Ridge Waveguide Lasers Research Articles

Investigation on the lasing characteristics of InAs/InGaAsP quantum dots with additional confinement structures

We report on morphological, optical, and lasing characteristics of InAs quantum dots (QDs) embedded in an In0.69Ga0.31As0.67P0.33 quantum well (having a bandgap energy corresponding to a wavelength of 1.35μm (1.35Q-InGaAsP)), which formed a dot-in-a-well (DWELL) structure. This DWELL was further sandwiched in In0.85Ga0.15As0.32P0.68 layers (1.15μm, 1.15Q-InGaAsP). A 2 monolayer-thick GaAs layer was simultaneously introduced right below the InAs QD layer in the DWELL structure (GDWELL). The emission wavelength of the InAs GDWELL was 1490nm, which was slightly shorter than that of the InAs QDs embedded only in 1.15Q-InGaAsP layers. To evaluate the effects of the GDWELL structure on lasing characteristics, gain-guided broad-area (BA) and index-guided ridge-waveguide (RW) laser diodes (LDs) were fabricated. The BA-LDs with the InAs QDs embedded only in 1.15Q-InGaAsP layers did not show the lasing at room temperature (RT) even in pulsed mode. For the GDWELL structure, however, the lasing emissions from both the BA-LDs and RW-LDs were successfully achieved at RT in continuous-wave mode.

Monolithic 626 nm single-mode AlGaInP DBR diode laser

Single-mode lasers below 630 nm are still realized using complex laser systems. We present distributed Bragg reflector (DBR) ridge waveguide lasers (RWL) based on AlGaInP. When packaged into sealed TO-3 housings and cooled internally to about 0°C the DBR-RWL emit more than 50 mW at a wavelength of 626.0 nm into a nearly diffraction-limited single longitudinal mode with a spectral width below 1 MHz. These new monolithic diode lasers have the potential to drastically miniaturize existing set-ups e.g. for quantum information processing.

Epitaxial-Side Mounting of Terahertz Quantum- Cascade Lasers for Improved Heat Management

First results on epitaxial-side (epi-down) mounting of terahertz quantum-cascade lasers (QCLs) on sapphire submounts using indium solder are presented. The single-plasmon ridge waveguide lasers emit in the range 3.1–3.3 THz. An epi-down mounting scheme for stressless assembly is realized, which provides enhanced heat dissipation at the corresponding operating temperature and high stability against thermal cycling. The thermal conductance of the devices is improved by 30%, and the maximum continuous-wave operating temperature is increased by 10 K for epi-down mounted lasers achieving output power levels ${>}{\rm 3}~{\rm mW}$ at 55 K.

Distinct Lasing Operation From Chirped InAs/InP Quantum-Dash Laser

We study the enhanced inhomogeneity across the InAs quantum-dash (Qdash) layers by incorporating a chirped AlGaInAs barrier thickness in the InAs/InP laser structure. The lasing operation is investigated via Fabry-Pérot ridge-waveguide laser characterization, which shows a peculiar behavior under quasi-continuous-wave (QCW) operation. Continuous energy transfer between different dash ensembles initiated quenching of lasing action among certain dash groups, causing a reduced intensity gap in the lasing spectra. We discuss these characteristics in terms of the quasi-zero-dimensional density of states (DOS) of dashes and the active region inhomogeneity.

Induced Anomalous Dispersion in Semiconductor Lasers

In semiconductor lasers, the nonlinear parametric interaction of spectral modes, with one of them being at sufficiently high intensity, results in anomalous dispersion. Consequently, in the vicinity of a strong driving wave (mode), the phase index, group index, linewidth broadening, and the gain experienced by a neighboring weak mode are strongly perturbed. The magnitude of nonlinear perturbation depends on driving wave intensity, frequency detuning between the modes, lifetime of the carriers in the system, and optical confinement factor of the laser structure. In this paper, the perturbation of optical characteristics of probe (weak) wave in presence of a strong driving wave is illustrated for GaAs/AlGaAs separate confinement heterostructure and InGaAs/AlGaAs/GaAs double-quantum-well semiconductor ridge waveguide lasers using numerical modeling.

Carrier transport in green AlInGaN based structures on c-plane substrates

In this paper, the carrier transport in (Al)InGaN based test structures with In-rich quantum wells on c-plane substrates is investigated under high current operation. To get access to the injection efficiency, the devices are processed as ridge waveguide lasers and examined above threshold. The slope efficiency reveals a slight decrease as a function of current even under pulsed operation that can be related to a reduction of the injection efficiency based on carrier leakage. As the test structure contains an InGaN detection layer on the n-side, it is possible to verify hole overflow across the active region. Moreover, by analysing the current dependence of the radiative recombination in the detection layer, the reduction of slope efficiency can be correlated to increasing hole leakage.

InAs/InGaAsP/InP Quantum Dot Lasers Grown by Metalorganic Chemical Vapor Deposition

We demonstrate InAs/InGaAsP/InP quantum dot (QD) lasers grown by metalorganic chemical vapor deposition. The active region of the lasers consists of five layers of InAs QDs. Ridge waveguide lasers with 6 μm width have been fabricated by standard optical lithography and wet etching. Under continuous wave operation at room temperature, a low threshold current density of 447A/cm2 per QD layer is achieved for a QD laser with a cavity length of 2 mm. Moreover, the lasing redshifts from 1.61 μm to 1.645 μm as the cavity length increases from 1.5 mm to 4 mm. A high characteristic temperature of up to 88K is obtained in the temperature range between 10°C and 40°C.

Laterally‐coupled distributed feedback laser with first‐order gratings by interference lithography

The first laterally-coupled distributed feedback (DFB) laser with first-order sidewall gratings fabricated by optical interference lithography is experimentally demonstrated. The gratings were first etched into a dielectric mask on the planar top surface of an InP/AlGaInAs laser epiwafer, and then transferred to both sidewalls of a 2 µm deep ridge-waveguide structure using a novel self-aligned process. DFB ridge-waveguide lasers with a cavity length of 650 µm and width of 2.6 µm (with 300 nm gratings on both sidewalls) achieved single longitudinal mode continuous-wave operation, with a sidemode suppression ratio of 37 dB. The threshold current density is 1.7 kA/cm2 at room temperature, and the slope efficiency is 0.14 mW/mA per facet (uncoated).

The single-longitudinal-mode operation of a ridge waveguide laser based on two-dimensional photonic crystals

An electrically driven, single-longitudinal-mode GaAs based photonic crystal (PC) ridge waveguide (RWG) laser emitting at around 850 nm is demonstrated. The single-longitudinal-mode lasing characteristic is achieved by introducing the PC to the RWG laser. The triangle PC is etched on both sides of the ridge by photolithography and inductive coupled plasma (ICP) etching. The lasing spectra of the RWG lasers with and without the PC are studied, and the result shows that the PC purifies the longitudinal mode. The power per facet versus current and current-voltage characteristics have also been studied and compared.

Multi-spectral lasing characteristics of InAs/GaAs quantum dot laser

The emission wavelength and mode structure of InAs/GaAs quantum dot (QD) lasers are reported. The active region consists of five-stacked QD layers with each QD layer formed by varying thickness of InAs gown by gas source molecular beam epitaxy. At operation temperature of 20°C, the ridge waveguide laser emits more than 33mW optical power from one of the cleaved facets under continuous-wave mode and broad gain spectra are obtained due to a large size distribution of InAs QDs. The lasing spectra are found to be a series of complicated longitudinal modes separated by non-lasing spectral regions. We proved experimentally that those behaviors are not relative to the cavity dimension or the supper radiance modulated by photon reflecting in vertical facets. The lasing characteristics can be explained in terms of spatially discrete nature from the non-uniformity size distribution of quantum dots.

Merged beam laser design for reduction of gain-saturation and two-photon absorption in high power single mode semiconductor lasers

In this paper we report a method to overcome the limitations of gain-saturation and two-photon absorption faced by developers of high power single mode InP-based lasers and semiconductor optical amplifiers (SOA) including those based on wide-waveguide or slab-coupled optical waveguide laser (SCOWL) technology. The method is based on Y-coupling design of the laser cavity. The reduction in gain-saturation and two-photon absorption in the merged beam laser structures (MBL) are obtained by reducing the intensity of electromagnetic field in the laser cavity. Standard ridge-waveguide lasers and MBLs were fabricated, tested and compared. Despite a slightly higher threshold current, the reduced gain-saturation in MBLs results in higher output power. The MBLs also produced a single spatial mode, as well as a strongly dominating single spectral mode which is the inherent feature of MBL-type cavity.

Integrated 13 GHz ps-pulse-source at 1064 nm

We present an integrated pulse source at 1064 nm and discuss design, fabrication and measurement results of the 3.5 mm long ridge-waveguide distributed Bragg reflector laser. The optical pulses with a peak power of 0.9 W, a temporal duration of 12.4 ps and a repetition frequency of 13 GHz are generated by passive mode-locking and are well suited for seeding master oscillator power amplifier systems for efficient green light generation with nonlinear frequency doubling in single pass configuration.

Chirped InAs/InP quantum-dash laser with enhanced broad spectrum of stimulated emission

We report on the demonstration of 50 nm (full-width at half-maximum) broadband stimulated emission from a chirped AlGaInAs barrier thickness multi-stack InAs/InP quantum dash (Qdash) laser. The 2 μm wide uncoated Fabry-Perot (FP) ridge-waveguide laser exhibits a total power of 0.18 W, corresponding to an average spectral power density of 3.5 mW/nm, under pulsed current conditions. Intentional extended inhomogeneity across the Qdash stacks have been attributed to the enhancement of broadband emission.

Ridge waveguide lasers in Nd:YAG crystals produced by combining swift heavy ion irradiation and precise diamond blade dicing

Ridge waveguides have been fabricated in Nd:YAG crystals by using ion irradiation and precise diamond blade dicing. Continuous-wave lasers at ~1064 nm have been realized in the ridge waveguides through optical pumping at 808 nm at room temperature. The ridge guiding structure shows superior lasing performance with respect to the planar counterpart with a slope efficiency of 43% and a maximum output power of 84 mW.

Narrow Linewidth of 633-nm DBR Ridge-Waveguide Lasers

Compact laser sources with long coherence lengths in the visible spectral region are sought for many applications. This letter presents distributed-Bragg-reflector (DBR) ridge-waveguide (RW) lasers with an emission wavelength at 633 nm and an optical output power >20 mW. The DBR-RW lasers exhibit a technical linewidth at full width at half maximum of ~1 MHz. The emission line can be tuned via current and temperature >200 GHz. At 14 mW, the lasers show a preliminary lifetime 4000 h.

Monolithic Integration of Single Facet Slotted Laser, SOA, and MMI Coupler

We demonstrate a monolithically photonic integrated circuit (PIC) comprising a single facet slotted laser (SFSL), a semiconductor optical amplifier (SOA), and a 1 × 2 multimode interference (MMI) coupler. The integrated SFSL generates a tunable single longitudinal mode output, and utilizes a simplified fabrication process for the PIC when compared with distributed feedback or distributed Bragg reflector lasers by eliminating the epitaxial regrowth as well as the ebeam or holographically generated gratings. The integration technique is implemented by biasing the MMIs to transparency, which makes the fabrication comparable the standard ridge waveguide laser. The demonstrated PIC can be used as a 1 × 2 splitter or by integrating with other waveguide devices, such as laser, modulators, or SOAs, to realize different functionality.

Dynamics of a gain-switched distributed feedback ridge waveguide laser in nanoseconds time scale under very high current injection conditions

We present detailed experimental investigations of the temporal, spectral and spatial behavior of a gain-switched distributed feedback (DFB) laser emitting at a wavelength of 1064 nm. Gain-switching is achieved by injecting nearly rectangular shaped current pulses having a length of 50 ns and a very high amplitude up to 2.5 A. The repetition frequency is 200 kHz. The laser has a ridge waveguide (RW) for lateral waveguiding with a ridge width of 3 µm and a cavity length of 1.5 mm. Time resolved investigations show, depending on the amplitude of the current pulses, that the optical power exhibits different types of oscillatory behavior during the pulses, accompanied by changes in the lateral near field intensity profiles and optical spectra. Three different types of instabilities can be distinguished: mode beating with frequencies between 25 GHz and 30 GHz, switching between different lateral intensity profiles with a frequency of 0.4 GHz and self-sustained oscillations with a frequency of 4 GHz. The investigations are of great relevance for the utilization of gain-switched DFB-RW lasers as seed lasers for fiber laser systems and in other applications, which require a high optical power.

Single-mode surface-emitting concentric-circular-grating terahertz quantum cascade lasers

We demonstrate single-mode surface-emitting terahertz frequency quantum cascade lasers utilising non-uniform second-order distributed feedback concentric-circular-gratings. The grating is designed for single-mode operation and surface emission for efficient and directional optical power out-coupling. The devices exhibit single-mode operation over the entire dynamic range with a side-mode-suppression-ratio of around 30 dB at 78 K, and a six-fold rotationally symmetric far-field pattern. In addition, the devices show a peak output power approximately three times higher than in ridge-waveguide lasers of similar size, whilst maintaining similar threshold current densities for the 3.8 THz emission and without remarkably sacrificing the maximum temperature operation performance. Owing to the high symmetry of the structure and the broad area light emission from surface, the devices are potentially very suitable for use as single-mode, high power emitters for integration into two-dimensional laser arrays.

InGaN/GaN self-organized quantum dot lasers grown by molecular beam epitaxy

Blue-and green-emitting quantum dots have been characterized and ridge waveguide lasers incorporating such quantum dots into the active region have been realized. The laser heteroscturctures were grown by plasma assisted molecular beam epitaxy. Injected carrier lifetimes in the quantum dots have also been measured by temperature dependent and time resolved photoluminescence. A threshold current density of 930A/cm2 in the blue-emitting lasers was measured under pulsed bias. A tunnel injection scheme to inject holes has been incorporated in the design of the green quantum dot lasers, and a threshold current density of 945A/cm2 in the green-emitting lasers has been measured under pulsed bias. Slope efficiencies of 0.41W/A and 0.25W/A have been measured, corresponding to differential quantum efficiencies of 13.9% and 11.3%, in the blue and green lasers, respectively.

High-performance InAs/GaAs quantum dot laser with dot layers grown at 425 oC

We investigate InAs/GaAs quantum dot (QD) lasers grown by gas source molecular beam epitaxy with different growth temperatures for InAs dot layers. The same laser structures are grown, but the growth temperatures of InAs dot layers are set as 425 and 500 °C, respectively. Ridge waveguide laser diodes are fabricated, and the characteristics of the QD lasers are systematically studied. The laser diodes with QDs grown at 425 °C show better performance, such as threshold current density, output power, internal quantum efficiency, and characteristic temperature, than those with QDs grown at 500 °C. This finding is ascribed to the higher QD density and more uniform size distribution of QDs achieved at 425 °C.