Magdalena Marciniak

Optimal parameters of monolithic high-contrast grating mirrors.

In this Letter a fully vectorial numerical model is used to search for the construction parameters of monolithic high-contrast grating (MHCG) mirrors providing maximal power reflectance. We determine the design parameters of highly reflecting MHCG mirrors where the etching depth of the stripes is less than two wavelengths in free space. We analyze MHCGs in a broad range of real refractive index values corresponding to most of the common optoelectronic materials in use today. Our results comprise a complete image of possible highly reflecting MHCG mirror constructions for potential use in optoelectronic devices and systems. We support the numerical analysis by experimental verification of the high reflectance via a GaAs MHCG designed for a wavelength of 980 nm.

Analysis of Threshold Currents and Transverse Modes in Nitride VCSELs With Different Resonators

This paper presents a comprehensive, self-consistent, room-temperature simulation of the operation of 414-nm nitride-based vertical-cavity surface-emitting lasers (VCSELs). We calculate the threshold currents and optical modes in a VCSEL structure based on the first continuous-wave nitride VCSEL reported to operate at room temperature, and in subsequent modifications of that structure. The effects of spectral detuning and of variations in resonator length and optical/electrical apertures are analyzed. Mechanisms of mode selection are described, and the fact that nitride VCSELs can operate on a very high-order mode is explained.

Optimization of VCSELs incorporating monolithic subwavelength high-refractive-index contrast surface grating mirrors

We present results of computer simulations of vertical cavity surface emitting lasers (VCSELs) using novel, highreflectivity monolithic high refractive-index contrast grating (MHCG) mirrors and their more advanced version, partially covered by a thin metal layer - metallic MHCG (mMHCG) mirrors. The first experimental realization of this new class of mirrors is presented and discussed. We show that the metal layer does not deteriorate the high reflectivity of an mMHCG mirror, but in contrary, is a crucial element which allows high reflectivity and additionally opens a way for a more efficient electrical pumping of a VCSEL. Comparison of results of thermal-electrical-carrier-gain self-consistent simulations of both MHCG- and mMHCG-based VCSELs is presented and discussed. It is shown that using mHCG mirror as a top mirror of a VCSEL improves electrical characteristics and greatly decreases the differential resistance of the device.

High contrast grating VCSELs for sensing applications

High Contrast Gratings (HCGs) become an attractive alternative for Distributed Bragg Reflectors (DBRs) used as high reflecting mirrors for VCSELs. In this paper we propose to implement HCG or monolithic HCG as a top mirror of the 1650nm InP-based VCSEL intended for use as a methane sensing device. Its unique feature is related to the fact that light taking part in the resonance can be accessed without opening the laser cavity due to the slow light phenomenon which occurs in HCG. Particular designs of HCGs allow to concentrate significant part of the mode between the HCG stripes. In such constructions the presence of the substance in the vicinity of the HCG which interacts with light resonating in the laser will change its emission properties. This enables sensing absorption or change to the refractive index in proximity of the laser based on the emission parameters of the laser. We present a numerical analysis of 1650nm MHCG and HCG mirrors based on fully vectorial optical model. We found optimal parameters of HCGs and MHCGs to detect absorption and refractive index variations in the vicinity of the gratings, based on changes in power reflectance of analysed mirrors. Additionally we consider HCG and MHCG constructions which allow for broad wavelength tuning by the change of the refractive index of substance surrounding mirror.

Monolithic high contrast grating VCSELs: Concept and prospects

Recent trend in the research focused on optical communication is to increase the speed and energy efficiency of the signal sources. In the same time, it is highly desirable to decrease the size of the source into submicron level. The driving forces for achieving these goals are growing market for optical interconnects which are widely used in large datacenters and the silicon photonics which in a short time will create a huge market for optical and electronic circuits integrated in a single chip. We present results of simulations of a novel, ultra-small VCSEL device of extremely simplified design. The device uses monolithic high contrast grating (MHCG) mirrors instead of the commonly used distributed Bragg reflectors (DBR). We show that very high reflectivity, required to sustain a VCSEL lasing, can be achieved by a shallow etching of the surface of the laser cavity only. Thanks to the extraordinary features of the MHCG mirror, the cavity and the mirror can be made of a single material. We show that the concept allows fabrication of VCSELs in all material systems used in optoelectronics, e.g. GaN, InP, GaSb, ZnO, Si, etc. Although several times smaller vertical dimensions of MHCG VCSELs in comparison to conventional VCSELs, their properties are comparable with standard DBR VCSELs.

Performance characteristics of GaSb-based TJ-VCSELs with emission wavelength above 2.6 µm

In this paper we present the results of the computer simulation of the GaSb-based multi-quantum-well GaInAsSb/GaSb vertical-cavity surface-emitting lasers (VCSELs) with the emission wavelength above 2.6 μm. Calculations have been performed with the aid of the comprehensive fully self-consistent numerical model developed by our group. The model combines electrical, thermal, gain, and optical effects, together with the mutual interactions between individual physical processes. For the selected active regions with various material contents and strains the influence of the ambient temperature and tunnel-junction diameter on continuous-wave performance characteristics has been taken into account. The results of the numerical analysis show that with the use of optimised active region it is possible to obtain stable single-fundamental-mode low-threshold operation of VCSEL with emission close to 2.8 μm. This wavelength is 0.2 μm longer than values reported so far for similar devices.

Simulation and optimization of 2.6–2.8 μm GaSb-based vertical-cavity surface-emitting lasers

We present the simulation results of threshold operation of mid-infrared GaSb-based vertical-cavity surface-emitting lasers obtained with the use of comprehensive fully self-consistent optical-electrical-thermal-recombination numerical model. The results show that by a proper design of the active region it is possible to achieve the stable single-fundamental-mode low-threshold operation with emission wavelengths longer than those reported so far for similar devices.

Monolithic high-index-contrast grating VCSELs

A new and radically simplified construction of the vertical-cavity surface-emitting laser (VCSEL) with monolithic high-index contrast grating will be investigated. Instead of hundreds of epitaxial layers as in conventional VCSELs, the proposed design consists of a thin active zone capturing and recombining the carriers positioned between two monolithic cladding layers of p-doped and n-doped material. In these semiconductor lasers the optical feedback is provided by one or two planar monolithic subwavelength gratings etched into the cladding layers on either side of the optical cavity.

Optimal parameters of monolithic high-index contrast grating VCSELs

Monolithic High refractive index Contrast Grating (MHCG) allows several-fold size reduction of epitaxial structure of VCSEL and facilitates VCSEL fabrication in all photonic material systems. MHCGs can be fabricated of material which refractive index is higher than 1.75 without the need of the combination of low and high refractive index materials. MHCGs have a great application potential in optoelectronic devices, especially in phosphide- and nitride-based VCSELs, which suffer from the lack of efficient monolithically integrated DBR mirrors. MHCGs can simplify the construction of VCSELs, reducing their epitaxial design to monolithic wafer with carrier confinement and active region inside and etched stripes on both surfaces in post processing. In this paper we present results of numerical analysis of MHCGs as a high reflective mirrors for broad range of refractive indices that corresponds to plethora of materials typically used in optoelectronics. Our calculations base on a three-dimensional, fully vectorial optical model. We investigate the reflectance of the MHCG mirrors of different design as the function of the refractive index and we show the optimal geometrical parameters of MHCG enabling nearly 100% reflectance and broad reflection stop-band. We show that MHCG can be designed based on most of semiconductors materials and for any incident light wavelength from optical spectrum.

Multi-parameter optimization of monolithic high-index contrast grating reflectors

Conventional High-index Contrast Gratings (HCG) consist of periodically distributed high refractive index stripes surrounded by low index media. Practically, such low/high index stack can be fabricated in several ways however low refractive index layers are electrical insulators of poor thermal conductivities. Monolithic High-index Contrast Gratings (MHCGs) overcome those limitations since they can be implemented in any material with a real refractive index larger than 1.75 without the need of the combination of low and high refractive index materials. The freedom of use of various materials allows to provide more efficient current injection and better heat flow through the mirror, in contrary to the conventional HCGs. MHCGs can simplify the construction of VCSELs, reducing their epitaxial design to monolithic wafer with carrier confinement and active region inside and etched stripes on both surfaces in post processing. We present numerical analysis of MHCGs using a three-dimensional, fully vectorial optical model. We investigate possible designs of MHCGs using multidimensional optimization of grating parameters for different refractive indices.