Return-to-zero On-off Keying Research Articles

10 Gbit/s RZ-OOK to RZ-BPSK format conversion using SOA and synchronous pulse carver

Conversion of return-to-zero on-off keying (RZ-OOK) to RZ binary phase-shift keying (RZ-BPSK) by transient cross-phase modulation in a semiconductor optical amplifier (SOA), and a synchronous pulse carver, is demonstrated for the first time using commercially available components. A receiver sensitivity gain of ∼1.5 dB was achieved for RZ-BPSK relative to baseline RZ-OOK.

Externally Modulated Optical Minimum Shift Keying Format

This paper presents the generation and the performance evaluation of optical minimum shift keying (MSK) for high-speed and high-spectral-efficiency wavelength-division multiplexing systems. The detailed principle on optical MSK generation and detection is derived and analyzed. Optical MSK data (10.7 Gb/s) are successfully generated by an experiment using the proposed scheme. The results show that the optical MSK signal exhibits a very compact optical spectrum. The performance of the optical MSK modulated system is evaluated and compared with those of 50% duty-cycle return-to-zero differential phase shift keying (RZ-DPSK) and 50% duty-cycle return-to-zero on-off keying (RZ-OOK) modulated systems, via both simulation and experiment, in terms of dispersion tolerance, linear crosstalk, self-phase modulation (SPM) tolerance, stimulated Brillouin scattering (SBS) threshold, optimal receiver filter bandwidth, and optimal link launch power into single-mode fibers and dispersion compensation fibers. Experimental and simulation results show that the MSK signal exhibits the largest tolerance against fiber dispersion and SPM effect as compared with RZ-DPSK and RZ-OOK. Experimental results also confirm the negative penalty against the SPM effect. The SBS threshold of both the MSK and RZ-DPSK systems is more than 10 dB higher than that of the RZ-OOK system. The MSK that is generated with conventional carrier-suppressed return-to-zero (CSRZ) pulses exhibits a narrower optimal optical filter bandwidth but a wider electrical filter bandwidth compared with those of RZ-OOK and RZ-DPSK. The MSK signal that is generated with pure dual-mode pulses has a similar optimum range to RZ-OOK and RZ-DPSK at a high optical signal-to-noise ratio (OSNR) but has a narrower optimal optical filter bandwidth at a low OSNR. The optimum fiber launch power study shows that the MSK signal that is generated using the conventional CSRZ pulses exhibits higher optimum launch power, which agrees with the SPM tolerance study.

Modeling and Analysis of the Contribution of Channel Walk-Off to Nondegenerate and Degenerate Four-Wave-Mixing Noise in RZ-OOK Optical Transmission Systems

A finite-band noise model for degenerate four-wave mixing (FWM) including channel walk-off in return-to-zero on-off-keying (RZ-OOK) transmission is extended to include nondegenerate FWM (ND-FWM). The model is verified by comparing the results for the noise variance for each type of FWM to split-step-Fourier (SSF) simulations for a 10-Gb/s single span link, and excellent agreement is obtained. A physical interpretation of the walk-off effect on the FWM noise is formulated in terms of intracollision and intercollision interference of the corresponding generated FWM waves. The author shows that the walk-off effect modifies the FWM noise power spectral density only at high frequencies by producing distinct peaks at locations determined by the channel spacing. In principle, the walk-off effect significantly increases the noise variance for both types of FWM before any filtering at the end of fiber. Upon demultiplexing, it is found that the walk-off effect is significant and observable for the degenerate FWM case but is no longer significant for the ND-FWM case. When a sub-bit-rate electrical filter is used in the receiver, the walk-off effect becomes insignificant for all types of FWM. They systematically conclude that the walk-off effect is unimportant for FWM in typical RZ-OOK systems when tight electrical filtering is used. They also illustrate the accuracy of the model for the more general case where more than one FWM tone is coincident on a probe channel by comparing the analytic model to SSF simulations for a five-channel example

Simultaneous PMD and OSNR monitoring by enhanced RF spectral dip analysis assisted with a local large-DGD element

In this letter, we propose and experimentally demonstrate an enhanced radio-frequency (RF) spectrum analysis technique to simultaneously monitor optical signal-to-noise ratio (OSNR) and polarization-mode dispersion (PMD) for return-to-zero ON- OFF keying (RZ-OOK) systems. In this method, by cascading a large differential group delay element at the monitoring module, the PMD and OSNR parameters can be derived from the analysis of the position shift and the minimum power of the RF spectral dip, respectively. Experimental results show that this scheme can monitor PMD from 0 to 90 ps with less than 2-ps error and OSNR from 16 to 35 dB with less than 1-dB error in a 10-Gb/s RZ-OOK transmission system with a pulsewidth of 2.5 ps. The scheme possesses the advantages of simple implementation, large monitoring range, and high PMD monitoring sensitivity by using the RF spectrum analysis only at low-frequency range.

Single-span transmission of WDM RZ-DPSK signal over 310-km standard SMF without using FEC and remote-pumping

To avoid significant stimulated Brillouin scattering (SBS) generation in a bidirectional Raman-pumped long single-span transmission system, the SBS threshold is studied in both return-to-zero on-off -keying (RZ-OOK) and RZ differential phase-shift keying (DPSK) systems. It shows that SBS threshold in an RZ-DPSK system is more than 10 dB higher than that in an RZ-OOK system, and SBS reflection is dominated by copumping, while counterpumping has minor effect. Error-free eight-channel single-span transmission is demonstrated over 310-km standard single-mode fiber using RZ-DPSK format and bidirectional Raman pumping, without applying forward-error correction and remote-pumping techniques.