Patent Publication Number: US-2011069968-A1

Title: Optical communication module and method for manufacturing the same

Description:
This application is based upon and claims the benefit of priority from Japanese patent application No. 2009-217802, filed on Sep. 18, 2009, the disclosure of which is incorporated herein in its entirety by reference. 
     TECHNICAL FIELD 
     The present invention relates to an optical communication module used in a large-capacity optical transmission system or the like and capable of oscillating light beams of plural wavelengths, and a method for manufacturing the optical communication module. 
     BACKGROUND ART 
     With the proliferation of broadband access, the diversification of access means, and the diversification of services, etc., traffic in a communication line is growing. In order to cope with an increase in the traffic, a wavelength division multiplexing (WDM) optical transmission technology for multiplexing a light signal in a wavelength region and transmitting it has been brought into practical use. 
     An element length of a semiconductor laser is a few 100 μm or less. Power consumption thereof is also as small as a few 10 mW or less. Thus, if a semiconductor laser is used as a light source, and a direct modulation system for modulating drive current of the semiconductor laser or a system for modulating light by an external modulator such as an LN (Lithium niobate) modulator, or an EA (Electro-absorption) modulator or the like is used, it is then possible to realize a size reduction in an optical transmission device or an optical communication device and a reduction in its power consumption. 
     Normally, in a wavelength division multiplexing optical transmission system, light sources corresponding to the number of wavelengths are prepared and the wavelengths of the respective light sources are set to a wavelength arrangement determined in advance. Then, light beams of respective wavelengths are combined together using a quartz waveguide or the like, followed by being output to an optical fiber (refer to, for example a patent document 1 (Japanese Patent Application Publication (JP-2000019362-A)). 
       FIG. 5  is a plan view showing a configuration of an optical coupling device including a semiconductor laser described in the patent document 1. The optical coupling device shown in  FIG. 5  has an array semiconductor laser  41 , a cylindrical lens  43 , and a light converger  50 . 
     The array semiconductor laser  41  includes a plurality of optical radiation parts  42   a  arranged in linear form. A plurality of LD light (laser light)  44  are radiated at predetermined divergence angles from optical radiation faces  42  of the optical radiation parts  42   a.    
     When an axis parallel to each of the optical radiation faces  42  is assumed to be a slow axis, an axis perpendicular to the optical radiation face  42  is assumed to be a traveling direction axis of each LD light, and an axis perpendicular to both of the LD-light traveling direction axis and the slow axis is assumed to be a first axis, each of the LD light  44  is greatly diverged in the direction of the first axis with the divergence angle in the slow-axis direction of the LD light  44  as a full-width-at-half-maximum of about 10 degrees and with the divergence angle thereof in the first-axis direction as a full-width-at-half-maximum of about 40 degrees. Thus, the light beams diverged in the first-axis direction are converted to parallel light by a cylindrical lens  43 . 
     The optical converger  50  has optical waveguides  46  of the same number as the number of the optical radiation parts.  42   a  in the array semiconductor laser  41 . The optical waveguides  46  are narrowed in their arrangement interval in the traveling direction of the LD light  44  and thereby combined into one by a coupling part  47 . The respective LD light  44  are launched from an outgoing port  48  as a high density LD light  49 . Incidentally, such a laser array as illustrated in a patent document 2 (Japanese Patent Application Publication (JP-07226563-A)) can be used as the array semiconductor laser  41 . 
     SUMMARY 
     An exemplary object of the present invention is to provide an optical communication module rendered high in optical coupling efficiency at low cost, and a method for manufacturing the optical communication module. 
     According to an exemplary aspect of invention, for attaining the above object, there is provided an optical communication module comprising an array semiconductor laser which emits light beams of plural wavelengths, an array lens which brings each of the light beams emitted from the array semiconductor laser to parallel light, and an array mirror which includes mirrors corresponding to the number of wavelengths and is provided at positions on which the light beams emitted from the array lens are incidentable, the respective mirrors selectively reflecting the light beams emitted from the array semiconductor laser. 
     According to an exemplary aspect of invention, for attaining the above object, there is provided a method for manufacturing an optical communication module, comprising the steps of forming an array semiconductor laser which emits light beams of plural wavelengths, on a substrate; forming an array lens which brings each of the light beams emitted from the array semiconductor laser to parallel light on the substrate; and forming an array mirror which includes mirrors corresponding to the number of wavelengths and in which the respective mirrors selectively reflect the light beams emitted from the array semiconductor laser, at positions on which the light beams emitted from the array lens on the substrate are incidentable. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view showing a configuration example of an exemplary embodiment of an optical communication module according to the invention; 
         FIG. 2  is a plan view illustrating the optical communication module held in a package; 
         FIG. 3  is a flowchart showing a method for manufacturing the optical communication module; 
         FIG. 4  is an explanatory view depicting a schematic configuration of an optical communication module according to the invention; and 
         FIG. 5  is a plan view showing a configuration of an optical coupling device including a semiconductor laser described in the patent document 1. 
     
    
    
     DESCRIPTION OF EMBODIMENT 
       FIG. 1  is a perspective view showing a configuration example of an exemplary embodiment of an optical communication module according to the invention. The optical communication module shown in  FIG. 1  includes an array semiconductor laser (which will be hereinafter referred to as array laser)  1 , an aspheric array lens (which will be hereinafter referred to as array lens)  2  on which light beams emitted from the array laser  1  are incident, an array mirror  3  on which the light beams emitted from the array lens  2  are incident, and a lens  4  which causes the light beams from the array mirror  3  to converge and emits the same to an optical fiber (not shown). 
     Incidentally, electrodes  11 ,  12 ,  13 , and  14  for supplying drive currents to the array laser  1 , a substrate  15  for holding the array laser  1  and the electrodes  11 ,  12 ,  13 , and  14 , and a carrier  16  for supporting the substrate  15  are also shown in  FIG. 1 . The electrodes  11 ,  12 ,  13 , and  14  are formed as, for example, microstrip lines. The substrate  15  is made of, for example, ceramic. The carrier  16  is made of, for example, CuW (copper tungsten). 
     The array laser  1  is of a semiconductor laser which emits a plurality of light beams different in wavelength. The array laser  1  emits the respective light beams modulated by an element (not shown) for carrying out direct modulation or an external modulator (not shown) such as an LN modulator or an EA modulator. The array lens  2  collimates the respective light beams emitted from the array laser  1  into parallel waves. The array mirror  3  changes the propagation direction of each light beam incident from the array lens  2  and launches the same into the lens  4 . 
     The array laser  1  is assumed to be a four-wave array laser which emits a light beam consisting of four waves. The light beams different in wavelength, which are emitted from the array laser  1 , are assumed to be a first light beam, a second light beam, a third light beam, and a fourth light beam respectively. The wavelength of the first light beam is assumed to be a first wavelength, the wavelength of the second light beam is assumed to be a second wavelength, the wavelength of the third light beam is assumed to be a third wavelength, and the wavelength of the fourth light beam is assumed to be a fourth wavelength. 
     The operation of the optical communication module illustrated in  FIG. 1  will next be explained. 
     The array laser  1  has a structure in which four laser resonators are assembled, and includes four light emitting active layers which produce optical gain by their energization. When a voltage is applied between the electrodes  11 ,  12 ,  13 , and  14  and their corresponding electrodes (not shown) provided on the back surface of the substrate  15 , the light emitting active layers emit light beams different from one another in wavelength. 
     The four light beams emitted from the array laser  1  are launched into the array lens  2 . The array lens  2  has a structure in which lenses for bringing the four light beams to parallel light are assembled. Thus, after the four light beams emitted from the array laser  1  have been brought to the parallel light by the array lens  2 , they are launched into the array mirror  3 . 
     Incidentally, the pitches of the four lenses that construct the array lens  2  (the intervals at which they are arranged) are respectively set to match with the intervals at which the four light emitting active layers of the array laser  1  are arranged. The intervals at which the four light emitting active layers are arranged, are the same. The respective lenses in the array lens  2  and their adjacent lenses are identical in spacing. Namely, the pitches of the four lenses are the same. Incidentally, the respective lenses and their adjacent lenses being identical in spacing means that the interval between a light incident position at each lens and a light incident position at its adjacent lens is the same with respect to any lens. 
     The array mirror  3  has a structure in which mirrors having filter functions for selectively reflecting the four light beams emitted from the array lens  2  are assembled. Namely, at the array mirror  3 , the mirror on which an n (where n: any of 1 to 4)th light beam falls reflects an nth wavelength component and changes the traveling direction of the light beam by 90 degrees. Further, the mirror causes other wavelength components to penetrate. In other words, the array mirror  3  is of one in which mirrors having filter functions for selecting four wavelengths are assembled. 
     The four light beams emitted from the array mirror  3  are condensed by the lens  4  and thereafter emitted to the optical fiber. 
     Incidentally, the pitches of the four mirrors that construct the array mirror  3  (the intervals at which they are arranged) are set so as to match with the intervals at which the four light emitting active layers of the array laser  1  are arranged. The respective mirrors and their adjacent mirrors in the array mirror  3  are identical in spacing. Namely, the pitches of the four mirrors are the same. Incidentally, the respective mirrors and their adjacent mirrors being identical in spacing means that the interval between a light incident position at each mirror and a light incident position at its adjacent mirror is the same with respect to any mirror. 
     Assuming that the light beams emitted from the array laser  1  are respectively of light beams modulated at a bit rate of 25 Gb/s or so, the capacity of transmission by the optical fiber can be brought to 100 Gb/s or so. Thus, the optical communication module according to the present embodiment can be applied to a field related to a 100 Gb/s transmission apparatus such as 100 Gb/s Ethernet (Trademark), a CFP optical module or the like. 
     An optical communication module manufacturing method according to the invention will next be explained.  FIG. 2  is a plan view showing an optical communication module held in a package.  FIG. 3  is a flowchart showing the manufacturing method of the optical communication module. The module stored in the package corresponds to the optical communication module shown in  FIG. 1 . Namely, in the manufacturing method to be described below, the sub-assembled optical communication module shown in  FIG. 1  is held within the package to thereby fabricate the packaged optical communication module. 
     A substrate  5  is provided on a carrier (not shown) made of CuW or Kovar or the like. 
     A water for the array laser  1  is fabricated (Step S 31 ). Namely, a lower clad layer, a multi-quantum well active layer, an upper clad layer, and the like are laminated on, for example, a GaAs (gallium arsenide) substrate to form light emitting active layers. Gratings are formed by electron beam exposure in such a manner that four regions in the active layers formed in the wafer emit light beams of wavelengths different from each other. The regions in the wafer, which respectively emit the light beams of wavelengths, are separated from one another (Step S 32 ). Namely, the wafer is diced to obtain four laser elements  101 ,  102 ,  103 , and  104 . 
     The diced four laser elements  101 ,  102 ,  103 , and  104  are mounted onto the substrate  5  in such a manner that they are disposed or arranged on the substrate  5  at equal intervals (Step S 33 ). Incidentally, the assembly of the laser elements  101 ,  102 ,  103 , and  104  corresponds to the array laser  1  shown in  FIG. 1 . The equal intervals mean that the intervals of outgoing parts of four light beams are the same. 
     Next, aspheric lenses (e.g., convex lenses: which will be hereinafter referred to as collimate lenses)  201 ,  202 ,  203 , and  204  for collimating the light beams emitted from the laser elements  101 ,  102 ,  103 , and  104  are fabricated and placed in positions on which the light beams emitted from the laser elements  101 ,  102 ,  103 , and  104  are incidentable, at equal intervals on the substrate  5  (Step S 34 ). The equal intervals mean that the intervals of incoming parts of the four light beams are the same. The intervals are the same as those at which the laser elements  101 ,  102 ,  103 , and  104  are arranged. Incidentally, the assembly of the collimate lenses  201 ,  202 ,  203 , and  204  corresponds to the array lens  2 . The collimate lenses  201 ,  202 ,  203 , and  204  may be fabricated in advance without forming them immediately before execution of the process of Step S 34 . 
     Since the collimate lenses  201 ,  202 ,  203 , and  204  are disposed at equal intervals, and the intervals at which the collimate lenses  201 ,  202 ,  203 , and  204  are disposed, are the same as the intervals at which the laser elements  101 ,  102 ,  103 , and  104  are disposed, for example, the optical axis of the collimate lens  201  may simply be matched with the optical axis (center of light emission) of the laser element  101 , and adjustment work for matching the optical axes of other collimate lenses  202 ,  203 , and  204  with the optical axes of the laser elements  102 ,  103 , and  104  respectively becomes unnecessary. This is because after the optical axis of the collimate lens  201  and the optical axis (center of light emission) of the laser element  101  have been matched with each other, the collimate lenses  202 ,  203 , and  204  may be arranged at equal intervals in sequence. 
     Four first through fourth multilayer film mirrors are fabricated which perform the function of reflecting a light beam of an n (where n: any of 1 to 4)th wavelength collimated by the array lens  2  as a light beam of a specific wavelength and causing a light beam of wavelength other than the specific wavelength to penetrate therethrough. The nth multilayer film mirror selectively reflects the light beam of the nth wavelength. Thus, the four multilayer film mirrors are hereinafter referred to as selective wavelength reflection mirrors  301 ,  302 ,  303 , and  304 . 
     The selective wavelength reflection mirrors  301 ,  302 ,  303 , and  304  are disposed on the substrate  5  at equal intervals (Step S 35 ). The equal intervals mean that the intervals of incoming and reflecting parts of the four light beams are the same. The intervals thereof are the same as the intervals at which the laser elements  101 ,  102 ,  103 , and  104  are disposed. Incidentally, the assembly of the selective wavelength reflection mirrors  301 ,  302 ,  303 , and  304  corresponds to the array mirror  3 . The selective wavelength reflection mirrors  301 ,  302 ,  303 , and  304  may be fabricated in advance without forming them immediately before execution of the process of Step S 35 . 
     Since the selective wavelength reflection mirrors  301 ,  302 ,  303 , and  304  are disposed at equal intervals, and the intervals at which the selective wavelength reflection mirrors  301 ,  302 ,  303 , and  304  are disposed, are the same as the intervals at which the laser elements  101 ,  102 ,  103 , and  104  are disposed, for example, the optical axis of the selective wavelength reflection mirror  301  may simply be matched with the position of incident light, and hence adjustment work for matching the optical axes of other selective wavelength reflection mirrors  302 ,  303 , and  304  with the position of the incident light becomes unnecessary. This is because after the optical axis of the selective wavelength reflection mirror  301  has been matched with the position of the incident light, the selective wavelength reflection mirrors  302 ,  303 , and  304  may be disposed at equal intervals in sequence. 
     The directions of reflection by the selective wavelength reflection mirrors  301 ,  302 ,  303 , and  304  are set such that the four reflected light are brought into a bundle. A lens  4  is provided on the optical path of the bundle of the reflected light. The lens  4  gathers the bundle of the reflected light. 
     Then, a carrier is mounted on a Peltier element  6  subjected to pre-soldering (Step S 36 ). The Peltier element  6  is of an element used for temperature control. Further, the optical communication module is mounted inside, for example, a Kovar-made package  7  to achieve its hermetic sealing (Step S 37 ). The package  7  is provided with a transmission hole  9  for causing a light beam from the lens  4  to pass therethrough. The light beam from the lens  4  passes through the transmission hole  9  and is thereafter coupled to an aligned optical fiber  8 . 
     In the above exemplary embodiment as described above, since the components for obtaining light beams of plural wavelengths are respectively brought into assembly, the optical communication module can be reduced in size. Incidentally, the components for obtaining the light beams of the plural wavelengths correspond to the array laser  1 , array lens  2 , and array mirror  3 . 
     Since the intervals at which the plural laser elements  101 ,  102 ,  103 , and  104  being of the components of the array laser  1  are disposed, and the intervals at which the plural collimate lenses  201 ,  202 ,  203 , and  204  being of the components of the array lens  2  are disposed, are the same respectively, the array laser  1  and the array lens  2  can be aligned with each other by simply performing the adjustment for matching the optical axis of one collimate lens with the optical axis of one laser element and providing other plural collimate lenses at equal intervals. Since the intervals at which the laser elements  101 ,  102 ,  103 , and  104  are disposed, and the intervals at which the plural selective wavelength reflection mirrors  301 ,  302 ,  303 , and  304  being of the components of the array mirror  3  are disposed, are the same respectively, the array laser  1  and the array mirror  3  can be aligned with each other by simply carrying out the adjustment for matching the optical axis of one selective wavelength reflection mirror with the position of the incident light from one collimate lens and locating other plural selective wavelength reflection mirrors at equal intervals. 
     Namely, in the above exemplary embodiment, the number of man-hours required for the adjustment upon fabrication of the optical communication module is reduced. 
     In the above exemplary embodiment as well, since there is not used an optical waveguide for combining light beams of plural wavelengths, the present optical communication module can be improved in optical coupling efficiency as compared with the optical communication module illustrated in  FIG. 5 , and the cost of the optical communication module is reduced. 
       FIG. 4  is an explanatory view showing a schematic configuration of an optical communication module according to the invention. As shown in  FIG. 4 , the optical communication module is equipped with an array semiconductor laser  10  which emits light beams of plural wavelengths, an array lens  20  which brings each of the light beams of the plural wavelengths emitted from the array semiconductor laser  10  to parallel light, and an array mirror  30  which includes mirrors corresponding to the number of wavelengths and is provided at positions on which the light beams emitted from the array lens  20  are incidentable, the respective mirrors selectively reflecting the light beams of the plural wavelengths emitted from the array semiconductor laser  10 . 
     The array semiconductor laser  10  includes a plurality of laser elements which respectively emit light beams having wavelengths different from one another. The array lens  20  includes a plurality of collimate lenses provided corresponding to the laser elements respectively. The intervals (p shown in  FIG. 4 ) at which the collimate lenses are arranged, are preferably identical to the intervals (p shown in  FIG. 4 ) at which the laser elements are arranged. 
     Preferably, the mirrors of the array mirror  30  are respectively provided corresponding to the laser elements, and the intervals (p shown in  FIG. 4 ) at which the mirrors are disposed, are respectively the same as the intervals (p shown in  FIG. 4 ) at which the laser elements are disposed. 
     As shown in  FIG. 4 , the mirrors of the array mirror  30  are preferably placed in such a manner that the light beams reflected by the mirrors of the array mirror  30  are brought to one light bundle. 
     The structure of the optical communication module may be of a structure in which the array semiconductor laser  10 , the array lens  20 , the array mirror  30 , and a lens for gathering a plurality of light beams emitted from the array mirror are held in a package made of a metal (refer to  FIG. 2 ). 
     Incidentally, in general, a waveguide consisting of quartz is comparatively high in cost, and an optical communication module using the quartz waveguide becomes expensive. Also, a problem arises in that since the optical coupling loss of the quartz waveguide is not small, the output level of multiplexed light is reduced. 
     An exemplary advantage according to the invention is, however, that an optical communication module rendered high in optical coupling efficiency can be obtained at low cost. 
     The invention can be applied suitably to an optical communication module used in a large-capacity optical transmission system or the like. 
     While the invention has been particularly shown and described with reference to exemplary embodiments thereof, the invention is not&#39;limited to these embodiments. It will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the claims. 
     The whole or part of the exemplary embodiments disclosed above can be described as, but not limited to, the following supplementary notes. 
     (Supplementary Note 1) 
     An optical communication module comprising an array semiconductor laser which emits light beams of plural wavelengths, an array lens which brings each of the light beams emitted from the array semiconductor laser to parallel light, and an array mirror which includes mirrors corresponding to the number of wavelengths and is provided at positions on which the light beams emitted from the array lens are incidentable, the respective mirrors selectively reflecting the light beams emitted from the array semiconductor laser. 
     (Supplementary Note 2) 
     In the optical communication module described in the supplementary note 1, the array semiconductor laser includes a plurality of laser elements which emit light beams of wavelengths different from one another respectively. The array lens includes a plurality of collimate lenses provided corresponding to the laser elements respectively. Intervals at which the collimate lenses are arranged, are respectively the same as intervals at which the laser elements are arranged. 
     (Supplementary Note 3) 
     In the optical communication module described in the supplementary note 1, the mirrors of the array mirror are provided corresponding to the laser elements respectively, and intervals at which the mirrors are arranged are respectively the same as the intervals at which the laser elements are arranged. 
     (Supplementary Note 4) 
     In the optical communication module described in the supplementary notes  1 , the mirrors of the array mirror are provided in such a manner that the light beams reflected by the mirrors of the array mirror are brought into one light bundle. 
     (Supplementary Note 5) 
     In the optical communication module described in the supplementary notes  1 , the array semiconductor laser, the array lens, the array mirror, and a lens for gathering the plural light beams emitted from the array mirror are held in a package made of a metal. 
     (Supplementary Note 6) 
     A method for manufacturing an optical communication module, comprising: forming an array semiconductor laser, which emits light beams of plural wavelengths, on a substrate, forming an array lens, which brings each of the light beams emitted from the array semiconductor laser to parallel light, on the substrate, and forming an array mirror which includes mirrors corresponding to the number of wavelengths and in which the respective mirrors selectively reflect the light beams emitted from the array semiconductor laser, at positions on which the light beams emitted from the array lens on the substrate are incidentable. 
     (Supplementary Note 7) 
     The method according to Supplementary note 6, further comprising: forming a plurality of laser elements respectively emitting light beams of wavelengths different from one another in a wafer and thereafter separating the laser elements from one another, mounting the laser elements on the substrate, forming a plurality of collimate lenses respectively provided corresponding to the laser elements as the array lens, mounting the collimate lenses on the substrate at positions on which the light beams emitted from the laser elements are incidentable, and setting intervals at which the collimate lenses are arranged, to be identical to intervals at which the laser elements are arranged. 
     (Supplementary Note 8) 
     The method according to Supplementary note 6, further comprising: setting intervals at which the mirrors of the array mirror are arranged, to be identical to the intervals at which the laser elements are arranged. 
     (Supplementary Note 9) 
     The method according to Supplementary notes  6 , further comprising: holding the array semiconductor laser, the array lens, the array mirror, and a lens for gathering the plural light beams emitted from the array mirror in a package made of a metal.