Coherent transmission system has been extensively studied in recent years, and it can use different modulation formats and different detection techniques. The modulation formats are ASK (Amplitude shift keying), PSK (Phase shift keying), and FSK (Frequency shift keying). The detection techniques are Homodyne detection and Heterodyne detection, and they need a laser in the receiver called as the LO (Local oscillator). In the previous study, the BPSK (Binary phase shift keying) modulation format was investigated, and the pilot carrier method realized the Homodyne Detection. The merit of the pilot carrier is that it do not need the LO in the receiver. In this master thesis, the QPSK (Quadrature phase shift keying) modulation format is investigated using the pilot carrier method, The BER is calculated using the matlab program. The performance of 20G bit/s, 50 km transmission system using the BPSK and the QPSK is compared to clarify the merits and demerits of the QPSK modulation.

The coherent system has been extensively studied in recent years. The reasons are that receiver sensitivity is better than Intensity Modulation with Direct Detection (IM/DD) and the spectral efficiency of wavelength division multiplexing (WDM) is increased. The modulation formats of the coherent system are Amplitude shift keying (ASK), Phase shift keying (PSK), and Frequency shift keying (FSK). The detection techniques are Homodyne detection and Heterodyne detection, both of them need a laser light source in the receiver called as the Local oscillator (LO). In the previous study, the Quadrature phase shift keying (QPSK) modulation format with Pseudo Random Binary Sequence (PRBS) 27-1 to transmit 51km was investigated, and the pilot carrier method realized the Homodyne Detection. The merit of the pilot carrier is that the LO is not necessary in the receiver. In this master thesis, the optical signal of the QPSK modulation format with PRBS 215-1 is transmitted over 500km using the pilot carrier method. A WDM system demonstration is also conducted to increase the system capacity. The Bit error rate (BER) is calculated by the MATLAB program. The BER performance of 20G bit/s, 500 km transmission system using the QPSK with single channel and multiplexed channels were measured.