Research On Ultra High Speed,High Sensitivity And High-Order Optical Modulation Signal Generation And Monitoring Technology

Detecting various parameters of optical field(for example: Amplitude,Phase and Polarization)and noise source in optical network,achieving real-time monitoring of optical signal quality have become very crucial to ensure the reliability of optical communication network.Measurement of ultrahigh-speed optical signal by using traditional electronic instruments becomes expensive or even impossible due to electronic bottleneck.Nonlinear optical sampling has been proposed as one of the key technologies for solving the electronic bottleneck,accordingly,completed ultrahigh-speed optical signal eye diagram measurement.With the rapid development of optical fiber communication technology,amplitude modulation formats have gradually been replaced by the complex modulation formats(combination of amplitude modulation,phase modulation and polarization modulation formats and so on).Optical high-order modulation,due to high optical spectrum efficiency,has become one of the key technologies in ultra-high-speed optical fiber communication.Non-linear optical sampling technology,due to phase insensitive,can not be used to detect the complex modulation formats signal.Optical coherent detection technology,overcoming phase insensitive of nonlinear optical sampling technology,achieves the constellation diagram measurement of phase modulated signal or phase correlation parameters measurement of the optical field.This paper is mainly devoted to ultra-high speed optical signal generation(Optical Time-Division Multiplexing,OTDM)and detection(optical nonlinear sampling technology),constant Carrier-Envelope Phase(CEP)measurement of optical frequency comb(optical linear sampling technology),optical advanced modulation signal generation(high quality multi-level signal generation)and detection(optical coherent detection and Digital Signal Processing,DSP)technology.The main achievements of this paper are summarized as follows:1.We successfully develop an optical sampling system based on the photonicIV crystal fiber(PCF)and a low noise amplifier.A two-stage bridge Erbium-doped optical fiber amplifier is established by using low-gain Erbium-doped fiber in first stage and high-gain Erbium-doped fiber in second stage.Double arms are bridged by using two wavelength division multiplexing(WDM)between two stages,which separate the optical signal and pump light.Spontaneous emission light from back scattering is suppressed by using optical isolator in signal arms,achieving high sensitive and high gain amplifier.Low noise ultra-short pulse sampling source with adjustable repetition frequency,optical sampling gate based on dispersion-flatten high nonlinear photonic crystal fiber,using low noise photoelectric detector,data acquisition card and software clock recovery,the eye diagram of quasi 800 Gbit/s optical signal is clearly displayed in the sampling system.2.Carrier Envelope Phase(CEP),i.e.,the relative phase between the carrier waveform and the pulses envelope,can be measured by using optical linear sampling technology.The optical linear sampling technique is theoretically derivated using different quadrature phase shift keying(DQPSK)optical signal as sampled signal and optical frequency comb pulses with constant CEP as sampling source.The feasibility for carrier-envelope phase accurate measurement using linear optical sampling technique is theoretically proved.We simulate the carrier-envelope phase measurement of femto optical pulses using labview software,and the effect of pulse width and pulse chirp on measurement results is also studied.3.The high quality four-level electrical signal is generated by using arbitrary waveform generator,which will be loaded on the narrow linewidth laser vias IQ modulator.The 16-QAM optical signal is generated by controlling the bias voltage of IQ modulator and optimizing the amplitude and phase of the input electrical signal.The amplitude and phase information of optical 16-QAM signal is acquired by using optical 90° hybrid,local oscillator with narrow linewidth laser,two balanced detectors and high-speed analog to digital conversion card.Different bit rate optical 16-QAM communication systems can be achieved by changing the sampling rate in arbitrary wavefrom generator.The damages in optical signal transmission can be compensated by using digital signal processing,such as carrierfrequency offset estimation and compensation,multi-modulus adaptive equalization algorithm and carrier phase noise estimation and compensation algorithm.Constellation diagram of 16-QAM is clearly displayed by optimizing the parameters of the digital signal processing.A novel carrier phase noise estimation and compensation algorithm is proposed and used in 16-QAM signal from Matlab simulation and experimental data.The results shows the carrier phase noise can be precisely estimated by uing this algorithm.The constellation diagram is clearly displayed by using the digital signal processing algorithm.