Waveguide Formation Research Articles

EFFECT OF LOW TEMPERATURE ON THE FABRICATION OF MICRORING RESONATOR BY WET ETCHING

Research related to semiconductor devices often relies on wafer fabrication. The fabrication of Silicon (Si) based devices by anisotropic wet etching can be affected by many etching parameters such as etching temperature, crystal orientation and percent of composition. Most of the anisotropic wet etchings by KOH solution done before were conducted at temperature over 70°C. We found that the temperatures are not suitable to fabricate ring waveguide as the waveguide wall will collapse at such high temperature. This study reports the etching characteristics of Si in KOH solution with 35% concentration at the temperature below 70°C. The etched wafer is targeted to be the basic structure for Microring Resonators (MRRs) based devices. This technique provides not only lower cost as compared to other etching technique, but also simple preparation. We found that low temperature manage to mold a good ring waveguide with low tendency to form rectangular structure due to crystal orientation. At 40°C, the best waveguide formation was obtained with a smooth waveguide surface, experiencing an etching rate of 0.066 µ min-1 and an appreciable ring waveguide structure. The effect of the low temperature on the fabrication of the MRRs devices has been investigated and studied.

Numerical Analysis of Waveguiding in Luminescence-Induced Spatial Soliton Channels

In this paper, we numerically investigate the formation and propagation characteristics of waveguides written by luminescence-induced spatial solitons (LISSs). Such waveguides, realized in erbium-doped lithium niobate crystals by photorefractive and Pockels effects, are analyzed in the transient regime by using a spatiotemporal numerical code for the photorefractive nonlinearity as well as for the erbium emission and light propagation within the induced waveguide. These calculations highlight a great LISS feasibility. Optical characterization of the waveguides indicates light propagation losses lower than 0.05 dB/cm at 1550 nm, pointing out high potentialities of LISS waveguides for active and passive electrooptic devices.

Tm3+ doped silicon thin film and waveguides for mid-infrared sources

A Tm3+ doped nanoparticulate silicon thin film and subsequent surface waveguides fully fabricated by using femtosecond (fs) pulsed laser are reported. The thin film exhibits strong room temperature fluorescence peaked at 2.04 μm when using an 808 nm diode laser. The fs-pulsed laser deposited film was then processed using fs-laser micromachining for the formation of channel waveguides, which were subsequently coupled with a 1550 nm laser and characterized for their infrared mode propagation.

Optical properties of in-vitro biomineralised silica

Silicon is the second most common element on the Earth's crust and its oxide (SiO2) the most abundant mineral. Silica and silicates are widely used in medicine and industry as well as in micro- and nano-optics and electronics. However, the fabrication of glass fibres and components requires high temperature and non-physiological conditions, in contrast to biosilica structures in animals and plants. Here, we show for the first time the use of recombinant silicatein-α, the most abundant subunit of sponge proteins catalyzing biosilicification reactions, to direct the formation of optical waveguides in-vitro through soft microlithography. The artificial biosilica fibres mimic the natural sponge spicules, exhibiting refractive index values suitable for confinement of light within waveguides, with optical losses in the range of 5–10 cm−1, suitable for application in lab-on-chips systems. This method extends biosilicification to the controlled fabrication of optical components by physiological processing conditions, hardly addressed by conventional technologies.

Optical properties of Yb3+-doped silicate glasses waveguides formed by low-dose oxygen ion implantation and effects of annealing

The planar waveguide, to our knowledge, has been firstly fabricated in the Yb3+-doped silicate glass by 6.0MeV O3+ ion implantation at a dose of 6×1014ions/cm2. The guiding properties are characterized by the prism-coupling and end-face coupling methods with a He–Ne beam. The dark-mode spectra and near-field intensity distribution are measured before and after annealing at 250°C for 1h in air. The results indicate that the thermal treatment can enhance the propagation properties with preserving the effective refractive indices well. The refractive index profile of the planar waveguide is reconstructed by the reflectivity calculation method, which shows a typical “enhanced well+optical barrier” distribution. The SRIM’2006 code is carried out to simulate the energy loss during the implantation in order to obtain a better understanding of the waveguide formation.

Analysis of Si+-implanted Nd:YVO4 crystal: the relation between lattice damage and waveguide formation

We report the lattice damage and annealing properties of the 500 keV Si+ ions implanted Nd:YVO4 crystal with different doses. The Rutherford backscattering spectrometry/channeling technique was used to analyze the damage profiles of ion-implanted samples. A series of post-implant annealing was performed at temperatures from 250 °C to 400 °C to investigate the relation between lattice damage profile and the waveguide formation. Implantations at doses of more than 5×10(14) ions/cm2 can result in high damage ratio in the near-surface region and the lattice structure cannot be restored even after annealing at 400 °C. Such seriously damaged lattice is relatively stable and contributes to the waveguide structure. Convergence of the refractive index at the surface region after ion implantation is believed mainly due to the elastic collisions with the target atoms caused by nuclear energy loss.

Visible and near-infrared waveguide properties in LiTaO3 crystal produced by swift Ar8+ ion irradiation

In this work, we report the optical waveguide formation in LiTaO3 crystal via Ar8+ ion irradiation at an energy of 180 MeV and a fluence of 2×1012 cm−2. The surface damage behavior of LiTaO3 crystal and structure change along the ion trajectory are studied through Rutherford backscattering/channeling spectra and micro-Raman spectra, respectively. The modal profile measurement through end-face coupling proves that the LiTaO3 waveguide can effectively support multimode propagation in the visible (633 nm) and single-mode propagation in the near-infrared (1539 nm) telecommunication wavebands. The waveguide propagation loss at 633 nm is measured by the back-reflection method.

Polarization behavior of femtosecond laser written optical waveguides in Ti:Sapphire

Ultrashort pulsed laser photoinscription of Ti:Sapphire crystals may result in the self-organization of nanoscale material redistribution regions in regular patterns within the laser trace and stress-induced birefringence around the laser trace. We report on the formation of anisotropic optical waveguides in Ti:Sapphire by a procedure that involves femtosecond laser inscription of adjacent nonguiding birefringent traces with nanopatterned crosssections and the accumulation of stress birefringence in the region between. Double parallel line structures with a separation of 25μm with vertical and horizontal nanoscale arrangements were written with a choice of orthogonal polarizations. Due to anisotropic light scattering on periodic nanostructures and stress-induced birefringence in the central zone, remarkable polarization dependent guiding effects were observed as a function of the microscopic geometry of the structures. Building on this polarization sensitivity, several structure such as 3 × 3 waveguide arrays, diamond and hexagon patterns are also investigated.

Monomode Optical Waveguides in Yb3+-Doped Silicate Glasses Produced by Low-Dose Carbon Ion Implantation

The planar waveguide has been fabricated in the Yb3+-doped silicate glass by 4.0 MeV C2+ ion implantation at a dose of 2×1014 ions/cm2. The guided modes are measured using a model 2010 prism coupler at 633 nm. The near-field profiles of the planar waveguide are obtained with an end-face coupling system. The refractive index profile of the waveguide is reconstructed by the intensity calculation method, which shows a typical “enhanced well + barrier” distribution. The SRIM'2006 code is carried out to simulate the energy loss during the implantation in order to obtain a better understanding of the waveguide formation. After post-implantation treatment at 260 °C for 1 h, the waveguide possesses a propagation loss of ∼1.42 dB/cm. The acceptable guiding properties suggest that further waveguide lasers may be realized on the C-implanted Yb3+-doped silicate glass waveguides.

Nd:Li6Y(BO3)3 crystal waveguide properties at wavelengths of 633 and 1539 nm produced by oxygen or silicon ion implantation

We report on the waveguide formation in the Nd:Li6Y(BO3)3 laser crystal by oxygen or silicon ion implantation, respectively, and how the waveguide structure effectively supports the fundamental mode in the visible and near-infrared telecommunication band. Compared with Si-ion, the waveguide produced by O-ion has a larger effective refractive index of fundamental mode and lower propagation loss, which shows that peak position of implanted ion nuclear energy loss has a significant impact on waveguide features. The investigation of the photoluminescence and Raman spectra demonstrates that the Nd3+ luminescence feature and crystal structure of the waveguide active region do not change significantly and gain good preservation after ion implantation.

Formation of slab waveguides in eulytine type BGO and CaF2 crystals by implantation of MeV nitrogen ions

Ion implantation, compared with other waveguide fabrication methods, has some unique advantages. It has proved to be a universal technique for producing waveguides in most optical materials. The authors of the present article reported fabrication of channel and slab waveguides in an Erbium-doped tungsten tellurite glass by implantation of MeV energy N+ ions. The present article reports successful adaptation of the same technique to the fabrication of slab waveguides in eulytine type bismuth germanate (BGO) and CaF2 crystals. This is the first report on successful waveguide fabrication in these materials using 3.5MeVN+ ions at implanted fluences between 5×1015 and 4×1016ions/cm2. Spectroscopic ellipsometric measurements revealed the existence of guiding structures in both materials. M-line spectroscopic measurements indicated guiding effect in the as-implanted BGO up to 1550nm and up to 980nm in the as-implanted CaF2. Ion implantation induced the appearance of three peaks in the UV/Vis absorption spectrum of CaF2, that can be attributed to colour centres.

Evanescent coupling in buried planar waveguide arrays written by a femtosecond laser in neodymium-doped yttrium lithium fluoride (Nd : YLiF4)

We report on the fabrication of buried planar waveguide arrays in neodymium-doped yttrium lithium fluoride (Nd : YLiF4) by femtosecond laser writing. With optimized fabrication parameters, the individual waveguide modes are coupled to each other through the evanescent tails of adjacent guided fields, while the coupling constant is calculated to be 1.18 cm−1 at 633 nm based on coupled-mode theory, which shows good agreement with the experiment results. Micro-luminescence spectra reveal that the Nd3+ fluorescence properties are not significantly affected by the waveguide formation processing, which indicates a fairly good potential for further laser actions in a compact device.

Refractive index change mechanisms in swift-heavy-ion-implanted Nd:YAG waveguide

A buried planar Nd:YAG waveguide has been fabricated by 20-MeV N-ion implantation. From Raman and optical characterization, it has been found that the refractive index has a larger increase when the crystal damage is heavier. According to our analysis, this crystal damage is caused by the electronic energy loss in the first several micrometers of irradiated regions, while nuclear energy loss also acts on the damage near the end of the ion range. This work is helpful to understand the mechanisms of swift-heavy-ion-implanted Nd:YAG waveguide formation.

Fluorescence-Quenching Free Channel Waveguides in Yb:YAG Ceramics by Carbon Ion Implantation

We report on the fabrication of channel waveguides in ytterbium-doped yttrium aluminum garnet (Yb:YAG) ceramics by carbon ion implantation. Confocal microfluorescence experiments revealed that the fluorescence efficiency of Yb ions is well preserved in the waveguide area, contrary to the case of helium ion-implanted waveguides characterized by a severe ion implantation-induced fluorescence quenching at waveguide's volume. The fluorescence images of the channel waveguides, and its comparison to those obtained from femtosecond direct laser written Yb:YAG waveguides, have been used to elucidate the waveguide formation mechanisms.

Analysis of Reflective Self-Organized Lightwave Network (R-SOLNET) for Z-Connections in 3-D Optical Circuits by the Finite-Difference Time-Domain Method

Reflective self-organized lightwave network (R-SOLNET) is a novel optical waveguide formation method that utilizes an attractive force induced between light beams in photo-induced refractive index increase materials, in which the refractive index increases as a result of write-beam exposure. R-SOLNET forms self-aligned optical couplings between optical devices, which tolerate the mutual positional misalignment, and it also forms optical waveguides in a free space. We propose R-SOLNET in 3-D optical circuits for board/chip-level optical interconnects to reduce the amount of effort that is required for optical device assembly and vertical optical waveguide formation. We predicted by the finite-difference time-domain method that an optical Z-connection of R-SOLNET would vertically connect two 2-μm-core optical waveguide films stacked with a 10-μm gap. A self-aligned vertical waveguide is formed even when misalignment exists between the films. A coupling efficiency of >;40% is achievable with 25% misalignment in waveguide core assembly.

Optical confinement achieved in ZnO crystal by O^+ ions implantation: analysis of waveguide formation and properties

Optical confinement in ZnO crystal was observed by O(+) implantation with different MeV energies and doses. Planar optical waveguides were formed in the as-implanted ZnO samples. The optical properties of the planar waveguide were investigated by the prism-coupling and the end-face coupling methods at the wavelength of 633 nm. The crystal lattice damage in the guiding region caused by the O(+) ions implantation was analyzed by the Rutherford backscattering/Channeling technique, results show that even high dose at 2 × 10(15) ions/cm(2) can hardly produce defect in near surface of ZnO. A theoretical model is developed to explain the principle of waveguide formation in ZnO crystal and the refractive index profile in the implanted waveguide was reconstructed accordingly. The experimental result and analysis are significant for application of ZnO crystal, especially for the design of ZnO light emitter devices.

Preservation of fluorescence and Raman gain in the buried channel waveguides in neodymium-doped KGd(WO_4)_2(Nd:KGW) by femtosecond laser writing

We report on the preservation of fluorescence and Raman gain in low-repetition-rate femtosecond laser written buried channel waveguides in neodymium-doped KGd(WO4)2. The propagation loss index, profile reconstruction, and calculation of the modal intensity distribution by the beam propagation method of the waveguide are presented. Microluminescence spectra of the waveguides show that the fluorescence properties of Nd3+ ions are not significantly affected by the waveguide formation processing, which indicates a fairly good potential for further laser actions in a compact device. Micro-Raman spectra are also performed to reveal the preservation of the characteristic 768 and 901 cm-1 Raman mode intensities in the guiding regions.

Application of swift and heavy ion implantation to the formation of chalcogenide glass optical waveguides

We demonstrate the application of swift and heavy ion implantation to generate optical waveguides in amorphous materials. Gallium lanthanum sulfide (GLS) and gallium lanthanum oxysulfide (GLSO) glass waveguides are fabricated using Ar implantation at 60MeV and 2×1012ions/cm2. A “well” region with increased refractive index (0.1% for GLS and 0.3% for GLSO) is formed near the surface of the glass based on the electronic energy deposition; a “barrier” layer with decreased refractive index is formed inside the glass due to the nuclear energy deposition. As a result, the waveguides exhibit a refractive index distribution of “well+barrier” type. It is supposed that the change in local structure order of the substrate causes the “well” formation. The propagation loss is 2.0dB/cm for GLS and 2.2dB/cm for the GLSO glass waveguide.

Femtosecond-laser-written, stress-induced Nd:YVO_4 waveguides preserving fluorescence and Raman gain

We report the formation of optical waveguides in the self-Raman Nd:YVO(4) laser crystal by femtosecond laser inscription. The confocal fluorescence and Raman images have revealed that the waveguide is constituted by a locally compressed area in which the original fluorescence and Raman gains of the Nd:YVO(4) system are preserved. Thus the obtained structures emerge as promising candidates for highly efficient self-Raman integrated laser sources.

Carbon ion implanted Nd:MgO:LiNbO_3 optical channel waveguides: an intermediate step between light and heavy ion implanted waveguides

We report on the micron-luminescent properties of carbon ion implanted optical channel waveguides in the Nd:MgO:LiNbO(3) laser crystals. The confocal fluorescence images of the waveguide's cross section are presented based on the analysis of the spatial variation of the Nd(3+) fluorescence properties. We have found that the carbon ion implanted waveguides exhibit hybrid fluorescence properties of both hydrogen and oxygen ion implanted waveguides, which clearly denotes a "boundary" effect of light and heavy ions for waveguide formation in lithium niobate crystals.