Electro-optic Lithium Niobate Research Articles

Electro-optic lithium niobate metasurfaces

Many applications of metasurfaces require an ability to dynamically change their properties in the time domain. Electrical tuning techniques are of particular interest, since they pave a way to on-chip integration of metasurfaces with optoelectronic devices. In this work, we propose and experimentally demonstrate an electro-optic lithium niobate (EO-LN) metasurface that shows dynamic modulations to phase retardation of transmitted light. Quasi-bound states in the continuum (QBIC) are observed from this metasurface. By applying external electric voltages, the refractive index of lithium niobate (LN) is changed by Pockels EO nonlinearity, leading to efficient phase modulations to the transmitted light around the QBIC wavelength. The EO-LN metasurface developed in this study opens up new routes for potential applications in the field of displaying, pulse shaping, and spatial light modulating.

20 GHz actively mode-locked thulium fiber laser.

A high repetition-rate actively mode-locked thulium fiber laser is demonstrated where an electro-optic lithium niobate phase modulator is used to synchronize the longitudinal modes in the cavity. The repetition rate of the actively mode-locked laser is tunable from 14.6 MHz to 19 GHz, where the 19 GHz pulses exhibit a super-mode suppression ratio of 46 dB. Furthermore, the output pulse width could be manipulated through finely controlling the detuning frequency or repetition rate. We have also experimentally observed rational harmonic mode-locking in the laser and obtained 14 GHz and 21 GHz repetition rate pulses using a 7 GHz modulating signal. To the best of our knowledge, we have improved the repetition-rate of actively mode-locked thulium fiber laser by more than one order of magnitude. Such a high repetition source can be readily synchronized to a master clock, which makes it very suitable for high speed optical data processing, communication and remote sensing.

Analytical tool for the design and optimisation of high‐speed lithium niobate thin‐film Mach–Zehnder modulator

An analytical tool for the design and optimisation of high-speed electro-optical lithium niobate Mach–Zehnder modulators is developed. This is obtained by merging a closed-form approach for the radio-frequency (RF) propagation parameters of the coplanar waveguide forming the electrodes, and closed-form expressions relating the RF propagation parameters with the modulator bandwidth, driving voltage and length.

Analysis of electric field for inclined electrodes and use of such configuration for generating tunable differential polarization phase

While analytical techniques to study electric field distribution for an electrode-pair placed on two parallel opposite faces of a crystal (or channel) exist, but for the configuration with inclined opposite crystal faces such analysis is not straightforward. Here Schwarz-Christoffel mapping method, a special form of Conformal mapping technique, is used to study electric field distribution for parallel and non-parallel electrode-pair respectively. Being an analytical technique, the simulations are fast compared to numerical methods. A scheme on how variable polarization phase can be introduced when the electrode-pair is placed on the non-parallel faces of a specially designed trapezoidal shaped electro-optic lithium niobate crystal is also given in this work. It is also shown that by using multiple strip electrodes, tunability of the polarization phase difference can be achieved. Random optimization based on genetic algorithm has been used to optimize the device structure parameters to obtain desired phase shift.

Design of tunable transmission filter using one-dimensional defective photonic crystal structure containing electro-optic material

A narrowband tunable transmission filter suitable for wavelength division multiplexing is designed. The basic structure is a one-dimensional Fabry–Perot structure formed by layers of dielectric magnesium fluoride and electro-optic lithium niobate, which act as low and high refractive index material layers, respectively. A narrowband phase shifted transmission peak occurs within the stopband of the reflectance spectra of the structure by introducing the defect of a low-index material at a suitable position in the structure. The bandwidth of the peak depends on the number of bilayers and also on the operating wavelength. The phase shift of the transmission peak is linearly related to the wavelength under consideration. By adjusting the defect layer width, this shift of the transmission peak from the operating wavelength can be avoided. The device dimensions are so chosen that such a structure can be fabricated and used with presently available technology. A linear transmission peak tunability of 4 nm/10 V is achieved for this device by varying the refractive index of the electro-optic lithium niobate layer with externally applied voltage along its z axis. All the simulations have been carried out using the finite difference time domain method in a MATLAB® environment.

Effect of annealing on the structure and phase composition of thin electro-optical lithium niobate films

We have studied the formation of thin textured LiNbO3 films in originally amorphous samples produced by rf magnetron sputtering of a single-crystal target on silicon substrates containing a native oxide layer. The results demonstrate that postgrowth annealing leads to the formation of two phases, LiNbO3 and LiNb3O8, and that the percentage of the nonferroelectric phase LiNb3O8 is minimal after annealing at a temperature of 700°C. Annealing at 700°C is optimal because it ensures the lowest surface roughness of the film, the highest degree of structuring of the ferroelectric phase, and the maximum contrasts corresponding to the vertical and lateral components of the ferroelectric polarization in piezoresponse force microscopy.

Mode-selective coupler for wavelength multiplexing using LiNbO3:Ti optical waveguides

Abstract A mode-selective directional coupler based on titanium in-diffused channel waveguides in lithium niobate is investigated. This coupler may be utilized as a key part of an add-drop multiplexer for dense wavelength division multiplexing in optical network nodes. The proposed coupler is based on evanescent coupling of the fundamental mode of a single-mode channel to the first higher mode of a parallel bi-modal waveguide. Our experimental results show that a compact directional coupler with coupling efficiencies larger than 90%, large bandwidth around 1550 nm, and with negligible polarization dependence can be realized using electro-optic lithium niobate substrates.

Photolithography by a tunable electro-optical lithium niobate phase array

Photolithography experiments are performed by means of an optical phase mask with electrooptically tunable phase step. The phase mask consists of a 2-dimensional hexagonal lattice of inverted ferroelectric domains fabricated on a z-cut lithium niobate substrate. The electro-optically tunable phase step, between inverted domain, is obtained by the application of an external electric field along the z axis of the crystal via transparent electrodes. The collimated beam of an argon laser passes through the phase mask and the near field intensity patterns, at different planes of the Talbot length and for different values of the applied voltage, are used for photolithographic experiments. Preliminary results are shown and further applications are discussed.

Electric field sensing system using coherence modulation of light

This paper describes an experimental setup for detecting electric fields using electrooptic lithium niobate (LiNbO/sub 3/) sensors and coherence modulation of light. In this detection scheme, the sensed electric fields modulate optical delays, which are introduced by LiNbO/sub 3/ coherence modulators when associated to low-coherence optical sources. The optical delays act as coherence-multiplexed carriers of the sensed electric fields and are transmitted through an optical fiber channel. At the receiver, the electric fields are detected by measuring the auto-correlation of the received light by using two-wave interferometers, which are matched to the introduced optical delays on the sensing devices.

Q-switching in a Cr3+:Yb3+:Ho3+:YSGG crystal laser based on the 5I6 — 5I7 (λ=2.92μm) transition

An investigation was made of the generation of giant pulses in a new yttrium scandium gallium garnet laser crystal doped with holmium (Cr3+:Yb3+:Ho3+:YSGG) operating on the basis of the self-terminating 5I6 — 5I7 transition. Q-switching was performed by an electro-optical lithium niobate switch, a passive switch based on an epitaxial film of indium arsenide on a gallium arsenide substrate, or a passive switch consisting of water. The 2.92 μm wavelength dominated giant pulse generation, whereas under free-running conditions the radiation was discretely tunable in the range 2.84 —3.05 μm. Depending on the Q-switching method, pulses of 60 — 160 ns duration were generated and the pulse energy was ∼20 mJ. The second and fourth harmonics of the holmium laser radiation were generated and the efficiency of each frequency-multiplication stage was ∼20%.

Tunable garnet laser with electroopticQswitching

A laser was constructed in which the active element was a Y3Al5O12:Nd3+ crystal placed in a dispersive resonator. This crystal emitted tunable radiation as a result of the 4F3/2→4I11/2 (λ = 1.064 μ) and 4F3/2→4I13/2 (λ = 1.318, 1.338, and 1.356 μ) transitions when the Q factor of the resonator was modulated by an electrooptic lithium niobate switch. The energy and time characteristics of the emitted lines were determined. When the pumping threshold was exceeded by a factor of 3, the energy of the output pulses at λ = 1.318 μ was comparable with the energy of the λ = 1.064 μ pulses. The duration of the pulses increased from 10 nsec (for the first transition) to 40–45 nsec (for the 4F3/2→4I13/2 transition).

Contrast and various configurations of lithium niobate switches used in YAG:Nd3+lasers

An investigation was made of the contrast of electrooptic lithium niobate switches allowing for the quality of the electrooptic elements and various ways of using these switches. The half-wave configuration ensured a contrast approximately two orders of magnitude greater than the quarter-wave scheme, and it made it possible to achieve higher output energies from YAG:Nd3+ lasers.