Abstract:
An optical element mounting substrate where a plurality of light emitting elements have been mounted on the same plane, a lens array for collimating a plurality of light emitted from the plurality of light emitting elements, and a wavelength multiplexing/demultiplexing device are prepared. The wavelength multiplexing/demultiplexing device has typically mounted both a wavelength selecting filter and a mirror on front and rear planes of a transparent substrate. These three components are mounted within a package at a desirable angle position. Optical axes of respective wavelengths of the wavelength multiplexing/demultiplexing device are determined based upon a thickness and an angle of the light emitting element mounting substrate, and are arrayed on a straight line of a horizontal plane. As a consequence, if the respective light emitting elements are arranged on the optical axes which are exclusively determined by a design work, then optical multiplexing/demultiplexing operations can be carried out.

Description:
INCORPORATION BY REFERENCE 
     The present application claims priority from Japanese application JP2007-273302 filed on Oct. 22, 2007, the content of which is hereby incorporated by reference into this application. 
     BACKGROUND OF THE INVENTION 
     The present invention is generally related to an optical module. More specifically, the present invention is directed to a structure of a multi-wavelength optical transmitter module which optically multiplexes a plurality of laser light having a plurality of wavelengths with each other and then transmits the multiplexed laser light, and also, directed to a structure of an optical receiver module which optically demultiplexes such a light whose plural wavelengths have been multiplexed so as to receive the demultiplexed light. 
     Semiconductor laser diode (LD) elements have been utilized in various sorts of technical fields such as information and telecommunication fields as compact light sources operable in higher efficiencies. Very recently, there are strong needs of technical ideas capable of providing laser diode light sources having a plurality of light emission wavelengths as compact light source mounted modules. Conventionally, the above-described technical needs have been made as light sources for wavelength multiplexing communications which employ light having plural wavelengths in optical communication fields. In addition thereto, LDs (laser diodes) of blue color series have been currently developed, and oscillatable wavelengths could be widened in blue color LDs. As a result, as reading/writing light sources of displays and optical disks, higher requirements for multi-wavelengths light source modules have been made even in wavelength ranges of visible light. 
     As one of application examples of the multi-wavelengths light source modules, there are light sources of laser projectors. Generally speaking, projectors imply such image display apparatuses which project images on screens, and the like, in response to image signals derived from various types of image supplying apparatuses (for example, computers etc.) so as to display the projected images. In general, as conventional projectors, the below-mentioned types of projectors are known, which have mainly employed transmission type liquid crystal panels, reflection type liquid crystal panels, or digital micromirror devices. On the other hand, laser projectors have been designed in such a system that while laser light is employed as light of light sources thereof, the laser light is scanned along a two-dimensional direction so as to display images. As a consequence, these laser projectors can be made compact, and can produce images having superior color reproduction, as compared with those as to the above-described other types of projectors. Conventionally, use places of projectors have been relatively limited only to, for example, meeting rooms, presentation rooms, living rooms of homes, and the like. However, since portable computers have been made compact and portable telephones equipped with higher functions have been marketed in the present stage, qualities and quantities of data which are portable for respective persons are considerably increased, so that these computers and portable telephones can be operated without restricting use places thereof. For example, there are some expectations as to development of ultracompact type projectors operable under low power consumption, which can be assembled in portable computers and portable telephones. As technical ideas related to laser projectors, for example, JP-A-2002-214705 has disclosed the below-mentioned color laser projector: That is, in this color laser projector, 3 sets of light emitted from 3 pieces of laser light sources having different light emission colors are scanned in the two-dimensional direction by optical scanning means which are different from each other, and then, 3 sets of the two-dimensionally scanned laser light are collected to each other in a synchronization manner so as to project color images. However, the color laser projector described in JP-A-2002-214705 has such a problem that since the plural sets of optical scanning means are required, whose total number is equal to that of the laser light sources, there is a limitation when the color laser projector is made compact. 
     Also, another technical idea has been proposed. That is, JP-A-2006-186243 has disclosed such a color laser projector that R (red), G (green), and B (blue) semiconductor LD (laser diodes) elements which are employed in light sources are stored in one package in order to improve compactness of the light sources and of optical systems thereof. However, in the color laser projector of the above-described JP-A-2006-186243, the light source are merely mounted in the proximity to each other, and three sets of the color laser light are not multiplexed with each other. As a result, the optical axes of the R, G, B laser diode elements are not coincident with each other. Under such a circumstance, in order to secure predetermined resolution, optical systems designed for respective wavelengths of the R, G, B semiconductor LD elements must be separately prepared. Otherwise, if a general technical idea is utilized in order to make the optical axes coincident with each other, then such an optical system as a dichroic prism and the like is required. Even if any of the above-described solving ideas is employed, there are certain limitations when a total number of optical components is reduced, and the optical systems are made compact. 
     SUMMARY OF THE INVENTION 
     As previously described, needs for using laser light having a plurality of light emission wavelengths by being multiplexed with each other have been increased, in which these laser light sources have been utilized in projectors as a first need. However, in the above-described conventional type of laser projector, while the plural light sources having the different wavelengths are separately prepared, the individual optical systems are assembled. Also, in the conventional method, plural sets of the laser light are multiplexed with each other by employing the dichroic mirror. These conventional system and method have such a drawback that the optical systems are made complex, and the quantity of optical components is increased. As a result, there are some limitations when the conventional systems are made compact and the cost thereof is reduced. 
     As a consequence, an object of the present invention is to provide a multi-wavelength optical transmitter/receiver module which can be made compact and can be manufactured in high yield, while the multi-wavelength optical transmitter/receiver module is capable of largely reducing a total number of structural components and a total quantity of mounting steps of a system in various sorts of application fields, for instance, projectors, optical transmission communications, information processing appliances, biological measuring fields and so on. 
     To solve the above-described problems, an optical multi-wavelength transmitter/receiver module, according to an aspect of the present invention, is featured by that while an optical element mounting substrate where a plurality of optical elements have been mounted on the same plane, and an optical wavelength multiplexing/demultiplexing device in which both a wavelength selecting filter and a mirror have typically been mounted on front and rear planes of a transparent substrate are prepared, these two components are mounted within a package in such an angle manner that an optical element mounting plane is located not parallel to a surface of the wavelength selecting filter. The optical elements having different use wavelengths from each other have been mounted at desirable positions on the optical element mounting substrate. The optical multiplexing/demultiplexing device is constituted in such a manner that while a substrate having a desirable thickness and one pair of parallel planes located opposite to each other is employed as a supporting substrate and has been made of a transparent material with respect to wavelengths of light, at least one sort of wavelength selecting filter is provided on one plane of the paired paralleled planes, and a mirror is provided on the other plane of the paired parallel planes in order to reflect thereon such a light having a wavelength which has not been selected by the wavelength selecting filter. In this case, windows for entering/projecting light are provided in these filter and mirror. 
     A description is made of operations of the optical module according to the present invention with reference to  FIG. 2 .  FIG. 2  is a diagram for schematically indicating functions in such a case that the inventive idea of the present invention has been applied to an optical module by which three sets of color light from optical sources are optically multiplexed with each other, and then, the multiplexed light is emitted. This optical module has such a function that a plurality of light having wavelengths “λ 1 ”, “λ 2 ”, “λ 3 ” emitted from light emitting elements  11 ,  12 ,  13  respectively are optically multiplexed with each other under such a condition that the plurality of light pass through the same optical axis, and then, the multiplexed light is emitted outside the optical module. Concretely speaking, the light having the wavelength “λ 3 ” emitted from the light emitting element  13  along a vertical direction with respect to a substrate reaches a multiplexing/demultiplexing device  2 . Since the multiplexing/demultiplexing device  2  has been mounted at an angle (not right angle) with respect to the optical axis, namely, at such an angle of “θ 1 ” (note that angle θ 1  is not equal to 2Nπ. Symbol N=0, 1, 2, - - - ), the light having the wavelength “λ 3 ” is refracted by a predetermined refraction at the multiplexing/demultiplexing device  2 , which is determined by a difference in refractive indexes. The light having the wavelength “λ 3 ” located within the multiplexing/demultiplexing device  2  is reflected on a mirror  8 , and then, reflected light reaches a filter  7 . Just under the filter  7 , the light emitting element  12  for emitting the light having the wavelength “λ 2 ” has been provided. Both the light emitting elements  12  and  13  have been mounted on an LD stem  10  in such a manner that an optical axis of the light emitted from the light emitting element  12  is intersected with an optical axis of the light emitted from the light emitting element  13  on either the filter  7  or the mirror  8 . It is so assumed that the filter  7  has such a property that this filter  7  reflects the light having the wavelength “λ 3 ”, and passes therethrough the light having the wavelength “λ 2 .” As a consequence, the light having the wavelength “λ 2 ” is multiplexed with the light having the wavelength “λ 3 ”, and the multiplexed light is propagated within the multiplexing/demultiplexing device  2  through the same optical axis. When the multiplexed light reaches the filter  6 , this multiplexed light is multiplexed with the light having the wavelength “λ 1 ” in a similar multiplexing manner. Finally, three sets of the light having the wavelengths “λ 1 ”, “λ 2 ”, “λ 3 ” are multiplexed with each other, so that the finally multiplexed light is emitted from the optical module. As indicated in  FIG. 2 , dimensions “x”, “y”, “z” among the optical axes of the respective wavelengths are determined based upon a thickness and an angle of the glass substrate. The respective optical axes are arranged along one column on the horizontal plane of the substrate in a predetermined interval. As a consequence, if the respective light emitting elements are arranged on the optical axes which are exclusively determined by a design work, then optical multiplexing/demultiplexing operations can be carried out for these wavelengths, so that the multiplexed light can be emitted. As previously described, in accordance with the present invention, since such a multiplexing/demultiplexing device is employed in which the filter and the mirror have been mounted on the front and rear planes of the transparent substrate, the compact optical transmitter module whose structural components are small can be provided. Also, the transparent substrate is once aligned, so that a plurality of filters can be automatically aligned, and thus, there is such a feature that the mounting steps thereof can be largely simplified while high precision is maintained. As previously explained, the optical module of the present invention may have such a function capable of multiplexing the light emitted from the plurality of light sources of the different wavelengths with each other. As a consequence, the optical module can be apparently suitably applied to projectors, but not limited only to these projectors, for instance, may be applied to light sources for wavelength multiplexing communications, reading/writing light sources for optical disks, and further, such a system utilizing light sources having a plurality of wavelengths (colors), for instance, a light source for a biological measuring system. Accordingly, there are such advantages that the apparatuses can be made compact, and the total numbers of structural elements thereof can be reduced. In this example, the optical transmitter module has been exemplified. If the traveling directions of the light are assumed as opposite directions, then the present invention may be realized as an optical receiver module. In this case, the optical multiplexing/demultiplexing device  2  separates the wavelengths. 
     As represented in  FIG. 2 , in such a case that a mounting angle of the substrate is selected to be “θ 1 ”, an angle (incident angle) of light entered from either the fiber or the light emitting element  11  with respect to the vertical direction of the front plane of the substrate becomes “θ 1 ”, and another angle “θ 2 ” of this incident light after being refracted in the substrate substance is given as follows by employing an external refractive index “n 1 ” and a refractive index “n 2 ” of the substrate in accordance with the Snell&#39;s law of refraction:
 
θ 2 =sin −1 ( n   1 *sin θ 1   /n   2 ).
 
     At this time, a time period “y” of multiple reflections within the substrate is given by “2d tan θ 2 ”, assuming now that the thickness of the transparent substrate is “d.” Also, in such a case that this multiple-reflected light is wavelength-separated by the filter based upon the above-described basic idea, and then, the wavelength-separated light is emitted to a plane located perpendicular to the optical axis when the light is entered, a time period “z” of this light is given as “2d sin θ 2 *cos θ 1 .” Since the above-described time period “z” corresponds to an interval of elements which are mounted on an element mounting substrate, the above-described values of “d” and “θ 1 ” must be selected in order to maintain a proper element interval. Generally speaking, there is no opportunity that sizes of elements (for example, as shown in  FIG. 2 , lateral widths of light emitting elements) become smaller than 100 μm. As a consequence, the value of the time period “z” must be selected to be larger than, or equal to 100 μm. 
     In accordance with an embodiment of the present invention, with respect to a multi-wavelength transmitter module for transmitting a plurality of light having a plurality of wavelengths by a single optical axis, and also, a multi-wavelength receiver module, it is possible to provide such a compact optical module capable of realizing a high yield, while a total number of structural elements and a total number of mounting steps are largely reduced. 
     In accordance with the present invention, there are specific effects when systems are made compact and in low cost in various application fields such as data projectors, optical transmission communications, information processing appliances, and biological measuring devices with respect to the multi-wavelength transmitter module for transmitting the plurality of light having the plurality of wavelengths by the single optical axis, and also, the multi-wavelength receiver module, while the total number of structural elements and the total number of mounting steps can be largely reduced. 
     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 
         FIG. 1  is a sectional view for schematically showing three color (RGB) light source optical transmitter module according to a first embodiment of the present invention. 
         FIG. 2  is an explanatory diagram for explaining operations of the optical transmitter module according to the first embodiment of the present invention. 
         FIG. 3  is a sectional view for indicating the three color (RGB) light source optical transmitter module according to the first embodiment, as viewed at an angle different from the viewing angle of  FIG. 1 . 
         FIG. 4  is a sectional view for indicating an optical module according to a second embodiment of the present invention, namely, a diagram for showing an example in which lens integrated vertically light emitting type LD elements have been employed as light emitting elements. 
         FIG. 5A  is a conceptional view for showing an optical module according to a third embodiment of the present invention, namely,  FIG. 5A  is a diagram for representing such an example that a red/blue light source package has been combined with a green light source package so as to construct the three color light source optical module of the third embodiment. 
         FIG. 5B  is a conceptional diagram for indicating a red/blue optical module employed in the third embodiment. 
         FIG. 6A  is a conceptional diagram for showing an optical module according to a fourth embodiment of the present invention. 
         FIG. 6B  is a sectional view for representing a can package which is employed in the optical module of the fourth embodiment. 
         FIG. 7  is a conceptional view for indicating a plane type optical module according to a fifth embodiment of the present invention. 
         FIG. 8  is a conceptional diagram for indicating a three-wavelength optical receiver module according to a sixth embodiment of the present invention. 
         FIG. 9  is a diagram for explanatorily showing a structure and operating conditions in such a case that an optical transmitter module of the present invention has been applied to a compact laser projector. 
         FIG. 10  is a conceptional diagram for indicating an example in which the compact laser projector shown in  FIG. 10  has been assembled in a portable telephone. 
         FIG. 11  is a diagram for explanatorily indicating a structure and operating conditions in such a case that the optical transmitter module of the present invention has been applied to a light source designed for an optical disk pick-up. 
         FIG. 12A  is a diagram for explanatorily indicating a structure and operating conditions in such a case that the optical transmitter module of the present invention has been applied to a light source for a brain function measuring-purpose infrared spectroscopic apparatus. 
         FIG. 12B  is a diagram for schematically representing a structure of a fiber coupling type optical transmitter module which is employed in the brain function measuring-purpose infrared spectroscopic apparatus shown in  FIG. 12A . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to drawings, various sorts of embodiments according to the present invention will be described in detail. 
     First Embodiment 
       FIG. 1  and  FIG. 3  are sectional views for showing an optical module according to a first embodiment of the present invention.  FIG. 1  is such an example that the present invention has been applied to an optical transmitter module with employment of light sources of three primary colors (R, G, B primary colors). 
       FIG. 1  shows an example in which the optical transmission module has been mounted in a can package  1 . That is, a stem  10  on which laser light sources  11 ,  12 ,  13  have been mounted has been mounted on a can stem  14 , and an optical multiplexing/demultiplexing device  2  has been mounted on a can cap  3 .  FIG. 3  is a sectional view of the optical transmitter module shown in  FIG. 1 , as viewed at a rotation angle of 90 degrees from a view point of  FIG. 1 . A lens array  9  has been mounted just above laser elements. It is so assumed that waveforms of laser light emitted from the respective laser light sources  11 ,  12 ,  13  correspond to blue laser light (for instance, approximately 400 nm to 500 nm), green laser light (for example, approximately 500 nm to 580 nm), and red laser light (for instance, 580 nm to 750 nm), respectively. As the blue laser light source  11 , such a semiconductor laser element may be employed which employs InGaN formed on a GaN substrate as an activation layer. As the green laser light source  12 , such a semiconductor laser element may be employed which employs InGaN formed on a GaN substrate as an activation layer, or another semiconductor laser element may be employed which employs ZnCdSe formed on a ZnSe substrate as an activation layer. As the red laser light source  13 , such a semiconductor laser element may be employed which employs either InGaP or an InGaAlP quantum well formed on a GaAs substrate as an activation layer. These semiconductor laser elements have been mounted on the stem  10  in a predetermined interval in a junction down manner. At this time, the blue semiconductor laser element, the green semiconductor laser element, and the red semiconductor laser element have been arranged from a left side of  FIG. 1  in this order from the short light emission wavelength to the long light emission wavelength. In the can cap  3 , concave/convex portions capable of mounting both the optical multiplexing/demultiplexing device  2  and the lens array  9  have been provided. The optical multiplexing/demultiplexing device  2  has been manufactured in such a manner that while a transparent glass substrate  5  is employed as a supporting substrate, both a first wavelength selecting filter  6  and a second wavelength selecting filter  7  have been mounted on one surface of the transparent glass substrate  5 , whereas both a first mirror  8  and a second mirror  9  have been mounted on another surface thereof which is located opposite to the first-mentioned surface. The optical multiplexing/demultiplexing device  2  was mounted in such a manner that the outer shape of the optical multiplexing/demultiplexing device  2  was aligned to the concave/convex portions of the can cap  3 , and then, this optical multipleixng/demultiplexing device  2  was adhered onto the concave/convex portions by using a UV hardening resin. A material of the glass substrate was selected from BK7, and a thickness thereof was set to 1136 μm. While the glass substrate has been mounted in such a manner that an angle of this glass substrate with respect to a plane becomes 20 degrees, symbol “z” indicated in  FIG. 2  is selected to be 500 μm, namely, a projection of a pitch of multiple reflections onto the plane is 500 μm. The first and second wavelength selecting filters  6  and  7  have been constituted by a dielectric multilayer film made of Ta 2 O 5  and SiO 2 . The first wavelength selecting filter  6  has been formed as a filter (so-called “short-pass filter”) having such a property that this short-pass filter  6  can pass therethrough blue light, and can reflect green light and red light. The second wavelength selecting filter  7  has been formed as a short-pass filter having such a property that this short-pass filter  7  can pass therethough blue light and green light, and can reflect red light. In the first mirror  8 , the dielectric multilayer film made of Ta 2 O 5 /SiO 2  capable of reflecting the light having the green and red wavelengths has been employed. Alternatively, a metal such as aluminum may be employed in this first mirror  8 . The lens array  9  has such a structure that three lenses have been formed on the glass substrate. These three lenses have been designed so as to have a function capable of suppressing widening angles of light emitted from the blue, green, red laser light sources  11 ,  12 ,  13 , and capable of collimating these emitted light. 
     Although there is no limitation as to materials of the transparent substrate  5  and the lens array  9  if these materials are transparent with respect to wavelengths to be used, it is preferable to employ such low cost materials having higher processing precision. As the materials capable of satisfying this condition, the material of BK7 has been employed in the first embodiment. Alternatively, other glass materials, dielectric materials, and semiconductor materials may be apparently employed. 
     Next, a description is made of operations of the optical transmitter/receiver module according to the first embodiment. Concretely speaking, red laser light emitted from the red semiconductor LD (laser diode) element  13  reaches the optical multiplexing/demultiplexing device  2 . Since the optical multiplexing/demultiplexing device  2  has been mounted at such an angle which is not equal to a right angle with respect to the optical axis, after the red laser light is refracted based upon a difference in refractive indexes, the refracted red laser light is propagated within the optical multiplexing/demultiplexing device  2 , and is reflected on the first mirror  8 , and then, the reflected red laser light reaches the second wavelength selecting filter  7 . Just under the second wavelength selecting filter  7 , the green semiconductor LD element  12  for emitting the green laser light has been mounted. Since the second wavelength selecting filter  7  has such a property that the red laser light is reflected and the green laser light passes therethrough, the red laser light is multiplexed with the green laser light, and then, the multiplexed laser light is propagated within the optical multiplexing/demultiplexing device  2 . When this multiplexed laser light has reached the first wavelength selecting filter  6 , this multiplexed laser light is further multiplexed with the blue laser light in a similar manner. Finally, the laser light as to the three primary colors (R, G, B) is multiplexed with each other, so that the finally multiplexed laser light is emitted outside the optical transmitter module. It should be understood that emission intensity of the respective R, G, B laser diode elements  11 ,  12 ,  13  can be controlled by drive circuits (not shown) connected to the respective later diodes elements  11 ,  12 ,  13 . 
     Second Embodiment 
       FIG. 4  is a sectional view for showing an optical module according to a second embodiment of the present invention. The second embodiment is such an example that lens integrated type vertical emission LD elements  21 ,  22 ,  23  have been employed in light sources of respective wavelengths so as to construct the optical module. A lens integrated type vertical emission LD element corresponds to such an LD (laser diode) element which emits collimated laser light with respect to a substrate along a vertical direction. 
     It should be noted that although a basic function of the optical module according to the second embodiment is similar to the basic function of the first embodiment, since the lenses have been integrated on the LD elements  21 ,  22 ,  23 , the above-described lens array  9  has not been assembled in the optical module. 
     Third Embodiment 
       FIG. 5A  and  FIG. 5B  are sectional views for showing an optical module according to a third embodiment of the present invention. The optical module of this third embodiment is such an optical module that a light source can  30  where two laser diode elements having two red and blue wavelengths have been stored in a single can, and another light source can  31  for emitting green laser light having a single wavelength have been assembled in a single package. A structure of the light source can  30  having the two red and blue wavelengths is represented in  FIG. 5B . The optical module of the above-described first embodiment has the function capable of multiplexing the laser light of three colors (three wavelengths) with each other, whereas the optical module of this third embodiment has the function capable of multiplexing only the laser light of the two colors (two wavelengths) with each other. In this third embodiment, as to the green color laser light source, the laser module  31  having the following technical idea has been employed: That is, laser light having a wavelength in the vicinity of 1000 nm is converted into secondary higher harmonic waves by utilizing a non-linear effect so as to emit such a laser light having a wavelength in the vicinity of 500 nm. The green color laser light source  31  has been equipped with an excitation laser element, a solid-state laser medium, a laser oscillator, and a wavelength converting element, which are not shown in the drawing. The solid-state laser medium is excited by the excitation laser element. The oscillator oscillates light generated from the solid-state laser medium so as to oscillate laser light. The wavelength converting element converts the laser light oscillated by the oscillator into such a laser light having a desirable wavelength. In this third embodiment, as the solid-state laser medium, crystal of vanadium acid chloride (Nd: YVO 2 ) into which neodymium has been added has been employed, while neodymium emits light having a wavelength of 1064 nm. Alternatively, even if other crystal capable of emitting light having wavelengths in the vicinity of 1000 nm, then the necessary function may be sufficiently realized. Also, as the above-described wavelength converting element, crystal of KTP (KTiOPO 4 ) has been employed. This crystal of KTP (KTiOPO 4 ) has been employed in order that the crystal receives infrared light having wavelengths in the vicinity of 1064 nm which has been excited by the solid-state laser medium, and thus, this crystal generates green light having wavelengths in the vicinity of 532 nm, while the green light corresponds to the second higher harmonic waves of the above-described infrared light. 
     As indicated in  FIG. 5A , a three-wavelength module  33  is operated as follows: That is, a filter  35  mounted on a glass substrate  34  multiplexes the light emitted from the red/blue two-wavelength module with the light emitted from the green color module  31 , and then, the multiplexed laser light is emitted via a package lens  36  outside this three-wavelength module  33 . 
     Fourth Embodiment 
       FIG. 6A  and  FIG. 6B  are diagrams for indicating an optical module according to a fourth embodiment of the present invention. In the fourth embodiment, a can package  40 , an optical multiplexing/demultiplexing device  2 , and a lens  41  have been mounted in a plane type package  42 , while LD elements have been mounted in the can package  40 , but an optical multiplexing/demultiplexing device has not been mounted in this can package  40 . As indicated in  FIG. 6B , as to a structure of the can package  40 , both a stem  10  on which LD elements  11 ,  12 ,  13  have been mounted, and also a lens array  9  have been mounted on a can stem  14 . 
     Fifth Embodiment 
       FIG. 7  is a diagram for indicating an optical module according to a fifth embodiment of the present invention. In this fifth embodiment, a stem  51 , a lens array  9 , an optical wavelength multiplexing/demultiplexing device  2 , and a package lens  41  have been mounted on a plane type package  50 , while LD elements  11 ,  12 ,  13  have been mounted on the above-described stem  51 . Concretely speaking, the plane type package  50  may employ a butterfly module, or the like. Although the optical module shown in  FIG. 7  can be operated in the three-wavelength mode, even when a total number of wavelengths is further increased, the optical module of this fifth embodiment may be relatively easily operated, which constitutes the feature of the fifth embodiment. 
     Sixth Embodiment 
       FIG. 8  is a diagram for representing an optical module according to a sixth embodiment of the present invention, namely, a diagram for showing one embodiment mode in such a case that the inventive idea of the present invention has been applied to an optical multi-wavelength receiver module. While a basic structure of the optical multi-wavelength receiver module is equal to that of the above-described first embodiment, light receiving elements  61 ,  62 ,  63  have been mounted, instead of the light emitting elements  11 ,  12 ,  13 . It should be understood that operations of the optical multi-wavelength receiver module corresponds to the temporally inverted operations of the optical module described in the above-explained summary. That is to say, such a light entered via the package lens  4  into the optical multi-wavelength receiver module, whose three wavelengths have been optically multiplexed with each other, is wavelength-separated by the first and second wavelength selecting filters  6  and  7  of the optical multiplexing/demultiplexing device  2 , and then, a plurality of the wavelength-separated light are entered to these light receiving elements  61 ,  62 ,  63 , respectively. The above-described sixth embodiment has exemplified that the optical receiver module has been constructed by employing the optical module of the first embodiment. Apparently, optical multi-wavelength receiver modules may be alternatively constructed even if the above-described other optical modules of the second to fifth embodiments are employed. 
     Seventh Embodiment 
       FIG. 9  is a schematic diagram for illustratively showing a seventh embodiment in such a case that a compact laser projector  70  has been arranged by employing the optical module  1  of the present invention. The compact laser projector  70  has been equipped with drive circuits  71 ,  72 ,  73  for driving at least red, green, blue LD elements. In response to drive signals from the drive circuits  71 ,  72 ,  73 , both intensity and timing as to respective color light outputted for the optical module  1  are controlled. The light emitted from the optical module  1  is reflected on a compact mirror  74 , so that the reflected light is projected toward a screen  76  positioned outside the laser projector  70 . Motion of the compact mirror  74  is controlled by a mirror driving apparatus  75 . In order to represent an image, such a laser light whose the respective colors (RGB) have been modulated based upon intensity and time is two-dimensionally scanned in a high speed on the screen  76 . 
     Eighth Embodiment 
       FIG. 10  illustratively shows an example in which the compact laser projector  70  described in the seventh embodiment has been assembled in a portable telephone. As apparent from the foregoing descriptions, as apparatuses into which the compact laser projector  70  is assembled, not only a portable telephone, but also other appliances may be assembled, for example, mobile computers, portable game machines, portable audio appliances, electronic dictionaries, and the like. Alternatively, these appliances may be apparently constructed as independent apparatuses as compact projectors. 
     Ninth Embodiment 
       FIG. 11  is a diagram for representing a ninth embodiment in such a case that the optical module of the present invention has been applied to an optical disk reading apparatus. 
     Laser light emitted from an optical multi-wavelength transmitter module  80  is entered via a diffraction grating  81 , a ½ wavelength plate  82 , a beam splitter  83 , a ¼ wavelength plate  84 , and a lens  85  onto an information recording plane formed on an optical disk  88 . Laser light reflected on the optical disk  88  is polarized/separated by the beam splitter  83 , and then, entered via another lens  86  to a light receiving element  87 . 
     In the multi-wavelength transmitter module  80 , a red laser element having a wavelength of 780 nm has been mounted as a CD reading-purpose LD element; a red laser element having a wavelength of 650 nm has been mounted as a DVD reading-purpose LD element; and a blue laser element having a wavelength of 405 nm has been mounted as a Blue-ray disk reading-purpose element. Normally, while these laser light sources are separately prepared, red laser light, green laser light, and blue laser light are optically multiplexed with each other by employing a dichroic prism. However, in accordance with this ninth embodiment, only one optical multi-wavelength transmitter module  80  may be merely employed, so that the optical system of the optical disk reading apparatus can be largely simplified. 
     Tenth Embodiment 
       FIG. 12A  and  FIG. 12B  are diagrams for illustratively showing a tenth embodiment of the present invention in such a case that the optical module of the present invention has been applied to a brain function measuring-purpose infrared spectroscopic apparatus (so-called “brain topography apparatus”). A basic function of this brain function measuring-purpose infrared spectroscopic apparatus is given as follows: That is, oxygen concentration within brain blood vessels is measured by absorptions of laser light. Laser light emitted from an optical multi-wavelength transmitter module  90  is conducted via a fiber  91  to a probe holder  93 , and then, the conducted laser light is projected from the probe holder  93 . After the projected laser light has been absorbed by a predetermined absorption level within a biological body, the absorbed laser light is detected by a light receiving element  92  mounted on the probe holder  93 . At this time, oxygen concentration within blood vessels is measured based upon intensity ratios of the respective wavelengths of the laser light. A concrete shape of the multi-wavelength transmitter module  90  is illustratively shown in  FIG. 12B . These sorts of LD elements having wavelengths of 705 nm, 754 nm, 830 nm, which are suitable for biological measurements, have been mounted on a can package  94 . 
     Since the optical module of the present invention is employed in the light source of the head mounting type probe holder  93  utilized in the biological measurement, cost and dimensions of the spectroscopic apparatus can be reduced. Also, since the spectroscopic apparatus is made simpler and compact, there is another effect that oppression senses felt by persons under examination can be reduced. 
     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.