Patent Publication Number: US-2019170953-A1

Title: Axial alignment of a lensed fiber in a grooved assembly

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 15/136,229, filed on Apr. 22, 2016, entitled “Axial Alignment of a Lensed Fiber in a Grooved Assembly,” which application is a divisional of U.S. patent application Ser. No. 14/857,580, filed on Sep. 17, 2015, entitled “Axial Alignment of a Lensed Fiber in a Silica V-Groove,” now U.S. Pat. No. 9,348,094, issued on May 24, 2016, which application claims priority to U.S. Provisional Application No. 62/136,504, filed on Mar. 21, 2015, and U.S. Provisional Application No. 62/136,503, filed on Mar. 21, 2015, the disclosures of which are incorporated by reference for all purposes. 
    
    
     BACKGROUND 
     Silicon integrated circuits have dominated the development of electronics, and many technologies based upon silicon processing have been developed over the years. Their continued refinement led to nano-scale feature sizes that can be important for making metal oxide semiconductor CMOS (complementary metal-oxide semiconductor) circuits. Silicon can be used as an optical medium, particularly for light having a wavelength of about 1.55 microns (m). Light having a wavelength of 1.55 μm is often used for fiber-optic telecommunication systems. 
     Some silicon devices have both electronic and optical components. 
     BRIEF SUMMARY OF THE INVENTION 
     This application relates to coupling optical waveguides. More specifically, and without limitation, to coupling an optical fiber with a semiconductor waveguide, such as a waveguide made in silicon. 
     A v-groove assembly is used to edge couple a lensed fiber (e.g., an optical fiber made of silica) with a waveguide in a photonic chip. For example the lensed fiber is butt-coupled to the photonic chip. The v-groove assembly is made from fused silica (e.g., by diamond dicing and/or etching). Fused silica is used so that resin used in bonding the lensed fiber to the v-groove assembly, and/or bonding the v-groove assembly to the photonic chip, can be cured, at least partially, by light (e.g., ultraviolet (UV) light used to cure the resin). In some embodiments, the photonic chip comprises silicon, and the waveguide comprises a crystalline-silicon core (e.g., the crystalline-silicon core being formed from a device layer of a silicon-on-insulator wafer). In some embodiments, photonic chips comprising other materials are used (e.g., II-VI and/or III-V compounds; including GaAs and/or InP and related compounds). In some embodiments, the photonic chip comprises two semiconductor materials. The photonic chip comprises an edge facet where the waveguide terminates and is coupled with the lensed fiber. 
     In some embodiments, a method for aligning an optical fiber with a v-groove assembly is described. A facet of the v-groove assembly is placed next to a mirror. A first end of the optical fiber is placed in a v-groove of the v-groove assembly, wherein the v-groove assembly comprises a base and a lid. The lid is placed over the optical fiber so that the optical fiber is between the base and the lid. An adhesive is applied to the v-groove assembly and/or the optical fiber for bonding the optical fiber to the v-groove assembly. A second end of the optical fiber is connected to a splitter, wherein the splitter is optically coupled with an optical source and a detector. Light of a first wavelength is transmitted from the optical source, through the splitter, to the optical fiber, and out the optical fiber through a tip of the first end of the optical fiber. With the mirror, light of the first wavelength is reflected back from the tip of the optical fiber back into the optical fiber through the tip. Light of the first wavelength is transmitted from the tip to the detector through the splitter. Feedback is received from the detector. A distance between the tip of the optical fiber and the mirror is adjusted based on feedback from the detector. The adhesive is at least partially cured using light of a second wavelength passing through the lid, after adjusting the distance between the tip of the optical fiber and the mirror. 
     In some embodiments, the lid is made of fused silica; the base is made of fused silica; light of the first wavelength is infrared light and light of the second wavelength is ultraviolet light; adjusting the distance between the tip of the optical fiber and the mirror includes moving the optical fiber in an axial direction to optimize received power at the detector; the chip comprises crystalline silicon and/or III-V material; and/or the adhesive is an epoxy resin configured to be at least partially cured by ultraviolet light. In some embodiments, the method further comprises bonding the v-groove assembly to a chip, after at least partially curing the adhesive. 
     A system for aligning an optical fiber with a v-groove assembly is described. The system comprises the optical fiber. The optical fiber has a first end and a second end; and the first end comprises a tip. The system comprises the v-groove assembly. The v-groove assembly comprises a base; a lid, wherein the first end of the optical fiber is between the base and the lid; and a facet for bonding to a chip, wherein the first end of the optical fiber is placed between the base and the lid such that the facet extends beyond the of the optical fiber. The system comprises an optical source, detector, and splitter. The splitter is coupled with the second end of the optical fiber, the optical source, and the detector. The system comprises a mirror for reflecting light from the optical source traveling out of the tip of the optical fiber back into the tip of the optical fiber and to the detector. 
     In some embodiments, in the system for aligning an optical fiber with a v-groove assembly, the optical source emits infrared light, the system further comprises a lamp, the lamp emits ultraviolet light, and/or the system further comprises an adhesive, at least partially cured by ultraviolet light, used to bond the optical fiber to the base and the lid; the v-groove assembly further comprises a v-groove, the optical fiber is in the v-groove, and the v-groove does not extend to the facet; the system further comprises an optical circulator or an optical isolator between the optical source and the splitter; the detector is a power meter; the lid is made of fused silica; and/or the base is made of fused silica. 
     An optical assembly for connecting an optical fiber to a semiconductor waveguide is described. The optical assembly comprises a v-groove assembly and adhesive. The v-groove assembly comprises a base; a lid; a v-groove; and a facet, wherein the facet is for bonding the v-groove assembly to a chip. The optical fiber in the v-groove, positioned between the base and the lid. The adhesive bonds the optical fiber to the base and the lid, wherein the adhesive is, at least partially, cured using light. In some embodiments, the base and/or the lid comprise fused silica. In some embodiments, the lid consists of fused silica. 
     Further areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating various embodiments, are intended for purposes of illustration only and are not intended to necessarily limit the scope of the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts a perspective view of an embodiment an optical adapter using a v-groove assembly. 
         FIG. 2  depicts a perspective view of an embodiment of a portion of the v-groove assembly. 
         FIG. 3  depicts a top view of an embodiment of the v-groove assembly aligned with a chip. 
         FIG. 4  depicts an embodiment of an alignment station. 
         FIG. 5  depicts a flowchart of an embodiment of a process for aligning an optical fiber in the v-groove assembly with a waveguide in a chip. 
         FIG. 6  depicts a simplified schematic top view of an embodiment of an alignment system. 
         FIG. 7  depicts a simplified front view of an embodiment of a v-groove assembly during working-distance alignment. 
         FIG. 8  depicts a simplified front view of another embodiment of a v-groove assembly. 
         FIG. 9  depicts a simplified view of a further embodiment of a v-groove assembly. 
         FIG. 10  depicts a flowchart of an embodiment of a process for aligning an optical fiber in the v-groove assembly. 
         FIG. 11  depicts a flowchart of an embodiment of a process for connecting an optical fiber, which is bonded to a v-groove assembly, with a photonic chip. 
     
    
    
     In the appended figures, similar components and/or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label by a dash and a second label that distinguishes among the similar components. If only the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label. 
     DETAILED DESCRIPTION 
     The ensuing description provides preferred exemplary embodiment(s), and is not intended to limit the scope, applicability, or configuration of the disclosure. Rather, the ensuing description of the preferred exemplary embodiment(s) will provide those skilled in the art with an enabling description for implementing a preferred exemplary embodiment. It is understood that various changes may be made in the function and arrangement of elements without departing from the spirit and scope as set forth in the appended claims. 
     In some embodiments, an optical fiber is optically coupled to a waveguide in a chip (in some embodiments the chip is also referred to as a photonic chip or optical chip) using a v-groove assembly. For example, the waveguide is crystalline silicon etched in a device layer of a silicon-on-insulator substrate. The v-groove assembly is made of silica. For example, the v-groove assembly is made by dicing, machining, grinding, etching, and/or polishing fused silica. Silica (SiO2) is used because silica is optically transparent to ultraviolet (UV) light in some forms. The optical fiber is bonded to the v-groove assembly using a resin cured by UV light, and/or the v-groove assembly is bonded to the chip using a resin cured by UV light. Forming the v-groove assembly from silica allows UV light to pass through parts of v-groove assembly for curing the resin. 
     Referring to  FIG. 1 , a perspective view of an embodiment an optical adapter  100  is shown. The optical adapter  100  optically couples a waveguide on a chip to a fiber-optics network. The optical adapter  100  comprises an optical fiber  104 , a v-groove assembly  108 , and a receptacle  112 . A first end  114  of the optical fiber  104  is attached to the v-groove assembly  108 , and a second end  115  of the optical fiber  104  is attached to the receptacle  112 . 
     In some embodiments, the optical fiber  104  is made of silica (e.g., Corning SMF-28 Ultra or similar fibers). The optical fiber  104  comprises a tip  116  at the first end  114  of the optical fiber  104 . In some embodiments, the tip  116  is lensed (e.g., a tapered tip) for focusing light exiting the tip  116  of the optical fiber  104 . In some embodiments, the optical fiber  104  has an ultra-high numerical aperture (NA). For example, ultra-high NA fibers have NA≥0.25. In some embodiments, 0.5≥NA≥0.25. 
     The first end  114  of the optical fiber  104  is secured to the v-groove assembly  108 . A lid  120  of the v-groove assembly  108  covers the optical fiber  104  to secure the optical fiber  104  in the v-groove assembly  108 . An adhesive that is cured by UV light (e.g., an epoxy resin, and/or UV/thermal curable, low-shrinkage epoxy resin) is used to secure the optical fiber  104  to the v-groove assembly  108 . 
     In some embodiments, the second end  115  of the optical fiber  104  is connected to the receptacle  112 . In some embodiments, the second end  115  of the optical fiber is fusion spliced to a fiber network. In some embodiments, the receptacle  112  is shaped as an LC connector (e.g., complying with IEC (International Electrotechnical Commission) standard 61754-20). The receptacle  112  allows for more simple and/or convenient optical connection to an optical network (e.g., for connecting to an intranet or to the Internet) than splicing optical fibers. 
       FIG. 2  depicts a perspective view of an embodiment of a portion of the v-groove assembly  108 . The v-groove assembly  108  comprises the lid  120 , and a base  202 . The base  202  comprises a v-groove  204  and one or more facets  208 . In  FIG. 2 , the base  202  comprises a first facet  208 - 1  and a second facet  208 - 2 . The first facet  208 - 1  is to one side of the v-groove  204  and the second facet  208 - 2  is to another side of the v-groove  204 . The facets  208  are for bonding the v-groove assembly  108  to a chip. 
     The first end  114  of the optical fiber  104  is placed in the v-groove  204 , and the lid  120  is placed over the optical fiber  104 . The facets  208  extend beyond, in an axial direction, the v-groove  204  for bonding to a chip. The axial direction is a direction along an axis of the optical fiber  104  (e.g., direction of beam propagation). A lateral direction is orthogonal to the axial direction; and the lateral direction can be further subdivided into a vertical direction and a horizontal direction. The tip  116  of the optical fiber  104  extends past the v-groove  204 , axially. In some embodiments, the facets  208  extend past the v-groove  204  so that an adhesive used to bond the v-groove assembly  108  to the chip is not as likely to cover the tip  116  of the optical fiber  104 . In some embodiments, the v-groove  204  comprises two bonding facets  208  to provide structural support when securing the v-groove assembly  108  to the photonic chip. The bonding facets  208  extend past the v-groove  204  a first length  212 . In some embodiments, the first length  212  is between 100 and 300 μm and/or 225 and 275 μm (e.g., 150, 200, 250, or 300 μm). 
       FIG. 3  depicts a top view of an embodiment of the v-groove assembly  108  aligned with a chip  308 . The chip  308  comprises a waveguide  312  (e.g., a semiconductor waveguide made of crystalline silicon). An adhesive  316  is used to bond the v-groove assembly  108  to the chip  308 . The adhesive  316  is applied to the bonding facet  208  of the v-groove assembly  108  and to an edge facet  320  of the chip  308 . 
     In some embodiments, the chip  308  comprises and/or is optically coupled with a receiver (e.g., photodiode). In some embodiments, the waveguide  312  is optically coupled with the receiver. In some embodiments, the chip  308  comprises one or more other chips (e.g., III-V chips for a gain medium) as described in U.S. application Ser. No. 14/509,914, filed on Oct. 8, 2014, which is incorporated by reference. The v-groove assembly  108  is aligned by applying adhesive  316  to the bonding facet  208  (or to the edge facet  320  of the chip  308 , or both), and the v-groove assembly  108  is roughly aligned with the chip  308  (e.g., bringing the v-groove assembly  108  near the edge facet  320  of the chip  308 ). Light is transmitted through the optical fiber  104  and into the waveguide  312 . A gripper holding the v-groove assembly  108  is adjusted to position the tip  116  of the optical fiber  104  in relation to the waveguide  312  to optimize optical transmission from the optical fiber  104  into the waveguide  312  (e.g., the receiver registers a maximum power; a percentage of maximum power, e.g., &gt;90%, 95%; or a predetermined threshold power). In some embodiments, the v-groove assembly  108  is actively aligned (e.g., using a computerized system). In some embodiments, a thickness of the adhesive  316  before a first cure is equal to or less than 10, 8, or 7 μm. In some embodiments, the bonding facets  208  are polished and the thickness of the epoxy resin before the first cure is equal to or less than 5 μm (e.g., separation of the bonding facet from the edge facet is equal to or less than 5 μm). In some embodiments, the bonding facets  208  are pitted and/or roughened for an adhesive  316  to better adhere to. In some embodiments, a thickness of the adhesive  316  before the first cure is 7-10 μm, because results from bonding show 7-10 μm forms a stable bond, which is sufficient for some applications. In some embodiments, the waveguide  312  has a height (vertical) and/or width (horizontal) equal to or less than 12, 10, 8, 5, 2, 1.7, 1.6, or 1.5 μm. In some embodiments, the waveguide has a height (vertical) and/or width (horizontal) greater than 1.0 or 1.5 μm for improved coupling with the optical fiber  104  (e.g., with a tapering waveguide). In some embodiments, only one dimension (e.g., a lateral dimension) is adjusted by the gripper holding the v-groove assembly  108 . For example, a vertical height (i.e., into and out of the page of  FIG. 3 ) is determined by a height of the v-groove  204  of the v-groove assembly  108 ; an axial distance (along a direction of beam propagation of the optical fiber  104 ) between the tip  116  of the optical fiber  104  and the edge facet  320  of the chip  308  is determined by a distance between the tip  116  of the optical fiber  104  and the bonding facet  208 . In some embodiments, the bonding facet  208  is placed to touch the edge facet  320  of the chip  308 , and then the v-groove assembly is moved away from the edge facet  320  of the chip  308  a predetermined distance (e.g., 7-10 μm) before adhesive  316  is applied between the bonding facet  208  and the edge facet  320 . 
     After the tip  116  of the optical fiber  104  is aligned to the waveguide  312  of the chip  308  (e.g., by the gripper holding the v-groove assembly  108 ), a first cure of the adhesive  316  is performed (e.g., by irradiating the adhesive  316  with light). In some embodiments, the adhesive  316  is an epoxy resin cured with ultraviolet (UV) light (e.g., light having a wavelength between 100 nm and 400 nm, or between 250 and 400 nm). In some embodiments, the v-groove assembly  108  is made of fused silica, which is made transparent to UV light, so that UV light can be shined through the v-groove assembly  108  to cure the adhesive  316  that is between the bonding facet  208  of the v-groove assembly  108  and the edge facet  320  of the chip  308 . In some embodiments, the v-groove assembly  108  is made of silica having greater than 60% or 70% transmission for wavelengths from 250 nm to 400 nm, or from 300 nm to 400 nm (e.g., UV-grade silica and/or broadband silica). It is noted that crystalline silicon has low transmission (e.g., &lt;20%) for wavelengths less than 900 nm. In some embodiments, additional epoxy resin is added after the first cure (e.g., to sides and/or other surfaces of the v-groove assembly  108 ), and a second cure is performed where the additional epoxy resin is cured with UV light. In some embodiments, two steps of curing epoxy resin is used because the first cure is used to set alignment of the v-groove, wherein using less epoxy resin has less shrinkage during UV cure. And the second cure, with the additional epoxy resin, is used to add more epoxy resin to form a more robust bond between the v-groove assembly  108  and the chip  308 . After the second cure (or in some embodiments after the first cure if the second cure is not used), a thermal cure is performed. The thermal cure further hardens the epoxy resin. 
     In some embodiments, coupling arrangement between the optical fiber  104  and the waveguide  312  shown in  FIG. 3  is compact, which reduces space on a printed circuit board assembly (PCBA). Further, coupling loss during adhesive  316  cure is reduced and reliability is improved. 
       FIG. 4  depicts an embodiment of an alignment station  400 . The alignment station  400  comprises a gripper  404  and a PCBA mount  408 . The PCBA mount  408  secures a PCBA  412 . The PCBA  412  comprises a first chip  308 - 1  and a second chip  308 - 2 . The gripper  404  is used to align the v-groove assembly  108  with the first chip  308 - 1  or the second chip  308 - 2 . In some embodiments, mechanical controls  416  are used to move the gripper  404 . In some embodiments, electrical connections  420  are used to automate alignment of the v-groove assembly  108  with the chip  308 . Such a system has demonstrated robust, high coupling efficiency alignment. In some embodiments, a sub mount is used instead of the PCBA  412 . 
       FIG. 5  depicts a flowchart of an embodiment of a process  500  for aligning the optical fiber  104 , which is in the v-groove assembly  108 , with the chip  308 . The process  500  for aligning the optical fiber  104  with the chip  308  begins in step  504  with loading the PCBA  412  (or a sub mount) on the PCBA mount  408 . In some embodiments, the PCBA  412  is loaded on the PCBA mount  408  after chip(s)  308  and/or wire bonding are added to the PCBA  412 . The gripper  404  picks up the v-groove assembly  108  (e.g., by the lid  120  of the v-groove assembly  108 ) and actively aligns the v-groove assembly  108  with the chip  308 , step  508 . In some embodiments, alignment involves providing active lateral and/or active axial (longitudinal) alignment. For reliability, and/or to minimize movement during adhesive  316  curing, in some embodiments, thickness of the adhesive  316  for butt-bonding between the v-groove assembly  108  and the chip  308  is reduced (e.g., &lt;10 μm). In some embodiments, an initial-alignment position is established. After an initial alignment, the v-groove assembly  108  is moved, using the gripper  404 , away from the chip  308 . In step  512 , adhesive  316  is applied to the v-groove assembly  108  (e.g., bonding facets  208 ). In some embodiments, a first amount of epoxy resin (e.g., a portion of adhesive  316 ) is applied to the bonding facet(s)  208  of the v-groove assembly  108 . The v-groove assembly  108  is moved back to the initial-alignment position using the gripper  404  (e.g., automatically using the gripper  404  and electrical connections  420  after the first amount of epoxy resin is applied). In some embodiments, a final alignment is performed. In some embodiments, a first cure of the adhesive  316  is performed, wherein the first cure at least partially cures the first amount of epoxy resin between the bonding facet  208  and the edge facet  320  of the chip  308  (e.g., UV curing by shining UV light through the v-groove assembly  108 , such as through the bonding facet  208 ). In some embodiments, a second amount of epoxy resin (e.g., a portion of adhesive  316 ) is applied to the v-groove assembly  108  and/or the chip  308 . In some embodiments, a second cure of the adhesive  316  is performed to further secure the v-groove assembly  108  to the chip  308  and/or the PCBA  412  (e.g., the adhesive is a two-step adhesive, which is thermally cured after UV curing). In some embodiments, the adhesive  316  is thermally cured after UV curing. In some embodiments, additional assembly of the PCBA  412  is performed after a UV curing and/or a thermal curing of the adhesive  316 . 
     In some embodiments, using a v-groove assembly  108  bonded to the chip  308  holds the optical fiber  104  with high stability for optical coupling; the fused silica optical properties enable UV curing of the adhesive  316  (e.g., epoxy resin) between the v-groove assembly  108  and the chip  308 . Shifting of the tip  116  of the optical fiber  104  during UV curing and/or thermal curing is small (e.g., is less than 0.5, 0.4, 0.3, 0.2, or 0.1 μm, in each of the three directions); and/or directly bonding the v-groove assembly  108  to the edge facet  320  of the chip  308  makes a stable bond when temperature varies. In some embodiments, a similar design can be applied to discrete optics coupling. For example, an optical assembly is formed that holds a discrete optical element (e.g., a lens). The optical assembly has facets for bonding to a photonic chip similar to the bonding facets  208  of the v-groove assembly  108 . The optical assembly is then bonded to the photonic chip (e.g., similarly as the v-groove assembly  108  is bonded to the chip  308 ). Because of a larger working distance that discrete optical elements normally have, a geometry with discrete optics would not likely be as compact as for a lensed fiber. However, attachment of an optical mount directly to the edge facet  320  of the chip  308  would still provide a more compact geometry and a direct attachment of the discrete optical element to the chip  308 , minimizing movement during curing and from thermal effects, and/or improving reliability. 
     In a previous approach by the applicant (and not admitted by the applicant to be prior art), a discrete lens plus a fiber collimator was used. Fiber output was collimated using a pigtailed collimator. A discrete lens coupled light into a waveguide (e.g., waveguide  312  on the chip  308 ). Some embodiments of this disclosure differ in that a lensed fiber is directly coupled to the waveguide (e.g., without a collimator and/or discrete lens); a v-groove assembly  108  is used to hold the optical fiber  104 ; the v-groove assembly  108  is attached directly to the chip  308  (e.g., by epoxy); higher optimal coupling efficiency during alignment is achieved; less movement during epoxy resin curing is achieved; improved final coupling efficiency is achieved; higher reliability is achieved; reduced temperature dependence of coupling efficiency due to thermal expansion due to compact geometry and/or limited epoxy thickness is achieved; and/or reduced board real estate is achieved. 
     Referring next to  FIG. 6 , a simplified schematic top view of an embodiment of an alignment system  600  is shown. The alignment system  600  is used to align and bond the optical fiber  104  to the v-groove assembly  108 . The alignment system  600  comprises the optical fiber  104 , the base  202  of the v-groove assembly  108 , an optical source  604 , an optical isolator  606 , a splitter  608 , a mirror  612 , a detector  616 , and a lamp  620 . 
     The optical source  604  is a laser, LED, or RCLED (resonant-cavity LED) emitting light of a first wavelength (e.g., light centered at a first wavelength). In some embodiments, the first wavelength is between 1000 nm and 1800 nm or between 1300 nm and 1600 nm (e.g., having a peak intensity at 1550 nm). The optical isolator  606  passes light traveling from the optical source  604 , and attenuates and/or blocks light from being transmitted to the optical source  604 . The optical source  604  is optically coupled with the splitter  608 , with the optical isolator  606  being between the optical source  604  and the splitter  608 . The splitter  608  is optically coupled with the second end  115  of the optical fiber  104 . For example, the splitter  608  is optically coupled with the receptacle  112  of the optical adapter  100 . 
     The base  202  of the v-groove assembly  108  shown in  FIG. 6  is similar to the base  202  of the v-groove assembly  108  show in  FIG. 3 . The lid  120  of the v-groove assembly  108  is not shown in  FIG. 6 . The bonding facet  208  of the base  202  of the v-groove assembly  108  is placed next to the mirror  612 . In some embodiments, the bonding facet  208  touches the mirror. In some embodiments, the bonding facet  208  is placed close to the mirror  612 , but not touching the mirror (e.g., less than 1, 2, 5, 7, or 10 μm away from the mirror). 
     The optical fiber  104  is placed in the v-groove  204  of the base  202  of the v-groove assembly  108 . The tip  116  of the optical fiber  104  is directed towards the mirror  612 . Adhesive is applied to the optical fiber  104  and/or the base  202  of the v-groove assembly  108  (e.g., to the v-groove  204 , to an interface between the base  202  and the lid  120 , and/or placing the lid  120  over the base  202 , at least partially covering the optical fiber  103 , and adhesive is applied between the optical fiber  104  and the lid  120 , such that capillary action brings the adhesive into interfaces between the lid  120 , the optical fiber  104 , and/or the base  202 ). In some embodiments, adhesive is applied to the lid  120  of the v-groove assembly  108 . In some embodiments, the adhesive applied to the optical fiber  104  and/or the base  202  of the v-groove assembly  108  is similar to the adhesive  316  applied between the bonding facet  208  and the edge facet  320  in  FIG. 3 . The bonding facet  208  helps orient the direction of beam propagation from the optical fiber  104  to be orthogonal a surface of the mirror  612 , because the bonding facet  208  is orthogonal to a length of the v-groove  204 . The lid  120  is placed over the v-groove  204 , at least partially covering the optical fiber  104 . The adhesive applied to the optical fiber and/or the base  202  of the v-groove assembly  108  is not cured until after aliment of the optical fiber  104  in the v-groove assembly  108 . The bonding facet  208  is not bonded to the mirror  612 . 
     The splitter  608  is optically coupled with the detector  616 . In some embodiments, the detector  616  is a power meter. Light of the first wavelength is transmitted from the optical source  604 , through the splitter  608  and into the optical fiber  104 . Light of the first wavelength is then transmitted out the tip  116  of the optical fiber  104 , to the mirror  612 , and reflected back into the tip  116  of the optical fiber  104 . Light of the first wavelength then travels from the tip  116  to the splitter  608  and to the detector  616 . 
     A distance, which is referred to as a working distance  624 , separates the tip  116  of the optical fiber  104  from the mirror  612 . The optical fiber  104  is moved longitudinally (in an axial direction), within the v-groove  204 , to adjust the working distance  624 . The tip  116  of the optical fiber  104  is lensed. As the working distance  624  approaches a focal length of the lens of the tip  116 , optical power at the detector  616  increases because more optical power is being reflected back into the optical fiber  104 . The working distance  624  is optimized (e.g., to have power above a predetermined threshold, or a percentage of maximum). In some embodiments, after the working distance  624  is optimized, the optical fiber  104  is then advanced so that the tip  116  goes toward the mirror  612  (i.e., reducing the working distance  624 ) a predetermined distance corresponding to an expected thickness of adhesive  316  between the bonding facet  208  and the edge facet  320  (e.g., 1-10 μm). 
     After the working distance  624  is set, adhesive applied to the lid  120 , the optical fiber  104 , and/or the base  202  of the v-groove assembly  108  is at least partially cured using a light source of a second wavelength. In the alignment system  600 , the lamp  620  is used as the light source of the second wavelength. The lid  120  is made of fused silica because fused silica transmits UV light. The lamp  620  emits UV light that is transmitted through the lid  120  to at least partially cure the adhesive applied to the optical fiber  104  and/or the base  202  of the v-groove assembly  108 . 
     In some embodiments, an epoxy resin is placed on the v-groove assembly  108  and/or the optical fiber  104  before alignment so that the fiber  104  can be fixed in position after optimization. In some embodiments, the lid  120  serves to retain and protect the optical fiber  104  and/or serve as a handle for gripper  404  to hold the v-groove assembly  108  for lateral and/or axial alignment with the chip  308 . In some embodiments, adhesive applied to the v-groove assembly  108  and/or the optical fiber  104  is also thermally cured. In some embodiments, the adhesive applied to the v-groove assembly and/or the optical fiber  104  has a first, initial cure followed by additional adhesive and a second cure. In some embodiments, the second cure is followed by a heat cure. 
     In some embodiments, once a set working distance  624  is known, then subsequent fibers can be positioned in v-groove assemblies  108  using a microscope and eyepiece (reticle scale). In some embodiments, in place of the splitter  608  and the isolator  606 , an optical circulator may be used. In some embodiments, the lid  120 , the v-groove  204 , and/or the bonding facets  208  are made of fused silica. In some embodiments, the lid  120  is fused silica for curing epoxy resin that secures the lid  120  to other portions of the v-groove assembly  108  and/or to the optical fiber  104 . 
       FIG. 7  depicts a simplified front view of an embodiment of a v-groove assembly  108  during working-distance alignment. The v-groove assembly comprises the v-groove  204 , a first bonding facet  208 - 1 , a second bonding facet  208 - 2 , and the lid  120 . The tip  116  of the optical fiber  104  is shown between the lid  120  and the v-groove  204 . Adhesive  704  between the lid  120  and the v-groove  204  bonds the optical fiber  104  to the v-groove assembly  108 . In some embodiments, the adhesive  704  is used to bond the lid  120  to the base  202  of the v-groove assembly  108 . In some embodiments, additional adhesive is used to bond the lid  120  to the base  202  of the v-groove assembly  108  (e.g., sides of the lid  120 ). 
     Referring next to  FIGS. 8 and 9 ,  FIGS. 8 and 9  depict additional embodiments of the v-groove assembly  108 .  FIG. 8  depicts a simplified front view of an embodiment of a v-groove assembly  108 .  FIG. 8  is similar to  FIG. 7 , except instead of having the first bonding facet  208 - 1  and the second bonding facet  208 - 2 , the v-groove assembly  108  in  FIG. 8  has only one bonding facet  208 . 
       FIG. 9  depicts a simplified view of an embodiment of a v-groove assembly  900 . The v-groove assembly  900  comprises a base  902  and a lid  920 . The lid  920  comprises a v-groove  904 . The base  902  comprises a bonding facet  908 . An optical fiber  104  is placed between the base  902  and the lid  920 . The base  902  further comprises a recess formed by a floor  912  and walls  916 . The recess helps prevent adhesive from getting on the tip  116  of the optical fiber  104 . 
       FIG. 10  depicts a flowchart of an embodiment of a process  1000  for aligning an optical fiber  104  in the v-groove assembly (e.g., v-groove assembly  108  or  900 ). The process  1000  for aligning an optical fiber  104  in the v-groove assembly  108  begins in step  1004  by placing a facet (e.g., bonding facet  208 ) of the v-groove assembly next to a mirror (e.g., mirror  612 ). In some embodiments, placing the bonding facet  208  next to the mirror  612  means the bonding facet  208  contacts the mirror  612 . In some embodiments, placing the bonding facet  208  next to the mirror  612  means the bonding facet  208  is close to, but not contacting, the mirror  612  (e.g., less than 15, 10, or 5 μm from the mirror  612 ). In some embodiments, the bonding facet  208  does not contact the mirror  612  in order to compensate for an estimated thickness of adhesive  316  for bonding the v-groove assembly  108  to the chip  308 . 
     In step  1008 , the first end  114  of the optical fiber  104  is placed in the v-groove  204  of the v-groove assembly  108 . The lid  120  is placed on the base  202  of the v-groove assembly  108 , covering at least a portion of the first end  114  of the optical fiber  104 . The optical fiber  104  is between the base  202  of the v-groove assembly  108  and the lid  120  of the v-groove assembly  108 . Then adhesive  704  (e.g. an epoxy resin) is applied between the optical fiber  104  and the lid  120 . Capillary action draws the adhesive into an interface between the lid  120 , the optical fiber  104 , and/or the base  202 . In step  1012 , the second end  115  of the optical fiber  104  is connected to the splitter  608 . 
     In step  1016 , light of a first wavelength is transmitted from the optical source  604 , through the splitter  608 , and to the first end  114  of the optical fiber  104 . In some embodiments, light of the first wavelength is transmitted through an optical isolator  606  positioned between the source  604  and the splitter  608 . In some embodiments, the light of the first wavelength is infrared (e.g., between 1250 nm and 1600 nm). Light of the first wavelength is transmitted out of the first end  114  of the optical fiber  104  through the tip  116  of the optical fiber  104 . 
     In step  1020 , light of the first wavelength transmitted out of the first end  114  of the optical fiber  104  through the tip  116  of the optical fiber  104  reflects off the mirror  612  and back into the first end  114  of the optical fiber  104  through the tip  116  of the optical fiber  104 . Reflected light of the first wavelength from the mirror  612  travels from first end  114  of the optical fiber  104 , to the second end  115  of the optical fiber  104 , to the splitter  608 , and from the splitter  608  to the detector  616 . The isolator  606  is used to keep light from reflecting back into the source  604 . 
     In step  1024 , a distance (e.g., the working distance  624 ) is adjusted between the tip  116  of the optical fiber  104  and the mirror  612  based on feedback from the detector  616 . For example, the detector  616 , in some embodiments, is a power meter. The tip  116  of the optical fiber  104  is moved axially (e.g., toward or away from the mirror  612 ) and a power reading of the detector  616  changes. Power increases as the working distance  624  approaches a focal length of the tip  116  (e.g., a lensed fiber). Power decreases as the working distance  624  departs from the focal length of the tip  116  of the optical fiber  104 . 
     Once the working distance  624  is adjusted based on feedback from the detector  616 , adhesive  704  in the v-groove  204  is cured using lamp  620 . To cure the adhesive  704  in the v-groove, light of a second wavelength (e.g., UV light), is transmitted through the lid  120  to cure the adhesive  704  in the v-groove  204 , step  1028 . Since the lid  120  is made of fused silica, UV light can penetrate through the lid  120  to cure the adhesive  704  in the v-groove  204 . Thus the optical fiber  104  can be aligned with, and bonded to, in the v-groove assembly  108  accurately and/or with less risk of altering alignment of the optical fiber  104  during curing than previous bonding techniques (e.g., alignment can be done before curing). 
     In some embodiments, the bonding facet  208  contacts the mirror  612  and adjusting the working distance  624  includes moving the tip  116  of the optical fiber  104  toward the mirror  612  to compensate for an estimated thickness of adhesive  316  for bonding the v-groove assembly  108  to the chip  308 . 
       FIG. 11  depicts a flowchart of an embodiment of a process  1100  for bonding a v-groove assembly  108 , which is bonded to an optical fiber  104 , to a chip  308 . In some embodiments, the chip  308  comprises silicon (e.g., a silicon-on-insulator (SOI) wafer having a waveguide in a device layer of the SOI wafer). The process  1100  for bonding the v-groove assembly  108  to the chip  308  begins in step  1104  where a v-groove assembly  108  is provided. For example, the optical adapter  100 , comprising the receptacle  112 , optical fiber  104 , and v-groove assembly  108 , is provided. 
     An adhesive (e.g., adhesive  316 , such as an epoxy resin) is applied to a facet (e.g., bonding facet  208 ) of the v-groove assembly  108 , step  1108 . In some embodiments, adhesive  316  is applied to the edge facet  320  in addition to, or in lieu of, applying adhesive  316  to the v-groove assembly  108 . In some embodiments, applying adhesive  316  to the v-groove assembly comprises applying adhesive  316  to the edge facet  320  of the chip  308  and bringing the v-groove assembly  108  near the edge facet  320  so that adhesive  316  touches the bonding facet  208 . 
     In step  1112 , the v-groove assembly  108  is aligned with the chip  308 . For example, the optical fiber  104 , bonded to the v-groove assembly  108 , is aligned with the waveguide  312  of the chip  308 . In some embodiments, the gripper  404  is used to align the v-groove assembly  108  with the chip  308  (e.g., by holding the lid  120  of the v-groove assembly  108 ). In some embodiments, light from the optical fiber  104 , which is coupled into the waveguide  312 , is used in aligning the v-groove assembly  108  with the chip  308 . For example, the waveguide  312  couples light from the optical fiber  104  to a photodetector (either on the chip  308 , such as a PIN diode formed in the device layer of the SOI wafer, or off the chip  308 ). Feedback from the photodetector is used to align the optical fiber  104  to the waveguide  312 . 
     In step  1116 , the adhesive  316  is cured. In some embodiments, the adhesive  316  is an epoxy resin and is cured with UV light (e.g., similar to lamp  620  producing light of a second wavelength). In some embodiments, light of the second wavelength is transmitted through the v-groove assembly  108  (e.g., and through the bonding facet  208 ). Light of the second wavelength is transmitted through the v-groove assembly  108  because the v-groove assembly  108  is made of fused silica, which is transparent to UV light. In some embodiments, a second cure is performed after a first cure (e.g., see discussion relating to  FIG. 3 ). In some embodiments, transmitting light of the second wavelength through the v-groove assembly  108  is done so that the gripper  404  can hold the v-groove assembly  108  in place after alignment and during cure so that the optical fiber  104  remains aligned with the waveguide  312 . In some embodiments, the term “v-groove” is used as a generic term for a groove configured to position an optical fiber in a material, and may include shapes such as a ‘v’, a trench (e.g., flat sides), and ‘u’-shaped grooves, depending on fabrication (e.g., trenches, in some embodiments, are easier to cut or etch in fused silica than a ‘v’; in some embodiments, a v-groove is cut or etched if the base  202  is made of crystalline material and etching can be done by etching on a crystalline plane). 
     The specific details of particular embodiments may be combined in any suitable manner without departing from the spirit and scope of embodiments of the invention. However, other embodiments of the invention may be directed to specific embodiments relating to each individual aspect, or specific combinations of these individual aspects. 
     The above description of exemplary embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form described, and many modifications and variations are possible in light of the teaching above. The embodiments were chosen and described in order to explain the principles of the invention and its practical applications to thereby enable others skilled in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. 
     For example, in some embodiments, the waveguide  312  of the chip  308  comprises a taper to more efficiently couple light into the waveguide  312 . In some embodiments, the waveguide  312  has rectangular cross section. In some embodiments, the waveguide is a ridge waveguide. In some embodiments, the mirror  612  comprises multilayers. In some embodiments, the mirror  612  comprises metal. In some embodiments, the mirror  612  is a block (e.g., a flat piece of metal). 
     In some embodiments, a tip  116  other than a lensed fiber is used (e.g., flat, cleaved end of a fiber). In some embodiments, the optical fiber  104  is aligned to a device other than the waveguide  312  of the chip  308 . For example, the tip  116  of the optical fiber  104  could be aligned to a photodiode or a laser in the chip  308 . In some embodiments, the lid  120  and/or the base  202  of the v-groove assembly are made of other material transparent to UV light (e.g., the lid  120  is made of quartz or UV-grade sapphire). 
     In some embodiments, the chip  308  comprises a light source (e.g., is made of III-V material as a gain medium for a laser). Light is coupled from the chip  308  to the optical fiber  104 . 
     Also, it is noted that the embodiments may be described as a process which is depicted as a flowchart, a flow diagram, a data flow diagram, a structure diagram, or a block diagram. 
     Although a flowchart may describe the operations as a sequential process, many of the operations can be performed in parallel or concurrently. In addition, the order of the operations may be re-arranged. A process is terminated when its operations are completed, but could have additional steps not included in the figure. A process may correspond to a method, a function, a procedure, a subroutine, a subprogram, etc. 
     A recitation of “a”, “an”, or “the” is intended to mean “one or more” unless specifically indicated to the contrary. 
     All patents, patent applications, publications, and descriptions mentioned here are incorporated by reference in their entirety for all purposes. None is admitted to be prior art.