Research On Optical Sampling Techniques

The optical sampling technique is a novel method to perform time-resolved measurements of optical data signals at high bit rates with a bandwidth that cannot be reached by conventional photodetectors and oscilloscopes. Applications of optical sampling systems include high bit rate waveform and eye diagram measurements, measurements of constellation diagrams of phase modulated data signals, time-resolved measurements of the state-of-polarization as well as investigations of fiber transmission impairments. Supported by the Science Fund for Distinguished Young Scholars of Hubei Province and the Program for the New Century Excellent Talents in University of Ministry of Education of China,the realization of optical sampling and its key techniques are studied in this paper. The main contents are listed as follows:(1) Different configurations of optical sampling systems and their principles are reviewed. The schemes of sampling pulse source, clock recovery, sampling gate, opto/electrical detection and data acquisition are summarized.(2) Three different theoretical models of semiconductor optical amplifier (SOA) are introduced. The optical power transmittance function of the ultrafast nonlinear interferometer (UNI) based on SOA is derived using the Jones formalism. Then the switch window properties of the UNI are simulated based on them. The switch window properties of the UNI at 20Gb/s are also experimentally studied using a folded structure.(3) Synchronous optical sampling eye diagrams of 20Gb/s NRZ and RZ pseudorandom binary sequence are simulated in different carriers lifetime conditions, with UNI and gain- transparent UNI (GT-UNI) as sampling gate respectively. And the results are analyzed comparatively.(4) All-optical data format conversion and differential phase-shift keying (DPSK) signals demodulation are experimentally studied. All-optical nonreturn-to-zero (NRZ) to pseudo-return- to-zero (PRZ) conversion has been achieved at different bit rate using UNI and delay polarization interferometer respectively. In addition, all-optical NRZ-DPSK to PRZ conversion at different bit rate, 40Gb/s NRZ-DPSK demodulation and 40Gb/s RZ-DPSK demodulation have been achieved using delay polarization interferometer. These works are beneficial to clock recovery in synchronous optical sampling system and DPSK signals sampling using traditional sampling technique.