A technique to generate polarization entangled photons using concurrent type-I and type-0 second-order nonlinear processes in monolithic Bragg reflection waveguides is presented and analyzed. Concurrent phase matching is achieved by lithographic tuning of the waveguide ridge width. Nearly perfect entanglement is achievable on-chip through appropriate epistructure design without the need of spectral filtering and group velocity compensation. Theoretical calculations predict that a high quantum interference visibility could be experimentally achieved with the pair generation rate of each process being approximately 3.0×10(6) pairs/s/mW/GHz.
A technique to generate polarization entangled photons using concurrent type-I and type-0 second-order nonlinear processes in monolithic Bragg reflection waveguides is presented and analyzed. Concurrent phase matching is achieved by lithographic tuning of the waveguide ridge width. Nearly perfect entanglement is achievable on-chip through appropriate epistructure design without the need of spectral filtering and group velocity compensation. Theoretical calculations predict that a high quantum interference visibility could be experimentally achieved with the pair generation rate of each process being approximately 3.0×10(6) pairs/s/mW/GHz.
Quantum states of photons such as entangled and single photons are indispensable components for applications in optical quantum information processing. Being able to generate and manipulate quantum states of photons on a chip is a crucial step towards realizing real-world quantum information processing systems such as an optical quantum computer. In this thesis, theoretical and experimental research was carried out for on-chip generation of quantum states of photons via the nonlinear process of spontaneous parametric down-conversion (SPDC), including polarization entangled photons, hyperentangled photons and heralded pure single photons. A majority of the study was based on III-V semiconductor AlGaAs, which could lead to monolithic integration of pump lasers and enable electrically pump sources operating at room temperature. The generation of cross-polarized entangled photons via a type-II SPDC in an AlGaAs Bragg reflection waveguide (BRW) was first investigated. The lack of material birefringence enables the direct generation of wavelength-multiplexed polarization entangled photons with a concurrence of at least 0.77 in a bandwidth of 95 nm. Second, a technique using concurrent type-0 and type-I processes on an AlGaAs chip to generate polarization entangled photon was developed. This technique allows the generation of both co-polarized and cross-polarized entangled photons on the same chip without the need of off-chip compensation, interferometer and bandpass filter. Third, a technique of generating hyperentangled photons on an AlGaAs chip was developed by utilizing spatial modes of different guiding mechanisms. High quality entanglement could be achieved with bandpass filtering of a few nanometers without off-chip phase compensation. Four, a generic technique using nonlinear photonic nanowires to engineer two-photon quantum states was proposed. Via dispersion engineering which controls the group velocity of each mode, maximally entangled polarization entangled photons and pure heralded single photons can be generated on-chip. Design examples were applied to III-V semiconductor and ferroelectric materials. Last, a strategy to enhance the bandwidths of wavelength conversion and SPDC spectrum was developed by tapering the waveguides. Combined with further integration of pump lasers, photonic circuits and detectors, the techniques developed in this thesis provides a viable route to achieve fully integrated generation and manipulations of photonic quantum qubits.
We propose and analyze the performance of a technique to generate mode and polarization hyperentangled photons in monolithic semiconductor waveguides using two concurrent type-II spontaneous parametric downconversion (SPDC) processes.These two SPDC processes are achieved by waveguide engineering which allows for simultaneous modal phase matching with the pump beam in a higher-order mode.Paired photons generated in each process are cross polarized and guided by different guiding mechanisms, which produces entanglement in both polarization and spatial mode.Theoretical analysis shows that the output quantum state has a high quality of hyperentanglement by spectral filtering with a bandwidth of a few nanometers, while off-chip compensation is not needed.This technique offers a path to realize an electrically pumped hyperentangled photon source.
We explore the potential of versatile and efficient entangled photon pair generation by spontaneous parametric downconversion in Bragg reflection waveguides. By employing a quantum treatment of modes in channel waveguides, and by accounting for group velocity dispersion in the modes, the quantum state of the generated biphotons is realistically calculated. The pair production rate is predicted to reach 4×108 pairs/s/nm/mW of pump light in a 2 mm-long structure, on par with or exceeding the performance of previously reported designs. This is attributable to an enhanced nonlinear interaction through tight mode confinement in the waveguide. Strategies for device performance optimization and phase matching wavelength tunability are outlined and numerically demonstrated. The proposed design platform is versatile and allows photon pair generation with controllable flux, bandwidth, Schmidt number, and degree of polarization entanglement. The possibility of monolithic integration with a diode laser pump offers a way to design an electrically pumped entangled photon source.
AlGaAs Bragg reflection waveguides are promising systems for the generation of single and entangled photons through the process of spontaneous parametric down-conversion (SPDC) [1]. We use a type II SPDC process where the downconverted photons are orthogonally polarized. The produced photons are inherently polarization-entangled eliminating the need for any additional entanglement setup. The material AlGaAs is our preferred choice as a nonlinear medium because it features a high nonlinear coefficient allowing for room temperature operation and has the advantage of being a non-birefringent material. Further, the material platform allows for the direct integration of a pump laser into the same chip.
We report the observation of polarization entangled photon pairs generated by means of type-II spontaneous parametric down-conversion (SPDC) within an Al x Ga 1-x As Bragg reflection waveguide (BRW).Even though SPDC in BRW had been observed before, the photons detected were not entangled in the polarization degree of freedom.As a necessary previous step, we also characterized the phasematching properties of the waveguides designed by means of the nonlinear process of second-harmonic generation (SHG).
Generating nonclassical states of photons such as polarization-entangled states on a monolithic chip is a crucial step towards practical applications of optical quantum information processing such as quantum computing and quantum key distribution. Here we demonstrate two polarization-entangled photon sources in a single monolithic semiconductor waveguide. The first source is achieved through the concurrent utilization of two spontaneous parametric down-conversion (SPDC) processes, namely, type-0 and type-I SPDC processes. The chip can also generate polarization-entangled photons via the type-II SPDC process, enabling the generation of both copolarized- and cross-polarized polarization-entangled photons in the same device. In both cases, polarization entanglement is generated directly on the chip without the use of any off-chip compensation, interferometry, or bandpass filtering. This enables direct, chip-based generation of both Bell states $(|H,H\ensuremath{\rangle}+|V,V\ensuremath{\rangle})/\sqrt{2}$ and $(|H,V\ensuremath{\rangle}+|V,H\ensuremath{\rangle})/\sqrt{2}$ simultaneously utilizing the same pump source. In addition, based on compound semiconductors, this chip can be directly integrated with it own pump laser. This technique ushers an era of self-contained, integrated, electrically pumped, room-temperature polarization-entangled photon sources.