Patent Publication Number: US-2005135738-A1

Title: Broadband light source and broadband optical module using the same

Description:
CLAIM OF PRIORITY  
      This application claims priority to an application entitled “Broadband Light Source and Broadband Optical Module Using the Same,” filed in the Korean Intellectual Property Office on Dec. 23, 2003 and assigned Serial No. 2003-95261, the contents of which are hereby incorporated by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a light source for generating light, and more particularly to a broadband light source for generating light of a broadband wavelength.  
      2. Description of the Related Art  
      A wavelength division multiplexed-passive optical network (WDM-PON) includes a central office for providing a communication service, a plurality of subscribers receiving the communication service from the central office, and a remote node connected to the central office through one optical fiber. The remote node receives optical signaling from the central office and demultiplexes the signaling downstream to the respective subscribers. The remote node likewise receives optical signals from the subscribers and outputs multiplexed optical signals upstream to the central office.  
      The downstream optical signals generated by the central office of mutually differing wavelengths so as to provide each downstream optical signals to a predetermined subscriber. Conversely, and the central office detects upstream optical signals having the mutually differing wavelengths inputted from subscribers.  
      The remote node is positioned adjacent to subscribers and linked to the central office through one optical fiber, so the optical fiber can be buried in an easy manner and it is possible to easily make communication lines.  
      The above-described wavelength division multiplexed-passive optical network uses mutually differing wavelength bands in such a manner that upstream optical signals are not overlapped with downstream optical signals, and may include a device capable of generating the upstream optical signals and downstream optical signals.  
      Such a device for generating the upstream optical signals and downstream optical signals may include one broadband light source and Fabry-Perot laser diodes fixed by the broadband light source.  
      The broadband light source uses spontaneous emitted light outputted through an erbium doped fiber amplifier (EDFA) or a semiconductor optical amplifier (SOA), and the spontaneous emitted light is de-multiplexed according to wavelengths thereof so as to lock each of wavelengths of the Fabry-Perot laser diodes.  
      However, the conventional method includes multiple broadband light sources in order to induce each of wavelength-locked upstream and downstream optical signals, entailing increased volume of the broadband light sources and cost.  
     SUMMARY OF THE INVENTION  
      The present invention has been made to solve the above-mentioned problem occurring in the prior art and provides additional advantages, by providing a broadband light source capable of generating light of mutually differing wavelength bands.  
      In order to accomplish the above object, according to the present invention, there is provided a broadband light source including a substrate, a plurality of waveguides including active layers for generating light of mutually differing wavelength bands, and formed on the substrate in order to extend from a first end to a second end of the broadband light source, a plurality of trenches located between waveguides in order to electrically and optically insulate the waveguides from each other, and a plurality of electrode devices for operating each of the waveguides. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above object, features and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which the same reference numerals are used to designate the same or similar components throughout the several views:  
       FIG. 1  is a sectional view showing a broadband light source according to a first embodiment of the present invention;  
       FIG. 2  is a plan view showing the broadband light source shown in  FIG. 1 ;  
       FIG. 3  is a view showing a structure of an optical module including a broadband light source according to a second embodiment of the present invention;  
       FIG. 4  is a view showing an optical axis alignment of a broadband light source, an optical fiber, and lens located between the optical fiber and the broadband light source shown in  FIG. 3 ; and  
       FIG. 5  is a spectrum showing a wavelength band of light outputted from a broadband light source according to one embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION  
       FIG. 1  is a sectional view showing a broadband light source according to a first embodiment of the present invention,  FIG. 2  is a plan view showing the broadband light source shown in  FIG. 1 . Referring to FIGS.  1  to  2 , the broadband light source according to the first embodiment of the present invention includes a substrate  101 , a plurality of waveguides  110 ,  120 ,  130  generating light of mutually differing wavelength bands and outputting the light to a first end (not shown), a plurality of trenches  102 ,  103  located between waveguides  110 ,  120 ,  130 , a plurality of electrode devices  141 ,  142 ,  143 ,  144  for operating each of waveguides  110 ,  120 ,  130 , an anti-reflective layer  160 , and a high-reflective layer  150 .  
      The substrate  101  is provided on an upper surface thereof with the waveguides  110 ,  120 ,  130 , and is provided at a lower surface thereof with a common electrode  144  of the waveguides  110 ,  120 ,  130 .  
      The waveguides  110 ,  120 ,  130  consists of a first waveguide  110 , a second waveguide  120 , and a third waveguide  130 , which generate light of mutually differing wavelength bands. The first to the third waveguides  110 ,  120 ,  130  output light of mutually differing wavelength bands towards the anti-reflective layer  160  of the broadband light source. The first to the third waveguides  110 ,  120 ,  130  respectively include active layers  111 ,  121 ,  131  having mutually differing band gaps, and clads  112 ,  122 ,  132  formed on the substrate  101  in such a manner that the clads surround the active layers.  
      The first waveguide  110  outputs light of an S-band corresponding to the wavelength band of 1490˜1530 mm through the anti-reflective layer  160  of the broadband light source. The second wavelength  120  outputs light of a C-band corresponding to a wavelength band of 1530˜1565 mm through the anti-reflective layer  160  of the broadband light source. Also, the third wavelength  130  outputs light of an L-band corresponding to a wavelength band of 1570˜1605 mm through the anti-reflective layer  160  of the broadband light source.  
      The first trench  102  is located between the first waveguide  110  and the second waveguide  120 , and the second trench  103  is located between the second waveguide  120  and the third waveguide  130 , so that the first to the third waveguides  110 ,  120  and  130  are electrically or optically insulated from each other.  
      The common electrode  144  is formed at a lower surface of the substrate  101 , and first to third upper electrodes  141 ,  142 ,  143  are formed on upper portions of the first to the third waveguides  110 ,  120 ,  130  such that they are insulated from each other. Thus, the electrode devices  141 ,  142 ,  143 .  144  independently apply current to the first to third waveguides  110 ,  120 ,  130  in order to operate each the waveguides.  
      The first upper electrode  141  is formed on the clad  112  of the first waveguide  110  in such a manner that the first upper electrode  141  is insulated from the second and the third upper electrodes  142 ,  143 , and, in conjunction with the common electrode  144 , applies a predetermined current to the first waveguide  110 . The second upper electrode  142  is formed on the clad  122  of the second waveguide  120 , and the third upper electrode  143  is formed on the clad  132  of the third waveguide  130 .  
      The anti-reflective layer  160  is coated on a first end of the broadband light source in order to output the light to an exterior of the broadband light source by minimizing an optical loss outputted from the first to the third waveguides  110 ,  120 ,  130 .  
      The high-reflective layer  150  is coated on a second end of the broadband light source so as to reflect light having mutually differing wavelengths created from the first to the third waveguides  110 ,  120 ,  130  towards the anti-reflective layer  160 .  
       FIG. 3  is a view showing a structure of an optical module including a broadband light source according to a second embodiment of the present invention, and  FIG. 4  is a view showing an optical axis alignment of a broadband light source, an optical fiber, and lens located between the optical fiber and the broadband light source shown in  FIG. 3 . Referring to  FIGS. 3 and 4 , the broadband light source according to the second embodiment of the present invention includes a broadband light source  210  generating light of mutually differing wavelength bands, an optical fiber  240 , a micro lens array  220 , a converged lens  230 , and an isolator  260 .  
      The broadband light source  210  includes first to third waveguides  215 ,  216 ,  217  grown on a substrate (not shown) in order to output light of the mutually differing wavelength bands, an anti-reflective layer  212  coated on one end of the broadband light source  210 , a high-reflective layer  211  coated on the opposite end of the broadband light source  210 , and first and second trenches  213 ,  214  located interleavingly between the first to third waveguides  215 ,  216 ,  217 .  
      Each of the first to third waveguides  215 ,  216 ,  217  includes active layers (not shown) having mutually differing band gaps, and clads (not shown) formed on the substrate to surround the active layers. In addition, driving current is separately applied to each of the first to third waveguides  215 ,  216 ,  217  by means of first to third upper electrodes  215   a ,  216   a ,  217   a  formed on upper surfaces of the first to third waveguides and a common electrode (not shown) grown at a lower surface of the substrate.  
      The broadband light source  210  is a reflective SOA that separately applies driving current to each of the active layers having the mutually differing band gaps, so light of mutually differing wavelength bands may be outputted.  
      The light of mutually differing wavelength bands outputted from the broadband light source  210  includes spontaneous emitted light, so a wavelength band of the light can be controlled according to band gaps of the active layers or intensity of driving current applied to waveguides. The light of mutually differing wavelength bands outputted from the broadband light source  210  is outputted to the micro lens array  220  through the anti-reflective layer  212 .  
      The micro lens array  220  is positioned opposed to the anti-reflective layer  212  of the broadband light source  210 . The micro lens array  220  collimates each of light outputted from the broadband light source  210  so as to output light to the converged lens  230 .  
      The converged lens  230  is located between the micro lens array  220  and the optical fiber  240 , so as to converge light collimated through the micro lens array  220  into the optical fiber  240 .  
      The optical fiber  240  outputs light inputted from the converged lens  230  to an exterior of the broadband light module.  
       FIG. 5  is a spectrum showing wavelength bands of light outputted from a broadband light source according to the present invention. Referring to  FIG. 5 , the broadband light source according to the present invention can output light of broad wavelength bands, such as C-band, L-band, and S-band, for optical communication.  
      The present invention integrates on a single substrate waveguides having mutually differing band gaps, making it is possible to output light of broad wavelength bands by using one broadband light source.  
      Although a preferred embodiment of the present invention has been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.