Crystal Mirror Research Articles

Modulation bandwidth of planar waveguide laser with 1D photonic crystal mirrors

AbstractAn analysis of the 3-dB modulation bandwidth in planar waveguide laser based on 1D photonic crystal structures is presented. The theoretical model takes into account the gain saturation effect, transverse and longitudinal field distribution. A small-signal perturbation solution of the coupled laser rate equation is used to obtain relations describing the dynamic operation. In paper, the distributed Bragg resonator DBR created as 1D photonic crystal is considered. The active waveguide is surrounded by 1D photonic crystal mirrors consisting of alternately placed stripes with different refractive indices. In particular, the influence of the photonic crystal parameters on the 3-dB modulation bandwidth is investigated.

Single layer silicon photonic crystal slab

We present here the fabrication and characterization of single layer silicon photonic crystal mirror on a silicon-on-insulator wafer. By a combination of electron beam lithography, fast atom beam etching with deep reactive ion etching, silicon photonic crystal slabs are achieved on 260nm freestanding silicon membrane and sandwiched with air on the top and bottom. Their high refractive index contrasts enable photonic crystal slabs function as dielectric mirrors for externally incident light. The optical performances of fabricated photonic crystal slabs can be tuned by varying the width of separation grooves or the air-hole size, which represents a significant advantage of offering various approaches for optical response control.

Quasi-3D Light Confinement in Double Photonic Crystal Reflectors VCSELs for CMOS-Compatible Integration

A novel architecture of one-dimensional photonic crystal membrane (PCM) reflectors embodying a heterostructure is proposed as a robust design aimed at a 3-D efficient confinement of light in single-mode polarization-controlled 1.55-μm vertical-cavity surface-emitting laser (VCSEL) microsources for heterogeneous integration on complementary metal-oxide-semiconductor (CMOS). On the basis of a theoretical approach, the paper focuses on the deep interweaving between the kinetics of light transport in the mirrors and the physical nature of the exploited Fano resonances. An example of VCSEL design for optical pumping employing heterostructure-confined photonic crystal mirrors is presented. The predicted photons kinetics along with the considerable improvement in cavity modal features owing to the enhanced mirror architecture have been confirmed by performing rigorous three-dimensional finite-difference time-domain (3-D FDTD) calculations. Finally, experimental observations of photoluminescence (PL) emission performed on first-ever fabricated devices for optical pumping show striking agreement with theoretical considerations and ab initio modelling.

Polarization conversion by a three-dimensional photonic crystal mirror with a diamond structure

We report experimental and numerical studies of a polarization conversion by a three-dimensional photonic crystal. The (001) surface of a photonic crystal with a diamond structure has been shown to act as a mirror-type polarization convertor under normal incidence. When the direction of the incident wave polarization is along [010], the direction of the reflected wave polarization is converted to [100]. This has been found to be due to approximately a half-wave phase shift between the eigenpolarizations of [110] and [1 1¯ 0] upon reflection. This result has been discussed in relation with a polarization-dependent Goos–Haenchen effect.

High-sensitivity temperature sensor based on an alcohol-filled photonic crystal fiber loop mirror

A compact temperature sensor based on a fiber loop mirror (FLM) combined with an alcohol-filled high-birefringence photonic crystal fiber (PCF) is proposed and experimentally demonstrated. The output of the FLM is an interference spectrum with many resonant dips, of which the wavelengths are quite sensitive to the change of the refractive index of the filled alcohol for the interference of the FLM. Simulation analysis predicts a high temperature sensitivity, and experimental results show it reaches up to 6.6 nm/°C for the 6.1-cm-long PCF used in the FLM.

A one-dimensional photonic-crystal nanocavity incorporating a fluorescent molecular dye

We model the optical properties of a SiN based one-dimensional waveguide photonic crystal nanocavity with three tapered air holes as a function of the photonic crystal mirror fill factor using finite difference time domain calculations. We show that the Q-factor of this type of cavity has a strong dependence on the mirror fill factor, with a Q-factor as high as 35 000 predicted. Experimental studies on a range of representative structures whose surface is coated with a layer of a fluorescent dye confirm our modeling and reveal that such structures are characterized by a single optical mode having a Q-factor of 2000.

Intensity measurement based temperature-independent strain sensor using a highly birefringent photonic crystal fiber loop mirror

A fiber-optic strain sensor is demonstrated by using a short length of highly birefringent photonic crystal fiber (HiBi-PCF) as the sensing element inserted in a fiber loop mirror (FLM). Due to the ultralow thermal sensitivity of the HiBi-PCF, the proposed strain sensor is inherently insensitive to temperature. When a distributed-feedback (DFB) laser passes through the FLM, the output power is only affected by the transmission spectral change of the FLM caused by the strain applied on the HiBi-PCF. Based on intensity measurement, an optical power meter is adequate to deduce the strain information and an expensive optical spectrum analyzer (OSA) would not be needed.

Final-state effects in high-resolution angle-resolved photoemission from Ni(110)

Angle-resolved photoemission with polarized synchrotron radiation is measured from a ferromagnetic single-crystal Ni(110) surface. Polarization dependence and dispersion with ${\mathbf{k}}_{\ensuremath{\parallel}}$ of spectral structures along the high-symmetry lines $\ensuremath{\Gamma}\text{-K-X}$ of the bulk Brillouin zone is discussed. An ab initio calculation within the one-step theory of photoemission reveals the relation of the observed structures to initial and final states. The energy-momentum distribution of photoemission intensity depending on the light polarization and experimental geometry is explained in terms of even and odd symmetry of the valence-band states with respect to the crystal mirror plane.

Numerical analysis of mode locking in multi-core photonic crystal fiber

With linearly coupled nonlinear Schrodinger equations, numerical analysis has been performed on the mode locking forming procedure of a fiber laser in the linear cavity configuration. The fiber is Yb-doped multi-core photonic crystal fiber and semiconductor saturable absorber mirror (SESAM) is adopted as the nonlinear transmission element to start mode locking. Because of the noise randomness, initial pulse would be picked out by SESAM in one or more cores which makes the multi-core mode locking quite different from single-core one. The two situations are compared and fully discussed. Mode locking in multi-core photonic crystal fiber laser can be realized only if the couple coefficient between the cores and the temporal overlap between the pulses in different cores are large enough.

Graphical Abstract: Eur. J. Inorg. Chem. 16/2010

AbstractThe cover picture shows the molecular structure of an atropochiral C,X‐chelating ligand with the 1,1′‐binaphthyl backbone of BINAP and P,X‐chelating X‐MOP analogues. The primal role of the carbon element in the determination of chemical chirality is symbolized in the background by the diamond crystal mirror and in the forefront by a universal asymmetric carbon atom. The weights symbolize the added value of the natural or eutomeric configuration of such atoms in molecules of biological interest, which can be controlled by atropochiral ligands in enantioselective transition‐metal‐catalyzed processes. Details are presented in the Microreview by Y. Canac and R. Chauvin on p. 2325 ff.

Atropochiral C,X‐ and C,C‐Chelating Carbon Ligands (Eur. J. Inorg. Chem. 16/2010)

AbstractThe cover picture shows the molecular structure of an atropochiral C,X‐chelating ligand with the 1,1′‐binaphthyl backbone of BINAP and P,X‐chelating X‐MOP analogues. The primal role of the carbon element in the determination of chemical chirality is symbolized in the background by the diamond crystal mirror and in the forefront by a universal asymmetric carbon atom. The weights symbolize the added value of the natural or eutomeric configuration of such atoms in molecules of biological interest, which can be controlled by atropochiral ligands in enantioselective transition‐metal‐catalyzed processes. Details are presented in the Microreview by Y. Canac and R. Chauvin on p. 2325 ff.

Multiwavelength fiber laser based on a photonic crystal fiber loop mirror with cooperative Rayleigh scattering

In this work, a multiwavelength fiber Raman laser based on a highly birefringent photonic crystal fiber loop mirror is presented. A laser resonator is formed when the Raman amplification with cooperative Rayleigh scattering in a dispersion-compensating fiber is used as a distributed mirror and combined with a photonic crystal fiber loop mirror filtering structure. Stable multiwavelength lasing at room temperature is achieved due to the low temperature sensitivity of the highly birefringent photonic crystal fiber.

Dynamically tunable mirrors for THz free electron laser applications

We have constructed and tested 1D-photonic crystal (PhC) mirrors with tunable reflectivity to be used as efficient, broadband outcouplers for THz free electron lasers (FELs). The test mirrors cover a spectral range between 0.5 and 1.5 THz. They are assembled by stacking up quarter-wave dielectric layers separated by vacuum. The adopted PhC mirror design enables dynamical (while lasing) adjustment of individual layer spacing. Single as well as multiple defects in the periodicity are introduced to invoke a continuous, well-defined tuning of reflectivity and outcoupling ratio. The scheme allows one to vary also the PhC period while the equidistant spacing between the layers is maintained. This feature is used to shift the photonic band gap (center) for achieving an effective extension in the reflectance spectrum. Because of the exceptional flexibility provided by the scheme in tailoring the characteristics of the PhC defects, additional features such as tunable (narrow) bandpass filtering as well as (fast) THz intensity modulation can be combined with the reflectivity/coupler properties of the proposed PhC mirrors for FELs.

Photonic crystal cavity embedded barium strontium titanate thin-film rib waveguide prepared by focused ion beam etching

A photonic crystal (PC) cavity embedded Ba 0.7Sr 0.3TiO 3 (barium strontium titanate, or BST) rib waveguide, which functions as an optical filter at λ = 1550 nm, is designed using finite-difference time-domain (FDTD) simulation. The PC cavity is composed of two 5-row photonic crystal mirrors, which are formed by air holes (radii 250 nm) arranged in triangular lattice (periodicity 625 nm) in the BST matrix. Calculations suggested that the required cavity length should be 800 nm for the resonant peak to be situated at 1550 nm. Based on this design, PC cavities were fabricated on BST thin-film rib waveguides by focused ion beam etching with satisfactory results. The transmission spectra of the BST thin-film rib waveguides with PC cavities have been measured. The results agreed well with the FDTD simulation.

Switchable dual-wavelength erbium-doped fiber laser based on the photonic crystal fiber loop mirror and chirped fiber Bragg grating

The switchable dual-wavelength erbium-doped fiber laser (EDFL) with a two-mode photonic crystal fiber (PCF) loop mirror and a chirped fiber Bragg grating (CFBG) at room temperature is proposed and experimentally demonstrated. The two-mode PCF loop mirror is formed by inserting a piece of two-mode PCF into a Sagnac loop mirror, with the air-holes of the PCF intentionally collapsing at the splices. By adjusting the state of the polarization controller (PC) appropriately, the laser can be switched between the stable single- and dual-wavelength operations by means of the polarization hole burning (PHB) and spectral hole burning (SHB) effects.

Demonstration and selection of a single-transverse higher-order-mode beam with radial polarization

Single-transverse higher-order radially polarized beams with multiple rings are selectively generated from a Nd:YAG laser cavity by using a reflectivity-modified and polarization-selective photonic crystal mirror. As predicted by theoretical analysis [A. A. Tovar, J. Opt. Soc. Am. A 15, 2705 (1998)], the intensity distribution and propagation characteristics of the higher-order radially polarized beams are expressed by a Laguerre-Gaussian formula.

Effect of photoconductivity and dielectric constant of the photorefractive materials on two-beam coupling gain and phase-shifts for a single unidirectional photorefractive ring resonator

Photoconductive dependence of two-beam coupling between the pump beam and the signal beam in photorefractive materials have been analyzed in case of non-degenerate wave mixing under the undepleted pump approximation method. During the two-wave mixing in photorefractive materials, steady state amplification of the signal beam and oscillation characteristics of a single unidirectional ring resonator has been studied. The domination of the two-beam coupling gain over the combined absorption and resonator losses such as Fresnel reflections from the crystal and imperfect mirrors builds up unidirectional oscillation. The buildup of such an oscillation leads to a saturation of the gain, which can be explained in terms of the photorefractive phase-shift. The existence of this phase-shift between the photorefractive index grating and the illumination intensity pattern, which is of characteristic of the photorefractive effect, leads to an energy transfer between the two beams. For a single unidirectional ring resonators, the effects of photoconductivity of the materials, two-beam energy coupling coefficient, dielectric constant, crystal thickness, and material's absorption coefficient on amplification of the two-beam coupling gain and photorefractive phase-shifts of the signal beam have also been studied in detail. It has been found that amplification of the signal beam and phase-shift can be enhanced by taking the photorefractive crystal having higher photoconductivity and lower dielectric constant, which improves performance of the resonators.

Difference between penetration and damping lengths in photonic crystal mirrors

Different mirror geometries in two-dimensional photonic crystal slabs are studied with fully vectorial calculations. We compare their optical properties and, in particular, we show that, for heterostructure mirrors, the penetration length associated with the delay induced by distributed reflection is not correlated with the characteristic damping length of the electromagnetic energy distribution in the mirror. This unexpected result evidences that the usual trade-off between short damping lengths and large penetration lengths that is classically encountered in distributed Bragg reflectors can be overcome with carefully designed photonic crystal structures.

EXPLORING VISUOSPATIAL THINKING IN LEARNING ABOUT MINERALOGY: SPATIAL ORIENTATION ABILITY AND SPATIAL VISUALIZATION ABILITY

This mixed-method research attempted to clarify the role of visuospatial abilities in learning about mineralogy. Various sources of data—including quantitative pre- and postmeasures of spatial visualization and spatial orientation tests and achievement scores on six measures and qualitative unstructured observations, interviews, and field trip notes—were utilized to document the abilities and learning of 27 university students. Results indicated that (a) some students had initial difficulty with certain visual concepts, such as 3D crystal models, symmetry elements, mirror symmetry, rotation, inversion, and combination of symmetry elements while they were learning about mineralogy; (b) learning about mineralogy and spatial ability are two interrelated components; while the mineralogy course improved students’ spatial ability, their existing spatial abilities had a strong influence on facilitating mineralogy learning; and (c) spatial visualization skill is a better predictor of mineralogy achievement than spatial orientation skill. While the discussions highlighted the role of visuospatial thinking in learning about mineralogy, it is argued that researchers and curriculum developers should focus on the productive role of visuospatial thinking in learning about science.

Performance Investigation of Photonic Crystal-Based Microring Resonator for Optical Signal Processing

A detailed theoretical analysis is presented to characterize wave propagation at 1,550 nm inside a glass (SiO2) microring resonator implemented using photonic crystal technology. A photonic crystal reflection is used at each microring resonator corner to enhance the bending efficiency. The characteristics of both photonic crystal beam splitter and microring resonator bending losses are analyzed and investigated using both effective refractive index and finite difference time domain methods. Analytical expressions are also derived to describe the field enhancement inside the microring resonator, the transfer function of the microring resonator, and the main parameters characterizing the resonator such as resonator band width and quality factor. The analysis is also extended to characterize a drop filter implemented using photonic crystal-based microring resonator. The results indicate clearly that the effective refractive index method can give accurate results if one starts the calculations with finite difference time domain-estimated beam splitter parameters. Further, bending efficiency as high as 99% can be obtained using a ten-post layer photonic crystal mirror at each microring resonator corner.