Control apparatus

In combination:

• a semiconductor laser;
• and apparatus for controlling the intensity and wavelength of light emitted by said laser, said wavelength being determined by an operating parameter of said laser;
• said apparatus comprising:
• means to supply drive current to said laser to cause said laser to emit light;
• first emission-responsive means to receive light emitted by said laser and to produce a first electrical output signal in dependence upon the intensity of said emitted light received thereby;
• current control means responsive to said first electrical output signal and coupled to said drive current supply means to control said drive current supplies to said laser to maintain said intensity of said emitted light substantially constant;
• second emission-responsive means to receive light emitted by said laser and to produce a second electrical output signal which varies in dependence upon said wavelength of said emitted light received thereby;
• a resonant cavity at the output of said laser;
• lens means and an optical grating in the path of said light emitted by said laser;
• and means to control the angle of said optical grating relative to the axis of said path under the control of said second output signal to maintain said wavelength of said emitted light substantially constant.