Silica-based Optical Waveguides Research Articles

Luminescence of Yb3+ ions in silica-based glasses synthesized by SPCVD

The spectra and decay kinetics of Yb3+ single-ion and cooperative luminescence in silica-based optical slab waveguides are investigated. The slab waveguides with a high content of Yb and various amounts of P and Al additives to the light-guiding core glass were fabricated on the basis of fused and unfused glassy layers synthesized via surface-plasma chemical vapor deposition (SPCVD). Luminescence was pumped by laser diodes at ∼904 nm and ∼967 nm wavelengths and recorded in the 450–1175 nm spectral band. For the pure silica host doped with Yb, only the influence of cluster sizes on the luminescence decay kinetics is determined. It is found that the profusion of deposited glass with increased Al content favors separation by geometry of the Yb3+ and Tm3+ ions; the latter are present in the glass as an uncontrollable contamination. Evidence was found that at least two different types of Yb clusters were formed in P doped silica as a result of profusion.

Fabrication and characterization of a fused silica-based optical waveguide with femtosecond fiber laser pulses

This study investigates the fabrication characteristics of a femtosecond fiber laser on a fused-silica-based optical waveguide. The wavelength and repetition rate of the femtosecond fiber laser are 532 nm and 1 MHz, respectively. We selected three main fabrication parameters for systematic adjustment: laser power (E), scanning speed (ν s ) and focus depth (d = 0 at the surface of substrate). We succeeded in fabricating a waveguide layer inside the silica subtracts. By analyzing the light translation path and the net fluence in the waveguide, the range of fabrication energy of the waveguide on the fused silica was kept within 0.973 – 1.438 KJ/cm2.

Control of birefringence using polymer as cladding layer in optical planar waveguides

We demonstrate theoretically that a polymer layer, when used as cladding layer for silica-based planar optical waveguides on a silicon substrate, can substantially reduce birefringence. Multilayer planar optical waveguides usually exhibit stresses that are caused by thermal-induced strains that originate from the bonding of the layers, in addition to intrinsic strains. Effect of various intrinsic properties on thermal stress as a function of thickness of the guiding layer is studied. It is shown that it is possible to achieve the thermal stress free and, hence, the stress-induced birefringence free waveguide devices by proper waveguide designs.

Low-loss silica-based optical film waveguides deposited by helicon-activated reactive evaporation

Planar silica-based optical waveguides have been deposited by a plasma helicon-activated reactive evaporation system, at a low temperature and with reduced hydrogen contamination, on thermally oxidized silicon wafers. The transmission loss of the rib waveguides, formed on the deposited films by etching with hydrofluoric acid, is determined to be lower than 0.1 and 0.7 dB/cm at wavelengths of 1310 and 1510 nm, respectively, for TE polarization. The influence of substrate leakage on propagation loss is determined numerically and compared with experimental results for TE and TM polarizations. The presence of the OH vibrational overtone band in the fabricated waveguides, at a wavelength of around 1385 nm, is discussed in terms of the waveguide structure.

Fabrication of Silica-Based Glass Optical Waveguide by UV Beam Scanning

UV induced refractive index increase, the photosensitivity, in Ge-doped silica glass has been utilized for the fabrication of fiber Bragg gratings and long period fiber gratings. Recently, this phenomenon has also been applied to the fabrication of optical channel waveguides in order to achieve cost efficiency and fabrication flexibility. In this work, the fabrication of various optical waveguides by UV beam scanning is demonstrated. 10-mm-long straight optical waveguides and a Y-Branch waveguide with a branching ratio of nearly 50% are realized. We also propose and demonstrate a technique for the simultaneous fabrication of an optical waveguide and a Bragg grating by scanning UV beam through a phase mask.

Reflection-type 2×2 optical waveguide switch using the Goos–Hänchen shift effect

We have designed a structure for a 2×2 silica-based optical waveguide switch that is based on a thermocapillarity effect. This switch can use the reflection walls on both sides of the slit, because the Goos–Hänchen shift effect was taken into account when the structure of the waveguides and the slit was designed. This switch can provide a cross/bar function through a single element, and the measured reflection losses in the reflection walls on both sides of the slit were consistent. The loss was comparable to the insertion loss of a Mach–Zender-interferometer-type thermo-optic switch.

Growth of polarisation crosstalk along a silica-based optical waveguide

The authors report the length dependence of polarisation crosstalk for a 10 m long silica-based waveguide in which the total polarisation crosstalk is 8.9 × 10–3. This is achieved by numerically integrating the coupling strength obtained by using low coherence interference between excited and orthogonally coupled light waves along the length of the waveguide. A comparison of the measured and theoretical crosstalk curves leads to confirmation that the bends in the waveguide are the main origin of the crosstalk. The polarisation crosstalk per bent section is 4.7 × 10–5.

Silica-based sol-gel optical waveguides on silicon

Silica-based waveguiding layers are readily obtained by the spin-coating of appropriate sols on silicon wafers. They may easily be doped with rare earth elements, for intended applications such as lasers or amplifiers. The authors describe the preparation and characterisation of such films. The film structure was investigated by X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopies (NEXAFS and EXAFS) and Fourier transform infrared spectroscopy (FTIR). Their surface area, evaluated by Brunauer-Emmett-Teller (BET) analysis, and their porosity, estimated from refractive index measurements, are reported. Finally, rare earth fluorescence lifetime data are presented and interpreted.

Silica-based optical integrated circuits

Silica-based integrated optical waveguide technology is reviewed. Low loss and manufacturable waveguides are made by chemical vapour, flame hydrolysis and electron beam deposition. Fibre to fibre insertion loss is as low as 0.3 dB for a 6 cm long waveguide. Bragg reflective add-drop filters are made with gratings formed by ultraviolet irradiation. The waveguide grating router has found important application as a multiplexer in dense wavelength multiplexed communications systems. Multiplexers with wide pass bands and stop bands are made with Fourier filters: these filters consist of a chain of alternating couplers and delaying arms. The good performance of waveguide grating routers and Fourier filters is due to the high degree of path delay and coupler control achievable by and processing in this technology.

Fabrication of high concentration rare-earth-doped silica-based waveguide by MCVD method

Reports a technique of fabricating a buried channel silica-based optical waveguide containing the largest rare-earth concentration ever reported, i.e., 3 wt% in Nd/sub 2/O/sub 3/. Instead of the flame hydrolysis technique, these waveguides are manufactured by the standard MCVD method originally designed for fiber preform fabrication.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Effective index drift from molecular hydrogen diffusion in hydrogen-loaded optical fibres and its effect on Bragg grating fabrication

When hydrogen loading is used to enhance the photosensitivity of silica-based optical waveguides and fibres, the presence of molecular hydrogen dissolved in the glass matrix changes the effective index of propagation of guided optical modes by as much as 0.05%. Real-time monitoring of the reflectivity spectrum of Bragg gratings written in such conditions shows that the centre wavelength follows the changes in hydrogen concentration due to diffusion and reaction with glass defects.

Silica-based finesse-variable ring resonator

A finesse-variable ring resonator with a free spectral range of 2.5 GHz is demonstrated using silica-based optical waveguides. The finesse is controlled with a coupling-ratio-variable coupler, which is composed of a symmetrical Mach-Zehnder interferometer and thermooptic phase shifters. The finesse of the resonator is changed continuously from 6 to 27.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Silica-based optical waveguide on terraced silicon substrate as hybrid integration platform

A silica-based optical waveguide on a silicon substrate with terrace regions is proposed. Because the substrate is equipped with a low-loss waveguide and an optical bench at the same time, it is applicable to a hybrid integration platform.

Increase in photosensitivity in silica-based optical waveguides on silicon

An increase in the photoinduced refractive-index change Δn in silica-based optical waveguides on silicon is described. The increase is attained by the consolidation of a core film in a reducing atmosphere. A maximum Δn of 3.9 × 10−4 is obtained for the TE mode by UV laser irradiation at 248nm. This is four times larger than that in conventional waveguides.

Propagation loss characteristics of long silica-based optical waveguides on 5 inch Si wafers

The propagation loss characteristics of silica-based optical waveguides with various bending curvatures fabricated on 5 inch Si wafers are investigated. Low loss waveguides more than lm long with a Δ of 0.75% are successfully fabricated and the loss is found to be independent of the curvature radius over 5mm. A minimum loss of 3.5dB/m at ∼1.55 μm is obtained in a waveguide 1.6 m long.

Polarization-insensitive arrayed-waveguide grating wavelength multiplexer on silicon

A wavelength-division multiplexer with no polarization dependence is demonstrated. It is based on an arrayed-waveguide grating fabricated with silica-based optical waveguides on a silicon substrate. The polarization dependence that is due to the birefringence of the waveguide is eliminated by inserting a quartz lambda/2 plate in the middle of the arrayed waveguide. Moreover the grating is designed to operate in the 115th order for high wavelength resolution. The polarization insensitivity and the high resolution lead to the successful multiplexing of 13 wavelength channels with 1-nm spacing. A passband width of 0.3 nm and a cross-talk level of -30 dB are achieved.

Design and fabrication of broad-band silica-based optical waveguide couplers with asymmetric structure

Waveguide-type directional couplers with different guide widths in the interactive region are designed and fabricated with silica-based waveguides on silicon substrates. It is demonstrated that these asymmetric couplers have broadband coupling-ratios of, for example, 50%+or-5%, 25%+or-3%, or 5%+or-2% over a wide wavelength range from 1.3 to 1.55 mu m, which are in good agreement with the results calculated using the beam propagation method (BPM). The excess loss of these couplers is as low as 0.7 dB, including input and output single-mode fiber coupling losses.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Hybrid-integrated 4*4 optical gate matrix switch using silica-based optical waveguides and LD array chips

The fabrication and characteristics of a hybrid-integrated optical gate matrix switch were studied. The switch was composed of a silica-based single-mode guided-wave circuit and two InGaAsP gate array chips, each of which comprised eight laser diode optical gates. The gate array chips were assembled on the guided-wave circuit using a hybrid integration technique. The insertion loss of the fabricated 4*4 matrix switch was scattered among switching paths and ranged from 26 to 33 dB. The switch was applicable to a 400 Mb/s signal system with a bit error rate of 10/sup -9/. The numerical analysis shows that the residual reflectivity at the LD gate and waveguide facets caused the loss scattering among the paths and that reduction of the residual reflectivity is essential for improving the switch characteristics. >

Silica-based optical waveguide ring laser integrated with semiconductor laser amplifier on Si substrate

A compact and stable ring laser at 1.3 μm was demonstrated using an InGaAsP semiconductor laser amplifier (SLA) and a silica-based optical waveguide ring resonator with an FSR of 2 GHz on an Si substrate. Two end facets of the SLA were coupled to lensed optical fibres, the other ends of which were attached without alignment to the waveguide resonator through fibre guiding grooves. A low threshold current of 17 mA was obtained in the ring laser.

Coherent optical transversal filter using silica-based waveguides for high-speed signal processing

A coherent optical transversal filter with a tapped delay-line structure is described. Utilizing phase information this filter can express arbitrary tap coefficients (including general complex numbers) by coherently combining tapped signals. Experimental filters using silica-based single-mode optical waveguides, monolithically integrated on silicon substrates were developed for stable and high-speed operation. Experimental results demonstrate the operating capabilities of the filters for high-speed signal processing. The operating bandwidth was experimentally estimated. Degradation of the frequency characteristics due to both deviation of fiber fabricating parameters and errors in setting tap-coefficients has been estimated theoretically.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>