Mode Cutoff Wavelength Research Articles

Single optical microfiber enabled tactile sensor for simultaneous temperature and pressure measurement

The ability to sense heat and touch is essential for healthcare, robotics, and human–machine interfaces. By taking advantage of the engineerable waveguiding properties, we design and fabricate a flexible optical microfiber sensor for simultaneous temperature and pressure measurement based on theoretical calculation. The sensor exhibits a high temperature sensitivity of 1.2 nm/°C by measuring the shift of a high-order mode cutoff wavelength in the short-wavelength range. In the case of pressure sensing, the sensor shows a sensitivity of 4.5% per kilopascal with a fast temporal frequency response of 1000 Hz owing to the strong evanescent wave guided outside the microfiber. The cross talk is negligible because the temperature and pressure signals are measured at different wavelengths based on different mechanisms. The properties of fast temporal response, high temperature, and pressure sensitivity enable the sensor for real-time skin temperature and wrist pulse measurements, which is critical to the accurate analysis of pulse waveforms. We believe the sensor will have great potential in wearable optical devices ranging from healthcare to humanoid robots.

Angstrom-precise fabrication of surface nanoscale axial photonics (SNAP) microresonators with a flame

We demonstrate the fabrication of surface nanoscale axial photonics bottle microresonators with angstrom precision using a flame. We observe strongly unscalable behavior of the whispering gallery mode cutoff wavelengths with different radial quantum numbers along the fibre length.

Calculation of Transmission Characteristics of Shielded Microstrip Lines Filled with Anisotropic Left-Handed and Right-Handed Materials

In this paper, the edge-based finite element formula for calculating the transmission characteristics of shielded microstrip lines filled with anisotropic materials with magnetic field as working variable is derived in detail. The filling materials include anisotropic left-handed materials and anisotropic right-handed materials, and the transmission characteristics include dominant mode cutoff wavelength and electric field structure. We mainly take Rectangular-shaped, V-shaped and Trapezoidal-shaped shielded microstrip lines as examples to calculate the transmission characteristics. The formulas and calculation examples derived in this paper have strong guiding significance for the application of anisotropic left-handed and right-handed materials in inhomogeneous transmission lines, which will further expand the use of shielded microstrip lines in optical devices such as electro-optic waveguide modulators.

Two-step manufacturing of hundreds of meter-long silicon micrometer-size core optical fibers with less than 0.2 dB/cm background losses

This work reports on the fabrication and the characterization of hybrid optical fibers with silicon core and silica cladding. Adopting a two-step manufacturing technique derived from the stack-and-draw method, silicon-core fibers with core dimensions ranging from about 0.8 μm to 3.5 μm have been successively drawn into hundreds of meter-long fibers. A 3.3 μm diameter core fiber has been more extensively characterized and background losses for this as-drawn fiber are less than 0.2 dB/cm between 1250 nm and 1650 nm, with a minimum of 0.12 dB/cm around 1600 nm. The crystalline state of the core and the limited impact of oxygen contamination were confirmed by Raman scattering, x-ray diffraction, HR-STEM, and ToF-SIMS analysis. Transmission peaks associated with specific modal distributions are evidenced under certain injection conditions and their positions are shown to be in good accordance with mode cut-off wavelengths of a step-index silicon-core fiber.

Discoveries and Explorations of Mode Splitting Phenomenon in Lossy Dielectric Waveguide

We discovered that a specific transmission mode in the fiber waveguide will split into two modes at near cut-off conditions when the fiber is coated with lossy dielectric nanofilms with higher refractive index. One of the two splitting modes is high lossy while the other is slightly lossy. We defined the “mode splitting coefficient” to describe the degree of mode splitting. We found that the biggest mode splitting coefficient was obtained at the mode cut-off wavelength using finite element method. Finally, we put forward an explanation towards the mode splitting phenomenon and expounded the relationship between the mode splitting and mode coupling.

Dielectric-loaded black phosphorus surface plasmon polariton waveguides.

By using the effective-index method (EIM) and the finite element methods (FEM), a surface plasmon polariton (SPP) waveguide structured by a dielectric ridge placed on monolayer black phosphorus is proposed and analyzed in the infrared spectral region. It is found that the strong anisotropic dispersion of the black phosphorus (BP) gives rise to direction-dependent waveguide modes in a dielectric-loaded black phosphorus waveguide (DLBPW). The effective mode index, propagation loss and cutoff wavelength of higher order modes are investigated along the armchair (AC) and the zigzag (ZZ) directions of the black phosphorus. Moreover, the propagation characteristics of single-mode are investigated for different widths of the dielectric ridge and different polarization directions of the black phosphorus. Via tuning the carrier density, the electromagnetic field propagation features can be effectively modified. Also, the coupling effect by adding more dielectric bridges can tune the propagation properties. These results will lead to great applications in black phosphorus-based optical integrated devices.

Spun-Related Effects on Optical Properties of Spun Silica Optical Fibers

Spun-related effects on optical properties of silica optical fibers have been investigated experimentally. In addition to the previously known spun effects on polarization mode dispersion (PMD), we observed previously unknown spun-related effects on mode field diameter (MFD), cutoff wavelength and Verdet constant. These effects are significant at highly spun (short pitch length) fibers which are draw at high rotation rate and low drawing speed. By fabricating and testing spun fibers of varying pitch lengths, we found that MFD, cutoff wavelength and PMD all decrease as the pitch length decreases, while the fiber loss increases significantly when the pitch length is lower than 1.5 mm. We have also investigated the spun and annealing effects on Verdet constant of spun fibers. Our experimental results reveal that, by increasing the spun rate (i.e., decreasing the spun pitch length), the Verdet constant is increased appreciably. One relevant finding is that the increase of Verdet constant of spun fibers after annealing is inversely proportional to the pitch length. The overall Verdet constant increase, due to spun and annealing processes, can reach about 4.5% at 1550 nm wavelength in a spun fiber with 1.0 mm pitch.

Acoustical mechanism for the extraordinary sound transmission through subwavelength apertures

An acoustical theory is developed for sound transmitting through subwavelength apertures. We show that the excitation of evanescent high-order modes induces, on each end of an aperture (either a slit or a hole), an additional acoustical reactance, which is singular as incident wavelength approaches one of cutoff wavelengths of high modes. The anomaly of the induced reactance greatly changes the resonant behaviors of the aperture, and makes the conjugate impedance matching possible at a wavelength slightly longer than the cutoff, thus leading to the extraordinary full transmission.

Mode field diameter and cut-off wavelength measurements of single mode optical fiber standards used in OTDR calibrations

This paper describes determination of the mode field diameter (MFD), and the cut-off wavelength of the single mode optical fiber standards used in OTDR calibrations, which was constructed in Optics Laboratory of National Metrology Institute of Turkey. Measurements of MFD were performed using computer controlled stepper motor unit with far field scanning (FFS) Method. For the same standard fibers, cut-off wavelength measurement was performed employing bend reference method, which is one of the transmitted power techniques. For both measurements, a nitrogen-cooled 5 mm InGaAs radiometer was used to detect optical flux. Detailed uncertainty analyses were presented for the MFD and cut-off measurements. While the total expanded uncertainties in MFD data at 1306.7 nm and 1550 nm were calculated as 0.8% and 1.0% (k=2), respectively, the total expanded uncertainty at determination of cut-off wavelength was found as 0.318% (k=2).

W-type fiber design for application in U- and S-band amplifiers by controlling the LP 01 mode long wavelength cut-off

We propose a novel passive band-pass filtering scheme to obtain a net gain in a band-competing system using a W-type fiber waveguide, slicing a shorter wavelength gain band out of a given stimulated emission cross-section. By controlling the location of the LP 01 mode cut-off, fiber design parameters are presented for obtaining a U-band gain from Tm ions and S-band from Er ions. The tolerance of the LP 01 mode cut-off wavelength and the accompanying bending loss are theoretically analyzed in terms of waveguide parameters.

Wideband tunable fiber short-pass filter based on side-polished fiber with dispersive polymer overlay

It is known that dispersive fiber has an LP01 mode cutoff wavelength that acts as a wavelength filter. With a dispersive polysiloxane polymer overlay on a side-polished single-mode fiber, an in-line tunable fiber short-pass filter with a tuning range of approximately 400 nm (1250-1650 nm) and a temperature variation of 15 degrees C was demonstrated. The rejection efficiency was greater than 50 dB, whereas the insertion and polarization-dependent losses were below 0.26 and 0.09 dB, respectively.

Ridged waveguide structures with improved fundamental mode cutoff wavelength and bandwidth characteristics

A new circular waveguide loaded with two T-shaped septa and a new triple ridge loaded trough rectangular waveguide are proposed and theoretically analyzed using the Finite Element Method. Numerical results are presented demonstrating that these structures offer a significant increase in both fundamental mode cutoff wavelength and bandwidth when compared to various unloaded and loaded waveguides. © 2002 Wiley Periodicals, Inc. Int J RF and Microwave CAE 12: 190–197, 2002.

Waveguiding properties of holey fibres and effective-Vmodel

The authors examine the waveguiding properties of holey optical fibres made with circular silica tubes. The effective index of the fundamental mode and the first higher-order mode cutoff wavelength have been obtained for different fibres. The effective-V model is found to be unsuitable in describing the guiding properties of such fibres.

Determination of mode-cutoff wavelengths and refractive-index profile of planar optical waveguides with a photon scanning tunneling microscope.

A method, using the photon scanning tunneling microscope, is proposed to measure the mode cutoff wavelengths of a planar optical waveguide with an arbitrary refractive index profile. From the measured values of the cutoff wavelengths, the characteristic thickness and the maximum refractive index of the guiding film are determined. Measurements, performed on a planar waveguide with a complementary error function profile, are in reasonably good agreement with the theoretical calculations.

Investigation of the microbending sensitivity of fibers

The microbending sensitivity of fibers was calculated as a function of the MAC value, which is the quotient of mode field diameter and cut-off wavelength. Two different methods, the expandable drum test and the sieve test, were used to simulate the additional losses due to microbending in fiber-optic cables: The theoretical and experimental results generally show an increase of the microbending sensitivity with increasing MAC value. In addition, the microbending loss of fibers strongly depends on the material and structure of the coating. Measurements of fibers in real cables confirmed the predicted correlation between attenuation and MAC value. >

The bending performance of single mode fibers with the similar mode field diameter and cutoff wavelength

Abstract Measurements of bending induced losses in matched‐cladding and depressed‐cladding single‐mode fibers with similar 1300‐nm mode field diameters and cutoff wavelengths are reported. It is found that the depressed‐cladding fiber demonstrates better microbending and macrobending performances than the matched‐cladding fiber.

Measurements on birefringent fibres: COST 217 interlaboratory measurement campaign

An interlaboratory comparison of measurements on three types of commercially available polarisation maintaining fibres was performed in the framework of COST 217. The obtained accuracy and reproducibility for the parameters as the mode field diameter, cutoff wavelength and chromatic dispersion was in the same range for these high birefringent fibres as for the conventional circular single mode fibres. Two setups were tested for the simultaneous determination of the birefringence and modal birefringence. The results characterising the polarisation properties of the fibres are presented in a 6-term Sellmeier expansion of the refractive index.

Characterization of asymmetric graded-index planar optical waveguides from the knowledge of TE/sub 0/-TE/sub 1/ mode cutoff wavelengths

The authors have proposed (1991) a simple method for predicting the index profile parameter (the profile exponent q in case of a power law profile or the aspect ratio S in case of trapezoidal index profile) of a graded-index optical fiber which is single moded in the 1.3-1.55 mu m wavelength range from a measurement of the LP/sub 11/ and LP/sub 02/ cutoff wavelengths. They extend the method with appropriate modification to determine the asymmetry parameter sigma , the maximum refractive index n/sub f/ and the characteristic thickness d of the guiding layer of a few-moded graded-index asymmetric planar optical waveguide from a measurement of the TE/sub 0/ and TE/sub 1/ cutoff wavelengths. The method is simple and can give firsthand information about these parameters with reasonably good accuracy.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A Müller-Stokes Description of Polarization-mode Transformation in Uniformly Perturbed Optical Fibres

Abstract On the basis of coupled-mode equations Müller matrices describing the polarization-mode transformation of twofold and fourfold degenerate LP-modes in the quasi-monochromatic case have been derived. Single-mode, two-mode and multimode regimes of operation have been studied. Improved polarization holding in W-type elliptical-core multimode optical fibres has been observed. It has been shown that the LP11 mode cut-off wavelength λC can be determined by measuring the wavelength dependence of the relative cross-coupled power.

Analysis of dielectric-loaded waveguide

The calculation of eigenvalues including propagation constants and cutoff wavelengths of longitudinal section electric and magnetic modes of different orders (LSE/sub nm/ and LSM/sub nm/ modes) in homogeneous and inhomogeneous lossless dielectric-slab-loaded rectangular waveguides using a modified variation-iteration method is presented. The initial eigenvalues used in the iteration are selected on the basis of a physical consideration. As shown in numerical examples, this method is very efficient for finding all the eigenvalues of LSE/sub nm/ and LSM/sub nm/ modes by a given free-space propagation constant calculation and a given lower bound of the cutoff wavelength for the cutoff wavelength calculation. In addition, the importance of the adaptive update factor in preventing the possibility of missing existing eigenvalues is also discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>