Buried Tunnel Junction Research Articles

掩埋隧道结垂直面激光器速率方程参量提取

In order to design and optimize high frequency performances of laser diodes,accurate extraction methods for the rate equation parameters are very important.A method for the rate equation parameter extraction for long-wavelength and high-bandwidth buried tunnel junction vertical-cavity surface-emitting lasers is presented.This method bases on the threshold current,output power,resonance frequency,damping factor and nonlinear effect of the gain compression factor under high bias currents.By fitting the chip frequency responses with different bias currents,resonance frequency and damping factor values can be obtained.Finally,by considering gain compression factor and nonlinear fitting resonance frequency and damping factor values under different currents,parameters of rate equation model can be extracted.

AlGaInAsPSb-based high-speed short-cavity VCSEL with single-mode emission at 1.3 μm grown by MOVPE on InP substrate

In this paper we present the first InP-based short-cavity Vertical-Cavity Surface-Emitting Laser with an AlGaInAsP/GaInAsP active region and a re-grown and structured GaAs0.51Sb:C/Ga0.47InAs:Si buried tunnel junction (BTJ), which serves as current aperture, grown by LP-MOVPE. We achieved over 1mW single-mode continuous-wave (cw) emission at around 1.3μm wavelength and room-temperature. The small-signal modulation bandwidth exceeds 7.5GHz, which is appropriate for 10Gb/s data transmission, and the series resistance is as low as 24Ω. The latter value indicates around three times lower dissipated power consumption than comparable MOVPE grown InP-based VCSELs.

Transverse-Mode Characteristics of GaSb-Based VCSELs With Buried-Tunnel Junctions

We report the transverse-mode characteristics of GaSb-based vertical-cavity surface-emitting lasers (VCSELs) with buried-tunnel junctions (BTJs). The optical-index guiding in the devices is achieved by an effective refractive index step due to the presence of a laterally structured BTJ in the cavity. All lasing modes in VCSELs of different active diameters are experimentally measured. Then the experimental results are compared against the theoretical data for two different VCSEL designs emitting at 2.3 and 2.6 μm yielding a good agreement. The transverse-mode spacing between the excited modes is also determined and the results are compared with the theory. The far-field patterns ensure that devices with reasonable aperture diameters operate in single-fundamental LP01 mode, showing that the devices are well-designed.

Vertical-Cavity Surface-Emitting Laser Light–Current Characteristic at Constant Internal Temperature

Two continuous-wave measurement methods for the laser P-I-characteristic at a constant internal temperature are presented (constant average cavity and constant junction (active region) temperature). The methods are used to correctly quantify the temperature dependence of threshold current and differential quantum efficiency without need for pulsed measurements. It is found that the deviations between both temperatures can be as high as 5 K in a 1390-nm InP-based buried tunnel junction vertical-cavity surface-emitting laser (BTJ-VCSEL), which is the reason for the slight sublinearity of the characteristics at constant cavity temperature.

Comprehensive analysis of electrically-pumped GaSb-based VCSELs

This paper discusses several performance-related aspects of electrically-pumped GaSb-based buried tunnel junction VCSELs with an emission wavelength of 2.6 μm based on theoretical and experimental results. These results allow a deeper insight into the internal device physics, such as radial diffusion of carriers, maximum continuous-wave operating temperature, diffraction loss, internal temperature, gain and loss parameters, internal quantum efficiency of the active region etc. These parameters can be taken into account while designing mid-infrared lasers which leads to an improved device performance. A simple thermal model of the devices based on the two-dimensional (2-D) finite element method using the material data from the literature is also presented. In addition, an application-based result utilizing these lasers for the measurement of absolute water vapor concentration by wavelength modulation spectroscopy (WMS) method are also described, hinting that devices are well-suited for the targeted sensing applications.

40 Gbit/s modulation of 1550 nm VCSEL

The modulation characteristics of vertical-cavity surface-emitting lasers with a buried tunnel junction emitting in the important wavelength regime around 1.55 m are presented. For the first time it was possible to demonstrate bit rates up to 40 Gbit/s also in this waveband. The 3 dB bandwidth measured under continuous-wave driving conditions was higher than 19 GHz. The present devices were found to be somehow sensitive to the bit-pattern length, especially at high temperatures or data rates resulting in some error-flooring. Error-free performance could be demonstrated up to 35 Gbit/s at room temperature and up to 25 Gbit/s at 55°C.

Evolution of high-speed long-wavelength vertical-cavity surface-emitting lasers

High-speed buried tunnel junction (BTJ) vertical-cavity surface-emitting lasers (VCSELs) covering the long-wavelength range from 1.3 µm to 1.6 µm have been developed in the last decade and achieved remarkable performance. The InP-based monolithic approach with a BTJ as a current aperture and an integrated gold heat sink, which originated at the Walter Schottky Institute, is reviewed in this review. Cutting-edge device performance like error-free operation at 25 Gb s−1 data rate, large VCSEL arrays with high output powers, widely tunable devices, or novel nano-photonic device concepts could be realized.

High-Speed Buried Tunnel Junction Vertical-Cavity Surface-Emitting Lasers

InP-based, vertical-cavity surface-emitting lasers (VCSELs) utilizing a buried tunnel junction (BTJ) emitting at 1.55 μm with improved active region and reduced parasitics are demonstrated. A superior modulation bandwidth > 10 GHz is achieved up to 85 °C. The VCSEL device is investigated in detail, analyzing all bandwidth-limiting elements. With their improved temperature range, these VCSELs are especially qualified for uncooled operation in passive optical networks. These lasers show open eyes and error-free transmission up to 25-Gb/s modulation speed at room temperature. Uncooled error-free operation over a wide temperature range under constant bias conditions for ultra-low-cost systems is demonstrated at a 12.5-Gb/s data rate up to 85 °C. Due to a well-tailored mode-gain detuning, the laser characteristics are practically invariant with temperature at fixed bias conditions. Further possible design optimizations targeting at data rates well above 25 Gb/s are discussed.

Small-Signal Equivalent-Circuit Model and Characterization of 1.55-μm Buried Tunnel Junction Vertical-Cavity Surface-Emitting Lasers

An equivalent-circuit model for a novel 1.55- μm buried tunnel junction vertical-cavity surface-emitting laser chip is proposed based on the structure of the device. The values of the equivalent-circuit elements are determined by fitting the reflection and transmission coefficients at different bias currents. Good agreement between measured and simulated results implies the validity of the equivalent-circuit model. The influences of the buried tunnel junction, active region, and parasitic parameters on the high-frequency responses are investigated based on measurements and theoretical predictions. It is shown that the impedance of the device will change with the bias current, even if the bias current is above threshold, which is different from the edge-emitting laser, and the frequency responses depend on both the buried tunnel junction and mesa diameters.

Long wavelength electrically pumped GaSb-based buried tunnel junction VCSELs

Long wavelength lasers are attractive light sources for free-space communications, military countermeasures, medical applications and trace-gas sensing systems by tunable diode laser absorption spectroscopy (TDLAS). As technically important gases, such as CO, CO2 or CH4, show strong absorption lines in a wavelength range from 2 to 3.5 μm, one is interested in the development of lasers emitting in that region. The (AlGaIn)(AsSb) material-system based on GaSb is the material of choice for devices in the near- to mid-infrared spectral region. In this paper, we present the device structure, design and results of an electrically-pumped GaSb-based VCSEL. The devices consist of an epitaxial GaSb/AlAsSb distributed Bragg reflector (DBR), a GaInAsSb quantum well gain section, a dielectric top DBR and a buried tunnel junction (BTJ) for electrical as well as optical confinement. Continuous-wave (cw) single-mode emission has been achieved up to a record high ambient temperature of 90 ∘C. The wavelength is (electro-) thermally tunable from 2345 nm to 2365 nm. A maximum output power of 800 μW has been measured at 0 ∘C.

Polarization Control in Buried Tunnel Junction VCSELs Using a Birefringent Semiconductor/Dielectric Subwavelength Grating

We present long-wavelength InGaAlAs-InP vertical-cavity surface-emitting lasers (VCSELs) with a buried tunnel junction (BTJ) and a well-defined polarization accomplished by a semiconductor/dielectric subwavelength grating (SWG). The grating is incorporated in the inner VCSEL cavity and exhibits an effective birefringence for polarizations parallel and perpendicular to the grating grooves. Theoretical modeling leads to distinct design rules for VCSELs with grating structure that deviate from the conventional design without grating. Due to the large polarization-mode separation, lasing activity is enabled only for one polarization mode. BTJ-VCSELs with properly chosen SWG parameters show predictable and full polarization stability. In addition, the relevant device parameters such as threshold current are comparable to conventional BTJ-VCSELs.

Single-mode electrically pumped GaSb-based VCSELs emitting continuous-wave at 2.4 and 2.6 μm

Vertical-cavity surface-emitting lasers (VCSELs) are perfect light sources for spectroscopic applications, where properties such as continuous-wave (cw) operation, single-mode emission, high lifetime and often low power consumption are crucial. For applications such as tunable diode laser absorption spectroscopy (TDLAS), there is a growing interest in laser devices emitting in the near- to mid-infrared wavelength range, where many environmentally and technologically important gases show strong absorption lines. The (AlGaIn)(AsSb) material system based on GaSb is the material of choice for covering the 2.0–3.3 μm range. In this paper, we report on electrically pumped single-mode VCSELs with emission wavelengths of 2.4 and 2.6 μm, operating cw at room temperature and beyond. By (electro-) thermal tuning, the emission wavelength can be tuned mode-hop free over a range of several nanometers. In addition, low threshold currents of several milliamperes promise mobile application. In the devices, a structured buried tunnel junction with subsequent overgrowth has been used in order to achieve efficient current confinement, reduced optical losses and increased electrical conductivity. Furthermore, strong optical confinement is introduced in the lasers due to laterally differing cavity lengths.

Gain peak–cavity mode alignment optimisation in buried tunnel junction mid-infrared GaSb vertical cavity surface emitting lasers using hydrostatic pressure

High-pressure techniques are used to investigate and optimise the design of GaInAsSb/AlGaAsSb vertical cavity surface emitting lasers (VCSELs) emitting at 2.4 µm. From measurements on edge emitting lasers it is found that non-radiative Auger recombination accounts for up to 85% of the threshold current at room temperature (RT) and is responsible for their strong temperature sensitivity. The effect of Auger recombination in VCSELs may be mitigated through judicious design of the gain peak–cavity mode (CM) alignment which may be investigated using high pressure. Results show that temperature insensitivity over the range −10 to +30°C may be obtained around RT if the gain peak is offset by approximately 10 meV higher in energy from the VCSEL CM.

Short-Cavity Long-Wavelength VCSELs With Modulation Bandwidths in Excess of 15 GHz

InP-based buried tunnel junction vertical-cavity surface-emitting lasers (VCSELs) incorporating a novel short-cavity (SC) design are presented. These highly single-mode devices emitting at 1.55 mum show record-high modulation bandwidths in excess of 15 GHz together with greatly enhanced intrinsic resonance frequencies. For elevated temperatures of 65degC and 80degC, 3-dB-modulation bandwidths beyond 13 and 10 GHz are demonstrated, respectively. Reasons for the improved modulation behavior are the smaller intrinsic damping due to reduced photon-lifetime, and the better heat-management of these SC-VCSELs.

Electrically pumped continuous-wave vertical-cavity surface-emitting lasers at ∼2.6 μm

In this paper, electrically pumped GaSb-based vertical-cavity surface-emitting lasers operating continuous wave at a record long emission wavelength of ∼2.6 μm are presented. Owing to the excellent thermal heat management, the devices exhibit single-mode operation up to a heat-sink temperature of 55 °C. Lateral current confinement and index guiding in the device are accomplished by utilizing the buried tunnel junction concept. Devices with aperture diameters of 6 μm show maximum output powers of 0.3 mW at room temperature with quantum efficiencies around 10%.

Long-Wavelength GaInNAs Vertical-Cavity Surface-Emitting Laser With Buried Tunnel Junction

A long-wavelength GaInNAs vertical-cavity surface-emitting laser with a buried tunnel junction (BTJ) has been demonstrated in this paper. It has been shown that a combination of a GaAs-based BTJ for a current confinement, GaInNAs multi-quantum wells for an active region, a dielectric distributed Bragg reflector (DBR) for a top mirror, and an AlGaAs/GaAs DBR for a bottom mirror is desirable to realize high-speed operation at high temperature. The maximum output power of 4.2 mW with a low resistance of 65 Omega has been obtained at 25degC. Operations of 10 Gb/s have been achieved over the temperature range of 25degC-85degC, with operation current of 6.9 mA and extinction ratio of 5.0 dB.

InP-Based Long-Wavelength VCSELs and VCSEL Arrays

Long-wavelength, InP-based, vertical-cavity surface-emitting lasers with buried tunnel junction (LW-BTJ-VCSELs) and VCSEL arrays are presented. Emitting at the telecommunications wavelengths around 1.3 and 1.55 mum, these devices show high modulation bandwidth in excess of 10 GHz over a wide temperature range. Small-signal equivalent circuits for the parasitic and intrinsic response are given. Various data-transmission experiments are performed with data rates up to 12.5 Gb/s over different fiber channels. 1-D LW-BTJ-VCSEL arrays can be used in wavelength-division multiplexing systems for high bandwidth per fiber channel. 2-D high-speed arrays with 64 individually addressable channels are presented that are particularly suited for optical ultrabroadband interconnects. Furthermore, large-scale arrays are investigated for high-power applications. In a detailed investigation, we derive scaling rules considering the influence of aperture, array size, and pitch on laser power. At room temperature, optical output powers in the watt regime have been realized at 1.55 mum. Divergence angles are as low as 13deg-17deg full-width at half-maximum. Wall plug efficiencies in excess of 20% over a wide current range and high-temperature operation up to 80degC are obtained.

GaSb-Based VCSEL With Buried Tunnel Junction for Emission Around 2.3 $\mu$m

In this paper, we present a device concept and results of an electrically pumped vertical-cavity surface-emitting laser in the (AlGaIn)(AsSb) material system grown on GaSb substrate. The structure consists of an n-doped GaSb/AlAsSb distributed Bragg reflector and a type-I GaInAsSb/AlGaAsSb active region, and incorporates a type-III p+-GaSb/n+-InAsSb buried tunnel junction for current as well as optical confinement. Continuous-wave operation up to 75degC has been achieved at a wavelength of 2.3 mum. The mid-IR emission, the large tunability over a wavelength range of more than 10 nm combined with its single-mode operation makes this device ideally suited for gas-sensing applications.

Diffraction loss in long-wavelength buried tunnel junction VCSELs analyzed with a hybrid coupled-cavity transfer-matrix model

Intra-cavity diffraction in VCSELs is a loss mechanism that potentially can cause a significant decrease in efficiency and a rise in the threshold current, particularly in cavities with small lateral features with a high index contrast. One such VCSEL type is the 2.3 microm GaSb-based buried tunnel junction (BTJ) VCSEL studied in this work, where the BTJ induced topology of the top layers gives rise to excess loss through diffraction. Diffraction loss is difficult to measure, and also the numerical estimation must be done with care because of the non-axial propagation of the diffracted fields. We present a simulation method with spatially varying dimensionality, such that the field is three-dimensional (3D) in the entire cavity, whereas the material structure of the cavity is modelled in 3D near the BTJ and the layers with a varying topology, but elsewhere is assumed to be 1D like in a regular DBR structure. We find that the diffraction loss displays a non-monotonic behaviour as a function of the BTJ diameter, but as expected it rapidly increases below a certain diameter of the BTJ and may even become the dominant cause of loss in some device designs. We also show that the diffraction loss can be much reduced if the layers above the BTJ can be deposited such that the surface profile becomes smoother with increasing distance from the BTJ.

Design of an InGaAs/InP 1.55 μm electrically pumped VCSEL

The design of an electrically pumped InGaAs quantum well based vertical cavity surface emitting laser (VCSEL) on InP substrate is presented. Such optically pumped VCSELs have already been demonstrated. To design electrically pumped VCSEL, three simulations steps are needed: optical simulation gives access to the standing-wave electric field distribution, to design the active region and the Bragg mirrors. Thermal simulation is helpful to design metallic contacts while the energy band diagram is obtained by electrical simulation to design the buried tunnel junction useful for carrier injection. All these simulations are compared to experiment.