Within the last decade, research and development in the field of silicon microring resonators have been accelerated due to their potential in a wide range of applications. In this study, we experimentally characterize the selfpulsing dynamics in active silicon ring cavities under the effects of varying the optical power, detuning, and free-carrier lifetime. Self-pulsing is measured by coupling a single laser source into the microring resonator’s input port. The light collected from the output grating is fiber coupled and sent to a photodetector, oscilloscope, power meter, and optical spectrum analyzer (OSA) for both time and frequency domain measurement.
We demonstrate both second harmonic generation (with a normalized efficiency of 0.20 %W−1 cm−2 ) and, to our knowledge, the first degenerate χ (2) optical parametric amplifier (with an estimated normalized gain of 0.6 dBW−1/2 cm−1 ) using silicon-on-insulator waveguides fabricated in a CMOS-compatible commercial foundry.
We study an all-optical Fredkin gate consisting of a Mach-Zehnder interferometer and a phase modulator based on silicon nitride ring resonators. Our study proposes an accurate, deterministic, and energy-efficient all-optical Fredkin gate utilizing the Kerr effect for optical computing. We firstly derive the mathematical model of the proposed controlled-swap gate from the Lugiato-Lefever equation taking into account the third-order optical nonlinearity. In addition, the mechanism of thermo-optical effect in the silicon nitride ring cavity is also included. The phase modulator built by the ring resonator with third-order nonlinearity can introduce a π phase shift to the signal when the Fredkin Gate is in the swap mode. However, it does not affect the overall phase shift of the parallel operation. Besides, the pump power introduces a phase shift to the signal by altering the intensity-dependent refractive index inside the micro-ring cavity. It dominates the switching of the Mach-Zehnder interferometer via cross-phase modulation. Moreover, we investigate the conditions of optical bistability for the silicon nitride cavities that can lead to the malfunctioning of the performance of the Fredkin gate. Lastly, we optimize the Fredkin gate performance by the pump power, pump detuning, and signal-pump wavelength difference sweeps.
Subwavelength grating (SWG) metamaterial structures are excellent platforms for guided-wave nonlinear optics, but their design and optimization are challenging due to the large number of geometric degrees of freedom and the need for compute-intensive 3D simulations. Here, we demonstrate inverse design of χ(2) SWG waveguides using an efficient and accurate differentiable plane-wave expansion (PWE) eigensolver. Our solver, which incorporates sparse iterative algorithms and subpixel smoothing, enables efficient eigensolution and end-to-end differentiation from geometric parameters to the SWG figure of merit, which depends both on the eigenvalues (first-order perturbation theory) and the eigenvectors and group indices (second-order perturbation theory), both in forward- and reverse-mode. We apply this solver to the design and optimization of metamaterial waveguides for two types of backward SHG: idler-reversed and pump-reversed. This approach may find use in designing periodic structures more generally, including nanobeam cavities, slow-light modulators, and vertically coupled resonators.
We theoretically study the nonlinear dynamics of silicon ring cavities with active carrier removal. In this system, linear dispersion, Kerr nonlinearity, two-photon absorption, and free-carrier dispersion / absorption play a key role in the dynamics and the steady-state behavior of the device. Placing the cavity inside a reverse-biased p-i-n junction allows one to reach a regime where both optical bistability and limit-cycle oscillations are accessible. Based on these phenomena, we propose and simulate a free-carrier based random number generator and an "Ising machine", consisting of interconnected ring cavities, which searches for the ground state of the NP-hard Ising XY problem.
An array of grating couplers is studied to be used for beam steering in a wireless optical communication system. This structure is designed using a rib waveguide with a silicon thickness of 220nm and an etch depth of 70nm using 2μm silica substrate. TE polarized input light with wavelength of 1550nm is coupled into the feed waveguide. The structure is optimized based on the angular coverage, directed power, and beam efficiency of the radiated main beam of an individual grating coupler. The main beam radiated by optimized grating coupler has a beamwidth of 10.3°×30.7°. The designed 1-D array of the fifteen grating couplers provides tunability in the range of around 30 degrees which is required for a point to pint wireless optical communication transmitter.
This paper presents a novel analytical model for the analysis of the electromagnetic field radiation in grating couplers. As will be shown, the radiation pattern of the grating couplers can be described with appropriate accuracy as periodic structures. The obtained field distribution of the coupler can be modeled as a sequence of Fourier series for particular distance values, periodicities and wavelengths. This is compatible with the Floquet-Bloch theory of periodic structures. With this model all relevant parameters for the radiation pattern can be investigated. The results of the proposed analytical model are compared with simulation results for a wavelength of 1550 nm. The model can be used for any periodic structure.
In this paper, we analytically describe the parametric amplification in ring resonators using silicon and silicon nitride waveguides. Achievable gain and bandwidth of the ring-based amplifiers are studied taking into account the Kerr nonlinearity for silicon nitride and Kerr nonlinearity as well as two photon absorption and free carrier absorption for silicon waveguides. Both telecom and 2-μm wavelengths are investigated in case of silicon. An approach for obtaining the optimum amplifier design without initiating the comb generation has been introduced. It is shown that there is a trade-off between the input pump and amplifier bandwidth. It is estimated that using optimum designs an amplifier with a gain and bandwidth of 10 dB and 10 GHz could be feasible with silicon ring resonators in 2 μm.
Due to their strong light confinement, waveguides with optical nonlinearities may be a promising platform for energy-efficient optical computing. Slow light can enhance a waveguide’s effective nonlinearity, which could result in devices that operate in low-power regimes where quantum fluctuations are important, and may also have quantum applications including squeezing and entanglement generation. In this manuscript, slow-light structures based on the Kerr (χ(3)) nonlinearity are analyzed using a semi-classical model to account for the quantum noise. We develop a hybrid split-step / Runge-Kutta numerical model to compute the mean field and squeezing spectrum for pulses propagating down a waveguide, and use this model to study squeezing produced in optical waveguides. Scaling relations are explored, and the benefits and limitations of slow light are discussed in the context of squeezing.
Simple RC model, which only considered PN junction capacitance and series resistor, and complete circuit model considering parasitic capacitances of a carrier depletion based optical modulators are studied. Modulation efficiency and bandwidth of the modulators are investigated using analytical models and numerical simulations respectively. Through particle swarm optimization (PSO) a repetitive algorithm is applied to find the feasible maximum of circuit bandwidth.
Optical sampling based on four wave mixing in silicon nano-waveguides is numerically investigated. A model for nonlinear propagation in silicon is developed which is used together with a mode-solver software to obtain optimum waveguide designs for optical sampling. Performance of the system using optimum waveguides is then evaluated.
Slow light effect based rib silicon waveguide structures are studied in this paper to enhance modulation efficiency of an
optoelectronic carrier plasma dispersion effect based phase modulator. Center frequency to achieve desired slow down
factor and band width limitations of the structures are investigated through finite element method simulations. Optical
modulation efficiency is modeled and the effects of doping, bias voltage and slow light on its performance are studied.
In this paper, we analyze the sensitivity degradation of a system due to various orders of chromatic dispersion. To do
this, the power penalty of the uncoded and encoded pulse of a coherent ultrashort light pulse Code Division Multiple
Access (CDMA) communication system due to various orders of chromatic dispersions are analyzed. Analysis of
uncoded pulse shows that the power penalty is unacceptably high when second order dispersion is not compensated.
However we can obtain acceptable level of power penalties while compensating second and third order dispersion. Also,
due to the high order of dispersion, the power of encoded pulse decreases as it propagates through the fiber which leads
to a better Multiple Access Interference (MAI) than reported in previous papers.
The concept of a nonlinear transfer function of a fibre-optic communication link is reviewed. Also an approximation of the nonlinear transfer function is introduced, which allows to define an equivalent single-span model of a dispersion-managed multi-span system. In this paper we will show its limits of validity and try to extent these limits by enhancing the theoretical model. In this respect we will discuss the impact of dispersion precompensation and show the influence of residual dispersion per span, number of spans and local dispersion on transmission systems with on-off keying and differential phase-shift keying modulation formats. This approach allows fast assessment of the performance of a given modulation format over various dispersion maps by reducing the need for extensive numerical simulations.
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