Abstract:
A semiconductor laser module comprising a semiconductor laser device, a collimating section collimating a laser beam emitted from the semiconductor laser device, a beam shaping section parallel-shifting at least part of a laser beam emitted from the collimating section to a position satisfying an effective numerical aperture of the optical fiber cable when the laser beam exceeds the effective numerical aperture of the optical fiber cable, and a collecting section collecting a laser beam emitted from the beam shaping section onto a light incident end face of the optical fiber cable.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2003-123704, filed Apr. 28, 2003, the entire contents of which are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a semiconductor laser module using a high output semiconductor laser device. The present invention relates to a method of controlling a semiconductor laser beam emitted from a high output semiconductor laser device. The present invention relates to a projection type video display apparatus using the semiconductor laser module as light source.  
         [0004]     2. Description of the Related Art  
         [0005]     As publicly known, there has been recently made technical development for using a semiconductor laser device as a light source in a projection type video display apparatus such as liquid crystal projector.  
         [0006]     This kind of video display apparatus takes a laser beam emitted from a semiconductor laser device generating high optical power such as several W to 10 W via optical fiber cable. The laser beam is used to special modulation by a video signal.  
         [0007]     In general, the semiconductor laser device has multimode when the power becomes high, and the beam emitting region, that is, the active layer becomes a thin and long shape. More specifically, the direction perpendicular to the active layer, that is, the shorter direction (fast axis direction) of the active layer is several μm. On the other hand, the direction parallel to the active layer, that is, the longer direction (slow axis direction) of the active layer is about 100 μm.  
         [0008]     The laser beam emitted from the semiconductor laser device is emitted having the following spread angles. One is a spread angle of several tens of degrees (±10°) in the fast axis direction with respect to the optical axis vertical to the beam emitting region surface. Another is a spread angle of ± several degrees in the slow axis direction with respect to the same as above.  
         [0009]     The receiving angle of the optical fiber cable on which the laser beam emitted from the semiconductor laser device is incident is symmetrical with respect to the optical axis vertical to a light incident end face. The receiving angle is about several 10° in both fast and slow axis directions.  
         [0010]     Currently, the laser beam emitted from the semiconductor laser device is shaped by an optical system composed of collimator lens and collective lens. By doing so, the laser beam is effectively incident on the optical fiber cable.  
         [0011]     In order to adapt the laser beam emitted from the semiconductor laser device to the receiving angle of the optical fiber cable, the laser beam is shaped by the optical system. However, the sine condition (relationship between beam diameter D and spread angle θ, Dsin θ=constant) is given. For this reason, the laser beam incident on the optical fiber cable has a thin and long beam shape having the fast axis direction of several μm and the slow axis direction of several 10 μm.  
         [0012]     On the contrary, the shape of the light incident end face of the optical fiber cable is circular in general. In order to enable the entire laser beam having the thin and long beam shape to be incident on the optical fiber cable, the following matter is required. The diameter of the optical fiber cable must be set to the beam diameter of the slow axis direction, that is, several 10 μm.  
         [0013]     By doing so, the entire laser beam emitted from the semiconductor laser device is incident on the optical fiber cable. However, the laser beam is incident with considerable margin in the fast axis direction. For this reason, a problem arises such that the optical density (incident light power/cross section of optical fiber cable) of the incident laser beam is reduced. In other words, it is desirable that the cross-sectional shape of the optical fiber cable coincides with the beam shape in order to enable the incidence of laser beam having high light density.  
         [0014]     JPN. PAT. APPLN. KOKAI Publications No. 10-300989, 11-316318 and 7-318854 disclose the following technique. According to the technique, the laser beam emitted from the semiconductor laser device is shaped using various lenses in order to enable the incidence of the laser beam with high efficiency and high light density.  
         [0015]     However, according to the laser beam shaping technique disclosed in each of the foregoing Publications, the effect adaptable to practical use is not sufficiently obtained. In addition, lenses having special shape must be employed; for this reason, the foregoing laser beam shaping technique is unsuitable for practical use.  
       BRIEF SUMMARY OF THE INVENTION  
       [0016]     According to one aspect of the present invention, there is provided a semiconductor laser module comprising: a semiconductor laser device; a collimating section collimating a laser beam emitted from the semiconductor laser device; a beam shaping section parallel-shifting at least part of a laser beam emitted from the collimating section to a position satisfying an effective numerical aperture of the optical fiber cable when the laser beam exceeds the effective numerical aperture of the optical fiber cable; and a collecting section collecting a laser beam emitted from the beam shaping section onto a light incident end face of the optical fiber cable.  
         [0017]     According to one aspect of the present invention, there is provided a method of controlling a semiconductor laser beam, comprising: collimating a laser beam emitted from the semiconductor laser device; parallel-shifting at least part of the laser beam to a position satisfying an effective numerical aperture of the optical fiber cable when the collimated laser beam exceeds the effective numerical aperture of the optical fiber cable; and collecting the collimated laser beam including the parallel-shifted laser beam onto a light incident end face of the optical fiber cable.  
         [0018]     According to one aspect of the present invention, there is provided a video display apparatus comprising: a semiconductor laser module parallel-shifting at least part of a laser beam collimated after being emitted from the semiconductor laser module to a position satisfying an effective numerical aperture of the optical fiber cable when the laser beam exceeds the effective numerical aperture of the optical fiber cable; a modulating section spatially modulating a laser beam outputted from the semiconductor laser module via the optical fiber cable based on a video signal; and a display section projecting and displaying optical output obtained from the modulating section on a screen. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
       [0019]      FIG. 1  is a view to explain a liquid crystal projection TV receiver according to one embodiment of the present invention;  
         [0020]      FIG. 2A  to  FIG. 2C  are views to explain a semiconductor laser device in the embodiment;  
         [0021]      FIG. 3A  and  FIG. 3B  are views to explain the structure of a semiconductor laser module in the embodiment;  
         [0022]      FIG. 4A  and  FIG. 4B  are views to explain the structure of a first beam shaping section in the embodiment;  
         [0023]      FIG. 5A  and  FIG. 5B  are views to explain the operation of the first beam shaping section in the embodiment;  
         [0024]      FIG. 6A  and  FIG. 6B  are views to explain the structure of a second beam shaping section in the embodiment;  
         [0025]      FIG. 7A  and  FIG. 7B  are views to explain the operation of the second beam shaping section in the embodiment; and  
         [0026]      FIG. 8A  and  FIG. 8B  are views to explain a modification example of the semiconductor laser module according to the embodiment. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0027]     One embodiment of the present invention will be described below with reference to the accompanying drawings.  FIG. 1  shows a video display apparatus described in the embodiment, that is, a liquid crystal projection TV (Television) receiver.  
         [0028]     In  FIG. 1 , reference numerals  11  to  13  individually denote a semiconductor laser modules. The semiconductor laser modules  11  to  13  emit R (Red), G (Green) and B (Blue) laser beams, respectively.  
         [0029]     R, G and B laser beams emitted from the semiconductor laser modules  11  to  13  are incident on spatial modulating means, that is, liquid crystal panels  14 ,  15  and  16 , which are located correspondingly to each beam.  
         [0030]     On the other hand, a tuner  18  selects a television broadcasting signal received by an antenna  17 . Thereafter, a signal processing section  19  demodulates the received television-broadcasting signal so that the signal can be generated as a video signal. The video signal is inputted to liquid crystal panels  14  to  16  via a driver  20 .  
         [0031]     The R, G and B laser beams incident on liquid crystal panels  14  to  16  receive spatial demodulation by the video signal, and are synthesized by synthesizing means such as dichroic prism  21 .  
         [0032]     The beam thus synthesized is enlarged and projected on a screen  23  via a projection lens  22 , and thereby, a television broadcasting video image is displayed thereon.  
         [0033]      FIG. 2A  shows the appearance of a semiconductor laser device  24  applied to the foregoing semiconductor laser modules  11  to  13 . The semiconductor laser device  24  is formed into an approximately rectangular shape, and a beam emitting region, that is, a thin and long active layer  24   a  is exposed on one side used as the beam emitting end face.  
         [0034]     Here, the direction perpendicular to the active layer  24   a , that is, the shorter direction of the active layer  24   a  is defined as the fast axis (y axis) direction. The length of the fast axis direction of the active layer  24   a  is several μm.  
         [0035]     The direction parallel to the active layer  24   a , that is, the longer direction of the active layer  24   a  is defined as the slow axis (x axis) direction. The length of the slow axis direction of the active layer  24   a  is several 100 μm.  
         [0036]     The traveling direction of the laser beam emitted from the active layer  24   a , that is, the direction vertical to the beam emitting end face is defined as the z-axis direction.  
         [0037]     As shown in  FIG. 2B , the laser beam from the active layer  24   a  is emitted having a spread angle θf of ± several 10° in the fast axis direction. As illustrated in  FIG. 2C , the laser beam from the active layer  24   a  is emitted having a spread angle θs of ± several degrees in the slow axis direction.  
         [0038]      FIG. 3A  and  FIG. 3B  are views to explain the structure of the semiconductor laser module  11  using the semiconductor laser device  24 . Other semiconductor laser modules  12  and  13  have the same structure as the module  11  except that the color of the laser beam emitted from the semiconductor laser device  24  is different. Therefore, the details of the modules  12  and  13  are omitted.  
         [0039]      FIG. 3A  shows a state that the semiconductor laser module  11  is viewed in the slow axis direction, that is, the y-z plane.  FIG. 3B  shows a state that the semiconductor laser module  11  is viewed in the fast axis direction, that is, the x-z plane.  
         [0040]     The laser beam emitted from the semiconductor laser device  24  is incident on a cylindrical lens  25  for fast-axis collimation so that it can be shaped into a beam parallel to the fast axis direction.  
         [0041]     Thereafter, the laser beam emitted from the cylindrical lens  25  is incident on a cylindrical lens  26  for slow-axis collimation so that it can be shaped into a beam parallel to the slow axis direction.  
         [0042]     The laser beam emitted from the cylindrical lens  26  is successively incident on first and second beam shaping sections  27  and  28 , and shaped therein. Thereafter, the laser beam is collected by a collective lens  29 , and thereafter, incident on the core of an optical fiber cable  30 .  
         [0043]      FIG. 4A  and  FIG. 4B  show the structure of the first beam shaping section  27 .  FIG. 4A  shows a state that the first beam shaping section  27  is viewed in the slow axis direction, that is, the y-z plane.  FIG. 4B  shows a state that the first beam shaping section  27  is viewed in the fast axis direction, that is, the x-z plane.  
         [0044]     The first beam shaping section  27  is composed of two flat-shaped lenses  27   a  and  27   b  each having a predetermined thickness. The lenses  27   a  and  27   b  are located together in the slow axis direction in a state that their plane is oriented toward the direction facing the traveling direction of the laser beam.  
         [0045]     In this case, the lenses  27   a  and  27   b  are arranged with a predetermined space dx in the slow axis direction. One lens  27   a  is inclined at only predetermined angle θx to the z-axis around the slow axis. The other lens  27   b  is inclined in the direction reverse to the lens  27   a  at only predetermined angle θx to the z-axis around the slow axis.  
         [0046]      FIG. 5A  shows a shape of a laser beam L 1 , which is incident on the first beam shaping section  27  after being emitted from the cylindrical lens  26 . More specifically, the laser beam L 1  has a thin and long shape, which is shorter in the fast axis direction while being longer in the slow axis direction.  
         [0047]     When being incident on the first beam shaping section  27 , the laser beam L 1  having the foregoing shape is emitted in the following manner. As seen from  FIG. 5B , the middle portion L 2  of the laser beam L 1  is intactly emitted through a space of the interval dx formed between lenses  27   a  and  27   b.    
         [0048]     One end portion L 3  of the laser beam L 1  is incident on the inclined flat-shaped lens  27   a . Thereafter, the end portion L 3  is emitted in a state of being shifted in parallel to the middle portion L 2  by a predetermined distance Δy in the fast axis direction.  
         [0049]     The other end portion L 4  of the laser beam L 1  is incident on the flat-shaped lens  27   b  inclined in the direction reverse to the lens  27   a . Thereafter, the other end portion L 4  is emitted in a state of being shifted in parallel to the middle portion L 2  by a predetermined distance Ay in the direction reverse to the end portion L 3  in the fast axis direction.  
         [0050]     In other words, the first beam shaping section  27  has a function of dividing the laser beam L 1  having a thin and long shape in the slow axis direction into three portions. The three portions are middle portion L 2 , end portions L 3  and L 4 , which are shifted in parallel to the middle portion L 2  by a predetermined distance Δy in the direction reverse to each other in the fast axis direction.  
         [0051]     The refractive index, inclined angle and thickness of the lenses  27   a  and  27   b  are varied, and thereby, the parallel shift of the end portions L 3  and L 4  of the laser beam L 1  is arbitrarily set. The ratio of dividing the laser beam L 1  into three is arbitrarily set by varying the interval dx between lenses  27   a  and  27   b.    
         [0052]      FIG. 6A  and  FIG. 6B  show the structure of the second beam shaping section  28 .  FIG. 6A  shows a state that the second beam shaping section  28  is viewed in the slow axis direction, that is, the y-z plane.  FIG. 6B  shows a state that the second beam shaping section  28  is viewed in the fast axis direction, that is, the x-z plane.  
         [0053]     The second beam shaping section  28  is composed of two flat-shaped lenses  28   a  and  28   b  each having a predetermined thickness. The lenses  28   a  and  28   b  are located together in the fast axis direction in a state that their plane is oriented toward the direction facing the traveling direction of the laser beam.  
         [0054]     In this case, the lenses  28   a  and  28   b  are arranged with a predetermined space dy in the fast axis direction. One lens  28   a  is inclined at only predetermined angle θy to the z-axis around the fast axis. The other lens  28   b  is inclined in the direction reverse to the lens  28   a  at only predetermined angle θy to the z-axis around the fast axis.  
         [0055]      FIG. 7A  shows each shape of laser beam L 2 , L 3  and L 4 , which is incident on the second beam shaping section  28  after being emitted from the first beam shaping section  27 . When the laser beams L 2  to L 4  are being incident on the second beam shaping section  28 , the middle portion L 2  is intactly emitted through a space of an interval dy formed between lenses  28   a  and  28   b , as seen from  FIG. 7B .  
         [0056]     One end portion L 3  of the laser beam is incident on the inclined flat-shaped lens  28   a . Thereafter, the end portion L 3  is emitted in a state of being shifted in parallel to the middle portion L 2  by a predetermined distance in the slow axis direction.  
         [0057]     The other end portion L 4  of the laser beam is incident on the flat-shaped lens  28   b  inclined in the direction reverse to the lens  28   a . Thereafter, the other end portion L 4  is emitted in a state of being shifted in parallel toward the middle portion L 2  by a predetermined distance in the slow axis direction.  
         [0058]     In this case, laser beams L 3  and L 4  are shifted in parallel that they come into line with the laser beam L 2  on the fast axis. In other words, the second beam shaping section  28  has the following function. Laser beams L 3  and L 4  shifted in parallel to the fast axis direction in the first beam shaping section  27  is shifted in parallel so that they can be arranged in ling via the middle portion L 2  in the fast axis direction.  
         [0059]     The refractive index, inclined angle and thickness of the lenses  27   a  and  27   b  are varied, and thereby, parallel shifting of the laser beams L 3  and L 4  in the slow axis is arbitrarily set.  
         [0060]     According to the embodiment, the laser beam emitted from the semiconductor laser device  24  is shaped into a parallel beam, that is, laser beam L 1  having the thin and long shape by cylindrical lenses  25  and  26 . The laser beam L 1  is divided into three in the longitudinal direction, and thereafter, divided three portions are shifted so that they can be arranged in line along the fast axis.  
         [0061]     Therefore, divided laser beams L 2  to L 4  are all incident on the circular core of the optical fiber cable  30  without generating wasteful beam space. As a result, the laser beam emitted from the semiconductor laser device  24  can be incident on the optical fiber cable  30  with high efficiency and high optical density.  
         [0062]     In other words, the laser beam emitted from the semiconductor laser device  24  has an area, which is not optically coupled with the optical fiber cable  30  because the effective numerical aperture of the slow axis exceeds that of the optical fiber cable. For this reason, the foregoing area of the laser beam is shifted in the fast axis having larger numerical aperture. By doing so, the laser beam can be optically coupled with the optical fiber cable  30  with high efficiency and high optical density.  
         [0063]     The first and second beam shaping sections  27  and  28  are composed of two flat-shaped lenses  27   a ;  27   b  and  28   a ;  28   b , respectively. Thus, the structure can be simplified without using lenses having special shape.  
         [0064]      FIG. 8A  and  FIG. 8B  show a modification example of the foregoing embodiment. In  FIG. 8A  and  FIG. 8B , the same reference numerals are used to designate the components identical to  FIG. 3A  and  FIG. 3B . Laser active substance is added to the core of the optical fiber cable  30 .  
         [0065]     The optical fiber cable  30  is provided with reflecting devices  31  and  32 . The reflecting device  31  transmits excitation light emitted from the semiconductor laser device  24 , and reflects laser beam generated in the optical fiber cable  30 . The reflecting device  32  partially reflects the laser beam generated in the optical fiber cable  30 .  
         [0066]     For example the following condition is given. More specifically, the semiconductor laser wavelength ranges from 830 to 850 nm, and the laser active substance added to the core of the optical fiber cable  20  is Pr 3+ /Yb 3+ . In this case, the reflecting device  31  totally transmits the wavelength ranging 830 to 850 nm while totally reflecting the wavelength of 635 nm. On the other hand, the reflecting device  32  partially reflects the wavelength of 635 nm.  
         [0067]     The excitation light incident on the optical fiber cable  30  is absorbed into the laser active substance; therefore, light having a wavelength of is generated. The generated light having 635 nm is generated as laser beam of 635 nm by a resonator composed of reflecting devices  31  and  32 , and thereafter, outputted from the reflecting device  32 .  
         [0068]     In this case, since high power and high density excitation light is required, it is specially effective to use the semiconductor laser module  11  shown in  FIG. 3A  and  FIG. 3B .  
         [0069]     The present invention is not limited to the embodiments described above, and various modifications of components may be made without departing from the spirit or scope of the general inventive concept. Several components disclosed in the foregoing embodiments are properly combined, and thereby, various inventions may be made. For example, some components may be deleted from all components shown in the embodiments. Components according to different embodiment may be properly combined.