Standard Single-mode Optical Fiber Research Articles

Mach-Zehnder Interferometer Biochemical Sensor Based on Silicon-on-Insulator Rib Waveguide with Large Cross Section.

A high-sensitivity Mach-Zehnder interferometer (MZI) biochemical sensing platform based on Silicon-in-insulator (SOI) rib waveguide with large cross section is proposed in this paper. Based on the analyses of the evanescent field intensity, the mode polarization and cross section dimensions of the SOI rib waveguide are optimized through finite difference method (FDM) simulation. To realize high-resolution MZI read-out configuration based on the SOI rib waveguide, medium-filled trenches are employed and their performances are simulated through two-dimensional finite-difference-time domain (2D-FDTD) method. With the fundamental EH-polarized mode of the SOI rib waveguide with a total rib height of 10 μm, an outside rib height of 5 μm and a rib width of 2.5 μm at the operating wavelength of 1550 nm, when the length of the sensitive window in the MZI configuration is 10 mm, a homogeneous sensitivity of 7296.6%/refractive index unit (RIU) is obtained. Supposing the resolutions of the photoelectric detectors connected to the output ports are 0.2%, the MZI sensor can achieve a detection limit of 2.74 × 10−6 RIU. Due to high coupling efficiency of SOI rib waveguide with large cross section with standard single-mode glass optical fiber, the proposed MZI sensing platform can be conveniently integrated with optical fiber communication systems and (opto-) electronic systems, and therefore has the potential to realize remote sensing, in situ real-time detecting, and possible applications in the internet of things.

Femtosecond laser inscription of asymmetric directional couplers for in-fiber optical taps and fiber cladding photonics.

Precise alignment of femtosecond laser tracks in standard single mode optical fiber is shown to enable controllable optical tapping of the fiber core waveguide light with fiber cladding photonic circuits. Asymmetric directional couplers are presented with tunable coupling ratios up to 62% and bandwidths up to 300 nm at telecommunication wavelengths. Real-time fiber monitoring during laser writing permitted a means of controlling the coupler length to compensate for micron-scale alignment errors and to facilitate tailored design of coupling ratio, spectral bandwidth and polarization properties. Laser induced waveguide birefringence was harnessed for polarization dependent coupling that led to the formation of in-fiber polarization-selective taps with 32 dB extinction ratio. This technology enables the interconnection of light propagating in pre-existing waveguides with laser-formed devices, thereby opening a new practical direction for the three-dimensional integration of optical devices in the cladding of optical fibers and planar lightwave circuits.

A robust high refractive index sensitivity fiber Mach–Zehnder interferometer fabricated by femtosecond laser machining and chemical etching

A fiberized refractive index (RI) Mach–Zehnder interferometer (MZI) based on a micro V-shaped slot in fiber core is fabricated in a standard single mode optical fiber by femtosecond laser machining and chemical etching. The interference fringe of the MZI would shift with the variation of the ambient RI. The experimental results show that the RI sensitivity for the sensor is about −104nm/RIU (refractive index unit) within the RI range between 1.332 and 1.352. Its robust structure and high sensitivity will have attractive potential application in chemical, biological and environmental monitoring.

Towards integration of a liquid-filled fiber capillary for supercontinuum generation in the 1.2-2.4 μm range.

We demonstrate supercontinuum generation in unspliced as well as in integrated CS(2)-filled capillary fibers at different pump wavelengths of 1030 nm, 1510 nm, and 1685 nm. A novel method for splicing a liquid-filled capillary fiber to a standard single-mode optical fiber is presented. This method is based on mechanical splicing using a direct-laser written polymer ferrule using a femtosecond two-photon polymerization process. We maintain mostly single-mode operation despite the multi-mode capability of the liquid-filled capillaries. The generated supercontinua exhibit a spectral width of over 1200 nm and 1000 nm for core diameters of 5 μm and 10 μm, respectively. This is an increase of more than 50 percent compared to previously reported values in the literature due to improved dispersion properties of the capillaries.

Enhanced sensitivity high temperature optical fiber FPI sensor created with the catastrophic fuse effect

ABSTRACTIn this work, we describe a novel and cost effective approach based on optical fiber microcavities, for sensing high temperature values (up to 1150°C). The proposed sensor is produced by splicing standard single mode optical fibers with fibers destroyed by the catastrophic fuse effect, resulting in a microcavity structure in the fiber core region. These microcavities have a thermal sensitivity of 10.43 ± 0.15 pm °C−1, for temperatures up to 1150°C, which compares well with the sensitivity of Fabry–Perot interferometric sensing cavities but with the advantage of substantially reduced manufacturing costs. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:972–974, 2015

Dependence of dark count rates in superconducting single photon detectors on the filtering effect of standard single mode optical fibers

We found that background radiation limits the dark count rates of superconducting single photon detectors coupled to standard single mode optical fibers to a minimum level when the source temperature of the photons is close to 300 K. We measured this level to be 103 cps, which was confirmed by a theoretical analysis of the background radiation influence. We also investigated the filtering-effect of cooled single mode optical fibers with different bending diameters and showed that for superconducting photon receivers with operating wavelengths below 2 µm the minimum dark count rate can be significantly decreased down to 0.1 cps.

Long-range surface plasmons on gold-coated single-mode fibers

A standard single-mode optical fiber, coated with low-index polymer (Cytop), then a thin Au sheath, immersed in fluid, is proposed as a structure for optical (bio)chemical sensing. The highest-order EH1m cladding modes are found to couple strongly to long- or short-range surface plasmons on the Au sheath, forming coupled modes that are sensitive to the refractive index of the fluid or to a biochemical adlayer formed on the outer surface of the Au sheath. Interrogation of the modes can be achieved with the help of a tilted grating photoinduced into the core of the fiber. We demonstrate experimentally, in this manner, the excitation of these modes, and their use for bulk sensing. Furthermore, negative bulk sensitivity was observed for some leaky modes beyond cutoff.

An optical fiber optofluidic particle aspirator

A fiberized optofluidic particle trapping device based on a micro-slot fabricated in a standard single-mode optical fiber by femtosecond laser micromachining is demonstrated. While fluidic convective motions move a large number of microparticles into the slot, the optical mode propagating in the nearby optical fiber core is exploited to trap and propel the particles inside the slot, thereby facilitating their collection at one of the slot extremities. The combined effect of fluidic and optical trapping allows for the collection of particles from as far as 60 μm away from the optical trap. Application to particle and live cell trapping and propulsion is demonstrated.

Analysis of surface plasmon resonance in bent single-mode waveguides with metal-coated cladding by eigenmode expansion method.

A numerical study is presented of surface plasmon waves excitation in a metal film applied to the cladding of a standard bent single-mode optical fiber. It was shown that by adjusting the bend radius and metal film thickness one can achieve effective coupling between the fiber fundamental mode and symmetric surface plasmon mode through the intermediary of whispering gallery modes supported by the cladding of the bent fiber. This effect is demonstrated to allow for refractometric measurement both in the wavelength and intensity-modulated regimes with a resolution of up to 10⁻⁸ RIU. Usage of standard noise reduction techniques for intensity-modulated optical signals promises further increase in accuracy.

Cryogenic Temperature Measurement Using Rayleigh Backscattering Spectra Shift by OFDR

We present a method to realize temperature variation measurement in the cryogenic environment (e.g., at 76 K) using Rayleigh backscattering spectra (RBS) shift in standard single mode optical fiber by optical frequency-domain reflectometry. By analyzing the relationship of effective sensing segment size of fiber (or sensing spatial resolution), minimal measurable temperature variation, and temperature response of RBS shift, we found minimal measurable temperature variation in the cryogenic environment can be improved by increasing effective sensing segment size. Our experiments show that at a relatively high temperature (e.g., above 195 K), minimal measurable temperature variation is 0.21 K with an effective sensing segment size of 8 cm. When the temperature is very low (e.g., at 76 K), minimal measurable temperature variation can still maintain 0.34 K by simply increasing the effective sensing segment size of fiber to 48 cm.

Surface plasmon polaritons in standard optical fibres with a metallised cladding

Abstract A numerical study is presented of a novel approach to fibre optic SPR-sensor development for biosensing applications. The proposed technique is based on a standard SMF-28 type bent single-mode optical fibre with a thin metal film applied to its optical cladding. It was shown that by adjusting the curvature radius and the metal film thickness, one can achieve effective coupling between the fundamental mode of the fibre and the surface plasmon mode supported by the metal/surrounding medium interface through the meditation of whispering gallery modes propagating along the bent inner surface of the fibre cladding. This effect is demonstrated to enable refractometric measurements, both in the wavelength and in the intensity-modulated regimes, with a resolution of up to 10-8 RIU. The use of standard noise reduction techniques for intensity-modulated optical signals promises further increase in accuracy.

Double-Layer Silicon Photonic Crystal Fiber-Tip Temperature Sensors

This letter describes the manufacture and performance of a monolithic double-layer silicon photonic crystal temperature sensor. The sensor is fabricated on standard silicon wafers using oxide passivation and a combination of isotropic and anisotropic etching, and mounted on the facet of a standard single-mode optical fiber using template-assisted epoxy bonding. The double-layer configuration leads to coupling of the guided resonances in the two photonic crystals and enables sharper resonances and consequently higher temperature sensitivity and better detection limit (0.011 °C) than the single-layer counterpart. We experimentally demonstrate that the sensor has a twofold increased temperature sensitivity in terms of reflectivity change at a fixed wavelength (-0.00576/°C), and report on electromagnetic simulations explaining the enhanced sensor operation. The photonic crystal fabrication method and template-assisted bonding enable batch-fabrication of the sensors. Their small size, robust construction, and fiber interface make the sensors promising for numerous applications, including sensing in harsh environments.

Overview of Stimulated Brillouin Scattering Effect and Various Types of Method to Eliminate this Effect

Stimulated Brillouin scattering (SBS) is a resonant nonlinear optical interaction with the material that results in transmitted light being scattered back towards the input. Although high power lasers are available to overcome the intrinsic loss of standard single mode optical transmission fibers (0.2 to 0.3 dB/km) but SBS places an upper limit on the optical power that can be transmitted through the link. Usually, SBS normally has a lower threshold power (≤1.4 mW) than other nonlinear effects. In this paper we see the SBS effect in optical fiber transmission system and different types of methods to eliminate this effect. Here we propose two new approaches to eliminate this effect.

Locally pressed photonic crystal fiber interferometer for multiparameter sensing.

A mode interferometer consisting of a short section of photonic crystal fiber (PCF) fusion spliced to a standard single-mode optical fiber with localized perturbations is proposed for multiparameter sensing. In this sensing configuration, the parameter being sensed changes the visibility (an absolute parameter) of the interference pattern and also causes a shift (a relative parameter) to the interference pattern. To achieve this dual effect, a portion of the PCF is squeezed on localized regions with a serrated mechanical piece. In this manner, we introduce attenuation losses and effective refractive index changes to the interfering modes, hence, visibility changes and a shift to the interference pattern. Our device is suitable for monitoring diverse physical parameters, such as weight, lateral force, pressure, load, etc., with the advantage that compensation to temperature or power fluctuations is not required. Moreover, the sensor sensitivity can be adjusted in a simple manner.

Fabricating optical fibre-top cantilevers for temperature sensing

In this paper, we propose techniques to fabricate micro-cantilevers onto the end of standard single mode optical fibres using a combination of picosecond laser machining and focused ion beam milling techniques and demonstrate their use as temperature sensors. Using this approach the cantilever can be pre-aligned with the core of the fibre during fabrication, therefore offering a stable and straightforward means of optically addressing the cantilever. The cantilever is designed to measure deflection over a range of 10 µm using a simple readout technique. A phase recovery algorithm is employed to reduce the interrogation error to around 2–3 nm. Finally, a temperature cycling experiment demonstrates that the cantilever could be used as a temperature sensor from room temperature to 500 °C with an average rms temperature error from 20 °C to 500 °C of ∼±1.4 °C.

Simple technique for integrating compact silicon devices within optical fibers

In this work, we present a simple fabrication process enabling the integration of a subwavelength amorphous silicon layer inside optical fibers by means of the arc discharge technique. To assess our method, we have fabricated a compact in-line Fabry-Perot interferometer consisting of a thin (<1 μm) a-Si:H layer completely embedded within a standard single-mode optical fiber. The device exhibits low loss (1.3 dB) and high interference fringe visibility (~80%) both in reflection and transmission, due to the high refractive index contrast between silica and a-Si:H. A high linear temperature sensitivity up to 106 pm/°C is demonstrated in the range 120°C-400°C. The proposed interferometer is attractive for point monitoring applications as well as for ultrahigh-temperature sensing in harsh environments.

The Usability Analysis of Different Standard Single-Mode Optical Fibers and Its Installation Methods for the Interferometric Measurements

With optical fibers we are able to measure a variety of physical quantities. Optical fiber sensors sensitive to the change of the light phase, so-called interferometers referred in this article are one of the most sensitive sensors. Because we are able to detect phase changes with extreme precision, these sensors are thus suitable for demanding applications, where cost is not the main requirement. We have used the Mach-Zehnder configuration. The paper deals with the usage of different types of standard single-mode optical fibers in the civil engineering as an integrated acoustic sensor. Further experiments are focused on the different types of fiber installation methods, such as placement in the mounting foam, into the polystyrene or attachment onto the wooden surface and their effect on the measurements. Through the repeated measurements of harmonic frequencies were obtained information about the usable frequency range and sensitivity of the particular arrangement. Measurement was performed for both cases, where the specific type of fiber or specifically installed fiber was used as the measurement or as the reference. The final evaluation is based both on the experience gained during measurements and also using the statistical calculations.

High-refractive-index transparent coatings enhance the optical fiber cladding modes refractometric sensitivity

The high order cladding modes of standard single mode optical fiber appear in quasi-degenerate pairs corresponding to mostly radially or mostly azimuthally polarized light. In this work, we demonstrate that, in the presence of a high-refractive-index coating surrounding the fiber outer surface, the wavelength spacing between the orthogonally polarized cladding modes families can be drastically enhanced. This behavior can be advantageously exploited for refractometric sensing purposes. For this, we make use of tilted fiber Bragg gratings (TFBGs) as spectral combs to excite the orthogonally polarized cladding modes families separately. TFBGs were coated with a nanometer-scale transparent thin film characterized by a refractive index value close to 1.9, well higher than the one of pure silica. This coating brings two important assets: an ~8-fold increase in refractometric sensitivity is obtained in comparison to bare TFBGs while the sensitivity is extended to surrounding refractive index (SRI) values above 1.45.

A chemical vapor sensor based on Rayleigh scattering effect in simplified hollow-core photonic crystal fibers

A novel optical fiber sensor for minor chemical vapor content detecting, based on Rayleigh scattering effect in simplified hollow-core photonic crystal fiber (HC-PCF), is proposed in this paper. Both ends of the simplified HC-PCF are aligned with standard single-mode optical fibers without splicing, leaving a very short air gap to allow molecules diffusing. As the concentration of volatile organic compounds (VOCs) in a chamber increases, molecules come into the air holes of the simplified HC-PCF so that the Rayleigh scattering is excited, resulting in an intensity loss of transmission light. We can detect the minor change of VOC content by monitoring the output transmission intensity using an optical power meter. The experimental results show that the ethanol concentration sensitivity is ~0.022dB/ppm, when a ~5.1cm long simplified HC-PCF is used. The sensitivity will be further improved when a longer simplified HC-PCF is used. When an optical power meter with 0.01dBm resolution is used, the ethanol concentration's resolution can reach ~0.45ppm.

Fiber-based pulse stretcher for narrowband terahertz pulse generation with a chirped-pulse beating method

We theoretically show that it is possible to generate chirp-free terahertz (THz) pulses with a chirped-pulse beating method by using an optical fiber as a pulse stretcher. Proper choices of the core radius and the dopant fraction of the core material of a step-index single-mode optical fiber eliminate the third-order spectral phase of the fiber, thus giving the pump laser pulse a purely linear chirp. We also show that even a standard commercial single-mode optical fiber can give THz pulses of lower chirp than the lower limit for a grating pair. We perform experiments to verify our theory.