Patent Publication Number: US-2005129359-A1

Title: Micro collimating lens system for optical communication

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a micro collimating system for optical communication, and more particularly, to a micro collimating system for optical communication used as an interface device of an optical communication network which is easy to fabricate and is constructed to reduce unit cost of fabrication.  
      2. Description of the Background Art  
      Recently, the technology related to information has made rapid progress together with the development of the high-speed technology of communications using optical fibers which are capable of transmitting/receiving much information. In particular, as multimedia information including various types of data such as a moving image, an audio signal and a text signal is transmitted at high speed, a two-way interactive communications environment is constructed, and users are tremendously increased, the communications network using previously available copper line is faced with a limit. The communications network having a form of an optical signal which has high carrier frequencies has been proposed as an alternative plan.  
      In case of an optical communication network using such light as a signal for transmitting information, an interface connecting a user with a repeater or with a communications provider should be constructed as an optical connector module instead of a logic integrated circuit having been applied to the communications network using the existing copper line.  
      The optical connector module, a data interface for the optical communication network, includes a line made of optical fibers; an optical receiving module used to receive an optical signal; an optical transmitting module used to transmit an optical signal; and an optical relay module used to relay an optical signal. However, since the optical connector module requires precision processing and close assembling, its manufacturing cost is high.  
      In addition to this, the optical connector module should meet requirements as follows: low power consumption, lightness and smallness for easy handling, and excellence of mechanical and optical characteristics. However, it is difficult to manufacture a module which satisfies such requirements.  
      In order to overcome such a limit, precise parts for optical fiber communication which use a semiconductor fabrication process and the micromachining technique have been researched and manufactured.  
       FIGS. 1 and 2  show the conventional micro collimating lens system for optical communication, as an optical communication module device, using a micro spherical lens.  FIG. 1  is a perspective view showing a construction of the conventional micro collimating lens system for optical communication using a micro spherical lens.  FIG. 2  is a side view of  FIG. 1  in the direction II, and  FIG. 3  is a side view of  FIG. 1  in the direction III.  
      As shown therein, the conventional micro collimating lens system for optical communication includes: a silicon substrate  1 ; a supporting groove  4  formed on the silicon substrate  1 ; an optical fiber  2  fixed to the supporting groove for transmitting an optical signal  7 ; a spherical lens  3  separated from one end of the optical fiber  2  by a predetermined distance and installed at the supporting groove  4  in order that the optical signal  7  from the optical fiber  2  can be collimated; light receiving elements  5  formed on the silicon substrate  1  and assembled by methods such as soldering; and electric wiring  6  for providing the power to the light receiving elements  5 .  
      An operation of the conventional micro collimating lens system for optical communication will be briefly described as follows.  
      When the optical signal  7  transmitted through the optical fiber  2  passes through the spherical lens  3 , it is collimated in a horizontal and vertical direction with respect to the silicon substrate  1 . As the collimated optical signal  7  passes through the spherical lens  3 , the amount of the light is increased and is made incident upon the light receiving elements  5 . Therefore, efficiency in transmitting the optical signal is improved.  
      However, since the spherical lens used in the conventional micro collimating lens system for optical communication is a micro lens of which diameter is less than 1 mm, efficiency of assembly is noticeably lowered when mounting the spherical lens at the micro collimating lens system.  
      In addition, the spherical lens is so expensive that the manufacturing cost of the collimating lens system for optical communication is entirely increased.  
     SUMMARY OF THE INVENTION  
      Therefore, an object of the present invention is to provide a micro collimating lens system for optical communication used as an interface device of an optical communication network which is easy to fabricate and is constructed to reduce unit cost of fabrication.  
      To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided a micro collimating lens system for optical communication, comprising: an optical fiber aligned on a silicon substrate in a certain direction for transmitting an optical signal; and at least two lenses aligned on the silicon substrate in order that the optical signal can be collimated at multiple stages.  
      The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention.  
      In the drawings:  
       FIG. 1  is a perspective view showing a construction of the conventional micro collimating lens system for optical communication using a spherical lens;  
       FIG. 2  is a side view of  FIG. 1  in the direction II;  
       FIG. 3  is a side view of  FIG. 1  in the direction III;  
       FIG. 4  is a perspective view showing the micro collimating lens system for optical communication in accordance with one embodiment of the present invention;  
       FIG. 5  is a side view showing an important construction of the micro collimating lens system for optical communication in accordance with one embodiment of the present invention; and  
       FIG. 6  is a front view showing the important construction of the micro collimating lens system for optical communication in accordance with one embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Hereinafter, reference will now be made in detail to the preferred embodiments of a micro collimating lens system for optical communication of the present invention, examples of which are illustrated in the accompanying drawings.  
      In addition, it should be understood that the above-described embodiments are not limited by any of the details of the foregoing specific embodiment, unless otherwise specified, but rather should be construed broadly within its spirit and scope as defined in the appended claims.  
      Hereinafter, a micro collimating lens system for optical communication in accordance with one embodiment of the present invention will be described in detail with reference to the accompanying drawings.  
      However, when describing the present invention, a detailed description with respect to well known technique or construction will be omitted in order to clearly show the gist of the present invention.  
      FIGS.  4  to  6  show a micro collimating lens system for optical communication in accordance with one embodiment of the present invention.  FIG. 4  is a perspective view showing the micro collimating lens system for optical communication in accordance with one embodiment of the present invention,  FIG. 5  is a side view showing an important construction of the micro collimating lens system for optical communication in accordance with one embodiment of the present invention, and  FIG. 6  is a front view showing the important construction of the micro collimating lens system for optical communication in accordance with one embodiment of the present invention.  
      As shown therein, the micro collimating lens system for optical communication in accordance with one embodiment of the present invention includes: an optical fiber  20  aligned on a silicon substrate  10  in a certain direction for transmitting an optical signal  50 ; and two lenses  30  and  40  aligned on the silicon substrate  10  in order that the optical signal  50  from the optical fiber  20  can be collimated at multiple stages.  
      Most preferably, the lenses  30  and  40  comprise a fist lens  30  aligned perpendicularly to a direction in which the optical signal  50  advances such that the Is optical signal  50  diverged from the optical fiber  10  can be collimated in one axial direction and a second lens  40  aligned parallel to the direction in which the optical signal  50  advances such that the optical signal having passed through the first lens  30  and thus been collimated in one axial direction can be collimated in another axial direction perpendicular to one axial direction in which the optical signal  50  has been collimated.  
      That is, as light coming from the optical fiber  20 , that is, the optical signal  50  passes through the two lenses  30  and  40 , a degree of divergence is reduced.  
      More in detail, when the optical signal  50  from the optical fiber  20  passes through the first lens  30 , a vertical divergence angle of the optical signal diverged in a direction (direction of axis X) perpendicular to the silicon substrate  10  on the basis of the axis of the optical fiber  20  is reduced. That is, as shown in  FIG. 5 , the vertical divergence angle of the optical signal  50  is reduced from α to α′. In addition, when the optical signal  50  passes through the second lens  40 , a horizontal divergence angle of the optical signal  50  diverged in a direction (direction of axis Y) horizontal to the silicon substrate  10  on the basis of the axis of the optical fiber  20  is reduced. That is, as shown in  FIG. 6 , the vertical divergence angle of the optical signal  50  is reduced from β to β′.  
      As the optical signal  50  from the optical fiber  20  passes through the first lens  30  and the second lens  40 , the divergence angles of the optical signal  50  are reduced in two axial directions (axis X and Y), respectively, perpendicular to the silicon substrate. Accordingly, the optical signal  50  is effectively collimated.  
      The first lens  30  is formed to have a certain radius of curvature in the direction (direction X) perpendicular to the silicon substrate  10 .  
      The first lens  30  is preferably aligned perpendicularly to a direction in which the optical fiber  20  is aligned, separated from the optical fiber  20  by a certain distance and formed as a cylindrical shape having a certain length. An optical fiber is typically used as materials of the first lens. Accordingly, a size of the lens can be enlarged, which makes alignment much easier.  
      As for the second lens  40 , one surface  41  which receives the optical signal  50  having passed through the first lens  30  is flat and another surface  42  from which the optical signal  50  goes out is formed to have a certain radius of curvature in the direction (direction of axis Y) horizontal to the silicon substrate  10 .  
      In addition, the second lens  40  is preferably formed of polymer materials.  
      The first lens  30  and the second lens  40  are aligned on the silicon substrate along a path to which light advances. In order to align parts according to the path to which light advances, a mounting layer  45  having an aligning groove structure is formed on the silicon substrate  10 .  
      Aligning grooves  11   a ,  11   b  and  11   c  formed at the mounting layer  45  and mounted to align the optical fiber  20 , the first lens  30  and the second lens  40  are formed simultaneously when forming the mounting layer  45 .  
      In addition, the mounting layer  45  is preferably made of a polymer, which is a material identical to the material of the second lens  40 .  
      That is, since the mounting layer  45  and the second lens  40  are formed of the same materials, it is possible to form the second lens  40  simultaneously with the aligning grooves  11   a ,  11   b  and  11   c  while the mounting layer  45  is patterned.  
      More in detail, the second lens  40  and the mounting layer  45  are formed by patterning a thick photoresist film formed at the silicon substrate  10  by a photolithography process. In addition, the second lens  40  and the mounting layer  45  can be also formed by patterning a film made of a photo sensitive polymer which has been formed at the silicon substrate  10  by the photolithography.  
      As the aligning groove structure is formed, parts to be installed on the silicon substrate  10  can be precisely aligned in three axial directions of X, Y and Z, respectively and passive alignment can be also easily done.  
      Light receiving elements  12  for receiving the optical signal  50  from the second lens  40  are formed on the mounting layer  45 , and electric wiring  13  is formed to connect them electrically.  
      Simple operation of the micro collimating lens system in accordance with the one embodiment of the present invention having such construction will be described as follows.  
      The optical signal  50  outputted from the optical fiber  20  passes through the cylindrical first lens  30  installed on the silicon substrate  10  in a direction perpendicular to the direction in which the optical signal  50  advances. At this time, as shown in  FIG. 5 , the divergence angle of the optical signal  50  being diverged is reduced in the direction (direction of axis A) perpendicular to the surface of the silicon substrate  10 . The optical signal  50  having passed through the first lens  30  passes through the second lens  40  made of polymer materials installed on the silicon substrate  10  parallel to the direction in which the optical signal  50  advances. At this time, as shown in  FIG. 6 , the divergence angle of the optical signal  50  is reduced again in the direction (direction of axis Y) horizontal to the surface of the silicon substrate  10 . As passing through the first lens  30  and the second lens  40  sequentially, the optical signal  50  is collimated at two stages and light efficiency is raised by increasing light flowing into the light receiving elements  12 .  
      As so far described, in order to collimate the optical signal outputted from the optical fiber, the micro collimating lens system for optical communication in accordance with the present invention is provided with the micro first lens having a certain size in the cylindrical shape, installed at the silicon substrate and the second lens installed, following the first lens so as to facilitate alignment and installation using the micromachining, so that the divergence angles of the optical signal are reduced by sequential multiple stages. Accordingly, without using the conventional spherical lens which is hard to fabricate and install, the same results can be obtained.  
      In addition, in the micro collimating lens system for optical communication in accordance with the present invention, an aligning groove structure for passively aligning an optical fiber, a lens or the like is not formed on the silicon substrate through etching, but is formed on the silicon substrate with a polymer-based film. At the same time, the second lens is also formed of polymer materials identical to materials of the aligning groove structure, and thus the aligning groove structure and the second lens can be simultaneously formed. Accordingly, since the following aligning process which is complicating like the conventional spherical lens is unnecessary, installation becomes very simplified, assembly of the collimating lens system becomes entirely easy, and its fabrication cost is also reduced.  
      In addition, because the micro collimating lens system for optical communication is a device for an optical communication module fabricated by a semiconductor process, it can be used to transmit/receive or relay an optical signal in a WDM (wavelength-division-multiplex) optical network and be applied to another optical interface device used to the optical communication network.  
      As the present invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, it should also be understood that the above-described embodiments are not limited by any of the details of the foregoing description, unless otherwise specified, but rather should be construed broadly within its spirit and scope as defined in the appended claims, and therefore all changes and modifications that fall within the metes and bounds of the claims, or equivalence of such metes and bounds are therefore intended to be embraced by the appended claims.