Broad Stripe Laser Diode Research Articles

Monolithic growth of GaAs laser diodes on Si(001) by optimal AlAs nucleation with thermal cycle annealing

A GaAs quantum-well laser diode was directly grown on silicon (001) substrate by a hybrid technique comprising AlAs nucleation and thermal cycle annealing. The hybrid technique provided the advantages of superior surface roughness, high quantum efficiency, and low threading dislocation density (TDD) of a thin buffer. The TDD was quantitatively characterized through the electron channeling contrast imaging method. Directly grown GaAs on Si exhibited a TDD of 5.45 × 107 /cm2 with small thickness of approximately 1.5 µm. The roughness and quantum efficiency of GaAs on Si was enhanced by adopting the nucleation layer of AlAs. We found that there exists an optimal thickness of AlAs nucleation to be 1.68 nm through structural and optical analysis. Based on optimized GaAs on Si, the GaAs quantum-well laser diode was directly grown with a TDD of 2.5 × 107 /cm2. Whole epitaxial layers were grown by metalorganic chemical vapor deposition. An edge-emitting broad stripe laser diode was successfully fabricated with a cavity length and width of 1120 µm and 60 µm, respectively. The continuous-wave lasing at room temperature was realized with a threshold current density of 643 A/cm2 and maximum output power of 19.7 mW at a single facet, where a threshold current density of 317 A/cm2 was obtained under pulsed operation condition. This result would constitute a building block to realize silicon-based on-chip light sources.

835 nm fiber Raman laser pulse pumped by a multimode laser diode at 806 nm

We present a fiber Raman laser (FRL) based on a highly nonlinear fiber that emits pulses at 835 nm when synchronously pumped by a broadstripe semiconductor laser diode (LD) at 806 nm. The slope efficiency reaches 65% in a 600 m long fiber for a 100 ns long pulse. Our results show that broadstripe LDs are now sufficiently bright for the Raman gain to overcome the relatively high background loss at wavelengths as short as 835 nm, which we believe is the shortest reported to date for any diode-pumped FRL.

Reliability study on high-power 638nm broad stripe laser diode

High-power laser diodes (LDs) are strongly demanded as a light source of display applications. In this work, the reliability of a high-power 638 nm broad stripe (BS) LD was studied from the viewpoint of not only gradual degradation but also catastrophic optical degradation (COD) at a front facet. Long term acceleration aging tests for the 638 nm BS-LD with the window-mirror structure by using Zn diffusion were performed. It was confirmed that COD only occurs at a high output power and this mode was dominant compared with gradual degradation. The result also revealed that the mean time to failure due to COD was proportional to optical density to the power of −3:2. It is clarified that maintaining a low optical output power density is essential to develop high-power and highly reliable red BS-LDs.

Homogeneous broadening and k-vector conservation in direct bandgap transitions

k-vector conservation is studied in direct bandgap optical transitions by examining edge emitted photoluminescent and electroluminescent spectra. Inhomogeneously and homogeneously broadened spectra are identified in tensile strained, single quantum well, broad stripe laser diode structures. In low excitation conditions, the molecular beam epitaxy (MBE) deposited test structures showed Urbach-tail like inhomogeneous broadening with small Urbach parameter values, typical for high quality materials. At high excitation conditions, significant deviations from Lorentzian line shape were observed and concluded to arise from k-vector conservation within the line broadening process.

500 nm electrically driven InGaN based laser diodes

Based on recent improvements of growth of In-rich InGaN quantum wells with low defect density, we demonstrate current driven InGaN laser diodes at wavelengths as long as 500 nm. The laser structures are grown on c-plane GaN substrate and are processed as broad oxide-insulated stripe laser diodes. We discuss the impact of the piezoelectric field on the emission energy of long wavelength laser diodes for this growth orientation. The combination of low threshold current density of 8.2 kA/cm2 with high slope efficiency of 650 mW/A enables high output powers up to several tens of milliwatts.

Generalised multiple-lateral-mode rate equation modelling of lasers with selective quantum-well intermixing for improved beam quality

A numerical model in terms of rate equations for lateral mode amplitudes for analysing static and dynamic properties of moderately broad stripe (tens of microns) laser diodes is proposed and used for modeling lasers with longitudinally or laterally intermixed passive areas. Introduction of passive diffractive regions is shown to offer some improvement of the laser beam, and the potential of further improvement of the beam by Intermixing lateral fringes along the stripe is discussed.

Stable dual-wavelength operation of InGaAs diode lasers with volume Bragg gratings

Stable dual-wavelength operation of InGaAs diode lasers coupled with volume Bragg gratings has been demonstrated for the continuous wave and gain-switching regimes. Spectral narrowing down to 0.33nm has been realized with maximum output power of up to 1.85W from a broad area stripe laser diode in a single-grating external cavity configuration. Spectral separation from 0.5 (0.16THz)to6.5nm (2.05THz) has been obtained and an output power of up to 1.75W was achieved in dual-wavelength operation.

General Discussion on Mode Selectivity Imposed by External Cavity used to Phase Lock Broad Stripe Diode Arrays

Without referring to specific devices, a general discussion on the selectivity of the phase locked super modes imposed by the external cavity has been made for the broad stripe laser diode arrays (LDAs) locked by extended cavities (ECs). For a phase locked LDA based on the diffraction coupling between the nearest neighbor emitters, analytical solutions have been derived for the coupling matrix equation, including the finite reflection of the front facet of the LDA facing the EC. Even though the thresholds of the super modes of an LDA are affected by the residual reflection at the front facet, it can still be analytically proved that the favored mode of the LDA is either the lowest or highest order super mode. In consistent with the mode coupling theory, analysis reveals that between z t /(4n + 3) and z t /(4n+1), with z t being the Talbot distance and n=0, 1, 2 ... , there exist EC length ranges favoring the operation of the lowest order super mode, and between z t /(4n + 5) and z t /(4n + 3) favoring the highest order super mode.

Analytically characterizing far field pattern of super-modes from external cavity phase locked diode array

Analytical studies have been made on multi-lobed far field patterns of super-modes (SMs) from a broad stripe laser diode array (LDA) phase locked with an external cavity. Irrespecting the order of an SM, the far field pattern of the SM is multi-lobed. The far field pattern of the highest super-mode (HSM) or the lowest super-mode (LSM) is composed of evenly-separated single lobes, and that of other SMs contains repeated pairs of lobes. It is difficult to distinguish the far field patterns of the HSM and the LSM unless the normal direction is accurately determined. Similar difficulty is also encountered when trying to discriminate the jth and (M−j+1)th SMs of the LDA containing M emitters.

Low dislocation density, high power InGaN laser diodes

We used single crystals of GaN, obtained from high-pressure synthesis, as substrates for Metalorganics Vapor Phase Epitaxy growth of violet and UV laser diodes. The use of high-quality bulk GaN leads to the decrease of the dislocation density to the low level of 105 cm−2, i.e. two orders of magnitude better than typical for the Epitaxial Lateral Overgrowth laser structures fabricated on sapphire. The low density and homogeneous distribution of defects in our structures enables the realization of broad stripe laser diodes. We demonstrate that our laser diodes, having 15 μm wide stripes, are able to emit 1.3-1.9 W per facet (50% reflectivity) in 30 ns long pulses. This result, which is among the best ever reported for nitride lasers, opens the path for the development of a new generation of high power laser diodes.

La2O3‐Al2O3‐SiO2Glasses for High‐Power, Yb3+‐Doped, 980‐nm Fiber Lasers

Single‐mode semiconductor pumps have failed to keep pace with the increasing power requirements of Er‐doped fiber amplifiers (EDFAs), so there is a need for high‐powered 980‐nm sources. Yb3+‐doped tapered fiber lasers can provide high‐power output by conversion of a low‐brightness, high‐powered, 920‐nm, multimode broad stripe laser diode to a high‐brightness, 980‐nm, single‐mode output. The tapered fiber laser requires a fiber with high numerical aperture (NA) (>0.4), a rectangular core, and good Yb3+spectroscopy for efficient operation. CVD‐based fiber fabrication methods are incapable of delivering fibers with an NA > ∼0.3 or with good efficiency at 980 nm so a new method of high‐NA fiber fabrication was developed. The core glass composition is critical for maintaining a high‐NA fiber with good power extraction while avoiding phase separation, loss, and clustering. The SiO2level controlled the NA and interdiffusion between core and clad, while the Al2O3/La2O3ratio controlled phase separation. A La2O3‐Al2O3‐SiO2glass was developed that is compatible with a pure SiO2cladding glass and has a laser slope efficiency of 70% at 980 nm. The optimized fiber composition yielded 450 mW of 980‐nm power in a single‐mode fiber.

A Novel Phase Conjugate Broad-Stripe Diode Laser with an External Ring Geometry

We present a highly bright output radiated from a single-stripe high power laser diode, known as a broad-stripe laser diode (BS-LD) with ring-type self-pumped phase conjugate mirror. Within a minute after the laser turning on, the lasing frequency was locked at the central wavelength of 808.9 nm within 0.1 nm. The BS-LD then generated a single-lobed far-field.

Suppression of Self-Frequency-Scanning and Brightness Improvement of a Broad-Stripe Laser Diode using Phase Conjugate Feedback

We present a new technique for suppressing the self-frequency-scanning in a single-stripe high power laser diode, known as a broad-stripe laser diode (BS-LD) with phase conjugate feedback. The lasing frequency was locked at the central wavelength of 808.7 nm within 0.1 nm for 20 min. The BS-LD was then operated in a narrow-band with a 0.4 nm line width and generated a single-lobed near-field radiation with a narrow divergence.

Highly efficient 4-W Yb-doped fiber amplifier pumped by a broad-stripe laser diode

A Yb-doped double-cladding fiber amplifier is v-groove side pumped by a 100-microm -wide, broad-stripe, 975-nm laser diode. The amplifier exhibits, separately, 39% electrical-to-optical conversion efficiency, 89% internal optical-to-optical conversion efficiency, 4-W output power at 1060 nm, and a small-signal gain of 53 dB.

GaAsSb: A novel material for 1.3 µm VCSELs

GaAsSb quantum wells (QWs) on GaAs substrate are proposed for the active layer of 1.3 /spl mu/m VCSELs. High-quality GaAsSb QWs showed intense 1.32 /spl mu/m photoluminescence at room temperature. Room-temperature pulsed operation of GaAsSb/GaAs broad stripe laser diodes at a wavelength of 1.22 /spl mu/m was demonstrated for the first time.

High-power superfluorescent source with a side-pumped Yb-doped double-cladding fiber

A compact superfluorescent source based on an Yb-doped double-cladding fiber amplifier is described. The packaged amplifier is pumped at 975 nm by side-coupling emission from a 2.0-W broad-stripe laser diode through an imbedded V groove. The fiber source generates 485 mW of broadband emission centered at 1055 nm with a 41-nm FWHM flat power spectrum.

Second harmonic generation applying injection-locked radiation from a high-power, broad-stripe laser diode

406 nm laser light is produced by second harmonic generation in a LiIO 3 crystal using the fundamental radiation of an injection-locked, broad-stripe, high-power laser diode. The efficiencies of injection locking as well as of second harmonic generation are discussed.

Investigation of photorefractive phase conjugate feedback on the lasing spectrum of a broad-stripe laser diode

We demonstrate single-longitudinal-mode operation of a 160 mW broad-stripe laser diode (BS-LD) with 0.2 nm line-width using an external semi-linear phase conjugator. The lasing spectrum of the BS-LD was insensitive to reflectivity fluctuations of the phase conjugator and the lasing wavelength was locked at 805.5 nm to within 0.02 nm over a period of 20 min. The stability of the lasing spectrum was due to the feedback beam being incoherent with the internal radiation of the BS-LD.

V-groove side-pumped 1.5 µm fibre amplifier

A side-pumping technique, using an imbedded v-groove is used to efficiently pump a double-clad Er/Yb doped fibre amplifier operating at 1.5 µm and pumped at 0.98 µm. A diode-to-fibre coupling efficiency of 76% was measured for a 100 µm wide broad stripe laser diode and a fibre with a 50 × 120 µm first cladding. A maximum output power of 185 mW, and separately, a small signal gain of 35 dB, are demonstrated.

FM mode-locked, laser-diode-pumped La_1−xNdxMgAl_11O_19 laser

We report the operation of a laser diode pumped La(1-x)Nd(x)MgAl(11)O(19) laser mode locked by an electro-optic phase modulator. The repetition rate of the laser was 230 MHz, and the average output power was 50 mW, when pumped by a 500-mW broad-stripe laser diode. Transform-limited pulses of 14 ps duration were obtained. We have also demonstrated the FM operation of this laser, with bandwidths of up to 440 GHz being obtained.