Gain-guided Laser Diodes Research Articles

Realization of GaN-based gain-guided blue laser diodes by helium ion implantation

The fabrication process and characteristics of gallium nitride (GaN) based gain-guided blue laser diodes (LDs) are studied, in which an ion implantation process is adopted to confine carrier injection into the active region. The implantation of helium ions with an energy of 85 keV, an angle of 0°, and a dosage of 4.7 × 1014 cm−2 is conducted in the experiment. The specific contact resistivity of p-type ohmic contact of implanted sample is determined to be 2.2 × 10–4 Ω cm2, which is comparable with the un-implanted sample. Then, both ion-implanted gain-guided and ridge waveguide LDs are fabricated at the same time. Similar threshold current density and slope efficiency are obtained, while the operation voltage of ion-implanted gain-guided LDs is 0.2 V lower than the ridge waveguide LDs at 0.56 kA cm−2. The ridge waveguide LDs show multi-mode operation after lasing. However, for ion-implanted gain-guided LDs, the far-field pattern indicates a single lateral mode operation up to twice of the threshold current, and the peak optical output power of blue single mode LDs at 450 nm exceeds 200 mW under pulsed condition.

InGaN-based true green laser diodes on novel semi-polar [formula omitted] GaN substrates

The crystal quality and emission characteristics of InGaN-based laser diodes (LDs) with lattice-matched quaternary InAlGaN cladding layers on novel semi-polar { 2 0 2 ¯ 1 } plane GaN substrates were investigated. Highly homogeneous InGaN quantum wells (QWs) with a suppressed piezoelectric field can be realized on the { 2 0 2 ¯ 1 } plane even in the green spectral region. Optical polarization measurements revealed that [ 1 ¯ 0 1 4 ] oriented stripes are advantageous for LDs on { 2 0 2 ¯ 1 } planes. Gain-guided LDs on the novel { 2 0 2 ¯ 1 } plane exhibited the longest lasing wavelength at 533.6 nm under pulsed operation. Continuous-wave (cw) operation at the lasing wavelength of 523.3 nm at 115 mA was also demonstrated. The I th , J th , V th , and the slope efficiency were 110 mA, 9.2 kA/cm 2, 7.4 V, and 0.04 W/A, respectively. These results indicate that the green LDs on semi-polar { 2 0 2 ¯ 1 } plane GaN substrates are promising candidates for laser display applications.

Laser Scribing for Facet Fabrication of InGaN MQW Diode Lasers on Sapphire Substrates

In this letter, a novel method for the fabrication of high-quality facets for III-nitride lasers grown on c -plane sapphire substrates as well as on GaN substrates is presented. Based on a laser scribing process gain-guided laser diodes with smooth facets were fabricated, which showed threshold current densities of 6.5 kA/cm2 at an emission wavelength of 405 nm under pulsed operation.

Ultraviolet semiconductor laser diodes on bulk AlN

Current-injection ultraviolet lasers are demonstrated on low-dislocation-density bulk AlN substrates. The AlGaInN heterostructures were grown by metalorganic chemical vapor deposition. Requisite smooth surface morphologies were obtained by growing on near-c-plane AlN substrates, with a nominal off-axis orientation of less than 0.5°. Lasing was obtained from gain-guided laser diodes with uncoated facets and cavity lengths ranging from 200 to 1500 μm. Threshold current densities as low as 13 kA/cm2 were achieved for laser emission wavelengths as short as 368 nm, under pulsed operation. The maximum light output power was near 300 mW with a differential quantum efficiency of 6.7%. This (first) demonstration of nitride laser diodes on bulk AlN substrates suggests the feasibility of using such substrates to realize nitride laser diodes emitting from the near to deep ultraviolet spectral regions.

1 W tunable near diffraction limited light from a broad area laser diode in an external cavity with a line width of 1.7 MHz

A novel unstable external cavity for a broad area laser diode is presented. The cavity is based on a V-shaped setup that improves the slow axis beam quality by coupling the internal modes of a gain guided laser diode. The novelty here is the compact unstable resonator design without lenses in direction of the slow axis. For frequency stabilisation and to narrow the line width of the laser diode emission a diffraction grating in a Littrow configuration is used. With this setup up to 1W of near diffraction limited light with a beam quality of M2⩽1.3 and a line width of 1.7MHz could be achieved. The external cavity laser was tunable over a range of 35nm (FWHM) around the center wavelength of 976nm.

InGaAs/AlGaAs Quantum Wire DFB Buried HeteroStructure Laser Diode by One-Time Selective MOCVD on Ridge Substrate

A quasi-buried heterostructure (BH) quantum wire (QWR)-distributed feedback (DFB) laser was realized by one-time selective metalorganic chemical vapor deposition (MOCVD) on a ridge substrate with a submicron grating. One-time selective MOCVD led to the formation of a ridge waveguide with a BH structure and a QWR array for gain-guided DFB laser diode (LD) without additional etching or regrowth process. The threshold current is 15 mA, and the threshold current density is 850 A/cm2. A stable single longitudinal mode was preserved until 3 Ith, after which another mode emerged at a high drive current at 813.6 nm. This suggests a complex-coupled DFB-mode operation. The elimination of the regrowth step enlarges the range of material for extended wavelengths and operational temperatures.

Ultraviolet AlGaN multiple-quantum-well laser diodes

We demonstrate ultraviolet emission from current-injection AlGaN multiple-quantum-well laser diodes grown on sapphire substrates by metalorganic chemical vapor deposition. Lasing was obtained in gain-guided laser diode test structures with uncoated facets and cavity length ranging from 400 to 1500 μm. Under pulsed bias conditions, threshold current densities as low as 23 kA/cm2 have been achieved for laser diodes with emission wavelengths between 359.7 and 361.6 nm. The maximum output power was 45 mW per facet with differential quantum efficiencies of 1.3%.

Laser Diode Facet Degradation Study

ABSTRACTWe study the degradation behaviour of GaN gain guided laser diodes (LDs) on SiC substrates with cleaved facets and reflective coatings on none, one, or both facets. This allows us to demonstrate that in addition to volume effects there is a contribution of the laser facets to laser degradation. We observe that for the uncoated LDs the threshold current density is increasing considerably faster compared to LDs with mirror coatings. Degradation is observed during operation but not during storage at ambient conditions and thus expected to be photon or current induced. Operation of the uncoated laser in a nitrogen atmosphere reduces the degradation rate with respect to operation in air.

Tuning high-power laser diodes with as much as 038 W of power and M^2 = 12 over a range of 32 nm with 3-GHz bandwidth

Gain-guided diode lasers usually have emission wavelengths determined by the manufacturing process, with typically 0.5-1-nm bandwidth. Furthermore, their beam quality is rather poor. We show that external cavities allow for tunable narrow-bandwidth operation of gain-guided diode lasers. At the same time the beam quality is drastically improved; almost diffraction-limited light of more than 200 mW has been achieved over the whole tuning range from 910 to 942 nm with narrow bandwidth.

Single aspherical lens for deastigmatism, collimation, and circularization of a laser beam

An astigmatic and elliptically diverging laser beam generated by a gain-guided laser diode can be converted into a collimated and circular beam with a single specially designed lens. The designed lens also corrects for the astigmatism present in the laser diode. The input surface of the lens has a different concave and convex aspherical profile in the transverse and the longitudinal direction, respectively, for astigmatism correction. The output surface possesses a convex aspherical and a straight profile in the transverse and the longitudinal direction, respectively, for collimation and circularization of the final output laser beam.

MOCVD growth and characterization of AlGaInN multiple quantum well heterostructures and laser diodes

We demonstrate room temperature, pulsed, current-injected operation of InGaAlN heterostructure laser diodes with mirrors fabricated by chemically assisted ion beam etching. The multiple quantum well devices were grown by organo–metallic vapor phase epitaxy on c-face sapphire substrates. The emission wavelengths of the gain-guided laser diodes were ∼400 nm. The lowest threshold current density obtained was 6 kA cm −2 with maximum output powers of 50 mW per facet. Optically-pumped distributed-feedback laser operation was also achieved.

Stripe-width dependence of threshold current for gain-guided AlGaInN laser diodes

The threshold current density of narrow-stripe gain-guided nitride laser diodes increases very rapidly as the stripe width is made narrow. To examine this behavior, waveguide simulations, incorporating the complex refractive indices associated with optical gain, have been used to analyze the lateral optical modes of gain-guided laser diodes. Threshold current was then determined from the gain–current relationship of our laser material, which was obtained experimentally. These evaluations reveal that gain guiding, coupled with a carrier-induced index depression, offer a reasonable explanation for the rapid increase in threshold when the stripe width becomes less than 5 μm.

On the Spectrum Characteristics of Laser Diodes

Consideration of the effect of laser-field-induced index grating is presented to qualitatively explain why index-guided laser diodes are more likely to operate with single longitudinal mode and gain-guided laser diodes are more likely to operate with multi-longitudinal mode, to explain the observed faster mode number decreasing of shorter wavelength laser diodes as their injection current is increased, and to explain the observed reluctant wavelength change of single longitudinal mode-operated laser diodes as their injection current and/or temperature are changed.

Characteristic of InGaN/GaN Laser Diode Grown by a Multi-Wafer MOCVD System

InGaN/GaN multi-quantum well (MQW) laser diodes (LDs) were grown on c-plane sapphire substrates using a multi-wafer MOCVD system. The threshold current for pulsed lasing was 1.6 A for a gain-guided laser diode with a stripe of 10 × 800 μm2. The threshold current density was 20.3 kA cm−2 and the threshold voltage was 16.5 V. The optical power ratio of transverse electric mode to transverse magnetic mode was found to be greater than 50. The characteristic temperature measured from the plot of threshold current versus measurement temperature was between 130 and 150K.

Electrical derivative characteristics of ion-implanted AlGaInP/GaInP multi-quantum well lasers

In this study, H + ion implantation was used to form high resistive regions in an AlGaInP/GaInP multi-quantum well (MQW) gain guided laser diode. The electrical derivative was used to characterize the properties of the fabricated laser diodes. The equivalent circuits were proposed to model the diodes for various structures. It was found that diodes fabricated with H + ion implantation, have lower threshold current density and better carrier confinement characteristics.

Single-mode operation of a laser-diode array with frequency-selective phase-conjugate feedback

A new technique for single-mode operation of laser-diode arrays is presented. A gain-guided GaAlAs laser diode array is coupled to an external frequency-selective phase-conjugate feedback system that contains a photorefractive barium titanate crystal, a Fabry-Perot etalon, and a spatial filter. The etalon is the key component, and it forces the array, which has low spatial and spectral coherence when it runs freely, to oscillate in a single spatial and a single longitudinal mode. At a drive current of two times the threshold current, the far-field pattern is reduced to only 1.4 times the diffraction limit, the spectral bandwidth is less than 0.02 nm, and the coherence length is increased by a factor of 70. The technique has general validity and can be applied to various other multimode laser systems.

Characteristics of InGaN-AlGaN multiple-quantum-well laser diodes

We demonstrate room-temperature pulsed current-injected operation of InGaAlN heterostructure laser diodes with mirrors fabricated by chemically assisted ion beam etching. The multiple-quantum-well devices were grown by organometallic vapor phase epitaxy on c-face sapphire substrates. The emission wavelengths of the gain-guided laser diodes were in the range from 419 to 432 nm. The lowest threshold current density obtained was 20 kA/cm/sup 2/ with maximum output powers of 50 mW. Longitudinal Fabry-Perot modes are clearly resolved in the high-resolution optical spectrum of the lasers, with a spacing consistent with the cavity length. Cavity length studies on a set of samples indicate that the distributed losses in the structure are on the order of 30-40 cm/sup -1/.

High-energy (59 pJ) and low-jitter (250 fs) picosecond pulses from gain-switching of a tapered-stripe laser diode via resonant driving

High-energy (59 pJ), low-jitter (250 fs), high-extinction ratio (800), and short (14.5 ps FWHM) pulses were generated by gain-switching of a tapered stripe gain-guided laser diode (LD) via resonant driving. These characteristics are attributed to a stable single-mode near-field pattern, a single-lobe far-field pattern, and multilongitudinal modes associated with the tapered stripe LD under high driving current pulses. These pulses from a comb generator were enhanced mainly from reflection at the LD-transmission line impedance mismatch; the line length was adjusted for resonance with the reflection from the step recovery diode, further increasing the driving current.

Paraxial-misalignment insensitive external-cavity semiconductor-laser array emitting near-diffraction limited single-lobed beam

We present a novel easy-to-align external cavity configuration for efficiently obtaining a near-diffraction limited single-lobed beam from gain-guided laser diode arrays. The external cavity has an external mirror (EM) in the image plane of the array. Two bulk-optics experimental setups are evaluated and a compact GRIN lens design is discussed. There are several advantages for the present geometry, including orders of magnitude lower misalignment-sensitivity and superior mode discrimination. Both experimental setups deliver near-diffraction limited single-lobed beams (of width /spl sim/0.8/spl deg/ at the rated output power of 100 mW of the array) in the entire current range. The light-current (L-I) characteristic is linear and kink-free and one of the setups shows higher efficiency than the free-running array. The broad-area laser (BAL) mode theory is discussed, introducing radiation losses to the analysis. Several aspects of amplification in laser arrays are theoretically explained, such as why the optimum angle of the far-field lobe is always greater than the tenth mode angle (for a uniform 10-stripe array). It is shown that the gain of the amplifying medium broadens the far-field profile. The width of the far-field lobe increases with gain and decreases with the lobe angle. An analytical expression for the broadened far-field profile of BAL modes is presented. The theory compares very well with the experiments.

Characteristics of Gain-Guided Laser Diodes with Cylindrical-Mirror Cavity

We have developed highly reliable etched-mirror laser diodes using a dry etching method. The lasers without facet-coating have been operating stably over 2500 h under automatic-power control (APC) at a power of 3 mW/facet at 50°C. The gain-guided laser diodes with a cylindrical-mirror cavity (CMC) have coaxial mirrors and a fan-shaped stripe structure. By decreasing the curvature radius of the inner facet or increasing the stripe width of the inner facet, the beam waist parallel to the junction plane can be moved outside of the laser diode, while the beam waist perpendicular to the junction plane stops at the mirror facet. A particular CMC laser has a low astigmatism of 4.1 μm and a low relative intensity of noise (RIN) less than –134 dB/Hz at 4 mW under 0–1% optical feedback without high frequency current superposition.