Digitally integrated self-trained pre-distortion curve finder for linearly frequency swept semiconductor laser systems

• US 10,574,028 B2
• Filed: 02/26/2019
• Issued: 02/25/2020
• Est. Priority Date: 07/21/2017
• Status: Active Grant

• Current Assignee: Rhode Island Council on Postsecondary Education
• Original Assignee: Rhode Island Council on Postsecondary Education
• Inventors: Wei, Tao, Yao, Zheyi, Sun, Yan
• Primary Examiner(s): Niu, Xinning(Tom)
• Assistant Examiner(s): Hagan, Sean P
• Application Number:
  US16/285,738
• Publication Number:
  US 20190190234A1
• Time in Patent Office: 364 Days
• CPC Class Codes: H01S 5/042 Electrical excitation ; Circuits therefor monolithically integrated laser drive components H01S5/0261
• CPC Class Codes: H01S 5/0617 using memorised or pre-programmed laser characteristics
• CPC Class Codes: H01S 5/0622 Controlling the frequency of the radiation
• CPC Class Codes: H01S 5/06223 using delayed or positive feedback
• CPC Class Codes: H01S 5/06817 Noise reduction
• CPC Class Codes: H01S 5/0683 by monitoring the optical output parameters
• CPC Class Codes: H01S 5/06835 Stabilising during pulse modulation or generation
• CPC Class Codes: H01S 5/0687 Stabilising the frequency of the laser

Abstract

The present disclosure provides a unique digitally integrated, self-trained pre-distortion curve generation method and apparatus for semiconductor lasers (SCLs) to generate linearly swept optical signals that are applicable to a wide range of sweep velocities and semiconductor laser types. The method requires no prior knowledge of the frequency response of the laser and is highly accurate.

Claims

1. A pre-distortion curve finder for a frequency-swept semi-conductor laser comprising:

a baseline pre-distortion curve stored in a memory;

an optical frequency discriminator (OFD) receiving an optical signal from said semiconductor laser and outputting an analog RF signal linearly proportional to the sweep velocity;

a digitizer receiving output from said OFD and converting said output into digital signals;

a digital phase frequency detector (PFD) receiving said digital signals from said digitizer, and generating an expected digital signal phase and a digital phase error signal;

a central loop controller receiving said expected digital phase signal and said digital phase error signal and generating a compensation signal to modify said baseline pre-distortion curve through a plurality of iterations, said loop controller counting iterations of digitized signals received;

a digital adder receiving said compensation signal;

a delay compensation loop providing a delayed version of said pre-distortion curve from a previous compensation iteration,

wherein said delayed version of said previous predistortion curve is summed with said current compensation signal to generate a newly modified pre-distortion curve which is written to said memory, and

wherein the laser diode is driven based on the newly modified iterative version of said pre-distortion curve stored in memory.

2. The pre-distortion curve finder of claim 1, wherein said OFD includes a photodetector.

3. The pre-distortion curve finder of claim 1, wherein said digitizer comprises an automatic grain control amplifier (AGC) and a comparator.

4. The pre-distortion curve finder of claim 1 wherein the loop controller is configured and arranged to cycle through at least 300 iterations.

5. The predistortion curve finder of claim 1 wherein the loop controller is configured and arranged to generate a new compensation signal every 1 ms.

6. The predistortion curve finder of claim 5 wherein the loop controller is configured and arranged to generate a compensation signal every 1 ms.

7. A linearly frequency swept semiconductor laser, comprising:

a laser diode;

a laser driver circuit operating the laser diode;

a baseline pre-distortion curve stored in a memory;

an optical frequency discriminator (OFD) receiving an optical signal from said semiconductor laser and outputting an analog RF signal linearly proportional to the sweep velocity;

a digitizer receiving output from said OFD and converting said output into digital signals;

a digital phase frequency detector (PFD) receiving said digital signals from said digitizer, and generating an expected digital signal phase and a digital phase error signal;

a central loop controller receiving said expected digital phase signal and said digital phase error signal and generating a compensation signal to modify said baseline pre-distortion curve through iterations, said loop controller further counting iterations of digitized signals received;

a digital adder receiving said compensation signal;

a delay compensation loop proving a delayed version of said pre-distortion curve from a previous compensation iteration,

wherein said delayed version of said previous predistortion curve is summed with said current compensation signal to generate a newly modified pre-distortion curve which is written to said memory, and

wherein the laser driver circuit uses the newly modified iterative version of said pre-distortion curve stored in memory to drive said laser diode.

8. The semiconductor laser of claim 7, wherein said OFD includes a photodetector.

9. The semiconductor laser of claim 7, wherein said digitizer comprises an automatic grain control amplifier (AGC) and a comparator.

10. The semiconductor laser of claim 7 wherein the loop controller is configured and arranged to cycle through at least 300 iterations.

11. The semiconductor laser of claim 7 wherein the loop controller is configured and arranged to generate a new compensation signal every 1 ms.

12. The semiconductor laser of claim 11 wherein the loop controller is configured and arranged to generate a compensation signal every 1 ms.

13. A method of finding the pre-distortion curve of a semiconductor laser comprising the steps of:

driving a semiconductor laser diode to generate an optical output;

storing a baseline pre-distortion curve store in a memory;

receiving an optical signal from said semiconductor laser and outputting an analog RF signal linearly proportional to a sweep velocity;

receiving output from said OFD and converting said output into digital signals;

receiving said digital signals and generating an expected digital signal phase and a digital phase error signal;

receiving said expected digital phase signal and said digital phase error signal and generating a compensation signal to modify said baseline pre-distortion curve;

providing a delayed version of said pre-distortion curve from a previous compensation iteration,

summing said delayed version of said previous predistortion curve with said current compensation signal to generate a newly modified pre-distortion curve;

writing said newly modified pre-distortion curve to said memory; and

driving said semiconductor laser diode to generate an optical output using the newly modified iterative version of said pre-distortion curve stored in memory.

14. The method of claim 13, wherein said steps of generating a compensation signal, providing said delayed version of said pre-distortion curve from the previous iteration, summing the delayed version with the compensation signal and generating a newly modified pre-distortion curve is repeated every 1 ms.

15. The method of claim 13, wherein the steps of generating a compensation signal, providing said delayed version of said pre-distortion curve from the previous iteration, summing the delayed version with the compensation signal and generating a newly modified pre-distortion curve is repeated every 1 ms for at least 300 iterations.

16. The method of claim 13, wherein the steps of generating a compensation signal, providing said delayed version of said pre-distortion curve from the previous iteration, summing the delayed version with the compensation signal and generating a newly modified pre-distortion curve is repeated every 1 ms for at least 500 iterations.

17. The method of claim 13, wherein the steps of generating a compensation signal, providing said delayed version of said pre-distortion curve from the previous iteration, summing the delayed version with the compensation signal and generating a newly modified pre-distortion curve is repeated every 1 ms for at least 1000 iterations.