Optoelectronic transceiver module laser diode stabilizer and bias control method

Abstract

A power stabilizer for maintaining a constant level of output power from a laser transmitter. The laser transmitter has a laser diode which produces an optical output which corresponds to the level of bias current received. In addition, the laser transmitter has a photodiode which produces a feedback signal which corresponds to the optical output power being produced by the laser diode. Furthermore, the power stabilizer consists of a digitally controlled potentiometer for producing a reference input signal and an op-amp for comparing the feedback signal and the reference input signal to produce a control signal to supply bias current.

We claim: 
     
       1. A power stabilizing circuit for maintaining a constant level of output power from a laser transmitter, wherein said laser transmitter includes a laser diode configured to emit an optical output signal having an output power level corresponding to a bias current input to said laser diode, and a photodiode for monitoring said optical output signal, providing a voltage feedback signal proportional to said output power level, said power stabilizing circuit comprising: a) a digitally controlled potentiometer, said potentiometer including a wiper contact having a variable output resistance for supplying an adjustable voltage reference signal;   b) an op-amp having first and second inputs, said adjustable voltage reference signal connected to said first input, and said voltage feedback signal connected to said second input, such that said op-amp compares said voltage reference signal and said voltage feedback signal to generate an output control signal corresponding to the voltage difference between said first and second input; and   c) a bias current driver driven by said output control signal for supplying said bias current to said laser diode.   
     
     
       2. The power stabilizing circuit of claim 1, wherein said current driver comprises a current drive transistor, having a base electrically connected to said output control signal, a collector connectted to said laser diode, and an emitter connected to a voltage source, whereby said transistor provides a bias current to said laser diode inversely proportional to said output control signal. 
     
     
       3. The power stabilizing circuit of claim 2, further comprising an RC filter disposed between said op-amp and said transistor such that said output control signal is filtered prior to connection to said base of said transistor. 
     
     
       4. The power stabilizing circuit of claim 1 wherein said potentiometer provides resistance trimming of said adjustable voltage reference signal by selectably altering said output resistance in a number of incremental steps between a maximum resistance value and zero ohms. 
     
     
       5. The power stabilizing circuit of claim 4 wherein said maximum resistance is 10k ohms. 
     
     
       6. The power stabilizing circuit of claim 4 wherein said number of incremental steps equals ninety-nine. 
     
     
       7. An apparatus for transmitting electrical data signals onto an optical transfer medium, said apparatus comprising: a) an AC driver for receiving said electrical data signals and providing a corresponding data signal;   b) a laser transmitter having a laser diode and a photodiode, said laser diode for producing optical power modulated by said data signal and transmittable over said optical transfer medium, and said photodiode for producing a feedback signal proportional to said optical output power produced by said laser diode; and   c) a power stabilizing circuit comprising; i) a digitally controlled potentiometer for producing a reference input signal;   ii) an op-amp for comparing said feedback and said reference input signal, said op-amp generating a output control signal; and   iii) a bias current drive transistor, responsive to said control signal, for supplying said bias current to said laser diode.     
     
     
       8. A method of maintaining a constant level of output power from a laser transmitter, comprising the steps of: a) providing a laser transmitter having a laser diode and a photodiode, said laser diode responsive to a reference voltage input which produces a level of bias current to produce a corresponding level of optical output power and said photodiode responsive to said optical output signal to produce a feedback signal which corresponds to said optical output power produced by said laser diode;   b) setting the resistance of a digitally controlled potentiometer to produce a reference input signal; and   c) comparing said feedback signal and said reference input signal to produce a control signal to supply said bias current. .Iadd.   
     
     
       9.  An apparatus for transmitting electrical data signals over an optical transfer medium; comprising: an AC driver circuit receiving said electrical data signals, generating a voltage signal based on said electrical data signals, and generating an AC data signal from said voltage signal;   a laser transmitter having a laser diode and a photodiode, said laser diode producing optical power modulated by said AC data signal and transmittable over said optical transfer medium, said photodiode producing a feedback signal based on said optical output power produced by said laser diode; and   a power stabilizing circuit including a comparator, a digitally controlled potentiometer and a bias current drive transistor, said comparator having inputs for each of said feedback signal and a voltage reference signal wherein said comparator compares said feedback signal and said voltage reference signal to generate an output control signal, said digitally controlled potentiometer operatively coupled to permit adjustment of one of said inputs for corresponding adjustment of said output control signal, and said bias current drive transistor responsive to said output control signal for supplying a bias current to said laser diode..Iaddend..Iadd.10. The apparatus as claimed in claim 9, wherein said comparator comprises an operational amplifier..Iaddend..Iadd.11. The apparatus as claimed in claim 9, wherein said digitally controlled potentiometer is operatively coupled to adjust a voltage of said feedback signal..Iaddend..Iadd.12. The apparatus as claimed in claim 9, wherein said digitally controlled potentiometer is operatively coupled to adjust a voltage of said voltage reference signal..Iaddend..Iadd.13. The apparatus as claimed in claim 9, further comprising:   a differential receiver in said AC driver circuit, said differential receiver comprising a pair of differential inputs for receiving said electrical data signals and an output via which said voltage signal is generated..Iaddend..Iadd.14. The apparatus as claimed in claim 13, further comprising:   a resistor electrically connected in series with said output of said differential receiver in said AC driver circuit; and   a capacitor electrically connected in parallel to said resistor..Iaddend..Iadd.15. The apparatus as claimed in claim 13, further comprising:   a pair of blocking capacitors, each blocking capacitor electrically connected to one of the inputs of said differential receiver..Iaddend..Iadd.16. A method of maintaining a constant level of output power from a laser transmitter, comprising the steps of:   providing a laser transmitter having a laser diode and a photodiode, said laser diode responsive to an output control signal which supplies a level of bias current to produce a corresponding level of optical output power, said photodiode responsive to said optical output power to produce a feedback signal which corresponds to a level of said optical output power;   receiving electrical data signals in an AC driver circuit;   generating a voltage signal in said AC driver circuit based on said electrical data signals;   generating said AC data signal from said voltage signal in said AC driver circuit;   modulating said optical output power with said AC data signal;   comparing said feedback signal and a voltage reference signal to produce said output control signal; and   adjusting the resistance of a digitally controlled potentiometer to adjust said output control signal..Iaddend.