AlGaAs Laser Diode Research Articles

High‐power ALGaAs single‐stripe laser diode with window‐grown‐on‐facets

AbstractA high‐power single‐stripe AlGaAs laser diode capable of reliable operation at an output power greater than 50 mW is useful for improvement in optical data storage systems and second harmonic generation elements. A novel window structure laser diode is developed and referred to as a window‐grown‐on‐facets (WGF) laser. Highly reliable operation is attained under 10 mW at 50°C beyond 10, 000 hours in the wavelength of 830 nm and under 70 mW at 60°C beyond 4000 hours in the wavelength of 780 nm, respectively. In the WGF laser, the window effects are found only in the case of the Al content of the window layer greater than that of the cladding layer. To explain the experimental results, calculation of carrier leakage from the active layer to the window layer is performed. The reduction of the window effects is caused by the carrier leakage.

Upconversion luminescence of Er3+ in CdX2 system glasses (X=Cl, Br, I)

Near-infrared to visible upconversion characteristics of Er3+ in CdX2-based halide glasses (X=Cl, Br, or I) has been investigated. When 4I9/2 state is pumped by 800 nm radiation from an AlGaAs laser diode, the upconverted green emissions (520–560 nm) of 2H11/2+4S3/2→I15/2 transition are clearly observed in all the glasses. The linewidth of green emission in these glasses becomes narrow in the order of chloride, bromide, and iodide. The CdCl2 and CdBr2 system glasses give blue upconversion luminescence (around 410 nm) due to the 2H9/2→I15/2 transition, but this emission is not observed in the CdI2 system glass because of the absorption edge at around 450 nm. The fluorescence spectra of CdX2 system glasses suggest that the multiphonon relaxation rate depends on choice of the X species.

High second-harmonic conversion efficiency of quasi-phase-matched LiTaO3 waveguides pumped by single-mode pulsed AlGaAs laser diodes

We show that the averaged second-harmonic conversion efficiency of quasi-phase-matched LiTaO3 waveguides can be increased by a factor larger than 15 with the use of single-mode pulsed AlGaAs laser diodes as the optical sources. The proton exchange followed by thermal annealing is used both to periodically change the sign in d33 nonlinear coefficient and to fabricate the waveguides. Laser pulses are produced by strong rf modulation of the diode current while single-mode operation is achieved with a grating-tuned external cavity. The averaged conversion efficiency is found to linearly increase with peak power of pulses even in the case of pulses whose spectral width is larger than the spectral acceptance of LiTaO3 waveguides. Experimental results are in agreement with calculated ones. The conversion efficiency of 450 %/W presently reached at optimum (i.e., 1% for 2.2 mW pump and 1 cm interaction length) is among the highest performances reported to date for frequency doubling of laser diodes.

Large-area wafer processing for 0.78-/spl mu/m AlGaAs laser diodes

Large-area wafer processing for buried-ridge loss-guided inner-stripe AlGaAs laser diodes (LD's) has been developed for the first time. High uniformity of ridge waveguides on a 3-in wafer is realized by introducing selective wet etching. The standard deviations of the ridge width and the remaining p-cladding layer thickness on either side of the ridge, which have a great influence on the device characteristics, are 0.07 μm and 0.01 μm, respectively. As a result, good uniformity of laser characteristics has been obtained, for example, the distribution of full width at half maximum angles of far-field pattern in the direction parallel to the junction plane (/spl theta//sub ///) is only 0.22/spl deg/ (1/spl sigma/) for 1000 chips across a 3-in wafer.

Nonlinear circuit model of laser diodes for large-signal microwave photonic CAD

The laser diode nonlinear equivalent circuit model is developed to be integrated as part of a microwave computer-aided design (CAD) software. Single-mode rate equations are numerically solved using a harmonic balance (HB) simulator to predict performance of laser diodes. The laser diode physical parameters are first extracted by fitting these parameters to the measured I- V, L- I and frequency response curves. Analytically calculated photon densities are employed in the CAD simulation model as seed values for a faster convergence time. The laser diode CAD simulation results compare very well with the large-signal modulation measurements for a DH InGaAsP laser diode. Moreover, the simulated nonlinear behavior of a AlGaAs laser diode is compared against the published measured and SPICE predicted results to assess accuracy of this simulation package. Also, this laser diode CAD simulation achieves a faster convergence speed than other approaches using harmonic balance simulators.

High energy CW Q-switched operation of multicontactsemiconductor laser

Continuous-wave passive Q-switched operation of multiple-contact AlGaAs laser diodes is described. Stable pulses having an energy of 300 pJ and a duration of 40 ps were obtained from 100 µm wide devices with an 800 Å thick active layer. The pulse repetition frequency was remarkably stable, having an RF linewidth of < 100 kHz.

0.78- and 0.98-μm ridge-waveguide lasers buried with AlGaAs confinement layer selectively grown by chloride-assisted MOCVD

The 0.78- and 0.98-/spl mu/m buried-ridge AlGaAs laser diodes (LD's) with a high Al-content AlGaAs confinement layer selectively grown by using a Cl-assisted MOCVD are demonstrated. By employing the AlGaAs confinement layer, the threshold current and the slope efficiency of the 0.78-/spl mu/m LD are improved by /spl sim/40%, compared to those of the conventional loss-guided LD with the GaAs confinement layer. In addition, the stable fundamental mode up to 150 mW and the small astigmatic distance less than 1 /spl mu/m are obtained. The 0.78-/spl mu/m LD also shows the excellent high-power and high-temperature characteristic such as 100 mW CW operation at 100/spl deg/C and the reliable 2,000-hour operation under the condition of 60/spl deg/C and 55 mW. In the 0.98-/spl mu/m LD, the narrow beam with the low aspect ratio of 1.86 and the stable fundamental transverse mode over 200 mW are exhibited. As a result, the 0.98-/spl mu/m LD realizes the high fiber-coupled-power of 148 mW. Moreover, the high-power and high-temperature operation of 150 mW at 90/spl deg/C is obtained. In the preliminary aging test, the LD's have been stably operating for over 900 hours under the condition of 50/spl deg/C and 100 mW. >

Two-dimensional analysis of self-sustained pulsation for narrow-stripe AlGaAs lasers

Self-sustained pulsation in narrow stripe geometry AlGaAs laser diodes is investigated numerically and experimentally. By taking account of the time-dependent two-dimensional optical field, carrier spreading in the cladding layers, and multilongitudinal modes, we succeeded in clarifying the mechanism for the pulsation. Fluctuation of the optical field plays an important role in forming saturable absorption. The numerical analysis clearly shows that our newly proposed real refractive index-guided structure is very suitable for a pulsation laser in which the optical field distribution and current spreading can be independently controlled. Furthermore, me show that the new structure gives much lower threshold current than that of a conventional loss-guided structure. These predicted advantages of the real refractive index-guided structure are verified experimentally with good agreement.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Potential for improving the Rubidium Frequency Standard with a novel optical pumping scheme using diode lasers

Frequency stability of a Rubidium Frequency Standard (RFS) is directly related to the signal-to-noise ratio (S/N) of the microwave-induced (6834 MHz) optical signal which is proportional to the fractional atomic population difference between the two M/sub F/=0 ground state sublevels of /sup 87/Rb. In the present RFSs this fractional population difference is small (<1%). S/N can be substantially improved by concentrating all of the atoms in one of the two M/sub F/=0 sublevels. Potentially, this could lead to a significant improvement in the short-term performance of RFSs. We have developed a novel scheme for concentrating a large fraction of the Rb atoms in one of the two M/sub F/=0 ground state sublevels. We optically pump the Rb vapor with circularly polarized light from a AlGaAs diode laser tuned to the D/sub 1/ transition (794.7 nm). Nearly all of the atoms are concentrated in one of the two high angular momentum states (M/sub F/=2 or -2 sublevels depending on the handedness of the circular polarization). The pumping laser is switched off and two radiofrequency (RF) /spl pi/-pulses are applied sequentially. The first /spl pi/-pulse transfers the atoms from the 2,2(F,M/sub F/) sublevel to the 2,1 sublevel and the second /spl pi/-pulse transfers the atoms from the 2,1 sublevel to the 2,0 sublevel. The resulting population distribution is diagnosed using a second AlGaAs diode laser (weak probe) in conjunction with a microwave field tuned to the 0-0 transition (6834 MHz). We obtain a fractional population difference of 0.7-0.9 between the two M/sub F/=0 sublevels. This should result in an improvement in the S/N by a factor of 70-90 over the lamp pumped RFSs. This could potentially be of considerable importance towards the development of future RFSs. Various relaxations and field inhomogeneities limit the transfer efficiency from being 100%. The details of the experimental technique and possible applications are discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Mass production of laser diodes by MBE

Molecular beam epitaxy (MBE) plays an important role in the mass production of AlGaAs laser diodes which have been widely used in a variety of opto-electronic applications. This paper provides an overview of self-aligned structure AlGaAs laser diodes fabricated by MBE (‘SAM laser diodes’)focusing on the GaAs passivation technique that we put into practical use for the first time, and on the modification of conventional MBE systems. Several features of SAM laser diodes for practical applications are also reviewed.

Tunable, narrow-linewidth output from an injection-locked high-power AlGaAs laser diode array

An injection-locking technique has been employed to produce single-frequency tunable output from a high-power AlGaAs laser diode array. A narrow-linewidth external cavity laser is used as a master oscillator. With an injected power of 15 mW, a total output power of 1.0 W was obtained from the laser diode array with a spectral linewidth of less than 38 kHz, a wavelength tuning range of 13 nm, and a 0.67 degrees -wide single-lobed far-field beam.

High purity AlGaAs from methyl-based precursors using in situ gettering of alkoxides

Atmospheric pressure metalorganic vapour phase epitaxy (MOVPE) has been used to prepare high purity AlGaAs from methyl metalorganic precursors and arsine. A low background concentration for carbon and oxygen was realized using a growth temperature of 600°C and processing of the metalorganic precursors using reactive metals dissolved in gallium. Comparisons have been made with unprocessed alkyl reagents using 10 K photoluminescence. A reduction of both carbon and oxygen through purification suggests alkoxide contamination is suppressed by this technique. MOVPE growth using oxygen gettering for all precursors has been applied to visible AlGaAs laser diodes. A 712 nm double quantum well design operating CW resulted in a maximum output power of 176mW/facet from an uncoated laser device with a 400 μ m×100 μ m oxide defined stripe.

Frequency control of a laser diode by a photothermal effect and its application to frequency stabilization

The frequency of an AlGaAs laser diode (LD) was controlled by using a photothermal effect. If intensity-modulated light from a heating LD is focused on the active domain of another LD, a heat spot changes the effective cavity length of the LD and thus modulates the lasting frequency. For frequency stabilization, frequency shift is detected by a Fabry-Pérot etalon, and it is compensated for by controlling the intensity of the heating LD via a proportional-integral-derivative controller. The highest stability obtained is 2.6x 10^-11 (π = 10 s), which is an improvement of 2 to 3 orders of magnitude over the free-running state. In this method, the concurrent intensity modulation is much smaller than in the current modulation method.

Diode-pumped amplification of Q-switched AlGaAsdiode laserto high power using fluoride fibre amplifier

A diode-pumped, thulium-doped, fluorozirconate fibre amplifier has been used to amplify high-power pulses from a modulated AlGaAs diode laser at 805 nm, using a 100 mW single-stripe diode laser at 785 nm as the pump source. Internal gains in excess of 18 dB were observed in the small-signal regime. The greatest peak output power, observed for a launched pump power of 47 mW, was 12.5 W for pulses of 15 ps duration driven at a repetition rate of 7 MHz.

A Tm 3+ sensitized Ho 3+ silica fibre laser at 2.04 μm pumped at 809 nm

Laser action at 2.04 μm has been achieved in a Tm 3+ sensitized Ho 3+: SiO 2 glass fibre laser. A high Tm 3+ concentration of 2000 ppm wt. allows optical pumping at 809 nm, in the wing of the Tm 3+ 786 nm absorption. Pumping was performed using a rhodamine 800 dye laser and a 809 nm AlGaAs laser diode operated in fundamental transverse mode. To our knowledge this is the first operation of a laser diode pumped Tm 3+: Ho 3+: SiO 2 fibre laser.

High-power laser diodes based on InGaAsP alloys

HIGH-POWER, high-coherence solid-state lasers, based on dielectric materials such as ruby or Nd:YAG (yttrium aluminium garnet), have many civilian and military applications. The active media in these lasers are insulating, and must therefore be excited (or ‘pumped’) by optical, rather than electrical, means. Conventional gas-discharge lamps can be used as the pumping source, but semiconductor diode lasers are more efficient, as their wavelength can be tailored to match the absorption properties of the lasing material. Semiconducting AlGaAs alloys are widely used for this purpose1, 2, but oxidation of the aluminium and the spreading of defects during device operation limit the lifetime of the diodes3, and hence the reliability of the system as a whole. Aluminium-free InGaAsP compounds, on the other hand, do not have these lifetime-limiting properties4–8. We report here the fabrication of high-power lasers based on InGaAsP (lattice-matched to GaAs substrates), which operate over the same wavelength range as conventional AlGaAs laser diodes and show significantly improved reliability. The other optical and electrical properties of these diodes are either comparable or superior to those of the AlGaAs system.

Beam magnification and the efficiency of optical trapping with 790-nm AlGaAs laser diodes

The efficiency of dielectric particle confinement with 790 nm AlGaAs laser diode optical traps is investigated as a function of beam magnification and polarization state. When an anamorphic prism pair is used to correct for diode beam ellipticity, trapping efficiencies of nearly 0.37 are achieved with a magnification factor of 3×, laser powers of 4-18 mW, and an overfilled microscope objective entrance aperture. Results are compared for diodes having small (8 μm) and large (57 μm) astigmatisms, but comparable far-field divergence angles.

A degradation rate study of MBE-grown high-power AlGaAs laser diodes

The influence of the growth temperature of ternary compounds on the degradation rate of AlGaAs/GaAs laser diodes was studied. The optimal temperature was found to be 700 degrees C. A further reduction in the degradation rate may be achieved by using a ridge-type stripe-array contact instead of a broad-area contact. The percentage of diodes with a lifetime exceeding 2500 hours (at Pout approximately=2 mW mu m-1 per facet) was four times larger for the former laser than for the latter.

Compound cavity gain of tandem-electrode multiple-quantum-well AlGaAs laser diodes

The compound cavity gain of multiple-quantum well AlGaAs semiconductor lasers with segmented contacts was measured in detail. A second peak of the gain curve is observed. We discuss the impact of the individual features of gain and absorption on the characteristics of the laser diode and demonstrate that, by changing the bias conditions, these features can be used to produce spectral switching of the lasing wavelength by more than 10 nm.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Laser diode wavelength-modulation spectroscopy for simultaneous measurement of temperature, pressure, and velocity in shock-heated oxygen flows

Wavelength modulation at 10 MHz of an AlGaAs laser diode, superposed on repetitive linear scans of wavelength, is applied to measure second-harmonic absorption line shapes of oxygen in the A band. Theoretical expressions of the harmonic line shapes, including the effect of laser amplitude modulation and varying modulation depth, are presented. A least-squares fit of the experimental line shapes to theoretical second-harmonic line shapes permits simultaneous determination of the temperature and the pressure. The use of high-repetition-rate (10-kHz) linear scans of the studied wavelength region permits application of the technique to high-speed unidimensional transient flows generated in a shock tube; velocity is derived from the Doppler shift of the absorption profiles.