Vladimir P. Minkovich

Temperature-insensitive photonic crystal fiber interferometer for absolute strain sensing

The authors report a highly sensitive (∼2.8pm∕μe) wavelength-encoded strain sensor made from a piece of photonic crystal fiber (PCF) spliced to standard fibers. The authors intentionally collapse the PCF air holes over a short region to enlarge the propagating mode of the lead-in fiber which allows the coupling of only two modes in the PCF. The transmission spectrum of the interferometer is stable and sinusoidal over a broad wavelength range. The sensor exhibits linear response to strain over a large measurement range, its temperature sensitivity is very low, and for its interrogation a battery-operated light emitting diode and a miniature spectrometer are sufficient.

Simple all-microstructured-optical-fiber interferometer built via fusion splicing

We report a compact and stable all-microstructured-optical-fiber interferometer built with two fusion splices separated a few centimeters from each other. The air-holes of the fiber are intentionally collapsed in the vicinity of the splices. This broadens the propagating optical mode, allowing coupling of two modes in the section between the splices. A truly sinusoidal interference pattern was observed from 800 nm to 1600 nm with fringe visibility reaching 80%. The fringe spacing was inversely proportional to the distance between the splices. The potential of the device for sensing applications is demonstrated.

Photonic crystal fiber interferometer for chemical vapor detection with high sensitivity.

We report an in-reflection photonic crystal fiber (PCF) interferometer which exhibits high sensitivity to different volatile organic compounds (VOCs), without the need of any permeable material. The interferometer is compact, robust, and consists of a stub of PCF spliced to standard optical fiber. In the splice the voids of the PCF are fully collapsed, thus allowing the excitation and recombination of two core modes. The device reflection spectrum exhibits sinusoidal interference pattern which shifts differently when the voids of the PCF are infiltrated with VOC molecules. The volume of voids responsible for the shift is less than 600 picoliters whereas the detectable levels are in the nanomole range.

Temperature-independent strain sensor made from tapered holey optical fiber

A large-mode-area holey fiber was tapered to a point in which the airholes collapsed, and its dependence on temperature and strain was studied. The transmission spectrum of such a fiber exhibits a series of peaks owing to the interference between the modes of the solid taper waist. We found that the interference peaks shifted to shorter wavelengths as the taper was elongated. However, the peaks were insensitive to temperature. The fabrication and advantages of our novel wavelength-encoded temperature-independent strain sensor compared with other optical fiber strain sensors are discussed.

Microstructured optical fiber coated with thin films for gas and chemical sensing

We propose the use of tapered microstructured fibers with collapsed air-holes coated with thin layers for gas sensing. The collapsing of the holes allows having access to the evanescent fields which can be absorbed or attenuated with gas-permeable thin films. On the other hand, a section of the holey fiber is transformed into a solid multimode fiber. The beating between the multiple modes of the latter makes the transmission spectra of the device to exhibit an oscillatory pattern. This evanescent-fields-plus-modal-interferometer structure may offer interesting properties for gas and chemical sensing. As an example we demonstrate a hydrogen sensor.

High-temperature sensing with tapers made of microstructured optical fiber

We report a simple and compact wavelength-encoded high-temperature sensor. It consists of a microstructured silica fiber taper with collapsed air holes in the waist. The transmission spectra of the taper exhibits a series of interference peaks owing to the beating between several modes of the solid taper waist. The interference peaks shift to longer wavelengths as the temperature increases from 200degC to 1000degC. The sensor exhibits a linear response and can be operated with different wavelengths which makes it attractive for diverse applications

Low-Loss Photonic Crystal Fiber Interferometers for Sensor Networks

This work addresses important issues of photonic crystal fiber (PCF) interferometers built by fusion splicing: high insertion loss, low mechanical strength, and complex multiplexing schemes. We have found that by decreasing the length of the collapsed region in these interferometers, the overall insertion losses diminish (down to 0.7 dB) without compromising their performance and mechanical strength. To multiplex such interferometers, we have used the frequency-division-multiplexing technique combined with a simple fast Fourier transform demodulation method. To avoid crosstalk between the interferometers, we have calculated the optimal relationship between their periods. The results reported here may allow the development of functional and competitive PCF devices or PCF-based sensor networks and can be adapted to multiplex any other optical fiber sensors that exhibit sinusoidal patterns.

Large-mode-area holey fibers with a few air channels in cladding: modeling and experimental investigation of the modal properties

Large-mode-area (LMA) silica holey fibers (HFs) are investigated both theoretically and experimentally with special attention paid to the effect of a limited number of air channels in the cladding on the main modal characteristics of the fibers. We applied the method of integral equations to model the LMA HF modes, and the results of our calculations are compared with the experimental data obtained for the so-called large-hole–large-spacing silica HFs. The effect of the relative holes’ diameter in the case of a few layers in the cladding on the LMA HF properties is addressed in detail because this parameter basically determines the limits of single-mode waveguide operation and transmission loss of the fabricated LMA HFs.

Capillary refractometer integrated in a microfluidic configuration

We propose a microfluidic method to measure the refractive index of liquids. This method is based on the dynamic focusing by a capillary when liquids with different refractive indexes are inserted into it. Fabrication of such a refractometer has been done by encapsulating two fibers and a capillary. A calibration method is proposed.

Photonic crystal fiber microtaper supporting two selective higher-order modes with high sensitivity to gas molecules

A photonic crystal fiber consisting of three rings of air holes was tapered down to 3–5μm. The voids of the fiber were collapsed so a solid microtaper was formed. In this microtaper two selective higher-order modes propagate and interfere. This makes the transmission of the taper to exhibit a sinusoidal pattern with subnanometric width fringes. It was found that the device was highly sensitive to gas molecules. The latter is attributed to surface refractive index changes, number of molecules enveloping the taper, and high sensitivity of the modes participating in the interference.