Low-loss polyimide-Ta2O5-SiO2hybrid ARROW waveguides

A low-loss polyimide-Ta₂O₅-SiO₂ hybrid antiresonant reflecting optical waveguide (ARROW) is presented. The ARROW device was fabricated using both the organic and dielectric thin-film technologies. It consists of the fluorinated polyimide, tantalum pentoxide (Ta₂O₅), and silicon dioxide (SiO₂) hybrid layers deposited on a Si substrate. For transverse electric polarized light, the propagation loss of the waveguide as low as 0.4 dB/cm was obtained at 1.31 μm. The propagation loss for transverse magnetic polarized light is 1.5 dB/cm. An ARROW waveguide fabricated using the polyimide-Ta₂O₅ -polyimide material system is also presented for comparison     

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     

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     

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)     

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     

ARROW-type polarizer utilizing form birefringence in multilayerfirst cladding

A waveguide polarizer using an ARROW (antiresonant reflecting optical waveguide) structure, of which the first cladding consists of three thin layers, is proposed. Theoretical calculation shows that this polarizer can achieve isolation over 30 dB/cm with an insertion loss of 0.01 dB/cm at 1.3 μm. Isolation of 83 dB/cm with insertion loss of 4.3 dB/cm was experimentally obtained at 0.633 μm. This structure is suitable for the integration of a polarization splitter and photodetector     

Zn indiffusion waveguide polarizer on a Y-cut LiNbO3 at1.32-μm wavelength

A polarization-dependent loss measurement of Zn indiffusion (ZI) waveguide on a Y-cut LiNbO₃ substrate is firstly reported. The measured results show that the waveguides support either a single extraordinary polarization or both extraordinary and ordinary polarizations depending on the fabrication process parameters. For the single extraordinary polarization waveguide, the measured propagation loss at 1.32-μm wavelength is 0.9 dB/cm and the best measured polarization extinction ratio is 44 dB at a distance of 1.5 cm from the input end, which are quite good for being a waveguide polarizer. Moreover, the voltage-length product measured for the ZI Mach-Zehnder modulator shows that the substrate electrooptic coefficient is not degraded     

AlGaAs/GaAs-ARROW waveguides

The first demonstration of a passive vertical antiresonant reflecting optical waveguide (ARROW) realised in the AlGaAs/GaAs material system is reported. Losses of 2.6 dB/cm for the TE- and 3.5 dB/cm for the TM-ARROW modes were obtained at a wavelength of 0.83 mu m for samples with 4 mu m-wide ridges.<>     

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.     

Prepatterned optical circuits in thin ion-sliced single-crystalfilms of LiNbO3

Crystal ion slicing was used in conjunction with conventional annealed proton exchange in Z-cut LiNbO₃ to result in prepatterned microns-thick single-crystal LiNbO₃ films with channel guides and a measured waveguide propagation loss of 0.2-0.7 dB/cm. Full optical circuit transfer, including a buffer layer and a patterned metal electrode structure for active control was demonstrated     

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.     

Low-loss electrooptic BaTiO/sub 3/ thin film waveguide modulator

A strip-loaded electrooptic waveguide modulator based on an epitaxial BaTiO/sub 3/ thin film was fabricated and characterized for the first time. The strip-loaded waveguide structure greatly improves waveguide propagation and polarization-dependent loss performance. A propagation loss of 1.1 dB/cm and polarization dependent loss of 0.1 dB/cm were measured. The electrooptic waveguide modulator exhibited a half-wave voltage-interaction length product of 4.5 V /spl middot/ cm at a wavelength of 1542 nm. The measured effective electrooptic coefficient of the as-grown BaTiO/sub 3/ waveguide modulator was 38 pm/V. The experimental results indicate that a strip-loaded thin film waveguide modulator is suitable for photonic applications.     

Finite element analysis of LiNbO3 waveguides with Si orSi/SiO2 overlay

LiNbO₃ waveguides with Si overlays are emerging as a basic building block for a variety of integrated-optic components, including modulators, high-efficiency gratings, and narrowband WDM filters. However, the development and optimization of these devices are, in large part, hindered by the lack of understanding of the specifics of the Si-on-LiNbO₃ structure which appear to differ dramatically from those of the Si and LiNbO₃ waveguides, considered separately. In this work, we provide a specific insight into the waveguiding properties of vertically stacked Si-on-LiNbO₃ waveguides. In particular, we present a detailed theoretical analysis of the effect of the Si film on the modal characteristics (propagation constant and field distribution) of the structure. The vectorial finite element method (VFEM) is used to numerically investigate a step-index and graded-index single-mode channel waveguide in LiNbO₃, with a Si or Si/SiO₂ multimode overlay. We show that for ~70% of all Si thicknesses, in the range from 0 to 1.6 μm, the highest order normal mode of the entire structure has more than 99.9% of the total energy confined in the LiNbO₃ region, i.e., beneath the Si overlay. This fact is quite intriguing given the fact a planar Si layer of submicron thickness on bulk LiNbO₃ is already multimoded. Furthermore, we show that the effective mode index of the structure is considerably modified compared to that of the LiNbO₃ waveguide while the propagation loss is, on the other hand, practically unaffected (~0.3 dB/cm) even in the presence of the lossy Si film, as confirmed by our previous experimental results. Evidently, large modulation of the effective index and low-loss propagation provide an ideal combination of properties suitable for the fabrication of high-reflectance corrugated waveguide gratings, essential for a number of practical devices, in particular, WDM filters     

Influence of temperature and initial titanium dimensions of fiber-Ti:LiNbO3waveguide insertion loss at λ = 1.3 µm

This paper describes the influence of fabrication parameters on fiber-Ti:LiNbO3waveguide-fiber insertion loss measured atlambda = 1.32 mum inc-cut LiNbO3. We present a systematic study of the influence of titanium thickness on insertion loss. Within the range examined, diffusion of 950 Å thick 6 μm wide strip of Ti at 1050°C for 6 h produced the minimum loss of 2.0 dB in a 2 cm long waveguide for both TE and TM modes. An analysis of fiber-waveguide coupling for the particular case of an asymmetric diffused waveguide is presented. In general, we find that coupling loss due to modal mismatch between the fiber and waveguide and propagation loss in the waveguide contribute approximately equally to total insertion loss.     

Low-loss polymeric optical waveguides fabricated with deuteratedpolyfluoromethacrylate

Deuterated polyfluoromethacrylate which has high transparency, low birefringence and good processability was newly synthesized for use as optical waveguide materials, and both single-mode and multimode optical waveguides were fabricated using the polymer. The propagation loss and waveguide birefringence of the single-mode waveguides were as low as 0.10 dB/cm and -5.5×10^-6 at 1.31 μm, respectively. The propagation losses of the multimode waveguides were less than 0.02 dB/cm at both 0.68 and 0.83 μm, and 0.07 dB/cm at 1.31 μm     

Blazed grating couplers on LiNbO3optical channel waveguides and their applications to integrated optical circuits

Blazed grating couplers on LiNbO3optical channel waveguides have been successfully designed, fabricated, and evaluated. A reactive ion beam etching technique was used to shape the groove profile of grating couplers. A large decay factor of 600 dB/cm along optical channel waveguide was obtained. The air coupling intensity ratio of 8:1 between positive and negative light propagation directions for ion beam angle of 55° indicated a strong blaze effect. Highly efficient optical coupling from channel waveguide to Si phototransistor was also demonstrated.     

Optical Channel Waveguides in $hbox {KTiOPO}_{4}$ Crystal Produced by Proton Implantation

We reported on, to our knowledge the first time, the channel waveguide formation in KTiOPO₄ crystal by the implantation of protons with a special designed photoresist mask. The 2-D refractive index profile was constructed according to the measured dark-mode spectroscopy (for longitudinally planar configuration) as well as the shape of the channel waveguide cross section. Based on this index distribution, the modal profile was calculated through a numerical simulation, which showed reasonable agreement with the near-field light intensity distribution of the guided mode that was obtained by an end-coupling method. After annealing at 200deg C for 30 min in air, propagation loss of the channel waveguides was determined to be as low as ~2.9 dB/cm at wavelength of 632.8 nm.     

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)     

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     

Photonic Crystal Slab Waveguides Based on Antiresonant Reflecting Optical Waveguide Structures

A novel two-dimensional photonic crystal slab waveguide based on an antiresonant reflecting optical waveguide (ARROW) structure is proposed and designed. Lightwaves propagating in this waveguide are confined by antiresonance reflection vertically and the photonic band gap laterally. In order to obtain the characteristics of the ARROW-based photonic crystal waveguides, the three-dimensional finite-difference time-domain simulations are performed. With a lateral adiabatic taper, a coupling efficiency of 80.3% from a single-mode fiber to the ARROW-based photonic crystal waveguide of a single-line defect is obtained. In addition, propagation losses less than 10 dB/mm and bend losses of 0.23 and 0.39 dB/bend for the designed 60$^{circ}$ and 120$^{circ}$ bends are achieved at an operating wavelength of $1.55~mu{hbox {m}}$.