Current control for an analog optical link

A control circuit for a laser to provide a minimal light output, comprising:

• a) a laser diode providing a light output;
• b) a feedback circuit receiving the light output and providing an output current Ifb;
• c) a current source providing a current Io;
• d) means for combining the currents Ifb and Io as a pre-bias current for the laser;
• and
• e) means for operating the feedback circuit to achieve a minimal pre-bias current to the laser and light output such that the laser average output power is at least equal to a predetermined light output value (Lo), where Lo is non-zero and wherein the pre-bias current does not fall below a minimum current level and is set to a minimum level defined by Imin=Ith(T=T')+Iac,max where:
• Ith=the laser threshold current at operating temperature T';
• Iac,max is the maximum of ›-1.times.Iac(t)!, (Iac(t) is the AC signal input to the laser);
• and T' is the temperature where (Iac,min).times.(the laser's slope efficiency)=Lo.

In a control circuit for a laser, the control circuit including a monitor diode coupled to the laser and to a feedback circuit which in conjunction with a current source provides a pre-bias current to the laser, a method for controlling the laser output power comprising the steps of:

• a) generating a feedback current (Ifb) in the feedback circuit;
• b) generating a current value Io from a current source;
• c) combining the feedback current and the current source current as a pre-bias current to the laser (Ipb) wherein the pre-bias current does not fall below a minimum current level and is set to a minimum level defined by Imin=Ith(T=T')+Iac,max where:
• Ith=the laser threshold current at operating temperature T';
• Iac,max is the maximum of ›-.times.Iac(t)!, (Iac(t) is the AC signal input to the laser);
• and T' is the temperature where (Iac,min).times.(the laser's slope efficiency)=Lo;
• d) providing an input signal to the laser as an input signal superimposed on the pre-bias current;
• e) generating a current Id in the monitor diode, the current Id being proportional to the laser output light;
• f) supplying Id to the feedback circuit;
• and
• g) varying the current from the feedback circuit to the laser so that the pre-bias current is above a minimal value (Imin) and as Id changes with respect to a preset value, the pre-bias current is adjusted so that the average light output from the laser is held above a minimum value (Lo).

A method of operating an optical transmission system comprising the steps of:

• a) setting a laser pre-bias current (Ipb) to be greater than, or equal to a predetermined value (Imin) wherein the minimum pre-bias current for the laser is set to Imin=Ith(T=T')+Iac,m where:
• Ith=(T) is the laser threshold current at operating temperature T';
• Iac,m is the maximum of ›-1.times.Iac(t)!, (Iac(t) is the AC signal input to the laser);
• and T' is the temperature where (Iac,m).times.(the laser's slope efficiency)=Lo;
• and
• b) maintaining Ipb above the predetermined value such that the laser average output power is at least equal to a predetermined light output value (Lo).

In a control circuit for a laser, the control circuit including a monitor diode coupled to the laser and to a feedback circuit which provides a pre-bias current to the laser, a method for controlling the laser output power comprising the steps of:

• a) generating a pre-bias current Ipb in the feedback circuit wherein the pre-bias current does not fall below a minimum current level and is set to a minimum level defined by Imin=Ith(T=T')+Iac,max where:
• Ith=the laser threshold current at operating temperature T':
• Iac,max is the maximum of ›-1.times.Iac(t)!, (Iac(t) is the AC signal input to the laser);
• and T' is the temperature where (Iac,min).times.(the laser's slope efficiency)=Lo;
• b) providing an input signal to the laser as an input signal superimposed on the pre-bias current;
• c) generating a current Id in the monitor diode, the current Id being proportional to the laser output light;
• d) supplying Id to the feedback circuit;
• and
• e) varying the current from the feedback circuit to the laser so that the pre-bias current is above a minimal value (Imin), and as Id changes with respect to a preset value, the pre-bias current is adjusted so that the average light output from the laser is held above a minimum value (Lo).

A method of operating an optical transmission system comprising the steps of:

• a) setting a laser pre-bias current (Ipb) to be greater than, or equal to a predetermined value (Imin);
• and
• b) maintaining Ipb above the predetermined value such that the laser average output power is at least equal to a predetermined light output value (Lo), where Lo is non-zero and wherein the pre-bias current does not fall below a minimum current level and is set to a minimum level defined by Imin=Ith(T=T')+Iac,max where:
• Ith=the laser threshold current at operating temperature T';
• Iac,max is the maximum of ›-1.times.Iac(t)!, (Iac(t) is the AC signal input to the laser);
• and T' is the temperature where (Iac,min).times.(the laser's slope efficiency)=Lo.