Numerical and theoretical analysis of the crosstalk in linear optical amplifiers

The dynamic characteristics, including the crosstalk and relaxation oscillation, of linear optical amplifiers (LOAs) are investigated by small-signal analysis under an averaging carrier density approximation and compared with the results of numerical simulation. The good agreement between the numerical simulation and the small-signal analysis indicated the averaging carrier density is an appropriate approximation for analyzing LOAs. Theoretical analyzes also show that the dynamic properties of the vertical laser fields dominate the dynamic performance of LOAs. Based on the small-signal analysis, a concise equation for the crosstalk under high bit rate was derived, which can be applied to measure the differential gain of LOAs.

Theoretical analysis about the influence of channel layer thickness on the 2D electron gas and its distribution in InP-based high-electron-mobility transistors

The principle of high-electron-mobility transistor (HEMT) and the property of two-dimensional electron gas (2DEG) have been analyzed theoretically. The concentration and distribution of 2DEG in various channel layers are calculated by numerical method. Variation of 2DEG concentration in different subband of the quantum well is discussed in detail. Calculated results show that sheet electron concentration of 2DEG in the channel is affected slightly by the thickness of the channel. But the proportion of electrons inhabited in different subbands can be affected by the thickness of the channel. When the size of channel lies between 20-25 nm, the number of electrons occupying the second subband reaches the maximum. This result can be used in parameter design of materials and devices.

Theoretical analysis of characteristics of GaxIn1-xNyAs1-y/GaAs quantum well lasers with different intermediate layers

Based on the band anticrossing model, the effects of the strain-compensated layer and the strain-mediated layer on the band structure, gain and differential gain of GaInNAs/GaAs quantum well lasers have been investigated. The results show that the GaNAs barrier has a disadvantage in increasing the density of states in the conduction band. Meanwhile, the multilayer quantum wells need higher transparency carrier density than the GaInNAs/GaAs single quantum well with the same wavelength. However, they help to suppress the degradation of the differential gain. The calculation also shows that from the viewpoint of band structure, the strain-compensated structure and the strain-mediated structure have similar features.

Theoretical analysis and experimental study of Fourier transformation of Franz-Keldysh oscillations in GaAs

Fourier transformation (FT) has been used in the theoretical line shape analysis of Franz-Keldysh oscillations (FKOs) in detail by numerical simulations. FKOs from the surface-intrinsic-n(+) GaAs structure were obtained in photoreflectance (PR) measurements with various modulation light intensities and with different strengths of bias light illumination, which were used to change the static electric field in the intrinsic layer of the sample. The FT spectra of the PR spectra, including the real part, imaginary part, and the modulus, were very consistent with the theoretical line shapes. The ratio of the square root of the reduced mass (root mu (L)/root mu (H)) and the ratio of transition strength of the electron heavy hole to the electron light hole were obtained from the PT spectra. In addition, the electric field in the intrinsic layer of the sample without and with bias illumination and the modulation field induced by photomodulation were also obtained. (C) 2000 American Institute of Physics. [S0021-8979(00)02123-X].

Theoretical investigation on quantum well lasers with extremely low vertical beam divergence and low threshold current

A specially designed quantum well laser for achieving extremely low vertical beam divergence was reported and theoretically investigated. The laser structure was characterized by two low index layers inserted between the waveguide layers and the cladding layers. The additional layers were intended to achieve wide optical spread in the cladding layers and strong confinement in the active region. This enabled significant reduction of beam divergence with no sacrifice in threshold current density. The numerical results showed that lasers with extremely low vertical beam divergence from 20 degrees down to 11 degrees and threshold current density of less than 131 A/cm(2) can be easily achieved by optimization of the structure parameters. Influences of individual key structure parameters on beam divergence and threshold current density are analyzed. Attention is also paid to the minimum cladding layer thicknesses needed to maintain low threshold current densities and low internal loss. The near and far field patterns are given and discussed. (C) 1998 American Institute of Physics.

Theoretical analysis of modal gain in p-doped 1.3 mu m InAs/GaAs quantum dot lasers

A theoretical study of modal gain in p-doped 1.3 mu m InAs/GaAs quantum dot (QD) lasers is presented. The expression of modal gain is derived, which includes an effective ratio that describes how many QDs contribute to the modal gain. The calculated results indicate that the modal gain with the effective ratio is much smaller than that without the effective ratio. The calculated maximum modal gain is is a good agreement with the experimental data. Furthermore, QDs with lower height or smaller aspect ratio are beneficial in achieving a larger maximum modal gain that leads to lower threshold current density and higher differential modal gain. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Theoretical and Experimental Studies of an Ultra-compact Photonic Crystal Corner Mirror Based on Silicon-On-Insulator

An ultra-compact silicon-on-insulator based photonic crystal corner mirror is designed and optimized. A sample is then successfully fabricated with extra losses 1.1 +/- 0.4dB for transverse-electronic (M) polarization for wavelength range of 1510-1630nm.

Theoretical analysis of the bandgap for the intermixed GaInP/AlGaInP quantum wells

Compositional distribution of the quantum well and barrier after quantum well intermixing for GaInP/AlGaInP system was theoretically analyzed on the basis of atom diffusion law. With the compositional distribution result, the valence subband structure of the intermixed quantum well was calculated on the basis of 6x6 Luttinger-Kohn Hamiltonian, including spin-orbit splitting effects. TO get more accurate results in the calculation, a full 6-band problem was solved without axial approximation, which had been widely used in the Luttinger-Kohn model to simplify the computational efforts, since there was a strong warping in the GaInP valence band. At last, the bandgap energy of the intermixed quantum well was obtained and the calculation result is of much importance in the analysis of quantum well intermixing experiments.

Experimental and theoretical analysis of nondegenerate ultrabroadband chirped pulse optical parametric amplification

Experimental investigations of nondegenerate ultrabroadband chirped pulse optical parametric amplification have been carried out. The general mathematical expressions for evaluating parametric bandwidth, gain and gain bandwidth for arbitrary three-wave mixing parametric amplifiers are presented. In our experiments, a type-I noncollinear phase-matched optical parametric amplifier based on lithium triborate, which was pumped by a 5-ns second harmonic pulses from a Q-switched Nd:YAG operating at 10 Hz, seeded by a 14-fs Ti:sapphire laser at 800 nm, was presented. The 0.85 nJ energy of input chirped signal pulse with 57-FWHM has been amplified to 3.1 muJ at pump intensity 3 GW/cm(2), the corresponding parametric gain reached 3.6 x 10(3), the 53 nm-FWHM gain spectrum bandwidth of output signal has been obtained. The large gain and broad gain bandwidth, which have been confirmed experimentally, provide great potentials to amplify efficiently the broad bandwidth femtosecond light pulses to generate new extremes in power, intensity, and pulse duration using optical parametric chirped pulse amplifiers pumped by powerful nanosecond systems.

Theoretical design or single-polarization single-mode microstructured polymer optical fibres

Using the full-vector plane-wave expansion method, a kind of PMMA-based polarization-maintaining microstructured optical fibre (PM-mPOF) is theoretically studied. Dependence of the cutoff wavelengths of the two orthogonal polarization states (polarized along the two principal axes of PM-mPOF) on the structure parameters of the fibre is investigated in detail. A single-polarization single-mode (SPSM) PM-mPOF working in the visible region is designed and optimized with the result of the maximum SPSM bandwidth of 140 nm.