TRANSMITTER IN OPTICAL COMMUNICATION SYSTEM, CONTROL METHOD FOR NEST TYPE MODULATOR, AND PROGRAM

To provide: a transmitter which minimizes a bit error rate at a reception side, by using a nest type modulator; a bias control method for the nest type modulator; an optical communication system; and a program.SOLUTION: In an optical communication system, a transmitter 10 comprises a nest type modulator 100 including a first modulation unit MZA and a second modulation unit MZB of a Mach-Zehnder (MZ) type and a phase shifter 101 which are connected in parallel. . The transmitter is configured to: perform Intensity phase modulation on two series of optical pulses by phase modulation for performing binary modulation on relative phases of the two series of optical pulses and intensity modulation for modulating any one of the two series of optical pulses into intensity 0 in accordance with transmission information, and transmit the two series of optical pulses to a receiver 20; on the basis of reception information and transmission information in the receiver, control, by a control unit 112, bias voltages DCA and DCB of the first modulator and the second modulator so as to minimize a first error rate ERZ relating to the intensity modulation; and control, by a control unit 111, a bias voltage DCC of the phase shifter 101 so as to minimize a second error rate ERY relating to the phase modulation.SELECTED DRAWING: Figure 2 【課題】ネスト型変調器を用いて受信側のビット誤り率を最小化する送信機、ネスト型変調器のバイアス制御方法、光通信システム及びプログラムを提供する。【解決手段】光通信システムにおいて、送信機１０は、並列接続されたマッハツェンダ（ＭＺ）型の第１変調部ＭＺＡおよび第２変調部ＭＺＢと位相シフタ１０１とを備えたネスト型変調器１００を有し、送信情報に従って２連光パルスの相対位相を２値変調する位相変調と２連光パルスのいずれか一方を強度０に変調する強度変調とにより２連光パルスを強度位相変調して受信機２０へ送信し、受信機での受信情報と送信情報とに基づいて、制御部１１２が強度変調に関する第１誤り率ＥＲＺを最小化するように第１変調器および第２変調器のそれぞれのバイアス電圧ＤＣＡ，ＤＣＢを制御し、制御部１１１が位相変調に関する第２誤り率ＥＲＹを最小化するように位相シフタ１０１のバイアス電圧ＤＣＣを制御する。【選択図】図２