Patent Publication Number: US-9851247-B2

Title: Spectrometer module

Description:
This is a continuation application of copending application Ser. No. 13/637,410, having a §371 date of Oct. 31, 2012, which is a national stage filing based on PCT International Application No. PCT/JP2011/056286, filed on Mar. 16, 2011. The copending application Ser. No. 13/637,410 is incorporated by reference herein in its entirety. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a spectroscopic module which disperses and detects light. 
     BACKGROUND ART 
     Known as a conventional spectroscopic module is one comprising a block-shaped support defining a biconvex lens having a first convex surface provided with a spectroscopic unit such as a blazed diffraction grating and a second convex surface provided with a photodetector such as a photodiode (see, for example, Patent Literature 1). In such a spectroscopic module, light incident on the second convex surface is dispersed by the spectroscopic unit, and thus dispersed light is detected by the photodetector. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: Japanese Patent Application Laid-Open No. 4-294223 
     SUMMARY OF INVENTION 
     Technical Problem 
     The above-mentioned spectroscopic module can be made smaller but is hard to enhance its detection sensitivity for light having a wide wavelength range or different wavelength regions of light. This is because the blazed diffraction grating characteristically exhibits a high efficiency for light in a specific wavelength region. 
     In view of such circumstances, it is an object of the present invention to provide a spectroscopic module which can accurately detect light in a wide wavelength range or different wavelength regions of light while being prevented from becoming larger in size. 
     Solution to Problem 
     For achieving the above-mentioned object, the spectroscopic module in accordance with the present invention comprises a main unit provided with a depressed portion having a concave curved surface and opening to one side; a first spectroscopic unit, formed on the curved surface, for dispersing light incident on the depressed portion and reflecting the light to the one side of the main unit; a first photodetector, supported so as to oppose the curved surface, for detecting a first light having a first order diffraction light and dispersed by the first spectroscopic unit; a reflection unit for reflecting a second light having a second order diffraction light and dispersed by the first spectroscopic unit; a second spectroscopic unit, formed on the curved surface, for dispersing the second light reflected by the reflection unit and reflecting the second light to the one side of the main unit; and a second photodetector, supported so as to oppose the curved surface, for detecting a third light dispersed by the second spectroscopic unit; wherein, on the one side of the main unit, a light entrance portion for letting the light into the depressed portion and a light-absorbing layer for absorbing the light are disposed between a first light detecting portion of the first photodetector and a second light detecting portion of the second photodetector; and wherein the reflection unit is located closer to the first and second spectroscopic units than are the first and second light detecting portions and the light-absorbing layer and opposes the light-absorbing layer. 
     In this spectroscopic module, light incident on the depressed portion unit is dispersed and reflected to one side of the main unit by the first spectroscopic unit. In the light dispersed by the first spectroscopic unit, the first light advances to the one side of the main unit and is detected by the first photodetector. In the light dispersed by the first spectroscopic unit, the second light advances to the one side of the main unit and is reflected to the other side of the main unit by the reflection unit. The second light reflected by the reflection unit is dispersed and reflected to the one side of the main unit by the second spectroscopic unit. In the light dispersed by the second spectroscopic unit, the third light advances to the one side of the main unit and is detected by the second photodetector. Since the second spectroscopic unit and second photodetector are thus provided in addition to the first spectroscopic unit and first photodetector, the detection sensitivity can be enhanced for light in a wide wavelength range or different wavelength regions of light. Further, the light entrance portion and the light-absorbing layer are provided between the first light detecting portion of the first photodetector and the second light detecting portion of the second photodetector, while the reflection unit is disposed so as to oppose the light-absorbing layer. Thus using a region between the first and second light detecting portions can prevent the spectroscopic module from becoming larger in size. When light is let into the depressed portion from the light entrance portion, ambient light, which is likely to reach the light entrance portion, is absorbed by the light-absorbing layer. Any part of ambient light transmitted through the light-absorbing layer is reflected to the light-absorbing layer by the reflection unit disposed so as to oppose the light-absorbing layer. This can inhibit stray light from being caused by the incidence of ambient light. Because of the foregoing, the present invention makes it possible to accurately detect light in a wide wavelength range or different wavelength regions of light, while preventing the size from becoming larger, 
     Preferably, a region between the first and second photodetectors in the light-absorbing layer is included in the reflection unit when seen from the one side of the main unit. In this structure, a part of the ambient light transmitted through the light-absorbing layer can be reflected more reliably to the light-absorbing layer. 
     Preferably, the spectroscopic module further comprises a substrate arranged on the one side of the main unit so as to cover the depressed portion, the first and second photodetectors are disposed on one surface of the substrate, and the reflection unit is disposed on the other surface of the substrate. In this structure, the reflection unit can be formed easily and accurately at a position, closer to the first and second spectroscopic units than is the light-absorbing layer, opposing the light-absorbing layer. When being provided on the other surface of the substrate, the reflection unit may be required to be formed as a multilayer structure including a reflection layer having a favorable reflection characteristic and a foundation layer compatible with the substrate. Here, the reflection unit is provided by forming the foundation layer on the other surface of the substrate and forming the reflection layer on the foundation layer, and the substrate and the main unit are joined to each other such that the reflection unit opposes the concave curved surface. This allows the reflection layer to face the first and second spectroscopic units, whereby the second light can be reflected reliably. 
     Advantageous Effects of Invention 
     The present invention can provide a spectroscopic module which can accurately detect light in a wide wavelength range or different wavelength regions of light while being prevented from becoming larger in size. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a plan view of a spectroscope in which a first embodiment of the spectroscopic module in accordance with the present invention is employed; 
         FIG. 2  is a sectional view of the spectroscopic module taken along the line II-II of  FIG. 1 ; 
         FIG. 3  is a sectional view taken along the line III-III of  FIG. 2 ; 
         FIG. 4  is a sectional view enlarging a main part of the spectroscopic module of  FIG. 2 ; 
         FIG. 5  is a sectional view for explaining a manufacturing process of the spectroscopic module of  FIG. 2 ; 
         FIG. 6  is a sectional view for explaining the manufacturing process of the spectroscopic module of  FIG. 2 ; 
         FIG. 7  is a sectional view for explaining the manufacturing process of the spectroscopic module of  FIG. 2 ; 
         FIG. 8  is a plan view of a spectroscope in which a second embodiment of the spectroscopic module in accordance with the present invention is employed; and 
         FIG. 9  is a sectional view enlarging a main part of another embodiment of the spectroscopic module in accordance with the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     In the following, preferred embodiments of the present invention will be explained in detail with reference to the drawings. In the drawings, the same or equivalent parts will be referred to with the same signs while omitting their overlapping descriptions. 
     First Embodiment 
     As illustrated in  FIG. 1 , a spectroscope  20  comprises a spectroscopic module  1  and a package  21  for accommodating the spectroscopic module  1 . The package  21  has a box  22  shaped like a rectangular parallelepiped box and a lid  23  formed into an oblong sheet. The box  22  and lid  23  are made of a light-absorbing material such as a resin or ceramic which absorbs light. The lid  23  is formed with a light entrance hole  23   a  for letting light into the box  22  from the outside, while a light entrance aperture plate  23   b  which transmits light therethrough is secured to the light entrance hole  23   a . The box  22  opens to the front side, while its opening is formed with a depressed portion  22   a  having an oblong cross section into which the lid  23  fits, A plurality of leads  24  are embedded in both side faces parallel to the longitudinal direction of the box  22 . Base end parts of the leads  24  are exposed into the box  22 , while their leading end parts extend to the outside of the box  22 . 
     As illustrated in  FIGS. 1 and 2 , the spectroscopic module  1  comprises a rectangular parallelepiped main unit  3  including a semispherical depressed portion  3   a  having a concave curved surface  3   b  and opening to the front side (one side), a substrate (light-absorbing layer)  2  arranged on the front side of the main unit  3  so as to cover the depressed portion  3   a , a spectroscopic unit (first spectroscopic unit)  7  which disperses light Lm incident on the depressed portion  3   a  through the substrate  2  and reflects it to the front side, and a photodetector (first photodetector)  4  which detects a light component (first light having a first order diffraction light) L 1  which is the −1st-order light dispersed by the spectroscopic unit  7 . The spectroscopic module  1  also comprises a reflection unit  6  which reflects a light component (second light having a second order diffraction light) L 2  which is the zero-order light dispersed by the spectroscopic unit  7  to the rear side (the other side), a spectroscopic unit  8  which disperses the light L 2  reflected by the reflection unit  6  and reflects it to the front side, and a photodetector (second photodetector)  9  which detects a light component (third light) L 3  dispersed by the spectroscopic unit  8 . 
     The substrate  2  is constituted by any of light-absorbing materials such as black resists, colored resins (such as silicone, epoxy, acrylic, urethane, polyimide, and composite resins) containing fillers (such as carbon and oxides) therein, metals such as Cr and Co or oxides thereof, their multilayer films, and porous ceramics and metals or metal oxides, for example, and has openings  2   c ,  2   d . The opening  2   c  is located on one side in the longitudinal direction of the substrate  2 , while the opening  2   d  is located on the other side in the longitudinal direction of the substrate  2 . The opening  2   c  is a hole through which the light Lm incident on the depressed portion  3   a  of the main unit  3  and the light L 1  dispersed by the spectroscopic unit  7  pass. The opening  2   c  is a hole through which the light L 3  dispersed by the spectroscopic unit  8  passes. 
     A wiring pattern  10  constituted by a single-layer film of Al, Au, or the like or a multilayer films of Cr—Pt—Au, Ti—Pt—Au, Ti—Ni—Au, Cr—Au, or the like is formed on the front face (one face)  2   a  of the substrate  2 . The wiring pattern  10  includes a plurality of pad units  10   a , a plurality of pad units  10   b , and a plurality of connection units  10   c  for connecting the corresponding pad units  10   a ,  10   b  to each other. The plurality of pad units  10   b  are arranged such as to correspond to the base end parts of the leads  24  embedded in the box  22 . An antireflection layer constituted by a single-layer film of CrO and the like or a multilayer film of Cr—CrO and the like is formed closer to the front face  2   a  of the substrate  2  than is the wiring pattern  10 . 
     Outer terminals of the oblong-sheet-shaped photodetectors  4 ,  9  are connected to their corresponding pad units  10   a  by facedown bonding through bumps  11 . The photodetector  4  is located on one side in the longitudinal direction of the substrate  2  such that its light detecting portion  4   a  opposes the opening  2   c  of the substrate  2 . The photodetector  9  is located on the other side in the longitudinal direction of the substrate  2  such that its light detecting portion  9   a  opposes the opening  2   d  of the substrate  2 . An underfill material is applied between the photodiodes  4 ,  9  and the front face  2   a  of the substrate  2  so as to cover the pad units  10   a  and the bumps  11 . 
     The light detecting portion  4   a  of the photodetector  4  is constructed by one-dimensionally arranging elongated photodiodes in a direction substantially perpendicular to their longitudinal direction. The photodetector  4  is arranged such that the one-dimensional arrangement direction of photodiodes substantially coincides with the longitudinal direction of the substrate  2  while the light detecting portion  4   a  is oriented to the front face  2   a  of the substrate  2 . The photodetector  4  is not restricted to the photodiode array, but may be a CMOS image sensor, a CCD-image sensor, or the like. 
     The photodetector  4  is provided with a light-transmitting hole (light entrance portion)  4   b  through which the light Lm incident on the depressed portion  3   a  of the main unit  3  passes. The light-transmitting hole  4   b  is located on the other side in the longitudinal direction of the substrate  2  and opposes the opening  2   c  of the substrate  2 . The light-transmitting hole  4   b , which is a slit extending in a direction substantially perpendicular to the longitudinal direction of the substrate  2  and substantially parallel to the front face  2   a  of the substrate  2 , is formed by etching or the like while being positioned highly accurately with respect to the light detecting portion  4   a.    
     As with the light detecting portion  4   a  of the photodetector  4 , the light detecting portion  9   a  of the photodetector  9  is constructed by one-dimensionally arranging elongated photodiodes in a direction substantially perpendicular to their longitudinal direction. The photodetector  9  is arranged such that the one-dimensional arrangement direction of photodiodes substantially coincides with the longitudinal direction of the substrate  2  while the light detecting portion  9   a  is oriented to the front face  2   a  of the substrate  2 . As with the photodetector  4 , the photodetector  9  is not restricted to the photodiode array, but may be a C-MOS image sensor, a CCD-image sensor, or the like. 
     The pad units  10   b  function as outer terminals of the spectroscopic module  1 . That is, the pad units  10   b  are electrically connected to the base end parts of their corresponding leads  24  with respective wires  25 . As a consequence, an electric signal generated when the light detecting portion  4   a  of the photodetector  4  receives the light L 1  is taken out of the spectroscope  20  through the bumps  11 , wiring pattern  10 , wires  25 , and leads  24  on the photodetector  4  side. Similarly, an electric signal generated when the light detecting portion  9   a  of the photodetector  9  receives the light L 3  is taken out of the spectroscope  20  through the bumps  11 , wiring pattern  10 , wires  25 , and leads  24  on the photodetector  9  side. 
     As illustrated in  FIG. 2 , the rectangular parallelepiped main unit  3  is joined to the rear face (other surface)  2   b  of the substrate  2 . The main unit  3  is constituted by a light-shielding or light-absorbing resin, examples of which include liquid-crystalline fully aromatic polyester resins, polycarbonate, and black epoxy. The curved surface  3   b  of the depressed portion  3   a  covered with the substrate  2  may also be aspheric. 
     As illustrated in  FIGS. 2 to 4 , the spectroscopic units  7 ,  8  are disposed near the bottom of the curved surface  3   b  of the depressed portion  3   a . The spectroscopic unit  7  is located on one side in the longitudinal direction of the substrate  2  so as to oppose the photodetector  4 . The spectroscopic unit  8  is located on the other side in the longitudinal direction of the substrate  2  so as to oppose the photodetector  9 . The spectroscopic unit  7  has a diffraction grating pattern  7   a  formed on a diffraction layer  5  and a reflection layer  12  formed so as to cover the diffraction grating pattern  7   a . Similarly, the spectroscopic unit  8  has a diffraction grating pattern  8   a  formed on the diffraction layer  5  and a reflection layer  13  formed so as to cover the diffraction grating pattern  8   a.    
     The diffraction layer  5  is formed into a circle when seen from the front side. The reflection layers  12 ,  13 , each formed into a circle when seen from the front side, are included in respective regions formed with their corresponding diffraction grating patterns  7   a ,  8   a.    
     The diffraction layer  5  is formed like a film in conformity to the curved surface  3   b  of the depressed portion  3   a . The diffraction layer  5  is provided by photocuring any of optical resins for a replica such as photocurable epoxy resins, acrylic resins, fluorine-based resins, PMMA, silicone, and organic/inorganic hybrid resins. The diffraction grating patterns  7   a ,  8   a , each of which is a blazed grading having a sawtooth cross section, are constructed by juxtaposing a plurality of grooves along the longitudinal direction of the substrate  2 . The reflection layers  12 ,  13  are formed into films by vapor-depositing Al or Au, for example. 
     As illustrated in  FIG. 2 , the reflection unit  6  is disposed on the rear face  2   b  of the substrate  2  so as to oppose the curved surface  3   b  of the depressed portion  3   a . As a consequence, the reflection unit  6  is located on the rear side of (i.e., on the side closer to the spectroscopic units  7 ,  8  than are) the light detecting portion  4   a  of the photodetector  4 , the light detecting portion  9   a  of the photodetector  9 , and the substrate  2 , The reflection unit  6  opposes a region R between the light detecting portions  4   a ,  9   a  in the substrate  2  and includes a region R 1  between the photodetectors  4 ,  9  in the substrate  2  (i.e., a part of the substrate  2  exposed to the front side through a gap between the photodetectors  4 ,  9 ) when seen from the front side. 
     In thus constructed spectroscopic module  1 , the light Lm incident on the depressed portion  3   a  from the light-transmitting hole  4   b  of the photodetector  4  through the opening  2   c  of the substrate  2  is dispersed and reflected to the front side by the spectroscopic unit  7 . In the light Lm dispersed by the spectroscopic unit  7 , the light L 1  advances to the front side and is detected by the photodetector  4 . In the light dispersed by the spectroscopic unit  7 , the light L 2  advances to the front side and is reflected to the rear side by the reflection unit  6 . The light L 2  reflected by the reflection unit  6  is dispersed and reflected to the front side by the spectroscopic unit  8 . In the light dispersed by the spectroscopic unit  8 , the light L 3  advances to the front side and is detected by the photodetector  9 . Since the spectroscopic unit  8  and the photodetector  9  are thus provided in addition to the spectroscopic unit  7  and the photodetector  4 , the detection sensitivity can be enhanced for light in a wide wavelength range or different wavelength regions of light, so as to widen the detectable wavelength range. 
     The light-transmitting hole  4   b  is disposed between the light detecting portions  4   a ,  9   a  of the photodetectors  4 ,  9 , while the reflection unit  6  is provided so as to oppose the region R in the substrate  2 . Thus using the region between the light detecting portions  4   a ,  9   a  can prevent the spectroscopic module  1  from becoming larger. 
     Ambient light La, which is likely to reach the light-transmitting hole  4   b  and thereabout when the light Lm is made incident on the depressed portion  3   a  from the light-transmitting hole  4   b , is absorbed in the region R in the substrate  2 . Any part of the ambient light La transmitted through the region R in the substrate  2  is reliably reflected to the region R in the substrate  2  by the reflection unit  6  disposed so as to oppose the region R in the substrate  2  and include the region R 1  thereof. This can inhibit stray light from being caused by the incidence of the ambient light La. 
     Any part of the ambient light La (a long wavelength light component in particular) entering the depression  3   a  through the region R in the substrate  2  constituted by a light-absorbing material becomes a part of stray light and increases the stray light unnecessary for spectrometer characteristics. The laser light L 2  mostly has a light intensity not so higher than that of the light L 1 , whereby the light L 3 , which is a diffracted light of the light L 2 , further lowers its light intensity. That is, the lights L 2 , L 3  are highly susceptible to the stray light caused by the ambient light La. Providing the reflection unit  6  as mentioned above is extremely effective in mitigating such a state. 
     Because of the foregoing, the spectroscopic module  1  can accurately detect light in a wide wavelength range or different wavelength regions of light, while being prevented from becoming larger. 
     A method of manufacturing the above-mentioned spectroscopic module  1  will now be explained. 
     First, as illustrated in  FIG. 5( a ) , the main unit  3  having the depressed portion  3   a  is molded from a resin. Subsequently, as illustrated in  FIG. 5( b ) , the photocurable resin material  14  is applied to the bottom of the curved surface  3   b  of the depressed portion  3   a  and thereabout. Then, as illustrated in  FIG. 6( a ) , a master grating  15  which is a die for forming the diffraction grating patterns  7   a ,  8   a  is pressed against the applied resin material  14 , while the resin material  14  is hardened by irradiation with light, so as to provide the diffraction layer  5  formed with the diffraction grating patterns  7   a ,  8   a . Here, when necessary, the diffraction layer  5  may be heat-treated, so as to be reinforced. A thermosetting resin may also be used as the resin material  14 , so as to form the diffraction layer  5  and the like by heat and pressure application alone. Further, as illustrated in  FIG. 6( b ) , Al, Au, or the like is vapor-deposited so as to cover the diffraction grating patterns  7   a ,  8   a , thereby forming the reflection layers  12 ,  13 . This forms the spectroscopic units  7 ,  8 . 
     On the other hand, as illustrated in  FIG. 7( a ) , the wiring pattern  10  is formed on the front face  2   a  of the substrate  2  having the openings  2   c ,  2   d . Subsequently, as illustrated in  FIG. 7( b ) , a foundation layer  6   a , an intermediate layer  6   b , and a reflection layer  6   c  are stacked on the rear face  2   b  of the substrate  2 , so as to form the reflection unit  6  constituted by a multilayer structure. An example of the multilayer structure of the reflection unit  6  comprises the foundation layer  6   a  made of Ti or Cr, the intermediate layer  6   b  made of Pt, and the reflection layer  6   c  made of Au. Thereafter, as illustrated in  FIG. 7( c ) , the photodetector  4  is mounted on its corresponding pad units  10   a  of the wiring pattern  10  by facedown bonding through the bumps  11  such that the light detecting portion  4   a  and light-transmitting hole  4   b  oppose the opening  2   c  of the substrate  2 . Similarly, the photodetector  9  is mounted on its corresponding pad units  10   a  of the wiring pattern  10  by facedown bonding through the bumps  11  such that the light detecting portion  9   a  opposes the opening  2   d  of the substrate  2 . 
     The reflection layer  6   c  is not limited to the Au layer, but may be a layer made of a high-reflectance metal film or metal oxide film based on Al or the like. The reflection unit  6  may also be formed by a dielectric multilayer mirror. As these materials, those having a high reflectance are selected according to wavelengths to be dealt with by the spectroscopic module. 
     Finally, the substrate  2  mounted with the photodetectors  4 ,  9  is joined to the main unit  3  so as to cover the depressed portion  3   a , whereby the spectroscopic module  1  is obtained as illustrated in  FIG. 2 . 
     As explained in the foregoing, the reflection unit  6  is disposed on the rear face  2   b  of the substrate  2  in the method of manufacturing the spectroscopic module  1 . This makes it possible to form the reflection unit  6  easily and accurately at a position, closer to the spectroscopic units  7 ,  8  than are the light detecting portions  4   a ,  9   a  of the photodetectors  4 ,  9  and the substrate  2 , opposing the region R in the substrate  2 . The reflection unit  6  is also provided by forming the foundation layer  6   a  on the rear face  2   b  of the substrate  2  and forming the reflection layer  6   c  on the foundation layer  7   a . This allows the reflection layer  6   c  to face the spectroscopic units  7 ,  8 , whereby the light L 2  can be reflected reliably. 
     Second Embodiment 
     As illustrated in  FIG. 8 , in a spectroscopic module  1  in a spectroscope  30 , a main unit  3  is formed with a depressed portion  3   c  having an oblong cross section into which a lid  23  fits, while a depressed portion  3   d  having an oblong cross section is formed on the bottom face of the depressed portion  3   c . A plurality of leads  24  are embedded in both side faces perpendicular to the longitudinal direction of the main unit  3 . Base end parts of the leads  24  are exposed into the depressed portion  3   d  while in contact with the bottom face of the depressed portion  3   d , whereas their leading end parts extend to the outside of the main unit  3 , Thus, the main unit  3  of the spectroscopic module  1  functions as a package in the spectroscope  30 . 
     A depressed portion  3   e  having an oblong cross section is formed on the bottom face of the depressed portion  3   d , while a semispherical depressed portion  3   a  having a concave curved surface  3   b  and opening to the front side (one side) is formed on the bottom face of the depressed portion  3   e . The curved surface  3   b  is provided with spectroscopic units  7 ,  8 . A light-transmitting substrate  2  formed into an oblong sheet from light-transmitting glass such as BK7, Pyrex (registered trademark), or silica, light-transmitting molded glass, light-transmitting plastics, or the like is fitted into the depressed portion  3   e  of the main unit  3  and bonded thereto with a resin or the like. 
     The bottom face of the main unit  3  is provided with a pair of grooves  29 . The grooves  29  are located on both sides of the spectroscopic units  7 ,  8  in a direction in which the diffraction grating patterns  7   a ,  8   a  are arranged, while extending along a direction orthogonal to a direction in which the grooves of the diffraction grating patterns  7   a ,  8   a  are arranged. While the grooves  29  are integrally formed with the main unit  3  when forming the latter, sinks occurring during the resin molding of the main unit  3  are mitigated by the pair of grooves  29  in the arrangement direction of the grooves of the diffraction grating patterns  7   a ,  8   a , whereby the positional deviation of the grooves of the diffraction grating patterns  7   a ,  8   a  is further suppressed in this direction. When a positional deviation occurs in the grooves of the diffraction grating patterns  7   a ,  8   a  with respect to their arrangement direction, the wavelength of light dispersed thereby may shift. Here, the positional deviation in the grooves of the diffraction grating patterns  7   a ,  8   a  with respect to their arrangement direction, i.e., spectral light dispersing direction, is suppressed, whereby spectroscopic characteristics can be inhibited from lowering. 
     A wiring pattern  10  having a plurality of pad units  10   a , a plurality of pad units  10   b , and a plurality of connection units  10   c  for connecting the corresponding pad units  10   a ,  10   b  to each other is formed on the front face  2   a  of a light-transmitting substrate  2 . The plurality of pad units  10   b  are arranged so as to correspond to respective base end parts of the leads  24  embedded in the main unit  3 . An antireflection layer constituted by a single-layer film of CrO and the like or a multilayer film of Cr—CrO and the like is formed closer to the front face  2   a  of the substrate  2  than is the wiring pattern  10 . 
     A light-absorbing layer  27  is formed on the front face  2   a  of the substrate  2 . The light-absorbing layer  27  covers the connection units  10   c  of the wiring pattern  10 , while exposing the pad units  10   a ,  10   b  of the wiring pattern  10 . The light-absorbing layer  27  is provided with openings  27   a ,  27   b ,  27   c . The opening  27   b  is located on one side in the longitudinal direction of the substrate  2 , while the opening  27   c  is located on the other side in the longitudinal direction of the substrate  2 . The opening  27   a  is located between the openings  27   b ,  27   c . The opening  27   a  is a hole through which light Lm incident on the substrate  2  and depressed portion  3   a  passes. The opening  27   b  is a hole through which the light L 1  dispersed by the spectroscopic unit  7  passes, while the opening  27   c  is a hole through which the light L 3  dispersed by the spectroscopic unit  8  passes. Examples of materials for the light-absorbing layer  27  include black resists, colored resins (such as silicone, epoxy, acrylic, urethane, polyimide, and composite resins) containing fillers (such as carbon and oxides) therein, metals such as Cr and Co or oxides thereof, their multilayer films, and porous ceramics and metals or metal oxides. 
     An insulating layer  26  is formed between the front face  2   a  of the substrate  2  and the light-absorbing layer  27 . The insulating layer  26  covers the connection units  10   c  of the wiring pattern  10 , while exposing the pad units  10   a ,  10   b  of the wiring pattern  10 . An insulating part  26   a  which is a part of the insulating layer  26  covers a part on one side in the longitudinal direction of the substrate  2  within the opening  27   b . An insulating part  26   b  which is a part of the insulating layer  26  covers a part on the other side in the longitudinal direction of the substrate  2  within the opening  27   c . The insulating parts  26   a ,  26   b  function as optical filters for cutting predetermined wavelength regions of light. 
     Outer terminals of photodetectors  4 ,  9  shaped into oblong sheets are connected by facedown bonding through bumps  11  to the pad units  10   a  exposed from the insulating layer  26  and light-absorbing layer  27 . An underfill material  28  which transmits therethrough at least the light L 1  fills a space on the substrate  2  side of the photodetector  4  (between the photodetector  4  and the substrate  2 , insulating layer  26 , or light-absorbing layer  27  here). Similarly, an underfill material  28  which transmits therethrough at least the light L 3  fills a space on the substrate  2  side of the photodetector  9  (between the photodetector  9  and the substrate  2 , insulating layer  26 , or light-absorbing layer  27  here). The underfill material  28  fills the whole space between the photodetector  4 ,  9  and the substrate  2  in the structure illustrated in  FIG. 8 , but may fill the surroundings of the bumps  11  alone. The pad units  10   b  exposed from the insulating layer  26  and light-absorbing layer  27  function as outer terminals. That is, the pad units  10   b  are wire-bonded by wires  25  to the base end parts of the leads  24 , so as to be electrically connected thereto. 
     In thus constructed spectroscopic module  1 , the light Lm incident on the depressed portion  3   a  through the substrate  2  from the light-transmitting hole  4   b  of the photodetector  4  and the opening  27   a  of the light-absorbing layer  27  is dispersed and reflected to the front side by the spectroscopic unit  7 . In the light dispersed by the spectroscopic unit  7 , the light L 1  advances to the front side and is detected by the photodetector  4 . In the light dispersed by the spectroscopic unit  7 , the light L 2  advances to the front side and is reflected to the rear side by the reflection unit  6 . The light L 2  reflected by the reflection unit  6  is dispersed and reflected to the front side by the spectroscopic unit  8 . In the light dispersed by the spectroscopic unit  8 , the light L 3  advances to the front side and is detected by the photodetector  9 . Since the spectroscopic unit  8  and the photodetector  9  are thus provided in addition to the spectroscopic unit  7  and the photodetector  4 , the detection sensitivity can be enhanced for light in a wide wavelength range or different wavelength regions of light. 
     The light-transmitting hole  4   b  is disposed between the light detecting portions  4   a ,  9   a  of the photodetectors  4 ,  9 , while the reflection unit  6  is provided so as to oppose the region R between the light detecting portions  4   a ,  9   a  in the light-absorbing layer  27 . Thus using the region between the light detecting portions  4   a ,  9   a  can prevent the spectroscopic module  1  from becoming larger. 
     Ambient light La, which is likely to reach the light-transmitting hole  4   b  and thereabout when the light Lm is made incident on the depressed portion  3   a  from the light-transmitting hole  4   b , is absorbed in the region R in the light-absorbing layer  27 . Any part of the ambient light La transmitted through the region R in the light-absorbing layer  27  is reliably reflected to the region R in the light-absorbing layer  27  by the reflection unit  6  disposed so as to oppose the region R in the light-absorbing layer  27  and include the region R 1  thereof (region between the photodetectors  4 ,  9  in the light-absorbing layer  27 ). This can inhibit stray light from being caused by the incidence of the ambient light La. 
     Because of the foregoing, the spectroscopic module  1  can accurately detect light in a wide wavelength range or different wavelength regions of light, while being prevented from becoming larger. 
     The present invention is not limited to the above-mentioned embodiment. 
     For example, as illustrated in  FIG. 9 , the diffraction grating patterns  7   a ,  8   a  may be formed on the curved surface  3   b  of the depressed portion  3   a  of the main unit  3  directly (without providing the diffraction layer  5 ). The type of the diffraction grating patterns  7 ,  8  may be a blazed grating having a sawtooth cross section as illustrated in  FIG. 9( a ) , a binary grating having a rectangular cross section as illustrated in  FIG. 9( b ) , or a holographic grating having a sinusoidal cross section. 
     Without providing the photodetector  4  with the light-transmitting hole  4   b , the region R 1  in the substrate  2  serving as a light-absorbing layer or the region R 1  in the light-absorbing layer  27  may be provided with a light-transmitting hole as a light entrance portion for letting the light Lm into the depressed portion  3   a . In terms of the diffraction order to be dealt with by the spectroscopic module, the lights L 1 , L 2  are not limited to the −1st-order and zero-order lights, respectively, as long as their orders differ from each other. 
     INDUSTRIAL APPLICABILITY 
     The present invention can provide a spectroscopic module which can accurately detect light in a wide wavelength range or different wavelength regions of light while being prevented from becoming larger in size. 
     REFERENCE SIGNS LIST 
       1  . . . spectroscopic module;  2  . . . substrate;  3  . . . main unit;  3   a  . . . depressed portion;  3   b  . . . curved surface;  4  . . . photodetector (first photodetector);  4   a  . . . light detecting portion (first light detecting portion);  4   b  . . . light-transmitting hole;  6  . . . reflection unit;  7  . . . spectroscopic unit (first spectroscopic unit);  8  . . . spectroscopic unit (second spectroscopic unit);  9  . . . photodetector (second photodetector);  9   a  . . . light detecting portion (second light detecting portion); R . . . region (region between the first and second light detecting portions); R 1  . . . region (region between the first and second light detecting portions); Lm . . . light to be measured; L 1  . . . light (first light); L 2  . . . light (second light); L 3  . . . light (third light)