Abstract:
An optical package for providing efficient coupling between a distributed feedback laser diode (DFB-LD) and a silicon photonic integrated-circuit chip (Si PIC) edge couplers with low return loss, as well as variations thereof, is described. The optical package may include a DFB-LD, a Si PIC, a single mode fiber or fiber array assembly, a lens and a spacer. The Si PIC may include an input edge coupler and an output edge coupler. The single mode fiber or fiber array assembly may be aligned to the output edge coupler. The lens may be disposed between the DFB-LD and the input edge coupler, and may be configured to minimize a mismatch between an output spot size of the DFB-LD and a spot size of the input edge coupler of the Si PIC. The spacer may be bonded to a facet of the input edge coupler with an index matching fluid.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION(S) 
       [0001]    The present disclosure is a non-provisional application of, and claims the priority benefit of, U.S. Provisional Patent Application No. 62/179,361, filed on 5 May 2015, which is herein incorporated by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure is related to optical packages. More particularly, the present disclosure is directed to an optical package for providing efficient coupling between a distributed feedback laser diode and a silicon photonic integrated-circuit chip edge couplers with low return loss. 
       BACKGROUND 
       [0003]    Silicon photonic integrated circuits (Si PIC) have attracted tremendous attention due to their high density integration capabilities of coupler, modulator, photodiode, avalanche photodiode, polarization diversity components and multimode interferometers. However, link budget deficiency has limited the application of Si PIC. In one aspect, the coupling efficiency of distributed feedback lasers (DFB-LD) and Si PIC has major influence on the link budget. 
         [0004]    Up to the present time, there are two coupling structures adopted in Si PICs. The first coupling structure is grating coupler, which is favored for its on-chip characterizing compatibilities and high coupling efficiency with less than 2 dB insertion loss. However, one disadvantage of grating coupler is its limited spectral bandwidth, and the typical bandwidth within 1 dB variation is less than 20 nm. Another less-apparent but significant disadvantage is that its vertical packaging structure cannot be easily designed into QSFP28 form factors which have been the main stream packaging form factors in data center applications. 
         [0005]    The second coupling structure is edge coupler, usually with an inverse tapered silicon waveguide surrounded by a SiO 2  cantilever structure. Edge couplers are in-plane structures which can be fully compatible with QSFP form factors. Edge couplers may provide less than 2 dB insertion loss to single mode fiber. Edge couplers may also demonstrate coupling tolerance comparable with single mode fiber and very wide spectral bandwidth supporting O-band and C-band simultaneously. Nevertheless, the coupling loss of a DFB-LD is still beyond the acceptable range, due to the mismatch of DFB-LD mode size and edge coupler mode size. Lenses have been adopted to overcome the mismatch between two modes. However, most commercially available lenses are not designed for the coupling between DFB-LD and Si PIC edge coupler, as shown in  FIG. 4 , but are designed for coupling between DFB-LD and single mode fiber. In  FIG. 4 , the conventional coupling scheme  400  simply utilizes a lens to couple an output optical beam into an edge coupler of a Si PIC. Thus, it is not easy to find a suitable lens to optimize the coupling between DFB-LD and Si PIC edge coupler. 
       SUMMARY 
       [0006]    The following summary is illustrative only and is not intended to be limiting in any way. That is, the following summary is provided to introduce concepts, highlights, benefits and advantages of the novel and non-obvious techniques described herein. Select implementations are further described below in the detailed description. Thus, the following summary is not intended to identify essential features of the claimed subject matter, nor is it intended for use in determining the scope of the claimed subject matter. 
         [0007]    The present disclosure aims to address aforementioned issues associated with conventional coupling structures. Advantageously, the present disclosure provides a novel high-efficient optical package that optimizes the coupling between DFB-LD and Si PIC edge coupler with suppressed return loss. 
         [0008]    In one aspect, an optical package may include a DFB-LD, a Si PIC, a single mode fiber or fiber array assembly, a lens and a spacer. The Si PIC may include at least one input edge coupler and at least one output edge coupler. The single mode fiber or fiber array assembly may be aligned to the at least output edge coupler of the Si PIC. The lens may be disposed between the DFB-LD and the at least one input edge coupler of the Si PIC, and may be configured to minimize a mismatch between an output spot size of the DFB-LD and a spot size of the at least one input edge coupler of the Si PIC. The spacer may be bonded to a facet of the at least one input edge coupler of the Si PIC with an index matching fluid. 
         [0009]    In another aspect, an optical package may include a DFB-LD, a Si PIC, a single mode fiber or fiber array assembly, a lens and an isolator. The Si PIC may include at least one input edge coupler and at least one output edge coupler. The single mode fiber or fiber array assembly may be aligned to the at least output edge coupler of the Si PIC. The lens may be disposed between the DFB-LD and the at least one input edge coupler of the Si PIC, and may be configured to minimize a mismatch between an output spot size of the DFB-LD and a spot size of the at least one input edge coupler of the Si PIC. The isolator may be bonded to a facet of the at least one input edge coupler of the Si PIC with an index matching fluid. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The accompanying drawings are included to provide a further understanding of the present disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure. The drawings may not necessarily be in scale so as to better present certain features of the illustrated subject matter. 
           [0011]      FIG. 1  is a diagram of a high-efficiency optical package in accordance with an embodiment of the present disclosure. 
           [0012]      FIG. 2  is a diagram of a high-efficiency optical package in accordance with another embodiment of the present disclosure. 
           [0013]      FIG. 3  is a diagram of a high-efficiency and low-return-loss optical package in accordance with an embodiment of the present disclosure. 
           [0014]      FIG. 4  is a diagram of a conventional coupling scheme in the prior art. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0015]    Detailed embodiments of the claimed subject matters are disclosed herein. However, it shall be understood that the disclosed embodiments are merely illustrative of the claimed subject matters which may be embodied in various forms. The present disclosure may, however, be embodied in many different forms and should not be construed as limited to the exemplary embodiments set forth herein. Rather, these exemplary embodiments are provided so that description of the present disclosure is thorough and complete and will fully convey the scope of the present disclosure to those skilled in the art. In the description below, details of well-known features and techniques may be omitted to avoid unnecessarily obscuring the presented embodiments. 
         [0016]    The present disclosure provides various embodiments of a novel high-efficient optical package which optimizes the coupling between DFB-LD and Si PIC edge coupler with low return loss. In general, a high-efficient optical package in accordance with the present disclosure may include a DFB-LD, a Si PIC, a lens, a single mode fiber or a fiber array assembly, and a spacer or an isolator. The lens may be inserted or otherwise disposed between the DFB-LD and an input edge coupler of the Si PIC. The single mode fiber or fiber array assembly may be coupled to an output edge coupler of the Si PIC with an index matching fluid filled in an air gap therebetween. The spacer may be a silica double-polished spacer bonded to a facet of the input edge coupler of the Si PIC with the index matching fluid filling the air gap, as shown in  FIG. 1 . The silica spacer may be utilized as a container or adhesion surface for filling the index matching fluid, thus allowing expansion of the mode size of the edge coupler. Furthermore, an opposite surface of the silica spacer may be anti-reflection coated to help reduce return loss. 
         [0017]      FIG. 1  illustrates a high-efficiency optical package  100  in accordance with an embodiment of the present disclosure. Optical package  100  may include a high-efficiency coupling structure between a DFB-LD  110  and a Si PIC  120 . Si PIC  120  may have at least one input edge coupler  122  and at least one output edge coupler  124 . A silica spacer (or isolator)  130  may be bonded to a facet of the at least one input edge coupler  122  with an index matching fluid  140 . A lens  150  may be inserted or otherwise disposed between DFB-LD  110  and spacer or isolator  130 . A single mode fiber or fiber array assembly  160  may be aligned to the at least output edge coupler  124  of the Si PIC  120 . The single mode fiber or fiber array assembly  160  may be bonded to a facet of the at least one output edge coupler  124  with the index matching fluid  140 . 
         [0018]      FIG. 2  illustrates a high-efficiency optical package  200  in accordance with another embodiment of the present disclosure. Optical package  200  may include a high-efficiency coupling structure between a DFB-LD  210  and a Si PIC  220 . Si PIC  220  may have at least one input edge coupler  222  and at least one output edge coupler  224 . A silica spacer (or isolator)  230  may be bonded to a facet of the at least one input edge coupler  222  with an index matching fluid  240 . The index matching fluid  240  may be ultra-violet (UV) curable and/or UV cured. A gradient index (GRIN) lens  250  may be inserted or otherwise disposed between DFB-LD  210  and spacer or isolator  230 . A single mode fiber or fiber array assembly  260  may be aligned to the at least output edge coupler  224  of the Si PIC  220 . The single mode fiber or fiber array assembly  260  may be bonded to a facet of the at least one output edge coupler  224  with the index matching fluid  240 . 
         [0019]      FIG. 3  illustrates a high-efficiency and low-return-loss optical package  300  in accordance with an embodiment of the present disclosure. Optical package  300  may include a high-efficiency coupling structure between a DFB-LD  310  and a Si PIC  320 . Si PIC  320  may have at least one input edge coupler  322  and at least one output edge coupler  324 . A silica spacer (or isolator)  330  may be bonded to a facet of the at least one input edge coupler  322  with an index matching fluid  340 . The index matching fluid  340  may be ultra-violet (UV) curable and/or UV cured. A lens  350  may be inserted or otherwise disposed between DFB-LD  310  and spacer or isolator  330 . A single mode fiber or fiber array assembly  360  may be aligned to the at least output edge coupler  324  of the Si PIC  320 . The single mode fiber or fiber array assembly  360  may be bonded to a facet of the at least one output edge coupler  324  with the index matching fluid  340 . A facet of the at least one input edge coupler  322  (e.g., the facet facing the spacer or isolator  330 ) may be tilt-polished. Alternatively or additionally, a facet of the at least one output edge coupler  324  (e.g., the facet facing the single mode fiber or fiber array assembly  360 ) may be tilt-polished. The Si PIC  320  may be covered with at least one silica cover lid  370 . 
         [0020]    In view of the above, select features of various embodiments in accordance with the present disclosure are described below. 
         [0021]    In one aspect, an optical package may include a DFB-LD, a Si PIC, a single mode fiber or fiber array assembly, a lens and a spacer. The Si PIC may include at least one input edge coupler and at least one output edge coupler. The single mode fiber or fiber array assembly may be aligned to the at least output edge coupler of the Si PIC. The lens may be disposed between the DFB-LD and the at least one input edge coupler of the Si PIC, and may be configured to minimize a mismatch between an output spot size of the DFB-LD and a spot size of the at least one input edge coupler of the Si PIC. The spacer may be bonded to a facet of the at least one input edge coupler of the Si PIC with an index matching fluid. 
         [0022]    In some embodiments, the spacer may include a silica spacer, a glass spacer, a polymer spacer, a polyimide spacer, an epoxy spacer, or a resin spacer. 
         [0023]    In some embodiments, the spacer may include a double-side polished spacer. 
         [0024]    In some embodiments, a first surface of the spacer facing toward the lens may be coated with an anti-reflection film. 
         [0025]    In some embodiments, the at least one input edge coupler may include a cantilever structure edge coupler or an anchored-cantilever structure edge coupler. 
         [0026]    In some embodiments, the optical package may also include at least one silica cover lid. The Si PIC may be covered with the at least one silica cover lid. In some embodiments, the facet of the at least one input edge coupler may be tilt-polished, as shown in  FIG. 3 . Alternatively or additionally, a facet of the at least one output edge coupler may be tilt-polished, as shown in  FIG. 3 . 
         [0027]    In some embodiments, the lens may include a ball lens, an aspheric lens, a GRIN lens, or a set of collimator lenses. 
         [0028]    In some embodiments, the single mode fiber may be fixed to a facet of the at least one output edge coupler with the index matching fluid. 
         [0029]    In some embodiments, the DFB-LD may be configured to operate at a wavelength range of C-band, O-band, or a combination thereof. 
         [0030]    In some embodiments, the DFB-LD and the lens may be packaged as one packaged component. In some embodiments, a type of the one packaged component is a transistor outline can (TO-can) type or a butterfly type. 
         [0031]    In some embodiments, the index matching fluid may be UV curable. 
         [0032]    In some embodiments, the lens may include a GRIN lens, as shown in  FIG. 2 . The GRIN lens may be bonded to a second surface of the spacer with UV-curable epoxy or resin. 
         [0033]    In another aspect, an optical package may include a DFB-LD, a Si PIC, a single mode fiber or fiber array assembly, a lens and an isolator. The Si PIC may include at least one input edge coupler and at least one output edge coupler. The single mode fiber or fiber array assembly may be aligned to the at least output edge coupler of the Si PIC. The lens may be disposed between the DFB-LD and the at least one input edge coupler of the Si PIC, and may be configured to minimize a mismatch between an output spot size of the DFB-LD and a spot size of the at least one input edge coupler of the Si PIC. The isolator may be bonded to a facet of the at least one input edge coupler of the Si PIC with an index matching fluid. 
         [0034]    In some embodiments, the isolator may include a double-side polished isolator. 
         [0035]    In some embodiments, a first surface of the isolator facing toward the lens may be coated with an anti-reflection film. 
         [0036]    In some embodiments, the at least one input edge coupler may include a cantilever structure edge coupler or an anchored-cantilever structure edge coupler. 
         [0037]    In some embodiments, the optical package may also include at least one silica cover lid. The Si PIC may be covered with the at least one silica cover lid. In some embodiments, the facet of the at least one input edge coupler may be tilt-polished, as shown in  FIG. 3 . Alternatively or additionally, a facet of the at least one output edge coupler may be tilt-polished, as shown in  FIG. 3 . 
         [0038]    In some embodiments, the lens may include a ball lens, an aspheric lens, a GRIN lens, or a set of collimator lenses. 
         [0039]    In some embodiments, the single mode fiber may be fixed to a facet of the at least one output edge coupler with the index matching fluid. 
         [0040]    In some embodiments, the DFB-LD may be configured to operate at a wavelength range of C-band, O-band, or a combination thereof. 
         [0041]    In some embodiments, the DFB-LD and the lens may be packaged as one packaged component. In some embodiments, a type of the one packaged component is a TO-can type or a butterfly type. 
         [0042]    In some embodiments, the index matching fluid may be UV curable. 
         [0043]    In some embodiments, the lens may include a GRIN lens, as shown in  FIG. 2 . The GRIN lens may be bonded to a second surface of the isolator with UV-curable epoxy or resin. 
         [0044]    Additional Notes 
         [0045]    Although some embodiments are disclosed above, they are not intended to limit the scope of the present disclosure. It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed embodiments of the present disclosure without departing from the scope or spirit of the present disclosure. In view of the foregoing, the scope of the present disclosure shall be defined by the following claims and their equivalents.