Integration Of Optical Elements Research Articles

III-V nanostructures with different dimensionality on silicon

The possibility of AlGaAs nanowires with GaAs quantum dots and InP nanowires with InAsP quantum dots growth by molecular-beam epitaxy on silicon substrates has been demonstrated. Results of GaAs quantum dots optical properties studies have shown that these objects are sources of single photons. In case of InP nanowires with InAsP quantum dots, the results we obtained indicate that nearly 100% of coherent nanowires can be formed with high optical quality of this system on a silicon surface. The presence of a band with maximum emission intensity near 1.3 μm makes it possible to consider the given system promising for further integration of optical elements on silicon platform with fiber-optic systems. Our work, therefore, opens new prospects for integration of direct bandgap semiconductors and singlephoton sources on silicon platform for various applications in the fields of silicon photonics and quantum information technology.

Active and Quantum Integrated Photonic Elements by Ion Exchange in Glass

Ion exchange in glass has a long history as a simple and effective technology to produce gradient-index structures and has been largely exploited in industry and in research laboratories. In particular, ion-exchanged waveguide technology has served as an excellent platform for theoretical and experimental studies on integrated optical circuits, with successful applications in optical communications, optical processing and optical sensing. It should not be forgotten that the ion-exchange process can be exploited in crystalline materials, too, and several crucial devices, such as optical modulators and frequency doublers, have been fabricated by ion exchange in lithium niobate. Here, however, we are concerned only with glass material, and a brief review is presented of the main aspects of optical waveguides and passive and active integrated optical elements, as directional couplers, waveguide gratings, integrated optical amplifiers and lasers, all fabricated by ion exchange in glass. Then, some promising research activities on ion-exchanged glass integrated photonic devices, and in particular quantum devices (quantum circuits), are analyzed. An emerging type of passive and/or reconfigurable devices for quantum cryptography or even for specific quantum processing tasks are presently gaining an increasing interest in integrated photonics; accordingly, we propose their implementation by using ion-exchanged glass waveguides, also foreseeing their integration with ion-exchanged glass lasers.

Integration of polymeric membrane/dielectric sphere assemblies in microfluidic chips for enhanced-contrast imaging with low-magnification systems

Current microscopy systems for the imaging of microorganisms are expensive because of their optimized design toward resolution maximization and aberration correction. In situations where such an optimization is not needed, for instance to merely detect the presence of pathogens in liquids for on-site analyses, a potential approach is to use highly refractive spheres in combination with low-magnification objectives to increase the resolution and the sensitivity of the optical sensing system in a cost-effective fashion. Indeed, for point-of-need assays, integration of optical elements on a microfluidic device can bring several advantages, such as test parallelization/automation and low-volume consumption. We report a study on BaTiO3 spheres that are partially embedded in thin polymeric membranes of mismatched refractive index. We computed the transformation that the polymeric membrane/dielectric sphere assembly (PMDSA) mediates on the light originating from the sample toward the optical detector and shows its enhanced-detection potential for a low-magnification objective. We then propose a method to easily fabricate chips with custom designs and precise location of such dielectric spheres relative to the microfluidic structures for enhanced imaging of microorganisms. We applied this concept to the detection of living fluorescent bacteria, either flowing in aqueous medium or immobilized in hydrodynamic traps. We quantified the contrast gain provided by the PMDSA for short exposure when used with a low-magnification objective. By comparing with a high-magnification objective, we also show how longer-term imaging can be still reliably performed with a more cost-effective system. Since the present PMDSA concept combines the optical enhancement of low-magnification systems with the flexibility of microfluidic handling, it can be highly suitable for portable and cost-effective systems for on-site analysis, from flow cytometry to longer-term antibiotic testing.

Absorption characteristics of silver ion-exchanged layers in chloride photo-thermo-refractive glass

Subject of Research. The paper considers effect of chloride in composition of photo-thermo-refractive glass on the spectral properties of silver nanoparticles formed in ion-exchanged layers after heat treatment. Method. Glasses based on Na2O–ZnO–Al2O3–SiO2–F doped with antimony oxide Sb2O3, cerium oxide CeО2 and a variable chloride content (0–1 mol%) were synthesized for the study. Silver ions were introduced by the low-temperature Na+–Ag+ ion exchange method into the synthesized glasses. For this purpose, glass samples were immersed in a mixture of 0.1AgNO3/99.9NaNO3 (mol%) nitrates at the temperature of 320 °С for 15 minutes. After the ion exchange glasses were irradiated with ultraviolet radiation and heat-treated at the temperature of 500 °C for 3 hours to achieve the growth of silver nanoparticles. Main Results. Spectrum properties of chloride photo-thermo-refractive glasses with silver nanoparticles in ion-exchanged layers are studied. It is found that the presence of chloride in the photo-thermo-refractive glass matrix results in a long-wavelength shift of the absorption band of silver nanoparticles. That may be attributed to the growth of the mixed AgCl/NaCl shell on silver nanoparticles. The formation of silver nanoparticles in ion-exchanged layers occurs both in the irradiated and unirradiated regions of the glass. Practical Relevance. The results can be used to create Bragg gratings inside photo-thermo-refractive glass for input and output radiation (pump and signal) into the waveguide structures formed by the ion exchange method, and to create monolithic integrated optical elements on a single substrate, that is very essential for integrated optics

Optical Properties Transformation under Laser Treatment of Hybrid Organic–Inorganic Thin Films

Thin films (50–100 nm) of hybrid materials (HM's) based on inorganic matrices and organic phosphor are prepared by layer‐by‐layer vacuum deposition on glass substrates. The possibility of an exchange solid‐phase reaction between the organometallic phosphor (tris‐(8‐hydroxyquinolate) aluminum) and inorganic compounds without thermal heating of the sample volume is demonstrated. The reaction is stimulated by Pharos SP laser (1030 nm wavelength, 180 fs pulse duration, 100 kHz pulse repetition rate, maximum power 6 W) with localization of the reaction region to the focused laser beam waist (diameter of ≈1 µm). The resulting products have a photoluminescence (PL) intensity exceeding the PL intensity of the original organometallic phosphor. Local modification of HM's thin films by femtosecond laser beam allows creating 2D integrated optics elements.

Control of waveguide properties by tuning femtosecond laser induced compositional changes

Local compositional changes induced by high repetition rate fs-laser irradiation can be used to produce high performance optical waveguides in phosphate-based glasses. The waveguide refractive index contrast is determined by the local concentration of La, which can be changed by the action of the writing laser pulses. In this work, we have investigated the degree of control that can be exerted using this waveguide writing mechanism over the cross-section of the guiding region, and the local refractive index and compositional changes induced. These variables can be smoothly controlled via processing parameters using the slit shaping technique with moderate Numerical Aperture (NA 0.68) writing optics. The combined use of X-ray microanalysis and near field refractive index profilometry evidences a neat linear correlation between local La content and refractive index increase over a broad Δn interval (>3 × 10−2). This result further confirms the feasibility of generating efficient, integrated optics elements via spatially selective modification of the glass composition.

Photorecording Polymeric Waveguide Film Based on 2,2-difluoro-4-(9-anthracyl)-6-methyl-1,3,2-dioksaborine for Photonics

In this paper the possibility of using the novel polymeric photosensitive medium for the fabrication of integrated optics elements was demonstrated. The medium is based on PMMA doped by beta-diketonatoboron difluorides. Planar and strip waveguides with the attenuation losses less than 1.8 dB/cm were fabricated in the layer of the medium. The photoinduced recording of the diffraction grating with the spatial frequency up to 3000 mm-1and diffraction efficiency ~5% in such waveguides was demonstrated. The possibility to improve the diffraction efficiency of recorded gratings up to 51% by chemical treatment was demonstrated.

Photoinduced record of waveguide structures in films of polymethylmethacrylate doped with beta-diketonatoboron difluorides

In this paper the possibility of using the novel polymeric photosensitive medium for the fabrication of integrated optics elements was demonstrated. The medium is based on PMMA doped by 2,2-difluoro-4-(9-anthracyl)-6-methyl-1,3,2-dioksaborine. Planar and strip waveguides with the attenuation losses less than 2dB/cm were fabricated in the layer of the medium. The photoinduced recording of the diffraction grating with the spatial frequency up to 2500mm−1 and diffraction efficiency ~5% in such waveguides was demonstrated. The possibility to improve the diffraction efficiency of recorded gratings up to 47% by chemical treatment was demonstrated.

Enhancement of radiation from dielectric waveguides using resonant plasmonic coreshells

Here, we present parametric studies of a method for enhancing radiation from a dielectric waveguide through the use of resonant coreshells. These coreshells act as a compact impedance matching element between the guided modes of the waveguide and radiation modes in free space. Furthermore, we also show that we can sense the distance between the waveguide end and the coreshell by monitoring the reflectance of the waveguide mode. Coreshell decoupled radiation from dielectric waveguides could hence find use for highly integrated optical coupling elements or nanometric distance sensors.

Passive integrated optics elements based on long-range surface plasmon polaritons

Waveguides and passive integrated optics elements constructed from thin metal films of finite width embedded in a homogeneous background dielectric and propagating long-range surface plasmon polaritons (LRSPPs) have been characterized experimentally at free-space optical wavelengths near 1550 nm. Straight and curved waveguides, s-bends, four-port couplers, y-junctions, and Mach-Zehnder interferometers have been carefully characterized. Additionally, rigorous models based on modal decomposition have been proposed for all of these elements and validated via comparisons with the measurements. Excellent qualitative and quantitative agreement between theory and experiment is observed for all structures over all measurement wavelengths. It is hoped that this work will help further establish this new integrated optics technology, taking it beyond demonstrators.

Demonstration of integrated optics elements based on long-ranging surface plasmon polaritons

An experimental investigation of long-ranging surface plasmonpolariton waves guided along thin finite width Au structures embedded in a homogeneous background dielectric is reported. The operation of key passive integrated optics elements such as straight waveguides, s-bends, y-junctions and couplers is demonstrated at a free space optical wavelength of 1550 nm. The influence of some important design parameters on the performance of these elements is presented and discussed.

Femtosecond waveguide writing: a new avenue to three-dimensional integrated optics

Using tightly focussed femtosecond laser pulses, waveguides can be fabricated inside various glasses and crystals. This technique has the potential to generate not only planar but three-dimensional photonic devices. In this paper we present, to the best of our knowledge, the first true three-dimensional integrated optical device, a 1×3 splitter fabricated in pure fused silica. The optical properties of this device and possibilities for the fabrication of complex high-density integrated optical elements are discussed.

Design tool for symbolic substitution

A design tool that aids in designing, evaluating, and comparing various implementations of optical symbolic substitution is presented. A hierarchical, modular approach to design similar to that used in digital electronics is supported to facilitate the design of large complex systems. This tool is composed of a schematic capture unit, a simulator unit, and an evaluation unit. Starting with the definition of certain basic or integrated optical elements performing well-defined functions, a schematic capture unit helps to design specific functions. The simulator tool helps to verify the design and the evaluation tool determines its complexity. The usefulness of this design tool is demonstrated with an example design of a simple four-function arithmetic logic unit.

Superimposed grating for use with magneto-optical disk heads

A superimposed grating comprising a diffraction grating and a high-frequency grating, whose aim is to achieve alignment-free and multifunctional integrated optical elements, is demonstrated for the first time. Then a lightweight and compact magneto-optical disk head that uses this superimposed grating is proposed. The superimposed grating, which simultaneously operates a polarizing beamsplitter and an off-axis cylindrical lens, has three functions required for optical heads: focusing error detection, tracking error detection, and signal detection. Measured focusing and polarizing characteristics suggest that the superimposed grating has the desirable error detection and signal detection for magneto-optical disk heads. A detailed investigation of this grating with an emphasis on clarifying both its basic principles and its use with magneto-optical disk heads is presented.

Surface waves in integrated-optics elements with distributed coupling (review)

A review is given of the literature on the interaction and conversion of surface waves in integrated-optics elements with distributed coupling. A general description is given of the distributed coupling of surface waves in thin-film waveguides and a detailed investigation is made of their interaction and conversion in waveguides with periodically modulated parameters. The different types of periodic modulation of the parameters of thin-film waveguides are discussed and compared. The main elements and devices in integrated-optics systems based on periodic diffraction-grating structures are examined. The possibility of using aperiodic grating structures in integrated optics is demonstrated and devices with tunnel distributed coupling are considered. PACS numbers: 42.82. + η Many phenomena in physics and engineering can be considered to be coupled wave effects. 1 In integrated optics many surface-wave distributed-coupling effects are also observed in elements and devices designed for different purposes. These include radiation scattering by irregularities in dielectric thin-film waveguides (TFW's), diffraction-induced conversion of surface waves at grating structures and directional power coupling, mode conversion, and nonlinear interactions. The devices and elements of greatest interest in integrated optics are those based on surface wave coupling and interaction effects in TFW's with periodically modulated parameters. These are used in the development of active devices such as distributed-feedback and distributed-Bragg-reflector lasers, various passive devices such as filters, radiation coupling elements, mode converters, diffraction modulators and deflectors, and are also used for spatially selective radiation filtering in TFW's. Many of these devices may find extensive applications in optical communication lines based on fiber waveguides. The present review gives a general description of the distributed coupling of surface waves in a TFW and a detailed analysis is made of the interaction and conversion of surface waves in waveguides with periodically modulated parameters. The main elements and devices in integrated-optics systems based on periodic grating structures are considered. The possibility of using aperiodic grating structures in integrated optics is demonstrated and devices with tunnel distributed coupling are examined.

VPE Growth of III/V Semiconductors

In recent years research on the epitaxial growth of IIIjV alloys has con­ centrated on those systems capable of producing lattice-matched hetero­ structures. The most important alloy of this type is AlxGal-xAs because the nearly exact lattice-parameter match between GaAs (ao = 5.654) and AlAs (ao = 5.661) allows the growth of lattice-matched heterostructures with nearly ideal interfaces and direct bandgap energies covering an important range for optoelectronic devices from 1 .43 to ,.., 2.0 eV. Other systems for which the lattice parameter of the epilayer can be made to match that of the substrate at a given composition such as GaxInl-xP / GaAs, or for a range of compositions, such as GaxIn 1 xAsyP 1 y/InP, are in much earlier stages of development. The ability to grow high quality lattice-matched AlxGa1-xAs heterostructures has resulted in dramatic improvements in the performance of such optoelectronic devices as lasers, high radiance IR LEDs for optical communication applications, visible LEDs, and integrated optics elements and circuits (1). In addition, two-layer devices where the top AlxGal-xAs layer acts to reduce surface recombination and to transmit effectively bandgap light to the junction have resulted in solar cells with air mass zero efficiencies of 19% (2) versus 14% for the best Si devices. If these could be produced cheaply, they could have significant impact on the feasibility of terrestrial photo voltaic solar energy converSlOn. A number of techniques used for the epitaxial growth of IIIjV semi­ conductors might be applied to the growth of AlxGal-xAs, including liquid phase, vapor phase, and molecular beam expitaxial growth (LPE, VPE, and MBE, respectively). Nearly all of the devices listed above are fabricated in AlxGal-xAs grown by the LPE technique. The LPE tech­ nique for a multilayer structure consists of a series of individual growth

Photodetector elements and relief-type diffraction gratings in thin films of As2S3for integrated optics

The possibility is investigated of constructing combined detection and recording integrated-optics elements and of making relief-type diffraction grating structures on the surfaces of thin-film waveguides utilizing amorphous chalcogenide semiconductors of the As–S–Se system. Photodetector elements and devices for radiation coupling and mode conversion in thin-film waveguides were made from As2S3.

Waveguide structures and functional elements of integrated optics systems based on volume holographic gratings in thin As2S3films

An investigation was made of functional integrated optics elements based on volume-phase holographic gratings in thin-film optical waveguides. The waveguides were films of arsenic trisulfide. Sinusoidal phase gratings were formed in the bulk of a thin-film waveguide and their function was the reflection and conversion of surface waves. A thin-film reflecting grating filter with a band half-width ~2.5 A and a maximum reflection coefficient of 0.9 was made. The calculated parameters of the grating structures were in satisfactory agreement with the experimental data.

Investigation of planar waveguides prepared for integratedoptics systems by solid-state diffusion

A report is given of an experimental investigation of the optical parameters of planar microscopic waveguides prepared by the diffusion of PbO. A physical explanation is given of the experimental dependences of the phase delay coefficient and of the waveguide losses on the duration of diffusion and thickness of PbO film. It is shown that planar integrated-optics elements and devices can be made from diffused waveguides.

A new device for realisation of gratings and modulation grids

Methods have already been described, to realise phase filters with either computer or optical methods. The new set-up, described here, allows the realisation of phase gratings, integrated-optics elements such as coupling systems, or amplitude filters used in Fourier spectroscopy. Each of these examples is a particular application of amplitude or phase profile.