Low Intensity Noise Research Articles

Low-intensity-noise single-frequency CW 1080 nm laser by employing a laser crystal with the small stimulated-emission cross section

An effective approach to obtain a single-frequency laser with low intensity noise is presented in this paper, which is implemented by employing a gain medium with the small stimulated-emission cross section (SECS). When the adopted Nd:YAP (Nd:YAlO3) gain medium with SECS of 4.6×10−19 cm2 is replaced by Nd:CYA (Nd:CaYAlO4) gain medium with SECS of 1.04×10−19 cm2, the frequency of measured intensity noise reached shot noise limit obviously reduces from 2.49 to 1.5 MHz, which agrees well with the theoretical predictions. On this basis, a single-frequency continuous-wave (CW) Nd:CYA laser with low intensity noise is first achieved. The attained output power of the Nd:CYA laser is 1.12 W. The achieved single-frequency CW 1080 nm laser will satisfy the requirements of the squeezed and entangled light generation.

An Unsupervised Noisy Sample Detection Method for Deep Learning-Based Health Status Prediction

Due to rough environment or data-acquisition equipment failure, the machine monitoring data may be contaminated with noise, which may lead to the generation of noisy samples. For the widely used deep learning-based prediction model, some noisy samples (with low-intensity noise) may improve model generalization while some noisy samples (with high-intensity noise) may hamper the prediction models. To detect the noisy samples that hamper the prediction models, an unsupervised noisy sample detection method is proposed, thereby promoting the accuracy of the deep learning-based prediction model. First, the transforming model with an attention mechanism is built to transform the multivariate input sequences of samples to attention weight vectors, which are related to the prediction task. Then, a clustering method without hyperparameters is proposed to cluster these attention weight vectors and the hierarchy of clusters is created. Afterward, the noisy samples that hamper the prediction models are detected and removed based on the clustering thresholds, and a prediction model with higher prediction accuracy can thus be obtained. The effectiveness of the proposed method is verified using a simulated turbofan engine degradation dataset and a real milling machine monitoring dataset. The results show that the prediction errors for the two datasets have been reduced by 13.44% and 12.97% on average after removing the noisy samples detected by the proposed method. The comparison results show that the proposed method outperforms other methods in terms of improving the prediction accuracy.

Influence of Pump Properties on the Tunability of 1.5 μm Low-Noise Single Frequency Fiber Amplifier

In this work, we investigate the impact of the pump configuration (wavelength and pump scheme i.e., backward forward) on the tuning range in a watt level low intensity noise single-frequency Erbium/Ytterbium doped fiber amplifier. Two different pump wavelengths, 976 nm and 940 nm, and three different pumping schemes were numerically and experimentally investigated. Tunability over 47 nm (1533 nm-1580 nm) with relative intensity noise level as low as −155 dB/Hz is achieved using an unconventional pumping scheme where the active fiber is pumped in both directions with two different pump wavelengths.

Frequency-stabilized Brillouin random fiber laser enabled by self-inscribed transient population grating.

A frequency-stabilized Brillouin random fiber laser (BRFL) realized by a self-inscribed transient population grating (TPG) is proposed and demonstrated for the first time, to the best of our knowledge. The TPG is formed via the redistribution of the population in erbium-doped fibers (EDFs) by bidirectionally injected phonon-controlled random laser beams. Long-lifetime metastable ion states in EDFs basically prolonged the time dynamics of a stimulated Brillouin scattering (SBS) laser up to milliseconds. Consequently, significant random modes are suppressed with low relative intensity noise, owing to reduced mode hopping in a Stokes random laser, hence one dominating lasing mode at milliseconds of lifetime is established from the competition of numerous random modes, which is proved theoretically and experimentally via TPG.

Five Different Noise Intensities Robustly Affects Corticosterone, Gastrin and Endothelin-1 Responses and Initiated Gastric Tissue Damage in Wistar Rats

Likewise other stress response noise stress is also affects the homeostasis of the biological systems and produce stress response in the form of Corticosterone to prevent the damage but if the exposure is longer with higher magnitude it may disrupt the robust ability of the homeostasis and could produce the damage to the biological systems. The goal of our study was to see how five different noise intensities affected stomach tissue damage. 42 healthy rats were divided into five different stress exposure group, normal control (NC) and sham control (SC) groups. Noise stress exposure was delivered for 1 hour per day continued for 30 days in all five noise exposed groups by specially designed noise chamber whereas sham control group of animals kept in noise chamber for 1 hour per day continued for 30 days without noise stress exposure and control group of animals neither exposed to noise stress of any intensities and nor kept in noise chamber without noise but remain in the same experimental room in their homecage for 30 days respectively. Results of the study showed that animals exposed to 60 and 80 dB noise give habituated and not significant Corticosterone, Gastrin and Endothelin-1 responses compared to NC and SC groups while animals exposed to 100, 120 and 140 dB had significantly higher Corticosterone, Gastrin and Endothelin-1 response and also chronic gastric damage was observed compared to later two noise exposed groups respectively. Study concluded that not only higher but also lower noise intensities also initiated the gastric damage even after the adaptation.

The relative intensity noise of a vertical-cavity surface-emitting laser with a fiber Bragg grating external cavity

The research deals with the topical problem of stabilizing the optical parameters of a single-mode vertical-cavity surface-emitting laser. A solution to the problem is proposed by forming an external cavity based on a Bragg grating induced into an optical polarization-maintaining fiber. In this experimental research, the authors estimated the contribution of an external cavity to the relative intensity noise of a vertical-cavity surface-emitting laser. The stability of the laser generation with a varying phase of back reflections at various pump currents is investigated. The relative intensity noise of laser radiation in the pump current range of 1.1–6.3 mA is estimated using a photodetector with a bandwidth of 8.5 MHz. The phase change of the back reflections was carried out by shifting the optical fiber end with a 100 nm step. As a result of the research, it was obtained that the vertical-cavity surface-emitting laser with such an external cavity shows a stable emission in the current range of 1.8–3.2 mA. However, one can observe instability with constant switching between adjacent longitudinal modes outside this range. The most stable laser operation mode with an external cavity against a change in the phase of back reflections is registered at a pump current of 2.78 mA. Utilizing an external cavity with the fiber Bragg grating made it possible to reduce the relative intensity noise from 7.2∙10–10 1/Hz to 1.5∙10–11 1/Hz in the currents range 1.86–3.2 mA. The study can be useful in applications that require an optical radiation coherent source with a low relative intensity noise level (such as coherent optical communication or fiber-optic sensors).

Active control of a diode laser with injection locking using a laser line filter.

We present a simple and effective method to implement an active stabilization of a diode laser with injection locking, which requires minimal user intervenes. The injection-locked state of the diode laser is probed by a photodetector, of which sensitivity is enhanced by a narrow laser-line filter. Taking advantage of the characteristic response of laser power to spectral modes from the narrow laser-line filter, we demonstrate that high spectral purity and low-intensity noise of the diode can be simultaneously maintained by active feedback to the injected laser. Our method is intrinsically cost-effective and does not require bulky devices, such as Fabry-Pérot interferometers or wavemeters, to actively stabilize the diode laser. Based on the successful implementation of this method in our quantum gas experiments, it is conceivable that our active stabilization will greatly simplify potential applications of injection locking of diode lasers in modularized or integrated optical systems.

CO2-based hollow-core fiber Raman laser with high-pulse energy at 1.95 µm.

In this Letter, we present a high-pulse energy (>10µJ) Raman laser at 1946 nm wavelength directly pumped with a 1533 nm custom-made fiber laser. The Raman laser is based on stimulated Raman scattering (SRS) in an 8 m carbon dioxide (CO2)-filled nested anti-resonant hollow-core fiber. The low-energy phonon emission combined with the inherent SRS process along the low-loss fiber allows the generation of high-pulse energy up to 15.4 µJ at atmospheric CO2 pressure. The Raman laser exhibits good long-term stability and low relative intensity noise of less than 4%. We also investigate the pressure-dependent overlap of the Raman laser line with the absorption band of CO2 at the 2 µm spectral range. Our results constitute a novel, to the best of our knowledge, and promising technology towards high-energy 2 µm lasers.

Determination of the beam waist position for the spin-orbit interaction effect observation

The spin angular momentum and the extrinsic orbital angular momentum of light are associated with the polarization of light and the light propagation trajectory, respectively. Those momenta are interdependent not only in an inhomogeneous or anisotropic medium but even in free space. This interaction is called the spin-orbit interaction of light. The effects of the spin-orbit interaction of light manifest themselves in a small transverse shift of the beam field longitudinal component from the beam propagation axis in the waist region under the circular polarization sign change. They can be observed both for Gaussian beams and for structured beams. The effects of the spin-orbit interaction of light should be taken into account when nanophotonics devices are created, but the detailed investigation of the effect had not been performed yet due to the low intensity noise image of the beam waist. Precise measurements of the focal waist centerline are needed to determine the transverse shift of the beam field longitudinal component of the asymmetric converging beam's waist under the circular polarization sign change. We propose methods for determining the transverse and longitudinal positions of the beam waist. Computer image processing methods made it possible to obtain the value of the beam waist's transverse position with an accuracy of 0.1 mkm. These methods will allow further testing of the shifts' theoretical predictions, the values of which are the order of 1 mkm. The results obtained can also be used for laser processing of materials by polarized light and precise positioning of the beam's focal spot at a surface.

High linear polarization, narrow linewidth hybrid semiconductor laser with an external birefringence waveguide Bragg grating.

We demonstrate a high linear polarization, narrow linewidth hybrid laser composed of a semiconductor gain chip and a high birefringence waveguide Bragg grating (WBG). The laser operates in the C-band, and a maximum output power of 8.07 mW is obtained in the fiber waveguide. With careful temperature tuning, the hybrid laser can operate in a single longitudinal mode state from above the threshold current to 410 mA. The side mode suppression ratio (SMSR) reaches a value of 50.2 dB, and the polarization extinction ratio exceeds 39.6 dB. We numerically analyze the linewidth suppression for the Bragg grating based on adiabatic chirp theory. The hybrid laser shows a narrow linewidth of 4.15 kHz and a low relative intensity noise (RIN) of <-155 dBc/Hz, providing a high-performance light source for coherent light communication.

Near-octave-spanning breathing soliton crystal in an AlN microresonator.

The soliton crystal (SC) was recently discovered as an extraordinary Kerr soliton state with regularly distributed soliton pulses and enhanced comb line power spaced by multiples of the cavity free spectral ranges (FSRs), which will significantly extend the application potential of microcombs in optical clock, signal processing, and terahertz wave systems. However, the reported SC spectra are generally narrow. In this Letter, we demonstrate the generation of a breathing SC in an aluminum nitride (AlN) microresonator (FSR ∼374GHz), featuring a near-octave-spanning (1150-2200 nm) spectral range and a terahertz repetition rate of ∼1.87THz. The measured 60 fs short pulses and low intensity-noise characteristics confirm the high coherence of the breathing SC. Broadband microcombs with various repetition rates of ∼0.75, ∼1.12, and ∼1.5THz were also realized in different microresonators of the same size. The proposed scheme shows a reliable design strategy for broadband soliton generation with versatile dynamic control over the comb line spacing.

Investigating well potential parameters on neural spike enhancement in a stochastic-resonance pre-emphasis algorithm

Objective. Background noise experienced during extracellular neural recording limits the number of spikes that can be reliably detected, which ultimately limits the performance of next-generation neuroscientific work. In this study, we aim to utilize stochastic resonance (SR), a technique that can help identify weak signals in noisy environments, to enhance spike detectability. Approach. Previously, an SR-based pre-emphasis algorithm was proposed, where a particle inside a 1D potential well is exerted by a force defined by the extracellular recording, and the output is obtained as the displacement of the particle. In this study, we investigate how the well shape and damping status impact the output signal-to-noise ratio (SNR). We compare the overdamped and underdamped solutions of shallow- and steep-wall monostable wells and bistable wells in terms of SNR improvement using two synthetic datasets. Then, we assess the spike detection performance when thresholding is applied on the output of the well shape-damping status configuration giving the best SNR enhancement. Main results. The SNR depends on the well-shape and damping-status type as well as the input noise level. The underdamped solution of the shallow-wall monostable well can yield to more than four orders of magnitude greater SNR improvement compared to other configurations for low noise intensities. Using this configuration also results in better spike detection sensitivity and positive predictivity than the state-of-the-art spike detection algorithms for a public synthetic dataset. For larger noise intensities, the overdamped solution of the steep-wall monostable well provides better spike enhancement than the others. Significance. The dependence of SNR improvement on the input signal noise level can be used to design a detector with multiple outputs, each more sensitive to a certain distance from the electrode. Such a detector can potentially enhance the performance of a successive spike sorting stage.

Mid-Infrared Random Fiber Laser Assisted by the Passive Feedback

Random fiber lasers (RFLs), featuring a simple open cavity but with unique lasing characteristics, have captured considerable attention in the past several decades. Particularly, RFLs assisted by the passive feedback exhibit excellent robustness and compactness owing to the combination of active amplification and passive feedback from random distributed Rayleigh scattering. However, RFLs with the aid of the passive feedback reported previously are primarily operating in the near-infrared wavelength region of 1.1 μm or 1.5 μm based on the ytterbium or erbium doped active fibers. Here, we propose and demonstrate a random fiber laser configuration combining the passive feedback from a piece of single mode fiber with the active gain based on the thulium doped fiber, and extend the operation wavelength to the critically important mid-infrared wavelength band of ~2 μm. The spectral and temporal characteristics of the lasing output are evaluated and compared with those generated in a single pass amplification structure and a conventional resonant structure. Our results show that the passive feedback assisted RFL has a stabilized lasing wavelength and notably suppressed temporal dynamics. This work not only advances the development of RFLs, but also provides a promising strategy to achieve mid-infrared laser emission with a comparatively low relative intensity noise.

Hedging futures performance with denoising and noise-assisted strategies

Noise processing is very important to improve hedging effectiveness. However, the existing methods are mainly considered from the view of denoising strategy, and the research on noise-assisted strategy is limited. In this paper, a framework that includes both denoising and noise-assisted strategies is proposed to comprehensively analyze the impact of noise proceeding on hedging effectiveness. In detail, the EMD technology is utilized to decompose the futures and spot original returns. Then, the decomposition terms are stepwise removed or added in the opposite way to obtain the denoised and noise-assisted returns. Finally, under the minimum-CVaR framework, the dynamic hedged portfolios based on original and processed returns are constructed to test the hedging effectiveness. Based on the daily prices of CSI300, S&P500, WTI crude oil, and gold futures contract which range from February 9, 2007, to January 10, 2020, the empirical results indicate that both denoising and noise-assisted hedging strategies can decrease CVaR compare with using original return. Furthermore, denoising or adding high-intensity noise has better hedging performance than low-intensity noise, adding uncorrelated noise performs better than adding correlated noise Robustness results by changing confidence level validate the above conclusions.

Optimizing Coherence Suppression in a Laser Broadened by Phase Modulation With Noise

Phase noise can be modulated onto the output of a laser with an electro-optic phase modulator (EOM) to create a highly incoherent broadened source with low intensity noise. This technique leaves a small but finite fraction of the coherent carrier power that can be highly detrimental in applications requiring incoherent light. This article shows that the carrier suppression in a laser broadened by this technique can be calculated for an arbitrary noise probability density function. The carrier suppression can be varied experimentally by adjusting the noise voltage standard deviation Gv <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">σ</sub> and saturation voltage V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sat</sub> of the amplifier that amplifies the noise source that drives the EOM. Simulations show that suppressions better than -30 dB are attainable for reasonable tolerances in Gv <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">σ</sub> , for example an EOM with a V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">π</sub> of 4.7 V, a V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sat</sub> of 6.3 V, and Gv <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">σ</sub> /V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">π</sub> = 0.73 ± 0.03. Even greater tolerances can be achieved with a higher V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sat</sub> (21 V), lower V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">π</sub> (3.5 V), and Gv <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">σ</sub> /V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">π</sub> ≈ 3.2 ± 2.3. This model aids in selecting these parameters such that the carrier suppression is resilient to fluctuations in these voltages due to temperature variations and aging of the components. The model predictions are validated by testing a fiber optic gyroscope interrogated with a broadened laser for various Gv <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">σ</sub> and V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sat</sub> and inferring the carrier suppression from its measured noise. A -44-dB carrier suppression was observed for a nonlinear amplifier with Gv <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">σ</sub> = 3.43 V, V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sat</sub> = 6.3 V, and an EOM with V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">π</sub> = 4.7 V, in agreement with predictions.

Low noise, self-phase-modulation-enabled femtosecond fiber sources tunable in 740-1236 nm for wide two-photon fluorescence microscopy applications

We have demonstrated widely tunable Yb:fiber-based laser sources, aiming to replace Ti:sapphire lasers for the nJ-level ultrafast applications, especially for the uses of nonlinear light microscopy. We investigated the influence of different input parameters to obtain an expansive spectral broadening, enabled by self-phase modulation and further reshaped by self-steepening, in the normal dispersion regime before the fiber damage. We also discussed the compressibility and intensity fluctuations of the demonstrated pulses, to reach the transform-limited duration with a very low intensity noise. Most importantly, we have demonstrated clear two-photon fluorescence images from UV-absorbing fluorophores to deep red dye stains.

HF-TPE: High-Fidelity Thumbnail- Preserving Encryption

With the popularity of cloud storage services, people are increasingly accustomed to storing images in the cloud. However, cloud storage services raise privacy concerns, e.g., leakage of images to unauthorized third parties and service providers may exploit image detection technologies to portrait users without permission. Although privacy concerns can be solved by encrypting images before they are uploaded to the cloud, traditional encryption methods significantly affect the usability and user experience, for example, users cannot preview images in the cloud. Recently, Marohn <i>et al.</i> proposed two approximate thumbnail-preserving encryption schemes, called DRPE and TPE-LSB, to balance the privacy and usability of images in the cloud. However, both schemes have defects that either the decryption may fail or the ciphertext images have poor performance in perceived quality and too many noise points after decryption. To this end, we pertinently propose a high-fidelity thumbnail-preserving encryption scheme (HF-TPE). Compared with the previous works, on the one hand, the HF-TPE scheme not only ensures the correct decryption of ciphertext images, but also makes the ciphertext thumbnails more close to the plaintext images perceptually. On the other hand, the decrypted thumbnails have lower noise intensity and upper limit of the number of noises. In addition, simulation experiments further show that the HF-TPE scheme can guarantee users&#x2019; usability.

Coherence resonance in neuronal populations: Mean-field versus network model.

The counterintuitive phenomenon of coherence resonance describes a nonmonotonic behavior of the regularity of noise-induced oscillations in the excitable regime, leading to an optimal response in terms of regularity of the excited oscillations for an intermediate noise intensity. We study this phenomenon in populations of FitzHugh-Nagumo (FHN) neurons with different coupling architectures. For networks of FHN systems in an excitable regime, coherence resonance has been previously analyzed numerically. Here we focus on an analytical approach studying the mean-field limits of the globally and locally coupled populations. The mean-field limit refers to an averaged behavior of a complex network as the number of elements goes to infinity. We apply the mean-field approach to the globally coupled FHN network. Further, we derive a mean-field limit approximating the locally coupled FHN network with low noise intensities. We study the effects of the coupling strength and noise intensity on coherence resonance for both the network and the mean-field models. We compare the results of the mean-field and network frameworks and find good agreement in the globally coupled case, where the correspondence between the two approaches is sufficiently good to capture the emergence of coherence resonance, as well as of anticoherence resonance.

The Immune System Can Hear Noise.

As a stressor widely existing in daily life, noise can cause great alterations to the immune system and result in many physical and mental disorders, including noise-induced deafness, sleep disorders, cardiovascular diseases, endocrine diseases and other problems. The immune system plays a major role in maintaining homeostasis by recognizing and removing harmful substances in the body. Many studies have shown that noise may play vital roles in the occurrence and development of some immune diseases. In humans, both innate immunity and specific immunity can be influenced by noise, and different exposure durations and intensities of noise may exert various effects on the immune system. Short-term or low-intensity noise can enhance immune function, while long-term or high-intensity noise suppresses it. Noise can lead to the occurrence of noise-induced hearing loss (NIHL) through the production of autoantibodies such as anti-Hsp70 and anti-Hsp60 and exert adverse effects related to other immune-related diseases such as some autoimmune diseases and non-Hodgkin lymphoma. The neuroendocrine system, mainly including the hypothalamic-pituitary-adrenal (HPA) axis and the sympathetic-adrenal-medullary (SAM) system, is involved in the mechanisms of immune-related diseases induced by noise and gut microbiota dysfunction. In addition, noise exposure during pregnancy may be harmful to the immune system of the fetus. On the other hand, some studies have shown that music can improve immune function and alleviate the adverse effects caused by noise.

Foraging dynamics of social insect colonies with resource constraints in random environments

Exploring foraging dynamics is central to our understanding of the complex behavior of social insect colonies. In this paper, a three-dimensional framework based on stochastic differential equations is presented to study the foraging dynamics of social insect colonies. Stochasticity and resource constraints are incorporated in the proposed framework. The stochastic dynamics, including the global existence and uniqueness of the positive solution and the existence of a unique stationary distribution (i.e., the ergodicity) are theoretically studied using stochastic analysis tools. The result suggests that higher resource growth rate, as well as lower noise intensity and colony size contribute to the sustainability of the foraging-resource system.