Abstract:
An optical communication module comprising: a light emitting element to emit light; a light transmission medium to receive incidence of the light from the light emitting element; a diverging unit to be provided on the light transmission medium and to diverge some proportion of the light emitted from the light emitting element to the light transmission medium and propagating within the light transmission medium; and a first light receiving element to receive the light from the light emitting element, which is diverged by the diverging unit.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2011-199779 filed on Sep. 13, 2011, the entire contents of which are incorporated herein by reference. 
       FIELD 
       [0002]    The present invention relates to an optical communication module and an optical communication device. 
       BACKGROUND 
       [0003]    In recent years, an optical communication module has been used in a variety of environments irrespective of whether indoor or outdoor. The optical communication module is requested to stabilize and thus output an optical signal. The output of the optical signal of the optical communication module is easy to be affected by usage environments such as variations in temperature and vibrations. It is therefore required to restrain fluctuations in optical output level of the optical communication module. 
         [0004]      FIG. 1  is a view illustrating an example (1) of a conventional optical communication module.  FIG. 1  depicts an example of a sectional structure parallel to an optical axis of an optical communication module  2100 . The optical communication module  2100  in  FIG. 1  is exemplified as a configuration of a transmission side. The optical communication module  2100  in  FIG. 1  includes an LD-CHIP (Laser Diode Chip)  2102 , a lens  2104 , a ferrule  2106 , an optical fiber  2108  and an M-PD (Monitor Photo Diode)  2110 . The optical fiber  2108  is held by a housing via the ferrule  2106 . Herein, light beams emitted from the LD-CHIP  2102  toward the lens  2104  are called front light (the light beams on a front side), while the light beams emitted from the LD-CHIP  2102  toward the M-PD  2110  are called back light (the light beams on a back side). In  FIG. 1 , the front side represents a side on which the lens  2104 , the optical fiber  2108 , etc exist in front of the LD-CHIP  2102 . In  FIG. 1 , the back side represents a side on which the M-PD  2110  exists in rear of the LD-CHIP  2102 . The front light emitted from the LD-CHIP  2102  toward the lens  2104  is output from the optical communication module  2100  via the lens  2104 , the optical fiber  2108 , etc. The light beams, which are output from the optical communication module  2100 , are received by an apparatus on the reception side. 
         [0005]    The LD-CHIP  2102  is a light emitting element. Light beams (front light) emitted from the LD-CHIP  2102  are condensed (converged) by the lens  2104  and are optically coupled (opto-coupled) by the optical fiber  2108  in the ferrule  2106 . The light beams, which are opto-coupled by the optical fiber  2108 , are output through the optical fiber  2108 . 
         [0006]    Further, the M-PD  2110  is a light receiving element. The M-PD  2110  monitors the back light of the LD-CHIP  2102 . An optical output level of the LD-CHIP  2102  is controlled so as to keep a fixed level of optical output by an APC (Auto Power Control) circuit on the basis of an intensity of the back light received by the M-PD  2110 . The APC based on the back light is capable of restraining fluctuations in optical output of the LD-CHIP  2102  itself. 
         [0007]      FIG. 2  is a view depicting an example (2) of the conventional optical communication module.  FIG. 2  illustrates an example of a sectional structure parallel to the optical axis of an optical communication module  2200 . The optical communication module  2200  in  FIG. 2  is exemplified by way of the configuration of the transmission side and a configuration on the reception side. The optical communication module  2200  includes an LD-CHIP  2202 , a first lens  2204 , a ferrule  2206 , an optical fiber  2208 , an M-PD  2210 , a first filter  2212 , a second filter  2222 , a second lens  2224  and a PD (Photo Diode)  2226 . 
         [0008]    The light beams (front light) emitted from the LD-CHIP  2202  is, similarly to the example in  FIG. 1 , output via the optical fiber. Further, an optical output level of the LD-CHIP  2202  is, similarly to the example in  FIG. 1 , controlled so as to keep a fixed level of optical output by the APC circuit on the basis of an intensity of the back light received by the M-PD  2210 . 
         [0009]    Moreover, the light beams inputted from the outside through the optical fiber  2208  are reflected by the first filter  2212 . The second filter  2222  selects a light beam having a predetermined wavelength from the reflected light beams. Further, the light beams passing through the second filter  2222  are converged by the second lens  2224  and received by the PD  2226 . 
       DOCUMENTS OF PRIOR ARTS 
     Patent Document 
       [0000]    
       
         [Patent document 1] Japanese Patent Application Laid-Open Publication No. 2010-239079 
         [Patent document 2] Japanese Patent Application Laid-Open Publication No. 2004-294513 
         [Patent document 3] Japanese Patent Application Laid-Open Publication No. 2002-252418 
       
     
       SUMMARY 
       [0013]    An optical system on the front side of an LD-CHIP  2102  of an optical communication module  2100  might cause optical fluctuations etc due to a tracking error and an external stress (vibration, impact, etc), in which optical coupling characteristics vary due to a change in temperature of a ferrule  2106  etc. The front-sided optical fluctuations etc of the LD-CHIP  2102  affect the light beams output from the optical communication module  2100  but hardly affect the light beams on the back side. Further, an optical output level of the front-sided light beams of the LD-CHIP  2102  does not depend on an optical output level of the back-sided light beams of the LD-CHIP  2102  in some cases according to characteristics, a malfunction, etc of the LD-CHIP  2102 . Hence, an intensity of the light beams output from the optical communication module  2100  does not depend on an intensity of the back-sided light beams of the LD-CHIP  2102  as the case may be. Accordingly, the optical communication module  2100  is unable to stabilize an optical output level even by conducting APC control in a way that uses the back-sided light beams of the LD-CHIP  2102  in some cases. This is the same with the optical communication module  2200 . What affects the light beams on the front side is exemplified such as thermal expansions, thermal contractions, vibrations and impacts of the respective components, the vibrations of the lenses and the vibrations of the fibers. 
         [0014]    One aspect of the disclosure is an optical communication module including: a light emitting element to emit light; a light transmission medium to receive incidence of the light from the light emitting element; a diverging unit to be provided on the light transmission medium and to diverge some proportion of the light emitted from the light emitting element to the light transmission medium and propagating within the light transmission medium; and a first light receiving element to receive the light from the light emitting element, which is diverged by the diverging unit. 
         [0015]    The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
         [0016]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is a view illustrating an example (1) of a conventional optical communication module. 
           [0018]      FIG. 2  is a view illustrating an example (2) of the conventional optical communication module. 
           [0019]      FIG. 3  is a view illustrating an example of a sectional structure parallel to an optical axis of an optical communication module (1). 
           [0020]      FIG. 4  is a view depicting an example of a wavelength demultiplexing multi-layered flat glass. 
           [0021]      FIG. 5  is a diagram illustrating an example of characteristics of a filter. 
           [0022]      FIGS. 6A ,  6 B and  6 C are a view illustrating an example (1-1) of how a ferrule is assembled. 
           [0023]      FIGS. 7A ,  7 B and  7 C are a view illustrating an example (1-2) of how the ferrule is assembled. 
           [0024]      FIGS. 8A ,  8 B and  8 C are a view illustrating an example (1-3) of how the ferrule is assembled. 
           [0025]      FIGS. 9A ,  9 B and  9 C are a view illustrating an example (1-4) of how the ferrule is assembled. 
           [0026]      FIG. 10  is a diagram illustrating examples of an LD-CHIP, M-PD and an APC circuit. 
           [0027]      FIG. 11  is a view illustrating an example of the sectional structure parallel to the optical axis of an optical communication module (2). 
           [0028]      FIG. 12  is a view illustrating an example (1) of a light shielding structure of a transparent ferrule. 
           [0029]      FIG. 13  is a view illustrating an example (2) of the light shielding structure of the transparent ferrule. 
           [0030]      FIG. 14  is a view illustrating an example (3) of the light shielding structure of the transparent ferrule. 
           [0031]      FIG. 15  is a view illustrating an example of the sectional structure parallel to the optical axis of an optical communication module (3). 
           [0032]      FIG. 16  is a view illustrating an example of the sectional structure parallel to the optical axis of an optical communication module (4). 
           [0033]      FIGS. 17A ,  17 B and  17 C are a view illustrating an example (2-1) of how the ferrule is assembled. 
           [0034]      FIGS. 18A ,  18 B and  18 C are a view illustrating an example (2-2) of how the ferrule is assembled. 
           [0035]      FIGS. 19A ,  19 B and  19 C are a view illustrating an example (2-3) of how the ferrule is assembled. 
           [0036]      FIGS. 20A ,  20 B and  20 C are a view illustrating an example (2-4) of how the ferrule is assembled. 
           [0037]      FIGS. 21A ,  21 B and  21 C are a view illustrating an example (2-5) of how the ferrule is assembled. 
           [0038]      FIG. 22  is a view illustrating an example of the sectional structure parallel to the optical axis of an optical communication module (5). 
           [0039]      FIG. 23  is a view illustrating an example of the sectional structure parallel to the optical axis of an optical communication module (6). 
           [0040]      FIG. 24  is a view illustrating an example of the sectional structure parallel to the optical axis of an optical communication module (7). 
           [0041]      FIG. 25  is a view illustrating an example of the sectional structure parallel to the optical axis of an optical communication module (8). 
           [0042]      FIG. 26  is a view illustrating an example of a configuration of an optical communication device. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0043]    Embodiments will hereinafter be described with reference to the drawings. Configurations in the embodiments are exemplifications, and a construction of the disclosure is not limited to the concrete configurations in the embodiments of the disclosure. Implementation of the construction of the disclosure may involve properly adopting the concrete configurations corresponding to the embodiments. 
       First Embodiment 
       [0044]    In an optical communication module of a first embodiment, part of light beams entering an optical fiber on the front side of an LD-CHIP are reflected by a filter installed within the optical fiber and received by an M-PD. The optical communication module controls an output of the LD-CHIP on the basis of an intensity of the light beams received by the M-PD. The optical communication module, which is incorporated into, e.g., an optical communication apparatus, converts an electric signal into an optical signal and transmits the optical signal. Further, the optical communication module is connected to a light transmission path (an optical fiber etc) through another ferrule etc and is thus enabled to transmit the optical signal to another apparatus on the reception side. 
         [0045]    (Example of Configuration) 
         [0046]      FIG. 3  is a view illustrating an example of a sectional structure parallel to an optical axis of the optical communication module. An optical communication module  100  transmits the optical signal. The optical communication module  100  in  FIG. 3  includes an LD-CHIP (Laser Diode Chip)  102 , a lens  104 , a ferrule  106 , an optical fiber  108 , an M-PD (Monitor Photo Diode)  110 , a filter  112  and an APC (Automatic Power Control) circuit  130 . The optical fiber  108  is held within a housing  116  of the optical communication module  100  through the ferrule  106  and a sleeve  114 . 
         [0047]    The LD-CHIP  102  is a light emitting element. The LD-CHIP  102  emits light beams having an intensity which depends on a current value of an inputted electric current. The APC circuit  130  controls the current value of the electric current inputted to the LD-CHIP  102 . The APC circuit  130  can operate as a control unit. Herein, the LD-CHIP is used as the light emitting element, however, other types of light emitting elements may also be utilized. A wavelength of the light beams emitted from the LD-CHIP  102  is, e.g., 1310 nm. The LD-CHIP  102  outputs the optical signal having the intensity based on the inputted electric signal. 
         [0048]    The lens  104  converges the light beams coming from the LD-CHIP  102  at an end portion of the optical fiber  108  and gets the light beams to be opto-coupled thereat. The lens  104  is exemplified such as a spherical lens, an aspherical lens and a ball lens. The lens  104  is not, however, limited to these types of lenses. The optical axis of the lens  104  is disposed coaxially with a central axis of, e.g., the optical fiber  108 . 
         [0049]    The ferrule  106  fixes the optical fiber  108  within the optical communication module  100 . A material exhibiting a small expansion coefficient is used for the ferrule  106 . Usable materials for the ferrule  106  are opaque materials such as zirconia ceramics, resins and metals. The ferrule  106  takes a cylindrical shape that is, e.g., 2.5 mm in diameter and 10 mm in length. The material and the shape of the ferrule  106  are not limited to those given above. The ferrule  106  is connected to another ferrule etc in a way that comes into contact therewith, whereby the optical fiber  108  within the ferrule  106  can be connected to the light transmission path (optical fiber etc). 
         [0050]    A hole, which penetrates a central portion of a circle of the cylinder, is bored in the ferrule  106 , thereby letting the optical fiber  108  therethrough. Further, the filter  112  is embedded in the ferrule  106 . The filter  112  is embedded so as to cut off the optical fiber  108 . Moreover, the ferrule  106  has a hole bored for taking out the light beams reflected by the filter  112 . The hole for taking out the light beams reflected by the filter  112  is, e.g., 1.0 mm in diameter. 
         [0051]    The ferrule  106  is press-fitted in the sleeve  114 . The sleeve  114  undergoing the press-fitting of the ferrule  106  is fixed within the housing  116 . The sleeve  114  and the housing  116  can be welded together by use of YAG (Yttrium Aluminum Garnet) and thus fixed. 
         [0052]    The optical fiber  108  is a light transmission medium. The optical fiber  108  propagates the light beams, which are opto-coupled at the end portion on the side of the LD-CHIP  102  and get incident thereon, toward the other end portion thereof. The optical fiber  108  is fixed by the ferrule  106 . The optical fiber  108  is 0.125 mm in diameter. Usable fibers as the optical fiber are a single-mode fiber (SMF) and a multi-mode fiber (MMF). Herein, the optical fiber is used as the light transmission medium, however, light transmission mediums other than the optical fibers may also be employed. 
         [0053]    The M-PD  110  is a light receiving element for a monitor. The M-PD  110  receives mainly the light beams emitted from the LD-CHIP  102  and reflected by the filter  112 . The M-PD  110  converts the received light beams into the electric signals (electric current) depending on the intensity of the received light beams. The M-PD  110  is connected to the APC circuit  130 . Herein, the PD (Photo Diode) is used as the light receiving element for the monitor, however, other types of light receiving elements may also be employed in place of the PD. A lens for the converging the light beams may also be provided in front of the M-PD  110 . 
         [0054]    The filter  112  reflects part of the light beams entering the optical fiber  108 . The filter  112  is inserted so as to cut off the optical fiber  108 . Accordingly, the filter  112  diverges part of optical signals outgoing from the LD-CHIP  102  and transmitted on the reception side through the optical fiber  108 . A size of the filter  112  is larger than the section of the optical fiber  108  to be cut off. The filter  112  is approximately, e.g., 0.1 mm to 0.5 mm in thickness. The filter  112  is one example of a diverging unit. 
         [0055]    The filter  112  transmits a large proportion of light beams in a predetermined wavelength range but reflects part of the light beams in the predetermined wavelength range. The filter  112  involves using, e.g., a wavelength demultiplexing multi-layered flat glass. The filter  112  is not limited to the wavelength demultiplexing multi-layered flat glass. 
         [0056]      FIG. 4  is a view depicting an example of the wavelength demultiplexing multi-layered flat glass. The wavelength demultiplexing multi-layered flat glass includes a multi-layered film composed of SiO 2  (a material having a low refractive index) and TiO 2  or Ta 2 O 5  (a material having a high refractive index) and a flat glass. 
         [0057]      FIG. 5  is a graphic chart illustrating an example of characteristics of the filter. In the graph of  FIG. 5 , the axis of abscissas represents a wavelength of the light, and the axis of ordinates represents a transmission loss. The filter having the characteristics indicated by the graph of  FIG. 5  transmits the large proportion of light beams in the vicinity of a wavelength of 1310 nm but reflects the large proportion of light beams in the vicinity of a wavelength of 1490 nm. Further, the filter having the characteristics indicated by the graph of  FIG. 5  reflects the light beams in the vicinity of the wavelength of 1310 nm at a predetermined rate. In the example of  FIG. 5 , the intensity of the transmitted light beams decreases by 0.3 dB at 1310 nm and decreases by 30 dB at 1490 nm. 
         [0058]    Herein, an assumption is that the filter having the characteristics indicated by the graph of  FIG. 5  is used as the filter  112 . A further assumption is that the wavelength of the light beams output from the LD-CHIP  102  is 1310 nm. At this time, the large proportion of light beams entering the optical fiber  108  from the LD-CHIP  102  pass through the filter  112 , while part of the light beams are reflected by the filter  112  and get incident on the M-PD  110 . 
         [0059]    An angle made by a reflection surface of the filter  112  or a vertical hole bored in the ferrule  106  in order for the M-PD  110  to receive the light beams and by the central axis of the ferrule  106  may be whatever angle if enabling the M-PD  110  to receive stably the light beams coming from the optical fiber. 
         [0060]    (Example of Assembling Ferrule) 
         [0061]      FIGS. 6A through 9C  are views illustrating how the ferrule  106  is assembled. The optical fiber  108  and the filter  112  are built in the ferrule  106 .  FIG. 6A  is a perspective view of the ferrule  106  etc. The near side of the ferrule  106  in  FIG. 6A  is the side of the end face on which the light beams coming from the LD-CHIP  102  get incident.  FIG. 6B  is a sectional view of the ferrule  106  etc on the plane embracing a line segment a 1 -a′ 1  and a line segment b 1 -b′ 1  in  FIG. 6A .  FIG. 6C  depicts a section of the ferrule  106  etc on the plane embracing a line segment c 1 -c′ 1  in  FIG. 6B  and being orthogonal to the section in  FIG. 6B . The same view configuration is applied to other similar views ( FIGS. 7A ,  7 B and  7 C, etc.). 
         [0062]    As in  FIG. 6A , the ferrule material such as the zirconia ceramics is formed in the cylindrical shape. One of the flat circular surfaces of the cylinder is defined as a lower surface, while the other is defined as an upper surface. The right side in  FIG. 6B  is defined as a lower surface side, while the left side is defined as an upper surface side. The upper surface side of the ferrule  106  is installed on the side of the LD-CHIP  102  in the optical communication module  100 . Furthermore, a curved surface of the cylinder is defined as a side surface. A straight line, which embraces a line segment extending from the center of the lower surface up to the center of the upper surface, is defined as the central axis. 
         [0063]    As in  FIGS. 6A ,  6 B and  6 C, a hole (a through-hole, a horizontal hole), through which the optical fiber is allowed to pass, is bored into the central axis of the cylinder. The hole takes a cylindrical shape, and the center of the hole is coincident with the central axis. If the optical fiber to be used is 125 μm in diameter, the diameter of the hole is set equal to or slightly larger than 125 μm. For example, the diameter of the hole is 125.5 μm. If the section of the optical fiber is not circular, the horizontal hole taking a shape matching with the section of the optical fiber may also be bored. 
         [0064]    Moreover, as in  FIGS. 6A ,  6 B and  6 C, the vertical hole is bored till reaching the hole for letting through the optical fiber from the side surface of the ferrule  106 . Namely, the hole is bored from the side surface of the optical fiber  108  down to the central axis. Some proportion of the light beams entering the optical fiber  108  are taken out of the thus-bored vertical hole. An angle made by the bored vertical hole and the central axis is, e.g., 90 degrees. The vertical hole may take the cylindrical shape and may also take a conical shape with its vertex formed in the vicinity of the central axis. 
         [0065]    Next, as in  FIGS. 7A ,  7 B and  7 C, the optical fiber  108  is inserted into the through-hole (the horizontal hole) filled with a bonding agent. Further, the optical fiber  108  coated with the bonding agent may also be inserted into the through-hole. The optical fiber  108  is fixed to the ferrule  106  upon hardening the bonding agent. The optical fiber  108  is inserted from the lower surface of the ferrule  106  up to the upper surface. The end faces (the upper and lower surfaces) of the ferrule  106  and the optical fiber  108  are polished. The (surface of) optical fiber  108  is polished, thereby facilitating the entrance of the light beams into the optical fiber  108 . 
         [0066]    Next, as in  FIGS. 8A ,  8 B and  8 C, a slit, into which to insert the filter  112 , is cut open from the side surface of the ferrule  106 . An angle made by the slit and the central axis is, e.g., 45 degrees. The slit is formed corresponding to a size of the filter  112 . The slit is cut open toward a connecting portion (intersection) between the central axis and the vertical hole. The slit receiving the insertion of the filter  112  is worked by, e.g., a dicing technique. At this time, the optical fiber is cut off. 
         [0067]    Next, as in  FIGS. 9A ,  9 B and  9 C, the filter  112  is inserted into the slit. The filter  112  is hardened by, e.g., the bonding agent. As the sizes of the filter  112  and the slit become smaller, a friction resistance between the filter  112  and the ferrule  106  gets smaller, thereby facilitating the insertion of the filter  112 . 
         [0068]    The vertical hole may be filled with a transparent resin. At this time, it is preferable that a resin having the same refractive index as the refractive index of a cladding portion of the optical fiber is used as the transparent resin. Further, on the occasion of hardening the optical fiber, the transparent bonding agent is used to fill the vertical hole, whereby the optical fiber may be thus hardened simultaneously with fixing this optical fiber. 
         [0069]    (APC Circuit) 
         [0070]      FIG. 10  is a diagram illustrating examples of the LD-CHIP, the M-PD and the APC circuit. The APC circuit  130  is not limited to the example in  FIG. 10 . The LD-CHIP  102  and the M-PD  110  are connected to the APC circuit  130 . The APC circuit  130  can be realized by hardware such as an Application Specific Integrated Circuit (ASIC) etc. 
         [0071]    The APC circuit  130  controls the electric power applied to the LD-CHIP  102  on the basis of the intensity of the light beams received by the M-PD  110 . The APC circuit  130  controls the electric power applied to the LD-CHIP  102  so that the intensity of the light beams received by the M-PD  110  is kept fixed. 
         [0072]    A backward bias is applied to the M-PD  110 . When the light beams enter the M-PD  110 , the electric current flows. That is, when the M-PD  110  receives the light beams reflected from the filter  112 , the light beams are converted into the electric signals (current). The electric signals converted by the M-PD  110  are amplified by a reference voltage and by an amplifier (Amp) and are inputted to a feedback loop control circuit. The setup of the reference voltage of the APC circuit and the configuration of the amplifier in  FIG. 10  are not limited to those in  FIG. 10 , and whatever setup and configuration are available if the electric signals converted by the M-PD  110 , i.e., the voltages at the both of terminals of a resistance R are amplified. Further, the electric signals converted by the M-PD  110  may also be amplified within the feedback loop control circuit. The electric current may be converted into the voltage. 
         [0073]    The feedback loop control circuit controls a bias current of the LD-CHIP  102  so that a magnitude of the inputted signal, i.e., the intensity of the light beams received by the M-PD  110  reaches the target value. The feedback loop control circuit compares the magnitude of the inputted signal with a predetermined reference value (the target value) of the signal, thus adjusting the bias current of the LD-CHIP  102 . 
         [0074]    For example, the feedback loop control circuit, if the intensity of the light beams received by the M-PD  110  is one-half of the reference value of the intensity of the light beams, adjusts the bias current so that the electric current supplied to the LD-CHIP  102  is doubled. This leads to such anticipation that the intensity of the light beams emitted from the LD-CHIP  102  is doubled, and the intensity of the light beams received by the M-PD  110  becomes equal to the reference value. 
         [0075]    (Operation, Effect of First Embodiment) 
         [0076]    The optical communication module  100  emits the light beams (the optical signals) from the LD-CHIP  102 . The light beams emitted from the LD-CHIP  102  are opto-coupled at the end portion of the optical fiber  108  in the ferrule  106  via the lens  104 . The opto-coupled light beams travel through within the optical fiber  108  and penetrate the filter  112 . The light beams penetrating the filter  112  are output from the optical communication module  100 . Moreover, some proportion of the opto-coupled light beams are reflected by the filter  112  and received by the M-PD  110 . The M-PD  110  receives the light beams emitted from the LD-CHIP  102 , entering the optical fiber and reflected by the filter  112 . Hence, the intensity of the light beams output from the optical communication module  100  depends on the intensity of the light beams received by the M-PD  110 . The light beams received by the M-PD  110  are converted into the electric signals depending on the intensity of the light beams. The APC circuit  130  controls the current value of the electric current supplied to the LD-CHIP  102 , corresponding to the intensity of the light beams received by the M-PD  110 . The APC circuit  130  controls the intensity of the light beams emitted from the LD-CHIP  102  so that the intensity of the light beams received by the M-PD  110  gets fixed. The optical communication module  100  can adjust the intensity of the light beams emitted from the LD-CHIP  102  on the basis of the intensity of the light beams which travel through the optical fiber  108  after being opto-coupled. 
         [0077]    The filter  112  reflects the light beams at a predetermined ratio, and consequently the intensity of the light beams received by the M-PD  110  gets fixed, thereby stabilizing the intensity of the light beams output from the optical communication module  100 . 
         [0078]    The optical communication module  100  controls the intensity of the light beams emitted from the LD-CHIP  102  so as to cancel influences of thermal expansions, thermal contractions, vibrations and impacts of the respective components, the vibrations of the lenses and the vibrations of the fibers, which are caused on the front side of the LD-CHIP  102 . 
         [0079]    The optical communication module  100  enables the stable optical output level to be kept against optical fluctuations (a change in temperature, an external stress) caused on the front side. The optical communication module  100 , for instance, if the intensity of the light beams entering the optical fiber  108  changes as the ferrule vibrates, receives the light beams on the front side, which are to be reflected by the filter  112 , whereby the output of the LD-CHIP  102  can be controlled in a way that reflects the change in intensity of the light beams. The optical communication module  100  can control the output of the LD-CHIP  102  by feeding back the influences due to the optical fluctuations on the front side. 
         [0080]    The optical communication module  100  outputs the light beams affected by the change in temperature and by the optical fluctuations on the front side. Further, the M-PD  110  similarly receives the light beams affected by the change in temperature and by the optical fluctuations on the front side. The APC circuit  130  controls, based on the intensity of the light beams received by the M-PD  110 , the intensity of the light beams emitted from the LD-CHIP  102 . The APC circuit  130  controls the intensity of the light beams so that the intensity of the light beams received by the M-PD  110  gets fixed, thereby enabling the optical communication module  100  to output the stable light beams even when affected by the change in temperature and by the optical fluctuations on the front side. 
       Second Embodiment 
       [0081]    Next, a second embodiment will be described. The second embodiment has common points to the first embodiment. Accordingly, the discussion will be focused on different points, while the descriptions of the common points are omitted. 
         [0082]    In the second embodiment, the ferrule involves using a transparent material. 
         [0083]    (Example of Configuration) 
         [0084]      FIG. 11  is a view illustrating an example of a sectional structure parallel to the optical axis of the optical communication module. An optical communication module  200  transmits the optical signal. The optical communication module  200  in  FIG. 11  includes an LD-CHIP  202 , a lens  204 , a ferrule  206 , an optical fiber  208 , an M-PD  210 , a filter  212  and an APC circuit  230 . The optical fiber  208  is held within a housing  216  of the optical communication module  200  through the ferrule  206  and a sleeve  214 . 
         [0085]    The ferrule  206  is a transparent ferrule which uses the transparent material. The transparent material such as a transparent resin and glass is employed as the material of the ferrule  206 . The transparent material connotes a material that is penetrated by the light beams having a wavelength band used for the optical communications, which involve using at least the optical fiber. The hole (vertical hole) for taking out the light beams reflected by the filter is bored in the ferrule  106  of the first embodiment, however, the vertical hole may not be bored in the ferrule  206  of the second embodiment. This is because the optical communication module  200  can receive the light beams reflected by the filter  212  with the M-PD  210  owing to the use of the transparent material without forming the vertical hole. Hence, the manufacture of the ferrule  206  is facilitated. An external configuration of the ferrule  206  is substantially the same as the external configuration of the ferrule  106  except the portion of the vertical hole. 
         [0086]    In the ferrule  206 , similarly to the ferrule  106  in  FIG. 6A  etc, one of the flat circular surfaces of the cylinder is defined as a lower surface, while the other is defined as an upper surface. The upper surface side of the ferrule  206  is installed on the side of the LD-CHIP  202  in the optical communication module  200 . Moreover, a curved surface of the cylinder is defined as a side surface. A straight line, which embraces a line segment extending from the center of the lower surface up to the center of the upper surface, is defined as the central axis. A portion vicinal to the upper surface of the ferrule  206  is also called an end portion. 
         [0087]    When the light beams enter from the upper surface side of the ferrule  206 , the light beams might become noises against the light beams traveling through within the optical fiber  208 . Accordingly, it is preferable to eliminate the light beams entering from other than the optical fiber  208 . 
         [0088]      FIG. 12  is a view depicting an example (1) of a light shielding structure of the transparent ferrule.  FIG. 12  is the view illustrating an example of the section passing through the central axis in the vicinity of the upper surface of the transparent ferrule. The light beams emitted from the LD-CHIP enter from the right side in  FIG. 12 . The transparent ferrule in  FIG. 12  has an upper surface that is roughly polished beforehand. The roughly-polished upper surface causes irregular reflections of the light beams on the upper surface itself, and the light beams become hard to enter the ferrule. Further, the optical fiber inserted into the transparent ferrule is inserted in a way that slightly projects from the roughly-polished upper surface. The end face of the optical fiber is polished. 
         [0089]      FIG. 13  is a view illustrating an example (2) of the light shielding structure of the transparent ferrule.  FIG. 13  is the view illustrating an example of the section passing through the central axis in the vicinity of the upper surface of the transparent ferrule. The light beams emitted from the LD-CHIP enter from the right side in  FIG. 13 . In the example of  FIG. 12 , the transparent ferrule in  FIG. 12  has the roughly-polished upper surface, however, the example in  FIG. 13  is that the upper surface is shielded from the light beams by covering a light shielding material over the upper surface. For example, a black resin is used as the light shielding material. Moreover, the optical fiber inserted into the transparent ferrule is inserted so as to project slightly from the upper surface covered with the black resin. The end face of the optical fiber is polished. Further, the black resin and the optical fiber may also be polished together. The upper surface of the ferrule excluding the portion of the optical fiber is thereby shielded from the light beams. 
         [0090]      FIG. 14  is a view illustrating an example (3) of the light shielding structure of the transparent ferrule.  FIG. 14  is the view illustrating an example of the section passing through the central axis in the vicinity of the upper surface of the transparent ferrule. The light beams emitted from the LD-CHIP enter from the right side in  FIG. 14 . In the example of  FIG. 14 , two holes each taking substantially a semicircular shape embracing the central axis are bored to intersect at a right angle the central axis in the vicinity of the upper surface. A distance between one hole and the upper surface is set different from a distance between the other hole and the upper surface. When viewing the transparent ferrule from the upper surface side, the two semicircular holes are disposed so as not to substantially overlap with each other. The light shielding materials are inserted into the two semicircular holes. For example, the black resin is used as the light shielding material. This light shielding material makes the light beams entering from the upper surface side of the transparent ferrule invisible from the lower surface side. Further, a hole, through which the optical fiber is allowed to pass, is bored along the central axis. The optical fiber is inserted into the bored hole and hardened therein. Thereafter, the upper surface side is polished. The light beams entering from the upper surface of the ferrule are cut off by the area excluding the portion of the optical fiber. 
         [0091]    For example, the transparent ferrule in  FIG. 12 ,  13  or  14  can be used as the ferrule  206  of the optical communication module  200 . The lower surface of the ferrule  206  may have, similarly to the upper surface of the ferrule  206 , the light shielding structures as in  FIGS. 12 through 14 . Each of the light shielding structures of the transparent ferrule as in  FIGS. 12 through 14  is an example of a light shielding portion. 
         [0092]    (Operation, Effect of Second Embodiment) 
         [0093]    The transparent material is employed for the ferrule  206  of the optical communication module  200 . The transparent material is used for the ferrule  206 , whereby the light beams on the front side can be received by the M-PD  210  without boring the vertical hole in the ferrule  206 . Further, the upper surface side of the ferrule  206  takes the light shielding structure as in  FIGS. 12 ,  13  and  14 , thereby reducing an error due to the noises caused by the light beams entering the transparent ferrule. 
       Third Embodiment 
       [0094]    Next, a third embodiment will be discussed. The third embodiment has common points to the first and second embodiments. Accordingly, the discussion will be focused on different points, while the descriptions of the common points are omitted. 
         [0095]    In the third embodiment, the optical communication module has a configuration on the reception side. The optical communication module, which is incorporated into, e.g., an optical communication device, converts the electric signal into the optical signal and vice versa, and transmits and receives the optical signal. Moreover, the optical communication module, which is connected to the light transmission path (the optical fiber etc) via another ferrule, can transmit and receive the optical signal to and from other devices. 
         [0096]    (Example of Configuration) 
         [0097]      FIG. 15  is a view illustrating an example of the sectional structure parallel to the optical axis of the optical communication module. An optical communication module  300  transmits and receives the optical signal. The optical communication module  300  in  FIG. 15  includes an LD-CHIP  302 , a first lens  304 , a ferrule  306 , an optical fiber  308 , an M-PD  310 , a first filter  312  and an APC circuit  330 . The optical communication module  300  includes a second filter  322 , a second lens  324  and a PD  326 . The optical fiber  308  is held within a housing  316  of the optical communication module  300  through the ferrule  306  and a sleeve  314 . 
         [0098]    The ferrule  306  is assembled in the same way as the ferrule  106  in the first embodiment is. A vertical hole (which passes through the central axis and has an angle of 90 degrees with the central axis) bored in the ferrule  306 , however, pieces the ferrule  306  throughout. The light beams coming from the LD-CHIP  302  pass through the vertical hole on one side, while the light beams inputted from the outside pass through the vertical hole on the other side. 
         [0099]    The first filter  312  transmits a large proportion but reflects some proportion of the light beams entering the optical fiber  308  from the LD-CHIP  302 . Moreover, the light beams inputted via the optical fiber  308  from the outside (the left side in  FIG. 15 ) are reflected by the first filter  312 . The second filter  322  transmits the light beams having a predetermined wavelength in the reflected light beams. Further, the light beams penetrating the second filter  322  are converged by the second lens  324  and received by the PD  326 . The light beams received by the PD  326  are converted into the electric signals. 
         [0100]    The first filter  312  involves using a filter having characteristics demonstrated by, e.g., a graph in  FIG. 5 . It is herein assumed that a wavelength of the light beams output from the LD-CHIP  302  is 1310 nm, and a wavelength of the light beams inputted via the optical fiber  308  from the outside is 1490 nm. At this time, the first filter  312  transmits a large proportion of the light beams entering the optical fiber  308  from the LD-CHIP  302 . Moreover, some proportion of the light beams entering the optical fiber  308  from the LD-CHIP  302  are reflected by the first filter  312  and enter the M-PD  310 . Further, the light beams inputted via the optical fiber  308  from the outside are reflected by the first filter  312  and enter the PD  326 . 
         [0101]    A wavelength different from the wavelength of the light beams inputted via the optical fiber  308  from the outside and received by the PD  326  is used as the wavelength of the light beams emitted from the LD-CHIP  302 . 
         [0102]    The second filter  322  cuts off the light beams emitted from the LD-CHIP  302  but transmits the light beams inputted via the optical fiber  308  from the outside. Namely, the second filter  322  cuts off the wavelength of the light beams emitted from the LD-CHIP  302  buts transmits the wavelength of the light beams inputted via the optical fiber  308  from the outside. The wavelength demultiplexing multi-layered flat glass as in  FIG. 4  can be used as the second filter  322 . 
         [0103]    The second lens  324  converges the light beams penetrating the second filter  322  at the PD  326 . The second lens  324  can be exemplified such as a spherical lens, an aspherical lens and a ball lens. The second lens  324  is not limited to these types of lenses. 
         [0104]    The PD  326  is a light receiving element. The PD  326  receives the light beams inputted via the optical fiber  308  from the outside. The received light beams are converted into the electric signals and then processed. 
         [0105]    (Operation, Effect of Third Embodiment) 
         [0106]    The optical communication module  300  outputs the light beams (the optical signals) emitted from the LD-CHIP  302  to the outside through the first filter  312  etc. Some proportion of the light beams (the optical signals) emitted from the LD-CHIP  302  are reflected by the first filter  312  and enter the M-PD  310 . The APC circuit  330  controls the intensity of the light beams emitted from the LD-CHIP  302  on the basis of the intensity of the light beams received by the M-PD  310 . The APC circuit  330  controls the intensity of the light beams emitted from the LD-CHIP  302  so that the intensity of the light beams received by the M-PD  310  becomes fixed. 
         [0107]    Furthermore, the first filter  312  reflects the light beams (the optical signals) inputted via the optical fiber  308  from the outside (the left side in  FIG. 15 ). The light beams reflected by the first filter  312  are received by the PD  326 . The first filter  312  can extract the light beams on the reception side and can extract the light beams on the transmission side. 
         [0108]    The optical communication module  300  enables the stable optical output level to be kept against the optical fluctuations (the change in temperature, the external stress) caused on the front side even in the case of including the configuration for receiving the optical signals from the outside. 
       Fourth Embodiment 
       [0109]    Next, a fourth embodiment will be discussed. The fourth embodiment has common points to the first through third embodiments. Accordingly, the discussion will be focused on different points, while the descriptions of the common points are omitted. 
         [0110]    In the fourth embodiment, the optical communication module has the configuration on the reception side, and the ferrule and the M-PD take an integral-type structure. 
         [0111]    (Example of Configuration) 
         [0112]      FIG. 16  is a view illustrating an example of the sectional structure parallel to the optical axis of the optical communication module. An optical communication module  400  transmits and receives the optical signal. The optical communication module  400  in  FIG. 16  includes an LD-CHIP  402 , a first lens  404 , a ferrule  406 , an optical fiber  408 , an M-PD  410 , a first filter  412  and an APC circuit  430 . The optical communication module  400  includes a second filter  422 , a second lens  424  and a PD  426 . The optical fiber  408  is held within a housing  416  of the optical communication module  400  through the ferrule  406  and a sleeve  414 . 
         [0113]    A hole piercing the central portion of the circle of the cylinder is thus bored in the ferrule  406 , and the optical fiber  408  is allowed to pass through this hole. Moreover, the first filter  412  is embedded in the ferrule  406 . The first filter  412  is embedded so as to cut (intercept) the optical fiber  408 . 
         [0114]    A hole for taking out the light beams reflected by the first filter  412  is bored in the ferrule  406 . The hole for taking out the light beams reflected by the first filter  412  is, e.g., 1.0 mm in diameter. Further, a hole for installing the M-PD  410  is bored in the ferrule  406 . The hole for installing the M-PD  410  is provided in the vicinity of the side surface of the ferrule  406  in a way that expands the hole for taking out the light beams reflected by the first filter  412 . 
         [0115]    The M-PD  410  is a light receiving element for a monitor. The M-PD  410  receives mainly the light beams emitted from the LD-CHIP  402 . A lens for converging the light beams may also be provided in front of the M-PD  410 . The M-PD  410  receives the light beams reflected by the first filter  412 . 
         [0116]    The M-PD  410  is mounted on the ferrule  406 . Namely, the M-PD  410  is fitted directly to the ferrule  406 . If the ferrule  406  vibrates due to the external stress etc, the M-PD  410  is mounted on the ferrule  406  and therefore vibrates together with the ferrule  406 . Hence, the M-PD  410  can receive, even when the ferrule  406  gets vibrating, the light beams reflected by the first filter  412  in the same way as when the ferrule  406  does not vibrate. If the M-PD is not fixed to the ferrule and when the ferrule vibrates, a part or the whole of the light beams reflected by the first filter  412  cannot be received as the case may be. 
         [0117]    (Example of Assembling Ferrule) 
         [0118]      FIGS. 17A through 21C  are views each depicting an example of how the ferrule  406  is assembled. The optical fiber  408  and the first filter  412  are built in the ferrule  406 .  FIG. 17A  is a perspective view of the ferrule  406  etc. The near side of the ferrule  406  in  FIG. 17A  is the side of the end face on which the light beams coming from the LD-CHIP  402  get incident.  FIG. 17B  is a sectional view of the ferrule  406  etc on the plane embracing a line segment a 5 -a′ 5  and a line segment b 5 -b′ 5  in  FIG. 17A .  FIG. 17C  depicts a section of the ferrule  406  etc on the plane embracing a line segment c 5 -c′ 5  in  FIG. 17B  and being orthogonal to the section in  FIG. 17B . The same view configuration is applied to other similar views ( FIGS. 18A ,  18 B and  18 C, etc). 
         [0119]    As in  FIGS. 17A ,  17 B and  17 C, the ferrule material such as the zirconia ceramics is formed in the cylindrical shape. One of the flat circular surfaces of the cylinder is defined as the lower surface, while the other is defined as the upper surface. The right side in  FIG. 17B  is defined as the lower surface side, while the left side is defined as the upper surface side. The upper surface side of the ferrule  406  is installed on the side of the LD-CHIP  402  in the optical communication module  400 . Furthermore, the curved surface of the cylinder is defined as the side surface. The straight line, which embraces the line segment extending from the center of the lower surface up to the center of the upper surface, is defined as the central axis. 
         [0120]    As in  FIGS. 17A ,  17 B and  17 C, the hole (the through-hole, the horizontal hole), through which the optical fiber is allowed to pass, is bored into the central axis of the cylinder. The hole takes the cylindrical shape, and the center of the hole is coincident with the central axis. If the optical fiber to be used is 125 μm in diameter, the diameter of the hole is set equal to or slightly larger than 125 μm. For example, the diameter of the hole is 125.5 μm. If the section of the optical fiber is not circular, the horizontal hole taking the shape matching with the section of the optical fiber may also be bored. 
         [0121]    Moreover, as in  FIGS. 17A ,  17 B and  17 C, the vertical hole is bored till passing through the hole for letting through the optical fiber from the side surface of the ferrule  406  and reaching the opposite side. Namely, the hole is bored to pass through the central axis from the side surface of the optical fiber  408  down to the side surface on the opposite side. Some proportion of the light beams entering the optical fiber  408  are taken out of the thus-bored vertical hole. The angle made by the bored vertical hole and the central axis is, e.g., 90 degrees. The vertical hole may take the cylindrical shape in principle and may also take other shapes. 
         [0122]    Furthermore, as in  FIGS. 17A ,  17 B and  17 C, a hole for fixing the M-PD  410  is bored so as to expand the vertical hole. The hole is bored in a manner that matches with the shape of the M-PD  410 . 
         [0123]    Next, as in  FIGS. 18A ,  18 B and  18 C, the optical fiber  408  is inserted into the through-hole (the horizontal hole) filled with the bonding agent. The optical fiber  408  is fixed to the ferrule  406  upon hardening the bonding agent. The optical fiber  408  is inserted from the lower surface of the ferrule  406  up to the upper surface. The end faces (the upper and lower surfaces) of the ferrule  406  and the optical fiber  408  are polished. 
         [0124]    Moreover, the vertical hole excluding the portion to which the M-PD  410  is fixed is filled with the transparent resin. At this time, it is preferable that the resin having the same refractive index as the refractive index of the cladding portion of the optical fiber is used as the transparent resin. Further, on the occasion of hardening the optical fiber, the transparent bonding agent is used to fill the vertical hole, whereby the optical fiber may be thus hardened simultaneously with fixing this optical fiber. The transparent resin may not fill the vertical hole. 
         [0125]    Next, as in  FIGS. 19A ,  19 B and  19 C, the slit, into which to insert the first filter  412 , is cut open from the side surface of the ferrule  406 . An angle made by the slit and the central axis is, e.g., 45 degrees. The slit is formed corresponding to the size of the first filter  412 . The slit is cut open toward the connecting portion (intersection) between the central axis and the vertical hole. The slit receiving the insertion of the first filter  412  is worked by, e.g., the dicing technique. At this time, the optical fiber is cut off. 
         [0126]    Next, as in  FIGS. 20A ,  20 B and  20 C, the first filter  412  is inserted into the slit. The first filter  412  is hardened by, e.g., the bonding agent. As the sizes of the first filter  412  and the slit become smaller, the friction resistance between the first filter  412  and the ferrule  406  gets smaller, thereby facilitating the insertion of the first filter  412 . 
         [0127]    Next, as in  FIGS. 21A ,  21 B and  21 C, the M-PD  410  is fixed by the bonding agent into the hole bored in a way that matches with the shape of the M-PD  410 . A relative position between the M-PD  410  and the first filter  412  is thereby fixed. The M-PD  410  is installed near the first filter  412 , whereby the light beams reflected by the first filter  412  can be received without any leakage even when a size of the light receiving portion of the M-PD  410  is small. 
         [0128]    (Operation, Effect of Fourth Embodiment) 
         [0129]    In the optical communication module  400 , the first filter  412  and the M-PD  410  are fixed to the ferrule  406 . The first filter  412  and the M-PD  410  are fixed to the ferrule  406 , and these components move together, and consequently the relative position between the first filter  412  and the M-PD  410  does not change. Hence, even when the ferrule  406  vibrates due to the external stress etc, the light beams reflected by the first filter  412  are not affected by the vibrations but are received by the M-PD  410 . Furthermore, the first filter  412  and the M-PD  410  are fixed to the ferrule  406 , thereby increasing a light convergence rate at the M-PD  410 . 
         [0130]    The intensity of the light beams received by the M-PD  410  depends on how much the light beams emitted from the LD-CHIP  402  are affected till being reflected by the first filter  412 . Hence, the optical communication module  400  can control the intensity of the light beams emitted from the LD-CHIP  402  on the basis of how much the light beams emitted toward the front side from the LD-CHIP  402  are affected till being reflected by the first filter  412 . 
         [0131]    The optical communication module  400  enables the stable output to be acquired even when causing the change in temperature and the external stress on the front side of the LD-CHIP  402 . 
         [0132]    The configuration of fixing the LD-CHIP to the ferrule as in the optical communication module  400  may be applied to the optical communication module including none of the configuration for receiving the optical signals from the outside as in the first and second embodiments. 
       Fifth Embodiment 
       [0133]    Next, a fifth embodiment will be described. The fifth embodiment has common points to the first through fourth embodiments. Accordingly, the discussion will be focused on different points, while the descriptions of the common points are omitted. 
         [0134]    In the fifth embodiment, the transparent material is used for the ferrule. 
         [0135]    (Example of Configuration) 
         [0136]      FIG. 22  are a view illustrating an example of a sectional structure parallel to the optical axis of the optical communication module. An optical communication module  500  transmits and receives the optical signal. The optical communication module  500  in  FIG. 22  includes an LD-CHIP  502 , a first lens  504 , a ferrule  506 , an optical fiber  508 , an M-PD  510 , a first filter  512  and an APC circuit  530 . The optical communication module 500  includes a second filter  522 , a second lens  524  and a PD  526 . The optical fiber  508  is held within a housing  516  of the optical communication module  500  through the ferrule  506  and a sleeve  514 . 
         [0137]    The ferrule  506  is the transparent ferrule which uses the transparent material. The transparent material such as a transparent resin and glass is employed as the material of the ferrule  506 . The hole (vertical hole) for taking out the light beams reflected by the first filter is bored in the ferrule  306  of the third embodiment, however, the vertical hole may not be bored in the ferrule  506  of the fifth embodiment. This is because the optical communication module  500  can receive the light beams reflected by the first filter  512  with the M-PD  510  and PD  526  owing to the use of the transparent material without forming the vertical hole. Hence, the manufacture of the ferrule  506  is facilitated. The light shielding structure as in  FIGS. 12 ,  13  and  14  of the second embodiment is applicable to the ferrule  506 . 
         [0138]    (Operation, Effect of Fifth Embodiment) 
         [0139]    The transparent material is employed for the ferrule  506  of the optical communication module  500 . The transparent material is used for the ferrule  506 , whereby the light beams on the front side can be received by the M-PD  510  without boring the vertical hole in the ferrule  506 . Further, similarly, the transparent material is used for the ferrule  506 , whereby the light beams from the outside can be received by the PD  526  without boring the vertical hole in the ferrule  506 . 
       Sixth Embodiment 
       [0140]    Next, a sixth embodiment will be discussed. The sixth embodiment has common points to the first through fifth embodiments. Accordingly, the discussion will be focused on different points, while the descriptions of the common points are omitted. 
         [0141]    In the sixth embodiment, the ferrule involves using the transparent material, and the ferrule and the M-PD take an integral-type structure. 
         [0142]    (Example of Configuration) 
         [0143]      FIG. 23  is a view illustrating an example of the sectional structure parallel to the optical axis of the optical communication module. An optical communication module  600  transmits and receives the optical signal. The optical communication module  600  in  FIG. 23  includes an LD-CHIP  602 , a first lens  604 , a ferrule  606 , an optical fiber  608 , an M-PD  610 , a first filter  612  and an APC circuit  630 . The optical communication module  600  includes a second filter  622 , a second lens  624  and a PD  626 . The optical fiber  608  is held within a housing  616  of the optical communication module  600  through the ferrule  606  and a sleeve  614 . 
         [0144]    The ferrule  606  is the transparent ferrule using the transparent material. Similarly to the ferrule  506  in the fifth embodiment, the vertical hole may not be bored in the ferrule  606 . Further, in the (configuration of) ferrule  606 , similarly to the ferrule  406  in the fourth embodiment, the M-PD  610  is fixed to the ferrule  606 . With this configuration, the optical communication module  600  exhibits at least the same operations and effects as those of the optical communication modules in the fourth and fifth embodiments. 
       Seventh Embodiment 
       [0145]    Next, a seventh embodiment will be discussed. The seventh embodiment has common points to the first through sixth embodiments. Accordingly, the discussion will be focused on different points, while the descriptions of the common points are omitted. 
         [0146]    The seventh embodiment adopts not the receptacle type of optical communication module as in the first through sixth embodiments but a pigtail type of optical communication module. 
         [0147]    (Example of Configuration) 
         [0148]      FIG. 24  is a view illustrating an example of the sectional structure parallel to the optical axis of the optical communication module. An optical communication module  700  transmits and receives the optical signal. The optical communication module  700  in  FIG. 24  includes an LD-CHIP  702 , a first lens  704 , a ferrule  706 , an optical fiber  708 , an M-PD  710 , a first filter  712  and an APC circuit  730 . The optical communication module  700  includes a second filter  722 , a second lens  724  and a PD  726 . The optical fiber  708  is held within a housing  716  of the optical communication module  700  through the ferrule  706  and a sleeve  714 . 
         [0149]    The optical communication modules in the first through sixth embodiments are the receptacle type of optical communication modules. In the receptacle type of optical communication module, the ferrule on the side of an external wire is press-fitted into the optical communication module and is thus optically connected to the ferrule of the optical communication module. In the receptacle type of optical communication module, the connecting portion between the ferrule of the optical communication module and the ferrule on the side of the external wire is called a receptacle portion. 
         [0150]    The optical communication module  700  is an optical communication module in which the receptacle portion of the optical communication module  300  in the third embodiment is replaced by the pigtail type. The receptacle portion of each of the optical communication modules in other embodiments may be replaced by the pigtail type. In the pigtail type, the optical fiber on the side of the external wire gets integral with the optical fiber within the ferrule of the optical communication module without being cut off. The optical communication module is configured as the pigtail type, thereby preventing a loss at the connection portion with another ferrule. 
         [0151]    The optical communication module, of which the receptacle portion is replaced by the pigtail type, also acquires the same operations and effects as those of the optical communication modules in other embodiments. 
       Eighth Embodiment 
       [0152]    Next, an eighth embodiment will be discussed. The eighth embodiment has common points to the first through seventh embodiments. Accordingly, the discussion will be focused on different points, while the descriptions of the common points are omitted. 
         [0153]    In the eighth embodiment, a light path of the light beams inputted from the outside via the second filter is changed. 
         [0154]    (Example of Configuration) 
         [0155]      FIG. 25  is a view illustrating an example of the sectional structure parallel to the optical axis of the optical communication module. An optical communication module  800  transmits and receives the optical signal. The optical communication module  800  in  FIG. 25  includes an LD-CHIP  802 , a first lens  804 , a ferrule  806 , an optical fiber  808 , an M-PD  810 , a first filter  812  and an APC circuit  830 . The optical communication module  800  includes a second filter  822 , a second lens  824  and a PD  826 . The optical fiber  808  is held within a housing  816  of the optical communication module  800  through the ferrule  806  and a sleeve  814 . 
         [0156]    Similarly to the ferrule  406  in the fourth embodiment, the M-PD  810  is built in the ferrule  806 . 
         [0157]    The second filter  822  cuts off the light beams emitted from the LD-CHIP  802  but transmits the light beams inputted via the optical fiber  808  from the outside. Namely, the second filter  822  cuts off the wavelength of the light beams emitted from the LD-CHIP  802  buts transmits the wavelength of the light beams inputted via the optical fiber  808  from the outside. The wavelength demultiplexing multi-layered flat glass as in  FIG. 4  can be used as the second filter  822 . 
         [0158]    The second filter  822  receives the incidence, at a predetermined angle, of the light beams reflected by the first filter  812 , thereby changing the light path of the incident light. Further, the second filter  822  gets the incident light to outgo at a predetermined angle, thereby making a PD  826  receive the light beams. The second filter  822  can change the light path of the light beams by deflecting the light beams. The light path of the light beams can be adjusted based on an angle between the incident light and the incident surface of the second filter  822 , an angle between the outgoing light and the outgoing surface of the second filter  822 , a refractive index of the second filter  822  and a size of the second filter  822 . 
         [0159]    The second filter  822  can, as in  FIG. 25 , change the light path of the light beams by adopting a shape such as of a prism. 
         [0160]    (Operation, Effect of Eighth Embodiment) 
         [0161]    According to the optical communication module  800 , a distance between the first lens  804  and the optical fiber  808  can be set similarly to the conventional optical communication module as in, e.g.,  FIG. 2 . The distance between the first lens  804  and the optical fiber  808  can be set similarly to the conventional optical communication module, whereby the same components as those of the conventional optical communication module can be used for, e.g., the optical communication module  800 . For example, the distance from the first lens  804  to the opto-coupling point remains unchanged, and therefore the same lens as that of the optical communication module can be used. 
       Ninth Embodiment 
       [0162]    Next, a ninth embodiment will be discussed. The ninth embodiment has common points to the first through eighth embodiments. Accordingly, the discussion will be focused on different points, while the descriptions of the common points are omitted. 
         [0163]    The discussion on the ninth embodiment will deal with an optical communication device incorporating the optical communication module in any one of the first through eighth embodiments. The optical communication device performs the process of converting the optical signal into the electric signal and vice versa. 
         [0164]    (Example of Configuration) 
         [0165]      FIG. 26  is a view depicting an example of a configuration of the optical communication device. The optical communication device converts the signal format used for the optical communications into the signal format used within the LAN, and vice versa. An optical communication device  1000  includes an optical communication module  1002 , a SERDES (Serialize Deserialize)  1004 , an LSI  1006 , a RAM  1008 , a ROM  1010 , a PHY  1012  and an RJ  45  ( 1016 ). The LSI  1006 , the RAM  1008  and the ROM  1010  can operate each as a signal converting unit. 
         [0166]    Herein, the signal flowing to the side of the optical communication module  1002  from the side of the RJ  45  ( 1016 ) is called the signal on the transmission side. Reversely, the signal flowing to the side of the RJ  45  ( 1016 ) from the side of the optical communication module  1002  is called the signal on the reception side. 
         [0167]    The optical communication module  1002  is the optical communication module in any one of the first through eighth embodiments described above. The optical communication module  1002  converts the signal (serial signal) on the transmission side, which is received from the SERDES  1004 , into the optical signal and outputs this optical signal to the outside device via the optical fiber. Further, the optical communication module  1002  converts the optical signal received from the outside device via the optical fiber into the electric signal, and outputs this electric signal to the SERDES  1004 . 
         [0168]    The SERDES  1004  is an interface between the optical communication module and the LSI. The SERDES  1004  serializes or deserializes the signal on the transmission side or the signal on the reception side. Namely, the SERDES  1004  converts the serial signal into the parallel signal, and vice versa. The SERDES  1004  can operate as a parallel-serial converting unit. 
         [0169]    The LSI (Large Scale Integration)  1006  converts the signal format used for the optical communication line into the signal format used for the telecommunication line (e.g., the LAN (Local Area Network)), and vice versa. Moreover, the LSI  1006  detects an abnormal state of the signal such as an interruption of the signal, and issues an alarm. The LSI  1006  converts the signal format on the basis of a program stored on the ROM  1010 . The ROM  1010  gets stored with the program etc employed in the LSI  1006 . The RAM  1008  temporarily gets stored with data etc used on the occasion of executing the program. The RAM  1008  temporarily gets stored with the signal on the transmission side or the signal on the reception side. 
         [0170]    The PHY  1012  is an interface related to a physical layer. The PHY  1012  takes charge of the interface between the LSI  1006  and the RJ  45  ( 1016 ). The PHY  1012  deserializes or serializes the signal on the transmission side or the signal on the reception side. That is, the PHY  1012  converts the serial signal into the parallel signal, and vice versa. 
         [0171]    The RJ  45  ( 1016 ) is a connector for connecting a LAN cable. A terminal device (information processing device) such as a personal computer is connected via the LAN cable to the RJ  45  ( 1016 ). 
         [0172]    The optical communication device can perform the optical communications exhibiting the stable optical output by including the optical communication module in any one of the first through eighth embodiments. 
         [0173]    [Others] 
         [0174]    The configurations of the respective embodiments, even other than those described above, can be properly combined and thus applied. For instance, the ferrule  606  in the sixth embodiment may also be applied as a substitute for the ferrule  806  to the eighth embodiment. 
         [0175]    All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.