Optical Background Noise Research Articles

Direct Measurement of Electrically Modulated Far-Field Thermal Infrared Emission and its Dynamics

Accurate direct measurements of far-field thermal infrared emission become increasingly important because conventional methods, relying on indirect assessments, such as reflectance/transmittance, are inaccurate or even unfeasible to characterize state-of-art devices with novel spectra, directionalities, and polarizations. The direct collection of the far-field emission from these tiny devices is also challenging because of their shrinking footprints and uncontrollable radiation noises from their surroundings. Here, we demonstrate a microscopic lock-in FTIR system that realizes significant improvement in signal-to-noise ratio (SNR) by combining a microscope and a lock-in amplifier with an FTIR. The lock-in FTIR is ultrasensitive, with a specific detectivity 10^6 times higher than commercial ones, to overcome the optical loss and background noise during the emission light collection. Based on an analytical model of the signal detection process, we also explore the combination of modulated Joule heating and global heating to fulfill the potential of our system for noise reduction. Our findings show that, compared to previous studies, more than 3 times lower temperatures are sufficient to generate a measurable signal. Under a heating temperature of around 125 {\deg}C, we can achieve an SNR of about 23.7, which is far above the true-signal-threshold (SNR of about 3.0). Furthermore, the system can respond fast enough (up to 175kHz) to record spectral-resolved dynamics of microdevices in the frequency domain. The measurable frequency range can be extended up to MHz or even GHz level by a high-speed circuit model. We believe the system together with the analytical signal processing can be beneficial for next-generation thermal infrared material and device exploration, boosting the applications in lighting, sensing, imaging, and energy harvesting on a small scale.

Hiding images in noise.

A limitation of free-space optical communications is the ease with which the information can be intercepted. This limitation can be overcome by hiding the information within background optical noise. We demonstrate the transfer of images over free-space using a photon-pair source emitting two correlated beams. One of these beams contains image information, to which noise is added, and the other correlated beam is used as a heralding trigger so that the intended recipient can differentiate this image signal from the background noise. The system uses spontaneous parametric down-conversion to create photon-pairs with a wide spectral bandwidth and a gated intensified camera to extract the image from the background noise. The high-dimensionality of the image space means that the information content can be many bits per detected photon, whereas the heralding photon can be restricted to a single spatial-mode within a secure fiber which itself could be protected against interception by traditional low-dimensionality quantum key protocols.

Enhanced tolerance against optical background noise in VLC link by using line coded signal with receiver filter

The performance of visible light communication (VLC) link is significantly affected by optical background noises generated by fluorescent light or AC driven light emitting diode (LED) and eventually degrades the data rate due to the in-band interference between signal and noise. Here, bandwidth efficient 8b10b dc-balanced line coding and post-detection electrical filter based VLC link is demonstrated to improve the system tolerance against the optical background noises. The 8b10b coded signal with low frequency components near DC ensure that the crosstalk noise is effectively minimized by spectral separation of signal and noise contributions. Moreover, the use of post detection filter for 8b10b coded signal gives an additional attenuation of noise frequency to further improve the system tolerance against optical background noise. The proposed VLC link is investigated thoroughly in several noise power levels as well as different noise frequencies, where the results indicate improved system tolerance against noise power by about 6.5 dB in compare to conventional data signal. The demonstration also shows that the proposed scheme maintains a low BER for the noise frequency up to 500 kHz for 10 Mb/s data modulation having a good eye opening.

Instant ghost imaging: improving robustness for ghost imaging subject to optical background noise

Ghost imaging (GI) is an imaging technique that uses the second-order correlation between two light beams to obtain the image of an object. However, standard GI is affected by optical background noise, which reduces its practical use. We investigated the robustness of an instant ghost imaging (IGI) algorithm against optical background noise and compare it with the conventional GI algorithm. Our results show that IGI is extremely resistant to spatiotemporally varying optical background noise that can change over a large range. When the noise is large in relation to the signal, IGI will still perform well in conditions that prevent the conventional GI algorithm from generating an image because IGI uses signal differences for imaging. Signal differences are intrinsically resistant to common noise modes, so the IGI algorithm is strongly robust against noise. This research is of great significance for the practical application of GI.

A 3D Non-Stationary GBSM for Vehicular Visible Light Communication MISO Channels

The potential of using visible light communication (VLC) technologies for vehicular communication networks has recently attracted much attention. The underlying VLC channels, as a foundation for the proper design and optimization of vehicular VLC communication systems, have not yet been sufficiently investigated. Vehicular VLC link impairments can have a significant impact on the system performance and capacity. Such impairments include the optical wireless channel distortion and background noise. This paper proposes a novel three-dimensional (3D) regular-shaped geometry-based stochastic model (RS-GBSM) for vehicular VLC multiple-input single-output (MISO) channels. The proposed 3D RS-GBSM combines a two-sphere model and an elliptic-cylinder model. Both the line-of-sight (LoS) and single-bounced (SB) components are considered. The proposed model jointly considers the azimuth and elevation angles by using von-Mises-Fisher (VMF) distribution. Based on the proposed model, the relationship between the communication range and the received optical power is analyzed and validated by simulations. The impact of the elevation angle in the 3D model on the received optical power is investigated by comparing with the received optical power of the corresponding two-dimensional (2D) model. Furthermore, the background noise is also modeled to evaluate the system's signal-to-noise ratio (SNR).

Improvement of LOD in Fluorescence Detection with Spectrally Nonuniform Background by Optimization of Emission Filtering.

The limit-of-detection (LOD) in analytical instruments with fluorescence detection can be improved by reducing noise of optical background. Efficiently reducing optical background noise in systems with spectrally nonuniform background requires complex optimization of an emission filter-the main element of spectral filtration. Here, we introduce a filter-optimization method, which utilizes an expression for the signal-to-noise ratio (SNR) as a function of (i) all noise components (dark, shot, and flicker), (ii) emission spectrum of the analyte, (iii) emission spectrum of the optical background, and (iv) transmittance spectrum of the emission filter. In essence, the noise components and the emission spectra are determined experimentally and substituted into the expression. This leaves a single variable-the transmittance spectrum of the filter-which is optimized numerically by maximizing SNR. Maximizing SNR provides an accurate way of filter optimization, while a previously used approach based on maximizing a signal-to-background ratio (SBR) is the approximation that can lead to much poorer LOD specifically in detection of fluorescently labeled biomolecules. The proposed filter-optimization method will be an indispensable tool for developing new and improving existing fluorescence-detection systems aiming at ultimately low LOD.

A terahertz EO detector with large dynamical range, high modulation depth and signal-noise ratio

The paper presents a novel design for terahertz (THz) free-space time domain electro-optic (EO) detection where the static birefringent phases of the two balanced arms are set close to zero but opposite to each other. Our theoretical and numerical analyses show this design has much stronger ability to cancel the optical background noise than both THz ellipsometer and traditional crossed polarizer geometry (CPG). Its optical modulation depth is about twice as high as that of traditional CPG, but about ten times as high as that of THz ellipsometer. As for the dynamical range, our improved design is comparable to the THz ellipsometer but obviously larger than the traditional CPG. Some experiments for comparing our improved CPG with traditional CPG agree well with the corresponding theoretical predictions. Our experiments also show that the splitting ratio of the used non-polarization beam splitter is critical for the performance of our design.

The mechanism and suppression methods of optical background noise in phase-sensitive optical time domain reflectometry

Phase-sensitive optical time domain reflectometry (-OTDR) has the advantages of fast response and high sensitivity. Therefore, it can realize fully distributed monitoring of weak vibrations along an optical fiber, which is of great value in many applications such as perimeter security and structural health monitoring. However, the optical background noise in the -OTDR will disturb the extraction of effective signals and limit the performance of this system. The optical background noise mainly includes the laser center frequency drift, the polarization-relevance noise and the distortion measurement due to the nonlinear relationship between optical fiber strain and interference intensity. In this paper, the generating mechanism of these optical background noise was analyzed and the corresponding noise suppression methods were proposed. The experiment results showed that the proposed methods could suppress the optical background noise effectively and improve the sensing performance significantly.

Simulation of VLC system under the influence of optical background noise using filtering technique

Visible light communication (VLC) has recently gained recognition as an alternate to RF communication. Optical background noise sources generated by conventional fluorescent light, optical shot noise and thermal noise demean the performance of the VLC system. In this paper, the simulation design and performance analysis of RZ-OOK VLC system under the influence of optical background noise using optisystem software is proposed. Rectangular optical filter, placed before the photo-diode and electrical low pass Bessel filter after the trans-impedance amplifier are used to mitigate the noise. Our proposed design of indoor VLC system helps to attain the best performance with minimum cost, effort and time, after that it can be applied physically in real-time experimentation. This paper also discusses the performance analysis of optical to electrical power conversion, BER, qualitative eye opening, evaluation of BER with respect to the distance between the transmitter and receiver for RZ-OOK VLC system. Simulation results make clear that the performance of RZ-OOK modulation is better achieved for data rate of 20 Kb/s and 20m distance between the transmitter and receiver.

3.375-Gb/s RGB-LED based WDM visible light communication system employing PAM-8 modulation with phase shifted Manchester coding.

Optical background noise and second-order nonlinear distortions are two main challenges faced by indoor high-speed VLC system. In this paper, a novel phase shifted Manchester (PS-Manchester) coding based on PAM-8 is proposed and experimentally demonstrated to mitigate these noise and distortions. With the aid of PS-Manchester coding and WDM, a total data rate of 3.375-Gb/s can be successfully achieved in the RGB-LED based VLC system. The BER is under 7% HD-FEC limit of 3.8x10-3 after 1-m indoor free space transmission. To the best of our knowledge, this is the highest data rate ever achieved in PAM VLC systems.

Adaptive spatial filtering of daytime sky noise in a satellite quantum key distribution downlink receiver

Spatial filtering is an important technique for reducing sky background noise in a satellite quantum key distribution downlink receiver. Atmospheric turbulence limits the extent to which spatial filtering can reduce sky noise without introducing signal losses. Using atmospheric propagation and compensation simulations, the potential benefit of adaptive optics (AO) to secure key generation (SKG) is quantified. Simulations are performed assuming optical propagation from a low-Earth-orbit satellite to a terrestrial receiver that includes AO. Higher-order AO correction is modeled assuming a Shack–Hartmann wavefront sensor and a continuous-face-sheet deformable mirror. The effects of atmospheric turbulence, tracking, and higher-order AO on the photon capture efficiency are simulated using statistical representations of turbulence and a time-domain wave-optics hardware emulator. SKG rates are calculated for a decoy-state protocol as a function of the receiver field of view for various strengths of turbulence, sky radiances, and pointing angles. The results show that at fields of view smaller than those discussed by others, AO technologies can enhance SKG rates in daylight and enable SKG where it would otherwise be prohibited as a consequence of background optical noise and signal loss due to propagation and turbulence effects.

Mitigation of the Influence of Optical Background Noise by Using Turbo-Coded DOOK

Mitigation of the Influence of Optical Background Noise by Using Turbo-Coded DOOK

Analysis of adaptive optics-based telescope arrays in a deep-space inter-planetary optical communications link between Earth and Mars

Earth-based telescope array receivers employing optical communications have the potential to fulfill the communication needs of technologically sophisticated, deep-space exploration missions. Atmospheric turbulence is the chief restrictive factor in an optical deep-space channel (ODSC). In this paper, investigation and design of adaptive optics (AO) subsystems are presented for the compensation of the coupled effects of optical turbulence and background noise in telescope array receivers. An end-to-end simulation platform for an ODSC between Mars and Earth is implemented, which incorporates pulse-position modulation (PPM), direct-detection receivers, and detectors with the capability of detection of single photon. The extreme conditions of atmospheric turbulence and background noise are also modeled in the analysis. AO subsystems are incorporated at individual telescopes in the array receiver to mitigate the turbulence effects. The performance of array receivers is evaluated in terms of the probability of error and communication throughput. The analysis in this research depicts that in worst-case turbulence and background noise conditions, inclusion of AO systems results in 8.5dB performance improvement in communication data rates. The performance improvement of 5.6dB is achievable in moderate channel conditions. Comparison of performance of array receivers with that of a large monolithic telescope shows that incorporation of AO systems is more feasible in arrays comprising telescopes with relatively smaller diameters.

Image processing for non-ratiometric measurement of membrane voltage using fluorescent reporters and pulsed laser illumination

The measurement of transmembrane voltages induced by pulsed electric field exposure can be achieved by using fluorescent dyes like ANNINE-6. Such approach requires a quantitative determination of the fluorescence intensity along the cell's membrane by image processing. When high temporal resolution is required, the illumination source is frequently a dye-laser which causes high fluctuations in the intensity of illumination which in turn affects the fluorescence intensity and thus the quality of the results. We propose an image processing technique that allows to overcome the fluctuations and to produce quantitative data. It uses the optical background noise as a correcting factor. Standard deviation in the fluctuations is thus efficiently reduced by at least a factor of 2.5. Additionally we draw attention to the fact that the parasitic component of the laser radiation (ASE) can also suppress fluctuations although it deteriorates wavelength precision.

Fluorescence Technologies for Evaluating Male Gamete (Dys)Function

For many years, andrologists have sought ways of assessing sperm fertility, especially of new sires entering the breeding chain. As knowledge of the complex processes that enable sperm to fertilize eggs has increased, it has become clearer that quantitative estimation of the fertilizing potential of a sire or an ejaculate is actually unlikely ever to be fully realized. Here, we propose that a better approach is to identify substandard males and semen samples. During the past decades, the use of fluorescence technologies in biomedical science has burgeoned, with the development of very powerful instrumentation such as confocal microscopy and flow cytometers of ever-increasing capabilities together with a vast range of fluorochromes and fluorochrome conjugates. This technology has been applied to andrology but thus far in only a relatively simple way. In this review, we offer strategies for assessing a large range of sperm functions thought to be related to fertilizing ability over a temporal window rather than at a single time point. From such an assessment profile, sperm samples that over-respond or do not respond sufficiently could be identified, termed dysfunctional and rejected. We outline the rationales behind such tests, present information on new potentially useful fluorochromes and current flow cytometer models that would be suitable for the multicolour multifunctional tests we propose, and we offer suggestions as to how andrologists might design such multicolour tests for themselves.

Mitigation of Optical Background Noise in Light-Emitting Diode (LED) Optical Wireless Communication Systems

One challenge faced by the in-home light-emitting diode (LED) optical wireless communication is the optical noises. Here, we first experimentally characterize the effect of optical background noise to the performance of the LED optical wireless communication channel. We demonstrate using Manchester coding for the LED to mitigate the optical noise. No adaptive monitoring, feedback, or optical filtering is required. The theoretical and numerical analysis of Manchester decoding process to mitigate the optical background noise is provided. Our experimental result shows that Manchester coding can significantly eliminate optical noise generated by the AC-LED operated at <; 500 kHz and fluorescent light.

Filterless optical oxygen sensor based on a CMOS buried double junction photodiode

We present a custom CMOS IC with a buried double junction (BDJ) photodiode to detect and process the optical signal, eliminating the need for any off-chip optical filters. The on-chip signal processing circuitry improves the desired signal extraction from the optical background noise. Since the IC is manufactured using standard commercial fabrication processes with no post-processing necessary, the system can ultimately be low cost to fabricate. Additionally, because of the CMOS integration, it will consume little power when operating, and even less during stand-by.

Subframe burst gating for Raman spectroscopy in combustion

We describe an architecture for spontaneous Raman scattering utilizing a frame-transfer CCD sensor operating in a subframe burst-gating mode to realize time-resolved combustion diagnostics. The technique permits all-electronic optical gating with microsecond shutter speeds (<5 micros) without compromising optical throughput or image fidelity. When used in conjunction with a pair of orthogonally polarized excitation lasers, the technique measures single-shot vibrational Raman scattering that is minimally contaminated by problematic optical background noise.

SNOM fluorescence techniques applied to cytoskeleton study in cell cultures

Introduction Scanning near field optical microscope (SNOM) is a tool which overcomes the diffraction limit of conventional optical microscopy and allows optical imaging with a resolution of less than 100 nm without having to go through any special sample preparation. Moreover one of the best advantages of SNOM is to produce topographic, transmission and reflection images simultaneously [1]. Several studies have been carried out by SNOM in the last years on biological specimens, but the fluorescence SNOM technique has been rarely applied on cell culture investigations. Here we set up a TriA-SNOM with a specific fluorescence equipment to develop the performance of this probe microscope and identify cytoskeleton elements in cell cultures, mainly primary rat podocytes cultures. Materials and methods The microscope used were a TriA-SNOM (APE Research, Trieste, Italy) equipped with a specific fluorescence set-up that allowed to obtain different SNOM images of the samples simultaneously: topography, SNOM fluorescence in reflection and SNOM-fluorescence in transmission. Cell cultures: Primary culture of rat podocytes were treated by immunofluorescence techniques with TRITC-phalloidin to visualize cytoskeletal elements such as actin filaments. Actin filaments were analyzed by SNOM-fluorescence and compared with conventional fluorescence. Results SNOMfluorescence, unlike all other techniques, may reconstruct a fluorescence mapping of the sample, and obtain a direct measure in height of the fluorescence structures. The major technical problem in this kind of microscopy is to reduce of the optical background noise. We actually obtained a SNOM-fluorescence set-up to adequately visualize the specimens, producing images with low background noise and high resolution. SNOM moreover allowed to discriminate the superficial actin filaments from the deep filaments by reflection system. Conclusions SNOM with fluorescence technique may be suitable method for detection of specific molecules in cell cultures, providing an overlapping of the fluorescence image on the 3D mapping of the sample. These studies open further possibilities for application of SNOM to biological materials, especially in cells observed in liquid environment.

Raman probe using a single hollow waveguide

A simple Raman probe was realized using a single flexible hollow waveguide (HW). A HW coated with a silver film, which had reasonable transmission and little optical background noise, was used as a bidirectional transmission fiber for both the excitation and collection of Raman scattered light. The HW itself generated no Raman scattering or fluorescence noise during transmission. A complex filtering system at the end of the waveguide was thus unnecessary. In addition, the measured Raman spectra showed better signal-to-noise ratios than a conventional Raman fiber probe. The HW's suitability as a Raman fiber probe was also demonstrated.