Novel Applications of Chirp Managed Laser in Optical Fiber Communication Systems.

摘要

Nowadays, with the dramatically growing bandwidth requirement of Internet, the number of wavelength division multiplexing (WDM) channels of the optical fiber communication systems is increasing rapidly. Hence, optical transmitters with cost effectiveness, high power efficiency, and excellent transmission performance are necessary. Especially, for access and metropolitan applications, simple configuration is the essential factor. The conventional optical transmitter is composed of a laser as continuous-wave (CW) source and one or more external modulators for modulation. However, the high insertion loss, large driving voltage, and extra cost of external modulator make it relatively bulky and power-hungry.;Chirp managed laser (CML), comprising a directly modulated semiconductor laser (DML) and a passive optical filter, is an alternative promising transmitter candidate. It has the merits of smaller device size, lower cost, less power consumption, and higher fiber chromatic dispersion (CD) tolerance, compared with that based on external modulator. In this thesis, we have investigated several novel applications of CML in optical fiber communication systems, taking advantage of its unique phase modulating and spectral reshaping properties. These topics include optical return-to-zero (RZ) pulses generation using CML, M-ary RZ differential phase-shift-keying (RZ-DPSK) signals generation using CML, and enhanced CD tolerance of CML with pre-emphasis. These CML-based designs consume low power for less electrical pre-coding, require reduced or no external modulator, and show notable transmission performances.;Optical RZ pulses generation using CML: RZ pulses have been widely used in optical fiber communication systems together with on-off-keying (OOK) and DPSK modulation formats, for its high robustness towards inter symbol interference (ISI) and nonlinear distortions. In this thesis, we propose and experimentally demonstrate the technique of 10-Gb/s optical RZ pulses generation using CML. No external modulator is used for pulse carving. The frequency of the sinusoidal driving signal is half the output RZ pulse rate. 70-km and 50-km error-free SSMF transmissions have been achieved for the 10-Gb/s 33%-duty-cycle and 67%-duty-cycle CML-RZ- pulses based RZ-DPSK signals, respectively. Later, we extend to demonstrate the scheme of 20-Gb/s RZ pulses generation using CML driven at one-fourth the output pulse rate and investigate the transmission performance of the 20-Gb/s CML-RZ-pulses based RZ-OOK signal.;M-ary RZ-DPSK signals generation using CML: M-ary RZ-DPSK is an attractive modulation format in optical fiber long-haul transmission systems, due to the advantages of high receiver sensitivity, increased spectral efficiency, and strong robustness against fiber nonlinearities. In this thesis, we propose and experimentally demonstrate the techniques of RZ-DPSK, ¾-RZ-DQPSK, and RZ-DQPSK signals generation using CML. First, we generate the 10-Gb/s RZ-DPSK signal using CML and pulse carver. It does not require any differential encoder or phase modulator (PM). The CML-based RZ-DPSK signal shows 3-dB higher receiver sensitivity after 70-km SSMF transmission without dispersion compensation and comparable nonlinear tolerance performance, compared with that generated by PM. Next, this proposal is generalized to generate the 10-Gbaud RZ-DQPSK signal using CML and pulse carver. Compared with the complex pre-coding required for the MZM-based RZ-DQPSK transmitter, only a simple exclusive-or (XOR) encoder is needed for that based on CML. Later, we demonstrate the scheme of 10-Gbaud ¾-RZ-DQPSK signal generation using single CML, without the need for external pulse carver. In this new signal format, the symbols with a differential phase shift of 0 remain non-return-to-zero (NRZ), while those with differential phase shifts of 0.5pi, pi, and 1.5pi are RZ. Error-free transmission is realized over 60-km SSMF without optical signal-noise-ratio (OSNR) penalty. Finally, we demonstrate the technique of 10.709-Gbaud RZ-DQPSK signal generation using single CML, without the need for differential encoder, external modulator, or pulse carver. The full RZ-shape is orientated from the combined effect of the designated driving signal and the narrow-bandwidth filter in CML. It realizes 40-km SSMF transmission at bit-error-rate (BER) of 10-9 .;Enhanced CD tolerance of CML with pre-emphasis: For optical access and metropolitan networks, CML is a promising transmitter for its low cost, compact footprint, low power consumption, and high CD tolerance. In this thesis, we propose and experimentally realize the 10-Gb/s 300-km SSMF transmission at BER of 10-9 using CML with a simple and passive pre-emphasis driver. The 10-Gb/s standard CML signal without pre-emphasis can only be transmitted up to 220 km, in comparison. No expensive optical dispersion compensation module (DCM) or power-hungry electronic dispersion compensation (EDC) technique is used. Later, we further demonstrate the 20-Gb/s 100-km SSMF transmission at BER of 10-9, using CML with pre-emphasis.