Semiconductor Gratings Research Articles

High-power distributed feedback lasers based on InP corrugated sidewalls at λ∼2 μm

We report a high-power single-mode InP-based 2 μm distributed feedback (DFB) laser with a second-order buried grating and corrugated sidewalls. A second-order semiconductor grating is used for in-plane feedback and vertical out-coupling. The corrugated sidewalls are used to eliminate higher-order transverse modes. For the DFB laser with a 2 mm long cavity and 15 μm wide ridge, the maximum continuous-wave edge-emitting and surface-emitting single-mode powers at 300 K are up to 81 and 42 mW, respectively. A single-lobed far-field radiation pattern with a low divergence angle of approximately 8.6° is achieved by a device with a ridge width of 15 μm. The single-longitudinal-mode emission wavelength of the fabricated laser can be adjusted from 2003.8 nm at 288 K to 2006.9 nm at 313 K without any mode hopping. Robust single-mode emission with a side-mode suppression ratio of 30 dB is achieved under all injection currents and temperature conditions.

Enhanced light absorption in Tamm metasurface with a bound state in the continuum

We consider light absorption in a germanium grating placed on top of photonic-crystalline substrate. Such a system supports an optical Tamm state decoupled from the continuous spectrum with its frequency within the photonic band gap. We have demonstrated that application of the Tamm state makes in possible to engineer extremely narrow absorber which provides a 100 % absorption in a semiconductor grating in the critical coupling regime. The proposed design may be used at both normal and oblique incidence at the telecom wavelength.

МЕТОД ВИЗНАЧЕННЯ ДІЕЛЕКТРИЧНОЇ ПРОНИКНОСТІ ДІЕЛЕКТРИКІВ У ММ ТА СУБММ ДІАПАЗОНАХ ДОВЖИН ХВИЛЬ НА ПІДСТАВІ ВИМІРЮВАННЯ ПАРАМЕТРІВ ПЛАЗМОН-ПОЛЯРИТОННОГО РЕЗОНАНСУ

МЕТОД ВИЗНАЧЕННЯ ДІЕЛЕКТРИЧНОЇ ПРОНИКНОСТІ ДІЕЛЕКТРИКІВ У ММ ТА СУБММ ДІАПАЗОНАХ ДОВЖИН ХВИЛЬ НА ПІДСТАВІ ВИМІРЮВАННЯ ПАРАМЕТРІВ ПЛАЗМОН-ПОЛЯРИТОННОГО РЕЗОНАНСУ

Laser-induced gratings in Ag3AsS3 semiconductors

We demonstrated experimentally an opportunity to form space grating patterns in Ag3AsS3 semiconductor crystals under an influence of coherent femtosecond (195 fs) laser beams. The observation of the laser stimulated gratings has been performed using a cw He–Ne laser with power about 15 mW at 1150 nm wavelength. The photoinducing femtosecond laser with pulse duration about 190 fs and frequency 65 MHz bandpass has been used in the two-beam coherent regime at wavelength 1045 nm. The set of dichroic mirrors, polarizers, and lenses have been applied to form two space-separated beams, which interact with the studied Ag3AsS3 trigonal single crystals. The treatment has been performed during additionally applied dc-electrical strength equal to about 8 kV/cm with a frequency about 20 kHz directed perpendicularly to the optical axis. The monitoring of the photo-thermal effects and photo-destruction have been done using the optical fiber spectrometer Ocean Optics with spectral resolution 1 nm.

Features of Light Transmission and Stark Effect in a Plasmonic Nanostructure Comprising Organic Semiconductor and Subwavelength Aluminum Grating

Specific features of light transmission and electroabsorption in a plasmonic nanostructure with organic semiconductor (zinc phthalocyanine, ZnPc) and subwavelength aluminum grating (AlGr) have been experimentally investigated. The glass–AlGr–ZnPc–Al nanostructure was prepared using layer-by-layer deposition. First, only a part of the structure has been analyzed to check the grating quality. After deposition of an organic semiconductor (ZnPc) layer on the grating, the transmission of TE and TM polarized light through AlGr and ZnPc layers upon excitation of plasmon resonances has been studied. Afterwards, a semitransparent aluminum layer has been deposited on the ZnPc layer (an additional electrode for measuring the electroabsorption effect). For TM polarized light, a multiple increase in the electroabsorption effect has been found (in comparison with a structure without subwavelength grating). This result can be explained by the Stark effect on exciton transitions and the presence of two cavities in the structure, which are related to the excitation of plasmonic states and the Fabry–Perot effect between aluminum electrodes. The presence of the cavities leads to a decrease in the group velocity of light and, accordingly, increases the density of exciton states, which are characterized by a large difference between polarizabilities in the excited and ground states.

Ultra-broadband and wide-angle perfect absorber based on composite metal–semiconductor grating

In this letter, we present an ultra-broadband and wide-angle perfect absorber based on composite Ge–Ni grating. Near perfect absorption above 90% is achieved in a wide frequency range from 150 nm to 4200 nm, which covers almost the full spectrum of solar radiation. The absorption keeps robust in a wide range of incident angle from 0º to 60º. The upper triangle Ge grating works as an antireflection coating. The lower Ni grating works as a reflector and an effective energy trapper. The guided modes inside Ge grating are excited due to reflection of the lower Ni grating surface. In longer wavelength band, gap surface plasmons (GSPs) in the Ni grating are excited and couple with the guided modes inside the Ge grating. The coupled modes extend the perfect absorption band to the near-infrared region (150 nm–4200 nm). This design has potential application in photovoltaic devices and thermal emitters.

Accelerating space-charge gratings in wide-bandgap semiconductors

The excitation of the non-steady-state photoelectromotive force and two-wave mixing signals is theoretically investigated for the case of uniformly accelerated motion of the recording light pattern. Such illumination is usually created by the linear frequency modulation of the interfering light beams. For the both effects we predict the pulsed response arising at the moments, when the velocities of the interference pattern and space-charge wave coincide. The application of the effects in laser Doppler velocimeters and accelerometers is discussed.

Broadband THz radiation through tapered semiconductor gratings on high-index substrate

We numerically demonstrate an extraordinary optical transmission (EOT) through semiconductor gratings with plasmonic properties on a high-index substrate over a broad terahertz (THz) bandwidth at the plasmonic Brewster channel. The THz EOT is due to impedance matching, an inherently non-resonant mechanism, at the grating entrance and exit faces, which are periodically carved with tapered slits. The optimal grating geometry provides a transmission of over 85% over a broad 0.2–1.0 THz bandwidth at a Brewster angle of incidence of 75°. In addition, we introduce a perfect THz absorber with low-loss and metal-free properties over a broad operating bandwidth based on the plasmonic Brewster transmission concept.

Highly efficient semiconductor grating structure for SOI optical circuits

This paper explores high efficiency of semiconductor grating structure at wavelength, 1550nm for silicon on insulator (SOI) optical circuits. Here semiconductor grating structure is realized by the combination of silicon and compound semiconductor materials, where compound semiconductor gratings are envisaged by indium phosphide, Al80Ga20As and Al42Ga58As. Different types of losses in terms of absorption, reflection and diffraction including polarization are cogitated to investigate the efficiency of grating SOI structure at wavelength, 1550nm. Interestingly, the absorption loss of above semiconductor grating is found to be zero at the above wavelength. Also the simulation was accomplished using plane wave expansion method, which leads to zero reflectance for the aforementioned structures at same wavelength. Simulation is also made for diffraction and polarization losses of above three semiconductor grating SOI structures. Simulation results reveal that diffraction efficiency is 1, (diffraction loss is zero) with respect to detune from Bragg’s angle which ranges from −12° to +12°. Additionally, the proposed structures encountered polarization losses. Present simulation results showed that polarization efficiency is more than 90% (polarization loss is less than 10%)in silicon −indium phosphide (Si-InP),silicon-Al80Ga20As (Si-Al80Ga20As) and silicon – Al42Ga58As (Si-Al42Ga58As) grating SOI structures with respect to same deviation. Since absorption, reflection and diffraction losses are zero, the overall transmitted efficiency depends on polarization efficiency and finally, with the combination of both absorption, reflection,diffraction and polarization loss,it is inferred that overall transmitted efficiency of semiconductor grating SOI structure is more than 90% with respect to same angle.

Laterally coupled distributed feedback lasers emitting at 2 μm with quantum dash active region and high-duty-cycle etched semiconductor gratings

Single-mode diode lasers on an InP(001) substrate have been developed using InAs/In0.53Ga0.47As quantum dash (Qdash) active regions and etched lateral Bragg gratings. The lasers have been designed to operate at wavelengths near 2 μm and exhibit a threshold current of 65 mA for a 600 μm long cavity, and a room temperature continuous wave output power per facet >5 mW. Using our novel growth approach based on the low ternary In0.53Ga0.47As barriers, we also demonstrate ridge-waveguide lasers emitting up to 2.1 μm and underline the possibilities for further pushing the emission wavelength out towards longer wavelengths with this material system. By introducing experimentally the concept of high-duty-cycle lateral Bragg gratings, a side mode suppression ratio of >37 dB has been achieved, owing to an appreciably increased grating coupling coefficient of κ ∼ 40 cm−1. These laterally coupled distributed feedback (LC-DFB) lasers combine the advantage of high and well-controlled coupling coefficients achieved in conventional DFB lasers, with the regrowth-free fabrication process of lateral gratings, and exhibit substantially lower optical losses compared to the conventional metal-based LC-DFB lasers.

Optically Induced Space-charge and Conductivity Gratings in Wide-bandgap Semiconductors

We report optical excitation of space-charge and conductivity gratings in wide-bandgap semiconductors. The approach is based on the illumination of semiconductor material with an oscillating interference pattern formed of two light waves, one of which is phase modulated with frequency ω. The non-steady-state photocurrent flowing through the short-circuited semiconductor is the measurable quantity in this technique. The alternating current results from the periodic relative shifts of the photoconductivity and space charge electric field gratings which arise in the volume of the crystal under illumination. The experiments are carried out in β-Ga2O3 crystal and the main parameters of the photoinduced carriers are determined.

Angle‐Insensitive and CMOS‐Compatible Subwavelength Color Printing

Photonic nanostructures for a wide-angle and complementary metal-oxide semiconductor-compatible structural color printing scheme exploiting strong resonance effects in ultrathin subwavelength semiconductor gratings are demonstrated. The proposed structures create distinctive colors with great homogeneity and high color saturation, easily tuned by varying a width of the subwavelength gratings, thereby enabling individual color pixels to be patterned via one-step process.

Surface plasmon-polariton resonance at diffraction of THz radiation on semiconductor gratings

Resonance diffraction of THz hidrogen cyanide laser radiation on a semiconductor (InSb) grating is studied both experimentally and theoretically. The specular reflectivity suppression due to the resonance excitation of the THz surface plasmon-polariton is observed on a pure semiconductor grating and on semiconductor gratings covered with a thin dielectric layer. The dielectric coating of the grating results in the resonance shift and widening depending both on the layer thickness and dielectric properties. A simple analytical theory of the resonance diffraction on rather shallow gratings covered with a dielectric layer is presented, and the results are in a good accordance with the experimental data. Analytical expressions for the resonance shift and broadening are essential for the resonance properties understanding and useful for sensing data interpretation of the agents deposited on the grating surface.

Almost-total absorption of light in thin, biperiodic, weakly-absorbing semiconductor gratings.

We consider the design of optical systems capable of providing near 100% absorption of visible light, consisting of a structured thin layer of a weakly absorbing semiconductor placed on top of a dielectric spacer layer and a metallic mirror layer. We generalise a system recently studied semi-analytically and experimentally by Stürmberg et al [Optica 3, 556 2016] which incorporated a grating layer of antimony sulphide and delivered high, narrow-band absorptance of normally-incident light for a single polarisation. We demonstrate that bi-periodic gratings can be optimised to deliver near-perfect absorptance of unpolarised light in the system, and comment on the wavelength and angular ranges over which the absorptance remains near 100%. We show that the properties of the systems studied depend on the interaction of multiple modes, and cannot be accurately modelled within the quasistatic approximation.

Total absorption of visible light in ultrathin weakly absorbing semiconductor gratings

The perfect absorption of light in subwavelength thickness layers generally relies on exotic materials, metamaterials, or thick metallic gratings. Here we demonstrate that total light absorption can be achieved in ultrathin gratings composed of conventional materials, including relatively weakly absorbing semiconductors, which are compatible with optoelectronic applications such as photodetectors and optical modulators. We fabricate a 41 nm thick antimony sulphide grating structure that has a measured absorptance of A=99.3% at a visible wavelength of 591 nm, in excellent agreement with theory. We infer that the absorption within the grating is A=98.7%, with only A=0.6% within the silver mirror. A planar reference sample absorbs A=7.7% at this wavelength.

Illumination artifacts in hyper-NA vector imaging

Off-axis polarized monopole illumination is applied to a hyper-numerical-aperture (NA) (NA>1) microscopic system. Illumination artifacts due to vector effects are observed, which are asymmetric and depend on illumination conditions. A model based on rigorous coupled wave theory is used to simulate image profiles for dielectric, semiconductor, and metal gratings with different monopole locations and polarization states. A solid immersion lens microscope is used to image different types of samples including MoSi photomask, patterned silicon wafer, and chrome photomask. The experimental images are in good agreement with simulation results.

All optical Flip-Flop based on a nonlinear DFB semiconductor laser: Theoretical study

A new design of an all optical Flip-Flop is proposed. It consists of a nonlinear distributed feedback (DFB) laser. The wave guiding layer of the DFB laser consists of linear grating section followed by a nonlinear one, and both sections are separated by a phase shift section. In the OFF-state, the real part of the refractive index in the wave guiding layer forms a Bragg grating. In the ON-state, it forms a Bragg grating with a phase shift section. Optical gain is achieved by current injection in the semiconductor active layer. Nonlinearity in the nonlinear layers of the semiconductor grating was achieved by direct absorption at the edge of the absorption band (Urbach tail). Numerical simulation shows that the device switches in a nanosecond time scale.

Microcavity polaritonlike dispersion doublet in resonant Bragg gratings

Periodic structures resonantly coupled to excitonic media allow the existence of extra intragap modes ('Braggoritons'), due to the coupling between Bragg photon modes and 3D bulk excitons. This induces unique and unexplored dispersive features, which can be tailored by properly designing the photonic bandgap around the exciton resonance. We report that one-dimensional Braggoritons realized with semiconductor gratings have the ability to mimic the dispersion of quantum-well microcavity polaritons. This will allow the observation of new nonlinear phenomena, such as slow-light-enhanced nonlinear propagation and an efficient parametric scattering at two 'magic frequencies'.

Controlling enhanced transmission through semiconductor gratings with subwavelength slits by a magnetic field: Numerical and analytical results

We exploit the change in the permittivity tensor of a conductor by a static magnetic field as a handle to control enhanced transmission in a semiconductor grating. Numerically, results of rigorous coupled-wave analysis (RCWA) incorporating the tensorial permittivity reveal that zeroth order transmission peaks at normal incidence can be shifted by about 15% to longer wavelengths and the peak values of transmission readily doubled when a moderate magnetic field is applied. Analytically, a single-mode theory incorporating anisotropy is developed and results are in quantitative agreement with RCWA, indicating that the tunability in the transmission stems from the waveguide mode.

Features of photoinduced dynamic gratings in semiconductors

The problem of influence of the diffusion process of nonequilibrium carriers on the efficiency of the dynamic grating photoinduced in a semiconductor material is studied theoretically and experimentally. An analytic expression is derived, which allows one to estimate the outlooks for applications of different semiconductor materials as active media for writing dynamic gratings.