Internal Optical Loss Research Articles

Absorption loss properties and Stokes shifts of InGaAs-based self-assembled well-wire-hybrid quantum structures

Stokes shift is an important physical property relating to emission and absorption of light-emitting diodes, which reflects photon self-absorption situation and affects the device performance. Nowadays, it is becoming more and more difficult to change Stokes shift and relevant physical properties to further improve device performance with traditional quantum structures from increasing requirements in application. Therefore, hybrid quantum structures have attracted an attention recently. However, the properties related to Stokes shift in the new configurations have not been revealed so far. In this paper, we investigate the absorption loss and Stokes shift of the newly proposed InGaAs self-assembled well-wire-hybrid quantum structure. By designing a new absorption loss measurement approach, we can conveniently extract internal optical mode loss of a quantum structure and explore its Stokes shift with the measured absorption spectra. Our findings reveal that the presence of quantum wires in the structure can significantly reduce the Stokes shift difference between transverse electric and transverse magnetic (TM) polarizations from 66.7% for a traditional quantum well to 15.4%. It suggests the potential for the reduction of TM-mode photon self-absorption in a compressive-strain quantum structure. This phenomenon offers new prospects for the development of polarization-insensitive devices.

Analysis of Internal Optical Loss of 1.3 μm Vertical-Cavity Surface-Emitting Laser Based on n++-InGaAs/p++-InGaAs/p++-InAlGaAs Tunnel Junction

Analysis of Internal Optical Loss of 1.3 μm Vertical-Cavity Surface-Emitting Laser Based on n++-InGaAs/p++-InGaAs/p++-InAlGaAs Tunnel Junction

High-Power Laser Diodes Based on InGaAs(P)/Al(In)GaAs(P)/GaAs Heterostructures with Low Internal Optical Loss

High-Power Laser Diodes Based on InGaAs(P)/Al(In)GaAs(P)/GaAs Heterostructures with Low Internal Optical Loss

Gain measurements on VCSEL material using segmented contact technique

We report direct measurements of the optical gain on vertical-cavity surface-emitting laser (VCSEL) material using a stripe-length method featuring segmented contacts. We utilise the similarity of the in-plane transverse electric (TE) polarised matrix element and that of the VCSEL lasing mode and a simple method to reduce round trip effects. The confinement factor is determined from cold-cavity simulations of the in-plane TE polarised slab waveguide mode and used to convert the measured in-plane modal gain into the vertical-cavity modal gain, as required for the VCSEL structure. This gives a threshold material gain of 1440 ± 140 cm−1 at 30 °C for this structure. A comparison with the threshold material gain values determined from the lasing condition, where internal optical losses due to doping induced absorption is included using parameters taken from the literature, indicates the presence of an additional source of optical loss in the experiment which increases the threshold material gain by ∼450 cm−1. A best fit is obtained by increasing the optical loss in the n-DBR (distributed Bragg reflectors) layers to 40 cm−1, which is consistent with previous work on additional scattering losses due to interface roughening in the n-DBR layers. To further demonstrate the utility of this method for rapid optimisation, the gain-peak wavelength is measured directly, and its temperature dependence is compared to the lasing wavelength.

Multiple increase in the radiative efficiency of 1060-nm laser diodes based on heterostructures with tunnel-coupled injection and a single waveguide mode.

An approach aimed at increasing the radiative efficiency in heterostructures operating in a single vertical mode at 1060 nm has been studied. Two types of heterostructures-the STJH (single tunnel junction heterostructure) and DTJH (double tunnel junction heterostructure)-have been developed to obtain the operation of a single waveguide mode of the first and second order, respectively. A multiple increase in the injection efficiency is realized by using tunnel junctions (TJs) embedded in the wide-gap barriers and placed between the active regions. An internal quantum efficiency of close to 100% and a transparency current density of 78 A/cm2 is demonstrated for both types of heterostructures, while the internal optical loss is 5.2 and 3.8 cm-1 for STJH and DTJH, respectively. The maximum radiative efficiency (for the initial linear part of the light-current curve) and the output optical power (for the current pulse of 1 µs and 9.6 A) reach 1.6 W/A and 7.8 W for STJH and 2.2 W/A and 15.8 W for DTJH.

Coupling Performance Enhancement of GaSb-Based Single-Transverse-Mode Lasers with Reduced Beam Divergence Obtained via near Field Modulation

Symmetric narrow waveguide structure has been developed and fabricated to achieve low beam divergence and improved coupling performance of the 1.95 μm GaSb-based single-transverse-mode diode lasers. The near-field expansion effect of the narrowed 150 nm vertical waveguide design leads to a reduced fast-axis beam divergence of 44.2° full width at half maximum (FWHM) as well as 62% single-mode fiber (SMF) coupling efficiency, which has 55% relative promotion compared to the 40% efficiency of the conventional 270 nm waveguide design with 60.4° FWHM. The highest SMF coupling power of 113 mW was obtained by the 210 nm narrow waveguide lasers with lower internal optical loss at a 55% coupling efficiency, which performed balanced optimal performance with a narrowed divergence of 53.4° and a relatively high optical power of 206 mW. The high coupling efficiency and power will provide more promising prospects for the GaSb-based single-transverse-mode lasers in the widespread fiber-based and external-cavity applications.

48 W Continuous-Wave Output From a High- Efficiency Single Emitter Laser Diode at 915 nm

Improving the power and efficiency of 9xx-nm broad-area laser diodes has a great help in reducing the cost of laser systems and expanding applications. This letter presents an optimized epitaxial structure with high power and conversion efficiency. Laser diodes with 230 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> emitter width and 5 mm cavity length deliver continuous-wave output power up to 48.5 W at 48 A, 30 °C, the highest power reported for 9xx-nm single emitter lasers so far. The slope efficiency is as high as 1.23 W/A due to a low internal optical loss of 0.31 cm−1 and a high internal efficiency of 96%. The maximum power conversion efficiency reaches 72.6% at 15.3 W and 67.3% at the operating power of 30 W under a heatsink temperature of 25 °C. Life test results show no failure in 1000 hours for 55 laser diodes.

Thermal Design of VCSEL Arrays for Optical Output Power Improvement

This study investigates the thermal design of 2-D vertical-cavity surface-emitting laser (VCSEL) arrays for optical output power improvement. Considering the temperature dependencies of bias current, internal quantum efficiency, internal optical loss, and thermal resistance of each array cell, a compact electro-opto-thermal model of 2-D VCSEL arrays with linear power dissipation and quadratic power dissipation in each array cell is established to study the effects of array cell spacing and layout on the device performance. At the same time, the power dissipation mechanisms contributing to thermal rollover are also studied. It is found that the array cell spacing has a strong influence on the linear power dissipation, and the layout (such as hexagonal design) influences quadratic power dissipation obviously. With the careful design of array cell spacing and layout, both the temperature profile and the thermal resistance matrix of VCSEL arrays are improved, which is helpful to delay the onset of thermal rollover and hence enhance the optical output power. The simulation results are consistent with experimental results.

Analysis of light – current characteristics of high-power semiconductor lasers (1060 nm) in a steady-state 2D model

This paper presents a 2D model of a high-power semiconductor laser, which takes into account carrier transport across the layers of its heterostructure and longitudinal spatial hole burning (LSHB), an effect related to the nonuniform gain distribution along the cavity axis. We show that the use of the 2D model which takes into account carrier transport across the layers of the heterostructure allows an appreciable contribution of LSHB to saturation of light – current characteristics to be demonstrated. The LSHB effect, causing a decrease in the output optical power of semiconductor lasers, is shown to be stronger at high drive currents and low output mirror reflectivities. In the case of high drive currents, the LSHB-induced drop in power is related to the faster growth of internal optical and recombination losses because of the nonuniform current density distribution along the cavity axis, such that the highest current density can be almost twice the lowest one. LSHB is shown to increase the power stored in a Fabry – Perot cavity, which is an additional mechanism reducing the output optical power.

High Power Single Mode 1300-nm Superlattice Based VCSEL: Impact of the Buried Tunnel Junction Diameter on Performance

High power single mode wafer-fused 1300-nm VCSELs with a gain region based on InGaAs/InAlGaAs short period superlattice are fabricated. An InP-based optical cavity and two AlGaAs/GaAs distributed Bragg reflector heterostructures were grown by molecular beam epita&#x00F5;y. The current and optical confinement is provided by a lateral-structured buried tunnel junction with etching depth of <inline-formula> <tex-math notation="LaTeX">$\sim 25$ </tex-math></inline-formula> nm. It is shown that optimal diameter of the buried tunnel junction for high-power single mode emission is <inline-formula> <tex-math notation="LaTeX">$\sim 5$ </tex-math></inline-formula>-<inline-formula> <tex-math notation="LaTeX">$6~\mu \text{m}$ </tex-math></inline-formula>. The VCSEL demonstrates more than 6 mW single mode continuous-wave power and a threshold current less than 1.5 mA at 20 &#x00B0;C. The output optical power exceeds 1 mW at 85 &#x00B0;C. A -3dB modulation bandwidth up to 8 GHz and 6 GHz is obtained at 20 &#x00B0;C and 85 &#x00B0;C, respectively. The gain coefficient of <inline-formula> <tex-math notation="LaTeX">$\sim 650$ </tex-math></inline-formula> cm^&#x2212;1 and the transparency current density of <inline-formula> <tex-math notation="LaTeX">$\sim 630$ </tex-math></inline-formula> A/cm² are estimated at zero gain-to-cavity detuning (\sim 60 &#x00B0;C). The ultimate low internal optical losses about 0.08 &#x0025; per round-trip (distributed losses &#x007E;3.2 cm^&#x2212;1) at 20 &#x00B0;C and 0.13 &#x0025; per round-trip (distributed losses &#x007E;5.5 cm^&#x2212;1) at 100 &#x00B0;C were obtained.

Designs for III-nitride edge-emitting laser diodes with tunnel junction contacts for low internal optical absorption loss

The lasing mode and internal optical absorption loss profiles of III-nitride edge-emitting laser diode (LD) designs operating at 440 nm were modeled using the transfer matrix method. These models indicate absorption losses are minimized in LDs utilizing tunnel junction (TJ) contacts that (1) optimize the TJ to be as close to fully depleted as possible; (2) spatially separate the metal contact from the lasing mode using lightly doped n-GaN located above the TJ; (3) in designs with optimized TJs, minimize the total thickness of p-type material. These features reduce absorption losses in the model, relative to comparable LD models with an unoptimized TJ contact or with a transparent conducting oxide p-contact, by up to 15.3% and 12.5%, respectively, while at the same time eliminating most or nearly all p-type material.

Influence of the a-directed off-cut on the opto-electrical properties of laser diodes grown on the 0.3° misoriented m-directed GaN substrate

We report on the results of the investigation of the influence of an additional a-directed off-cut of the substrate on the opto-electrical properties of the laser diodes grown on bulk GaN with initial misorientation 0.3° towards the m-direction. The investigated a-directed off-cut is varied from 0° up to 1° by means of multilevel laser lithography and dry etching. The results show that the increase of the a-directed off-cut causes the decrease of internal optical losses and increase of injection efficiency. In consequence, the devices fabricated on the wafer areas characterized by higher a-directed off cut are characterized by the lower threshold current, and higher slope and wall-plug efficiencies.

Analysis of internal optical loss of 1.3 μm vertical-cavity surface-emitting laser based on n-=SUP=-++-=/SUP=--InGaAs/p-=SUP=-++-=/SUP=--InGaAs/p-=SUP=-++-=/SUP=--InAlGaAs tunnel junction

The analysis of internal optical loss and internal quantum efficiency in 1.3 μm-range InAlGaAsP/AlGaAs a composite n+-InGaAs/p+-InGaAs/p+-InAlGaAs tunnel junction obtained in the frame of molecular-beam epitaxy and wafer fusion technology. The level of internal optical losses in the lasers under study was varied by depositing a dielectric layer on the surface of the output mirror. It is shown that it is possible in principle to achieve low internal optical loss of less than 0.08% and 0.14% per one pass (round-trip) at temperatures of 20oC and 90oC, respectively. Keywords: vertical-cavity surface-emitting laser, wafer fusion, tunnel junction, superlattice, internal optical loss.

Internal optical loss and light-current characteristic in injection lasers

Possibility of tailoring the light-current characteristic (LCC) shape in quantum dot (QD) lasers by varying uniformity of QDs is discussed. Making the QD ensemble less uniform results in roll-over in the LCC. The second branch in the LCC appears with making the QD ensemble even less uniform.

Effect of Internal Optical Losses on the Generation of Mid-IR Stimulated Emission in Waveguide Heterostructures with HgCdTe/CdHgTe Quantum Wells

Effect of Internal Optical Losses on the Generation of Mid-IR Stimulated Emission in Waveguide Heterostructures with HgCdTe/CdHgTe Quantum Wells

Internal optical loss and internal quantum efficiency of a high-power GaAs laser operating in the CW mode

We continue the comparative studies of high-power AlGaAs/InGaAs/GaAs semiconductor lasers with different waveguide designs. In this work, measurements were carried out for a continuous-wave mode of operation: light–current and current–voltage characteristics, threshold characteristics and their temperature dependences and crystal temperature depending on the pump current. The data obtained made it possible to reconstruct the dependences of internal optical losses and internal quantum efficiency using calculations. It was shown that the main factor affecting the power characteristics in the continuous mode of operation is the temperature stability of the laser and its relationship with internal optical losses and internal quantum efficiency. Thus, lasers based on a heterostructure with a doped GaAs waveguide with characteristic temperatures T 0 and T 1 of 120 K and 170 K, respectively, demonstrated an increase in internal optical losses to 2 cm−1 and a drop in the quantum efficiency to 90%, which led to saturation of the output power by high pump currents. Lasers based on the heterostructure with an AlGaAs waveguide, which are characterized by higher temperature stability (T 0 = 161 K and T 1 = 280 K), had lower internal optical losses and a higher quantum efficiency. This made it possible to obtain optical power 1 W higher than that for lasers with GaAs waveguides.

High-power operation and lateral divergence angle reduction of broad-area laser diodes at 976 nm

Broad-area diode lasers with high output power and low lateral divergence angle are highly desired for extensive scientific and industrial applications. Here, we report on the epitaxial design for higher output power and a flared waveguide design for reduced divergence, which leads to high power operation with a low lateral divergence angle. A vertically asymmetric epitaxial structure was employed and optimized for low internal optical loss and high efficiency to realize high output power operation. Using a flared waveguide design, the lateral divergence angle was efficiently reduced by decreasing the number of high-order lateral optical modes significantly. The flared waveguide design introduces a smooth modification of the ridge width along the cavity without deteriorating laser performance. Based on the optimized epitaxial and waveguide design, we scaled the waveguide width to realize high continuous-wave power of 34.5 W at 25 °C. A low lateral divergence angle of 8° and high power conversion efficiency of 60% were achieved at the operating power level of 25 W. The life test data (30 A at 45 °C for 39 units, 0 failures in 1000 h) demonstrated reliable operation illustrating the efficient design for reduced lateral divergence angle and high operating power.

Novel 900 nm diode lasers with epitaxially stacked multiple active regions and tunnel junctions

A multi-active-region bipolar-cascade edge-emitting laser emitting at nearly 900 nm is presented. The three active regions and two tunnel junctions located in a single waveguide core share the same third-order vertical mode. A slope efficiency of 3.6 W/A was measured with a threshold current density of 230 A/cm2. The epitaxial layer stack developed features with very low internal optical losses of 0.7 cm−1. The voltage extrapolated to vanishing current is only 0.3 V larger than 3 times the voltage of 1.4 V originating from the photon energy.

Optical gain and absorption of 1.55 μm InAs quantum dash lasers on silicon substrate

This Letter reports on the temperature-dependent optical gain and absorption features, including the quantum confined Stark effect, of an InAs/InGaAs quantum-dash laser directly grown on a (001) Si substrate, with the lasing wavelength within the range of 1.5–1.6 μm. The maximum optical net gain was 22 cm−1, and the internal optical loss was ∼–17 cm−1 at 20 °C. Measurements as a function of injection level indicate that while the required current densities are still high, the intrinsic performance is significantly better than that of similarly operated InAs quantum dots operating at 1.3 μm, and further effort on growth could be made to reduce the internal optical losses and non-radiative current density. Optical modal absorption spectra were measured as a function of reverse bias from 0 V to 6 V, and a 40 nm redshift was observed in the absorption edge due to the quantum confined Stark effect, suggesting potential applications of these materials in electro-absorption modulators grown on silicon.

Анализ внутренних оптических потерь вертикально-излучающего лазера спектрального диапазона 1.3 &amp;mu;m с туннельным переходом на основе слоев n-=SUP=-+-=/SUP=--InGaAs/p-=SUP=-+-=/SUP=--InGaAs/p-=SUP=-+-=/SUP=--InAlGaAs

The analysis of internal optical loss and internal quantum efficiency in 1.3 μm-range InAlGaAsP/AlGaAs a composite n++-InGaAs/р++-InGaAs/р++-InAlGaAs tunnel junction obtained in the frame of molecular-beam epitaxy and wafer fusion technology. The level of internal optical losses in the lasers under study was varied by depositing a dielectric layer on the surface of the output mirror. It is shown that it is possible in principle to achieve low internal optical loss of less than 0.08% and 0.14% per one pass (round-trip) at temperatures of 20°С and 90°С, respectively.