Lateral Gratings Research Articles

In-Plane Radiation of Surface Plasmon Polaritons Excited by Free Electrons.

Surface plasmon polaritons (SPPs) have become a research hotspot due to their high intensity and subwavelength localization. Through free-electron excitation, a portion of the momentum of moving electrons can be converted into SPPs. Converting highly localized SPPs into a radiated field is an approach with the potential to aid in the development of a light radiation source. Reducing losses of SPPs is currently a critical challenge that needs to be addressed. The lifetime of SPPs in metal films is longer than that in metal blocks. Traditional optical gratings can transform SPPs into radiation to avoid the decay of SPPs in metal; however, they are created by etching metal films, so they tend to alter the dispersion characteristics of these films and will emit radiation in the direction perpendicular to the metal surface. This paper proposes an approach to converting the SPPs of a metal film excited by free electrons into a radiation field via lateral grating and obtaining in-plane radiation. We investigate the properties of SPP lateral radiation. The study of lateral radiation from metal films holds significant importance for SPP radiation sources and SPP on-chip circuit development.

High‐Power, Narrow‐Linewidth, and Low‐Noise Quantum Dot Distributed Feedback Lasers

AbstractSingle‐frequency semiconductor lasers represent a critical role in optical communications, light detection and ranging systems, photonics integrated circuits, etc. Here, combining atom‐like quantum dot (QD) materials and advanced lateral gratings, a high‐power, ultra‐low‐noise 1.3 µm InAs/GaAs QD distributed feedback laser is demonstrated. Stable single‐longitudinal‐mode output power of 100 mW from 25 ℃ to 85 ℃ is achieved with a maximum side mode suppression ratio of 62.6 dB, and the variations of threshold current and slope efficiency over the temperature range are slight, indicting a high temperature stability. A record‐narrow intrinsic linewidth of 1.62 kHz is achieved at 55 ℃ with a white noise level of merely 515 Hz2 Hz–1, and a minimum averaged relative intensity noise of only –166 dB/Hz between 0.1 GHz and 20 GHz is obtained at 25 ℃. Furthermore, a strong tolerance to external optical feedback (〉 –14 dB) is demonstrated in the range from 25 ℃ to 85 ℃, with a maximum value of –8 dB at 85 ℃. This high‐quality single‐frequency laser fabricated with simplified processes and compact size paves the way for its future large‐scale applications such as high‐capacity optical communication, high‐precision optical detection, high‐speed optical interconnections, etc.

Engineering the anisotropy of AlAs wet oxidation using silicon implantation

We investigate the influence of silicon implantation on wet lateral oxidation of AlAs and show that the introduction of n-type doping silicon ions permits the adjustment of the oxidation kinetics and anisotropy. Using mesas with selectively patterned implantation regions, we demonstrate the fabrication of oxide apertures unachievable using the standard process such as oxide lateral gratings whose pitch can range down to 4 µm and crosses with 40°-angle tips. This approach thus constitutes an easy and flexible way to engineer the oxidation process and opens the path to new confinement geometries for lateral confinement patterns in photonics devices and in particular VCSELs.

侧向非对称光栅光场耦合特性的理论研究

侧向非对称光栅光场耦合特性的理论研究

Form deviations caused by lateral displacement errors in annular subaperture stitching interferometry

Annular subaperture stitching interferometry (ASSI) is a common approach for the measurement of aspherical surfaces. A common obstacle of ASSI is the occurrence of lateral displacement errors when the sensor or specimen is repositioned between the subaperture measurements. Our contribution focuses on modeling of the statistical displacement errors. A virtual experiment is presented simulating the propagation of the displacement errors through a cumulative and a global stitching algorithm to the retrieved surface form. For the considered experimental setup, the uncertainty in lateral position depends on the positioning uncertainties of the employed motion system and the uncertainty in the absolute distance measurement between the sensor and specimen. The lateral displacement uncertainty is determined experimentally employing a calibratable lateral grating. Thus, it is traceable to the SI unit of the length (meter). The experimental results show that the lateral displacement errors may be modeled by a normal distribution, and the results of the virtual experiment indicate that the statistical lateral displacement errors transfer linear through the stitching procedure and also cause a normal distributed topography error. This enables the assignment of an expanded uncertainty to each individual sample point employing the Zernike polynomial expression of the topography measurement.

Terahertz quantum cascade lasers with sampled lateral gratings for single mode operation.

In this paper, we presented single mode terahertz quantum cascade lasers (THz QCLs) with sampled lateral grating emitting approximately 3.4 THz. Due to strong mode selection, the implementation of sampled lateral grating on THz QCL ridges can result in stable single longitudinal mode emission with a side-mode suppression ratio larger than 20 dB. The measured peak power of the grating laser is improved by about 11.8% compared to the power of devices with uniform distributed feedback gratings. Furthermore, the far-field pattern of the presented device is uninfluenced by grating structures.

Dynamical Theory of X-Ray Diffraction in a Crystal with a Surface Grating of Another Material

A general theory is developed for dynamical X-ray diffraction in a crystal on the surface of which a lateral periodic structure of thin-film lines (strips) of another material is formed. On the basis of the model of edge forces, the fields of elastic lattice displacements in the substrate are calculated that arise as a result of formation of a lateral surface grating (SG). With the use of the formalism of diffraction of spatially restricted X-ray beams, solutions are obtained for the amplitudes of X-ray waves reflected from a crystal with an SG whose chemical composition differs from the composition of the substrate. A numerical simulation is carried out of X-ray diffraction in a silicon substrate with SGs of tungsten and SiO2 oxide. It is shown that the angular distributions of the scattering intensity by a silicon crystal with tungsten and oxide lines of identical size differ significantly, and the physical nature of such difference is established.

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.

Lateral grating DFB AlGaInN laser diodes for optical communications and atomic clocks.

AlGaInN laser diode technology is of considerable interest for telecom applications and next generation atomic optical clocks based on Sr (by using 422nm & 461nm) and Rb at 420.2nm.Very narrow linewidths (<1MHz) are required for such applications. We report lateral gratings on AlGaInN ridge waveguide laser diodes to achieve a single wavelength device with a good side mode suppression ratio (SMSR) that is suitable for atomic clock and telecom applications.

Role of the different eyes in the visual odometry in the wolf spider Lycosa tarantula (Araneae, Lycosidae)

The wolf spider Lycosa tarantula returns home by means of path integration. Previous studies demonstrated: (i) that the angular component of the outbound run is measured using a polarized-light compass associated with the anterior median eyes; (ii) changes in direction of the substratum are detected by the anterior lateral eyes (ALEs); and (iii) in relation to the linear component of the outbound run, an increase of optic flow, in either the lateral or ventral fields of view, caused spiders to search for the burrow at a point nearer to the goal. However, the role of the secondary eyes [ALEs, posterior lateral eyes (PLEs) and posterior median eyes (PMEs)] in the perception of this optic flow and the importance of them for gauging the distance walked is still unknown. In this study, lateral or ventral gratings of wavelength λ=1 cm were used, with two groups of spiders in each setup: (1) PLEs+PMEs covered and (2) ALEs covered. The largest reduction in the distance walked to return to the burrow was observed with the ventral grating/ALEs covered. These results show the importance of the previously neglected ALEs for the visual behavior of these spiders. The possibility of gathering information for locomotion from the three pairs of secondary eyes in the mushroom bodies is discussed.

Nanophotonic Ultrashort Coupler Based on Hybrid Plasmonic Waveguide With Lateral Subwavelength Grating

A nanophotonic vertical coupler with ultrashort coupling length based on hybrid plasmonic (HP) waveguide with a lateral subwavelength grating (LSG) is proposed. An ultrashort coupling length of 0.461 μ m is achieved through the lateral resonances in the subwavelength grating. The combined effect of LSG and the metal layer sandwiched between the coupling dielectric-regions makes it possible to realize efficient coupling and low-loss guiding of hybrid modes with a propagation lengths of 123 and 53 μm, respectively, for odd and even modes. The vertical coupling influenced by the lateral resonances through LSG also exhibits broadband nature where the coupling length remains acceptably small and the coupling performance remains high over a broad range of wavelengths. The coupling performance of 192 and a low propagation loss of 0.035 dB/μm are reported with the analysis based on finite element method. LSG introduced into the HP waveguide is shown to provide multifold benefits of increased fabrication tolerance, enhanced coupling efficiency and expanded coupling regime.

Optical refractive index biosensor using evanescently coupled lateral Bragg gratings on silicon-on-insulator

In this paper, we present a compact silicon-on-insulator optical biosensor based on lateral Bragg gratings evanescently coupled to a waveguide. The device is fabricated by electron-beam lithography and dry-etched in a single step with inductive coupled plasma reactive ion etching (ICP-RIE). Fully etched grating couplers are used to couple the light in and out of the chip, while lateral Bragg gratings are used as the sensing element of the device. A sensitivity of 22 nm/RIU is obtained by exposing the device to deionized water with different NaCl concentrations with a footprint area of 15 × 4 µm2 that allows for densely multiplexed solutions.

High Spectral Purity High-Power GaSb-Based DFB Laser Fabricated by Nanoimprint Lithography

The development of single-mode distributed feedback (DFB) lasers emitting high output powers in a broad wavelength range from 1980 to 2035 nm is reported. A unique feature of the development is the fabrication of lateral feedback gratings by nanoimprint lithography. We have varied a wide range of design parameters and studied their effect on the performance of the laser. The best uncoated devices exhibited a side-mode suppression ratio as high as $>50$ dB at output powers in excess of 14 mW. Moreover, a tuning range of over 12 nm was measured. After coating the facets with dielectric mirrors, the laser diodes could deliver an output power of more than 25 mW. In this letter, we prove the suitability of nanoimprint lithography to the fabrication of GaSb-DFB laser diodes by demonstrating the state-of-the-art devices made using imprint lithography.

Single-mode tapered terahertz quantum cascade lasers with lateral gratings

We report on tapered terahertz quantum cascade lasers with lateral gratings. The proposed devices exhibit not only low horizontal divergence due to tapered structure but also single-mode operation by using lateral grating structure. The tapered region and lateral gratings can be fabricated with the ridged waveguide in one etching step without inducing complexity into the fabrication. Side-mode suppression ratio ∼20dB is obtained for proposed devices from threshold to rollover currents at all measure temperatures, with the peak output power of ∼30mW at 10K in pulsed mode and lateral divergence angle reduced by half. The proposed devices are good candidates for high-power, single-mode operation and low-divergence laser with easy fabrication.

InAs-based distributed feedback interband cascade lasers

Single mode emission of InAs-based interband cascade lasers using lateral metal gratings that provide distributed feedback is presented. A double ridge configuration was developed, where the grating is placed above the active region while a second, slightly wider ridge ensures current confinement in the active region. Side mode suppression ratios above 30 dB have been obtained, and single mode emission was observed at wavelengths around 6 μm in continuous-wave operation up to a temperature of −10 °C. Current- and temperature-tuning rates of 0.011 nm/mA and 0.50 nm/ °C, respectively, have been found, and a total tuning range of 6.5 nm has been covered by one device. As a reference, ridge waveguide devices without a grating made from the same material were able to emit in pulsed mode up to 49 °C and in continuous-wave operation at temperatures up to 0 °C around 6 μm.

Near field of terahertz radiation transmitted through a lateral non-centrosymmetric grating

The transmission of a terahertz (THz) wave through a grating of metallic strips deposited on a flat surface of a dielectric medium has been considered. It has been assumed that the unit cell of the lateral grating does not have a spatial inversion center and the grating period is small compared to the radiation wavelength. The found amplitudes and phases of the spatial harmonics of the transmitted wave in the near field have been used to calculate the components of the tensor of asymmetry parameters responsible for the generation of photocurrents in a doped quantum well embedded in the non-centrosymmetric system under consideration. It has been found that, at a strip height greater than the skin depth, the parameters of the transmitted spatial harmonics are nearly independent of the height. It has been shown that the metallic grating exhibits strong birefringence, and the radiation polarized either circularly or linearly at an angle of 45° with respect to the principal axes of the lateral grating induces superposition of photocurrents owing to the circular or linear electronic ratchet effects.

Single mode interband cascade lasers based on lateral metal gratings

Single mode distributed feedback (DFB) interband cascade lasers were realized by placing metal gratings laterally to dry etched ridges. A discrete tuning range of 104 nm could be realized on the same gain material by a variation of the grating period. At room temperature, a 2.4 mm long and 9.8 μm wide ridge with as-cleaved facets emitted more than 6 mW of single mode output power in continuous-wave (cw) mode at a wavelength around 3.8 μm. With typical temperature- and current-tuning rates of 0.31 nm/ °C and 0.065 nm/mA, respectively, a total tuning bandwidth of more than 10 nm could be covered with a single device.

Visual odometry in the wolf spider Lycosa tarantula (Araneae: Lycosidae)

The wolf spider Lycosa tarantula homes using path integration. The angular component of the displacement is measured using a polarized-light compass associated with the functioning of the anterior median eyes. However, how L. tarantula estimates the linear component of the displacement was not known prior to this investigation. The ability of L. tarantula to gauge the distance walked after being displaced from its burrow was investigated using experimental channels placed in an indoor setup. Firstly, we manipulated the perception of visual stimuli by covering all the spider's eyes. Secondly, we changed the optic flow supplied by a black-and-white grating (λ=2 cm) perceived either in the lateral or in the ventral field of view. Finally, the period of the lateral or ventral grating was changed from λ=2 cm to λ=1 cm. Our results indicate that visual information contributes to distance estimation because when the spider's eyes were covered, the spiders tended to search for the burrow at very variable distances. This visual information is created by the motion of the image as the spider walks, the motion in the lateral field of view being the most important. The preference of a lateral optic flow over the ventral flow can be explained by the difference in the resolution capacity of the posterior lateral eyes and the anterior lateral eyes.

Quantum Cascade Laser With Unilateral Grating

We report on distributed feedback quantum cascade lasers at a wavelength of 3.58 μm operating at room temperature. Single-mode emission with a side-mode suppression ratio of 30 dB is achieved by manufacturing single-sided third-order lateral gratings. The devices exhibit watt level peak powers with a threshold current density of ~ 4.3 kA/cm2 at room temperature and remain in single-mode operation over the temperature range of 280-420 K.

Lateral distributed-feedback gratings for single-mode, high-power terahertz quantum-cascade lasers

We report on terahertz quantum-cascade lasers (THz QCLs) based on first-order lateral distributed-feedback (lDFB) gratings, which exhibit continuous-wave operation, high output powers (>8 mW), and single-mode emission at 3.3-3.4 THz. A general method is presented to determine the coupling coefficients of lateral gratings in terms of the coupled-mode theory, which demonstrates that large coupling strengths are obtained in the presence of corrugated metal layers. The experimental spectra are in agreement with simulations of the lDFB cavities, which take into account the reflective end facets.