Mach-Zehnder Interferometer Sensor Research Articles

Design and fabrication of a heterostructured cladding solid-core photonic bandgap fiber for construction of Mach-Zehnder interferometer and high sensitive curvature sensor.

A heterostructured cladding solid-core photonic bandgap fiber (HCSC-PBGF) is designed and fabricated which supports strong core mode and cladding mode transmission in a wide bandgap. An in-line Mach-Zehnder interferometer (MZI) curvature sensor is constructed by splicing single mode fibers at both ends of a HCSC-PBGF. Theoretical analysis of this heterostructured cladding design has been implemented, and the simulation results are consistent with experiment results. Benefiting from the heterostructured cladding design, an enhanced curvature sensing sensitivity of 24.3 nm/m-1 in the range of 0-1.75 m-1 and a high quality interference spectrum with 20 dB fringe visibility are achieved. In order to eliminate the interference of longitudinal strain and transverse torsion on the result of the curvature sensing experiment, we measure the longitudinal strain and transverse torsion sensing properties of HCSC-PBGF, and the results show that the impact is negligible. It is obvious that this high-sensitivity and cost-effective all fiber sensor with a compact structure will have a promising application in fiber sensing.

Analysis of the use of fiber-optic sensors in the road traffic

This publication focuses on the use of fiber-optic sensors in the transport applications. Fiberoptic sensors are based on the fiber-optic communications, using nearly identical elements and components as classic fiber-optic communications. The fundamental difference is that in the fiber-optic communications we limit the effects of the environment on the transmission of the information itself, whereas, in the case of fiber-optic sensors, different arrangements are sought to maximize these impacts. In this publication, so-called interferometric sensors are described which work on the basis of comparison of light phases in two parts (the measuring and reference arm). These phase differences can be measured with extreme sensitivity, so fiber-optic interferometers are much more accurate than most other sensors. The base of the structure is an optical fiber, so sensors are immune to electromagnetic interference (EMI) and offer the simplicity of implementation, as the sensors do not require destructive installation on the roads. The publication describes the use of a Mach-Zehnder interferometric sensor type. This type of sensor has been practically validated and discussed for the automotive applications. The primary tracked parameter is the monitoring of the traffic density. The results presented in this publication are based on the evaluation of long-term time series containing hundreds of samples and confirm the idea of using fiber-optic sensors in transport applications.

Sensitivity amplification of fiber-optic in-line Mach-Zehnder Interferometer sensors with modified Vernier-effect.

In this paper, a novel sensitivity amplification method for fiber-optic in-line Mach-Zehnder interferometer (MZI) sensors has been proposed and demonstrated. The sensitivity magnification is achieved through a modified Vernier-effect. Two cascaded in-line MZIs based on offset splicing of single mode fiber (SMF) have been used to verify the effect of sensitivity amplification. Vernier-effect is generated due to the small free spectral range (FSR) difference between the cascaded in-line MZIs. Frequency component corresponding to the envelope of the superimposed spectrum is extracted to take Inverse Fast Fourier Transform (IFFT). Thus we can obtain the envelope precisely from the messy superimposed spectrum. Experimental results show that a maximum sensitivity amplification factor of nearly 9 is realized. The proposed sensitivity amplification method is universal for the vast majority of in-line MZIs.

A stepped Mach-Zehnder interferometric humidity sensor based on lateral offset fusion splicing

A novel optical fiber relative humidity (RH) sensor based on a Mach-Zehnder interferometer (MZI) is proposed and demonstrated in this paper. The sensor head is formed by a single-mode-multimode-single-mode-single-mode(SM-MM-SM-SM) fiber structure through lateral offset fusion splicing. The intermodal interference is achieved by two lateral offset points. The change of relative humidity will cause the optical path difference changed of the core mode and cladding modes, which gives rise to the interference pattern change. The ambient RH change can be determined by monitoring the energy variation of the interference pattern. The experimental results show the dip energy of the transmission spectrum changes with respect to surrounding RH with good linearity. The MZI with a interferometer length of 15mm offers the enhanced RH sensitivity of −0.0487dB/%RH in the range of 35–95%RH with linearity of 0.9966. The proposed humidity has compact size, simple fabrication procedure and does not need any functional coating, making it a good candidate for RH measurements.

Detection of Refractive Index Change From the Critical Wavelength of an Etched Few Mode Fiber

A novel scheme for the detection of refractive index change based on the mode interference in a special few mode fiber (FMF) is proposed in this paper. The parameters and index profile of the FMF used in the measurement are specifically designed so that only LP01 and LP02 modes are transmitted within the operation wavelength, and the propagation constant difference Δβ between these two modes reaches maximum at critical wavelength (CWL). An inline Mach–Zehnder interferometric sensor for the detection of surrounding refractive index (SRI) is constructed by splicing FMF with two sections of conventional single mode fiber. We demonstrated at the first time that the CWL will change monotonically with the change of SRI in the measurement range of 1.316–1.439. The experimental sensitivity of the CWL increases with the increase of SRI. A sensitiviy of 140.626 ± 12.560 nm/RIU in the range of 1.316–1.383 and a maximum sensitivity of 2489.796 ± 190.179 nm/RIU in the range of 1.433–1.439 were obtained, respectively, in the experiment. At present parameters of the etched FMF, the limit of detection of the refractive index is 3.413 × 10–4 RIU in the SRI range of 1.316–1.383, and 1.928 × 10–5 RIU in the SRI range of 1.433–1.439, respectively. The detection of SRI via monitoring the shift of CWL is superior to the traditional detection method via monitoring merely the shift of peak or dip wavelength of the transmission spectrum, since the latter usually suffers from limited measurement range and multivalue problem because it is difficult to identify and follow one specific peak or dip from the transmission spectrum especially if the system needs to reset in practical application. The novel detection scheme based on monitoring the shift of the exclusive CWL of FMF is promising in practical applications.

Mach–Zehnder Interferometer-Based Integrated Terahertz Temperature Sensor

A plasmonic Mach–Zehnder interferometer (MZI) for temperature sensing is reported in the terahertz (THz) regime. The MZI is formed by embedding a semiconductor (SC) layer into a silicon membrane, where the SC layer supports two independent propagating surface plasmon polariton (SPP) waves on both surfaces. The temperature-sensitive phase difference between these two SPP waves gives rise to the modulation of the transmitted intensity. The results show that the MZI sensor possesses a sensitivity and a figure of merit as high as 8.9 × 10−3 THz/K and 117, respectively. Theoretical calculations indicate that the further improvement in sensing performance is still possible through optimization of the structure Moreover, an investigation of structural perturbations indicates that the MZI has a good tolerance to the fabrication errors. The compact MZI-based waveguide structure may find important applications in areas of sensing and integrated THz circuits.

Semiconductor-based plasmonic interferometers for ultrasensitive sensing in a terahertz regime.

A robust plasmonic semiconductor-based Mach-Zehnder interferometer (MZI), which consists of a semiconductor layer with a microslit flanked by two identical microgrooves, is proposed and investigated for the terahertz sensing. The microgrooves reflect the surface plasmon polariton waves toward the microslit, where they interfere with the transmitted terahertz wave. The interference pattern is determined by the permittivities of the sensing material and semiconductor (i.e., temperature dependent), making the structure useful for the refractive index (RI) and temperature detection. A quantitative theoretical model is also developed for performance prediction and validated with a finite element method. The numerical results show that the Mach-Zehnder interferometer sensor possesses an RI sensitivity as high as 140000 nm/RIU (or 0.42 THz/RIU) and a relative intensity sensitivity of 1200%RIU-1. In addition, a temperature sensitivity of 1470 nm/K (or 4.7×10-3 THz/K) is determined. Theoretical calculations indicate that the further improvement in sensing performance is still possible through optimization of the structure. The proposed sensing scheme may pave the way for applications in terahertz sensing and integrated terahertz circuits.

Plasmonic Mach–Zehnder interferometric sensor based on a metal–insulator-metal nanostructure**Project supported by the National Natural Science Foundation of China (Grant Nos. 51405240 and 61178044), the Natural Science Foundation of Jiangsu Province of China (Grant No. BK20161559), the Natural Science Foundation of the Higher Education Institutions of Jiangsu Province of China (Grant No. 16KJB510018), and University Postgraduate Research and Innovation Project of

A plasmonic Mach–Zehnder interferometric sensor based on a semicircular aperture-slit nanostructure patterned on a metal–insulator–metal film is proposed and demonstrated by finite difference time domain (FDTD) simulation. Due to the interference between two different surface plasmon polariton modes in this design, the transmission spectra exhibit oscillation behaviors in a broad bandwidth, and can be readily tailored by changing the SPP path length and core layer thickness. Based on this principle, the characteristics of refractive index sensing are also demonstrated by simulation. This structure is illuminated with a collimated light source from the back side to avoid impacts on the interference. Meanwhile, these results show that the proposed structure is promising for portable, efficient, and sensitive biosensing applications.

Design of optical channel waveguide Mach-Zehnder interferometer (MZI) for environmental sensor applications

High sensitivity environmental sensors with a simple and compact structure are required to monitor unwanted pollution such as liquid waste. In this research, a component of environmental sensor based on optical channel waveguide Mach-Zehnder interferometer (MZI) has been designed and also simulated. The materials used in the design were titanium dioxide (TiO2) as a core and silicon dioxide (SiO2) with air as cladding. The sensitivity value of the MZI sensor obtained by simulation using computer program was 11 nm/RIU at the angle of 16°. Meanwhile, the obtained fixed length of MZI sensing arm was 4 μm. The proposed design can be used for identifying the existence of liquid material precisely.

Hollow hybrid plasmonic Mach-Zehnder sensor.

A Mach-Zehnder interferometer (MZI)-based liquid refractive index sensor, utilizing a hollow hybrid plasmonic (HP) waveguide as the sensing element, has been investigated, showing large sensitivity to the refractive index changes of the tested liquids, as well as lower propagation loss in comparison to typical plasmonic waveguide-based ones. The sensor is fabricated using conventional silicon-on-insulator (SOI) technology; therefore, it is compatible to other standard SOI devices. The waveguide sensitivity, Sw, is experimentally demonstrated to be 0.64, with a propagation loss less than 0.25 dB/μm. Using a 20 μm long hollow HP waveguide in the sensing arm, the sensitivity of the MZI sensor (device sensitivity, Sd) is about 160 nm/RIU, with an extinction ratio larger than 40 dB.

Mach–Zehnder interferometer based on tapered PCF with an up-tapered joint for curvature, strain and temperature interrogation

We propose a Mach–Zehnder interferometric sensor based on tapered Photonic Crystal Fiber (PCF) with up-tapered collapsed region for measurement of parameters such as curvature, strain and temperature. The up-tapered collapsed region helps in excitation of the cladding modes in PCF and these modes interfere with each other at the tapered region of PCF which is completely collapsed. Three tapered PCFs with varying geometry are fabricated and their effect on curvature sensitivity is analyzed. Experimental results show that the proposed sensor has a curvature sensitivity of 7.56 nm m−1 with negligible hysteresis effect. Moreover, the proposed sensor shows a strain sensitivity of 1.6 pm/με along with a maximum temperature sensitivity of 51.6 pm °C−1. In addition to this, the response of the interference pattern to all these parameters is found to be linear.

Intensity-modulated abrupt tapered Fiber Mach-Zehnder Interferometer for the simultaneous sensing of temperature and curvature

An abrupt tapered fiber In-Line Mach-Zehnder Interferometer sensor for simultaneous measurement of temperature and curvature is proposed and experimentally demonstrated. The sensor head is fabricated by arcing Corning SMF-28 using a commercial arc fusion splicer. The individual parameters discrimination was achieved by manipulating the unequal sensitivities of optical power to temperature and curvature obtained at two wavelengths within the sensing spectrum. The curvature and temperature sensitivities at λ1 (1537nm) and λ2 (1568.7nm) were found to be 11.8264dBm/m−1, 12.4885dBm/m−1 and 0.0829dBm/°C, 0.0833dBm/°C, respectively. The experimental results show unperturbed readings with rms deviation of ±0.1801m−1 and ±0.0826°C, for curvature and temperature measurements, respectively, through measurement of optical power response of the sensor. With this simultaneous sensing technique, the proposed sensor can be deployed for many field applications such as nondestructive structural health monitoring of civil infrastructure.

Analysing surface plasmon resonance phase sensor based on Mach-Zehnder interferometer technique using glycerin

Surface Plasmon Resonance (SPR) based on Mach-Zehnder interferometer (MZI) is a very accurate tool for the detection and analysis of molecular interactions. The performance of the proposed SPR phase sensor is dependent upon multiple performance parameters that include sensitivity, repeatability, drift and the induction speed of fluid into the flow cell. The SPR Mach-Zehnder interferometer is tested for different glycerin–water concentrations to check its performance based on the different parameters. This paper highlights the enhancement of the performance of SPR phase technique based on MZI that is influenced by different parameters, measured using glycerin solutions. These four performance parameters can affect the performance of SPR based on MZI and have a particular impact on the sensor output. It also provides us information about suitable working conditions for the SPR Mach-Zehnder interferometer sensor. The experiment data shows that the sensor's sensitivity is high for small concentrations of glycerin–water mixtures. Also, any change in drift as well as in induction speed of fluid can affect the performance of SPR Mach-Zehnder interferometer. The sensitivity of SPR phase sensor is high as it can measure glycerin concentration as low as 0.05%.

A Continuous Wavelet Transform Based Time Delay Estimation Method for Long Range Fiber Interferometric Vibration Sensor

We propose a time delay estimation (TDE) method based on a continuous wavelet transform (CWT), which can be applied to the different-wavelength-based fiber interferometric vibration sensors. Using a CWT-based characteristic extraction algorithm, we successfully eliminate the asymmetry of the interference outputs that would seriously deteriorate the positioning accuracy of the sensor. A positioning measurement experiment using an asymmetric dual Mach-Zehnder interferometric sensor was carried out to verify the effectiveness of the proposed method. The experiment achieved a positioning accuracy of 0.029% at the sensing length of 85 km, with a mean processing time of 591.2 ms.

Local functionalization of CMOS-compatible Si3N4 Mach-Zehnder interferometers with printable functional polymers

A CMOS-compatible integrated four-channel silicon nitride (Si3N4) waveguide based Mach-Zehnder interferometric (MZI) sensor platform was realized with the goal to take maximum advantage of the inherent self-referencing property of MZI-sensors with both sensing and reference waveguides exposed to the sample liquid. To study the self-referencing characteristics of the MZI-sensor system, we compared two sensor configurations—an asymmetric MZI configuration, where the reference waveguide was covered by a cladding, and a symmetric MZI configuration, where the reference waveguide was also in contact with the measurement liquid.To enable biomolecular measurements, we developed an inkjet printing procedure for functional polymers (biotin-modified polyethyleneimine (PEI-B) macromolecules), which allows for local functionalization of sensing waveguides in a cost effective mass-fabrication compatible manner. We could show that for high refractive index changes of the measurement liquid (Δn=0.007) the background signal can be suppressed by a factor of ∼42 for the symmetric MZI configuration compared to the asymmetric MZI configuration. For the characterization of the functional polymer printing procedure we compared locally functionalized asymmetric and symmetric MZIs with non-locally functionalized asymmetric MZIs, which were prepared with silanization/biotinylation based approach.These locally functionalized MZIs where used for the detection of single stranded DNA (150bp) with concentrations ranging from 2.5 to 100nM. The limits of detection were 1.9nM and 1.6nM for the non-locally and locally functionalized asymmetric MZI-sensors, respectively. The locally functionalized symmetric MZI-sensors had a four times better LOD of 0.4nM. These results proof the superior performance of symmetric biosensor arrays with locally deposited functional polymers by means of inkjet printing.

Bulk sensing using a long-range surface-plasmon triple-output Mach–Zehnder interferometer

A triple-output Mach–Zehnder interferometric sensor operating with long-range surface plasmon–polaritons at free-space wavelengths near 1310 nm was constructed by etching a microfluidic channel through the top cladding (Cytop) of one arm of the interferometer to expose the Au stripe embedded therein. Optical bulk (refractometric) sensing was conducted by sequentially flowing sample solutions with different refractive indices through the microfluidic channel and measuring the optical powers of the three outputs, which responded sinusoidally and were separated by ∼2π/3 rad as expected in theory. Three detection schemes are analyzed and compared, demonstrating that the device benefits from a 3× larger dynamic range and the ability to suppress common perturbations relative to its single-output counterpart, thus improving the detection limit. The device is promising for biosensing applications.

Design of Compact Mach–Zehnder Interferometer-Based Slow-Light-Enhanced Plasmonic Waveguide Sensors

We investigate slow-light-enhanced ultracompact plasmonic Mach–Zehnder interferometer sensors. The sensing arm consists of either a conventional metal–dielectric–metal plasmonic waveguide or a waveguide system based on a plasmonic analogue of electromagnetically induced transparency. Such plasmonic electromagnetically induced transparency waveguide systems can be engineered to support slow-light modes. We find that, as the slowdown factor increases, the sensitivity of the effective index of the mode to variations of the refractive index of the material filling the structures increases. Such slow-light enhancements of the sensitivity to refractive index variations lead to enhanced sensing performance. We show that the Mach–Zehnder interferometer sensor using the plasmonic electromagnetically induced transparency waveguide system leads to approximately an order of magnitude enhancement in the refractive index sensitivity, and therefore, in the minimum detectable refractive index change, compared to the sensor using a conventional metal–dielectric–metal plasmonic waveguide. We also find that the refractive index sensitivity for such a plasmonic Mach–Zehnder interferometer sensor is approximately two times larger than the sensitivity of a waveguide-cavity sensor in which the plasmonic electromagnetically induced transparency waveguide system is sandwiched between two conventional metal–dielectric–metal waveguides.

Slow light Mach-Zehnder interferometer as label-free biosensor with scalable sensitivity.

The design, fabrication, and characterization of a label-free Mach-Zehnder interferometer (MZI) optical biosensor that incorporates a highly dispersive one-dimensional (1D) photonic crystal in one arm are presented. The sensitivity of this slow light MZI-based sensor scales with the length of the slow light photonic crystal region. The numerically simulated sensitivity of a MZI sensor with a 16 μm long slow light region is 115,000 rad/RIU-cm, which is sevenfold higher than traditional MZI biosensors with millimeter-length sensing regions. An experimental bulk refractive index detection sensitivity of 84,000 rad/RIU-cm is realized and nucleic acid detection is also demonstrated.

Surface Modification of Integrated Optical MZI Sensor Arrays Using Inkjet Printing Technology

In order to enable local functionalisation of label-free optical waveguide biosensors in a cost effective mass-fabrication compatible manner, we investigate surface modification employing inkjet printing of a) functional polymers (biotin-modified polyethyleneimine (PEI-B)) to implement high receptor densities at the surface and b) UV-curable benzophenone dextran (benzo-dextran) to form a voluminous porous hydrogel matrix. The combination of these approaches on a single chip is promising for the detection of biomolecules. We evaluate these functional polymers and hydrogels on an integrated four-channel silicon nitride (Si3N4) waveguide based Mach-Zehnder interferometric (MZI) sensor platform operating at a wavelength of 850nm (TM-Mode).

Mach–Zehnder interferometer sensor based on the U-shaped probe for concentration sensing

A newly compact bent tapered optical fibre sensor is proposed and demonstrated for the detection of levofloxacin concentration. The structure of micro fibre Mach–Zehnder interferometer (MMZI) is fabricated using a glass processing system, demonstrating a 30mm-long single mode fibre between two tapered fibres which has a waist diameter of 15μm and tapering length of 6mm. A combination of bending and tapering acts as a sensor, which results in high penetration depth of evanescent field. The sensor is sensitive to concentration variation. Upon exposure to Levofloxacin concentrations varying from 50 to 250ppm, the U-shaped MMZI sensor sensitivity is 21pm/ppm and a linearity of more than 98.7%, which is about 1.49 fold greater than that of a straight MMZI sensor. In addition, the U-shaped MMZI sensor is very compact in size which make this type of fibre sensor is easily measuring concentration variation in small volume.