Control loop circuit and method therefor
First Claim
1. A control loop circuit apparatus for compensating modulation amplitude control of a laser device, the apparatus comprising:
- a first receiver for receiving a first signal and outputting the first signal to a laser driver;
a comparator;
a second receiver for receiving a second signal generated by a sensor for monitoring the laser device and outputting the second signal to the comparator;
a simulator arrangement for receiving the first signal and simulating the second signal in response to the first signal and outputting the simulated second signal to the comparator;
the comparator being adapted to (a) receive both the second signal and the simulated signal, and (b) generate an output signal for compensating for modulation amplitude control of the laser device, the output signal providing an indication of the relative values of the amplitudes of the second signal and the simulated second signal.
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Accused Products
Abstract
In an optical communications system, it is necessary to control the extinction ratio of a laser device (192) of an optical transmission unit. The laser device (192) is typically used to transmit a signal that can be approximated by a pseudo-random bit stream. The bit stream is monitored by collecting light from a back facet of the laser device (192) using a photodiode (194) in a control loop. Due to band limiting effects of the photodiode (194) and parasitic circuit track capacitances, a feedback signal generated by the photodiode (194) becomes distorted, leading to difficulties in controlling the extinction ratio. The present invention therefore provides an apparatus that simulates a signal generated by the photodiode (194) and subsequent processing of the photodiode signal. The simulated signal and the processed photodiode signal are compared so as to generate a control signal for controlling modulation amplitude of the laser device (192) and hence the extinction ratio.
27 Citations
22 Claims
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1. A control loop circuit apparatus for compensating modulation amplitude control of a laser device, the apparatus comprising:
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a first receiver for receiving a first signal and outputting the first signal to a laser driver;
a comparator;
a second receiver for receiving a second signal generated by a sensor for monitoring the laser device and outputting the second signal to the comparator;
a simulator arrangement for receiving the first signal and simulating the second signal in response to the first signal and outputting the simulated second signal to the comparator;
the comparator being adapted to (a) receive both the second signal and the simulated signal, and (b) generate an output signal for compensating for modulation amplitude control of the laser device, the output signal providing an indication of the relative values of the amplitudes of the second signal and the simulated second signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 11, 12, 13, 14, 15, 21, 22)
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9. A method of compensating modulation amplitude control of a laser device, the method comprising the steps of:
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receiving a first signal and outputting the first signal to a laser driver;
receiving a second signal generated by a sensor monitoring the laser device;
generating a simulated signal corresponding to the second signal by using the first signal; and
generating an output signal that compensates the modulation amplitude control of the laser device by comparing the relative values of the amplitudes of the received second signal and the simulated signal.
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10. A control loop circuit apparatus for compensating modulation amplitude control of a laser device, the apparatus comprising:
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a first input for receiving a first signal and outputting the first signal to a laser driver;
a comparator;
a second input for receiving a second signal adapted to be generated by a sensor for monitoring the laser device and outputting the second signal to the comparator;
a simulation arrangement for receiving the first signal and simulating the second signal in response to the first signal and outputting the simulated second signal to the comparator, the comparator being adapted to receive both the second signal and the simulated second signal for generating an output signal for compensating the modulation amplitude control of the laser device, the output signal providing an indication of the relative values of the amplitudes of the second signal and the simulated second signal.
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16. An optical transmitter for a data signal, comprising:
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a laser adapted to be responsive to the data signal;
a feedback loop for controlling the laser output, the feedback loop including a sensor for optical energy the laser derives in response to the data signal; and
circuitry adapted to be connected to be responsive to the data signal for simulating the response of the feedback loop to the optical energy the laser derives in response to the data signal and for affecting the control the feedback loop provides for the laser output in response to the simulated response of the feedback loop to the optical energy the laser derives in response to the data signal. - View Dependent Claims (17, 18)
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- 19. A method of controlling a laser that emits an optical signal in response to a data signal comprising sensing the optical energy in the optical signal the laser emits in response to the laser being responsive to the data signal, controlling the laser output in response to the sensed optical energy, simulating the response of the control of the laser output in response to the data signal, and modifying the response of the control of the laser output based on the simulation.
Specification