Tunable photonic nanojet achieved using a core–shell microcylinder with nematic liquid crystal

A tunable photonic nanojet achieved using a core–shell microcylinder with nematic liquid crystal is reported. The core–shell microcylinder can be obtained by the infiltration of liquid crystal into the air core of a microcylinder. The refractive indices of the liquid crystals can be changed by rotating the directors of the liquid crystals. Therefore, we were able to control the flow direction of the photonic nanojet in two-dimensional core–shell microcylinder structures. Using high resolution finite-difference time-domain simulation, we demonstrate that the photonic nanojet can be continuously tuned in the core–shell microcylinder. The horizontal and vertical shifts of photonic nanojet depend strongly on the director of the liquid crystals. Such a mechanism of nanojet adjustment should open up a new application for using visible light to detect nanoparticles, optical gratings, and single molecules with subwavelength spatial resolution.     

A high sensitivity refractive index sensor based on photonic crystal fibre Mach–Zehnder interferometer

A compact and high sensitivity refractive index sensor based on a photonic crystal fibre Mach–Zehnder mode–mode interferometer is proposed. The sensing part is formed by in fibre SMF-PCF-SMF structure (SMF: single-mode fibre; PCF: photonic crystal fibre) using fusion splicing method. The fully collapse air holes of photonic crystal fibre make coupling of fibre core and cladding mode in the splicing collapse region which establish a Mach–Zehnder interferometer. The Mach–Zehnder interferometers with different photonic crystal fibre length are fabricated to investigate refractive index sensing characteristics. The refractive index measuring sensitivity can reach 224.2 nm/RIU (RIU: Refractive Index Unit) with a length of PCF L = 4 cm, experimentally. The proposed refractive index sensor is attractive due to its simple production process, compact size and high sensitivity.     

Tunable ring-coupled Mach–Zehnder interferometer based on lithium niobate

The fabrication and characterization are reported of a Fano resonance-based electro-optically tunable ring resonator-coupled Mach–Zehnder interferometer device based on a chalcogenide–lithium niobate hybrid waveguide system. The experiments reveal inherent asymmetric lineshapes that can be flipped to a near symmetrical resonance by applying a dc voltage of ~10 V across the electrode at the MZI non-resonator arm. Further increase in voltage yields the reverse of initial asymmetry. The optical filter-based transfer-matrix model easily explains the experimental data and indicates ways to further enhance the usability of such architecture.     

Implementation of high speed optical universal logic gates using the electro-optic effect-based Mach–Zehnder interferometer structures

The universal logic gates are the most important logic gates responsible for optimized design of different types of complex digital logic circuits. It is of great interest to implement the function of universal logic gates such as NAND and NOR logic gates using the concepts of electro-optic effect. The smart use of electro-optic effect can provide very effective optical power switching devices. The implementation of universal logic gates operation in the optical domain can improve the performance of the devices and includes the advantages of the optical communication system. The proper configuration of Mach–Zehnder interferometer working on the principle of electro-optic effect can provide the optical responses equivalent to the NAND and NOR logic gates. The proposed devices can be analyzed to check the various performance affecting parameters in order to specify the physical parameters.     

Filters based on spoof surface plasmon polaritons composed of planar Mach–Zehnder interferometer

Abstract

Filter characteristics of a planar Mach–Zehnder interferometer (MZI) structure composed of periodically thin corrugated metal films were studied here. From theoretical simulation, spoof surface plasmon polaritons can propagate along the periodically thin corrugated metal films in microwave frequency, which can be excited by a coplanar waveguide. When the two arms of the MZI have the same length with the angle between them being 60°, the MZI structure has a very wide bandwidth with 8.6 GHz. By changing the length of one of the interference arms, a novel low-pass filter based on the planar MZI structure with two notched frequencies was proposed. The proposed planar structure can find potential applications in developing surface wave devices in integrated microwave circuits and systems.     

Spatially resolved phase objects using Mach–Zehnder interferometry

Phase characterization with a good spatial resolution is crucial for focused beams in nonlinear media. The phase-shifting interferometry technique, using the least-squares error criterion for several interferograms, is implemented using a reflective spatial light modulator (SLM). The method provides a convenient calibration for any phase-shift steps. The reliability of the proposed method is checked by direct comparison with results obtained by the Fourier transform method as well as using a previously characterized circular phase object.     

Switchable triple-wavelength thulium-doped fibre laser based on a Mach–Zehnder interferometer and fibre ring filter

A switchable triple-wavelength thulium-doped fibre laser based on an all-fibre Mach–Zehnder interferometer and fibre ring filter with a polarization-maintaining fibre is proposed and experimentally demonstrated. In the proposed fibre laser, a Mach–Zehnder interferometer comprising two 1 × 2 optical couplers is inserted into the optical cavity to produce the comb filter effect. The fibre ring filter comprises two optical couplers with a 3:7 splitting ratio and a 2-m-long polarization-maintaining fibre to improve lasing stability. Single-wavelength lasing can be tuned continuously from 1864.4 to 1884.5 nm, and five different modes of dual-wavelength and switchable triple-wavelength lasers can be realized by changing the polarization state. The signal-to-noise ratios of all lasers are more than 33 dB. The maximum power fluctuations and wavelength variations are less than 1.5 dB and 0.3 nm at room temperature, respectively, and the 3 dB bandwidth is less than 0.2 nm. The results demonstrate that stable and switchable single- or dual-wavelength lasers can be generated using the designed fibre laser.     

All-fibre Mach–Zehnder interferometer based on seven-core and coreless fibres for generating stable wavelength-switchable laser

In order to realize a wavelength-tuneable fibre-laser output, a ring-cavity erbium-doped fibre laser based on an all-fibre Mach–Zehnder interferometer (MZI) is proposed and experimentally tested. The MZI consists of a single-mode fibre, two segments of coreless fibre, and a seven-core fibre. For the proposed fibre laser, the length of the gain medium is 4?m and the lasing threshold is 75?mW. By adjusting the loss of the laser cavity, switchable single-wavelength laser emission is realized across the range of 1527.6–1549.9?nm and the wavelength interval is less than 2.4?nm; the peak power difference of each lasing wavelength is less than 7.9?dB. Tuneable dual- and three-wavelength laser outputs were obtained by adjusting the polarization controller. The 3-dB linewidth was less than 0.57?nm. The single- and dual-wavelength laser output power fluctuations were less than 1.4 and 1.7?dB, respectively, when monitored over a period of 30?min.     

Analysis of the dual-parallel Mach–Zehnder modulator-based equivalent phase modulation

In a dual polarization quadrature phase shift keyed (DP-QPSK) modulator, it is desired that one dual-parallel Mach–Zehnder (MZ) modulator in it is operated as a phase modulator (PM) to achieve some functions in conjunction with the other dual-parallel MZ modulator. Equivalent phase modulation is realized by controlling the bias points of a dual-parallel MZ modulator. If the parameters are accurately set, it functions as a true PM. However, the amplitude imbalance and the different arrival time of the two RF signals applied to the dual-parallel MZ modulator, and the deviations of the three bias points in the dual-parallel MZ modulator influence the performance of the equivalent phase modulator (e-PM). In this paper, we study the influences of these non-ideal factors on the performance of the e-PM. The results show important guidelines for significance for the further use of the dual-parallel MZ modulator-based equivalent phase modulation in a DP-QPSK modulator.     

L-Band multi-wavelength erbium-doped fibre laser based on non-linear optical loop mirror and dual-channel Mach–Zehnder interferometer

In this letter, we propose and demonstrate an L-Band linear cavity tunable multi-wavelength erbium-doped fibre laser based on non-linear optical loop mirror (NOLM) and dual-channel Mach–Zehnder interferometer (MZI) . The NOLM provides the intensity-dependent transmissivity, can effectively alleviate the mode competition and beating caused by the homogeneous gain broadening, so that the multi-wavelength lasing can be achieved at room temperature. The dual-channel MZI, configured by linking the two outputs of the single-channel MZI, serves as comb filter. By adjusting the polarization controller in NOLM and pump power, the tunable multi-wavelength output at 1600 nm can be achieved. Moreover, the output stability of the laser has also been accomplished .     

Performance improvement in Mach–Zehnder interferometer-based refractive index sensor using elliptical photonic nanowires

We propose a modified Mach–Zehnder interferometer design based on elliptical silica photonic nanowires. The use of the interferometer as an evanescent field-based refractive index (RI) sensor was numerically investigated. Single-mode operation, maintaining polarization and very high sensitivity, is achieved at short optical wavelengths by simply using elliptical nanowires. The proposed sensor is capable of determining the RI of benzene solutions with different concentrations in water and detecting a RI variation of the order of 10^?6 RI units in only a 1-mm length sensitive area. Extremely high sensitivity of 4.63?rad/μm is achieved using an 800?nm elliptical silica nanowire diameter. The operating wavelengths (λ = 650?nm and 970?nm) were chosen to avoid high water absorption. The sensor is shown to be an alternative solution to small circular-nanowire-based sensor whose core size needs to be significantly reduced below 400?nm to achieve comparable performance.     

Double Imaging Mach–Zehnder Spatial Carrier Digital Shearography

This paper presents a Double Imaging Mach–Zehnder Spatial Carrier Digital Shearography (DIM-SCDS) system. Compared to traditional Spatial Carrier Mach–Zehnder shearography, DIM-SCDS has two advantages: one is that it can adjust shearing amount and spatial carrier frequency independently; the other one is that it can measure a larger area with a shorter working distance. Two pairs of imaging lenses and apertures are placed in the two arms of Mach–Zehnder interferometry, respectively. Shearing amount is adjusted by the mirrors in the two arms, and spatial carrier frequency is determined by the angle between the two apertures when they are mapped to the same optical axis. Shearograms of the object under test are recorded using a CCD. Shearogram phases are calculated as the measurement results. Finally, the performance of DIM-SCDS is proved by experiments.     

A wide-view twisted nematic liquid crystal cell with improved image quality obtained by decreasing γ-curve distortion

Wide-view (WV) film, which was introduced by Fuji Co., has been commercialized to block light leakage of twisted nematic (TN)-liquid crystal (LC) cells in a dark state when the viewing angles are in the off-axis direction. In this investigation, we designed an optical compensation structure of a TN-LC cell with an improved γ-curve, as well as a viewing angle property in the dark state. Basically, we used a pair of optical films consisting of a positive and a negative A-plate in order to avoid affecting the viewing angle property in the dark state. Then, we optimized the positive and negative A-plate to improve the viewing angle property in the gray levels by calculating polarization variations as a function of the optical axis and the retardation of the pair of the A-plates. From this calculation, we were able to show that the proposed normally white (NW) WV-TN cell exhibits wide viewing angle performance, including good γ-curve stability.     

Modelling nanofiber Mach–Zehnder interferometers for refractive index sensors

In a single-mode silica nanofibre a large amount of the energy of the guided light is in the form of evanescent waves, making it possible to develop a novel sensing element with high sensitivity. Based on theoretical modelling, a highly-sensitive sensor employing a nanofibre-assembled Mach–Zehnder structure is suggested and investigated here. The sensor is used to measure the refractive indices of isopropyl alcohol (IPA) solutions of different concentrations. A phase shift of the guided mode, originating from the change of refractive index of the ambient medium, is obtained. In addition, the important parameters, including sensitivity and detection limit, are also estimated. The results show that Mach–Zehnder interferometric sensor based on nanofibres exhibits the capability of measuring an index variation of ～10^?6. Our simulations are helpful for studying and developing new miniaturised high-performance sensors with high sensitivity.     

Multi-directional shearography based on multiplexed Mach–Zehnder interference system

ABSTRACT

Shearography is only sensitive to deformation in the shearing direction, and the deformation of object defects after loading may occur in multiple directions. This work reports a multi-direction shearography system that uses spatial phase-shift methods to detect the object from multi-shearing directions, effectively avoiding the missed detection of directional defects. A single laser is utilized to illuminate an object, and a single CCD camera records images in the multiplexed Mach–Zehnder interference system. First, the aperture stops in suitable size and location are set to produce different spatial carrier frequencies. Second, the shearing amount is independently adjusted by using different devices. Finally, the Fourier transform method is used to extract the phase information from the frequency domain. This system can be used for nondestructive testing of multi-directional defects and the feasibility of the method is verified by theoretical analysis and experiment.     

Nonlinearity suppression of Mach–Zehnder modulator based on optical carrier processing in radio-over-fiber links

A highly linear transmitter that consists of a dual-drive Mach–Zehnder modulator (DD-MZM), an optical gain, and an optical phase shifter in radio-over-fiber links is proposed and demonstrated by simulation. The optical carrier is split equally with one part driving the DD-MZM, while the other part remaining unmodulated. By properly adjusting the magnitude and phase shift of unmodulated optical carrier, two kinds of main origins of third-order IMD (IMD3) have equal intensity and opposite phase, and cancel each other out. The comparison of the proposed technique and double-sideband modulation by MZM is presented. Simulation results shown that the spurious-free dynamic range of 125.3 dB Hz^2/3 is achieved, which is about 26 dB more than a quadrature biased MZM.     

Self-catalyzed vapor–liquid–solid growth of large-scale single crystal GaN whiskers

Based on self-catalyzed vapor–liquid–solid mechanism, large-scale hexagonal GaN whiskers were synthesized via a two-step reaction of GaS powders with H₂ and NH₃ at 1000 °C. These whiskers were characterized using XRD, SEM, TEM, SAED, HRTEM, and Raman spectroscopy, in which the results obtained show that these GaN whiskers have the single crystal wurtzite structure with width of 20–200 nm and length of several micrometers.     

Miscibility and morphology of poly p-phenylene sulphide–liquid crystal polymer blends

Blends of poly p-phenylene sulphide (PPS) and a liquid crystalline polymer (LCP) were made by two methods: (i) mixing and capillary extrusion (samples A), and (ii) injection moulding (samples B). To study miscibility in the melt and solid states and the resulting morphology, techniques like polarized light optical microscopy, capillary rheometry, dynamic mechanical thermal analysis and scanning electron microscopy with X-ray microanalysis were used. It was observed that the miscibility of the amorphous fractions of both polymers increased with increasing intensity (rates and stresses) of deformational flow (shear and elongational). Samples A had a morphology composed of fibrils of both polymers, but a matrix made of only one polymer i.e. PPS. Samples B had a mainly fibrillar morphology, with no observable matrix, made of both polymers. Formation of pure LCP fibrils was not observed neither in the extruded blends nor in the injection moulded samples. The addition of LCP to PPS improved its mechanical properties. At a molecular level, these blends can be considered to be molecular composites.