Photonic bandgap fiber bundle spectrometer

Single-pixel reconstructive mid-infrared micro-spectrometer

Miniaturized spectrometers in the mid-infrared (MIR) are critical in developing next-generation portable electronics for advanced sensing and analysis. The bulky gratings or detector/filter arrays in conventional micro-spectrometers set a physical limitation to their miniaturization. In this work, we demonstrate a single-pixel MIR micro-spectrometer that reconstructs the sample transmission spectrum by a spectrally dispersed light source instead of spatially grated light beams. The spectrally tunable MIR light source is realized based on the thermal emissivity engineered via the metal-insulator phase transition of vanadium dioxide (VO₂). We validate the performance by showing that the transmission spectrum of a magnesium fluoride (MgF₂) sample can be computationally reconstructed from sensor responses at varied light source temperatures. With potentially minimum footprint due to the array-free design, our work opens the possibility where compact MIR spectrometers are integrated into portable electronic systems for versatile applications.

Applications of nanotechnology in smart textile industry: A critical review

Background

In recent years, nanotechnology has been playing an important role in designing smart fabrics. Nanomaterials have been employed to introduce in a sustainable manner, antimicrobial, ultraviolet resistant, electrically conductive, optical, hydrophobic and flame-retardant properties into textiles and garments. Nanomaterial based smart devices are now also being integrated with the textiles so as to perform various functions such as energy harvesting and storage, sensing, drug release and optics. These advancements have found wide applications in the fashion industry and are being developed for wider use in defence, healthcare and on-body energy harnessing applications.

Aim of review

The objective of this work is to provide an insight into the current trends of using nanotechnology in the modern textile industries and to inspire and anticipate further research in this field. This review provides an overview of the most current advances concerning on-body electronics research and the wonders which could be realized by nanomaterials in modern textiles in terms of total energy reliance on our clothes.

Key scientific concepts of review

The work underlines the various methods and techniques for the functionalization of nanomaterials and their integration into textiles with an emphasis on cost-effectiveness, comfort, wearability, energy conversion efficiency and eco-sustainability. The most recent trends of developing various nanogenerators, supercapacitors and photoelectronic devices on the fabric are highlighted, with special emphasis on the efficiency and wearability of the textile. The potential nanotoxicity associated with the processed textiles due to the tendency of these nanomaterials to leach into the environment along with possible remediation measures are also discussed. Finally, the future outlook regarding progress in the integration of smart nano-devices on textile fabrics is provided.

Compact fiber-integrated scattering device based on mixed-phase TiO2 for speckle spectrometer

A universal, repeatable, and controllable integration of single-mode optical fiber and mixed-phase TiO₂ is used to manufacture a compact fiber-integrated scattering device. Based on the device, we achieve a high-performance and compact fiber-based speckle spectrometer, which has a resolution of 20 pm over a bandwidth of 15 nm, in the 1550 nm range. We test the capability of our proposed spectrometer to reconstruct narrow linewidth and broadband optical spectrums, and compare the performance with that of a traditional optical spectrum analyzer.

Miniaturization of optical spectrometers

Spectroscopic analysis is one of the most widely used analytical tools in scientific research and industry. Although laboratory benchtop spectrometer systems offer superlative resolution and spectral range, their miniaturization is crucial for applications where portability is paramount or where in situ measurements must be made. Advancement in this field over the past three decades is now yielding microspectrometers with performance and footprint near those viable for lab-on-a-chip systems, smartphones, and other consumer technologies. We summarize the technologies that have emerged toward achieving these aims—including miniaturized dispersive optics, narrowband filter systems, Fourier transform interferometers, and reconstructive microspectrometers—and discuss the challenges associated with improving spectral resolution while device dimensions shrink ever further.

Study of a fiber spectrometer based on offset fusion

A near-infrared spectrometer based on offset fused multimode fiber (MMF) is investigated in this study. The light spectrum is recovered by analyzing the speckle images when light is passing through the MMF. In order to generate adequate speckles, a polarization maintaining fiber (PMF) and a 30 cm long MMF are fused with a vertical offset. Seven different offset displacements are implemented in the fiber fusion. The follow-up experiments show that the fiber offset fusion has a significant influence on the spectral correlation and the resolution. Larger offset fusion can excite more high-order modes in the MMF, and it greatly improves the spectrometer's performance. The simulation results also show that more modes are excited in MMF, and the increase of mode number leads to lower correlation coefficients of the neighboring spectral channels. However, large offset fusion increases the fusion and the insertion loss of the whole system, which may bring difficulties in the low-light cases. In addition, an image denoising algorithm based on dynamic threshold filtering and a spectral reconstruction algorithm originated from complete orthogonal decomposition were used to remove the speckle pattern noise and recover the spectrum. The final speckle-based spectrometer has a spectral resolution of 0.6∼0.016nm depending on the different offset fusions.

Broadband Spectrometer with Single-Photon Sensitivity Exploiting Tailored Disorder

Harnessing tailored disorder for broadband light scattering enables high-resolution signal analysis in nanophotonic spectrometers with a small device footprint. Multiple scattering events in the disordered medium enhance the effective path length which leads to increased resolution. Here we demonstrate an on-chip random spectrometer cointegrated with superconducting single-photon detectors suitable for photon-scarce environments. We combine an efficient broadband fiber-to-chip coupling approach with a random scattering area and broadband transparent silicon nitride waveguides to operate the spectrometer in a diffusive regime. Superconducting nanowire single-photon detectors at each output waveguide are used to perform spectral-to-spatial mapping via the transmission matrix at the system, allowing us to reconstruct a given probe signal. We show operation over a wide spectral range with sensitivity down to powers of -111.5 dBm in the telecom band.

High-performance compact spectrometer based on multimode interference in a tapered spiral-shaped waveguide

Multimode interference patterns are strongly dependent on spectral components and can be used as fingerprints to reconstruct a spectrum with random amplitudes. Motivated by this concept, we designed and realized a high-performance compact spectrometer based on a tapered spiral-shaped waveguide with a detector array integrated directly on top. The device relies on imaging the multimode interference from leaky modes, resulting in a resolution of 20 pm in the visible range and a bandwidth from 545 to 725 nm with a 250 µm radius structure. Spectra of multiple narrow lines and synthesized broadband are well reconstructed. The ability to achieve such high resolution and broad bandwidth in a compact footprint is expected to have a significant role in low-cost and multifunctional integrated systems.

Snapshot fiber spectral imaging using speckle correlations and compressive sensing

Snapshot spectral imaging is rapidly gaining interest for remote sensing applications. Acquiring spatial and spectral data within one image promotes fast measurement times, and reduces the need for stabilized scanning imaging systems. Many current snapshot technologies, which rely on gratings or prisms to characterize wavelength information, are difficult to reduce in size for portable hyperspectral imaging. Here, we show that a multicore multimode fiber can be used as a compact spectral imager with sub-nanometer resolution, by encoding spectral information within a monochrome CMOS camera. We characterize wavelength-dependent speckle patterns for up to 3000 fiber cores over a broad wavelength range. A clustering algorithm is employed in combination with l₁-minimization to limit data collection at the acquisition stage for the reconstruction of spectral images that are sparse in the wavelength domain. We also show that in the non-compressive regime these techniques are able to accurately reconstruct broadband information.

Harnessing speckle for a sub-femtometre resolved broadband wavemeter and laser stabilization

The accurate determination and control of the wavelength of light is fundamental to many fields of science. Speckle patterns resulting from the interference of multiple reflections in disordered media are well-known to scramble the information content of light by complex but linear processes. However, these patterns are, in fact, exceptionally rich in information about the illuminating source. We use a fibre-coupled integrating sphere to generate wavelength-dependent speckle patterns, in combination with algorithms based on the transmission matrix method and principal component analysis, to realize a broadband and sensitive wavemeter. We demonstrate sub-femtometre wavelength resolution at a centre wavelength of 780 nm, and a broad calibrated measurement range from 488 to 1,064 nm. This compares favourably to the performance of conventional wavemeters. Using this speckle wavemeter as part of a feedback loop, we stabilize a 780 nm diode laser to achieve a linewidth better than 1 MHz.

Speckle-based hyperspectral imaging combining multiple scattering and compressive sensing in nanowire mats

Encoding of spectral information onto monochrome imaging cameras is of interest for wavelength multiplexing and hyperspectral imaging applications. Here, the complex spatiospectral response of a disordered material is used to demonstrate retrieval of a number of discrete wavelengths over a wide spectral range. Strong, diffuse light scattering in a semiconductor nanowire mat is used to achieve a highly compact spectrometer of micrometer thickness, transforming different wavelengths into distinct speckle patterns with nanometer sensitivity. Spatial multiplexing is achieved through the use of a microlens array, allowing simultaneous imaging of many speckles, ultimately limited by the size of the diffuse spot area. The performance of different information retrieval algorithms is compared. A compressive sensing algorithm exhibits efficient reconstruction capability in noisy environments and with only a few measurements.

Broadband multimode fiber spectrometer

A general-purpose all-fiber spectrometer is demonstrated to overcome the trade-off between spectral resolution and bandwidth. By integrating a wavelength division multiplexer with five multimode optical fibers, we have achieved 100 nm bandwidth with 0.03 nm resolution at wavelength 1500 nm. An efficient algorithm is developed to reconstruct the spectrum from the speckle pattern produced by interference of guided modes in the multimode fibers. Such an algorithm enables a rapid, accurate reconstruction of both sparse and dense spectra in the presence of noise.

Nanotechnology in Textiles

Increasing customer demand for durable and functional apparel manufactured in a sustainable manner has created an opportunity for nanomaterials to be integrated into textile substrates. Nanomoieties can induce stain repellence, wrinkle-freeness, static elimination, and electrical conductivity to fibers without compromising their comfort and flexibility. Nanomaterials also offer a wider application potential to create connected garments that can sense and respond to external stimuli via electrical, color, or physiological signals. This review discusses electronic and photonic nanotechnologies that are integrated with textiles and shows their applications in displays, sensing, and drug release within the context of performance, durability, and connectivity. Risk factors including nanotoxicity, nanomaterial release during washing, and environmental impact of nanotextiles based on life cycle assessments have been evaluated. This review also provides an analysis of nanotechnology consolidation in the textiles market to evaluate global trends and patent coverage, supplemented by case studies of commercial products. Perceived limitations of nanotechnology in the textile industry and future directions are identified.

Miniature spectrometer based on diffraction in a dispersive hole array

We present an ultra-compact spectrometer that uses a 10×10 hole array as the dispersive component. Our analysis shows that the two-dimensional intensity distribution can be modeled by a system of simultaneous linear equations when the size of each hole in the dispersive component has been pre-designed appropriately. One can readily recover the spectral contents of the input radiation by solving the linear equation system with regularized procedure. Experimental results show that the reconstruction range is at least within the entire visible band, which can be further extended if a near-infrared CCD is used. One therefore envisions strong potential for many wavelength analysis applications.

Noise analysis of spectrometers based on speckle pattern reconstruction

Speckle patterns produced by a disordered medium or a multimode fiber can be used as a fingerprint to uniquely identify the input light frequency. Reconstruction of a probe spectrum from the speckle pattern has enabled the realization of compact, low-cost, and high-resolution spectrometers. Here we investigate the effects of experimental noise on the accuracy of the reconstructed spectra. We compare the accuracy of a speckle-based spectrometer to a traditional grating-based spectrometer as a function of the probe signal intensity and bandwidth. We find that the speckle-based spectrometers provide comparable performance to a grating-based spectrometer when measuring intense or narrowband probe signals, whereas the accuracy degrades in the measurement of weak or broadband signals. These results are important to identify the applications that would most benefit from this new class of spectrometer.

All-fiber spectrometer based on speckle pattern reconstruction

A standard multimode optical fiber can be used as a general purpose spectrometer after calibrating the wavelength dependent speckle patterns produced by interference between the guided modes of the fiber. A transmission matrix was used to store the calibration data and a robust algorithm was developed to reconstruct an arbitrary input spectrum in the presence of experimental noise. We demonstrate that a 20 meter long fiber can resolve two laser lines separated by only 8 pm. At the other extreme, we show that a 2 centimeter long fiber can measure a broadband continuous spectrum generated from a supercontinuum source. We investigate the effect of the fiber geometry on the spectral resolution and bandwidth, and also discuss the additional limitation on the bandwidth imposed by speckle contrast reduction when measuring dense spectra. Finally, we demonstrate a method to reduce the spectrum reconstruction error and increase the bandwidth by separately imaging the speckle patterns of orthogonal polarizations. The multimode fiber spectrometer is compact, lightweight, low cost, and provides high resolution with low loss.

Using a multimode fiber as a high-resolution, low-loss spectrometer

We propose and demonstrate that a conventional multimode fiber can function as a high-resolution, low-loss spectrometer. The proposed spectrometer consists only of the fiber and a camera that images the speckle pattern generated by interference among the fiber modes. Although this speckle pattern is detrimental to many applications, it encodes information about the spectral content of the input signal, which can be recovered using calibration data. We achieve a spectral resolution of 0.15 nm over 25 nm bandwidth using 1 m long fiber, and 0.03 nm resolution over 5 nm bandwidth with a 5 m fiber. The insertion loss is less than 10%, and the signal-to-noise ratio in the reconstructed spectra is more than 1000.