Distributed Bragg Reflector Ridge Waveguide Research Articles

Miniaturizing a coherent beam combining system into a compact laser diode module.

We present a laser module with dimensions of 76×43×15m m 3 that for the first time to our knowledge realizes a coherent beam combination in such a compact device, using two tapered amplifiers seeded by a distributed Bragg reflector ridge waveguide laser diode operating at 761nm in a single longitudinal mode. The generated combined optical power is up to 5W continuous wave with a combing efficiency of 85%. The phase of the system is controlled by the current in the ridge waveguide section of one of the tapered amplifiers. The phase-stabilization process is automated using a reverse hill-climbing algorithm and an ATmega328P microcontroller.

UV generation via periodically poled MgO:LiTaO3 circular waveguide crystal and diode-based master oscillator power amplifier.

Lasers with emission wavelengths in the near-ultraviolet (UV) spectral range have been used in many applications across various fields, and the demand for these lasers has been on the rise. For example, in medicine, near-UV light has been used for fluorophore excitation. Although laser diodes emitting in this region exist, single longitudinal mode lasers emitting at 380nm with high optical power are limited. One of the solutions to this problem is the use of second harmonic generation by a non-linear crystal. In this work, single-longitudinal-mode laser emission at 380.5nm with an optical power of up to 13mW has been achieved. The emission was realized by frequency doubling using a periodically poled circular waveguide crystal of stoichiometric L i T a O 3 doped with MgO (PPMgSLT) pumped by a master oscillator power amplifier with optical power up to 5W. A distributed Bragg reflector ridge waveguide laser diode at 761nm was used as the master oscillator and a tapered amplifier as the power amplifier.

Compact, Watt-class 785 nm dual-wavelength master oscillator power amplifiers

785 nm micro-integrated, dual-wavelength master oscillator power amplifiers with a footprint of 5 mm × 25 mm are presented. They are based on Y-branch distributed Bragg reflector ridge waveguide diode lasers and anti-reflection coated tapered amplifiers. In order to reduce the impact of potential optical feedback, devices with master oscillator front facet reflectivities of 5% and 30% as well as with an integrated miniaturized optical isolator have been realized. A comparison up to 1 W shows narrowband dual wavelength laser emission with a spectral distance of 0.6 nm (10 cm−1) and individual spectral widths <20 pm. As expected, a higher front facet reflectivity leads to a significant reduction of feedback related mode hops. Longitudinal modes corresponding to the master oscillator resonator length remain within spectral windows <0.15 nm (3 cm−1), suitable for applications such as Raman spectroscopy and especially shifted excitation Raman difference spectroscopy. Integrating a compact 30 dB optical isolator completely eliminates the observed optical feedback effects. Lateral beam propagation ratios of 1.2 (1/e2) enable easy beam shaping and fiber coupling. Outside of the experimental comparison, the developed MOPAs provide up to 2.7 W of optical output power available for applications.

Comparison of individual and common wavelength-operation for 785 nm Y-branch DBR ridge waveguide diode lasers with adjustable spectral distance.

An experimental comparison between individual and common wavelength-operation of a Y-branch distributed Bragg reflector (DBR) ridge waveguide (RW) laser at 785 nm with an electrically adjustable spectral distance is presented. The dual-wavelength Y-branch laser combines two laser cavities via a Y-section to a common output section. DBR gratings with different grating periods are associated with the two cavities, which set the emission wavelengths of the two branches. Implemented resistive heater elements allow separate wavelength tuning of the two branches, which can be operated individually for alternating emission wavelengths in applications such as differential absorption spectroscopy or shifted excitation Raman difference spectroscopy. Common wavelength operation simultaneously generates two emission lines suitable for the generation of THz radiation using difference frequency mixing. Hereby, the devices could potentially be used as single-chip light sources for a combination of Raman and THz applications. For the wavelength-operation comparison presented, the devices were operated up to optical output powers of about 105 and 185 mW in individual and common wavelength-operation mode, respectively. In individual operation mode, the devices show spectral single-mode emission over the whole operation range. In common operation mode, the spectral emission is predominantly single mode up to an optical output power of 65 mW. In both operation modes, mode hops typical for DBR lasers occur. At an optical output power of 50 mW, tuning of the spectral distance between the two wavelengths using the implemented resistor heaters is demonstrated. In both modes of wavelength operation, a flexible frequency difference between 0 and 0.8 THz (0 and 1.6 nm) with predominantly single-mode spectral emission is obtained.

Characterization and comparison between two coupling concepts of four-wavelength monolithic DBR ridge waveguide diode laser at 970 nm

Compact laser sources emitting at multiple wavelengths from a single aperture are interesting in a multiple of applications. In this work, we characterize and compare two concepts of four-arm monolithic distributed Bragg reflector (DBR) ridge waveguide (RW) diode lasers emitting at four different wavelengths around 970 nm. The first concept has a single intersection point, where the four arms are joined before being emitted from the output aperture. The second concept has two intersection points: the first where the inner two arms are combined and a second where those are joined by the outer two arms. In the first case, the inner and outer arms show difference in performance, in particular the outer arms show worse opto-electrical and spatial parameters compared to the inner arms. In the second concept, similar performance is observed from all four arms, with smaller deviations between the inner and outer arms in the mentioned parameters. This study suggests that a serial combination of pairs of bends is preferable in this kind of multi-wavelength laser sources.

Freely Triggerable Picosecond Pulses From a DBR Ridge Waveguide Diode Laser Near 1120 nm

In this letter, we present results on the pulsed operation of a distributed Bragg reflector ridge waveguide diode laser with wavelength close to 1120 nm. Picosecond optical pulses were generated by gain-switching at variable repetition frequencies up to 80 MHz. In single-pulse operation, a pulse width of 92 ps with a pulse peak power of 1.7 W at 10 MHz could be obtained. Investigations in operation at higher injection current pulse amplitude increased the pulse peak power to 2.6 W, but also showed significant trailing pulses which is typical for gain-switched diode lasers. The shape of the pulses is stable over the whole range of the investigated repetition frequencies from 5 to 80 MHz. At an operation temperature of 25 °C, the emitted radiation has a wavelength of 1114.7 nm and increases to 1116.4 nm at 45 °C. The central wavelength does not change significantly at higher output power.

Generation of second harmonic light with a wavelength of 560 nm in a compact module

We demonstrate a continuous wave 133mW laser module at 560.5nm on a 50mm·10mm optical bench. The setup consists of a 1121nm distributed Bragg reflector ridge waveguide laser and a MgO:LiNbO3 quasi-phase matched ridge waveguide crystal, which are coupled by a grin lens, as well as two cylindrical lenses for beam collimation behind the crystal. A novel approach to ensure phase matching is used. The laser and the crystal are stabilized by the same heat sink and only the wavelength of the laser is tuned by heating the distributed Bragg reflector section of the laser. This reduces the influence of temperature variations on the module's performance enabling operation with output power variations <10% over a temperature range of 20K. The size and robustness against temperature variations of this setup make it an interesting candidate for future biomedical applications.

InGaAs ridge-waveguide distributed Bragg reflector laser with first-order grating fabricated by nanoimprint lithography

A distributed Bragg reflector (DBR) laser with a surface relief grating was fabricated by a simple process using room-temperature nanoimprint lithography. An imprint mold for first-order DBR gratings with a period of 151 nm was formed using a silica plate. The grating pattern was imprinted on a nanoimprint layer and then transferred into an InGaAs quantum well waveguide by reactive ion etching. A single-mode lasing at a wavelength of 984.3 nm with a side-mode suppression ratio of 30 dB and a maximum output power of 42 mW were obtained under CW operation.

Fabrication of widely tunable ridge waveguide DBR lasers for WDM-PON

We report the fabrication of widely tunable ridge waveguide distributed Bragg reflector (DBR) lasers with InGaAsP butt-joint as grating material. The shape of the butt-joint interface is found to have significant effect on the properties of the lasers. It is shown that irregular mode jumps during wavelength tuning can be avoided by a V-shaped butt-joint interface. From the fabricated device, 23 channels with 0.8 nm spacing and greater than 35 dB side mode suppression ratios are obtained. The different tuning characteristics of the ridge waveguide and the previously reported buried ridge stripe DBR lasers are discussed. Combined with the wide tuning range and the simple structure, the ridge waveguide DBR lasers are promising for use in wavelength division multiplexing passive optical networks (WDM-PONs).

High Brightness, Narrow Bandwidth DBR Diode Lasers at 1120 nm

In this letter, we report on monolithic distributed Bragg reflector ridge waveguide diode lasers. The lasers feature highly strained InGaAs quantum wells and fifth order surface gratings for a stabilized emission wavelength ~1120 nm. Output powers up to 1 W and a maximum conversion efficiency of ~34% were achieved in a spatial and spectral single-mode. In a preliminary reliability test, at 0.4 W a lifetime of could be demonstrated. Therefore, the laser sources should allow for an efficient non-linear frequency doubling to 560 nm.

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.

96 mW longitudinal single mode red-emitting distributed Bragg reflector ridge waveguide laser with tenth order surface gratings

Red-emitting ridge waveguide lasers with integrated tenth order surface distributed Bragg reflector gratings were developed. The grating was implemented by the use of a BCl3-Ar-plasma, while the shape of the grating trench was controlled by additional He-backside cooling of the wafer. The devices exhibit longitudinal single mode operation up to 96 mW at 635.3 nm with a side mode suppression ratio of 18 dB and a good beam quality of M2<3. The spectrum is free of mode hops for a span of more than 55 pm.

High-power, spectrally stabilized, near-diffraction-limited 970 nm laser light source based on truncated-tapered semiconductor optical amplifiers with low confinement factors

High-power spectrally single-moded coherent emission with high beam quality is demonstrated using a master-oscillator (MO) power-amplifier (PA) system. The MO is a single-moded distributed Bragg reflector ridge-waveguide (DBR-RW) laser and the PA is a semiconductor amplifier with a truncated-tapered gain region. The spectrum of the DBR-RW is found to be preserved, with >40 dB of noise suppression. Peak output powers from the PA of >50 W (250 µs, 100 Hz) are demonstrated for laser designs with conventional confinement factors in the active region, Γ = 1%, but only with substantial degradation in the beam quality (M2 at 1/e2 level of >30). The use of alternative designs with low confinement (Γ = 0.4%) reduces the gain and hence peak power, but dramatically improves the beam quality (M2 at 1/e2 level of ∼3), enabling ∼11 W emission into a diffraction-limited central lobe, with temperature and current invariant central wavelength and a spectral width of ∼40 pm.

Narrowing the linewidth of 852nm diode lasers

Tunable semiconductor lasers with narrow spectral linewidths at specific wavelengths are of interest for both communication and spectroscopy applications. In communications, narrowlinewidth lasers are necessary to reduce optical dispersion, enabling high-speed data rates. Such lasers can also be used for spectroscopic applications that require tuning to the specific wavelengths of an atomic transition. The optical pumping of a cesium transition at 852nm is of particular interest for applications like optical inertial guidance systems. Both types of applications require lasers that operate with a single optical mode and that exhibit spectral linewidths narrower than 1MHz. Most edge-emitting semiconductor lasers, however, have multiple longitudinal modes spaced closely together. Incorporating a distributed Bragg reflector (DBR) or distributed feedback (DFB) grating selects a single longitudinal mode, which allows the laser to operate in a single spectral mode. DBR and DFB gratings are typically located at the interface between the core and cladding of a laser to provide the necessary feedback for narrow-linewidth performance. However, locating the grating between the core and cladding requires epitaxial regrowth, which is difficult for devices with AlGaAs barriers due to the rapid oxidation of Al-containing compounds. Surface-grating ridge-waveguide DBR lasers have been developed as a method for achieving narrow-linewidth lasers with a single epitaxial-growth step. By incorporating an asymmetric cladding, one can reduce the etch depth and form first-order gratings in the DBR section. 3 These devices exhibit narrow-linewidth operation with a minimum spectral linewidth of 36kHz, as determined by the self-heterodyning measurement technique. We recently reported fabricating narrow-linewidth 852nm asymmetric-cladding ridge-waveguide DBRs with firstorder gratings in the AlGaAs/GaAs material system. Figure 1. Scanning electron micrographs of the (a) top view and (b) cross section of the first-order distributed Bragg reflector (DBR) grating. The schematic diagram shows structure of the asymmetriccladding DBR laser diode.

Narrow-linewidth asymmetric cladding distributed Bragg reflector semiconductor lasers at 850 nm

Narrow-linewidth ridge-waveguide distributed Bragg reflector (DBR) single quantum well lasers for spectroscopic applications have been demonstrated. These devices, which were fabricated in the AlGaAs-GaAs material system, use an asymmetric cladding and a first-order surface grating to realize single-mode operation in the range from 850 to 860 nm. To our knowledge, these devices contain the shortest period surface etched gratings DBRs to date, demonstrating spectral linewidth values lower than 40 kHz.

Dual-wavelength InGaAs-GaAs ridge waveguide distributed Bragg reflector lasers with tunable mode separation

The design and operation of integrated dual-wavelength sources are reported. These InGaAs-GaAs ridge waveguide (RW) distributed Bragg reflector (DBR) lasers consist of a common gain section and two, separate DBR sections. Multiple current injection is not necessary for these lasers to operate in dual-wavelength. Dual-wavelength operation is easily achieved by simply biasing the gain section. A relatively low coupling coefficient /spl kappa/ in the front grating reduces the added cavity loss for the back grating mode. Therefore, the back grating mode reaches threshold easily. Also, the addition of a spacing section lowers the current induced thermal interaction between the two uniform grating sections, significantly reducing the inadvertent wavelength drift. As a result, biasing the front DBR section results in tunable mode pair separations (/spl Delta//spl lambda/) as small as 0.3 nm and as large as 6.9 nm.

Monolithically integrated distributed Bragg reflector lasers for 1.5 μm operation with band gap shifted grating section

The design and operation of long wavelength ridge waveguide distributed Bragg reflector lasers in both InGaAs–InGaAlAs and InGaAs–InGaAsP materials with deeply dry-etched surface gratings are presented. To our knowledge, quantum well intermixing was used for the first time in these systems to widen the band gap in the grating region, and significant improvement in performance is obtained from the distributed Bragg reflector (DBR) lasers with intermixed grating region.

Single and tunable dual-wavelength operation of an InGaAs-GaAs ridge waveguide distributed Bragg reflector laser

The design and operation of an InGaAs-GaAs asymmetric cladding ridge waveguide (RW) distributed Bragg reflector (DBR) laser that can be operated in both a single-wavelength mode and a stable, dual-wavelength mode with tunable mode pair separation are reported. The asymmetric cladding RW-DBR laser consists of a conventional DBR laser with an additional, separate tuning contact pad over a part of the grating. The laser operates on a single-wavelength with no current applied to the tuning DBR pad, and dual-wavelength operation is achieved when current is applied to the tuning DBR pad. Tunable mode pair separations as small as /spl sim/13 nm and as large as /spl sim/17 nm can be achieved in various tuning conditions.

Dual-wavelength asymmetric cladding InGaAs-GaAs ridge waveguide distributed Bragg reflector lasers

The design and operation of dual-wavelength InGaAs-GaAs asymmetric cladding ridge waveguide distributed Bragg reflector (DBR) lasers are reported. DBR lasers with mode pair separations of 4.1, 8.4, and 16.9 nm exhibit stable, simultaneous, dual-wavelength operation in current ranges of 40-52 mA, 32-42 mA, and 28-35 mA, respectively. Within the stated current ranges, all lasing modes exhibit at least 20-dB sidemode suppression, and approximately 30-dB sidemode suppression under optimum operating conditions.

InGaAsP-InP ridge-waveguide DBR lasers with first-order surface gratings fabricated using CAIBE

The design and operation of InGaAsP-InP ridge-waveguide (RW) distributed Bragg reflector (DBR) multiple quantum-well lasers with first-order surface gratings are presented. The RW DBR lasers are fabricated using only a single growth step without growth on a corrugated surface. Uncoated devices with grating etch depths of 0.6 and 0.5-μm exhibit pulsed threshold currents of 32 and 43 mA with slope efficiencies of 0.34 and 0.24 W/A, respectively. The device with a grating etch depth of 0.5-μm operates on a single longitudinal mode with about 40 dB side-mode suppression. All these results are from devices with Bragg condition wavelengths which are red-shifted from the peak spontaneous emission wavelength by over 400 /spl Aring/.