Patent Publication Number: US-6668140-B2

Title: Module for optical communication

Description:
This is a continuation application of U.S. Ser. No. 09/037,541, filed Mar. 10, 1998 now U.S. Pat. No. 6,341,027. 
    
    
     BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT 
     The present invention relates to a module for optical communication or an optical fiber device. 
     In a conventional module for optical communication, a metallic package receiving an end of an optical fiber and an optical element in a hermetic sealing manner is used. A replacement of the metallic package by a synthetic resin package is desired to decrease a producing cost of the module. 
     OBJECT AND SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a module for optical communication or an optical fiber device in which a reliability of an optical transmission between an optical fiber and an optical element is kept high without a significantly-precise relationship in position and attitude between the optical fiber and the optical element, and/or a metallic hermetic sealing. 
     According to the present invention, since in a module for optical communication comprising an optical fiber including an axial-end surface, and an optical element including an optical surface facing to the axial-end surface in such a manner that a light is transmitted between the optical surface and the axial-end surface, a transparent solid-state medium, for example, a synthetic resin or glass, is arranged between the optical surface and the axial-end surface so that the light is transmitted through the transparent solid-state medium between the optical surface and the axial-end surface, a volume of atmosphere including humidity between the optical surface and the axial-end surface is minimized to restrain a deterioration of the optical fiber and/or the optical element caused by the humidity. The transparent solid-state medium may be a high-rigidity or hard member such as glass or epoxy-resin, a low-rigidity or soft member such as an elastomer, a soft viscoelastic elastomer such as silicone resin or the like. 
     For restraining strongly the deterioration of the optical fiber (the axial-end surface) and/or the optical element (the optical surface) and/or preventing an undesirable reflection at the optical surface toward the axial-end surface, a contact between the transparent solid-state medium and the axial-end surface, and/or a contact between the transparent solid-state medium and the optical surface is effective. For preventing securely the deterioration of the optical fiber (the axial-end surface) and/or the optical element (the optical surface) and/or preventing the undesirable reflection at the optical surface toward the axial-end surface, it is preferable for the transparent solid-state medium to extend continuously or fill completely between the optical surface and the axial-end surface. For preventing securely the deterioration of the optical fiber (the axial-end surface) and/or the optical element (the optical surface) and making an optical characteristic between the optical surface and the axial-end surface constant and correct, it is preferable for the transparent solid-state medium to extend monolithically between the optical surface and the axial-end surface to cover monolithically both of the optical surface and the axial-end surface. 
     If the optical surface is prevented from extending perpendicularly to a direction of a longitudinal axis of the optical fiber or optical-light-proceeding axis of the optical fiber at the axial-end surface, the light from the axial-end surface is prevented from being reflected toward the axial-end surface by the optical surface. 
     If a refractive index of the transparent solid-state medium facing to or contacting the axial-end surface is more than that of the atmosphere to decrease a difference between that of the transparent solid-state medium and that of the axial-end surface or optical fiber, for example, not more than that of the optical fiber or axial-end surface, the light is restrained from being reflected or returned by the axial-end surface. If the refractive index of the transparent solid-state medium facing to or contacting the optical surface is more than that of the atmosphere to decrease a difference between that of the transparent solid-state medium and that of the optical element or optical surface, for example, not more than that of the optical element or optical surface, the light is restrained from being reflected or returned by the optical surface. The axial-end surface may extend substantially Perpendicularly to the longitudinal axis of the optical fiber at the axial-end surface. The transparent solid-state medium, for example, a glass or synthetic resin, may comprise or be a substantially transparent silicone resin and/or a substantially transparent epoxy resin. 
     The optical element may perform through the optical surface at least one of emitting the light toward the axial-end surface so that the optical element generates an optical signal to be transmitted through the optical fiber and receiving the light from the axial-end surface so that the optical element generates an electric signal from the light transmitted through the optical fiber. The optical element may include a light generator and a light beam cross-sectional area expanding element arranged between the light generator and the axial-end surface to increase a cross-sectional area of the light (along an imaginary plane perpendicular to a proceeding axis or direction of the light) supplied to the axial-end surface in comparison with that of the light at the light generator, and the optical surface may be formed on the light beam cross-sectional area expanding element. 
     The optical fiber may be substantially surrounded at an axial-end thereof by the solid-state medium in an airtight sealing manner, so that the axial-end of the optical fiber is securely prevented from being deteriorated by the atmosphere. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a partial front view of a first embodiment of the invention. 
     FIG. 2 is a partial cross-sectional side view of the first embodiment. 
     FIG. 3 is another partial cross-sectional side view of the first embodiment. 
     FIG. 4 is another partial front view of the first embodiment. 
     FIG. 5 is a partial side view of the first embodiment. 
     FIG. 6 is another partial front view of the first embodiment. 
     FIG. 7 is a partial front view of a second embodiment of the invention. 
     FIG. 8 is a front view showing a pair of optical fiber devices of the present invention for mutual optical communication. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     As shown in FIGS. 1-5, a plastic case  12  made through an injection or transfer molding receives a die pad  14  and a lead frame  15 , and a part of the lead frame and the die pad  14  are joined. A substrate  3  with a V-shaped groove  4  is adhered onto the die pad  14  by an electrically conductive adhesive, an optical fiber  1  is mounted in the V-shaped groove  4 , and an axial end surface of the optical fiber  1  extends substantially perpendicularly to a longitudinal axis of the optical fiber  1  or a light proceeding axis in the optical fiber  1  at an axial end of the optical fiber  1 . An optical element  2  (a semiconductor laser generator emitting a light through an optical surface thereof and/or a photo-electric detector receiving the light from the axial-end surface through the optical surface thereof so that the photo-electric detector generates an electric signal from the light or optical signal transmitted through the optical fiber  1 ) and a reflection-type or wave-guide type optical detector  6  for monitoring an output of the semiconductor laser generator  2  are mounted on the substrate  3 , an electrode  8  is arranged on the substrate  3  to be electrically connected to the optical element  2 , and the optical surface of the optical element  2  is inclined by an angle θ (for example, not less than 0.5 degrees when a distance between the optical surface of the optical element  2  and the axial end of the optical fiber  1  is not more than 100 μm, not less than 1.0 degree when the distance therebetween is not more than 80 μm, or not less than 1.6 degree when the distance therebetween is not more than 50 μm) relative to an imaginary plane perpendicular to the light proceeding axis in the optical fiber  1  at the axial end of the optical fiber  1  so that an amount of light supplied from the optical fiber  1  and returned or reflected by the optical surface of the optical element  2  to the axial end of the optical fiber  1  is decreased. 
     An index mark  5  is formed on the substrate  3  on the basis of which another index mark (not shown) on a reverse surface of the optical element  2  is positioned correctly to making a positional relationship between the optical element  2  and the optical fiber  1  correct. The optical element  2  is soldered to the substrate  3 . The axial end of the optical fiber  1 , the optical element  2 , the optical detector  6  and the substrate  3  form a sub-assembly  19 , and a glass or synthetic resin  7  as a solid-state medium substantially transparent relative to a wavelength of the light (for example, a silicone resin or an epoxy resin) receives therein or covers the sub-assembly  19 , that is, is cured to fill a space between the axial end of the optical fiber  1  and the optical surface of the optical element  2 , without a clearance, gas or air between the sub-assembly  19  and the glass or synthetic resin  7 , so that the light passes through the glass or synthetic resin  7  filling between the axial-end surface of the optical fiber  1  and the optical surface of the optical element  2  and between the optical element  2  and the optical detector  6 . A cap  16  is adhered to the plastic case  12  to form a plastic package  20  receiving the glass or synthetic resin  7  surrounding the sub-assembly  19 . 
     A reflectance R between two substances contacting each other is calculated through the following formula, when a refractive index of one of the substances is n1, and that of another thereof is n2. 
     
       
           R =( n 1− n 2) 2/( n 1+ n 2)2 
       
     
     A refractive index of a glass forming the axial-end surface of the optical fiber  1  is 1.5, that of the silicone resin  7  is 1.45, and that of the atmosphere is 1.0. Therefore, a reflectance R between the axial-end surface of the optical fiber  1  and the synthetic resin  7  is significantly smaller than a reflectance R between the axial-end surface of the optical fiber  1  and the atmosphere so that a reflection of the light by the axial-end surface of the optical fiber  1  is prevented by the silicone resin  7  contacting the axial-end surface of the optical fiber  1 . 
     Further, since a difference between the refractive index of the synthetic resin  7  and that of the axial-end surface of the optical fiber  1  contacting the synthetic resin  7  is small, the cross sectional shape and size of the light are restrained from being changed between the synthetic resin  7  and the axial-end surface of the optical fiber  1 . 
     Since the optical surface of the optical element  2  is prevented from extending perpendicularly to a direction of the light proceeding axis in the optical fiber  1  at the axial end of the optical fiber  1 , the light reaching the optical surface of the optical element  2  through the synthetic resin  7  from the axial-end surface of the optical fiber  1  is prevented from being reflected or returned toward the axial-end surface of the optical fiber  1  by the optical surface of the optical element  2 . 
     An angle of diffraction θ by medium is calculated through the following formula, when a refractive index of the medium is  n , a spot or cross-sectional diameter of the light beam reaching or taken into a light inlet face of the medium is D, and a wavelength of the light is λ. 
     
       
         θ=μ/( n×D ) 
       
     
     Since the refractive index of the silicone or epoxy resin  7  is larger than that of the atmosphere, an angle of diffraction θ by the silicone or epoxy resin  7  is smaller than an angle of diffraction θ by the atmosphere. Since the smaller the refractive index is, the larger a tolerance for positional relationship between the optical surface of the optical element  2  and the axial end surface of the optical fiber  1  is, a positioning between the optical surface of the optical element  2  and the axial end surface of the optical fiber  1  can be easily performed. 
     As shown in FIG. 6, the optical element  27  includes a monolithic combination of the semiconductor laser generator and a light beam cross-sectional area or spot-diameter expanding element  9 , for example, a tapered wave guide whose wave guide layer is tapered gradually in a thickness direction thereof. Since a light strength distribution is expanded by the wave guide  9 , an angle of diffraction of the light emitted from the optical surface (formed on the wave guide  9 ) through the synthetic resin  7  toward the axial-end surface of the optical fiber  1  is decreased. Therefore, the light is effectively transmitted to the optical fiber  1 . 
     As shown in FIG. 7, the optical element  2  is replaced by a photo-electric element  10  for generating an electric signal in accordance with the light transmitted through the optical surface from the optical fiber  1  and a preamplifier  11  for amplifying the electric signal. The optical surface is formed on the photo-electric element  10  as the optical element, and is prevented from extending perpendicularly to the direction of the light proceeding axis in the optical fiber  1  at the axial end of the optical fiber  1 . The axial end of the optical fiber  1 , the photo-electric element  10 , the preamplifier  11  and the substrate  3  form a sub-assembly. The synthetic resin  7  (for example, the silicone resin) receives therein or covers the sub-assembly without a clearance between the sub-assembly and the silicone resin  7 . 
     FIG. 8 shows a pair of optical fiber modules for mutual optical communication, each of the optical fiber modules having an optical signal generating part  17  including the semiconductor laser generator and an electric signal generating part  18  including the photo-electric detector. The optical fiber module may have a plurality of the electric signal generating parts  18  diverging from the optical fiber  1 .