Donald R. Scifres

Effect of external reflectors on longitudinal modes of distributed feedback lasers

The effect of external reflectors on longitudinal modes of distributed feedback (DFB) lasers is analyzed. The general case of dissimilar reflectors arbitrarily located relative to the phase of the DFB structure is considered. An eigenvalue equation for the propagation constants is derived and solved numerically for a variety of practical cases. Longitudinal mode thresholds, wavelengths, separations, and field distributions are obtained for GaAs lasers and for DFB lasers with a single reflector. It is shown that these quantities are very sensitive not only to the relative strength of the discrete and DFB, but also to the relative phases. Quite asymmetric transmitted powers are shown to occur under a variety of circumstances.

Coupling coefficients for distributed feedback single- and double-heterostructure diode lasers

We compute coupling coefficients for TE modes as a function of tooth height, active layer thickness, and Bragg scattering order in single-heterostructure (SH) and double-hetetostructute (DH) distributed feedback (DFB) diode lasers for a variety of corrugation shapes. In particular, equations for rectangular, sinusoidal, and triangular shapes are evaluated; the last both in the symmetric and saw-tooth cases. It is shown that the coupling coefficient for rectangular and sawtooth gratings decreases much less rapidly with increasing Bragg order than do the sinusoidal and symmetric triangular.

Coupled wave analysis of DFB and DBR lasers

The familiar coupled mode equations are extended in a self-consistent fashion to include radiation and other partial wave coupling effects in distributed feedback (DFB) and distributed Bragg reflector (DBR) lasers, as well as orthogonal radiating couplers. This general formulation takes into account the joint interaction of the two coherent contradirectional guided waves with arbitrarily shaped gratings. In addition to the modified coupled mode equations, which contain added constants characterizing the interactions, expressions for radiated waves are also obtained. A particular waveguide geometry is studied in detail. The interaction constants are evaluated for all Bragg orders up to the fourth and various blazing angles. Then the equations are solved for both a DBR and DFB laser. In the former case it is shown that the reflection is smaller than that computed without the interaction constants. Furthermore, reflection is asymmetrical relative to the Bragg condition. The DFB laser is shown to have an asymmetrical longitudinal mode structure even for symmetrical boundary conditions and to have only slightly higher thresholds than previously calculated.

Analysis of grating-coupled radiation in GaAs:GaAlAs lasers and waveguides - I

Grating-coupled radiation in GaAs:GaAlAs lasers and waveguides is analyzed. A general formulation is developed for arbitrary-shaped gratings which need not be small in size. Two methods are used to solve the resulting equations in the case of rectangular-shaped gratings. The first is a perturbation technique and the second is iterative in nature. The iterative procedure converges to a numerical exact solution in many cases of practical interest and indicates that the perturbation results are quite accurate. Curves are presented for radiated power from traveling waves as a function of grating tooth height, tooth width, refractive index, waveguide thickness, and period for rectangular gratings in heterostructure waveguiding geometries. It is shown that radiation is not a monotonically increasing function of tooth height, but rather maxima occur when the teeth are half the optical wavelength in the material. Also, in particular geometries with an air:GaAs grating interface, radiated power of a mode can exceed 100 cm-1.

Distributed‐feedback single heterojunction GaAs diode laser

Laser operation utilizing distributed feedback (DFB) in single heterojunction (SH) GaAs/GaAlAs diodes is reported. Laser wavelengths ranging from 8430 to 8560 A were observed in various samples depending on grating period. The threshold current densities required were comparable to those of normal SH diodes.

Experimental and analytic studies of coupled multiple stripe diode lasers

Experimental and analytic studies of coupled multiple stripe (CMS) phase-locked, room-temperature diode lasers are reported. Such devices generate high-power well-collimated beams, which potentially may be electronically scanned in the manner of phased array radar. For the tested devices with ten conducting 3 μm stripe contacts on centers separated by D and coupled by curved waveguide sections, data from four stripe geometries with D ranging from 10 μm to 27.4 μm are compared and overall optimal characteristics occur for D = 10 \mu m. In that case, threshold current densities are comparable to solid area lasers, differential quantum efficiency is approximately 60 percent, and maximum observed pulsed power per facet is on the order of 1 W.

Operating characteristics of a high-power monolithically integrated flared amplifier master oscillator power amplifier

High-power monolithically integrated flared amplifier master oscillator power amplifiers (MFA-MOPAs) that operate up to 2 W continuous wave (CW) in a single diffraction-limited lobe have been fabricated. The spectral output of the MFA-MOPA is single longitudinal mode with a side-mode suppression ratio greater than 25 dB. Several operating characteristics of the MFA-MOPA, including the beam astigmatism, amplifier gain saturation, linewidth, far-field extinction ratio, and beam quality metrics are investigated and discussed. >

Advances in diode laser pumps

Diode laser pumps for solid-state lasers are reviewed with special emphasis on current and future capabilities. Included are discussions of pumps for CW (continuous-wave) and quasi-CW operation, and end- and side-pumping configurations. >

Wavelength modification of AlxGa1−xAs quantum well heterostructure lasers by layer interdiffusion

Data are presented showing that thermal annealing (875–‐900 °C) can be used to modify the wavelength of a photopumped, low threshold AlxGa1−xAs quantum well heterostructure (QWH) laser from ∼8200 to ∼7300 A with a threshold change from 150 to 1700 W/cm2. The energy levels of the annealed single quantum well crystal are approximated by fitting a modified Poschl–Teller potential to the band‐edge profile as modified by layer (Al–Ga) interdiffusion. The layer (Al–Ga) interdiffusion coefficient (at 875 °C) is found to be smaller, by a factor of 3–4, than previously reported. We suggest that this is due to the high quality, i.e., low defect density, of the ultralow threshold QWH crystals of this work.

Etched buried heterostructure GaAs/GaAlAs injection lasers

An injection laser is described in which a semicircular GaAs active region is completely surrounded by Ga1−xAlxAs by using selective etching and a single liquid‐phase epitaxial growth.The active region dimensions can be made much more symmetric than those obtained with conventional stripe geometry lasers resulting in improved optical characteristics and low room‐temperature threshold currents.