Abstract:
An optical multiplexer/demultiplexer comprising a member, of which first and second opposite planar surfaces are parallel to each other. The member includes therein a void, of which third and fourth opposite planar surfaces are in parallel to each other. An extension of a first line lying on the first planar surface and an extension of a third line lying on the third planar surface intersect each other in a cross section including the void of the member, a smaller one of intersection angles thereof being φ 1.  An extension of a second line lying on the second planar surface and an extension of a fourth line lying on the fourth planar surface intersect each other, a smaller one of intersection angles thereof being φ 1.  The third planar surface is provided on a part thereof with at least one high reflection coating film. The fourth planar surface is provided on a part thereof with at least one optical wavelength filter. At least parts of the high reflection coating film and the first optical wavelength filter are opposed to each other. The first optical wavelength filter transmits therethrough light of wavelength λ 1  and reflects light of wavelength λ 2  (here, wavelength λ 1 ≠wavelength λ 2 ). The member and an interior of the void are different in value of refractive index from each other.

Description:
CLAIM OF PRIORITY 
       [0001]    The present application claims priority from Japanese application JP 2007-131204 filed on May 17, 2007, the content of which is hereby incorporated by reference into this application. 
       BACKGROUND OF THE INVENTION  
       [0002]    The present invention relates to an optical multiplexer/demultiplexer, and more particular, to the construction of an optical multiplexer/demultiplexer for use in wavelength division multiplexing optical transmission and bidirection transmission over a single optical fiber, and a method of manufacturing the same. 
         [0003]    With an increase in communications traffic in recent years, wavelength division multiplexing optical transmission, in which a plurality of wavelengths are transmitted over a single optical fiber, and bidirection transmission over a single optical fiber are going to spread. In these optical transmission, an optical multiplexer/demultiplexer is essential, in which optical signals having different wavelengths and transmitted through a plurality of separate optical fibers are multiplexed in a single optical fiber and conversely, optical signals having different wavelengths and transmitted through a single optical fiber are demultiplexed in a plurality of separate optical fibers. 
         [0004]      FIG. 26  is a cross sectional view showing the conventional construction of an optical multiplexer/demultiplexer disclosed in JP-A-61-149906. An exemplary operation of this optical multiplexer/demultiplexer is as follows. 
         [0005]    Optical signals having different wavelengths λ 1 , λ 2  . . . enter a prism  90  through a spacer prism  91  from an optical fiber collimator  40 . Here, the prism  90  is arranged by the spacer prisms  91 ,  92  so that light incoming and outgoing surfaces have an angle φ 1  to a direction perpendicular to an optical axis of the optical fiber collimator  40 . Also, the prism  90  and the spacer prisms  91 ,  92  are made of the same material and their refractive indexes are equal to one another. With this construction, light goes on a straight line also when entering the prism  90  from the spacer prism  91  and reaches an optical wavelength filter  21  provided on a surface of the prism  90  opposed to the spacer prism  91 . Here, when the optical wavelength filter  21  is set in characteristics so as to transmit therethrough only light of wavelength λ 1  and to reflect light of other wavelengths, the light of wavelength λ 1  enters an optical fiber collimator  41  via the spacer prism  92 . Also, the light reflected by the optical wavelength filter  21  reaches the other surface of the prism  90  to be reflected by a high reflection coating film  31  provided there to reach an optical wavelength filter  22  provided in a further location on that surface, on which the optical wavelength filter  21  is provided. Here, when the optical wavelength filter  22  is set in characteristics so as to transmit therethrough only light of wavelength λ 2  and to reflect light of other wavelengths, the light of wavelength λ 2  enters an optical fiber collimator  42  via the spacer prism  92 . With the construction, lights of wavelength λ 1 , λ 2 , . . . can be sequentially demultiplexed to the optical fiber collimators  41 ,  42 , . . . . In addition, while an explanation is given taking demultiplexing as an example, multiplexing can be performed when a sense, in which light advances, is reversed. Also, when light  1  enters the prism  90  from the optical fiber collimator  41  and light having a different wavelength from that of the light  1  is simultaneously enters the prism  90  from at least one of the optical fiber collimators  41 ,  42 , bidirection transmission over a single optical fiber becomes possible. In addition, while multiplexing is taken as an example in all the following descriptions, it goes without saying that the multiplexer/demultiplexer according to the invention disclosed herein has not only the demultiplexing function but also the multiplexing function and the function of bidirection transmission over a single optical fiber. Also, while anti-reflection coating is not referred to in the above description, anti-reflection coating is applied to all interfaces, on which the optical wavelength filter and the high reflection coating are not formed, and the same is the case with all constructions described later. In this manner, with the construction of the conventional example, a multiplexer/demultiplexer is formed but it is especially necessary to make the prism  90  distant from a fiber array formed by the optical fiber collimators  41 ,  42 , . . . and so miniaturization becomes difficult because it is necessary to arrange the prism  90  obliquely to the collimators. 
         [0006]      FIG. 27  is a cross sectional view showing an optical multiplexer/demultiplexer disclosed in JP-A-2006-285280 and thought of in order to solve the problem of the conventional example described above. The multiplexer/demultiplexer is constructed such that a prism block  93  with a plurality of prism functions accumulated therein, an optical wavelength filter array  94 , and a light transmission block  95  are laminated. Here, inclined surfaces  603 ,  604  are formed on an upper surface of the prism block  93  to provide for the prism function. The inclined surfaces  603 ,  604  are formed so that angles of inclination thereof are made symmetrical with respect to a plane perpendicular to a plane of the drawing. Also, an air is present above the prism block  93 , and all the prism block  93 , the optical wavelength filter array  94 , and the light transmission block  95  are made the same in refractive index. An example of an operation of the optical multiplexer/demultiplexer is as follows. 
         [0007]    For example, optical signals having different wavelengths λ 1 , λ 2 , . . . enter the inclined surfaces  604  at an angle perpendicular to the upper surface of the prism block  93  from an optical fiber collimator  40 . After being refracted by the inclined surfaces  604 , the incident light goes on a straight line to a lower surface of the light transmission block  95  to be reflected by a high reflection coating film  31  provided there. Here, an angle θ 2  of reflection is determined by an angle φ 1  of inclination of the inclined surfaces  604 , and refractive indexes of the prism block  93  and an air. Subsequently, the reflected light reaches an optical wavelength filter  21  provided in the optical wavelength filter array  94 . Here, when the optical wavelength filter  21  is set in characteristics so as to transmit therethrough only light of wavelength λ 1  and to reflect light of other wavelengths, the light of wavelength λ 1  is transmitted through the optical wavelength filter  21  and then reaches the inclined surface  603  provided below an optical fiber collimator  41 . At this time, since an angle of inclination of the inclined surface  603  to the upper surface of the prism block  93  assumes an absolute value φ 1 , which is equal to that of the inclined surface  604 , the light of wavelength λ 1  outgoes perpendicularly to the upper surface of the prism block  93  on the basis of Snell&#39;s law to enter the optical fiber collimator  41 . Also, light reflected by the optical wavelength filter  21  reaches the high reflection coating film  31  again to be reflected thereby to reach the optical wavelength filter  22 . Here, when the optical wavelength filter  22  is set in characteristics so as to transmit therethrough only light of wavelength λ 2  and to reflect light of other wavelengths, the light of wavelength λ 2  can enter an optical fiber collimator  42  in the same manner as the light of wavelength λ 1 . In this manner, with the construction, optical signals having wavelengths λ 1 , λ 2 , . . . can be demultiplexed into the optical fiber collimators  41 ,  42 , . . . . Further, with the construction, since the upper surface of the prism block  93  and optical axes of the optical fiber collimators can be made perpendicular to each other, a distance between the both suffices to be small, thus enabling miniaturization of the optical multiplexer/demultiplexer. 
         [0008]    With the construction disclosed in JP-A-2006-285280, however, the prism block  93  is complex in structure, so that it is necessary to fabricate it one by one by means of a casting mold or the like and so it is difficult to achieve mass-production and reduction in cost. Also, it is necessary to arrange all incoming and outgoing optical fiber collimators on a side of the upper surface of the prism block  93 , which makes it difficult to provide a construction, in which input side fiber collimators and output side fiber collimators are arranged in opposition to each other, so that the structural design of a whole light module is decreased in freedom. Also, when it is tried to enable making an opposed arrangement of the fiber collimators in the above construction, an increase in number of constituent parts such prism blocks, etc. is brought about to lead to difficulty not only in mass-production and reduction in cost but also in miniaturization. 
         [0009]    Hereupon, it is an object of the present invention to provide a construction capable of miniaturization of an optical multiplexer/demultiplexer for use in wavelength division multiplexing optical transmission, in which a plurality of wavelengths are transmitted over a single optical fiber, and bidirection transmission over a single optical fiber, a decrease in number of parts, and simplification of mounting and fabricating processes. 
       SUMMARY OF THE INVENTION  
       [0010]    According to one aspect of the present invention, there is provided an optical multiplexer/demultiplexer comprising a member, of which first and second opposite, planar surfaces are parallel to each other, and wherein the member includes therein a void, of which third and fourth opposite, planar surfaces are parallel to each other, an extension of a first line lying on the first planar surface and an extension of a third line lying on the third planar surface intersect each other in a cross section including the void of the member, a smaller one of intersection angles thereof being φ 1 , an extension of a second line lying on the second planar surface and an extension of a fourth line lying on the fourth planar surface intersect each other, a smaller one of intersection angles thereof being φ 1 , the third planar surface is provided on a part thereof with at least one high reflection coating film, the fourth planar surface being provided on a part thereof with at least one optical wavelength filter, at least parts of the high reflection coating film and the first optical wavelength filter are opposed to each other, the first optical wavelength filter transmits therethrough light of wavelength λ 1  and reflects light of wavelength λ 2  (here, wavelength λ 1 ≠wavelength λ 2 ), and the member and an interior of the void are different in value of refractive index from each other. 
         [0011]    According to a further aspect of the present invention, there is provided an optical multiplexer/demultiplexer comprising a member, of which first and second opposite, planar surfaces are parallel to each other, and wherein the member includes therein a void, of which third and fourth opposite, planar surfaces are parallel to each other, the first planar surface and the third planar surface are parallel to each other, the first planar surface is partially removed to provide a fifth planar surface, a normal direction of the first planar surface and a normal direction of the fifth planar surface intersecting each other at an angle φ 1 , a high reflection coating film is provided on a part of the first planar surface, a first optical wavelength filter being provided on a part of the third or fourth planar surface, at least parts of the high reflection coating film and the first optical wavelength filter are opposed to each other with a part of the member therebetween, the second planar surface is partially removed to provide sixth and seventh planar surfaces separately from each other, a normal direction of the second planar surface and a normal direction of the sixth and seventh planar surfaces intersecting each other at an angle φ 1 , the fifth planar surface, the sixth planar surface, and the seventh planar surface being parallel to one another, and the first optical wavelength filter transmits therethrough light of wavelength λ 1  and reflects light of wavelength λ 2 . 
         [0012]    According to a still further aspect of the present invention, there is provided an optical multiplexer/demultiplexer comprising a member having first and second planar surfaces, which are parallel to each other, and wherein at least one high reflection coating film is provided on the first planar surface, at least one optical wavelength filter being provided on the second planar surface, at least parts of the high reflection coating film and the first optical wavelength filter are opposed to each other, and the first optical wavelength filter transmits therethrough light of wavelength λ 1  and reflects light of wavelength λ 2 , which is different from the wavelength λ 1 . 
         [0013]    According to the present invention, it is possible to enable miniaturization of an optical multiplexer/demultiplexer for use in wavelength division multiplexing optical transmission, in which a plurality of wavelengths are transmitted over a single optical fiber, and bidirection transmission over a single optical fiber, a decrease in number of parts, and simplification of mounting and fabricating processes. 
         [0014]    Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0015]      FIG. 1  is a plan view showing Embodiment 1 of an optical multiplexer/demultiplexer according to the invention; 
           [0016]      FIG. 2  is a cross sectional view taken along the line II-II in  FIG. 1 ; 
           [0017]      FIG. 3  is a cross sectional view taken along the line III-III in  FIG. 1 ; 
           [0018]      FIG. 4  is a cross sectional view being the same as  FIG. 2  and illustrating an operation of Embodiment 1; 
           [0019]      FIG. 5  is a view illustrating a method of fabricating Embodiment 1; 
           [0020]      FIG. 6  is a view illustrating a method of fabricating Embodiment 1; 
           [0021]      FIG. 7  is a plan view showing Embodiment 1 in the case where an optical signal is of dual wavelength; 
           [0022]      FIG. 8  is a cross sectional view taken along the line VIII-VIII in  FIG. 7 ; 
           [0023]      FIG. 9  is a cross sectional view taken along the line IX-IX in  FIG. 7 ; 
           [0024]      FIG. 10  is a cross sectional view being the same as  FIG. 7  and illustrating an operation of Embodiment 1 in the case where an optical signal is of dual wavelength; 
           [0025]      FIG. 11  is a view illustrating a method of fabricating Embodiment 1 in the case where an optical signal is of dual wavelength; 
           [0026]      FIG. 12  is a cross sectional view being the same as  FIG. 2  and showing Embodiment 2 of an optical multiplexer/demultiplexer according to the invention; 
           [0027]      FIG. 13  is a cross sectional view being the same as  FIG. 2  and showing Embodiment 2 in the case where an optical signal is of dual wavelength; 
           [0028]      FIG. 14  is a cross sectional view being the same as  FIG. 2  and showing Embodiment 3 of an optical multiplexer/demultiplexer according to the invention; 
           [0029]      FIG. 15  is a cross sectional view being the same as  FIG. 2  and showing Embodiment 3 in the case where an optical signal is of dual wavelength; 
           [0030]      FIG. 16  is a cross sectional view being the same as  FIG. 2  and showing Embodiment 4 of an optical multiplexer/demultiplexer according to the invention; 
           [0031]      FIG. 17  is a cross sectional view being the same as  FIG. 2  and showing Embodiment 4 in the case where an optical signal is of dual wavelength; 
           [0032]      FIG. 18  is a cross sectional view being the same as  FIG. 2  and showing Embodiment 5 of an optical multiplexer/demultiplexer according to the invention; 
           [0033]      FIG. 19  is a cross sectional view being the same as  FIG. 2  and showing Embodiment 5 in the case where an optical signal is of dual wavelength; 
           [0034]      FIG. 20  is a cross sectional view being the same as  FIG. 2  and showing Embodiment 6 of an optical multiplexer/demultiplexer according to the invention; 
           [0035]      FIG. 21  is a cross sectional view being the same as  FIG. 2  and showing Embodiment 6 in the case where an optical signal is of dual wavelength; 
           [0036]      FIG. 22  is a cross sectional view being the same as  FIG. 2  and showing Embodiment 7 of an optical multiplexer/demultiplexer according to the invention; 
           [0037]      FIG. 23  is a cross sectional view being the same as  FIG. 2  and showing Embodiment 7 in the case where an optical signal is of dual wavelength; 
           [0038]      FIG. 24  is a cross sectional view being the same as  FIG. 2  and showing Embodiment 8 of an optical multiplexer/demultiplexer according to the invention; 
           [0039]      FIG. 25  is a cross sectional view being the same as  FIG. 2  and showing Embodiment 8 in the case where an optical signal is of dual wavelength; 
           [0040]      FIG. 26  is a cross sectional view showing an optical multiplexer/demultiplexer according to the related art; and 
           [0041]      FIG. 27  is a cross sectional view showing an optical multiplexer/demultiplexer according to the related art. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0042]    Embodiments of the invention will be described in detail with reference to the drawings. 
       Embodiment 1  
       [0043]    Embodiment 1 of the invention will be described with reference to  FIGS. 1 to 6 . 
         [0044]    A construction comprises silicon substrates  11 ,  12  as worked. An inclined surface  301  having an angle φ 1  to a substrate surface is formed on the silicon substrate  11 . Further, optical wavelength filters  21 ,  22 ,  23  are formed on the inclined surface  301 . Also, an inclined surface  302  having an angle φ 1  to a substrate surface is formed on the silicon substrate  12 . Further, a high reflection coating film  31  is formed on the inclined surface  302 . The silicon substrates  11 ,  12  are bonded together so as to make the inclined surfaces  301 ,  302  in parallel to and in opposition to each other, thereby enabling fabricating an optical multiplexer/demultiplexer according to Embodiment 1 of the invention. In addition, an air surrounds the silicon substrates  11 ,  12 . In addition, an air is not necessarily present between the inclined surface  301  and the inclined surface  302  but a material will do, which is permeable to transmitted light and has a different refractive index from that of silicon. 
         [0045]      FIG. 4  is a cross sectional view showing an operation of Embodiment 1 of the invention. Here, an explanation is given taking a demultiplexing function as an example. First, an optical fiber collimator  40  is arranged perpendicularly to a substrate surface  304  of the silicon substrate  12 , on which the inclined surface  302  is not formed, and multiplexed signal light having different wavelengths λ 1 , λ 2 , . . . , λn is entered toward the inclined surface  302  from the substrate surface  304 . A combination of wavelengths is conceivable, in which, for example, 1.31 μm, 1.49 μm, and 1.55 μm, which transmits through silicon, are made λ 1 , λ 2 , λ 3 , respectively. The light is refracted by the inclined surface  302  and then reaches the optical wavelength filter  21  formed on the inclined surface  301 . Here, when the optical wavelength filter  21  is fabricated so as to transmit therethrough only light of wavelength λ 1  and light of adjacent wavelength but to reflect light of other wavelengths, it is possible to make the light of wavelength λ 1  outgo toward the optical fiber collimator  41 . Also, light reflected by the optical wavelength filter  21  is reflected by the high reflection coating film  31  formed on the inclined surface  302  to reach the optical wavelength filter  22 . Thereafter, by changing the optical wavelength filters  22 ,  23 , . . . in characteristics, it is possible to make lights of wavelengths λ 2 , λ 3 , . . . enter optical fiber collimators  42 ,  43 , . . . . Here, the optical wavelength filters  22 ,  23 , . . . may be separate from, or in contact with one another. In this manner, the construction realizes the demultiplexing function. Here, since the inclined surfaces  301 ,  302  are parallel to each other, the substrate surfaces  303 ,  304  are parallel to each other, and incident light from the optical fiber collimator  40  is perpendicular to the substrate surface  304 , incident light to the optical fiber collimators  41 ,  42 , . . . is made perpendicular to the substrate surface  303 . Accordingly, the optical fiber collimators  41 ,  42 , . . . can be arranged perpendicularly to the substrate surface  303 , thus enabling miniaturization. Also, those parts, which determine the size of the present optical multiplexer/demultiplexer, are only two, that is, the silicon substrates  11 ,  12 , thus enabling fabricating a small-sized optical multiplexer/demultiplexer in this respect. 
         [0046]      FIG. 5  illustrates a method of fabricating the present optical multiplexer/demultiplexer. First, an etching mask  71  is formed on silicon substrates  11 ,  12  cut with an off angle so that a substrate surface has an angle of φ 1  to a (111) plane ( FIG. 5(   a )). 
         [0047]    Subsequently, an etchant, such as KOH water solution, which will expose the (111) plane of silicon, is used to subject the silicon substrates  11 ,  12  to wet etching to form inclined surfaces  301 ,  302 , and then the etching masks  71  are removed ( FIG. 5(   b )). Subsequently, optical wavelength filters  21  to  23  are formed on the inclined surface  301  of the silicon substrate  11  by deposition or bonding ( FIG. 5(   c )). Also, a high reflection coating film  31  is formed on the inclined surface  302  of the silicon substrate  12  by deposition or bonding ( FIG. 5(   d )). Finally, when the silicon substrate  11  and the silicon substrate  12  are bonded together so that the inclined surfaces  301 ,  302  are opposed to each other, the present optical multiplexer/demultiplexer is completed ( FIG. 5(   e )). Here, it goes without saying that fabrication in the processes (a) to (d) can be performed in an ordinary wafer process. 
         [0048]    Further, fabrication in the process (e) can be performed in wafer level.  FIG. 6  illustrates a manner, in which the fabrication is performed. First, in the processes shown in  FIGS. 5(   a ) to  5 ( d ), a silicon substrate  11  is fabricated, in which inclined surfaces  301  and optical wavelength filters  21  to  23  are formed in addresses  110 - 1 ,  110 - 2 , ,  110 -N on a substrate surface  11 - 1  ( FIG. 6(   a )). Further, in the processes shown in  FIGS. 5(   a ) to  5 ( d ), inclined surfaces  302  and high reflection coating films  31  are formed on a substrate surface  12 - 1  of a silicon substrate  12 , on which addresses  120 - 1 ,  120 - 2 , . . . ,  120 -N correspond to those on the silicon substrate  11  ( FIG. 6(   b )). Finally, when a substrate formed by bonding the substrate surface  11 - 1  and the substrate surface  12 - 1  to stick the silicon substrate  11  and the silicon substrate  12  together with the addresses  110 - 1 ,  110 - 2 ,  110 -N overlapping the addresses  120 - 1 ,  120 - 2 , . . . ,  120 -N is subjected to dicing along boundaries of the addresses, a multiplicity of optical multiplexer/demultiplexers  130 - 1 ,  130 - 2 , . . . ,  130 -N are fabricated in a lump ( FIG. 6(   c )). 
         [0049]    As described above, the construction can realize a small-sized optical multiplexer/demultiplexer, of which parts are small in number, in simple processes capable of readily achieving mass-production. 
         [0050]    In addition, an optical fiber collimator used herein can be replaced with an ordinary optical fiber. In this case, it suffices to arrange a collimator lens between an optical fiber and the silicon substrate  12 . 
         [0051]    The present construction is of course effective in the case where an optical signal as used is of dual wavelength.  FIGS. 7 ,  8 ,  9 ,  10 , and  11 , respectively, illustrate a construction, an operation, and a fabrication method in case of dual wavelength. Also, it goes without saying that fabrication in wafer processes shown in  FIG. 6  is possible also in case of dual wavelength. 
       Embodiment 2  
       [0052]      FIG. 12  is a cross sectional view showing Embodiment 2 of the invention. Lenses  50 ,  51 ,  52 ,  53 ,  54  are integrated on light paths on the substrate surfaces  303 ,  304  of the silicon substrate in the construction of Embodiment 1 shown in  FIG. 4 . With the construction, an optical multiplexer/demultiplexer has lens function whereby instead of expensive optical fiber collimators, ordinary optical fibers  80 ,  81 ,  82 ,  83 ,  84  can be used in incoming and outgoing of light, so that further reduction in cost is enabled. Here, in order to integrate the lenses  50 ,  51 ,  52 ,  53 ,  54 , it suffices to subject, for example, the substrate surfaces  303 ,  304  to etching. 
         [0053]    The present construction is of course effective in the case where an optical signal as used is of dual wavelength.  FIG. 13  is a cross sectional view in case of dual wavelength. Also, it goes without saying that fabrication in wafer processes shown in  FIG. 6  is possible in case of dual wavelength. 
       Embodiment 3  
       [0054]      FIG. 14  is a cross sectional view showing Embodiment 3 of the invention. This is an example, in which a similar construction to that of Embodiment 2 shown in  FIG. 12  is used to fabricate an optical transmitter and receiver for bidirection transmission over a single optical fiber. In the present construction, the optical multiplexer/demultiplexer shown in  FIG. 12  is laminated and integrated on an optical device mount plate  13  having an optical device mount surface  311 . Here, the optical device mount plate  13  can be fabricated by subjecting, for example, a silicon substrate to wet etching. In the optical transmitter and receiver, light (optical signal subjected to wavelength division multiplexing and referred to in the invention ordinarily indicates such multiplexed light. The same is the case in the following.), into which lights having two wavelengths of λ 1  and λ 2  are multiplexed, is made entered perpendicularly to the substrate surface  304  from an optical fiber  85 . The light is collimated by a lens  55  provided on the substrate surface  304  to be refracted by the inclined surface  302  to reach an optical wavelength filter  24  formed on the substrate surface  301 . Here, when the optical wavelength filter  24  is set in characteristics so as to transmit therethrough only light of wavelength λ 1  and to reflect light of other wavelengths, the light of wavelength λ 1  is refracted and transmitted through the optical wavelength filter  24  to advance in a direction perpendicular to the substrate surface  303 , and adjusted in beam diameter by a lens  56  formed on the substrate surface  303  to be thereafter received by a photo-detector  61 . On the other hand, the light of the wavelength λ 2  is reflected by the optical wavelength filter  24  to be thereafter reflected further by a high reflection coating film  32  formed on an inclined surface  302  to reach an optical wavelength filter  25  formed on an inclined surface  301 . Here, when the optical wavelength filter  25  is set in characteristics so as to transmit therethrough only light of wavelength λ 2  and to reflect light of other wavelengths, the light of wavelength λ 2  is received by a photo-detector  62  in the same manner as the light of wavelength λ 1 . Also, a laser diode  63  mounted on the optical device mount surface  311  causes light of wavelength λ 3  to outgo perpendicularly to the substrate surface  303  of the silicon substrate  11 , which forms the optical multiplexer/demultiplexer. The light of wavelength λ 3  is collimated by a lens  58  to be thereafter refracted by the inclined surface  301  to reach a high reflection coating film  32  formed on an inclined surface  302  to be thereafter reflected to reach an optical wavelength filter  25  formed on the inclined surface  303 . Here, since the optical wavelength filter  25  is designed to reflect light of wavelength λ 3 , the light of wavelength λ 3  is repeatedly reflected between the optical wavelength filter  25  and the high reflection coating film  32  to reach an optical wavelength filter  24  formed on the inclined surface  301 . Since the optical wavelength filter  24  is also designed to reflect the light of wavelength λ 3 , the light of wavelength λ 3  is reflected to reach the inclined surface  302  to be refracted thereby to advance in a direction perpendicular to the substrate surface  304  to pass through the lens  55  to be transmitted to the optical fiber  85 . In this manner, the present optical multiplexer/demultiplexer is used to enable realizing a small-sized optical transmitter and receiver for bidirection transmission over a single optical fiber, which can be readily fabricated. In addition, the optical fiber  85  is fixed by a package  701  made of metal or the like. Also, the package  701  is omitted in the following descriptions. 
         [0055]    The present construction is of course effective in the case where an optical signal as used is of dual wavelength.  FIG. 15  is a cross sectional view in case of dual wavelength. In the construction shown in  FIG. 15 , the light of wavelength λ 1  from the optical fiber  85  enters a photo-detector  61  and the light of wavelength λ 3  from a laser diode  63  enters the optical fiber  85 . Also, the construction is not limited only to duplex communication. When optical devices as mounted are all photo-detectors or all laser diodes, it is possible to form an optical module for unidirectional wavelength division multiplexing optical transmission. 
       Embodiment 4  
       [0056]      FIG. 16  is a cross sectional view showing Embodiment 4 of the invention. In the present construction, a silicon substrate  112  is laminated on a silicon substrate  111  with a spacer member  72  therebetween. Here, it is possible to fill an air, gases, or fill a substance such as filler, etc. between the silicon substrate  112  and the silicon substrate  111 , or to put the substance in voids. In short, it suffices that the voids be permeable to transmitted light. 
         [0057]    Optical wavelength filters  21 ,  22 ,  23  are formed on a substrate surface  401  of the silicon substrate  112 , which are in contact with the spacer member  72 , and a high reflection coating film  31  is formed on the other substrate surface  402 . Also, an inclined surface  404  having an angle φ 1  of inclination is formed on the substrate surface  402  of the silicon substrate  112 . Also, two or more inclined surfaces  403  having an angle φ 1  of inclination are formed on that substrate surface of the silicon substrate  111 , which are not in contact with the spacer member  72 . The silicon substrate  111  and the silicon substrate  112  are arranged so that the inclined surfaces  403  and the inclined surface  404  are in parallel with each other. Also, an optical fiber collimator  40  is arranged above the inclined surface  404  so as to make an optical axis thereof perpendicular to the substrate surface  402 . Also, optical fiber collimators are arranged one by one below the inclined surfaces  403 . Here, in the case where the present construction is used for an optical demultiplexer, it suffices that a signal light having different wavelengths λ 1 , λ 2 , . . . be made entered in a direction toward the inclined surface  404  and perpendicular to the substrate surface  402 . The light is refracted by the inclined surface  404  to thereafter advance in the silicon substrate  112  to reach the optical wavelength filter  21 . Here, when the optical wavelength filter  21  is set in characteristics so as to transmit therethrough only light of wavelength λ 1  and to reflect light of other wavelengths, the light of wavelength λ 1  is transmitted through the optical wavelength filter  21  to pass through an air layer and the silicon substrate  111  to pass through the inclined surface  403  to outgo toward the optical fiber collimator  41 . Here, when substrate surfaces of the silicon substrate  112  and the silicon substrate  111  are arranged in parallel to each other, light outgoing toward the optical fiber collimator  41  is made perpendicular to the substrate surface of the silicon substrate  111  on the basis of Snell&#39;s law because the inclined surfaces  403 ,  404  are arranged in parallel to each other. Accordingly, it suffices to arrange the optical fiber collimator  41  perpendicularly to the silicon substrate  111 . Also, light reflected by the optical wavelength filter  21  reaches a high reflection coating film  31  provided on the substrate surface  402  of the silicon substrate  112  to be thereafter reflected to reach the optical wavelength filter  22  formed on the substrate surface  401  of the silicon substrate  112 . Here, by adjusting the optical wavelength filters  22 ,  23  in characteristics, it is possible to make light of wavelength λ 2 , light of wavelength λ 3 , and light of wavelength λ 4 , respectively, enter the optical fiber collimators  42 ,  43 ,  44  in the same manner as the light of wavelength λ 1 . Here, light outgoing toward any one of the optical fiber collimators is made perpendicular to the substrate surface of the silicon substrate  111  in the same manner as the light of wavelength λ 1 . Accordingly, since any one of the optical fiber collimators can be arranged perpendicularly to the substrate surface of the silicon substrate  111 , the present optical multiplexer/demultiplexer can be formed to be made small. Also, the construction of the present embodiment enables fabrication in simple wafer processes shown in  FIGS. 5 and 6  and suited to mass-production in the same manner as that of Embodiment 1. 
         [0058]    In addition, with the construction, a part or a whole of the optical wavelength filters  21 ,  22 ,  23 ,  . . . may be provided on a substrate surface  401 - 2  of the silicon substrate  111  opposed to the substrate surface  401  of the silicon substrate  112  with the spacer member  72  therebetween. 
         [0059]    The present construction is of course effective in the case where an optical signal as used is of dual wavelength.  FIG. 17  is a cross sectional view in case of dual wavelength. Also, it goes without saying that fabrication in wafer processes shown in  FIG. 6  is possible in case of dual wavelength. 
       Embodiment 5  
       [0060]      FIG. 18  is a cross sectional view showing Embodiment 5 of the invention. This is an example, in which a similar construction to that of Embodiment 4 shown in  FIG. 16  is used to fabricate an optical transmitter and receiver for bidirection transmission over a single optical fiber. In the present construction, the optical multiplexer/demultiplexer shown in  FIG. 16  is laminated and integrated on an optical device mount plate  13  having an optical device mount surface  311 . Here, a lens array substrate  114  fabricated by working a silicon substrate is interposed between the optical multiplexer/demultiplexer and the optical device mount plate  13 . Here, the optical device mount plate  13  can be fabricated by subjecting, for example, a silicon substrate to wet etching. In the optical transmitter and receiver, the same operation of an optical transmitter and receiver for bidirection transmission over a single optical fiber as that of the optical transmitter and receiver of Embodiment 3 is obtained on the basis of the same principle as that of Embodiment 4. In addition, according to the embodiment, since no lens is formed on a silicon substrate  112 , a lens  96  is arranged between an optical fiber  85  and an inclined surface  404 . 
         [0061]    The present construction is of course effective in the case where an optical signal as used is of dual wavelength.  FIG. 19  is a cross sectional view in case of dual wavelength. In the construction shown in  FIG. 19 , the light of wavelength λ 1  from an optical fiber  85  enters a photo-detector  61  and the light of wavelength λ 3  from a laser diode  63  enters the optical fiber  85 . Also, the construction is not limited only to duplex communication. When optical devices as mounted are all photo-detectors or all laser diodes, it is possible to form an optical module for unidirectional wavelength division multiplexing optical transmission. 
       Embodiment 6  
       [0062]      FIG. 20  is a cross sectional view showing Embodiment 6 of the invention. In the embodiment, the construction of Embodiment 4 shown in  FIG. 16  is modified so that both incoming and outgoing of light are performed on the same plane. In the construction, a silicon substrate  112  is laminated on a silicon substrate  111  with a spacer member  72  therebetween. Here, an air is present between the silicon substrate  112  and the silicon substrate  111 . Optical wavelength filters  21 ,  22  are formed on a substrate surface  401  of the silicon substrate  112 , which is in contact with the spacer member  72 , and a single inclined surface  404  having an angle φ 1  of inclination is formed on the other substrate surface  402 . Further, the substrate surface  402  and a plurality of inclined surfaces  405  made symmetrical with respect to a plane perpendicular to a plane of the drawing are formed on the substrate surface  402 . Also, a high reflection coating film  31  is formed on that substrate surface of the silicon substrate  111 , which is not in contact with the spacer member  72 . Here, in the case where the present construction is used for an optical demultiplexer, it suffices that from an optical fiber collimator  40 , a signal light having different wavelengths λ 1 , λ 2 , . . . is put in a direction toward the inclined surface  404  and perpendicular to the substrate surface  402 . The light signal is refracted by the inclined surface  404  to thereafter advance in the silicon substrate  112 , an air layer, and the silicon substrate  111  to reach the high reflection coating film  31  and thereafter advances again in the silicon substrate  111  and the air layer to reach the optical wavelength filter  21 . 
         [0063]    Here, when the optical wavelength filter  21  is set in characteristics so as to transmit therethrough only light of wavelength λ 1  and to reflect light of other wavelengths, the light of wavelength λ 1  is transmitted through the optical wavelength filter  21  to pass through the silicon substrate  112  to pass through the inclined surface  405  to outgo toward an optical fiber collimator  41 . Here, when substrate surfaces of the silicon substrate  112  and the silicon substrate  111  are arranged in parallel to each other, light outgoing toward the optical fiber collimator  41  is made perpendicular to the substrate surface of the silicon substrate  111  on the basis of Snell&#39;s law because angles of inclination of the inclined surfaces  403 ,  404  are the same in absolute value. Accordingly, it suffices to arrange the optical fiber collimator  41  perpendicularly to the silicon substrate  112 . 
         [0064]    Also, light reflected by the optical wavelength filter  21  passes through the air layer and the silicon substrate  111  to reach the high reflection coating film  31  to be reflected and advances again in the silicon substrate  111  and the air layer to reach an optical wavelength filter  22  formed on the substrate surface  401  of the silicon substrate  112 . Here, by adjusting the optical wavelength filters  22 ,  23  in characteristics, it is possible to make light of wavelength λ 2  and light of wavelength λ 3 , respectively, enter the optical fiber collimators  42 ,  43  in the same manner as the light of wavelength λ 1 . Here, light outgoing toward any one of the optical fiber collimators is made perpendicular to the substrate surface  402  of the silicon substrate  112  in the same manner as the light of wavelength λ 1 . Accordingly, since any one of the optical fiber collimators can be arranged perpendicularly to the substrate surface  402  of the silicon substrate  112 , the present optical multiplexer/demultiplexer can be formed to be made small. Also, the construction of the present embodiment enables fabrication in simple wafer processes shown in  FIGS. 5 and 6  and suited to mass-production in the same manner as that of Embodiment 1. Here, in the case where it is difficult to form angles of the inclined surfaces  404 ,  405  by means of wet etching, fabrication may be made by means of dry etching. 
         [0065]    The present construction is of course effective in the case where an optical signal as used is of dual wavelength.  FIG. 21  is a cross sectional view in case of dual wavelength. Also, it goes without saying that fabrication in wafer processes shown in  FIG. 6  is possible in case of dual wavelength. 
       Embodiment 7  
       [0066]      FIG. 22  is a cross sectional view showing Embodiment 7 of the invention. The present construction comprises a silicon substrate  201  as worked. In the construction, an inclined surface  501  having an angle φ 1  of inclination is formed on one  503  of substrate surfaces of the silicon substrate  201  and an inclined surface  502  having the same angle φ 1  of inclination is formed on the other  504  of the substrate surfaces so as to be made parallel to the inclined surface  501 . At this time, as shown in the drawing, silicon is present between the inclined surfaces  501 ,  502 . Also, in the construction, optical wavelength filters  21 ,  22  are formed on the inclined surface  501  and a high reflection coating film  31  is formed on the inclined surface  502 . Here, in the case where the present construction is used for an optical demultiplexer, it suffices that from an optical fiber collimator  40 , a signal light having different wavelengths λ 1 , λ 2 , . . . enters in a direction toward the inclined surface  502  and perpendicular to the substrate surface  504 . The light is refracted by the inclined surface  502  to thereafter advance in the silicon substrate  201  to reach a high reflection coating film  21 . Here, when the optical wavelength filter  21  is set in characteristics so as to transmit therethrough only light of wavelength λ 1  and to reflect light of other wavelengths, the light of wavelength λ 1  is refracted and transmitted through the optical wavelength filter  21  to advance in a direction perpendicular to the substrate surface  503  to be directed toward an optical fiber collimator  41 . Also, light reflected by the optical wavelength filter  21  passes through the silicon substrate  201  to reach the high reflection coating film  31  to be reflected and advances again in the silicon substrate  201  to reach an optical wavelength filter  22  formed on the substrate surface  501  of the silicon substrate  201 . Here, by adjusting the optical wavelength filter  22  in characteristics, it is possible to make light of wavelength λ 2  and light of wavelength λ 3 , respectively, enter the optical fiber collimators  42 ,  43  in the same manner as the light of wavelength λ 1 . 
         [0067]    Here, light outgoing toward any one of the optical fiber collimators is perpendicular to the substrate surface  503  of the silicon substrate  201  in the same manner as light of wavelength λ 1 . Accordingly, since any one of the optical fiber collimators can be arranged perpendicularly to the substrate surface  503  of the silicon substrate  201 , the present optical multiplexer/demultiplexer can be formed to be made small. 
         [0068]    Also, the construction of the present embodiment enables fabrication in simple wafer processes shown in  FIGS. 5 and 6  and suited to mass-production in the same manner as Embodiment 1. 
         [0069]    The present construction is of course effective in the case where an optical signal as used is of dual wavelength.  FIG. 23  is a cross sectional view in case of dual wavelength. Also, it goes without saying that fabrication in wafer processes shown in  FIG. 6  is possible in case of dual wavelength. 
       Embodiment 8  
       [0070]      FIG. 24  is a cross sectional view showing Embodiment 8 of the invention. The present construction comprises silicon substrates  211 ,  212  as worked. In the construction, an inclined surface  501  having an angle φ 1  of inclination is formed on one  503  of substrate surfaces of the silicon substrate  211  and an inclined surface  502  having the same angle φ 1  of inclination is formed also on the other  504  of substrate surfaces of the silicon substrate  212 . A substrate surface  505  of the silicon substrate  211 , on which the inclined surface  501  is not formed, and a substrate surface  506  of the silicon substrate  212 , on which the inclined surface  502  is not formed, are stuck together so as to make the inclined surface  501  of the silicon substrate  211  and the inclined surface  502  of the silicon substrate  212  in parallel to each other. Further, optical wavelength filters  21 ,  22  are formed on the inclined surface  501  and a high reflection coating film  31  is formed on the inclined surface  502 . Here, in the case where the present construction is used for an optical demultiplexer, it suffices that from an optical fiber collimator  40 , a signal light having different wavelengths λ 1 , λ 2 , . . . enters in a direction toward the inclined surface  502  and perpendicular to the substrate surface  504 . The light is refracted by the inclined surface  502  to thereafter advance in the silicon substrates  212 ,  211  to reach the optical wavelength filter  21 . Here, when the optical wavelength filter  21  is set in characteristics so as to transmit therethrough only light of wavelength λ 1  and to reflect light of other wavelengths, the light of wavelength λ 1  is refracted and transmitted through the optical wavelength filter  21  to advance in a direction perpendicular to the substrate surface  503  to be directed toward an optical fiber collimator  41 . Also, light reflected by the optical wavelength filter  21  passes through the silicon substrates  211 ,  212  to reach the high reflection coating film  31  to be thereafter reflected and advances again in the silicon substrates  212 ,  211  to reach the optical wavelength filter  22  formed on the substrate surface  501  of the silicon substrate  211 . Here, by adjusting the optical wavelength filter  22  in characteristics, it is possible to make light of wavelength λ 2  and light of wavelength λ 3 , respectively, enter the optical fiber collimators  42 ,  43  in the same manner as the light of wavelength λ 1 . Here, all lights outgoing toward the optical fiber collimators are made perpendicular to the substrate surface  503  of the silicon substrate  211  in the same manner as the light of wavelength λ 1 . Accordingly, since any one of the optical fiber collimators can be arranged perpendicularly to the substrate surface  503  of the silicon substrate  211 , the present optical multiplexer/demultiplexer can be formed to be made small. Also, the construction of the present embodiment enables fabrication in simple wafer processes shown in  FIGS. 5 and 6  and suited to mass-production in the same manner as that of Embodiment 1. 
         [0071]    The present construction is of course effective in the case where an optical signal as used is of dual wavelength.  FIG. 25  is a cross sectional view in case of dual wavelength. Also, it goes without saying that fabrication in wafer processes shown in  FIG. 6  is possible in case of dual wavelength. 
         [0072]    While a material of an optical multiplexer/demultiplexer has been described taking silicon as an example, the invention is effective irrespective of a material. Also, while the function has been described mainly taking a demultiplexer as an example, it goes without saying that the optical multiplexer/demultiplexer according to the invention has a multiplexing function and a multiplexing and demultiplexing function. 
         [0073]    It should be further understood by those skilled in the art that although the foregoing description has been made on embodiments of the invention, the invention is not limited thereto and various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims.