P Ivanov

Investigations of mode control in proton-implanted and oxide-confined VCSELs using PBGs: modelling and experiment

We have investigated theoretically the influence on transverse optical modes of a two-dimensional photonic crystal (PC) defect waveguide embedded into a vertical-cavity surface-emitting laser. In gain-guided structures, where the index profile is weak, the effect of the PC is efficient. In the oxide-confined structures, where the index guidance provided by the oxide is larger, this is not the case, but the efficiency of the PC can be increased by oxide in the node position. It is shown that the thermal lensing effect leads to increased sensitivity of the single-mode conditions on the current injection change.

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

Theoretical optimization of transverse waveguiding in oxide-confined VCSELs with internal photonic crystals

We systematically investigate transverse optical modes in oxide-confined vertical-cavity surface-emitting lasers (VCSELs) with photonic crystal (PC) structures embedded within the cavity of the VCSEL. We consider the interplay between the effective refractive index step of the oxide and the semiconductor and the oxide aperture size. The PC lattice period a, the diameter of the holes d, and the number of lattice periods around the central defect are considered. We evaluate confinement factors for the various transverse modes and consider their spatial extent in the transverse plane which we relate to the output power. Results suggest that the power of the single-mode photonic crystal vertical-cavity surface-emitting lasers (PC-VCSELs) is limited by the smaller radius of the fundamental mode of the PC-VCSEL compared to the VCSEL with no PC. We discuss various designs aimed to optimize power into the single-fundamental mode and to discriminate from power going into other modes.

Comparative Study of Mode Control in Vertical-Cavity Surface-Emitting Lasers With Photonic Crystal and Micropillar Etching

The dependence of spectral, power versus current and small-signal modulation characteristics versus the etch depth in two types of surface-etched vertical-cavity surface-emitting lasers (VCSELs) are experimentally and theoretically investigated. One type has a photonic crystal (PC) fabricated in the top distributed Bragg reflector (DBR), whereas the second type has a micropillar (MP) created by removing the DBR surrounding it. The aim of both fabrication designs is to improve the single-mode high-power output. Theoretical and experimental results are found to be in qualitative agreement. It is shown that mode-selective optical losses, introduced by the etched holes of the PC in the DBR, control the optical modes of the PC-VCSEL. Single-fundamental-mode radiation is observed for deeply etched PC- and MP-VCSELs. In contrast, improved modulation characteristics are found for shallowly etched devices. Higher-order single-mode generation with improved modulation characteristics is demonstrated for PC-VCSELs with an etch depth of 1.54 μm. PC-VCSELs demonstrate higher slope efficiency, lower threshold current, and series resistance compared with MP-VCSELs of the same etching depth.

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.

FDTD Simulation of Inverse 3-D Face-Centered Cubic Photonic Crystal Cavities

We present the modeling and simulation of 3-D face-centered cubic photonic crystal (PhC) cavities with various defects. We use the plane-wave expansion method to map the allowed modes and photonic bandgaps. Having determined the photonic bands we design specific defects and input-output waveguides and model the coupling between defects and waveguides using the 3-D finite-difference time-domain method. We have calculated the Q-factors and modal volumes (Veff) of the resonant cavity modes for the PhC structures made of materials including germanium (Ge), silicon (Si), gallium phosphide (GaP), titanium dioxide (TiO2), and silica (SiO2). We then use our estimates of Q and Veff to quantify the enhancement of spontaneous emission and possibility of achieving strong coupling with color centers and quantum dots.

Optimal design of single-photon source emission from a quantum-dot in micro-pillar microcavity

We have modelled wavelength scale micro-pillar microcavities of group III-V semiconductor materials using the 3-D finite difference time domain (FDTD) method. A broad band dipole source within the microcavity probes the microcavity mode structure and spectrum. We then investigated the modifications to spontaneous emission of photons form narrowband emitters (e.g. quantum dots) at the centre of the resonance. We find strongly enhanced emission due to small modal volumes and high quality factor (Q-factor). A large fraction of the quantum-dot spontaneous emission is coupled into the fundamental cavity mode. Increasing the number of mirror pairs in the bottom distributed Bragg reflector (DBR) obviously reduces the bottom light leakage, leading to light collection efficiency up to 90%. Moreover, we are now looking at more sophisticated structures with both lateral and perpendicular confinements based on annular and photonic crystal defect cavities in order to suppress the remaining sidewall scattering.

Static and Dynamic Properties of Vertical-Cavity Surface-Emitting Semiconductor Lasers with Incorporated Two-Dimensional Photonic Crystals

In oxide-confined Vertical-Cavity Surface-Emitting Lasers (VCSELs) the single-mode radiation is desirable for many applications. The single longitudinal mode is typical in VCSELs, however transverse optical modes can be controlled either with a small oxide aperture size [2] or small micropillar-like etched top distributed Bragg reflectors (DBRs) [3]. However, the power radiated from single-mode VCSELs is low and it results in low transmission distance in optical telecommunication networks. The power can be increased due to the fabrication of wider oxide aperture and wider top DBR, but than a VCSEL becomes multimode. Since the last decade photonic crystals had been introduced to control transverse optical modes of VCSELs [4-8]. The PC is created by periodic modulation of the refractive index in one, two or three space directions. In the VCSELs, the PC is positioned in top DBR and fabricated due to etching air-filled holes in the DBR. It was demonstrated that the PC reduces the transverse optical mode number, spectral linewidth [4-8] and increases the modulation bandwidth of VCSELs [9]. In this paper we present results of the investigated VCSELs with incorporated photonic crystals fabricated using the focused ion beam (FIB) machine. Power versus current, spectral and modulation characteristics of VCSELs with PC are investigated and compared to similar VCSELs with etched mesa.

Experimental study of temperature sensitivity of carrier lifetime and recombination coefficients in GaInNAs SQW lasers

This paper deals with the characterization of the differential carrier lifetime and the calculation of the monomolecular, radiative and non-radiative recombination coefficients and their temperature dependence as an evidence of the excellent temperature performance of this material system. The device characterized is a 1.25 /spl mu/m GaInNAs laser structure grown on a GaAs substrate. The active region consists of a single 6 nm thick single quantum well. Light current (L-I) characteristics performed over a temperature range of 20/spl deg/C to 80/spl deg/C, show a characteristic temperature of 50 K. Similar than in the case of commercial InGaAs. Good temperature performance of optical gain using Hakki-Paoli method, lasing wavelength and efficiency will also be presented and compared with modelling work.

Web-oriented interactive environment for distance education in study of semiconductor lasers

We present development results of the web-oriented environment for distance education in the field of the semiconductor laser physics. The paper includes description of the Interactive Environment for Distance Education (IEDE) focused on connection of lecture courses and the laser simulation package LaserCAD III, which allows considering lasers directly during reading of lectures via Internet. Some examples of the package using are presented.