Feasibility study on optical heterodyne MSK receiver using synchronous demodulation

The feasibility study of an optical heterodyne MSK (minimum shift keying) synchronous receiver based on a Costas loop circuit is presented. The theoretical performance of the receiver is evaluated in terms of the laser linewidth requirements, loop bandwidth, and quantum noise limited sensitivity for the permissible phase error and bit rate. The optimum loop bandwidth has been found to be 32.7% of the bit rate and the theoretical quantum noise limited receiver sensitivity is evaluated to be 29.63×10^-19 R_b. The signal power required for reliable phase-locking is found to be 12.05×10^-16 Δν watts. It is shown that an IF (intermediate frequency) linewidth of less than 0.24% of the bit rate is required to avoid performance degradation of approximately 1.0 dB due to imperfect phase locking. Therefore, the synchronous MSK receiver can be implemented using the presently available semiconductor lasers. The receiver sensitivity has been improved due to the compact spectrum of the MSK signal, giving an advantage over other schemes for high-speed optical systems operating in the multigigabit range