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This circuit simplifies the control system needed to maintain constant optical power out of a semiconductor injection laser over a range of temperatures.
English (United States)
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Injection Laser Biasing Circuit Using Temperature Dependent Resistors
This circuit simplifies the control system needed to maintain constant optical
power out of a semiconductor injection laser over a range of temperatures.
Semiconductor injection lasers have lasing threshold currents
that increase with temperature (I(t) = I(o) exp (T/T(o))). For many
applications, it is imperative that the light power out of the laser
remain constant over a range of temperatures. To maintain a
constant optical power level, the biasing current must be controlled.
Most circuits which do this are based on the feedback principle;
the optical power is monitored off the back mirror of the laser and
is used to control the bias current.
If a resistor 10 with a negative temperature coefficient is placed in series with
the laser 12, the current through the laser will increase with temperature. This
increase in current with temperature maintains the laser at or near threshold.
The figure shows this circuit.
The circuit has the advantage of being simple; that is, it uses very few
components. The components are passive. The back mirror of the laser need
not be exposed for monitoring. The circuit is physically small.
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