Active APD gain control for an optical receiver
AssigneeTektronix, Inc.
InventorDuwayne R. Anderson
Life of this patent
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Abstract
An active avalanche photo-diode, APD, gain control circuit for use in an optical receiver includes a bias generator for varying the bias on a variable gain APD in response to bias control values generated by a controller. The controller receives the output of the optical receiver and determines the system noise of the receiver for the various bias control values. The system noise is compared to a threshold value for establishing the optimum bias for optimum gain of the APD. The gain control circuit is useable in an optical receiver in an optical time domain reflectometer, OTDR, for increasing the dynamic range of the OTDR.
Claims22
An active gain control circuit for a variable gain avalanche photo-diode usable in an optical receiver having a signal-to-noise ratio being a function of the gain of the variable gain avalanche photo-diode comprising:
- a bias generator producing a bias that is coupled to the avalanche photo-diode to vary the gain the avalanche photo-diode;
- and
- a controller coupled to receive the output of the optical receiver and producing varying bias control values that are coupled to the bias generator to vary the bias on the avalanche photo-diode with the receiver output being generated without an optical signal present on the avalanche photo-diode and the controller determining system noise levels of the optical receiver for the various bias control values and comparing the system noise levels to a threshold value derived from a statistical measure of the optical receiver system noise without an optical signal present for establishing an optimum bias for optimizing the gain of the avalanche photo-diode for increasing the signal-to-noise ratio in the optical receiver.
An optical time domain reflectometer having an optical source for generating an optical output coupled into an optical fiber under test and an optical receiver having a signal-to-noise ratio for receiving an optical return signal from the test fiber with the optical receiver having a variable gain avalanche photo-diode responsive to an active gain control circuit for converting the optical return signal into an electrical signal comprising:
- a bias generator producing a bias that is coupled to the avalanche photo-diode for biasing the avalanche photo-diode;
- and
- a controller coupled to receive the output of the optical receiver and producing varying bias control values that are coupled to the bias generator to vary the bias on the avalanche photo-diode with the receiver output is generated without the optical return signal being present on the avalanche photo-diode and the controller determining system noise levels of the optical receiver for the various bias control values and comparing the system noise levels to a threshold value derived from a statistical measure of the optical receiver system noise without the optical return signal present for establishing an optimum bias for optimizing the gain of the avalanche photo-diode for increasing the signal-to-noise ratio in the optical receiver.
A method of optimizing the gain of a variable gain avalanche photodiode in an optical receiver having a signal-to-noise ratio comprising the steps of:
- a) generating bias control values for driving a bias generator for varying the gain of the avalanche photo-diode;
- b) measuring a system noise level of the optical receiver for each bias control value using the receiver output with the output being generated without an optical signal being present on the avalanche photo-diode;
- c) comparing the measured system noise level at each bias control value to a threshold value derived from a statistical measure of the optical receiver system noise without an optical signal present;
- and
- d) selecting the bias control value that produces the bias on the avalanche photo-diode for optimizing the gain of the avalanche photo-diode and increasing the signal-to-noise ratio in the optical receiver.
A method for increasing the dynamic range of an optical time domain reflectometer having an optical receiver with a variable gain avalanche photo-diode comprising the steps of:
- a) generating bias control values for driving a bias generator for varying the gain of the avalanche photo-diode;
- b) measuring system noise levels of the optical receiver for each bias control value using the receiver output with the output being generated without an optical signal being present on the avalanche photo-diode;
- c) comparing the measured system noise level at each bias control value to a threshold value derived from a statistical measure of the optical receiver system noise without an optical signal present;
- and
- d) selecting the bias control value that optimizes the bias on the avalanche photo-diode while producing system noise no greater than the threshold for optimizing the gain of the avalanche photo-diode and increasing the dynamic range of the optical time domain reflectometer.
Dependencies are inferred from the claim text.