We developed an iterative method for calculating the solutions to mixed boundary value problems. First, we demonstrate the method by calculating injection current densities from a metal contact plane into a single layer of finite conductivity material. Next, we show how the method adapts to much more complicated cases by calculating injection profiles for several semiconductor laser geometries. The method proves to be practical and accurate for calculating injection current profiles for semiconductor epitaxial structures.
A 2-D symmetric hybrid surface plasmonic waveguide is proposed and numerical analysis is carried out to study its supported mode properties, including the field distribution of the mode, the effective index, propagation length, and normalized mode area of the fundamental modes. Results show that this type of hybrid waveguide can support a longer propagation length fundamental mode as well as three types of high loss modes when the working wavelength is 1550 nm. By tuning the geometrical parameters and choosing a proper fundamental mode in terms of its characteristics, it is shown that this hybrid surface plasmonic waveguide has potential applications in low loss and high density photonic integration, biosensors, nanolasers, and nonlinear photonics.
We present an experimental and numerical study of the dynamics of a semiconductor laser subject to filtered optical feedbacks (FOFs) from two separate external cavities. Our results show that the inclusion of a second FOF introduces a rich control over the frequency of the dynamics. The period of frequency oscillations of the laser light is determined by the two time scales related to the feedback loops, and the frequency corresponding to this period is given by the average of the fundamental frequencies of the two cavities. The average frequency is dependent on the relative feedback from the cavities. Proper adjustment of the cavity lengths leads to the oscillations at a frequency which represents the average of the higher harmonics of one cavity and the fundamental frequency of the other cavity. The amplitudes of the frequency components in the single-FOF can be controlled by adding a second FOF, and in particular, the amplitude of the fundamental frequency is suppressed while the amplitude of the second harmonic becomes larger than that of the fundamental frequency. A cascade of period doubling bifurcations leads the dynamics to a chaotic state.
A study of frequency stability and power scaling of single-mode GaSb-based 2.05-
Using an approach unlike that in the literature, the effects induced by waveguides on the gain in infrared free-electron lasers are analyzed for both the low and the high gain regimes. By analyzing the relation of the detuning parameter to the radiation frequency and the waveguide parameter, the radiation frequency and the slippage are analyzed not merely for the resonance case, but for more general cases. Their dependence on the waveguide parameter is analytically presented for an arbitrary value of the detuning, the features of the gain and the requirements for the waveguide parameter can be easily revealed. It is found that the derivative of the detuning parameter with respect to the radiation wavenumber is proportional to the slippage. The analysis shows that the zero slippage always exists, and to have gain at the zero-slippage frequency corresponds to obtaining a gain curve with a single broadband peak. This can be realized for both the high gain and the low gain regions by choosing the appropriate dimension of the waveguide. It is also shown that the higher order modes of the waveguide have greater effect on the high gain than on the low gain regime.
We derive analytical approximations to the threshold gain, detuning, and power distribution ratios of distributed-feedback lasers with a variable phase shift at a variable longitudinal position. These closed-form approximations exhibit the direct influence of the grating parameters, and are in excellent agreement with the exact solution of the coupled mode equations for a wide range of phase shifts, positions, grating strengths and lengths. It is shown that the product of grating strength and phase shift offset distance from the grating center has a dominant influence on most threshold parameters. The threshold gain and output power splitting ratio grow exponentially with this product, whereas the intracavity peak power and the
The randomness enhancement of physical chaos generated by slave vertical-cavity surface-emitting lasers (S-VCSEL) subject to dual-path polarization-preserved optical injection (DP-PPOI) from single master VCSEL (M-VCSEL) with variable-polarization optical feedback (VPOF) is investigated numerically. The randomness of chaotic signals is evaluated quantitatively by an information-theory-based quantifier, the permutation entropy. The randomness properties for S-VCSEL with DP-PPOI and S-VCSEL with single-path PPOI are compared, as well as the effects of injection strength, frequency detuning, and VPOF are considered. It is shown that, the PE values for S-VCSELs with two different injection schemes are both much higher than those for M-VCSEL, and increase initially and then decrease until they saturate at a constant level. The region of injection parameter space contributing to randomness-enhanced chaos in S-VCSEL can be greatly broadened by adopting DP-PPOI. The generation of randomness-enhanced chaos via photonic approach is highly desirable for high-speed random number generators based on chaotic VCSELs.
We present a procedure based on the combined use of analytical and numerical tools, useful for understanding the relative interplay between the various components of a free electron laser (FEL) self-amplified spontaneous emission (SASE) device. We take as reference case the Sorgente Pulsata Auto-amplificata di Radiazione Coerente (SPARC) experiment to analyze how electron beam transverse matching conditions affect the lasing conditions itself and discuss the possibility of implementing new configurations. In particular we show that the procedure can be extended to account for the effect of an on line inserted cavity, with the role of inducing a transverse longitudinal correlation allowing a transfer of the longitudinal and transverse emittance. We discuss the associated benefit on the FEL operation, with particular reference to the nonlinear harmonic generation. The possibility of completing the tool with regards to the beam degradation effects due to CSR is briefly accounted for.
We use the nonlinear dynamics approach for studying delayed feedback optoelectronic oscillators (OEOs) formed by hybrid integration of resonant tunneling diode (RTD) photo-detectors with laser diodes, in both single and dual optical fiber feedback routes. In the single loop topology, the performance of the RTD-OEO free-running self-sustained oscillator is improved in terms of phase noise, with a compromise between the delay line and the strength of the optical re-injection. In the dual-loop configuration, superior performance is achieved due to the suppression of the side modes associated with the optical cavity length, resulting in a side mode suppression ratio of up to