Waveguide-type Devices Research Articles

Wavelength Dependence of Optical Waveguide-Type Devices for Recognition of QPSK Routing Labels

In photonic label routing networks, recognition of optical labels is one of the key functions. We have proposed passive waveguide-type devices for recognition of optical labels coded in quadri-phase-shift-keying (QPSK) form. In this paper, we consider wavelength dependence of the devices. The basic module of the proposed device consists of a 3-dB directional coupler, two Y-junctions, and an asymmetric X-junction. The Y-junction and an asymmetric X-junction have basically no wavelength dependence. Although the 3-dB directional coupler has weak wavelength dependence, the device for two-symbol label recognition is found to work in wavelength 1.5-1.6 μm. The performance of the device is confirmed by simulation using beam propagation method (BPM).

Waveguide-Type Optical Circuit for Recognition of Optical QPSK Coded Labels in Photonic Router

In photonic label routing networks, optical recognition of optical labels is one of the key functions. We propose a In photonic label routing networks, optical recognition of optical labels is one of the key functions. We propose a passive waveguide-type device for recognition of optical coded labels. We consider quadrature-phase-shift-keying (QPSK) coded labels. The basic module of the proposed device consists of a 3-dB directional coupler, two Y-junctions, and an asymmetric X-junction. By using interference between an optical pulse of each coded bit and a identifying bit pulse, the basic module distinguishes optical phase of the QPSK signal in a self-routing fashion of the identifying bit pulse. QPSK codes consisting of plural bits can also be recognized by connecting the basic module device in a tree structutre through a phase adjustment circuit. The performance of the proposed basic module is confirmed by simulation using beam propagation method (BPM).passive waveguide-type device for recognition of optical coded labels. We consider quadrature-phase-shift-keying (QPSK) coded labels. The basic module of the proposed device consists of a 3-dB directional coupler, two Y-junctions, and an asymmetric X-junction. By using interference between an optical pulse of each coded bit and a identifying bit pulse, the basic module distinguishes optical phase of the QPSK signal in a self-routing fashion of the identifying bit pulse. QPSK codes consisting of plural bits can also be recognized by connecting the basic module device in a tree structure through a phase adjustment circuit. The performance of the proposed basic module is confirmed by simulation using beam propagation method (BPM).

Poled Electrooptic Polymers and Waveguide Type Devices

In recent broadband photonic network system, high speed optical data transmission is required. Electrooptic (EO) polymers are attractive because of their large nonlinearity, fast response time and ease of device fabrication. Therefore the EO polymers are expected for the application of ultra-high speed EO switch and/or wide bandwidth EO modulator, both of which will be used in future photonic network. In this report, recent progress of EO polymers and their application to waveguide type devices are described.

High-Resolution Pattern Reproduction by Cold Ultra Violet Stamping in Optical Polymeric Films

In this paper, we present a new method of waveguide-type device fabrication using an optical polymer. This method is applied to the fabrication of a grating on top of a polymeric waveguide film where, we used a mixture of pentaerythritol triacrylate, N-methyldiethanolamin, and eosin as a polymer material. This mixture, called henceforward PNME, acts as a negative-type photoresist polymeric material. Exposure of the material to light of specific wavelength makes the material solidify. Using this particular property of PNME and the fact that before the solidification PNME material is liquid, and thus copies the volume of the vessel where it is contained, we were able to fabricate polymeric films and waveguides with a relief grating on their surfaces. It was also determined that the interface between the side walls of the vessel and the PNME material plays a vital role in the fabrication process. Moreover, the presented method of fabrication is a high-resolution, high-output, and low-cost method of optical device fabrication and thus it is particularly suitable for commercial use.

NANO-CRYSTALS OF c-DIAMOND, n-DIAMOND AND i-CARBON GROWN IN CARBON-ION IMPLANTED FUSED QUARTZ

Combined high-resolution transmission electron microscopy, selected area electron diffraction and parallel electron energy loss spectroscopy are used to characterise carbon nano-phases found embedded in fused quartz. These appear after implantation of 1 MeV carbon ions, followed by annealing in argon, oxygen and forming gas for 1 hour at 1100°C. For Ar, virtually all of the carbon diffuses out of the substrate with no observable carbon clusters for all doses studied. After annealing in oxygen, a crystalline CO x phase is identified at the end of range, following a dose of 5×1017 C/cm 2. Three nano-crystalline carbon phases, including diamond, appear after annealing in forming gas: these form a layer 170 nm beneath the fused quartz surface for all ion doses. The average size of these clusters and the corresponding phases depend on the ion dose; the smallest size of 5–7 nm diameter crystallise as fcc [Formula: see text] diamond following a dose of 0.5× 1017 C/cm 2, whereas clusters of 8–13 nm diameter, for a higher dose of 2× 1017 C/cm 2, have a [Formula: see text] modified phase of diamond known as n-diamond. The largest clusters, diameter 15–40 nm, for a dose of 5× 1017 C/cm 2, have the cubic P2 13 (or P4 232) structure known as i-carbon. These buried layered diamond and diamond-related materials may have applications for field emission and optical waveguide type devices.

Ultrafast all optical modulation based on intersubband transition in semiconductor quantum wells

Ultrafast modulation of interband-resonant light by intersubband-resonant light in n-doped GaAs/AlGaAs and GaN/AlGaN quantum wells was investigated by femtosecond pump-probe technique. A planar-type AlGaAs/GaAs modulation device shows a modulation speed of ∼1 ps at room temperature. The observed modulation efficiency indicates that 99% modulation can be achieved with a control pulse energy of ∼1 pJ when a waveguide-type device structure is utilized. The feasibility of the all-optical modulation in GaN/AlGaN quantum wells is also investigated. The intersubband carrier relaxation time, which mainly determines the modulation speed, is measured and is found to be extremely fast (130–170 fs). The results indicate that the optical modulation at a bit rate of over 1 Tb/s will be possible by utilizing the intersubband transition in GaN/AlGaN quantum wells. The modulation efficiency in GaN/AlGaN quantum wells is also discussed in comparison with that in GaAs/AlGaAs quantum wells.

Pump-probe measurement of ultrafast all-optical modulation based on intersubband transition in n-doped quantum wells

Modulation of interband-resonant light (∼800 nm) by intersubband-resonant light (5–7 μm) was investigated in n-doped AlGaAs/GaAs multiple quantum wells by a two-color femtosecond pump-probe technique. Modulation with a recovery time of ∼1 ps is observed in a plainer-type modulation device at room temperature. The modulation of interband absorption coefficient is ∼1000 cm−1 when the energy density of the intersubband light pulse is ∼4 fJ/μm2. The modulation efficiency indicates that 99% modulation can be achieved with a control pulse energy of ∼1 pJ when a conventional waveguide-type device structure is utilized. The mechanism which determines the modulation speed is discussed in terms of carrier relaxation process. It is shown that the modulation speed is mainly determined by the inter- and intrasubband relaxation times, where the latter is influenced by hot phonon effects.

Electro-optic effect, propagation loss, and switching speed in polymers containing nano-sized droplets of liquid crystal

Polymers containing droplets of liquid crystal smaller than 100 nm, which have good transparency and easily form films, were prepared under various conditions to evaluate their potential as electro-optic materials for waveguide-type devices. By varying the liquid crystal concentration and the strength of the UV irradiation causing photo-induced phase separation of the droplets, we were able to control the droplet size and density. We have clarified how the birefringence generated in an applied electric field, switching speed, and optical loss of light propagating in the film depend on droplet size and density. Polymer materials having a large electro-optic effect (δn = 0.001 at 8 V μm-1), low propagation loss (~2.5 dB cm-1), and fast response time (~10 μs) have been developed.

All-optical switching by use of cascading of phase-matched sum-frequency generation and difference-frequency generation processes

We have investigated proposed all-optical switching by use of cascading of phase-matched sum-frequency-generation (SFG) and difference-frequency-generation (DFG) processes. The switching operation is accomplished by both a π phase change and an amplitude change of the signal field in SFG–DFG processes. We theoretically confirmed that the proposed switch requires the least operation power of any switch that uses cascading SFG–DFG processes. The switching characteristics have been numerically clarified, and the experimental full-switching characteristics when a bulk-type periodically poled LiNbO3 is used correspond to the numerical analysis. An ultrafast all-optical switch with low switching power and small size can be expected from use of waveguide-type devices.

All-optical waveguide-type gain switch utilizing intersubband transition

All-optical switching performance of waveguide-type device utilizing intersubband transition is investigated by analyzing the position-dependent change of optical power densities and carrier densities in the waveguide. In the device, the three lowest energy-level subbands in the conduction band structure of asymmetric coupled quantum wells are used. The optical excitation pulse excites the electrons in the first subband to the third subband and the stimulated emission between the third subband and second subband amplifies the optical signal pulse. We find that the signal pulse is notably amplified when the excitation pulsewidth is less than the relaxation time of the third subband. The calculated results show that wavelength conversion from 1.35 to 1.6 /spl mu/m with a gain of more than 10 dB is achieved by the excitation using an optical pulse with 1.5-ps width. This demonstrates the effectiveness of using a waveguide-type device structure with pulsed operation to make devices with a high-optical gain. We also derive a simple approximation for the optical gain. We show that the approximation gives results in good agreement with the results of the rigorous simulation using a finite difference method and the approximation is useful for designing devices.

Optical Mode Conversion by Magnetostatic Surface Waves in Optical Waveguide-Type Devices Using Cerium- and Bismuth-Doped Garnet Crystalline Films

Optical devices using magnetostatic surface waves (MSSWs) have important applications in optical signal processing and optical computing. In this paper we propose the analysis and design of an optical mode conversion device that features improved switching efficiency achieved by the use of a new material with increased magneto-optic effect. The device consists of cerium- and bismuth-doped thin and thick garnet films. The design features 100% mode conversion over an interaction length of about 5 mm for an applied microwave power density in the range 1–10 mW/mm. Cerium- and bismuth-doped Yttrium Iron Garnet (YIG) films are fabricated by rf sputtering and their crystal properties are studied using X-ray microanalyzer and X-ray diffractometer.

Material Dependence of Strain Distributions of Surface Acoustic Waves in Multilayered Thin-Film Acousto-Optic Devices

The acoustic strain distributions in thin acousto-optic waveguides consisting of two-layered thin amorphous films on a Y-cut, X-propagation LiNbO3 substrate are studied. The theoretical relation between the elastic properties and the strain distributions in layered thin films is discussed. The strains contributing to acousto-optic interactions in the film increase as the Poisson ratio of the film material decreases. The strain amplitude in each of the layered thin films can be controlled over a wide range by suitable selection of choosing the film materials. The results give important information on improving the mode-conversion efficiency in thin-film acousto-optic devices and for designing various waveguide-type devices using acousto-optic interactions. Further, method of evaluating the elastic properties of amorphous films is discussed.

Research of a Stationary High Power Microwave Plasma at Atmospheric Pressure

The optimum configuration of the rectangular waveguide type device is given for producing a stable high power microwave plasma. It is shown that helical flow of nitrogen gas stabilizes the plasma beam and contributes to the formation of a virtual “gas wall” between the plasma beam and the pyrex wall. It is clarified that the change in the pyrex tube diameter strongly affects the plasma parameters and the comparison of experimental results with a theory of energy absorption by Meierovich shows a better agreement by assuming the existence of a “gas wall”.