Optically-based frequency synthesizer for generating an electric output signal at a preselected frequency that can be changed over a wide band of frequencies for communication purpose

An optically-based frequency synthesizer for generating an electric output signal at a preselected frequency having a given period that can be changed over a wide band of frequencies for communication purposes, comprising:

• modulating means having an input for receiving a command signal corresponding to said preselected frequency, and an output for generating a current driving signal having a DC component, and a modulating component formed of an AC signal having a predetermined time period which is an integer multiple of the period of said preselected frequency, and an amplitude responsive to said command signal;
• a laser having an input for receiving said current driving signal so that said laser is driven to emit a coherent light signal at at least two different wavelengths during the predetermined time period, said coherent light signal having a given coherence time;
• optical isolating means for receiving said light signal emitted by said laser for preventing undesirable optical feedback into said laser;
• an optical splitting device having an input optically connected to an output of said isolating means, and first and second outputs;
• a first optical path having an end optically connected to the first output of said splitting device;
• a second optical path having an end optically connected to the second output of said splitting device, and a delay means along its length for producing a time delay in light signal transmitted through said second path with respect to light signal transmitted through said first path, said time delay being shorter than said coherence time;
• an optical recombining device having first and second inputs optically connected to other ends of said first and second paths respectively, so that said light signal transmitted through said first path can be beat with said light signal transmitted through said second path, said light signals transmitted through said paths having a frequency difference determined by said time delay;
• a non-linear device having an input optically connected to an output of said recombining device, and an output for generating said electric output signal at said preselected frequency which corresponds to said frequency difference;
• and
• means for stabilizing operation of said synthesizer with respect to ambient temperature, whereby by applying said command signal to said modulating means, said output signal can be generated for communication purposes.