Microfiber Mach-Zehnder Interferometer Research Articles

Ultra-sensitive seawater temperature sensor using an FBG-cascaded microfiber MZI operating at dispersion turning point

We proposed an ultra-sensitive seawater temperature sensor with extended measurement range by using an optical fiber Bragg grating (FBG) cascaded with a microfiber Mach-Zehnder interferometer (MZI) working at dispersion turning point (DTP). The FBG works as a rough temperature measurement tool, while the ultra-sensitive polydimethylsiloxane (PDMS)-packaged microfiber MZI plays the role of a precise measurement tool. The cooperation of these two measurement tools can realize temperature measurement with ultrahigh sensitivity and extended measurement range by using a single compact sensing structure. The proposed structure can solve the trade-off between ultrahigh sensitivity and large range of the microfiber MZI resulting from the periodic optical spectrum. A temperature sensitivity of about 38 nm/°C in the seawater temperature measurement range of 2.28–38.38 °C is obtained by the FBG-cascaded microfiber MZI which works at DTP. The corresponding temperature measurement resolution is estimated to be 0.0005 °C when the resolution of the interrogation device is 0.01 nm, which is better than that of the commercial electronic seawater temperature sensor. The temperature measurement range of the MZI can be enlarged from around 2 °C to about 36 °C with the aid of an FBG. Besides ultrahigh sensitivity and extended measurement range, the seawater temperature sensor has advantages of compact structure, easy fabrication, economical cost, low loss, making it promising in ocean monitoring.

RI sensing system with high sensitivity and large measurement range using a microfiber MZI and a photonic crystal fiber MZI

A dual-channel optical fiber sensing system for refractive index (RI) measurement with ultra-high sensitivity and large measurement range is proposed and demonstrated by combining a rough measurement sensor and a precise measurement sensor. One sensing channel consists of an optical microfiber Mach-Zehnder interferometer (MZI), which works as a RI precise measurement sensor. The microfiber MZI is fabricated on a single mode fiber (SMF) by using a two-step tapering method. The microfiber MZI operating around dispersion turning point (DTP) shows an ultra-high sensitivity of up to 44271 nm/RIU, however, its measurement range is limited to be only 0.0015 owing to the periodic interference spectrum. The other sensing channel contains an SMF-photonic crystal fiber (PCF)-SMF MZI, which works as a RI rough measurement sensor. RI sensitivity of the SMF-PCF-SMF MZI is 143.67 nm/RIU in 1.3317–1.3710. RI measurement range of the microfiber MZI is expanded by firstly read a rough RI value from the SMF-PCF-SMF MZI and then determine the observation window of the interference spectrum of the microfiber MZI. This proposed sensing scheme solves the trade-off between high sensitivity and large measurement range caused by the periodic interference spectrum, and it is promising in liquid RI-related sensing fields with high requirements of both sensitivity and measurement range.

In-line microfiber MZI operating at two sides of the dispersion turning point for ultrasensitive RI and temperature measurement

An in-line microfiber Mach-Zehnder interferometer (MZI) is demonstrated for ultrasensitive refractive index (RI) and temperature measurement by operating at two sides of the dispersion turning point (DTP), respectively. An ultrahigh RI sensitivity of 24,209 nm/RIU (RI unit) around 1.3320 and a high temperature sensitivity of -2.47 nm/℃ are experimentally achieved by a microfiber MZI with taper waist diameter of about 4.8 μm. By embedding this microfiber MZI into polydimethylsiloxane (PDMS), the temperature sensitivity is improved from -2.47 nm/℃ to about 8.33 nm/℃. The positive temperature sensitivity of this PDMS-coated microfiber MZI and the negative thermo-optic coefficient of PDMS show that this microfiber MZI has a negative RI sensitivity around the material RI of PDMS (about 1.405), which indicates that the microfiber MZI works at two sides of the DTP for RI measurement and temperature measurement, respectively. The PDMS-coated microfiber MZI could achieve a temperature measurement resolution of about 0.0024 ℃ if the resolution of the optical spectrum analyzer were 0.02 nm, making it suitable for temperature measurement applications with high precision requirement. The bare microfiber MZI is promising for liquid analytical measurement in fields like biochemistry for its advantages of ultrahigh sensitivity, small size, and little sample consumption.

Micro-fiber Mach-Zehnder interferometer based on ring-core fiber.

A micro-fiber Mach-Zehnder interferometer (MZI), with a thousands-µm-long ring-core fiber (RCF), is demonstrated, and its performance investigation is also implemented. In this paper, the proposed MZI is manufactured by ends-splicing the short RCF segment with single-mode fiber (SMF-28), respectively. The scheme of the MZI is a typically core-mismatch structure, which has the advantages of miniaturization and simplification. Due to the core mismatch between RCF and SMF, the light from the SMF can be well separated into ring core (RC) and silica center (SC) of the RCF at the first splicing point. After transmitting through the RC and SC, the two separated light beams encounter each other and interfere at the second splicing point. Different from conventional micro-fiber MZIs using SMFs or few-mode fibers, the RCF has a higher numerical aperture, which can generate a larger optical path-length difference with a short length fiber, accumulates a higher extinction ratio and suppresses the crosstalk between the core and cladding modes. Therefore, our proposed MZI is more stable and the best extinction ratios can reach up to 18.2 dB. Meanwhile, owing to the core structure of RCF (where SC is surrounded by high-index ring core), the power propagating through low-index area of RCF is mostly confined into SC (termed the silica-center modes). These characteristics would lead to the lower sensitivity to external disturbances.

Tapered Fiber-Optic Mach-Zehnder Interferometer for Ultra-High Sensitivity Measurement of Refractive Index.

A Mach-Zehnder interferometer (MZI) based fiberoptic refractive index (RI) sensor is constructed by uniformly tapering standard single mode fiber (SMF) for RI measurement. A custom flame-based tapering machine is used to fabricate microfiber MZI sensors directly from SMFs. The fabricated MZI device does not require any splicing of fibers and shows excellent RI sensitivity. The sensor with a cladding diameter of 35.5 µm and length of 20 mm exhibits RI sensitivity of 415 nm/RIU for RI range of 1.332 to 1.384, 1103 nm/RIU for RI range of 1.384 to 1.4204 and 4234 nm/RIU for RI range of 1.4204 to 1.4408, respectively. The sensor reveals a temperature sensitivity of 0.0097 nm/°C, which is relatively low in comparison to its ultra-high RI sensitivity. The proposed inexpensive and highly sensitive optical fiber RI sensors have numerous applications in chemical and biochemical sensing fields.

Graphene-assisted all-optical tunable Mach–Zehnder interferometer based on microfiber

We experimentally demonstrate a compact all-optical tunable Mach–Zehnder interferometer (MZI) based on microfiber. The graphene-assisted sandwich structure (GASS) integrated on the microfiber is adopted to form the all-optical tunable structure. The effective footprint of the fabricated device is about 7.31×8.66 mm2 which is much more compact than other reported all-optical tunable MZIs based on fiber system. An out-fiber 1535 nm continuous-wave pump light is employed to irradiate the GASS vertically, which can produce the strong interaction of light-graphene. As a result, the device’s response spectrum occurs red-shift due to the graphene’s photothermal effect. Compared with the microfiber MZI with only the bottom graphene film, the tuning efficiency of the microfiber MZI with GASS is improved by 6 times, which is about 0.856 pm/mW. Meanwhile, the red-shift range can exceed one free spectral range (FSR) that means the resonant wavelength can be tuned to arbitrary wavelength in the range of the transparent window. This microfiber MZI with GASS featured with wavelength tunability, all-in-fiber, compact size, easy fabrication, and simple packaging is expected for the fabricated device to be used as all-optical modulator, tunable optical filter and optical switch, etc.

Single longitudinal mode laser generation using coupled microfiber Mach–Zehnder interferometer filter

The fabrication and operation of a single longitudinal mode (SLM) laser using a compact coupled microfiber Mach–Zehnder interferometer (CM-MZI) in an erbium doped fiber (EDF) laser cavity is demonstrated. The CM-MZI is created by first fabricating an optical microfiber using the flame-brushing technique before being cut and rejoined to form a half-loop, which is the basis for the CM-MZI structure. The CM-MZI is inserted into an EDF laser cavity; the filtering effect of the CM-MZI induces a stable SLM lasing output with a consistent 3 dB bandwidth of 0.02 nm at different a pumping power and signal-to-noise ratio of ~50 dB. The output also exhibits minimal wavelength and power fluctuations of 0.02 nm and 0.15 dB, respectively, over a time period of 60 min.

A PDMS microfiber Mach-Zehnder interferometer and determination of nanometer displacements

Abstract A polydimethylsiloxane (PDMS) microfiber Mach-Zehnder interferometer (MZI), integrated between single-mode optical fibers (SMFs), is proposed and demonstrated experimentally. One arm of the interferometer consists of a microfiber of diameter 7 µm and length 270 µm; the second is an air arm. Due to the good elastic properties of PDMS microfiber, the length of the air arm of MZI can be changed by changing the distance between SMFs. The change in length of the air arm results in a change in the transmission characteristics of the MZI; thus, the relative displacement can be measured in the range 10–250 nm. By measuring the peak-to-peak amplitude of the difference in transmission powers (in dB), the smallest displacement by prepared MZI was determined as being on the order of a few nm for a ratio of intensities of 0.135. For a higher ratio of intensities of transmission functions, the smallest displacement could be determined on the order of subnanometers.

Investigation of Temperature Sensitivity of a Polymer-Overlaid Microfiber Mach-Zehnder Interferometer.

The temperature sensitivity of the free spectral range (FSR) for a polymer-overlaid microfiber Mach-Zehnder interferometer (MZI) is investigated both theoretically and experimentally. The waist diameter of the optical microfiber can be controlled to alter the thermal expansion and optic properties of the polymer-coated MZI. Inserting an optical microfiber with a strong evanescent field into the MZI, a low index polymer with high thermal characteristics is deposited on the surface of the microfibers to realize a polymer-overlaid microfiber MZI. It was found that the thermal expansion factor in the proposed MZI plays an important role in the temperature sensitivity of the FSR. The temperature sensitivity of the polymer-overlaid microfiber MZI is improved, which is measured to be −8.29 nm/°C at 25 °C. The optical transmission spectrum of the polymer-overlaid microfiber MZI is converted to the spatial frequency spectrum via fast Fourier transform. The temperature sensitivity of the spatial frequency in the proposed polymer-overlaid MZI is estimated to be 18.31 pm−1 °C−1, which is 17 times higher than that of the microfiber MZI without polymer coating (1.04 pm−1 °C−1).

A highly stable and switchable dual-wavelength laser using coupled microfiber Mach-Zehnder interferometer as an optical filter

The generation and switching of dual-wavelength laser based on compact coupled microfiber Mach-Zehnder interferometer (CM-MZI) is reported. The CM-MZI is constructed by overlapping two portions of a single tapered optical fiber which has a diameter of 9μm as to create multi-mode interference and also to produce spatial mode beating as to suppress mode competition in the homogeneous gain medium. The system is able to generate a dual-wavelength laser output that can be switched with the aid of the polarization rotation technique. Four dual-wavelength oscillation pairs are obtained from the interference fringe peaks of the CM-MZI comb filter with a switched channel spacing of 1.5nm, 3.0nm, and 6.0nm. The wavelength spacing is stable at different pump powers. The lasing wavelength has a 3-dB linewidth of about 30pm and peak-to-floor ration of about 55dB at a pump power of 38mW.

Poly (N-vinylcarbazole)-polypyrrole/graphene oxide nanocomposites based microfiber interferometer for high stability temperature sensor

An all-optical, highly stable temperature sensor based built around Poly (N-vinylcarbazole)-polypyrrole/graphene oxide nanocomposites (PNVC-PPy-GO) deposited on an inline Microfiber Mach-Zehnder interferometer (IMMZI) is investigated and demonstrated. Depositing the PNVC-PPy-GO solution on the IMMZI is seen to enhance the temperature sensing stability, and the resulting wavelength shift as a result of heating the IMMZI with a heating element was linearly proportional to temperature variations, and observed to be stable and uniform. The sensitivity and resolution of the sensor after deposition improves by about 7pm/°C and 0.18°C respectively, as compared to the sensor before deposition. The IMMZI with PNVC-PPy-GO coating will be a highly viable candidate for sensing applications requiring highly stable and precise measurements.

Performance enhancement of multi-wavelength generations based on SOAs with a microfiber Mach–Zehnder interferometer

Functionality improvement of a non-linear semiconductor optical amplifier for multi-wavelength generation is reported. A microfiber Mach–Zehnder interferometer (MMZI) is incorporated to enhance the multi-wavelength generation performance in terms of optical signal-to-noise ratio (OSNR) and full-width-half-maximum linewidth. The proposed scheme offers better dynamic functionality, with flexible tunable and switchable properties. Incorporating the MMZI causes spatial mode beating interference, resulting in narrow bands and power-efficient modes. Tunable and switchable octuple wavelength is demonstrated using non-linear polarization rotation (NPR), with frequency separation with respect to the free spectral range of the implemented MMZI over a greater than 30 nm span. The NPR effect is induced to suppress mode competition within the homogeneous broadening linewidth of the employed semiconductor optical amplifier.

Stable C-band fiber laser with switchable multi-wavelength output using coupled microfiber Mach-Zehnder interferometer

Abstract A compact coupled microfiber Mach-Zehnder interferometer (CM-MZI) is proposed and experimentally demonstrated for C-band region multi-wavelength tuning and switching in a fiber laser. The CM-MZI is fabricated using a 9 μm single tapered silica optical microfiber fabricated by flame-drawing technique and exploits multi-mode interference to produce spatial mode beating and suppress mode competition of the homogeneous gain medium. The output wavelength spacing is immune to changes in the external environment, but can be changed from 1.5 nm to 1.4 nm by slightly modifying the path-length difference of the CM-MZI. The proposed laser is capable of generating single, dual, triple, quintuple, and sextuple stabilize wavelengths outputs over a range of more than 32 nm using polarization rotation (PR) and macro-bending. The lasers having a 3 dB line-width of less than ∼30 pm and peak-to-floor of about 55 dB at a pump power of 38 mW.

Simultaneous Measurement of Seawater Temperature and Salinity Based on Microfiber MZ Interferometer With a Knot Resonator

It is significant to develop new methods for temperature and salinity measurement in seawater since they are two important parameters in physical oceanography application. In this paper, a new approach for simultaneous measurement of temperature and salinity in seawater based on microfiber Mach-Zehnder (MZ) interferometer with a knot resonator is proposed. The typical transmission spectra show the combined effect of MZ interference and knot resonance. When the temperature and salinity change, both the interference dip and the resonance dip shift linearly. Based on the linear relation, the measurement matrix is established, and the temperature and salinity of seawater sample can be obtained simultaneously by collecting the transmission spectra. The hybrid structure demonstrated here shows advantages of high sensitivity and good accuracy, which may have great potential for temperature and salinity measurement in ocean and other liquid surroundings.

Bragg Grating Embedded in Mach-Zehnder Interferometer for Refractive Index and Temperature Sensing

Fiber Bragg grating (FBG) embedded in a microfiber Mach–Zehnder interferometer (MZI) is presented for sensing multiparameters, such as temperature and refractive index. The MZI is constructed by splicing a short length of 40- $\mu \text{m}$ -diameter microfiber between standard single mode fibers. A millimeter long FBG is then written in the microfiber using direct point-by-point ultrafast laser inscription method. The microfiber MZI shows moderate sensitivity to ambient refractive index and temperature changes. In contrast, the microfiber FBG is insensitive to ambient refractive index change while it exhibits typical sensitivity to temperature variation. These distinct characteristics of the FBG and MZI sensors enable the simultaneous measurement of refractive index and temperature, and temperature compensation in ambient refractive index measurement.

Temperature-Insensitive Microfiber Mach–Zehnder Interferometer for Absolute Strain Measurement

A temperature-insensitive microfiber Mach–Zehnder interferometer (MZI) for absolute strain measurement is investigated theoretically and experimentally depending on the diameter of the microfiber. The thermo-optic quantity of the microfiber MZI is effectively controlled by optimizing the diameter of the microfiber within the MZI incorporating an external coating overlay. Consequently, the positive thermal property of the microfiber MZI is successfully compensated by the negative thermo-optic factor of the microfiber resulting in suppression of the temperature sensitivity of the microfiber MZI. The transmission spectra of the microfiber MZI with variations in temperature are converted to the spatial frequency spectra by using the fast Fourier transform. When the diameter of the microfiber is ∼7 μm, the temperature sensitivity of the spatial frequency of the microfiber MZI is dramatically mitigated to be $1.94 \times 10^{-6} \,{\rm nm}^{-1}\cdot ^{\circ}{\rm C}^{-1}$ . We apply the proposed microfiber MZI for absolute strain measurement and its strain sensitivity is measured to be $7.53 \times 10^{-4} \,nm^{-1}\cdot \mu \varepsilon ^{-1}$ in the spatial frequency domain.

Highly stable and tunable narrow-spacing dual-wavelength ytterbium-doped fiber using a microfiber Mach–Zehnder interferometer

We describe a successful demonstration of highly stable and narrowly spaced dual-wavelength output via an ytterbium-doped fiber laser. A microfiber-based Mach-Zehnder interferometer and a tunable bandpass filter were both placed into the laser ring cavity for the purpose of ensuring a stable and narrowly spaced dual-wavelength output. Experimental results comprised three sets of dual-wavelength lasing output with wavelength spacing of 0.06, 0.09, and 0.22 nm, respectively, and side-mode suppression ratio of ∼50 dBm. A subsequent stability test provided evidence that maximum power and wavelength fluctuation were less than 0.8 dB and 0.01 nm, respectively, and thus, the obtained output was considered to be highly stable in dual-wavelength operation. The proposed system offers advantages of flexibility in dual-wavelength laser generation in addition to excellent reliability.

Tunable dual-wavelength ytterbium-doped fiber laser using a strain technique on microfiber Mach-Zehnder interferometer.

In this paper, stable dual-wavelength generation using a strain technique for a ytterbium-doped fiber laser is successfully demonstrated. A microfiber-based Mach-Zehnder interferometer is inserted into the laser ring cavity and stretched using the xyz translation stage. Four sets of dual-wavelength output lasing are obtained when the strain is applied onto a microfiber. The dual-wavelength output possesses spacing between 7.12 and 11.59nm, with displacement from 2 to 190μm from the central wavelength. The obtained side-mode suppression ratio is ∼48 dBm, while the maximum power fluctuation and wavelength shift are less than 0.6dB and 0.01nm, respectively. The results demonstrate that this setup generates a stable dual-wavelength laser in the 1μm region.

Realization of spectral tunable filter based on thermal effect in microfiber structure

Abstract This paper demonstrates a new approach for tuning the extinction ratio of a complex microfiber structure output using thermal effect. The microfiber filter device comprises of a microfiber Mach–Zehnder interferometer followed a knot structure, where temperature is controlled by a DC current applied to a copper wire placed inside the knot. This enables electrical tuning, where applying electrical current increases the temperature and affects the optical path. The change of temperature facilitates the fine tuning of the resonance output spectrum. From the experiment, it was observed that the extinction ratio of the output comb spectrum can be controlled within 2 dB to 10 dB by varying the current rating from 0 A to 1.22 A.

Highly responsive NaCl detector based on inline microfiber Mach–Zehnder interferometer

This paper details the fabrication and performance evaluation of a sodium chloride (NaCl) detector based on an inline microfiber Mach–Zehnder interferometer (IMMZI) that had been fabricated via a glass fiber processing system (Vytran GPX-3400). Spectral characteristics of IMMZIs possessing a variety of waist diameters and situated within assorted concentrations of NaCl solutions are also reported. An optimally high responsitivity to NaCl solutions of about 2913.7nm per refractive-index unit (RIU) was exhibited by an IMMZI with a total length of 34mm and a tapered waist diameter of 10μm, in which the RI ranged from 1.31837 to 1.31928.