Automatic optical reflectometer power adjustment

Abstract

The adjustment of output power of a transmitter is described. In one embodiment, a first laser diode of a transmitter is directed to transmit a first pulse of light at a first wavelength over a fiber cable. A second laser diode of the transmitter is also directed to transmit a second pulse of light at a second wavelength over the fiber cable. An output tap of the transmitter is monitored to detect a first timing of a first reflection event on the fiber cable, and the output tap of the transmitter is also monitored to detect a second timing of a second reflection event on the fiber cable. An output power of the first laser diode is tuned or adjusted based on the first timing, and an output power of the second laser diode is tuned or adjusted based on the second timing.

Therefore, the following is claimed: 
     
         1 . A method to reduce transmitter power, comprising:
 directing a first laser diode of a photonic integrated circuit (PIC) transmitter to transmit a first pulse of light at a first wavelength over a fiber cable;   monitoring an output tap of the PIC transmitter to detect a reflection event at the first wavelength on the fiber cable in response to transmission of the first pulse of light;   directing a second laser diode of the PIC transmitter to transmit a second pulse of light at a second wavelength over the fiber cable;   monitoring the output tap of the PIC transmitter to detect a reflection event at the second wavelength on the fiber cable in response to transmission of the second pulse of light; and   tuning an output power of the first laser diode based on a timing of the reflection event at the first wavelength and tuning an output power of the second laser diode based on a timing of the reflection event at the second wavelength.   
     
     
         2 . The method of  claim 1 , wherein:
 tuning the output power of the first laser diode comprises reducing at least one of a bias voltage or a modulation voltage supplied to at least one of the first laser diode or an optical modulator for the first laser diode; and   tuning the output power of the second laser diode comprises reducing at least one of a bias voltage or a modulation voltage supplied to at least one of the second laser diode or an optical modulator for the second laser diode.   
     
     
         3 . The method of  claim 1 , wherein the reflection event at the first wavelength comprises a final reflection event and at least one intervening reflection event between the transmission of the first pulse of light and the final reflection event. 
     
     
         4 . The method of  claim 1 , wherein tuning the output power of the first laser diode comprises reducing the output power of the first laser diode based on an interval of time between the transmission of the first pulse of light and the reflection event at the first wavelength. 
     
     
         5 . The method of  claim 1 , wherein the timing of the reflection event at the first wavelength comprises an interval of time between the transmission of the first pulse of light and detection of the reflection event at the first wavelength. 
     
     
         6 . The method of  claim 5 , further comprising estimating a length of the fiber cable based on the interval of time and an average refractive index value of the fiber cable. 
     
     
         7 . The method of  claim 6 , further comprising determining whether the length of the fiber cable is acceptable for optical data communications by the PIC transmitter. 
     
     
         8 . The method of  claim 6 , wherein at least one of tuning the output power of the first laser diode and tuning the output power of the second laser diode comprises tuning the output power based on the length of the fiber cable. 
     
     
         9 . A device, comprising:
 a photonic transmitter, the photonic transmitter comprising a plurality of laser diodes and an output tap;   a driver; and   a controller configured to:
 direct a first laser diode among the plurality of laser diodes to transmit a first pulse of light at a first wavelength over a fiber cable; 
 monitor the output tap to detect a reflection event at the first wavelength on the fiber cable in response to transmission of the first pulse of light; 
 direct a second laser diode among the plurality of laser diodes to transmit a second pulse of light at a second wavelength over the fiber cable; 
 monitor the output tap to detect a reflection event at the second wavelength on the fiber cable in response to transmission of the second pulse of light; and 
 adjust an output power of the first laser diode based on a timing of the reflection event at the first wavelength and adjust an output power of the second laser diode based on a timing of the reflection event at the second wavelength. 
   
     
     
         10 . The device of  claim 9 , wherein the controller is further configured to:
 reduce at least one of a bias voltage or a modulation voltage supplied to at least one of the first laser diode or an optical modulator for the first laser diode; and   reduce at least one of a bias voltage or a modulation voltage supplied to at least one of the second laser diode or an optical modulator for the second laser diode.   
     
     
         11 . The device of  claim 9 , wherein the reflection event at the first wavelength comprises a final reflection event and at least one intervening reflection event between the transmission of the first pulse of light and the final reflection event. 
     
     
         12 . The device of  claim 9 , wherein the controller is further configured to reduce the output power of the first laser diode based on an interval of time between the transmission of the first pulse of light and the reflection event at the first wavelength. 
     
     
         13 . The device of  claim 9 , wherein the timing of the reflection event at the first wavelength comprises an interval of time between the transmission of the first pulse of light and detection of the reflection event at the first wavelength. 
     
     
         14 . The device of  claim 13 , wherein the controller is further configured to estimate a length of the fiber cable based on the interval of time and an average refractive index value of the fiber cable 
     
     
         15 . The device of  claim 14 , wherein the controller is further configured adjust at least one of the output power of the first laser diode and the output power of the second laser diode based on the length of the fiber cable. 
     
     
         16 . A method to reduce transmitter power, comprising:
 monitoring an output tap of a photonic integrated circuit (PIC) transmitter to detect a timing of a reflection event at a first wavelength on a fiber cable in response to transmission of a first pulse of light at the first wavelength over the fiber cable by a first laser diode;   monitoring the output tap of the PIC transmitter to detect a timing of a reflection event at a second wavelength on the fiber cable in response to transmission of a second pulse of light at the second wavelength over the fiber cable by a second laser diode;   tuning an output power of the first laser diode based on the timing of the reflection event at the first wavelength; and   tuning an output power of the second laser diode based on the timing of the reflection event at the second wavelength.   
     
     
         17 . The method of  claim 16 , wherein:
 tuning the output power of the first laser diode comprises reducing at least one of a bias voltage or a modulation voltage supplied to at least one of the first laser diode or an optical modulator for the first laser diode; and   tuning the output power of the second laser diode comprises reducing at least one of a bias voltage or a modulation voltage supplied to at least one of the second laser diode or an optical modulator for the second laser diode.   
     
     
         18 . The method of  claim 16 , wherein the reflection event at the first wavelength comprises a final reflection event and at least one intervening reflection event between the transmission of the first pulse of light and the final reflection event. 
     
     
         19 . The method of  claim 16 , further comprising estimating a length of the fiber cable based on an average refractive index value of the fiber cable and at least one of the timing at the reflection event at the first wavelength and the timing of the reflection event at the second wavelength. 
     
     
         20 . The method of  claim 19 , further comprising determining whether the length of the fiber cable is acceptable for optical data communications by the PIC transmitter.