Bragg Reflection Waveguide Research Articles

Experimental quantum Byzantine agreement on a three-user quantum network with integrated photonics.

Quantum communication networks are crucial for both secure communication and cryptographic networked tasks. Building quantum communication networks in a scalable and cost-effective way is essential for their widespread adoption. Here, we establish a complete polarization entanglement-based fully connected network, which features an ultrabright integrated Bragg reflection waveguide quantum source, managed by an untrusted service provider, and a streamlined polarization analysis module, which requires only one single-photon detector for each user. We perform a continuously working quantum entanglement distribution and create correlated bit strings between users. Within the framework of one-time universal hashing, we provide the experimental implementation of source-independent quantum digital signatures using imperfect keys circumventing the necessity for private amplification. We further beat the 1/3 fault tolerance bound in the Byzantine agreement, achieving unconditional security without relying on sophisticated techniques. Our results offer an affordable and practical route for addressing consensus challenges within the emerging quantum network landscape.

Fabrication of low-loss III-V Bragg-reflection waveguides for parametric down-conversion

Entangled photon pairs are an important resource for many types of quantum protocols. Semiconductor Bragg-reflection waveguides are a promising photon-pair source due to mature fabrication, integrability, large transparency window in the telecom wavelength range, integration capabilities for electro-optical devices as well as a high second-order nonlinear coefficient. To increase performance, we improved the fabrication of Bragg-reflection waveguides by employing fixed-beam-moving-stage optical lithography, low-pressure, and low chlorine concentration etching, and resist reflow. The reduction in sidewall roughness yields a low optical loss coefficient for telecom wavelength light of αreflow = 0.08 (6) mm−1. Owing to the decreased losses, we achieved a photon-pair production rate of 8800 (300) (mW · s · mm)−1, which is 15-fold higher than in previous samples.

Full characterization of spontaneous parametric down conversion in non-ideal quarter-wavelength semiconductor Bragg reflection waveguide

Entangled photons are important for testing foundations of quantum physics and are at the heart of quantum technology. Integrated photonics has overwhelming dominance in terms of density and performance, making it a promise route for scalable quantum information processing. AlGaAs-based materials having large second-order non-linearities, direct bandgap and strong electro-optical effect can offer distinct advantages in quantum light source. Here we report a non-ideal quarter-wavelength Bragg reflection waveguide for generating three types of spontaneous parametric down-conversion processes. A general solution to the dispersion equation is derived and employed for designing high efficiency devices by taking into account the influence of core layer aluminium concentration. We further design and fabricate a Bragg reflection waveguide sample based on the analysis, and experimentally characterize its phase matching types and spectral brightness. Our work paves the path for the development of portable quantum light sources.

AlGaAs Bragg reflection waveguides for hybrid quantum photonic devices

Hybrid photonic devices represent a promising solution to the effective on-chip integration of all the components required for the generation, manipulation and detection of non-classical states of light encoding quantum information. We present an AlGaAs source of highly entangled photon pairs envisioned for the hybridization with silicon-on-insulator integrated platforms, in order to take benefit from the strong second order nonlinearity and the compliance with electrical pumping of the III-V platform and the maturity and CMOS compatibility of silicon photonic circuitry, enabling a wide variety of quantum information applications.

Nonlinear Quantum Photonics With AlGaAs Bragg-Reflection Waveguides

Integrated photonics is playing a key role in the development of quantum technologies covering applications ranging from quantum communication to computing and from simulations to sensing. In this context, material platforms enabling the chip-scale integration of quantum components are a key issue on the way towards real-world and large-scale technological implementations. In this paper, we review our last achievements on AlGaAs Bragg reflection waveguides emitting nonclassical states of light by spontaneous parametric down conversion. The choice of this platform combines the advantages of a mature fabrication technology, room temperature operation, emission in the telecom C-Band and compliance with electrical injection. We demonstrate the ability of these devices to generate a large variety of quantum states spanning from biphoton frequency combs to broadband polarization entanglement enabling promising applications in quantum processing as well as flexible quantum networks.

High-efficiency non-ideal quarter-wavelength Bragg reflection waveguide for photon-pair generation

Quantum light source is a promising resource for quantum-enhanced technologies and tests of quantum mechanics. In the race towards scalable quantum information processing, integrated photonics has recently emerged as a powerful platform. Semiconductor AlGaAs is arising as an outstanding platform due to its strong second-order nonlinearities, direct bandgap, manufacturability and reconfigurability. Here, we conduct an analytical investigation of semiconductor Bragg reflection waveguide (BRW), in which the core layer is surrounded by periodic claddings. A general solution to the mode dispersion equation is deduced independently of whether each cladding layer has an ideal quarter-wavelength thickness or not, and used for the analysis of AlGaAs/GaAs material. Different than before, we propose a novel structure with the core layer having high-index and achieve high modal overlap after full parameter optimization in a BRW slab structure, which can provide a practical way for designing high efficiency devices. The influence of thickness variation on overlap factor and system dispersion as well as biphoton spectral properties generated from type-II spontaneous parametric down conversion are also shown. Our approach can serve as a quick guideline for the design of polarization-entangled sources and contribute to large scale processing devices for practical applications by leveraging the structure’s versatile architecture.

An Optical Parametric Amplifier via $ \chi ^{(2)}$ in AlGaAs Waveguides

We report parametric gain by utilizing $ \chi^{(2)} $ non-linearities in a semiconductor Bragg Reflection Waveguide (BRW) waveguide chip. Under the two-mode degenerate type II phase matching, it can be shown that more than 18 dBs of parametric gain for both TE and TM modes is tenable in 100s of micrometers of device length. Polarization insensitive parametric gain can be attained within the 1550 nm region of the spectrum. These AlGaAs BRW waveguides exhibit sub-photon per pulse sensitivity. This is in sharp contrast to other types of parametric gain devices which utilize $ \chi^{(3)} $, where the pump wavelength is in the vicinity of the signal wavelength. This sensitivity, which reached 0.1~photon/pulse, can usher a new era for on-chip quantum information processing using compact, micrometer-scale devices.

Light dynamics around an exceptional point in a 1D photonic bandgap waveguide

Exceptional points (EP) in a system parameter space at which eigenvalues and corresponding eigenvectors coalesce are ubiquitous in non-Hermitian systems. Many unconventional applications have been proposed while encircling around the EPs. One of the unique application is the direction-dependent mode conversion. Here the appearance of an EP has been investigated in a planar 1D Bragg reflection waveguide(BRW) geometry, which has provided an additional degree of freedom to explore EP-based exotic light dynamics. A planar 1D BRW consists of periodic dielectric arrays and a defect dielectric layer forming the core. An inhomogeneous customized gain-loss profile is incorporated in the core region to couple two quasi-guided transverse electric (TE) modes so that the waveguide hosts an EP of order two. Here, we propose a dynamical EP encirclement scheme and corresponding asymmetric mode conversion phenomenon between two photonic bandgap quasi-guided TE modes in a 1D photonic bandgap-guided structure. Our findings will be potentially important to open up a fertile platform using the paradigm of non-Hermitian coupling to meet a wide range of exotic integrated chip-scale applications in the context of mode selectivity for switching and conversion.

Implementation of Bragg reflection waveguide microring resonator for optical second-harmonic generation

We propose a microring resonator with Bragg reflection waveguide (BRW) capable of simultaneously establishing the quasi-phase-matching, Bragg, and resonance conditions to achieve optical second-harmonic generation (SHG). Using numerical simulations, we suggest a comprehensive design procedure for a monolithic AlGaAs BRW microring. Due to the sensitive nature of BRW-based devices to material and fabrication tolerances, precise thermo-optic tuning method is proposed. It is shown that the designed structure can be thermally tuned in such a way that by only 6 °C, it can be switched to adjacent working wavelengths. Furthermore, being able to design microrings with different radii on the same wafer for SHG investigation is another advantage of our proposed device.

A Bragg reflection waveguide laser operating at an exceptional point

A vertical Bragg reflection waveguide (BRW) laser is proposed and simulated for reaching single-mode output, which operates at an exceptional point (EP). We study the properties of the EP-BRW laser using both the transfer matrix method and the traveling wave model. The mode selection mechanism for the EP-BRW laser and the key design parameters for optimum performance are analyzed. The effect of the EP on laser performance is investigated to achieve high confinement transversely of the optical field and low threshold gain. At the EP, such laser system exhibits exotic behaviors, such as high transverse gain, high single-mode stability, and high slope efficiency.

Research on a novel temperature indicating device based on Bragg reflection waveguide of planar texture cholesteric liquid crystal layer

In this paper, a temperature indicating device with double-layer planar texture cholesteric liquid crystal (PTCLC) is designed, which has great advantages over temperature card. It works based on the temperature dependence of the cholesteric liquid crystal helical pitch and the Bragg Reflection of PTCLC. A white light source is placed on one side of the waveguide element of the temperature indicating device, and only light of a particular wavelength can form guided wave due to the Bragg Reflection. The feasibility of the temperature indicating device was verified by measuring the Bragg reflectance spectrum and chromaticity coordinates at different temperatures.

χ2-based AlGaAs phase sensitive amplifier with record gain, noise, and sensitivity

Phase sensitive amplifiers (PSAs) have the potential to empower substantial advances in emerging generations of optical communication systems as well as classical and quantum on-chip signal processing. While second order nonlinearity ( χ 2 ) is stronger than third order nonlinearity ( χ 3 ), it is seldom utilized in semiconductors to realize PSAs owing to the challenges of effectively phase matching the interacting waves as well as countering the two-photon absorption of the pump. In this work, we demonstrate the successful design, fabrication, and characterization of, to our knowledge, the first χ 2 -based semiconductor PSA using an efficient phase matching approach and a pulsed pump, in an AlGaAs Bragg reflection waveguide. The reported AlGaAs PSA achieves on-chip in-phase gain approaching 30 dB, with a sensitivity of 0.005 photons per pulse. Its performance also approaches the theoretical minimal noise figure of 0 dB. With such performance metrics and its capability to operate in the single mode regime, this PSA could usher in a new era of on-chip quantum circuits.

Difference-frequency generation in an AlGaAs Bragg-reflection waveguide using an on-chip electrically-pumped quantum dot laser

Nonlinear frequency conversion is ubiquitous in laser engineering and quantum information technology. A long-standing goal in photonics is to integrate on-chip semiconductor laser sources with nonlinear optical components. Engineering waveguide lasers with spectra that phase-match to nonlinear processes on the same device is a formidable challenge. Here, we demonstrate difference-frequency generation in an AlGaAs Bragg reflection waveguide which incorporates the gain medium for the pump laser in its core. We include quantum dot layers in the waveguide that generate electrically driven laser light at ∼790 nm, and engineer the structure to facilitate nonlinear processes at this wavelength. We perform difference-frequency generation between 1540 nm and 1630 nm using the on-chip laser, which is enabled by the broad modal phase-matching of the AlGaAs waveguide, and measure normalized conversion efficiencies up to ()% W−1 cm−2. Our work demonstrates a pathway towards devices that utilize on-chip active elements and strong optical nonlinearities to enable highly integrated photonic systems-on-chip.

Distributed feedback lasers using surface gratings in Bragg waveguides.

This Letter presents, to the best of our knowledge, the first report of a narrow-linewidth ∼790-800nm edge-emitting semiconductor distributed feedback Bragg reflection waveguide diode laser (DFB2RL). The DFB2RLs were fabricated using a ridge waveguide structure with 5th order, surface-etched grating forming the wavelength selective element. Unbonded devices with a 500 µm cavity length exhibited continuous wave threshold currents in the region of 25 mA with an output power of 2.5 mW per (uncoated) facet at 100 mA drive current. The devices operated in a single longitudinal mode, with side-mode suppression ratio (SMSR) as high as 49 dB and linewidths as low as 207 kHz. Devices maintained single mode operation with high SMSR over a 9 nm wavelength range as the temperature was swept from 15°C to 50°C.

Compact solid-state optical phased array beam scanners based on polymeric photonic integrated circuits

Optical phased array (OPA) devices are being actively investigated to develop compact solid-state beam scanners, which are essential in fields such as LiDAR, free-space optical links, biophotonics, etc. Based on the unique nature of perfluorinated polymers, we propose a polymer waveguide OPA with the advantages of low driving power and high optical throughput. Unlike silicon photonic OPAs, the polymer OPAs enable sustainable phase distribution control during beam scanning, which reduces the burden of beamforming. Moreover, by incorporating a tunable wavelength laser comprising a polymer waveguide Bragg reflector, two-dimensional beam scanning is demonstrated, which facilitates the development of laser-integrated polymeric OPA beam scanners.

Understanding photoluminescence in semiconductor Bragg-reflection waveguides

Compared to traditional non-linear optical crystals, like BaB2O4, KTiOPO4 or LiNbO3, semiconductor integrated sources of photon pairs may operate at pump wavelengths much closer to the bandgap of the materials. This is also the case for Bragg-reflection waveguides (BRWs) targeting parametric down-conversion (PDC) to the telecom C-band. The large non-linear coefficient of the AlGaAs alloy and the strong confinement of the light enable extremely bright integrated photon pair sources. However, under certain circumstances, a significant amount of detrimental broadband photoluminescence has been observed in BRWs. We show that this is mainly a result of linear absorption near the core and subsequent radiative recombination of electron–hole pairs at deep impurity levels in the semiconductor. For PDC with BRWs, we conclude that devices operating near the long wavelength end of the S-band or the short C-band require temporal filtering shorter than 1 ns. We predict that shifting the operating wavelengths to the L-band reduces the amount of photoluminescence by 70% and making small adjustments in the material composition results in its total reduction of 90%. Such measures enable us to increase the average pump power and/or the repetition rate, which makes integrated photon pair sources with on-chip multi-gigahertz pair rates feasible for future devices.

Non-mechanical beam scanner based on VCSEL integrated amplifier with resonant wavelength detuning design

We demonstrate the non-mechanical beam steering and amplifier operation of a vertical cavity surface emitting laser (VCSEL) integrated Bragg reflector waveguide amplifier with a cut-off wavelength detuning design, which enables unidirectional lateral coupling, continuous electrical beam steering, and diffraction-limited divergence angle. We present the modeling of the proposed structure for unidirectional coupling between a seed single-mode VCSEL and slow-light amplifier. We also present the detailed operating characteristics including the near-field and far-field patterns, light/current characteristics, and lasing spectrum. The experimental measurements exhibit a single-mode output of over 8 mW under CW operation, a continuous beam steering range of 16°, and beam divergence below 0.1° as an optical beam scanner. The integrated amplifier length is as small as 0.9 mm, and thus we could expect much higher powers and higher resolution points by increasing the amplifier lengths.

Non-ideal quarter-wavelength Bragg-reflection waveguides for nonlinear interaction: eigen equation and tolerance.

A general eigen equation has been deduced that can handle ideal and non-ideal quarter-wavelength cases of Bragg-reflection waveguide structure for nonlinear interaction with matching layers on each side of the active region. In particular, this equation allows for solving the cases when the Bragg reflectors are non-ideal quarter-wavelength thick. With this equation, we propose a Bragg-reflection waveguide structure based on the AlxGa1-xAs/GaAs material system with high figure-of-merit |ξdeff| total nonlinearity and checked the influence if the thickness of the quarter-wavelength Bragg reflectors is off by 10%.

Photon-number parity of heralded single photons from a Bragg-reflection waveguide reconstructed loss-tolerantly via moment generating function

Due to their strict photon-number correlation, the twin beams produced in parametric down-conversion (PDC) work well for heralded state generation. Often, however, this state manipulation is distorted by the optical losses in the herald and by the higher photon-number contributions inevitable in the PDC process. In order to find feasible figures of merit for characterizing the heralded states, we investigate their normalized factorial moments of the photon number that can be accessed regardless of the optical losses in the detection. We then perform a measurement of the joint photon statistics of twin beams from a semiconductor Bragg-reflection waveguide with transition-edge sensors acting as photon-number-resolving detectors. We extract the photon-number parity of heralded single photons in a loss-tolerant fashion by utilizing the moment generating function. The photon-number parity is highly practicable in quantum state characterization, since it takes into account the complete photon-number content of the target state.

Design of Surface Defects Loaded Selectively Notched W-Band Waveguide Filter for Millimeter Wave Diagnostic in Fusion Reactor

In the fusion experiment, sensitive radio frequency signal diagnostic instruments need to be protected against high power stray radiation coming from the Electron Cyclotron Resonance Heating. The design of a stopband notch filter in the transmission path of the diagnostic system is helpful to avoid the stray radiations. This work presents the study and design methodology of the notch filter based on a circular corrugated waveguide Bragg reflector that provides a single stopband between 75 and 105 GHz. The existence of the HE11 mode, i.e. the only propagating mode in the W-band notch filter is the key aspect in the design of the filter. The proposed notch filter is compact and spans only 46.62 cm in length with an inner diameter of 16.4 mm. By optimizing the number of corrugation to 140, their period to λ through parametric analysis and unconventionally introducing uniformly spaced surface defects within the filter structure, a single stopband at 90 GHz is obtained corresponding to the LP12 Bragg resonance. The notch filter may be useful in wideband diagnostics like Electron Cyclotron Emission and reflectometry in the fusion plasma experiments.