Method and apparatus for digital signal processing enhanced laser performance compensation

Abstract

Methods for controlling lasers or other light emitting devices to compensate for performance degradations due to temperature changes and aging without disrupting the transmission of information are presented. Disclosed embodiments describe various methods of applying mathematical models and digital signal processing algorithms to continuously calculate and execute precise output power adjustments. A synthesized test signal is injected into the normal data stream is applied to the laser system. The magnitude of the test signal is sufficiently small that it is buried in system noise and will not alter the noise margin of the signal or the transmitted data. Micro-detection, recovery and digital signal processing of the embedded test signal produces precisely monitored output power and modulation amplitude measurements used to accurately adjust performance characteristics regardless of temperature or age.

1 . A method for controlling a light emitting device during and without disrupting data transmission, comprising: 
 modulating a light emitting device with a noise-level test signal embedded in a data signal to produce a modulated signal output;    acquiring the modulated signal from the light emitting device;    extracting the noise-level test signal from the acquired signal;    digitally processing the extracted noise-level test signal to calculate power control adjustments; and    controlling output power of the light emitting device by applying the calculated power control adjustments to the light emitting device.    
     
     
         2 . A method for controlling a laser during and without disrupting data transmission, comprising: 
 generating a noise-level test signal having a predetermined characteristic;    generating a data signal having a predetermined characteristic;    modulating a laser with the generated noise-level test signal and the data signal to produce a modulated output signal;    acquiring the modulated output signal;    extracting a noise-level test signal from the acquired modulated output signal;    determining an average value of the extracted noise-level test signal;    determining a characteristic of the extracted noise-level test signal;    calculating a bias current adjustment from the characteristic of the extracted noise-level test signal;    calculating a modulation current adjustment from a ratio of the characteristic of the generated noise-level test signal to the characteristic slope of the extracted noise-level test signal;    controlling a laser bias current by applying the calculated bias current adjustment to a laser driver; and    controlling a laser modulation current by applying the calculated modulation current adjustment to the laser driver.    
     
     
         3 . The method of  claim 2  wherein the noise-level test signal is a sinusoidal signal.  
     
     
         4 . The method of  claim 2  wherein the noise-level test signal is a saw tooth signal.  
     
     
         5 . The method of  claim 2  where the noise-level test signal is a composite signal.  
     
     
         6 . The method of  claim 2  wherein the noise-level test signal is extracted by applying a digital signal processing lock-in detector algorithm and filtering to the acquired modulated output signal.  
     
     
         7 . The method of  claim 2  wherein the noise-level test signal is extracted by a applying a digital signal processing quadrature detector algorithm and filtering to the acquired modulated output signal.  
     
     
         8 . The method of  claim 2  wherein the noise-level test signal is extracted by a applying a digital signal processing regression detector algorithm and filtering to the acquired modulated output signal.  
     
     
         9 . An apparatus for controlling a laser during and without disrupting data transmission, comprising: 
 a laser driver for modulating the laser with a noise-level test signal embedded in a data signal to produce a modulated output signal from the laser;    a monitor photodiode for acquiring the modulated signal from the laser;    a digital signal processor for extracting a noise-level test signal from the acquired signal and digitally processing the extracted noise-level test signal to calculate power control adjustments; and    a servo for controlling output power of the laser by applying the calculated power control adjustments to the laser driver.    
     
     
         10 . A method for controlling output power of a laser during and without disrupting data transmission, comprising: 
 embedding an original test signal in system noise;    modulating the original test signal and system noise;    mathematically extracting the embedded test signal from the modulated system noise;    applying digital signal processing algorithms to the extracted test signal to calculate power control adjustments from differences between the original test signal and the extracted test signal; and    applying the calculated power control adjustments to the laser.    
     
     
         11 . An apparatus for controlling a laser during and without disrupting data transmission, comprising: 
 a laser driver for modulating the laser with data to produce a modulated output signal;    a high frequency monitor photodiode for acquiring the modulated output signal from the laser and following amplitudes of the modulated output signal;    a digital signal processor for performing peak and valley detection of the followed amplitudes of the acquired output signal, and for calculating power control adjustments from the peak and valley detection; and    a servo for controlling output power of the laser by applying the calculated power control adjustments to the laser driver.    
     
     
         12 . An method for controlling a laser system during and without disrupting data transmission, comprising: 
 embedding a noise-level test signal in system noise of a data signal in a first laser transceiver;    transmitting a data signal containing the noise-level test signal embedded in system noise from the first laser transceiver to a second laser transceiver using optical path;    receiving the transmitted signal at the second laser transceiver.    detecting, recovering and digitally processing the noise-level test signal at the second transceiver to determine characteristic information about the first laser transceiver and the optical path;    sending the characteristic information from the second laser transceiver to the first laser transceiver;    receiving the characteristic information at the first transceiver; and    adjusting the output characteristics of the first laser transceiver according to the received characteristic information.    
     
     
         13 . A method for extracting a noise-level test signal from a modulated data signal during and without disrupting data transmission, comprising: 
 modulating a data signal containing an original noise-level test signal to produce a modulated output signal;    acquiring the modulated output signal;    multiplying the acquired modulated output signal by a copy of the original noise-level test signal to shift the frequency of an acquired noise-level test signal within the acquired modulated signal; and    filtering the frequency shifted noise-level test signal from the acquired modulated signal.    
     
     
         14 . A method for extracting a noise-level test signal from a modulated data signal during and without disrupting data transmission, comprising: 
 modulating a data signal containing an original sinusoidal noise-level test signal to produce a modulated output signal;    acquiring the modulated output signal;    splitting the acquired modulated signal into a first half and a second half;    multiplying the first half of the acquired modulated output signal by a sinusoidal copy of the original sinusoidal noise-level test signal to shift the frequency of an acquired noise-level test signal within the acquired modulated signal;    filtering the frequency shifted sinusoidal noise-level test signal from the acquired modulated signal;    squaring the filtered sinusoidal noise-level test signal;    multiplying the second half of the acquired modulated output signal by a cosinusoidal copy of the original sinusoidal noise-level test signal to produce a cosinusoidal noise-level test signal and shift the frequency of the acquired cosinusoidal noise-level test signal within the acquired modulated signal;    filtering the frequency shifted cosinusoidal noise-level test signal from the acquired modulated signal;    squaring the filtered cosinusoidal noise-level test signal; and    adding the squared sinusoidal and cosinusoidal acquired test signals to produce an amplitude of the acquired noise-level test signal.