We present simulation results for a 5 Gb/s optically pre-amplified, differential phase shift keying communication
system achieving -48.1 dBm (about 24.7 photons/bit) receiver sensitivity at 10-9 bit-error-rate and using an optical delay
line interferometer made by ourselves with 1 bit delay as the demodulator. The system is also experimental tested and
sensitivity of the receiver is -36.5 dBm (about 106.6 photons/bit). The experimental results have some penalty in
sensitivity comparing to the results in the simulation because the 1 bit delay interferometer is sensitive to the
environment such as temperature, tremble and so on. To our knowledge if the interferometer is well designed and
optimized, the experimental results can correspond with the simulative results and an optically pre-amplified direct
detection DPSK receiver with high sensitivity can be realized.
Lots of researches have simulated performance of optical system based on plane wave or spherical wave model, but
optical field is Gauss distribution in real optical communication system. So we derive the relationships between the
signal-to-noise ratio (SNR), bit error rate (BER), channel capacity (C) and the transmission distance of the space laser
communication system, which is obtained by the Gaussian beam propagation model for on-off keying (OOK) modulated
signal under horizontal link. We numerically study the influence of atmospheric turbulence on system performance. we
get the conclusions: Under weak turbulence intensity, as the turbulence intensity increases, the C and SNR for OOK
modulated space laser communication system decrease while the BER increase; In the case of strong turbulence intensity,
the intensity scintillation and the BER dramatically increase with the increase of transmission distance, and then become
saturated; In the condition of turbulence intensity and transmission distance are both constant, the longer the wavelength
results in greater C, higher SNR and lower BER. Selecting longer communication wavelength can mitigate the impact of
the atmosphere turbulence on the communication system in some extent.
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