Tun Cao

Three-Dimensional FDTD Simulation of Micro-Pillar Microcavity Geometries Suitable for Efficient Single-Photon Sources

We present the results of calculations of the microcavity mode structure of distributed-Bragg-reflector (DBR) micro-pillar microcavities of group III-V semiconductor materials. These structures are suitable for making single photon sources when a single quantum dot is located at the center of a wavelength scale cavity. The 3-D finite difference time domain (FDTD) method is our primary simulation tool and results are validated against semi-analytic models. We show that high light extraction efficiencies can be achieved (>90%) limited by sidewall scattering and leakage. Using radial trench DBR microcavities or 2-D photonic crystal structures, we can further suppress sidewall emission, however, light is then redirected into other leaky modes

Modeling of chirped pulse propagation through a mini-stop band in a two-dimensional photonic crystal waveguide

The finite-difference time-domain (FDTD) and frequency-domain finite-element (FE) methods are used to study chirped pulse propagation in 2D photonic crystal (PhC) waveguides. Chirped pulse FDTD has been implemented, which allows the study of pulse propagation in a direct way. The carrier wavelength of the pulse is swept across the bandwidth of a mini-stop-band (MSB) feature, and pulse compression behavior is observed. Both round-hole and square-hole PhC waveguides are studied, with the latter giving increased pulse compression. A group-delay analysis is then used to understand the compression behavior, and this shows how the fast-light regime that occurs within the MSB plays an important role in the observed pulse compression.

Fabrication and Measurement of a Photonic Crystal Waveguide Integrated with a Semiconductor Optical Amplifier

A III-V semiconductor photonic crystal (PhC) waveguide is integrated into a semiconductor optical amplifier (SOA); this has the potential to reshape pulses that are distorted and chirped on propagation through the SOA. The PhC waveguide is modeled using the three-dimensional (3D) finite difference time domain (FDTD) method initially for the ideal case of infinite depth holes, and this shows a ministop band close to 1600 nm. The PhC waveguide is then fabricated into a commercial SOA using focused ion beam etching. The optical power measured at the output of the PhC-SOA waveguide shows evidence of a ministop band but with a small stopband depth. More realistic 3D FDTD modeling including effects of finite hole depth and vertical layer structure is then shown to give much better agreement with measured results. Finally predictions are made for the performance of a membrane structure.

Modelling of a 2D photonic crystal waveguide pulse reshaper integrated with a SOA

In this paper, an arbitrary chirped pulse (ACP)-finite difference time domain (FDTD) method is developed where pulse data can be read in from a data file. This has allowed the FDTD code to be used in combination with a semiconductor optical amplifier (SOA) model to study 2R regeneration using 2D photonic crystal waveguide for sub-picosecond pulses

Fast-Light Based Pulse Compression in 2-D Photonic Crystal Waveguides

Chirped-pulse propagation close to a mini-stopband (MSB) in short photonic crystal (PhC) waveguides is studied using the 2-D finite-difference time-domain method. The group delay (GD) is calculated for different length waveguides and is shown to have a nonlinear relationship with length, implying that dispersion diagram based design approaches may not be applicable in these cases. Pulse compression is then observed directly in the time domain, and a GD-based analysis is used to explain the results. It is shown that the fast-light or negative GD region that is found within the MSB plays a more important role than pulse filtering effects, which can also induce compression. The GD analysis is then used to find the optimum length waveguide for the maximum pulse compression, and this is found to be in agreement with direct time-domain results. Finally, a different PhC waveguide structure is studied based on square holes, which results in an increased GD and, hence, increased pulse compression.

Modelling the polarisation mode control of single quantum-dot emission in elliptical micro-pillar microcavities based on DBR mirror pairs using the FDTD method

We use the finite difference time domain method (FDTD) to investigate polarisation control of single-photon emission from single quantum dots confined in elliptical micro-pillar microcavities. In contrast to circular pillars, one of the cavity modes has smaller modal volume and maintains high Q-factor.

Electromagnetic Modelling of a Monolithic Pulse Reshaper based on a Photonic Crystal Waveguide Integrated with a SOA

Finite difference time domain (FDTD) and finite element (FE) frequency domain methods are used to study the propagation of arbitrary chirped pulses in photonic crystal (PhC) waveguide. An arbitrary chirped pulse is derived from a separate Semiconductor optical amplifier (SOA) model and is passed through a mini-stop band (MSB) in a photonic crystal waveguide. Good agreement is shown between the FDTD and FE models and pulse compression is observed

Modelling quantum-dot in quasi-3D photonic crystal defect microcavity for single-photon sources

We model wavelength scale III-V photonic crystal defect microcavities containing a single quantum-dot using 3-D FDTD. These microcavities have small modal volume while maintaining high Q-factors to make efficient single-photon sources for quantum information applications.

Modelling of a 2R regenerator based on a photonic crystal waveguide pulse reshaper integrated with a SOA

In this proceedings the Finite Difference Time Domain (FDTD) and frequency domain Finite Element (FE) methods are used to model both linear chirped pulse and arbitrary chirped pulse propagation in 2D Photonic Crystal (PhC) waveguides. An in-house FDTD code has been implemented which allows the study of pulse propagation in a very direct way. The carrier wavelength of the pulse is swept across the bandwidth of a mini-stopband feature and pulse compression behaviour is observed. In the case of linear chirped pulse, both round hole and square hole PhC waveguides are studied with the latter giving increased pulse compression. An input pulse is then derived from a SOA model which has arbitrary chirp. This is passed through a mini-stop band in a narrowed W3 PhC waveguide and pulse compression is observed.

FDTD modelling of chirped pulse propagation through a mini-stopband in a 2D photonic crystal waveguide

The FDTD method is used to study chirped pulse propagation in photonic crystal waveguides. In particular the carrier wavelength of the pulse is swept across the bandwidth of a mini-stopband feature and interesting, nonstandard pulse compression behaviour is observed. To further study this, increased frequency resolution across the MSB feature is used and the pulse width is varied.