Submicrometer Gratings Research Articles

Single-detecting-path high-resolution displacement sensor based onself-interference effect of a single submicrometer grating.

On the basis of the self-interference effect between ±1 st-order diffraction beams from a single optical submicrometer grating, we demonstrate a single-detecting-path optical displacement sensor with high resolution. Using a quadrant optoelectronic detector, a single-detecting-path system without any wave plates is realized experimentally. Combined with an interpolation circuit, we demonstrate the system for displacement measurement within a range of 200 µm. The results indicate a detecting sensitivity of 905.4°/µm and an accuracy of ±1.9µm. It is worth mentioning that, considering a maximum subdividing factor of 9674 used in experiment, the resolution goes down to 41.1 pm in principle. We demonstrate a compact optical sensor with high resolution, which is promising in developing miniaturized displacement systems.

Pattern Transfer of Sub-micrometre-scaled Structures into Solid Copper by Laser Embossing

Abstract Laser embossing allows the micron and submicron patterning of metal substrates that is of great interest in a wide range of applications. This replication process enables low-cost patterning of metallic materials by non-thermal, high-speed forming which is driven by laser-induced shock waves. In this study the surface topography characteristics as well as the material structure at laser embossing of sub-micrometre gratings into solid copper is presented. The topography of the laser-embossed copper pattern is analysed with atomic force microscopy (AFM) in comparison to the master surface. The height of the embossed structures and the replicated pattern fidelity increases up to a laser fluence of F∼10 J/cm 2 . For higher laser fluences the height of the embossed structures saturates at 75% of the master pattern height and the shape is adequate to the master. Structural modifications in the copper mono crystals after the laser embossing process were investigated with transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD). Almost no modifications were detected. The residual stress after laser embossing of 32 MPa(F = 30 J/cm 2 ) has only a limited influence on the surface pattern formation.

Sub-micrometric patterns written using a DIL method coupled to a TiO2 photo-resist

An all-inorganic TiO2 photo-resist has been formulated through an optimized sol–gel route. This photo-resist has been coupled to an original dynamic interferometric lithography technique to propose a cost effective method compatible with the formation of sub-micrometric diffraction gratings on rather large surfaces using a single-step lithography and a reduced-size set-up. For that purpose, a phase mask has firstly been designed in relation to the specificities of the TiO2 photo-resist. The optical characteristics arising from such a photo-resist have also been assessed. We finally discuss the formation of sub-micrometric gratings in relation to device features (phase mask design, writing light power) and specificities of the all-inorganic photo-resist.

Broadband highly transparent sapphires with biomimetic antireflective compound submicrometer structures for optical and optoelectronic applications

We reported the broadband highly transparent sapphires with biomimetic antireflective compound submicrometer structures (c-SMSs) made of disordered nanocone arrays on closely packed ordered hemispherical submicrometer gratings (o-SMGs). The o-SMGs and nanocones were fabricated using the spin-coated silica spheres and thermally dewetted gold (Au) nanoparticles, respectively, as the etch masks by a dry etching. The silica spheres with an average diameter of ∼700±10  nm were synthesized. The dot-like Au nanoparticles were formed from the Au thin films with different thicknesses by a proper heat treatment. The total and diffuse transmission characteristics of the fabricated c-SMSs on sapphires were investigated at wavelengths of 350–1100 nm, together with theoretical predictions using a rigorous coupled wave analysis simulation. For the c-SMSs with taller and larger nanocone arrays at 7 nm of Au film, an average total transmittance (Tavg) of ∼90.7% was obtained, exhibiting haze ratios (H) of ∼33.3 and 26% at λ=525 and 635 nm, respectively. These values were much higher than those of bare sapphire (i.e., Tavg∼85.4%, H∼5.4 and 3.7% at λ=525 and 635 nm, respectively). The surface of fabricated c-SMSs also exhibited a strong hydrophilic property with a low water contact angle of ∼10°.

Submicrometer grating light bar for a color-separation backlight

A light bar patterned using a submicrometer grating was designed to replace conventional dye color filters for color liquid crystal displays. The light bar generates color rays by transmitting them from side-lit color light-emitting diodes through the submicrometer grating. These angular color rays are then redirected by a V-grooved light guide, and then converged by a lens array and mapped to corresponding subpixel positions to efficiently display color images. The results show that 106% of the National Television System Committee (NTSC) color space in a blue-green-red-green (B-G-R-G) repeating pattern display pixel layout can be achieved.

Submicrometric gratings fabrication from photosensitive organo-silica-hafnia thin films elaborated by sol–gel processing

The aim of this study is the elaboration of a high index sol–gel material in order to prepare submicrometric grating. The gratings were obtained after few seconds of UV exposure in one step using an organically modified silica-hafnia matrix. The chemical composition of thin films after UV and annealing treatments were studied using Fourier Transform Infrared Spectroscopy and X-Ray Photoelectron Spectroscopy. The study of optical properties revealed that the annealed films are transparent from 200 to 1000nm and have a refractive index from 1.550 to 1.701 depending on the hafnium concentration.

Bragg Grating Optical Filters by UV Nanoimprinting

Results on an optical waveguide filter operating in the near IR region are reported. The device consists of a hybrid sol‐gel ‐based grating loaded waveguide, obtained through the merging of conventional photolithography and UV‐nanoimprinting. Starting from submicrometric gratings, fabricated by electron beam lithography, a soft mould has been produced and the original structures were replicated onto sol‐gel photosensitive films. A final photolithographic step allowed the production of grating‐loaded channel waveguides. The devices were optically characterized by transmission measurements in the telecom range 1450–1590 nm. The filter extinction ratio is −11 dB and the bandwidth is 1.7 nm.

Surface plasmon interference on the surface of an aluminum-covered fiber core array for solgel fabrication of submicrometer gratings

An interesting method to fabricate submicrometer gratings (SMGs) utilizing the interference of surface plasmon waves (SPWs) is presented. The stationary wave field off the aluminum (Al) layer surface of an Al-covered UV fiber core, formed by the interference of the induced SPWs, has been employed as a submicrometer photolithography tool to inscribe SMGs on the surface of a self-processing hybrid HfO(2)/SiO(2) solgel film. Using atomic force microscopy, the period of the fabricated SMGs was measured as 105 nm. The intensity distribution of the stationary wave field was measured by a near-field scanning optical microscope and anastomosed with theoretical values calculated by using FDTD simulations.

Antireflective submicrometer gratings on thin-film silicon solar cells for light-absorption enhancement

This study reports highly efficient light-absorbing structures based on submicrometer gratings (SMGs) for thin-film crystalline silicon solar cells. The integration of SMGs into the cell structure leads to superior broadband antireflection properties compared to conventional antireflection coatings. With careful design optimization, an improvement of the cell efficiency of nearly 25.1% was obtained compared to double-layer coated solar cells. Optimized SMG structures were fabricated on a silicon substrate using interference lithography and a lenslike shape transfer process. The fabricated SMG structures exhibited low reflectivity in the wavelength range of 300-1200 nm, indicating good agreement with the simulated results.

Color filter based on a two-dimensional submicrometer metal grating

A color filter incorporating a two-dimensional (2D) submicrometer metal grating is proposed. The device is designed by utilizing rigorous coupled-wave analysis (RCWA) and consists of four parts: a polymethyl methacrylate (PMMA) substrate, a dielectric film of high refractive index, a submicrometer grating, and a dielectric overlay of low refractive index. Its performance is enhanced effectively by applying a dielectric film of high refractive index. With a dielectric film height of 30 nm, a grating depth of 70 nm, and an overlay height of zero, three different devices are designed with the following structural parameters: a period of 420 nm for the red, a period of 350 nm for the green, and a period of 260 nm for the blue. For the red filter, the center wavelength is 645 nm and the peak transmission is 72%; for the green one, the center wavelength is 546 nm and the peak transmission is 75%; and for the blue one, the center wavelength is 455 nm and the peak transmission is 71%. The calculated result shows that its peak transmission efficiency increased more than 14% compared to the previous color filters incorporating a grating.

Plasmonic structure generation by laser illumination of silica colloid spheres deposited onto prepatterned polymer-bimetal films

Plasmonic structures are prepared on bimetal films evaporated onto glass substrates applying a multi-step process, and atomic force microscopy is utilized to study the structures after each step. Sub-micrometer gratings are generated on polycarbonate films spin-coated onto silver-gold bimetal layers by interference lithography (IL) applying the fourth harmonics of a Nd:YAG laser. These polymer gratings are used as prepatterned templates in order to deposit silica colloid spheres by spin-coating. It is shown that the conditions of periodic silica sphere-array formation along the template valleys are sufficiently large grating modulation depth, appropriate ratio of silica sphere diameter to grating period, and optimized speed of spinning. The periodic silica sphere arrays are illuminated by a homogeneous KrF excimer laser beam, and periodically arrayed sub-wavelength holes are drilled into bimetal films via colloid sphere lithography (CSL). The characteristic dimensions of the resulted plasmonic structures are defined by the polymer grating period and by the silica colloid sphere diameter. Attenuated total reflection spectroscopy is performed exciting plasmons on different metal-dielectric interfacial structures by the second harmonic of a continuous Nd:YAG laser. The polar and azimuthal angle dependent grating-coupling and scattering effects of the complex periodic structures on the resonance characteristic of plasmons is demonstrated.

Diffraction characteristics of a submicrometer grating for a light guide plate

The diffraction transmission characteristics of submicrometer gratings (SMGs) designed for coupling tricolor light out of a light guide plate (LGP) are discussed. Three discrete SMGs are designed for three special wavelengths: red (700 nm), green (546.1 nm), and blue (435.8 nm). The propagation direction of the output tricolor light is perpendicular to the surface of the LGP and can pass through the corresponding pixels of liquid crystal. Calculated by the rigorous coupled-wave theory, the first-order transmission efficiency as a function of grating depth is found to be approximate to a sinusoidlike curve and can be utilized to obtain uniform illumination. The theoretical maximum transmission is as much as 44%. The performance of the LGP composed of SMGs is also demonstrated by our experiments. Compared with other types of LGP, the present device has the advantage of flexible control of illumination angle and wavelengths. Additionally, lossy and costly color filters are unnecessary in the proposed configuration.

Brillouin scattering studies of polymeric nanostructures *

AbstractFor a range of applications, polymers are now being patterned into nanometer‐sized features. In these applications, the robust mechanical properties of the nanostructures are critical for performance and stability. Brillouin light scattering is presented as a nondestructive, noncontact tool used to quantify the elastic constants in such nanostructures. We demonstrate this through a series of thin films and parallel ridges and spacings (gratings) with ridge widths ranging from 180 to 80 nm. For the set of films and structures presented here, the room‐temperature elastic moduli did not change with decreasing film thickness or grating ridge width, and this implied that one‐dimensional and two‐dimensional confinement‐induced changes of the mechanical properties were not significant down to feature sizes of 80 nm. Additionally, Brillouin spectra of submicrometer gratings revealed new modes not present in the spectra of thin films. The origin of these new modes remains unclear. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1106–1113, 2004

Poly(p-phenylenevinylene) derivatives: new promising materials for nonlinear all-optical waveguide switching

Several new derivatives of poly(p-phenylenevinylene) (PPV) are investigated regarding their linear and nonlinear optical material and waveguide properties, including their nonlinear photonic bandgap properties that are induced by photoablated periodic Bragg gratings. The new materials were prepared by means of the polycondensation route, which yields polymers with excellent solubilities and film-forming properties. Comparative data suggest that the new polycondensation-type MEH-PPV (completely soluble, strictly linear and fully conjugated), in particular, is the most promising polymer under investigation to fulfill the requirements for all-optical switching in planar waveguide photonic bandgap structures. UV-photobleaching techniques and photoablation in the UV, VIS, and near-infrared ranges at different pulse durations are investigated. Homogeneous submicrometer gratings that serve as Bragg reflectors have been fabricated in MEH-PPV thin films by application of these methods. The great potential of this type of materials for nonlinear all-optical switching applications that arises from their unique optical properties and their patterning behavior is discussed in detail. Numerical simulations of a switching device based on gap-soliton formation in a nonlinear periodic waveguide structure with the newly obtained material data have been carried out. We show that one can expect photonic bandgap all-optical switching in MEH-PPV planar waveguides. Device performance considering different grating parameters is discussed.

Subpicosecond time resolved ablation studies of submicrometer gratings on metals and semiconductors

Subpicosecond time resolved ablation studies of submicrometer gratings on metals and semiconductors

Subpicosecond time resolved ablation studies of submicrometer gratings on metals and semiconductors

Time-resolved studies on the ablation of metals (Ni, Ag, Au, Cu) and semiconductors (Ge, Si) by short UV laser pulses (500 fs at 248 nm) are presented. Submicron-period grating structures were created on the sample surface by UV pump pulses and the diffracted signals (0th, 1st, 2nd order) of a weak probe pulse (500 fs at 496 nm) were recorded as a function of pump-probe delay. These signals provide direct information about electronic excitations, phase transitions and the onset of material removal.

Diffraction gratings in sol–gel films by direct contact printing using a UV-mercury lamp

We report on the fabrication of diffraction gratings in photosensitive sol–gel thin films by direct contact printing using a UV-mercury lamp. Titanium amplitude masks were used to replicate diffraction gratings into photosensitive sol–gel films by contact printing with an incoherent UV-light source. Gratings with 1-μm period were fabricated in sol–gel films. The diffraction efficiencies of each diffracted order were measured and compared to theoretical values. The demonstrated process of contact printing using a regular UV-light source in the optically compatible sol–gel material has potential for large-scale fabrication of submicrometer gratings at very low cost.

High-resolution transmission electron microscopy studies of quantum wire structures grown on submicrometre gratings of V-grooves

We present an extensive characterization of a quantum wire (QWR) structure using transmission electron microscopy (TEM). The structure consisted of a single GaAs layer in between AlGaAs barriers, grown on a GaAs substrate patterned with a submicrometre grating of V-grooves. For reference we also studied other QWR, as well as, quantum well (QW) samples, fabricated under similar conditions. We used bright field and dark field imaging to study the overall structure, high-resolution TEM to study the layer thickness and the interface quality, and chemical lattice imaging to study the compositional variations across the interfaces. In the QWR sample, there were mainly two distinctly different areas of the QW: on the (100) planes between the V-grooves, the QW was flat, whereas the QW on the near side walls of the V-grooves had a flat lower interface and a saw-tooth shaped upper interface. The QWRs at the bottom of the V-grooves were crescent shaped. We also observed a fundamental difference in growth of the GaAs and the AlGaAs on the side wall, where the AlGaAs formed straight interfaces, determined by high-index planes, whereas the GaAs tended to form alternating low-index planes giving a saw-tooth appearance of the GaAs QW.

Effective carrier confinement of a short-period GaAs/AlGaAs quantum wire array

Quantum wire (QWR) arrays grown on a GaAs substrate with V-grooved submicrometre gratings were investigated by high-resolution scanning electron microscopy (SEM) and temperature-dependent photoluminescence (PL) spectra. All samples were grown by atmospheric pressure metalorganic chemical vapour deposition (MOCVD). Elliptical QWR arrays having a central thickness of 20 nm and an effective width of 40 nm were produced at the bottom of the V-grooved gratings. An intense and sharp PL peak with a full width at half maximum (FWHM) of 6 meV was observed from the QWR array at 21 K, which shows a sufficient mode coupling among the neighbouring QWRs and an effective carrier confinement at the quantum wire subbands. The distinct temperature dependence of the PL spectra also provides evidence of a well-fabricated QWR array. The small variation of the FWHM and peak energy from the temperature-dependent PL spectra implies that the carrier confinement at the QWR subbands is retained up to elevated temperatures.

Crystallographically limited submicrometer gratings in (100) and (211) silicon

We demonstrate the fabrication of submicrometer gratings in (100) and (211) Si with periodicities that are appropriate for normal-incidence coupling into Ge-Si waveguides. Gratings of periodicities in the 0.25-0.75microm range were fabricated by a standard holographic lithography technique. Crystallographically preferential wet etching that effectively terminates at the {111} family of planes facilitates the fabrication of symmetric gratings in (100) Si and of blazed gratings in (211) Si. The gratings used in this study are appropriate for the fabrication of integrated first- and second-order, normal-incidence grating couplers at a 1.30-microm wavelength. The blazed gratings show a preferential coupling of more than 80% of the total diffraction into the (+1) diffraction order at normal incidence. The maximum first-order diffraction efficiency obtained with these gratings was approximately 28% in (100) Si and 23% in (211) Si.