Recently, we presented the idea of a single-element gas detector based on a VCSEL, in which the top mirror is realised as subwavelength grating (SWG). The presence of gas in the vicinity of the grating causes a change in its reflectivity, which leads to a change in the quality factor of the laser cavity. We investigate the possibility of a realisation of a single-element detector based on the SWG VCSEL, in which a Fano-resonance occurs in the SWG. We analyse the performance of such a detector based on the example of an antimonide VCSEL designed as an ethane detector.
We experimentally demonstrate that circular oxide apertures with small side deformations of large-area 980 nm VCSELs contribute to an increase in the optical output power by more than 60% and in the quantum efficiency by more than 10%. We elaborate on the physical background of this behavior and its applicability to small aperture VCSELs. We show that the efficiency of stimulated emission can be enhanced by engineering the spectral structure of the resonator. Such an approach is used already to enhance spontaneous emission,but has been left unexplored in the context of the stimulated emission of VCSELs.
Monolithic High Contrast Gratings (MHCGs) are a special type of high-contrast grating (HCGs). In MHCGs, the stripes and the substrate on which they are implemented are made of the same material. MHCGs provide up to 100% power reflectance and thus are expected to find numerous applications in modern optoelectronics. We present thorough experimental analysis of spectral properties of GaAs MHCG mirrors designed at the wavelength of 1000 nm. Our results show that MHCG mirrors can be high-reflectivity mirrors as well as efficient polarizer and their properties can be modified by variation of lateral parameters of MHCG stripes.
We experimentally demonstrate and elucidate by numerical simulations that breaking circular symmetry of large apertures of vertical-cavity surface-emitting lasers (VCSELs) significantly enhances their emission properties by increasing the optical density of states. Specifically, deformed shapes of circular oxide apertures of VCSELs enhance stimulated emission and suppress undesired non-radiative recombination contributing to an increase in output optical output power of more than 60% and in quantum efficiency of more than 10%. Our example deformed VCSEL structures demonstrate that the optical density of states appears to be of high importance for conventional optoelectronic devices in accordance to the predictions of quantum electrodynamics theory.
High contrast gratings (HCGs) are diffraction gratings whose period is less than the wavelength of light, made of a material with a high refractive index. Monolithic HCGs (MHCGs) are made of the same material as the cladding. They can be made of almost any material used in optoelectronics. We show experimentally and via simulations that shaping the cross-section of the MHCG stripes enables very broad high reflection spectrum.
We design and process more than 100 different 980 nm MHCG mirror designs, to determine optimal parameters for the use of the MHCGs as mirrors for VCSELs. We present measured power reflectance spectra and compare the results to our with numerical simulations. We discuss the impact of the actual processed geometric shape of the MHCG stripes on the measured power reflectance of the MHCGs..
980 nm VCSELs with different numbers of top dielectric DBR periods added to a 5.5-period top semiconductor DBR and with various oxide aperture diameters are investigated to determine the impact of the added dielectric DBR’s impact on the static and dynamic properties of the VCSELs. For VCSELs with the same oxide aperture diameter we observe smaller small-signal modulation bandwidth and lower D-factor for the VCSELs with more pairs of dielectric DBRs. For the VCSELs with 4 μm oxide aperture diameters with 8 and 12 periods of added top dielectric DBRs we measured bandwidths of 29 and 26 GHz, respectively.
High contrast gratings (HCGs) are an attractive alternative to distributed Bragg reflectors (DBRs) as highly reflective mirrors for VCSELs. In our previous work we proposed the use of monolithic HCGs (MHCGs) to reduce the vertical thickness and simplify the epitaxial structure of VCSELs. In this work we discuss the optimization and fabrication of MHCGs. We also analyze the impact of processing imperfections on the power reflectance of MHCGs.
Since the very first demonstration of a vertical-cavity surface-emitting laser (VCSEL) incorporating subwavelength high refractive index contrast grating (HCG) membrane mirror in 2007 by the group of Prof. Chang-Hasnain, numerous research groups around the world have presented devices based on the same concept emitting at wavelengths from ~400 to 1550 nm manufactured in gallium nitride (GaN), gallium arsenide (GaAs) and indium phosphide (InP) material systems. On one hand, an open access to a VCSEL cavity through an air gap combined with a very low inertia of an HCG mirror opened a way for a large range of emission wavelengths in MEMS tunable VCSELs. On the other hand, an air gap in a cavity generally hinders heat and current flow, while the potentially rather fragile HCG membrane is prone to mechanical instability. We present electrically-injected VCSELs incorporating monolithic HCG (MHCG) mirrors. An MHCG mirror being a special case of an HCG mirror, keeps the extraordinary features of an HCG such as scalability with wavelength, ultra-low thickness and very large power reflectance, but doesn't have to be surrounded by a low refractive index material and hence can be monolithically integrated with an all-semiconductor VCSEL cavity. We present an extensive analysis of the impact of the MHCG parameters on the modal properties and thermal stability of single- and double-mode devices, with various oxide apertures. We additionally compare MHCG VCSELs and generic distributed Bragg reflector VCSELs in terms of modal properties and temperature stability based on measured data and the results of computer simulations.
In this paper, we present a novel design of a nitride-based VCSEL emitting at 414 nm and perform numerical analysis of optical, electrical and thermal phenomena. The bottom mirror of the laser is a Al(In)N/GaN DBR (Distributed Bragg Reflector), whereas the top mirror is realized as a semiconductor-metal subwavelength-grating, etched in GaN with silver stripes deposited between the stripes of the semiconductor grating. In this monolithic structure simulations show a uniform active-region current density on the level of 5.5 kA/cm2 for the apertures as large as 10 μm. In the case of a broader apertures, e.g. 40 μm, we showed that, assuming a homogeneous current injection at the level of 5.5 kA/cm2 , the temperature inside the laser should not exceed 360 K, which gives promise to improve thermal management by uniformisation of the current injection.
Here we investigate the influence of the p- and n-oxide-aperture radii in all-semiconductor GaAs-based verticalcavity surface-emitting lasers (VCSELs), designed for 980 nm, on the modulation time constant (τ). Our analysis shows that the minimum value of τ is obtained if the oxide layers on both sides of the junction have identical depths. The simulations of the number of oxide layers on both p- and n-type sides reveal that double p- and n-oxidations are the most effective in the reduction of the modulation time constant as compared to single oxide layers.
We propose a novel optical sensing system based on one device that both emits and detects light consisting of a verticalcavity surface-emitting laser (VCSEL) incorporating an high contrast grating (HCG) as a top mirror. Since HCGs can be very sensitive to the optical properties of surrounding media, they can be used to detect gases and liquid. The presence of a gas or a liquid around an HCG mirror causes changes of the power reflectance of the mirror, which corresponds to changes of the VCSEL’s cavity quality factor and current-voltage characteristic. By observation of the current-voltage characteristic we can collect information about the medium around the HCG. In this paper we investigate how the properties of the HCG mirror depend on the refractive index of the HCG surroundings. We present results of a computer simulation performed with a three-dimensional fully vectorial model. We consider silicon HCGs on silica and designed for a 1300 nm VCSEL emission wavelength. We demonstrate that our approach can be applied to other wavelengths and material systems.
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 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.
Different structures of nitride Vertical-Cavity Surface-Emitting Lasers (VCSELs) have been developed in recent years. However there is still many problems with such constructions, especially with electrical and optical confinement, current injection and construction and fabrication of mirrors. In this paper we present novel approach to nitride VCSEL designing. We investigated structure with tunnel junction (TJ) and top and bottom dielectric distributed Bragg reflectors (DBRs). Using our three-dimensional self-consistent model we investigated thermal and electrical properties of such laser. We also proposed replacing bottom DBR by monolithic high contrast grating mirror (MHCG) and presented optical properties of VCSEL with such mirrors.
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.
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.
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