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Direct Detection Frequency Discrimination Optical Receiver for Minimum-Shift Keying Format Transmission

An incoherent detection scheme based on frequency discrimination for minimum-shift keying (MSK) optical transmission systems is proposed to significantly extend the reach of uncompensated transmission distance. The receiver consists of dual narrowband optical filters in association with an optical delay line. This photonic front end operates based on frequency discrimination principles of matched filters, rather than relying on the phase of the optical carrier. Hence, its performance is less sensitive to the all-pass quadratic phase transfer function of the fiber transmission medium and is thus less susceptible to fiber chromatic dispersion. The photonic front-end optical receiver for 40-Gb/s optical MSK offers a dispersion tolerance of up to plusmn340 ps/nm for 1-dB power penalty at a bit-error rate of 10-9. This achievement is approximately five to seven times better than that of the existing value based on the Mach-Zehnder delay interferometer (MZDI) optical balanced receiver. Furthermore, the receiver is shown to be robust to polarization-mode dispersion.