Electro-optic Waveguide Modulators Research Articles

UV integrated optics devices based on beta-barium borate

We report on our recent progress in development of ultraviolet (UV) integrated optics devices based on beta-barium borate (BBO). Planar optical waveguides with a thickness of a few micrometers have been formed by the implantation of He+ ions with energies of around 2MeV. Two alternative methods based on the femtosecond-laser assisted micromachining and lithographic structuring for the fabrication of ridge-type channel optical waveguides in implanted BBO crystals have been developed, and the transmission properties of the obtained waveguides have been studied. We demonstrate a big potential of the fabricated channel waveguides for the second harmonic generation of continuous-wave deep-UV laser light with a power of the order of 1mW, exploiting the nonlinear optical properties of BBO crystal. In addition, a low-voltage electro-optic waveguide modulator for the deep-UV light (half-wave voltage times electrode length Vπ×l=43Vcm at 257nm) was realized for the first time.

Optical properties of BaTiO3 thin films: Influence of oxygen pressure utilized during pulsed laser deposition

The crystallographic properties of BaTiO3 thin films, grown by pulsed laser deposition on MgO substrates, were found to be strongly influenced by the oxygen pressure used during growth. Low pressure grown films were c-oriented while increasing oxygen pressure produced films with preferred a-orientation. The crystal reorientation resulted in the shift of optical birefringence from +0.04 to −0.025 with low levels of birefringence in films possessing low tetragonal distortion. Mach-Zehnder electro-optic waveguide modulators were fabricated to characterize the electro-optic properties of the deposited films and to evaluate the suitability of these films for planar optical applications. An effective electro-optic coefficient of 23 pm/V was obtained for a c-axis oriented film near the crystal c→a reorientation point.

基于电光调制的激光光谱整形技术

A new spectrum shaping method, based on electro-optic modulation, to alleviate gain narrowing in chirped pulse amplification (CPA) system, is described and numerically simulated. Near-Fourier transform-limited seed laser pulse is chirped linearly through optical stretcher. Then the chirped laser pulse is coupled into integrated waveguide electro-optic modulator driven by an aperture-coupled-stripline (ACSL) electrical-waveform generator, and the pulse shape and amplitude are shaped in time domain. Because of the direct relationship between frequency interval and time interval of the linearly chirped pulse, the laser pulse spectrum is shaped correspondingly. Spectrum-shaping examples are modeled numerically to determine the spectral resolution of this technique. The phase error introduced in this method is also discussed.

Very low voltage single drive domain inverted LiNbO_3 integrated electro-optic modulator

Domain inversion is used in a simple fashion to improve significantly the performance of a waveguide electro-optic modulator in z-cut LiNbO(3). The waveguide arms of the Mach-Zehnder interferometer are placed in opposite domain-oriented regions under the same, narrower and more efficient electrode, so that opposite phase shifts (push-pull effect) can still be achieved despite the arms being subjected to the same electric field. Switching voltages close to 2 V are obtained, which allow 10Gb/s modulation with inexpensive drivers, such as those used for electro-absorption modulators, which deliver driving voltages well below 3V.

Ba Ti O 3 – Sr Ti O 3 multilayer thin film electro-optic waveguide modulator

Mach-Zehnder electro-optic waveguide modulators were fabricated based on BaTiO3 (BTO)-SrTiO3 (STO) multilayer thin film stacks grown on single crystal MgO substrates by pulsed laser deposition. X-ray diffraction measurements confirmed the formation of a BTO-STO superlattice with periodicity of 11unit cells. Strip-loaded waveguides were formed by patterning a SixNy film deposited onto the BTO-STO stack while Al electrodes of 3mm length and 13μm separation were fabricated in the vicinity of the active waveguide arm of the Mach-Zehnder modulator. An effective electro-optic coefficient of 73pm∕V at 1550nm wavelength was determined for the deposited BTO-STO superlattice by measuring the output intensity as a function of applied electric field.

ELECTRO-OPTIC EFFECT IN RELAXOR FERROELECTRIC FILMS AND SUPERLATTICES

ABSTRACT Electro-optic (EO) effect in single crystalline thin films and superlattices made from relaxor ferroelectric lead titanate doped lead magnesium niobate (PMN-PT) and rare-earth doped PMN-PT materials have been investigated. Strong in-plane EO anisotropy has been found in both single crystalline thin films and superlattices. A large out-of-plane EO coefficient was observed in PMN-PT superlattices. Such a significant enhancement can be attributed to the spontaneous polarization coupling between the two crystalline phases in superlattices when the stacking period is below 90 nm. When doping with erbium, the EO effect in PMN-PT single crystalline film films decreases as the erbium concentration increases. This research has been motivated by the development of various promising integrated photonic devices such as waveguide EO modulators, waveguide lasers, and photonic bandgap devices.

Performance of an electro-optic waveguide modulator fabricated using a deoxyribonucleic-acid-based biopolymer

An electro-optic (EO) planar waveguide modulator using a deoxyribonucleic acid (DNA)-based biopolymer for both the waveguide core and cladding layers has been fabricated and its performance evaluated. A cross-linked DNA-surfactant biopolymer was used for the top and bottom cladding layers and the core layer was a cross-linked DNA-surfactant biopolymer with 3wt% Disperse Red 1. The EO coefficient r33 was induced through contact poling. The fabricated device was found to exhibit EO modulating behavior. Using an estimated value of r33=0.5pm∕V, a sine-squared fit to the modulating data was obtained with Vπ=263V±10%.

Waveguide electro-optic modulator in fused silica fabricated by femtosecond laser direct writing and thermal poling

An integrated electro-optic waveguide modulator is demonstrated in bulk fused silica. A Mach-Zehnder interferometer waveguide structure is fabricated by direct writing with a femtosecond laser followed by thermal poling. A 20 degrees electro-optic phase shift is achieved at an operating wavelength of 1.55 microm with an applied voltage of 400 V and an interaction length of 25.6 mm, which correspond to an estimated effective electro-optic coefficient of 0.17 pm/V for the TE-polarized mode.

High-speed travelling-wave BaTiO 3 thin-film electro-optic modulators

The first successful realisation of high-speed travelling-wave BaTiO3 thin-film electro-optic waveguide modulators with 3 dB modulation bandwidth of 15 GHz at 1.55 µm wavelength is reported. Quasi-velocity-matched electrodes for BaTiO3 thin-film modulators are achieved by addition of a SiO2 buffer layer. Its microwave and electro-optic response are characterised.

Performance simulation for ferroelectric thin-film based waveguide electro-optic modulators

We simulate thin-film based electro-optic modulator structures to target low drive voltage, high-speed modulation, and small device size by using BaTiO3 ferroelectric film as an exemplary device material with optimizing film thickness. The calculations are performed for both the case of an experimental film having reff=35pm/V and the case of an ideal thin-film having r51=730pm/V. For the case of r51=730pm/V, a new relation between the drive voltage and the interaction length is derived with respect to the special configuration of BaTiO3 thin-films. For the optimal case of the film thickness and the waveguide design, the frequency–voltage-size performances that can be achieved include: >2.5GHz with 0.75 V Vπ and 31.1mm length, 10GHz with 1.5 V Vπ and 7.8mm length, >40GHz with 3.0 V Vπ and 1.9mm length, and >100GHz with 4.8 V Vπ and 0.8mm length. Various physical factors unique to the frequency–voltage-size performance trade-off of the thin-film EO modulator structures are discussed.

Modeling of electrooptic polymer electrical characteristics in a three-layer optical waveguide modulator

The electrical characteristics of electrooptic polymer waveguide modulators are often described by the bulk reactance of the individual layers. However, the resistance and capacitance between the layers can significantly alter the electrical performance of a waveguide modulator. These interface characteristics are related to the boundary charge density and are strongly affected by the adhesion of the layers in the waveguide stack. An electrical reactance model has been derived to investigate this phenomenon at low frequencies. The model shows the waveguide stack frequency response has no limiting effects below the microwave range and that a true dc response requires a stable voltage for over 1000 h. Thus, reactance of the layers is the key characteristic of optimizing the voltage across the core layer, even at very low frequencies (>10/sup -6/ Hz). The results of the model are compared with experimental data for two polymer systems and show quite good correlation.

Numerical modeling of polarization conversion in semiconductor electro-optic modulators

An accurate numerical simulation study of a polarization conversion phenomenon in deeply etched semiconductor electro-optic waveguide modulators is presented. Based on a powerful and versatile finite element package, the effect of various imperfect fabrication conditions on unwanted and unexpected polarization conversion in electro-optic semiconductor modulators is, for the first time to our knowledge reported and explained in terms of its origin.

BaTiO_3 thin-film waveguide modulator with a low voltage–length product at near-infrared wavelengths of 098 and 155 µm

A BaTiO3 thin-film electro-optic waveguide modulator with a low half-wave voltage-length product has been demonstrated at near-infrared wavelengths of 1-1.6 microm. Half-wave voltage-length products as small as 0.25 and 0.5 V cm were measured for a 5-mm-long device at wavelengths of 973 and 1561 nm, respectively. The effective electro-optic coefficients were calculated as 420 pm/V at 973 nm and 360 pm/V at 1561 nm. Further improvements in device performance by optimizing the ferroelectric domain structure are anticipated.

Visible and IR Light Waveguiding in Ferroelectric Na0.5K0.5NbO3Thin Films

ABSTRACTHigh-quality ferroelectric thin films are attractive materials for integrated optics applications including electro-optic waveguide modulators and frequency doubling second-harmonic generators. Several ferroelectric thin film materials, such as BaTiO3, KNbO3, LiNbO3, and (Pb,La)(Zr,Ti)O3, have been investigated regarding their optical and waveguiding properties. Recently the first results on waveguiding in ferroelectric Na0.5K0.5NbO3 (NKN) thin films were presented. Perovskite NKN films have previously been investigated as electrically tunable material for low loss rf and microwave applications. Na0.5K0.5NbO3 thin films of thickness 0.5–1.0 μm have been deposited on Nd:YAlO3(001) and Al2O3(0112) substrates using rf-magnetron sputtering of a stoichiometric, high-density ceramic target. X-ray diffraction measurements confirmed films grown highly (00 l) oriented on the perovskite Nd:YAlO3 substrate and preferentially c-axis oriented on the single crystal r-cut sapphire substrate. Optical and waveguiding properties were characterized using a Metricon 2010 prism-coupling apparatus with a rutile prism. Dark-line spectra were obtained at visible light (λ = 632.8 nm) as well as at infrared optical communication wavelengths, λ = 1319 nm and λ = 1549 nm, in both transverse electric ( TE) and transverse magnetic ( TM) polarizations. Sharp dips corresponding to waveguide propagation modes in the thin film layers where observed for both substrates. The calculated refractive index values and corresponding birefringence (Δ n = n TM− n TE = n e − n o ) as a function of wavelength has been compared. Generally a larger birefringence is observed for the NKN film on Nd:YAlO3, which is in agreement with the larger degree of preferential c-axis orientation measured by XRD.

Modeling and analysis of high-speed electro-optic modulation in high confinement silicon waveguides using metal-oxide-semiconductor configuration

We analyze the electrical and optical properties of a silicon electro-optic waveguide modulator using a metal-oxide-semiconductor (MOS) configuration. The device performance is studied under different modes of operation of the MOS diode and gate oxide thicknesses. Our calculations indicate that this scheme can be used for achieving high-speed submicron waveguide active devices on silicon on insulator. A microring resonator intensity modulator is predicted to exhibit switching times on the order of tens of picoseconds with modulation depth of 73% by employing a bias voltage of only 5 V.

Low-voltage, polarization-insensitive, electro-optic modulator based on a polydomain barium titanate thin film

A BaTiO3 thin-film electro-optic waveguide modulator with a half-wave voltage-interaction length product (VπL) of 1.1Vcm at 1.55-μm wavelength is demonstrated. The half-wave voltage and the measured effective electro-optic coefficient are 3.3V and 162pm∕V, respectively. The half-wave voltage increases less than 10% over a temperature range of 23–90°C. Polarization-independent electro-optic modulation was observed and attributed to the polydomain structure of the BaTiO3 film. The unique combination of large electro-optic coefficient and polarization independence illustrates how engineered domain structures in ferroelectric thin films can enable properties and performance unachievable in bulk single crystals.

Low-Loss Electrooptic BaTiO<tex>$_3$</tex>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.

Lasing dynamics of tunable single-frequency fiber-optic and waveguide lasers

The dynamics of the wavelength tuning of the radiation of fiber-optic and waveguide lasers with a short linear cavity are analyzed. It is shown that the tuning time is minimized in lasers in which the output diffraction grating has a reflectance of about 95% and which possess the maximum lasing efficiency. The additional losses that appear when the optical fiber is coupled with a controllable diffraction grating written on a waveguide electrooptic modulator reduce the tuning time of the laser radiation, but its lasing efficiency is also reduced in this case.

Continuous tuning of radiation frequency in fibre and waveguide lasers by a controllable Bragg grating

A method for fast radiation wavelength tuning is proposed for a single-frequency fibre laser. A diffraction grating written on a waveguide electrooptical modulator serves as the mirror of the external cavity and as the selector. The voltage supplied to the grating electrodes shifts the reflection band of the grating and hence tunes the emitted radiation range. The radiation frequency tuning within the grating reflection band is carried out by using an intracavity waveguide electrooptical cell. The spectral characteristics of laser radiation are calculated. It is shown that the tuning range of such a laser achieves 0.2 nm for a control voltage up to 5 V, the switching time being shorter than 0.7 ns.

High-speed continuous tuneable fibre and waveguide lasers with controllable Bragg grating

The method for fast controllable tuning of radiation wavelength of fibre and waveguide lasers is proposed. Bragg grating written on waveguide electrooptic modulator is used both as a wavelength selective element and as laser cavity mirror. By applying control voltage to grating electrodes it is possible to shift grating reflectivity spectrum and, thus, to tune laser generation region. Further, frequency is continuously tuned within the grating reflectivity bandwidth by means of intracavity waveguide electrooptic cell. Spectral parameters of laser radiation as well as efficiency of generation and switching time have been calculated. The region of continuous tuning of such a laser for control voltage up to 5 V is about 0.2 nm and switching time is less than 0.7 ns.