Patent Publication Number: US-2021181407-A1

Title: Optical Device and Optical Coupling Method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a national phase entry of PCT Application No. PCT/JP2019/016944, filed on Apr. 22, 2019, which claims priority to Japanese Application No. 2018-090419, filed on May 9, 2018, which applications are hereby incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to an optical coupling form of an optical device. 
     BACKGROUND 
     On board optics (OBO) are a form in which a component group is directly attached to a printed substrate or board in a communication apparatus without packaging an optical transceiver. In the OBO, wafer level packaging (WLP) is often used which packages optical components at a chip level. However, because a packaging process is performed prior to formation of a chip, it is difficult to perform an examination prior to packaging of an element extracting light from an element end surface in a wafer state. Thus, it is necessary to obtain optical coupling in the wafer state and in a detachable form with respect to an optical device. 
     A waveguide type optical device in related art has used a grating coupler (GC) (see Non-Patent Literature 1) or a jump mirror (45° mirror) having an angle of approximately 45° (see Non-Patent Literature 2) when an attempt is made to examine optical input and output in the wafer state. 
     However, there has been a problem that as represented by a Si waveguide, the GC may be used only in a case where the refractive indices of a waveguide core and a clad are plural times different. 
     Further, there has been a problem that the 45° mirror bents the optical path of an output of the waveguide at 90° and may thus not be applied to the waveguide actually used for operation. 
     CITATION LIST 
     Non-Patent Literature 
     
         
         Non-Patent Literature 1: Frederik Van Laere et al., “Compact Focusing Grating Couplers for Silicon-on-Insulator Integrated Circuits”, IEEE Photonics Technology Letters, Vol. 19, No. 23, pp. 1919-1921, 2007. 
         Non-Patent Literature 2: W.-J. Lee et al., “Surface Input/Output Optical Splitter Film for Multilayer Optical Circuits”, IEEE Photonics Technology Letters, Vol. 24, No. 6, pp. 2012-2014, 2012. 
       
    
     SUMMARY 
     Technical Problem 
     Embodiments of the present invention have been made to solve the above problem, and an object thereof is to provide an optical device that may easily obtain optical coupling in a wafer state and in a detachable form. 
     Means for Solving the Problem 
     An optical device of embodiments of the present invention includes a first waveguide configured with a core guiding light and a clad surrounding the core, in which a thickness of the clad between a surface of a coupling unit of the first waveguide and the core is a thickness with which optical evanescent coupling is capable of being performed with a second waveguide or an optical fiber for monitoring in a case where the second waveguide or the optical fiber for monitoring is arranged in a vicinity of the surface of the coupling unit. 
     Further, in one configuration example of the optical device of embodiments of the present invention, the thickness of the clad of the first waveguide gradually becomes thinner from a region other than the coupling unit toward the coupling unit. 
     Further, in one configuration example of the optical device of embodiments of the present invention, a width of a core in a direction perpendicular to an optical propagation direction of the first waveguide in the coupling unit is narrower than a width of a core in a region other than the coupling unit. 
     Further, in one configuration example of the optical device of embodiments of the present invention, the coupling unit is provided in a region of the first waveguide connecting integrated circuit configuration components of the optical device or in a region of the first waveguide through which light is input to and output from the integrated circuit configuration components of the optical device. 
     Further, in one configuration example of the optical device of embodiments of the present invention, the integrated circuit configuration components include a laser and an optical modulator modulating light from the laser, and the coupling unit is provided in a region of the first waveguide connecting the laser with the optical modulator and in a region of the first waveguide outputting light from the optical modulator. 
     Further, in one configuration example of the optical device of embodiments of the present invention, the integrated circuit configuration components include a laser, a 90° hybrid coupler mixing main signal light with local light from the laser, and a photodiode receiving output light from the 90° hybrid coupler, and the coupling unit is provided in a region of the first waveguide inputting the main signal light to the 90° hybrid coupler, a region of the first waveguide connecting the laser with the 90° hybrid coupler, and a region of the first waveguide connecting the 90° hybrid coupler with the photodiode. 
     An optical coupling method of an optical device of embodiments of the present invention includes arranging a second waveguide or an optical fiber for monitoring configured with a second core and a second clad surrounding the second core in a vicinity of a surface of a coupling unit of a first waveguide with respect to the optical device including the first waveguide configured with a first core and a first clad surrounding the first core, in which a thickness of the first clad between the surface of the coupling unit of the first waveguide and the first core is a thickness with which optical evanescent coupling is capable of being performed with the second waveguide or the optical fiber for monitoring, and a thickness of the second clad facing the surface of the coupling unit and provided between a surface of the second waveguide or the optical fiber for monitoring and the second core is a thickness with which optical evanescent coupling is capable of being performed with the first waveguide. 
     Further, in one configuration example of the optical coupling method of an optical device of embodiments of the present invention, the first waveguide is a compound semiconductor waveguide in which the first core and the first clad are formed of a compound semiconductor, and the second waveguide for monitoring arranged in the vicinity of the surface of the coupling unit of the first waveguide is a semiconductor waveguide in which at least a second core is formed of a semiconductor. 
     Effects of Embodiments of the Invention 
     In embodiments of the present invention, the thickness of a clad between a surface of a coupling unit of a first waveguide of an optical device and a core is set to a thickness with which optical evanescent coupling is capable of being performed with a second waveguide or optical fiber for monitoring, and optical coupling with the second waveguide or optical fiber for monitoring may thereby be obtained easily. In embodiments of the present invention, the detachable second waveguide or optical fiber for monitoring may be used, light may be input to or output from the optical device while a wafer state is maintained, and an examination of the optical device at a wafer level may thus be realized easily. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates vertical cross-sectional views and horizontal cross-sectional views for explaining a fabrication method of a coupling unit for monitoring of an optical device according to a first embodiment of the present invention. 
         FIG. 2  is a cross-sectional view illustrating a state where an optical fiber for monitoring is provided adjacently to an upper surface of the coupling unit of the optical device according to the first embodiment of the present invention. 
         FIG. 3  is a diagram representing calculation results of an optical coupling constant and a coupling length between the optical device according to the first embodiment of the present invention and the optical fiber for monitoring, the optical coupling constant and the coupling length being calculated while the thickness of a clad is changed. 
         FIG. 4  is a cross-sectional view illustrating a structure of an optical device according to a second embodiment of the present invention. 
         FIG. 5  is a cross-sectional view illustrating a structure of an optical device according to a third embodiment of the present invention. 
         FIG. 6  is a plan view illustrating another structure of the optical device according to the third embodiment of the present invention. 
         FIG. 7  is a cross-sectional view illustrating a state where an optical fiber for monitoring is provided adjacently to an upper surface of a coupling unit of an optical device according to a fourth embodiment of the present invention. 
         FIG. 8  is a diagram representing calculation results of the optical coupling constant and the coupling length between the optical device according to the fourth embodiment of the present invention and the optical fiber for monitoring, the optical coupling constant and the coupling length being calculated while the thickness of the clad is changed. 
         FIG. 9  illustrates cross-sectional views for explaining a fabrication method of a coupling unit of an optical device according to a fifth embodiment of the present invention. 
         FIG. 10  illustrates cross-sectional views for explaining another fabrication method of the coupling unit of the optical device according to the fifth embodiment of the present invention. 
         FIG. 11  is a cross-sectional view illustrating a state where a waveguide for monitoring is provided adjacently to an upper surface of a coupling unit of an optical device according to a sixth embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     Principle of the Invention 
     To solve the above problem, in embodiments of the present invention, an upper clad of a waveguide of an optical device is partially thinned. The thickness of the upper clad is thinned to the extent that evanescent coupling is capable of being performed with a waveguide or optical fiber for monitoring whose clad is similarly thinned. When the waveguide or optical fiber for monitoring is caused to approach a section in which the upper clad of the waveguide of the optical device is thinned, the section acts as a directional coupler in the perpendicular direction to a wafer. Thus, output light of the waveguide of the optical device may be output to the waveguide or optical fiber for monitoring, or input light from the waveguide or optical fiber for monitoring may be input to the waveguide of the optical device. Further, when the waveguide or optical fiber for monitoring is moved away, the optical device with the thinned upper clad may act as an optical device without any change. 
     First Embodiment 
     Embodiments of the present invention will hereinafter be described with reference to drawings.  FIG. 1(A)  to  FIG. 1(E)  are vertical cross-sectional views for explaining a fabrication method of a coupling unit for monitoring of an optical device according to a first embodiment of the present invention, and  FIG. 1(F)  to  FIG. 1(J)  are horizontal cross-sectional views in a case where respective optical devices of  FIG. 1(A)  to  FIG. 1(E)  are sectioned in the position of A. 
     Here, as an example of the optical device, an optical waveguide of a dielectric body will be raised. The fabrication method of the coupling unit for monitoring of the optical device of this embodiment is as follows. 
     First, as illustrated in  FIG. 1(A)  and  FIG. 1(F) , films of a lower clad layer  2  and a core layer  3  are formed on a substrate  1  by a method such as CVD (chemical vapor deposition), sputtering, or evaporation. Then, the core layer  3  is processed by using lithography and etching, and a waveguide core  4  is formed as illustrated in  FIG. 1(B)  and  FIG. 1(G) . 
     Next, as illustrated in  FIG. 1(C)  and  FIG. 1(H) , a film of an upper clad layer  5  is formed so as to cover the whole waveguide core  4 . Then, as illustrated in  FIG. 1(D)  and  FIG. 1(I) , the upper clad layer  5  only in the region of a coupling unit  6  for monitoring is etched. Finally, as illustrated in  FIG. 1(E)  and  FIG. 1(J) , the upper clad layer  5  is polished as needed such that the film thickness of the upper clad layer  5  does not steeply change. 
     In the above method, an optical device  10  in which the upper clad layer  5  of the coupling unit  6  for monitoring becomes thin may be fabricated. A waveguide or optical fiber for monitoring in which a clad layer is thinned similarly is provided adjacently to such a coupling unit  6  from an upper surface, and optical coupling may thereby be obtained between the optical device  10  and the waveguide or optical fiber for monitoring. 
     The light propagated in the optical device  10  is trapped in the core  4  of a waveguide formed with the lower clad layer  2 , the waveguide core  4 , and the upper clad layer  5  but may leak into regions of the clad layers  2  and  5 . When the film thickness of the upper clad layer  5  sharply changes as illustrated in  FIG. 1(D) , the light leaking out to the upper clad layer  5  may be scattered and become loss. In addition, this may become a factor of reflection of light in the point that the film thickness of the upper clad layer  5  sharply changes. Accordingly, such scattering or reflection may be inhibited by making a slope of the upper clad layer  5  gentle as illustrated in  FIG. 1(E) . 
     In this embodiment, it is assumed that a dielectric optical waveguide is provided which uses partially doped SiO 2 , SiOx, or the like as a material of the clad layer. However, this embodiment may be applied to a polymer waveguide using a polymer as a material of the clad layer or a semiconductor waveguide using a semiconductor as a material of the core and the clad layer. 
     Further, because a power monitor, a laser, a modulator, and so forth described later may be fabricated with compound semiconductors, monolithic integration may be intended when a waveguide of a compound semiconductor is used as a waveguide for coupling. 
     Next, a description will be made about optical mode calculation results for explaining effects of this embodiment.  FIG. 2  is a cross-sectional view illustrating a state where an optical fiber  20  for monitoring is provided adjacently to an upper surface of the coupling unit of the optical device  10  of this embodiment. The optical fiber  20  for monitoring is configured with a core  21  and a clad  22 . The clad  22  of a surface provided adjacently to the upper surface of the coupling unit of the optical device  10  is processed to be thin to the extent that evanescent coupling is capable of being performed with the optical device  10 . 
     Here, it is presumed that the optical device  10  contacts with the optical fiber  20  for monitoring with no gap. Further, the refractive index of the clad layers  2  and  5  and the clad  22  is presumed to be 1.45, and the refractive index ratio between the core  4  and the clad layers  2  and  5  and the refractive index ratio between the core  21  and the clad  22  are presumed to be 3%. Further, the cross-sectional dimensions of the cores  4  and  21  are set to 3 μm-square. 
     Under the above conditions, the coupling coefficient and coupling length between the optical device  10  and the optical fiber  20  have been calculated by an optical mode analysis while the respective thicknesses (clad thicknesses) of the thinned upper clad layer  5  of the coupling unit of the optical device  10  and the thinned clad  22  contacting with the upper clad layer  5  are changed, and the calculation results are indicated in  FIG. 3 . In  FIG. 3 , a reference numeral  30  denotes the coupling coefficient, and a reference numeral  31  denotes the coupling length. The coupling length is a distance necessary for optical energy to completely move from the optical device  10  to the optical fiber  20  and is a length in the direction perpendicular to the page in the example of  FIG. 2 . 
     In  FIG. 3 , even if the respective thicknesses of the thinned upper clad layer  5  of the coupling unit of the optical device  10  and the thinned clad  22  contacting with the upper clad layer  5  are 1.0 μm, light may be extracted from the optical device  10  when a coupling length of 750 μm is provided. Further, if the respective thicknesses of the upper clad layer  5  and the clad  22  may be thinned to 0.5 μm, light may be extracted from the optical device  10  with a coupling length of 240 μm. 
     Note that it is matter of course that a waveguide for monitoring in which a clad layer of a surface provided adjacently to the upper surface of the coupling unit of the optical device  10  is processed to be thin may be used instead of the optical fiber  20  for monitoring. 
     Second Embodiment 
     Next, a second embodiment of the present invention will be described.  FIG. 4  is a cross-sectional view illustrating a structure of an optical device according to the second embodiment of the present invention, and the same reference numerals are given to the same configurations as  FIG. 1 . In the first embodiment, it is assumed that one simple waveguide is provided as the optical device  10 . An optical device  10   a  of this embodiment is a transmission-side optical integrated circuit for communication, and a laser  7 , a power monitor  8  detecting output of the laser  7 , and an optical modulator  9  modulating light from the laser  7  are integrated on the substrate  1 . 
     In this embodiment, coupling units  6   a  are respectively provided in the region of a waveguide connecting the laser  7  with the optical modulator  9  and in the region of a waveguide connecting the optical modulator  9  with a next-stage element (not illustrated). The upper clad layer  5  of the coupling unit  6   a  is processed to be thin similarly to the first embodiment to the extent that evanescent coupling is capable of being performed with the optical fiber or waveguide for monitoring, and the light input from the laser  7  to the optical modulator  9  and the light input from the optical modulator  9  to the next-stage element may thereby be measured directly without forming a chip. A coupling method with the optical fiber or waveguide for monitoring is as described in the first embodiment. 
     Third Embodiment 
     Next, a third embodiment of the present invention will be described.  FIG. 5  is a cross-sectional view illustrating a structure of an optical device according to the third embodiment of the present invention, and the same reference numerals are given to the same configurations as  FIG. 1 . An optical device  10   b  of this embodiment is a reception-side optical integrated circuit for communication, and a laser  7   b  for generating local light, the power monitor  8  detecting output of the laser  7   b , a 90° hybrid coupler  11  that mixes main signal light with local light from the laser  7   b , separates signal light into a quadrature component, and outputs the quadrature component, and a photodiode  12  receiving the output light of the 90° hybrid coupler  11  are integrated on the substrate  1 . 
     In this embodiment, coupling units  6   b  are respectively provided in the region of a waveguide connecting the laser  7   b  with the 90° hybrid coupler  11  and in the region of a waveguide connecting the 90° hybrid coupler  11  with the photodiode  12 . The upper clad layer  5  of the coupling unit  6   b  is processed to be thin similarly to the first embodiment to the extent that evanescent coupling is capable of being performed with the optical fiber or waveguide for monitoring, and the light input from the laser  7   b  to the 90° hybrid coupler  11  and the light input from the 90° hybrid coupler  11  to the photodiode  12  may thereby be measured directly without forming a chip. The coupling method with the optical fiber or waveguide for monitoring is as described in the first embodiment. 
     Note that although an input port of the main signal light is omitted in  FIG. 5 , a plan view of an assumed configuration is illustrated in  FIG. 6 . In an optical device  10   c  illustrated in  FIG. 6 , coupling units  6   c  are respectively provided in the region of a waveguide inputting the main signal light to the 90° hybrid coupler  11  (an upper left region in  FIG. 6 ), in the region of a waveguide connecting the laser  7   b  with the 90° hybrid coupler  11 , and in the region of a waveguide connecting the 90° hybrid coupler  11  with the photodiode  12 , and the upper clad layer  5  of the coupling unit  6   c  is processed to be thin similarly to the first embodiment. 
     The coupling units  6   c  are provided in such regions, and the main signal light input from the outside of the optical device  10   c  to the 90° hybrid coupler  11 , the light input from the laser  7   b  to the 90° hybrid coupler  11 , and the light input from the 90° hybrid coupler  11  to the photodiode  12  may thereby be measured directly without forming a chip. 
     Fourth Embodiment 
     Next, a fourth embodiment of the present invention will be described.  FIG. 7  is a cross-sectional view illustrating a state where an optical fiber  20   d  for monitoring is provided adjacently to an upper surface of a coupling unit of an optical device  10   d  according to a fourth embodiment of the present invention, and the same reference numerals are given to the same configurations in  FIG. 1  and  FIG. 2 . In the first to third embodiments, it is presumed that the cross-sectional shapes of the waveguide core  4  of the optical devices  10  to  10   c  and the core  21  of the optical fiber  20  (or waveguide) for monitoring are squares (3 μm-square in the example of  FIG. 2 ). However, optical coupling may be obtained in a wider range by changing the dimensions of the cores. 
     In this embodiment, the widths of a waveguide core  4   d  of the optical device  10   d  and a core  21   d  of the optical fiber  20   d  in the perpendicular direction to a light propagation direction (the dimensions in the left-right direction in  FIG. 7 ) are each set to 1 μm, and the heights are set to 3 μm similarly to  FIG. 2 . Similarly to  FIG. 2 , it is presumed that the optical device  10   d  contacts with the optical fiber  20   d  for monitoring with no gap. Further, the refractive index of the clad layers  2  and  5  and the clad  22  is presumed to be 1.45, and the refractive index ratio between the core  4   d  and the clad layers  2  and  5  and the refractive index ratio between the core  21   d  and the clad  22  are presumed to be 3%. 
     Under the above conditions, the coupling coefficient and the coupling length between the optical device  10   d  and the optical fiber  20   d  have been calculated by an optical mode analysis while the respective thicknesses (clad thicknesses) of the thinned upper clad layer  5  of the coupling unit of the optical device  10   d  and the thinned clad  22  contacting with the upper clad layer  5  are changed, and the calculation results are indicated in  FIG. 8 . In  FIG. 8 , a reference numeral  80  denotes the coupling coefficient, and a reference numeral  81  denotes the coupling length. Similarly to the example of  FIG. 2 , the coupling length is the length in the direction perpendicular to the page in  FIG. 8 . 
     It may be understood from  FIG. 8  that the coupling constant is large and the coupling length is short even in a case where the thinned upper clad layer  5  of the coupling unit of the optical device  10   d  and the thinned clad  22  contacting with the upper clad layer  5  become thick compared to the example of  FIG. 2 . 
     In a case where a structure as illustrated in  FIG. 7  is fabricated, a core is fabricated whose cross-sectional shape is square except the coupling unit, and the width of the core may thereby be narrowed in the coupling unit. For example, in the example of  FIG. 6 , the waveguide cores  4  are fabricated whose cross-sectional shape is square in the other regions than the coupling units  6   c , and the widths of the waveguide cores  4  may thereby be narrowed in three coupling units  6   c.    
     Note that it is matter of course that a waveguide for monitoring in which a clad layer of a surface provided adjacently to the upper surface of the coupling unit of the optical device  10   d  is processed to be thin may be used instead of the optical fiber  20   d  for monitoring. 
     Fifth Embodiment 
     Next, a fifth embodiment of the present invention will be described.  FIG. 9(A)  and  FIG. 9(B)  are cross-sectional views illustrating a fabrication method of a coupling unit of an optical device according to the fifth embodiment of the present invention, and the same reference numerals are given to the same configurations as  FIG. 1 . In the first embodiment, a polymer waveguide is mentioned which uses a polymer (resin) as a material of a clad layer. In an optical device  10   e  of this embodiment, a lower clad layer and an upper clad layer are formed of a resin. 
     A description will be made in the following about advantages in a case where an upper clad layer  5   e  is formed of a resin compared to other clad materials. For example, in a case where SiO 2  is used as the upper clad layer  5 , a polishing process for smoothly changing the thickness of the upper clad layer  5  as illustrated in  FIG. 1(E)  is necessary. 
     Differently, in this embodiment, the upper clad layer  5   e  formed of a resin is etched only in the region of a coupling unit  6   e  as illustrated in  FIG. 9(A) , and a resin  13  is thereafter coated onto the upper clad layer  5   e  so as to cover that by a procedure such as spin coating. Because the resin  13  itself has a function of flattening a stepped structure, an upper clad layer  5   f  with no sharp step may be obtained without performing the polishing process ( FIG. 9(B) ). The resin  13  used here may be any material having a smaller refractive index than the waveguide core  4  and being capable of forming a film by coating. 
     Another advantage by using a resin as the clad material will be described by using  FIG. 10(A)  and  FIG. 10(B) . Here, it is assumed that a configuration is provided in which plural function elements are connected as in  FIG. 4  or  FIG. 5 . In order to form the upper clad layer whose thickness smoothly changes in the configuration in  FIG. 4  or  FIG. 5 , in a case where the material of the upper clad layer is a hard substance such as SiO 2 , either one of methods is possible between: (I) a method in which integrated circuit configuration components, for example, such as a laser, a modulator, and a photodiode are mounted and a film of the upper clad layer is thereafter formed and polished; and (II) a method in which integrated circuit configuration components are mounted on a waveguide having the upper clad layer which is in advance polished and whose thickness smoothly changes. 
     Although realization is possible by either method, because upper surfaces of the integrated circuit configuration components are polished in a case of the method of (I), an unnecessary pressure, a peeling stress, and so forth are exerted on the components, and there is a concern about degradation of the components. Although degradation factors about the integrated circuit configuration components are considered to be few in a case of the method of (II), there is a concern that as illustrated in  FIG. 10(A) , abrasions  16  occur to the upper clad layer  5  in end portions on which integrated circuit configuration components  14  and  15  are mounted due to characteristics of polishing for smoothing an upper surface of the upper clad layer. 
     On the other hand, the above two concerns may be avoided by using a material capable of being coated such as a resin. As illustrated in  FIG. 10(B) , in an optical device  10   g  of this embodiment, the integrated circuit configuration components  14  and  15  are mounted on a waveguide in which the upper clad layer is not present or is in a very thin state. Subsequently, the resin  13  is coated onto the lower clad layer  2 , the waveguide core  4 , and the integrated circuit configuration components  14  and  15  so as to cover those by a procedure such as spin coating. 
     In such a manner, in this embodiment, an upper clad layer  5   g  may automatically be obtained in which a sharp step is not present and the thickness smoothly changes and which becomes thin to the extent that evanescent coupling is capable of being performed with an optical fiber or waveguide for monitoring in a coupling unit  6   g . This embodiment has an advantage of enabling avoidance of occurrence of a stress on the integrated circuit configuration components  14  and  15  due to polishing and avoidance of abrasions of the upper clad layer Sg in boundary portions between the waveguide and the integrated circuit configuration components  14  and  15 . 
     Sixth Embodiment 
     Next, a sixth embodiment of the present invention will be described.  FIG. 11  is a cross-sectional view illustrating a state where a waveguide  23  for monitoring is provided adjacently to an upper surface of a coupling unit of an optical device  10   h  according to the sixth embodiment of the present invention, and the same reference numerals are given to the same configurations in  FIG. 1  and  FIG. 2 . The optical device  10   h  of this embodiment is a compound semiconductor waveguide including a waveguide core  4   h  formed of a compound semiconductor and a clad layer  5   h  formed of the compound semiconductor. 
     Also in the compound semiconductor waveguide, it is possible to partially thin the clad layer  5   h  of a coupling unit  6   h  (an upper surface in the example of  FIG. 11 ) by etching or the like. However, in order to couple light with an optical fiber or waveguide for monitoring provided adjacently from a substrate upper surface direction as in embodiments of the present invention, the light propagation constants (or equivalent refractive indices) of the optical device  10   h  and the optical fiber or waveguide for monitoring have to be close to each other. There is a problem that because the waveguide configured with a compound semiconductor in general has a higher refractive index than a dielectric body such as glass, it is difficult to obtain coupling of light by an optical fiber or waveguide mainly formed of glass. 
     Thus, a combination is possible in which the optical fiber or waveguide for monitoring provided adjacently to the coupling unit  6   h  of the optical device  10   h  from the upper surface side is also configured with a semiconductor. 
     The example of  FIG. 11  illustrates a case where a rib waveguide using an SOI (silicon on insulator) wafer as the waveguide  23  for monitoring is provided adjacently to the optical device  10   h . The waveguide  23  is configured with an Si substrate  24 , a clad layer  25  formed of SiO 2 , a waveguide layer  26  formed of Si, and a clad layer  27  formed of SiO 2 . A reference numeral  28  denotes a core of the rib waveguide. The clad layer  27  of a surface provided adjacently to the coupling unit  6   h  of the optical device  10   h  is processed to be thin to the extent that evanescent coupling is capable of being performed with the optical device  10   h.    
     When an Si waveguide is employed as the waveguide  23  for monitoring as described above, the dimensions such as thickness and width are adjusted, substantially the same propagation constant as the compound semiconductor may thereby be obtained, and light may be also extracted from a compound semiconductor having a relatively high refractive index. Because the integrated circuit configuration components such as the power monitor, the laser, and the modulator may be fabricated with compound semiconductors, monolithic integration may be intended when the compound semiconductor waveguide (optical device  10   h ) illustrated in  FIG. 11  is used as a waveguide for coupling between the integrated circuit configuration components. 
     INDUSTRIAL APPLICABILITY 
     Embodiments of the present invention may be applied to a technique for examining an optical device in a wafer state. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1  substrate 
               2 ,  2   e  lower clad layer 
               3  core layer 
               4 ,  4   d ,  4   h  waveguide core 
               5 ,  5   e  to  5   h  upper clad layer 
               6 ,  6   a  to  6   c ,  6   e ,  6   g ,  6   h  coupling unit 
               7 ,  7   b  laser 
               8  power monitor 
               9  optical modulator 
               10 ,  10   a  to  10   h  optical device 
               11  90° hybrid coupler 
               12  photodiode 
               13  resin 
               14 ,  15  integrated circuit configuration component 
               20 ,  20   d  optical fiber 
               21 ,  21   d ,  28  core 
               22  clad 
               23  waveguide 
               24  Si substrate 
               25 ,  27  clad layer 
               26  waveguide layer.