In an optically preamplified differential phase-shift keying (DPSK) receiver with Mach–Zehnder interferometer (MZI) demodulation, it is essential to couple free space light into a single-mode fiber, by which the received optical signal can be guided into the amplifier and MZI. Random angular jitter has a profound impact on fiber coupling efficiency, in that it would significantly deteriorate the receiver performance. In this paper, the average bit error rate (BER) of fiber-coupled DPSK receivers is obtained in the presence of random angular jitter. It is shown that the degradation is significant when the random angular jitter normalized by the mode field radius is larger than 0.3. We further analyze the impact of other factors, including central obstruction and optical filter transfer functions. Our results show that the super-Gaussian filter outperforms other filters and leads to lower average BER at a fixed optical signal-to-noise ratio. This work can be used to improve the design of fiber-coupled DPSK receivers.
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