ФОРМИРОВАНИЕ ОДНОПОЛОСНОЙ КВАДРАТУРНОЙ ФАЗОВОЙ МАНИПУЛЯЦИИ РАДИОСИГНАЛОВ НА ПОДНЕСУЩИХ ЧАСТОТАХ В КОГЕРЕНТНОЙ ОПТИЧЕСКОЙ СИСТЕМЕ КОММУНИКАЦИИ

Abstract

The coherent optical communication technology allows to create a transmission system overlong distances with high bandwidth. Higher order modulation formats such as Quadrature PhaseShift Keying (QPSK) provide high data rates in a simple, reliable and cost-effective manner. Thesemulti-bit modulation methods are transmitted as a symbol implementing simple in-phase andquadrature (IQ) modulation formats. To increase throughput in coherent optical systems, opticalsubcarrier multiplexing is used, when several radio signals are multiplexed on one optical carrier.This multiplexing is limited by double sideband, resulting in reduced received subcarrier powerand degraded carrier-to-noise ratio. To accumulate these effects, many ways of implementingoptical single sideband (OSSB) are proposed. The paper proposes an analysis of a coherent opticaltransmission system for generating single-sideband QPSK modulation using an optical I/Qmodulator and M-ary RF pulse shaping. The pseudo-random bit sequence generator generates a10 Gb/s modulation baseband signal. Each bit sequence is converted into an M-ary sequence ofsymbols from binary signals using phase shift keying (PSK). The M-ary pulse generator generatesa multi-level pulse shaping according to the sequence of M-ary input symbols. Electrical pulsesare applied to the electrodes of the electro-optical modulator according to the Mach–Zehnderinterferometer (MZM) scheme. The I/Q modulator operated at the quadrature operating point inboth the in-phase and quadrature branches, with an extinction ratio 60 dB and 3 V switching voltage.The light wave is emitted by a CW laser with a wavelength of 1550 nm.