Extinction ratio calculation and control of a laser

• US 20030018453A1
• Filed: 07/17/2001
• Published: 01/23/2003
• Est. Priority Date: 07/17/2001
• Status: Active Grant

• Current Assignee: Tellabs Operations Incorporated (Infinera Corp.)
• Original Assignee: Tellabs Operations Incorporated (Infinera Corp.)
• Inventors: Carrick, John C.
• Granted Patent: US 6,993,459 B2
• Time in Patent Office: Days
• US Class Current: 702/189
• CPC Class Codes: H04B 10/504 using direct modulation
• CPC Class Codes: H04B 10/564 Power control

Abstract

A laser driver outputs a data protocol signal as controlled by an extinction control signal. The data protocol signal has a header section including a first sub-section having a first bit pattern and a second sub-section having a second bit pattern which is different than the first bit pattern. A laser outputs an optical signal in response to being excited by the data protocol signal, with the optical signal being converted to an electrical signal which is low-pass filtered to produce a signal based on the first and second bit patterns. A sequence of the signals are convolved with a reference signal to produce a convolved signal, with a peak of the convolved signal being located, this location being further used to locate the first and second subsections in the low-pass filtered signal. The located first and second subsections are then measured and used to calculate an extinction ratio in accordance with a predetermined formula. The calculated extinction ratio is compared with a desired extinction ratio to generate the extinction control signal.

Claims

1. A method of calculating an extinction ratio of a laser, said method comprising the steps of:

applying a data protocol signal to said laser for exciting said laser, the data protocol signal having repetitive sections including at least first and second sub-sections, the first sub-section having a first predetermined bit pattern, and the second sub-section having a second predetermined bit pattern which is different than the first predetermined bit pattern, said laser outputting an output data protocol signal;

detecting the first predetermined bit pattern and the second predetermined bit patten in the output data protocol signal; and

calculating the extinction ratio based on the detected first predetermined bit pattern and the second predetermined bit pattern in the output protocol signal.

2. The method according to claim 1, wherein the first predetermined bit pattern has a different distribution of ONE bits than a distribution of ONE bits in the second predetermined bit pattern.

3. The method according to claim 1, including:

comparing the calculated extinction ratio with a desired extinction ratio to generate an extinction control signal for controlling an extinction ratio of said laser.

4. The method according to claim 1, wherein the first predetermined bit pattern has a preponderance of ONE bits, and the second redetermined bit pattern has a preponderance of ZERO bits.

5. The method according to claim 1, wherein the first predetermined bit pattern has on average six ONE bits and two ZERO bits per eight bits, and the second predetermined bit pattern has on average two ONE bits and six ZERO bits per eight bits.

6. The method according to claim 1, wherein the data protocol is a SONET protocol, and the first repetitive sub-section of the header is an A1 framing byte and the second relative sub-section of the header is an A2 framing byte.

7. A method of calculating an extinction ratio of a laser, said method comprising the steps of:

applying a sequence of data protocol signals, each having a header section and a data section, to said laser for exciting said laser, with the header section having at least first and second sub-sections, the first sub-section having a first predetermined bit pattern, and the second sub-section having a second predetermined bit pattern which is different than the first predetermined bit pattern, said laser outputting a sequence of optical signals, each having a bit pattern corresponding to the bit pattern of the data protocol signal;

converting the sequence of optical signals to a sequence of electrical signals;

low-pass filtering the sequence of electrical signals to pass a sequence of analog signals, each having a HIGH portion corresponding to filtering the first predetermined number of bits in the first sub-section of the header, and having a LOW portion corresponding to filtering the second predetermined number of bits in the second sub-section of the header;

converting the sequence of analog signals to a sequence of digital signals;

convolving the sequence of digital signals with a reference digital signal to generate a convolved signal;

finding a peak of the convolved signal corresponding to an alignment between the first and second subsections and the reference digital signal;

measuring the digital signal at the first and second sub-sections based on the alignment; and

calculating an extinction ratio based on the measured digital signal at the first and second sub-sections.

8. The method according to claim 7, including:

comparing the calculated extinction ratio with a desired extinction ratio to generate an extinction control signal for controlling an extinction ratio of said laser.

9. The method according to claim 7, wherein the first predetermined bit pattern has a preponderance of ONE bits, and the second predetermined bit pattern has a preponderance of ZERO bits.

10. The method according to claim 7, wherein the first predetermined bit pattern has on average six ONE bits and two ZERO bits per eight bits, and the second predetermined bit pattern has on average two ONE bits and six ZERO bits per eight bits.

11. The method according to claim 7, wherein the data protocol is a SONET protocol, and the first sub-section has an A1 framing byte and the second sub-section has an A2 framing byte.

13. The apparatus according to claim 12, wherein the first predetermined bit pattern has a different distribution of ONE bits than a distribution of ONE bits in the second predetermined bit pattern.

14. The apparatus to claim 12, including:

a comparator adapted to compare the calculated extinction ratio with a desired extinction ratio to generate an extinction control signal for controlling the extinction ratio of said laser.

15. The apparatus according to claim 12, wherein the first predetermined bit pattern has a preponderance of ONE bits, and the second predetermined bit pattern has a preponderance of ZERO bits.

16. The apparatus according to claim 12, wherein the first predetermined bit pattern has on average six ONE bits and two ZERO bits per eight bits, and the second predetermined bit pattern has an average two ONE bits and six ZERO bits per eight bits.

17. An apparatus according to claim 12, wherein the data protocol in a SONET protocol, and the first sub-section has an A1 framing byte and the second sub-section has an A2 framing byte.

19. The apparatus according to claim 18 including:

another comparator adapted to comparing the calculated extinction ratio with a desired extinction ratio to generate an extinction control signal for controlling an extinction ratio of said laser.

20. The apparatus according to claim 18, wherein the first predetermined bit pattern has a preponderance of ONE bits and the second predetermined bit pattern has preponderance of ZERO bits.

21. The apparatus according to claim 18, wherein the first predetermined bit pattern has on average six ONE bits and two ZERO bits per eight bits, and the second predetermined bit pattern has on average two ONE bits and six ZERO bits per eight bits.

22. The apparatus according to claim 18, wherein the data protocol is a SONET protocol, and the first sub-section has an A1 framing byte and the second sub-section has an A2 framing byte.

24. The computer program product according to claim 23, including:

program code for a comparing step of comparing the calculated extinction ratio with a desired extinction ratio to generate an extinction control signal for controlling an extinction ratio of said laser.

25. The computer program product according to claim 23, wherein the first predetermined bit pattern has a preponderance of ONE bits, and the second predetermined bit pattern has a preponderance of ZERO bits.

26. The program product according to claim 23, wherein the first predetermined bit pattern has on average six ONE bits and two ZERO bits per eight bits, and the second predetermined bit pattern has on average two ONE bits and six ZERO bits per eight bits.

27. The program product according to claim 23, wherein the data protocol is a SONET protocol, and the first sub-section has an A1 framing byte and the second sub-section has an A2 framing byte.

12. An apparatus for calculating an extinction ratio of a laser, comprising:

an input device adapted to excite said laser with a data protocol signal, the data protocol signal having repetitive sections including at least first and second sub-sections, the first sub-section having a first predetermined bit pattern, and the second sub-section having a second pre-determined bit pattern which is different than the first predetermined bit pattern, said laser outputting an output data protocol signal;

a detector adapted to detect the first predetermined bit pattern and the second predetermined bit pattern in the output data protocol signal; and

a calculator adapted to calculate the extinction ratio based on the detected first predetermined bit pattern and the second predetermined bit pattern in the output protocol signal.

18. An apparatus for calculating an extinction ratio of a laser, comprising:

an input device adapted to excite said laser with a sequence of data protocol signals, each having a regularly repetitive header section and a data section, with the header section having at least first and second sub-sections, the first sub-section having a first predetermined bit pattern, and the second sub-section having a second predetermined bit pattern which is different than the first predetermined bit pattern, said laser outputting a sequence of optical signals, each having a bit pattern corresponding to the bit pattern of the data protocol signal;

a first converter adapted to convert the sequence of optical signals to a sequence of electrical signals;

a low-pass filter adapted to low-pass filtering the sequence of electrical signals to pass a sequence of analog signals, each having a HIGH portion corresponding to filtering the first predetermined number of bits in the first sub-section of the header, and having LOW portion corresponding to filtering the second predetermined number of bits in the second subsection of the header;

a second converter adapted to converting the sequence of analog signals to a sequence of digital signals;

a convolver adapted to convolving the sequence of digital signals with a reference digital signal to generate a convolved signal;

a first measuring device adapted to finding a peak of the convolved signal corresponding to an alignment between the first and second sub-sections and the reference digital signal;

a second measuring device adapted to measuring the digital signal at the first and second sub-sections based on the alignment; and

a calculator adapted to calculating an extinction ration based on the measured digital signal at the first and second subsections.

23. A computer program product embodying a program for implementing a method of calculating an extinction ratio of a laser, wherein an input device is adapted to excite said laser with a sequence of data protocol signals, each having a regularly repetitive header section and a data section, with the header section having at least first and second sub-sections, the first sub-section having a first predetermined bit pattern, and the second sub-section having a second predetermined bit pattern which is different than the first predetermined bit pattern, said laser outputting a sequence of optical signal, each having a bit pattern corresponding to the bit pattern of the data protocol signal, a first converter is adapted to convert the sequence of optical signals to a sequence of electrical signals, a low-pass filter is adapted to low-pass filtering the sequence of electrical signals to pass a sequence of analog signals, each having a HIGH portion corresponding to filtering the first predetermined number of bits in the first sub-section of the header, and having LOW portion corresponding to filtering the second predetermined number of bits in the second subsection of the header, and a second converter is adapted to converting the seqence of analog signals to a sequence of digital signals, the program comprising:

program code for a convolving step of convolving the sequence of digital signals with a reference digital signal to generate a convolved signal;

program code for a finding step of finding a peak of the convolved signal corresponding to an alignment between the first and second subsections and the reference digital signal;

program code for a measuring step of measuring the digital signal at the first and second sub-sections based on the alignment; and

program code for a calculating step of calculating an extinction ratio based on the measured digital signal at the first and second sub-sections.