Circular Lasers Research Articles

Semiconductor circular ring lasers fabricated with the cryo-etching technique

GaAs-AlGaAs multiple quantum well semiconductor circular ring lasers with a /spl sigma/ shape were fabricated by using the deep UV laser-assisted cryo-etching technique. Most of the fabricated lasers had external quantum efficiencies of more than 18% which mere higher than similar devices previously reported. The modal spacing observed from the resonance spectrum near threshold was always several times that corresponding to the circular oscillation of the ring cavity. The observed modal spacing was quite consistent with the theoretical result based on a coupled-cavity model.

Low threshold room temperature pulsed and -57 degrees C CW operations of 1.3 mu m GaInAsP/InP circular planar buried heterostructure surface-emitting lasers

Room temperature pulsed lasing operation of a 1.3- mu m GaInAsP/InP vertical-cavity surface-emitting laser has been achieved by using an effective carrier confinement of circular planar buried heterostructure (CPBH) and high reflectivity SiO/sub 2//Si dielectric multilayer mirrors. The threshold current for a device having a nearly 12- mu m-diameter active region was 34 mA at 24 degrees C under pulsed operation. The optimized window cap structure reduces the series resistance to 6 approximately 15 Omega . Continuous wave lasing was also obtained up to -57 degrees C, and the threshold below -61 degrees C was still lower than 22 mA.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

In/sub x/Ga/sub 1-x/As-Al/sub y/Ga/sub 1-y/As-GaAs strained-layer quantum-well heterostructure circular ring lasers

The growth, processing, and optical characterization of a single Y-junction In/sub x/Ga/sub 1-x/As-Al/sub y/Ga/sub 1-y/As-GaAs strained-layer quantum-well heterostructure circular ring laser (6 mu m width, 11 approximately 251 mu m outer radius) are described. The circular ring lasers have been grown by metalorganic chemical vapor deposition, etched by SiCl/sub 4/ reactive ion etching, and planarized by polyimide. The dependences of laser threshold current density and peak emission wavelength (950 approximately 1015 nm) on outer radius are presented. The emission spectra show that the circular ring lasers lase mainly in high-order whispering gallery modes, with smaller outer radius ring lasers operating in low-order whispering gallery modes.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Linear theory of generalized circular free electron lasers

A linear theory of generalized circular free electron lasers (FEL) is presented. A relativistic electron beam rotates azimuthally under an axial magnetic field and/or a radial electric field, superimposed by an azimuthally periodic wiggler magnetic field in the radial direction. The characteristics of these circular FELs depend largely on the effective azimuthal inertia of the equilibrium circular motion. The electric field type, in which only a radial electric field force is applied to balance the centrifugal force, has the maximum growth rate among circular FELs. The growth rate of the magnetic field type, in which only an axial magnetic field is applied, is as high as that of the electric field for highly relativistic cases. In these two types, the weak pump regime found in conventional linear FELs is replaced by a negative mass instability regime. The crossed field type, in which both fields are applied to balance the centrifugal force, has a very small growth rate for highly relativistic cases.

Reproducible fabrication of AlGaAs/GaAs circular buried heterostructure (CBH) surface-emitting lasers with low thresholds

The fabrication process for circular buried-heterostructure surface-emitting lasers has been improved to increase the uniformity of the active region diameter. Circular mesas of approximately=8 mu m diameter can now be consistently prepared and low-threshold surface-emitting lasers (30-60 mA at room temperature pulsed conditions) are obtained.

Coupling loss theory of single-mode waveguide resonators

The past dozen years have seen several important publications on mode coupling losses in circular and rectangular waveguide lasers. It is frequently assumed that the laser mode is pure EH11 (quasi-TEM00). We note a flaw in the widely quoted Laguerre-Gaussian mode expansion method as it originally appeared and show how to reconcile it with later results. Also we summarize and try to remove several discrepancies in the published accounts of how the EH11 loss behaves for the popular near-Case I reflector (i.e., a plane mirror placed within a few guide widths of the guide aperture).

Off-Axial mode selection in solid-state lasers due to nonuniformities

It is shown that the nonuniformity of excitation produced in circular cross-section solid-state lasers due to the focusing of pump power leads to a coupling of certain modes and reduction in their threshold of oscillation. These modes correspond in plane-wave representation to simple closed paths in the cavity. The off-axial radiation observed in the form of rings by Collins and Giordmaine and others is explained on the basis of the theory.