Ti-diffused Waveguide Research Articles

Polarization mode converters in ZnO-diffused LiNbO3 waveguides

The linear electro-optic effect in lithium niobate is capable of realizing a variety of polarization transformations, including TE-to-TM and left-to-right circular polarization conversion. Several types of devices have been demonstrated in Ti-diffused waveguides. LiNbO3 devices have historically been based on either Ti-diffused or proton-exchanged waveguides. The proton-exchanged waveguides only guide light polarized along the optic axis, and therefore, are not applicable to polarization transforming devices. Zinc oxide diffusion is an alternative waveguide fabrication technology that guides both e- and o-waves with much higher power-handling capability than Ti : LiNbO3 waveguides. ZnO : LiNbO3 waveguides exhibit a highly circular mode field with lower anisotropy than Ti-diffused waveguides. We report the design, fabrication, and testing of ZnO : LiNbO3 devices for polarization mode conversion.

Photorefractive long-period waveguide grating filter in lithium niobate strip waveguide

To fabricate a long-period waveguide grating (LPWG) filter in a simple, reliable and low-cost way, a novel LPWG scheme based on photorefractive grating is designed and theoretically analyzed in a Ti-diffused strip waveguide embedded in a Ti-diffused planar \(\hbox {LiNbO}_{3}\) waveguide. By means of effective index method and coupled-mode theory, the processing conditions of the planar and the strip waveguide have been calculated. The minimum 100 % filtering length \(L=1.40\) cm and the coupling coefficient \(\kappa =112.23\,\hbox {m}^{-1}\) are obtained. The photorefractive LPWG filter can be used in coarse wavelength division multiplexing system.

Linear photonic frequency discriminator on As_2S_3-ring-on-Ti:LiNbO_3 hybrid platform

We report a photonic frequency discriminator built on the vertically integrated As₂S₃-ring-on-Ti:LiNbO₃ hybrid platform. The discriminator consists of a Mach Zehnder interferometer (MZI) formed by the optical path length difference (OPD) between polarization modes of Ti-diffused waveguide on LiNbO₃ substrate and a vertically integrated As₂S₃ race-track ring resonator on top of the substrate. The figures of merit of the device, enhancement of the signal-to-3rd order intermodulation distortion (IMD3) power ratio and corresponding 3rd order intercept point (IP3) over a traditional MZI, are demonstrated through device characterization.

Electro-Optically Tunable ${\rm As}_{2}{\rm S}_{3}$ Mach–Zehnder Interferometer on ${\rm LiNbO}_{3}$ Substrate

An electro-optically tunable vertically integrated As2S3 Mach-Zehnder interferometer side coupled to a Ti-diffused waveguide on LiNbO3 substrate was designed and fabricated. Asymmetric coplanar strip electrodes were placed along the As2S3 path, which show strong electro-optic tuning capability, shifting the FSR of the interferometer. The tuning of the TM polarization with 7-mm-long electrodes having a 7-μm gap was observed with VπL = 15.9 V-cm, giving a tuning rate of 0.028 nm/V at 1530 nm. To our knowledge, this is the first demonstration of electro-optic tuning of an As2S3 guided mode on LiNbO3 substrate.

Change of the refractive index in PPLN waveguides due to the photorefractive effect

In this work we report the results of the experimental investigation of the refractive index change due to the photorefractive effect in periodically poled lithium niobate (PPLN) Ti-diffused waveguides in dependence on light intensity and sample temperature. We show an experimental method that allows for the direct determination of the refractive index change. The saturation state of the change of the refractive index is reached at 775 nm with input power of 50 μW.

Optical Performance of Bragg Gratings Fabricated in Ti:LiNbO$_3$ Waveguides by Focused Ion Beam Milling

In this paper we propose an efficient technique for micromachining lithium niobate that is used in Ti-diffused waveguides. The use of Focused Ion Beam (FIB) etching allows obtaining homogeneous periodic microstructures. Bragg gratings with a period of 1.05 μm and an aspect ratio of 6:1 (depth-to-half period ratio) have been achieved. A reflectivity greater than 95 % associated with a bandwidth at half maximum of about 100 nm within a window centered at 1550 nm, is demonstrated for a Bragg grating of period Λ = 1.8 μm and a length of 144 μm, in good agreement with theoretical predictions.

Šolc-Type Wavelength Filters Based on TE↔TM Mode Conversion Utilizing Periodically Poled Ti-Diffused Lithium Niobate Channel Waveguides

We have demonstrated the Šolc-type wavelength filters in a 52 mm long periodically poled Ti-diffused lithium niobate channel waveguide which has a domain period of 16.6 μm. At room temperature, the center wavelength and the full-width at half maximum of the filter were about 1272.49 nm and 0.23 nm, respectively. The nearest side-lobe is about 7 dB. New structure of optical add/drop multiplexer (OADM) utilizing Šolc-type TE↔TM mode converters was proposed for the first time.

Compact Bends for Achieving Higher Integration Densities for LiNbO$_{3}$ Waveguides

A new waveguide platform is demonstrated that allows the bend radii to be substantially decreased for titanium-diffused lithium-niobate (LiNbO3) waveguides using vertically integrated arsenic-trisulfide (As2S3) overlay waveguides. Power is transferred from a Ti-diffused waveguide into the overlay waveguide using tapers, guided by the As2S3 waveguide through the S-bend region and transferred back into another Ti-diffused waveguide. This structure also behaves like a polarization beam splitter. We present simulation results as well as measurements to show the feasibility of achieving low loss and reduced bend radii for electrooptic waveguides.

Gain Improvement in Waveguide-typed Er-Light Amplifier with Yb Co-dope Technique

In this letter, Er-doped LiNbO3 waveguide-typed light amplifiers made with Yb co-dope technique are investigated from the point of view of gain improvement. The Ti-diffused waveguide light amplifiers are fabricated in Er/Yb co-doped LiNbO3 substrate, and benefits of Yb co-doping are provided by comparing with the conventional Er-single doping in gain measurement. It is also shown experimentally that the high-index clad-loaded waveguide configuration is more advantageous in the gain improvement than the conventional non-clad waveguide.

Reciprocating Optical Modulation on Erbium-Doped LiNbO$_{3}$ for Harmonic Generation

We demonstrated reciprocating optical modulation using erbium-doped LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> crystal for high-order sideband generation and selective amplification. A Ti-diffused waveguide, formed on the crystal, had a gain of 2.1 dB/cm for 1531.4-nm signal light pumped at 1480 nm with a pump power of 200 mW/port. A sideband component of 40 GHz was successfully enhanced and a gain of 12 dB was realized.

Optical amplification characteristics of Ti-diffused waveguides on Erbium-doped LiNbO3 crystal

We have first fabricated and characterized Ti-diffused channel waveguides on Er-doped LiNbO3 single crystal. We achieved an optical gain of 2.1dB/cm at 1531.4nm signal light (TM mode) by optical pumping at 1480nm with pump power of 200mW/port for a 40mm long Ti-diffused Z-cut 0.5mol% Er-doped LiNbO3 waveguide. The total gain of a pig tailed device was 3.8dB.

An optical grating filter dry-etched on a LiNbO3 substrate

We fabricated an etched grating filter on a Ti-diffused waveguide in LiNbO3 using inductively coupled plasma etching with C4F8/Ar as an etching gas, which has an etching rate of 85.1nm/min. The etched grating filter had a reflectivity of 35% and a bandwidth of 0.02nm. Maximum reflectivity was obtained when the electric field of an incident beam was perpendicular to the grating.

Zero-chirp broadband Z-cut Ti:LiNbO/sub 3/ optical modulator using polarization reversal and branch electrode

In this paper, a novel zero-chirp Z-cut LiNbO/sub 3/ optical modulator using ferroelectric polarization reversal and a branch electrode is proposed. The optical modulator with a Ti-diffused optical waveguide had a very small chirp parameter, which was less than 0.02. The performance showed a preferable 10-Gb/s eye opening and bias stability.

Laser-Induced Fracturing: An Alternative to Mechanical Polishing and Patterning of&amp;lt;tex&amp;gt;$rm LiNbO_3$&amp;lt;/tex&amp;gt;Integrated Optics Chips

We report a method for cutting z-oriented LiNbO/sub 3/ substrates into nearly arbitrary shapes using a pulsed UV laser to controllably fracture the crystal. The end surfaces appear optically smooth. Ti-diffused waveguides terminated using this technique have fiber-waveguide-fiber insertion losses which are equal to the lowest values reported for waveguide end faces prepared using conventional mechanical polishing techniques.

Group velocity modified Ti-diffused LiNbO 3 waveguides with dual Bragg gratings

Experimental results are reported on the modification of the group velocity in the Ti-diffused LiNbO/sub 3/ waveguides with dual Bragg gratings. The Bragg gratings were fabricated along the Ti-diffused waveguides. The average bandwidth was measured to be approximately 30 GHz separated by 30 GHz. Calculation showed approximately 10% modification of the group velocity between the stop bands.

Diffusion and structural modification of Ti:LiNbO3, studied by high-resolution x-ray diffraction

The ability of high-resolution x-ray diffraction, as a nondestructive method, to provide information on atomic diffusion is analyzed. The analysis focuses on studying Ti-diffused waveguide layers of LiNbO3 crystals for optoelectronic applications. Samples were prepared by a deposition of a 35-nm-thick Ti layer on the 3-in.-Y-cut LiNbO3 wafer and subsequent annealing at 995 °C for periods of 0.5–6 h. Depth-resolved profiles of the interplanar spacing derived from x-ray diffraction data are compared with the Ti-concentration profiles measured by secondary ion mass spectrometry. It is shown that both results can be used with confidence to determine the Ti-diffusion coefficients in LiNbO3. Comparison of the two techniques allowed us to obtain a numerical factor, K, relating the Ti concentration and the modification of lattice parameters, i.e., to characterize quantitatively the extent of lattice contraction due to Ti incorporation in the LiNbO3 crystal. The K factor was found to increase with annealing time, indicating a variable strain contribution to the structural parameters of the waveguide layer. These variations are attributed to high-temperature phase transformation processes, which accompany Ti diffusion.

Thermally Nd-diffused Z-propagation Ti:LiNbO 3 waveguide laser pumped by laser diode

The authors present results of the demonstration of laser oscillation in a Z-propagation Ti-diffused waveguide, which is immune from optical damage, on thermally Nd-diffused X-cut LiNbO3. Laser emission at a wavelength of 1093 nm was obtained with a threshold as low as 2.9 mW using a laser diode as the pump source.

Original method for measurement of optical mode fields

We report on a new method for measurement of mode spot sizes of fibers or waveguides (Ti-diffused or proton-exchanged waveguides on LiNbO(3)) that uses neither camera nor optics and works at any wavelength with a 1-μm resolution. The measurements are in good agreement with a finite element simulation.

Non-photorefractive CW Tm-indiffused Ti:LiNbO3 waveguide laser operating at room temperature

We report laser operation at 1.81 μm and 1.85 μm in a Tm/sup 3+/:LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Ti-diffused waveguide doped by thermal indiffusion at high temperature. We believe this is the first time lasing has been seen in Tm:LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> at room temperature. Continuous-wave operation was achieved at room temperature with a threshold of 42 mW launched pump power. The output power was observed to be stable, without any sign of photorefractive damage.

Characterization of optical waveguide layers in LiNbO3 by high-resolution X-ray diffraction

Abstract Ti-diffused and He-implanted optical waveguides in Y -cut LiNbO 3 wafers were, for the first time, studied by means of highresolution X-ray diffraction and revealed widely differing distortions of the shapes of (030)LiNbO 3 rocking curves. The depth strain profiles obtained as well as the corrlations found between rocking curve broadenings and variations in lattice constant demonstrated the high sensitivity of this technique to the structural properties of waveguides, as dependent on the processing parameters.