Titanium Indiffused Lithium Niobate Research Articles

A Pulsed Lidar System With Ultimate Quantum Range Accuracy

A light detection and ranging (lidar) system using a multi-output quantum pulse gate (mQPG) for quantum uncertainty limited range resolution is presented. Due to the inherent phase-sensitivity of the process, the proposed mQPG enhanced lidar system is able to beat the theoretical Rayleigh range resolution limit and the single detection Craméer-Rao bound (CRB) of classic pulsed lidar. To achieve this behavior, gating pulses interact with the backscattered lidar pulse while propagating through the optically non linear waveguide within the mQPG. The intensity of the discrete spectral channels of the mQPG contains finally the target distance informations. The mQPG was fabricated in a periodically poled (PP) titanium-indiffused lithium niobate waveguide and the entire system was built up in a lab environment. Measurement up to 1500 μm were performed around an arbitrary set reference point, and show excellent agreement with the theory up to 600 μm for a pulse length of 1.56ps, and up to 1100 μm for a pulse length of 2.12ps.

General analytic theory of classical collinear three-wave mixing in a monolithic cavity

Integrated, monolithic nonlinear cavities are of great interest in both classical and quantum optics experiments due to their high efficiency and stability. However, a general analytic theory of classical three-wave mixing in such monolithic systems, including both linear and nonlinear regions with arbitrary finesse and non-zero propagation losses, is a challenging task. Here, we derive such a model for any three-wave mixing process (second harmonic, sum frequency and difference frequency generation) under the sole assumption of low single-pass conversion efficiency. We demonstrate remarkable agreement between the presented model and the experimentally obtained highly complex second-harmonic spectrum of a titanium-indiffused lithium niobate waveguide cavity that includes both a linear and nonlinear section. We then show the effect that reversing the linear and nonlinear regions has on the output spectrum, highlighting the importance of system design. Finally, we demonstrate that the model can be extended to include the effect of phase modulation applied to the cavity.

Integrated superconducting nanowire single-photon detectors on titanium in-diffused lithium niobate waveguides

We demonstrate the integration of amorphous tungsten silicide superconducting nanowire single-photon detectors on titanium in-diffused lithium niobate waveguides. We show proof-of-principle detection of evanescently coupled photons of 1550 nm wavelength using bidirectional waveguide coupling for two orthogonal polarization directions. We investigate the internal detection efficiency as well as detector absorption using coupling-independent characterization measurements. Furthermore, we describe strategies to improve the yield and efficiency of these devices.

Cryogenic Second-Harmonic Generation in Periodically Poled Lithium Niobate Waveguides

We demonstrate second-harmonic generation in a fiber-coupled periodically poled titanium in-diffused lithium niobate waveguide over the temperatures range from 292 to 4.4 K. We observe a reproducible shift in the phase-matched pump wavelength within the telecom band, which is at odds with the phase matching arising from existing models of the refractive indices in this temperature regime. We further investigate transient discontinuities while temperature cycling, which we attribute to the build-up and discharge of pyroelectric fields. Our results show that modifications of the Sellmeier coefficients for lithium niobate are required in the cryogenic temperature regime for our waveguides, but also establish titanium in-diffused waveguides in lithium niobate as a versatile nonlinear photonic integration platform compatible with cryogenic quantum technologies.

Waveguide resonator with an integrated phase modulator for second harmonic generation.

We report second harmonic generation from a titanium indiffused lithium niobate waveguide resonator device whose cavity length is locked to the fundamental pump laser using an on-chip phase modulator. The device remains locked for more than 5 minutes, producing more than 80% of the initial second harmonic power. The stability of the system is seen to be limited by DC-drift, a known effect in many lithium niobate systems that include deposited electrodes. The presented device explores the suitability of waveguide resonators in this platform for use in larger integrated networks.

Cryogenic electro-optic polarisation conversion in titanium in-diffused lithium niobate waveguides.

Many technologies in quantum photonics require cryogenic conditions to operate. However, the underlying platform behind active components such as switches, modulators and phase shifters must be compatible with these operating conditions. To address this, we demonstrate an electro-optic polarisation converter for 1550 nm light at 0.8 K in titanium in-diffused lithium niobate waveguides. To do so, we exploit the electro-optic properties of lithium niobate to convert between orthogonal polarisation modes with a fiber-to-fiber transmission >43%. We achieve a modulation depth of 23.6±3.3 dB and a conversion voltage-length product of 28.8 V cm. This enables the combination of cryogenic photonics and active components on a single integration platform.

Interferometric method for determining the losses of spatially multi-mode nonlinear waveguides based on second harmonic generation.

The characterisation of loss in optical waveguides is essential in understanding the performance of these devices and their limitations. Whilst interferometric-based methods generally provide the best results for low-loss waveguides, they are almost exclusively used to provide characterization in cases where the waveguide is spatially single-mode. Here, we introduce a Fabry-Pérot-based scheme to estimate the losses of a nonlinear (birefringent or quasi-phase matched) waveguide at a wavelength where it is multi-mode. The method involves measuring the generated second harmonic power as the pump wavelength is scanned over the phase matching region. Furthermore, it is shown that this method allows one to infer the losses of different second harmonic spatial modes by scanning the pump field over the separated phase matching spectra. By fitting the measured phase matching spectra from different titanium indiffused lithium niobate waveguides to the model presented in this paper, it is shown that one can estimate the second harmonic losses of a single spatial-mode, at wavelengths where the waveguides are spatially multi-mode.

Design of reversible optical Feynman gate using directional couplers

Currently, reversible logic has gained a lot of interest, and it is a reliable solution in optical computing, low-power CMOS, quantum computing, and nanotechnology. Being reversible logic, one-to-one mapping between input and output causes minimal loss of information. In fact, optical Feynman gate (FG), one among many reversible logic gates, is a potential candidate for the realization of low-power photonic computational circuits. We propose and design a reversible optical FG using four titanium indiffused lithium niobate (Ti : LiNbO3) directional couplers. The elaborate design and analysis of uniform Δβ electrodes configuration of directional coupler has been presented preceded by in-depth design details and analysis of single-mode waveguides, fabrication tolerance, and S-type bend waveguides at 1.55-μm transmitting wavelength, using effective-index-based matrix method. Switching voltage of directional coupler, considering z-cut substrate, for a 134-nm-thick SiO2 buffer layer, is obtained as 24 V. The chip dimension of optical Feynman gate is of 23.8 mm length and 0.63 mm width.

RETRACTED: Apprehension of parity generator through array of Mach–Zehnder modulation process

Abstract Optical communication relies on electro optic effect for switching and modulation processes for various purposes. In order to achieve this, Mach-Zehnder interferometer (MZI) structure is utilized to achieve influential optical switching based on the function of electro-optic effect. This function is widely investigated in this paper and the same is implemented in a parity generator/checker for obtaining electro-optic effect by using MZI structure. Simulation is devised in a computer by applying a Titanium (Ti) in-diffused lithium niobate profile of MZI. Basic 2 × 2 switch is transformed as MZI for the design of parity device over a functional wavelength range of 1.3 µm to 1.65 µm. This simulated design is analyzed with different Ti LiNbO3 stripe thicknesses, in order to attain the optimum Ti-LiNbO3 stripe thickness and also to improve the performance of the switch on its cross talk, power imbalance, extinction ratio and transition losses. Opti BPM and Optisystem software is the tool used to design, implement and investigate the outputs obtained. The result set has proved to be efficient than all previous standards.

Characterisation of fabrication inhomogeneities in Ti:LiNbO3 waveguides

Nonlinear processes in integrated, guiding systems are fundamental for both classical and quantum experiments. Integrated components allow for compact, modular and stable light-processing systems and as such their use in real-world systems continues to expand. In order to use these devices in the most demanding applications, where efficiency and/or spectral performance are critical, it is important that the devices are fully optimised. In order to achieve these optimisations, it is first necessary to gain a thorough understanding of current fabrication limits and their impact on the devices’ final performance. In this paper we investigate the current fabrication limits of titanium indiffused lithium niobate waveguides produced using a masked photolithographic method. By dicing a long (∼8 cm) sample into smaller pieces and recording the resulting phase matching spectra, the fabrication error present in the UV photolithographic process is characterised. The retrieved imperfections fit well with theoretical expectations and from the measured imperfection profile it is shown that one can directly reconstruct the original distorted phase matching spectrum. Therefore, our measurements directly quantify the intrinsic limitations of the current standard UV photolitographically produced titanium-indiffused lithium niobate waveguides.

Array of Mach Zehnder Modulators for Realization of Parity Generator/Checker

The electro-optic effect is one of the most important techniques for modulation and switching purpose in optical communication. The Mach–Zehnder interferometer (MZI) structure functioning on the principle of electro-optic effect behaves as the influential optical switching device. This paper contains discussion of electro-optic effect based MZI structure and its efficient application to construct parity generator and checker. Titanium (Ti) in-diffused lithium niobate profile of MZI through computer simulation has been used for this purpose. Basic 2*2 switch is transformed as MZI for the design of parity device over a functional wavelength range of 1.3 µm to 1.65µm. This simulated design is analyzed with different Ti-LiNbO3 stripe thicknesses, in order to attain the optimum Ti-LiNbO3 stripe thickness and also to improve the performance of the switch on its crosstalk, power imbalance, extinction ratio and transition losses. The simulation model of proposed optical parity device has been implemented using the OptiBPM and OptiSystem softwares have been used for suitable verification of the discussed schemes.

Integrated transition edge sensors on titanium in-diffused lithium niobate waveguides

We show the proof-of-principle detection of light at 1550 nm coupled evanescently from a titanium in-diffused lithium niobate waveguide to a superconducting transition edge sensor. The coupling efficiency strongly depends on the polarization, the overlap between the evanescent field, and the detector structure. We experimentally demonstrate polarization sensitivity of this coupling as well as photon-number resolution of the integrated detector. The combination of transition edge sensors and lithium niobate waveguides can open the field for a variety of new quantum optics experiments.

Estimation of Fiber-Waveguide Coupling Loss and Waveguide Propagation Loss by Spectral Analysis

This letter presents a non-destructive and simple method for simultaneous measurement of fiber-waveguide coupling loss and propagation loss of single-mode optical waveguides. The experiment includes the coupling of a medium bandwidth laser source to optical waveguide under test and the analysis of its transmission spectra by using a grating monochromator. The technique has been demonstrated for a 46.5-mm-long fabricated titanium-indiffused lithium niobate (Ti:LiNbO3) waveguide for transverse magnetic polarization, and our first experiment yields a 2.18-dB fiber-waveguide coupling loss and a 0.58-dB/cm propagation loss at around 1557-nm transmitting wavelength. The measurement process needs no external perturbation, such as electric field or controlled heating, and hence is applicable for optical waveguides as-fabricated.

Towards optical-frequency-comb generation in continuous-wave-pumped titanium-indiffused lithium-niobate waveguide resonators

Much progress, both experimentally and theoretically, has recently been made towards optical frequency comb generation from continuously pumped second-order nonlinear systems. Here, we present the first observations towards finding an integrated solution for such a system, using a titanium indiffused lithium niobate waveguide resonator. These results are compared to recently developed theory for equivalent systems. The system is seen to exhibit strong instabilities, which require further investigation in order to fully determine the suitability of this platform for stable optical frequency comb generation.

Waveguide Cavity Resonator as a Source of Optical Squeezing

We present the generation of continuous-wave optical squeezing from a titanium-indiffused lithium niobate waveguide resonator. We directly measure 2.9\pm 0.1 dB of single-mode squeezing, which equates to a produced level of 4.9\pm 0.1 dB after accounting for detection losses. This device showcases the current capabilities of this waveguide architecture and precipitates more complicated integrated continuous-wave quantum devices in the continuous-variable regime.

Two-photon interference of weak coherent laser pulses recalled from separate solid-state quantum memories

Quantum memories allowing reversible transfer of quantum states between light and matter are central to quantum repeaters, quantum networks and linear optics quantum computing. Significant progress regarding the faithful transfer of quantum information has been reported in recent years. However, none of these demonstrations confirm that the re-emitted photons remain suitable for two-photon interference measurements, such as C-NOT gates and Bell-state measurements, which constitute another key ingredient for all aforementioned applications. Here, using pairs of laser pulses at the single-photon level, we demonstrate two-photon interference and Bell-state measurements after either none, one or both pulses have been reversibly mapped to separate thulium-doped lithium niobate waveguides. As the interference is always near the theoretical maximum, we conclude that our solid-state quantum memories, in addition to faithfully mapping quantum information, also preserve the entire photonic wavefunction. Hence, our memories are generally suitable for future applications of quantum information processing that require two-photon interference.

Construction and generation of OCDMA code families using a complete row-wise orthogonal pairs algorithm

A new code construction algorithm for incoherent Multi-Dimensional Optical Code Division Multiple Access (MD-OCDMA) for asynchronous fiber optic communication is proposed. We refer multi-dimensionality to two-dimensional (2D) wavelength–time or space–time domains and three-dimensional (3D) space–wavelength–time domains. The application of the algorithm in constructing 2D multiple pulses per row codes and 3D multiple pulses per plane codes is given. The performance of the codes is discussed. In the applications discussed, this construction ensures a maximum crosscorrelation of 1 between any two codes. The proposed codes have complete 1D code allocation, which increases the cardinality. The performance of some codes in literature is compared with the proposed codes. The analyzed performance measure is bit error rate due to multiple access interference for different numbers of active users. The performance analysis shows that the proposed 2D construction offers very low bit error rate at lower spectral efficiency when compared with other 2D constructions. A comparison of the proposed 3D construction with existing 3D constructions shows lower bit error rate for equivalent code dimension. New integrated optic designs for the generation of OCDMA codes using titanium indiffused lithium niobate technology are explored, which can enable compact encoders and decoders for computer communications.

Bandstructure measurement in nonlinear optical waveguide arrays

We demonstrate a technique for measuring the linear bandstructure of periodic systems with quadratic nonlinearity. The phase-matching constraints of parametric optical frequency mixing are employed to probe the longitudinal wavevectors of the eigenmodes. The method is verified experimentally by measuring the diffraction relation of eigenmodes in periodically poled titanium-indiffused lithium niobate waveguide arrays with second-harmonic generation.

Modeling of a 2x2 electro-optic Mach-Zehnder Interferometer optical switch with s-bend arms

In this paper, we present a 2×2 electro-optic switch based on a Mach-Zehnder interferometer (MZI) with tapered (s-bend) interferometric arms. All structures have been designed with a channel profile of titanium indiffused lithium niobate waveguides. The crosstalk analysis of the switch suggests that the crosstalk levels become worse (-12dB) when both interferometric arms of the structure are tapered. We have optimized the structure in order to reduce the overall switch losses ( 20dB). Full Text: PDF

Laser-induced-forward-transfer: a rapid prototyping tool for fabrication of photonic devices

We propose a rapid prototyping method for the fabrication of optical waveguides based on the direct laser-printing method of ultrafast Laser-Induced Forward Transfer (LIFT) followed by further processing. The method was implemented for the fabrication of titanium in-diffused lithium niobate channel waveguides and X-couplers by LIFT-depositing titanium metal followed by diffusion. Propagation loss as low as 0.8 dB/cm was measured in preliminary experiments.