Abstract:
A wavelength variable light source is provided with: a light emitting layer containing therein light emitting substance having a carbon-carbon inter-atomic bond; a pair of electrodes disposed on both sides of the light emitting layer while holding the light emitting layer therebetween; a pair of main reflectors disposed on both sides of the light emitting layer so as to hold the light emitting layer therebetween, thereby to constitute an optical resonator with respect to light emitted from the light emitting layer; and refractive index modulating means disposed on the optical path of the optical resonator, wherein the refractive index modulating means can reversibly vary the length of the optical path of the optical resonator so as to control the wavelength of the light emitted from the light source.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a light source capable of varying a light emitting wavelength in a light source including an organic electroluminescence (organic EL) element or the like. 
   2. Related Art 
   An organic EL element using an amorphous thin film made of organic substance has been actively developed in recent years. In a light source for allowing the organic substance of the organic EL element or the like to emit light, it has been difficult to modulate a light emitting wavelength because the width of a light emitting spectrum has been great. For example, in a light source disclosed in Japanese Patent Publication Laid-open No. 08-315983, a light emitting layer includes an organic light emitting material having a light emitting peak wavelength ranging from 450 nm to 570 nm and a half-value breadth ranging from 100 nm to 200 nm. 
   Consequently, it has been difficult to use the light source for allowing the organic substance of the organic EL element or the like to emit the light as a light source for performing optical communications at a high speed by a frequency modulating system. Furthermore, since a response speed during the flickering of the light source has ranged from several micro seconds to several hundred micro seconds, it has been difficult to perform the optical communications at the high speed even by a pulse width modulation system or a pulse code modulation system. 
   SUMMARY OF THE INVENTION 
   A first object of the present invention is to provide a wavelength variable light source which has a narrow width of a light emitting spectrum and can readily vary a light emitting wavelength in the light source for allowing organic substance of an organic EL element or the like to emit light. 
   A second object of the present invention is to provide a wavelength variable light source which can widen an angle of view and limit the same for protection of an privacy. 
   The wavelength variable light source according to the present invention comprises: a light emitting layer containing therein light emitting substance having a carbon-carbon inter-atomic bond; a pair of electrodes disposed on both sides of the light emitting layer while holding the light emitting layer therebetween; a pair of main reflectors disposed on both sides of the light emitting layer while holding the light emitting layer therebetween, so as to constitute an optical resonator with respect to light emitted from the light emitting layer; and refractive index modulating means disposed on the optical path of the optical resonator, wherein the refractive index modulating means can reversibly vary the length of the optical path of the optical resonator so as to control the wavelength and/or directivity of the light emitted from the light source. 
   Examples of the refractive index modulating means according to the present invention include means consisting of a piezoelectric member held between the pair of electrodes. With the application of a voltage to the piezoelectric member by the pair of electrodes, the thickness of the piezoelectric member is varied by a piezoelectric effect, so that its refractive index can be varied. The above-described piezoelectric member is provided on the optical path of the optical resonator, thereby varying the length of the optical path of the optical resonator, so as to control the variations of the length of the wavelength of the light emitted from the light source. 
   Either one of the pair of electrodes holding the piezoelectric member therebetween may be constituted of either one of the pair of electrodes holding the light emitting layer therebetween. 
   Besides the above-described piezoelectric member, means having a refractive index which is varied according to a stimulus such as a voltage, a current, an electromagnetic wave, an elastic wave or heat can be used as the refractive index modulating means according to the present invention. Specifically, there can be used substance exhibiting an electrooptic effect, an acoustooptic effect, a magnetooptic effect, a thermooptic effect or a nonlinear optical effect. 
   According to the present invention, the pair of main reflectors may be constituted of the pair of electrodes holding the light emitting layer therebetween. That is to say, in the case where the electrode is formed of a metallic thin film, this metallic thin film can be used as the main reflector. 
   Since the pair of main reflectors constitute the optical resonator according to the present invention, it is preferable that the length of the optical path between the pair of main reflectors should be substantially equal to a multiple of a natural number of a half of a predetermined peak wavelength (i.e., a designed peak wavelength) of the light emitted from the light source. Specifically, for example, it is preferable that the length of the optical path between the pair of main reflectors should range from 99/200 to 101/200 of a multiple of a natural number of a predetermined peak wavelength of the light emitted from the light source. 
   According to the present invention, it is preferable that the length of the optical path from the center of a region in the light emitting layer, in which the light emission occurs most strongly, to the main reflector should be substantially equal to a multiple of a natural number of a half of a predetermined peak wavelength of the light emitted from the light source. Specifically, for example, it is preferable that the length of the optical path from the center of a region in the light emitting layer, in which the light emission occurs most strongly, to the main reflector should range from 99/200 to 101/200 of a multiple of a natural number of a predetermined peak wavelength of the light emitted from the light source. With this setting, it is possible to further enhance a wavelength selecting effect. 
   The region in the light emitting layer, in which the light emission occurs most strongly, may be located in the vicinity of the end face of the light emitting layer or at the center of the light emitting layer. Otherwise, it may be located inside of the layer adjacent to the light emitting layer. Therefore, it is preferable that the length of the optical path between the end face of the light emitting layer and the main reflector should be set as follows: 
   Namely, it is preferable that the length of the optical path from an end face nearer a region in the light emitting layer, in which the light emission occurs most strongly, to the main reflector nearer the end face should be substantially equal to or slightly smaller than a multiple of a natural number of a half of a predetermined peak wavelength of the light emitted from the light source. Specifically, for example, it is preferable that the length of the optical path from an end face nearer a region in the light emitting layer, in which the light emission occurs most strongly, to the main reflector nearer the end face should range from 101/200 to 88/200 of a multiple of a natural number of a predetermined peak wavelength of the light emitted from the light source. 
   It is preferable that the length of the optical path from an end face nearer a region in the light emitting layer, in which the light emission occurs most strongly, to the main reflector more remote from the end face should be substantially equal to or slightly greater than a multiple of a natural number of a half of a predetermined peak wavelength of the light emitted from the light source. Specifically, for example, it is preferable that the length of the optical path from an end face nearer a region in the light emitting layer, in which the light emission occurs most strongly, to the main reflector more remote from the end face should range from 99/200 to 112/200 of a multiple of a natural number of a predetermined peak wavelength of the light emitted from the light source. 
   According to the present invention, an auxiliary electrode having light transmittance may be disposed outside of at least either one of the pair of electrodes holding the light emitting layer therebetween. Such an auxiliary electrode is disposed in such a manner as to be brought into contact with the electrode made of the metallic thin film, thereby constituting a composite electrode consisting of the electrode made of the metallic thin film and the auxiliary electrode. With the auxiliary electrode having the light transmittance, the thickness of the electrode made of the metallic thin film can be reduced, thereby achieving both characteristics of conductivity and light transmittance. Consequently, the light can be emitted on the side on which the above-described auxiliary electrode is disposed. 
   It is preferable that the length of the optical path of the auxiliary electrode should be substantially equal to a multiple of a natural number of a half of a predetermined peak wavelength of the light emitted from the light source. Specifically, for example, it is preferable that the length of the optical path of the auxiliary electrode should range from 99/200 to 101/200 of a multiple of a natural number of a predetermined peak wavelength of the light emitted from the light source. 
   Although the light emitting layer according to the present invention is, for example, an organic EL light emitting layer containing therein organic EL light emitting substance, the present invention is not limited to this. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic cross-sectional view showing a wavelength variable light source in a preferred embodiment according to the present invention; 
       FIG. 2  is a schematic cross-sectional view showing a wavelength variable light source in another preferred embodiment according to the present invention; 
       FIG. 3  is a schematic cross-sectional view showing a wavelength variable light source in a further preferred embodiment according to the present invention; and 
       FIG. 4  is a schematic diagram illustrating a high-speed optical communication system by the use of the wavelength variable light source according to the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   EXAMPLE 1 
     FIG. 1  is a schematic cross-sectional view showing a wavelength variable light source in a preferred embodiment according to the present invention. A thin film (having a thickness of 200 nm) made of gold serving as a first electrode  2  is formed on a substrate  1  made of glass by sputtering method. On the first electrode  2 , a piezoelectric thin film  3  (having a thickness of 50 nm) having light transmittance is formed as refractive index modulating means by reactive sputtering method with an electron cyclotron resonance (abbreviated as “ECR”) plasma in an atmosphere of argon and nitrogen. The piezoelectric thin film  3  is made of aluminum nitride (AlN). On the piezoelectric thin film  3 , a transparent conductive thin film made of In 2 O 3—SnO   2  (ITO) (having a thickness of 50 nm) is formed as a second electrode  4  by sputtering method. 
   On the second electrode  4 , a hole injecting layer  5  (having a thickness of 9 nm) made of copper phthalocyanine (CuPc) expressed by the following chemical formula is formed: 
   
     
               
       
           
           
       
    
   
   On the hole injecting layer  5 , a hole transporting layer  6  (having a thickness of 30 nm) made of 4,4′-bis[N-(1-napthyl)-N-phenyl-amino]biphenyl (NPB) expressed by the following chemical formula is formed: 
   
     
               
       
           
           
       
    
   
   On the hole transporting layer  6 , a light emitting layer  7  (having a thickness of 150 nm) made of aluminumtris(8-hydroxyquinoline) (Alq) expressed by the following chemical formula is formed: 
   
     
               
       
           
           
       
    
   
   On the light emitting layer  7 , an electron injecting layer  10  (having a thickness of 1 nm) made of lithium fluoride (LiF) is formed. On the electron injecting layer  10 , a layer (having a thickness of 10 nm) as a third electrode  11  which has light semi-transmittance and is made of an magnesium alloy (Mg:In) containing 20% by mass of indium is formed. On the third electrode  11 , an ITO thin film (having a thickness of 136 nm) is formed by a sputtering method as an auxiliary electrode  12  having light transmittance. The third electrode  11  and the auxiliary electrode  12  constitute a composite electrode. 
   Each of the hole injecting layer  5 , the hole transporting layer  6 , the light emitting layer  7 , the electron injecting layer  10 , and the third electrode  11  are formed by a vacuum evaporation method. 
   Here, the simplified molecular formula of CuPc is expressed by C 32 H 16 N 8 Cu, which has a mol mass of 576.08 g/mol. The simplified molecular formula of NPB is expressed by C 44 H 32 N 2 , which has a mol mass of 588.75 g/mol, a melting point of 277° C., a glass transition temperature of 96° C. , an ionization potential of 5.4 eV and an energy gap between HOMO and LUMO of 3.1 eV. The simplified molecular formula of Alq is expressed by C 27 H 18 N 3 O 3 Al, which has a mol mass of 459.4318 g/mol, a thermal decomposition temperature of 412° C., a glass transition temperature of 175° C., an ionization potential of 5.7 eV and an energy gap between HOMO and LUMO of 2.7 eV without any melting point. 
   Table 1 shows below the material, refractive index, actual thickness and optical thickness of each of the above-described layers. 
                   TABLE 1                                                                  
In Table 1, reference number  2   a  designates the position of the end face of the first electrode  2 ;  7   a , the position of the end face of the light emitting layer  7 ; and  11   a , the position of the end face of the third electrode  11 .
 
   In the present example, the first electrode  2  and the third electrode  11  are disposed on both sides of the light emitting layer  7  while holding the light emitting layer  7  therebetween, and further, they constitute main reflectors, respectively. These main reflectors further constitute a Fabry-Përot type optical resonator. Moreover, with the application of a voltage to the piezoelectric thin film  3  from the first electrode  2  and the second electrode  4 , the thickness of the piezoelectric thin film  3  can be varied, and further, the refractive index of the piezoelectric thin film  3  can be varied. Consequently, the length of the optical path of the optical resonator constituted of the first electrode  2  and the third electrode  11  can be varied by varying the refractive index of the piezoelectric thin film  3 . Thus, the wavelength peak of the light emitted from the optical resonator can be varied by varying the length of the optical path of the optical resonator. 
   Table 2 shows the lengths of the optical paths between the main reflectors in the present example: namely, the length of the optical path between the end face  2   a  of the first electrode and the end face  11   a  of the third electrode, the length of the optical path between the end face  2   a  of the first electrode and the end face  7   a  of the light emitting layer, the length of the optical path between the end face  2   a  of the first electrode and the center of a region in the light emitting layer, in which light emission occurs most strongly (hereinafter referred to as “a light emitting region”), the length of the optical path between the end face  7   a  of the light emitting layer and the end face  11   a  of the third electrode, and the length of the optical path between the light emitting region and the end face  11   a  of the third electrode; and the length of the optical path within the auxiliary electrode  12 . Incidentally, in the present specification, a designed peak wavelength signifies a light emitting peak wavelength from the light source in the case where no voltage is applied to the piezoelectric thin film  3 . Moreover, in the present example, the light emitting region in the light emitting layer is located at a position inward by 2.7 nm of the optical thickness from the end face  7   a  of the light emitting layer. 
   
     
       
             
           
             
             
             
           
             
             
             
           
         
             
               TABLE 2 
             
           
           
             
                 
             
             
               Example 1 
             
             
               Light Emitting Region: Inward by 2.7 nm from End 
             
             
               Face 7a of Light Emitting Layer 
             
             
               Designed Peak Wavelength: 525 nm 
             
           
        
         
             
                 
               Length 
               Length 
             
             
                 
               of the 
               of the 
             
             
                 
               Optical 
               Optical Path/ 
             
             
                 
               Path 
               Designed Peak 
             
             
                 
               (nm) 
               Wavelength 
             
             
                 
             
           
        
         
             
               From the End Face 2a of the 1st Electrode 
               525.5 
               200/200 
             
             
               to the End Face 11a of the 3rd Electrode 
             
             
               From the End Face 2a of the 1st Electrode 
               260.1 
                99/200 
             
             
               to the End Face 7a of the Light Emitting 
             
             
               Layer 
             
             
               From the End Face 2a of the 1st Electrode 
               262.8 
               100/200 
             
             
               to the Light Emitting Region 
             
             
               From the End Face 7a of the Light Emitting 
               265.4 
               101/200 
             
             
               Layer to the End Face 11a of the 3rd 
             
             
               Electrode 
             
             
               From the Light Emitting Region to the End 
               262.7 
               100/200 
             
             
               Face 11a of the 3rd Electrode 
             
             
               Within the Auxiliary Electrode 12 
               262.5 
               100/200 
             
             
                 
             
           
        
       
     
   
   The lengths of the optical paths shown in Table 2 are values obtained by summing the optical thicknesses of the predetermined layers shown in Table 1, respectively. Here, the length of the optical path having the light emitting region at one end is obtained in consideration of 2.7 nm of the optical thickness since the light emitting region is located by 2.7 nm of the optical thickness inward of the end face  7   a  of the light emitting layer. In addition, the end face of the light emitting layer near the light emitting region is the end face  7   a , so that the length of the optical path having the end face  7   a  at one end is obtained. 
   As shown in Table 2, the length of the optical path between the main reflectors (that is, the length of the optical path from the end face  2   a  of the first electrode to the end face  11   a  of the third electrode) is substantially equal to a multiple of a natural number of a half of the designed peak wavelength. Therefore, the phase of the light of the designed peak wavelength matches with that of the optical resonator, thereby strengthening the interference of the optical wave, such that the light emission having the matched designed peak wavelength is selectively strengthened. Thus, the shape of the light emitting peak of the light to be emitted from the light source is sharpened, thereby reducing the full width at half maximum (hereinafter referred to as “the half-value breadth”). 
   Moreover, the lengths of the optical paths between the light emitting region and the main reflectors (that is, the length of the optical path from the end face  2   a  of the first electrode to the light emitting region and the length of the optical path from the light emitting region to the end face  11   a  of the third electrode) also are substantially equal to a multiple of a natural number of a half of the designed peak wavelength. Therefore, the phase of the light of the designed peak wavelength matches with that of the optical resonator, so that the light emission having the matched designed peak wavelength is more selectively strengthened. 
   Additionally, the length of the optical path from the end face  2   a  of the first electrode to the end face  7   a  of the light emitting layer ranges from 101/200 to 88/200 of a multiple of a natural number of the designed peak wavelength. In addition, the length of the optical path from the end face  7   a  of the light emitting layer to the end face  11   a  of the third electrode ranges from 99/200 to 112/200 of a multiple of a natural number of the designed peak wavelength. 
   The length of the optical path within the auxiliary electrode  12  is substantially equal to a multiple of a natural number of a half of the designed peak wavelength. Therefore, the phase of the light of the designed peak wavelength matches with that of the optical resonator, so that the light emission having the matched designed peak wavelength is more selectively strengthened. 
   The first electrode and the second electrode in the light source in the present example were electrically short-circuited to set a control voltage Vc to zero, and a current was supplied with the application of a DC voltage of 14 V between the second electrode and the third electrode. In the case of the observation on the front axis of a light emitting face parallel to the normal of the light emitting face (that is, an observation angle θ was 0), the emission of green light having a light emitting peak wavelength of 525 nm and a half-value breadth of a light emitting peak of 40 nm was observed. Even in the case where the voltage to be applied between the second electrode and the third electrode was varied, no variation of the light emitting peak wavelength was observed. In the case of the observation in a direction inclined by the angle θ from the normal of the light emitting face, the emission of green light having a light emitting peak wavelength of 493 nm and a half-value breadth of a light emitting peak of 30 nm was observed when the angle θ was 20°. Furthermore, the emission of weak blue-green light having a light emitting peak wavelength of about 450 nm was observed when the angle θ was 30°. Moreover, the light emission was hardly observed when the angle θ was 35° or more. 
   Subsequently, while an AC voltage of 200 V as the control voltage was applied to the first electrode and the second electrode, the current was supplied with the application of a DC voltage of 14 V between the second electrode and the third electrode. In the case of the observation on the front axis of the light emitting face parallel to the normal of the light emitting face (that is, the observation angle θ was 0), the emission of green light having the light emitting peak wavelength shifted to 521 nm and a half-value breadth of a light emitting peak of 40 nm was observed. In the case of the observation in a direction inclined by the angle θ from the normal of the light emitting face, the emission of green light having a light emitting peak wavelength of 489 nm and a half-value breadth of a light emitting peak of 25 nm was observed when the angle θ was 20 . Furthermore, the emission of very weak blue-green light having a light emitting peak wavelength of about 450 nm was observed when the angle θ was 30°. Moreover, no light emission was observed at all when the angle θ was 35° or more. 
   Next, while a DC voltage of 200 V was applied between the first electrode and the second electrode, the current was supplied with the application of a DC voltage of 14 V between the second electrode and the third electrode. In the case of the observation on the front axis of the light emitting face parallel to the normal of the light emitting face (that is, the observation angle θ was 0), the shift of the light emitting peak wavelength to 515 nm was observed. In the case of the observation in a direction inclined by the angle θ from the normal of the light emitting face, the emission of green light having a light emitting peak wavelength of 484 nm and a half-value breadth of a light emitting peak of 20 nm was observed when the angle θ was 20°. The light emission was hardly observed when the angle θ was 30° or more. 
   COMPARATIVE EXAMPLE 1 
   Neither the first electrode  2  and nor the piezoelectric thin film  3  in Example 1 were formed, and a second electrode  4  was formed directly on a substrate  1 . On the second electrode  4 , layers were formed in the same manner as in Example 1, thus fabricating a light source for comparison. The constitution and thickness of each of the layers were the same as those in Example 1. 
   A current was supplied with the application of a DC voltage of 14 V between the second electrode and a third electrode in the light source for comparison. In the case of the observation on the front axis of a light source parallel to the normal of a light emitting face, the emission of green light having a light emitting peak wavelength of 533 nm and a half-value breadth of a light emitting peak of 80 nm was observed. The light emitting intensity was as low as less than 40% in comparison with that in Example 1. Even in the case where the voltage to be applied between the second electrode and the third electrode was varied, no variation of the light emitting peak wavelength was observed. In the case of the observation in a direction inclined by the angle θ from the normal of the light emitting face, no variation of the light emitting peak wavelength was observed when the angle θ ranged from 0° to 75°. Although it was difficult to measure a light emitting spectrum when the angle θ exceeded 75°, no variation of the emitted light color was observed even as viewed almost sideways. 
   EXAMPLE 2 
     FIG. 2  is a schematic cross-sectional view showing a wavelength variable light source in another preferred embodiment. A thin film (having a thickness of 50 nm) made of gold serving as a first electrode  2  was formed on a (110) surface of a sapphire substrate serving as a substrate  1  by sputtering method. Subsequently, on the first electrode  2  was formed a thin film (having a thickness of 74 nm) as a piezoelectric thin film  3  made of zinc oxide (ZnO) by reactive sputtering method with an electron cyclotron resonance (abbreviated as “ECR”) plasma in an atmosphere of argon and oxygen. On the piezoelectric thin film  3 , an ITO thin film (having a thickness of 50 nm) was formed serving as a second electrode  4  by sputtering method. 
   On the second electrode  4 , the same hole injecting layer  5  and the same hole transporting layer  6 , as those in Example 1, were formed. 
   On the hole transporting layer  6 , a mixture light emitting layer (having a thickness of 35 nm) was formed by a vacuum evaporation method, as a light emitting layer  7  containing 92.5% by mass of Alq, 5% by mass of 5,6,11,12-tetraphenylnaphthacene (Rubrene) expressed below by a chemical formula and 2.5% by mass of 2-methyl-6-[2-(2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene]propane-dinitrile (DCM2) expressed by the following chemical formula. 
   
     
               
       
           
           
       
    
   
   The simplified molecular formula of Rubrene is expressed by C 42 H 28 , which has a mol mass of 532.68 g/mol. The simplified molecular formula of DCM2 is expressed by C 23 H 21 ON 3 , which has a mol mass of 355.43 g/mol. 
   On the light emitting layer  7 , a layer (having a thickness of 142 nm) was formed as an electron transporting layer  9  made of pure substance of Alq. On the electron transporting layer  9 , a layer (having a thickness of 6 nm) was formed as an electron injecting layer  10  made of lithium oxide (Li 2 O) Both of the above-described layers were formed by a vacuum evaporation method. 
   On the electron injecting layer  10 , a silver layer (having a thickness of 10 nm) was formed as a third electrode  11 ; and further, on the third electrode  11 , an ITO layer (having a thickness of 168 nm) was formed as an auxiliary electrode  12 . 
   Table 3 shows below the material, refractive index, actual thickness and optical thickness of each of the layers. 
   
     
       
             
           
         
             
               TABLE 3 
             
             
                 
             
           
           
             
               
                 
                           
                   
                       
                       
                   
                 
               
             
             
                 
             
           
        
       
     
   
   Similarly to Table 2, Table 4 shows below the lengths of optical paths in the present example. In the present example, a designed peak wavelength is 620 nm, and further, a light emitting region is located at a position inward by 2.9 nm of the optical thickness from the end face  7   a  of the light emitting layer. 
   
     
       
             
           
             
             
             
           
             
             
             
           
         
             
               TABLE 4 
             
           
           
             
                 
             
             
               Example 2 
             
             
               Light Emitting Region: Inward by 2.9 nm from End 
             
             
               Face 7a of Light Emitting Layer 
             
             
               Designed Peak wavelength: 620 nm 
             
           
        
         
             
                 
               Length 
               Length 
             
             
                 
               of the 
               of the 
             
             
                 
               Optical 
               Optical Path/  
             
             
                 
               Path 
               Designed Peak 
             
             
                 
               (nm) 
               Wavelength 
             
             
                 
             
           
        
         
             
               From the End Face 2a of the 1st Electrode 
               619.9 
               200/200 
             
             
               to the End Face 11a of the 3rd Electrode 
             
             
               From the End Face 2a of the 1st Electrode 
               307.1 
                99/200 
             
             
               to the End Face 7a of the Light Emitting 
             
             
               Layer 
             
             
               From the End Face 2a of the 1st Electrode 
               310 
               100/200 
             
             
               to the Light Emitting Region 
             
             
               From the End Face 7a of the Light Emitting 
               312.8 
               101/200 
             
             
               Layer to the End Face 11a of the 3rd 
             
             
               Electrode 
             
             
               From the Light Emitting Region to the End 
               309.9 
               100/200 
             
             
               Face 11a of the 3rd Electrode 
             
             
               Within the Auxiliary Electrode 12 
               309.1 
               100/200 
             
             
                 
             
           
        
       
     
   
   As shown in Table 4, also in the present example, the length of each of the optical paths is substantially equal to a multiple of a natural number of a half of the designed peak wavelength, like in Example 1. 
   The first electrode and the second electrode in the light source in the present example were electrically short-circuited, and a current was supplied with the application of a DC voltage of 15 V between the second electrode and the third electrode. In the case of observation on the front axis of the light source parallel to the normal of a light emitting face, the emission of red light having a light emitting peak wavelength of 620 nm and a half-value breadth of a light emitting peak of 60 nm was observed. Even in the case where the voltage to be applied between the second electrode and the third electrode was varied, no variation of the light emitting peak wavelength was observed. In the case of the observation in a direction inclined by the angle θ from the normal of the light emitting face, the emission of yellow light having a light emitting peak wavelength of 585 nm and a half-value breadth of a light emitting peak of 50 nm was observed when the angle θ was 20°. Furthermore, the emission of very weak green light having a light emitting peak wavelength of about 540 nm was observed when the angle θ was 30°. Moreover, no light emission was observed at all when the angle θ was 35° or more. 
   Subsequently, while an AC voltage of 200 V was applied between the first electrode and the second electrode, the current was supplied with the application of a DC voltage of 14 V between the second electrode and the third electrode. In the case of the observation on the front axis of the light source parallel to the normal of the light emitting face, the shift of the light emitting peak wavelength to 611 nm was observed according to the application of the AC voltage. In the case of the observation in a direction inclined by the angle θ from the normal of the light emitting face, the emission of yellow light having a light emitting peak wavelength of 574 nm and a half-value breadth of a light emitting peak of 45 nm was observed when the angle θ was 20°. Furthermore, the emission of very weak green light having a light emitting peak wavelength of about 530 nm was observed when the angle θ was 30°. Moreover, no light emission was observed at all when the angle θ was 35° or more. 
   COMPARATIVE EXAMPLE 2 
   Neither the first electrode  2  and nor the piezoelectric thin film  3  in Example 2 were formed, and a second electrode  4  was formed directly on a substrate  1 . On the second electrode  4 , layers were formed in the same manner as in Example 2, thus fabricating a light source for comparison. Here, the constitution and thickness of each of the layers were the same as those in Example 2. 
   A current was supplied with the application of a DC voltage of 15 V between the second electrode and a third electrode in the light source. Then, the emission of slightly orangy red light having a light emitting peak wavelength of 645 nm and a half-value breadth of a light emitting peak of 100 nm was observed. The light emitting intensity was as low as less than 40% in comparison with that in Example 2. Even in the case where the voltage to be applied between the second electrode and the third electrode was varied, no variation of the light emitting peak wavelength was observed. In the case of the observation in a direction inclined by the angle θ from the normal of the light emitting face, no variation of the light emitting peak wavelength was observed when the angle θ ranged from 0° to 75°. Although it was difficult to measure a light emitting spectrum when the angle θ exceeded 75°, no variation of the emitted light color was observed even as viewed almost sideways. 
   EXAMPLE 3 
     FIG. 3  is a schematic cross-sectional view showing a wavelength variable light source in a further preferred embodiment. A thin film (having a thickness of 50 nm) made of gold as a first electrode  2  was formed on a (110) surface of a sapphire substrate as a substrate  1  by sputtering method. Subsequently, on the first electrode  2 , a thin film (having a thickness of 50 nm) made of zinc oxide (ZnO) was formed as a piezoelectric thin film  3  by the same reactive sputtering method as in Example 2. On the piezoelectric thin film  3 , an ITO thin film (having a thickness of 48 nm) was formed as a second electrode  4  by sputtering method. Thereafter, a hole transporting layer  6  (having a thickness of 20 nm) made of NPB was formed. 
   On the hole transporting layer  6 , a mixture light emitting layer (having a thickness of 30 nm) was formed as a light emitting layer  7  containing 94% by mass of 4,4′-bis(carbazol-9-yl)-biphenyl (CBP) expressed below by a chemical formula and 6.0% by mass of iridium(III)bis(4,6-difluorophenyl)-pyridinato-N,C2′)picolinato (IrX) expressed by the following chemical formula. 
   
     
               
       
           
           
       
    
   
   Subsequently, on the light emitting layer  7 , a hole inhibitable electron transporting layer  8  (having a thickness of 10 nm) was formed, that is made of 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) expressed by the following chemical formula. 
   
     
               
       
           
           
       
    
   
   Thereafter, an electron transporting layer  9  (having a thickness of 85 nm) made of Alq was formed, and further, on the electron transporting layer  9  was formed an electron injecting layer  10  (having a thickness of 6 nm) made of Li 2 O. Both of the above-described layers were formed by a vacuum evaporation method. 
   Subsequently, a third electrode  11  (having a thickness of 10 nm) made of Ag and an auxiliary electrode  12  (having a thickness of 117 nm) made of ITO were formed in sequence by sputtering method. 
   The simplified molecular formula of CBP is expressed by C 36 H 24 N 2 , which has a mol mass of 484.60 g/mol. The simplified molecular formula of BCP is expressed by C 26 H 20 N 2 , which has a mol mass of 360.45 g/mol. The simplified molecular formula of IrX is expressed by C 28 H 16 N 3 O 2 Ir, which has a mol mass of 502.44 g/mol. 
   Table 5 shows below the material, refractive index, actual thickness and optical thickness of each of the layers. 
                   TABLE 5                                                                  
A designed peak wavelength of the wavelength variable light source in the present example is 470 nm. Furthermore, a light emitting region is located at a position inward by 2.3 nm of the optical thickness from the end face  7   a  of the light emitting layer.
 
   Similarly to Table 2 in Example 1, Table 6 shows below the lengths of optical paths in the present example. 
   
     
       
             
           
             
             
             
           
             
             
             
           
         
             
               TABLE 6 
             
           
           
             
                 
             
             
               Example 3 
             
             
               Light Emitting Region: Inward by 2.3 nm from End 
             
             
               Face 7a of Light Emitting Layer 
             
             
               Designed Peak wavelength: 470 nm 
             
           
        
         
             
                 
               Length 
               Length 
             
             
                 
               of the 
               of the  
             
             
                 
               Optical 
               Optical Path/  
             
             
                 
               Path 
               Designed Peak 
             
             
                 
               (nm) 
               Wavelength 
             
             
                 
             
           
        
         
             
               From the End Face 2a of the 1st Electrode 
               469.7 
               200/200 
             
             
               to the End Face 11a of the 3rd Electrode 
             
             
               From the End Face 2a of the 1st Electrode 
               232.6 
                99/200 
             
             
               to the End Face 7a of the Light Emitting 
             
             
               Layer 
             
             
               From the End Face 2a of the 1st Electrode 
               234.9 
               100/200 
             
             
               to the Light Emitting Region 
             
             
               From the End Face 7a of the Light Emitting 
               237.1 
               101/200 
             
             
               Layer to the End Face 11a of the 3rd 
             
             
               Electrode 
             
             
               From the Light Emitting Region to the End 
               234.8 
               100/200 
             
             
               Face 11a of the 3rd Electrode 
             
             
               Within the Auxiliary Electrode 12 
               234.0 
               100/200 
             
             
                 
             
           
        
       
     
   
   As shown in Table 6, the length of each of the optical paths is substantially equal to a multiple of a natural number of a half of the designed peak wavelength. 
   The first electrode and the second electrode in the light source in the present example were electrically short-circuited, and a current was supplied with the application of a DC voltage of 12 V between the second electrode and the third electrode. In the case of observation on the front axis of the light source parallel to the normal of a light emitting face, the emission of blue light having a light emitting peak wavelength of 470 nm and a half-value breadth of a light emitting peak of 35 nm was observed. Even in the case where the voltage to be applied between the second electrode and the third electrode was varied, no variation of the light emitting peak wavelength was observed. In the case of the observation in a direction inclined by the angle θ from the normal of the light emitting face, the emission of blue light having a light emitting peak wavelength of 441 nm and a half-value breadth of a light emitting peak of 30 nm was observed when the angle θ was 20°. Furthermore, the emission of very weak blue light was observed when the angle θ was 30°, wherein it was difficult to measure a light emitting spectrum. Moreover, no light emission was observed at all when the angle θ was 35° or more. 
   Subsequently, while an AC voltage of 200 V was applied between the first electrode and the second electrode, the current was supplied with the application of a DC voltage of 14 V between the second electrode and the third electrode. In the case of the observation on the front axis of the light source parallel to the normal of the light emitting face, the shift of the light emitting peak wavelength to 465 nm was observed according to the application of the AC voltage. In the case of the observation in a direction inclined by the angle θ from the normal of the light emitting face, the emission of blue light having a light emitting peak wavelength of 437 nm and a half-value breadth of a light emitting peak of 20 nm was observed when the angle θ was 20°. Furthermore, no light emission was observed at all when the angle θ was 30° or more. 
   COMPARATIVE EXAMPLE 3 
   Neither the first electrode  2  and nor the piezoelectric thin film  3  in Example 3 were formed, and a second electrode  4  was formed directly on a substrate  1 . On the second electrode  4 , layers were formed in the same manner as in Example 3, thus fabricating a light source for comparison. The constitution and thickness of each of the layers were the same as those in Example 3. 
   A current was supplied with the application of a DC voltage of 12 V between the second electrode and a third electrode in the light source. In the case of the observation on the front axis of the light source parallel to the normal of a light emitting face, the emission of considerably cyanic blue light having a light emitting peak wavelength of 480 nm and a half-value breadth of a light emitting peak of 70 nm was observed. The light emitting intensity was as low as less than 40% in comparison with that in Example 3. Even in the case where the voltage to be applied between the second electrode and the third electrode was varied, no variation of the light emitting peak wavelength was observed. In the case of the observation in a direction inclined by the angle θ from the normal of the light emitting face, no variation of the light emitting peak wavelength was observed when the angle θ ranged from 0° to 75°. Although it was difficult to measure a light emitting spectrum when the angle θ exceeded 75°, no variation of the emitted light color was observed even as viewed almost sideways. 
     FIG. 4  is a schematic diagram illustrating a high-speed optical communication system by the use of the wavelength variable light source according to the present invention. As illustrated in  FIG. 4 , a plurality of wavelength variable light sources  20   a  is disposed, thereby configuring a transmitting device  20 . Furthermore, a plurality of photodiodes  21   a  are disposed at positions corresponding to the wavelength variable light sources  20   a , respectively, thereby configuring a receiving device  21 . The wavelength of a light emitting spectrum to be emitted from the wavelength variable light source  20   a  can be varied by providing the refractive index modulating means in the wavelength variable light source  20   a  with variations in voltage corresponding to an electric signal. The photodiode  21   a  receives the variation of the light emitting spectrum, thereby converting an optical signal sent from the wavelength variable light source  20   a  into an electric signal. 
   The high-speed optical communication device illustrated in  FIG. 4  is merely one example of communication devices using the wavelength variable light source according to the present invention. In other words, the wavelength variable light source according to the present invention is not limited to the device illustrated in  FIG. 4 . 
   EXAMPLE 4 
   A light source having a structure shown below in Table 7 was fabricated in the same process as in Example 1. 
   
     
       
             
             
             
             
             
             
             
             
             
           
             
             
             
             
             
             
             
             
             
           
         
             
               TABLE 7 
             
             
                 
             
             
                 
                 
                 
                 
                 
                 
                 
                 
               Length of 
             
             
                 
                 
                 
                 
                 
                 
                 
                 
               the 
             
             
                 
                 
                 
                 
                 
                 
               Total 
               Total 
               Optical 
             
             
                 
                 
                 
                 
                 
                 
               Length of 
               Length of 
               Path 
             
             
                 
                 
                 
                 
                 
                 
               the 
               the 
               Between a 
             
             
                 
                 
                 
                 
               Actual 
               Optical 
               Optical 
               Optical 
               Main 
             
             
               Ref. 
                 
                 
               Refractive 
               Thickness 
               Thickness 
               Paths 
               Paths 
               Reflectors 
             
             
               No. 
                 
               Material 
               Index 
               (nm) 
               (nm) 
               (nm) 
               (nm) 
               (nm) 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
                1 
               Substrate 
               Glass 
                 
                 
                 
                 
                 
                 
             
             
                2 
               First Electrode 
               Al 
               — 
               200.0 
               — 
             
             
                2a 
               End Face 
                 
                 
                 
                 
                 
               (2a)  
               (2a)  
             
             
                3 
               Refractive Index 
               AlN 
               1.9 
               76.3 
               145.0 
                 
               432.3 
               580.0 
             
             
                 
               Modulating 
             
             
                 
               Means 
             
             
                4 
               Second 
               ITO 
               1.93 
               75.1 
               145.0 
               287.3 
             
             
                 
               Electrode 
             
             
                5 
               Hole Injecting 
               CuPc 
               1.76 
               9.0 
               15.8 
             
             
                 
               Layer 
             
             
                6 
               Hole 
               NPB 
               1.76 
               71.9 
               126.5 
             
             
                 
               Transporting 
             
             
                 
               Layer 
             
             
                7a 
               Interface 
                 
                 
                 
                 
                 
               (7a)  
             
             
                7 
               Light Emitting 
               Alq 
               1.76 
               83.1 
               146.3 
                 
               147.7 
             
             
                 
               Layer 
             
             
               10 
               Electron 
               LiF 
               1.39 
               1.0 
               1.4 
             
             
                 
               Injecting Layer 
             
             
               11a 
               Interface 
                 
                 
                 
                 
                 
               (11a) 
               (11a) 
             
             
               11 
               Third Electrode 
               Al 
               — 
               10.0 
               — 
             
             
               12 
               Auxiliary 
               ITO 
               1.93 
               150.3 
               290.0 
                 
               290.0 
             
             
                 
               Electrode 
             
             
                 
             
           
        
       
     
   
   A designed peak wavelength in the present example is 580 nm. Furthermore, a light emitting region is located at a position inward by 2.7 nm of the optical thickness from the end face  7   a  of the light emitting layer. 
   EXAMPLE 5 
   A light source having a structure shown below in Table 8 was fabricated in the same process as in Example 2. 
   
     
       
             
             
             
             
             
             
             
             
             
           
             
             
             
             
             
             
             
             
             
           
         
             
               TABLE 8 
             
             
                 
             
             
                 
                 
                 
                 
                 
                 
               Total 
               Total 
               Total 
             
             
                 
                 
                 
                 
               Actual 
               Optical 
               Length of 
               Length of 
               Length of 
             
             
               Ref. 
                 
                 
               Refractive 
               Thickness 
               Thickness 
               the Optical 
               the Optical 
               the Optical 
             
             
               No. 
                 
               Material 
               Index 
               (nm) 
               (nm) 
               Paths (nm) 
               Paths (nm) 
               Paths (nm) 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
                1 
               Substrate 
               Glass 
                 
                 
                 
                 
                 
                 
             
             
                2 
               First 
               Au 
               — 
               200.0 
               — 
               — 
               — 
               — 
             
             
                 
               Electrode 
             
             
                2a 
               Interface 
                 
                 
                 
                 
                 
               (2a)  
               (2a)  
             
             
                3 
               Refractive 
               ZnO 
               2 
               95.0 
               190.0 
                 
               362.9 
               720.2 
             
             
                 
               Index 
             
             
                 
               Modulating 
             
             
                 
               Means 
             
             
                4 
               Second 
               ITO 
               1.84 
               75.6 
               139.1 
               172.9 
             
             
                 
               Electrode 
             
             
                5 
               Hole 
               CuPc 
               1.72 
               8.0 
               13.8 
             
             
                 
               Injecting 
             
             
                 
               Layer 
             
             
                6 
               Hole 
               NPB 
               1.72 
               11.6 
               20.0 
             
             
                 
               Transporting 
             
             
                 
               Layer 
             
             
                7a 
               Interface 
                 
                 
                 
                 
                 
               (7a)  
             
             
                7 
               Light 
               Alq + 
               1.72 
               8.7 
               15.0 
               169.0 
               357.3 
             
             
                 
               Emitting 
               Rubrene + 
             
             
                 
               Layer 
               DCM2 
             
             
                9 
               Electron 
               Alq 
               1.72 
               89.5 
               154.0 
             
             
                 
               Transporting 
             
             
                 
               Layer 
             
             
               10 
               Electron 
               Li 2 O 
               1.39 
               6.0 
               8.3 
             
             
                 
               Injecting 
             
             
                 
               Layer 
             
             
               12 
               Auxiliary 
               ITO 
               1.84 
               97.8 
               180.0 
             
             
                 
               Electrode 
             
             
               11a 
               Interface 
                 
                 
                 
                 
                 
               (11a) 
               (11a) 
             
             
               11 
               Third 
               Ag 
               — 
               10.0 
               — 
               — 
               — 
               — 
             
             
                 
               Electrode 
             
             
                 
             
           
        
       
     
   
   A designed peak wavelength in the present example is 720 nm. Furthermore, a light emitting region is located at a position inward by 2.9 nm of the optical thickness from the end face  7   a  of the light emitting layer. 
   EXAMPLE 6 
   Dielectric layers  21  to  24 , which were different in refractive index from each other, were laminated on a glass substrate  1 , thereby obtaining a dielectric multi-layer mirror. An ITO layer as an electrode  2  layer was formed by sputtering method. 
   Thereafter, a light source having a structure shown below in Table 9 was fabricated in the same process as in Example 5. 
   
     
       
             
             
             
             
             
             
             
             
             
           
             
             
             
             
             
             
             
             
             
           
         
             
               TABLE 9 
             
             
                 
             
             
                 
                 
                 
                 
                 
                 
               Total 
               Total 
               Total 
             
             
                 
                 
                 
                 
               Actual 
               Optical 
               Length of 
               Length of 
               Length of 
             
             
               Ref. 
                 
                 
               Refractive 
               Thickness 
               Thickness 
               the Optical 
               the Optical 
               the Optical 
             
             
               No. 
                 
               Material 
               Index 
               (nm) 
               (nm) 
               Paths (nm) 
               Paths (nm) 
               Paths (nm) 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
                1 
               Substrate 
               Glass 
                 
                 
                 
                 
                 
                 
             
             
               24 
               Low Refractive 
               SiO 2   
               1.46 
               119.9 
               175.0 
             
             
                 
               Index Layer 
             
             
               23 
               High Refractive 
               TiO 2   
               2.35 
               74.5 
               175.0 
             
             
                 
               Index Layer 
             
             
               22 
               Low Refractive 
               SiO 2   
               1.46 
               119.9 
               175.0 
             
             
                 
               Index Layer 
             
             
               21 
               High Refractive 
               TiO 2   
               2.35 
               74.5 
               175.0 
             
             
                 
               Index Layer 
             
             
                2 
               First Electrode 
               ITO 
               1.84 
               97.8 
               180.0 
             
             
                2a 
               Interface 
                 
                 
                 
                 
                 
               (2a)  
               (2a)  
             
             
                3 
               Refractive Index 
               ZnO 
               2 
               95.0 
               190.0 
                 
               362.9 
               720.2 
             
             
                 
               Modulating Means 
             
             
                4 
               Second Electrode 
               ITO 
               1.84 
               75.6 
               139.1 
               172.9 
             
             
                5 
               Hole Injecting 
               CuPc 
               1.72 
               8.0 
               13.8 
             
             
                 
               Layer 
             
             
                6 
               Hole Transporting 
               NPB 
               1.72 
               11.6 
               20.0 
             
             
                 
               Layer 
             
             
                7a 
               Interface 
                 
                 
                 
                 
                 
               (7a)  
             
             
                7 
               Light Emitting 
               Alq + Rubre 
               1 .72 
               8.7 
               15.0 
               169.0 
               357.3 
             
             
                 
               Layer 
               ne + DCM2 
             
             
                9 
               Electron 
               Alq 
               1.72 
               89.5 
               154.0 
             
             
                 
               Transporting Layer 
             
             
               10 
               Electron Injecting 
               Li 2 O 
               1.39 
               6.0 
               8.3 
             
             
                 
               Layer 
             
             
               12 
               Auxiliary Electrode 
               ITO 
               1.84 
               97.8 
               180.0 
             
             
               11a 
               Interface 
                 
                 
                 
                 
                 
               (11a) 
               (11a) 
             
             
               11 
               Third Electrode 
               Ag 
               — 
               10.0 
               — 
               — 
               — 
               — 
             
             
                 
             
           
        
       
     
   
   A designed peak wavelength in the present example is 720 nm. Furthermore, a light emitting region is located at a position inward by 2.9 nm of the optical thickness from the end face  7   a  of the light emitting layer. 
   EXAMPLE 7 
   A substrate  1  was made of quartz glass. An electrode  2   b  was formed by depositing a silver thin film in the vacuum by an electron beam heating method. 
   Subsequently, on the electrode  2   b , a zinc oxide (ZnO) layer was formed as a piezoelectric thin film  3   b  by laser ablation method using a KrF excimer pulse laser having a wavelength of 248 nm. At that time, the partial pressure of oxygen was set within the range of 10 −6  Pa to 10 −7  Pa, and further, the temperature of the substrate was set to 600° C. The temperature of the substrate was able to be set variably within the range of 500° C. to 700° C. As a result of an analysis of the resultant zinc oxide (ZnO) layer by X-ray diffraction, it was confirmed that the c-axes of zinc oxide were aligned in a direction perpendicular to the surface of the substrate. 
   Subsequently, on the piezoelectric thin film  3   b , an ITO layer was formed as an auxiliary electrode  2   c  by sputtering method. 
   Next, on the auxiliary electrode  2   c , a silver thin film was formed as a first electrode  2  by sputtering method. 
   Thereafter, on the electrode  2 , a zinc oxide layer was formed as a piezoelectric thin film  3  by the laser ablation method in the same manner as described above. 
   And then, on the piezoelectric thin film  3 , an ITO layer was formed as an electrode  4  by sputtering method. 
   Thereafter, a light source having a structure shown below in Table 10 was fabricated in the same process as in Example 3. IrX for use in a light emitting layer  7  was replaced by an organic metal compound ReX containing rhenium therein, expressed by the following chemical formula. 
   
     
       
             
           
             
             
             
             
             
             
             
             
             
           
             
             
             
             
             
             
             
             
             
           
         
             
               TABLE 10 
             
           
           
             
                 
             
             
               
                 
                           
                   
                       
                       
                   
                 
               
             
             
                 
             
           
        
         
             
                 
                 
                 
                 
                 
                 
               Total 
               Total 
               Total 
             
             
                 
                 
                 
                 
               Actual 
               Optical 
               Length of 
               Length of 
               Length of 
             
             
               Ref. 
                 
                 
               Refractive 
               Thickness 
               Thickness 
               the Optical 
               the Optical 
               the Optical 
             
             
               No. 
                 
               Material 
               Index 
               (nm) 
               (nm) 
               Paths (nm) 
               Paths (nm) 
               Paths (nm) 
             
             
                 
             
           
        
         
             
               1 
               Substrate 
               Quartz 
                 
                 
                 
                 
                 
                 
             
             
                 
                 
               Glass 
             
             
               2b 
               Electrode 2b 
               Ag 
               — 
               100.0 
               — 
               — 
               — 
               — 
             
             
               3b 
               Refractive Index 
               ZnO 
               2 
               67.5 
               135.0 
                 
               265.0 
             
             
                 
               Modulating 
             
             
                 
               Means 
             
             
               2c 
               Auxiliary 
               ITO 
               2 
               65.0 
               130.0 
             
             
                 
               Electrode 
             
             
               2 
               First Electrode 
               Ag 
               — 
               10.0 
               — 
               — 
               — 
               — 
             
             
               2a 
               Interface 
                 
                 
                 
                 
                 
               (2a) 
               (2a) 
             
             
               3 
               Refractive Index 
               ZnO 
               2 
               67.5 
               135.0 
                 
               263.0 
               530.0 
             
             
                 
               Modulating 
             
             
                 
               Means 
             
             
               4 
               Second 
               ITO 
               2 
               49.0 
               98.0 
               128.0 
             
             
                 
               Electrode 
             
             
               6 
               Hole 
               NPB 
               1.83 
               16.4 
               30.0 
             
             
                 
               Transporting 
             
             
                 
               Layer 
             
             
               7a 
               Interface 
                 
                 
                 
                 
                 
               (7a) 
             
             
               7 
               Light Emitting 
               CBP + 
               1.83 
               60.3 
               110.4 
                 
               267.0 
             
             
                 
               Layer 
               ReX 
             
             
               8 
               Hole Inhibitable 
               BCP 
               1.83 
               10.0 
               18.3 
               156.6 
             
             
                 
               Electron 
             
             
                 
               Transporting 
             
             
                 
               Layer 
             
             
               9 
               Electron 
               Alq 
               1.83 
               71.0 
               130.0 
             
             
                 
               Transporting 
             
             
                 
               Layer 
             
             
               10 
               Electron Injecting 
               Li 2 O 
               1.39 
               6.0 
               8.3 
             
             
                 
               Layer 
             
             
               11a 
               Interface 
                 
                 
                 
                 
                 
               (11a)  
               (11a)  
             
             
               11 
               Third Electrode 
               Ag 
               — 
               10.0 
               — 
               — 
               — 
               — 
             
             
               12 
               Auxiliary 
               ITO 
               2 
               65.5 
               131.0 
                 
               131.0 
             
             
                 
               Electrode 
             
             
                 
             
           
        
       
     
   
   A designed peak wavelength of a wavelength variable light source in the present example is 530 nm. Furthermore, alight emitting region is located at a position inward by 2.0 nm of the optical thickness from the end face  7   a  of the light emitting layer. 
   (Light Emitting Characteristics) 
   Light emitting characteristics in each of the above-described examples and comparative examples are shown below in Tables 11 to 14. 
   
     
       
             
             
             
             
             
             
             
             
           
             
             
             
             
             
             
             
             
           
         
             
               TABLE 11 
             
             
                 
             
             
                 
                 
                 
                 
               Light 
               Half-Value 
                 
                 
             
             
                 
                 
                 
                 
               Emitting 
               Breadth of 
             
             
                 
               Control 
               Control 
                 
               Peak 
               Light 
             
             
                 
               Voltage 
               Voltage 
               θ 
               Wavelength 
               Emitting 
               Relative 
               Emitted Light 
             
             
                 
               Vc/V 
               Vc 
               (°) 
               (nm) 
               Peak (nm) 
               Luminance 
               Color 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
               Ex. 1 
               0 
               none 
               0 
               525 
               40 
               1 
               Green 
             
             
               Ex. 1 
               0 
               none 
               10 
               517 
               39 
               0.9 
               Green 
             
             
               Ex. 1 
               0 
               none 
               20 
               493 
               30 
               0.6 
               Green 
             
             
               Ex. 1 
               0 
               none 
               30 
               450 
               Cannot be 
               0.1 
               Blue-Green 
             
             
                 
                 
                 
                 
                 
               Measured 
             
             
               Ex. 1 
               0 
               none 
               35 
               Cannot be 
               Cannot be 
               0.01 
               Cannot be 
             
             
                 
                 
                 
                 
               Measured 
               Measured 
                 
               Measured 
             
             
               Ex. 1 
               200 
               a.c. 
               0 
               521 
               40 
               1 
               Green 
             
             
               Ex. 1 
               200 
               a.c. 
               10 
               513 
               38 
               0.85 
               Green 
             
             
               Ex. 1 
               200 
               a.c. 
               20 
               489 
               25 
               0.5 
               Green 
             
             
               Ex. 1 
               200 
               a.c. 
               30 
               450 
               Cannot be 
               0.1 
               Blue-Green 
             
             
                 
                 
                 
                 
                 
               Measured 
             
             
               Ex. 1 
               200 
               a.c. 
               35 
               No Light 
               No Light 
               0 
               No Light Emission 
             
             
                 
                 
                 
                 
               Emission 
               Emission 
             
             
               Ex. 1 
               200 
               d.c. 
               0 
               515 
               35 
               0.95 
               Green 
             
             
               Ex. 1 
               200 
               d.c. 
               10 
               507 
               34 
               0.8 
               Green 
             
             
               Ex. 1 
               200 
               d.c. 
               20 
               484 
               20 
               0.3 
               Green 
             
             
               Ex. 1 
               200 
               d.c. 
               30 
               Cannot be 
               Cannot be 
               0.05 
               Cannot be 
             
             
                 
                 
                 
                 
               Measured 
               Measured 
                 
               Measured 
             
             
               Ex. 1 
               200 
               d.c. 
               35 
               No Light 
               No Light 
               0 
               No Light Emission 
             
             
                 
                 
                 
                 
               Emission 
               Emission 
             
             
               Comp. Ex. 1 
               none 
               none 
               0 
               533 
               80 
               1 
               Green 
             
             
               Comp. Ex. 1 
               none 
               none 
               45 
               533 
               80 
               0.6 
               Green 
             
             
               Comp. Ex. 1 
               none 
               none 
               75 
               533 
               80 
               0.2 
               Green 
             
             
               Ex. 4 
               0 
               none 
               0 
               550 
               25 
               0.8 
               Green 
             
             
               Ex. 4 
               0 
               none 
               10 
               540 
               30 
               0.9 
               Green 
             
             
               Ex. 4 
               0 
               none 
               20 
               530 
               40 
               1 
               Green 
             
             
               Ex. 4 
               0 
               none 
               30 
               520 
               40 
               1 
               Green 
             
             
               Ex. 4 
               0 
               none 
               35 
               480 
               18 
               0.7 
               Green 
             
             
               Ex. 4 
               0 
               none 
               40 
               460 
               15 
               0.5 
               Blue-Green 
             
             
               Ex. 4 
               0 
               none 
               45 
               450 
               Cannot be 
               0.1 
               Blue-Green 
             
             
                 
                 
                 
                 
                 
               Measured 
             
             
               Ex. 4 
               0 
               none 
               50 
               No Light 
               No Light 
               0 
               No Light Emission 
             
             
                 
                 
                 
                 
               Emission 
               Emission 
             
             
               Ex. 4 
               100 
               d.c. 
               0 
               535 
               35 
               0.9 
               Green 
             
             
               Ex. 4 
               100 
               d.c. 
               10 
               530 
               40 
               1 
               Green 
             
             
               Ex. 4 
               100 
               d.c. 
               20 
               515 
               38 
               0.9 
               Green 
             
             
               Ex. 4 
               100 
               d.c. 
               30 
               470 
               15 
               0.3 
               Blue-Green 
             
             
               Ex. 4 
               100 
               d.c. 
               35 
               450 
               Cannot be 
               0.1 
               Blue-Green 
             
             
                 
                 
                 
                 
                 
               Measured 
             
             
               Ex. 4 
               100 
               d.c. 
               40 
               No Light 
               No Light 
               0 
               No Light Emission 
             
             
                 
                 
                 
                 
               Emission 
               Emission 
             
             
               Comp. Ex.4 
               none 
               none 
               0 
               533 
               80 
               1 
               Green 
             
             
               Comp. Ex.4 
               none 
               none 
               45 
               533 
               80 
               0.6 
               Green 
             
             
               Comp. Ex.4 
               none 
               none 
               75 
               533 
               80 
               0.2 
               Green 
             
             
                 
             
           
        
       
     
   
   
     
       
             
             
             
             
             
             
             
             
           
             
             
             
             
             
             
             
             
           
         
             
               TABLE 12 
             
             
                 
             
             
                 
                 
                 
                 
                 
               Half-Value 
                 
                 
             
             
                 
                 
                 
                 
               Light Emitting 
               Breadth of 
             
             
                 
               Control 
               Control 
                 
               Peak 
               Light 
             
             
                 
               Voltage 
               Voltage 
               θ 
               Wavelength 
               Emitting 
               Relative 
               Emitted Light 
             
             
                 
               Vc/V 
               Vc 
               (°) 
               (nm) 
               Peak (nm) 
               Luminance 
               Color 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
               Ex. 2 
               0 
               none 
               0 
               620 
                60 
               1 
               Red 
             
             
               Ex. 2 
               0 
               none 
               10 
               611 
                55 
               0.8 
               Red 
             
             
               Ex. 2 
               0 
               none 
               20 
               585 
                50 
               0.5 
               Yellow 
             
             
               Ex. 2 
               0 
               none 
               30 
               540 
               Cannot be 
               0.1 
               Green 
             
             
                 
                 
                 
                 
                 
               Measured 
             
             
               Ex. 2 
               0 
               none 
               35 
               No Light 
               No Light 
               0 
               No Light 
             
             
                 
                 
                 
                 
               Emission 
               Emission 
                 
               Emission 
             
             
               Ex. 2 
               200 
               a.c. 
               0 
               611 
                60 
               1 
               Yellow 
             
             
               Ex. 2 
               200 
               a.c. 
               10 
               602 
                50 
               0.7 
               Yellow 
             
             
               Ex. 2 
               200 
               a.c. 
               20 
               574 
                45 
               0.2 
               Yellow 
             
             
               Ex. 2 
               200 
               a.c. 
               30 
               530 
               Cannot be 
               0.1 
               Green 
             
             
                 
                 
                 
                 
                 
               Measured 
             
             
               Ex. 2 
               200 
               a.c. 
               35 
               No Light 
               No Light 
               0 
               No Light 
             
             
                 
                 
                 
                 
               Emission 
               Emission 
                 
               Emission 
             
             
               Ex. 2 
               100 
               d.c. 
               0 
               605 
                50 
               0.8 
               Yellow 
             
             
               Ex. 2 
               100 
               d.c. 
               10 
               600 
                45 
               0.6 
               Yellow 
             
             
               Ex. 2 
               100 
               d.c. 
               20 
               570 
               Cannot be 
               0.1 
               Yellow 
             
             
                 
                 
                 
                 
                 
               Measured 
             
             
               Ex. 2 
               100 
               d.c. 
               30 
               No Light 
               No Light 
               0 
               No Light 
             
             
                 
                 
                 
                 
               Emission 
               Emission 
                 
               Emission 
             
             
               Ex. 2 
               100 
               d.c. 
               35 
               No Light 
               No Light 
               0 
               No Light 
             
             
                 
                 
                 
                 
               Emission 
               Emission 
                 
               Emission 
             
             
               Comp. Ex.2 
               none 
               none 
               0 
               645 
               100 
               1 
               Red 
             
             
               Comp. Ex.2 
               none 
               none 
               45 
               645 
               100 
               0.6 
               Red 
             
             
               Comp. Ex.2 
               none 
               none 
               75 
               645 
               100 
               0.2 
               Red 
             
             
               Comp. Ex.5 
               none 
               none 
               0 
               645 
               100 
               1 
               Red 
             
             
               Comp. Ex.5 
               none 
               none 
               45 
               645 
               100 
               0.6 
               Red 
             
             
               Comp. Ex.5 
               none 
               none 
               75 
               645 
               100 
               0.2 
               Red 
             
             
                 
             
           
        
       
     
   
   
     
       
             
             
             
             
             
             
             
             
           
             
             
             
             
             
             
             
             
           
         
             
               TABLE 13 
             
             
                 
             
             
                 
                 
                 
                 
               Light 
               Half-Value 
                 
                 
             
             
                 
                 
                 
                 
               Emitting 
               Breadth of 
             
             
                 
               Control 
               Control 
                 
               Peak 
               Light 
             
             
                 
               Voltage 
               Voltage 
               θ 
               Wavelength 
               Emitting 
               Relative 
               Emitted Light 
             
             
                 
               Vc/V 
               Vc 
               (°) 
               (nm) 
               Peak (nm) 
               Luminance 
               Color 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
               Ex. 5 
               0 
               none 
               0 
               710 
               30 
               0.6 
               Red 
             
             
               Ex. 5 
               0 
               none 
               10 
               700 
               40 
               0.7 
               Red 
             
             
               Ex. 5 
               0 
               none 
               20 
               680 
               55 
               1 
               Red 
             
             
               Ex. 5 
               0 
               none 
               30 
               640 
               60 
               1 
               Red 
             
             
               Ex. 5 
               0 
               none 
               35 
               620 
               50 
               0.6 
               Red 
             
             
               Ex. 5 
               0 
               none 
               40 
               600 
               30 
               0.2 
               Red 
             
             
               Ex. 5 
               0 
               none 
               45 
               Cannot be 
               Cannot be 
               0.05 
               Red 
             
             
                 
                 
                 
                 
               Measured 
               Measured 
             
             
               Ex. 5 
               0 
               none 
               50 
               No Light 
               No Light 
               0 
               No Light 
             
             
                 
                 
                 
                 
               Emission 
               Emission 
                 
               Emission 
             
             
               Ex. 5 
               100 
               d.c. 
               0 
               680 
               60 
               1 
               Red 
             
             
               Ex. 5 
               100 
               d.c. 
               10 
               680 
               60 
               1 
               Red 
             
             
               Ex. 5 
               100 
               d.c. 
               20 
               650 
               60 
               0.7 
               Red 
             
             
               Ex. 5 
               100 
               d.c. 
               30 
               600 
               40 
               0.2 
               Red 
             
             
               Ex. 5 
               100 
               d.c. 
               35 
               580 
               Cannot be 
               0.1 
               Red 
             
             
                 
                 
                 
                 
                 
               Measured 
             
             
               Ex. 5 
               100 
               d.c. 
               40 
               No Light 
               No Light 
               0 
               No Light 
             
             
                 
                 
                 
                 
               Emission 
               Emission 
                 
               Emission 
             
             
               Ex. 6 
               0 
               none 
               0 
               710 
               30 
               0.5 
               Red 
             
             
               Ex. 6 
               0 
               none 
               10 
               700 
               35 
               0.6 
               Red 
             
             
               Ex. 6 
               0 
               none 
               20 
               680 
               50 
               1 
               Red 
             
             
               Ex. 6 
               0 
               none 
               30 
               640 
               50 
               0.9 
               Red 
             
             
               Ex. 6 
               0 
               none 
               35 
               620 
               50 
               0.5 
               Red 
             
             
               Ex. 6 
               0 
               none 
               40 
               600 
               30 
               0.1 
               Red 
             
             
               Ex. 6 
               0 
               none 
               45 
               Cannot be 
               Cannot be 
               0.05 
               Red 
             
             
                 
                 
                 
                 
               Measured 
               Measured 
             
             
               Ex. 6 
               0 
               none 
               50 
               No Light 
               No Light 
               0 
               No Light 
             
             
                 
                 
                 
                 
               Emission 
               Emission 
                 
               Emission 
             
             
               Ex. 6 
               100 
               d.c. 
               0 
               680 
               55 
               1 
               Red 
             
             
               Ex. 6 
               100 
               d.c. 
               10 
               680 
               55 
               0.9 
               Red 
             
             
               Ex. 6 
               100 
               d.c. 
               20 
               650 
               55 
               0.6 
               Red 
             
             
               Ex. 6 
               100 
               d.c. 
               30 
               600 
               35 
               0.1 
               Red 
             
             
               Ex. 6 
               100 
               d.c. 
               35 
               Cannot be 
               Cannot be 
               0.05 
               Red 
             
             
                 
                 
                 
                 
               Measured 
               Measured 
             
             
               Ex. 6 
               100 
               d.c. 
               40 
               No Light 
               No Light 
               0 
               No Light 
             
             
                 
                 
                 
                 
               Emission 
               Emission 
                 
               Emission 
             
             
               Comp. Ex.6 
               none 
               none 
               0 
               645 
               100 
               1 
               Red 
             
             
               Comp. Ex.6 
               none 
               none 
               45 
               645 
               100 
               0.6 
               Red 
             
             
               Comp. Ex.6 
               none 
               none 
               75 
               645 
               100 
               0.2 
               Red 
             
             
                 
             
           
        
       
     
   
   
     
       
             
             
             
             
             
             
             
             
           
             
             
             
             
             
             
             
             
           
         
             
               TABLE 14 
             
             
                 
             
             
                 
                 
                 
                 
               Light 
               Half-Value 
                 
                 
             
             
                 
                 
                 
                 
               Emitting 
               Breadth of 
             
             
                 
               Control 
               Control 
                 
               Peak 
               Light 
             
             
                 
               Voltage 
               Voltage 
               θ 
               Wavelength 
               Emitting 
               Relative 
               Emitted Light 
             
             
                 
               Vc/V 
               Vc 
               (° ) 
               (nm) 
               Peak (nm) 
               Luminance 
               Color 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
               Ex. 3 
               0 
               none 
               0 
               470 
               35 
               1 
               Blue 
             
             
               Ex. 3 
               0 
               none 
               10 
               465 
               35 
               0.8 
               Blue 
             
             
               Ex. 3 
               0 
               none 
               20 
               441 
               30 
               0.5 
               Blue 
             
             
               Ex. 3 
               0 
               none 
               30 
               Cannot be 
               Cannot be 
               0.1 
               Blue 
             
             
                 
                 
                 
                 
               Measured 
               Measured 
             
             
               Ex. 3 
               0 
               none 
               35 
               No Light 
               No Light 
               0 
               No Light 
             
             
                 
                 
                 
                 
               Emission 
               Emission 
                 
               Emission 
             
             
               Ex. 3 
               200 
               a.c. 
               0 
               465 
               35 
               1 
               Blue 
             
             
               Ex. 3 
               200 
               a.c. 
               10 
               460 
               35 
               0.7 
               Blue 
             
             
               Ex. 3 
               200 
               a.c. 
               20 
               437 
               20 
               0.3 
               Blue 
             
             
               Ex. 3 
               200 
               a.c. 
               30 
               No Light 
               No Light 
               0 
               No Light 
             
             
                 
                 
                 
                 
               Emission 
               Emission 
                 
               Emission 
             
             
               Ex. 3 
               200 
               a.c. 
               35 
               No Light 
               No Light 
               0 
               No Light 
             
             
                 
                 
                 
                 
               Emission 
               Emission 
                 
               Emission 
             
             
               Ex. 3 
               100 
               d.c. 
               0 
               450 
               30 
               0.8 
               Blue 
             
             
               Ex. 3 
               100 
               d.c. 
               10 
               445 
               25 
               0.5 
               Blue 
             
             
               Ex. 3 
               100 
               d.c. 
               20 
               435 
               20 
               0.1 
               Blue 
             
             
               Ex. 3 
               100 
               d.c. 
               30 
               No Light 
               No Light 
               0 
               No Light 
             
             
                 
                 
                 
                 
               Emission 
               Emission 
                 
               Emission 
             
             
               Ex. 3 
               100 
               d.c. 
               35 
               No Light 
               No Light 
               0 
               No Light 
             
             
                 
                 
                 
                 
               Emission 
               Emission 
                 
               Emission 
             
             
               Comp. Ex. 3 
               none 
               none 
               0 
               480 
               70 
               1 
               Blue 
             
             
               Comp. Ex. 3 
               none 
               none 
               75 
               480 
               70 
               0.2 
               Blue 
             
             
               Comp. Ex. 7 
               none 
               none 
               0 
               460 
               50 
               1 
               Blue 
             
             
               Comp. Ex. 7 
               none 
               none 
               75 
               460 
               50 
               0.2 
               Blue 
             
             
               Ex. 7 
               0 
               none 
               0 
               500 
               50 
               0.8 
               Blue 
             
             
               Ex. 7 
               0 
               none 
               10 
               480 
               40 
               0.9 
               Blue 
             
             
               Ex. 7 
               0 
               none 
               20 
               460 
               30 
               1 
               Blue 
             
             
               Ex. 7 
               0 
               none 
               30 
               460 
               30 
               1 
               Blue 
             
             
               Ex. 7 
               0 
               none 
               35 
               440 
               25 
               0.8 
               Blue 
             
             
               Ex. 7 
               0 
               none 
               40 
               420 
               20 
               0.4 
               Blue 
             
             
               Ex. 7 
               0 
               none 
               45 
               400 
               Cannot be 
               0.1 
               Blue 
             
             
                 
                 
                 
                 
                 
               Measured 
             
             
               Ex. 7 
               0 
               none 
               50 
               No Light 
               No Light 
               0 
               No Light 
             
             
                 
                 
                 
                 
               Emission 
               Emission 
                 
               Emission 
             
             
               Ex. 7 
               100 
               d.c. 
               0 
               460 
               35 
               1 
               Blue 
             
             
               Ex. 7 
               100 
               d.c. 
               10 
               460 
               30 
               1 
               Blue 
             
             
               Ex. 7 
               100 
               d.c. 
               20 
               445 
               25 
               0.9 
               Blue 
             
             
               Ex. 7 
               100 
               d.c. 
               30 
               400 
               Cannot be 
               0.1 
               Blue 
             
             
                 
                 
                 
                 
                 
               Measured 
             
             
               Ex. 7 
               100 
               d.c. 
               35 
               No Light 
               No Light 
               0 
               No Light 
             
             
                 
                 
                 
                 
               Emission 
               Emission 
                 
               Emission 
             
             
               Ex. 7 
               100 
               d.c. 
               40 
               No Light 
               No Light 
               0 
               No Light 
             
             
                 
                 
                 
                 
               Emission 
               Emission 
                 
               Emission 
             
             
                 
             
           
        
       
     
   
   As described above, according to the present invention, it is possible to reduce the light emitting spectrum width and readily vary the light emitting wavelength in the light source for allowing the organic substance in the organic EL element to emit the light. Thus, the wavelength variable light source according to the present invention can be used in the high-speed optical communications or the like.