Hertzvasquez2189

Sampling frequency offset (SFO) is an important issue in the orthogonal frequency-division multiplexing (OFDM)-based visible light communication (VLC) systems with low-cost analog-to-digital or digital-to-analog converters (ADCs/DACs). A digital interpolation or resampling filter can be used to effectively compensate the SFO. In such case, oversampling at the receiver ADC is required to mitigate the aliasing effect due to imperfect DACs and nonlinearity of visible light sources that cause extra frequency components inside/outside the OFDM signal spectrum. The oversampling factor (rate) is mainly determined by the order of the digital interpolation filter and nonlinear VLC links. The design of the OFDM-VLC receiver incorporating the digital interpolation filter is vital as it affects not only the transmission performance but also the complexity of digital signal processing (DSP). To evaluate the feasibility of the digital interpolation-based SFO compensation schemes for cost-sensitive VLC applications, in this paper, a real-time OFDM-VLC receiver incorporating the 2nd/3rd/4th order interpolation filters is experimentally demonstrated. An OFDM frame structure is designed for the synchronization including SFO estimation and compensation, in which the precision and latency of DSP are considered. On the basis of the real-time OFDM-VLC receiver, the comparison in the VLC transmission performance and DSP complexity between different interpolation-based SFO compensation schemes is discussed.Wide field fluorescence microscopy is the most commonly employed fluorescence imaging modality. However, a major drawback of wide field imaging is the very limited imaging depth in scattering samples. TGFbeta inhibitor By experimentally varying the control of illumination, we found that the optimized illumination profile can lead to large contrast improvement for imaging at a depth beyond four scattering path lengths. At such imaging depth, we found that the achieved image signal-to-noise ratio can rival that of confocal measurement. As the employed illumination control is very simple, the method can be broadly applied to a wide variety of wide field fluorescence imaging systems.We present the design and construction of an all-fiber high-power optical parametric chirped-pulse amplifier working at 1700 nm, an important wavelength for bio-photonics and medical treatments. The laser delivers 1.42 W of output average power at 1700 nm, which corresponds to ∼40 nJ pulse energy. The pulse can be de-chirped with a conventional grating pair compressor to ∼450 fs. Furthermore, the laser has a stable performance with relative intensity noise typically below the -130 dBc/Hz level for the idler pulses at 1700 nm from 10kHz to 16.95 MHz, half of the laser repetition rate f/2.Compared with multicolor-chip integrated white LEDs, phosphor-based white LEDs are more attractive for daily illumination due to lower cost and complexity, and thus they are preferable for future commercial use of visible light communication (VLC) systems. However, the application of phosphorescent white LEDs has a lower data rate than multicolor-chip integrated LEDs because of severe nonlinear impairments and limited bandwidth caused by the slow-responding phosphor. In this paper, for the first time we propose to employ phosphorescent white LEDs based on silicon substrate with adaptive bit-loading discrete multitone (DMT) modulation and a memoryless polynomial based nonlinear equalizer to achieve a high-speed VLC system. We also present a comprehensive comparison among nonlinear equalizers based on the Volterra series model, memory polynomial model, memoryless polynomial model and deep neural network (DNN) with experimental results utilizing a silicon substrate phosphorescent white LED, and provide detailed suggestions on how to choose the most suitable nonlinear mitigation scheme considering different practical conditions and the tradeoff between complexity and performance. Beyond 3.00 Gb/s DMT VLC transmission over 1-m indoor free space is successfully demonstrated with bit error rate (BER) under the 7% forward error correction (FEC) limit of 3.8×10-3. As far as we know, this is the highest data rate ever reported for VLC systems based on a single high-power phosphorescent white LED.Entanglement purification is an indispensable ingredient in extended quantum communication networks and usually determines the efficiency and communication rate of quantum communication protocols. Different from all existing entanglement purification protocols (EPPs) where two or more copies of low quality mixed entangled states are selected from the same ensemble, here we describe a general and optimal EPP for arbitrary initial mixed states from different ensembles. We show that the successful operation of EPP may not obtain a higher fidelity mixed state, while the discarded source pair, which is usually regarded as a failure in existing EPPs, may have residual entanglement and can be reused to increase the yield of entanglement purification. We give the criterions of both the successful purification to obtain a higher fidelity mixed state and the existence of residual entanglement. Moreover, we reveal that entanglement purification procedure causes some entanglement loss. Finally, we provide an optimal approach to reduce the entanglement loss. This approach can also be used to increase the yield of entanglement purification. Our EPP may have potential application in long-distance quantum communications.We study the problem of determining the photon number statistics of an unknown quantum state using conjugate optical homodyne detection. We quantify the information gain in a single-shot measurement and show that the photon number statistics can be recovered in repeated measurements on an ensemble of identical input states without scanning the phase of the input state or randomizing the phase of the local oscillator used in homodyne detection. We demonstrate how the expectation maximization algorithm and Bayesian inference can be utilized to facilitate the reconstruction and illustrate our approach by conducting experiments to study the photon number distributions of a weak coherent state and a thermal state source.