Patent Publication Number: US-2023134543-A1

Title: Optical fiber cable and raceway therefor

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. patent application Ser. No. 16/822,103, filed on Mar. 18, 2020, and U.S. provisional patent application 63/145,368, filed on Feb. 3, 2021. The entire contents of the above applications are incorporated by reference. 
    
    
     BACKGROUND 
     Field 
     Various example embodiments relate to optical communication equipment and, more specifically but not exclusively, to fiber-optic cables. 
     Description of the Related Art 
     This section introduces aspects that may help facilitate a better understanding of the disclosure. Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is in the prior art or what is not in the prior art. 
     As the input/output (I/O) capacities of electronic processing chips increase, electrical signals may not provide sufficient I/O capacity across the limited size of a practically viable electronic chip package. A feasible alternative may be to interconnect electronic chip packages using optical signals, which can typically be delivered with a much higher I/O capacity per unit area compared to electrical I/Os. 
     SUMMARY OF THE INVENTION 
     Disclosed herein are various embodiments of (i) a fiber-optic cable having a cable sheath that enables significant changes in the cable&#39;s cross-sectional shape when the cable is bent and (ii) a raceway that can be used to deploy such a fiber-optic cable. 
     According to an example embodiment, provided is a fiber-optic cable comprising a cable segment that has a plurality of optical fibers laterally encased by a cable sheath; and the cable segment is constructed to permit relative lateral movement of at least some of the optical fibers within the cable sheath to change a cross-sectional shape of the cable segment. 
     In some embodiments of the above fiber-optic cable, the cable segment is configured to change the cross-sectional shape in response to being bent. 
     In some embodiments of any of the above fiber-optic cables, in a bent portion of the cable segment, a pair of the optical fibers is laterally separated by a larger distance than any two of the optical fibers in a straight portion of the cable segment. 
     In some embodiments of any of the above fiber-optic cables, in a bent portion of the cable segment, a pair of the optical fibers is laterally separated by a larger distance than any two points in an orthogonal cross-section of a straight portion of the cable segment. 
     In some embodiments of any of the above fiber-optic cables, the cable sheath comprises a layer of a laterally flexible material. 
     In some embodiments of any of the above fiber-optic cables, the cable sheath comprises a layer of a laterally stretchable material. 
     In some embodiments of any of the above fiber-optic cables, the plurality of optical fibers comprises at least 100 optical fibers. 
     In some embodiments of any of the above fiber-optic cables, the plurality of optical fibers comprises at least 1000 optical fibers. 
     In some embodiments of any of the above fiber-optic cables, the cable segment further comprises one or more strength members. 
     In some embodiments of any of the above fiber-optic cables, the cable segment is constructed to permit lateral movement of at least some of the optical fibers with respect to the one or more strength members. 
     In some embodiments of any of the above fiber-optic cables, at least some of the strength members are distributed throughout an interior of the cable. 
     In some embodiments of any of the above fiber-optic cables, at least some of the strength members are more concentrated near a center of the cable. 
     In some embodiments of any of the above fiber-optic cables, at least some of the strength members are attached to an inner surface of the cable sheath. 
     In some embodiments of any of the above fiber-optic cables, at least some of the strength members are embedded within the cable sheath. 
     In some embodiments of any of the above fiber-optic cables, at least some of the strength members are attached to an outer surface of the cable sheath. 
     According to another example embodiment, provided is an apparatus comprising a raceway having a hollow cable conduit, the hollow cable conduit having a curved portion and a straight portion connected to the curved portion, the curved portion of the hollow cable conduit having a larger cross-sectional size measured orthogonally to a main plane of the raceway than a corresponding cross-sectional size of the straight portion of the hollow cable conduit. 
     In some embodiments of the above apparatus, the raceway has a substantially constant height along the curved and straight portions, said height being measured orthogonally to the main plain. 
     In some embodiments of any of the above apparatus, the raceway has a larger height along the curved portion than along the straight portion, said height being measured orthogonally to the main plain. 
     In some embodiments of any of the above apparatus, the apparatus further comprises a fiber-optic cable laid in the hollow cable conduit of the raceway. 
     In some embodiments of any of the above apparatus, the fiber-optic cable comprises a cable segment that has a plurality of optical fibers laterally encased by a cable sheath; and the cable segment is constructed to permit relative lateral movement of at least some of the optical fibers within the cable sheath to change a cross-sectional shape of the cable segment. 
     In a general aspect, a fiber-optic cable including a cable segment that has a plurality of optical fibers laterally encased by a cable sheath is provided. The plurality of optical fibers are permitted to move laterally relative to one another to become relatively spatially rearranged from a first cross-section of the cable segment to a second cross-section of the cable segment. The cable sheath includes a laterally stretchable material that permits a cross-sectional shape of the cable segment to change in response to movement of the optical fibers within the cable sheath. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other aspects, features, and benefits of various disclosed embodiments will become more fully apparent, by way of example, from the following detailed description and the accompanying drawings, in which: 
         FIG.  1    shows a block diagram of an optical communication system in which at least some embodiments can be practiced; 
         FIGS.  2 A- 2 C  illustrate certain features of an optical fiber cable that can be used in the optical communication system of  FIG.  1    according to an embodiment; 
         FIGS.  3 A- 3 C  pictorially illustrate an optical fiber cable that can be used in the optical communication system of  FIG.  1    according to another embodiment; 
         FIGS.  4 A- 4 F  schematically show example cross-sections of the optical fiber cable of  FIG.  3    according to some embodiments; 
         FIGS.  5 A- 5 B  schematically show example branching optical fiber cables that can be used in the optical communication system of  FIG.  1    according to some embodiments; 
         FIGS.  6 A- 6 E  schematically show a raceway that can be used in the optical communication system of  FIG.  1    according to an embodiment; and 
         FIGS.  7 A- 7 C  schematically show a section of a raceway that can be used in the optical communication system of  FIG.  1    according to another embodiment. 
         FIG.  8    is a diagram an optical communications system. 
         FIGS.  9  and  10    are diagrams of co-packaged optical interconnect modules. 
         FIG.  11    is a diagram of an example of an optical communications system. 
         FIG.  12    is a block diagram of an example of an optical communication system. 
         FIG.  13 A  is a diagram of an example of an optical communication system. 
         FIG.  13 B  is a diagram of an example of an optical cable assembly used in the optical communication system of  FIG.  13 A . 
         FIG.  13 C  is an enlarged diagram of the optical cable assembly of  FIG.  13 B . 
         FIG.  13 D  is an enlarged diagram of the upper portion of the optical cable assembly of  FIG.  13 B . 
         FIG.  13 E  is an enlarged diagram of the lower portion of the optical cable assembly of  FIG.  13 B . 
         FIG.  14    is a block diagram of an example of an optical communication system. 
         FIG.  15 A  is a diagram of an example of an optical communication system. 
         FIG.  15 B  is a diagram of an example of an optical cable assembly. 
         FIG.  15 C  is an enlarged diagram of the optical cable assembly of  FIG.  15 B . 
         FIG.  15 D  is an enlarged diagram of the upper portion of the optical cable assembly of  FIG.  15 B . 
         FIG.  15 E  is an enlarged diagram of the lower portion of the optical cable assembly of  FIG.  15 B . 
         FIG.  16    is a block diagram of an example of an optical communication system. 
         FIG.  17 A  is a diagram of an example of an optical communication system. 
         FIG.  17 B  is a diagram of an example of an optical cable assembly. 
         FIG.  17 C  is an enlarged diagram of the optical cable assembly of  FIG.  17 B . 
         FIGS.  18  to  20 B  are diagrams of examples of data processing systems. 
         FIG.  21    is a diagram of an example of connector port mapping for an optical fiber interconnection cable. 
         FIGS.  22  and  23    are diagrams of examples of fiber port mapping for optical fiber interconnection cables. 
         FIGS.  24  and  25    are diagrams of examples of viable port mapping for optical fiber connectors of universal optical fiber interconnection cables. 
         FIG.  26    is a diagram of an example of a port mapping for an optical fiber connector that is not appropriate for a universal optical fiber interconnection cable. 
         FIGS.  27  and  28    are diagrams of examples of viable port mapping for optical fiber connectors of universal optical fiber interconnection cables. 
         FIGS.  29 ,  30 ,  31 A, and  31 B  are diagrams of examples of optical fiber connectors. 
     
    
    
     DETAILED DESCRIPTION 
     Emerging optical interconnects aim to co-package and even co-integrate optical transponders and electronic processing chips, which necessitates transponder solutions that consume relatively low power and that are sufficiently robust against significant temperature variations often present within an electronic processing chip package. Of significant interest are massively spatially parallel optical interconnect solutions that multiplex information signals onto relatively few wavelengths and use a relatively large number of parallel spatial paths for chip-to-chip interconnection. Although some optical cables carrying as many as 3456 strands of optical telecommunication fiber are commercially available, their relatively large cross-section, relative bend-inflexibility, and relatively high weight may make such optical cables unfavorable or even unusable for chip-to-chip interconnection applications. 
       FIG.  1    shows a block diagram of a communication system  100  in which at least some embodiments can be practiced. As shown, system  100  comprises integrated optical communication devices  101   1 - 101   6  suitably interconnected by optical fiber cables  102   1 - 102   11  establishing communication paths between the communication devices. Communication system  100  can also comprise one or more external optical power supply modules  103  producing continuous-wave (CW) light or producing one or more trains of periodic or non-periodic optical pulses for use in one or more of the integrated optical communication devices  101   1 - 101   6 . Some end-to-end communication paths can pass through external optical power supply modules  103  (e.g., see the communication path between devices  101   2  and  101   6 ). For example, the communication path between devices  101   2  and  101   6  can be jointly established by optical fiber cables  102   7  and  102   8 , whereby light from external optical power supply  103  is multiplexed onto optical fiber cables  102   7  and  102   8 . Some end-to-end communication paths can pass through a multiplexing unit  104  (e.g., see the communication path between devices  101   2  and  101   6 ). For example, the communication path between devices  101   2  and  101   6  can be jointly established by optical fiber cables  102   10  and  102   11 , whereby light from external optical power supply  103  can be multiplexed within multiplexing unit  104  onto optical fiber cables  102   10  and  102   11 . 
       FIGS.  2 A- 2 C  illustrate certain features of optical fiber cable  102  that can be used in system  100  ( FIG.  1   ) according to some embodiments. More specifically,  FIG.  2 A  shows an example longitudinal-section  201  of optical fiber cable  102  according to some embodiments.  FIG.  2 B  shows an example cross-section  202  of optical fiber cable  102  according to some embodiments.  FIG.  2 C  shows an example cross-section  203  of a cable sheath  210  of optical fiber cable  102  according to some embodiments. The shown longitudinal-section  201  and cross-sections  202  and  203  may or may not correspond to the same optical fiber cable  102 . 
     As shown in  FIGS.  2 A and  2 B , each of optical fiber cables  102  comprise a respective sheath  210 , a respective plurality of optical fiber strands  220  (shown in dotted gray in  FIG.  2 A ), and respective one or more strength members  230  (shown in dashed black in  FIG.  2 A ). Individual cables  102  can be terminated by connectors  240  that are designed to make the connection thereof to system elements  101 ,  103 , and/or  104  relatively effortless and/or straightforward. In various embodiments, fiber strands  220  can be loosely contained within sheath  210 , can be arranged in ribbons, or can be compartmentalized into tubes or sectors. In some embodiments, individual fiber strands  220  can be coated by a relatively thin layer of soft plastic (e.g., up to the cross-sectional diameter of about 250 micrometers) and optionally additionally be coated by a thicker layer of harder plastic (e.g., up to the cross-sectional diameter of about 900 micrometers). 
     In various embodiments, strength members  230  can be variously arranged, e.g., in the middle of cable  102 , near sheath  210 , embedded within sheath  210 , and/or distributed throughout the cable cross-section.  FIG.  2 B  shows a non-limiting example of the latter distribution. Example materials from which strength members  230  can be made include but are not limited to steel, fiberglass, and aramid yarn. In some embodiments, some strength members  230  can be attached to sheath  210  and/or to the cable end points at the housing of connector(s)  240 . Sheath  210  can be designed to approximately maintain a certain cross-sectional shape, such as a substantially circular cross-sectional shape, across the cable&#39;s length (e.g., see  FIG.  2 B ), even if the cable is bent or curved to create segments having a minimum recommended bend radius. For some cables  102 , tighter-than-recommended bending may result in kinking and/or buckling of sheath  210  or irreversible damage inside the cable, e.g., when the tensile strain (at the outer side of the bend) or the compressive stress (at the inner side of the bend) exceeds the elastic-deformation limits of some of the materials making up the cable. Kinking, buckling, or breaking may, inter alia, result in damaged optical fiber strands  220 . 
     Some cable features directed at the prevention of the cable  102  kinking, buckling, and/or breaking can include: (i) hard-to-bend sheaths, such as sheaths made of stiff materials; (ii) relatively thick sheaths; (iii) braided sheaths; (iv) spiral wraps; (v) mono-coil sheaths; and (vi) bend-restricting sheaths, such as the interlocking hose designs and interlocking vertebrae bend restrictors. 
     A typical recommended bend radius for conventional optical cables can be approximately 10 times the outer cable diameter. Conventional, commercially available cables for carrying one thousand or more fiber strands can have outer cable diameters on the order of one inch, which corresponds to a recommended minimum bend radius on the order of inches. The latter cable characteristic can make some conventional cables unsuitable for some compact applications, such as those corresponding to some embodiments of system  100  ( FIG.  1   ). 
     These and possibly other related problems in the state of the art can be addressed using at least some embodiments of cables  102 , in which sheaths  210  are constructed to be laterally flexible and/or laterally stretchable, e.g., as explained in more detail below, in reference to  FIGS.  2 C and  3 A- 3 C . Such laterally flexible/stretchable sheaths  210  can be very different from and should be contrasted with typical conventional sheaths, e.g., used in outdoor cabling environments. For example, some embodiments of cables  102  disclosed herein can advantageously afford bend radii that are very close to the bend radii afforded by individual optical fiber strands  220  used therein. Such tight bend radii may not be achievable with conventional sheaths, e.g., because the latter can force the corresponding cable to maintain a substantially fixed cross-sectional shape throughout its entire length, including the bent segments of the cable. In contrast, some embodiments of laterally flexible/stretchable sheaths  210  can allow for significant changes of the cross-sectional shape of cable  102  when the latter is bent or otherwise deformed to fit into a restricted and/or confined geometry of the available cable conduit, thereby providing a capability to achieve tighter cable turns than the above-mentioned conventional cables without inflicting any internal damage onto the cable. 
     As shown in  FIG.  2 C , one can define a circumference C, a longest cross-sectional dimension A, and a shortest cross-sectional dimension B of sheath  210 . While these quantities are shown for an example elliptical cross-section, they can be defined on any geometrical shape representing the cross-section of fiber-optic cable  102 . According to some embodiments, one or more of the three geometric parameters A, B, and C associated with fiber-optic cable  102  can change when the cable is bent. We refer to the three geometric parameters of a straight section of cable as A 0 , B 0 , and C 0 , respectively. In some embodiments, the cross-section of an unperturbed, straight section of cable can be essentially circular, in which case A 0 ≈B 0  and C 0 ≈πA 0 . In some embodiments, the cross-section of an unperturbed, straight section of cable can be essentially square, in which case A 0 ≈B 0  and C 0 ≈4A 0 . In some embodiments, the cross-section of an unperturbed, straight section of cable can be essentially elliptical, in which case C 0 ≈π([A 0   2 +B 0   2 ]/2) 1/2 . 
     When fiber-optic cable  102  is being bent, e.g., to accommodate a 90-degree turn, laterally flexible/stretchable sheath  210  can change its cross-sectional shape from, e.g., circular ( FIG.  2 B ) to, e.g., elliptical ( FIG.  2 C ). In some embodiments, such a shape change can be nearly permanent and/or at least partially irreversible (e.g., if laterally flexible/stretchable sheath  210  is made from a plastically deformable or malleable material) or substantially reversible (e.g., if laterally flexible/stretchable sheath  210  is made from a deformable material whose elastic limit is not exceeded when the cable is bent). When laterally flexible/stretchable sheath  210  is made from an elastically deformable material, laterally flexible/stretchable sheath  210  can substantially return to its original shape once fiber-optic cable  102  is straightened out after having been bent. 
     As used herein, the term “laterally flexible” refers to a cable sheath that can maintain a substantially constant cable circumference while allowing the cross-sectional shape of the cable to change in a significant way. For example, in some embodiments, it may be possible to change the circumference of a laterally flexible cable sheath  210  in a bent cable section without damage to optical fiber strands  220  by no more than 10% relative to the circumference C 0 , i.e., 0.9 C 0 ≤C≤1.1 C 0 . At the same time, it may also be possible in such embodiments to change one or both of the dimensions A and B of a laterally flexible cable sheath  210  in a bent cable section without damage to optical fiber strands  220  by more than 20% relative to the dimensions A 0  and B 0 , i.e., in accordance with one or more of the inequalities: A&lt;0.8A 0 , A&gt;1.2A 0 , B&lt;0.8B 0 , and B&gt;1.2B 0 . 
     As used herein, the term “laterally stretchable” refers to a cable sheath  210  that can expand and/or contract the cable circumference without damage to optical fiber strands  220 , e.g., by more than 10% when subjected to bending strain and/or stress, i.e., C&lt;0.9C 0  or C&gt;1.1C 0 . In some embodiments, a laterally stretchable sheath  210  can allow the overall cross-sectional shape to be approximately maintained while the area of the cross-section expands or contracts during the cable bending without damage to optical fiber strands  220 . For example, a generally oval or circular cross-sectional shape can be maintained along the length of the cable while the area of the corresponding cross-sectional oval or circle changes along said length. In some other embodiments, a laterally stretchable sheath can allow the cross-sectional shape of the cable to change in a significant way during bending without damage to optical fiber strands  220 . For example, it may be possible to change one or both of the dimensions A and B of a laterally stretchable sheath  210  in a bent cable section without damage to optical fiber strands  220  by more than 20% relative to the dimensions A 0  and B 0 , i.e., in accordance with one or more of the inequalities: A&lt;0.8A 0 , A&gt;1.2A 0 , B&lt;0.8B 0 , and/or B&gt;1.2B 0 . 
     In some embodiments, a laterally flexible/stretchable sheath  210  can comprise a relatively thin layer of a suitable elastic material, with the thickness thereof being selected such that: (i) said layer is thick enough to provide sufficient sheath strength for holding the optical fiber strands  220  and strength members  230  appropriately laterally confined and restrained under the sheath; and (ii) said layer is still thin enough to provide sufficient effective elasticity and/or plasticity for changing the cable&#39;s cross-sectional shape and/or area along the length of the cable. Example materials that can be used for this purpose include, but are not limited to: (i) various natural and artificial fabrics; (ii) plastic and metal foils; (iii) cellulose and its derivatives; (iv) rubber; (v) neoprene; (v) latex; (vi) lycra; (vii) elastane; and (viii) spandex. 
       FIGS.  3 A- 3 C  pictorially illustrate optical fiber cable  102  that can be used in system  100  ( FIG.  1   ) according to another embodiment. More specifically,  FIG.  3 A  shows a top view of cable  102 .  FIG.  3 B  shows a side view of the same cable  102 .  FIG.  3 C  shows a three-dimensional (3D) perspective cutout view of a middle segment  300  of said same cable  102 . The XYZ-coordinate triads shown in  FIGS.  3 A- 3 C  indicate the relative orientations of the shown views. 
     Referring to  FIG.  3 A , optical fiber cable  102  is shown therein in a configuration that has a sharp (e.g., approximately 90-degree) bend near plane  321 . Individual fiber strands  220  are such that each of them can accommodate such a bend without cracking or breaking. 
     Referring to  FIG.  3 B , the sheath  210  of the shown cable  102  is laterally flexible and/or stretchable as explained above. This characteristic enables cable  102  to change its cross-sectional shape along its length. For example,  FIG.  3 B  clearly shows that the vertical size (i.e., the size measured along the Z-coordinate axis) of cable  102  is larger in a middle segment  300  thereof than in the end segments thereof immediately adjacent to connectors  240 . 
       FIG.  3 C  schematically shows the middle segment  300  in more detail. In particular,  FIG.  3 C  schematically shows three cross-sections of the middle segment  300 , which cross-sections are labeled  302 ,  304 , and  306 , respectively. Cross-section  306  corresponds to plane  321  (also see  FIGS.  3 A- 3 B ). Cross-sections  302  and  306  correspond to the respective planes that are locally orthogonal to the (bent) longitudinal axis of cable  102  and located closer to the opposite ends thereof (e.g., near respective connectors  240 ). 
     Cross-section  302  has an approximately pentagonal shape, with rounded corners. Cross-section  304  has an approximately oval shape characterized by a relatively large aspect ratio (e.g., &gt;4). Cross-section  306  has an irregular non-convex shape. A person of ordinary skill in the art will understand that the shown shapes represent non-limiting examples and that many other cross-sectional shapes are possible. Visual inspection of the shown example cross-sectional shapes  302 ,  304 , and  306  reveals that fiber strands  220  and strength members  230  can be relatively spatially rearranged from one cross-section to the next, e.g., to spread out laterally within sheath  210  more in some segments than in other segments. The latter property enables, inter alia, the sharp cable bend near plane  321 . 
     During bending, at least some of the optical fiber strands  220  contained within the flexible/stretchable sheath  210  may be subject to relative lateral movement, whereby the relative positions between at least some of optical fiber strands  220  may change in a bent section of the cable compared to a straight section thereof. In one example embodiment, the largest distance between two optical fiber strands contained within the sheath in a bent section of the cable (a in  FIG.  3 C ) can become larger than the largest distance between two optical fiber strands contained within the sheath in an unperturbed, straight section of the cable (a 0  in  FIG.  3 C ), i.e., a&gt;a 0 . In some embodiments, the largest distance between two optical fiber strands contained within the sheath in a bent section of the cable (a in  FIG.  3 C ) can become larger than the largest dimension of the cross-sectional area of the sheath in an unperturbed, straight section of cable (A 0  in  FIG.  3 C ), i.e., a&gt;A 0 . 
       FIGS.  4 A- 4 F  schematically show cross-section  302  ( FIG.  3 C ) according to some embodiments. More specifically,  FIGS.  4 A- 4 F  provide some examples of how strength members  230  can be placed and/or distributed in cable  102 . 
       FIG.  4 A  illustrates an embodiment in which no dedicated strength members  230  are being used. In this particular embodiment, the plurality of fiber strands  220  themselves also act as strength elements of the cable. In some embodiments, sheath  210  can have some axial strength that contributes to the overall axial strength of cable  102 . 
       FIG.  4 B  illustrates an embodiment in which strength members  230  are relatively widely distributed (e.g., approximately uniformly or non-uniformly) throughout the interior of cable  102  within sheath  210 . Strength members  230  can be redistributed within sheath  210 , e.g., as indicated in  FIG.  3 C , when cable  102  is bent. 
       FIG.  4 C  illustrates an embodiment in which multiple strength members  230  are located near the cross-sectional center of cable  102 . Such multiple strength members may or may not be connected to form a structural bundle. 
       FIG.  4 D  illustrates an embodiment in which strength members  230  are located near the inner surface of sheath  210 . In some embodiments, one or more such strength members  230  can be attached (e.g., glued) to the inner surface of sheath  210 . 
       FIG.  4 E  illustrates an embodiment in which strength members  230  are embedded into sheath  210 . In one possible embodiment, strength members  230  can be woven into a laterally flexible/stretchable fabric used in sheath  210 . Alternatively or in addition, strength members  230  can be sandwiched between different thin layers of flexible/stretchable material used in sheath  210 . 
       FIG.  4 F  illustrates an embodiment in which strength members  230  are positioned at the outer surface of sheath  210 . In some embodiments, one or more such strength members  230  can be attached (e.g., glued) to sheath  210 . 
     Alternatively or in addition, in any of the above embodiments, strength members  230  can be attached to the housing(s) of connector(s)  240  at the opposite ends of cable  102 , or can be fed through sheath  210  to the outside of the cable, e.g., to make the strength members directly accessible during cable pulling. 
       FIGS.  5 A- 5 B  schematically show some alternative embodiments of cable  102 . More specifically, in such embodiments, cable  102  can comprise more than one connector  240  at one end or both ends thereof. 
       FIG.  5 A  illustrates an embodiment in which a sheathed trunk  510  splits into sheathed branches  511  and  512 , each having a respective subset of optical fiber strands  220  of the trunk  510 . At least one of trunk  510  and branches  511  and  512  includes sheath  210 . The remainder can have sheaths that may or may not be laterally flexible or stretchable. In some embodiments, the sheaths of trunk  510  and branches  511  and  512  can comprise the same material. In some embodiments, the sheaths of trunk  510  and branches  511  and  512  can comprise different respective materials. 
       FIG.  5 B  illustrates an embodiment in which cable  102  comprises cables  521  and  522  and connectors  240   1 ,  240   2 , and  240   3 . Cables  521  and  522  share connector  240   1  and have connectors  240   2  and  240   3 , respectively, at the other cable end. Near connector  240   1 , cables  521  and  522  are arranged in a trunk  520  that has laterally flexible or stretchable sheath  210  at an outer surface thereof. The sheath  210  of trunk  520  encloses the corresponding segments of cables  521  and  522 , each carrying a respective subset of optical fibers  220 . In some embodiments, the sheath  210  of trunk  520  can enclose more than two cables similar to cables  521  and  522 . 
     Cables  521  and  522  can have respective sheaths that may or may not be laterally flexible or stretchable. Embodiments with any number of connectors  240  on either end of cable  102  and with at least one laterally flexible or stretchable sheath  210  are also contemplated. In view of this disclosure, a person of ordinary skill in the art will be able to make and use such embodiments without any undue experimentation. Although strength members  230  are not explicitly shown in  FIGS.  5 A- 5 B , such strength members can be incorporated into the corresponding cables  102 , e.g., in accordance with any of  FIGS.  4 B- 4 F . 
     Referring back to  FIG.  1   , in some embodiments, at least some cables  102  in system  100  can be deployed using one or more cable raceways. In cable-management arts, a raceway (also sometimes referred to as a raceway system) is a rigid enclosed or semi-enclosed channel or conduit that protects, routes, and/or hides cables and wires. Raceways can protect wires and cables from heat, humidity, corrosion, water intrusion, and other physical threats. A well-grounded metallic raceway can also provide radio frequency (RF) shielding that reduces electromagnetic interference (EMI). A plastic raceway can be used, e.g., when EMI is not relevant. For example, cables  102  can be deployed using metallic or plastic raceways. 
       FIGS.  6 A- 6 E  schematically show a section of a raceway  600  that can be used to deploy one or more cables  102  in system  100  according to an embodiment. More specifically,  FIG.  6 A  shows a top view of a section of raceway  600 .  FIGS.  6 B- 6 D  show three cross-sectional views of a section of raceway  600  at positions  611 ,  612 , and  613  indicated in  FIG.  6 A .  FIG.  6 E  pictorially shows a curved middle portion  610  of a section of raceway  600  in more detail (also see  FIG.  6 A ). The XYZ-coordinate triads shown in  FIGS.  6 A,  6 B, and  6 D  indicate the relative orientations of the shown views. 
     Referring to  FIGS.  6 A- 6 D , a section of raceway  600  comprises walls  601  forming an inner opening  602  as a hollow conduit for one or more fiber-optic cables  102 . Within a section of raceway  600 , the hollow conduit proceeds substantially along a main plane  620  of that section. One or more cables  102  can be deployed substantially along the main plane  620  of that raceway section. As used herein, the term “main plane” refers to a plane drawn approximately through the geometrical centroids of the inner opening&#39;s local cross-sections of raceway  600 . In some embodiments, the main plain can be parallel to the surface of the floor on which raceway  600  is laid down. 
     In an example embodiment, one or more of the cross-sectional dimensions of the inner opening  602  of raceway  600  can change within the curved middle portion  610  of raceway  600 , e.g., as indicated in  FIGS.  6 B- 6 D . 
     In one possible embodiment, the largest cross-sectional dimension (D in  FIG.  6 C ) of the inner opening  602  in the curved middle portion  610  of raceway  600  (e.g., at position  612 ), measured in the direction orthogonal to the main plane  620  can be larger than the largest cross-sectional dimension (D 0  in  FIGS.  6 B and  6 D ) of the inner opening  602  in a straight portion (e.g., at positions  611  and  613 ) of raceway  600 , measured in the direction orthogonal to the main plane, i.e., D&gt;D 0 . This feature enables raceway  600  to accommodate the lateral expansion of cable  102  at a bend, e.g., such as the lateral expansion near plane  321  illustrated in  FIGS.  3 B- 3 C . In the example embodiment illustrated by  FIGS.  6 B- 6 D , the inner opening  602  of raceway  600  is shaped to expand up and down with respect to the main plane  620  (also see  FIG.  6 E ). 
       FIG.  6 E  pictorially illustrates example three-dimensional geometry of the inner opening  602  of raceway  600  within curved middle portion  610 . As shown in  FIG.  6 E , raceway  600  comprises a bottom part  650  and a top part  660  that can be joined together as indicated by the double-headed arrows to form walls  601  and inner opening  602 . The dashed lines  651 ,  652 ,  661 , and  662  indicate the inner edges of the inner opening  602 . The curvature of the inner edges  651 ,  652 ,  661 , and  662  is such that the cross-sectional dimension changes indicated in  FIGS.  6 B- 6 D  are realized. 
     In some embodiments, inner opening  602  of raceway  600  can be completely surrounded by walls  601 . In some other embodiments, inner opening  602  of raceway  600  may only be partially surrounded by walls  601 , e.g., the hollow conduit may not have a top wall. 
       FIGS.  7 A- 7 C  schematically show a section of raceway  600  that can be used to deploy one or more cables  102  in system  100  according to another embodiment. More specifically,  FIGS.  7 A- 7 C  show three cross-sectional views of a section of raceway  600  at positions  611 ,  612 , and  613  indicated in  FIG.  6 A . The XYZ-coordinate triads shown in  FIGS.  7 A and  7 C  indicate the relative orientations of the shown views. In this particular embodiment, at position  612 , the inner opening  602  expands asymmetrically above and below the main plane  620  corresponding to positions  611  and  613 . For example, there is a larger expansion above said main plane  620  than below said main plane, e.g., as indicated in  FIG.  7 B . 
     In some embodiments, the external height of raceway  600  can change between a value H 0  for a straight section and a value H&gt;H 0  for a curved section, as visualized in  FIGS.  6 B- 6 D . In some other embodiments, the external height of raceway  600  can have a substantially constant value H C  for both a straight section and a curved section, as visualized in  FIGS.  7 A- 7 C . In some embodiments, the external height of raceway  600  can be the sum of the height of a bottom part H B  and the height of a top part H T , as visualized in  FIG.  6 E . 
     According to an example embodiment disclosed above, e.g., in the summary section and/or in reference to any one or any combination of some or all of  FIGS.  1 - 7   , provided is a fiber-optic cable (e.g.,  102 ,  FIG.  1   ) comprising a cable segment (e.g.,  300 ,  FIGS.  3 B- 3 C ;  520 ,  FIG.  5 B ) that has a plurality of optical fibers (e.g.,  220 ,  FIG.  2 ,  3 ,  4   , or  5 ) laterally encased by a cable sheath (e.g.,  210 ,  FIG.  2 ,  3 ,  4   , or  5 ); and the cable segment is constructed to permit relative lateral movement of at least some of the optical fibers within the cable sheath (e.g., as illustrated by comparison of  302 ,  304 ,  306 ,  FIG.  3 C ) to change a cross-sectional shape of the cable segment. 
     The fiber optic cables described above (e.g.,  102  of  FIGS.  2 A to  5 B ) can be used in various systems, such as the communication system  100  of  FIG.  1   . For example, the fiber optic cables can transmit data and control signals, as well as optical power supply light that can be used as light sources for modulators in photonic integrated circuits. 
       FIGS.  8  to  11    show examples of optical communications systems  800  and  1100  in which in each system an optical power supply or photon supply provides optical power supply light to photonic integrated circuits hosted in multiple communication devices (e.g., optical transponders), and the optical power supply is external to the communication devices. The optical power supply can have its own housing, electrical power supply, and control circuitry, independent of the housings, electrical power supplies, and control circuitry of the communication devices. This allows the optical power supply to be serviced, repaired, or replaced independent of the communication devices. Redundant optical power supplies can be provided so that a defective external optical power supply can be repaired or replaced without taking the communication devices off-line. The external optical power supply can be placed at a convenient centralized location with a dedicated temperature environment (as opposed to being crammed inside the communication devices, which may have a high temperature). The external optical power supply can be built more efficiently than individual power supply units, as certain common parts such as monitoring circuitry and thermal control units can be amortized over many more communication devices. The following describes implementations of the fiber cabling for remote optical power supplies. Additional information about the fiber cabling for remote optical power supplies is provided in U.S. provisional patent application 63/145,368, filed on Feb. 3, 2021 (referred to as “the &#39;368 application”), the entire contents of which are incorporated by reference. 
       FIG.  8    shows an optical communications system  800  providing high-speed communications between a first chip  802  and a second chip  804  using co-packaged optical interconnect modules  806 ,  807 , respectively, that include photonic integrated circuits. Each of the first and second chips  802  and  804  can be a high-capacity chip, e.g., a high bandwidth Ethernet switch chip. The first and second chips  802  and  804  communicate with each other through an optical fiber interconnection cable  808  that includes a plurality of optical fibers. In some implementations, the optical fiber interconnection cable  808  can be implemented using one or more of the optical fiber cables  102  described above (e.g., see  FIGS.  2 A to  5 A ). In the example of  FIG.  8   , the optical fiber interconnection cable  808  includes optical fiber cores that transmit data and control signals between the first and second chips  802 ,  804 . The optical fiber interconnection cable  808  also includes one or more optical fiber cores that transmit optical power supply light from an optical power supply or photon supply to photonic integrated circuits that provide optoelectronic interfaces for the first and second chips  802 ,  804 . The optical fiber interconnection cable  808  can include single-core fibers or multi-core fibers. Each single-core fiber includes a cladding and a core, typically made from glasses of different refractive indices such that the refractive index of the cladding is lower than the refractive index of the core to establish a dielectric optical waveguide. Each multi-core optical fiber includes a cladding and multiple cores, typically made from glasses of different refractive indices such that the refractive index of the cladding is lower than the refractive index of the core. More complex refractive index profiles, such as index trenches, multi-index profiles, or gradually changing refractive index profiles can also be used. More complex geometric structures such as non-circular cores or claddings, photonic crystal structures, photonic bandgap structures, or nested antiresonant nodeless hollow core structures can also be used. 
     The example in  FIG.  8    illustrates a switch-to-switch use case. An external optical power supply or photon supply  810  provides optical power supply signals, which can be, e.g., continuous-wave light, one or more trains of periodic optical pulses, or one or more trains of non-periodic optical pulses. The power supply light is provided from the photon supply  810  to the photonic integrated circuits through optical fibers  812  and  814 , respectively. For example, the optical power supply  810  can provide continuous wave light, or both pulsed light for data modulation and synchronization, as described in U.S. patent application Ser. No. 16/847,705, filed on Apr. 14, 2020 (referred to as “the &#39;705 application”), the entire contents of which are incorporated by reference. This allows the first chip  802  to be synchronized with the second chip  804 . 
     For example, the photon supply  810  can correspond to the optical power supply  103  of  FIG.  1   . The pulsed light from the photon supply  810  can be provided to the co-packaged optical interconnect modules  806 ,  807 . In some implementations, the photon supply  810  can provide a sequence of optical frame templates, in which each of the optical frame templates includes a respective frame header and a respective frame body, and the frame body includes a respective optical pulse train. The modulators in the co-packaged optical interconnect modules  806 ,  807  can load data into the respective frame bodies to convert the sequence of optical frame templates into a corresponding sequence of loaded optical frames that are output through optical fiber links. The implementation shown in  FIG.  8    uses a packaging solution corresponding to  FIG.  9    in which a photonic integrated circuit  900  is directly attached to a serializers/deserializers module  902 .  FIG.  10    shows another example in which the photonic integrated circuit  900  is directly attached to the serializers/deserializers  902 . 
     The optical fiber cable  808  includes a first optical fiber connector  822  and a second optical fiber connector  832 . The first optical fiber connector  822  mates with a corresponding connector optically coupled to the co-packaged optical interconnect module  806 , and the second optical fiber connector  832  mates with a corresponding connector optically coupled to the co-packaged optical interconnect module  807 . Each of the first optical fiber connector  822  and the second optical fiber connector  832  includes one or more power supply fiber ports, one or more transmitter fiber ports, and one or more receiver fiber ports. One or more optical fibers that includes a plurality of optical fiber cores is optically coupled between the first optical fiber connector  822  and the second optical fiber connector  832  to enable communication between the chips  802  and  804 . 
     Each power supply fiber port of the first optical fiber connector  822  provides optical power supply light to the co-packaged optical interconnect module  806 . The co-packaged optical interconnect module  806  transmits output optical signals to the one or more transmitter fiber ports of the optical fiber connector  822 , and receives input optical signals from the one or more receiver fiber ports of the optical fiber connector  822 . In a similar manner, each power supply fiber port of the second optical fiber connector  832  provides optical power supply light to the co-packaged optical interconnect module  807 . The co-packaged optical interconnect module  807  transmits output optical signals to the one or more transmitter fiber ports of the optical fiber connector  832 , and receives input optical signals from the one or more receiver fiber ports of the optical fiber connector  832 . The optical fiber connectors  822  and  832  can have symmetric properties described below so that the optical fiber connectors  822  and  832  are interchangeable, e.g., the optical fiber connector  832  can be connected to connector associated with the co-packaged optical interconnect module  806 , and the optical fiber connector  822  can be connected to connector associated with the co-packaged optical interconnect module  807 . Each of the optical fiber connectors  822  and  832  can be invariant against a 180-degree rotation or a 90-degree rotation so that it is more convenient for the user. 
     One or more portions of the optical fiber cable  808  can have a cable sheath (e.g., similar to the cable sheath  210  of  FIGS.  2 A to  5 B ). The optical fiber cable  808  can have strength members (e.g., similar to the strength members  230 ). In some implementations, the optical fiber cable  808  can include a cable segment constructed to permit relative lateral movement of at least some of the optical fibers within the cable sheath to change a cross-sectional shape of the cable segment. In some implementations, the optical fiber cable  808  can include a cable segment that has a plurality of optical fibers laterally encased by a cable sheath, in which the plurality of optical fibers are permitted to move laterally relative to one another to become relatively spatially rearranged from a first cross-section of the cable segment to a second cross-section of the cable segment, and wherein the cable sheath includes a laterally stretchable material that permits a cross-sectional shape of the cable segment to change in response to movement of the optical fibers within the cable sheath. 
       FIG.  11    shows an example of an optical communications system  1100  providing high-speed communications between a high-capacity chip  1102  (e.g., an Ethernet switch chip) and multiple lower-capacity chips  1104   a ,  1104   b ,  1104   c , e.g., multiple network interface cards (NICs) attached to computer servers using co-packaged optical interconnect modules  806 ,  807  similar to those shown in  FIG.  8   . The high-capacity chip  1102  communicates with the lower-capacity chips  1104   a ,  1104   b ,  1104   c  through an optical fiber cable  1114  that includes a high-capacity optical fiber interconnection cable  1106  that later branches out into several lower-capacity optical fiber interconnection cables  1108   a ,  1108   b ,  1108   c  that are connected to the lower-capacity chips  1104   a ,  1104   b ,  1104   c , respectively. This example illustrates a switch-to-servers use case. 
     An external optical power supply or photon supply  1110  provides optical power supply signals, which can be continuous-wave light, one or more trains of periodic optical pulses, or one or more trains of non-periodic optical pulses. The power supply light is provided from the photon supply  1110  to the optical interconnect modules  806 ,  807  through optical fibers  1116 ,  1112   a ,  1112   b ,  1112   c , respectively. For example, the optical power supply  1110  can provide both pulsed light for data modulation and synchronization, as described in U.S. patent application Ser. No. 16/847,705. This allows the high-capacity chip  1102  to be synchronized with the lower-capacity chips  1104   a ,  1104   b , and  1104   c.    
     In some implementations, the optical fiber cable  1114  can include a cable segment that has a plurality of optical fibers laterally encased by a cable sheath, in which the cable segment is constructed to permit relative lateral movement of at least some of the optical fibers within the cable sheath to change a cross-sectional shape of the cable segment. In some implementations, the optical fiber cable  1114  can include a cable segment that has a plurality of optical fibers laterally encased by a cable sheath, in which the plurality of optical fibers are permitted to move laterally relative to one another to become relatively spatially rearranged from a first cross-section of the cable segment to a second cross-section of the cable segment, and wherein the cable sheath includes a laterally stretchable material that permits a cross-sectional shape of the cable segment to change in response to movement of the optical fibers within the cable sheath. 
     Some aspects of the systems  8000  and  11000  are described in more detail in connection with  FIGS.  12  to  17 C . 
       FIG.  12    is a system functional block diagram of an example of an optical communication system  1200  that includes a first communication transponder  1202  and a second communication transponder  1204 . Each of the first and second communication transponders  1202 ,  1204  can include one or more co-packaged optical modules described above. Each communication transponder can include, e.g., one or more data processors, such as network switches, central processing units, graphics processor units, tensor processing units, digital signal processors, and/or other application specific integrated circuits (ASICs). In this example, the first communication transponder  1202  sends optical signals to, and receives optical signals from, the second communication transponder  1204  through a first optical communication link  1206 . The one or more data processors in each communication transponder  1202 ,  1204  process the data received from the first optical communication link  1206  and outputs processed data to the first optical communication link  1206 . The optical communication system  1200  can be expanded to include additional communication transponders. The optical communication system  1200  can also be expanded to include additional communication between two or more external photon supplies, which can coordinate aspects of the supplied light, such as the respectively emitted wavelengths or the relative timing of the respectively emitted optical pulses. 
     A first external photon supply  1208  provides optical power supply light to the first communication transponder  1202  through a first optical power supply link  12910  and a second external photon supply  1212  provides optical power supply light to the second communication transponder  1204  through a second optical power supply link  1214 . In one example embodiment, the first external photon supply  1208  and the second external photon supply  1212  provide continuous wave laser light at the same optical wavelength. In another example embodiment, the first external photon supply  1208  and the second external photon supply  1212  provide continuous wave laser light at different optical wavelengths. In yet another example embodiment, the first external photon supply  1208  provides a first sequence of optical frame templates to the first communication transponder  1202 , and the second external photon supply  1212  provides a second sequence of optical frame templates to the second communication transponder  1204 . For example, as described in U.S. patent Ser. No. 16/847,705, each of the optical frame templates can include a respective frame header and a respective frame body, and the frame body includes a respective optical pulse train. The first communication transponder  1202  receives the first sequence of optical frame templates from the first external photon supply  1208 , loads data into the respective frame bodies to convert the first sequence of optical frame templates into a first sequence of loaded optical frames that are transmitted through the first optical communication link  1206  to the second communication transponder  1204 . Similarly, the second communication transponder  1204  receives the second sequence of optical frame templates from the second external photon supply  1212 , loads data into the respective frame bodies to convert the second sequence of optical frame templates into a second sequence of loaded optical frames that are transmitted through the first optical communication link  1206  to the first communication transponder  1202 . 
     In some implementations, each of the communication links  1206 ,  1210 ,  1214  can include an optical fiber cable that includes a cable segment that has a plurality of optical fibers laterally encased by a cable sheath, in which the cable segment is constructed to permit relative lateral movement of at least some of the optical fibers within the cable sheath to change a cross-sectional shape of the cable segment. In some implementations, each of the communication links  1206 ,  1210 ,  1214  can include an optical fiber cable that includes a cable segment that has a plurality of optical fibers laterally encased by a cable sheath, in which the plurality of optical fibers are permitted to move laterally relative to one another to become relatively spatially rearranged from a first cross-section of the cable segment to a second cross-section of the cable segment, and wherein the cable sheath includes a laterally stretchable material that permits a cross-sectional shape of the cable segment to change in response to movement of the optical fibers within the cable sheath. 
       FIG.  13 A  is a diagram of an example of an optical communication system  1300  that includes a first switch box  1302  and a second switch box  1304 . Each of the switch boxes  1302 ,  1304  can include one or more data processors, such as network switches. The first and second switch boxes  1302 ,  1304  can be separated by a distance greater than, e.g., 1 foot, 3 feet, 10 feet, 100 feet, or 1000 feet. The figure shows a diagram of a front panel  1306  of the first switch box  1302  and a front panel  1308  of the second switch box  1304 . In this example, the first switch box  1302  includes a vertical ASIC mount grid structure  1310 . A co-packaged optical module  1312  is attached to a receptor of the grid structure  1310 . The second switch box  1304  includes a vertical ASIC mount grid structure  1314 . A co-packaged optical module  1316  is attached to a receptor of the grid structure  1314 . The first co-packaged optical module  1312  communicates with the second co-packaged optical module  1316  through an optical fiber bundle  1318  that includes multiple optical fibers. Optional fiber connectors  1320  can be used along the optical fiber bundle  1318 , in which shorter sections of optical fiber bundles are connected by the fiber connectors  1320 . 
     In some implementations, each co-packaged optical module (e.g.,  1312 ,  1316 ) includes a photonic integrated circuit configured to convert input optical signals to input electrical signals that are provided to a data processor, and convert output electrical signals from the data processor to output optical signals. The co-packaged optical module can include an electronic integrated circuit configured to process the input electrical signals from the photonic integrated circuit before the input electrical signals are transmitted to the data processor, and to process the output electrical signals from the data processor before the output electrical signals are transmitted to the photonic integrated circuit. In some implementations, the electronic integrated circuit can include a plurality of serializers/deserializers configured to process the input electrical signals from the photonic integrated circuit, and to process the output electrical signals transmitted to the photonic integrated circuit. The electronic integrated circuit can include a first serializers/deserializers module having multiple serializer units and deserializer units, in which the first serializers/deserializers module is configured to generate a plurality of sets of first parallel electrical signals based on a plurality of first serial electrical signals provided by the photonic integrated circuit, and condition the electrical signals, in which each set of first parallel electrical signals is generated based on a corresponding first serial electrical signal. The electronic integrated circuit can include a second serializers/deserializers module having multiple serializer units and deserializer units, in which the second serializers/deserializers module is configured to generate a plurality of second serial electrical signals based on the plurality of sets of first parallel electrical signals, and each second serial electrical signal is generated based on a corresponding set of first parallel electrical signals. The plurality of second serial electrical signals can be transmitted toward the data processor. 
     The first switch box  1302  includes an external optical power supply  1322  (i.e., external to the co-packaged optical module) that provides optical power supply light through an optical connector array  1324 . In this example, the optical power supply  1322  is located internal of the housing of the switch box  1302 . Optical fibers  1326  are optically coupled to an optical connector  1328  (of the optical connector array  1324 ) and the co-packaged optical module  1312 . The optical power supply  1322  sends optical power supply light through the optical connector  1328  and the optical fibers  1326  to the co-packaged optical module  1312 . For example, the co-packaged optical module  1312  includes a photonic integrated circuit that modulates the power supply light based on data provided by a data processor to generate a modulated optical signal, and transmits the modulated optical signal to the co-packaged optical module  1316  through one of the optical fibers in the fiber bundle  1318 . 
     In some examples, the optical power supply  1322  is configured to provide optical power supply light to the co-packaged optical module  1312  through multiple links that have built-in redundancy in case of malfunction in some of the optical power supply modules. For example, the co-packaged optical module  1312  can be designed to receive N channels of optical power supply light (e.g., N 1  continuous wave light signals at the same or at different optical wavelengths, or N 1  sequences of optical frame templates), N 1  being a positive integer, from the optical power supply  1322 . The optical power supply  1322  provides N 1 +M 1  channels of optical power supply light to the co-packaged optical module  1312 , in which M 1  channels of optical power supply light are used for backup in case of failure of one or more of the N 1  channels of optical power supply light, M 1  being a positive integer. 
     The second switch box  1304  receives optical power supply light from a co-located optical power supply  1330 , which is, e.g., external to the second switch box  1304  and located near the second switch box  1304 , e.g., in the same rack as the second switch box  1304  in a data center. The optical power supply  1330  includes an array of optical connectors  1332 . Optical fibers  1334  are optically coupled to an optical connector  1336  (of the optical connectors  1332 ) and the co-packaged optical module  1316 . The optical power supply  1330  sends optical power supply light through the optical connector  1336  and the optical fibers  1334  to the co-packaged optical module  1316 . For example, the co-packaged optical module  1316  includes a photonic integrated circuit that modulates the power supply light based on data provided by a data processor to generate a modulated optical signal, and transmits the modulated optical signal to the co-packaged optical module  1312  through one of the optical fibers in the fiber bundle  1318 . 
     In some examples, the optical power supply  1330  is configured to provide optical power supply light to the co-packaged optical module  1316  through multiple links that have built-in redundancy in case of malfunction in some of the optical power supply modules. For example, the co-packaged optical module  1316  can be designed to receive N 2  channels of optical power supply light (e.g., N 2  continuous wave light signals at the same or at different optical wavelengths, or N 2  sequences of optical frame templates), N 2  being a positive integer, from the optical power supply  1322 . The optical power supply  1322  provides N 2 +M 2  channels of optical power supply light to the co-packaged optical module  1312 , in which M 2  channels of optical power supply light are used for backup in case of failure of one or more of the N 2  channels of optical power supply light, M 2  being a positive integer. 
       FIG.  13 B  is a diagram of an example of an optical cable assembly  1340  that can be used to enable the first co-packaged optical module  1312  to receive optical power supply light from the first optical power supply  1322 , enable the second co-packaged optical module  1316  to receive optical power supply light from the second optical power supply  1330 , and enable the first co-packaged optical module  1312  to communicate with the second co-packaged optical module  1316 .  FIG.  13 C  is an enlarged diagram of the optical cable assembly  1340  without some of the reference numbers to enhance clarity of illustration. 
     The optical cable assembly  1340  includes a first optical fiber connector  1342 , a second optical fiber connector  1344 , a third optical fiber connector  1346 , and a fourth optical fiber connector  1348 . The first optical fiber connector  1342  is designed and configured to be optically coupled to the first co-packaged optical module  1312 . For example, the first optical fiber connector  1342  can be configured to mate with a connector part of the first co-packaged optical module  1312 , or a connector part that is optically coupled to the first co-packaged optical module  1312 . The first, second, third, and fourth optical fiber connectors  1342 ,  1344 ,  1346 ,  1348  can comply with an industry standard that defines the specifications for optical fiber interconnection cables that transmit data and control signals, and optical power supply light. 
     The first optical fiber connector  1342  includes optical power supply (PS) fiber ports, transmitter (TX) fiber ports, and receiver (RX) fiber ports. The optical power supply fiber ports provide optical power supply light to the co-packaged optical module  1312 . The transmitter fiber ports allow the co-packaged optical module  1312  to transmit output optical signals (e.g., data and/or control signals), and the receiver fiber ports allow the co-packaged optical module  1312  to receive input optical signals (e.g., data and/or control signals). Examples of the arrangement of the optical power supply fiber ports, the transmitter ports, and the receiver ports in the first optical fiber connector  1342  are shown in  FIGS.  13 D,  22 , and  23   . 
       FIG.  13 D  shows an enlarged upper portion of the diagram of  FIG.  13 B , with the addition of an example of a mapping of fiber ports  1750  of the first optical fiber connector  1342  and a mapping of fiber ports  1752  of the third optical fiber connector  1346 . The mapping of fiber ports  1750  shows the positions of the transmitter fiber ports (e.g.,  1753 ), receiver fiber ports (e.g.,  1755 ), and power supply fiber ports (e.g.,  1751 ) of the first optical fiber connector  1342  when viewed in the direction  1754  into the first optical fiber connector  1342 . The mapping of fiber ports  1752  shows the positions of the power supply fiber ports (e.g.,  1757 ) of the third optical fiber connector  1346  when viewed in the direction  1756  into the third optical fiber connector  1346 . 
     The second optical fiber connector  1344  is designed and configured to be optically coupled to the second co-packaged optical module  1316 . The second optical fiber connector  1344  includes optical power supply fiber ports, transmitter fiber ports, and receiver fiber ports. The optical power supply fiber ports provide optical power supply light to the co-packaged optical module  1316 . The transmitter fiber ports allow the co-packaged optical module  1316  to transmit output optical signals, and the receiver fiber ports allow the co-packaged optical module  1316  to receive input optical signals. Examples of the arrangement of the optical power supply fiber ports, the transmitter ports, and the receiver ports in the second optical fiber connector  1344  are shown in  FIGS.  13 E,  22 , and  23   . 
       FIG.  13 E  shows an enlarged lower portion of the diagram of  FIG.  13 B , with the addition of an example of a mapping of fiber ports  1760  of the second optical fiber connector  1344  and a mapping of fiber ports  1762  of the fourth optical fiber connector  1348 . The mapping of fiber ports  1760  shows the positions of the transmitter fiber ports (e.g.,  1763 ), receiver fiber ports (e.g.,  1765 ), and power supply fiber ports (e.g.,  1761 ) of the second optical fiber connector  1344  when viewed in the direction  1764  into the second optical fiber connector  1344 . The mapping of fiber ports  1762  shows the positions of the power supply fiber ports (e.g.,  1767 ) of the fourth optical fiber connector  1348  when viewed in the direction  1766  into the fourth fiber connector  1348 . 
     The third optical connector  1346  is designed and configured to be optically coupled to the power supply  1322 . The third optical connector  1346  includes optical power supply fiber ports (e.g.,  1757 ) through which the power supply  1322  can output the optical power supply light. The fourth optical connector  1348  is designed and configured to be optically coupled to the power supply  1330 . The fourth optical connector  1348  includes optical power supply fiber ports (e.g.,  1762 ) through which the power supply  1322  can output the optical power supply light. 
     In some implementations, the optical power supply fiber ports, the transmitter fiber ports, and the receiver fiber ports in the first and second optical fiber connectors  1342 ,  1344  are designed to be independent of the communication devices, i.e., the first optical fiber connector  1342  can be optically coupled to the second switch box  1304 , and the second optical fiber connector  1344  can be optically coupled to the first switch box  1302  without any re-mapping of the fiber ports. Similarly, the optical power supply fiber ports in the third and fourth optical fiber connectors  1346 ,  1348  are designed to be independent of the optical power supplies, i.e., if the first optical fiber connector  1342  is optically coupled to the second switch box  1304 , the third optical fiber connector  1346  can be optically coupled to the second optical power supply  1330 . If the second optical fiber connector  1344  is optically coupled to the first switch box  1302 , the fourth optical fiber connector  1348  can be optically coupled to the first optical power supply  1322 . 
     The optical cable assembly  1340  includes a first optical fiber guide module  1350  and a second optical fiber guide module  1352 . The optical fiber guide module depending on context is also referred to as an optical fiber coupler or splitter because the optical fiber guide module combines multiple bundles of fibers into one bundle of fibers, or separates one bundle of fibers into multiple bundles of fibers. The first optical fiber guide module  1350  includes a first port  1354 , a second port  1356 , and a third port  1358 . The second optical fiber guide module  1352  includes a first port  1360 , a second port  1362 , and a third port  1364 . The fiber bundle  1318  extends from the first optical fiber connector  1342  to the second optical fiber connector  1344  through the first port  1354  and the second port  1356  of the first optical fiber guide module  1350  and the second port  1362  and the first port  1360  of the second optical fiber guide module  1352 . The optical fibers  1326  extend from the third optical fiber connector  1346  to the first optical fiber connector  1342  through the third port  1358  and the first port  1354  of the first optical fiber guide module  1350 . The optical fibers  1334  extend from the fourth optical fiber connector  1348  to the second optical fiber connector  1344  through the third port  1364  and the first port  1360  of the second optical fiber guide module  1352 . 
     A portion (or section) of the optical fibers  1318  and a portion of the optical fibers  1326  extend from the first port  1354  of the first optical fiber guide module  1350  to the first optical fiber connector  1342 . A portion of the optical fibers  1318  extend from the second port  1356  of the first optical fiber guide module  1350  to the second port  1362  of the second optical fiber guide module  1352 , with optional optical connectors (e.g.,  1320 ) along the paths of the optical fibers  1318 . A portion of the optical fibers  1326  extend from the third port  1358  of the first optical fiber connector  1350  to the third optical fiber connector  1346 . A portion of the optical fibers  1334  extend from the third port  1364  of the second optical fiber connector  1352  to the fourth optical fiber connector  1348 . 
     The first optical fiber guide module  1350  is designed to restrict bending of the optical fibers such that the bending radius of any optical fiber in the first optical fiber guide module  1350  is greater than the minimum bending radius specified by the optical fiber manufacturer to avoid excess optical light loss or damage to the optical fiber. For example, the minimum bend radii can be 2 cm, 1 cm, 5 mm, or 2.5 mm. Other bend radii are also possible. For example, the fibers  1318  and the fibers  1326  extend outward from the first port  1354  along a first direction, the fibers  1318  extend outward from the second port  1356  along a second direction, and the fibers  1326  extend outward from the third port  1358  along a third direction. A first angle is between the first and second directions, a second angle is between the first and third directions, and a third angle is between the second and third directions. The first optical fiber guide module  1350  can be designed to limit the bending of optical fibers so that each of the first, second, and third angles is in a range from, e.g., 30° to 180°. 
     For example, the portion of the optical fibers  1318  and the portion of the optical fibers  1326  between the first optical fiber connector  1342  and the first port  1354  of the first optical fiber guide module  1350  can be surrounded and protected by a first common sheath  1366 . The optical fibers  1318  between the second port  1356  of the first optical fiber guide module  1350  and the second port  1362  of the second optical fiber guide module  1352  can be surrounded and protected by a second common sheath  1368 . The portion of the optical fibers  1318  and the portion of the optical fibers  1334  between the second optical fiber connector  1344  and the first port  1360  of the second optical fiber guide module  1352  can be surrounded and protected by a third common sheath  1369 . The optical fibers  1326  between the third optical fiber connector  1346  and the third port  1358  of the first optical fiber guide module  1350  can be surrounded and protected by a fourth common sheath  1367 . The optical fibers  1334  between the fourth optical fiber connector  1348  and the third port  1364  of the second optical fiber guide module  1352  can be surrounded and protected by a fifth common sheath  1370 . Each of the common sheaths can be laterally flexible and/or laterally stretchable, as described in, e.g., U.S. patent application Ser. No. 16/822,103. 
     In some implementations, the optical cable assembly  1340  includes cable segments, in which each cable segment includes optical fibers laterally encased by a cable sheath (e.g.,  1366 ,  1367 ,  1368 ,  1369 ,  1370 ). Each cable segment is constructed to permit relative lateral movement of at least some of the optical fibers within the cable sheath to change a cross-sectional shape of the cable segment. In some implementations, the plurality of optical fibers are permitted to move laterally relative to one another to become relatively spatially rearranged from a first cross-section of the cable segment to a second cross-section of the cable segment. The cable sheath includes a laterally stretchable material that permits a cross-sectional shape of the cable segment to change in response to movement of the optical fibers within the cable sheath. 
     One or more optical cable assemblies  1340  ( FIGS.  13 B,  13 C ) and other optical cable assemblies (e.g.,  1400  of  FIG.  15 B,  15 C,  1490    of  FIG.  17 B,  17 C ) described in this document can be used to optically connect switch boxes that are configured differently compared to the switch boxes  1302 ,  1304  shown in  FIG.  13 A , in which the switch boxes receive optical power supply light from one or more external optical power supplies. For example, in some implementations, the optical cable assembly  1340  can be attached to a fiber-optic array connector mounted on the outside of the front panel of an optical switch, and another fiber-optic cable then connects the inside of the fiber connector to a co-packaged optical module that is mounted on a circuit board positioned inside the housing of the switch box. The co-packaged optical module (which includes, e.g., a photonic integrated circuit, optical-to-electrical converters, such as photodetectors, and electrical-to-optical converters, such as laser diodes) can be co-packaged with a switch ASIC and mounted on a circuit board that can be vertically or horizontally oriented. For example, in some implementations, the front panel is mounted on hinges and a vertical ASIC mount is recessed behind it. The optical cable assembly  1340  provides optical paths for communication between the switch boxes, and optical paths for transmitting power supply light from one or more external optical power supplies to the switch boxes. The switch boxes can have any of a variety of configurations regarding how the power supply light and the data and/or control signals from the optical fiber connectors are transmitted to or received from the photonic integrated circuits, and how the signals are transmitted between the photonic integrated circuits and the data processors. 
     One or more optical cable assemblies  1340  and other optical cable assemblies (e.g.,  1400  of  FIG.  15 B,  15 C,  1490    of  FIG.  17 B,  17 C ) described in this document can be used to optically connect computing devices other than switch boxes. For example, the computing devices can be server computers that provide a variety of services, such as cloud computing, database processing, audio/video hosting and streaming, electronic mail, data storage, web hosting, social network, supercomputing, scientific research computing, healthcare data processing, financial transaction processing, logistics management, weather forecast, or simulation, to list a few examples. The optical power light required by the optoelectronic modules of the computing devices can be provided using one or more external optical power supplies. For example, in some implementations, one or more external optical power supplies that are centrally managed can be configured to provide the optical power supply light for hundreds or thousands of server computers in a data center, and the one or more optical power supplies and the server computers can be optically connected using the optical cable assemblies (e.g.,  1340 ,  1400 ,  1490 ) described in this document and variations of the optical cable assemblies using the principles described in this document. 
       FIG.  14    is a system functional block diagram of an example of an optical communication system  1380  that includes a first communication transponder  1282  and a second communication transponder  1284 , similar to those in  FIG.  12   . The first communication transponder  1282  sends optical signals to, and receives optical signals from, the second communication transponder  1284  through a first optical communication link  1290 . The optical communication system  1380  can be expanded to include additional communication transponders. 
     An external photon supply  1382  provides optical power supply light to the first communication transponder  1282  through a first optical power supply link  1384 , and provides optical power supply light to the second communication transponder  1284  through a second optical power supply link  1386 . In one example, the external photon supply  1282  provides continuous wave light to the first communication transponder  1282  and to the second communication transponder  1284 . In one example, the continuous wave light can be at the same optical wavelength. In another example, the continuous wave light can be at different optical wavelengths. In yet another example, the external photon supply  1282  provides a first sequence of optical frame templates to the first communication transponder  1282 , and provides a second sequence of optical frame templates to the second communication transponder  1284 . Each of the optical frame templates can include a respective frame header and a respective frame body, and the frame body includes a respective optical pulse train. The first communication transponder  1282  receives the first sequence of optical frame templates from the external photon supply  1382 , loads data into the respective frame bodies to convert the first sequence of optical frame templates into a first sequence of loaded optical frames that are transmitted through the first optical communication link  1290  to the second communication transponder  1284 . Similarly, the second communication transponder  1284  receives the second sequence of optical frame templates from the external photon supply  1382 , loads data into the respective frame bodies to convert the second sequence of optical frame templates into a second sequence of loaded optical frames that are transmitted through the first optical communication link  1290  to the first communication transponder  1282 . 
       FIG.  15 A  is a diagram of an example of an optical communication system  1390  that includes a first switch box  1302  and a second switch box  1304 , similar to those in  FIG.  13 A . The first switch box  1302  includes a vertical ASIC mount grid structure  1310 , and a co-packaged optical module  1312  is attached to a receptor of the grid structure  1310 . The second switch box  1304  includes a vertical ASIC mount grid structure  1314 , and a co-packaged optical module  1316  is attached to a receptor of the grid structure  1314 . The first co-packaged optical module  1312  communicates with the second co-packaged optical module  1316  through an optical fiber bundle  1318  that includes multiple optical fibers. 
     As discussed above in connection with  FIGS.  13 A to  13 E , the first and second switch boxes  1302 ,  1304  can have other configurations. For example, horizontally mounted ASICs can be used. A fiber-optic array connector attached to a front panel can be used to optically connect the optical cable assembly  1340  to another fiber-optic cable that connects to a co-packaged optical module mounted on a circuit board inside the switch box. The front panel can be mounted on hinges and a vertical ASIC mount can be recessed behind it. The switch boxes can be replaced by other types of server computers. 
     In an example embodiment, the first switch box  1302  includes an external optical power supply  1322  that provides optical power supply light to both the co-packaged optical module  1312  in the first switch box  1302  and the co-packaged optical module  1316  in the second switch box  1304 . In another example embodiment, the optical power supply can be located outside the switch box  1302  (cf.  1330 ,  FIG.  13 A ). The optical power supply  1322  provides the optical power supply light through an optical connector array  1324 . Optical fibers  1392  are optically coupled to an optical connector  1396  and the co-packaged optical module  1312 . The optical power supply  1322  sends optical power supply light through the optical connector  1396  and the optical fibers  1392  to the co-packaged optical module  1312  in the first switch box  1302 . Optical fibers  1394  are optically coupled to the optical connector  1396  and the co-packaged optical module  1316 . The optical power supply  1322  sends optical power supply light through the optical connector  1396  and the optical fibers  1394  to the co-packaged optical module  1316  in the second switch box  1304 . 
       FIG.  15 B  shows an example of an optical cable assembly  1400  that can be used to enable the first co-packaged optical module  1312  to receive optical power supply light from the optical power supply  1322 , enable the second co-packaged optical module  1316  to receive optical power supply light from the optical power supply  1322 , and enable the first co-packaged optical module  1312  to communicate with the second co-packaged optical module  1316 .  FIG.  15 C  is an enlarged diagram of the optical cable assembly  1400  without some of the reference numbers to enhance clarity of illustration. 
     The optical cable assembly  1400  includes a first optical fiber connector  1402 , a second optical fiber connector  1404 , and a third optical fiber connector  1406 . The first optical fiber connector  1402  is similar to the first optical fiber connector  1342  of  FIGS.  13 B,  13 C,  13 D , and is designed and configured to be optically coupled to the first co-packaged optical module  1312 . The second optical fiber connector  1404  is similar to the second optical fiber connector  1344  of  FIGS.  13 B,  13 C,  13 E , and is designed and configured to be optically coupled to the second co-packaged optical module  1316 . The third optical connector  1406  is designed and configured to be optically coupled to the power supply  1322 . The third optical connector  1406  includes first optical power supply fiber ports (e.g.,  1770 ,  FIG.  15 D ) and second optical power supply fiber ports (e.g.,  1772 ). The power supply  1322  outputs optical power supply light through the first optical power supply fiber ports to the optical fibers  1392 , and outputs optical power supply light through the second optical power supply fiber ports to the optical fibers  1394 . The first, second, and third optical fiber connectors  1402 ,  1404 ,  1406  can comply with an industry standard that defines the specifications for optical fiber interconnection cables that transmit data and control signals, and optical power supply light. 
       FIG.  15 D  shows an enlarged upper portion of the diagram of  FIG.  15 B , with the addition of an example of a mapping of fiber ports  1774  of the first optical fiber connector  1402  and a mapping of fiber ports  1776  of the third optical fiber connector  1406 . The mapping of fiber ports  1774  shows the positions of the transmitter fiber ports (e.g.,  1778 ), receiver fiber ports (e.g.,  1780 ), and power supply fiber ports (e.g.,  1782 ) of the first optical fiber connector  1402  when viewed in the direction  1784  into the first optical fiber connector  1402 . The mapping of fiber ports  1776  shows the positions of the power supply fiber ports (e.g.,  1770 ,  1772 ) of the third optical fiber connector  1406  when viewed in the direction  1786  into the third optical fiber connector  1406 . In this example, the third optical fiber connector  1406  includes 8 optical power supply fiber ports. 
     In some examples, optical connector array  1324  of the optical power supply  1322  can include a first type of optical connectors that accept optical fiber connectors having 4 optical power supply fiber ports, as in the example of  FIG.  13 D , and a second type of optical connectors that accept optical fiber connectors having 8 optical power supply fiber ports, as in the example of  FIG.  15 D . In some examples, if the optical connector array  1324  of the optical power supply  1322  only accepts optical fiber connectors having 4 optical power supply fiber ports, then a converter cable can be used to convert the third optical fiber connector  1406  of  FIG.  15 D  to two optical fiber connectors, each having 4 optical power supply fiber ports, that is compatible with the optical connector array  1324 . 
       FIG.  15 E  shows an enlarged lower portion of the diagram of  FIG.  15 B , with the addition of an example of a mapping of fiber ports  1790  of the second optical fiber connector  1404 . The mapping of fiber ports  1790  shows the positions of the transmitter fiber ports (e.g.,  1792 ), receiver fiber ports (e.g.,  1794 ), and power supply fiber ports (e.g.,  1796 ) of the second optical fiber connector  1404  when viewed in the direction  1798  into the second optical fiber connector  1404 . 
     The port mappings of the optical fiber connectors shown in  FIGS.  13 D,  13 E,  15 D, and  15 E  are merely examples. Each optical fiber connector can include a greater number or a smaller number of transmitter fiber ports, a greater number or a smaller number of receiver fiber ports, and a greater number or a smaller number of optical power supply fiber ports, as compared to those shown in  FIGS.  13 D,  13 E,  15 D, and  15 E . The arrangement of the relative positions of the transmitter, receiver, and optical power supply fiber ports can also be different from those shown in  FIGS.  13 D,  13 E,  15 D, and  15 E . 
     The optical cable assembly  1400  includes an optical fiber guide module  1408 , which includes a first port  1410 , a second port  1412 , and a third port  1414 . The optical fiber guide module  1408  depending on context is also referred as an optical fiber coupler (for combining multiple bundles of optical fibers into one bundle of optical fiber) or an optical fiber splitter (for separating a bundle of optical fibers into multiple bundles of optical fibers). The fiber bundle  1318  extends from the first optical fiber connector  1402  to the second optical fiber connector  1404  through the first port  1410  and the second port  1412  of the optical fiber guide module  1408 . The optical fibers  1392  extend from the third optical fiber connector  1406  to the first optical fiber connector  1402  through the third port  1414  and the first port  1410  of the optical fiber guide module  1408 . The optical fibers  1394  extend from the third optical fiber connector  1406  to the second optical fiber connector  1404  through the third port  1414  and the second port  1412  of the optical fiber guide module  1408 . 
     A portion of the optical fibers  1318  and a portion of the optical fibers  1392  extend from the first port  1410  of the optical fiber guide module  1408  to the first optical fiber connector  1402 . A portion of the optical fibers  1318  and a portion of the optical fibers  1394  extend from the second port  1412  of the optical fiber guide module  1408  to the second optical fiber connector  1404 . A portion of the optical fibers  1394  extend from the third port  1414  of the optical fiber connector  1408  to the third optical fiber connector  1406 . 
     The optical fiber guide module  1408  is designed to restrict bending of the optical fibers such that the radius of curvature of any optical fiber in the optical fiber guide module  1408  is greater than the minimum radius of curvature specified by the optical fiber manufacturer to avoid excess optical light loss or damage to the optical fiber. For example, the optical fibers  1318  and the optical fibers  1392  extend outward from the first port  1410  along a first direction, the optical fibers  1318  and the optical fibers  1394  extend outward from the second port  1412  along a second direction, and the optical fibers  1392  and the optical fibers  1394  extend outward from the third port  1414  along a third direction. A first angle is between the first and second directions, a second angle is between the first and third directions, and a third angle is between the second and third directions. The optical fiber guide module  1408  is designed to limit the bending of optical fibers so that each of the first, second, and third angles is in a range from, e.g., 30° to 180°. 
     For example, the portion of the optical fibers  1318  and the portion of the optical fibers  1392  between the first optical fiber connector  1402  and the first port  1410  of the optical fiber guide module  1408  can be surrounded and protected by a first common sheath  1416 . The optical fibers  1318  and the optical fibers  1394  between the second optical fiber connector  1404  and the second port  1412  of the optical fiber guide module  1408  can be surrounded and protected by a second common sheath  1418 . The optical fibers  1392  and the optical fibers  1394  between the third optical fiber connector  1406  and the third port  1414  of the optical fiber guide module  1408  can be surrounded and protected by a third common sheath  1420 . Each of the common sheaths can be laterally flexible and/or laterally stretchable. 
     In some implementations, the optical cable assembly  1400  includes cable segments, in which each cable segment includes optical fibers laterally encased by a cable sheath (e.g.,  1416 ,  1418 ,  1420 ). Each cable segment is constructed to permit relative lateral movement of at least some of the optical fibers within the cable sheath to change a cross-sectional shape of the cable segment. In some implementations, the optical fibers are permitted to move laterally relative to one another to become relatively spatially rearranged from a first cross-section of the cable segment to a second cross-section of the cable segment. The cable sheath includes a laterally stretchable material that permits a cross-sectional shape of the cable segment to change in response to movement of the optical fibers within the cable sheath. 
       FIG.  16    is a system functional block diagram of an example of an optical communication system  1430  that includes a first communication transponder  1432 , a second communication transponder  1434 , a third communication transponder  1436 , and a fourth communication transponder  1438 . Each of the communication transponders  1432 ,  1434 ,  1436 ,  1438  can be similar to the communication transponders  1282 ,  1284  of  FIG.  12   . The first communication transponder  1432  communicates with the second communication transponder  1434  through a first optical link  1440 . The first communication transponder  1432  communicates with the third communication transponder  1436  through a second optical link  1442 . The first communication transponder  1432  communicates with the fourth communication transponder  1438  through a third optical link  1444 . 
     An external photon supply  1446  provides optical power supply light to the first communication transponder  1432  through a first optical power supply link  1448 , provides optical power supply light to the second communication transponder  1434  through a second optical power supply link  1450 , provides optical power supply light to the third communication transponder  1436  through a third optical power supply link  1452 , and provides optical power supply light to the fourth communication transponder  1438  through a fourth optical power supply link  1454 . 
       FIG.  17 A  is a diagram of an example of an optical communication system  1460  that includes a first switch box  1462  and a remote server array  1470  that includes a second switch box  1464 , a third switch box  1466 , and a fourth switch box  1468 . The first switch box  1462  includes a vertical ASIC mount grid structure  1310 , and a co-packaged optical module  1312  is attached to a receptor of the grid structure  1310 . The second switch box  1464  includes a co-packaged optical module  1472 , the third switch box  1466  includes a co-packaged optical module  1474 , and the third switch box  1468  includes a co-packaged optical module  1476 . The first co-packaged optical module  1312  communicates with the co-packaged optical modules  1472 ,  1474 ,  1476  through an optical fiber bundle  1478  that later branches out to the co-packaged optical modules  1472 ,  1474 ,  1476 . 
     In one example embodiment, the first switch box  1462  includes an external optical power supply  1322  that provides optical power supply light through an optical connector array  1324 . In another example embodiment, the optical power supply can be located external to switch box  1462  (cf.  1330 ,  FIG.  80 A ). Optical fibers  1480  are optically coupled to an optical connector  1482 , and the optical power supply  1322  sends optical power supply light through the optical connector  1482  and the optical fibers  1480  to the co-packaged optical modules  1312 ,  1472 ,  1474 ,  1476 . 
       FIG.  17 B  shows an example of an optical cable assembly  1490  that can be used to enable the optical power supply  1322  to provide optical power supply light to the co-packaged optical modules  1312 ,  1472 ,  1474 ,  1476 , and enable the co-packaged optical module  1312  to communicate with the co-packaged optical modules  1472 ,  1474 ,  1476 . The optical cable assembly  1490  includes a first optical fiber connector  1492 , a second optical fiber connector  1494 , a third optical fiber connector  1496 , a fourth optical fiber connector  1498 , and a fifth optical fiber connector  1500 . The first optical fiber connector  1492  is configured to be optically coupled to the co-packaged optical module  1312 . The second optical fiber connector  1494  is configured to be optically coupled to the co-packaged optical module  1472 . The third optical fiber connector  1496  is configured to be optically coupled to the co-packaged optical module  1474 . The fourth optical fiber connector  1498  is configured to be optically coupled to the co-packaged optical module  1476 . The fifth optical fiber connector  1500  is configured to be optically coupled to the optical power supply  1322 .  FIG.  17 C  is an enlarged diagram of the optical cable assembly  1490 . 
     In some implementations, the optical cable assembly  1490  includes cable segments, in which each cable segment includes optical fibers laterally encased by a cable sheath. Each cable segment is constructed to permit relative lateral movement of at least some of the optical fibers within the cable sheath to change a cross-sectional shape of the cable segment. In some implementations, the optical fibers are permitted to move laterally relative to one another to become relatively spatially rearranged from a first cross-section of the cable segment to a second cross-section of the cable segment. The cable sheath includes a laterally stretchable material that permits a cross-sectional shape of the cable segment to change in response to movement of the optical fibers within the cable sheath. 
     Optical fibers that are optically coupled to the optical fiber connectors  1500  and  1492  enable the optical power supply  1322  to provide the optical power supply light to the co-packaged optical module  1312 . Optical fibers that are optically coupled to the optical fiber connectors  1500  and  1494  enable the optical power supply  1322  to provide the optical power supply light to the co-packaged optical module  1472 . Optical fibers that are optically coupled to the optical fiber connectors  1500  and  1496  enable the optical power supply  1322  to provide the optical power supply light to the co-packaged optical module  1474 . Optical fibers that are optically coupled to the optical fiber connectors  1500  and  1498  enable the optical power supply  1322  to provide the optical power supply light to the co-packaged optical module  1476 . 
     Optical fiber guide modules  1502 ,  1504 ,  1506 , and common sheaths are provided to organize the optical fibers so that they can be easily deployed and managed. The optical fiber guide module  1502  is similar to the optical fiber guide module  1408  of  FIG.  15 B . The optical fiber guide modules  1504 ,  1506  are similar to the optical fiber guide module  1350  of  FIG.  13 B . The common sheaths gather the optical fibers in a bundle so that they can be more easily handled, and the optical fiber guide modules guide the optical fibers so that they extend in various directions toward the devices that need to be optically coupled by the optical cable assembly  1490 . The optical fiber guide modules restrict bending of the optical fibers such that the bending radiuses are greater than minimum values specified by the optical fiber manufacturers to prevent excess optical light loss or damage to the optical fibers. 
     The optical fibers  1480  that extend from the include optical fibers that extend from the optical  1482  are surrounded and protected by a common sheath  1508 . At the optical fiber guide module  1502 , the optical fibers  1480  separate into a first group of optical fibers  1510  and a second group of optical fibers  1512 . The first group of optical fibers  1510  extend to the first optical fiber connector  1492 . The second group of optical fibers  1512  extend toward the optical fiber guide modules  1504 ,  1506 , which together function as a 1:3 splitter that separates the optical fibers  1512  into a third group of optical fibers  1514 , a fourth group of optical fibers  1516 , and a fifth group of optical fibers  1518 . The group of optical fibers  1514  extend to the optical fiber connector  1494 , the group of optical fibers  1516  extend to the optical fiber connector  1496 , and the group of optical fibers  1518  extend to the optical fiber connector  1498 . In some examples, instead of using two 1:2 split optical fiber guide modules  1504 ,  1506 , it is also possible to use a 1:3 split optical fiber guide module that has four ports, e.g., one input port and three output ports. In general, separating the optical fibers in a 1:N split (N being an integer greater than 2) can occur in one step or multiple steps. 
       FIG.  18    is a diagram of an example of a data processing system (e.g., data center)  1520  that includes N servers  1522  spread across K racks  1524 . In this example, there are 6 racks  1524 , and each rack  1524  includes 15 servers  1522 . Each server  1522  directly communicates with a tier 1 switch  1526 . The left portion of the figure shows an enlarged view of a portion  1528  of the system  1520 . A server  1522   a  directly communicates with a tier 1 switch  1526   a  through a communication link  1530   a . Similarly, servers  1522   b ,  1522   c  directly communicate with the tier 1 switch  1526   a  through communication links  1530   b ,  1530   c , respectively. The server  1522   a  directly communicates with a tier 1 switch  1526   b  through a communication link  1532   a . Similarly, servers  1522   b ,  1522   c  directly communicate with the tier 1 switch  1526   b  through communication links  1532   b ,  1532   c , respectively. Each communication link can include a pair of optical fibers to allow bi-directional communication. The system  1520  bypasses the conventional top-of-rack switch and can have the advantage of higher data throughput. The system  1520  includes a point-to-point connection between every server  1522  and every tier 1 switch  1526 . In this example, there are 4 tier 1 switches  1526 , and 4 fiber pairs are used per server  1522  for communicating with the tier 1 switches  1526 . Each tier-1 switch  1526  is connected to N servers, so there are N fiber pairs connected to each tier-1 switch  1526 . 
     Referring to  FIG.  19   , in some implementations, a data processing system (e.g., data center)  1540  includes tier-1 switches  1526  that are co-located in a rack  1540  separate from the N servers  1522  that are spread across K racks  1524 . Each server  1522  has a direct link to each of the tier-1 switches  1526 . In some implementations, there is one fiber cable  1542  (or a small number &lt;&lt;N/K of fiber cables) from the tier-1 switch rack  1540  to each of the K server racks  1524 . 
       FIG.  20 A  is a diagram of an example of a data processing system  1550  that includes N=1024 servers  1552  spread across K=32 racks  1554 , in which each rack  1554  includes N/K=1024/32=32 servers  1552 . There are 4 tier-1 switches  1556  and an optical power supply  1558  that is co-located in a rack  1560 . 
     Optical fibers connect the servers  1552  to the tier-1 switches  1556  and the optical power supply  1558 . In this example, a bundle of 9 optical fibers is optically coupled to a co-packaged optical module  1564  of a server  1552 , in which 1 optical fiber provides the optical power supply light, and 4 pairs of (a total of 8) optical fibers provide 4 bi-directional communication channels, each channel having a 100 Gbps bandwidth, for a total of 4×100 Gbps bandwidth in each direction. Because there are 32 servers  1552  in each rack  1554 , there are a total of 256+32=288 optical fibers that extend from each rack  1554  of servers  1552 , in which 32 optical fibers provide the optical power supply light, and 256 optical fibers provide 128 bi-directional communication channels, each channel having a 100 Gbps bandwidth. 
     For example, at the server rack side, optical fibers  1566  (that are connected to the servers  1552  of a rack  1554 ) terminate at a server rack connector  1568 . At the switch rack side, optical fibers  1578  (that are connected to the switch boxes  1556  and the optical power supply  1558 ) terminate at a switch rack connector  1576 . An optical fiber extension cable  1572  is optically coupled to the server rack side and the switch rack side. The optical fiber extension cable  1572  includes 256+32=288 optical fibers. The optical fiber extension cable  1572  includes a first optical fiber connector  1570  and a second optical fiber connector  1574 . The first optical fiber connector  1570  is connected to the server rack connector  1568 , and the second optical fiber connector  1574  is connected to the switch rack connector  1576 . At the switch rack side, the optical fibers  1578  include 288 optical fibers, of which 32 optical fibers  1580  are optically coupled to the optical power supply  1558 . The 256 optical fibers that carry 128 bi-directional communication channels (each channel having a 100 Gbps bandwidth in each direction) are separated into four groups of 64 optical fibers, in which each group of 64 optical fibers is optically coupled to a co-packaged optical module  1582  in one of the switch boxes  1556 . The co-packaged optical module  1582  is configured to have a bandwidth of 32×100 Gbps=3.2 Tbps in each direction (input and output). Each switch box  1556  is connected to each server  1552  of the rack  1554  through a pair of optical fibers that carry a bandwidth of 100 Gbps in each direction. 
     The optical power supply  1558  provides optical power supply light to co-packaged optical modules  1582  at the switch boxes  1556 . In this example, the optical power supply  1558  provides optical power supply light through 4 optical fibers to each co-packaged optical module  1582 , so that a total of 16 optical fibers are used to provide the optical power supply light to the 4 switch boxes  1556 . A bundle of optical fibers  1584  is optically coupled to the co-packaged optical module  1582  of the switch box  1556 . The bundle of optical fibers  1584  includes 64+16=80 fibers. In some examples, the optical power supply  1558  can provide additional optical power supply light to the co-packaged optical module  1582  using additional optical fibers. For example, the optical power supply  1558  can provide optical power supply light to the co-packaged optical module  1582  using 32 optical fibers with built-in redundancy. 
     Referring to  FIG.  20 B , the data processing system  1550  includes an optical fiber guide module  1590  that helps organize the optical fibers so that they are directed to the appropriate directions. The optical fiber guide module  1590  also restricts bending of the optical fibers to be within the specified limits to prevent excess optical light loss or damage to the optical fibers. The optical fiber guide module  1590  includes a first port  1592 , a second port  1594 , and a third port  1596 . The optical fibers that extend outward from the first port  1592  are optically coupled to the switch rack connector  1576 . The optical fibers that extend outward from the second port  1594  are optically coupled to the switch boxes. The optical fibers that extend outward from the third port  1596  are optically coupled to the optical power supply  1558 . 
     In some implementations, one or more of fiber-optic cables in  FIGS.  20 A and  20 B  each includes a cable segment that has a plurality of optical fibers laterally encased by a cable sheath. The cable segment is constructed to permit relative lateral movement of at least some of the optical fibers within the cable sheath to change a cross-sectional shape of the cable segment. In some implementations, the optical fibers are permitted to move laterally relative to one another to become relatively spatially rearranged from a first cross-section of the cable segment to a second cross-section of the cable segment. The cable sheath includes a laterally stretchable material that permits a cross-sectional shape of the cable segment to change in response to movement of the optical fibers within the cable sheath. 
       FIG.  21    is a diagram of an example of the connector port mapping for an optical fiber interconnection cable  1600 , which includes a first optical fiber connector  1602 , a second optical fiber connector  1604 , optical fibers  1606  that transmit data and/or control signals between the first and second optical fiber connectors  1602 ,  1604 , and optical fibers  1608  that transmit optical power supply light. Each optical fiber terminates at an optical fiber port  1610 , which can include, e.g., lenses for focusing light entering or exiting the optical fiber port  1610 . The first and second optical fiber connectors  1602 ,  1604  can be, e.g., the optical fiber connectors  1342  and  1344  of  FIGS.  13 B,  13 C , the optical fiber connectors  1402  and  1404  of  FIGS.  15 B,  15 C , or the optical fiber connectors  1570  and  1574  of  FIG.  20 A . The principles for designing the optical fiber interconnection cable  1600  can be used to design the optical cable assembly  1340  of  FIGS.  13 B,  13 C , the optical cable assembly  1400  of  FIGS.  15 B,  15 C , and the optical cable assembly  1490  of  FIGS.  17 B,  17 C . 
     In some implementations, a segment of the optical fiber interconnection cable  1600  includes the optical fibers  1606  laterally encased by a cable sheath. The cable segment is constructed to permit relative lateral movement of at least some of the optical fibers within the cable sheath to change a cross-sectional shape of the cable segment. In some implementations, the optical fibers  1606  are permitted to move laterally relative to one another to become relatively spatially rearranged from a first cross-section of the cable segment to a second cross-section of the cable segment. The cable sheath includes a laterally stretchable material that permits a cross-sectional shape of the cable segment to change in response to movement of the optical fibers within the cable sheath. 
     In the example of  FIG.  21   , each optical fiber connector  1602  or  1604  includes 3 rows of optical fiber ports, each row including 12 optical fiber ports. Each optical fiber connector  1602  or  1604  includes 4 power supply fiber ports that are connected to optical fibers  1608  that are optically coupled to one or more optical power supplies. Each optical fiber connector  1602  or  1604  includes 32 fiber ports (some of which are transmitter fiber ports, and some of which are receiver fiber ports) that are connected to the optical fibers  1606  for data transmission and reception. 
     In some implementations, the mapping of the fiber ports of the optical fiber connectors  1602 ,  1604  are designed such that the interconnection cable  1600  can have the most universal use, in which each fiber port of the optical fiber connector  1602  is mapped to a corresponding fiber port of the optical fiber connector  1604  with a 1-to-1 mapping and without transponder-specific port mapping that would require fibers  1606  to cross over. This means that for an optical transponder that has an optical fiber connector compatible with the interconnection cable  1600 , the optical transponder can be connected to either the optical fiber connector  1602  or the optical fiber connector  1604 . The mapping of the fiber ports is designed such that each transmitter port of the optical fiber connector  1602  is mapped to a corresponding receiver port of the optical fiber connector  1604 , and each receiver port of the optical fiber connector  1602  is mapped to a corresponding transmitter port of the optical fiber connector  1604 . 
       FIG.  22    is a diagram showing an example of the fiber port mapping for an optical fiber interconnection cable  1660  that includes a pair of optical fiber connectors, i.e., a first optical fiber connector  1662  and a second optical fiber connector  1664 . The optical fiber connectors  1662  and  1664  are designed such that either the first optical fiber connector  1662  or the second optical fiber connector  1664  can be connected to a given communication transponder that is compatible with the optical fiber interconnection cable  1660 . The diagram shows the fiber port mapping when viewed from the outer edge of the optical fiber connector into the optical fiber connector (i.e., toward the optical fibers in the interconnection cable  1660 ). 
     The first optical fiber connector  1662  includes transmitter fiber ports (e.g.,  1614   a ,  1616   a ), receiver fiber ports (e.g.,  1618   a ,  1620   a ), and optical power supply fiber ports (e.g.,  1622   a ,  1624   a ). The second optical fiber connector  1664  includes transmitter fiber ports (e.g.,  1614   b ,  1616   b ), receiver fiber ports (e.g.,  1618   b ,  1620   b ), and optical power supply fiber ports (e.g.,  1622   b ,  1624   b ). For example, assume that the first optical fiber connector  1662  is connected to a first optical transponder, and the second optical fiber connector  1664  is connected to a second optical transponder. The first optical transponder transmits first data and/or control signals through the transmitter ports (e.g.,  1614   a ,  1616   a ) of the first optical fiber connector  1662 , and the second optical transponder receives the first data and/or control signals from the corresponding receiver fiber ports (e.g.,  1618   b ,  1620   b ) of the second optical fiber connector  1664 . The transmitter ports  1614   a ,  1616   a  are optically coupled to the corresponding receiver fiber ports  1618   b ,  1620   b  through optical fibers  1628 ,  1630 , respectively. The second optical transponder transmits second data and/or control signals through the transmitter ports (e.g.,  1614   b ,  1616   b ) of the second optical fiber connector  1664 , and the first optical transponder receives the second data and/or control signals from the corresponding receiver fiber ports ( 1618   a ,  1620   a ) of the first optical fiber connector  1662 . The transmitter port  1616   b  is optically coupled to the corresponding receiver fiber port  1620   a  through an optical fiber  1632 . 
     A first optical power supply transmits optical power supply light to the first optical transponder through the power supply fiber ports of the first optical fiber connector  1662 . A second optical power supply transmits optical power supply light to the second optical transponder through the power supply fiber ports of the second optical fiber connector  1664 . The first and second power supplies can be different (such as the example of  FIG.  13 B ) or the same (such as the example of  FIG.  15 B ). 
     In the following description, when referring to the rows and columns of fiber ports of the optical fiber connector, the uppermost row is referred to as the 1 st  row, the second uppermost row is referred to as the 2 nd  row, and so forth. The leftmost column is referred to as the 1 st  column, the second leftmost column is referred to as the 2 nd  column, and so forth. 
     For an optical fiber interconnection cable having a pair of optical fiber connectors (i.e., a first optical fiber connector and a second optical fiber connector) to be universal, i.e., either one of the pair of optical fiber connectors can be connected to a given optical transponder, the arrangement of the transmitter fiber ports, the receiver fiber ports, and the power supply fiber ports in the optical fiber connectors have a number of properties. These properties are referred to as the “universal optical fiber interconnection cable port mapping properties.” The term “mapping” here refers to the arrangement of the transmitter fiber ports, the receiver fiber ports, and the power supply fiber ports at particular locations within the optical fiber connector. The first property is that the mapping of the transmitter, receiver, and power supply fiber ports in the first optical fiber connector is the same as the mapping of the transmitter, receiver, and power supply fiber ports in the second optical fiber connector (as in the example of  FIG.  22   ). 
     In the example of  FIG.  22   , the individual optical fibers connecting the transmitter, receiver, and power supply fiber ports in the first optical fiber connector to the transmitter, receiver, and power supply fiber ports in the second optical fiber connector are parallel to one another. 
     In some implementations, each of the optical fiber connectors includes a unique marker or mechanical structure, e.g., a pin, that is configured to be at the same spot on the co-packaged optical module, similar to the use of a “dot” to denote “pin  1 ” on electronic modules. In some examples, such as those shown in  FIGS.  22  and  23   , the larger distance from the bottom row (the third row in the examples of  FIGS.  22  and  23   ) to the connector edge can be used as a “marker” to guide the user to attach the optical fiber connector to the co-packaged optical module connector in a consistent manner. 
     The mapping of the fiber ports of the optical fiber connectors of a “universal optical fiber interconnection cable” has a second property: When mirroring the port map of an optical fiber connector and replacing each transmitter port with a receiver port as well as replacing each receiver port with a transmitter port in the mirror image, the original port mapping is recovered. The mirror image can be generated with respect to a reflection axis at either connector edge, and the reflection axis can be parallel to the row direction or the column direction. The power supply fiber ports of the first optical fiber connector are mirror images of the power supply fiber ports of the second optical fiber connector. 
     The transmitter fiber ports of the first optical fiber connector and the receiver fiber ports of the second optical fiber connector are pairwise mirror images of each other, i.e., each transmitter fiber port of the first optical fiber connector is mirrored to a receiver fiber port of the second optical fiber connector. The receiver fiber ports of the first optical fiber connector and the transmitter fiber ports of the second optical fiber connector are pairwise mirror images of each other, i.e., each receiver fiber port of the first optical fiber connector is mirrored to a transmitter fiber port of the second optical fiber connector. 
     Another way of looking at the second property is as follows: Each optical fiber connector is transmitter port-receiver port (TX-RX) pairwise symmetric and power supply port (PS) symmetric with respect to one of the main or center axes, which can be parallel to the row direction or the column direction. For example, if an optical fiber connector has an even number of columns, the optical fiber connector can be divided along a center axis parallel to the column direction into a left half portion and a right half portion. The power supply fiber ports are symmetric with respect to the main axis, i.e., if there is a power supply fiber port in the left half portion of the optical fiber connector, there will also be a power supply fiber port at the mirror location in the right half portion of the optical fiber connector. The transmitter fiber ports and the receiver fiber ports are pairwise symmetric with respect to the main axis, i.e., if there is a transmitter fiber port in the left half portion of the optical fiber connector, there will be a receiver fiber port at a mirror location in the right half portion of the optical fiber connector. Likewise, if there is a receiver fiber port in the left half portion of the optical fiber connector, there will be a transmitter fiber port at a mirror location in the right half portion of the optical fiber connector. 
     For example, if an optical fiber connector has an even number of rows, the optical fiber connector can be divided along a center axis parallel to the row direction into an upper half portion and a lower half portion. The power supply fiber ports are symmetric with respect to the main axis, i.e., if there is a power supply fiber port in the upper half portion of the optical fiber connector, there will also be a power supply fiber port at the mirror location in the lower half portion of the optical fiber connector. The transmitter fiber ports and the receiver fiber ports are pairwise symmetric with respect to the main axis, i.e., if there is a transmitter fiber port in the upper half portion of the optical fiber connector, there will be a receiver fiber port at a mirror location in the lower half portion of the optical fiber connector. Likewise, if there is a receiver fiber port in the upper half portion of the optical fiber connector, there will be a transmitter fiber port at a mirror location in the lower half portion of the optical fiber connector. 
     The mapping of the transmitter fiber ports, receiver fiber ports, and power supply fiber ports follow a symmetry requirement that can be summarized as follows: 
     (i) Mirror all ports on either one of the two connector edges. 
     (ii) Swap TX (transmitter) and RX (receiver) functionality on the mirror image. 
     (iii) Leave mirrored PS (power supply) ports as PS ports. 
     (iv) The resulting port map is the same as the original one. 
     Essentially, a viable port map is TX-RX pairwise symmetric and PS symmetric with respect to one of the main axes. 
     The properties of the mapping of the fiber ports of the optical fiber connectors can be mathematically expressed as follows:
         Port matrix M with entries PS=0, TX=+1 RX=−1;   Column-mirror operation  ;   Row-mirror operation  ;      A viable port map either satisfies − =M or − M=M.       

     In some implementations, if a universal optical fiber interconnection cable has a first optical fiber connector and a second optical fiber connector that are mirror images of each other after swapping the transmitter fiber ports to receiver fiber ports and swapping the receiver fiber ports to transmitter fiber ports in the mirror image, and the mirror image is generated with respect to a reflection axis parallel to the column direction, as in the example of  FIG.  22   , then each optical fiber connector should be TX-RX pairwise symmetric and PS symmetric with respect to a center axis parallel to the column direction. If a universal optical fiber interconnection cable has a first optical fiber connector and a second optical fiber connector that are mirror images of each other after swapping the transmitter and receiver fiber ports in the mirror image, and the mirror image is generated with respect to a reflection axis parallel to the row direction, as in the example of  FIG.  23   , then each optical fiber connector should be TX-RX pairwise symmetric and PS symmetric with respect to a center axis parallel to the row direction. 
     In some implementations, a universal optical fiber interconnection cable:
         a. Comprises n_trx strands of TX/RX fibers and n_p strands of power supply fibers, in which 0≤n_p≤n_trx.   b. The n_trx strands of TX/RX fibers are mapped 1:1 from a first optical fiber connector to the same port positions on a second optical fiber connector through the optical fiber cable, i.e. the optical fiber cable can be laid out in a straight manner without leading to any cross-over fiber strands.   c. Those connector ports that are not 1:1 connected by TX/RX fibers may be connected to power supply fibers via a break-out cable.       

     In some implementations, a universal optical module connector has the following properties:
         d. Starting from a connector port map PM 0 .   e. First mirror port map PM 0  either across the row dimension or across the column dimension.   f. Mirroring can be done either across a column axis or across a row axis.   g. Replace TX ports by RX ports and vice versa.   h. If at least one mirrored and replaced version of the port map again results in the starting port map PM 0 , the connector is called a universal optical module connector.       

     In  FIG.  22   , the arrangement of the transmitter, receiver, and power supply fiber ports in the first optical fiber connector  1662 , and the arrangement of the transmitter, receiver, and power supply fiber ports in the second optical fiber connector  1664  have the two properties described above. First property: When looking into the optical fiber connector (from the outer edge of the connector inward toward the optical fibers), the mapping of the transmitter, receiver, and power supply fiber ports in the first optical fiber connector  1662  is the same as the mapping of the transmitter, receiver, and power supply fiber ports in the optical fiber connector  1664 . Row  1 , column  1  of the optical fiber connector  1662  is a power supply fiber port ( 1622   a ), and row  1 , column  1  of the optical fiber connector  1664  is also a power supply fiber port ( 1622   b ). Row  1 , column  3  of the optical fiber connector  1662  is a transmitter fiber port ( 1614   a ), and row  1 , column  3  of the optical fiber connector  1664  is also a transmitter fiber port ( 1614   b ). Row  1 , column  10  of the optical fiber connector  1662  is a receiver fiber port ( 1618   a ), and row  1 , column  10  of the optical fiber connector  1664  is also a receiver fiber port ( 1618   b ), and so forth. 
     The optical fiber connectors  1662  and  1664  have the second universal optical fiber interconnection cable port mapping property described above. The port mapping of the optical fiber connector  1662  is a mirror image of the port mapping of the optical fiber connector  1664  after swapping each transmitter port to a receiver port and swapping each receiver port to a transmitter port in the mirror image. The mirror image is generated with respect to a reflection axis  1626  at the connector edge that is parallel to the column direction. The power supply fiber ports (e.g.,  1662   a ,  1624   a ) of the optical fiber connector  1662  are mirror images of the power supply fiber ports (e.g.,  1622   b ,  1624   b ) of the optical fiber connector  1664 . The transmitter fiber ports (e.g.,  1614   a ,  1616   a ) of the optical fiber connector  1662  and the receiver fiber ports (e.g.,  1618   b ,  1620   b ) of the optical fiber connector  1664  are pairwise mirror images of each other, i.e., each transmitter fiber port (e.g.,  1614   a ,  1616   a ) of the optical fiber connector  1662  is mirrored to a receiver fiber port (e.g.,  1618   b ,  1620   b ) of the optical fiber connector  1664 . The receiver fiber ports (e.g.,  1618   a ,  1620   a ) of the optical fiber connector  1662  and the transmitter fiber ports (e.g.,  1618   b ,  1620   b ) of the optical fiber connector  1664  are pairwise mirror images of each other, i.e., each receiver fiber port (e.g.,  1618   a ,  1620   a ) of the optical fiber connector  1662  is mirrored to a transmitter fiber port (e.g.,  1618   b ,  1620   b ) of the optical fiber connector  1664 . 
     For example, the power supply fiber port  1622   a  at row  1 , column  1  of the optical fiber connector  1662  is a mirror image of the power supply fiber port  1624   b  at row  1 , column  12  of the optical fiber connector  1664  with respect to the reflection axis  1626 . The power supply fiber port  1624   a  at row  1 , column  12  of the optical fiber connector  1662  is a mirror image of the power supply fiber port  1622   b  at row  1 , column  1  of the optical fiber connector  1664 . The transmitter fiber port  1614   a  at row  1 , column  3  of the optical fiber connector  1662  and the receiver fiber port  1618   b  at row  1 , column  10  of the optical fiber connector  1604  are pairwise mirror images of each other. The receiver fiber port  1618   a  at row  1 , column  10  of the optical fiber connector  1662  and the transmitter fiber port  1614   b  at row  1 , column  3  of the optical fiber connector  1664  are pairwise mirror images of each other. The transmitter fiber port  1616   a  at row  3 , column  3  of the optical fiber connector  1662  and the receiver fiber port  1620   b  at row  3 , column  10  of the optical fiber connector  1664  are pairwise mirror images of each other. The receiver fiber port  1620   a  at row  3 , column  10  of the optical fiber connector  1662  and the transmitter fiber port  1616   b  at row  3 , column  3  of the optical fiber connector  1664  are pairwise mirror images of each other. 
     In addition, and as an alternate view of the second property, each optical fiber connector  1662 ,  1664  is TX-RX pairwise symmetric and PS symmetric with respect to the center axis that is parallel to the column direction. Using the first optical fiber connector  1662  as an example, the power supply fiber ports (e.g.,  1622   a ,  1624   a ) are symmetric with respect to the center axis, i.e., if there is a power supply fiber port in the left half portion of the first optical fiber connector  1662 , there will also be a power supply fiber port at the mirror location in the right half portion of the first optical fiber connector  1662 . The transmitter fiber ports and the receiver fiber ports are pairwise symmetric with respect to the main axis, i.e., if there is a transmitter fiber port in the left half portion of the first optical fiber connector  1662 , there will be a receiver fiber port at a mirror location in the right half portion of the first optical fiber connector  1662 . Likewise, if there is a receiver fiber port in the left half portion of the optical fiber connector  1662 , there will be a transmitter fiber port at a mirror location in the right half portion of the optical fiber connector  1662 . 
     If the port mapping of the first optical fiber connector  1662  is represented by port matrix M with entries PS=0, TX=+1, RX=−1, then − =M, in which   represents the column-mirror operation, e.g., generating a mirror image with respect to the reflection axis  1626 . 
       FIG.  23    is a diagram showing another example of the fiber port mapping for an optical fiber interconnection cable  1670  that includes a pair of optical fiber connectors, i.e., a first optical fiber connector  1672  and a second optical fiber connector  1674 . In the diagram, the port mapping for the second optical fiber connector  1674  is the same as that of optical fiber connector  1672 . The optical fiber interconnection cable  1670  has the two universal optical fiber interconnection cable port mapping properties described above. 
     First property: The mapping of the transmitter, receiver, and power supply fiber ports in the first optical fiber connector  1672  is the same as the mapping of the transmitter, receiver, and power supply fiber ports in the second optical fiber connector  1674 . 
     Second property: The port mapping of the first optical fiber connector  1672  is a mirror image of the port mapping of the second optical fiber connector  1674  after swapping each transmitter port to a receiver port and swapping each receiver port to a transmitter port in the mirror image. The mirror image is generated with respect to a reflection axis  1640  at the connector edge parallel to the row direction. 
     Alternative view of the second property: Each of the first and second optical fiber connectors  1672 ,  1674  is TX-RX pairwise symmetric and PS symmetric with respect to the central axis that is parallel to the row direction. For example, the optical fiber connector  1672  can be divided in two halves along a central axis parallel to the row direction. The power supply fiber ports (e.g.,  1678 ,  1680 ) are symmetric with respect to the center axis. The transmitter fiber ports (e.g.,  1682 ,  1684 ) and the receiver fiber ports (e.g.,  1686 ,  1688 ) are pairwise symmetric with respect to the center axis, i.e., if there is a transmitter fiber port (e.g.,  1682  or  1684 ) in the upper half portion of the first optical fiber connector  1672 , then there will be a receiver fiber port (e.g.,  1686 ,  1688 ) at a mirror location in the lower half of the optical fiber connector  1672 . Likewise, if there is a receiver fiber port in the upper half portion of the optical fiber connector  1672 , then there is a transmitter fiber port at a mirror location in the lower half portion of the optical fiber connector  1672 . In the example of  FIG.  23   , the middle row  1690  should all be power supply fiber ports. 
     In general, if the port mapping of the first optical fiber connector is a mirror image of the port mapping of the second optical fiber connector after swapping the transmitter and receiver ports in the mirror image, the mirror image is generated with respect to a reflection axis at the connector edge parallel to the row direction (as in the example of  FIG.  90   ), and there is an odd number of rows in the port matrix, then the center row should all be power supply fiber ports. If the port mapping of the first optical fiber connector is a mirror image of the port mapping of the second optical fiber connector after swapping the transmitter and receiver ports in the mirror image, the mirror image is generated with respect to a reflection axis at the connector edge parallel to the column direction, and there is an odd number of columns in the port matrix, then the center column should all be power supply fiber ports. 
       FIG.  24    is a diagram of an example of a viable port mapping for an optical fiber connector  1700  of a universal optical fiber interconnection cable. The optical fiber connector  1700  includes power supply fiber ports (e.g.,  1702 ), transmitter fiber ports (e.g.,  1704 ), and receiver fiber ports (e.g.,  1706 ). The optical fiber connector  1700  is TX-RX pairwise symmetric and PS symmetric with respect to the center axis that is parallel to the column direction. 
       FIG.  25    is a diagram of an example of a viable port mapping for an optical fiber connector  1710  of a universal optical fiber interconnection cable. The optical fiber connector  1710  includes power supply fiber ports (e.g.,  1712 ), transmitter fiber ports (e.g.,  1714 ), and receiver fiber ports (e.g.,  1716 ). The optical fiber connector  1710  is TX-RX pairwise symmetric and PS symmetric with respect to the center axis that is parallel to the column direction. 
       FIG.  26    is a diagram of an example of a port mapping for an optical fiber connector  1720  that is not appropriate for a universal optical fiber interconnection cable. The optical fiber connector  1720  includes power supply fiber ports (e.g.,  1722 ), transmitter fiber ports (e.g.,  1724 ), and receiver fiber ports (e.g.,  1726 ). The optical fiber connector  1720  is not TX-RX pairwise symmetric with respect to the center axis that is parallel to the column direction, or the center axis that is parallel to the row direction. 
       FIG.  27    is a diagram of an example of a viable port mapping for a universal optical fiber interconnection cable that includes a pair of optical fiber connectors, i.e., a first optical fiber connector  1800  and a second optical fiber connector  1802 . The mapping of the transmitter, receiver, and power supply fiber ports in the first optical fiber connector  1800  is the same as the mapping of the transmitter, receiver, and power supply fiber ports in the second optical fiber connector  1802 . The port mapping of the first optical fiber connector  1800  is a mirror image of the port mapping of the second optical fiber connector  1802  after swapping the transmitter and receiver ports in the mirror image. The mirror image is generated with respect to a reflection axis  1804  at the connector edge parallel to the column direction. The optical fiber connector  1800  is TX-RX pairwise symmetric and PS symmetric with respect to the center axis  1806  that is parallel to the column direction. 
       FIG.  28    is a diagram of an example of a viable port mapping for a universal optical fiber interconnection cable that includes a pair of optical fiber connectors, i.e., a first optical fiber connector  1810  and a second optical fiber connector  1812 . The mapping of the transmitter, receiver, and power supply fiber ports in the first optical fiber connector  1810  is the same as the mapping of the transmitter, receiver, and power supply fiber ports in the second optical fiber connector  1812 . The port mapping of the first optical fiber connector  1810  is a mirror image of the port mapping of the second optical fiber connector  1812  after swapping the transmitter and receiver ports in the mirror image. The mirror image is generated with respect to a reflection axis  1814  at the connector edge parallel to the column direction. The optical fiber connector  1810  is TX-RX pairwise symmetric and PS symmetric with respect to the center axis  1816  that is parallel to the column direction. 
     In the example of  FIG.  28   , the first, third, and fifth rows each has an even number of fiber ports, and the second and fourth rows each has an odd number of fiber ports. In general, a viable port mapping for a universal optical fiber interconnection cable can be designed such that an optical fiber connector includes (i) rows that all have even numbers of fiber ports, (ii) rows that all have odd numbers of fiber ports, or (iii) rows that have mixed even and odd numbers of fiber ports. A viable port mapping for a universal optical fiber interconnection cable can be designed such that an optical fiber connector includes (i) columns that all have even numbers of fiber ports, (ii) columns that all have odd numbers of fiber ports, or (iii) columns that have mixed even and odd numbers of fiber ports. 
     The optical fiber connector of a universal optical fiber interconnection cable does not have be a rectangular shape as shown in the examples of  FIGS.  22 ,  23 ,  25  to  28   . The optical fiber connectors can also have an overall triangular, square, pentagonal, hexagonal, trapezoidal, circular, oval, or n-sided polygon shape, in which n is an integer larger than 6, as long as the arrangement of the transmitter, receiver, and power supply fiber ports in the optical fiber connectors have the three universal optical fiber interconnection cable port mapping properties described above. 
     In the examples of  FIGS.  13 A,  15 A,  17 A, and  20 A , the switch boxes (e.g.,  1302 ,  1304 ) includes co-packaged optical modules (e.g.,  1312 ,  1316 ) that is optically coupled to the optical fiber interconnection cables or optical cable assemblies (e.g.,  1340 ,  1400 ,  1490 ) through fiber array connectors. For example, the fiber array connector can correspond to a first optical connector part, and the optical fiber connector (e.g.,  1342 ,  1344 ,  1402 ,  1404 ,  1492 ,  1498 ) of the optical cable assembly can correspond to a second optical connector part. The port map (i.e., mapping of power supply fiber ports, transmitter fiber ports, and receiver fiber ports) of the fiber array connector (which is optically coupled to the photonic integrated circuit) is a mirror image of the port map of the optical fiber connector (which is optically coupled to the optical fiber interconnection cable). The port map of the fiber array connector refers to the arrangement of the power supply, transmitter, and receiver fiber ports when viewed from an external edge of the fiber array connector into the fiber array connector. 
     As described above, universal optical fiber connectors have symmetrical properties, e.g., each optical fiber connector is TX-RX pairwise symmetric and PS symmetric with respect to one of the main or center axes, which can be parallel to the row direction or the column direction. The fiber array connector also has the same symmetrical properties, e.g., each fiber array connector is TX-RX pairwise symmetric and PS symmetric with respect to one of the main or center axes, which can be parallel to the row direction or the column direction. 
     In some implementations, a restriction can be imposed on the port mapping of the optical fiber connectors of the optical cable assembly such that the optical fiber connector can be pluggable when rotated by 180 degrees, or by 90 degrees in the case of a square connector. This results in further port mapping constraints. 
       FIG.  29    is a diagram of an example of an optical fiber connector  1910  having a port map  1912  that is invariant against a 180-degree rotation. Rotating the optical fiber connector  1910  180 degrees results in a port map  1914  that is the same as the port map  1912 . The port map  1912  also satisfies the second universal optical fiber interconnection cable port mapping property, e.g., the optical fiber connector is TX-RX pairwise symmetric and PS symmetric with respect to the center axis parallel to the column direction. 
       FIG.  30    is a diagram of an example of an optical fiber connector  1920  having a port map  1922  that is invariant against a 90-degree rotation. Rotating the optical fiber connector  1920  180 degrees results in a port map  1924  that is the same as the port map  1922 . The port map  1922  also satisfies the second universal optical fiber interconnection cable port mapping property, e.g., the optical fiber connector is TX-RX pairwise symmetric and PS symmetric with respect to the center axis parallel to the column direction. 
       FIG.  31 A  is a diagram of an example of an optical fiber connector  1930  having a port map  1932  that is TX-RX pairwise symmetric and PS symmetric with respect to the center axis parallel to the column direction. When mirroring the port map  1932  to generate a mirror image  1934  and replacing each transmitter port with a receiver port as well as replacing each receiver port with a transmitter port in the mirror image  1934 , the original port map  1932  is recovered. The mirror image  1934  is generated with respect to a reflection axis at the connector edge parallel to the column direction. 
     Referring to  FIG.  31 B , the port map  1932  of the optical fiber connector  1930  is also TX-RX pairwise symmetric and PS symmetric with respect to the center axis parallel to the row direction. When mirroring the port map  1932  to generate a mirror image  1936  and replacing each transmitter port with a receiver port as well as replacing each receiver port with a transmitter port in the mirror image  1936 , the original port map  1932  is recovered. The mirror image  1936  is generated with respect to a reflection axis at the connector edge parallel to the row direction. 
     Additional information about the optical communication systems described in this document can be found in U.S. patent application Ser. No. 16/816,171, filed on Mar. 11, 2020, U.S. patent application Ser. No. 16/888,890, filed on Jun. 1, 2020, U.S. provisional patent application 63/080,528, filed on Sep. 18, 2020, U.S. provisional patent application 63/088,914, filed on Oct. 7, 2020, U.S. provisional patent application 63/116,660, filed on Nov. 20, 2020, and U.S. provisional patent application 63/146,421, filed on Feb. 5, 2021. The entire contents of the above applications are incorporated by reference. 
     In some embodiments of the above fiber-optic cable, the cable segment is configured to change the cross-sectional shape in response to being bent. 
     In some embodiments of any of the above fiber-optic cables, in a bent portion of the cable segment, a pair of the optical fibers is laterally separated by a larger distance than any two of the optical fibers in a straight portion of the cable segment (e.g., a&gt;a 0 ,  FIG.  3 C ). 
     In some embodiments of any of the above fiber-optic cables, in a bent portion of the cable segment, a pair of the optical fibers is laterally separated by a larger distance than any two points in an orthogonal cross-section of a straight portion of the cable segment (e.g., a&gt;A 0 ,  FIG.  3 C ). 
     In some embodiments of any of the above fiber-optic cables, the cable sheath comprises a layer of a laterally flexible material. 
     In some embodiments of any of the above fiber-optic cables, the cable sheath comprises a layer of a laterally stretchable material. 
     In some embodiments of any of the above fiber-optic cables, the plurality of optical fibers comprises at least 100 optical fibers. 
     In some embodiments of any of the above fiber-optic cables, the plurality of optical fibers comprises at least 1000 optical fibers. 
     In some embodiments of any of the above fiber-optic cables, the cable segment further comprises one or more strength members (e.g.,  230 ,  FIGS.  3 - 4   ). 
     In some embodiments of any of the above fiber-optic cables, the cable segment is constructed to permit lateral movement of at least some of the optical fibers with respect to the one or more strength members (e.g., as illustrated by comparison of  302 ,  304 ,  306 ,  FIG.  3 C ). 
     In some embodiments of any of the above fiber-optic cables, at least some of the strength members are distributed throughout an interior of the cable (e.g.,  230 ,  FIG.  4 B ). 
     In some embodiments of any of the above fiber-optic cables, at least some of the strength members are more concentrated near a center of the cable (e.g.,  230 ,  FIG.  4 C ). 
     In some embodiments of any of the above fiber-optic cables, at least some of the strength members are attached to an inner surface of the cable sheath (e.g.,  230 ,  FIG.  4 D ). 
     In some embodiments of any of the above fiber-optic cables, at least some of the strength members are embedded within the cable sheath (e.g.,  230 ,  FIG.  4 E ). 
     In some embodiments of any of the above fiber-optic cables, at least some of the strength members are attached to an outer surface of the cable sheath (e.g.,  230 ,  FIG.  4 F ). 
     According to another example embodiment disclosed above, e.g., in the summary section and/or in reference to any one or any combination of some or all of  FIGS.  1 - 7   , provided is an apparatus comprising a raceway (e.g.,  600 ,  FIG.  6   ) having a hollow cable conduit (e.g.,  602 ,  FIG.  6   ), the hollow cable conduit having a curved portion and a straight portion connected to the curved portion, the curved portion of the hollow cable conduit having a larger cross-sectional size (e.g., D,  FIG.  6 C ) measured orthogonally to a main plane of the raceway than a corresponding cross-sectional size (e.g., D 0 ,  FIG.  6 B ) of the straight portion of the hollow cable conduit. 
     In some embodiments of the above apparatus, the raceway has a substantially constant height along the curved and straight portions (e.g., as in  FIGS.  7 A- 7 C  and in  FIG.  6 E ), said height being measured orthogonally to the main plain. 
     In some embodiments of any of the above apparatus, the raceway has a larger height along the curved portion than along the straight portion (e.g., compare  FIGS.  6 B and  6 C ), said height being measured orthogonally to the main plain. 
     In some embodiments of any of the above apparatus, the apparatus further comprises a fiber-optic cable (e.g.,  102 ,  FIG.  1   ) laid in the hollow cable conduit of the raceway. 
     In some embodiments of any of the above apparatus, the fiber-optic cable comprises a cable segment (e.g.,  300 ,  FIGS.  3 B- 3 C ;  520 ,  FIG.  5 B ) that has a plurality of optical fibers (e.g.,  220 ,  FIG.  2 ,  3 ,  4   , or  5 ) laterally encased by a cable sheath (e.g.,  210 ,  FIG.  2 ,  3 ,  4   , or  5 ); and the cable segment is constructed to permit relative lateral movement of at least some of the optical fibers within the cable sheath (e.g., as illustrated by comparison of  302 ,  304 ,  306 ,  FIG.  3 C ) to change a cross-sectional shape of the cable segment. 
     While this disclosure includes references to illustrative embodiments, this specification is not intended to be construed in a limiting sense. Various modifications of the described embodiments, as well as other embodiments within the scope of the disclosure, which are apparent to persons skilled in the art to which the disclosure pertains are deemed to lie within the principle and scope of the disclosure, e.g., as expressed in the following claims. 
     Some embodiments can be implemented as circuit-based processes, including possible implementation on a single integrated circuit. 
     It will be further understood that various changes in the details, materials, and arrangements of the parts which have been described and illustrated in order to explain the nature of this disclosure may be made by those skilled in the art without departing from the scope of the disclosure, e.g., as expressed in the following claims. 
     Unless explicitly stated otherwise, each numerical value and range should be interpreted as being approximate as if the word “about” or “approximately” preceded the value or range. 
     The use of figure numbers and/or figure reference labels in the claims is intended to identify one or more possible embodiments of the claimed subject matter in order to facilitate the interpretation of the claims. Such use is not to be construed as necessarily limiting the scope of those claims to the embodiments shown in the corresponding figures. 
     Although the elements in the following method claims, if any, are recited in a particular sequence with corresponding labeling, unless the claim recitations otherwise imply a particular sequence for implementing some or all of those elements, those elements are not necessarily intended to be limited to being implemented in that particular sequence. 
     Reference herein to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the disclosure. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments necessarily mutually exclusive of other embodiments. The same applies to the term “implementation.” 
     Unless otherwise specified herein, the use of the ordinal adjectives “first,” “second,” “third,” etc., to refer to an object of a plurality of like objects merely indicates that different instances of such like objects are being referred to, and is not intended to imply that the like objects so referred-to have to be in a corresponding order or sequence, either temporally, spatially, in ranking, or in any other manner. 
     Throughout the detailed description, the drawings, which are not to scale, are illustrative only and are used in order to explain, rather than limit the disclosure. The use of terms such as height, length, width, top, bottom, is strictly to facilitate the description of the embodiments and is not intended to limit the embodiments to a specific orientation. For example, height does not imply only a vertical rise limitation, but is used to identify one of the three dimensions of a three-dimensional structure as shown in the figures. Such “height” would be vertical where the raceway is horizontal, but would be horizontal where the raceway is vertical, and so on. 
     Also for purposes of this description, the terms “couple,” “coupling,” “coupled,” “connect,” “connecting,” or “connected” refer to any manner known in the art or later developed in which energy is allowed to be transferred between two or more elements, and the interposition of one or more additional elements is contemplated, although not required. Conversely, the terms “directly coupled,” “directly connected,” etc., imply the absence of such additional elements. 
     The description and drawings merely illustrate the principles of the disclosure. It will thus be appreciated that those of ordinary skill in the art will be able to devise various arrangements that, although not explicitly described or shown herein, embody the principles of the disclosure and are included within its spirit and scope. Furthermore, all examples recited herein are principally intended expressly to be only for pedagogical purposes to aid the reader in understanding the principles of the disclosure and the concepts contributed by the inventor(s) to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. Moreover, all statements herein reciting principles, aspects, and embodiments of the disclosure, as well as specific examples thereof, are intended to encompass equivalents thereof