Semiconductor optical amplifier

Abstract

A semiconductor optical amplifier includes: a laminated structure sequentially including a first compound semiconductor layer composed of GaN compound semiconductor and having a first conductivity type, a third compound semiconductor layer having a light amplification region composed of GaN compound semiconductor, and a second compound semiconductor layer composed of GaN compound semiconductor and having a second conductivity type; a second electrode formed on the second compound semiconductor layer; and a first electrode electrically connected to the first compound semiconductor layer. The laminated structure has a ridge stripe structure. When widths of the ridge stripe structure in a light output end face and the ridge stripe structure in a light incident end face are respectively W out , and W in , W out >W in is satisfied. A carrier non-injection region is provided in an internal region of the laminated structure from the light output end face along an axis line of the semiconductor optical amplifier.

What is claimed is: 
     
       1. A semiconductor optical amplifier comprising:
 a laminated structure including (i) a first compound semiconductor layer that has a first conductivity type and is composed of GaN compound semiconductor, (ii) a second compound semiconductor layer that has a second conductivity type different from the first conductivity type and is composed of GaN compound semiconductor, and (iii) a third compound semiconductor layer that has a light amplification region composed of GaN compound semiconductor, the first compound semiconductor layer, the third compound semiconductor layer, and the second compound semiconductor layer being sequentially layered; 
 a second electrode on the second compound semiconductor layer; and 
 a first electrode electrically connected to the first compound semiconductor layer, 
 wherein,
 the laminated structure has a ridge stripe structure, 
 when a width of the ridge stripe structure in a light output end face is W out , and a width of the ridge stripe structure in a light incident end face is W in , W out >W in  is satisfied, and 
 a carrier non-injection region is provided in the laminated structure, the carrier non-injection region extending from the light output end face of the ridge stripe structure and towards the light incident end face of the ridge stripe structure along an axis line of the semiconductor optical amplifier, the first, second, and third compound semiconductor layers being present in the carrier non-injection region, and the second electrode not being present in the carrier non-injection region. 
 
 
     
     
       2. The semiconductor optical amplifier according to  claim 1 , wherein W out  is greater or equal to 5 μm. 
     
     
       3. The semiconductor optical amplifier according to  claim 1 , wherein W in  is from 1.4 μm to 2.0 μm, both inclusive. 
     
     
       4. The semiconductor optical amplifier according to  claim 1 ,
 wherein the second electrode is composed of a first section and a second section separated by an isolation trench, and 
 the second section of the second electrode is provided in the carrier non-injection region. 
 
     
     
       5. The semiconductor optical amplifier according to  claim 4 , wherein a voltage equal to or less than a built-in voltage is applied to the second section of the second electrode. 
     
     
       6. The semiconductor optical amplifier according to  claim 1 , wherein the axis line of the semiconductor optical amplifier intersects with an axis line of the ridge stripe structure at a given angle that ranges from 0.1 to 10 degrees. 
     
     
       7. The semiconductor optical amplifier according to  claim 1 , wherein a value of (width of the ridge stripe structure in the light output end face)/(width of laser light outputted from the semiconductor optical amplifier) is from 1.1 to 10, both inclusive. 
     
     
       8. A light output device comprising:
 a laser light source; and   a semiconductor optical amplifier according claim 1 that optically amplifies laser light from the laser light source and outputs amplified light.    
     
     
       9. The light output device according to claim 8, further comprising a mirror and a light isolator positioned such that laser light output from the laser light source passes through the light isolator and then is reflected by the mirror.  
     
     
       10. The light output device according to claim 9, further comprising a half-wave plate and a lens positioned such that laser light reflected by the mirror passes through the half-wave plate and lens and then enters the semiconductor optical amplifier.  
     
     
       11. The light output device according to claim 10, wherein the light isolator is positioned to prevent light returned from the semiconductor optical amplifier from returning to the laser light source.  
     
     
       12. The light output device according to claim 11, further comprising an output lens, wherein the laser light is optically amplified in the semiconductor optical amplifier, and is output outside the system through the output lens. 
     
     
       13. The light output device according to claim 8, wherein the laser light source is a mode locking laser diode device, and pulse laser light output from the mode locking laser diode device enters the semiconductor optical amplifier.  
     
     
       14. A light output device comprising:
 a laser light source;   a semiconductor optical amplifier according claim 1;   an alignment device that adjusts a relative position of the semiconductor optical amplifier with respect to laser light entering the semiconductor optical amplifier; and   a semiconductor optical amplifier control device that controls operation of the semiconductor optical amplifier.    
     
     
       15. The light output device according to claim 14, further comprising a mirror and a light isolator positioned such that laser light output from the laser light source passes through the light isolator and then is reflected by the mirror.  
     
     
       16. The light output device according to claim 15, further comprising a half-wave plate and a lens positioned such that laser light reflected by the mirror passes through the half-wave plate and lens and then enters the semiconductor optical amplifier.  
     
     
       17. The light output device according to claim 16, wherein the light isolator is positioned to prevent light returned from the semiconductor optical amplifier from returning to the laser light source.  
     
     
       18. The light output device according to claim 17, further comprising an output lens, wherein the laser light is optically amplified in the semiconductor optical amplifier, and is output outside the system through the output lens.  
     
     
       19. The light output device according to claim 14, wherein the laser light source is a mode locking laser diode device, and pulse laser light output from the mode locking laser diode device enters the semiconductor optical amplifier.  
     
     
       20. The light output device according to claim 14, wherein the reflecting mirror, the half-wave plate, and the lens are on the alignment device. 
     
     
       21. The light output device according to claim 20, wherein the alignment device comprises an XYZ stage and when the thickness direction of the laminated structure in the semiconductor optical amplifier is the Y direction and an axis line direction of the semiconductor optical amplifier is the Z direction, the reflecting mirror and the lens are moved in the X direction, the Y direction, and the Z direction by the alignment device.  
     
     
       22. A light output device comprising:
 a laser;   a semiconductor optical amplifier that amplifies light output by the laser;   a light isolator between the laser and the semiconductor optical amplifier;   a mirror between the light isolator and the semiconductor optical amplifier;   a half-wave plate between the mirror and the semiconductor optical amplifier; and   a lens between the half-wave plate and the semiconductor optical amplifier,   wherein,
 (1) the semiconductor optical amplifier comprises
 (a) a laminated structure including (i) a first compound semiconductor layer that has a first conductivity type and is composed of GaN compound semiconductor, (ii) a second compound semiconductor layer that has a second conductivity type different from the first conductivity type and is composed of GaN compound semiconductor, and (iii) a third compound semiconductor layer that has a light amplification region composed of GaN compound semiconductor, the first compound semiconductor layer, the third compound semiconductor layer, and the second compound semiconductor layer are sequentially layered, 
 (b) a second electrode on the second compound semiconductor layer, and 
 (c) a first electrode electrically connected to the first compound semiconductor layer, 
 
 (2) the laminated structure has a ridge stripe structure, and 
 (3) a carrier non-injection region is provided in the laminated structure, the carrier non-injection region extending from the light output end face of the ridge stripe structure and towards the light incident end face of the ridge stripe structure along an axis line of the semiconductor optical amplifier, the first, second, and third compound semiconductor layers being present in the carrier non-injection region, and the second electrode not being present in the carrier non-injection region.  
   
     
     
       23. The light output device of claim 22, wherein, for the semiconductor optical amplifier, when a width of the ridge stripe structure in a light output end face is W out  and a width of the ridge stripe structure in a light incident end face is W in , W out >W in  is satisfied.