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Quantitative polymerase chain reaction (qPCR) is the most important quantitative sensing technique for pathogens, especially for emerging pandemics such as the coronavirus outbreak this year. The qPCR chip and device were investigated to meet the unmet needs of ultrafast inspection time, high accuracy, and small system volume. Therein, the fluorescence intensity was the most important signal in qPCR quantification of DNA amplifications, which is essential not only in the confirmative diagnosis of positive or negative infection, but also in the assessment of viral load for therapeutic and quarantine decision making. As the target DNAs got amplified, the interaction of fluorescence dye and double strand DNA will generate fluorescence signal proportional to amplified DNA in the intensity when excited by certain wavelength. A miniature spectro-detector was employed to receive the fluorescence scattering for digital output of the intensity in the qPCR chip in this study, and the optical simulation and actual experimental design and results according to the optical simulation results were performed to study the effect of the stray light shutter (SLS) in the improvement of the signal in fluorescence detection. The analysis results showed that the signal-to-noise ratio (SNR) of the fluorescence can be enhanced significantly for five times of the control using the SLS with a shape of extended component aperture, where the protruding structure was positioned away from the center. The experimental results showed that fluorescence intensity can be enhanced by 15.50% and 9.86% when adding the above shape of SLS in resin- and in glass-based chip, respectively. The results also demonstrated that the optical setup had good stability and repeatability in fluorescence detection, and variation was less than 1.00%. Our results can provide important reference to the development of qPCR chip to obtain the high SNR fluorescence signal in DNA quantification process. [ABSTRACT FROM AUTHOR]

Optical fibre backscatter reflectometry is an important technique for Structural Health Monitoring (SHM). In recent years, increasing the intensity of backscattered light in backscatter reflectometry has shown the advantage of improving the signal detection in shape sensing and temperature detection due to the increase of signal to noise ratio and this approach could potentially be used to improve the performance of an SHM system. Doping nanoparticles (NPs) is a method to increase the intensity of backscattered light in distributed fibre optic sensing. The increased intensity of light backscattered by the NPs needs to be investigated to design suitable optical sensing fibres with NPs for backscatter reflectometry. In this work NPs were added to refractive index matching liquid and tested with commercial NP suspensions experimentally between the tips of two optical fibres. An estimate of the intensity of backscattered light from the NPs in this structure was performed by simulation to give a better understanding of the expected levels of intensities of scattered light from NPs in this distributed fibre optic sensing configuration. We present analytical models based on Mie theory and the Monte Carlo Method. Simulated results are presented, for a broad bandwidth Gaussian spectra shape incident light with a central wavelength around 1550 nm, to match the experimental conditions in this work. The novelty is in developing this model for scattered light by NPs at optical fibre interfaces and the evaluation of the possibility of detection by the calculated scattered intensity levels. [ABSTRACT FROM AUTHOR]

We demonstrate theoretically and experimentally a method to break the Rayleigh limit of an imaging system by modulating only the aperture of the imaging optics. By fully utilizing the useful information extracted from an image sequence, a superresolution image with high-frequency components beyond the cutoff frequency of the imaging system is reconstructed. Resolution enhancement of 2 times is achieved experimentally. Simulation results show that the method can still work with the signal-to-noise ratio of ~ 10 for the acquired images. [ABSTRACT FROM AUTHOR]

We characterize the performance of standard and micro genetic algorithms when applied to focusing inside of an opaque media using feedback from a fluorescent guidestar particle. Using this feedback modality we find that the algorithms optimize more quickly (but to a lower enhancement) than when using reflective feedback, with the underlying mechanism being the fluorescence signal's multimodal nature and lower signal-to-noise ratio. We also find that both algorithms' performance decrease at very large numbers of bins due to decoherence effects related to a bin-dependent iteration time. To mitigate this effect we implement multithreaded functionality in the genetic algorithms and find that for our specific computer we obtain a 3.3 × improvement in speed utilizing multithreading. These results demonstrate the usefulness of both algorithms for focusing inside of opaque media, which has applications in biological imaging and the study of subsurface chemical reactions in heterogeneous materials. [ABSTRACT FROM AUTHOR]

The stability of the spatial information transmission in communication is very important, and the ghost imaging mechanism has shown advantages in resistance to the external interference factors and in the low-light detection. A Rician fading channel typically describes the environment with a direct path and an infinite number of multi-path scatters, and the channel quality could be directly reflected by the estimation of the Rician factor. We propose a theoretical model of ghost imaging in a Rician fading channel with additive random noise. By calculating the peak signal-to-noise ratio and the resolution, the impact of the path loss and the Rician distribution on the imaging quality are numerically investigated. In addition, the comparative studies between the traditional non-correlated imaging and ghost imaging under the same conditions are also discussed, and it is shown that ghost imaging technique presents higher robustness and longer transmission distance. Our results establish a link between communication channels and ghost imaging, and provide reference and guidance for the spatial information transmission through a Rician fading channel. [ABSTRACT FROM AUTHOR]

Cross polarized optical coherence tomography (OCT) offers enhanced contrast in certain pathological conditions. Traditional cross-polarized OCT systems require a defined input polarization and thus require several polarization controlling elements increasing the overall complexity of the system. Our proposed system requires a single quarter wave plate as a polarization controller thus simplifying the system significantly. The majority of cross-polarized OCT systems are spectrometer based, which suffers from slow speed and low signal to noise ratio. In this work, we present a swept source based cross-polarized OCT system that works for any input polarization state. The system was tested against known birefringent materials such as quarter wave plate. Furthermore, biological samples such as finger, nail and chicken breast were imaged to demonstrate the potential of our technique. [ABSTRACT FROM AUTHOR]

In recent years, various studies have been conducted to illustrate the vulnerability of double random phase encoding (DRPE). In this paper, we propose a novel method via phase reservation and compression to enhance DRPE security. Only a compressed phase distribution is available in the CCD plane, and the amplitude component is not available or requested for optical decryption. Since only noise-like distributions can be obtained by using the correct security keys during optical decryption, a nonlinear correlation algorithm is further applied for authenticating the decrypted image. It is demonstrated that valid conditions for attack algorithms are broken and high security can be achieved for the DRPE system. [ABSTRACT FROM AUTHOR]

A novel method is proposed for designing optimized three-dimensional computer-generated holograms (CGHs). A series of spherical wave factors are introduced into the conventional optimal rotation angle (ORA) algorithm to achieve a varying amount of defocus along the optical axis, and the distraction terms are minimized during the iterative process. Both numerical simulation and experimental reconstructions are presented to demonstrate that this method is able to yield excellent multilayer patterns with high uniformity and signal-to-noise ratio (SNR). This method is significant for applications in laser 3D printing and multilayer data recording. [ABSTRACT FROM AUTHOR]

A method to evaluate quantitatively the performance of the phase shift extraction algorithms in generalized phase-shifting interferometry (GPSI) is proposed. A parameter named as reconstruction signal-to-noise ratio (R-SNR) is used as the evaluation measure. The R-SNR is defined with the reconstructed object image as the signal and the residual of the DC term and conjugate image as noise. The more accurate the extracted phase shift is, the less residual of the DC term and conjugate image there is, and then the higher R-SNR is obtained. To avoid the overlap of the DC term and conjugate image and the object image, the off-axis digital holography configuration is adopted. The correctness and effectiveness of the proposed method have been verified by both computer simulation and optical experiments. The major advantage of the proposed method is that it utilizes the experimental detectable data and not only the computer simulation results. [ABSTRACT FROM AUTHOR]

We describe a quasi-all-optical extension dedicated to simplifying the deployment of submarine cabled observatories. Based on power-over-fiber technologies, high power supply and data are both transmitted in one optical fiber of a few kilometers in length. We study the Raman amplification on the down- and up-stream data in the static regime with the high optical power varying from 100 mW to 4 W over a 10 km long single-mode optical fiber. We focus on the data optical budget and signal to noise ratio dependence with respect to the high optical power value and the data optical wavelength. We also present the transmission quality in the dynamic regime of this quasi-all-optical extension. [ABSTRACT FROM AUTHOR]

A dual-wavelength random distributed feedback fiber laser with external micro-air cavity (MAC) is experimentally demonstrated. The structure that comprises of a fixed 200 μm air-gap distance between two flat-angle fiber-end facets behaves similarly to the role of reflectors. The generation of dual-wavelength lasing at 1552.5 and 1557.7 nm was achieved. The accomplishment is associated to the filtering effect of MAC superimposed with Raman gain spectrum. Equal peak power of approximately −12.7 dBm was attained at maximum 2.0 W pump power. In this case, the respective optical signal-to-noise ratios were 18.79 and 18.73 dB. Excellent stability of the spectral width was realized over 60 min observation time at room temperature, which denotes the practicality of this device in addition to the relatively simpler architecture. [ABSTRACT FROM AUTHOR]

Ghost imaging (GI) has great potential applications in remote sensing because of its obvious advantage of high sensitivity in detection. However, there is rare investigation for GI in the scenario of background light environment or signal disturbance. In this paper, based on the theory of statistical optics, the imaging signal-to-noise ratio (SNR) of GI in background light environments is deduced and the influence of background light to the quality of GI is clarified. The analytical results suggest that the imaging SNR of GI is not only related with the measurement number and the object’s transmission area, but also depends on the signal power to background power ratio illuminating on the object and the speckle’s coherence areas of signal light and background light at the object plane. Furthermore, the latter analytical results are also backed up experimentally. [ABSTRACT FROM AUTHOR]

A dynamic encryption scheme is demonstrated based on chirp z-transform (CZT). The novel design of this setup allows us to protect multiple images in a multiplexed format and fully recover them without the influence of crosstalk and sample noise. The encoding stage is implemented using the 2D CZT and a Fourier lens. The CZT works with proper frequency parameters to control the position and size of the input frequency spectrum. The accurate positioning leads to an efficient packing of the multiplexed images and a remarkable improvement of the signal-to-noise ratio of the decrypted pictures. The introduction of the CZT in the field of encryption is significant, since it can expand the functionality to a dynamic regime of optical and digital architectures for static encoding. We validated the feasibility of our proposal with the encryption and decryption of a color image sequence and a set of binary images. [ABSTRACT FROM AUTHOR]

In this paper, we have experimentally demonstrated light focusing through strongly scattering media by performing binary amplitude optimization with a genetic algorithm. In the experiments, we control 160 000 mirrors of digital micromirror device to modulate and optimize the light transmission paths in the strongly scattering media. We replace the universal target-position-intensity (TPI) discriminant with signal-to-background ratio (SBR) discriminant in genetic algorithm. With 400 incident segments, a relative enhancement value of 17.5% with a ground glass diffuser is achieved, which is higher than the theoretical value of for binary amplitude optimization. According to our repetitive experiments, we conclude that, with the same segment number, the enhancement for the SBR discriminant is always higher than that for the TPI discriminant, which results from the background-weakening effect of SBR discriminant. In addition, with the SBR discriminant, the diameters of the focus can be changed ranging from 7 to 70 μm at arbitrary positions. Besides, multiple foci with high enhancement are obtained. Our work provides a meaningful reference for the study of binary amplitude optimization in the wavefront shaping field. [ABSTRACT FROM AUTHOR]

Vortex light beams can provide a tremendous alphabet for encoding information. We derive a symbol decoding algorithm for a direct detection matrix detector vortex beam receiver using Laguerre Gauss (LG) modes, and develop a mathematical model of symbol error rate (SER) for this receiver. We compare SER as a function of signal to noise ratio (SNR) for our algorithm and for the Pearson correlation algorithm. To our knowledge, this is the first comprehensive treatment of a decoding algorithm of a matrix detector for an LG receiver. [ABSTRACT FROM AUTHOR]

We propose a new plasmonic biosensor based on a birefringent partial-solid-core microstructured optical fiber where a single core mode can interact resonantly with the corresponding plasmon mode. This structure can be scaled to a larger radius of the gold layer with simultaneous increase in the number of rings and thus of the holes. The different configurations obtained by changing the geometry and relative positions of the holes can be best exploited depending on the analyte refractive index value na. Thus, for na = 1.35, the advantages of the proposed plasmonic sensor are larger values of the signal-to-noise ratio, maximum value of the amplitude sensitivity, power fraction in the gold layer and transmission loss as compared with that for a solid-core microstructured optical fiber. Another advantage of the proposed plasmonic sensor for na = 1.35 is related to the smaller values of the resonance spectral width and the difference between maximal amplitude sensitivity and resonant wavelengths. [ABSTRACT FROM AUTHOR]

We present dichroic x-ray lensless magnetic imaging by Fourier transform holography with an extended reference scheme via a modified uniformly redundant array (mURA). Holographic images of magnetic domains simultaneously generated by a single pinhole reference as well as by a mURA reference are compared with respect to the signal-to-noise ratio (SNR) as a function of exposure time. We apply this approach for spectro-holographic imaging of ferromagnetic domain patterns in Co/Pt multilayer films. Soft x-rays with wavelengths of 1.59 nm (Co L3 absorption edge) and 20.8 nm (Co M2,3 absorption edges) are used for image formation and to generate contrast via x-ray magnetic circular dichroism. For a given exposure time, the mURA-based holography allows to decouple the reconstruction SNR from the spatial resolution. For 1.59 nm wavelength, the reconstruction via the extended reference scheme shows no significant loss of spatial resolution compared to the single pinhole reference. In contrast, at 20.8 nm wavelength the single pinhole reveals some very intricate features which are lost in the image generated by the mURA, although overall a high-quality image is generated. The SNR-advantage of the mURA scheme is most notable when the hologram has to be encoded with few photons, while errors associated with the increased complexity of the reconstruction process reduce the advantage for high-photon-number experiments. [ABSTRACT FROM AUTHOR]

We propose an efficient method to accurately identify two mode indices (p and l) of Laguerre–Gaussian (LG) beams simultaneously with weak value measurement (WVM). Concise relations between the spatial displacements from the WVM and two mode indices of LG beams have been obtained. Compared with the traditional measurements, the advantage of using our method is that LG beams with large p and l can be identified precisely. A joint spatial WVM with a looser approximate condition has been presented, which realizes better identification than the individual spatial WVM with correction terms or strict approximation. Furthermore, the signal-to-noise ratio (SNR) of the spatial WVM is also discussed. [ABSTRACT FROM AUTHOR]

This work presents an angular and polarization multiplexing technique for synthetic aperture (SA) imaging in digital holographic microscopy by using a pair of phase-type spatial light modulators (SLMs) to achieve resolution enhancement through a single hologram acquisition. Angular multiplexing is applied to adjust the incident wave propagation at different specific deflection angles by modulating a SLM panel as a binary phase grating. The other SLM panel is introduced to control the polarization of the propagating object beams and thus ensure orthogonal polarization between these waves to avoid mutual interference of the conjugated first-order diffracting beams derived from the same phase grating. Experimental results indicate that the spatial resolution and signal-to-noise ratio of the reconstructed image are efficiently improved. Furthermore, an electrically addressed SLM pair creates the possibility to perform a dynamic and precise manipulation for realizing angular-polarization multiplexing SA imaging without the use of mechanical scanning mirrors. [ABSTRACT FROM AUTHOR]

Confocal laser scanning microscopy (CLSM) has wide applications in biological research and medical diagnosis. However, the spatial resolution and signal to noise ratio (SNR) of CLSM is reduced in the presence of an aberration. Here we improve the pupil-segmentation method to measure and compensate for aberrations in focus modulation CLSM (FM-CLSM), which uses Gaussian-type and doughnut-like foci to scan a sample in sequence. As a result, FM-CLSM can provide images with a high resolution and a high SNR for biomedical or industrial applications. [ABSTRACT FROM AUTHOR]

In this paper, we report a widely tunable, narrow linewidth, low noise continuous-wave double-clad Er:Yb doped fiber ring laser. Tunability is demonstrated in wide range spanning from 1520 to almost 1620 nm covering the C and L spectral bands. The cavity design is optimized in order to achieve the largest tuning range with very high optical signal-to-noise ratio (SNR). The output coupling ratio greatly influences the tuning range of the laser while the position of the spectral filter determines the SNR. The obtained laser exhibits a tuning range over 98 nm with a nearly constant SNR of about 58.5 dB. [ABSTRACT FROM AUTHOR]

In this paper, a magnetic field sensor based on a multilongitudinal mode fiber laser has been proposed by employing a rotary apparatus modulated by an external magnetic field. Due to the remarkable birefringence change caused by the fiber twist, the polarimetric mode beat frequency (PMBF) of the laser is sensitive to the applied magnetic field intensity. Experimental results show that the PMBF linearly shifts with the variation of the magnetic field intensity and the sensitivity reaches up to 10.4 KHz Oe−1 in the range of 0–270 Oe. Moreover, such a device has the advantages of easy fabrication, low cost and high resolution, offering potentials in the weak magnetic field applications. [ABSTRACT FROM AUTHOR]

We propose and numerically verify a scheme of frequency-shift free mid-span spectral inversion (MSSI) for nonlinearity mitigation in an optical transmission system. Spectral inversion is accomplished by optical phase conjugation, realized by counter-propagating dual pumped four-wave mixing in a highly nonlinear fiber. We examine the performance of MSSI due to critical parameters such as nonlinear fiber length, pump and signal power. We demonstrate the near complete nonlinearity mitigation of 40 Gbps DQPSK modulated data transmitted over 1000 km standard single mode fiber using our method of MSSI. We perform simulation of bit-error rate as a function of optical signal to noise ratio to corroborate the effect of frequency-shift free MSSI. [ABSTRACT FROM AUTHOR]

Single pixel imaging (SPI) is a novel technique capturing 2D images using a bucket detector with a high signal-to-noise ratio, wide spectrum range and low cost. Conventional SPI projects random illumination patterns to randomly and uniformly sample the entire scene’s information. Determined by Nyquist sampling theory, SPI needs either numerous projections or high computation cost to reconstruct the target scene, especially for high-resolution cases. To address this issue, we propose an efficient single pixel imaging technique (eSPI), which instead projects sinusoidal patterns for importance sampling of the target scene’s spatial spectrum in Fourier space. Specifically, utilizing the centrosymmetric conjugation and sparsity priors of natural images’ spatial spectra, eSPI sequentially projects two -phase-shifted sinusoidal patterns to obtain each Fourier coefficient in the most informative spatial frequency bands. eSPI can reduce requisite patterns by two orders of magnitude compared to conventional SPI, which helps a lot for fast and high-resolution SPI. [ABSTRACT FROM AUTHOR]

According to the reconstruction feature of fluctuation-correlation ghost imaging (GI), we define a normalized characteristic matrix and the influence of the property of random coded patterns on GI is investigated based on the theory of matrix analysis. Both simulative and experimental results demonstrate that for different random coded patterns, the quality of fluctuation-correlation GI can be predicted by some parameters extracted from the normalized characteristic matrix, which suggests its potential application in the optimization of random coded patterns for GI system. [ABSTRACT FROM AUTHOR]

The noise-to-signal transitions are very interesting processes in physics, as they might transform environmental noise to useful mechanical effects. We theoretically analyze stochastic noise-to-signal transition of overdamped Brownian motion of a particle in the cubic potential. The particle reaches thermal equilibrium with its environment in the quadratic potential which is suddenly swapped to the cubic potential. We predict a simultaneous increase of both the displacement and signal-to-noise ratio in the cubic potential for the position linearly powered by the temperature of the particle environment. The short-time analysis and numerical simulations fully confirm different dynamical regimes of this noise-to-signal transition. [ABSTRACT FROM AUTHOR]

An all-fiber Yb-doped kHz-linewidth low-noise linearly polarized single-frequency master-oscillator power-amplifier (MOPA) laser with a stable CW output power of >52 W is demonstrated. By suppressing the intensity noise of the DBR phosphate fiber oscillator, the linewidth of MOPA laser is not noticeably broadened, and an ultra-narrow linewidth of <3 kHz is obtained. Furthermore, the low-noise behavior of MOPA lasers is investigated. A measured relative intensity noise of < −130 dB Hz−1 at frequencies of over 2 MHz, a phase noise above 1 kHz of <5 μrad/Hz1/2, and a signal-to-noise ratio of >63 dB are achieved. [ABSTRACT FROM AUTHOR]

We propose and demonstrate a long-range Brillouin optical time-domain analysis (BOTDA) sensor based on the pre-pumped Simplex coding technique. This approach combines Simplex coding with the pulse pre-pump technique, which takes full advantage of the signal-to-noise ratio enhancement provided by optical pulse coding and achieves meter-scale spatial resolution with an unbroadened Brillouin gain spectrum by the use of pre-pumped short pump pulse. Compared to the widely used differential pulse-width pair technique, a comparable performance can be realized while the measurement time is reduced by half. The theoretical analysis of pre-pumped Simplex coding applied to BOTDA systems is presented and a proof-of-concept experiment is carried out along a ∼51 km single-mode fiber composed of two fiber segments with slightly different Brillouin frequency shift values. With the proposed technique, Brillouin frequency shifts of the two different fiber sections at the end of the sensing fiber are clearly distinguished, and the obtained spatial resolution and temperature/strain accuracy along the sensing fiber are respectively 1 m and . According to the experimental results, we believe that the BOTDA employing pre-pumped Simplex coding is able to realize extra-long distance sensing without Raman amplification, while keeping a high spatial resolution and measurement accuracy. [ABSTRACT FROM AUTHOR]

In this paper, we analyze numerically the effect of phase noise from the laser in Brillouin optical time-domain analysis (BOTDA) sensors. Due to laser phase noise, the phase shift between pump and probe beams is a stochastic variable with zero mean and variance changing with the position along the fiber. The numerical results, carried out for various fiber lengths and pump pulse durations, show that laser phase noise induces a reduction of the average Brillouin gain, as well as an increase of the overall system noise. Preliminary experimental results, carried out by use of a conventional BOTDA system and two DFB diode lasers having different linewidth (63 and 900 kHz), support the numerical analysis. [ABSTRACT FROM AUTHOR]

In this communication, a novel technique to measure the temporal width of an ultra-short optical pulse using an electrically focus-tunable lens (EFTL) is proposed and implemented (no need for a mechanical translation stage). The principle is based on the time delay experienced by the pulse when it passes through the deformed membrane of the EFTL as the focal length changes by an applied current. The resolution of the system is approximately 0.23 fs, with a total time delay of 0.69 ps. A typical autocorrelation can be performed in less than 5 s with an excellent Signal to Noise Ratio. The same technique can be implemented to study ultrafast phenomena like electronic relaxation or ultrafast fluorescence in a pump-probe configuration. [ABSTRACT FROM AUTHOR]

In this paper we experimentally demonstrate the effect of large effective area fiber length on the performance of a multiwavelength Brillouin–Raman fiber laser in which the forward and backward generated Stokes lines due to Brillouin scattering are combined together through a 3 dB coupler. Thus, the demonstrated laser is dubbed a forward–backward scattering combination multiwavelength Brillouin–Raman fiber laser (FBSC-MBRFL). This laser system utilizes a large effective area fiber and a dispersion compensating fiber that act as Brillouin and Raman gain media, respectively. It is demonstrated that by employing forward pumping schemes, the demonstrated laser system is capable of generating a good flat amplitude Brillouin Stokes line with an average optical to noise ratio of 17 dB along the spectral spans. However, the backward pumping scheme is able to produced high bandwidth spans. At the optimal large effective area fiber length of 50 km, a Raman pump power of 1100 mW at Brillouin pump wavelengths of 1550 mm and 1560 nm is identified to produce the maximum bandwidth with values of approximately 28.45 nm and 24.08 nm, respectively. [ABSTRACT FROM AUTHOR]

In this paper, we propose an integratable spectral quantization scheme for all-optical analog-to-digital conversion (AOADC) by slicing the supercontinuum, which is generated in a chalcogenide (As2S3) horizontal slot waveguide. The numerical simulation results show that a 4-bit quantization resolution is successfully achieved along with a signal-to-noise ratio of 23.96 dB and an effective number of bit (ENOB) of 3.98 bit. The required As2S3 waveguide length and input peak power are only 1.5 cm and 900 mW, respectively, owing to the high nonlinear coefficient of 115.8 W−1/m. It is believed that this proposed scheme can find important applications in the photonic integratable AOADC with low power consumption. [ABSTRACT FROM AUTHOR]

A novel technique is proposed for the direct two-dimensional phase derivatives estimation based on the matrix pencil approach in digital holographic interferometry. The interference field is represented as a two-dimensional complex sinusoidal signal in an analysis window around each pixel. The method provides high resolution frequency estimates and does not require the two-dimensional search in the spectral domain. A simple denoising procedure is proposed based on singular value decomposition of the interference field. The uncertainty in the frequency estimate is utilized as a parameter to identify the regions containing high fringe concentration on the object surface. Simulation and experimental results are provided to show the noise robustness and the practical applicability of the proposed method. [ABSTRACT FROM AUTHOR]

In the pursuit of realizing quantum optical networks, a large variety of different approaches have been studied to achieve a single photon source on-demand. The common goal for these approaches is to harvest all the emission from a quantum emitter into a single spatial optical mode while maintaining a high signal-to-noise ratio. In this work, we use a single nitrogen vacancy center in diamond as a quantum emitter operating at ambient conditions and we demonstrate an increased photon count rate up to a factor of 1.76 by placing a silver mirror fabricated on the end facet of an optical fiber near the emitter. [ABSTRACT FROM AUTHOR]

It is very important for daytime Raman lidar measurement of water vapor to determine the parameters of a band-pass filter, which are pertinent to the lidar signal to noise ratio (SNR). The simulated annealing (SA) algorithm method has an advantage in finding the extremum of a certain cost function. In this paper, the Raman spectrum of water vapor is simulated and then a first realization of a simulated annealing algorithm in the optimization of a band-pass filter of a Raman lidar system designed to detect daytime water vapor is presented. The simulated results indicate that the narrow band-pass filter has higher SNR than the wide filter does but there would be an increase in the temperature sensitivity of a narrowband Raman water vapor lidar in the upper troposphere. The numerical simulation indicates that the magnitude of the temperature dependent effect can reach 3.5% or more for narrow band-pass Raman water vapor measurements so it is necessary to consider a new water vapor Raman lidar equation that permits the temperature sensitivity of these equations to be confined to a single term. [ABSTRACT FROM AUTHOR]

A multi-wavelength fibre laser utilizing the four-wave mixing (FWM) effect in a 100 m long highly non-linear fibre (HNLF) is proposed and demonstrated. The multi-wavelength fibre laser is configured in a ring cavity and only needs a low power erbium doped fibre amplifier (EDFA) as the gain medium to generate 11 lines in the range of 1582-1600 nm with a signal-to-noise ratio (SNR) of 43 dB. The proposed system is very stable, with only minor fluctuations of 0.1 dB in the output power of the generated multi-wavelengths observed for a test period of more than an hour. The multi-wavelength fibre laser has many potential applications in optical communications and optical sensing systems. [ABSTRACT FROM AUTHOR]