Two-dimensional Distributed Feedback Lasers Research Articles

Two-dimensional distributed feedback lasers with thermally-nanoimprinted perylenediimide-containing films

Two-dimensional (2D) distributed feedback (DFB) lasers with gratings imprinted by thermal nanoimprint lithography on the active film are reported. They show thresholds for lasing of ∼10 kW/cm2, similar to the most efficient imprinted DFB lasers reported; and long operational lifetimes (under ambient conditions) of ∼12 × 104 pump pulses. The key for their successful operation has been the selection of a highly efficient and stable dye, perylene orange (PDI-O), and a proper matrix to host it, the fluoro-modified thermoplastic resist mr-I7030R, which has enabled 2D imprinting while preserving the dye optical properties. The use of the UV-curable resist SU8 as an alternative matrix for PDI-O to be imprinted by combined nanoimprint and photolithography was also investigated, and was concluded to be unsuccessful due to severe photoluminescence quenching. By replacing PDI-O with Rhodamine 6G, lasers with reasonable thresholds, but with significantly inferior operational lifetimes in comparison to PDI-O/mr-I7030R devices, were obtained.

Review of recent progress of III-nitride nanowire lasers

One-dimensional compound semiconductor nanolasers, especially nanowire (NW)-based nanolasers utilizing III-nitride (AlGaInN) materials system, are an emerging and promising area of research. Significant achievements have been made in developing III-nitride NW lasers with emission wavelengths from the deep ultraviolet (UV) to the near-infrared spectral range. The types of lasers under investigation include Fabry-Pérot, photonic crystal, plasmonic, ring resonator, microstadium, random, polariton, and two-dimensional distributed feedback lasers. The lasing thresholds vary by several orders of magnitude, which are a direct consequence of differing NW dimensions, quality of the NWs, characteristics of NW cavities, and coupling with the substrate. For electrically injected, such as ultralow-threshold and continuous-wave III-nitride NW lasers that can operate at room temperature, the following obstacles remain: carrier loss mechanisms including defect-related nonradiative surface recombination, electron overflow, and poor hole transport; low radiative recombination efficiency and high surface recombination; poor thermal management; and highly resistive ohmic contacts on the p -layer. These obstacles must be overcome to fully realize the potential of these lasers.

Two-dimensional distributed feedback lasers based on static and dynamic Bragg structures**Reported at the Conference on ‘Laser Optics’, St. Petersburg, Russia, 2011.

In order to increase the output power of DFB lasers, we consider the possibility of using two-dimensional distributed feedback. Within the framework of this scheme, the feedback circuitincludes four partial wave fluxes propagating in mutually orthogonal directions, which makes it possible to provide coherent radiation from a spatially extended planar active medium characterised by large values of the Fresnel parameter. By analogy with the onedimensional distributed feedback, the wave coupling can be ensured by using both the structures with a periodically varying effectiverefractive index (static two-dimensional Bragg structures) and the gain modulation (photo-induced two-dimensional Bragg structures). Within the semiclassical approximation, the initial conditions andnonlinear dynamics of lasers with the above-described two-dimensional Bragg structures are analysed. Self-similarity conditions are found, allowing one to scale the laser parameters with increasing active region size, which is accompanied by an increase in the integratedoutput power.

Two-dimensional distributed feedback lasers with excitation of TE waves in the active medium

Two-dimensional Bragg resonators with the coupling of TE- and TM-polarised waves are proposed. The selective properties of such resonators are analysed. Within the semiclassical approach, the nonlinear dynamics of laser radiation with a two-dimensional (in the xy plane) distributed feedback is studied, at which TE-polarised waves, propagating in the ±z directions, are amplified in the active medium (in particular, based on quantum wells). The latter, on a two-dimensional Bragg structure, are scattered into TM-polarised waves propagating in the ±x directions. These partial wave flows do not interact with the active medium but provide the spatial radiation synchronisation. The conditions of the solution self-similarity are obtained with increasing the dimensions of the active medium and the corresponding increase in the integral output power. It is shown that when an additional end mirror is mounted, almost unidirectional radiation coupling can be realised.

Mode selection in two-dimensional Bragg resonators based on planar dielectric waveguides

Two-dimensional Bragg resonators based on planar dielectric waveguides are analysed. It is shown that the doubly periodic corrugation deposited on the dielectric surface in the form of two gratings with translational vectors directed perpendicular to each other ensures effective selection of modes along two coordinates at large Fresnel parameters. This result is obtained both by the method of coupled waves (geometrical optics approximation) and by the direct numerical simulations. Two-dimensional Bragg resonators make it possible to fabricate two-dimensional distributed feedback lasers and to provide generation of spatially coherent radiation in large-volume active media.

Improved operational lifetime of semiconducting polymer lasers by encapsulation

We report polymer distributed feedback lasers with dramatically extended operational lifetimes by using a simple encapsulation process. The lasers are configured as surface emitting, two-dimensional distributed feedback lasers based on the polymer poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene vinylene]. The microstructure is transferred to the polymer surface through solvent assisted micromolding. Once encapsulated, a 2500-fold improvement in lifetime is demonstrated under ambient conditions, compared to the unencapsulated device. A blueshift of the emission wavelength observed during operation is characterized by absorption and ellipsometry measurements and attributed to a change in effective index due to a loss of conjugation in the polymer.

Operating characteristics of a semiconducting polymer laser pumped by a microchip laser

We report the demonstration of a compact, all-solid-state polymer laser system featuring a microchip laser as the pump source. The laser was configured as a surface-emitting, two-dimensional distributed feedback laser, based on the conjugated polymer poly(2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene vinylene). Pulsed, band-edge lasing was observed at 636 nm above a threshold pump energy of 4 nJ. The laser exhibited an energy slope efficiency of 6.8%, with a maximum output energy of 1.12 nJ at a pump energy of 20.4 nJ. The output beam had an azimuthally polarized annular profile with a beam quality factor (M2) of 2.2, close to the theoretical value of the lowest-order Laguerre–Gaussian and Bessel–Gaussian annular modes. We explain the origin of the azimuthal polarization as due to a coherent combination of the resonant fields supported by the two gratings.

Two-dimensional rectangular lattice distributed feedback lasers: A coupled-mode analysis of TE guided modes

Two-dimensional rectangular lattice distributed feedback lasers in a waveguide geometry are described by a coupled-mode analysis of a scalar wave equation derived from a vector field for TE guided modes. A detailed analysis is provided for a two-dimensional grating which allows the method of separation of variables for the scalar wave equation so that the threshold conditions are described by those of two orthogonal one-dimensional gratings. We present the correct definitions of threshold gain and detuning of the two-dimensional distributed feedback laser, and also the optimum design conditions for the minimization of the threshold gain. It is found that there is an optimum structural angle for the given area and periods of the two-dimensional grating.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Two-dimensional distributed-feedback lasers and their applications

We report the operation of two-dimensional distributed-feedback (DFB) lasers in which periodic thickness variations exist in two orthogonal directions in the plane of the film. By using photoresist and chemical etching, two-dimensional gratings with periods of 0.635 and 4.34 μm are formed on fused silica substrates. For the gain medium, a polyurethane film doped with rhodamine 6G is used. Emission characteristics and potential applications of two-dimensional DFB lasers are discussed.