Oxide Aperture Research Articles

垂直腔面发射激光器氧化孔结构对器件激射性能的影响

垂直腔面发射激光器氧化孔结构对器件激射性能的影响

Anisotropic lateral oxidation of Al-III–V semiconductors: inverse problem and circular aperture fabrication

The lateral wet oxidation of aluminum-containing III–V-semiconductors is a technological process which converts a buried (thin) cristalline material into an amorphous insulator and, as such, tends to exhibit an anisotropic behavior. As a result, the shape of the interface between the semiconductor and the insulator, often referred as the oxide aperture, differs from the etched mesa contour from which the oxidation proceeds. This, in turn, complicates the design of the devices relying on this process especially when specific oxide patterns are needed. In this paper, we introduce a method based on a morphological dilatation to determine the shape of the mesas which will lead to a specific targetted contour upon an anisotropic oxidation over a modest extent. The approach is experimentally validated by demonstrating the fabrication of circular oxide apertures which are inherently difficult to make because of their high degree of symmetry but which also turn out to be of critical importance in obtaining efficient single-mode vertical-cavity surface-emittting lasers.

Performance Analysis of Modulation Response of a Designed 1550 nm Oxide Confined Vertical Cavity Surface Emitting Laser

This paper aims to present the impact of using oxidized layer and the effect of oxide aperture size on VCSEL’s modulation performance. After the introduction of oxidized layer, the characteristics of VCSEL have improved immensely, especially in modulation performance. The peak material gain of Al0.06Ga0.24In0.70As/InP MQW VCSEL found from the MATLAB simulation tools has been utilized for investigating the modulation characteristics of the laser model. The optical output power of 27.23 dBm is found at 2.5 mA of current injection. Later, by varying the injection current up to 2.5 mA a maximum frequency of resonance of 10.75 GHz and the equivalent -3dB cut off frequency of 11.85 GHz are achieved. It is seen that with the reduction of oxide aperture size and increase of injection current, the frequency of resonance in addition to the -3dB cut off frequency of the laser increases. The use of oxidized layer and impact of aperture size effect on VCSEL’s -3dB cut off frequency.

Polarization-controlled and single-transverse-mode vertical-cavity surface-emitting lasers with eye-shaped oxide aperture

We presented a single-transverse-mode and single-polarization vertical-cavity surface-emitting laser (VCSEL) with an eye-shaped oxide aperture, obtained by enhanced anisotropic oxidation of oxide layer. For apertures with dimensions of 2 × 4.6 and 3 × 6 µm2, the orthogonal polarization suppression ratio (OPSR) of the VCSEL was 22 and 19 dB, respectively. A single-mode suppression ratio (SMSR) of more than 25 dB at an output power of 0.5 mW was also achieved for the VCSEL with aperture dimension of 2 × 4.6 µm2. We believe that the proposed method to realize the mode and polarization control of VCSELs has great potential in future applications.

Electro-optic polarization tuning of microcavities with a single quantum dot.

We present an oxide aperture microcavity with embedded quantum dots which utilizes a three-contact design to independently tune the quantum dot wavelength and birefringence of the cavity modes. A polarization splitting tuning of ∼5 GHz is observed. For a typical microcavity polarization splitting, the method can be used to achieve perfect polarization degeneracy that is required for many polarization-based implementations of photonic quantum gates. The embedded quantum dot wavelength can be tuned into resonance with the cavity, independent of the polarization tuning.

Novel single-transverse-mode control of VCSELs with dielectric mode filter**Project supported by the National Key Research and Development Project, China (Grant No. 2017YFB0503200), the National Natural Science Foundation of China (Grant Nos. 61434005, 61474118, 11774343, and 11674314), the Science and Technology Program of Jilin Province, China (Grant No. 20160203013GX), and the Youth Innovation Promotion Association, China (Grant No. 2017260).

We establish a novel method of controlling the transverse modes of vertical cavity surface emitting lasers (VCSELs) to achieve 1 mW single-fundamental-mode lasing. A dielectric mode filter is installed on top of the VCSEL. The dielectric layer (SiO2) is deposited and patterned to modify the mirror reflectivity across the oxide aperture via antiphase reflections. This mode selection is nondestructive and universally applicable for other structures under single transverse mode. Destructive etching techniques (dry/wet) or epitaxial regrowth are also not required. This method simplifies the preparation process and improves the repeatability of the device. Measurements show that under continuous-wave current injection, the side-mode suppression ratio exceeds 30 dB.

Anisotropy in the wet thermal oxidation of AlGaAs: influence of process parameters

The crystallographic anisotropy of the lateral selective thermal oxidation of AlGaAs alloys is experimentally studied. The anisotropic behavior of this oxidation process, used primarily for building a lateral confinement in vertical surface emitting lasers (VCSEL), is quantified by varying different process parameters and the geometrical shapes of laterally oxidized mesa structures. This experimental study aims to have a better control of the oxide aperture shape used in oxide-confined photonics devices.

Modelling anisotropic lateral oxidation from circular mesas

In this paper, an iterative method to model the anisotropic lateral oxidation of circular structures is proposed and validated by confrontation to experimental data. The described model enables the efficient calculation of the temporal bi-dimensional evolution of the oxidation front shape, starting from a circular mesa, and progressing inward as a result of an anisotropic process combining an isotropic diffusion with an anisotropic reaction. The result of the developed model shows that the oxide aperture smoothly deforms from a circle to become more diamond-like, mimicking the experimental situation encountered when fabricating vertical-cavity surface-emitting lasers (VCSELs) on (100) wafers or, more generally, when oxidizing circular mesas of aluminum-containing III-V semiconductor on similarly oriented substrates.

Semiconductor nanostructures for flying q-bits and green photonics

Abstract Breakthroughs in nanomaterials and nanoscience enable the development of novel photonic devices and systems ranging from the automotive sector, quantum cryptography to metropolitan area and access networks. Geometrical architecture presents a design parameter of device properties. Self-organization at surfaces in strained heterostructures drives the formation of quantum dots (QDs). Embedding QDs in photonic and electronic devices enables novel functionalities, advanced energy efficient communication, cyber security, or lighting systems. The recombination of excitons shows twofold degeneracy and Lorentzian broadening. The superposition of millions of excitonic recombinations from QDs in real devices leads to a Gaussian envelope. The material gain of QDs in lasers is orders of magnitude larger than that of bulk material and decoupled from the index of refraction, controlled by the properties of the carrier reservoir, thus enabling independent gain and index modulation. The threshold current density of QD lasers is lowest of all injection lasers, is less sensitive to defect generation, and does not depend on temperature below 80°C. QD lasers are hardly sensitive to back reflections and exhibit no filamentation. The recombination from single QDs inserted in light emitting diodes with current confining oxide apertures shows polarized single photons. Emission of ps pulses and date rates of 1010+bit upon direct modulation benefits from gain recovery within femtoseconds. Repetition rates of several 100 GHz were demonstrated upon mode-locking. Passively mode-locked QD lasers generate hat-like frequency combs, enabling Terabit data transmission. QD-based semiconductor optical amplifiers enable multi-wavelength amplification and switching and support multiple modulation formats.

Optimized design and epitaxy growth of high speed 850 nm vertical-cavity surface-emitting lasers

Using transfer matrix method and TFcalc thin film design software,the reflectance spectrum of distributed Bragg reflector (DBR) and vertical cavity surface emitting laser (VCSEL) are simulated.The reflectance spectra from the cavity and surface are compared with each other,thus providing the basis for white light source (WLS) optical reflectance spectrum of the VCSEL epitaxial wafer.When using WLS to characterize VCSEL wafer,it is necessary to combine the simulation results and the shape of optical reflectance spectrum to speculate the reflectance seen from the cavity.The influences of different cap layers on the reflectance of DBRs are discussed theoretically and experimentally.With a 1/4 GaAs cap layer,the reflectance reaches up to 97.8% seen from the cavity.This design can make the wavelength of the VCSEL etalon picked easily because of avoiding the influence of test noise. The active region has higher heat accumulation due to the small area and poor thermal conductivity.The characteristics of the gain spectrum of InGaAs/AlGaAs strained quantum well (QW) under different temperatures and the temperature distribution in VCSEL are simulated by Crosslight software.The gain-to-cavity wavelength detuning is used to improve the slope efficiency and the temperature stability.The temperature in active region ranges from 360 K to 370 K.The gain peak wavelength and the Fabry-Perot cavity wavelength are designed in the ranges of 829-832 nm and 845-847 nm,respectively.Epitaxial wafer with top-emitting VCSEL structure grown by metal-organic chemical vapor deposition is characterized.The room temperature photoluminescence peak is at 827.5 nm and the etalon cavity wavelength measured by optical reflectance is 847.7 nm,which are consistent with designed values. The oxide restricted VCSELs with 7.5 m oxide aperture are fabricated.The image of the infrared light source CCD shows that the oxide aperture is circular.A passivation layer of 120 nm SiO2 is finally deposited to insulate water vapor.The threshold current is 0.8 mA,and the maximum output power reaches up to 9 mW at 13.5 mA.The optical spectrum at 6.0 mA reveals multiple transverse modes.The center wavelength is 852.3 nm and the root mean square (RMS) spectrum width is 0.6 nm,meeting the high-speed Datacom standards.Shannon theory indicates that the maximum data rate is not only proportional to bandwidth but also related to signal-to-noise ratio (SNR).It is effective to reduce relative intensity noise and enhance the SNR by increasing output power.From the eye diagram of 25 Gbit/s on-off key VCSEL,it is demonstrated that fall time is 38.66 ps,rise time is 41.54 ps,SNR is 5.6,and jitter RMS is 1.57 ps.Clear eye opening is observed from eye diagram of 25 GBaud/s PAM-4 VCSEL,which indicates the qualified 50 Gbit/s high speed performance.

采用BCB平整技术的高速850 nm垂直面发射激光器

Vertical-cavity surface-emitting lasers(VCSELs) are widely used in short-reached optical interconnects and data communication links because of their low energy consumption and high modulation speed. Capacitance, as the parasitic parameters, affects the modulation bandwidth. In this paper, parasitic capacitance of VCSELs is reduced by using a low-k benzocyclobutene(BCB) planarization technique. The detail BCB planarization technique has been discussed with optimal process parameters, which is useful for high-speed VCSEL fabrication. The small signal modulation bandwidth of the low-k BCB planarization VCSEL with 7 μm oxide aperture has been achieved to 15.2 GHz.

Large Bandwidth, Small Current Density, and Temperature Stable 980-nm VCSELs

A low-cost method to adjust the mirror reflectivity of vertical-cavity surface-emitting lasers (VCSELs) helps to optimize the cavity photon lifetime. The joint variation of photon lifetime and the oxide aperture diameter of our 980-nm VCSELs allows optimization procedures between the laser parameters. A new indicator helps to judge the optimum mirror reflectivity to enable increased bit rates in concert with reduced energy consumption, as well as temperature stability, and a smaller bias current density. Error-free back-to-back data transmission at 50 Gb/s over a wide temperature range from 25 °C to 75 °C for completely unchanged driving conditions is presented amongst other progress, including a 400-fJ/b data transmission energy efficiency at 50 Gb/s.

Few-mode vertical-cavity surface-emitting lasers for space-division multiplexing**Project supported by the National Basic Research Program of China (No. 2014CB3400102), the National Natural Science Foundation of China (No. 61335004), the National High Technology Research and Development Program of China (No. 2015AA017101), and the National Key Technologies R & D Program of China (No. 2016YFB0400603).

In order to choose the proper radius of oxide aperture for few-mode vertical-cavity surface-emitting lasers (VCSELs), the influences of oxide aperture size on the multi-transverse-mode behaviors are investigated in detail. By establishing the effective refractive index model to simulate VCSELs with different radii of oxide apertures, the wavelength and corresponding order of different modes are obtained. VCSELs with three kinds of oxide apertures are manufactured. Then the multi-transverse-mode spectra and near-field are measured. It is found that when the radius is between 1.5 and , few-mode VCSELs can be implemented. The VCSEL manufactured in this paper only emits LP01 mode and LP21 mode. Since the space distance between the two modes is , it is expected to realize direct-modulation few-mode VCSELs by channel etching or ion implantation between the two modes.

Mode Behavior of VCSELs With Impurity-Induced Disordering

This letter explores the modal behavior of oxide-confined vertical-cavity surface-emitting lasers (VCSELs) with varying emission apertures defined by impurity-induced disordering (IID) via closed ampoule zinc diffusion. A 1-D plane wave propagation method is used to calculate the mirror loss as a function of IID strength and depth. The devices are fabricated with masked areas ranging from approximately 70%-110% of the oxide aperture defining an unmodified emission aperture designed to overlap mainly with the fundamental mode. An analysis of the transverse mode lasing characteristics and mode-dependent thermal characteristics demonstrates a decrease in thermal performance associated with the increasing overlap between the IID ring and supported optical modes of the VCSEL cavity. A single-mode output power of 1.6 mW with over 30 dBm side-mode suppression ration is achieved from a 3 μm device with an IID-defined output aperture of approximately 1.3 μm. The optimal IID emission aperture to oxide aperture ratio for maximizing the single-fundamental-mode output power is experimentally measured.

50 Gb/s PAM4 Modulated 1065 nm Single-Mode VCSELs Using SMF-28 for Mega-Data Centers

Optical interconnections for mega-data centers will require longer link lengths than can be readily provided with today's low-cost vertical-cavity surface-emitting laser (VCSEL)based multi-mode technologies. We demonstrate a solution based on 1065-nm single-mode bottom emitting VCSELs to transmit data at 50 Gb/s using four-level pulse-amplitude modulation over a distance of 2 km using a standard single-mode fiber (SMF-28). We address potential concerns regarding the unwanted higher order LP11 mode that can propagate in the SMF-28 fiber. The single-mode VCSELs have oxide apertures in the 6-7 μm range to reduce series resistance and increase output power.

Polarization- and Modal-Control in a Vertical-Cavity Surface-Emitting Laser With an External-Cavity Formed by a Liquid Crystal Overlay

By utilizing a fully-vectorial three-dimensional cold-cavity optical simulation, we analyze the spectral, polarization, and modal-losses behavior of a vertical-cavity surface-emitting laser with a nematic liquid-crystal (LC) overlay. We identify phenomena responsible for mode and polarization selectivities and show how they can be controlled by varying design geometry parameters, such as LC thickness and oxide aperture diameter, or by electrooptically tuning the LC director. We present possibility of achieving voltage-controlled polarization switching of a fundamental mode or transverse mode switching within the same polarization. Furthermore, we show that it is theoretically possible to obtain improved single-mode operation by means of increased higher order transverse mode discrimination. Finally, we point out a way to destabilize the diode by equalizing the modal losses of all the analyzed modes.

Single fundamental mode photonic crystal VCSEL with high power and low threshold current optimized by modal loss analysis**Project supported by the National Basic Research Program of China (Grant Nos. 2010CB934104, 2009CB320300, and 2011CBA00608) and the National Natural Foundation of China (Grant Nos. 61604007, 61378058, 61376049, 61575008, and 61574011).

The characteristics of the photonic crystal vertical cavity surface emitting lasers (PhC-VCSELs) were investigated by using the full vector finite-difference time-domain (FDTD) method through the transverse mode loss analysis. PhC-VCSELs with different photonic crystal structures were analyzed theoretically and experimentally. Through combining the dual mode confinement of oxide aperture and seven-point-defect photonic crystal structure, the PhC-VCSELs with low threshold current of 0.9 mA and maximum output power of 3.1 mW operating in single fundamental mode were demonstrated. Mode loss analysis method was proven as a reliable and useful way to analyze and optimize the PhC-VCSELs.

Design of oxide-confined and temperature stable long wavelength Vertical Cavity Surface Emitting Laser for optical interconnects

One of the important attributes of Vertical Cavity Surface Emitting Laser for applications in optical interconnects is stable high temperature performance. In addition to temperature insensitivity, power dissipation is other major concern in the field of on-chip optical interconnects. With ever increasing chip size and functionalities, researchers are aggressively looking for temperature stability and power reduction in each department. Also the future emerging system of on-chip devices require long wavelength laser for high capacity applications. This paper deals with the designing of oxide-confined VCSEL structure operating at long wavelength i.e. 1310nm. Atlas Silvaco frame work is used to design VCSEL and to analyze its electrical and thermal behavior with state of the art modules. The static properties of the proposed VCSEL are analyzed at different oxide aperture diameter and temperature. It is observed that the future obligatory performance can be attained with this proposed design of VCSEL structure model even operating at low current densities and reduced oxide-aperture diameter equal to 3μm. The average error between the simulated and analytical power conversion efficiency is less than 5%.

Facilitating Single-Transverse-Mode Lasing in VCSELs via Patterned Dielectric Anti-Phase Filters

A novel method to achieve single-fundamental-mode lasing and higher order mode suppression using a multi-layer, patterned, dielectric anti-phase filter is employed on the top of oxide-confined vertical-cavity surface-emitting lasers (VCSELs). Dielectric layers are deposited and patterned on individual VCSELs in a wafer-scale process to modify (increase/decrease) the mirror reflectivity across the oxide aperture via anti-phase reflections, creating spatially dependent threshold material gain and VCSEL lasing-mode control. A 1-D plane-wave propagation method is used to calculate the dielectric layer thicknesses in each spatial region needed to facilitate or suppress lasing. A single-fundamental-mode, continuous-wave output power of 3.5 mW is achieved at a lasing wavelength of 850 nm. This additive, non-destructive method allows for mode selection at any lasing wavelength and for any VCSEL layer structure without the need for destructive etching techniques or epitaxial regrowth. It also offers the capability of a tailored filter design based on available materials and deposition methods.

Optically Controlled Current Confinement in Vertical-Cavity Surface-Emitting Lasers

We present a concept for optically controlled current confinement in vertical-cavity surface-emitting lasers (VCSELs) based on the monolithic integration of a phototransistor. Omitting the usual oxide aperture improves the manufacturability and prevents built-in strain near the active zone. Measured continuous-wave operation characteristics of fabricated devices show hysteresis loops in the current–voltage and light–current curves or a negative differential resistance region. Moreover, the optoelectronic influence of the integrated phototransistor is compared with a regular VCSEL. Requirements for the switch-on point of the laser are defined and explained.