Optical assembly for aligning an active optical device and an optical fiber and method of forming such assembly

Abstract: An optical assembly (10) is disclosed which utilizes a pair of separate members (12,30) to support an optical device (14) and an associated optical fiber (32). Header (12) further comprises a pair of fiducial features (20) and (22) located, in this particular example, on either side of electrically conductive bonding means (24). Conductive means (24) may comprise a solder preform, an electroplated layer of conductive material, a deposited layer of conductive material, or any other suitable arrangement capable of providing physical and electrical attachment of device (14) to header (12). The remaining electrical contact to device (14) may be provided by a wirebond (not shown) between electrical contact pad (16) and the top side of device (14). Alternatively, if both contacts are located on the same side of device (14), a pair of (electrically isolated) conductive means may be utilized. In accordance with the teachings of the present invention, fiducials (20,22) are utilized to provide alignment between optical device (14) and an associated optical fiber. In particular, member (12) is processed to locate fiducials (10,22) as well as conductive means (24), with sufficient certainty such that self-alignment between the device and fiber is achieved. Fiducials (20,22) may comprise a pair of pyramidal openings formed in top surface (26) of header (12). If header (12) comprises a semiconductor material such as silicon, fiducials (20,22) may be formed by etching top surface (26) of member (12). Optical assembly (10) further comprises a second member (30), also referred to a base, for supporting an oprical fibre (32) within a groove (34). Groove (34) may include a first enlarged portion (36) for supporting a plastic-coated optical fiber, and a second, narrowed portion (38) for supporting a stripped, bare glass fiber section. Base (30) further comprises a pair of fiducials (40,42) formed on surface (39) of base (30) and intercepting an orthogonal sidewall (44). As indicated by the arrows, header (12) and base (30) are moved toward each other such that fiducials (20,22) align with fiducials (40,42) resulting in the optical alignment between device (14) and fiber (32). A coupling lens (50) may also be disposed in an opening (52) formed in sidewall (44) of base (30). Lens (50) is utilized to improve the coupling efficiency between optical device (14) and optical fiber (32). Alternatively, a lensed optical device and/or lensed optical fiber may be used to increase the coupling efficiency. Mechanical attachement of header (12) and base (30) is accomplished by utilizing a pair of spherical members (46,48) positioned within the pair of cavities created by the aligned fiducials.

Description: Background of the Invention Technical Field The present invention relates to an optical assembly including an aligned fiber attachment and, more particularly, to an assembly capable of providing self-alignment between an active optical device and the associated optical fiber. The present invention also relates to a method of forming such assembly. Description of the Prior Art An exemplary utilization of silicon in the formation of a subassembly for optoelectronic devices is disclosed in U. S. Patent 4,945,400, (Blonder et aL) issued July 31, 1990 and assigned to the assignee of record in this application. In general, Blonder et al. disclose a subassembly including a semiconductor (e..g, silicon) base and lid including a variety of etched features (e.g., grooves, cavities, alignment detents) and metallization patterns (e.g., contacts, reflectors) which enable the optoelectronic device to be reliably and inexpensively mounted on the base and coupled to a communicating optical fiber. In particular, Blonder et al. disclose an arrangement wherein the optoelectronic device (e.g., LED) is disposed within a cavity formed by a lid member and the communicating fiber is positioned along a groove formed in a base member. A reflective metallization is utilized to optically couple the device to the fiber. Therefore, positioning of the device over the reflector is the only active alignment step required to provide coupling. Any remaining alignments are accomplished utilizing fiducial features formed in the base and lid members. Although the Blonder et aL subassembly represents a significant advance in the field of silicon optical bench packaging, a need remains for providing an arrangement which requires no active alignments to be performed. The provision of a completely passive optical packaging arrangement being considered both more reliable and less expensive than virtually any alternative requiring active alignment between components. EP-A-0331 334 shows a connector providing optical alignment between optical fibers. One of the fibers may be formed in a groove in a substrate including an optical device and a waveguide. EP-A-0413 489 shows a device for coupling a fiber to an optical device employing fiducials on a member to which the device is bonded and on a guide member attached to a tubular member holding the fiber. Summary of the Invention The need remaining in the prior art is addressed by the present invention which relates to an optical assembly including an aligned fiber and, more particularly, to an assembly capable of providing self-alignment between an active optical device and an associated optical fiber. According to the present invention, there is provided an assembly as defined in claim 1 or a method as defined claim 9. In accordance with an exemplary embodiment of the present invention, an optical assembly may comprise a first member (i.e., header) for supporting an active optical device and a second member (i.e., base) including a groove for holding an associated optical fiber. The first and second members further comprise fiducial features (e.g., detents and spheres) which function to align and mechanically attach the first member to the second member. The attachment is accomplished such that the first and second members are positioned to form a direct signal path between the fiber and the optical device. The optical device is disposed on and attached to an electrically conductive bonding means (e.g., solder preform, electroplated solder material, or deposited solder material), the attachment means being positioned with respect to the fiducial features such that self-alignment between the optical device and fiber is achieved. A third member may be utilized in accordance with the teachings of the present invention as a lid to cover the surface of the second member containing the optical fiber. Another set of fiducial features may be utilized to attach the third member to the second member. Brief Description of the Drawing FIG 1. illustrates an exemplary optical assembly formed in accordance with the teachings of the present invention; FIG. 2. illustrates cut-away side view of an exemplary first member, utilized as a support for an optical device; FIG. 3 illustrates a top view of an alternative first member, showing the co-location of an electronic circuit associated with the active optical device; FIG. 4 illustrates an exemplary leadframe structure which may be utilized in the batch processing of a plurality of first members as illustrated in FIG. 2; FIG. 5 illustrates an exemplary section of a wafer, supporting a plurality of first members and associated leadframe structure, as illustrated in FIG. 4; FIG. 6 illustrates an exemplary arrangement of a second member, utilized as a support for an optical fiber; FIG. 7 illustrates an exemplary substrate arrangement which may be processed to form a second member as illustrated in FIG. 5; FIG. 8 includes a top view of an optical assembly formed in accordance with the present invention; and FIG. 9 illustrates an alternative optical array assembly formed in accordance with the teachings of the present invention. Detailed Description An exemplary optical assembly 10 formed in accordance with the present invention is illustrated (in an exploded view) in FIG. 1. Optical assembly 10 comprises a first member 12, also referred to as a header, for supporting an optical device (e.g., LED) 14 and associated electrical contact pads 16, 18. As will be discussed in detail below, first member 12 (as well as other members described hereinafter) may comprise any suitable material capable of being processed to include the requisite alignment fiducials. For example, semiconductor substrate materials such as silicon or GaAs may be used and etched to form the alignment fiducials. Alternatively, a plastic material, such as a high-performance engineering plastic, may be used and molded to form the alignment fiducials. Header 12 further comprises a pair of fiducial features 20 and 22 located, in this particular example, on either side of electrically conductive bonding means 24. Conductive bonding means 24 may comprise a solder preform, an electroplated layer of conductive material, a deposited layer of conductive material, or any other suitable arrangement capable of providing physical and electrical attachment of device 14 to header 12. The remaining electrical contact to device 14 may be provided by a wirebond (not shown) between electrical contact pad 16 and the top side of device 14. Alternatively, if both contacts are located on the same side of device 14, a pair of (electrically isolated) conductive means may be utilized. In accordance with the teachings of the present invention, fiducials 20,22 are utilized to provide alignment between optical device 14 and an associated optical fiber. In particular, member 12 is processed to locate fiducials 20,22, as well as conductive bonding means 24, with sufficient certainty such that self-alignment between the device and fiber is achieved. Fiducials 20,22 may comprise a pair of pyramidal openings formed in top surface 26 of header 12. If header 12 comprises a semiconductor material such as silicon, fiducials 20,22 may be formed by etching top surface 26 of member 12. Optical assembly 10 further comprises a second member 30, also referred to as a base, for supporting an optical fiber 32 within a groove 34. Groove 34 may include a first enlarged portion 36 for supporting a plastic-coated optical fiber, and a second, narrowed portion 38 for supporting a stripped,bare glass fiber section. Base 30 further comprises a pair of fiducials 40,42 formed on surface 39 of base 30 and intercepting an orthogonal sidewall 44. As indicated by the arrows in FIG. 1, header 12 and base 30 are moved toward each other such that fiducials 20,22 align with fiducials 40,42, resulting in the optical alignment between device 14 and fiber 32. A coupling lens 50 may also be disposed in an opening 52 formed in sidewall 44 of base 30. Lens 50 is utilized to improve the coupling efficiency between optical device 14 and optical fiber 32. Alternatively, a lensed optical device and/or lensed optical fiber may be used to increase the coupling efficiency. Mechanical attachment of header 12 and base 30 is accomplished by utilizing a pair of spherical members 46,48 positioned within the pair of cavities created by the aligned fiducials. As shown, spherical members are in physical contact with both header 12 and base 30, resulting in a gap between surfaces 26 and 44 (cf. Fig. 8). The gap allows for process variations in the formation of base 30 without affecting the alignment of the optical device to the fiber. It is to be noted that in the formation of the fiducials, any number of separate alignment features may be utilized, the pair of fiducials illustrated in FIG. 1 being considered as exemplary only. Further, there may exist other types of fiducial features which could be utilized in place of the pyramidal openings and spheres illustrated in FIG. 1. For example, alignment grooves and ridges may be included in the separate members and utilized to provide both alignment and mating therebetween. FIG. 2 illustrates a cut-away side view of an exemplary first member (header) 12. Important to the self-aligning feature of the present invention is the ability to locate device 14 with respect to fiducials 20,22 such that when header 12 and base 30 are mated, fiber 32 will be optically aligned with device 14. The utilization of conductive means 24 has been found to provide the desired alignment. As shown, device 14 is attached to conductive means 24, where means 24 is disposed between fiducials 20 and 22. In the assembly of the illustrated arrangement, device 14 is placed on solder means 24 (which may comprise a tin-gold compound or any other suitable/compatible well-known conductive material), and the combination heated to a temperature sufficient to liquify conductive means 24 (without affecting device 14) and thus cover (i.e. "wet") an underlying electrical pad (not shown). The surface tension created by liquified means 24 results in forming a dome-like mass of material, defined by the boundary of the underlying electrical pad. Device 14 will thus "float" on the surface thereof so as to align with the material. Therefore, as long as the underlying electrical pad is properly positioned with respect to fiducials 20,22, device 14 will be properly disposed so as to be in optical alignment with an attached fiber 32 (FIG. 1). FIG. 3 illustrates a top view of an alternative header 12' which is formed to include the electronic circuitry 13 associated with the operation of optical device 14. For example, when silicon or another semiconductor substrate material is used to form header 12', the circuit may be directly fabricated in/on the surface of the header. Alternatively, when a plastic material is used, the circuitry may be physically attached to the top surface thereof. The ability to co-locate the circuitry with the optical device thus reduces the overall size of the resulting arrangement. Further, in the case of an optical receiving arrangement, the ability to form a circuit, such as a pre-amplifier, in close proximity to the optical receiving device (e..g, photodiode) reduces the electrical path lengths required to connect the devices, and thus reduces any parasitics associated with the arrangement. It is to be understood that a transmitting arrangement may also be so formed, with a optical transmitting device such as an LED or laser co-located with a driver circuit. An advantage of the arrangement of the present invention is the ability to batch fabricate, as well as test, the header assemblies. FIG. 4 illustrates an exemplary arrangement illustrating a leadframe 54 attached to a plurality of headers 12, each each being of the type illustrated in detail in FIG. 2. As shown, leadframe 54 comprises a plurality of lead pairs 56,58, each lead pair being bonded to a separate pair of electrical pads 16, 18 located on header 12. A wirebond 60 (illustrated in FIGs. 2,3) may be utilized to provide the final electrical connection between lead 56, electrical pad 16, and the top side of device 14. In general, the plurality of headers 12 may be subjected to a number of electrical tests to assess the operability of the individual units prior to being mated with the an associated base member 30. The ability to batch test the header assemblies may thus result in a cost saving in the final optical subassembly. A wafer 57 containing the plurality of headers 12 may be pre-cut along the edges 59 of headers 12, as shown in FIG. 5, through a predetermined portion of the wafer thickness. Upon completion of the batch testing, the individual headers may then simply be snapped apart. A fiber subassembly, including an optional third member 60 (lid) is illustrated in FIG. 6. In some packaging applications, it may be advantageous to include a lid 60 which substantially covers fiber 32 as supported by groove 34 in base member 30. Alignment and attachment of lid 60 to base 30 may be accomplished, in accordance with the present invention, by utilizing an additional set of fiducial features. In particular, base 30 of FIG. 6 is illustrated as including a pair of fiducials 62,64, formed as a pair of pyramidal openings in top surface 31 of base 30. In general, any suitable number (as well as location) of fiducials may be utilized. An associated pair of fiducials 66,68 are formed in lid 60 so as to be in alignment with fiducials 62,64. A pair of spheres 70,72 are positioned between base 30 and lid 60 so as to be located within the cavities formed by the aligned fiducials and provide mechanical attachment therebetween. An important aspect of the present invention is the ability to form fiducials 40,42 in an intercepting sidewall 44 of second member 30 with sufficient accuracy such that alignment with first member 12 is achieved. FIG. 7 illustrates a top view of an exemplary starting substrate 80 (which may comprise silicon, plastic, or any other suitable material) which may be processed to form second member 30. As shown in the illustration of second member 30, starting substrate 80 is processed to form groove 34 for supporting fiber 32, as well as alignment fiducials 62,64 (optional) for attaching lid 60 to second member 30. Substrate 80 is further processed, as shown in FIG. 7, to form a pair of pyramidal openings 82 and 84 on either side of a relatively large pyramidal opening 86. Second member 30 is formed from substrate 80 by dicing substrate 80 along line A-A, as shown in FIG. 7. As shown , therefore, line A-A forms sidewall 44 of second member 30. FIG. 8 contains a cut-away top view of an exemplary optical assembly formed in accordance with the present invention, illustrating in particular the configuration of fiducials 40 and 42 (as well as opening 52) in second member 30. The mating of first member 12 to second member 30 is also shown. The size of opening 52 is formed sufficiently large to allow for the coupling of optical device 14 to fiber 32, as well as the placement (optional) of coupling lens 50. FIG. 9 illustrates an alternative array embodiment of the present invention. As shown, a first member 120 is formed to include a plurality of active optical devices 140 disposed as shown on surface 260 of member 120. Associated electrical bond pads 160, 180 are also illustrated. Fiducials 200 may be formed as shown in FIG. 9. It is to be understood that a smaller number of such fiducials may be required with an array embodiment, since separate fiducials are not required for each optical device location. In particular, the arrangement as illustrated in FIG. 9 includes only a single fiducial between adjacent devices. A second member 300 may be formed as shown in FIG. 9 to include a plurality of grooves 340 for supporting an associated plurality of optical fibers 320. Fiducials 400 are formed as shown in member 300 to provide alignment with fiducials 200 of first member 120. Mechanical attachment between first member 120 and second member 300 is achieved by including a plurality of spheres 420 between the aligned plurality of fiducials 200 and 400, as shown. In an exemplary arrangement of the embodiment of FIG. 9, the array may comprise a pair of device-fiber couplings, forming either a transmitter-receiver pair or a sparing arrangement. Finally, it will be appreciated that although today's technology suggests that silicon is the preferred material from which the principal piece parts of the invention are made, it is possible that different circumstances (e.g., system specifications and cost considerations) might render it desirable to utilize a different semiconductor material (e.g., Ge, GaAs), or a plastic which may be molded (e.g., injection molded) to form the requisite alignment fiducials.

Claims: An optical assembly (10) for aligning at least one active optical device (14;140) with at least one optical fiber (32;320), comprising a first member (12;120) for the mounting of said at least one active optical device (14;140) on a surface (26) thereof, said first member comprising a first set of fiducial features (20,22;200) and including electrically conductive bonding means (24;240) for the attachment of said active optical device, said electrically conductive bonding means being disposed in a predetermined location with respect to said first set of fiducial features; and a second member (30;300) for the support of said at least one optical fiber (32;320), said second member including at least one longitudinal groove (34;340) formed along a major surface (39) thereof for the placement of said at least one optical fiber, the second member further comprising a second set of fiducial features (40,42;400) exposed in a surface (44) of said member orthogonal to said major surface and in the direction of which the longitudinal groove extends, the fiducial features of said second set being arranged with respect to one another on said second member in a manner identical to that according to which the fiducial features of said first set are arranged with respect to one another on said first member, and the longitudinal groove being disposed with respect to said second set of fiducial features in the same predetermined location according to which the electrically conductive bonding means are disposed with respect to said first set of fiducial features, said second and said first member being intended to be moved towards to each other in a manner such that said second set of fiducial features comes into alignment and cooperates with said first set of fiducial features so as to result in the direct alignment of the active optical device to be attached to the first member with the optical fiber to be received in the second member; said fiducial features of said first and said second set being adapted with respect to one another in a manner such as to leave a gap between the two confronting surfaces (26,44), supporting the respective two sets of fiducial features, of the first and second member when the latter are pressed against each other. An optical assembly as defined in claim 1, wherein the first member (120) is capable of mounting a plurality of active optical devices (140) and the second member (300) is capable of supporting an associated plurality of optical fibers (320). An o tical assembly as defined in claim 1, wherein the first and second members (12,30;120,300) comprise a semiconductor material, such as comprising silicon, or comprise a plastic. An optical assembly as defined in claim 1 wherein the electrically conductive bonding means (24;240) comprises a solder preform, such as is capable of being liquified when heated such that an optical device placed on the surface thereof will align to said preform upon heating. the solder preform comprising a tin-gold combination. An optical assembly as defined in claim 1, wherein the first and second fiducial features (20,22,40,42;200,400) comprise a set of openings formed in the associated surfaces (26, 44) of the first and second members respectively, the fiducial features further comprising a plurality of spherical members (46,48;420) disposed between associated openings so as to provide mechanical mating of the first and second members, the first and second members comprising silicon, and wherein the fiducial openings comprise features etched into the silicon surface. An optical assembly as defined in claim 1, wherein the first and second fiducial features comprise set of grooves and ridges, the set of grooves being formed on either one of the first and second members and the ridges formed on the remaining member, the grooves and ridges being disposed to provide alignment between the first and second members upon mating. An optical assembly as defined in claim 1, further comprising a third member (60) disposed to cover the major surface of the second member (30) supporting the optical fiber (32), the second and third members formed to include a plurality of fiducial features (62,64,66,68) to facilitate the alignment and attachment therebetween, said plurality of fiducial features comprising a first plurality of openings (62,64) formed in the top major surface (31) of the second member (30) and an associated plurality of openings (66,68) formed in the attaching surface of the third member, with a plurality of spherical members (70,72) disposed therebetween. An optical assembly as defined in claim 1 wherein the first member (12) further includes a pair of electrical lead pads (16,18) attached to the surface (26) of the member to provide an electrical signal path to the active optical device (14), the first member further including electronic circuitry (13), disposed along the top surface thereof, associated with the operation of the active optical device. A method of forming an optical assembly (10) for aligning at least one optical device (14;140) with at least one optical fiber (32;320), comprising the steps of: a) providing first (12;120) and second (30;300) separate support members, each including a top major surface (26,39) and sidewalls (44) orthogonal thereto; b) forming fiducial alignment features (20,22,40,42;200,400) on the top major surface (26) of said first support member and on a sidewall (44) of said second support member, in a manner such that the fiducial features (20,22;200) on the second member are arranged with respect to one another in a manner identical to that according to which the fiducial features (40,42;400) on the first member are arranged with respect to one another; c) forming electrically conductive bonding means (24;240) on said top major surface (26) of said first member for the attachment of said active optical device (14;140), said electrically conductive bonding means being formed at a predetermined location with respect to said fiducial alignment features associated to said first member; d) forming a longitudinal groove (34) along the top major surface (39) of said second support member for the placement of said optical fiber (32;320), the longitudinal groove extending in the direction of that sidewall (44) supporting the fiducial features associated to the second member and being formed with respect to said fiducial features in the same predetermined location according to which the electrically conductive bonding means are disposed with respect to the fiducial features associated to the first member; and e) attaching said first support member to said second support member by aligning and attaching the fiducial alignment features (20,22; 200) of said first member to the fiducial alignment features (40,42;400) of said second member, so that the top surface (26) of the first member supporting the bonding means and the sidewall (44) of the second member onto which the groove emerges are facing each other, to provide direct alignment between the active optical device on said bonding means and the optical fiber in said groove; said fiducial features of said first member and said second member being adapted with respect to one another so as to leave a gap between the confronting top surface of the first member and the sidewall of the second member once said first and second member have been attached to each other; wherein, in performing step a), semiconductor substrate support members are provided, said support members comprising silicon, or plastic substrate support members are provided. The method according to claim 9, wherein in performing steps b) and d), etching is used to form the longitudinal groove as well as openings constituting the fiducial align features and wherein in performing step e), spheres are inserted between and attached to the etched openings to achieve alignment and attachment of the first support member to the second support member. The method according to claim 9, wherein the method comprises the further steps of f) placing an active optical device (14) on the conductive bonding means (24) of step c); and g) heating the conductive bonding means to liquify and allow said active optical device to align with the underlying conductive bonding means.

Inventors: BLONDER GREG E, DAUTARTAS MINDAUGAS FERNAND, WONG YIU-HUEN, BLONDER, GREG. E., DAUTARTAS, MINDAUGAS FERNAND, WONG, YIU-HUEN
Applicants: AT & T CORP, AT&T CORP.
Application year: 1992
Main classification: G02B6
IPC codes: G02B6, H01L33