Polyimide/Ta2O5/polyimide antiresonantreflecting optical waveguides

A novel antiresonant reflecting optical waveguide (ARROW) fabricated using both the organic and dielectric thin film technologies is presented for the first time. The ARROW consisted of the fluorinated polyimide and tantalum pentoxide (Ta₂O₅) hybrid layers deposited on a Si substrate. For TE polarized light, the propagation loss of the waveguide as low as 0.8 dB/cm is obtained at 632.8 nm. The propagation loss for TM polarized light is 2.7 dB/cm. Some design considerations of the hybrid ARROW are also discussed in this work     

Hybrid polyimide/Ta2O5/polyimide antiresonantreflecting optical waveguides

A hybrid polyimide/Ta₂O₅/polyimide antiresonant reflecting optical waveguide (ARROW) is presented. The ARROW consists of fluorinated polyimide and tantalum pentoxide hybrid layers deposited on Si substrates. The propagation losses of the device are 0.6 and 2.6 dB/cm at 1.3 μm for TE and TM polarised lights, respectively     

Low-loss proton-exchanged waveguide in MgO-doped LiNbO3fabricated with pyrophosphoric acid using Ta2O5protective mask

The authors describe low-loss proton-exchanged channel waveguides in MgO-doped LiNbO₃. The authors demonstrate the application of a Ta₂O₅ film for the protective mask material in proton-exchanging instead of a Ta film in order to reduce the propagation loss. A Ta₂O₅ sputtered film was applied as a protective mask with pyrophosphoric acid. The propagation loss of the waveguide, measured with laser diode light (λ=0.83 μm) was 0.5 dB/cm. It is shown that the use of a Ta₂O₅ mask reduces the propagation loss compared with the use of a Ta mask (1.5 dB/cm)     

Wavelength multiplexer based onSiO2-Ta2O5 arrayed-waveguide grating

The characteristics of a wavelength multiplexer based on an arrayed-waveguide grating are carefully investigated by using the grating theory and related experiments. A 28-channel multiplexer is designed and fabricated as SiO₂-Ta₂O₅ waveguides on a 1 cm×2 cm substrate. The designed wavelength channel spacing of 1 nm is obtained. The crosstalk to an adjacent channel is -15 dB. The measured minimum loss is 4.2 dB, which is composed of 3.4 dB excess loss and 0.8 dB grating loss     

Loss reduction of an ARROW waveguide in shorter wavelength and itsstack configuration

The reduction of the propagation loss of an antiresonant reflecting optical waveguide (ARROW) to 0.3 dB/cm in a short-wavelength band by using transparent TiO₂/SiO₂ interference cladding is discussed. An analysis method for ARROW is developed to analyze its propagation characteristics. Two uncoupled parallel ARROWs were stacked with 2-μm spacing, to obtain three-dimensional optical interconnection     

A polarized brightness-enhancedNd:Y3Al5Ol2 planar waveguide laser

A simple method for the production of a polarized Nd:Y₃Al₅0₁₂ on Y₃Al₅ O₁₂ planar waveguide laser is reported. A 50-nm layer of Au deposited on the surface of an unclad, 8.3-μm thick core region has produced an improvement in the TE/TM polarization extinction ratio from 7 to 27 dB. The M² of the beam in the guided plane has been reduced from 1.53±0.01 in an uncoated region of the waveguide to 1.17±0.01 in the Au-coated region using optimum pump launch conditions     

Reliable Low-Cost Fabrication of Low-Loss $hbox{Al}_{2}hbox{O} _{3}{:}hbox{Er}^{3+}$ Waveguides With 5.4-dB Optical Gain

A reliable and reproducible deposition process for the fabrication of Al₂O₃ waveguides with losses as low as 0.1 dB/cm has been developed. The thin films are grown at ~ 5 nm/min deposition rate and exhibit excellent thickness uniformity within 1% over 50times50 mm² area and no detectable OH^- incorporation. For applications of the Al₂O₃ films in compact, integrated optical devices, a high-quality channel waveguide fabrication process is utilized. Planar and channel propagation losses as low as 0.1 and 0.2 dB/cm, respectively, are demonstrated. For the development of active integrated optical functions, the implementation of rare-earth-ion doping is investigated by cosputtering of erbium during the Al₂O₃ layer growth. Dopant levels between 0.2-5times10²⁰ cm^-3 are studied. At Er³⁺ concentrations of interest for optical amplification, a lifetime of the ⁴I_13/2 level as long as 7 ms is measured. Gain measurements over 6.4-cm propagation length in a 700-nm-thick Al₂O₃:Er³⁺ channel waveguide result in net optical gain over a 41-nm-wide wavelength range between 1526-1567 nm with a maximum of 5.4 dB at 1533 nm.     

New polarization-insensitive antiresonant reflecting opticalwaveguide (ARROW-B)

A type of antiresonant reflecting optical waveguide (ARROW-B) is proposed to reduce the polarization dependence of propagation loss in ARROW. A low-loss propagation (<1 dB/cm) for both transverse electric (TE) and transverse magnetic (TM) modes is demonstrated. The features of the conventional waveguide, ARROW, and ARROW-B are summarized. The conventional ARROW is advantageous in constructing some functional devices such as a waveguide-type polarizer or wavelength demultiplexer. On the other hand, the ARROW-B seems to be suitable for applications requiring a primarily polarization-insensitive function, such as optical interconnection     

Low Rayleigh scatteringP2O5-F-SiO2 glasses

The Rayleigh scattering and infrared absorption losses of P₂ O₅-F-doped silica glass, which is a candidate material for ultra-low-loss optical fiber, were investigated experimentally. The Rayleigh scattering loss of 8.5 wt.% P₂O₅ and 0.3 wt.% F-doped SiO₂ glass is found to be 0.8 times that of pure silica glass. It is also found that the infrared absorption property of P₂O₅-F-SiO₂ glass is almost the same as that of pure silica glass. The minimum loss for the proposed composition is estimated to be 0.11 dB/km at 1.55 μm wavelength, and 0.21 dB/km at 1.3 μm wavelength     

CO2laser annealing of Si3N4, Nb2O5, and Ta2O5thin-film optical waveguides to achieve scattering loss reduction

Significant reductions in the optical scattering losses of Si3N4, Nb2O5, and Ta2O5waveguides fabricated on SiO2/Si substrates have been measured following CO2laser annealing. The largest improvements were observed for Si3N4waveguides, where waveguide attenuation values of about 6.0 dB/cm before laser annealing were reduced to as low as 0.1 dB/cm afterwards. An improvement of more than an order of magnitude was obtained for a Nb2O5waveguide upon laser annealing, the attenuation coefficient decreasing from 7.4 to 0.6 dB/cm. In the case of one Nb2O5waveguide no improvement was obtained upon laser annealing. The attenuation coefficient of a reactively sputtered Ta2O5waveguide was found to decrease from 1.3 dB/cm before laser annealing to 0.4 dB/cm afterwards. In the case of a thermally oxidized Ta2O5waveguide a small initial improvement in waveguide attenuation was followed by degradation upon further laser annealing.     

An ARROW optical wavelength filter: design and analysis

A novel ARROW (antiresonant reflecting optical waveguide)-based optical wavelength filter is proposed. The modal characteristics of the coupled ARROW structures is analyzed rigorously by the transverse resonance method. As an alternative configuration to the conventional directional coupler filter, the proposed device features large core size compatible with fiber and nearly periodic dependence of the coupling-length on the waveguide separation, which provides more flexibility for fabrication of the device. A design procedure for this type of coupled ARROW structure used for wavelength filtering is presented. The devices designed are simulated and verified by the beam propagation method. An ARROW wavelength filter based on SiO₂/TiO₂ has a FWHM bandwidth narrower than 7 Å     

A Minimized SiO2 Waveguide With an Antiresonant Reflecting Structure for Large-Scale Optical Integrations

A minimized SiO₂ waveguide with an antiresonant reflecting buffer, a SiO₂ core, and an air cladding is presented. The buffer includes multiple periods of antiresonant reflecting structure to lower leakage loss to the substrate. Theoretically speaking, when there are three periods of etch-through antiresonant reflecting structures, one obtains a straight minimized SiO ₂ waveguide with a low leakage loss (<0.01 dB/cm) and a bending radius as small as 15 mum (because of the large index contrast between the core (SiO₂) and the air cladding in the lateral direction)     

Fabrication and characterization of Si-MOSFET's with PECVDamorphous Ta2O5 gate insulator

Silicon MOS transistors having amorphous Ta₂O₅ insulator gates have been fabricated. The Ta₂O₅ films were deposited using a low pressure (a few mtorr) plasma-enhanced CVD process in a microwave (2.45 GHz) excited electron cyclotron resonance reactor. The source gas was TaF₅. Electrical characteristics of p-channel Al gate transistors are presented     

ARROW-type vertical coupler filter: design and fabrication

Vertical coupler filters (VCF) exhibiting narrow bandwidth and low sidelobe levels have been designed and demonstrated. Narrow bandwidth filter response is achieved due to the strong asymmetry between the waveguides of the filter and the nondispersive characteristics of the anitresonant reflecting optical waveguide (ARROW) structure. An ARROW-type VCF with a conventional parallel coupled directional coupler configuration with a full width at half-maximum (FWHM) of 1.36 nm and a maximum sidelobe level of -8.5 dB was fabricated using a compound glass consisting of SiO₂ and SiO₂-Ta₂O₅ . The filter sidelobe levels were then further suppressed by using an X-crossing arrangement to provide coupling strength apodization along the device. The sidelobe levels of this modified X-crossing filter were suppressed to below -23 dB and the measured FWHM was 3.9 nm. The central wavelength of the reported filters are in the 1.55 μm region. The measured results are in good agreement with theoretical results from an analysis procedure that combines the coupled mode theory with the finite difference complex mode solver     

Film-level hybrid integration of AlGaAs laser diode with glasswaveguide on Si substrate

A ridge-waveguide AlGaAs laser diode (LD) was integrated with a SiO₂-Ta₂O₅ embedded waveguide on a Si substrate by using a film-level hybrid integration technique of semiconductor epitaxial film. CW operation of the LD was achieved at room temperature. The LD-waveguide butt-coupling loss was 9 dB, and the loss due to misalignment was estimated at 3 dB, which corresponds to a displacement of about 1 μm in both the vertical and lateral directions     

Low Dit, thermodynamically stable Ga2O3-GaAs interfaces: fabrication, characterization, and modeling

Thermodynamically stable, low D_it amorphous Ga₂ O₃-(100) GaAs interfaces have been fabricated by extending molecular beam epitaxy (MBE) related techniques. We have investigated both in situ and ex situ Ga₂O₃ deposition schemes utilizing molecular beams of gallium oxide. The in situ technique employs Ga₂O₃ deposition on freshly grown, atomically ordered (100) GaAs epitaxial films in ultrahigh vacuum (UHV); the ex situ approach is based on thermal desorption of native GaAs oxides in UHV prior to Ga₂O₃ deposition. Unique electronic interface properties have been demonstrated for in situ fabricated Ga₂O₃-GaAs interfaces including a midgap interface state density D_it in the low 10¹⁰ cm^-2 eV^-1 range and an interface recombination velocity S of 4000 cm/s. The existence of strong inversion in both n- and p-type GaAs has been clearly established. We will also discuss the excellent thermodynamic and photochemical interface stability. Ex situ fabricated Ga₂O₃-GaAs interfaces are inferior but still of a high quality with S=9000 cm/s and a corresponding D_it in the upper 10¹⁰ cm^-2 eV^-1 range. We also developed a new numerical heterostructure model for the evaluation of capacitance-voltage (C-V), conductance-voltage (G-V), and photoluminescence (PL) data. The model involves selfconsistent interface analysis of electrical and optoelectronic measurement data and is tailored to the specifics of GaAs such as band-to-band luminescence and long minority carrier response time τ_R. We will further discuss equivalent circuits in strong inversion considering minority carrier generation using low-intensity light illumination     

Semiconductor lasers with 2-D-photonic crystal mirrors based on awet-oxidized Al2O3-mask

We have fabricated and investigated AlGaAs-InGaAs-based ridge waveguide (RWG) lasers with two-dimensional (2-D) triangular photonic crystal (PC) mirrors using a wet-oxidized Al₂O₃ mask for the dry etching of the PC at one end of the ridge. The laser structure includes a 60-nm-thick AlAs layer positioned in the upper cladding, which is converted into Al₂O₃ after the definition of the PC by electron beam lithography and shallow etching. Etching of the holes is then continued using the Al₂O₃ mask, to a final depth of 600 nm. The continuous-wave characteristics of the lasers show a clear dependence on the period of the PC including a significant decrease of the threshold current and an increase of the efficiency for properly adjusted crystal parameters     

Low-loss CaxBa1−xNb2O6 ridge waveguide for electro-optic devices

Optical ridge waveguide using calcium barium niobate (CBN) on silicon substrate for the first time is designed, fabricated and characterized for future integrated electro-optic devices. To obtain single-mode propagation, the CBN thin strip is designed to be surrounded by thick silicon dioxide layer forming a ridge waveguide. Deposition of CBN film on profiled silicon dioxide introduces spatial separation which solves the CBN etching problem. Fabrication, edge polishing and near-field mode profile measurement of the waveguide are carried out. The measurement is in good agreement with the simulation and an exact loss as low as 2.15 dB/cm was obtained for the fabricated waveguide.     

Ta2O5/silicon barrier height measured fromMOSFETs fabricated with Ta2O5 gate dielectric

N-channel metal oxide semiconductor field effect transistors with Ta₂O₅ gate dielectric were fabricated. The Ta₂O₅/silicon barrier height was calculated using both the lucky electron model and the thermionic emission model. Based on the lucky electron model, a barrier height of 0.77 eV was extracted from the slope of the ln(I_g/I_d) versus ln(I_sub/I_d) plot using an impact ionization energy of 1.3 eV. Due to the low barrier height, the application of Ta₂ O₅ gate dielectric transistors is limited to low supply voltage preferably less than 2.0 V     

MOS transistors with stacked SiO2-Ta2O5-SiO2 gate dielectrics for giga-scale integration ofCMOS technologies

Advances in lithography and thinner SiO₂ gate oxides have enabled the scaling of MOS technologies to sub-0.25-μm feature size. High dielectric constant materials, such as Ta₂O₅ , have been suggested as a substitute for SiO₂ as the gate material beyond t_ox≈25 Å. However, the Si-Ta ₂O₅ material system suffers from unacceptable levels of bulk fixed charge, high density of interface trap states, and low silicon interface carrier mobility. In this paper we present a solution to these issues through a novel synthesis of a thermally grown SiO₂(10 Å)-Ta₂O₅ (MOCVD-50 Å)-SiO₂ (LPCVD-5 Å) stacked dielectric. Transistors fabricated using this stacked gate dielectric exhibit excellent subthreshold behaviour, saturation characteristics, and drive currents