Abstract:
A testing structure formed on a photonic integrated circuit including a plurality of first photonic components and having a given functionality corresponding to a given interconnectivity of the first photonic components, the testing structure including: at least one second photonic component being suitable for testing at least one of the first photonic components; and, at least one photonic pathway optically coupling the at least one first photonic component to the at least one second photonic component. The at least one photonic pathway is unique from the given interconnectivity.

Description:
FIELD OF INVENTION  
         [0001]    The present invention relates generally to photonic devices and methods for the same.  
         BACKGROUND OF THE INVENTION  
         [0002]    The use of photonic components such as type III-V semiconductor compound photonic components in photonic devices and Photonic Integrated Circuits (PICs) is desirable. Such circuits may be monolithic in nature. Monolithic integration of photonic components on a single chip may present advantages over discrete devices in fiber optic communications and other applications.  
           [0003]    Many processes are conventionally used in manufacturing such components, devices and PICs, such as epitaxial growth, etching and photolithography for example. Due to a number of well known factors, such processes typically lead to less than optimum production yields. That is, a certain percentage of components are expected not to operate as intended. As devices and PICs become more complex and include a greater number of photonic components, the percentage of defective devices and PICs likewise increases. This is believed to have the undesirable effect of driving up costs associated with photonic devices and PICs. In other words, when a multitude of photonic components are integrated into a single device or PIC, the compound yield of the device or PIC will be the product of that of photonic components used for the device or PIC. As the yield of individual components decreases, the compound yield of the device or PIC is believed to quickly decrease with the total number of components incorporated.  
         SUMMARY OF INVENTION  
         [0004]    A testing structure formed on a photonic integrated circuit including a plurality of first photonic components and having a desired functionality corresponding to a given interconnectivity of the first photonic components, the testing structure including: at least one second photonic component being suitable for testing at least one of the first photonic components; and, at least one photonic pathway optically coupling the at least one first photonic component to the at least one second photonic component; wherein, the at least one photonic pathway is unique from the given interconnectivity. 
       
    
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0005]    Understanding of the present invention will be facilitated by consideration of the following detailed description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings, wherein like numerals refer to like parts and in which:  
         [0006]    FIGS.  1 - 6  illustrate PICs according to aspects of the present invention; and,  
         [0007]    [0007]FIG. 7 illustrates a flow diagram according to an aspect of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0008]    It is to be understood that the figures and descriptions of the present invention have been simplified to illustrate elements that are relevant for a clear understanding of the present invention, while eliminating, for purposes of clarity, many other elements found in typical photonic components, devices, Photonic Integrated Circuits (PICs), optical waveguides and manufacture methods relating thereto. Those of ordinary skill in the art will recognize that other elements are desirable and/or required in order to implement the present invention. However, because such elements are well known in the art, and because they do not facilitate a better understanding of the present invention, a discussion of such elements is not provided herein. The disclosure herein is directed to all such variations and modifications to such components, devices, PICs, waveguides and methods known to those skilled in the art.  
         [0009]    According to an aspect of the present invention, active components, such as lasers, receivers, amplifiers and optoelectronic switches for example, may be interconnected in planar PICs using passive waveguides. The interconnecting waveguides may be used to define which photonic components, or sets of components, are ultimately used in the PIC.  
         [0010]    According to an aspect of the present invention, redundant photonic components, from the standpoint of the finalized PIC, may be provided as part of the PIC. By creating and then using removable waveguides, defective components may be identified, and interconnect circuitry modified or designed so as to avoid use of the identified defective components.  
         [0011]    According to an aspect of the present invention, such on-chip testing can be accomplished by making the waveguides in the form of a sacrificial testing optical circuit that can be constructed and then removed without deteriorating photonic component performance.  
         [0012]    According to an aspect of the present invention, amorphous silicon (a-Si) materials, including for example a-Si:H and a-Si:F based alloys such as a-SiC x  where 0&lt;x&lt;1, a-SiN y  where 0&lt;y&lt;1.33, a-SiO z  where 0&lt;z&lt;2 and a-SiGe w  where 0&lt;w&lt;1 may be utilized to form waveguides for integrating the sacrificial testing structure with the active photonic components. According to an aspect of the present invention, polymer based waveguiding structures may be analogously utilized.  
         [0013]    According to an aspect of the present invention, a-Si based alloy material, such as a-Si:H or a-Si:F based alloy waveguides may be fabricated using Plasma Enhanced Chemical Vapor Deposition (PECVD), resulting in a low intrinsic optical absorption coefficient (approximately 0.1 cm −1  at 1.55 μm), allowing the development of low-loss waveguide structures.  
         [0014]    Referring now to FIG. 1, there is shown a schematic representation of a PIC  100  at a first processing stage according to an aspect of the present invention. PIC  100  includes a sacrificial testing structure for an integrated laser array device for sake of non-limiting explanation only. In addition to the intended laser array  110  which has been formed with redundancy, an array of receivers  120  are also fabricated on the same chip. These detectors  120  may or may not be part of the intended eventual device design and PIC  100  intended functionality.  
         [0015]    The array of type III-V semiconductor compound based laser components  110  includes a number of individual devices  110  greater than the required number for PIC  100  intended operability. That is, if X components are needed to accomplish the desired functionality of PIC  100 , Y components may be fabricated on the PIC  100 , where X&lt;Y. The difference between X and Y may be dependent upon a number of factors, including for example anticipated production yields for each of the components  110  and/or  120 , and the desired production yield of PICs  100 . Further, if a PIC having a different desired functionality which requires Z number of components  110 , and Z&lt;Y, a desired production of such PICs may also be considered, based upon the anticipated production yield of the components  110 ,  120 , for example.  
         [0016]    PIC  100  includes a number of testing components suitable for testing devices  110 , in the case of PIC  100 , an array of receivers, or photonic detectors,  120 . Components  120  may or may not be useful for the intended operation of PIC  100 , or optionally may be used to provide enhanced functionality therefore, for example.  
         [0017]    Components  110 ,  120  are communicatively coupled to one another using an array of waveguides  130 . For example, each of the components  110  may be optically coupled to a corresponding component  120  using a corresponding photonic waveguide  130 . Alternatively, more than one component  110  may be coupled to a single component  120 , provided each of the components  110  are selectively operable for example. Likewise, a number of components  120  may be coupled to a single component  110  to provide for redundancy in testing, for example.  
         [0018]    PIC  100  may be tested by activating components  110 , either sequentially or in parallel for example, and checking their operation using components  120 , as is conventionally understood. If an output is not received at a particular receiver  120  for example, it may be assumed that either: 1) component  120  is defective in some manner, 2) the corresponding component  110  is defective in some manner and/or 3) the corresponding waveguide  130  is defective in some manner. Regardless, use of either the particular component  110  and/or  120  may be avoided in continued processing of PIC  100 . Significantly however, those components whose operability has been confirmed through such on-chip testing can be used in further processing of PIC  100 .  
         [0019]    Referring now also to FIG. 2, there is shown a schematic representation of PIC  100  at a second processing stage according to an aspect of the present invention. Sacrificial waveguides  130  have been removed, leaving arrays of components  110 ,  120 .  
         [0020]    Referring now also to FIG. 3, there is shown a schematic representation of PIC  100  at a third processing stage according to an aspect of the present invention. Waveguides  140  are fabricated so as to provide the desired functionality of PIC  100  using components  110  whose operability has been confirmed by testing using components  120  and waveguides  130 .  
         [0021]    Referring now also to FIG. 4, as has been set forth components  120  may be used to provide enhanced functionality for PIC  100 . Waveguides  150  may be fabricated so as to provide communicability with components  120  and the enhanced functionality associated therewith.  
         [0022]    Referring now also to FIG. 5, in the case where a greater number of components have failed to be confirmed as operable by on-chip testing, different functionality for the PIC  100  may be achieved using waveguides  140 . In the non-limiting and illustrative case of FIG. 5, using components  120  for example. Of course, any combination of components  110  and/or  120  whose operability has been confirmed through testing may be used to provide this alternative functionality.  
         [0023]    For example, and referring now also to FIG. 6, PIC  100  could use devices  110  and/or  120  whose operability has been confirmed for purposes of achieving enhanced alternative functionality in such a case.  
         [0024]    Referring again to FIG. 1, and now also to FIGS.  3 - 6 , according to an aspect of the present invention, amorphous silicon (a-Si) materials may be used to provide flexible, index matched, low loss waveguide coupling to active and passive device components in a monolithically integrated optoelectronic product, such as PIC  100 . According to an aspect of the present invention, amorphous silicon (a-Si) materials, including a-Si:H and a-Si:F based alloys such as a-SiC x  where 0&lt;x&lt;1, a-SiN y  where 0&lt;y&lt;1.33, a-SiO z  where 0&lt;z&lt;2 and a-SiGe w  where 0&lt;w&lt;1 may be utilized to form waveguides for integrating active and passive components in optoelectronic products, such as PIC  100 .  
         [0025]    Moreover, etching selectivity between such a-Si materials and type III-V semiconductor materials is good, helping make it particularly suitable for use as a sacrificial on-chip testing technology. For example, a-Si based alloy material waveguides can be fabricated at approximately 250° C. and be readily removed after testing. Because of their amorphous nature, a-Si based alloy materials do not have the lattice match requirements of crystalline materials. Furthermore, the ability to tune the optical index substantially continuously, from 1.5 to 4 for example, provides for improved index matching and low loss waveguide coupling to active components as compared to conventional techniques.  
         [0026]    In the case of such a-Si based alloy materials, optical absorption at an operating wavelength of 1.55 μm is desirably low, leading to low loss and good optical transmission properties as will be understood by those possessing an ordinary skill in the pertinent arts. For example, the absorption coefficient corresponding to a-Si:H may be approximately 0.1 cm −1 , advantageously providing for waveguide losses on the order of approximately 0.5 dB/cm at 1.55 μm, for example.  
         [0027]    Further, by mixing the main gas that undergoes plasma assisted decomposition in the a-Si based alloy material PECVD process, such as SiH 4 , with other chemicals, such as CH 4 , CO 2 , N 2 , NH 3  or N 2 O, wider energy gaps may be achieved with lower refractive indices.  
         [0028]    Referring now also to FIG. 7, there is shown a flow diagrammatic view of a method  1000  for forming a PIC, such as PIC  100  (FIG. 1), according to an aspect of the present invention. Method  1000  generally includes forming photonic components  1010 , forming a testing interconnection structure  1020  including sacrificial waveguides, testing the photonic components  1030 , removing the testing interconnecting structure  1040  and forming waveguides  1050 .  
         [0029]    Photonic components, such as the components  110 ,  120  (FIG. 1), may be formed  1010  using any suitable methodology and materials. Such methodologies and materials are well known to those possessing an ordinary skill in the pertinent arts. Such methodologies may include conventional type III-V semiconductor compound photonic device manufacture methods such as epitaxial growth, etching and photolithography to name a few. Utilized materials may include type III-V semiconductor compound materials as will be readily understood by those possessing an ordinary skill in the pertinent arts. Some examples of materials which may be suitable for use depending upon the nature of the intended device  110 ,  120  include for example: GaAs, AlGaAs, InGaAs, GaAsSb, InGaAsP, GaN, to name a few. The photonic components may be formed  1010  on any suitable substrate, such as silicon (c-Si), InP or GaAs, for example.  
         [0030]    According to an aspect of the present invention, redundant components may be formed. That is, if X components are needed to achieve a desired functionality of the final PIC, Y components may be formed  1010 , where X&lt;Y.  
         [0031]    The testing structure may be formed  1020  according to an aspect of the present invention, using Plasma Enhanced Chemical Vapor Deposition (PECVD) of a-Si based alloy materials, such as a-Si:H or a-Si:F based alloys. Resulting waveguides may exhibit a low intrinsic optical absorption coefficient (approximately 0.1 cm −1  at 1.55 μm) and low-loss characteristics. The electronic and optical characteristics of a-Si based alloy materials may be altered depending on the waveguide formation method, such as sputtering or PECVD. For example, sputtered a-Si has been generally characterized as having a high density of states in the forbidden band and optical absorption coefficients greater than 10 cm −1  at 1.55 μm. However, PECVD a-Si based alloy materials may exhibit lower absorption coefficients in the infrared wavelengths, such as in the range of 1.3 and 1.55 μm.  
         [0032]    Waveguides  130  may take the form of an a-Si alloy material layer having a refractive index of approximately 3.4 deposited upon an a-Si alloy materiaunder-cladding layer having a refractive index of approximately 3.2 in turn deposited on a c-Si wafer. The a-Si alloy under-cladding layer may be approximately 1 μm thick, while the a-Si:H alloy core may be approximately 0.5 μm thick. An a-Si alloy material layer having a refractive index of approximately 3.2 may be provided as an overcladding layer, and have a thickness of approximately 1 μm for example. The a-Si alloy under-and overcladding may be formed using RF or DC plasma assisted decomposition of SiH 4  or N 2  (see FIG. 4), for example. In the case of N 2 , an N 2  to SiH 4  flow ratio of approximately 0.9 may be used while the substrate temperature is held at approximately 250° C. To form the a-Si alloy core layer, the N 2  to SiH 4  flow ratio may be approximately 0.45, while the substrate temperature is held at approximately 250° C. Processing pressure may be approximately 1.5 torr, while the 13.56-MHz RF power is held approximately at 50 W, for example.  
         [0033]    The sacrificial waveguides, and cores thereof, may be defined using standard photolithographic patterning of the planar amorphous stack and plasma etching, for example. The sacrificial waveguides may be monolithically formed with the formed devices, for example.  
         [0034]    Thereafter, the composite structure may be tested  1030  using conventional techniques. For example, the laser array  110  of FIG. 1 may be activated and tested using detector array  120  of FIG. 1 and conventional methodologies. Such testing identifies which of the formed device pairs are operating properly. For example, upon activation of lasers  110 , those detectors  120  that output a signal indicative of detecting an operating laser  110  may be identified as operable laser  110 —detector  120  pairs.  
         [0035]    Thereafter, the testing structure may be removed  1040 . The sacrificial waveguides may be removed using any suitable technique, such as etching for example. The process of removing the waveguides  1030  may occur at a relatively low temperature, such as approximately room temperature for example. Etchants which may be utilized include CF 4 , SF 6  and SiC 4 , by way of non-limiting example only.  
         [0036]    Thereafter, suitable waveguide connections to those of the formed components whose operability has been confirmed via testing may be made  1040  to accomplish the desired functionality of the final PIC. These waveguide connections can take the form of, and be formed, consistently with the formation of the testing interconnection structure  1020 , for example.  
         [0037]    According to an aspect of the present invention, the desired functionality of the PIC may be determined based upon the testing. For example, if a first desired functionality requires X number of operable components, and a second desired functionality requires Y number of operable components, and Z number of operable components have been formed and confirmed as operable, the following may occur. If X&lt;Z, the first functionality may be achieved using suitable interconnection of the operable components. If Y&lt;Z, the second functionality may be achieved using suitable interconnection of the operable components. If X&lt;Z&lt;Y, the first functionality may be achieved using suitable interconnection of the operable components, even if it was originally desired to achieve the second functionality. If Y&lt;Z&lt;X, the second functionality may be achieved using suitable interconnection of the operable components, even if it was originally desired to achieve the first functionality.  
         [0038]    Of course, where multiple functionalities may be achieved, such as where X&lt;Z and Y&lt;Z, conventional methodologies, such as the principles of supply and demand, may be used to determine which functionality is to ultimately be achieved.  
         [0039]    It will be apparent to those skilled in the art that various modifications and variations may be made in the apparatus and process of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modification and variations of this invention provided they come within the scope of the appended claims and their equivalents.