Abstract:
Disclosed are a broadband light source and a method of fabricating the same. The method includes the steps of forming a lower clad on a substrate, forming an active layer having a multiple well structure on the lower clad (so as to generate light having a broad wavelength band), sequentially depositing an upper clad and a cap on the active layer, depositing a cover layer including at least two regions having bandgaps different from each other on the cap, and heat-treating the broadband light source including the cover layer.

Description:
CLAIM OF PRIORITY  
       [0001]     This application claims priority to an application entitled “Broadband Light Source And Method For Fabricating The Same,” filed with the Korean Intellectual Property Office on Oct. 20, 2004 and assigned Serial No. 2004-83898, the contents of which are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a broadband light source, and more particularly to a broadband light source having a quantum well structure.  
         [0004]     2. Description of the Related Art  
         [0005]     Optical fiber amplifiers or semiconductor amplifiers capable of generating incoherent spontaneous emission are used as broadband light sources. Such broadband light sources may be used as a light source for a Fabry-Perot laser, to generate external injection light for inducing a wavelength-lock or to generate light for creating multiple channels in a WDM (wavelength division multiplex) optical communication system.  
         [0006]     In addition, a semiconductor light source having a multiple quantum well structure can be used as a broadband light source. In order to generate broadband wavelength light using such semiconductor light sources, quantum wells are formed having mutually different energy levels (or various light generated with different energy levels are combined with each other), thereby creating broadband wavelength light.  
         [0007]     However, such a semiconductor light source cannot easily control the thickness of a quantum well. Further, it is difficult to control the wavelength characteristic of the quantum well after the quantum well has been grown. Since the optical gain may vary depending on the sort of the quantum well, it is difficult to constantly obtain light having a desired wavelength band through the semiconductor light source having the multiple quantum well structure.  
       SUMMARY OF THE INVENTION  
       [0008]     Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the prior art and provides additional advantages, by providing a semiconductor light source having a multiple quantum well structure capable of stably generating light having a broad wavelength band by controlling a bandgap after the semiconductor light source has been grown on a substrate.  
         [0009]     In accordance with the principles of the present invention, a method of fabricating a broadband light source is provided. The method comprises the steps of forming a lower clad on a substrate; forming an active layer having a multiple well structure on the lower clad; sequentially depositing an upper clad and a cap on the active layer; depositing a cover layer including at least two regions having bandgaps different from each other on the cap; and heat-treating the broadband light source including the cover layer.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     The present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:  
         [0011]      FIG. 1  is a view illustrating a broadband light source having a quantum well structure according to a first embodiment of the present invention;  
         [0012]      FIG. 2  is a view illustrating an energy bandgap of first and second regions shown in  FIG. 1 ;  
         [0013]      FIG. 3  is a view illustrating wavelengths of light outputted from first and second regions shown in  FIG. 1 ;  
         [0014]      FIG. 4  is a plan view illustrating a broadband light source shown in  FIG. 1  according to one embodiment of the present invention;  
         [0015]      FIG. 5  is a plan view illustrating a broadband light source shown in  FIG. 1  according to another embodiment of the present invention;  
         [0016]      FIGS. 6 and 7  are graphs for explaining a relationship between areas of the first and second regions shown in  FIG. 5  and a gain of light;  
         [0017]      FIG. 8  is a plan view illustrating a broadband light source according to a second embodiment of the present invention; and  
         [0018]      FIG. 9  is a plan view illustrating a broadband light source according to a third embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION  
       [0019]     Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. For the purposes of clarity and simplicity, a detailed description of known functions and configurations incorporated herein will be omitted as it may make the subject matter of the present invention unclear.  
         [0020]      FIG. 1  is a view illustrating a broadband light source having a quantum well structure according to a first embodiment of the present invention. As shown in  FIG. 1 , the broadband light source  100  according to the first embodiment of the present invention includes a substrate  110 , a lower clad  120  formed on the substrate  110 , an active layer  140  deposited on the lower clad  120  so as to generate light having a broad wavelength band, an upper clad  160  formed on the active layer  140 , a cap layer  170  deposited on the upper clad layer  160 , a cover layer  180  deposited on the cap layer  170  and formed with a plurality of regions made from different kinds of materials, and first and second protective layers  130  and  150 . The first protective layer  130  is grown between the lower clad  120  and the active layer  140 . The second protective layer  150  is grown between the upper clad  160  and the active layer  140 . The cover layer  180  includes a first region  181  made from SiO 2  and a second region  182  made from SiN x .  
         [0021]      FIG. 2  is a view illustrating an energy bandgap of the first and second regions  181  and  182 . As shown in  FIG. 2 , broadband light source is heat-treated at a temperature above 700° C. in such a manner that the energy gap formed in the cover layer  180  can be locally controlled. That is, the quantum well structure shown in  FIG. 2  is changed into a smooth curve structure through a heat-treatment process.  
         [0022]      FIG. 3  is a view illustrating wavelengths of light outputted from first and second regions shown in  FIG. 1  As shown in  FIG. 3 , the broadband light source  100  may generate light having the broad wavelength band. When the broadband light source  100  formed with the cover layer  180  is heat-treated, the quantum well structure is changed, so the bandgap and the wavelength band of the light are also changed. That is, the bandgap of the cover layer  180  is changed after the heat-treatment process, so the wavelength thereof is also change. At this time, variation of the bandgap and the wavelength band of the first region  181  is different from that of the second region  182 .  
         [0023]      FIG. 4  is a plan view illustrating the broadband light source  100  shown in  FIG. 1 . When the energy bandgap of the second region  182  is higher than the energy bandgap of the first region  181 , light generated from the broadband light source  100  including the second region  182  has a wavelength band shorter than a wavelength band of light generated from the broadband light source  100  including the first region  181 . A high-reflective layer  102  is coated on one end of the broadband light source  100  including the first region  181 , and a non-reflective layer  101  is coated on the other end of the broadband light source  100  including the first region  181 .  
         [0024]     The broadband light source  100  is subject to an impurity free vacancy disordering (IFVD) process at a temperature above 700° C. after the cover layer  180  has been formed on the cap layer  170 , so that the bandgap thereof is changed. In addition, such variation of the bandgap in the first region  181  is different from that of the second region  182 . The broadband light source  100  according to the first embodiment of the present invention may locally control the bandgap of each region, thereby generating light having the broad wavelength band.  
         [0025]      FIG. 5  is a plan view of a broadband light source  100  for illustrating the first and second regions of the cover layer shown in  FIG. 1  according to another embodiment of the present invention.  FIGS. 6 and 7  are graphs for explaining the relationship between widths G 1  and G 2  of first and second regions  181 ′ and  182 ′ shown in  FIG. 5  and a gain of light.  
         [0026]     As shown in  FIGS. 5 and 6 , when the gain of the first region  181 ′ is larger than the gain of the second region  182 ′, areas A 1  and A 2  of the first and second regions  181 ′ and  182 ′ are adjusted in such a manner that intensity of light generated from the first and second regions  181 ′ and  182 ′ can be constantly adjusted. That is, the gain of each region forming the cover layer  180 ′ is proportional to the area thereof, so the gains of lights having mutually different wavelengths can be constantly controlled by adjusting the areas of the regions. The broadband light source  100  includes a high-reflective layer  102  and a non-reflective layer  101 .  
         [0027]      FIG. 8  is a plan view illustrating a multi-wavelength light source  200  including a cover layer formed with first and second regions  210  and  220  made from different kinds of materials according to a second embodiment of the present invention.  
         [0028]     The multi-wavelength light source  200  shown in  FIG. 8  includes a high-reflective layer coated on one surface of the multi-wavelength light source  200  having the first region  210  and a non-reflective layer coated on the other surface of the multi-wavelength light source  200  having the second region  220 . Light is generated through the non-reflective layer. An active layer  230  is tapered from the second region  220  to the first region  210 , so the gain of light may increase along a proceeding direction of the light.  
         [0029]      FIG. 9  is a plan view illustrating a reflective type semiconductor optical amplifier  300  including a cover layer formed with first and second regions  310  and  320  made from different kinds of materials according to a third embodiment of the present invention.  
         [0030]     The reflective type semiconductor optical amplifier  300  shown in  FIG. 9  includes a high-reflective layer coated on one surface of the reflective type semiconductor optical amplifier  300  having the first region  310  and a non-reflective layer coated on the other surface of the reflective type semiconductor optical amplifier  300  having the second region  320 . The reflective type semiconductor optical amplifier  300  includes an spot size converter (SSC) having an active layer  330 , which is tapered at the second region  320 . That is, the reflective type semiconductor optical amplifier  300  having the above active layer  330  according to the third embodiment of the present invention improves an far-field pattern (FFP), so it can be coupled with optical fiber with a high coupling efficiency.  
         [0031]     As described above, a broadband light source according to the present invention includes a cover layer having a plurality of regions made from different kinds of materials. The regions have bandgaps different from each other after the broadband light source has been subject to an IFVD process, such as a heat-treatment process. Thus, the broadband light source can stably generate light having the broad wavelength band. In addition, the broadband light source can be integrated on a single substrate, so productivity for the broadband light source may improve. Furthermore, the present invention can easily control the gain and the wavelength band of light by adjusting areas of the regions and the bandgaps thereof, so it is possible to produce articles having various specifications.  
         [0032]     While the invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.