Robert D. Burnham

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.

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.

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.

High power coupled multiple stripe quantum well injection lasers

Operation of a coupled multiple stripe quantum well injection laser array is described. The device emits up to 400 mW of continuous output power and 2.1 W of peak pulsed (75 ns) output power from an uncoated mirror facet. Its far‐field pattern is invariant to over three times threshold, and over 140 mW cw are coupled into a 100‐μm core 0.3‐numerical aperture (N.A.) optical fiber.

Longitudinal mode spectra of diode lasers

A theory is presented which explains the longitudinal mode spectra of diode lasers. The theory is based on spontaneous emission coupling into the longitudinal modes and the excellent agreement with experimental data for both gain guided and real refractive index waveguide diode lasers is obtained because of the more accurate and detailed modeling of the spontaneous emission coupling and the laser itself.

Analysis of grating-coupled radiation in GaAs:GaAlAs lasers and waveguides - II: Blazing effects

Grating-coupled radiation in lasers and waveguides is analyzed for trapezoidal-shaped grating teeth which includes all triangular shapes. A perturbation technique is used which involves calculating the modes in a geometry with an inhomogeneous refractive index profile in the grating region. Curves are presented for radiated power from traveling waves as a function of blazing angle, grating tooth height, refractive index, and grating period. It is shown that the ratio of power radiated into the outer media depends greatly on tooth shape and size. By judiciously selecting parameters this ratio can exceed 50:1.

Symmetrical and asymmetrical waveguiding in very narrow conducting stripe lasers

Two-dimensional waveguiding is analyzed in very narrow conducting stripe lasers. Relatively simple closed form analytic expressions are derived for modes with both symmetrical and asymmetrical lateral distributions of gain and real refractive index. We show that the calculated far-field radiation patterns agree with those measured only if substantial real refractive index antiguiding is introduced. At higher pumping levels the dual far-field peaks observed for symmetrical lasers operating in the lowest order (TE 00 ) mode are reproduced analytically by reducing the optical absorption in the modal wings. Highly asymmetrical far-field radiation patterns previously observed are also demonstrated to result from asymmetrical gain and refractive index variations. We conclude that measured very narrow stripe laser far-field radiation patterns can only occur if the real refractive index is significantly depressed in the region of maximum gain; that is, substantial antiguidance must be present.

Experimental realization of a resonant tunneling transistor

We report experimental realization of a three‐terminal negative differential resistance (NDR) device. As proposed by A. R. Bonnefoi, T. C. McGill, and R. D. Burnham [IEEE Electron. Dev. Lett. EDL‐6, 636 (1985)], the structure consists of a GaAs‐AlxGa1−xAs double‐barrier tunneling heterostructure, the current through which is controlled by an integrated vertical field‐effect transistor. We present results for two samples grown by metalorganic chemical vapor deposition. Both samples exhibit NDR in their source‐drain current‐voltage characteristics at 77 K, with peak‐to‐valley current ratios ranging between 3 and 5.3. One sample exhibits NDR at room temperature. The position and peak‐to‐valley current ratio of the NDR can be modulated by gate voltage. Due to asymmetry in the doping levels of the two GaAs cladding layers, resonant tunneling peaks occur at much larger voltages in reverse bias than in forward bias.

Low threshold, high efficiency Ga1−xAlxAs single quantum well visible diode lasers grown by metalorganic chemical vapor deposition

Laser threshold current density and emission wavelength were investigated for broad area single quantum well double heterostructure (SQW DH) Ga1−xAlxAs lasers grown by metalorganic chemical vapor deposition (MOCVD) under pulsed operation at room temperature. The shortest lasing emission wavelength was 7065 A. At that wavelength, the threshold current density was 1 kA/cm2 for a Fabry–Perot diode of 500‐μm cavity length and the external differential quantum efficiency was 48%. These values are significantly better than those previously reported for Ga1−xAlxAs DH lasers operating under similar conditions at the same wavelengths. We attribute the improved performance in part to the quantum size effect (active layer thickness 400– 600 A).