Question

i want report for DIRECT MODULATION OF LASER DIODES include introduction and conclusion

Answer 1

It is possible to internally modulate the output of a semiconductor laser by controlling either the current flow through the device or some internal cavity parameter.
Such direct modulation of the laser output has the advantages of simplicity and potential for high frequency operation.

Principle

The light output of a semiconductor laser can be directly modulated, i.e., made to vary in response to changes within the laser cavity, so as to produce amplitude modulation (AM), optical frequency modulation (FM), or pulse modulation (PM). Most often, the laser output is either amplitude or pulse modulated by controlling the current flow through the device. However, other parameters, such as the dielectric constant
or the absorptivity of the laser cavity material can be varied to produce FM, as weIl as AM and PM of the output. The basic principles of these modulation techniques, most of which were developed during the late 1960's and 1970's. More sophisticated improvements, which have led to reliable direct modulation of laser diodes at microwave frequencies.