Conventional Nonlinear Optical Loop Mirror Research Articles

All-optical multi-level amplitude regenerator in a polarization-effect optimized nonlinear-optical loop mirror (PE-NOLM) configuration.

We propose a modified configuration of the nonlinear-optical loop mirror (NOLM) unit by introducing the polarization-effect optimization (PE) into a nonlinear Sagnac interferometer through a polarization-maintaining optical coupler, enabling significant extension of the regeneration region (RR) of the all-optical multi-level amplitude regenerator. We carry out the thoughtful investigations on this PE-NOLM subsystem, and reveal the collaboration mechanism between the Kerr nonlinearity and the PE effect in only one unit. Moreover, the proof-of-concept experiment and its theoretical discussion of multiple-level operation have been performed, observing the 188% enhancement on the RR extending and the consequent 4.5 dB signal-to-noise ratio (SNR) improvement for a 4-level pulse amplitude modulated (PAM4) signal compared to the conventional NOLM scheme.

Extinction ratio improvement by an advanced NOLM setup

We present a nonlinear optical loop mirror (NOLM)-based setup which is optimized for regeneration of signals with a poor extinction ratio caused by, e.g., high powered ghost pulses. In a conventional NOLM, the improvement of the extinction ratio is limited by the input extinction ratio or insufficient amplitude jitter reduction. These limitations can be overcome by an additional directional phase shifter. According to numerical simulation, the extinction ratio can be improved from 6 dB up to several 10 dB.

160-gb/s operation of nonlinear optical loop-mirror with an optical bias controller

All-optical signal regeneration at 160 Gb/s is demonstrated with a nonlinear optical loop-mirror (NOLM). We introduce an optical bias controller into the conventional NOLM composed of a polarization-maintaining fiber, which can suppress degradation of the extinction ratio due to cross-phase modulation between counterpropagating lights; accordingly, full-swing operation is achieved at the bit rate of 160 Gb/s, enabling all-optical signal regeneration.

NOLM-based RZ-DPSK signal regeneration

We present a nonlinear optical loop mirror (NOLM)-based 2R-regenerator setup, which is capable of regenerating signals modulated in phase-sensitive modulation formats. In a conventional NOLM, fluctuations of the signal amplitude are converted into phase fluctuations. Therefore, it is not suitable for regeneration of signals, modulated in formats such as differential phase-shift keying (DPSK) or duobinary. In this letter, we present a modified NOLM setup for 2R-regeneration taking return-to-zero DPSK as an example.

Nonlinear Optical Loop Mirror With an Optical Bias Controller for Achieving Full-Swing Operation of Gate Switching

Cross-phase modulation between counterpropagating lights degrades the extinction ratio of nonlinear optical-loop-mirror (NOLM) switches. To suppress such effect, we propose an NOLM with an optical-bias controller that can give a proper amount of optical bias between lights propagating through an NOLM in opposite directions. Implementing such optical bias controller in a conventional NOLM composed of a polarization-maintaining fiber, we demonstrate, for the first time, wavelength conversion of a nonreturn-to-zero signal under the full-swing condition with the maximum extinction ratio.

All-optical polarization-insensitive time-division demultiplexer using a nonlinear optical loop mirror with a pair of short polarization-maintaining fibers

We propose an all-optical polarization-insensitive time-division demultiplexer using a nonlinear optical-loop mirror (NOLM) with a pair of short polarization maintaining (PM) fibers. This configuration enables us to realize polarization-diversity operation of a conventional NOLM consisting of a non-PM fiber. When a signal pulse is launched on a PM fiber placed at the input port of the NOLM, the pulse is temporally separated into two pulses with orthogonal linear polarizations. Each polarization component is switched independently by the NOLM, and recombined by another piece of a PM fiber placed at the output port of the NOLM. We experimentally demonstrate that a 40-Gb/s signal is demultiplexed into 10-Gb/s channels independently of. signal polarizations.

Polarization-independent optical demultiplexing by conventional nonlinear optical loop mirror in a polarization-diversity loop configuration

All-optical demultiplexing schemes based on cross-phase modulation in a conventional nonlinear optical fiber loop mirror (NOLM) switch generally suffer from a polarization dependence. In this letter, we propose a polarization-diversity loop configuration that allows polarization-independent all-optical demultiplexing by a conventional NOLM switch. We demonstrate polarization-independent all-optical demultiplexing of 40 Gbit/s signal pulses using the proposed scheme.

All-optical switching with pulsed signals in an all-semiconductor-optical-amplifier loop device

Picosecond pulsed-signal operation for efficient self- and cross-switching in an all-semiconductor-optical-amplifier loop device was implemented. Although the configuration of the device is similar to a conventional nonlinear optical loop mirror, the operation principles are quite different. For cw signals, the device operation relies on the nonlinear coupling effect in a multi-mode interference waveguide amplifier and the lateral field redistribution and amplification by the active loop. However, for pulsed signals the crucial factor of asymmetric gain distribution in the loop needs to be added for the device operation. The pump–probe experiments provided efficient cross-switching results and indicated that GHz-range operation is feasible by redesigning the device configuration for pump signal injection.

Numerical study on a compact all-semiconductor-optical-amplifier Sagnac interferometer device

The nonlinear switching effect of an all-semiconductor-optical-amplifier Sagnac interferometer is numerically investigated. The device, stemming from the conventional nonlinear optical loop mirror made of fiber, has a much more compact size and a latency several hundred times smaller than the conventional ones. Numerical simulations are conducted for the case of cw signal operation. It is found that the nonlinear coupling in the MMIWA and the lateral field redistribution as well as the amplification of the signal through the loop structure contribute together to the nonlinear switching. Besides investigating the physical mechanism of the device, we vary relevant parameters to evaluate their influences on device performance. The numerical simulations show good agreement in trend with the experimental results.

Nonlinear switching behaviours in a compact all-semiconductor optical-amplifier Sagnac interferometer device

Nonlinear switching effects in a GaAs-AlGaAs all-semiconductor optical-amplifier loop device with a multimode interference waveguide amplifier (MMIWA) for closing the loop was investigated experimentally and numerically. The miniaturized device, designed to imitate a nonlinear optical loop mirror (NOLM), has a latency more than one hundred times smaller than that of a NOLM. Also, because it used an MMIWA for replacing a coupler in a conventional NOLM, its operation was quite different from that previously reported. In CW signal operation, the nonlinear switching behaviour resulted from the combined effect of nonlinear coupling in the MMIWA and the amplification and lateral field redistribution of the signal through the loop structure. Efficient self-switching and cross-polarized switching were observed. Numerical simulations showed consistent trends in varying device parameters.

Control pulse-induced crosstalk in propagation diversity and conventional nonlinear optical loop mirrors

The conventional nonlinear optical loop mirror (NOLM) is known to suffer from control pulse power induced crosstalk that may give a substantial receiver sensitivity penalty. Here, we compare the conventional NOLM with a polarization independent propagation diversity NOLM which is shown to not give this penalty. When demultiplexing 40 to 10 Gb/s, the conventional NOLM gave 6.5-dB penalty while the propagation diversity NOLM gave only 0.7-dB penalty in agreement with a simple theory.

Nonlinear fiber loop mirror with optical feedback

The performance of a conventional nonlinear optical loop mirror (NOLM) with optical feedback for cw radiation is theoretically investigated. The results indicate that the device shows the feature of single output for low input power, when the input power is increased to some extent a significant property as bistability occurs. Furthermore, if the input power is continually increased, multistability or even chaos will occur.

Nonlinear fiber loop mirror with an inserted half-mirror

A nonlinear optical device for all-optical ultrafast processes is proposed and theoretically investigated. It is based on a conventional nonlinear optical loop mirror, with a half-mirror inserted in the middle of the fiber loop. The device is equivalent to a combination of a nonlinear Sagnac loop and a nonlinear Michelson interferometer. Our results show that the modulation property of the switch is improved.