Abstract:
To provide an optical device whereby the optical characteristics of a lightwave circuit element can be varied with low power consumption. There is provided an optical device comprising a lightwave circuit element having one or plurality of optical waveguides, and also having a refractive index adjusting portion composed of resin located in the one or plurality of optical waveguides and/or in a portion of the area in the one or plurality of optical waveguides. The lightwave circuit element comprises an adjustment-light waveguide for guiding adjustment light that varies the refractive index of the resin, and directing the adjustment light to the adjusting portion.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an optical device having a lightwave circuit element.  
         [0003]     2. Description of the Background Art  
         [0004]     An example of an optical device is a directional coupler that has first and second optical waveguides disposed in mutual proximity in a fixed range and lightwaves guided respectively through each of the waveguides are coupled therebetween.  
         [0005]     The optical device disclosed in Japanese Patent Application Publication No. 2003-215647 is provided with a hollow area filled with resin between the first and second optical waveguides in the optical coupling area of the directional coupler which is formed on a substrate. The temperature of the resin is adjusted via an overcladding layer or the substrate. By modifying the temperature of the resin, the refractive index of the resin is changed, and the optical characteristics (optical branching ratio, for example) of the directional coupler are thereby changed.  
         [0006]     The optical device disclosed in Japanese Patent Application Publication No. 2000-066044 (corresponding European patent application publication No. 981 064) uses a polymer material in the core area or cladding area. The refractive index of the polymer material is changed and the state (phase, for example) of the light guided through the core area is modified by changing the temperature of the polymer material.  
         [0007]     The optical device disclosed in Japanese Patent Application Publication No. 2000-111964 (corresponding U.S. Pat. No. 6,310,999) uses a polymer material in the periphery of the first and second waveguides in the optical coupling area of the directional coupler which is formed on a substrate. The refractive index of the polymer material is changed by modifying the temperature of the polymer material and thereby the optical branching ratio of the directional coupler is changed.  
         [0008]     The power required to vary the temperature of the resins is considerable with the optical devices disclosed in the prior art.  
       SUMMARY OF THE INVENTION  
       [0009]     An object of the present invention is to provide an optical device in which the optical characteristics of a lightwave circuit element can be varied with low power consumption.  
         [0010]     In order to achieve the stated object, there is provided an optical device comprising a lightwave circuit element having one or plurality of optical waveguides, and also having a refractive index adjusting portion composed of resin and located in the one or plurality of optical waveguides and/or in a portion of the area in the vicinity thereof. The lightwave circuit element comprises an adjustment-light waveguide for guiding adjustment light that varies the refractive index of the resin, and directing the adjustment light to the adjusting portion.  
         [0011]     As used herein, the phrase “area in the vicinity” refers to an area in which there is light energy being guided through one or a plurality of waveguides, and is an area in which the state, phase, for example, of the guided waves can be varied by varying the refractive index in the area and thereby the characteristics of the lightwave circuit element can be varied.  
         [0012]     Advantages of the present invention will become apparent from the following detailed description, which illustrates the best mode contemplated to carry out the invention. The invention is capable of other and different embodiments, the details of which are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the accompanying drawing and description are illustrative in nature, not restrictive. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0013]     The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawing in which like reference numerals refer to similar elements.  
         [0014]      FIG. 1  is a schematic diagram of the optical device of the first embodiment according to the present invention;  
         [0015]      FIG. 2  is a sectional view along the line II-II of  FIG. 1 ;  
         [0016]      FIG. 3  is a schematic diagram of the optical device of the second embodiment of according to the present invention;  
         [0017]      FIG. 4  is a sectional view along the line IV-IV of  FIG. 3 ; and  
         [0018]      FIG. 5  is a schematic diagram of the optical device of the specific example of the first embodiment according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
     First Embodiment  
       [0019]      FIG. 1  is a schematic diagram of the optical device of the first embodiment according to the present invention. The optical device  1  is provided with a lightwave circuit element  10 , a light source  31 , and a lens  32 . An optical waveguide  11   a , an optical waveguide  11   b , and an optical waveguide  12  are formed in the lightwave circuit element  10 , and a refractive index adjusting portion  13  composed of resin is also provided. In the lightwave circuit element  10 , the optical waveguide  11   a  extends from the end face P 1  to the end face P 2 , the optical waveguide  11   b  extends from the end face P 3  to the end face P 4 , and the optical waveguide  12  extends from the end face P 5  to the adjusting portion  13 . The optical waveguide  11   a  and optical waveguide  11   b  are mutually proximate in a fixed range, form an optical coupling area in which guided waves are coupled therebetween, and constitute a directional coupler.  
         [0020]     The refractive index adjusting portion  13  is disposed in the optical waveguides  11   a  and  11   b  or in a portion of the area in the vicinity thereof, and is heated by the incidence of light (adjustment light) guided through the optical waveguide  12 . The refractive index can be changed by the evolved heat. The adjusting portion  13  can change the optical branching characteristics of the directional coupler by changing the refractive index of the resin. In the first embodiment, a part of the adjusting portion  13  is disposed in the optical coupling area.  
         [0021]     The light source  31  outputs light (adjustment light) with a wavelength that is capable of changing the refractive index of the refractive index adjusting portion  13 . The light source  31  is configured so that the optical output power is variable or that switching is possible between light output and stoppage. The wavelength of the adjustment light output from the light source  31  is preferably located in the absorption band of resin, and more preferably matches the wavelength of the absorption peak. The refractive index of the adjusting portion  13  can be effectively changed in this case. The lens  32  condenses the light output from the light source  31  to the end face P 5 , and the light is directed from the end face P 5  to the optical waveguide  12 . The optical waveguide  12  guides the light directed to the end face P 5  toward the adjusting portion  13 , causing the light to enter the adjusting portion  13 .  
         [0022]     The refractive index adjusting portion  13  is narrow since the material is disposed in the narrow area between the optical waveguide  11   a  and the optical waveguide  11   b . Therefore, light can be efficiently directed to the adjusting portion  13  by making the width of the optical waveguide  12  in the position from which light is emitted from the optical waveguide  12  to the adjusting portion  13  substantially the same as the width of the adjusting portion  13 . Conversely, light can be efficiently directed from the exterior to the end face P 5  by increasing the width of the optical waveguide  12  in the vicinity of the end face P 5 . Therefore, the width of the optical waveguide  12  is preferably gradually narrowed from the end face P 5  side toward the adjusting portion  13  within a fixed range in the lengthwise direction in the vicinity of the adjusting portion  13 .  
         [0023]      FIG. 2  is a sectional view along the line II-II of  FIG. 1 . The lightwave circuit element  10  has an undercladding layer  15  formed on a flat substrate  14 , optical waveguides  11   a ,  11   b , and  12  and a refractive index adjusting portion  13  that are formed on a portion of the undercladding layer  15 , and an overcladding layer  16  further formed thereon. The adjusting portion  13  is disposed in a position between the optical waveguide  11   a  and optical waveguide  11   b . In this embodiment, the optical waveguides  11   a ,  11   b , and  12 ; the substrate  14 ; the undercladding layer  15 ; and the overcladding layer  16  are composed of silica glass.  
         [0024]     The refractive indexes of the optical waveguides  11   a ,  11   b , and  12  are higher than the refractive indexes of the undercladding layer  15  and the overcladding layer  16 . The refractive index of the refractive index adjusting portion  13  differs depending on the intensity of the light directed to the adjusting portion  13 . In certain cases, it is advantageous for the refractive index of the resin to be equal to the refractive index of the optical waveguides  11   a  and  11   b  at the time when the adjustment light is not being directed into the adjusting portion  13 . In other cases, it is advantageous for the refractive index of the resin to be equal to the refractive index of the optical waveguides  11   a  and  11   b  at the time when the adjustment light at a predetermined power is incident on the adjusting portion  13 .  
         [0025]     Next, a specific example of the optical device  1  is described.  FIG. 5  is a schematic diagram of the optical device of the specific example of the first embodiment according to the present invention. In this example, the optical waveguide  31   a , optical waveguide  31   b , optical waveguide  12 , substrate  14 , undercladding layer  15 , and overcladding layer  16  are principally composed of silica glass. GeO 2  is added to the optical waveguide  31   a , optical waveguide  31   b , and optical waveguide  12 . The refractive index at the wavelength of 1.55 μm is 1.45.  
         [0026]     The thicknesses of the optical waveguide  31   a  and optical waveguide  31   b  are 7.5 μm, and the widths thereof are 7.5 μm. The thickness of the optical waveguide  12  is 7.5 μm, and the width thereof is 7.5 μm in a fixed range in the lengthwise direction in the vicinity of the end face P 5 , but the width gradually decreases toward the refractive index adjusting portion  13  within a fixed range in the lengthwise direction in the vicinity of the adjusting portion  13 , and is 3 μm at the position where the light exits to the adjusting portion  13 . The space between optical waveguide  31   a  and optical waveguide  31   b  in the center portion, linear waveguide portion,  38  of the optical coupling area  37  is 5 μm, and the lengths of the optical waveguides  31   a  and  31   b  in the linear waveguide portion  38  are 160 μm.  
         [0027]     The refractive index adjusting portion  13  is an epoxy resin, of which the refractive index at a wavelength of 1.55 μm is 1.45, the temperature dependency of the refractive index is −0.0002/K. The resin  13  has absorption peaks in the vicinity of the wavelengths 1.65 μm and 1.1 μm due to its organic groups. The adjusting portion  13  is disposed from 700 μm to 40 μm away from the beginning edge of the linear waveguide portion  38 .  
         [0028]     The wavelength of the light emitted from the light source  31  is 1.61 μm, substantially matching the absorption peak wavelength of the refractive index adjusting portion  13 . The power of the light output from the light source  31  and directed to the adjusting portion  13  is 10 mW. Light with a wavelength of 1.55 μm is directed from the end face P 1  to the optical waveguide  31   a.    
         [0029]     As a result, when light with a power of 10 mW and a wavelength of 1.61 μm enters the refractive index adjusting portion  13 , the loss of light with a wavelength of 1.55 μm entering the end face P 1  and exiting from the end face P 2  is 1.5 dB, and the loss of light with a wavelength of 1.55 μm entering the end face P 1  and exiting from the end face P 4  is 5.3 dB. Conversely, when light with a wavelength of 1.61 μm is not allowed to enter the adjusting portion  13 , the loss of light with a wavelength of 1.55 μm entering the end face P 1  and exiting from the end face P 2  is 3.1 dB, and the loss of light with a wavelength of 1.55 μm entering the end face P 1  and exiting from the end face P 4  is 3.1 dB.  
         [0030]     Thus, the optical branching ratio of the optical device  1  differs based on whether light with a wavelength of 1.61 μm enters the refractive index adjusting portion  13 . Also, the optical branching ratio changes when the power of the light with a wavelength of 1.61 μm entering the adjusting portion  13  changes. It should be noted that even if light with a wavelength of 1.61 μm enters the optical waveguides  31   a  and  31   b  at the optical coupling area, the light with a wavelength of 1.61 μm is leaked away from the curved portions of the optical waveguides  31   a  and  31   b.    
         [0031]     As described above, since the light to be directed to the refractive index adjusting portion  13  is guided by the optical waveguide  12  in the first embodiment, the light is guided with good efficiency to the adjusting portion  13 , and the optical branching ratio of the directional coupler can be varied with low power consumption.  
       Second Embodiment  
       [0032]      FIG. 3  is a schematic diagram of the optical device of the second embodiment according to the present invention. The optical device  2  is provided with a lightwave circuit element  20 , a light source  31 , and a lens  32 . An optical waveguide  21   a , an optical waveguide  21   b , and an optical waveguide  22  are formed in the lightwave circuit element  20 , and a refractive index adjusting portion  23  composed of resin is also provided. In the lightwave circuit element  20 , the optical waveguide  21   a  extends from the end face P 1  to the end face P 2 , the optical waveguide  21   b  extends from the end face P 3  to the end face P 4 , and the optical waveguide  22  extends from the P 5  to the adjusting portion  23 . The optical waveguide  21   a  and optical waveguide  21   b  mutually intersect to form an intersecting area.  
         [0033]     The refractive index adjusting portion  23  is disposed in the optical waveguides  21   a  and  21   b  or in a portion of the area in the vicinity thereof, and is heated by the incidence of light (adjustment light) guided through the optical waveguide  22 . The refractive index of the adjusting portion can be changed by the evolved heat. The polymer material  23  can change the optical propagation characteristics of the optical waveguides  21   a  and  21   b  by changing the refractive index thereof. In the second embodiment, the polymer material  23  is disposed in the intersecting area.  
         [0034]     The light source  31  outputs light with a wavelength capable of changing the refractive index of the refractive index adjusting portion  23 . The light source  31  is configured so that the optical output power is variable or that switching is possible between light output and stoppage. The wavelength of the adjustment light output from the light source  31  preferably matches the wavelength of the absorption peak of the adjusting portion  23 . The refractive index of the adjusting portion  23  can be effectively changed in this case. The lens  32  condenses the light output from the light source  31  to the end face P 5 , and the light is directed from the end face P 5  to the optical waveguide  22 . The optical waveguide  22  guides the light directed to the end face P 5  toward the adjusting portion  23 , causing the light to enter the adjusting portion  23 .  
         [0035]      FIG. 4  is a sectional view along the line IV-IV of  FIG. 3 . The lightwave circuit element  20  has an undercladding layer  25  formed on a flat substrate  24 ; optical waveguides  21   a ,  21   b , and  22  formed on a portion of the undercladding layer  25  together with a refractive index adjusting portion  23  provided thereto; and an overcladding layer  26  further formed thereon. The adjusting portion  23  is disposed in the intersecting area where the optical waveguide  21   a  and optical waveguide  21   b  mutually intersect. In the second embodiment, the optical waveguides  21   a ,  21   b , and  22 ; the substrate  24 ; the undercladding layer  25 ; and the overcladding layer  26  are composed of silica glass.  
         [0036]     The refractive indexes of the  21   a ,  21   b , and  22  are higher than the refractive indexes of the undercladding layer  25  and the overcladding layer  26 . The refractive index of the refractive index adjusting portion  23  differs depending on the intensity of the light output and directed from the light source  31 . In certain cases, it is advantageous for the refractive index of the resin to be equal to the refractive index of the optical waveguides  21   a  and  21   b  when the adjustment light is not being directed into the adjusting portion  23 . In other cases, it is advantageous for the refractive index of the resin to be equal to the refractive index of the optical waveguides  21   a  and  21   b  when the adjustment light at a predetermined power is incident on the adjusting portion  23 .  
         [0037]     Next, a specific example of the optical device  2  is described. In this example, the optical waveguide  21   a , the optical waveguide  21   b , the optical waveguide  22 , the substrate  24 , undercladding layer  25 , and the overcladding layer  26  are principally composed of silica glass. GeO 2  is added to the optical waveguide  21   a , the optical waveguide  21   b , and the optical waveguide  22 , and the refractive index at the wavelength of 1.55 μm is 1.45. The heights of the optical waveguide  21   a , the optical waveguide  21   b , and the optical waveguide  22  are 7.5 μm, and the widths thereof are 7.5 μm.  
         [0038]     The refractive index adjusting portion  23  is an epoxy resin, the refractive index at a wavelength of 1.55 μm is 1.45, the temperature dependency of the refractive index is −0.0002/K, and the resin has absorption peaks in the vicinity of the wavelengths 1.65 μm and 1.1 μm due to organic groups. The adjusting portion  23  is disposed in the intersecting area.  
         [0039]     The wavelength of the light emitted from the light source  31  is 1.1 μm, substantially matching the absorption peak wavelength of the refractive index adjusting portion  23 . The power of the light directed to the adjusting portion  23  is 100 mW. Light with a wavelength of 1.55 μm is directed from the end face P 1  to the optical waveguide  21   a.    
         [0040]     As a result, when light with a power of 100 mW and a wavelength of 1.1 μm is incident on the refractive index adjusting portion  23 , the light with a wavelength of 1.55 μm directed to the end face P 1  travels through the optical waveguide  21   a  and arrives at the adjusting portion  23 , whereupon the light is reflected by the polymer material  23 , guided by the optical waveguide  21   b , and emitted to the exterior from the end face P 4 . When light with a wavelength of 1.1 μm does not enter the adjusting portion  23 , the light with a wavelength of 1.55 μm incident on the end face P 1  travels through the optical waveguide  21   a  and arrives at the adjusting portion  23 , whereupon the light is transmitted by the adjusting portion  23 , guided by the optical waveguide  21   a , and emitted to the exterior from the end face P 2 .  
         [0041]     Thus, depending on whether the light with a wavelength of 1.1 μm is incident on the refractive index adjusting portion  23 , the optical device  2  can switch between whether the light with the wavelength of 1.55 μm directed to the end face P 1  is emitted from the end face P 2  or the end face P 4 . In other words, the optical device  2  can operate as an optical switch.  
         [0042]     As described above, since the light to be directed to the refractive index adjusting portion  23  is guided by the optical waveguide  22  in the second embodiment, the light is guided with good efficiency to the adjusting portion  23 , and switching operations can be carried out with low power consumption.  
         [0043]     While this invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, the invention is not limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.  
         [0044]     The entire disclosure of Japanese Patent Application Publication No. 2004-145395 filed on May 14, 2004 including specification, claims, drawings, and summary are incorporated herein by reference in its entirety.