Broadband Light Source Research Articles

Noise Suppression Method of Fiber Optic Sensors Driven by Broadband Light Source

Noise Suppression Method of Fiber Optic Sensors Driven by Broadband Light Source

Sensitivity improvement of the closed-loop resonant fiber-optic gyroscope interrogated with a broadband source

The resonant fiber-optic gyroscope (RFOG), interrogated with a broadband light source, represents an intriguing optical gyroscope that has been proposed as an extension of the traditional RFOG, which is driven by a narrow linewidth laser source. The implementation of a closed-loop detection system enhances the linearity and dynamic range of the gyroscope output. This paper is devoted to improving the sensitivity of the closed-loop broadband source-driven RFOG. First, a model for analysis and optimization of the feedback loop gain of a closed-loop broadband source-driven resonant fiber-optic gyroscope (RFOG) is developed, and the feedback loop gain is optimized. The experimental results indicate that the influence of the feedback loop noise on the gyro performance can be neglected. Subsequently, the noise contributions, including the shot noise, detector noise, and relative intensity noise, in the broadband source-driven RFOG system are investigated. A theoretical derivation and experimental verification of an expression for the reduction of the relative intensity noise by a fiber-optic ring resonator are presented. Finally, a packaged broadband source-driven RFOG prototype using a 175 m long fiber coil with an average diameter of 5.7 cm was constructed and evaluated. The experimental results demonstrate that the prototype achieves navigation-grade precision with an angular random walk of 0.003∘/h1/2 and a bias instability of 0.005°/h.

Design and Analysis of Ridge and Sub-Wavelength Grating Waveguide Based Micro Ring-Resonator Sensor

The subwavelength grating microring resonator based filter shows great promise in optical sensing and communication. However, it spectrum nature makes it unsuitable for tracking or extracting a single wavelength from a broadband light source. In this paper, we used side-mode suppression, based on an angular grating- subwavelength microring resonator which offer high flexibility in wavelength design within the silicon-on-insulator (SOI) waveguide. By periodically arranging silicon waveguide pieces in three different widths, we can set the effective index along the inner sidewall of subwavelength microring resonator. thereby can achieve the precise wavelength selection. We examine the effects of various key parameters on the center wavelength, side-mode suppressed ratio, and quality factor of this filter.The proposed structure's isalso analysed for coupling strength between the bus and subwavelength grating ring resonator. The wavelength selection, compact size, compatibility with other similar nature waveguide-based devices and design flexibility highlight its significant potential in compact optical sensing and optical communication

Primary realization of spectral responsivity in the near infrared using a laser-driven light source

Abstract The National Research Council (NRC) Canada has realized the spectral responsivity scale from 900 nm to 1600 nm using a Xe-based laser driven light source, double subtractive monochromator system, and an absolute cryogenic radiometer. An NRC-designed InGaAs sphere transfer standard radiometer was calibrated with combined relative standard uncertainties below 0.135 % (k=1). The scale realization was also performed with a 100 W tungsten lamp, as previously done at NRC. Calibration results and uncertainties in spectral responsivity measurements with each broadband light source are compared and presented.

Enhanced Cherenkov radiation in twisted hyperbolic Van der Waals crystals

AbstractCherenkov radiation in artificial structures experiencing strong radiation enhancements promises important applications in free‐electron quantum emitters, broadband light sources, miniaturized particle detectors, etc. However, the momentum matching condition between swift electrons and emitted photons generally restricts the radiation enhancement to a particular momentum. Efficient Cherenkov radiation over a wide range of momenta is highly demanded for many applications but still remains a challenging task. To this end, we explored the interaction between swift electrons and twisted hyperbolic Van der Waals crystals and observed enhanced Cherenkov radiation at the flatband resonance frequency. We show that, at the photonic magic angle of the twisted crystals, the electron momentum, once matching with that of the flatband photon, gives rise to a maximum energy loss (corresponding to the surface phonon generation), one‐order of magnitude higher than that in conventional hyperbolic materials. Such a significant enhancement is attributed to the excitation of flatband surface phonon polaritons over a broad momentum range. Our findings provide a feasible route for highly directional free‐electron radiation and radiation shaping.

High-Precision Chromatic Confocal Technologies: A Review

Chromatic confocal technology is widely used for precise, steady, and efficient displacement measurement in many industrial fields. It employs the confocal and dispersion principles to encode axial positions with the wavelengths of the reflected broad spectrum. The typical chromatic confocal sensor includes a light source, a dispersion objective, conjugate pinholes, and a spectral detection device. This study offers an overview of the current research on chromatic confocal technology. Because of its good performance in displacement detection, chromatic confocal technology has been widely used in contour measurement, biomedical imaging, and thickness measurements, as part of global and professional research. Due to its structural flexibility, it is also easily integrated into industrial equipment for in-machine and online profile measurements. It holds significant potential for future applications in industrial manufacturing and scientific research. However, there are also some challenges to be explored in terms of the broadband light source, dispersive optics design, and the balance between speed and accuracy in signal processing.

Bright compact ultrabroadband source by orthogonal laser-sustained plasma

Laser-sustained plasma (LSP) source featuring high brightness and broadband spectral coverage is found to be powerful in various fields of scientific and industrial applications. However, the fundamental limit of low conversion efficiency constrains the system compactness and widespread applications of such broadband light sources. In this paper, we propose an innovative orthogonal LSP to break through the conversion efficiency limitation. Driven by the elevated conversion efficiency from absorbed laser power to ultraviolet (UV) emission, a compact broadband source (250–1650 nm) with UV spectral radiance exceeding 210 mW/(mm2⋅sr⋅nm)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${mW}/({{mm}}^{2}\\,\\cdot\\, {sr}\\,\\cdot\\, {nm})$$\\end{document} is achieved with >100 W pump laser. With the plot of a two-dimensional refractive index model, we report an important conceptual advance that the orthogonal design eliminates the influence of the negative lensing effect on laser power density. Experimental results unambiguously demonstrate that we achieve a bright compact UV-VIS-NIR source with negligible thermal loss and the highest conversion efficiency to our knowledge. Significant enhancement of 4 dB contrast-to-noise ratio (CNR) in spectral single-pixel imaging has been demonstrated using the proposed ultrabroadband source. By establishing the quantitative link between pumping optics design and plasma absorption, this work presents a compact broadband source that combines superior conversion efficiency and unprecedented brightness, which is essential to high-speed inspection and spectroscopy applications.

Fiber Bragg Grating Pulse and Systolic Blood Pressure Measurement System Based on Mach-Zehnder Interferometer.

A fiber Bragg grating (FBG) pulse and systolic blood pressure (SBP) measurement system based on the edge-filtering method is proposed. The edge filter is the Mach-Zehnder interferometer (MZI) fabricated by two fiber couplers with a linear slope of 52.45 dBm/nm. The developed system consists of a broadband light source, an edge filter, fiber Bragg gratings (FBGs), a coarse wavelength-division multiplexer (CWDM), and signal-processing circuits based on a field-programmable gate array (FPGA). It can simultaneously measure pulse pulsations of the radial artery in the wrist at three positions: Cun, Guan and Chi. The SBP can be calculated based on the pulse transit time (PTT) principle. The measurement results compared to a standard blood pressure monitor showed the mean absolute error (MAE) and standard deviation (STD) of the SBP were 0.93 ± 3.13 mmHg. The system meets the requirements of the Association for the Advancement of Medical Instrumentation (AAMI) equipment standards. The proposed system can achieve continuous real-time measurement of pulse and SBP and has the advantages of fast detection speed, stable performance, and no compression sensation for subjects. The system has important application value in the fields of human health monitoring and medical device development.

Ultrabroadband Optical Diffraction Tomography.

Optical diffraction tomography (ODT) is a powerful noninvasive 3D imaging technique, but its combination with broadband light sources is difficult. In this study, we introduce ultrabroadband ODT, covering over 150 nm of visible spectral bandwidth with a lateral spatial resolution of 150 nm. Our work addresses a critical experimental gap by enabling the measurement of broadband refractive index changes in 3D samples, crucial information that is difficult to assess with existing methodologies. We present broadband, spectrally resolved ODT images of HeLa cells, obtained via pulse-shaping-based Fourier transform spectroscopy. The spectral observations enabled by ultrabroadband ODT, combined with material-dependent refractive index responses, allow for precise three-dimensional identification of nanoparticles within cellular structures. Our work represents a crucial step toward time and spectrally resolved tomography of complex 3D structures with implications for life and materials science applications.

A wavelength-division-multiplex depolarized Sagnac-based interferometer for noise suppression

The Sagnac-based interferometer (SI) has been developed over several decades and is widely recognized for its sensitivity and stability. Most SIs utilize polarization-maintaining (PM) fiber and polarizers to ensure polarization reciprocity, or depolarizers to mitigate the effects of polarization non-reciprocity. The depolarizing method was considered more promising from a marketability standpoint. Additionally, broadband optical sources were typically used in SIs to eliminate the Kerr effect and backscatter. However, broadband light source SIs are hindered by high excess relative intensity noise (excess RIN) generated by the self-interference of different spectral components. To enhance the performance of SIs, it is crucial to suppress the excess RIN. In this study, we demonstrate a wavelength-division-multiplex depolarized Sagnac-based interferometer and suppress the excess RIN by utilizing the overlap of two interfering lights, which shifts the primary frequency of noise outside the detection range. Experimental results show that the noise equivalent displacement at a light intensity of 42 μW achieves 170.18 fm/√Hz, which encompasses both shot noise and non-optical noise, indicating successful suppression of excess RIN.

Controlled dispersive waves emission via swallowtail-type catastrophe pulses.

The dispersive waves (DWs) emission has emerged as an efficient way to extend the spectral range of a light source. However, the applications of the DWs are limited because of its narrowband and low power. It is crucial to find novel ways to manipulate the DWs radiation. We investigate a kind of catastrophe pulses, called swallowtail pulses, which can radiate DWs with broadband and high power. By exploiting the dependence of the temporal and spectral structure of swallowtail pulses on the initial control parameter within the catastrophe integral, we can effectively manipulate the emission of DWs in terms of resonant frequency and conversion efficiency. Furthermore, we observe that the swallowtail pulses can shed two solitons, and that both of them radiate DWs with different frequencies. In comparison to fundamental solitons, the minimum value of third-order dispersion required for the onset of DWs emission becomes significantly smaller for that of swallowtail pulses. The results of this study clearly reveal the impact of the inherent behaviors of swallowtail pulses on the DWs emission, which should be relevant for applications requiring broadband light sources and optical frequency combs based on the mechanism of DWs emission.

Super broadband light source: a promising master oscillator source for high brightness and high-power fiber amplifiers.

Stimulated Raman scattering (SRS) and transverse mode instability (TMI) effects are crucial limitation factors for further power scaling of high-power fiber amplifiers with near-diffraction-limited beam quality. It is an important research direction to carry out laser system optimization from the perspective of seed construction. In this work, we experimentally investigated the impact of utilizing different seed lasers on the SRS and TMI characteristics in high power ytterbium-doped fiber amplifiers. Both the phase modulated single frequency fiber laser (PMSFL), fiber oscillator laser (FOL), and superfluorescent fiber source (SFS) as a typical type of temporally stable broadband light source (SBLS) are employed as seed lasers. The experimental results indicated that the SRS intensity in the fiber amplifier is influenced by the properties of the seed laser source. Notably, the SRS threshold of the SBLS could be comparable to that of a low-noise PMSFL source. There is a significant increase in TMI threshold when employing SBLS as a seed laser in high-power fiber amplifiers, which is 3.86times that of the injected seed laser with a 3dB narrow linewidth of 0.74nm. Considering the combined threshold characteristics of SRS and TMI, it can be found that SBLS is a promising master oscillator source for high brightness and high-power fiber amplifiers. Our work could provide a good reference for the selection of a master oscillator source, and we believe that it is an important direction to go beyond the power limitation of high-power fiber lasers by constructing a light source with broader spectral linewidth and temporal stability.

Octave spanning and flat-top supercontinuum generation in standard foundry-compatible process-made Ge–Sb–Se chalcogenide glass waveguide

We reported near octave-spanning supercontinuum generation in Ge28Sb12Se60 chalcogenide glass rib waveguides. The waveguides were fabricated using foundry-compatible deep ultra-violet lithography, followed by plasma etching. We demonstrated an average propagation loss of ∼1.3 dB/cm at the 1550 nm telecommunication wavelength. With dispersion engineering, optimizing waveguide geometry, and pumping by a multi-wavelength femtosecond soliton fiber laser, we achieved a flat-top supercontinuum generation spanning from 1290 to 2400 nm and beyond . It has a 3 dB bandwidth of 436 nm and a 20 dB bandwidth of more than 900 nm. The implementation of such waveguides provides a practical broadband light source solution for on-chip spectroscopy and sensing systems.

Resonant fiber optic gyroscope driven by a broadband light source based on an over-coupled state fiber ring resonator

The resonant fiber optic gyroscope (RFOG) driven by a broadband light source has advantages over conventional RFOGs in terms of structure, solution, etc., and provides new ideas for the commercialization of RFOGs. In this paper, the basic working principle of RFOG driven by a broadband light source is introduced. The optimal modulation coefficients are provided for sinusoidal wave modulation. The influence of the length of the fiber-optic ring resonator (FRR) and the coupling coefficient of the fiber coupler on the sensitivity is analyzed. The FRR is constructed in the over-coupled state to improve the utilization of optical power, and thus significantly increase the system sensitivity. In experiments, an RFOG prototype with a diameter of 13 cm, a height of 7 cm, and a fiber ring length of 210 m is produced. A bias instability (BI) of 0.06°/h and an angular random walk (ARW) of 0.01∘/h are obtained.

Inverse design of coherent supercontinuum generation using free-form nanophotonic waveguides

Many key functionalities of optical frequency combs, such as self-referencing and broad spectral access, rely on coherent supercontinuum generation (SCG). While nanophotonic waveguides have emerged as a compact and power-efficient platform for SCG, their geometric degrees of freedom have not been fully utilized due to the underlying complex nonlinear and noise-dependent stochastic physics. Here, we introduce inverse design to unlock free-form waveguides for coherent SCG. The efficacy of our design is numerically and experimentally demonstrated on Si3N4 waveguides, producing flat and coherent spectra from visible to mid-infrared wavelengths. Our work has direct applications in developing chip-based broadband light sources for spectroscopy, metrology, and sensing across multiple spectral regimes.

Time-domain Vernier effect-based optical fiber sensor.

In this Letter, we demonstrate an easy-to-fabricate time-domain Vernier-effect-based sensor. An all-fiber variable optical delay line (VODL) is utilized to drive an OPD scan of two interferometers simultaneously, and fiber Bragg gratings are used to filter out two slightly detuned time-domain interferometric signals. Then two normalized interferograms with different spatial frequencies can be achieved and utilized to generate an envelope modulation, viz., a Vernier envelope, with enhanced sensitivity in comparison to the native state of the interferometers used. The sensitivity magnification factor of our structure can be regulated simply via altering the resonant wavelength difference of FBGs rather than optimizing the OPDs of the interferometers. The proposed sensor is independent of the precise and complicated fabrication procedures. The Vernier signal can be demodulated without a broadband light source and spectrometer. We argue that the proposed structure may inspire a new concept for constructing simple and cheap Vernier effect-based sensors that are well suited for practical applications.

Influence of the average wavelength on the scale factor stability of interferometric fiber optic gyroscope

The introduction of closed-loop mechanisms has significantly enhanced the performance of interferometric fiber optic gyroscopes (IFOGs). However, the poor scale factor (SF) stability limits its further application due to the use of broadband light sources. This study first reviewed the impact of the average wavelength of a light source on SF stability in a closed-loop IFOG setup. A simulation model is developed according to modulation and demodulation principles, and the SF error is found to be proportional to the wavelength drift in a closed-loop IFOG. Additionally, employing a laser with a more stable average wavelength instead of a super fluorescent fiber source (SFS) for driving the IFOG enhanced the SF stability by an order of magnitude to 0.38 ppm in ambient-air experiments, which is one of the best SF performances achieved thus far. With the significant improvement in stability during the variable temperature tests, the IFOG measures rotation rates more accurately.

Spurious signals identification in Brillouin light scattering spectrum

AbstractBrillouin light scattering (BLS) is the inelastic scattering of light from elementary excitations with periodic density modulation. The characteristics of non‐contact, high sensitivity, and high resolution in energy, wavevector, time, space, and phase make the BLS spectrometer widely used in investigating many intriguing physical phenomena, including the acoustic phonon confinement effects, Bose‐Einstein condensation (BEC), supercurrent, and soliton formation. Generally, the quick and correct assignment of the signals in the BLS spectra is a prerequisite for further investigations. Herein, we experimentally identify the high‐order spurious signals in the BLS spectra, which make the interpretation of the spectra difficult. The additional signals are demonstrated to originate from the laser and the temperature‐controlled laser filter used for laser filtering. Our results would contribute to the rapid assignment of the signals from the sample after excluding the spurious signals reported here. Moreover, the series of high‐order modes spaced by the free spectral range can serve as a weak broadband light source, which has great potential for investigating the optical responses of materials.

Theoretical prediction of broadband ambient light optogenetic vision restoration with ChRmine and its mutants

Vision restoration is one of the most promising applications of optogenetics. However, it is limited due to the poor-sensitivity, slow-kinetics and narrow band absorption spectra of opsins. Here, a detailed theoretical study of retinal ganglion neurons (RGNs) expressed with ChRmine, ReaChR, CoChR, CatCh and their mutants, with near monochromatic LEDs, and broadband sunlight, halogen lamp, RGB LED light, and pure white light sources has been presented. All the opsins exhibit improved light sensitivity and larger photocurrent on illuminating with broadband light sources compared to narrow band LEDs. ChRmine allows firing at ambient sunlight (1.5 nW/mm2) and pure white light (1.2 nW/mm2), which is lowest among the opsins considered. The broadband activation spectrum of ChRmine and its mutants is also useful to restore color sensitivity. Although ChRmine exhibits slower turn-off kinetics with broadband light, high-fidelity spikes can be evoked upto 50 Hz. This limit extends upto 80 Hz with the improved hsChRmine mutant although it requires double the irradiance compared to ChRmine. The present study shows that ChRmine and its mutants allow activation of RGNs with ambient light which is useful for goggle-free white light optogenetic retinal prostheses with improved quality of restored vision.

Spontaneously Integrated Multicolor InGaN Micro‐Light‐Emitting Diodes for Spectrum‐Controllable Broadband Light Sources

Spontaneously integrated multicolor InGaN micro‐light‐emitting diodes with a microstripe topography achieve selective electrical operation with four different color emissions: green, bluish‐green, bluish‐purple, and purple. The entire microstripe displays broadband emissions because the stripe topography with a convex lens‐like cross section induces a continuous emission wavelength gradient in the overgrown InGaN active layers. Since each wavelength component is distributed along the stripe direction, multiple narrow p‐electrodes are positioned side by side across the stripe width. This design supports selective current injection into the corresponding local areas. This work represents an important step for realizing broadband visible light emitters where individual wavelength components comprising the broad spectra can be modulated and switched independently.