Self-Triggered Harmonic Mode-Locking WRC-FPLD Based Synthesizer-Free 10 Gbit/s RZ Data Transmission System
Date Issued
2011
Date
2011
Author(s)
Lin, Chun-Ju
Abstract
A self-triggered harmonic mode-locked weak-resonant-cavity Fabry-Perot laser diode is employed as the 10 Gbit/s RZ data generator. Derived from the rate equation, the pulsewidth formula in actively mode-locking theory is modified and illuminates the shortening of the pulse as a function of optical feedback ratio and microwave power gain. The pulsewidth is narrower with higher optical injection and microwave gain due to the gain saturation of the laser diode and the increase of the modulation depth. The timing jitter, pulsewidth of the pulse train and phase noise of the microwave signal under different biased current, optical injection and microwave gain are measured. The optimized jitter and pulsewidth are 0.9 ps and 20 ps, respectively. With higher microwave gain, the SNR and ER are improved to 10.2 dB and 13.8 dB due to the enhancement of the peak power and elimination of the residual carrier. At the optimized operation condition, the receiving sensitivity of -18.5 dBm and -16.5 dBm before and after channelization, respectively, are obtained with 10 Gbit/s RZ-OOK data.
To further enhance the cavity Q-value, 100-m single mode fiber is added in the OEO loop. The minimal single sided-band phase noise of -70 dBc/Hz at 100Hz offset is measured while significant degradation is observed with cavity length longer than 200 m. The optimized pulse train exhibits timing jitter of 0.67 ps and pulsewidth of 18.5 ps with 100-m single mode fiber. Chirping, mode-partition noise, spurious signal and environmental fluctuation are enlarged with longer loop length and these factors oppose the expected improvement induced by longer cavity and the resultant higher Q-value. The optimized RZ pulsed carrier modulated by MZM with 10 Gbit/s RZ-OOK data shows high SNR of 11 dB and lower receiving sensitivity of -19.2 dBm than the system with original cavity length. With 200-GHZ spacing AWG, the channelization is performed and the power penalty of only 2.5 dB can be attributed to the narrow linewidth of 0.77 nm since most signal on the carrier can transmit through the passband of the AWG.
To suppress the spurious signal, the dual OEO loop structure is employed. A theoretical analysis based on the relationship between closed-loop intensity transfer function, power ratio between two loops and the cavity lengths is derived for exploring the optimized principle of dual-loop OEO structure. The dual-loop scheme in the proposed system is realized with different cavity length and the optimized condition is 100-m, 120-m loop length with equal power. The spurious signal in the system with longer cavity is vanished with the use of dual-loop structure. The phase noise is about -100 dBc/Hz at 10-kHz and the RMS timing jitter and pulsewidth are 0.67 ps and 18.3 ps, respectively. These parameters have no obvious change compared with single loop case except the elimination of the spurious signal. The SNR slightly decays to 10.9 dB and the receiving power at BER of 10-9 is -19.2 dBm in the optimized condition with 10 Gbit/s RZ-OOK data from PRBS source triggered by the OEO microwave signal.
Subjects
return-to-zero data
weak-resonant-cavity Fabry-Perot laser diode (WRC-FPLD)
harmonic mode-locking
self-feedback
optoelectronic oscillator
Type
thesis
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