This thesis describes the establishment of a new fabrication facility for the realization of annealed and reverse proton exchanged waveguides in congruent lithium niobate at Grith University{Centre for Quantum Dynamics, and their application in dierent contexts of integrated quantum photonics technologies. We demonstrated the development of an accurate numerical model for the design of waveguides in X-cut and Z-cut substrates and high quality fabrication of both quasi-phase matched quadratic nonlinear waveguides and fast electro-optic waveguide modulators. Within the context of nonlinear optical processes, we demonstrated a newly proposed method which eciently reconstruct the biphoton state produced through spontaneous parametric down-conversion by the use of only classical measurements. The validity of the method is tested by a direct comparison with photon-coincidence counting measurements in a multi-channel integrated nonlinear device fabricated in our facility. We also implemented the rst frequency conversion of 369:5 nm light {resonant with the transition of Yb+ trapped ions{ to the 1550 nm telecom wavelength range with a periodically poled waveguide fabricated by the reverse proton exchange technique. Within the context of electro-optical processes, we showed the rst active demultiplexing of single-photons emitted from a quantum dot source with a single integrated device made of a network of electro-optically tunable directional couplers.
This thesis describes the establishment of a new fabrication facility for the realization of annealed and reverse proton exchanged waveguides in congruent lithium niobate at Grith University{Centre for Quantum Dynamics, and their application in dierent contexts of integrated quantum photonics technologies. We demonstrated the development of an accurate numerical model for the design of waveguides in X-cut and Z-cut substrates and high quality fabrication of both quasi-phase matched quadratic nonlinear waveguides and fast electro-optic waveguide modulators. Within the context of nonlinear optical processes, we demonstrated a newly proposed method which eciently reconstruct the biphoton state produced through spontaneous parametric down-conversion by the use of only classical measurements. The validity of the method is tested by a direct comparison with photon-coincidence counting measurements in a multi-channel integrated nonlinear device fabricated in our facility. We also implemented the rst frequency conversion of 369:5 nm light {resonant with the transition of Yb+ trapped ions{ to the 1550 nm telecom wavelength range with a periodically poled waveguide fabricated by the reverse proton exchange technique. Within the context of electro-optical processes, we showed the rst active demultiplexing of single-photons emitted from a quantum dot source with a single integrated device made of a network of electro-optically tunable directional couplers.
Entanglement is the hallmark of quantum mechanics. Quantum entanglement -- putting two or more identical particles into a non-factorable state -- has been leveraged for applications ranging from quantum computation and encryption to high-precision metrology. Entanglement is a practical engineering resource and a tool for sidestepping certain limitations of classical measurement and communication. Engineered nonlinear optical waveguides are an enabling technology for generating entangled photon pairs and manipulating the state of single photons. This dissertation reports on: i) frequency conversion of single photons from the mid-infrared to 843nm as a tool for incorporating quantum memories in quantum networks, ii) the design, fabrication, and test of a prototype broadband source of polarization and frequency entangled photons; and iii) a roadmap for further investigations of this source, including applications in quantum interferometry and high-precision optical metrology. \n \nThe devices presented herein are quasi-phase-matched lithium niobate waveguides. Lithium niobate is a second-order nonlinear optical material and can mediate optical energy conversion to different wavelengths. This nonlinear effect is the basis of both quantum frequency conversion and entangled photon generation, and is enhanced by i) confining light in waveguides to increase conversion efficiency, and ii) quasi-phase matching, a technique for engineering the second-order nonlinear response by locally altering the direction of a material's polarization vector. Waveguides are formed by diffusing titanium into a lithium niobate wafer. Quasi-phase matching is achieved by electric field poling, with multiple stages of process development and optimization to fabricate the delicate structures necessary for broadband entangled photon generation. \n \nThe results presented herein update and optimize past fabrication techniques, demonstrate novel optical devices, and propose future avenues for device development. Quantum frequency conversion from 1848nm to 843nm is demonstrated for the first time, with >75% single-photon conversion efficiency. A new electric field poling methodology is presented, combining elements from multiple historical techniques with a new fast-feedback control system. This poling technique is used to fabricate the first chirped-and-apodized Type-II quasi-phase-matched structures in titanium-diffused lithium niobate waveguides, culminating in a measured phasematching spectrum that is predominantly Gaussian (R^2 = 0.80), nearly eight times broader than the unchirped spectrum, and agrees well with simulations.
In this paper, we will see in more detail how the modal dispersion present in any waveguide can replace or be combined with the birefringence to fulfil the phase-matching condition. Chapter Contents: 8.1 Introduction 8.2 Proton exchange in LiNbO3, 8.2.1 The first discoveries: High δne, low loss 8.2.2 Combination with birefringence phase matching 8.2.3 Cerenkov configuration 8.2.4 Destruction of the X2 and strain-induced losses in channel waveguides 8.3 Periodic poling 8.3.1 Surface domains: Titanium diffusion and heat treatment 8.3.2 E-Field poling 8.3.3 The different PE processes and their impact on the nonlinearity of the crystal 8.3.3.1 Direct exchange 8.3.3.2 Annealing 8.3.3.3 IR absorption 8.3.3.4 Nonlinear optical properties of PE lithium niobate waveguides 8.3.4 PE and periodic poling 8.3.4.1 PE in PPLN crystals 8.3.4.2 E-field poling of PE samples 8.3.5 Components 8.3.5.1 SHG 8.3.5.2 Parametric fluorescence 8.3.5.3 DFG and amplification 8.4 Single photon pair generators 8.5 Quantum photonics integrated circuits on PPLN 8.5.1 Quantum relay 8.5.2 Squeezed states 8.6 Further improvements 8.6.1 Power-resistant materials 8.6.2 Highly confining waveguides 8.6.2.1 High-index soft proton-exchanged (HISoPE) waveguides 8.6.2.2 Thin-film lithium niobate 8.7 Today's issues 8.7.1 Control of the domains 8.7.1.1 E-beam poling of PE samples 8.7.2 Insensitive phase-matching configurations 8.7.2.1 Experimental observation of insensitive phase-matching configurations 8.7.2.2 Numerical studies of the phase mismatch 8.8 Conclusion Acknowledgments References Inspec keywords: ion exchange; optical phase matching; optical dispersion; optical waveguides; lithium compounds Other keywords: classical optics; LiNbO3; modal dispersion; quantum optics; nonlinear integrated optics; proton-exchanged lithium niobate waveguides; birefringence; phase-matching condition Subjects: Optical waveguides; Optical propagation, transmission and absorption; Nonlinear optics; Optical waveguides and couplers; Nonlinear optics and devices
Entangled photons generation is an interesting field of research, since progress in this area will directly affect the development of photonic quantum technologies, including quantum computing, simulation and sensing. Several methods have been sifted to increase the performances of entangled photon sources and the integrated optics approach represents a promising strategy. In particular, integrated waveguide sources represent a robust tool, thanks to their stability and the enhancement of nonlinear light-crystal interaction provided by waveguide field confinement. Here, we show the versatility of a hybrid approach, realizing an integrated optical source for the generation of entangled photon-pairs at telecom wavelength. The nonlinear active medium used is lithium niobate, while the routing and manipulation of the generated signal is performed in aluminum-borosilicate glass photonic circuits. The system is composed of three cascaded devices. First, a balanced directional coupler at the fundamental wavelength equally splits the pump in the lithium niobate waveguides, which generate single-photon pairs through type 0 spontaneous parametric down-conversion process. A third chip, encompassing directional couplers and waveplates, closes the interferometer and recombines the generated photons, thus giving access to different quantum states of light: path-entangled or polarization-entangled states. A thermal phase shifter, which controls the relative phase between the interferometer arms, gives an additional degree of freedom for engineering the output state of the presented photon pairs source. All these components are entirely fabricated by femtosecond laser micromachining, a direct and very versatile technique that allows to process different kind of materials and realize high quality optical circuits.
Herewithin we present multiplexed integrated photonics as a realisable route to large-scale quantum technologies. Quantum photonics is one many platforms for experimental demonstrations of quantum information science. The technological advantages afforded by the combination of integrated photonic circuits with multiplexing techniques can enable performance enhancements to make photonics a leading infrastructure for implementation of real-world quantum information systems. For this purpose, we create integrated circuits to solve technical challenges in the fields of quantum cryptography, discrete variable and continuous variable quantum computation. These circuits were fabricated in a facility developed at Griffith University, Centre for Quantum Dynamics, for the production of annealed and reverse proton exchange waveguides in congruent lithium niobate and have found applications across the fields of quantum optics and cryptography. We develop and demonstrate the first integrated many-mode active optical demultiplexing of single photons from a solid-state source. This scheme enables the production of a multiphoton Fock state across multiple spatial modes from a single high brightness solid-state source with temporal indistinguishability. This work addressed a major hurdle in the development of photonic quantum computers, namely generation of a large number of indistinguishable single photons on demand. To perform the demultiplexing of single photons we develop two key technologies; a high-speed 1:4 integrated photonic switch and a many channel arbitrary pulse sequence generator. Cryptography as a field is increasingly reliant on quantum random number generators for added security. With increased demand comes a requirement for higher bitrate random number generators, and as such we demonstrate multiplexing of a random number generation scheme based on measurements of quantum vacuum fluctuations. Furthermore, we show an increased level of security at high bitrates by implementing a new signal processing scheme We demonstrate integrated generation, manipulation and homodyning of squeezed light on a single chip for the first time. This scheme is the first successful demonstration of full integration of all the major components needed for continuous variable quantum computation in a temporally multiplexed architecture. These results represent contributions to several fields of study, demonstrating the advantages of integrated quantum photonic multiplexing, and are of interest to the quantum computing, information security, integrated optics, and electronic control communities.
Ion-sliced thin-film lithium niobate (LN) compact waveguide technology has facilitated the resurgence of integrated photonics based on lithium niobate. These thin-film LN waveguides offer over an order of magnitude improvement in optical confinement, and about two orders of magnitude reduction in waveguide bending radius, compared to conventional LN waveguides. Harnessing the improved confinement, a variety of miniaturized and efficient photonic devices are demonstrated in this work. First, two types of compact electrooptic modulators are presented – microring modulators, and Mach-Zehnder modulators. Next, two distinct approaches to nonlinear optical frequency converters are implemented – periodically poled lithium niobate, and mode shape modulation (grating assisted quasi-phase matching). Following this, stochastic variations are added to the mode shape modulation approach to demonstrate random quasi-phase matching. Afterward, broadband photon-pair generation is demonstrated in the miniaturized periodically poled lithium niobate, and spectral correlations of the biphoton spectrum are reported. Finally, extensions of the aforementioned results suitable for future work are discussed.
Lithium niobate (LiNbO3) serves as one of the most competitive materials in nonlinear integrated photonics and becomes a key platform for the realization of integrated optical quantum technology, because it is physically and chemically very stable and it has a larger refractive index, a wider transparent wavelength range and better nonlinear optical characteristics than most of the traditional materials. Using the second-order nonlinear effect of periodically polarized lithium niobate (PPLN) crystal, single-photon frequency conversion was successfully realized to satisfy the quantum measurement requirements. LiNbO3and PPLN Waveguides were widely developed to solve the problems such as easy beam divergence in crystals, so that the improved nonlinear conversion effect promotes the successful fabrication of many quantum devices such as single photon sources, entangled photon sources and single photon detectors etc. By combining LiNbO3waveguides with other waveguide technologies, one can fabricate various LiNbO3integrated optical components serving as the core devices of quantum interfaces, quantum memories and etc. Based on these progresses, we see the attractive potential of LiNbO3material to play a deterministic role in quantum information technology.