Waveguide Formation Research Articles

Optical Waveguide Formed in RbTiOPO4 Crystal by 6.0 MeVO3+ Implantation

A planar optical waveguide was formed in RbTiOPO4 crystal by6.0-MeV oxygen ion implantation with the dose of 2×1015 ions/cm2 at room temperature. Annealing at 200°Cfor 30 min in air is performed to improve the thermal stability of thewaveguide. The dark modes of the waveguide are measured at wavelengths633 and 1539 nm, respectively. The refractive index profiles in theguiding layer are reconstructed by using the reflectivity calculationmethod. TRIM'98 code was carried out to simulate the damage profilescaused by the implantation process to obtain a better understanding ofthe waveguide formation.

Direct observation of waveguide formation in KGd(WO4)2 by low dose H+ ion implantation

In this letter, a direct measurement of a refractive index change in potassium gadolinium tungstate (KGW) created by a low-dose ion implantation of 1MeV hydrogen ions is reported. The characterization was performed using both microreflectivity and Raman spectroscopy measurements. The microreflectivity results show both negative and positive changes in refractive index in the damage region when measuring refractive index along different polarization axes. Micro-Raman spectroscopy analysis shows preservation of the Raman characteristics of KGW in the nondamaged crystal regions. These results show that ion implantation in KGW has a great potential for fabricating waveguide structures in Raman-based photonic devices.

Self-Aligned Single-Mode Polymer Waveguide Interconnections for Efficient Chip-to-Chip Optical Coupling

Single-mode (SM) ultrashort optical interconnections between the fibers and waveguides using self-forming polymeric waveguides with low optical losses at 1300 and 1550 nm were demonstrated. The localized refractive index in the SM regime is estimated by measuring the surface topography induced by monomer diffusion during the waveguide formation. A loss less than -1 dB can be obtained from self-aligning SM-to-multimode (MM) fibers and SM-to-SM fibers interconnections, respectively. A self-formed waveguide-to-fiber interconnection is fabricated and measured with loss less than 0.2 dB at 1550 nm. The polymer waveguide relaxes the positioning requirements for single-mode chip-to-chip optical interconnections, showing great potential to improve the short-term yield and long-term reliability

Characterization of optical planar waveguide in Ce:KNSBN crystal formed by triple-energy helium ion implantation

We report on the optical planar waveguide formation and modal characterization in a Ce:KNSBN crystal by triple helium ion implantation at energies of (2.0, 2.2 and 2.4MeV) and fluences of (1.5, 1.65 and 2.25)×1015cm−2. The prism-coupling method is used to investigate the dark-line spectroscopy at wavelength of 632.8 and 1539nm, respectively. The refractive index profiles of the waveguide are reconstructed by an effective refractive index method. It is found that the ion-beam irradiation creates slight increase of extraordinary index whilst decreases ordinary one in the guide region. The modal analysis shows, at wavelength of 632.8nm, the fields of one TE and three TM modes are well restricted in the guiding region, which means the formation of non-leaky waveguide in the crystal. The damping coefficients of the waveguide are 0.6 and 1.6cm−1 for ordinary and extraordinary polarized light at 632.8nm, respectively.

Formation of planar optical waveguide by multi energy Si ion implantation into Nd:YVO 4 crystal

The planar waveguides have been fabricated in Nd:YVO 4 crystals by single and multi energy Si ion implantation. Optically polished Nd:YVO 4 samples were implanted at room temperature by 2.6 MeV Si ions and multi energy (3.0 MeV, 2.6 MeV and 2.2 MeV) Si ions, to the dose of 6 × 10 14 ions/cm 2. The prism-coupling method was carried out to measure the dark modes in the Nd:YVO 4 crystal waveguides by using a model 2010 prism coupler. In both waveguides 3 modes were observed before annealing and after annealing the effective refractive index of all these modes gets smaller. The two waveguides show much similarity in prism-coupling results. Reflectivity Calculation Method was applied to fitting the single energy ion implanted waveguide refractive index profile. TRIM'98 (Transport of Ions in Matter) code was used to simulate the damage profile in Nd:YVO 4 by a single and multi energy ion implantation, respectively. It is found that the electronic energy loss in ion implantation may play an important role in Nd:YVO 4 waveguide formation.

Formation of waveguides in LiNbO3 by 6.0MeV F3+ implantation

6.0 MeV F3+ ions are implanted into x-cut LiNbO3 crystals in doses ranging from 3.0×1013to1.0×1015ions∕cm2 at room temperature. Planar waveguide formations are confirmed and dark modes are measured by prism coupling technique with a wavelength of 633nm. TE modes due to both raised extraordinary index and barrier-confined waveguides are demonstrated. The Rutherford backscattering∕channeling technique is used to investigate the damage produced by implantation. The experimental results are analyzed. With a fiber probe technique, the waveguide loss from TE0 mode in sample implanted with the dose of 1.0×1014ions∕cm2 is measured which is about 0.76dB∕cm after annealing.

3D-soliton waveguides in lithium niobate for femtosecond light pulses

We show that efficient waveguides can be written by bright spatial solitons in the volume of lithium niobate photorefractive crystals by cw and pulsed laser beams. Using high-repetition-rate femtosecond laser pulses, an efficient formation of soliton waveguides (SWGs) is possible, after accumulating a large number of pulses, because the characteristic photorefractive build-up time is much longer than the pulse period and the efficient two-photon absorption may contribute to the solitonic confinement. These results open the possibility of writing reconfigurable single SWGs and SWG arrays (with any spatial orientation and large range of periods) and optimally guiding the femtosecond pulsed laser beams through them, creating a graded refractive-index profile matched to the spatial beam profile. Our experiments also show a small increase in pulse duration (small dispersion) in these waveguides.

Optical Planar Waveguides in KTiOPO4 Crystals by MeVOxygen Ion Implantation

We report on the optical planar waveguide formation in KTiOPO4crystals by single or double oxygen ion implantation at energies of2.4–3.0 MeV and doses of 1015 ions/cm2. The dark-linespectroscopy properties are investigated by a prism-coupling method.With an effective refractive index method, the refractive indexprofiles of the waveguides are reconstructed. The program codeTRIM'98 (transport of ions in matter) is used to simulate theimplantation process of oxygen ions into the KTiOPO4 crystal. Itis found that an inherent relationship exists between the nucleardamage and the refractive index changes induced by the ion-beamimplantation.

Densification of silica glass induced by 0.8 and 1.5μm intense femtosecond laser pulses

We investigate the physical mechanisms responsible for waveguide formation in silica glass induced by 1kHz intense femtosecond laser pulses from a Ti-sapphire laser at 0.8μm as well as from a femtosecond optical parametric amplifier at 1.5μm. It is demonstrated that the densification taking place at the irradiated region is the principal cause for refractive index change in the waveguides written with both 0.8 and 1.5μm pulses. The birefringence induced by the stress arising from such densification and its behavior against thermal annealing are also studied.

Optical waveguides formed in Nd:YVO4 crystals by C2+ implantation

This work reports the formation of planar and channel waveguides in Nd:YVO4 by carbon implantation, using doses as low as 5 × 1014 ions/cm2. The analysis includes refractive index profiles, propagation losses and spectroscopic properties. The results indicate that there is an index convergence, the ordinary index increases while the extraordinary index decreases. The spectroscopic studies show that emission bands coming from the 4F3/2 level are not altered by the ion beam process, shedding light on the potential of carbon implanted waveguides for laser integrated devices.

Optical waveguides in Nd:YVO4 crystals by multi-implants with protons and helium ions

This work reports the formation of planar waveguides by proton and helium implantation in Nd:YVO4. Double and triple implants were realised using energies between 0.4MeV and 1.75MeV and doses around 1016ions/cm2, thus generating wide barriers; in particular a double waveguide was generated with a triple implantation. The analysis includes refractive index profiles, spectroscopic properties and near field imaging.

Parametric instability in the formation of plasma waveguides

Plasma waveguides generated by focusing a moderate intensity laser into neutral gas with an axicon lens can be unstable to the generation of axial modulations in the channel parameters. A model is proposed in which the modulations are due to the nonlinear coupling between the axicon field and a scattered mode in the evolving channel. Good agreement is found with experimental measurements of these modulations.

Modelling the formation of optical waveguides produced in LiNbO3 by laser induced thermal diffusion of lithium ions

Analytical and numerical modelling of the fabrication of optical waveguides in lithium niobate (LiNbO3) through direct writing with a continuous wave ultraviolet (UV) laser has been performed. It is proposed that the UV illumination induces heating of the surface and subsequent thermal diffusion of lithium which alters the refractive index in accordance with the lithium concentration dependence of the Sellmeier equations.

Optical channel waveguides in Nd:YVO4 crystal produced by O+ ion implantation

In this letter, we report on optical channel waveguides in Nd:YVO4 crystals produced by photographic masking and following direct O+ ion implantation at 3.0MeV. Annealing treatments of the samples are performed to improve the waveguide stability and to reduce losses. An increase of the ordinary refractive index induced by the implantation is believed to be responsible for waveguide formation. Quasi-TM guided modes are observed, while no quasi-TE ones are detected. The optical damping coefficients are of 0.43, 0.63, and 0.54cm−1 for channel waveguides with widths of 4, 5, and 6μm, respectively. The result of modal analysis is in agreement with the experimental data.

Side diffusion modeling by the explicit consideration of a space-charge buildup under the mask during strip waveguide formation in the Ag^+-Na^+ field-assisted ion-exchange process

A space-charge buildup under the blocking mask in a field-assisted Ag+ -Na+ ion-exchange modeling is assumed. It results in the distortion of electric field lines in the direction under the mask edges. As a result, side diffusion occurs and the numerical model shows the same range of side diffusion as the experimental data. Explicit consideration of the space-charge buildup under the mask and solving the Poisson equation for the electric field determination make it possible to use more realistic boundary conditions in the numerical model, compared to the boundary conditions generally used.

Design Methodology for Ti:LiNbO3 Waveguides

The purpose of this work was to develop a design methodology for the fabrication of waveguides in LiNbO3 operating in the single-mode regime at several wavelengths, with specific characteristics required to optimize integrated devices. To achieve this, it is necessary to obtain the relations between the optical characteristics of the waveguides and their respective fabrication conditions, and to introduce models of the waveguide formation process. The relations between fabrication conditions and optical characteristics of planar waveguides realized by titanium in-diffusion are documented extensively in the literature. However, reports on the characterization of waveguide fabrication processes, performed in a systematic way, could not be found, resulting in the need to combine information from several sources. Discrepancies among results from different researches are evident, resulting from different experimental methodologies and calibrations of equipment. Therefore, aiming at extracting a consistent data set, optical characterization techniques for the refractive index profile were employed to study series of samples.

Coupling efficiencies in reflective self-organized lightwave network (R-SOLNET) simulated by the beam propagation method

The reflective self-organized lightwave network (R-SOLNET) enables the formation of self-aligned waveguides in the photorefractive (PR) material between misaligned optical devices by introducing a write beam. The incident write beam from one device and the reflected write beam from the second device induce self-focusing in the PR material and construct a coupling waveguide. A wavelength filter on the waveguide edge is used to facilitate the reflected beam. The beam propagation method reveals that R-SOLNET exhibits higher coupling efficiencies and better tolerances than the one-beam-writing SOLNET and the free-space coupling. The apparent usefulness of R-SOLNET is remarkable for gaps wider than 100 /spl mu/m in 8-/spl mu/m-wide waveguide circuits. For 240-/spl mu/m gap, coupling efficiency better than 50% can be achieved even when the lateral misalignment is as large as 4 /spl mu/m. The results indicate that R-SOLNET may be useful for vertical waveguide constructions of optical z-connections in three-dimensional intrachip optical interconnects and switching systems, as well as for self-aligned optical couplings with devices that cannot emit write beams such as vertical-cavity surface-emitting lasers, photodetectors, and electrooptic switches.

Fabrication of light-induced self-written waveguides with a W-shaped refractive index profile

This paper proposes a novel technique for automatic waveguide formation by means of the self-trapping effect of optical fiber irradiation into a photopolymerizing resin. We investigate experimentally the phenomenon of thin cladding layer formation surrounding the core following the core creation. In the proposed technique, a counterdiffusion effect involving polymerizing monomers via the core/cladding interface causes enrichment of a low refractive index monomer, and a resultant "W-shaped" refractive index profile is realized. The measured propagation loss of the fabricated waveguide is 1.7 dB/cm at 0.68 /spl mu/m wavelength. This technology is appropriate for the fabrication of large-core optical waveguides of greater than 0.5 mm in diameter and is useful for automating the optical fiber connection and packaging process by virtue of being an all-passive optically induced process.

Mechanisms of refractive index modification during femtosecond laser writing of waveguides in alkaline lead-oxide silicate glass

We report on the mechanisms responsible for the formation of optical waveguides upon femtosecond laser irradiation of an alkaline lead-oxide silicate glass. MicroRaman spectroscopy and nonlinear fluorescence were employed to probe the local glass network structure and the formation of optically active defects respectively. At low laser pulse energies, the laser modified region is formed by a single light guiding region, whereas for pulses above 14 μJ the modified region is formed by a central dark zone, which does not guide light, accompanied by light guiding zones located in the surrounding of the dark one. This behavior is different from that observed in common silica glass systems but agrees with recent results obtained in phosphate and heavy metal oxide glasses. However, our results show that, unlike the latter glass, local densification of the glass occurs in the whole laser modified region, i.e., in the dark and the guiding zones. The suppression of light guiding in the dark region is explained by a high density of absorbing color centers.

Microcavity filters based on hexagonal lattice 2-D photonic crystal structures embedded in ridge waveguides

Two-dimensionally periodic photonic crystal microcavity filters in a ridge waveguide format have been designed and fabricated. Transition mode-matching features were added to increase the optical throughput by more than a factor of two. An increase of Q-factor (more than 100%) was achieved by the addition of two further rows of photonic crystal holes to the microcavity filters. Attempts have also been made to tailor the filter response by applying design concepts used in other Bragg-grating optical filter technologies.