N. Finger

Analysis of TM-polarized DFB laser structures with metal surface gratings

An analysis of distributed feedback (DFB) laser structures with metallized surface grating structures in TM polarization is presented. The modal properties of these structures are described using coupled-mode theory where the coupling coefficients are derived from rigorously computed on-resonant Floquet-Bloch solutions of the waveguide grating problem. Based on this theory, first- and second-order DFB quantum cascade laser structures operating at a wavelength of 10 /spl mu/m are investigated numerically. We show that, utilizing a metal stripe grating structure, second-order laser structures are feasible showing efficient surface emission, whereas radiation into the substrate is strongly suppressed. The fraction of stimulated emission power being emitted via the surface can be as high as 17.5% whereas a low threshold gain of 20 cm/sup -1/ is maintained.

Analysis of metallized-grating coupled twin-waveguide structures

In this paper, we present an analysis of grating coupled twin-waveguide structures consisting of a semitransparent metal-low-index waveguide on top of a corrugated high-index laser waveguide. A rigorous Floquet analysis of TE modes is performed for trapezoid shaped gratings. Starting from on-resonant Floquet solutions, we establish a relation to simple coupled-mode equations yielding results, that show excellent agreement with the rigorous Floquet solutions. Grating coupled radiation plays a crucial role in the waveguide structures under consideration: when phase matching of the guided modes occurs, narrow-band resonant suppression of radiation loss with linewidths in the subnanometer regime can be achieved. The grating geometry has an important impact on these resonances, which is made evident by various numerical examples demonstrated in this paper.

Continuous-wave operation of distributed feedback AlAs/GaAs quantum cascade lasers

Summary form only given. Quantum cascade lasers QCLs are powerful light emitters in the mid infrared. For chemical sensing, single mode emission is advantageous. We fabricated first order distributed feedback lasers to achieve single mode emission. The emission wavelength is continuously tunable according to the temperature dependence of the effective refractive index, which shifts the Bragg wavelength. A rigorously on-resonant Floquet-Bloch analysis of the waveguide grating problem was used to design the grating geometry and the cladding layer thickness. The active material consists of 40 periods of an AlAs/GaAs chirped superlattice, grown by solid source molecular beam epitaxy. A double plasmon enhanced waveguide is used for vertical optical confinement while lateral electrical and optical confinement is achieved by deep etched ridges. The Bragg grating is defined by contact lithography and etched into the surface of the top cladding layer, thus avoiding the need of regrowth. The whole grating region is covered with gold, resulting in a large contact area. The lasers, with as cleaved facets, are soldered with In on Cu-plates (epilayer up) and mounted in a flow cryostat.

Wavelength-graded surface-emitting laser array with contradirectional surface-mode coupling

Summary form only. The wavelength division multiplexing (WDM) scheme is utilized to increase significantly the transmission rate of optical communication systems. Monolithic arrays of wavelength-graded laser diodes are considered as a compact choice for WDM light sources. Lasers in the visible regime are suitable to be used as emitters in optical short-range data transmission since the attenuation minimum of polymethylmethacrylate (PMMA) fibres lies near 650 nm. We have developed a wavelength-graded GaInP-AlGaInP surface-emitting laser array with horizontal cavities.

Analysis of surface-mode coupled semiconductor laser structures with adjustable emission wavelength

An analysis of semiconductor laser structures with adjustable single-mode emission based on a contradirectionally grating coupled twin-waveguide structure consisting of a semitransparent metal (or ITO)/low-index dielectric waveguide on top of a corrugated active laser waveguide is presented. A coupled mode theory, where the coupling coefficients are expressed in terms of field overlap integrals between the unperturbed fields and on-resonant Floquet-fields, is applied to describe the optical fields of the laser resonators with a high degree of accuracy, although the modulation of the refractive index in the grating region is large. At resonance between the laser mode and the surface mode the grating-coupled radiation losses show a sharp drop with a linewidth comparable to the longitudinal Fabry-Perot-mode spacing of the laser cavity, thus preferring a single longitudinal mode. Intermodal discrimination of up to 20 cm -1 and moderate threshold gain of ∼ 50 cm -1 can be obtained. Since the resonance wavelength depends on the optical thickness of the surface waveguide, a simple post-processing adjustment of the emission wavelength with a tuning range in excess of ∼ 15 nm can be achieved.

Quasi-single-mode surface-emitting laser diodes based on surface mode emission

First results from surface mode emitting (SME)-laser diodes utilizing a first-order grating are presented. The use of a first-order grating instead of a third-order grating strongly improves the radiation characteristics of surface emitting SME-laser diodes. Although a real single mode operation from SME-laser diodes is not yet achieved, the tunability of the main emission wavelength by changes of the waveguide thickness is clearly demonstrated. The crucial feature of the SME-technique is that it provides a high flexibility, when processing surface emitting laser diodes with desired radiation pattern and wavelength emission characteristics. These features are discussed to demonstrate the high application potential of the SME-laser diodes.