Absorptive Grating Research Articles

Two-dimensional plasmon induced grating in a double V-type quantum system

We theoretically study a two-dimensional electromagnetically induced phase grating in a four-level quantum system located near plasmonic metamaterials consisting of a periodic two-dimensional array of metal-coated dielectric nanospheres. The four-level quantum system interacts with a weak-probe laser field and a strong coherent coupling field with a standing-wave pattern. In the presence of plasmonic metamaterials the quantum system becomes sensitive to the relative phase between applied light. Therefore, the linear absorption and Kerr nonlinearity of the medium become phase dependent. Here, due to the standing-wave pattern of coupling light, an absorptive grating or phase grating can be formed in the quantum system. In our proposed model, we show that the diffraction efficiencies of the grating are related to the relative phase between applied fields, when the quantum system is located at different distances from plasmonic metamaterials.

Analysis of Absorptive Nickel Grating with a Dielectric Layer

Background: Nickel grating absorber has been studied and shows good absorption property in the visible band. In order to further improve the absorption performance, reflection should be reduced, and anti-reflection layer should be added upon or under the gratings. Method: In this paper, the dielectric layer is added between and upon the nickel gratings. Equivalent medium theory is used to analyze the role of dielectric layer on absorption mechanism of nickel gratings. photoresist is used to illustrate the possible practical usage of the proposed method. Results: Absorption efficiency of TM (transverse magnetic) and TE (transverse electric) polarization show growing trend with the increase of refractive index of the dielectric material. PMMA and TU7 are chosen as the dielectric material. The simulation results show that TM absorption reduced slightly in visible band, and improved by up to 86% in the near infrared region. TE absorption shows up to 79% improvement in the whole visible to near infrared waveband. Conclusion: Nickel grating based broadband absorber is analyzed in this paper. Dielectric layer is added upon the gratings, and act as the anti-reflection layer. The refractive index and layer thickness is analyzed by using equivalent medium theory. Dielectric material that has high refractive index is more desired. The designed nickel grating shows high absorption property from 450nm to 800nm for both TM and TE polarization.

Wavelength detuning of DFB laser incorporating compressively strained MQW and automatically buried absorptive grating

The thermal effect on wavelength detuning of the uncooled packaged complex (loss)-coupled distributed feedback (DFB) edge emitting 1.55-μm laser has been investigated for wide temperature range of −40°C to 85°C. The InGaAsP/InP laser diode incorporates a thin 1% compressively strained multiple quantum well (MQW) structure as well as an automatically buried InAsP buried layer in the grating region to simplify the steps of the epitaxial growth during the fabrication processes. As an experimental result, it has been found that the wavelength detuning between the gain medium (Fabry–Perot cavity) and the Bragg grating (for distributed feedback) should be optimized around −10nm at the room temperature to accommodate their differently shifting center wavelengths for temperature changes where the gain profile changes faster than DFB wavelength for predicting a single mode operation in a wide temperature range. Based on the measured optical characteristics (threshold current, slope efficiency) of the fabricated diode laser, the characteristic temperature was estimated to be approximately 46K and the slope efficiency ratio between room and high temperatures was around 70%.

EFFECT OF PSEUDOMORPHIC MULTIPLE QUANTUM WELL LAYERS ON CHARACTERISTICS OF UNCOOLED ELECTROLUMINESCENT DIODE

We have fabricated and characterized the uncooled light emitting device having a pseudomorphic structure of multiple quantum wells. The effect of numbers of compressively strained quantum well layers on the semiconductor diode laser characteristics was experimentally demonstrated, depending on room and high temperatures. In addition to the automatically embedded absorptive grating which can reduce the epitaxial growth step, the laser performance can be optimized for both threshold current and differential slope efficiency when the quantum well numbers are reduced to five layers for optical communication systems.

Erratum for ‘High device yield and performance of InGaAsP MQW DFB lasers with absorptive grating’

Erratum for ‘High device yield and performance of InGaAsP MQW DFB lasers with absorptive grating’

High device yield and performance of InGaAsP MQW DFB lasers with absorptive grating

AR/HR-coated, loss-coupled, InGaAsP multiple quantum well distributed feedback lasers emitting at 1.55 µm are reported, indicating a high device yield of ∼66% for the quarter of a two-inch wafer and a good reliability as long as 5000 h operation at 85°C with a constant power of 5 mW. The high device yield was achieved by the automatically buried InAsP absorptive grating formed during the heat-up process on InP corrugations and the uniform surface-facing upward wet chemical etching process.

Resonant atomic diffraction: real versus imaginary potentials

In 1997, Zeilinger's group claimed to have observed atomic diffraction from a purely imaginary potential, that is an absorptive grating, made with resonant light waves. In a 1990 summary of their previous research, Kazantsev et al. stated that the diffraction of atoms from resonant light waves is due to a real potential (a resonant phase grating). We resolve this conflict and argue that absorptive gratings of light do not exist for atoms. Analysis of our metastable argon experiments with resonant 801.7 nm light supports this view. We discuss why these issues are important for understanding transverse momentum conservation in diffraction processes.

Contribution of Absorptive and Refractive Gratings to Mixed Holograms Using Xanthene-Dye-Doped Films

The contribution of absorptive and refractive gratings to a mixed hologram is investigated by means of two-wave coupling technique by moving a hologram. Polyvinyl alcohol films doped with xanthene-dyes such as erythrosin B,eosin Y, uranin and fluorescein which absorb an argon-ion laser light of 488 nm and 515 nm are used as hologram recording materials in our experiment. A simple model of the two-level one-step photo-bleaching well explains the growth of an absorptive grating and the refractive index and also the working wavelength dependence of growth of the refractive grating in the xanthene-dye-doped films.

Atomic focusing and near field imaging: A combination for producing small-period nanostructures

We present a scheme which combines focusing of atomic de Broglie waves by standing light waves and fractional Talbot imaging to produce nanostructures. Masking of the incoming atomic wave by an absorptive grating is used to eliminate atom-optical aberrations that would otherwise wash out the fractional Talbot images. The scheme allows the creation of structures of very small feature size as well as small period.

High Output Power Operation of a 1.3 µm Gain-Coupled Distributed Feedback Laser with Narrow Spectral Linewidth

High output power and narrow spectral linewidth operation of 1.3 µm gain-coupled distributed feedback (DFB) lasers with InAsP buried absorptive grating is reported. In this study, we have investigated the effect of the thickness of a separate-confinement-heterostructure (SCH) layer on the single-mode stability and the spectral-linewidth property of 1.3 µm gain-coupled DFB lasers. As a result, we clarified that decreasing the thickness of the SCH layer led to stable single-mode operation at high output power and the reduction of the product of the spectral linewidth and the output power. For the fabricated gain-coupled DFB laser, a record high output power of 230 mW and a minimum spectral linewidth of 100 kHz at an output power of 150 mW were realized.

High output-power and narrow spectral-linewidth operation of a 1.3-/spl mu/m gain-coupled DFB laser with InAsP buried absorptive grating

High output-power and narrow spectral-linewidth operation of 1.3-/spl mu/m gain-coupled distributed feedback lasers with grating are reported. The fabricated output power of 230 mW and a linewidth of 100 kHz by reducing optical confinement in multiple quantum wells to improve the single-mode stability at high output-power operation.

Influence of standing waves on DFB lasers including saturable absorptive gratings

The influence of standing waves on the performance of distributed feedback (DFB) lasers is investigated, whereby local changes of the wavenumber as induced by gain compression or inhomogeneous saturation of an absorptive grating are incorporated into the coupled wave equations. With the help of this model, it is shown that gain compression ultimatively limits the maximum output power for monomode operation. As compared to in-phase complex-coupled lasers, it is shown that the worse monomode capability of antiphase complex-coupled lasers is related to the better stability properties of these lasers. Additionally, a characteristic interaction between the saturable absorptive grating and the optical field is found, which furthermore reduces the maximum monomode output power of antiphase complex-coupled lasers with saturable absorptive gratings.

Measurements of photorefractive and absorptive gratings in GaAs:EL2 and their use in extracting material parameters

Simultaneous measurements of the photorefractive and the absorptive grating gain components in GaAs:EL2 are made and are shown to display qualitative behavior consistent with linearized solutions of a two-carrier rate equation model. These two components, together with the linear absorption coefficient, permit determination of four independent material parameters, e.g., the ionized and the nonionized EL2 densities, the hole photoionization cross section (σh), and the electro-optic coefficient (r41). Data obtained at optical wavelengths of 0.96 and 1.06 µm indicate that σh and r41 are larger than published values.

High-power, wide-temperature range operation of 1.3-μm gain-coupled DFB lasers with automatically buried InAsP absorptive grating

DFB lasers operating at 1.3 μm with gain-coupling structure show single-mode operation over a wide temperature range of -20/spl sim/85/spl deg/C and up to a high power of 130 mW. These lasers have InAsP absorptive grating, which can be formed by a substantially simplified fabrication process, involving annealing a corrugated InP substrate in an atmosphere of mixed arsine and phosphine.

Coupling coefficients of gain-coupled distributedfeedback lasers with absorptive grating

An effective coupling coefficient is introduced for gain-coupled distributed feedback lasers with absorptive grating. When radiation and other partial wave coupling effects are considered, the effective coupling coefficient will change significantly. In some cases, it will become real, although both loss and index coupling are presented.

New Structure of 1.3 µm Strained-Layer Multi-Quantum Well Complex-Coupled Distributed Feedback Lasers

A new structure of 1.3 µm strained-layer multi-quantum well (MQW) complex-coupled distributed feedback lasers having an InAsP absorptive grating is demonstrated. In this structure, the InAsP absorptive grating and the strained-layer MQW active layer can be fabricated by a metalorganic vapor phase epitaxy process involving only one step. Furthermore, the fabricated laser has a low threshold current (16.8 mA) and a high efficiency (0.45 mW/mA).

Dynamics of gain-switching operation in gain-coupled distributed-feedback semiconductor lasers with absorptive grating

Very-low-chirping optical short-pulse generation in gain-coupled (GC) distributed-feedback (DFB) semiconductor lasers of absorptive-grating type is investigated. First, we have observed time-resolved spectra of gain-switched optical pulses. The GC DFB laser has shown a very small and characteristic lasing wavelength shift with time. Moreover, we have noticed uncommon bias-dependence of the pulse width and pulse tailing at high bias regime. Then, we have examined spontaneous emission from the grating to probe carrier generation by the optical pulse. Next, we have conducted a rate equation analysis to understand the uncommon pulse dynamics of the GC DFB laser by taking the carrier generation in the grating into account, consequently, all the anomalies observed in the GC DFB laser have successfully been explained. Finally, by making use of the analysis, we have shown a guideline to further improve the pulse shape without sacrificing the low chirping property. >

Gain-coupled DFB lasers with atitanium surface Bragg grating

The improved performance of gain-coupled DFB lasers incorporating a titanium surface Bragg grating and a strained layer multiquantum well active region for operation at 1.55 mu m is presented. Besides the essentially simplified fabrication process, the incorporation of the metallic, absorptive grating yields stable singlemode operation with a high sidemode suppression.

Origin of low dynamic wavelength chirp in shortoptical pulsesfrom absorptive-grating gain-coupled distributed feedback semiconductor lasers

The instantaneous wavelength shift in gain-switched short optical pulses from absorptive-grating gain-coupled distributed feedback semiconductor lasers showed unusual behaviour which resulted in much smaller chirping than that in conventional lasers. Measurements of spontaneous emission from the absorptive grating layer indicate carrier accumulation in that layer. The origin of the low chirping has been attributed to the fact that the index increase due to carrier depletion in the active layer is compensated for by an index decrease due to carrier accumulation in the grating layer.

Advanced 1.55 µm Quantum-Well GaInAlAs Laser Diodes with Enhanced Performance

The fabrication and characteristics of advanced 1.55 µ m quantum-well GaInAlAs laser diodes are presented. The strained layer laser structures were grown by metal organic vapor phase (MOVPE). By employing InP-cladding layers and an etch-stop layer, ridge-waveguide lasers with different longitudinal resonator types were processed by conventional chip technology. The following characteristics have been obtained, which mostly represent best values for 1.55 µ m GaInAlAs laser diodes: for Fabry-Perot (FP) lasers, cw operation at 130°C and a characteristic temperature of 95 K were observed; maximum output power was 46 mW; and the 3 dB bandwidth as high as 17 GHz. Gain-coupled distributed feedback (DFB) lasers with an absorptive grating show a single-mode yield about 75%, their 3 dB bandwidth being 11 GHz. Two-section gain-coupled DFB devices were continuously tunable over 3 nm. For negatively detuned index-coupled DFB devices an ultrahigh 3 dB bandwidth of 18.5 GHz was measured. All these characteristics are comparable to those of 1.55 µ m InGaAsP ridge-waveguide lasers. We report for the first time, the broad-area folded-cavity surface-emitting lasers using GaInAlAs which exhibit a threshold current density of 2 kA/cm2.