Abstract:
An optical module comprises: an optical element array comprising plural optical elements that emits or receives light; and an optical waveguide comprising a clad and plural cores respectively with optical path changing portions, the cores being disposed in the clad with an interval. The optical path changing portions are optically connected to the optical elements. The optical path changing portions are arranged in a first direction having an angle with respect to a formation direction of the cores, the first direction being corresponding to an arrangement direction of said plurality of optical elements.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2007-260147 filed Oct. 3, 2007. 
       BACKGROUND 
       [0002]    (i) Technical Field 
         [0003]    The present invention relates to an optical module. 
         [0004]    (ii) Related Art 
         [0005]    Generally, an electronic device includes plural elements in many cases. For example, a copier includes an image inputting unit and an image outputting unit. In the copier, image data input from the image inputting unit is sent to the image outputting unit through an electrical cable to be printed on a printing medium such as a paper sheet. 
         [0006]    In recent years, with development of high capability of an electronic device, a volume of transmission capacity between devices has been increased. In order to deal with the high capacity using a known parallel transmission method, a method of increasing the number of channels or a method of speeding up synchronous clock can be taken into consideration. However, an error caused due to skew between channels caused by a difference of a wiring length or a decrease in timing margin may easily occur. Accordingly, in order to solve this problem, a serial transmission method of transmitting data signals through one transmission path has become attracted. 
         [0007]    However, since a transmission rate increases in the serial transmission method, it is difficult to embody signal transmission while maintaining good signal quality in an electrical cable by nature. As a technique for solving such a problem, a method of using an optical signal which can perform broadband signal transmission has been under examination. 
       SUMMARY 
       [0008]    According to an aspect of the invention, there is provided an optical module comprising: an optical element array comprising plural optical elements that emits or receives light; and an optical waveguide comprising a clad and plural cores respectively with optical path changing portions, the cores being disposed in the clad with an interval, wherein the plural optical path changing portions are optically connected to the plural optical elements, and the plural optical path changing portions are arranged in a first direction having an angle with respect to a formation direction of the cores, the first direction being corresponding to an arrangement direction of the plural optical elements. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    Exemplary embodiments of the present invention will be described in detail based on the following figure, wherein: 
           [0010]      FIGS. 1A and 1B  are diagrams illustrating an optical module according to a first exemplary embodiment of the invention, in which  FIG. 1A  is a side view illustrating the optical module and  FIG. 1B  is a partly expanded view illustrating an optical waveguide; 
           [0011]      FIG. 2  is a top view illustrating the optical module shown in  FIG. 1A ; 
           [0012]      FIG. 3  is a top view illustrating the optical waveguide shown in  FIG. 1A ; 
           [0013]      FIG. 4  is a front view illustrating an optical module according to a second exemplary embodiment of the invention; 
           [0014]      FIG. 5  is a top view illustrating the optical module shown in  FIG. 4 ; 
           [0015]      FIG. 6  is a top view illustrating an optical waveguide shown in  FIG. 4 ; 
           [0016]      FIG. 7  is a top view illustrating a configuration of an optical module according to a third exemplary embodiment of the invention; 
           [0017]      FIG. 8  is a top view illustrating an optical waveguide of the optical module according to the third exemplary embodiment; 
           [0018]      FIG. 9  is a top view illustrating a configuration of an optical module according to a fourth exemplary embodiment of the invention; 
           [0019]      FIG. 10  is a top view illustrating an optical waveguide of the optical module according to the fourth exemplary embodiment; and 
           [0020]      FIG. 11  is a sectional view illustrating an optical module according to a fifth exemplary embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
     First Exemplary Embodiment 
     (Configuration of Optical Module) 
       [0021]      FIGS. 1A and 1B  are diagrams illustrating an optical module according to a first exemplary embodiment of the invention.  FIG. 1A  is a side view illustrating the optical module and  FIG. 1B  is a partly expanded view illustrating an optical waveguide.  FIG. 2  is a top view illustrating the optical module shown in  FIG. 1A .  FIG. 3  is a top view illustrating the optical waveguide shown in  FIG. 1A . 
         [0022]    The optical module  100  has a configuration for converting electric signals of four channels into optical signals to simultaneously transmit the converted optical signals and for simultaneously receiving the optical signals of the four channels to convert the optical signals into the electric signals. In addition, the number of channels is four in this exemplary embodiment, but any number of channels can be set. The same is also applied to the following exemplary embodiments. 
         [0023]    As shown in  FIGS. 1A ,  1 B, and  2 , the optical module  100  includes a board  1  which is a mounting board for mounting optical elements; a light-emitting element array  2  which is mounted on the board  1 ; a light-receiving element  3  which is mounted on the board  1  and gets away from the light-emitting element array  2  by a gap g between the light-emitting elements and receiving elements; a driving IC  4  which is electrically connected to the light-emitting element array  2  to be mounted on the board  1 ; an amplifying IC  5  which is electrically connected to the light-receiving element array  3  and mounted on the board  1 ; a spacer  6  which is mounted on the board  1 ; and an optical waveguide  7  which is fixed onto the spacer  6  and includes mirrors  74 A to  74 D and  75 A to  75 D as a light path changing portion formed on a 45° inclined surface on each one end thereof. 
         [0024]    The board  1 , which is made of an epoxy resin, for example, includes electrode pads  11 A to  11 D connected to the light-emitting element array  2 , the light-receiving element array  3 , the driving IC  4 , and the amplifying IC  5 . 
       (Configuration of Light-Emitting Element Array  2 ) 
       [0025]    The light-emitting element array  2  is composed of four VCSELs (Vertical Cavity Surface Emitting Laser)  20 A to  20 D for generating modulation light of four channels, for example. In this exemplary embodiment, as shown in  FIG. 2 , in order to facilitate connection with the driving IC  4 , the light-emitting element array  2  is arranged so that an element mount direction thereof is reverse to the element mount direction of the light-receiving element array  3 . At this time, the element mount direction refers to a direction of taking out a bonding wire from the light element array. In this exemplary embodiment, the element mount directions of the light-emitting element array  2  and the light-receiving element array  3  are reverse to each other by 180°. 
         [0026]    The VCSELs  20 A to  20 D each include an light-emitting portion having a laminated configuration in which an n-type lower reflector layer, an active layer, a current narrowing layer, a p-type upper reflector layer, a p-type contact layer, and a p-side electrode are laminated on an n-type GsAs board having an n-side electrode on the rear thereof. In addition, each of the p-side electrodes is connected to each of electrode pads  11 B of the board  1  by the bonding wire (signal line)  2   a.    
       (Configuration of Light-Receiving Element Array  3 ) 
       [0027]    The light-receiving element array  3  is composed of, for example, four photodiodes (PD)  30 A to  30 D as a light-receiving element for performing an optical-electric conversion of four channels. In particular, it is preferable to use GaAs series in the PDs  30 A to  30 D since a high-speed response can be obtained. 
         [0028]    As shown in  FIG. 2 , the light-receiving element array  3  is mounted so that a gap g between the VCSELs  20 A to  20 D and the PDs  30 A to  30 D is larger than a pitch p, that is, a relation of g&gt;p is satisfied, assuming that the pitch p is a pitch between the elements in a direction in which the VCSELs  20 A to  20 D and the PDs  30 A to  30 D are adjacent to each other. 
         [0029]    For example, on the GaAs board, the PD  30 A to  30 D include a p layer, an I layer, and an N layer, which form PIN junction, a p-side electrode formed on the p layer, and an n-side electrode formed on the N layer. The p-side electrode has an opening, and the inside of the opening is a light-receiving portion for receiving a laser beam. Each p-side electrode and each n-side electrode of the light-receiving element array  3  are connected on each electrode pad  11 C of the board  1  by a bonding wire (signal line)  3   a.    
       (Configurations of Driving IC  4 , Amplifying IC  5 , and Spacer  6 ) 
       [0030]    The driving IC  4  is a driving circuit for performing current-driving of the light-emitting element array  2  on the basis of transmitting data. In this exemplary embodiment, a flat package (FP) type surface-mounting package is used in the driving IC  4 . 
         [0031]    The amplifying IC  5  is a amplifying circuit which includes transimpedance amplifiers (TIA) (not shown) of four channels for converting current variation of the light-receiving element array  3  into voltage variation and limiting amplifiers (LA) (not shown) of four channels for amplifying and outputting the output voltage of the TIA so as to become predetermined output voltage. In this exemplary embodiment, a flat package (FP) type surface-mounting package is used in the amplifying IC  5 . 
         [0032]    The spacer  6  positions and fixes the optical waveguide  7  so as to maintain an optical connection distance between the light-emitting element array  2  and the light waveguide  7  and between the light-receiving element array  3  and the light waveguide  7 . The spacer  6  is formed of an insulating material board such as an epoxy resin board or a Si board. The spacer  6  is adhered to the optical waveguide  7  by an adhesive, but may be positioned by means of a different supporting adhering way such as fitting. 
       (Configuration of Optical Waveguide  7 ) 
       [0033]    As shown in  FIG. 3 , the optical waveguide  7  includes cores  71 A to  71 D of four channels for transmitting a transmitting optical signal, cores  72 A to  72 D of four channels for transmitting a receiving optical signal, and a clad  73  for surrounding the cores  71 A to  71 D and the cores  72 A to  72 D. 
         [0034]    The cores  71 A to  71 D and the cores  72 A to  72 D are made of an acrylic resin or an epoxy resin, for example. The clad  73  can be made of a film material which has a refractive index smaller than that of the cores  71 A to  71 D and the cores  72 A to  72 D, an optical property such as optical transparency, mechanical strength, heat resistance, flexibility, etc. Examples of the film material include an acrylic resin, a styrene resin, an olefinic resin, and a vinyl chloride series resin. 
         [0035]    As shown in  FIG. 1B , each one end (front ends) of the cores  71 A to  71 D and the cores  72 A to  72 D is formed so as to have a 45° inclined surface. In addition, each of mirrors  74 A to  74 D and mirrors  75 A to  75 D is formed on the inclined surface  7   a.  The mirrors  74 A to  74 D and the mirrors  75 A to  75 D are each formed in a manner in which the 45° inclined surface  7   a  is formed by removing each one end of the cores  71 A to  71 D and the cores  72 A to  72 D, and an Au film or the like is deposited on the surface of each one end by electron beams. In addition, the mirrors may be formed by a precision mold. As shown in  FIG. 3 , a gap G of the mirrors  74 A to  74 D and the mirrors  75 A to  75 D is configured so as to be equal to the gap g between the VCSELs  20 A to  20 D and the PD  30 A to  30 D. 
       (Operation of Optical Module  100 ) 
       [0036]    Next, an operation of the optical modules  100  will be described. When a transmitting signal is input to the driving IC  4 , a modulation signal is applied to the light-emitting element array  2  in accordance with the transmitting signal, and driving current flows to the VCSELs  20 A to  20 D. The VCSELs  20 A to  20 D emit light in accordance with the drive current, and the output light is incident to the mirrors  74 A to  74 D provided in the cores  71 A to  71 D of the optical waveguide  7 . 
         [0037]    The optical signal incident to the mirrors  74 A to  74 D is incident to the cores  71 A to  71 D after the optical signal is reflected on the mirrors  74 A to  74 D and the optical path thereof is changed. The optical signal incident to the cores  71 A to  71 D propagates through the cores  71 A to  71 D in the right direction of  FIG. 3  and reaches the end of the cores  71 A to  71 D to be transmitted to a different optical module which is not shown. 
         [0038]    On the other hand, when an optical signal is incident to the cores  72 A to  72 D of the optical waveguide  7 , the optical signal propagates through the cores  72 A to  72 D from the right direction to the left direction of  FIG. 3  to be incident to the mirrors  75 A to  75 D. The optical signal incident to the mirrors  75 A to  75 D is incident to the PD  30 A to  30 D after the optical signal is reflected on the mirrors  75 A to  75 D and the optical path thereof is changed. 
         [0039]    The PD  30 A to  30 D converts the incident optical signal into current. An electric output generated from the PD  30 A to  30 D is sent to an image processing IC, which is not shown, after the amplifying IC  5  converts the current into voltage to obtain an electric signal and performs predetermined amplifying. 
         [0040]    In the first exemplary embodiment, the arrangement of the light-emitting element array  2  and the light-receiving element array  3  is just an example, and the arrangement of light-emitting element array  2  and the light-receiving element array  3  may be changed with each other to be mounted in the board  1 . 
       Second Exemplary Embodiment 
       [0041]      FIG. 4  is a front view illustrating an optical module according to a second exemplary embodiment of the invention.  FIG. 5  is a top view illustrating the optical module shown in  FIG. 4 .  FIG. 6  is a top view illustrating an optical waveguide shown in  FIG. 4 . In addition, in  FIGS. 4 to 6 , a configuration of a light-receiving side is now shown. 
         [0042]    In this exemplary embodiment, the VCSELs  20 A to  20 D of the light-emitting element array  2  according to the first exemplary embodiment are disposed at a predetermined angle θ (for example, 45°) with respect to a direction in which the cores  71 A to  71 D of the optical waveguide  7  are formed. In addition, the rest configuration is the same as that according to the first exemplary embodiment. 
         [0043]    As shown in  FIG. 5 , the VCSELs  20 A to  20 D are disposed at the angle θ with respect to the end surface of the optical waveguide  7  and at an angle α with respect to the direction in which the cores  71 A to  71 D and the cores  72 A to  72 D are formed. A pitch p of the cores  71 A to  71 D of the optical waveguide  7  satisfies a relation of p=P cos θ for a pitch P between the VCSELs  20 A to  20 D. That is, the pitch p between the cores  71 A to  71 D is narrower than the pitch P of the VCSELs  20 A to  20 D. 
         [0044]    In the second exemplary embodiment, the light-emitting element array  2  may be configured in place of the light-receiving element array  3 . Moreover, a light-receiving element array  3  and the corresponding cores may be added to the configuration shown in  FIG. 5 . Moreover, a plurality of the light-emitting element arrays  2  may be configured. 
       Third Exemplary Embodiment 
       [0045]      FIG. 7  is a top view illustrating a configuration of an optical module according to a third exemplary embodiment of the invention.  FIG. 8  is a top view illustrating an optical waveguide of the optical module according to the third exemplary embodiment. 
         [0046]    In this exemplary embodiment, the light-emitting element array  2  and the light-receiving element array  3  according to the first exemplary embodiment are disposed at an angle θ with respect to the end surface of the cores  71 A to  71 D and the cores  72 A to  72 D of the optical waveguide  7  and are disposed at an angle α with respect to a direction in which the cores  71 A to  71 D and the cores  72 A to  72 D are formed, in the same manner as that according to the second exemplary embodiment. In  FIG. 7 , the spacer described in the first exemplary embodiment is not shown. Likewise, the optical waveguide  7  is configured in a manner in which mirrors  74 A to  74 D and mirrors  75 A to  75 D are provided so that each end surface of the cores  71 A to  71 D and each end surface of the cores  72 A to  72 D are disposed at the angle θ with respect to the end surface  7   b  of the optical waveguide  7  and the two optical waveguide  7  according to the second exemplary embodiment are arranged in parallel with each other which is shown in  FIG. 6 . 
         [0047]    As shown in  FIG. 7 , the driving IC  4  and the amplifying IC  5  are arranged more outside than the light-emitting element array  2  and the light-receiving element array  3 , so that the light-emitting element array  2  and the light-receiving element array  3  are approximated to each other and the mirrors  74 A to  74 D and the mirrors  75 A to  75 D shown in  FIG. 8  get together in the end of the optical waveguide  7 . A gap g between the VCSELs  20 A to  20 D and the PDs  30 A to  30 D is larger than the pitch P, that is, a relation of g&gt;P is satisfied. 
       Fourth Exemplary Embodiment 
       [0048]      FIG. 9  is a top view illustrating a configuration of an optical module according to a fourth exemplary embodiment of the invention.  FIG. 10  is a top view illustrating an optical waveguide of the optical module according to the fourth exemplary embodiment. 
         [0049]    In this exemplary embodiment, the light-receiving element array  3  according to the third exemplary embodiment rotates by 90° to be mounted so that PDs  30 A to  30 D of the light-receiving element array  3  is disposed at right angles with respect to a direction in which VCSELs  20 A to  20 D of the light-emitting element array  2  are arranged. Mirrors  74 A to  74 D and mirrors  75 A to  75 D of the optical waveguide  7  are arranged in accordance with the arrangement of the light-emitting element array  2  and the light-receiving element array  3 . The rest configuration is the same as that according to the third exemplary embodiment. 
         [0050]    In this case, the light-receiving element array  3  is disposed so that the cores  71 A to  71 D and the cores  72 A to  72 D of the optical waveguide  7  have the same pitch and the PDs  30 A to  30 D have the same pitch p as that of the VCSELs  20 A to  20 D. 
         [0051]    In the fourth exemplary embodiment, the mirrors  74 A to  74 D and the mirrors  75 A to  75 D of the optical waveguide  7  may be arranged in a V shape. In this case, the light-emitting element array  2  and the light-receiving element array  3  are arranged so that the VCSELs  20 A to  20 D and the PDs  30 A to  30 D shown in  FIG. 9  are formed in a V shape. 
       Fifth Exemplary Embodiment 
       [0052]      FIG. 11  is a sectional view illustrating an optical module according to a fifth exemplary embodiment of the invention. 
         [0053]    In this exemplary embodiment, the optical waveguide  7  according to the first exemplary embodiment is disposed on the board  1  and the spacer  6  is removed. In addition, the light-emitting element array  2  is mounted as an optical wiring of the board in a face-down manner. The rest configuration is the same as that according to the first exemplary embodiment. Moreover, the fifth exemplary embodiment may be also applied to the second to fourth exemplary embodiments. 
         [0054]    An optical module  100  includes the board  1  on which the optical waveguide  7  is mounted and a light-emitting unit  200  mounted on the board  1 . 
         [0055]    The board  1  includes an insulating layer  1   a;  a clad portion  70  which is formed on the insulating layer  1   a  and on which the optical waveguide  7  is formed; a core portion  71  of which a refractive index is larger than that of the clad portion  70 ; and a wiring layer  1   b  which is formed on the upper surface of the waveguide  7  and on which electrode pads  12 A and  12 B are provided. 
         [0056]    Like the description according to the first exemplary embodiment, in the optical waveguide  7  according to the this exemplary embodiment, cores  71 A to  71 D are formed on the clad portion  70  and mirrors  74 A to  74 D are each formed on an inclined surface  7   a  formed on each one end of the cores  71 A and  71 D. A translucent resin material having the same refractive index as that of the clad portion  70  fills up portions of each inclined surface  7   a  and the mirrors  74 A to  74 D. 
         [0057]    The light-emitting unit  200  includes a wiring board  201  with electrode pads  202 A and  202 B on the rear surface thereof; solder balls  203  mounted on the electrode pads  202 A and  202 B, a light-emitting element array  2  mounted on the rear surface of the wiring board  201 ; and a driving IC  4  mounted on the surface of the wiring board  201 . 
       Other Exemplary Embodiments 
       [0058]    The invention is not limited to the above-described exemplary embodiments, but may be modified in various forms within the scope of the invention without departing the gist of the invention. For example, in the first, third, and fourth exemplary embodiments, only one of the light-emitting side and the light-receiving side may be configured. 
         [0059]    In the above-described exemplary embodiments, the board  1  may include cores  75 A to  75 D of four channels for receiving light in addition to the cores  74 A to  74 D of four channels for transmitting light. Moreover, the electric wiring layer for transmitting the electric signal may be configured as a multi-layer. 
         [0060]    The foregoing description of the exemplary embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The exemplary embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.