Laser control circuit

• US 20060291510A1
• Filed: 06/22/2005
• Published: 12/28/2006
• Est. Priority Date: 06/22/2005
• Status: Active Grant

• Current Assignee: Intel Corporation
• Original Assignee: Intel Corporation
• Inventors: Juluri, Raghavendra V.
• Granted Patent: US 7,515,619 B2
• Time in Patent Office: Days
• US Class Current: 372/29.021
• CPC Class Codes: H01S 5/0617 using memorised or pre-programmed laser characteristics
• CPC Class Codes: H01S 5/06804 by monitoring an external parameter, e.g. temperature
• CPC Class Codes: H01S 5/06808 by monitoring the electrical laser parameters, e.g. voltage or current
• CPC Class Codes: H01S 5/06825 Protecting the laser, e.g. during switch-on/off, detection of malfunctioning or degradation
• CPC Class Codes: H01S 5/0683 by monitoring the optical output parameters
• CPC Class Codes: H01S 5/06832 Stabilising during amplitude modulation

Abstract

An apparatus and method to safely control the power output of a laser source. A power monitor is optically coupled to monitor a power output of laser source generating an optical signal. The power monitor is coupled to generate power feedback data indicative of the power output. A processor is coupled to control the power output of the laser source in real-time in response to the power feedback data from the power monitor.

Claims

1. An apparatus, comprising:

a laser source to generate an optical signal;

a power monitor optically coupled to monitor a power output of the laser source and to generate power feedback data indicative of the power output; and

a processor coupled to control the power output of the laser source in real-time in response to the power feedback data from the power monitor.

2. The apparatus of claim 1, further comprising:

a firmware unit coupled to the processor to store a lookup table, the lookup table including power data points indexed to temperature data points; and

a temperature sensor thermally coupled to the laser source to measure an operating temperature of the laser source and coupled to generate temperature data indicative of the operating temperature to the laser source,

wherein the processor is coupled in a feedback control loop with the laser source and power monitor to control the power output of the laser source based at least in part on the temperature data and with reference to the power data points indexed to the temperature data points of the firmware unit.

3. The apparatus of claim 1, further comprising:

a power regulator coupled to provide power to the laser source during operation of the laser source; and

a hardware watchdog circuit coupled to receive an alternating current (“

AC”

) safety shutoff signal from the processor and further coupled to disable the power regulator when the AC safety shutoff signal is disrupted.

4. The apparatus of claim 3, wherein the hardware watchdog circuit comprises:

a high-pass filter coupled to receive the AC safety shutoff signal from the processor;

a peak rectifier coupled to rectify the AC safety shutoff signal; and

a discharge resistor coupled to discharge an output of the peak rectifier, if the AC safety shutoff signal fails.

5. The apparatus of claim 4, wherein the hardware watchdog circuit comprises:

a capacitor C1 coupled between an input and a node N1;

a diode D1 coupled between node N1 and a ground node;

a diode D2 having an anode coupled to node N1;

a resistor R1 coupled between to a cathode of diode D2 and to an output;

a capacitor C2 coupled between the ground node and the output; and

a resistor R2 coupled between the ground node and the output.

6. The apparatus of claim 2, further comprising:

a laser driver to drive the laser source with a DC bias current and an AC signal current, the processor coupled to the laser driver to control the DC bias current in real-time; and

a laser bias monitor coupled to monitor the DC bias current and coupled to provide bias current data to the processor.

7. The apparatus of claim 1, wherein the laser source comprises a vertical cavity surface emitting laser (“

VCSEL”

) and wherein the power monitor comprises a photo diode positioned to receive a portion of the optical signal to monitor the power output of the VCSEL.

8. A method of operation, comprising:

monitoring an optical signal output from a laser source to generate power feedback data indicative of a power output of the laser source;

monitoring an operating temperature of the laser source to generate temperature data indicative of the operating temperature; and

controlling a bias current driving the laser source with a processor in real-time based at least in part on the temperature data and the power feedback data to achieve a desired power output of the laser.

9. The method of claim 8, further comprising referencing a lookup table indexing power data points to temperature data points for the laser source, and wherein controlling the bias current comprises adjusting the bias current to trend the power feedback data towards one of the power data points indexed to one of the temperature data points corresponding to the temperature data.

10. The method of claim 9, wherein the temperature data points and the power data points of the lookup table are generated uniquely for the laser source by testing the laser source.

11. The method of claim 9, further comprising:

periodically validating the lookup table against a checksum; and

disabling the laser source if the lookup table fails to validate.

12. The method of claim 8, further comprising:

generating an alternating current (“

AC”

) safety shutoff signal by the processor indicating healthy operation of the processor;

generating a power enable signal in response to the AC safety shutoff signal while the AC safety shutoff signal oscillates within a limited frequency range; and

enabling a power supply of the laser source with the power enable signal while the AC safety shutoff signal oscillates within the limited frequency range.

13. The method of claim 8, further comprising executing a short circuit test to test for a closed circuit condition, the short circuit test including:

generating a control signal by the processor to drive a bias current through the laser source;

monitoring a power monitor of the laser source for a first condition where the power monitor detects the power output as exceeding an expected power output for the control signal; and

monitoring a laser bias monitor of the laser source for a second condition where the laser bias monitor detects the bias current as greater than expected for the control signal.

14. The method of claim 8, further comprising executing an open circuit test to test for an open circuit condition, the open circuit test including:

generating a control signal by the processor to drive a bias current through the laser source; and

monitoring a laser bias monitor of the laser source for a condition where the laser bias monitor detects the bias current as less than expected for the control signal.

15. The method of claim 8, further comprising executing a power monitor test to verify operation of a power monitor optically coupled to monitor the laser source, the power monitor test including:

generate a control signal by the processor to drive a bias current through the laser source; and

monitoring the power monitor for a condition where the power monitor detects the power output as exceeding a threshold power level.

16. The method of claim 8, further comprising:

referencing a fault register prior to enabling the laser source to determine whether one or more laser safety tests previously executed to monitor safe operation of the laser source have failed; and

enabling the laser source only if the fault register indicates no failure of the one or more laser safety tests.

17. The method of claim 8, further comprising:

executing one or more laser safety tests within the processor to monitor safe operation of the laser source;

notifying a task monitor by each of the one or more laser safety tests upon execution that the corresponding laser safety tests was executed;

monitoring the task monitor to determine whether any of the one or more safety tests failed to notify the task monitor; and

periodically resetting a software watchdog timer prior to expiration if all of the one or more laser safety tests notify the task monitor within a set time period, the software watchdog timer configured to disable the laser source upon expiration.

18. An optical transmitter system, comprising:

a laser source coupled to generate an optical signal in response to an electrical signal; and

a control circuit to control the laser source, the control circuit including;

a power monitor optically coupled to monitor the power output of the laser source and to generate power feedback data indicative of the power output;

a processor coupled to control the power output of the laser source in real- time in response to the power feedback signal from the power monitor; and

synchronous dynamic random access memory (“

SDRAM”

) coupled to the processor to execute instruction therefrom.

19. The optical transmitter system of claim 18, wherein the control circuit further includes:

a firmware unit coupled to the processor to store a lookup table, the lookup table including power data points indexed to temperature data points; and

a temperature sensor thermally coupled to the laser source to measure an operating temperature of the laser source and coupled to generate temperature data indicative of the operating temperature to the laser source,

wherein the processor is coupled in a feedback control loop with the laser source and power monitor to control the power output of the laser source based at least in part on the temperature data and with reference to the power data points indexed to the temperature data points of the firmware unit.

20. The optical transmitter system of claim 19, further comprising:

a power regulator coupled to provide power to the laser source during operation of the laser source; and

a hardware watchdog circuit coupled to receive an alternating current (“

AC”

) safety shutoff signal from the processor and further coupled to disable the power regulator when the AC safety shutoff signal is disrupted.