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Wen Qi Zhang

Publications and source records attributed to Wen Qi Zhang.

8 recordsLinked to original sources

Stein-Weiss, and power weight Korn type Hardy-Sobolev Inequalities in $L^1$ norm

We extend the $L^1$ Stein-Weiss inequalities studied by De Nápoli and Picon [4] in two ways: First we address an open question posed by the authors about whether the cocanceling condition was necessary for some of their Stein-Weiss inequalities. We replace the cocanceling condition with a weaker vanishing moment assumption, and under this assumption extend the $L^1$ Stein-Weiss inequalities to $L^1(|x|^{a } dx)$ data for all positive, non-integer exponents $a$. Second, in relation to integer exponents, while [4] showed that Stein-Weiss fails for $L^1(|x| dx)$ data, we prove a weaker Korn type Hardy-Sobolev inequality. These inequalities were previously inaccessible due to the growth of $|x|$, and we demonstrate a specific example on $\mathbb{R}^2$ of where the original duality estimate by Bousquet and Van Schaftingen [2] for canceling operators can be improved.

math.CA↗

Unseeded One-Third Harmonic Generation in Optical Fibers

We propose a new concept to generate efficient one-third harmonic light from an unseeded third harmonic process in optical fibers. Our concept is based on the dynamic constant (Hamiltonian) of the nonlinear third harmonic generation in optical fibers and includes a periodic array of nonlinear fibers and phase compensation elements. We test our concept with a simulation of the nonlinear interaction between the fundamental and third harmonic modes of a realistic optical fiber, demonstrating high-efficiency one-third harmonic generation. Our work opens a new approach to achieving the so far elusive one-third harmonic generation in optical fibers.

physics.optics↗

A neural network for forward and inverse nonlinear Fourier transforms for fiber optic communication

We propose a neural network for both forward and inverse continuous nonlinear Fourier transforms, NFT and INFT respectively. We demonstrate the network's capability to perform NFT and INFT for a random mix of NFDM-QAM signals. The network transformations (NFT and INFT) exhibit true characteristics of these transformations; they are significantly different for low and high-power input pulses. The network shows adequate accuracy with an RMSE of 5e-3 for forward and 3e-2 for inverse transforms. We further show that the trained network can be used to perform general nonlinear Fourier transforms on arbitrary pulses beyond the training pulse types.

eess.SP↗

Correlated Eigenvalues Optical Communications

There is a fundamental limit on the capacity of fibre optical communication system (Shannon Limit). This limit can be potentially overcome via using Nonlinear Frequency Division Multiplexing. Dealing with noises in these systems is one of the most critical parts in implementing a practical system. In this paper, we discover and characterize the correlations among the NFT channels. It is demonstrated that the correlation is universal (i.e., independent of types of system noises) and can be exploited to maximize transmission throughput. We propose and experimentally confirm a noise model showing that end-to-end noise can be modeled as the accumulation of noise associated with each segment of optical communication which can be dealt with independently. Also, each point noise can be further decomposed into different components, some of which are more significant (and even dominating) than others. Hence, one can further approximate and simplify the noise model by focusing on the significant component.

cs.IT↗

Ultrafast pulse generation in a mode-locked Erbium chip waveguide laser

We report mode-locked ~1550 nm output of transform-limited ~180 fs pulses from a large mode-area (diameter ~ 50 μm) guided-wave erbium fluorozirconate glass laser. The passively mode-locked oscillator generates pulses with 25 nm bandwidth at 156 MHz repetition rate and peak-power of 260 W. Scalability to higher repetition rate is demonstrated by transform-limited 410 fs pulse output at 1.3 GHz. To understand the origins of the broad spectral output, the laser cavity is simulated by using a numerical solution to the Ginzburg-Landau equation. This paper reports the widest bandwidth and shortest pulses achieved from an ultra-fast laser inscribed waveguide laser.

physics.optics↗

Study of noise impact on nonlinear frequency division multiplexing

In this work, how the noise contaminates signals propagating in an optical fibre is discussed in the nonlinear spectral domain after applying the nonlinear Fourier transform. Simulation results about how the soliton parameters in the nonlinear spectral domain perturb is shown.

physics.optics↗

Nonlinear self-flipping of polarization states in asymmetric waveguides

Waveguides of subwavelength dimensions with asymmetric geometries, such as rib waveguides, can display nonlinear polarization effects in which the nonlinear phase difference dominates the linear contribution, provided the birefringence is sufficiently small. We demonstrate that self-flipping polarization states can appear in such rib waveguides at low (mW) power levels. We describe an optical power limiting device with optimized rib waveguide parameters that can operate at low powers with switching properties.

physics.optics↗

Full vectorial analysis of polarization effects in optical nanowires

We develop a full theoretical analysis of the nonlinear interactions of the two polarizations of a waveguide by means of a vectorial model of pulse propagation which applies to high index subwavelength waveguides. In such waveguides there is an anisotropy in the nonlinear behavior of the two polarizations that originates entirely from the waveguide structure, and leads to switching properties. We determine the stability properties of the steady state solutions by means of a Lagrangian formulation. We find all static solutions of the nonlinear system, including those that are periodic with respect to the optical fiber length as well as nonperiodic soliton solutions, and analyze these solutions by means of a Hamiltonian formulation. We discuss in particular the switching solutions which lie near the unstable steady states, since they lead to self-polarization flipping which can in principle be employed to construct fast optical switches and optical logic gates.

physics.optics↗