Improving source-in-the-middle continuous-variable quantum key distribution using a heralded hybrid linear amplifier

A hybrid linear amplifier is inserted at the output of the source-in-the-middle distribution protocol to overcome the shortcomings of the transmission distance.The modified protocol aims to maintain a high key rate for long-distance transmission under high noise.It has the potential to significantly broaden the application range of the continuous variable quantum key distribution protocol.The effects of amplifier parameters and noise on the modified protocol are analyzed in detail with regard to applying it to a practical system.To make the simulation more realistic,the effect of finite size on the new protocol is taken into account.It will serve as a guideline for the future use of hybrid linear amplifiers.Different parameters can be adjusted to achieve the best performance for key rates of different quantum channels.

Quantum Illumination with Noiseless Linear Amplifier

Quantum illumination, that is, quantum target detection, is to detect the potential target with two-mode quan- tum entangled state. For a given transmitted energy, the quantum illumination can achieve a target-detection probability of error much lower than the illumination scheme without entanglement. We investigate the useful- ness of noiseless linear amplification （NLA） for quantum illumination. Our result shows that NLA can help to substantially reduce the number of quantum entangled states collected for joint measurement of multi-copy quan- tum state. Our analysis on the NLA-assisted scheme could help to develop more efficient schemes for quantum illumination.

Hybrid linear amplifier-involved detection for continuous variable quantum key distribution with thermal states

Continuous-variable quantum key distribution(CVQKD)can be integrated with thermal states for short-distance wireless quantum communications.However,its performance is usually restricted with the practical thermal noise.We propose a method to improve the security threshold of thermal-state(TS)CVQKD by employing a heralded hybrid linear amplifier(HLA)at the receiver.We find the effect of thermal noise on the HLA-involved scheme in near-and-mid infrared band or terahertz band for direct and reverse reconciliation.Numerical simulations show that the HLA-involved scheme can compensate for the detriment of thermal noise and hence increase the security threshold of TS-CVQKD.In near-and-mid infrared band,security threshold can be extended by 2.1 dB in channel loss for direct reconciliation and 1.6 dB for reverse reconciliation,whereas in terahertz band,security threshold can be slightly enhanced for the gain parameter less than 1 due to the rise in thermal noise.

FPGA Implementation of a Power Amplifier Linearizer for an ETSI-SDR OFDM Transmitter

Most satellite digital radio （SDR） systems use orthogonal frequency-division multiplexing （OFDM） transmission, which means that variable envelope signals are distorted by the RF power amplifier （PA）. It is customary to back off the input power to the PA to avoid the PA nonlinear region of operation. In this way, linearity can be achieved at the cost of power efficiency. Another attractive option is to use a linearizer, which compensates for the nonlinear effects of the PA. In this paper, an OFDM transmitter conforming to European Telecommunications Standard Institute SDR Technical Specifications 2007-2008 was designed and implemented on a low-cost field-programmable gate array （FPGA） platform. A weakly nonlinear PA, operating in the L-band SDR frequency, was used for signal transmission. An adaptive linearizer was designed and implemented on the same FPGA device using digital predistortion to correct the undesired effects of the PA on the transmitted signal. Test results show that spectral distortion can be suppressed between 6-9 dB using the designed linearizer when the PA is driven close to its saturation region.

Radio Frequency Low Noise Amplifier with Linearizing Bias Circuit

A 1.34 GHz-1=60 MHz low noise amplifier （LNA） designed in a 0.35 pm SiGe process is presented. The designed LNA exhibits a power gain of 21.46 dB and a noise figure （NF） of 1.27 dB at 1.34 GHz. The linearity is improved with an active biasing technique. The post-layout simulation shows an input referred 1-dB compression point （IPldn） of-11.52 dBm. Compared with the recent reported high gain LNAs, the proposed LNA has a much better linearity without degrading other performance. The LNA draws 10 mA current from a 3.3 V power supply.

Adaptation of a Digitally Predistorted RF Amplifier Using Selective Sampling

In this paper, a reduced-cost method of measuring residual nonlinearities in an adaptive digitally predistorted amplifier is proposed. Measurements obtained by selective sampling of the amplifier output are integrated over the input envelope range to adapt a fourth-order polynomial predistorter with memory correction. Results for a WCDMA input with a 101 carrier configuration show that a transmitter using the proposed method can meet the adjacent channel leakage ratio （ACLR） specification. Inverse modeling of the nonlinearity is proposed as a future extension that will reduce the cost of the system further.

国外模拟集成电路近期发展动态

近年来,由于器件工艺水平的提高和电路设计技术的改进,模拟集成电路获得了很大的发展。席卷世界先进工业国家的三“A”革命(工厂自动化、办公室自动化和家庭自动化)和各种高精尖的军事装备,使品种繁多的模拟电路找到了用武之地。目前,国外半导体厂家正在竞相开发新的品种,并且不断扩大其应用范围,本文拟对应用比较广泛的几种主要模拟集成电路在国外的发展情况作一简单介绍。

Multi-Wavelength Conversion Using FP-LD with Linear Optical Amplifier

We propose and demonstrate a multi-wavelength converter using FP-LD with linear optical amplifier (LOA) which based on cross-gain modulation can convert an input signal to many wavelengths simultaneously for reconfigurable wavelength conversion in OXC and broadcasting in WDM systems.

All-fiber linear polarization and orbital angular momentum modes amplifier based on few-mode erbium-doped fiber and long period fiber grating

A few-mode erbium-doped fiber（FM-EDF） is fabricated using modified chemical vapor deposition in combination with liquid solution. The core and cladding diameters of the fiber are approximately 19.44 and 124.12 μm,respectively. The refractive index difference is 0.98%, numerical aperture（NA） is 0.17, and normalized cut-off frequency at 1550 nm is 6.81. Therefore, it is a five-mode fiber, and can be used as a higher-order mode gain medium. Furthermore, a long period fiber grating（LPFG） is fabricated, which can convert LP〈01 mode to LP11 mode, and its conversion efficiency is up to 99%. The first-order orbital angular momentum（OAM） is also generated by combining the LPFG and polarization controller（PC）. Then, an all-fiber amplification system based on the FM-EDF and LPFG, for LP11 mode and first-order OAM beams, is built up. Its on-off gain of the LP11 mode beam is 37.2 d B at 1521.2 nm. The variation, whose transverse mode field intensity of first-order OAM is increased with the increase of pumping power, is obvious. These show that both the LP11 mode and first-order OAM beams are amplified in the all-fiber amplification system. This is a novel all-fiber amplification scheme,which can be used in the optical communication fields.

Performance of a recursive algorithm for polynomial predistorter design

In this article, based on least square estimation, a recursive algorithm for indirect learning structure predistorter is introduced. Simulation results show that of all polynomial predistorter nonlinear terms, higher-order （higher than 7th-order） nonlinear terms are so minor that they can be omitted in practical predistorter design. So, it is unnecessary to construct predistorter with higher-order polynomials, and the algorithm will always be stable. Further results show that even when 15th-order polynomial model is used, the algorithm is convergent after 10 iterations, and it can improve out-band spectrum of 20 MHz bandwidth signal by 64 dB, with a 1.2×10^11 matrix condition number.