20 April 1995 Experimental and numerical determination of crosstalk in a coherent optical multichannel receiver
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We developed a multichannel receiver concept for densely packed optical channels which are to be demodulated simultaneously. In each channel, the input is a binary phase modulated optical signal of approximately the same optical power. For experimental verification of the concept we designed, realized and tested a dualchannel system working at 2 X 8.45 Mbit/s, employing DPSK modulation of Nd:YAG ring lasers at 1.064 micrometers . In the transmitter, the channel distance is set by means of a synthesizer-stabilized optical PLL. In the receiver, a balanced frontend based on a polarization-preserving fiber directional coupler, InGaAs photodiodes, and a 5 mW local laser oscillator transposes the optical input channels to a first intermediate frequency. To achieve good channel separation and reliable simultaneous demodulation, conversion to a second and third intermediate frequency is implemented. If only one channel carries information, a sensitivity of 3.2 dB above the shot noise limit is achieved. The crosstalk penalty depends on the optical channel distance, on the channel selection filter, and the post-detection filter. The power penalty due to crosstalk is investigated experimentally and is compared with theoretically predicted results. For a channel distance of twice the data rate a crosstalk penalty of less than 2 dB is achieved.
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Martin A. Schreiblehner, Michael M. Rasztovits-Wiech, Walter R. Leeb, Arpad L. Scholtz, "Experimental and numerical determination of crosstalk in a coherent optical multichannel receiver", Proc. SPIE 2381, Free-Space Laser Communication Technologies VII, (20 April 1995); doi: 10.1117/12.207416; https://doi.org/10.1117/12.207416

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