Ridge Waveguide Lasers Research Articles

Optoelectronic Noise and Photocurrent Measurement on GaAs/AlGaAs Laser Diode with Single Quantum Well

The current progress in optomechatronic applications needs more efficient devices and components with higher reliability, operational lifetime, reduced cost, and dimensions as laser diodes, fast photodetectors, and modulators. The laser is one key technology in a highly industrialized economy. To understand modern efficient laser diode (LD) structures and evaluate their performance, an electrical and optical characterization is necessary. Therefore, low-frequency electrical and optical fluctuation spectra and their cross-correlation factor have been investigated in GaAs/AlGaAs ridge waveguide laser diode with an active region containing a single quantum well layer. It is shown that in the lasing region the intensive Lorentzian-type electrical and optical noises with negative cross-correlation factor are characteristic. This noise is due to charge carrier recombination processes in the interfaces between the active layer and the neighboring layers. To verify it, a complementary insight into the same laser diode structure provided by near-field-induced photocurrent technique with 100 nm spatial resolution is also discussed.

High-Temperature and High-Frequency Operation of 1.3 μm AlGaInAs ∕ InP Laser Diodes Using Silicon Oxide Planarization

In this article, a self-terminated oxide polish (STOP) planarization technique is utilized to fabricate high-temperature and high-speed ridge-waveguide laser diodes (LDs). The as-cleaved LDs fabricated by this STOP technique exhibit a threshold current of 8.5 and , and a light output power of 27 and at for 0 and , respectively. The characteristic temperature is from 0 to and from 80 to . The full width at half maximum of the lateral far-field angle is for the conventional ridge LDs and reduces to for the LDs by the STOP technique. The modulation bandwidth at of the LDs can reach 16.9 at and at .

Metamorphic growth of 1.25–1.29 μm InGaAs quantum well lasers on GaAs by molecular beam epitaxy

We demonstrate 1.25–1.29 μm metamorphic laser diodes grown on GaAs by molecular beam epitaxy (MBE) using an alloy-graded buffer layer (GBL). Use of Be in the GBL is effective to reduce surface/interface roughness and improves optical quality. The RMS surface roughness of the optimized metamorphic laser is only two atomic monolayers for 1×1 μm 2. Cross-sectional transmission electron microscopy (TEM) images confirm that most dislocations are blocked in the GBL. Ridge waveguide lasers with 4 μm wide ridge were fabricated and characterized. The average threshold current under the pulsed excitation is in 170–200 mA for a cavity length of 0.9–1.5 mm. This value can be further reduced to about 100 mA by high-reflectivity coating. Lasers can work in an ambient temperature up to at least 50 °C.

Period-doubling and total mode-locking, and chaotic pulsations in a GaAs ridge wave-guide external-cavity diode laser

We report on the experimental observations of a period-doubling route to chaos and a total mode-locking between two lowest-order lateral modes of a GaAs ridge wave-guide diode laser at 795 nm. A self-starting passively mode-locking was achieved in an extended-cavity diode laser (ECDL) operating in a gain saturation regime. In the period-doubling mode-locked state, the RF spectra associated with the coherently coupled lateral TE(0) and TE(1) modes, consisted of harmonics (nf(rep)/2, n is an integer) of the half of pulse repetition rate f(rep)/2 and the period (2T) of the pulse train was two-times longer than the pulse round-trip time T. On the other hand, in the total mode-locked state, the RF spectra and the pulse train corresponding to the TE(0) and TE(1) modes had exactly the same features compared to those of the period-doubling mode-locked state, except the RF spectra and the pulse train of the TE(1) mode were shifted by f(ref)/4 in frequency and by T in time, respectively, indicating the pulses actually traveled alternatively through two lateral modes. The total mode-locking and also chaotic pulsations were observed at slightly different operation parameters, e.g. at different feedback angle of the grating, which was used as an output coupler of the ECDL.

Nitrides optoelectronic devices grown by molecular beam epitaxy

AbstractWe report on the characteristics of our recent room temperature continuous‐wave InGaN quantum well laser diodes grown by by molecular beam epitaxy (MBE). Uncoated ridge waveguide lasers fabricated on freestanding GaN substrates have a continuous‐wave (cw) threshold current of 110 mA, corresponding to a threshold current density of 5.5 kA cm–2. We report on our steps taken to reduce threshold voltage to 7 V. Lasers with uncoated facets have a maximum cw output power of 14 mW and a cw characteristic temperature T 0 of 123 K. Cw laser lifetime vs. power dissipation data is presented, with a maximum lifetime of 2.6 hours for the best laser. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Transition From Perturbed to Coupled-Cavity Behavior With Asymmetric Spectral Emission in Ridge Lasers Emitting at 1.55 $\mu$m

We have investigated a series of ridge waveguide lasers with deeply etched slots in the ridges. The slots do not penetrate the active region, but are deep enough to strongly perturb the longitudinal modes. By the addition of slots, a transition between perturbed-mode and coupled-cavity behavior is crossed. With a group of four or more slots, the below-threshold amplified spontaneous emission spectrum from each end of the laser has different periods and the facet-facet oscillations are suppressed indicating that the different sections have become quasi-independent. A model using a distributed emitter in the cavity reproduces this behavior. Above threshold, the single contact coupled cavity lasers are single mode with greater than 30-dB sidemode suppression ratio over a wide range of currents

Fast Tuneable InGaAsP DBR Laser Using Quantum-Confined Stark-Effect-Induced Refractive Index Change

We report a monolithically integrated InGaAsP DBR ridge waveguide laser that uses the quantum-confined Stark effect (QCSE) to achieve fast tuning response. The laser incorporates three sections: a forward-biased gain section, a reverse-biased phase section, and a reverse-biased DBR tuning section. The laser behavior is modeled using transmission matrix equations and tuning over ~8 nm is predicted. Devices were fabricated using post- growth shallow ion implantation to reduce the loss in the phase and DBR sections by quantum well intermixing. The lasing wavelength was measured while varying the reverse bias of the phase and DBR sections in the range 0 V to <-2.5 V. Tuning was noncontinuous over a ~7-nm-wavelength range, with a side-mode suppression ratio of ~20 dB. Coupled cavity effects due to the fabrication method used introduced discontinuities in tuning. The frequency modulation (FM) response was measured to be uniform within plusmn2 dB over the frequency range 10 MHz to 10 GHz, indicating that tuning times of 100 ps are possible.

Intra-cavity absorption spectroscopy with narrow-ridge microfluidic quantum cascade lasers

We demonstrate microfluidic laser intra-cavity absorption spectroscopy with mid-infrared lambda approximately 9mum quantum cascade lasers. A deepetched narrow ridge waveguide laser is placed in a microfluidic chamber. The evanescent tails of the laser mode penetrate into a liquid on both sides of the ridge. The absorption lines of the liquid modify the laser waveguide loss, resulting in significant changes in the laser emission spectrum and the threshold current. A volume of liquid as small as ~10pL may, in principle, be sufficient for sensing using the proposed technique. This method, similar to the related gas-phase technique, shows promise as a sensitive means of detecting chemicals in small volumes of solutions.

Effect of layer stacking and p-type doping on the performance of InAs∕InP quantum-dash-in-a-well lasers emitting at 1.55μm

The authors report the growth of 6-, 9-, and 12-layer InAs∕InP quantum-dash-in-a-well (DWELL) laser structures using gas source molecular beam epitaxy. Broad area laser performance has been investigated as a function of number of layers. The highest modal gain at 48cm−1 is achieved for an optimized nine-DWELL layer structure. The effect of layer stacking and p-type doping on the characteristic temperature is also reported. Nine-DWELL layer single mode ridge waveguide lasers showed high slope efficiency (0.2W∕A per facet) and output power (Pout=20mW), close to those of conventional quantum well devices.

Characteristics of InGaN multiple quantum well blue-violet laser diodes

Studies on InGaN multiple quantum well blue-violet laser diodes have been reported. Laser structures with long-period multiple quantum wells were grown by metal-organic chemical vapor deposition. Triple-axis X-ray diffraction (TAXRD) measurements show that the multiple quantum wells were high quality. Ridge waveguide laser diodes were fabricated with cleaved facet mirrors. The laser diodes lase at room temperature under a pulsed current. A threshold current density of 3.3 kA/cm2 and a characteristic temperature T0 of 145 K were observed for the laser diode.

Stacking, polarization control, and lasing of wavelength tunable (1.55 μm region) InAs/InGaAsP/InP (1 0 0) quantum dots

We report the growth, device fabrication, and performance of stacked InAs/InGaAsP/InP (1 0 0) quantum dots (QDs) in telecom lasers. Wavelength tuning of the QDs grown by metalorganic vapor-phase epitaxy (MOVPE) over the 1.55-μm region at room temperature (RT) is achieved using ultrathin GaAs interlayers underneath the QDs, which suppress As/P exchange to reduce the QD height in a controlled way. Unpolarized photoluminescence from the cleaved side, important for realization of polarization-insensitive semiconductor optical amplifiers, is obtained for closely stacked QDs due to vertical electronic coupling. The wavelength shift due to group-V-atom intermixing in the QDs during growth at higher temperatures of device structures is compensated by adjusting the GaAs interlayer thickness and V/III flow ratio during QD growth. Device quality of the QDs is highlighted by continuous-wave ground-state lasing at RT of narrow ridge-waveguide QD lasers.

Low-threshold GaInNAs single-quantum-well lasers with emission wavelength over 1.3 µm

Low-threshold GaInNAs single-quantum-well (SQW) lasers with emission wavelength over 1.3 µm are demonstrated. Epitaxial layers of the lasers are grown using an aluminium-free gas-source molecular-beam epitaxy (GS-MBE) to prevent any impurity or contamination related to aluminium that might be incorporated into the GaInNAs active layer. The fabricated laser is believed it exhibit the lowest threshold-current density (200 A/cm2) among GaInNAs-SQW lasers grown by MBE. Moreover, record low threshold current (5.2 mA) and long-wavelength (1.31 µm) emission were achieved in a ridge-waveguide laser at 25°C under continuous-wave operation.

Gain and lifetime of GaInNAsSb narrow ridge waveguide laser diodes in continuous-wave operation at 1.56μm

The continuous-wave (cw) operation of GaInNAsSb lasers at 1560nm is reported. Light-current measurements were made before and after a 100h cw burn in at 20°C, during which a 3×890μm2 device with 72mA initial threshold current and 14mW maximum output power experienced a 15% drop in peak output power. These preliminary lifetime results provide insight into the reliability of GaInNAsSb active regions and reinforce the promise of this material for C-band devices. High-resolution modal gain spectra were extracted from the amplified spontaneous emission spectra acquired after the burn in, providing reliable values for the internal loss, transparency current, and differential gain.

Multi-active region laser diode with a narrow beam divergence angle

A novel large optical cavity laser diode, which consists of multi-active regions cascaded together through tunnel junctions, is proposed. After growing the epi-layers with LP-MOCVD system on GaAs substrate, the ridge waveguide laser structure is fabricated, and it shows a transverse divergence angle as low as 14.4°.

Lasing of wavelength-tunable (1.55μm region) InAs∕InGaAsP∕InP (100) quantum dots grown by metal organic vapor-phase epitaxy

The authors report lasing of InAs∕InGaAsP∕InP (100) quantum dots (QDs) wavelength tuned into the 1.55μm telecom region. Wavelength control of the InAs QDs in an InGaAsP∕InP waveguide is based on the suppression of As∕P exchange through ultrathin GaAs interlayers. The narrow ridge-waveguide QD lasers operate in continuous wave mode at room temperature on the QD ground state transition. The low threshold current density of 580A∕cm2 and low transparency current density of 6A∕cm2 per QD layer, measured in pulsed mode, are accompanied by low loss and high gain with an 80-nm-wide gain spectrum.

1.34 µm GaInNAs quantum well lasers with low room-temperature threshold current density

The quaternary GaInNAs barrier layer was used to improve the performance of 1.3 µm GaInNAs single quantum well lasers grown by MBE. A record low threshold current density of 178 A/cm2 and a record low transparent current density of 63 A/cm2 were achieved by a ridge waveguide laser with emission at 1336 nm.

High-modal gain 1300-nm In(Ga)As-GaAs quantum-dot lasers

A semiconductor laser containing seven InAs-InGaAs stacked quantum-dot (QD) layers was grown by molecular beam epitaxy. Shallow mesa ridge-waveguide lasers with stripe width of 120 mum were fabricated and tested. A high modal gain of 41 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> was obtained at room temperature corresponding to a modal gain of ~6 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> per QD layer, which is very promising to enable the realization of 1.3-mum ultrashort cavity devices such as vertical-cavity surface-emitting lasers. Ground state laser action was achieved for a 360-mum-cavity length with as-cleaved facets. The transparency current density per QD layer and internal quantum efficiency were 13 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and 67%, respectively

Continuous Wave Performance and Tunability of MBE Grown2.1 μm InGaAsSb/AlGaAsSb MQW lasers

InGaAsSb/AlGaAsSb multi quantum well ridge waveguide lasers at2.1 μm wavelength are fabricated by using molecular beam epitaxy.Continuous wave performance and tunability of the lasers are evaluatedin a wide temperature range extend to 80°C. Output power of the laserat 30°C exceeds 30 mW/facet at driving current of 0.5 A, thecharacteristic temperature T0 is 89 K in 0–50°C range. Nofast degradation is observed in accelerated aging test at 90°C forthose lasers with lower Al content in cladding layers. Temperaturetunability of the lasers is 1.36 nm/K. Single-mode output with side modesuppression ratios greater than 20 dB is achieved in a certaindriving current region; current tunability is 8×10−3 nm/mAregardless of mode hopping.

Wavelength controlled InAs/InP quantum dots for telecom laser applications

This article reviews the recent progress in the growth and device applications of InAs/InP quantum dots (QDs) for telecom applications. Wavelength tuning of the metalorganic vapor-phase epitaxy grown single layer and stacked InAs QDs embedded in InGaAsP/InP (100) over the 1.55-μm region at room temperature (RT) is achieved using ultra-thin GaAs interlayers underneath the QDs. The GaAs interlayers, together with reduced growth temperature and V/III ratio, and extended growth interruption suppress As/P exchange to reduce the QD height in a controlled way. Device quality of the QDs is demonstrated by temperature-dependent photoluminescence (PL) measurements, revealing zero-dimensional carrier confinement and defect-free InAs QDs, and is highlighted by continuous-wave ground-state lasing at RT of narrow ridge-waveguide QD lasers, exhibiting a broad gain spectrum. Unpolarized PL from the cleaved side, important for realization of polarization insensitive semiconductor optical amplifiers, is obtained from closely stacked QDs due to vertical electronic coupling.

Continuous-wave operation of GaInAsSb-GaSb type-II ridge waveguide lasers emitting at 2.8 /spl mu/m

We have realized compressively strained GaInAsSb-GaSb type-II double quantum-well lasers with an emission wavelength of 2.8 mum. Using broad area devices, an internal absorption of 9.8 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> and an internal quantum efficiency of 0.57 is determined. For the increase of the threshold current with temperature, a T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> of 44 K is obtained. Narrow ridge waveguide lasers show continuous-wave laser operation at temperatures up to 45 degC, with room-temperature (RT) threshold current of 37 mA. At RT, the maximum optical output power per facet of an uncoated 800times7 mum <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ridge waveguide laser exceeds 8 mW