Abstract:
An optical device, such as optical coupling devices, optical switches, optical isolators, optical attenuators, laser diodes, photo diodes are provided having a substrate with a groove in order to locate a optical fiber. A lens, such as a graded index lens, is secured to the end of the optical fiber, with the lens located outside the groove, thereby avoiding difficulties with axial alignment of the lens caused by the interface of the optical fiber to the lens. In one implementation, the groove in the prototype is a V-groove, thereby providing stable positioning of the optical fiber within the groove.

Description:
TECHNICAL FIELD 
   The present invention relates generally to optical devices. Examples of optical devices include optical coupling devices, optical switches, optical isolators, optical attenuators, laser diodes, photo diodes and other devices involving optical fibers. 
   BACKGROUND 
   The use of optical signals for communication and signal transmission has become commonplace. Typically, in the design of an optical network, additional expense and complexity is incurred because of signal loss at coupling locations. Additionally, because of signal loss, additional amplifiers and other devices are often added, thereby increasing noise levels and reducing efficiency. 
   One method of coupling optical signals between two optical fibers is shown in  FIG. 1. A  coupling device  100  is provided with a ball lens  110  in proximity to the end of each of the optical fibers  120 . The ball lenses are typically 2-3 millimeters in diameter and are separated from each other. Typically, the diameter of the optical fiber  120  is in the neighborhood of 125 microns. 
   With reference to  FIG. 1 , difficulties reside in the assembly of coupling devices  100  in locating the ball lens  110  with respect to the optical fiber  120  and also with respect to the neighboring ball lens  110 . Further difficulties arise due to the large amount of space required for the two ball lenses and associated separation distance. One example of the use of a ball lens configuration can be found in U.S. Pat. No. 5,257,332. 
   SUMMARY 
   The present invention may be adapted to position a lens coupled to an optical fiber, such that the lens can be precisely and accurately located, both in position and angle. The present invention may also minimize the effort required in configuring and assembling an optical device, while simultaneously enabling precise, accurate and reliable positioning of a lens coupled to an optical fiber. 
   The present invention uses a substrate having a groove in order to locate a optical fiber. A lens, such as a graded index lens, is secured to the end of the optical fiber, with the lens located outside the groove, thereby avoiding difficulties with axial alignment of the lens, such as those caused by differing diameters of the lens and the optical fiber and/or irregularities of the interface of the optical fiber to the lens. In one implementation, the groove is a V-groove, thereby providing stable positioning of the optical fiber within the groove. 
   According to one embodiment of the invention, a device is provided for alignment of a lens. The device includes a substrate having a groove in which an optical fiber is located. A lens is mounted to the end of the optical fiber, such that the lens is located out of the groove and is held in position by the fiber. 
   According to another embodiment of the invention, an optical coupling device is provided with a first substrate. The first substrate has a groove in which an optical fiber is located. A lens is mounted to the end of the optical fiber such that the lens is located out of the groove and is held in position by the fiber. A second substrate is also provided having a second groove. Another optical fiber is located in the second groove and another lens is mounted to an end of the optical fiber in the second groove, such that the lens is located out of the second groove and is held in position by the second fiber. According to this embodiment of the invention, the lenses face each other. Optionally, the first substrate and second substrate may be a continuous substrate. 
   According to variations of embodiments of the invention, an optical isolator may be located between the first lens and the second lens to allow light to pass from said first lens to said second lens and inhibit back reflection light. Another variation involves an optical attenuator located between the first lens and the second lens to selectively inhibit light traveling between the first lens and the second lens. 
   According to another embodiment of the invention, a laser device is provided with a substrate. The substrate has a groove in which an optical fiber is located. A lens is located at an end of the optical fiber, such that the lens is located out of the groove and is held in position by the fiber. A laser is coupled to the substrate and faces the lens and is located to direct light into the fiber. 
   A further embodiment of the invention provides a photodetector having a substrate with a groove. An optical fiber is located in the groove with a lens having a first end mounted to the optical fiber, such that the lens is located out of the groove and is held in position by the fiber. A photodetector is coupled to the substrate and faces a second end of the lens and is located to detect light in the fiber. 
   A further embodiment of the invention provides an optical switch having a substrate with a groove. A first optical fiber is located in a first groove with a first lens mounted to the end of the optical fiber such that the first lens is located out of the first groove and is held in position by the first fiber. A first mirror is coupled to the substrate and is selectively located to obliquely face the first lens to be adapted to selectively redirect light travelling from the first lens. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be apparent from the description herein and the accompanying drawings, in which like reference characters refer to the same parts throughout the different views. 
       FIG. 1  illustrates a known optical coupling using ball lenses; 
       FIG. 2  illustrates an optical coupling using GRIN lenses. 
       FIGS. 3A-3C  illustrate various couplings of GRIN lenses to optical fibers; 
       FIG. 4  illustrates varying diameters of splice locations between an optical fiber and a lens. 
       FIG. 5  illustrates a coordinate system for purposes of discussion; 
       FIG. 6  illustrates an example lens positioning device according to an embodiment of the invention; 
       FIG. 7  illustrates a close-up view of the device of  FIG. 6 ; 
       FIG. 7A  illustrates a close-un view of a variation of the device of  FIG. 6 ; 
       FIGS. 8 and 9  illustrate cross-sectional views of grooves according to examples of the invention; 
       FIG. 10  illustrates a groove formed in a substrate according to an embodiment of the invention; 
       FIGS. 11A-11C  illustrate various mountings of optical fibers to lenses; 
       FIG. 12A  illustrates an example laser device according to an embodiment of the invention; 
       FIG. 12B  illustrates an example photodetector according to an embodiment of the invention; 
       FIGS. 13 and 14  illustrates examples of optical coupling devices according to embodiments of the invention; 
       FIG. 15  illustrates an optical isolator according to an embodiment of the invention; 
       FIG. 16  illustrates an example optical attenuator according to an embodiment of the invention; and 
       FIG. 17  illustrates an example optical switch according to an embodiment of the invention. 
   

   DETAILED DESCRIPTION 
   The present invention, in various embodiments, provides optical coupling devices, including lens positioning devices, optical isolators, optical attenuators, laser devices, photodetector devices and optical switches using a lens mounted to the end of an optical fiber. According to various embodiments of the invention, a substrate is provided with a groove. One or more optical fibers are located in the groove, such as a V-groove or other groove capable of inhibiting movement of the optical fiber. The lens is located out of the groove, such that the coupling of the optical fiber to the lens does not degrade the orientation of the fiber within the groove. 
   An optical coupling is illustrated in FIG.  2 . In this approach, the ball lens is replaced by a smaller, graded index (GRIN) lens  130 . The GRIN lens  130  may also be known as a graded index fiber (GIF) lens. A good optical coupling using a GRIN lens  130  can result in less than 1 dB of signal loss. An example of the use of a GRIN lens can be found in U.S. Pat. No. 4,701,011. 
   The GRIN lens  130  may be provided with a diameter of approximately 125 microns, similar to the example optical fiber  120 . As shown in  FIG. 2 , the external diameter A of the optical fiber  120  is approximately 125 microns. The core diameter B of the optical fiber is approximately 10 microns. Typically, the GRIN lens  130  is directly affixed to the optical fiber  120 . 
   In the example configuration shown in  FIG. 2 , the GRIN lens  130  and optical fiber  120  assemblies have a separation distance C of approximately 3 millimeters and a beam spot size D of approximately 40-80 microns. The working distance can be less or more than 3 millimeters, and the beam spot can be less or more than 40-80 microns. These values can vary depending on characteristics of the GRIN lens  130 , such as the index profile and the length of the GRIN lens  130 . It is understood that the example configuration of  FIG. 2  is not limiting and is merely presented for purposes of discussion of embodiments of the invention. Examples of considerations in optical fiber coupling can be found in Marcuse, D., Loss Analysis of Single-Mode Fiber Splices,  The Bell System Technical Journal,  vol 56, no. 5, May-June 1977. Examples of considerations in GRIN lens selection can be found in Emkey W. L. et al., Analysis and Evaluation of Graded-Index Fiber-Lenses,  Journal of Lightwave Technology,  vol. LT-5, no. 9, September 1987. 
   The coupling of the GRIN lens  130  and the optical fiber  120  often results in a configuration that will not lie flat along a flat surface. As shown in  FIG. 3A , the diameter of the optical fiber  120  may be smaller or larger than the diameter of the GRIN lens  130 . The different diameter of the GRIN lens  130  from the optical fiber  120  will likely cause the GRIN lens  130  to be located non-parallel to a flat surface  152 , as shown in FIG.  3 B. This may occur regardless of whether the transition  125  between the GRIN lens  130  and the optical fiber  120  is smooth, such as by tapering the GRIN lens  130  or optical fiber  120  so that the diameters match at the transition  125 . 
   Another example of a configuration that will not lie flat along a flat surface is provided in FIG.  3 C. The example shown in  FIG. 3C  can occur during fusion splicing or adhesive dispensing. In this example, the transition  125  where the GRIN lens  130  and optical fiber  120  are coupled has a larger diameter than either of the GRIN lens  130  or optical fiber  120 , likely resulting in a non-parallel location of the GRIN lens  130  relative to a flat surface. 
   A further difficulty encountered with the coupling of a GRIN lens  130  and optical fiber  120  is the frequent non-round condition of the splice, or coupling location, between the GRIN lens  130  and optical fiber  120 . Measurements taken by Applicants of various samples are illustrated in FIG.  4 . Each row of  FIG. 4  signifies a different sample. As shown in the first sample, a diameter in a first direction was measured as 127.2 microns, while the diameter of the same portion in a second direction, orthogonal to the first direction, was 127.0 microns. 
   One drawback of the GRIN lens  130  is that it requires precise axial alignment relative to its counterpart GRIN lens  130  in an optical coupling. In some applications, axial misalignment greater than 0.1° can result in substantial signal loss. By way of example,  FIG. 5  illustrates a coordinate system for purposes of discussion of the relationship between two GRIN lenses  130 A,  130 B and optical fiber  120  assemblies. A z axis is provided generally along a longitudinal axis of a GRIN lens  130 A. The angle θ illustrates the axial orientation of GRIN lens  130 B relative to GRIN lens  130 A. Further axes, the x axis and the y axis, are provided to form a three-dimensional Cartesian coordinate system with the z axis. As shown in  FIG. 5 , the x axis and y axis are orthogonal to each other and the z axis. 
   In the example configuration shown in  FIG. 2 , the tolerances for a coupling loss of less than 1 dB require that the GRIN lenses  130  be placed ±5 microns in the x and y directions. Substantial flexibility exists in placement along the z axis, as the GRIN lenses  130  are to be located ±400 microns of their focusing locations in the example. In view of the parameters specified, θ needs to be ±0.1° in order to maintain coupling loss of less than 1 dB. These tolerances for θ assume the 40 micron beam spot size, illustrated by the letter D in  FIG. 2 , and a 3 millimeter separation distance C. It is understood that the example configuration of  FIG. 2  is not limiting and is merely presented for purposes of discussion of embodiments of the invention. 
   A lens positioning device  200 , according to an example of an embodiment of the invention, is shown in  FIG. 6. A  lens  230  is mounted to an optical fiber  220 . The optical fiber  220  is located in a groove  240  of a substrate  250 . According to the invention, the lens  230  is located outside of the groove  240 . The lens  230  is mounted to the optical fiber  220 . 
     FIG. 7  provides a top view of the end of the groove  240 . Although the lens  230  is illustrated as located a short distance from the end of the groove  240 , the invention is not so limited. The lens  230  may be located at the end of the groove  240 k optionally contacting the substrate  250 , or may be a greater or lesser distance than illustrated from the end of the groove  240 .  FIG. 7A  illustrates an example of the lens  230  contacting the substrate  250 . 
   The groove  240  may be formed in the substrate  250  according to a wide variety of methods known in the art. One example is a V-groove  240 , as shown in  FIGS. 8 and 9 . A V-groove is well suited to the invention, as the V-groove helps to locate the optical fiber  220  by inhibiting movement of the optical fiber in an x direction. The V-groove shape also serves to align the optical fiber along the direction of the groove, by contacting the optical fiber at two locations along its circumference. 
   As shown in  FIG. 8 , the optical fiber  220  may be located all or substantially within the groove  240 , when viewed in cross-section.  FIG. 9  illustrates a groove  240  in which the optical fiber  220  is located partially outside of the groove  240  in cross-section. The optical axis of the optical fiber  220  may optionally be located within a plane formed by the upper surface of the substrate  250 . By way of example, angle G may optionally vary between 60° and 70°, or may be any angle such that the optical fiber  220  movement along an x axis is inhibited. All or only a portion of the optical fiber  200  may be located within the groove  240  when viewed in cross-section. 
   As will be apparent to one of skill in the art, other groove shapes may also be used, such as a U-groove, including U-grooves with square or rounded lower corners. Grooves capable of receiving at least a portion of the optical fiber are within the scope of the invention. According to one example, the groove will provide contact with the optical fiber at least at two locations along the circumference of the optical fiber. 
   The substrate  250  may be formed of a wide variety of materials. Performance of the resulting device benefits by the use of substrate materials and groove-forming methods that provide a precise and accurate groove. Examples of substrate materials include Si, SiO 2 , InP, GaAs, InGaAs, InGaAsP and the like. 
   As will be apparent to one of skill in the art, the method of forming the groove  240  in the substrate  250  may vary according to the type of substrate material selected. As shown in  FIG. 10 , a sample embodiment of the invention provides the groove  240  by etching through a portion of a substrate  250 . One example of forming the groove  240  involves wet-etching the groove  240  into a Si substrate. Other methods of forming the groove in the substrate will be apparent to one of skill in the art and are within the scope of the invention. Various examples of ways of forming the groove in a substrate are discussed in Madou, M. J.,  Fundamentals of Microfabrication,  pp. 163-187, CRC Press, Boca Raton, Fla., 1997. 
   The lens  230  may be mounted to the optical fiber  220 , such that the lens  230  and optical fiber  220  are optically coupled, in a variety of ways known to those in the art. As shown in  FIG. 11A , one example of mounting is a fusion splice  222 .  FIG. 11B  illustrates adhesive  224  as another example. The adhesive  224  is located and/or formulated to allow transmission of optical signals from the lens  230  to the optical fiber  220 , while fixedly securing the lens  230  to the optical fiber  220 . Although the invention is not so limited, examples of adhesives include ABLELUX, A4021T, and AA50T by ABLESTIK, of Rancho Dominguez, Calif. A further example of an adhesive is 301-2 by EPOXY TECHNOLOGIES of Billerica, Mass. 
   A further example of mounting the lens  230  to the optical fiber  220  is a clamp  226 . An example of a clamp  226  is shown in FIG.  11 C. According to the example of the invention, the clamp  226  is located outside of the groove  240  of the substrate  250 . It will be apparent to one in the art that the clamp  226  may be a variety of mechanical devices capable of fixedly positioning the optical fiber  220  and lens  230  relative to each other. One example is a compression clamp. 
   The optical fiber  220  may be any optical fiber capable of allowing light to pass through. Examples include a single-mode fiber and a multi-mode fiber. The optical fiber  220  may be selected from a wide variety of sizes. According to one implementation of the invention, the diameter of the optical fiber is 125 microns±1 micron. The lens  230  may be a wide variety of optical lenses. An example is a graded index lens. As used herein, the term “light” includes any form of optical signal capable of transmission by optical fiber. 
     FIGS. 12A and 12B  illustrate other embodiments of the invention. According to one embodiment, illustrated in  FIG. 12A , a laser device  275  is provided by orienting the lens  230  toward a laser  280 . The substrate  250  is provided with the groove  240  for locating the optical fiber  220 . According to this embodiment, the laser  280  is fixedly located relative to the substrate  250  and oriented to providing at least a portion of its output into the lens  230 . The lens  230  is selected and separated from the laser  280  to achieve a desired optical result of the laser light traveling into and through the optical fiber  220 . 
   According to a further embodiment illustrated in  FIG. 12B , a photodetector device is  285  provided. The substrate  250  is provided with the groove  240  for locating the optical fiber  220 . A photodetector  290  is fixedly located relative to the substrate  250  such that the photodetector  290  receives at least a portion of any light emitted from the optical fiber  220  through the lens  230 . The lens  230  is selected and separated from the photodetector  290  to achieve a desired optical result of any light emitted from the optical fiber  220  traveling to the photodetector  290 . 
     FIG. 13  shows an example of an optical coupling  300  according to a further embodiment of the invention. The optical coupling  300  is the functional equivalent of two lens positioning devices  200  oriented such that the lenses  230  are in optical communication with each other and are located outside of the grooves  240 . 
   The substrate  250  of the optical coupling  300  may be a single, continuous piece, or may be two or more pieces fixedly mounted to each other. The optical coupling  300  may be formed to fixedly locate lenses  230 , such as GRIN lenses, in optical communication with each other. As shown in  FIG. 14 , the optical coupling  300  may optionally be formed with solder plating  305  and/or one or more electrodes  310  and/or an alignment mark  320 . The solder plating  305  and electrodes  310  may be formed of a variety of materials known in the art. Examples of the solder plating include Au—Sn, Sn and Pb—Sn. Examples of the electrodes include Cr/Au, Ti/Ni/Au and Cr/Cu/Au. Therefore, an example electrode may have Cr deposited on a substrate and Au as a second, outermost layer. Although the invention is not so limited, the other examples are three-layer electrodes, having Ti on a substrate, Ni as a second layer and Au as a top layer or Cr on a substrate and Cu and Au as second and third layers, respectively. 
   An optical isolator  400  is illustrated in FIG.  15 . The optical isolator can allow light to pass from a first optical fiber  420  to a second optical fiber  422  and inhibit back reflection light. Lenses  430 ,  432 , such as GRIN lenses, are mounted to the ends of the optical fibers  420 ,  422 . The optical fibers  420 ,  422  are located in grooves  440  of substrate  450 , while lenses  430 ,  432  are outside the grooves  440 . Between the lenses  430 ,  432 , a magneto-optical crystal  405  is provided. A cylindrical magnet  410  is provided along the magneto-optical crystal  405 . Polarizers  406  are located between the lenses  430 ,  432  and the magneto-optical crystal  405 . Upon activation of magnets  410  or rotation of the polarizers  406  relative to the magneto-optical crystal  405 , the light transmitted through the magneto-optical crystal  405  can be adjusted. The magneto-optical crystal  405 , magnet  410  and polarizers  406  are mounted to the substrate  450 , which has a lower surface level than the portions of the substrate  450  having the grooves  440 , such that the optical path between the lenses  430 ,  432  passes through the magneto-optical crystal  405  and polarizers  406 . 
   An example of an optical attenuator  500  according to another embodiment of the invention is shown by way of example in FIG.  16 . This optical attenuator  500  provides a substrate  550  having grooves  540  to position optical fibers  520 ,  522 . Lenses  530 ,  532  are mounted to ends of the optical fibers  520 ,  522 . One or more shutters  505 ,  506  are positioned to selectively block the optical path between the lenses  530 ,  532 . One or more shutters  505 ,  506  are moved in and out of the optical path by the use of one or more actuators  510 ,  511 . Optionally, only a single shutter  506  and actuator  510  may be provided, such that the shutter  506  extends across the optical path between lenses  530 ,  532 . For further detail regarding examples of actuators and substrate configuration that may be used with this implementation, please see U.S. Pat. No. 6,275,320, to Dhuler, et. al. 
     FIG. 17  illustrates a further example of an optical switch  600  using one or more mirrors  605  that can be selectively placed to redirect light. Optical fibers  620  are arranged in grooves  640  formed in substrates  650 . Lenses  630  are mounted to a first end of the optical fibers  620 , such that the lenses  630  are outside of the grooves  640 . 
   With reference to  FIG. 17 , the example optical switch  600  operates as follows. By way of example, optical fiber  620 A directs light into the optical switch  600 . If mirror  605 A has been moved up, the mirror  605 A will redirect the light from the optical fiber  620  to optical fiber  620 B. In  FIG. 17 , mirrors  605  in an up position are illustrated as a solid line, while mirrors  605  in a down position are illustrated in dashed lines. If the mirror  605 A is down, light from optical fiber  620 A will continue to travel to optional optical fiber  620 C. In another example, light from optical fiber  620 D will travel to optical fiber  620 E and not be directed into optical fibers  620 F,  620 G,  620 H or  620 B, because each of the mirrors between optical fiber  620 D and optical fiber  620 E are down. Mirrors  605  may be moved from an up position to a down position by actuators. Although many types of actuators may be used with this embodiment of the invention, examples of actuators that may be used with this implementation, see U.S. Pat. No. 6,449,406 to Fan, et al. 
   Although  FIG. 17  illustrates a matrix of mirrors  605  and corresponding optical fibers  620  and lenses  630 , it is understood that the invention is not so limited. One or more mirrors  605  may be used and may be arranged linearly or some other pattern or randomly. Similarly, optical fibers  620 , lenses  630  and grooves  640  may be arranged as desired. 
   The entire contents of each of the patents and publications cited herein are hereby incorporated herein by reference. 
   The present invention has been described by way of example, and modifications and variations of the described embodiments will suggest themselves to skilled artisans in this field without departing from the spirit of the invention. Aspects and characteristics of the above-described embodiments may be used in combination. The described embodiments are merely illustrative and should not be considered restrictive in any way. The scope of the invention is to be measured by the appended claims, rather than the preceding description, and all variations and equivalents that fall within the range of the claims are intended to be embraced therein.