Adaptive power supply for avalanche photodiode

• US 6,222,660 B1
• Filed: 06/09/1998
• Issued: 04/24/2001
• Est. Priority Date: 06/09/1998
• Status: Expired due to Fees

• Current Assignee: Tektronix Incorporated (Fortive Corp.)
• Original Assignee: Tektronix Incorporated (Fortive Corp.)
• Inventors: Traa, Einar O.
• Primary Examiner(s): Chan, Jason
• Assistant Examiner(s): Leung, Christina Y
• Application Number:
  US09/094,438
• Time in Patent Office: 1,050 Days
• Field of Search: 359/189, 359/193, 359/194, 359/195, 359/161, 359/158
• US Class Current: 398/213
• CPC Class Codes: H04B 10/077 using a supervisory or additional signal
• CPC Class Codes: H04B 10/07955 Monitoring or measuring power
• CPC Class Codes: H04B 10/6911 Photodiode bias control, e.g. for compensating temperature variations

Abstract

An adaptive power supply for an avalanche photodiode (APD) is used to determine an optimum bias voltage. Without an optical signal input the adaptive power supply applies a swept voltage to the APD while monitoring the photodiode current. When breakdown occurs, the voltage is noted and the bias voltage from the adaptive power supply is set at a specified offset below the breakdown voltage. Where a source of optical digital data signal is present, it is coupled to the input of the APD via a programmable optical attenuator. The electrical digital signal output from the APD is input to a bit error rate counter, the output of which is monitored. For different optical power levels the APD bias voltage is swept by the adaptive power supply, determining a constant power level curve over which the bit error rate is virtually zero. This is repeated for a plurality of optical power levels, the resulting family of curves defining a region within the bit error rate is virtually zero. The adaptive power supply is set to a value that falls within the virtually zero bit error rate region for the expected optical power level input.

Claims

1. A method of determining an optimum bias voltage for an avalanche photodiode that converts an optical data signal to an electrical data signal for optical digital data applications comprising the steps of:

applying a calibrated optical data signal via a programmable optical attenuator to the avalanche photodiode;

obtaining from the electrical data signal from the avalanche photodiode in response to the calibrated optical data signal a bit error rate;

adjusting a bias voltage for the avalanche photodiode over a range of values to determine a constant optical power level curve for the calibrated optical data signal where the bit error rate is virtually zero; and

selecting as the optimum bias voltage a value of the bias voltage at one end of the constant optical power level curve closest to a breakdown voltage for the avalanche photodiode.

2. The method as recited in claim 1 further comprising the steps of:

repeating the applying, obtaining and adjusting steps at different settings of the programmable optical attenuator corresponding to different optical power levels to generate a family of constant optical power level curves where the bit error rate is virtually zero; and

selecting as the optimum bias voltage a value of the bias voltage at one end of the constant optical power level curve corresponding to a current setting of the programmable optical attenuator closest to the breakdown voltage for the avalanche photodiode.

3. An apparatus for determining an optimum bias voltage for an avalanche photodiode that converts an optical data signal to an electrical data signal for optical data applications comprising:

a programmable optical attenuator to which the optical data signal is applied as an input, an attenuated optical data signal being output from the programmable optical attenuator and coupled to the avalanche photodiode;

an adjustable bias voltage source coupled to the avalanche photodiode; and

means for generating an attenuator control signal to select a setting of the programmable optical attenuator as a function of the electrical data signal from the avalanche photodiode and for adjusting the adjustable bias voltage source as a function of a constant optical power curve where a bit error rate for the electrical data signal is virtually zero corresponding to the setting of the programmable optical attenuator to provide the optimum bias voltage at a point at one end of the constant optical power curve closest to a breakdown voltage for the avalanche photodiode.

4. The apparatus as recited in claim 3 wherein the controlling means comprises:

means for extracting from the electrical data signal digital data and a recovered clock;

means for detecting the bit error rate from the digital data and recovered clock; and

means for processing the bit error rate so that when the bit error rate is non-zero the attenuator control signal is generated to select a different setting for the programmable optical attenuator and the optimum bias voltage from the adjustable bias voltage source is adjusted according to the constant optical power curve for the different setting of the programmable optical attenuator.