Deviation modulation with applications in optical communications

A new nonlinear angle modulation method for digital communications systems named Deviation Modulation (DM) is introduced. It falls in a general class of continuous phase modulation. DM places the information on the deviation of a carrier that is frequency modulated with a single tone. DM is suited for communications in systems where the baseband is modulated on a very high frequency carrier, such as light or millimeter wavelength carriers. It is shown that DM is a viable method of modulation by performing: (1) a baseband analysis of bit error rate for four different types of detectors, (2) a systems simulation of a coherent optical receiver that uses DM, and (3) a feasibility study using DM to accurately measure the half wave voltage of an optical phase modulator.; The four DM detectors analyzed are: (1) a distance metric (2) a winner take all (WTA) scheme where the input signal is found based only on the highest output, (3) a two/channel method that uses the two highest outputs, (4) and a 3-out-of-4 detector that uses the 3 highest outputs. The best performance was obtained from the distance metric. The WTA detector is within 3dB of the distance metric and is easily implemented, but it requires a large number of channels in some applications. The other detectors address this practical drawback. Simulations of a DM optical communications link with a homodyne receiver, a channelizer demodulator and the WTA detector were done for a representative rate of 250MB/sec. There is no fundamental limit to the data rate DM can use.; DM offers four significant system advantages over other modulation methods for use at optical frequencies: (1) no requirement for a phase coherent local oscillator, (2) ease of modulation, (3) ease of demodulation, (4) low sensitivity to laser linewidth. We demonstrated DM by measuring the half wave voltage of an optical phase modulator. The deviation in the optical carrier is dependent upon both the applied modulating voltage and the half wave voltage. Measuring the deviation to determine the half wave voltage demonstrated the feasibility of DM communication systems.