Banghong Guo

Spin-orbit hybrid entanglement quantum key distribution scheme

We propose a novel quantum key distribution scheme by using the SAM-OAM hybrid entangled state as the physical resource. To obtain this state, the polarization entangled photon pairs are created by the spontaneous parametric down conversion process, and then, the q-plate acts as a SAM-to-OAM transverter to transform the polarization entangled pairs into the hybrid entangled pattern, which opens the possibility to exploit the features of the higher-dimensional space of OAM state to encode information. In the manipulation and encoding process, Alice performs the SAM measurement by modulating the polarization state |θ〉π on one photon, whereas Bob modulates the OAM sector state |χ〉l on the other photon to encode his key elements using the designed holograms which is implemented by the computer-controlled SLM. With coincidence measurement, Alice could extract the key information. It is showed that N-based keys can be encoded with each pair of entangled photon, and this scheme is robust against Eve’s individual attack. Also, the MUBs are not used. Alice and Bob do not need the classical communication for the key recovery.

Characterization of passive optical components with ultra-fast speed and high-resolution based on DD-OFDM.

The passive optical components with very fine structures in wavelength domain are very sensitive to the mechanical vibrations or thermal fluctuations. If the measurement speed is lower than the temperature and mechanical fluctuation, we cannot measure the dynamic characteristics of the optical components. In this paper, we propose and demonstrate a novel method with ultra-fast measurement speed and high-resolution based on optical channel estimation using direct-detected orthogonal frequency division multiplexing (DD-OFDM) signal, which can be used to measure the dynamic characteristics and fine structure of the passive optical components. In experiment, by using fast Fourier transform (FFT) and a low-cost electro-absorption modulated laser (EML), we can achieve the transfer function characteristics with 3.9 MHz resolution. Compared with the optical channel estimation using coherent OFDM signal reported before, the proposed measurement technique is cost-effective.

Encoding random hot spots of a volume gold nanorod assembly for ultralow energy memory

Data storage with ultrahigh density, ultralow energy, high security, and long lifetime is highly desirable in the 21st century and optical data storage is considered as the most promising way to meet the challenge of storing big data. Plasmonic coupling in regularly arranged metallic nanoparticles has demonstrated its superior properties in various applications due to the generation of hot spots. Here, the discovery of the polarization and spectrum sensitivity of random hot spots generated in a volume gold nanorod assembly is reported. It is demonstrated that the two-photon-induced absorption and two-photon-induced luminescence of the gold nanorods adjacent to such hot spots are enhanced significantly because of plasmonic coupling. The polarization, wavelength, and spatial multiplexing of the hot spots can be realized by using an ultralow energy of only a few picojoule per pulse, which is two orders of magnitude lower than the value in the state-of-the-art technology that utilizes isolated gold nanorods. The ultralow recording energy reduces the cross-talk between different recording channels and makes it possible to realize rewriting function, improving significantly both the quality and capacity of optical data storage. It is anticipated that the demonstrated technology can facilitate the development of multidimensional optical data storage for a greener future.

Measuring topological charges of Laguerre–Gaussian vortex beams using two improved Mach–Zehnder interferometers

Abstract. We demonstrate, theoretically and experimentally, a new method to measure high-order topologicalcharges (TCs) of Laguerre–Gaussian vortex beams, including the magnitude and the sign, by analyzing theinterference intensity patterns. The magnitude is determined by analyzing the interference intensity patternsbetween the vortex beam and its conjugate beam, and using an improved Mach–Zehnder interferometerwith a dove prism. Counting the number of interference bright petals attests to the magnitude of high-orderTCs through half of the bright petal number. After the TC is modulated by a spiral phase plate, the sign isacquired by comparing the counting results of two charge-coupled devices. Just by this method, we havebeen able to measure both the magnitude and the sign of the TCs up to l ¼ 90. Our experimental resultsare in good agreement with the numerical simulations.

Novel wavelength division multiplex-radio over fiber-passive optical network architecture for multiple access points based on multitone generation and triple sextupling frequency

Abstract. An innovative wavelength division multiplex-radio over fiber-passive optical network architecture for multiple access points (AP) based on multitone generation and triple sextupling frequency is proposed and demonstrated. A dual-drive Mach–Zehnder modulator (DD-MZM) is utilized to realize the multitone generation. Even sidebands are suppressed to make the adjacent frequency separation twice the frequency of the local oscillator by adjusting the modulation voltage of the DD-MZM. Due to adopting three fiber Bragg gratings to reflect the unmodulated sidebands for uplink communications source free at optical network unit (ONU), is achieved. The system can support at least three APs at one ONU simultaneously with a 30 km single-mode fiber (SMF) transmission and 5  Gb/s data rate both for uplink and downlink communications. The theoretical analysis and simulation results show the architecture has an excellent performance and will be a promising candidate in future hybrid access networks.

A gain-flatness optimization solution for feedback technology of wideband low noise amplifiers *

The S parameter expression of high-frequency models of the high electron mobility transistors (HEMTs) with basic feedback structure, especially the transmission gain S21, is presented and analyzed. In addition, an improved feedback structure and its theory are proposed and demonstrated, in order to obtain a better gain-flatness through the mutual interaction between the series inductor and the parallel capacitor in the feedback loop. The optimization solution for the feedback amplifier can eliminate the negative impacts on transmission gain S21 caused by things such as resonance peaks. Furthermore, our theory covers the shortage of conventional feedback amplifiers, to some extent. A wideband low-noise amplifier (LNA) with the improved feedback technology is designed based on HEMT. The transmission gain is about 20 dB with the gain variation of 1.2 dB from 100 MHz to 6 GHz. The noise figure is lower than 2.8 dB in the whole band and the amplifier is unconditionally stable.

Pure Dielectric Waveguides Enable Compact, Ultrabroadband Wave Plates

The ability to manipulate polarization of light on a chip is of fundamental importance for many applications. Here, we demonstrate an ultrabroadband quarter-wave plate for silicon photonics based on pure dielectric waveguides. The concept of birefringence is used to introduce a phase lag of π/2 between two orthogonally polarized modes in nanophotonic waveguides, such that a quasi-linearly polarized mode is converted into a quasi-circularly polarized mode, which is accompanied with a longitudinal optical vortex component due to the spin-orbit interaction. Our device is ultracompact (2.3 μm) with low insertion losses (around 0.05 dB), and it allows for an ultrabroad operation bandwidth of 280 nm around 1.55 μm. We also propose a half-wave plate structure, which can either serve as a chiral converter for quasi-circularly polarized modes or a polarization rotator for quasi-linearly polarized modes. These results may find important applications in many fields, such as integrated quantum computing and polarization handling on a chip.

Wavelength division multiplexing quantum key distribution network using a modified plug-and-play system

This paper proposes and analyzes a multi-user wavelength division multiplexing–quantum key distribution (WDM-QKD) network that employs a modified plug-and-play system; this system employs a multi-wavelength laser diode to generate wavelength pulses for Bobs and utilizes a single phase modulator to modulate the returned pulses for all users. Benefitting from the time delay and delay line in Bobs, the returned pulses remain independent of Rayleigh backward scattering caused by strong pulse signals. Numerical simulations and results show that the key rate per user maintains a high level compared with a point-to-point link, because the communications between Alice and four Bobs can be carried out simultaneously.

Wavelength selective switch with superflat passbands based on a microelectromechanical system micromirror array

Abstract. We propose and experimentally demonstrate an industrial wavelength selective switch (WSS) architecture based on a microelectromechanical system (MEMS) micromirror array. An anisotropic uniaxial crystal and a half-wave plate are employed as the polarization-diversity solution to reduce the polarization-dependent loss (PDL) of the WSS, and an achromatic lens composed of a positive lens and a negative lens is adopted to eliminate chromatic aberration. Experimental results show that it is possible to select and switch any wavelength channel from an input port to any output port through a two-stage beam steering process. The measured insertion loss and PDL are 4.78 and 0.5 dB, respectively. Benefiting from the customized MEMS micromirror array with a high fill factor of 96%, the 3 dB bandwidth is about 90 GHz. The results also show that the proposed WSS possesses uniform and superflat passbands for different wavelength channels.

A characterization measurement of passive optical components with ultra-fast speed and high-resolution based on DD-OFDM

We demonstrate a novel method based on DD-OFDM to measure the property of passive optical components. In experiment, we realize the transfer function measurement of the delay interferometer (DI) with 3.9-MHz resolution and an ultra-fast measurement speed.