Showing papers on "Mach–Zehnder interferometer published in 2022"

In-situ DNA detection with an interferometric-type optical sensor based on tapered exposed core microstructured optical fiber

Abstract: A label-free DNA biosensor based on exposed core microstructured optical fiber for in-situ real-time DNA detection has been presented and experimentally demonstrated. The sensor is fabricated by splicing a section of tapered exposed core fiber (ECF) between two single-mode fibers (SMFs), forming a multimode Mach-Zehnder interferometer (MZI). The ECF design provides the evanescent field with the sensitivity of a micro/nano optical fiber. In this paper, the ECF has a large cladding diameter (160 µm) but a small core (9 µm), and the core of the ECF is further reduced by tapering, which significantly improves the refractive index (RI) sensitivity. The sensor can detect local RI changes that occur on the surface of the optical fiber due to the binding of biomolecules. We immobilized probe DNA (pDNA) on the exposed side of the core to detect the complementary DNA (cDNA), demonstrating use for specific and label-free sensing of DNA hybridization. Experimental results show that the sensor can qualitatively detect cDNA with the sensitivity of 0.0618 nm/nM and a detection limit of 0.31 nM at a temperature of 25 °C. The proposed DNA biosensor has potential applications in fast developing fields such as medical diagnostics, cancer screening, drug testing, and environmental engineering.

In-situ DNA detection with an interferometric-type optical sensor based on tapered exposed core microstructured optical fiber

Abstract: A label-free DNA biosensor based on exposed core microstructured optical fiber for in-situ real-time DNA detection has been presented and experimentally demonstrated. The sensor is fabricated by splicing a section of tapered exposed core fiber (ECF) between two single-mode fibers (SMFs), forming a multimode Mach-Zehnder interferometer (MZI). The ECF design provides the evanescent field with the sensitivity of a micro/nano optical fiber. In this paper, the ECF has a large cladding diameter (160 µm) but a small core (9 µm), and the core of the ECF is further reduced by tapering, which significantly improves the refractive index (RI) sensitivity. The sensor can detect local RI changes that occur on the surface of the optical fiber due to the binding of biomolecules. We immobilized probe DNA (pDNA) on the exposed side of the core to detect the complementary DNA (cDNA), demonstrating use for specific and label-free sensing of DNA hybridization. Experimental results show that the sensor can qualitatively detect cDNA with the sensitivity of 0.0618 nm/nM and a detection limit of 0.31 nM at a temperature of 25 °C. The proposed DNA biosensor has potential applications in fast developing fields such as medical diagnostics, cancer screening, drug testing, and environmental engineering.

Wavelength-interval-switchable multi-wavelength thulium-doped fiber laser with a nonlinear dual-pass Mach-Zehnder interferometer filter in 2-μm-band

Abstract: A wavelength-interval-switchable multi-wavelength thulium-doped fiber laser (MWTDFL) is proposed and demonstrated, based on a nonlinear dual-pass Mach-Zehnder interferometer (NDP-MZI) filter for the first time. We investigate the NDP-MZI filter theoretically and experimentally, which has both the transmission characteristics of a dual-pass Mach-Zehnder interferometer (DP-MZI) for wavelength selection and a nonlinear optical loop mirror (NOLM) for suppressing wavelength competition. By tuning two polarization controllers (PCs), two 20-wavelength operations with an opposite phase and a same wavelength-interval of 0.46 nm are obtained and switched between each other flexibly. The maximum power fluctuation and wavelength drift measured are 0.612 dB and 0.04 nm, respectively. In addition, due to the power-equalizing effect resulting from the NOLM, 60 lasing wavelengths within a 3-dB bandwidth with an adjacent wavelength-interval of 0.23 nm are also obtained by adjusting the PCs carefully, and the stability of the MWTDFL is measured experimentally. Furthermore, the performance of the NDP-MZI using an 80 m highly nonlinear fiber has been studied in detail as well. The proposed MWTDFL may find great applications in optical communication and optical sensing.

SU(2)-in-SU(1,1) Nested Interferometer for High Sensitivity, Loss-Tolerant Quantum Metrology

Abstract: We present experimental and theoretical results on a new interferometer topology that nests a SU(2) interferometer, e.g., a Mach-Zehnder or Michelson interferometer, inside a SU(1,1) interferometer, i.e., a Mach-Zehnder interferometer with parametric amplifiers in place of beam splitters. This SU(2)-in-SU(1,1) nested interferometer (SISNI) simultaneously achieves a high signal-to-noise ratio (SNR), sensitivity beyond the standard quantum limit (SQL) and tolerance to photon losses external to the interferometer, e.g., in detectors. We implement a SISNI using parametric amplification by four-wave mixing (FWM) in Rb vapor and a laser-fed Mach-Zehnder SU(2) interferometer. We observe path-length sensitivity with SNR 2.2 dB beyond the SQL at power levels (and thus SNR) 2 orders of magnitude beyond those of previous loss-tolerant interferometers. We find experimentally the optimal FWM gains and find agreement with a minimal quantum noise model for the FWM process. The results suggest ways to boost the in-practice sensitivity of high-power interferometers, e.g., gravitational wave interferometers, and may enable high-sensitivity, quantum-enhanced interferometry at wavelengths for which efficient detectors are not available.

Wavelength-interval-switchable multi-wavelength thulium-doped fiber laser with a nonlinear dual-pass Mach-Zehnder interferometer filter in 2-μm-band

Abstract: A wavelength-interval-switchable multi-wavelength thulium-doped fiber laser (MWTDFL) is proposed and demonstrated, based on a nonlinear dual-pass Mach-Zehnder interferometer (NDP-MZI) filter for the first time. We investigate the NDP-MZI filter theoretically and experimentally, which has both the transmission characteristics of a dual-pass Mach-Zehnder interferometer (DP-MZI) for wavelength selection and a nonlinear optical loop mirror (NOLM) for suppressing wavelength competition. By tuning two polarization controllers (PCs), two 20-wavelength operations with an opposite phase and a same wavelength-interval of 0.46 nm are obtained and switched between each other flexibly. The maximum power fluctuation and wavelength drift measured are 0.612 dB and 0.04 nm, respectively. In addition, due to the power-equalizing effect resulting from the NOLM, 60 lasing wavelengths within a 3-dB bandwidth with an adjacent wavelength-interval of 0.23 nm are also obtained by adjusting the PCs carefully, and the stability of the MWTDFL is measured experimentally. Furthermore, the performance of the NDP-MZI using an 80 m highly nonlinear fiber has been studied in detail as well. The proposed MWTDFL may find great applications in optical communication and optical sensing.

Low-power all-optical switch based on a graphene-buried polymer waveguide Mach-Zehnder interferometer.

Abstract: We propose a low-power all-optical switch based on the structure of a graphene-buried balanced Mach-Zehnder interferometer (MZI), where the signal light is switched between the two output ports of the MZI by the heat generated from graphene's absorption of the pump light. We use orthogonal polarizations for the pump and the signal light to maximize pump absorption and minimize graphene-induced signal loss. Our experimental device fabricated with polymer waveguides buried with 5-mm long graphene shows a pump absorption of 10.6 dB (at 980 nm) and a graphene-induced signal loss of 1.1 dB (at 1550 nm) and can switch the signal light with a pump power of 6.0 mW at an extinction ratio of 36 dB. The actual pump power absorbed by graphene for activating switching is estimated to be 2.2 mW. The rise and fall times of the switch are 1.0 and 2.7 ms, respectively. The switching characteristics are weakly sensitive to ambient temperature variations. Our device can be butt-coupled to single-mode fibers and could find applications in fiber-based and on-chip all-optical signal processing.

High-performance silicon polarization switch based on a Mach–Zehnder interferometer integrated with polarization-dependent mode converters

Abstract: Abstract As the key element for optical systems, polarization controllers with versatile functionalities are highly desired. Here, a CMOS-compatible polarization switch is proposed and realized by using a Mach–Zehnder interferometer integrated with two polarization-dependent mode converters (PDMCs) at the input/output ends. The PDMCs, which utilize the mode hybridness and adiabatic mode evolution in a silicon-on-insulator (SOI) ridge waveguide taper, provide a low-loss adiabatic transmission for the launched TE0 mode as well as efficient mode conversion from the launched TM0 mode to the TE1 mode. For the MZI structure, there are two 1 × 2 dual-mode 3-dB power splitters based on a triple-core adiabatic taper, and two thermally-tunable phase-shifters embedded in the arms. The polarization state and the polarization extinction ratio (PER) of the transmitted light can be dynamically tuned by introducing some phase difference between the MZI arms electrically. The fabricated device has an excess loss of ∼0.6 dB for the TE0 and TM0 modes. When the switch is off, the TE0 and TM0 modes go through the device without exchange. In contrast, when the switch is on, the TE0–TM0 conversion occurs and the measured PER is about 20 dB.

Tunable filter based on two concatenated symmetrical long period fiber gratings as Mach-Zehnder interferometer and its fiber lasing application

Abstract: • Switchable and tunable multi-wavelength laser. • Mach-Zehnder interferometer. • Symmetric long-period fiber grating. • Fiber optics. This work presents a highly stable switchable and tunable erbium-doped fiber laser based on a Mach-Zehnder interferometer (MZI) made with two symmetrical LPFGs separated by an SMF segment of 5 cm in length. The core and the cladding of the SMF central segment act like the MZI arms, whereas the LPFG 1 -SMF and SMF-LPFG 2 splices act as optical couplers. The emission is switchable from one single emission at 1563.6 nm, a side mode suppression ratio (SMSR) of ∼55 dB, and linewidth of 0.15 nm, to a dual emission located at 1563.98 and 1573.89 nm, reaching a high SMSRs of 56 dB, and linewidths ∼0.10 nm. Moreover, the laser emission can be tuned from 1569 to 1572 nm applying torsion to the MZI from 0° to 330° obtaining a nearly linear sensitivity of 9.2 pm/° with low hysteresis. Additionally, the laser operation stability was tested over 60 min, obtaining the power and wavelength fluctuations lower than 0.086 dB and 0.028 nm respectively. To the best of our knowledge, this is the first time that symmetric LPFGs have been used as a torsion sensitive WSF. For its high wavelength stability and SMSR, the MZI can be a low-cost alternative WSF while the switchable and tunable laser can be useful as an optical source for spectroscopy and communications applications.

Eight-Channel LAN WDM (De)Multiplexer Based on Cascaded Mach–Zehnder Interferometer on SOI for 400GbE

Abstract: In this paper, we design and experimentally demonstrate an eight-channel cascaded Mach–Zehnder interferometer (MZI) based Local Area Network (LAN) Wavelength Division Multiplexing (WDM) (de)multiplexerwith channel spacing of 800 GHz on a silicon-on-insulator. By cascading a three-stage MZI, eight target wavelengths are (de)multiplexed. The length difference of the third-stage MZI delay arms is adjusted so that the output channels skip the guard band. In order to keep the central wavelength of each channel from shifting, we utilize a wide waveguide for the phase delay arm in MZI to achieve large fabrication tolerance, and the multi-mode interference (MMI) couplers as power splitters with weak dispersions. The measurement results of the fabricated device show the precise wavelength alignment over the whole working wavelength range.

Optimization of Silicon Nitride Waveguide Platform for On-Chip Virus Detection

Abstract: This work presents a rigorous and generic sensitivity analysis of silicon nitride on silicon dioxide strip waveguide for virus detection. In general, by functionalizing the waveguide surface with a specific antibodies layer, we make the optical sensor sensitive only to a particular virus. Unlike conventional virus detection methods such as polymerase chain reaction (PCR), integrated refractive index (RI) optical sensors offer cheap and mass-scale fabrication of compact devices for fast and straightforward detection with high sensitivity and selectivity. Our numerical analysis includes a wide range of wavelengths from visible to mid-infrared. We determined the strip waveguide’s single-mode dimensions and the optimum dimensions that maximize the sensitivity to the virus layer attached to its surface at each wavelength using finite difference eigenmode (FDE) solver. We also compared the strip waveguide with the widely used slot waveguide. Our theoretical study shows that silicon nitride strip waveguide working at lower wavelengths is the optimum choice for virus detection as it maximizes both the waveguide sensitivity (Swg) and the figure of merit (FOM) of the sensor. The optimized waveguides are well suited for a range of viruses with different sizes and refractive indices. Balanced Mach–Zehnder interferometer (MZI) sensors were designed using FDE solver and photonic circuit simulator at different wavelengths. The designed sensors show high FOM at λ = 450 nm ranging from 500 RIU−1 up to 1231 RIU−1 with LMZI = 500 µm. Different MZI configurations were also studied and compared. Finally, edge coupling from the fiber to the sensor was designed, showing insertion loss (IL) at λ = 450 nm of 4.1 dB for the design with FOM = 500 RIU−1. The obtained coupling efficiencies are higher than recently proposed fiber couplers.

Design and analysis of an all-optical NAND logic gate using a photonic crystal semiconductor optical amplifier based on the Mach–Zehnder interferometer structure

Abstract: In this study, a high-speed all-optical NAND logic gate (AO-NAND-LG) was designed and numerically simulated. The simulation was performed using the photonic crystal-semiconductor optical amplifier (PC-SOA) structure based on the Mach–Zehnder interferometer and nonlinear cross-phase modulation mechanism. The input optical pulse sequence used in the design was the return-to-zero type. Moreover, two PC-SOAs were utilized in the design of the NAND-LG. The rate and propagation equations were solved using the finite difference method. The optimal mode was achieved for NAND-LG with an energy value of 2.2 fJ for input pulse trains A and B, and an injection current of 1 mA at a bit rate of 80 Gbps. Furthermore, the impacts of the pattern effect, conversion efficiency, extinction ratio, and gain recovery on the design of the AO-NAND-LG were analyzed for the first time in simulations to enhance the performance and efficiency of the PC-SOA. Furthermore, the results demonstrated that the PC-SOA exhibited better logical performance than the ordinary SOA, and it is a suitable candidate for integrated optical circuits because it is much shorter than the SOA.

An All Fiber Mach-Zehnder Interferometer Based on Tapering Core-Offset Joint for Strain Sensing

Abstract: A Mach-Zehnder interferometer, composed of two core-offset tapered joints (COTJ-MZI), is proposed and experimentally verified for high sensitivity strain sensing. The COTJ-MZI is handily fabricated by core-offset fusion splicing and tapering based on all single-mode fiber (SMF). The fiber cores form stepped cores within the COTJs. The transmission spectra with different core-offset values and interference lengths are obtained and theoretically analyzed. Benefitting from the stepped cores in the COTJ structure, the mode coupling points are able to be modulated easily by the applied strain. A strain sensitivity of −108.0 pm/ $\mu \varepsilon $ (0- $400~\mu \varepsilon$ ) and −47.6 pm/ $\mu \varepsilon $ (400-1200 $\mu \varepsilon$ ) is achieved. In addition, the temperature response is also characterized as low as 23.3 pm/°C. With the advantages of low cost and high sensitivity, the COTJ-MZI sensor is competitive candidates in the field of strain measurement.

Tension and Torsion Sensing With a Double-Taper Mach-Zehnder Interferometer

Abstract: A novel setup for a Double-Taper Mach-Zehnder Interferometer (DTMZI) is presented to measure axial strain and torsion. An epoxy section is added between the two tapers as a fixture to ensure torsion sensing. The modal filtering effect of the epoxy upon the interferometry response is experimentally verified. The transmission spectrum of DTMZI under strain and torsion is modelled and further analyzed through the differential accumulated phase between the beating modes.The experimental spectral observation confirms our estimate. The relationships between the spectral shifts in wavelength and applied displacements are obtained. The sensor shows a very high sensitivity against the applied strain and twists.

Tapered-open-cavity-based in-line Mach-Zehnder interferometer for highly sensitive axial-strain measurement.

Abstract: An in-line Mach-Zehnder interferometer based on a multimode-fiber-assisted tapered open-cavity (TOC) is proposed. Light field distributions of the TOC were investigated using beam propagation method with different offsets and diameters of the taper waist. Bias and uniform taper (BT and UT)-based structures were fabricated and compared using one- and two-step arc-discharge methods, and comprehensive tests were then conducted considering axial-strain. The experimental results show that the UT structure has more than -45 pm/µɛ linear wavelength shift with the applied axial-strain. Owing to its compact size and low cost, the proposed sensor is promising for axial-strain-related high-precision engineering applications.

Linearity-Enhanced Dual-Parallel Mach–Zehnder Modulators Based on a Thin-Film Lithium Niobate Platform

Abstract: In this work, we report a linearity-enhanced dual-parallel Mach–Zehnder modulator (MZM) on a thin-film lithium niobate platform. By setting the optical and electrical splitting ratios at a specific condition, the third-order intermodulation distortions (IMD3) of the child MZMs cancel with each other, whereas the first-order harmonics (FH) reach the maximum. Passive devices instead of thermo-optical switches are used to control the optical power and phase of the child MZMs, which greatly improve the device stability and simplify the operation complexity. To the best of our knowledge, the experimental results show a record-high spurious-free dynamic range on a thin-film lithium niobate platform (110.7 dB·Hz2/3 at 1 GHz). The E-O response decayed about 1.9 dB from 10 MHz to 40 GHz, and the extrapolated E-O 3 dB bandwidth is expected to be 70 GHz. A half-wave voltage of 2.8 V was also achieved. The proposed modulator provides a promising solution for high-bandwidth and low-voltage analog optical links.

Sensitivity Enhanced Refractive Index Sensor With In-Line Fiber Mach-Zehnder Interferometer Based on Double-Peanut and Er-Doped Fiber Taper Structure

Abstract: A fiber-optic Mach Zehnder interferometer (MZI) refractive index (RI) sensor based on a double peanut-shaped structure in Er-doped fiber with a section of tapered fiber was fabricated using fusion splicer and experimentally demonstrated. The double peanut-shaped structures placed at both ends of the sensor function as beam splitting/combining. Besides, the tapered region works as the sensing area. With RI changes, the optical path difference between the core mode and the cladding modes will change correspondingly, resulting in interference spectrum shifting. By monitoring the shift, the measured RI can be obtained. The experimental results show that the RI sensitivity was significantly improved compared with other types of peanut-shaped fiber sensors. By comparing different taper diameters, it is found that the finer the tapered fiber, the higher the sensitivity of measuring RI.High RI sensitivity of 441.56 nm/RIU is obtained in the experiments. Compared with the similar-structure sensor consisted of single-mode fiber (SMF), the sensitivity of the proposed sensor based on Er-doped fiber is 115.22 nm/RIU higher than that of the former. The proposed sensor has the characteristics of a compact structure. In addition, it has potential in environmental, medical, and aerospace monitoring applications.

Photonic crystal based interferometric design for label-free all-optical sensing applications.

Abstract: Optical sensing devices has a great potential in both industrial and biomedical applications for the detection of biochemicals, toxic substances or hazardous gases thanks to their sustainability and high-selectivity characteristics. Among different kinds of optical sensors based on such as fibers, surface plasmons and resonators; photonic crystal (PC) based optical sensors enable the realization of more compact and highly efficient on-chip sensing platforms due to their intriguing dispersive relations. Interferometric devices based on PCs render possible the creation of biochemical sensors with high sensitivity since a slight change of sensor path length caused by the captured biochemicals could be detected at the output of the interferometer via the interferences of separated beams. In this study, a new type of Mach-Zehnder Interferometer (MZI) using low-symmetric Si PCs is proposed, which is compatible with available CMOS technology. Intended optical path difference between the two MZI channels is provided by the periodic alignments of symmetry-reduced PC unit cells in the MZI arms. Unlike the conventional symmetrical PC based MZIs, Fano resonances exist for the proposed MZI design, i.e. transmission dips and peaks appear in the output spectrum, and the location of dip and peak frequencies in transmission spectra can be efficiently controlled by utilizing interference phenomenon. Exploiting this effect, any refractive index change at the surrounding medium could be distinctly observed at the transmission spectra. In the view of such results, it is convenient to say that the proposed MZI configuration is suitable for efficient optical sensing of toxic gases as well as liquids. The designed all-dielectric MZI system is numerically investigated in both spectral and spatial domains to analyze its interferometric tunability: an optical sensitivity of about 300 nm/RIU is calculated for gaseous analytes whereas that sensitivity value is around 263.2 nm/RIU in the case of liquid analytes. Furthermore, high quality factor of Q > 45000 is obtained at Fano resonances with Figure-of-Merit (FoM) value of FoM ∼ 8950 RIU-1(7690 RIU-1) in the case of gas analytes (liquid analytes), which is the indication of enhanced optical sensing performance of the proposed MZI design. Considering all the above-mentioned advantages, the proposed interferometric configurations based on low-symmetric PCs could be utilized for efficient photonic sensor applications that require controllable output power or sensing of gaseous and liquid substances.

Optimal phase sensitivity of an unbalanced Mach-Zehnder interferometer

Abstract: In this paper we address the problem of optimizing an unbalanced Mach-Zehnder interferometer, for a given pure input state and considering a specific detection scheme. While the optimum transmission coefficient of the first beam splitter can be uniquely determined via the quantum Fisher information only [Phys. Rev. A 105, 012604 (2022)], the second beam splitter transmission coefficient is detection-scheme dependent, too. We systematically give analytic solutions for the optimum transmission coefficient of the second beam splitter for three types of widely used detection schemes. We provide detailed examples including both Gaussian and non-Gaussian input states, showing when an unbalanced Mach-Zehnder interferometer can outperform its balanced counterpart in terms of phase sensitivity.

Asymmetric Self-Coherent Detection Based on Mach-Zehnder Interferometers

Abstract: We propose an asymmetric self-coherent detection scheme (ASCD) based on Mach-Zehnder interferometers (MZI) for the field reconstruction of self-coherent (SC) complex double-sideband (DSB) signals. The MZI-ASCD scheme approaches the high electrical spectral efficiency (ESE) of homodyne coherent detection via a direct detection (DD) receiver having only two photodiodes (PD) and two analog-to-digital converters. The incoming SC-DSB signal is split into two parts at the receiver in this approach, one of which is delayed and beats with the other part at the outputs of an MZI. We show that the field reconstruction can be performed from the two tributaries of photocurrents. In addition, we present a modified MZI-ASCD scheme referred to as AUX-ASCD which introduces an auxiliary DD branch to improve the SNR of the detected signal. It is found that both the MZI-ASCD scheme and the AUX-ASCD scheme achieve higher OSNR sensitivity compared to the Kramers-Kronig scheme and in the meantime increases the ESE by a factor of 2 using a cost-effective DD receiver. These advantages make the ASCD scheme attractive for short-reach optical communications including edge cloud connections and mobile X-haul systems.

Pb2+ fiber optic sensor based on smart hydrogel coated Mach-Zehnder interferometer

Abstract: A fiber optics sensor based on the structure of no-core fiber/few-mode fiber coated with a smart hydrogel membrane/no-core fiber, cascading a fiber Bragg grating for temperature monitoring was developed to detect the concentration of Pb2+ in aqueous solution. It is the first time that a phase-modulated fiber sensor is used to measure the concentration of Pb2+ in aqueous solution. When the concentration of Pb2+ changes, the specific adsorption of the hydroxyethyl methacrylate crosslinked hydrogel on Pb2+ will change the refractive index of the sensing membrane, and will shift the interference fringe of the sensor in optical spectrum. The process is simple and friendly to environment, and does not produce any harmful substance. The fiber sensor with high sensitivity of 8.155 × 105nm/(mol/L) and the estimated detection limit of Pb2+ concentration of 2.452 × 10−8 mol/L at the spectral resolution of 0.02 nm. The sensor has the advantages of high concentration resolution, low cost, remote detection ability, etc. It has good application prospect in the detection of Pb2+ concentration.

Realistic non-Gaussian operations scheme in parity detection based Mach-Zehnder quantum interferometry

Abstract: We theoretically analyze phase sensitivity using parity detection based Mach Zehnder interferometer (MZI) with the input states generated by performing non-Gaussian operations, viz., photon subtraction, photon addition, and photon catalysis on a two-mode squeezed vacuum (TMSV) state. Since these non-Gaussian operations are probabilistic, it is of utmost importance to take the success probability into account. To this end, we consider the realistic model of photon subtraction, addition, and catalysis and derive a single expression of the Wigner function for photon subtracted, added, and catalyzed TMSV state. The Wigner function is used to evaluate the lower bound on the phase sensitivity via quantum Cramer-Rao bound and parity detection based phase sensitivity in MZI. We identify the ranges of squeezing and transmissivity parameters where the non-Gaussian states provide better phase sensitivity than the TMSV state. On qualitatively taking the success probability into account, it turns out that the photon addition is the most advantageous non-Gaussian operation. We hope that the generalized Wigner function derived in this work will be useful in various quantum information protocols and state characterization.

An Integrated-Plasmonic Chip of Bragg Reflection and Mach-Zehnder Interference Based on Metal-Insulator-Metal Waveguide

Abstract: Abstract In this paper, a Bragg reflector is proposed by placing periodic metallic gratings in the center of a metal-insulator-metal (MIM) waveguide. According to the effective refractive index modulation caused by different waveguide widths in a period, a reflection channel with a large bandwidth is firstly achieved. Besides, the Mach-Zehnder interference (MZI) effect arises by shifting the gratings away from the waveguide center. Owing to different optical paths with unequal indices on both sides of the grating, a narrow MZI band gap will be obtained. It is interesting to find out that the Bragg reflector and Mach-Zehnder interferometer are immune to each other, and their wavelengths can be manipulated by the period and the grating length, respectively. Additionally, we can obtain three MZI channels and one Bragg reflection channel by integrating three different gratings into a large period. The performances are investigated by finite-difference time-domain (FDTD) simulations. In the index range of 1.33–1.36, the maximum sensitivity for the structure is as high as 1 500 nm/RIU, and it is believed that this proposed structure can find widely applications in the chip-scale optical communication and sensing areas.

Strain and Temperature Discrimination Based on a Mach-Zehnder Interferometer With Cascaded Single Mode Fibers

Abstract: Abstract An in-fiber Mach-Zehnder interferometer is proposed for the discrimination of strain and temperature. The sensor is based on two cascaded standard single mode fibers using three peanut tapers fabricated by simple splicing. The cascaded structure excites more frequency components, which induce four sets of interference dips in the transmission spectrum. One set of the spectrum dips have different sensitivities to temperature and strain from those of the other three. The sensor can discriminate strain and temperature by monitoring the wavelength shifts of two spectrum dips. Repeated experiments are taken both for strain and temperature increasing and decreasing scenarios. Experimental results show that Dip 1 has an average strain sensitivity of −0.911 pm/µε and an average temperature sensitivity of 49.98 pm/°C. The strain sensitivity for Dip 2 is negligible and its average temperature sensitivity is 60.52 pm/°C The strain and temperature resolutions are ±3.82 µε and ±0.33 °C.

High-performance Mach–Zehnder modulator using tailored plasma dispersion effects in an ITO/graphene-based waveguide

Abstract: A high-performance electro-optic Mach-Zehnder modulator (MZM) with outstanding characteristics is proposed. The MZM is in a push-pull configuration that is constructed using an ITO/graphene-based silicon waveguide. A novel idea for engineering of the plasma dispersion effect in an ITO/graphene-based waveguide is proposed so that the modulation characteristics of the MZM are highly improved. Plasma dispersion effects of ITO and graphene layers are tailored in such a way that a large difference between real parts of guided mode effective index of the two arms is achieved while their corresponding imaginary parts are equal. As a result, a very low [Formula: see text] of [Formula: see text] is achieved. To the best of our knowledge, this is one of the lowest [Formula: see text] reported for an electro-optic modulator. In addition, the proposed modulator exhibits a very high extinction ratio of more than 30 dB, low insertion loss of 2.8 dB and energy consumption of as low as 10 fJ/bit, which are all promising for optical communication and processing systems.