Top DBR Research Articles

Surface-Emitting Lasers with Surface Metastructures

Vertical-cavity surface-emitting lasers (VCSELs) have been widely used in consumer electronics, light detection and ranging, optical interconnects, atomic sensors, and so on. In this paper, a VCSEL with the surface metastructure like one-dimensional high-contrast grating (HCG), based on the HCG-DBR vertical cavity, was first designed and fabricated. The polarization characteristic of the HCG-VCSEL were experimentally studied. The p-doped top 4-pair DBR for the current spreading and the direction shift between the HCG and the elliptical oxide aperture may result in a low orthogonal polarization suppression ratio in the HCG-VCSEL. Then, the Bloch surface wave surface-emitting laser (BSW-SEL), based on the HCG-DBR metastructure, is proposed for single-mode, high-efficiency, and high-power output with a low divergence angle. The mode field and the far field profile of the BSW-SEL are calculated for verification. The surface-emitting lasers with surface metastructures are useful for the sensing applications and optical interconnects.

Efficient Tunnel Junction Lithographic Aperture 940 nm VCSEL

We report on oxide free 940 nm VCSELs based on a buried tunnel junction acting as a lithographic aperture and achieving power conversion efficiency above 40%. We present the fabrication flow implementing a 2-step epitaxial growth as well as a detailed electro-optical characterization of the fabricated devices. The tunnel junction based VCSELs benefit from a uniform current distribution thanks to a low resistive n-doped top DBR. The mesa-free lithographically defined aperture enables the arrangement of compact arrays constituted of small single mode emitters. Such array configuration allows to scale up the generated optical power while maintaining a diffraction-limited Gaussian beam and limiting the impact of thermal rollover.

Transferrable dielectric DBR membranes for versatile GaN-based polariton and VCSEL technology

We present an innovative process to realize planar GaN microcavities, based on transferrable high-quality oxide-based Distributed-Bragg-Reflector (t-DBR) membranes. Unlike the widely used direct DBR deposition, which is not always feasible, the concept of t-DBR membranes allows their versatile use as top mirrors in all kinds of vertical-cavity surface emitting geometry devices, including light emitting diodes and lasers. The process illustrated here starts by evaporating first a 4-pair SiO2/Ta2O5 DBR centered around 400 nm on a lithographically patterned GaAs substrate. The GaAs substrate is subsequently removed by wet-etching, and the released DBR membranes are transferred onto other templates for their use as top mirrors in microcavities. By transferring a 4-pair top DBR on an 8-pair bottom SiO2/Ta2O5 DBR, a distinct cavity mode appears due to the formed λ/2 oxide cavity with a Q-factor of 110. If the 4-pair top DBR is transferred on 200 nm-thick GaN/AlGaN quantum well-containing membranes sitting on 10-pair bottom DBRs, complete all-dielectric nitride polariton structures are fabricated with pronounced strong-coupling characteristics.

Impact of damping on high speed 850 nm VCSEL performance * * Project supported by the National Natural Science Foundation of China (Nos. 61335004, 61675046, 61505003), the Open Fund of IPOC2017B011 (BUPT).

High speed VCSELs are important optical devices in short-reach optical communication links and interconnects because of their low cost and high modulation speeds. In this paper, the impact of damping on the their static and dynamic characteristics is analyzed and demonstrated. Through the shallow corrosion of the top layer DBR, the VCSELs with different damping is designed and fabricated. With the increase of the surface etch depth from 0 to ~55 nm for 9 μm oxide-aperture VCSEL, the K factor related with the damping is reduced from 0.31 to 0.23 ns−1. When the etch depth of the VCSEL with 9 μm oxide-aperture is decreased to ~25 nm, output power is increased from 4.03 to 4.70 mW and small signal modulation bandwidth is also increased from 15.46 to 16.37 GHz. It shows that there is a tradeoff between damping and differential gain for improving modulation speed.

Design and performance of high temperature operating resonant-cavity photodiodes based on 795 nm-VCSEL structure

We present detailed simulated and experimental results on spectral response of high temperature operating resonant-cavity photodiodes (RCPDs). Room temperature external quantum efficiency (EQE) spectrum shows peaks at resonance wavelength, ground-state emission, and lower reflectivity position. The EQE is ∼1.25, ∼0.7, and ∼3.75%, respectively, at the above three peak positions, i.e., 793, 778, and 743 nm. The maximum EQE increases from ∼1.25 to ∼18% as incident light angle increasing from 0 to 60°. The bandgap of AlGaAs barrier layer was also obtained by the angle dependence of EQE measurement. The amount of EQE/responsivity peak shift with temperature can be determined to be Δλ = T × 0.065 nm K−1, which is consistent with the temperature dependence of CM. The maximum responsivity increases from ∼0.01 to ∼0.19 A W−1 when temperature increasing from 300 to 370 K at −1 V bias. For high temperature operating RCPDs, the EQE/responsivity are largely governed by the total absorption within the active region. The performance of RCPDs can be further improved by increasing the pairs of bottom DBR and optimizing the pairs of top DBR.

Design and simulation of a high contrast grating organic VCSEL under electrical pumping

We propose an electrically pumped high-index-contrast grating (HCG)-based organic vertical-cavity surface-emitting laser (OVCSEL). The microcavity structure consists of an organic light emitting diode inserted in a very high quality factor hybrid photonic crystal (HPC) in which the top DBR is replaced by a sub-wavelength HCG layer. The results of simulation show that quality factor of the proposed microcavity is at least 280,000. Therefore, a considerable reduction of the laser threshold under electrical pump is expected. We also investigate the threshold behavior and the dynamics of the OVCSEL under electrical pump. Results from numerical simulation show that the structure can reach the lasing condition under electrical pump with a current density above 2 A/cm2.

SOI基RCE光电探测器谐振腔结构的设计与优化

由于CMOS光电探测器存在量子效率低、工作带宽窄等性能问题，为实现更高量子效率的CMOS光电探测器，结合工艺实现性，本文构建了一种新型的SOI CMOS工艺可兼容的光电探测器谐振腔结构。基于底镜采用一层1/4波长(850 nm光波长)奇数倍厚度SiO2，顶镜采用1/4波长偶数倍厚度SiO2的DBR反射镜，形成的SOI基谐振腔结构适用于光通信850 nm光波长的RCE PD器件。数值仿真结果表明，RCE PD器件比CMOS PD器件提高了量子效率，验证了谐振腔结构的正确性。 Due to the functional problems of CMOS photodetectors such as low quantum efficiency, narrow bandwidth and so on, this paper proposed a new resonant cavity structure compatible with SOI CMOS process to fabricate the CMOS photodetector with a higher quantum efficiency based on process optimization. By adopting the SiO2 with the thickness of odd number of a layer of 1/4 wavelength (850 nm optical wavelength) as the bottom DBR mirror, and using the SiO2 mirror with the thickness of an even multiple of 1/4 wavelength as the top DBR mirror, the SOI resonant cavity structure was prepared and demonstrated being suitable for the PD RCE device with the optical communication wavelength of 850 nm. Numerical simulation results showed that the PD RCE device could improve the quantum efficiency effectively compared with the PD CMOS device, which verifies the correctness of the resonant cavity structure.

Increasing single mode power of 1.3-μm VCSELs by output coupling optimization.

We report on the single mode emission power enhancement of 1.3-μm VCSELs by adjusting the reflectivity of the top GaAs-based DBR for output coupling optimization using selective removal of Bragg reflector layers. Devices with record single mode power of 6.8-mW at room temperature and 2.8-mW at 80°C, with more than 30 dB single mode suppression ratio, have been obtained.

Integrated Duo Wavelength VCSEL Using an Electrically Pumped GaInAs/AlGaAs 980 nm Cavity at the Bottom and an Optically Pumped GaInAs/AlGaInAs 1550 nm Cavity on the Top.

In this work, an integrated single chip dual cavity VCSEL has been designed which comprises an electrically pumped 980 nm bottom VCSEL section fabricated using GaInAs/AlGaAs MQW active region and a 1550 nm top VCSEL section constructed using GaInAs/AlGaInAs MQW active region but optically pumped using half of the produced 980 nm light entering into it from the electrically pumped bottom cavity. In this design, the active region of the intracavity structure 980 nm VCSEL consists of 3 quantum wells (QWs) using Ga0.847In0.153As, 2 barriers using Al0.03Ga0.97As, and 2 separate confinement heterostructures (SCH) using the same material as the barrier. The active region of the top emitting 1550 nm VCSEL consists of 3 QWs using Ga0.47In0.52As, 2 barriers using Al0.3Ga0.17In0.53As, and 2 SCHs using the same material as the barrier. The top DBR and the bottom DBR mirror systems of the 1550 nm VCSEL section plus the top and bottom DBR mirror systems of the 980 nm VCSEL section have been formed using GaAs/Al0.8Ga0.2As. Computations show that the VCSEL is capable of producing 8.5 mW of power at 980 nm from the bottom side and 2 mW of power at the 1550 nm from top side.

Intra-cavity patterning - new method of single mode emission enhancement

We demonstrate the results of numerical simulations of 1.3μm InAlGaAs/InP VCSEL with a ring pattern etched at the interface between the cavity and top DBR. We show that the proposed design offers selective confinement of the fundamental mode and strong discrimination of higher order modes. Consequently, VCSEL with ring confinement is capable to operate in a broad range of injected currents in the single mode regime, which facilitates the improvement of maximal emitted power and increase of the wavelength tuning range with very narrow spectral characteristics. High power, single-mode emitting vertical-cavity surface-emitting lasers (VCSELs) are of great interest, since they can serve as high-power, smoothly tuned with current and temperature, coherent-optical sources. Emerging applications include inexpensive and portable gas sensors, telecommunication emitters, and so on. For these applications, it is preferable to have a low-threshold, high side-mode suppression ratio (SMSR) light source. VCSELs inherently emit in a single longitudinal mode; controlling the lateral mode is far more complicated. It can be achieved using a well-established wet oxidation technology, which makes possible single-mode operation only for relatively narrow apertures (providing less than 5 mW of output power) (1). Other methods provide up to twofold higher emitted power but exploit more challenging technologies (2-5). The limitation of high power single mode operation comes from small optical apertures or multimode operation under high injection levels. This paper provides numerical analysis of the ring pattern etched in the cavity of the VCSEL which eliminates higher order mode emission. The ring pattern provides confinement for a fundamental mode and forces higher order modes to be pushed out of the active region. The analyzed structure (Fig. 1a) (6) incorporates InAlGaAs quantum wells within an InP cavity. The cavity is bounded by 35 pairs of Al0.9Ga0.1As/GaAs DBRs from the bottom and 20.5 pairs of Al0.9Ga0.1As/GaAs DBRs from the top. Laterally patterned tunnel junction (TJ) layers are responsible for tunnelling carriers into the

Designing a High Speed 1310nm AlGaInAs/AlGaInAs VCSEL using MgO/Si Top DBR and GaInAsP/InP Bottom DBR

In this paper, a 1310nm intracavity structure Vertical Cavity Surface Emitting Laser (VCSEL) has been designed using quaternary compound material of AlGaInAs in both QW and barrier but with different composition. This choice has been made instead of choosing widely used GaInAsP/ InP, GaInAsN/ GaAs to gain some advantages. This combination has shown good band offset in the conduction band. Lattice matching has been obtained in the layers from the substrate up to the top contact layer except the quantum well (QW) layers where small amount of compressive strain of 1.55% has been used. From the substrate up to the top contact layer, fabrication can be done by epitaxial growth without any difficulty. Reduction in height by using 5 pairs of the top dielectric DBR mirror system of MgO/ a-Si is an attraction of this design which can be fabricated by evaporation technique. Dissipation in the bottom DBR due to current flow has been eliminated by using intracavity structure which also gave a way out for the current flow bypassing the dielectric top DBR. The active material compositions have been chosen to obtain a peak gain at 1310nm. The end result of this design is a top emitting VCSEL based on InP substrate using a different structure which is capable of producing 1310nm light output and which can be constructed easily using widely used epitaxial techniques mixed with the evaporation technique for the top DBR mirror system. The structure is suitable for use in optical ICs.

Effect of SiO2 Reflection Reducing Coating on the Vertical Cavity Surface Emitting Laser

The effects of epitaxis SiO2 film on the characteristics of DBR reflectivity were simulated, and the reflectivity of graded interface DBR is lower than the abrupt one was studied. 850nm vertical-cavity surface-emitting lasers were fabricated, the DBR is formed by graded heterojunction of AlxGa1–xAs, the top and bottom DBR have 22 and 34 pairs of mirror, and current was confined by oxide aperture, and then different thickness of SiO2 film were grew on the top DBR. and found that a certain thickness (λ/4) of the SiO2 reflection reducing coating could make the vertical-cavity surface-emitting lasers output power increased about 3–5 mW, the threshold current does not increase obviously, the reason is external quantum efficiency increases more than the threshold current. So the SiO2 reflection reducing coating does not affect the lasing of lasers and threshold current obviously, but It can significantly improve the output power. The experimental results agree well with the theoretical expectation.

Full 3D FDTD analysis of Electromagnetic Field in Photonic Crystal VCSEL

The effect of etch damage to the mode characteristics of photonic crystal vertical cavity surface emitting lasers was simulated in this paper. The devices simulated in this paper are 850-nm GaAs-based VCSELs with photonic crystal. And the devices were simulated by using finite difference time domain (FDTD) method. Limited to the computer resource, the top DBR was simulated only, and the traverse size was smaller than the real size. In order to highlight the impact of the etch damage, several kinds of light sources and photonic crystal structures were simulated separately, and each situation is calculated in the condition of ideal photonic crystal and photonic crystal with etch damage respectively. All parameters of device and light feature are referred to the real condition.

Thermal analysis of asymmetric intracavity-contacted oxide-aperture VCSELs for efficient heat dissipation

The asymmetric intracavity-contacted oxide-aperture vertical-cavity surface-emitting lasers (VCSELs), operating at λ ∼ 980 nm, with different oxide aperture diameters were fabricated and their thermal analysis was theoretically performed using a three-dimensional cylindrical heat dissipation model. The heat flux, temperature profile, and thermal resistance ( R th) of the devices were investigated by incorporating heat source values, obtained from experimentally measured results, into the thermal simulation. For the fabricated VCSELs with benzocyclobutene passivation layer, the R th decreased from 4612 K/W to 1130 K/W as the oxide aperture diameter ( D a) increased from 8 μm to 16 μm and it increased significantly below 8 μm. The use of the thin substrate and the passivation layer with a high conductivity enhances the heat dissipation, allowing for a low R th. Furthermore, thick Au layers on contact pads and top DBR in intracavity-contacted VCSEL structures help increase heat removal from the active region. For D a = 8 μm and 16 μm, the VCSELs with SiN x passivation layer, 5 μm thick extra Au layer, and 100 μm thick substrate indicate R th = 3050 K/W and 778 K/W, respectively, leading to an improvement by >30% compared to the fabricated devices.

Performance optimisation of epitaxially regrown 1.3-μm vertical-cavity surface-emitting lasers

A number of GaAs-based long-wavelength, vertical-cavity, surface-emitting laser structures with optical and electrical confinement based on selective area epitaxy have been fabricated and evaluated. The influence on output power, threshold current, thermal stability and modal properties from design parameters such as bottom-distributed Bragg reflector (DBR) doping, cavity doping, dielectric top DBR design and carrier confinement barriers is evaluated. More than 7 mW of output power is emitted from multimode devices with a square active region size of 10 µm. Single-mode power from smaller devices is restricted to 1.5 mW because of a non-optimal cavity shape.

High performance resonant cavity light emitting diodes for POF application

A device structure of resonant cavity light emitting diodes （RCLED） at 650nm wavelength was proposed by using AlGaAs as the n-type bottom DBR, AlGaInP as the p-type top DBR, and GaInP/AlGaInP MQW as the active region. The device was designed according to the transfer matrix method, and both RCLED and normal LED were fabricated for comparison. Results showed that the efficiency of RCLED is 30% higher than the normal LED, and the peak wavelength of RCLED changed only 1nm when the driving current increased from 3mA to 30mA, compared with that of 7nm for the normal LED. Meanwhile, RCLED has a narrower spectrum and a smaller far field divergence angle.

Threshold characteristics of bottom-emitting long wavelength VCSELs with photonic-crystal within the top mirror

We present self-consistent modeling of InP-based 1300-nm AlInGaAs photonic-crystal vertical-cavity surface-emitting diode laser. We investigate the influence of photonic-crystal parameters on threshold characteristics. We show that a shallow photonic crystal can significantly deteriorate the VCSEL threshold current. The significant reduction of threshold current can be assured by the photonic-crystal etched through the whole top DBR mirror.

VCSELs with monolithic coupling to internal horizontal waveguides using integrated diffraction gratings

A VCSEL structure with output coupling to an internal waveguide using integrated diffraction gratings has been demonstrated. The design and fabrication of the monolithically integrated structure, including epitaxial regrowth, is discussed and initial device characteristics are presented. While horizontal waveguides can be used to route optical signals between monolithically integrated components, a small amount of transmission is retained in the top DBR to enable on-wafer testing. This monolithic structure has the potential to enable VCSEL-based photonic integrated circuits on GaAs.

Green monolithic II–VI vertical‐cavity surface‐emitting laser operating at room temperature

AbstractThe realization of a monolithic all II–VI‐based vertical cavity surface emitting laser (VCSEL) for the green spectral region is reported. Optically pumped lasing operation was achieved up to room temperature using a planar VCSEL structure. Taking advantage of distributed Bragg‐reflectors based on MgS/Zn(Cd)Se superlattices as the low‐refractive index material and ZnS0.06Se0.94 layers as the high‐index material with a refractive index contrast of Δn = 0.6, a quality factor exceeding Q = 2000 is reached by using only 18 Bragg periods for the bottom DBR and 15 Bragg periods for the top DBR. The threshold power density is 0.32 MW/cm2 at a temperature of 10 K (emission wavelength 498.5 nm) and 1.9 MW/cm2 at room temperature (emission wavelength 502.3 nm). (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Design and analysis of anti-resonant reflecting photonic crystal VCSEL lasers

Anti-resonant reflecting photonic crystal structure is employed in vertical cavity surface emitting lasers (VCSELs) to achieve photon confinement in lateral direction. Such a design is promising in supporting large-aperture single-mode emission. In the configuration, hexagonal arrays of high-index cylinders which run vertically in the cladding region are introduced in the VCSEL's top DBR (p-DBR) mirror region. The transverse modal property of the proposed structure, especially leakage loss, has been theoretically investigated. An optimum design for the minimum radiation loss while maintaining single-mode operation has been discussed in this paper.