AlGaAs Laser Diode Research Articles

Blue Laser Devices Using Frequency-Doubled Laser Diodes.

Modulatable, stable, and highly efficient small-size blue laser sources are recently considered very promising for high-density optical data storage, laser printer, and so on. A frequency-dou-bled AlGaAs laser diode using a monolithic KNbO3 resonator is expected to be more practical be-cause of its high SH power. We developed compact blue laser devices by this method. These devices, with size of 50×30×20mm3, have an SH output above 10mW with relative intensity noise of - 136dB/Hz and slightly elliptical Gaussian beam profile. We also found a new techni-que for direct modulation of blue radiation by using the EO-effect of KNbO3 crystal.

Laser-absorption mass flux sensor for high-speed airflows

We present a laser-based concept for an air mass flux sensor based on the simultaneous measurement of density and velocity of O(2). The sensor uses wavelength modulation absorption spectroscopy at 10 MHz of an AlGaAs laser diode in the b(1)Sigma(g)(+)(v' = 0)-X(3)Sigma(g)(-)(v'' = 0) system of O(2), combined with second-harmonic detection. The apparatus is demonstrated on a high-speed oxygen flow generated behind the incident shock wave in a shock tube. The measurement time is 0.5 ms for typical absorption levels of 0.5%.

Novel all-optical 10 μm waveguide modulator based on intersubband absorption in GaAs/AlGaAs quantum wells

Efficient all-optical modulation of mid-infrared radiations based on photoinduced intersubband absorption of a GaAs/AlGaAs multiquantum well structure is demonstrated at room temperature. The sample designed for mid-infrared waveguiding was grown by molecular beam epitaxy. A double-resonance spectroscopy of both interband and intersubband transitions of the quantum wells is presented. The intersubband resonance is found at 9.56 μm. An AlGaAs laser diode is used to optically pump the quantum wells. On/off modulation ratios as high as 150:1 are obtained with only 45 mW pump power and for mid-infrared input powers up to 0.5 W. The frequency bandwidth of the device is presently comparable to that of acousto-optic modulators available at mid-infrared wavelengths.

Laser-diode frequency control by resonant phase-conjugate reflection from an atomic vapor

We report our first results on the frequency control of an AlGaAs laser diode by resonant phase-conjugate reflection from an atomic rubidium vapor. When the electrical feedback technique is used, the Allan variance reaches a flicker floor such that sigma(y)(2)(tau) = 1.6 x 10(-19) tau(0) for tau > 1s. We also demonstrate that laser frequency locking can be achieved by using the phase-conjugate reflection directly as a resonant optical feedback. This approach leads to a self-controlled optical frequency standard at 780 nm.

Ultrashort pulse generation from a Q-switched AlGaAs laser with cw injection

Injection of a weak cw radiation in a Q-switched AlGaAs laser diode is shown to produce single-mode pulses with a quasi-linear downchirp of very large amplitude. Strong pulse compression can be achieved by using single-mode dispersive fibers at the laser output. Time-resolved spectroscopic measurements of the laser pulses are presented. Optical solitary pulses shorter than 2 ps are obtained after compression, which corresponds to a pulse compression factor larger than 15. Although the laser-fiber coupling is not fully optimized, peak powers exceeding 3 W are measured at the fiber output. These performances are believed to be the best ever reported for an electrically pumped Q-switched AlGaAs laser diode.

Ultrafast refractive index dynamics in AlGaAs diode laser amplifiers

Ultrafast refractive index dynamics in AlGaAs diode laser amplifiers were studied using 440 fs optical pulses. Refractive index changes consistent with a free carrier heating model proposed to explain earlier studies of gain dynamics in diode lasers are exhibited. We also observe an apparently instantaneous refractive index change that corresponds to an n2⊥ of −5×10−12 cm2/W.

Long-term 60 mW operation of 780 nm AlGaAa lasers with extended beam by additional low-Al-content layer in p -type cladding layer

The catastrophic optical damage level of a 780 nm AlGaAs laser diode is increased by extending the optical beam profile by using a low-Al-content layer in the cladding layer. A higher light output power can be obtained without increasing threshold current, and reliable operation for more than 1000 h at 60 mW output and 50 degrees C ambient is obtained. >

15 W CW monolithic AlGaAs laser diode arrays

Good continuous-wave lifetimes have been demonstrated for 1 cm wide monolithic AlGaAs laser diode arrays with a 3500 μm total aperture width at a power level of 15 W. This represents the highest CW power level at which long lifetimes have been obtained.

Electronically tunable single-mode external-cavity diode laser

A six-stage birefringent filter placed in an external cavity of an AlGaAs diode laser is used to scan the laser electronically over 10.3 nm, hopping single modes of the external cavity. Continuous electronic tuning of the single mode over the free spectral range of the external cavity, 182 MHz, is also demonstrated by using a variable-phase plate. All tuning mechanisms use nematic liquid-crystal electro-optic effects operating at <2 V.

Autocorrelation measurements of picosecond laser-diode pulses by means of quasiphase-matching LiNbO 3 channel waveguides

Autocorrelation measurements of picosecond optical pulses have been carried out using a quasiphase-matching channel waveguide in lithium niobate as the doubling element. The use of waveguides instead of bulk crystals can drastically reduce the demands on power level. A pulse duration of 12 ps was measured for pulses from a gain-switched AlGaAs laser diode with ion-bombarded facets.

Bistability and mode hopping in a semiconductor laser

We investigated mode hopping and bistability in an AlGaAs laser diode. The dwell times of a laser mode intensity in the on and off states are measured as a function of the mode suppression ratio. Predictions of the laser behavior made from a multidimensional laser model with Langevin noise sources are compared with experimental results. The model utilizes an asymmetric nonlinear gain that accounts for the experimentally observed bistable and multimode regimes.

Injection-locking of Q-switched AlGaAs laser with fast saturable absorber

Injection of a weak CW laser beam in a Q-switched AlGaAs laser diode with a fast saturable absorber is shown to produce powerful single-mode picosecond pulses at 0.82μm. The saturable absorber regions are obtained by deep implantation of heavy ions through the diode facets. Single-mode operation is achieved with CW injection powers as low as 50μW. Peak powers exceeding 1.5W are detected at the laser output. A time-resolved spectroscopy of the laser pulses reveals an overall downchirp of 1.5nm.

Hybrid integration of laser diode and monomode high contrast slab waveguide on silicon

The hybrid integration of an AlGaAs laser diode and a monomode high contrast optical slab waveguide on silicon is reported. The laser was placed upside down in an anisotropically etched well and mounted by thermocompression. The power coupled into the waveguide was 1mW and a coupling efficiency of more than 5% has been achieved.

Low‐temperature LPE technique for the performance of visible AlGaAs (SC) lasers

AbstractThe possibilities of the low‐temperature (LT)‐LPE technique in the performance of visible AlGaAs laser diodes are studied. Low current density visible lasers λ ˜ 746 nm has been fabricated and characterized. The laser diode structures are of the separate confinement type (SC) to obtain low threshold current (Jth = 190 A/cm2 at λ = 848 nm for a cavity length L = 1.15 mm). The threshold current density Jth versus lasing wavelength λ characteristic, as well as the dependences of the threshold current density Jth and the reciprocal of differential quantum efficiency 1/ηd with the cavity length L are reported. The expected linear behaviour of the Jth and 1/ηd with the cavity length characteristics appears to break down for the shortest cavity length which is larger for shorter lasing wavelengths.

Frequency locking of laser diode using metallic vapor optogalvanic spectrum: UI

The frequency of a AlGaAs diode laser has been locked to the 8118-cm(-1)(f(3)d(2)s(5)M(0)(7))-20,218-cm(-1) transition of UI at 826.20570 nm using the optogalvanic effect. A hollow cathode vapor generator has been utilized to produce a density of 10(12) atoms/cm(3) of uranium in vapor phase. The absolute frequency stability for a 10-min run was estimated to be better than 500 kHz P-P at an integration time of 1 s. This preliminary result shows that the rich optogalvanic spectrum of uranium can be efficiently used for the frequency-locking of semiconductor lasers.

High power, high brightness 2 W (200 μm) and 3 W (500 μm) CW AlGaAs laser diode arrays with long lifetimes

Continuous-wave lifetimes in excess of ten thousand hours have been demonstrated for single aperture AlGaAs laser diode arrays with 200 μm and 500 μm aperture widths at power levels of 2 and 3 W, respectively.

High-reliability silicon microchannel submount for high average power laser diode arrays

A simple and highly reliable package consisting of a 1-cm-long AlGaAs laser diode array mounted directly on a silicon microchannel cooler has been demonstrated. 3.4×109 shots were logged on this device at an average optical output of 8.75 W with only a 6% increase in current required to hold the light output constant. This extrapolates to a current doubling lifetime of 1.6×1011 shots. The thermal impedance was also measured to be 0.014 °C/(W/cm2).

Word timing recovery in direct detection optical PPM communication systems with avalanche photodiodes using a phase lock loop

A technique for word timing recovery in a direct detection optical pulse position modulation (PPM) communication system is described. It tracks on back-to-back pulse pairs in the received random PPM data sequences with the use of a phase locked loop. The experimental system consisted of an AlGaAs laser diode transmitter ( lambda =833 nm) and a silicon avalanche photodiode photodetector, and its used Q=4 PPM signaling at a source data rate of 25 Mb/s. The mathematical model developed to characterize system performance is shown to be in good agreement with the experimental measurements. Use of this recovered PPM word clock, along with a slot clock recovery system described previously, caused no measurable penalty in receiver sensitivity when compared to a receiver which used common transmitter/receiver clocks. The completely self-synchronized receiver was capable of acquiring and maintaining both slot and word synchronizations for input optical signal levels as low as 20 average detected photons per information bit. The receiver achieved a bit error probability of 10/sup -6/ at less than 60 average detected photons per information bit. >

Performance characteristics of high power CW, 1 cm wide monolithic AlGaAs laser diode arrays with a 2 mm total aperture width

1 cm wide monolithic laser diode arrays emitting around 810 nm with a 2 mm total aperture width have been characterised under CW conditions. CW operation up to 16 W has been achieved at a heatsink temperature of 70°C. Several arrays have been lifetested at 10 W CW at a 20°C heatsink temperature for a few thousand hours and have projected lifetimes of between 5000 and 17000 hours. The temperature dependence of the degradation rate was characterised, from which data an activation energy of 0.2 eV was obtained.

A 780 nm high-power and highly reliable laser diode with a long cavity and a thin tapered-thickness active layer

Conventional AlGaAs laser diodes with uniform thickness active layers of various cavity lengths are investigated. It is recognized that the extension of the cavity length is effective in the improvement of the maximum output power, the temperature characteristics, and the operating life in high-temperature conditions. A 780-nm, high-power laser diode having a 350- mu m-long cavity with a thin tapered-thickness active layer was fabricated. The optical power density near the mirror facets, the thermal resistance, the current density, and the carrier density were reduced by this structure. The laser emitted over 100 mW of CW (continuous-wave) output power at temperatures up to 80 degrees C. A maximum output power level of 160 mW was achieved at room temperature. The fundamental transverse mode was confirmed at least up to 120 mW. >