Fiber Mach-Zehnder Interferometer Research Articles

Intensity modulation type fiber-optic strain sensor based on a Mach–Zehnder interferometer constructed by an up-taper with a LPG

A highly sensitive and compact fiber-optic strain sensor was presented and experimentally demonstrated. The sensor is based on an in-line fiber Mach–Zehnder interferometer (MZI), which is constructed by connecting a long-period fiber grating (LPG) with an up-taper. With the increasing of the axial strain on the sensor, both of the up-taper's diameter and the light coupling efficiency decreased. By measuring the transmission intensity changes of the resonant dips at wavelength ~1553.4nm under the fiber axial strain ranging from 0 to 590με, the sensitivity of 0.026dB/με was obtained, which is almost 2 times of the existing similar strain sensor. And the results were also confirmed by simulations.

Temporal manipulation of light propagation via cross-intensity modulation in unbalanced fiber Mach-Zehnder interferometers.

We theoretically propose and experimentally demonstrate an approach to achieve temporal manipulation of light propagation via cross-intensity modulation (XIM) effect in an unbalanced fiber Mach-Zehnder interferometer (MZI). By changing the optical loss indices (which can also be gain indices theoretically) discrepantly in the two branches of the MZI, we can obtain the largest time shifts at the minima of the transmission frequency spectrum, while there shows no time shifts at the maxima. This scheme provides a flexibility of ultra-wide bandwidth operation both on optical wavelength and modulation frequency.

Fourier-transform spectroscopy using an Er-doped fiber femtosecond laser by sweeping the pulse repetition rate.

Femtosecond lasers allow for simultaneous detection of multiple absorption lines of a specimen over a broad spectral range of infrared or visible light with a single spectroscopic measurement. Here, we present an 8-THz bandwidth, 0.5-GHz resolution scheme of Fourier-transform spectroscopy using an Er-doped fiber femtosecond laser. A resolving power of 1.6 × 104 about a 1560-nm center wavelength is achieved by sweeping the pulse repetition rate of the light source on a fiber Mach-Zehnder interferometer configured to capture interferograms with a 0.02-fs temporal sampling accuracy through a well-stabilized 60-m unbalance arm length. A dual-servo mechanism is realized by combining a mechanical linear stage with an electro-optic modulator (EOM) within the fiber laser cavity, enabling stable sweeping control of the pulse repetition rate over a 1.0-MHz scan range with 0.4-Hz steps with reference to the Rb clock. Experimental results demonstrate that the P-branch lines of the H13CN reference cell can be observed with a signal-to-noise ratio reaching 350 for the most intense line.

Effect of waist diameter and twist on tapered asymmetrical dual-core fiber MZI filter.

A compact in-fiber Mach-Zehnder interferometer (MZI) filter fabricated from custom-designed asymmetrical dual-core fiber is numerically analyzed in detail and experimentally verified. The asymmetrical dual-core fiber has core diameters and a core pitch of 6.9, 6, and 19.9 μm, respectively. The fiber tapering technique is introduced to fuse the originally uncoupled cores into strong coupling tapered regions. The length and diameter of the waist region have a close impact on the splitting ratio, which further affects the spectral properties of the MZI filter. The field evolution with varied waist parameters is characterized by the finite element method and beam propagation method. Repeatable comb filters with ∼15 dB extinction ratio are successfully achieved under the guidance of simulated optimum conditions. The twist-induced circular birefringence gives rise to a retardance that causes the spectral shifts of the MZI filter. The theoretical and experimental results confirm that the relative wavelength shift is proportional to the retardance, which follows a sinc function in the limit of a large twist rate.

Linewidth Measurement of Distributed-Feedback Semiconductor Lasers Operating Near 2.05 <inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula>

The first unambiguous linewidth measurements are reported for fiber-pigtailed high-power distributed feedback (DFB) semiconductor lasers operating near 2.05 $\mu \text{m}$ wavelength range. The DFB lasers are packaged inside standard 14-pin butterfly package with polarization- maintaining output fiber and an integrated optical isolator. The Schawlow-Townes linewidth was measured using the coherent frequency-discriminator technique with a fiber Mach-Zehnder interferometer and the total linewidth was characterized using a heterodyne setup. Our measurements indicate less than 100 KHz Schawlow-Townes linewidth and a total linewidth of less than 200 KHz over 50 ms measurement time.

Peak-to-peak tracking method for measurement of optical path difference: Revisited

This paper reports on the measurement of optical path difference of spectral interference signal by using the peak-to-peak tracking method in the wavelength domain. Numerical simulations are performed to produce the interference spectrum based on an all fibre Mach–Zehnder interferometer with a white light source. The peak-to-peak tracking method is improvised by measuring the wavelength value corresponding to bright fringes from the phase plot for determination of the optical path difference. The results are compared to the conventional peak-to-peak tracking method and measurement of the slope of phase against wavenumber plot. Optical path difference determined from the improvised method yields higher accuracy with lower uncertainty.

An optical fiber magnetic field sensor based on fiber spherical structure interferometer coated by magnetic fluid

A novel magnetic field sensor based on optical fiber Mach-Zehnder interferometer (MZI) coated by magnetic fluid (MF) is proposed. The MZI consists of two spherical structures formed on standard single mode fiber (SMF). The interference wavelength and the power of the sensing structure are sensitive to the external refractive index (RI). Since RI of the MF is sensitive to the magnetic field, the magnetic field measurement can be realized by detecting the variation of the interference spectrum. Experimental results show that the wavelength and the power of interference dip both increase with the increase of magnetic field intensity.

Mach–Zehnder Interferometer Based on S-Tapered All-Solid Photonic Bandgap Fiber

We propose an S-tapered fiber Mach-Zehnder interferometer based on all-solid photonic bandgap fibers. Theoretical and experimental results reveal that the interference pattern originates from the coupling between core modes LP01 and LP11, LP01 cladding supermode. The proposed structure exhibits quite sensitive to temperature and nearly insensitive to surrounding refractive index (RI). Moreover, the temperature-strain cross sensitivity is only 0.0092 °C/ $\mu \varepsilon $ . The strain/surrounding RI responses show little impact on the temperature sensing precision. Such a structure is easy to fabricate and can be a promising temperature sensor, eliminating the RI/strain-induced cross sensitivity.

Bent Fiber Interferometer

We report a novel fiber-optic interferometer based on Mach–Zehnder interferometer (MZI) from a bent single-mode fiber (SMF) and experimentally demonstrated that it can be used as a fiber-optic refractometer. The interferometer has a simple structure including a standard SMF with a bare fiber semicircular bending region of a given diameter. A fiber MZI is formed by the different optical paths taken by the core and cladding modes from the designed bending fiber structure. We also realize a dual-channel interferometer by using a 9 and 11 mm bending diameter fiber structure and measure the refractive index of the ambient environment by monitoring the wavelength shift of the resonance dips in its transmission spectrum. Additionally, we investigate the relationship between the wavelength shifts of the resonant dips with temperature changes. This dual-channel interferometer can be potentially used for simultaneous measurement of dual chemical parameters.

Microwave photonic filter with two independently tunable passbands based on paralleled fiber Mach–Zehnder interferometers and dispersive medium

In this article, we propose and experimentally demonstrate a novel microwave photonics filter (MPF) with two independently tunable passbands. The MPF is based on a sliced broadband optical source and a dispersive medium, and two paralleled fiber Mach–Zehnder interferometers (FMZIs) have been employed as the optical spectrum slicer. A coil of single-mode fiber has been used as a dispersion medium, which introduces time delay for each tap. A stable dual-passband MPF has been obtained, and the experimental results show that each passband of the MPF can be tuned freewill by adjusting the variable optical delay line (VODL) in each of the FMZIs.

All-Fiber Mach–Zehnder Interferometer for Liquid Level Measurement

A new liquid level sensor based on in fiber Mach-Zehnder interferometer (MZI) is proposed and demonstrated. The MZI is formed by cascading two peanut-shaped fiber structures in single-mode fiber. In the water level experiment, the sensitivities of sensors with lengths of 53.5 and 75.4 mm are -0.1025 and -0.0279 nm/mm, respectively. The absolute value of sensitivity increases with the refractive index of liquid. The MZI presented in this paper has advantages of low cost and ease of fabrication, which can be a potential advantage in the liquid level measurement.

Compact Mach–Zehnder Interferometer Based on Tapered Hollow Optical Fiber

A compact fiber Mach–Zehnder interferometer based on tapered hollow optical fiber (THOF) has been demonstrated. The THOF is sandwiched between two single mode fibers (SMFs), forming a SMF-THOF-SMF (STS) structure. The discharging during the splicing and tapering processes induces the collapsed regions in the hollow fiber, which form the modal coupling/re-coupling areas of the interferometer. The THOF has a length of about 2 mm and the taper waist diameter is about 66.5 $\mu \text{m}$ . The refractive index (RI), stress, and temperature response properties of the STS interferometer have been investigated, which show a high RI sensitivity and low temperature cross-sensitivity. The STS interferometer holds the merits of compact structure, low cost and easy fabrication, making it a suitable candidate in the biochemical and physical sensing fields.

Novel method of detecting movement of the interference fringes using one-dimensional PSD.

In this paper, a method of using a one-dimensional position-sensitive detector (PSD) by replacing charge-coupled device (CCD) to measure the movement of the interference fringes is presented first, and its feasibility is demonstrated through an experimental setup based on the principle of centroid detection. Firstly, the centroid position of the interference fringes in a fiber Mach-Zehnder (M-Z) interferometer is solved in theory, showing it has a higher resolution and sensitivity. According to the physical characteristics and principles of PSD, a simulation of the interference fringe’s phase difference in fiber M-Z interferometers and PSD output is carried out. Comparing the simulation results with the relationship between phase differences and centroid positions in fiber M-Z interferometers, the conclusion that the output of interference fringes by PSD is still the centroid position is obtained. Based on massive measurements, the best resolution of the system is achieved with 5.15, 625 μm. Finally, the detection system is evaluated through setup error analysis and an ultra-narrow-band filter structure. The filter structure is configured with a one-dimensional photonic crystal containing positive and negative refraction material, which can eliminate background light in the PSD detection experiment. This detection system has a simple structure, good stability, high precision and easily performs remote measurements, which makes it potentially useful in material small deformation tests, refractivity measurements of optical media and optical wave front detection.

Switchable and tunable microwave frequency multiplication based on a dual-passband microwave photonic filter.

In this paper, a novel approach to implement switchable and tunable microwave frequency multiplication has been proposed and experimentally demonstrated. High order harmonics of microwave signal with external modulation technique can be selected by using a novel switchable dual-passband microwave photonic filter (MPF) based on a modified fiber Mach-Zehnder interferometer (FMZI) and a dispersive medium. By adjusting the polarization controllers in the modified FMZI, the passbands of the MPF can switch between lower frequency, higher frequency or dual-passband states, and by changing the length of the variable optical delay line (VODL) in the modified FMZI, the central frequencies of these passbands can also be tuned. Therefore, tunable and switchable microwave signal frequency multiplication can be achieved. The experimental results show that by modulating a driving signal with frequency of 2.5 GHz, a signal with frequency of 7.5 GHz, which is three times of the driving frequency, the other one with the frequency of 15 GHz, which is six times of the driving frequency can be generated and freely switchable between two frequencies and dual frequency states by simply adjusting the polarization controllers in the modified FMZI.

High Sensitivity Fiber Laser Temperature Sensor

This paper presents an erbium-doped fiber laser temperature sensor, which is based on an intracavity fiber filter immersed in glycerol/water solutions. The sensing element is the intracavity fiber filter, consisting of a two-taper fiber Mach-Zehnder interferometer (MZFI). The high refractive index dispersion of glycerol/water solutions with temperature allowed the modification of the MZFI spectral characteristics and hence determines the lasing wavelength. The sensitivity of 1089 pm/°C and a signal-to-noise ratio of 50 dB make the proposed sensor suitable for real applications.

Fourier Analysis Applied on MZI Transmission Spectrum for Refractive Index Measurement

An approach for surrounding refractive index (SRI) measurement is proposed and demonstrated using all fiber Mach-Zehnder interferometer (MZI) formed by fusion splicing a short section of thin-core fiber between two sections of single-mode fibers with lateral offsets. The transmission spectrum of the MZI is dominantly formed by the superposition of two cladding modes separately interference with the core mode, which correspond to two frequency components in its fast Fourier transform (FFT) spectrum, respectively. In this letter, the two frequency components are extracted to take the inverse FFT, respectively, thus we can obtain two dual-mode interference (DMI) patterns between the cladding modes and the core mode. As the SRI changes, the shifts of the two DMI patterns with SRI will be observed. Through this way, we can eliminate the influence of multiple interferences and improve the accuracy of the sensor. The approach can also be utilized with other modal interferometric sensors.

A tunable dual-passband microwave photonic filter based on optical slicing and dual-path fiber delay lines

In this article, a dual-passband microwave photonics filter (MPF) based on spectrally sliced broadband optical source (BOS) and a dual-path fiber delay line has been proposed and experimentally demonstrated. Continuous optical samples are obtained when a BOS is sliced by a fiber Mach–Zehnder interferometer (FMZI). Dual-passband frequency response has been realized by utilizing two dispersive fiber delay lines with different length and recombining two groups of delayed samples on the photodiode (PD). The proposed dual-passband MPF is stable and the central frequencies of the passbands can be tuned continuously by either changing the free spectral range of the FMZI or the length of dispersive fiber delay lines. Furthermore, multi-passband MPF with desirable passband central frequencies can be achieved by using the proposed technique, which shows good application potentials in the wireless communication and measurement systems.

Simultaneous measurement of temperature and strain or temperature and curvature based on an optical fiber Mach–Zehnder interferometer

A compact optical fiber Mach–Zehnder interferometer (MZI) is proposed and experimentally demonstrated for simultaneous measurement of temperature and strain or temperature and curvature. This device consists of input single mode fiber (SMF), a fiber Bragg grating (FBG), a short section of multimode fiber (MMF) and output SMF, of which the FBG is offset spliced with upstream input SMF. The high-order cladding modes can be excited at the core offset plane and then be recoupled to the output SMF through the MMF. The interference dip of 1563nm is selected to demonstrate the interferometer's response to strain and curvature, and the Bragg peak is used to monitor temperature variation. The experimental results demonstrate that the strain and curvature sensitivities of the proposed MZI are −0.12pm/με and −164pm/m−1, and the temperature sensitivities of FBG and MZI are 9pm/°C and 52pm/°C, respectively. The simultaneous measurement of temperature and strain or temperature and curvature can be realized through the demodulation matrixes.

A variable coefficient microwave photonic filter based on multi-wavelength fiber laser and Mach-Zehnder interferometer

A microwave photonic filter (MPF) with variable coefficient is proposed and demonstrated, which is constructed by a multi-wavelength fiber laser and Mach-Zehnder interferometer (MZI). Through changing the slope characteristics of Mach-Zehnder interference spectrum adjusted by optical variable delay line (OVDL), the conversion from phase modulation (PM) to intensity modulation (IM) is realized. The multi-wavelength fiber laser with Lyot-Sagnac optical filter has variable wavelength spacing. So the designed filter has a variable number of taps and tap weights. As a result, the tunable range of passband center frequency is 2.6 GHz. The reconfigurability of MPF can be also realized by adjusting the output of fiber laser.

Asymmetrical dual tapered fiber Mach-Zehnder interferometer for fiber-optic directional tilt sensor.

This work proposes a novel, highly sensitive and directional fiber tilt sensor that is based on an asymmetrical dual tapered fiber Mach-Zehnder interferometer (ADTFMZI). The fiber-optic tilt sensor consists of two abrupt tapers with different tapered waists into which are incorporated a set of iron spheres to generate an asymmetrical strain in the ADTFMZI that is correlated with the tilt angle and the direction of inclination. Owing to the asymmetrical structure of the dual tapers, the proposed sensor can detect the non-horizontal/horizontal state of a structure and whether the test structure is tilted to clockwise or counterclockwise by measuring the spectral responses. Experimental results show that the spectral wavelengths are blue-shifted and red-shifted when the sensor tilts to clockwise (-θ) and counterclockwise ( + θ), respectively. Tilt angle sensitivities of about 335 pm/deg. and 125 pm/deg. are achieved in the -θ and + θ directions, respectively, when the proposed sensing scheme is utilized.