In this paper we report a mid-infrared sensor based on an anti-resonant hollow core fiber. A quantum cascade laser operating around 4.53 µm is used to target one of the strongest transition of ...nitrous oxide near 2203.7 cm
. The system provides 1-second minimum detection limit at single parts-per-billion level using 3.2-m-long fiber with the response time of less than 30 seconds. Presented sensing approach shows a good perspective for compact and sensitive mid-infrared fiber-based spectrometers.
Hollow-core optical fibers have been used for laser gas sensing for almost two decades. However, to date, the vast majority of sensing systems have used hollow-core fiber only as a replacement for ...bulky gas cells (single- or multi-pass). Here, we investigate a reflective, dual-pass configuration in which light enters and exits hollow-core fiber from the same side. The advantage of this approach is the fact that the hollow-core fiber can be used not only as a cell but also as an endoscope-like probe, which does not need any additional tubing for sample delivery.
In this paper, we identify unwanted reflections from various fiber-to-fiber connections in the setup as the main challenge limiting the performance of the sensor in reflective configuration. We propose and experimentally demonstrate that the problem of reflections can be addressed using heterodyne-based detection, which allows for identifying and extracting useful signals in the radio frequency domain. Absorption and dispersion spectroscopy of methane are performed as a proof-of-concept with a detection limit of methane concentration below 10 ppm. Discussion insights into further development are provided, including strategies for miniaturization and detection limit improvement.
We present the pedestal-free thulium doped silica fiber with a large nanostructured core optimized for fiber lasers. The fiber is composed of over 6 thousand thulium doped silica nanorods with a ...diameter of 71 nm each which form a nanostructured step-index core. We study the influence of non-continuous distribution in nanoscale active areas on gain, beam quality, and fiber laser performance. The proof-of-concept fiber is effectively single mode for wavelength above 1.8 µm. We demonstrate the performance of the fiber in a laser setup pumped at 792 nm. Single mode laser emission with a slope efficiency of 29% at quasi-continuous output power of 4 W with M
= 1.3 at the emission spectrum 1880-1925 nm is achieved.
In this paper, we present a laser-based sensing inside anti-resonant hollow core fiber. A distributed feedback laser diode operating near 2004 nm and a 1.35-m-long silica-based fiber are used to ...demonstrate carbon dioxide detection with sensitivity down to ~5 ppmv. Gas exchange time as low as 5 seconds is obtained. This performance was achieved in a very simple optical configuration, without any mirrors or lenses in the setup.
In this paper we present a light field camera system where a flat-surface hexagonal array of nanostructured gradient index lenses was used as a lens matrix. In our approach we use an array of 469 ...gradient index microlenses with a diameter of 20 µm and 100% fill factor. To develop the single lens and the lenslet array we used a modified stack-and-draw technology. In this technique, variation of refractive index is achieved by using quantized gradient index profiles and rods from different types of glasses. We show experimental results of using this type of lenses for imaging in a system of two kinds of light field cameras. In the first one, the microlens array is located in the focal plane of the main lens. The image is reconstructed, in this case using a Fourier slice photography algorithm. This allowed a partial reconstruction of a 3D scene with spatial and depth resolution of 20 µm and field of view of 500×500×500 µm. In the second configuration, the microlens array is located between a sample and a microscopic objective, thus allowing for superresolution 3D reconstruction of a microscopic image. The scale-invariant feature transform method was used for image reconstruction and obtained a partial 3D reconstruction with a field of view of 150×115×80 µm and a spatial resolution of 2 µm and depth resolution of 10 µm.
For over a decade hollow-core fibers have been used in optical gas sensors in the role of gas cells. However, very few examples of actual real-life applications of those sensors have been ...demonstrated so far. In this paper, we present a highly-sensitive hollow-core fiber based methane sensor. Mid-infrared distributed feedback interband cascade laser operating near 3.27 µm is used to detect gas inside anti-resonant hollow-core fiber. R(3) line near 3057.71 cm
located in ν
band of methane is targeted. Compact, lens-free optical setup with an all-silica negative curvature hollow-core fiber as the gas cell is demonstrated. Using wavelength modulation spectroscopy and 7.5-m-long fiber the detection limit as low as 1.54 ppbv (at 20 s) is obtained. The demonstrated system is applied for a week-long continuous monitoring of ambient methane and water vapor in atmospheric air at ground level. Diurnal cycles in methane concentrations are observed, what proves the sensor's usability in environmental monitoring.
We report the development of microscopic size gradient index vortex masks using the modified stack-and-draw technique. The vortex mask has a form of flat surface all-glass plate. Its functionality is ...determined by an internal nanostructure composed of two types of soft glass nanorods. The generation of optical vortices with charges 1 and 2 is demonstrated.
All-optical switching of 75 fs pulses centered at 1560 nm, driven by 270 fs, 1030 nm pulses in a dual-core optical fiber exhibiting high index contrast is presented. The fiber is made of a thermally ...matched pair of lead silicate and borosilicate glasses used as core and cladding material, respectively. The novel switching approach is based on nonlinear balancing of dual-core asymmetry, by control pulse intensity induced group velocity reduction of the fast fiber channel. Due to the fiber core made of soft glass with high nonlinearity high switching contrast exceeding 20 dB is reached by using control pulses of only few nanojoule energy. The optimum fiber length is 14 mm, which closely match the calculated coupling length at the signal wavelength. The results express significant progress in comparison to similar studies based on self-switching of solitonic pulses in dual-core fibers and represent high application potential.
The paper presents a new approach to developing exposed-core fibers. We designed a new asymmetric structure of suspended core fibers with series of additional air holes in the cladding. Using the ...standard wet etching method we removed a part of glass, demonstrating that the method allows to open a selected air hole surrounding the suspended core. Such modified of fibers can be used to build sensors and devices dedicated to chemical and biological studies and based on the interaction of light with liquids. We used the developed fiber to develop an interferometric sensor that measures changes in the refractive index with a high accuracy. As a proof of concept, we present the experimental measurement results of the ethanol concentration in water.
A nanostructured core silica fiber with active and photosensitive areas implemented within the fiber core is demonstrated. The photosensitivity, active and passive properties of the fiber can be ...independently shaped with this new approach. We show that discrete local doping with active ions in form of nanorods allow to obtain effective laser action as in case of continuous distribution of the ions in the core. Co-existing discrete photosensitive nanostructure of germanium doped silica determine single-mode performance and allow inscription of highly efficient Bragg grating over the entire core area. Each nanostructure do not degrade performance of other one since physical interaction between active and photosensitive areas are removed. As a proof of concept, we have designed and fabricated the nanostructured, ytterbium single-mode silica fiber laser with the Bragg grating inscribed in the entire core area. We demonstrated fiber laser with good quality of generated laser beam (M
=1.1) with lasing efficiency of 44% and inscribed Bragg grating with 98.5% efficiency and -18 dB contrast.
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