Electro-optic Tuning Research Articles

Polymer-Filled Silica Fibers as a Step Towards Electro-Optically Tunable Fiber Devices

Microstructured fibers offer the possibility of being filled with unconventional materials in order to influence the propagation properties in an optical fiber waveguide. We have studied the filling of microstructured silica fibers with electro-optic polymers. For this purpose a new electro-optic polymer formulation has been developed which is well suited for the complete filling of capillaries in microstructured optical fibers. Such filling could be of special interest for all-solid bandgap fibers thanks to the high refractive index of electro-optic polymers compared with silica, for fiber integrated electro-optical modulation, or for tunable fiber Bragg gratings. We demonstrate waveguiding with such filled fibers, investigate the integration of electrodes for poling and prove the possibility of long-period grating inscription in such fibers.

Electric-field-tuned color in photonic crystal elastomers

Electrically tuned photonic crystals are produced by applying fields across shear-assembled elastomeric polymer opal thin films. At increasing voltages, the polymer opal films stretch biaxially under Maxwell stress, deforming the nanostructure and producing marked color changes. This quadratic electro-optic tuning of the photonic bandgap is repeatable over many cycles, switches within 100 ms, and bridges the gap between electro-active materials and photonic crystals.

Integrated Tunable Quantum-Dot Laser for Optical Coherence Tomography in the 1.7 <formula formulatype="inline"><tex Notation="TeX">$\mu{\rm m}$</tex></formula> Wavelength Region

In this paper, we present the design and characterization of a monolithically integrated tunable laser for optical coherence tomography in medicine. This laser is the first monolithic photonic integrated circuit containing quantum-dot amplifiers, phase modulators, and passive components. We demonstrate electro-optical tuning capabilities over 60 nm between 1685 and 1745 nm, which is the largest tuning range demonstrated for an arrayed waveguide grating controlled tunable laser. Furthermore, it demonstrates that the active-passive integration technology designed for the 1550 nm telecom wavelength region can also be used in the 1600-1800 nm region. The tunable laser has a 0.11 nm effective linewidth and an approximately 0.1 mW output power. Scanning capabilities of the laser are demonstrated in a free space Michelson interferometer setup where the laser is scanned over the 60 nm in 4000 steps with a 500 Hz scan frequency. Switching between two wavelengths within this 60 nm range is demonstrated to be possible within 500 ns.

Polarization-independent rapidly tunable optical add-drop multiplexer utilizing non-polarizing beam splitters in Ti:LiNbO3

A polarization-independent four-port wavelength-tunable optical add drop multiplexer (OADM) that utilizes non-polarizing relaxed beam splitters has been analyzed and demonstrated in Ti:LiNbO3 at the 1530nm wavelength regime. The design utilizes an asymmetric interferometer configuration with strain induced index grating for polarization coupling along its arms that are shifted in position relative to each other. Experimental results of the filter response agree with theoretical predictions. Electrooptic tuning over a range of 15.7nm at a rate of 0.08nm/V has been measured. A temporal response <46ns to a 20V step change in tuning voltage has been demonstrated. Fiber-to-fiber insertion loss is ~6.5dB.

Electro-Optic Tuneable of Direct Current Voltage in Ring Resonator

In this paper, a new design of the electro-optical tuning voltage in buried fiber ring resonator (BFRR) system is proposed. The crystals of LiNbO3, (Ba, Sr)TiO3, K(Ta, Nb)O3 and KH2PO4 are used as electro-optic core materials. The applied voltage can generate different refractive index deformation when used different electro-optic crystals. Different electro-optic crystals produce distinct maximum power loss within BFRR. The power loss in an electro-optic crystal can be controlled by tuning the applied voltage. The K(Ta, Nb)O3 crystal produce maximum power loss with lower voltage compared to other crystals.

Optical group-velocity control in a phase-shifted narrowband filter

We demonstrate group-velocity control with an optically reconfigurable narrow-band filter at 1550 nm based on a volume-holographic Bragg grating. The filter is dynamically addressed to obtain different tunable magnitude and phase function by modification of the length, coupling strength, apodization, and phase discontinuities. We characterize the switching behavior, group-delay, electro-optical tuning, and Gaussian pulse propagation.

Coherent recovery of the degree of polarization of light propagating in random anisotropy media

We report on the study of light polarization behavior in random anisotropy scattering media. It is shown that, in the case of low scattering events, the degree of polarization (DOP) demonstrates oscillatory behavior due to the coherent character of light scattering. A strong increase in the DOP is demonstrated by using electro-optic fine tuning of the refractive index modulation depth of the scattering media.

A high-speed widely tunable Šolc-type flat-top filter based on the dual transverse Pockelseffect

A high-speed widely tunable Šolc-type flat-top filter based on the dualtransverse Pockels effect is presented. The filter employs single-domainLiNbO3 (LN) with two pairs of transverse electrodes, where the one along they-axis is periodic and theother one along the z-axis is continual. The periodic electrode provides periodic electro-optic modulation alongthe light propagation direction, which results in a folded Šolc-type filter. The continualelectrode giving a uniform electric field is in charge of tuning the transmitted centralwavelength of the filter. Compared to a conventional PPLN Šolc-type filter, oursetup has double electro-optic tuning efficiency and a much broader operatingrange of intensity of the control electric field. In a safe region of electric fieldintensity, the transmitted central wavelength can extend from 1488 to 1562 nm.Since the tuning is via the Pockels effect, it has very fast response time (tens ofnanoseconds).

Semiconductor Cavity Quantum Electrodynamics with Single Quantum Dots

Semiconductor cavity quantum electrodynamics (cQED) with single quantum dots as artificial atoms and high quality factor cavies is a rapidly developing research field. Solid state platforms are a prerequisite for more wide spread exploitation of cQED effects, which hold promise for the realization of several key devices for quantum information processing and nano-optoelectronics, like single photon sources or ultra-low threshold lasers. Semiconductor systems are particularly attractive because they offer routes for electrical injection or electro-optical tuning. This talk will mainly focus on the presentation of cQED experiments in high-quality factor micropillar cavities containing semiconductor quantum dots (see Fig. 1). After a general introduction into semiconductor cQED with micropillar cavities, the recent progress made in our group on electrically driven micropillar cavities will be reported [1, 2]. By developing a process for planarizing and contacting quantum dot micropillars we fabricated devices with quality factors up to 16.000 for pillar diameters of 4 μm. Such devices feature pronounced cQED effects, like enhanced spontaneous emission, photon antibunching, high-β lasing and electro-optical tuning in both the weak or strong (see Fig. 2) coupling regime. Spatial determinism in cQED is of major importance for the exploitation of related effects on larger scale or for the realization of more complex device functionalities, e.g. the deterministic photonic coupling of remote quantum dots via spatially separated cavities and waveguides. Another main part of the talk will discuss our recent progress made in the field of device integration of site-controlled quantum dots into photonic crystal as well as micropillar cavities (see Fig. 3) [3, 4].

Optical Microring Resonators in Fluorine-Implanted Lithium Niobate for Electrooptical Switching and Filtering

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> We present a new approach for the fabrication of electrooptically tunable microring resonators in lithium niobate. Planar optical waveguides for vertical light confinement <formula formulatype="inline"><tex Notation="TeX">$(\Delta n_{ o} = 0.17)$</tex></formula> are produced by fluorine ion implantation. Optical microrings and bus waveguides are then formed by laser lithography masking and Ar<formula formulatype="inline"><tex Notation="TeX">$^{+}$</tex> </formula> plasma etching. Electrodes are optically isolated from the optical microrings by a polyvinyl alcohol buffer layer with a high dielectric constant (<formula formulatype="inline"><tex Notation="TeX">$\varepsilon \sim 70$</tex> </formula> at 10 Hz) to improve electrooptic tuning. The microrings with a radius of 80 <formula formulatype="inline"><tex Notation="TeX">$\mu$</tex> </formula>m exhibit optical resonances with a modulation depth of 11 dB, a free spectral range of 2 nm, and an electrooptical tunability of 10 pm/V. </para>

Electro-optic tuning and modulation of single-crystalline organic microring resonators

We present, for the first time to our knowledge, the fabrication and electro-optic (EO) tuning of single-crystalline organic microring resonators. In recent years, optical microring resonators have proven to be highly suitable building blocks for the realization of very large-scale integrated photonic circuits. In particular, microresonators based on organic materials are very promising for ultrafast EO applications, due to the electronic nature of the EO response preserving the modulation performances beyond 100 GHz. In contrast to polymer waveguiding structures realized previously, our crystalline thin-film devices feature an excellent long-term stability of the chromophore orientation and superior photochemical stability, and they do not require high-field poling prior to operation. The introduced thin-film fabrication method significantly reduces fabrication complexity of organic crystalline EO waveguides, compared to previously developed techniques. We have fabricated crystalline COANP (2-cyclo-octylamino-5-nitropyridine) microring resonators with resonance contrast up to 10 dB, ring waveguide propagation losses of about 10 dB/cm, a free spectral range of 1.6 nm, a finesse of up to 20, and a corresponding Q-factor of about 20,000, measured in the telecom wavelength range around 1.55 μm. We have demonstrated resonance wavelength tuning at the rate of 0.13 GHz/V(1.1 pm/V).

A Hybrid Electrooptic Microring Resonator-Based $1 \times 4\times 1$ ROADM for Wafer Scale Optical Interconnects

Pairing high-quality factor ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> ) silicon-on-insulator microring resonators with rapidly tunable organic electrooptic claddings has allowed the first demonstration of a silicon-organic hybrid electrooptic reconfigurable optical add/drop multiplexer (ROADM). A coplanar electrode geometry provides up to 0.36 GHz/V of electrooptic voltage tuning for each channel, corresponding to an electrooptic coefficient of r <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">33</sub> = 64 pm/V at wavelengths around 1550 nm. Individual ring resonator devices have 40- mum ring radii, 2.7-nm free spectral range, and tuning ranges of 180 GHz. The 1 times 4 times1 ROADM has a footprint of less than 1 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and has been shown to reconfigure in less than a microsecond.

Optical properties of holographically generated twisted nematic liquid-crystal gratings

By use of a trans-cis photoisomerization process occurring in an azo-benzene side chain, various twisted nematic liquid-crystal (LC) gratings are fabricated in LC cells. Two counterpropagating orthogonally polarized beams produce a polarization modulation, which inscribes the replica polarization modulation inside LC cells holographically, providing twisted nematic LC gratings. Microstructure, diffraction properties, and electro-optic tunability of diffraction efficiency are examined experimentally. From the Fourier transformation of the Jones matrix of twisted nematic LC gratings, Stokes parameters of the zeroth and first diffraction orders are calculated and compared with the optical measurements, resulting in a good agreement.

Demonstration of strong coupling via electro-optical tuning in high-quality QD-micropillar systems

We demonstrate electro-optical tuning of single quantum dots (QDs) embedded in high-quality (high-Q) micropillar cavities by exploiting the quantum confined Stark effect (QCSE). Combining electrically contacted high-Q micropillars and large In(0.3) Ga(0.7)As QDs with high oscillator strength facilitates the realization of strong coupling. In our experiments a single QD exciton was electrically tuned on resonance with a cavity mode of a micropillar with 1.9 microm diameter and a quality-factor (Q-factor) of 14,000 enabling the observation of strong coupling with a vacuum Rabi-Splitting of 63 microeV.

Analysis of Ti:LiNbO 3 zero-gap directional coupler for wavelength division multiplexer/demultiplexer

For the purpose of multichannel integrated-optical wavelength division MUX/DEMUX design, the wavelength tuning method of Ti:LiNbO 3 zero-gap directional coupler is analysed by effective-index based matrix method (EIMM). In this method, first, the 2D refractive index profile of the Ti:LiNbO 3 zero-gap directional coupler is transformed into lateral 1D effective-index profile by WKB method. Finally, matrix method is applied to this effective-index profile and the propagation constants are computed from the resonance peaks of the excitation efficiency versus propagation constant characteristics. It has been shown that the channel wavelength tuning can be achieved by varying the Y-branching angle at the input and output of the device or by a slight variation of two-mode-section length. The method of electro-optic fine tuning of the channel wavelength and channel separation of the device has also been investigated. A cascaded structure with proper parameters for four-channel application is also simulated and the results are presented.

Electro-optically tunable microring resonators on lithium niobate

Electro-optical tuning of a microring resonator fabricated on lithium niobate (LiNbO3) is presented. The device structure, including microring resonator and couplers, is designed in detail and is produced by titanium diffusion on the wet-etched LiNbO3 ridge surface. The resonance wavelengths for TM and TE polarizations can be tuned by electro-optic effect. The output characteristics of through port and drop port in the microring resonators are measured, and the effect of applied voltage on the shift of resonant wavelength is discussed. The presented microring resonators have the features of fast tuning speed, high material stability, bidirection wavelength shift, and no heating interference. Realization of such a microring resonator on LiNbO3 makes the utilization of electro-optic tuning and nonlinear effects in the versatile photonic applications of microring resonators achievable.

Bragg Reflector Waveguide and Electro-Optic Modulator Based on Barium Titanate Epitaxial Thin Films

AbstractWe report the nanofabrication of Bragg reflector waveguide structure based on barium titanate (BTO) epitaxial thin film grown on MgO substrate and characterized its optical transmission. A low pressure (~1 Torr) nano-lithography was used for the formation of Bragg reflector waveguide structure. We demonstrate that there is sufficient refractive index contrast to form a well-defined stop band by forming gratings in a top strip layer of Si3N4 that was grown on BTO thin film. Simulation of the optical transmission and stop band of TE mode, and electro-optic (EO) modulator tunability are discussed as well. The non-linear photonic crystal waveguides are potentially suitable as tunable optical filters and ultra-wide bandwidth modulators.

Light-enhanced electro-optic spectral tuning in annealed proton-exchanged periodically poled lithium niobate channel waveguides

We report the observation of light-enhanced electro-optic spectral tuning in annealed proton-exchanged, asymmetric domain-duty-cycle periodically poled lithium niobate (PPLN) channel waveguides for second-harmonic generation. The spectral tuning rate was increased rapidly from 0.07 nm/(kV/mm) to a saturated value of 0.32 nm/(kV/mm) in a 30%/70% domain-duty-cycle PPLN waveguide when the fundamental pump power near 1534 nm was increased from 0.6 to 46 mW. The second-harmonic laser power at 767 nm was identified to be the source enhancing the spectral tuning.

Electrically tunable two-dimensional holographic photonic crystal fabricated by a single diffractive element

An electrically tunable two-dimensional holographic photonic crystal was fabricated in polymer-dispersed liquid crystal using a single diffraction element, which was a specially designed photomask consisting of three diffraction gratings, which had a period of 4μm, oriented 120° relative to one another. With the photomask subjected to a collimated Ar+ laser beam operating at 514.5nm, a two-dimensional spatial light intensity pattern was created by interference of the three first order diffracted beams produced by the mask. The spatial light intensity pattern was then recorded inside a cell filled with the liquid crystal/prepolymer mixture to create a photonic crystal. The photonic crystal structures were observed under an optical microscope. It showed triangular structures with a lattice constant of about 2.50μm. The diffraction properties and electro-optic tunability were also presented.

Tunable two-dimensional hexagonal phase array in domain-engineered Z-cut lithium niobate crystal

An optical phase array with tunable phase step is demonstrated. The phase array consists of a two-dimensional hexagonal lattice of inverted ferroelectric domains fabricated on a Z-cut lithium niobate substrate. The electro-optically tunable phase step is obtained by the application of an external electric field along the z axis of the crystal via transparent electrodes. Theoretical analysis and experimental results are presented, showing that a tunable and flexible adaptive optical illuminator device can be realized by combining the electro-optic tunability with the Talbot effect. Generation of a multiplicity of light patterns is shown.