Optical solitons in fibre Bragg gratings with third- and fourth-order dispersive reflectivities

The existence, stability and collision dynamics of moving Bragg grating solitons in a semilinear dual-core system where one core has the Kerr nonlinearity and is equipped with a Bragg grating with dispersive reflectivity, and the other core is linear are investigated. It is found that moving soliton solutions exist as a continuous family of solutions in the upper and lower gaps of the system’s linear spectrum. The stability of the moving solitons are investigated by means of systematic numerical stability analysis, and the effect and interplay of various parameters on soliton stability are analyzed. We have also systematically investigated the characteristics of collisions of counter-propagating solitons. In-phase collisions can lead to a variety of outcomes such as passage of solitons through each other with increased, reduced or unchanged velocities, asymmetric separation of solitons, merger of solitons into a quiescent one, formation of three solitons (one quiescent and two moving ones) and destruction of both solitons. The outcome regions of in-phase collisions are identified in the plane of dispersive reflectivity versus frequency. The effects of coupling coefficient, relative group velocity in the linear core, soliton velocity and dispersive reflectivity and the initial phase difference on the outcomes of collisions are studied.

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Moving Bragg grating solitons in a semilinear dual-core system with dispersive reflectivity.

The existence and stability of moving gap solitons in coupled Bragg gratings with cubic–quintic nonlinearity are investigated. It is shown that the model supports two disjoint families of solitons, known as Type 1 and Type 2 solitons, which fill the entire bandgap. There exist symmetric and asymmetric moving gap solitons within each family of solitons. By means of systematic numerical stability analysis, the stability regions in the plane of the coefficient of quintic nonlinearity versus frequency have been identified. We have analyzed the effects and interplay of quintic nonlinearity, coupling coefficient, and velocity on the stability of solitons and the stability regions.

Stability of moving gap solitons in linearly coupled Bragg gratings with cubic–quintic nonlinearity

The interactions between stable quiescent Bragg grating solitons are investigated systematically in a dual-core system where one core is uniform and has Kerr nonlinearity and other is linear and is equipped with a Bragg grating with dispersive reflectivity. In a previous work, it has been shown that the model supports stable quiescent Bragg solitons which may contain sidelobes in their profile in case of strong dispersive reflectivity. The interactions of in-phase solitons may lead to a variety of outcomes in the absence of sidelobes including merger into a quiescent soliton, destruction of both solitons, symmetric or asymmetric separation of solitons and generation of three solitons. In case of $$\pi $$
 -out-of-phase solitons without sidelobes, the solitons repel each other. However, in the presence of sidelobes, for both in-phase and $$\pi $$
 -out-of-phase solitons, the interactions may result in the repulsion of solitons or the formation of a long-lasting bound state that eventually disintegrates into two separating solitons. We have identified the regions for different interaction outcomes in the plane of dispersive reflectivity and frequency.

Soliton-soliton dynamics in a dual-core system with separated nonlinearity and nonuniform Bragg grating

Optical solitons in fiber Bragg gratings with dispersive reflectivity by sine-Gordon equation approach

We investigate return-to-zero (RZ) to non-return-to-zero (NRZ) format conversion by means of the linear time-invariant system theory. It is shown that the problem of converting random RZ stream to NRZ stream can be reduced to constructing an appropriate transfer function for the linear filter. This approach is then used to propose novel optimally-designed single fiber Bragg grating (FBG) filter scheme for RZ-OOK/DPSK/DQPSK to NRZ-OOK/DPSK/DQPSK format conversion. The spectral response of the FBG is designed according to the optical spectra of the algebraic difference between isolated NRZ and RZ pulses, and the filter order is optimized for the maximum Q-factor of the output NRZ signals. Experimental results as well as simulations show that such an optimally-designed FBG can successfully perform RZ-OOK/DPSK/DQPSK to NRZ-OOK/DPSK/DQPSK format conversion.

Optimally-designed single fiber Bragg grating filter scheme for RZ-OOK/DPSK/DQPSK to NRZ-OOK/DPSK/DQPSK format conversion

A novel multichannel carrier-suppressed return-to-zero (CSRZ) to non-return-to-zero (NRZ) format conversion scheme based on a single custom-designed fiber Bragg grating (FBG) with comb spectra is proposed. The spectral response of each channel is designed according to the algebraic difference between the CSRZ and NRZ spectra outlines. The tailored group delays are introduced to minimize the maximum refractive index modulation. Numerical results show that four-channel 200-GHz-spaced CSRZ signals at 40 Gbits/s can be converted into NRZ signals with high Q-factor and wide-range robustness. It is shown that our proposed FBG is robust to deviations of bandwidth and central wavelength detuning. Another important merit of this scheme is that the pattern effects are efficiently reduced owing to the well-designed spectra response.

Simultaneous multichannel carrier-suppressed return-to-zero to non-return-to-zero format conversion using a fiber Bragg grating.

We propose a novel carrier-suppressed return-to-zero (CSRZ) to non-return-to-zero (NRZ) conversion scheme based on a single custom-designed fiber Bragg grating (FBG) with a knife-shaped spectrum. The structure of the FBG is designed and synthesized using a discrete layer-peeling inverse scattering technique. It is shown that such an FBG can replace the combination of interferometer and the cascaded filter that is invariably employed in the reported schemes for CSRZ to NRZ format conversion. Simulation results show that conversion of 40 Gbit/s CSRZ into NRZ signals results in a Q factor that is 4.5 dB greater than the previously reported schemes.

Carrier-suppressed return-to-zero to non-return-to-zero format conversion based on a single fiber Bragg grating with knife-shaped spectra

We propose a novel notch-filtering scheme for bit-rate transparent all-optical NRZ-to-PRZ format conversion. The scheme is based on a two-degree-of-freedom optimally designed fiber Bragg grating. It is shown that a notch filter optimized for any specific operating bit rate can be used to realize high-Q-factor format conversion over a wide bit rate range without requiring any tuning.

https://iopscience.iop.org/article/10.1088/2040-8978/17/2/025702/pdf

Bangyun Xiong

Papers

Optimally-designed single fiber Bragg grating filter scheme for RZ-OOK/DPSK/DQPSK to NRZ-OOK/DPSK/DQPSK format conversion

Simultaneous multichannel carrier-suppressed return-to-zero to non-return-to-zero format conversion using a fiber Bragg grating.

Carrier-suppressed return-to-zero to non-return-to-zero format conversion based on a single fiber Bragg grating with knife-shaped spectra

Fiber Bragg grating based notch filter for bit-rate-transparent NRZ to PRZ format conversion with two-degree-of-freedom optimization