Light-receiving method of an avalanche photodiode and a bias control circuit of the same

Abstract

The present invention provides a method to maintain a multiplication factor of an avalanche photodiode independent on temperatures without additional devices. The light-receiving apparatus of the invention includes an avalanche photodiode (APD), a dividing circuit, and a bias supplying circuit. The APD has a first region, where a significant multiplication factor appears, and a second region without any multiplication factor. The dividing circuit extracts a second signal

1 . An optical apparatus for receiving signal light, comprising: 
 an avalanche photodiode having a light-receiving surface including a first region and a second region, said avalanche photodiode outputting a photo current including a signal component generated in said first region and a monitor component generated in said second region;    a bias control circuit for outputting a bias voltage to be provided to said avalanche photodiode, said bias control circuit comprising,    a high-pass-filter for extracting said signal component from said photo current output from said avalanche photodiode,    a variable gain amplifier having a preset gain, said variable gain amplifier extracting said monitor component from said photo current by comparing said photo current with said signal component output from said high-pass-filter, and amplifying said extracted monitor component by said preset gain; and    a comparator for comparing said signal component and said amplified monitor component,    wherein said bias voltage applied to said avalanche photodiode is controlled such that said signal component is substantially equal to said amplified monitor component.    
   
   
       2 . The optical apparatus according to  claim 1 , wherein said bias control circuit further comprises a peak hold circuit for holding a peak value of said extracted signal component, said comparator comparing said peak value with said amplified monitor component, and 
 wherein said bias voltage applied to said avalanche photodiode is controlled such that said peak value output from said peak hold circuit is equal to said amplified monitor component.    
   
   
       3 . The optical apparatus according to  claim 1 , wherein said bias control circuit further comprises a low-pass filter for smoothing said monitor signal and for outputting a smoothed monitor signal, said variable gain amplifier extracting said gained monitor signal from said signal component and said smoothed monitor signal.  
   
   
       4 . The optical apparatus according to  claim 1 , wherein said bias control circuit further comprises an extracting amplifier for extracting said monitor component by comparing said photo current with said signal component extracted by said high-pass-filter, said preset gain of said variable gain amplifier being controlled based on said monitor component extracted by said extracting amplifier.  
   
   
       5 . An avalanche photodiode for outputting a photo current corresponding to received signal light by applying a bias voltage, said avalanche photodiode including a first electrode, a semiconductor substrate of a first conduction type provided on said first electrode, a light-sensitive layer of the first conduction type provided on said semiconductor substrate, a highly-doped layer of a second conduction type provided in said light-sensitive layer, and a second electrode contacting to said highly-doped layer, said bias voltage being applied between said first electrode and said second electrode, said avalanche photodiode comprising: 
 a first region including said highly-doped layer and having a significant multiplication factor, said first region receiving a portion of said signal light and generating a first photo current; and    a second region having a multiplication factor of substantially unity, said second region receiving a portion of said signal light and generating a second photo current,    wherein said bias voltage is mainly applied to said first region.    
   
   
       6 . The avalanche photodiode according to  claim 5 , wherein said second region surrounds said first region.  
   
   
       7 . A method for controlling a multiplication factor of an avalanche photodiode having a light-receiving surface including a first region and a second region, said avalanche photodiode outputting a photo current including a signal component generated in said first region and a monitor component generated in said second region, said method comprising steps of 
 (a) extracting said signal component from said photo current;    (b) extracting said monitor component from said photo current by comparing said photo current with said extracted signal component;    (c) amplifying said extracted monitor component by a preset gain; and    (d) comparing said amplified monitor component with said extracted signal component,    wherein said bias voltage applied to said avalanche photodiode is controlled such that said extracted signal component is substantially equal to said amplified monitor component.    
   
   
       8 . The method according to  claim 7 , further comprising a step of, before step (c), determining said preset gain based on said monitor component extracted from said photo current by comparing said photo current with said extracted signal component.