Apparatus and method for measurement for dynamic laser signals

Abstract

A system contains a laser output measurement circuit used in a laser control system ( 210 ). The circuits contain a photodiode sensor ( 109 ), sample and hold amplifier ( 202 ), IC with synchronizer and delay circuits ( 206 ), and an analog to digital converter ( 204 ). The circuits measure the laser light output ( 107 ) while the laser Module ( 106 ) transmits signals. The measurement circuit tracks and stores the laser light output ( 107 ) signal using a Photodiode Sensor ( 109 ) and with a Sample/hold ( 202 ). The methods calculate the value of the laser light output ( 107 ) from mathematical relationships, which correlate the light output ( 107 ) of the laser Module ( 106 ) to the current value of the drive signal ( 100 ). Some of the distinguishing features in the present invention are 1) feedback information from the photodiode is obtained in a synchronous manner as a snapshot of the laser performance, and 2) the measurements are precise and calibrated, and 3) no disruption of the signal transmission occurs.

1. A method for synchronizing capture of laser output samples comprising:
 buffering an analog laser drive signal; 
 delaying the buffered drive signal to produce a set of delayed analog drive signals from the buffered drive signal; 
 selecting a particular delayed analog drive signal from the set of delayed analog drive signals; 
 capturing the selected signal in a sample and hold amplifier to produce a delayed analog signal sample; 
 placing the sample and hold amplifier in a hold mode during an analog to digital conversion of the delayed analog signal sample; 
 converting the delayed analog signal sample to a digital signal sample; and, 
 resetting the sample and hold amplifier for a next sample capturing cycle. 
 
     
     
       2. An A circuit for synchronizing capture of laser output samples comprising:
 a buffer for buffering an analog laser drive signal; 
 a set of signal propagation delays for producing a set of delayed analog drive signals from the buffered drive signal; 
 a digital multiplexer for selecting a particular delayed analog signal from the set of delayed analog drive signals; 
 a sample and hold amplifier for capturing the selected signal to produce a delayed analog signal sample; 
 a set reset latch for causing a sample and hold controller to place the sample and hold amplifier in a hold mode during an analog to digital conversion of the delayed analog signal sample, and to reset the sample and hold amplifier for a next sample capturing cycle; and, 
 an analog to digital converter for converting the delayed analog signal sample to a digital signal sample. 
 
     
     
       3. The method of  claim 1  further comprising:
 opening a first switch to disconnect a laser drive signal from a laser driver; 
 concurrently closing a second switch to connect a know known test pulse signal to the laser drive driver; and, 
 calibrating timing for output signal sampling using the known test pulse signal. 
 
     
     
       4. The method of  claim 1  further comprising:
 opening a first switch to disconnect a laser drive signal from a laser driver; 
 concurrently closing a second switch to connect a known test pulse signal to the laser driver; and, 
 calibrating an extinction ratio using the known test pulse signal. 
 
     
     
       5. The circuit of  claim 2  further comprising:
 a first switch for disconnecting a laser drive signal from a laser driver; and, a second switch for connecting a known test pulse signal to the laser driver. 
 
     
     
       6. An apparatus comprising:
 a sampler configured to sample a photodiode signal to provide a sample signal, wherein the sample signal is configured to serve as at least a partial basis for calibration of a laser module; and   a synchronization module operatively coupled with the sampler and configured to:
 receive a drive signal configured to drive the laser module; 
 delay the drive signal, based at least in part on an input signal received from a controller, to provide a delayed drive signal; and 
 control the sampler to sample the photodiode signal based at least in part on the delayed drive signal. 
   
     
     
       7. The apparatus of claim 6, further comprising the controller operatively coupled with the sampler and the synchronization module and configured to provide the input signal to the synchronization module to correlate sampling of the photodiode signal with the drive signal. 
     
     
       8. The apparatus of claim 7, wherein the controller is further configured to provide one or more control signals based at least in part on the sample signal and the apparatus further comprises:
 the laser module to provide light output; and   a driver operatively coupled with the laser module and the controller and configured to:
 receive the drive signal; 
 receive the one or more control signals from the controller; and 
 drive the laser module, based at least in part on the drive signal and the one or more control signals, to provide the light output. 
   
     
     
       9. The apparatus of claim 8, wherein the controller is further configured to:
 provide the one or more control signals based at least in part on an extinction ratio or a bit error rate associated with the laser module.   
     
     
       10. The apparatus of claim 8, wherein the one or more control signals comprise bias and modulation control signals. 
     
     
       11. The apparatus of claim 8, further comprising:
 a photodiode configured to provide the photodiode signal based at least in part on the light output.   
     
     
       12. The apparatus of claim 7, wherein the controller is configured to:
 select a delay value from a plurality of delay values that results in a peak value of the sample signal; and   provide the input signal to implement the delay value.   
     
     
       13. The apparatus of claim 6, wherein the synchronization module comprises synchronizer and delay circuits. 
     
     
       14. The apparatus of claim 6, wherein the synchronization module is further configured to control the sampler to transition from a sample mode to a hold mode at a time that corresponds to a peak value of the sample signal. 
     
     
       15. A method comprising:
 receiving, by a synchronization module, a drive signal configured to drive a laser module;   driving, by the synchronization module, the laser module based at least in part on the drive signal, to provide light output;   delaying, by the synchronization module based at least in part on an input signal received from a controller, the drive signal to provide a delayed drive signal; and   sampling, by a sampler controlled by the synchronization module, a photodiode signal that corresponds to the light output, based at least in part on the delayed drive signal, to provide a sample signal,   wherein said delaying of the drive signal is configured to correlate the sample signal with the drive signal to enable the sample signal to serve as at least a partial basis for calibration of the laser module.   
     
     
       16. The method of claim 15, wherein said delaying the drive signal is further configured to provide a sampling transition at a time that corresponds to a peak value of the sample signal. 
     
     
       17. The method of claim 16, wherein the sampling transition is a transition from a sample mode to a hold mode of a sampler. 
     
     
       18. The method of claim 15, further comprising:
 calibrating the laser module based at least in part on the sample signal.   
     
     
       19. The method of claim 18, wherein said calibrating the laser module comprises:
 adjusting at least a bias control signal or a modulation control signal.   
     
     
       20. The method of claim 19, further comprising adjusting at least the bias control signal or the modulation control signal based on an extinction ratio or bit error rate associated with the laser module.