Stable Transverse Mode Research Articles

Visible GaAlAs Laser with a Buried-Convex Waveguide Structure

A new buried-heterostructure visible GaAlAs laser, called a buried-convex waveguide structure (BCS) laser, has been developed. BCS lasers exhibit a highly stable transverse and single longitudinal mode operation in the 750 to 870 nm wavelength range. Very low threshold currents of 10–20 mA are obtained for the wavelength at about 750 nm. The output beam of BCS lasers has an aspect ratio of 2.0–2.5 and has no astigmatism. The relative intensity noise of BCS laser is very low at a level below -150 dB/Hz and is constant in the temperature range between 10 and 50°C. The maximum output power ofBCS lasers with facet coating is almost independent of the lasing wavelength between 750 and 870 nm.

Visible GaAlAs V-channeled substrate inner stripe laser with stabilized mode using p-GaAs substrate

A new visible laser, the V channeled substrate inner stripe laser, is developed. This laser can internally confine the current into the V-channel by using a thin n-GaAs layer grown on the p-GaAs substrate. cw threshold currents were 35–45 mA in the visible spectral range of 770–790 nm. And highly stable transverse and single longitudinal mode operation were observed because the built-in optical waveguide was formed within the V channel.

Transverse mode controlled in inGaAsP inP lasers at 1.5 µm range with buffer-layer loaded piano-convex waveguide (BL-PCW) structures

A modified plano-convex waveguide structure is studied analytically and successfully applied to InGaAsP/InP lasers in the 1.5- 1.6 \mu m wavelength region to realize stable transverse mode operation. The structure of these lasers is characterized by a standard buffer layer between an active layer and an upper cladding layer and a waveguide layer of varying thickness between the active layer and the substrate. A theoretical analysis of this structure showed that, for a given channel depth, increases in buffer-layer thickness give rise to larger maximum channel widths of the substrate for fundamental transverse mode operation. It was also shown that the optical confinement factor in the active layer decreases little as the buffer-layer thickness is increased from 0.1 to 0.3 μm. Buffer-layer loaded plano-convex waveguide lasers in the 1.5 μm range were prepared by liquid phase epitaxy and fundamental transverse mode operation up until I = 2I_{th} was obtained. The dc threshold current was 100-300 mA and the differential quantum efficiency per facet was 10-15 percent. Continuous CW operation for over 2000 h at 25°C has been achieved.

Narrow-stripe injection lasers in GaInAsP/InP

Results are reported on CW and pulsed operation of GaInAsP/InP narrow-stripe (3 μm) injection lasers emitting at the 1.3 μm wavelength. These lasers operate with linear light-current characteristics, stable zeroth-order transverse mode, and no transient oscillations. Their far-field emission pattern in the plane parallel to the junction is double peaked and their spectral emission is multimode.

Transverse mode control in InGaAsP/InP buried crescent diode lasers

Transverse mode stabilisation of InGaAsP/InP buried crescent laser diodes emitting at 1.3 ?m is described. Width and thickness of the active region have been reduced to stabilise the transverse mode. Operation up to 17 mW/facet in a stable transverse mode and threshold current as low as 12 mA in CW operation have been obtained.

High power output InGaAsP/InP buried heterostructure lasers

A novel InGaAsP/InP buried heterostructure (BH) laser was fabricated on a p-InP substrate. This laser can provide a peak pulse output of 0.8 W per facet with a stable lateral transverse mode oscillation and enables the fault location measurement of a single mode fibre cable over 20 km.

Buried heterostructure AlGaAs lasers on semi-insulating substrates

Buried heterostructure (BH) AlGaAs lasers were fabricated on Cr-doped semi-insulating substrates. Low threshold current (8 mA/μm stripe width for cavity length of 300 μm), a high differential quantum efficiency (55%), and stable transverse mode operation were realised.

GaAs-Al<inf>x</inf>Ga<inf>1-x</inf>As strip buried heterostructure lasers

A new laser structure, the strip buried heterostructure (SBH) laser, using an active strip on a low-loss waveguide is described, theoretically analyzed, and experimentally characterized under both pulsed and CW operations. The waveguiding properties and laser threshold conditions are analyzed using the effective refractive index approximation. The calculated results agree fairly well with measured results. Pulsed output powers as high as 400, 230, and 130 mW/mirror without AR coating have been obtained at "catastrophic" mirror failure for SBH lasers with 10, 5, and 3 μm strips, respectively. Throughout this entire current injection range, stable transverse mode operation and excellent linearity and symmetry in light-current characteristic from each mirror were obtained. Intermodulation products were measured for 5 μm strip SBH lasers. At an average power of 4 mW and modulation depth of 80 percent, the third-order component was about 48 dB below the fundamental. Excess noise above threshold was not present. For SBH lasers with efficient injection current confinement and active strip area of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">380 \times 10 \mu</tex> m, pulsed and CW current thresholds were about 74 and 85 mA, respectively. The average external quantum efficiency was about 45 percent. CW operation has been achieved at a heat-sink temperature as high as 115°C. The current threshold has an exponential variation with temperature exp ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T/T_{0}</tex> ) where <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T_{0} = 110</tex> K. For SBH lasers with strip widths <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\sim5 \mu</tex> m, stable fundamental mode oscillation in both transverse directions was observed up to 9 times threshold. Far-field beam divergences of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8-10\deg</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">26-30\deg</tex> were obtained in directions parallel and perpendicular to the junction plane, respectively. Single-longitudinal-mode operation up to twice threshold was obtained for SBH lasers with strip widths <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\lsim5 \mu</tex> m under both pulsed and CW operations. Relaxation oscillation and self-pulsation were not observed for SBH lasers with clean transverse modes in pulsed response up to current injection levels as high as <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4 \times I_{th}</tex> . For these particularly good diodes, self-pulsation was not observed before aging under CW operation in preliminary experiments. Aging studies have not yet been performed. Densely packed monolithic linear arrays of SBH lasers with center-to-center spacing of 15 μm were also studied. They exhibited similar laser characteristics as in single SBH lasers, but with increased maximum pulsed output power/mirror, approximately ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">310 \times N</tex> ) and ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">150 \times N</tex> ) mW for arrays with ∼10 and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\sim4 \mu</tex> m strips, respectively. <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</tex> is the number of lasers in the array. Spectral behavior of these arrays was also studied as a function of injection current and temperature.

OPERATION OF A LASER WITH A PLANAR RESONATOR AT HIGH PUMPING LEVELS

It is shown that the laser action in a resonator with plane-parallel mirrors is of single-mode nature if the pumping level is high. Stable transverse oscillation modes are characterized by waves which are generated near one edge of the resonator and travel at right angles to the laser axis.