Patent Document

RELATED APPLICATIONS 
       [0001]    This application claims all benefits accruing under 35 U.S.C. §119 from China Patent Application No. 201010260139.1, filed on Aug. 23, 2010 in the China Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
       BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    The present disclosure relates to a grating coupler and a package structure incorporating the grating coupler. 
         [0004]    2. Description of Related Art 
         [0005]    Grating couplers can include an isolation layer, a waveguide layer, a reflector layer, and an under-cladding layer, disposed on a substrate in turns. The reflector layer is disposed between the under-cladding layer and the waveguide layer. The isolation layer defines a hole for receiving an optical fiber. Optical signals through the optical fiber transmit through the isolation layer, and are captured by the grating coupler, and then optically coupled into an integrated optical chip. However, because the reflector layer is disposed between the under-cladding layer and the waveguide layer, the fabrication technology of the grating coupler is not compatible with conventional CMOS (Complementary Metal Oxide Semiconductor) technology and has a high cost, which makes mass production prohibitive. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    Many aspects of the embodiments can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the embodiments. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
           [0007]      FIG. 1  is a schematic view of one embodiment of a grating coupler. 
           [0008]      FIG. 2  is an enlarged view of a substrate of the grating coupler of  FIG. 1 . 
           [0009]      FIG. 3  is a schematic view of another embodiment of a grating coupler. 
           [0010]      FIG. 4  is an enlarged view of a substrate of the grating coupler of  FIG. 3 . 
           [0011]      FIG. 5  shows a bottom view of the substrate of  FIG. 4 . 
           [0012]      FIG. 6  shows a side view of the substrate of  FIG. 4  with an addition of a fixing element. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    The disclosure is illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements. It should be noted that references to “an” or “one” embodiment in this disclosure are not necessarily to the same embodiment, and such references mean at least one. 
         [0014]    Referring to  FIG. 1  and  FIG. 2 , one embodiment of a grating coupler  10  includes a reflector layer  100 , an isolation layer  110 , a waveguide layer  120 , an under-cladding layer  130 , and a substrate  140 . The substrate  140  has a first surface  141 , an opposite second surface  142 , and a third surface  143  extending between the first surface  141  and the second surface  142 . The under-cladding layer  130  is disposed on the first surface  141 . The reflector layer  100 , the isolation layer  110 , the waveguide layer  120 , and the under-cladding layer  130  are stacked on each other in sequence along a direction from the first surface  141  to the second surface  142 . The reflector layer  100  is disposed on a surface of the isolation layer  110  and is away from the first surface  141  of the substrate  140 . 
         [0015]    The waveguide layer  120  can be made of silicon, and have a thickness in a range of about 200 nanometers to about 300 nanometers. The refractive index of the waveguide layer  120  is greater than the refractive index of the isolation layer  110  and the refractive index of the under-cladding layer  130 . The waveguide layer  120  is disposed on a surface of the under-cladding layer  130 , and the under-cladding layer  130  is sandwiched between the waveguide layer  120  and the substrate  140 . The waveguide layer  120  is embedded in the isolation layer  110 . 
         [0016]    The waveguide layer  120  includes a ridge waveguide  122  and a grating  121  connected to the ridge waveguide  122 . The grating  121  includes a plurality of substantially parallel grooves with a rib between every two adjacent grooves. The grooves are defined in one surface of the grating  121  away from the under-cladding layer  130 . In one embodiment, the grating  121  has a width of about 20 microns and a length of about 20 microns. The grooves have a depth in a range of about 70 nanometers to about 100 nanometers. The grating period of the grating  121 , that is, a sum of a width of one groove and a width of an adjacent rib, is in a range of about 300 nanometers to about 600 nanometers. 
         [0017]    The isolation layer  110  can be made of silicon dioxide or silicon nitride. The isolation layer  110  has a thickness in a range of about 0.5 microns to about 5 microns. 
         [0018]    The reflector layer  100  can be made from one of gold, silver, copper, and aluminum. The reflector layer  100  can have a thickness in a range of about 50 nanometers to about 200 nanometers. The reflector layer  100  is disposed on a surface of the isolation layer  110  and is away from the under-cladding layer  130 . The reflector layer  100  can be easily formed through metal evaporation at low cost. 
         [0019]    The substrate  140  can be made of silicon and have a thickness in a range of about 300 nanometers to about 500 nanometers. The substrate  140  has a fiber aligned groove  150  defined therein. The fiber aligned groove  150  allows installation of an optical fiber  50  therein. The fiber aligned groove  150  is depressed from the second surface  142  towards the first surface  141 . A cross section of the fiber aligned groove  150  along a surface substantially parallel to the second surface  142  can be substantially square, circular, or triangular. In one embodiment, cross sections of the fiber aligned groove  150  along surfaces substantially parallel to the second surface  142  have about the same shape and size. It should be noted that the shape and the size of the cross section of the fiber aligned groove  150  along a surface substantially parallel to the second surface  142  can be adjusted to match the shape and size of the optical fiber  50  installed in the fiber aligned groove  150 . 
         [0020]    The fiber aligned groove  150  includes an opening  151 , an end surface  153 , and a lateral surface  152 . The opening  151  is defined in the second surface  142 . The end surface  153  is opposite to the opening  151 . The end surface  153  is away from the first surface  141 . The lateral surface  152  extends along a periphery of the end surface  153  to the opening  151 . The fiber aligned groove  150  can be fabricated through wet etching or dry deep etching. The fiber aligned groove  150  can be aligned with the grating  121  through double sided lithography, so that a geometric center of the grating  121  is located on an extended line of a center line or an axis of the fiber aligned groove  150 . Further, a geometric center of the end surface  153  is also located on the extended line of the center line or the axis of the fiber aligned groove  150 . If the optical fiber  50  is installed in the fiber aligned groove  150 , the optical fiber  50  will automatically be aligned with the grating  121 . 
         [0021]    The under-cladding layer  130  can be made of silicon dioxide and have a thickness in a range of about 2 microns to about 5 microns. 
         [0022]    Moreover, the grating coupler  10  can include a plurality of overlapping gratings  121 . The gratings  121  are connected to the same ridge waveguide  122 . 
         [0023]    In assembling the grating coupler  10  and the optical fiber  50 , the optical fiber  50  is inserted into the fiber aligned groove  150  through the opening  151 , and is then encapsulated or packaged therein. As a result, a grating coupler package structure is formed. In one embodiment, the optical fiber  50  can be encapsulated or packaged in the fiber aligned groove  150  using glue. In one embodiment, the optical fiber  50  has a flat end surface which is substantially perpendicular to an axis of the optical fiber  50 . In one embodiment, the flat end surface of the optical fiber  50  can be in close contact with the end surface  153  of the fiber aligned groove  150 . 
         [0024]    In operation of the grating coupler package structure, the optical fiber  50  can be connected to an external photo-conducting device and receive optical signals from the external photo-conducting device. Optical signals from the optical fiber  50  can be optically coupled into an integrated optical chip through the grating coupler  10 . 
         [0025]    Referring to  FIGS. 3-5 , one embodiment of a grating coupler  20  is shown. The grating coupler  20  is similar to the grating coupler  10 , and also includes a reflector layer  200 , an isolation layer  210 , a waveguide layer  220 , an under-cladding layer  230 , and a substrate  240 . The main difference between the grating coupler  20  and the grating coupler  10  is that, the substrate  240  is different from the substrate  140 . 
         [0026]    The substrate  240  includes a first surface  241 , an opposite second surface  242 , a third surface  243 , and a fourth surface  244 . The third surface  243  and the fourth surface  244  are located at opposite sides of the substrate  240 . The third surface  243  and the fourth surface  244  extend between the first surface  241  and the second surface  242 . When the substrate  240  is positioned in the position shown in  FIG. 4 , the third surface  243  and the fourth surface  244  are two lateral surfaces of the substrate  240 . 
         [0027]    The substrate  240  includes a fiber aligned groove  250 . The fiber aligned groove  250  includes a first opening  2520 , a second opening  251 , an end surface  253  and two lateral surfaces  252 . The first opening  2520  is defined in the second surface  242 , and the second opening  251  is defined in the third surface  243 . The first opening  2520  and the second opening  251  intersect with each other at a joint of the second surface  242  and the third surface  243 . The end surface  253  is substantially parallel to and away from the fourth surface  244 . The two lateral surfaces  252  extend from edges of the end surface  253  towards the first opening  2520 , and the second opening  251 , respectively. 
         [0028]    The fiber aligned groove  250  is depressed from the second surface  242  towards the first surface  241 , and is away from the first surface  241 , as well as being depressed from the third surface  243  towards the fourth surface  244 , and away from the third surface  243 . A cross section of the fiber aligned groove  250  along a surface substantially parallel to the fourth surface  244  can be square, circular, or a triangular. 
         [0029]    In one embodiment, cross sections of the fiber aligned groove  250  along surfaces substantially parallel to the fourth surface  244 , are substantially triangular. The first opening  2520  is substantially rectangular. The second opening  251  is substantially triangular. The shape and the size of the cross section of the fiber aligned groove  250  along a surface substantially parallel to the fourth surface  244  can be adjusted to match the shape and size of an optical fiber  60  installed in the fiber aligned groove  250 . 
         [0030]    As shown in  FIG. 6 , the grating coupler  20  can further include a fixing element  300 . The fixing element  300  can be a clip or an adhesive tape. In the embodiment shown in  FIG. 6 , the fixing element  300  can be a clip, which includes a protrusion  310  and two flanges  320  extending from opposite ends of the protrusion  310 . The protrusion  310  protrudes up from the flanges  320  with a cavity defined below. The cavity corresponds to and matches with the fiber aligned groove  250  to receive the optical fiber  60  therebetween. 
         [0031]    In assembling the grating coupler  20  and the optical fiber  60 , the optical fiber  60  is inserted into the fiber aligned groove  250  through the first and second openings  2520 ,  251 , and is then encapsulated or packaged therein. As a result, a grating coupler package structure is formed. In one embodiment, the optical fiber  60  can be encapsulated or packaged in the fiber aligned groove  250  by coating glue on the lateral surfaces  252 . 
         [0032]    In one embodiment, the optical fiber  60  has a flat end surface which defines an included angle of about 45 degrees with respect to an axis of the optical fiber  60 . The optical fiber  60  is installed in the fiber aligned groove  250  with the flat end surface towards the second surface  242 . The flat end surface defines an included angle of about 45 degrees with respect to the second surface  242 . A line passing through a geometric center of the flat surface and a geometric center of the grating  221  is substantially perpendicular to the second surface  242 . 
         [0033]    In operation of the grating coupler package structure shown in  FIG. 3 , the optical fiber  60  can be connected to an external photo-conducting device and receive optical signals from the external photo-conducting device. Optical signals travel to the flat surface of the optical fiber  30 , and are then reflected to the grating  221  by the flat surface of the optical fiber  60 . The optical fiber  60  optically couples the optical signals into an integrated optical chip. During this process, some optical signals may transmit through the grating  221  and travel towards the reflector layer  200 , and the reflector layer  200  can reflect back these optical signals and prevent signal leakage, so that the coupling efficiency of the grating coupler  200  can be enhanced. 
         [0034]    As described above, the reflector layer  100 / 200  can be disposed on a surface of the isolation layer  110 / 210  and is away from the first surface  141 / 241  of the substrate  140 / 240 , the reflector layer  100 / 200  can be easily formed through metal evaporation at low cost. Further, the fabrication technology of the grating coupler  100 / 200  can be compatible with conventional CMOS technology and has a low cost, which makes it possible for mass production. Further, because the fiber aligned groove  150 / 250  is defined in the second surface  142 / 242  of the substrate  140 / 240 , it is convenient for aligning the optical fiber  50 / 60  with the grating  121 / 221 . 
         [0035]    It is to be understood that the above-described embodiments are intended to illustrate rather than limit the disclosure. Variations may be made to the embodiments without departing from the spirit of the disclosure as claimed. It is understood that any element of any one embodiment is considered to be disclosed to be incorporated with any other embodiment. The above-described embodiments illustrate the scope of the disclosure but do not restrict the scope of the disclosure. 
         [0036]    Depending on the embodiment, certain of the steps of methods described may be removed, others may be added, and the sequence of steps may be altered. It is also to be understood that the description and the claims drawn to a method may include some indication in reference to certain steps. However, the indication used is only to be viewed for identification purposes and not as a suggestion as to an order for the steps.

Technology Category: 3