Fiber Michelson Interferometer Research Articles

Graphene decorated twin-core fiber Michelson interferometer for all-optical phase shifter and switch

We investigated an all-optical phase shifter and switch based on a graphene decorated side-polished twin-core fiber (TCF) Michelson interferometer (MI). The MI was fabricated by tapering the splicing point between the TCF and single-mode fiber. The flat surface of exposed polished core in the TCF was coated with monolayer graphene. A 980 nm pump laser is used to produce a photothermal effect. The graphene’s ohmic heating changes the effective refractive index of the exposed core, resulting in the phase shift of the MI. The MI with a polished length of 5 mm has a significant modulation phase shift with a nearly linear slope of 0.0102 π / m W near the wavelength of 1550 nm and can obtain an extinction ratio of 7 dB for optical switching with a rise (fall) time of 55.8 ms (15.5 ms). The high-density integration and all-optical control enable the proposed device to have great potential in the miniaturization of optical devices and all-optical signal processing.

Optimal design for spectral narrowing and fast frequency sweep of an interferometer-stabilized laser

Self-heterodyne fiber interferometers have been shown to be capable of stabilizing lasers to ultra-narrow linewidths and present an excellent alternative to high-finesse cavities for frequency stabilization. In addition to suppressing frequency noise, these devices are highly tunable and can be manipulated to produce high-speed frequency sweeps over the entire range of the laser. We present an analytic approach for choosing a delay-line length for both optimal noise suppression and highest in-loop frequency sweep rate. Based on this model, we stabilize an extended cavity diode laser to a fiber Michelson interferometer and demonstrate a linewidth of 700 Hz over millisecond timescales while also allowing for a frequency scan rate of 1 THz/s. We independently measure the maximum deviation from linearity of the sweep to be only 100 kHz.

A liquid refractive index sensor based on 3-core fiber Michelson interferometer

A liquid refractive index (RI) sensor based on in-fiber Michelson interferometer (MI) is proposed and experimentally demonstrated, which consists of a segment of 3-core fiber (3CF) fusion spliced with a short piece of multimode fiber (MMF). The operation principle of the MI lies in the intermodal interference of the 3CF via employing MMF to excite high-order modes, and the 3CF end face reflects the interference spectrum which loaded the surrounding RI information. By measuring the reflection spectrum variation, the RI can be determined. Experimentally, a linearly RI sensitivity of -151.56 dB/RIU is achieved in the sensing range of 1.3335-1.3720 RIU, and the temperature sensitivity in water is 0.048 nm/°C.

Bending sensor with parallel fiber Michelson interferometers based on Vernier-like effect

A highly sensitive bending sensor based on two parallel fiber Michelson interferometers (MIs) with a Vernier-like effect is proposed and demonstrated. The interferometric structure consists of a dual-core fiber (DCF) spliced with a short section of dual-side-hole fiber (DSHF). The centric core of the DCF is aligned with one air-hole of the DSHF to form a reflective interface. The centric core of the DCF is connected to the core of the DSHF with a little lateral offset to make the light in the centric core couple to both the core and cladding of the DSHF. The light beams reflected by the end of the DSHF and the DCF interfere with each other, forming two parallel MIs. The free spectral range (FSR) difference between the two MIs is very small due to the tiny difference in refractive index (RI) between the core and cladding of the DSHF, which results in a Vernier-like effect. The most novel feature of the mentioned structure is that both MIs are sensitive to bending with the same sensitive direction. Experimental results indicate that the bending sensitivity of the sensor can reach 38.53 nm/m−1. This kind of sensor has far-reaching significance in the research of structural safety monitoring.

All-optical or logic gate based on a photonic crystal fiber Michelson interferometer operating with pulse-position modulation

We present a numerical investigation of the study of the Michelson interferometer by exploring the potential of such a device to act as an all-optical logic gate when excited with ultrashort pulses of 100 fs. The input pulse is controlled by a pulse-position modulation (PPM) modulator, which has the role of controlling the value and direction of the temporal displacement from the variation of the PPM modulating factor. We present the study on the signal-to-noise ratio (SNR), which served as the basis for constructing a merit figure of the studied logic gates in order to verify their performance. We considered pulse propagation under the influence of dispersive effects, as well as the nonlinear effects in the propagation regime with no loss for the input pulses. It was possible to implement the OR logic operation in at least one interval of the modulation adjustment parameter in each of the distinct pumping power regimes, thus obtaining a total of nine intervals of OR logic gate. The situation with the best SNR = 29.36 dB, for the suggested logic gate operation, was found at the power of 150 kW with the modulation adjustment parameter e = 43 fs. Numerical studies were done from the coupled–coupled equations solved using the fourth-order Runge–Kutta method. The implementation of fully optical logic gates tends to revolutionize digital systems in the field of data storage, such as optical memory, “replacement” of electronic circuits among other applications.

Highly Sensitive Vector Curvature Sensor Based on Two Juxtaposed Fiber Michelson Interferometers With Vernier-Like Effect

In this paper, a highly sensitive vector curvature sensor based on two juxtaposed fiber Michelson interferometers (MI) with Vernier-like effect has been proposed and verified. Different from the structures of the conventional Vernier effect which are composed of the cascaded elements, the proposed configuration consists of two juxtaposed MIs. A triple-core fiber (TCF) is connected with a quite short piece of dual-side-hole fiber (DSHF), and the core of the DSHF and the two eccentric cores of the TCF are respectively constituted two juxtaposed MIs. The Vernier-like effect is caused by the very small refractive index difference between the two eccentric cores of the TCF. The most outstanding feature of the proposed structure is that the two MIs are both sensitive to curvature with opposite sensitivities, which makes the curvature sensitivity magnification factor twice that of the conventional Vernier effect structure. Experimental results show that the curvature sensitivity of the structure can reach $-60.84~{\mathrm {nm/m}}^{-1}$ .

All-optical graphene-oxide humidity sensor based on a side-polished symmetrical twin-core fiber Michelson interferometer

A high-sensitive graphene-oxide (GO) humidity sensor based on a side-polished twin-core fiber (SPTCF) Michelson interferometer (MI) has been demonstrated. The MI was fabricated by splicing a section of TCF to a standard single mode fiber (SMF) and tapering the splicing point. The exposed polished core has a stronger evanescent field and enhances the interaction between light and external environment. The GO-SPTCFMI can operate in the wavelength- and intensity- modulated sensor. The super-high humidity sensitivities of ˜2.72 nm/RH% in the RH range of 40–75% and ˜3.76 dB/RH% in the RH range of 60–62.1% are obtained experimentally. The high-performance GO-SPTCFMI is a promising candidate for potential applications, such as gas sensing and biochemical detection.

Experimental study on 1/f intrinsic thermal noise in optical fibers

Intrinsic thermal noise in optical fibers is an ultimate factor limiting the performances of fiber-based sensors and measurement systems. Therefore, it is important to have a thorough understanding of this kind of noise. However, the mechanism of the intrinsic thermal noise which has a 1/<i>f</i> spectral density remains unclear so far. There are two theoretical models to explain the mechanism of this kind of noise: thermoconductive noise model and thermomechanical noise model. The thermoconductive noise model states that the noise is caused by diffusion of local entropy fluctuations associated with random spontaneous emission events, while the thermomechanical noise model says that the noise is caused by spontaneous fluctuations of fiber length induced by mechanical dissipation. Which theoretical model is correct is still an open question. In this paper, we experimentally investigate the intrinsic thermal noise in optical fibers by using a balanced fiber Michelson interferometer with heterodyne detection technique. When a fiber-stabilized laser with ultralow frequency noise is used as a laser source and other noise sources are carefully controlled, the 1/<i>f</i> spectral intrinsic thermal noise can be observed down to infrasonic frequency. According to these measurements, in order to verify which theoretical model is the mechanism of generating the intrinsic thermal noise with 1/<i>f</i> spectral density, we study the relationship between the level of the intrinsic thermal noise and the concentration of the dopant in fibers and the applied tension of fibers. We observe that the level of the 1/<i>f</i> spectral intrinsic thermal noise is independent of the concentration of the dopant in fibers. This means that the thermoconductive noise model is not suitable to this case. We also observe that the level of the 1/<i>f</i> spectral intrinsic thermal noise can be reduced by increasing the tension exerted on the optical fibers. Because the mechanical loss of a fiber can be lower than the loss of the material which the fiber is made of when the fiber is subjected to a certain tension, this observation proves the fact that the 1/<i>f</i> spectral intrinsic thermal noise in optical fibers originates from the mechanical dissipation process inside optical fibers. This is consistent with the predictions of the thermomechanical noise model. Finally, the inconsistency between the experimental data and the theoretical results for thermomechanical noise is discussed.

Spacing-adjustable multi-wavelength erbium-doped fiber laser using a fiber Michelson interferometer

We demonstrate a stable spacing-adjustable multi-wavelength erbium-doped fiber laser by employing an adjustable fiber Michelson interferometer. The central wavelength of the multi-wavelength laser can be tuned by adjusting the polarization controllers, while the wavelength spacing can be continuously tuned by adjusting the optical delay line in the Michelson interferometer. Tunable wavelength spacing is achieved in the range of 0.045 to 0.7 nm. More than 60 wavelengths within a flatness of 3 dB and wavelength spacing of 0.0474 nm can be achieved.

Highly sensitive liquid level sensor based on an optical fiber Michelson interferometer with core-offset structure

A highly sensitive liquid level sensor based on an optical fiber Michelson interferometer with core-offset structure has been proposed and demonstrated. The sensor was fabricated by offset splicing a section of single-mode fiber (SMF) between another two SMFs and coated the reflection film at the end-face of the pigtail. This sensor was then used to measure liquid level and the dip of the measured reflection spectra caused by Michelson interference shifted obvious when the sensor is immersed in pure water. A good linear relationship between the liquid level and spectrum dip wavelength shift was detected (R2 = 0.9971), while the dip intensity of the interference fringes fluctuates very little. The measured sensitivity up to 77 pm/mm was shown when the water level changed from 0 to 40 mm. In summary, this optical fiber sensing system would be appreciated in applications to liquid level measurement due to its good linearity, sensitivity, simple structure, and low cost.

Phase derivative thermo-spatiogram for distributed temperature sensing based on chirped grating-Michelson Interferometer

A novel thermometric measurement based on chirped fiber Bragg grating (CFBG) and Michelson Interferometer is proposed. The interrogation technique is based on the linear relation between the temperature and the phase derivative function of the grating, which is determined through Fourier transformation of the output spectrum. The Michelson interferometer configuration offers the flexibility in adjusting the position of coupling coefficient curve in the spatiogram, enabling the interrogation to be done at a shorter optical spectrum record length which can reduce the interrogation time and computation load.

In-Line Fiber Michelson Interferometer for Enhancing the Q Factor of Cone-Shaped Inwall Capillary Coupled Resonators

An in-line fiber Michelson interferometer in a cone-shaped inwall capillary with the whispering gallery mode microsphere resonator integrated inside is demonstrated for enhancing the Q factor, which is fabricated on the etched capillary by the femtosecond laser micromachining to decrease the coupling paths. The modulated symmetric WGM resonances and asymmetric Fano resonances induced by the Michelson interferometer are observed in the reflection spectra, with a slope of 91.87 dB/nm and Q factor as 3.85 × 104 achieved. Numerical simulations with the transfer matrix method also validate the resonator spectra modulated by the Michelson interference. This method shows a perspective potential for the enhancement of the Q factor by tailoring interacting paths through the femtosecond laser micromachining.

Double‐clad fiber Michelson interferometer for measurement of temperature and refractive index

AbstractAn all‐fiber Michelson interferometer based on double‐clad fiber (DCF) is proposed for temperature and refractive index (RI) sensing. The sensor is formed by continuous splicing between single mode fiber, multimode fiber, and DCF. Temperature measurement is achieved by monitoring the dip wavelength shift of the interferometer spectra resulting from thermo‐optic effect on core and first cladding of DCF. RI measurement is established from the power change in spectra due to the Fresnel's reflection at the DCF tip. Experimental result on 18.5 mm sensor manifests that temperature and RI responses are distinguishable. For instance, power level at 1540.5 nm exhibits quadratic shift to RI changes while unaffected to temperature changes. Dip wavelengths of sensor spectra demonstrate linear shift to temperature changes while unaffected by RI changes. The proposed sensor is cost effective as sensor fabrication only requires conventional splicing. Sensor capability to distinguish temperature and RI parameters makes it practical for broad range applications including for biomedical and food industries.

An Integrated Fiber Michelson Interferometer Based on Twin-Core and Side-Hole Fibers for Multiparameter Sensing

An integrated fiber Michelson interferometer (MI) based on an asymmetrical twin-core fiber (TCF) cascaded with a side-hole fiber (SHF) for multiparameter sensing is proposed and demonstrated. The asymmetrical TCF consists of a centric core and an eccentric core with same refractive index. The centric core of the TCF is aligned with the core of the SHF and the eccentric core is aligned with one air hole of the SHF. Because the eccentric core of the TCF is off the axis of the fiber, a bend or twist will cause a variation of the optical path difference of the MI, which makes the MI structure be suitable for twist and vector curvature measurements. Experimental results show that the bending sensitivities of the sensor are −6.968 and 6.978 nm/m−1 at the bending directions of 0° and 180° in the curvature ranges of 0–10.708 m−1, respectively, and the twist sensitivity of the sensor is 0.639 nm/(rad/m) in the twist ranges of 0–7.44 rad/m. The structure is also sensitive to strain and temperature, and the strain and temperature sensitivities of the interferometer are 1.36 pm/ ${{\mu \varepsilon }}$ and 10.37 pm/°C, respectively.

Fiber Optical Coherence Domain Polarimetry for PM Fiber Measurements

Optical coherence domain polarimetry (OCDP) utilizes incoherent light and is based on Michelson interferometer. This paper presents a polarization maintaining (PM) Michelson fiber interferometer utilizing a single PM fiber loop mirror (Sagnac Loop) that replaces the conventional free space mirrors for OCDP systems. This implementation is environmentally robust and alleviates much of the mechanical complications necessary to reduce temperature and vibrations effects. A piezoelectric transducer (PZT) is inserted in one of the arms of the interferometer and driven near its resonance. This enables a detailed measurement of polarization coupling around any point in the device under test. An analytical model is given, based on Pauli matrices algebra, that includes the side effects due to component imperfections. It is shown that the polarization coupling in the PZT has the largest side effect on the OCDP output. Experimental investigations verify the accuracy of the theoretical model. Measurements are done on two PM PANDA fibers of lengths 20 and 150 m, respectively. In addition, the new system successfully measures distributed polarization mode coupling, group birefringence, and group birefringence dispersion for the fiber under test.

Quadrature Michelson Interferometer for Temperature Measurement in the Core of Active Fiber of a High-Power Fiber Laser

We propose a new way for temperature measurement in the core of active optical fiber under high-power laser generation. The technique is based on quadrature fiber Michelson interferometer assisted with lock-in amplification for separated amplitude and phase modulations of the probe light, which allows to perform measurements in arbitrary heat transfer conditions. The technique is demonstrated on the Yb-doped fiber laser. The pump power up to 25 W under natural convection was applied. The value of convective heat transfer coefficient and its dependence on temperature difference between fiber and environment are determined from these measurements.

High-birefringence photonic crystal fiber Michelson interferometer with cascaded fiber Bragg grating for pressure and temperature discrimination

A simple and compact interferometer for temperature and pressure discrimination is proposed and demonstrated experimentally. It consists of a short section of high-birefringence photonic crystal fiber (Hi-Bi PCF) and a cascaded fiber Bragg grating (FBG). In the Hi-Bi PCF, two orthogonal polarized modes are employed as optical arms to construct, such as a Michelson interferometer. Combined with a cascaded FBG, pressure and temperature measurements are discriminated by a matrix method, and the pressure sensitivity of Hi-Bi PCF is determined to be around 3.65 nm/MPa. The proposed Michelson interferometer is easy-to-fabricate, flexible, and low-cost, which shows great potential in future applications of remote sensing.

Real-time drift error compensation in a self-reference frequency-scanning fiber interferometer

In order to eliminate the fiber drift errors in a frequency-scanning fiber interferometer, we propose a self-reference frequency-scanning fiber interferometer composed of two fiber Michelson interferometers sharing common optical paths of fibers. One interferometer defined as reference interferometer is used to monitor the optical path length drift in real time and establish a measurement fixed origin. The other is used as a measurement interferometer to acquire the information from the target. Because the measured optical path differences of the reference and measurement interferometers by frequency-scanning interferometry include the same fiber drift errors, the errors can be eliminated by subtraction of the former optical path difference from the latter optical path difference. A prototype interferometer was developed in our research, and experimental results demonstrate its robustness and stability.

Fiber optofluidic biosensor for the label-free detection of DNA hybridization and methylation based on an in-line tunable mode coupler

An optical fiber optofluidic biosensor for the detection of DNA hybridization and methylation has been proposed and experimentally demonstrated. An in-line fiber Michelson interferometer was formed in the photonic crystal fiber. A micrhole in the collapsed region, which combined the tunable mode coupler and optofluidic channel, was fabricated by using femtosecond laser micromachining. The mode field diameter of the guided light is changed with the refractive index in the optofluidic channel, which results in the tunable coupling ratio. Label-free detections of the DNA hybridization and methylation have been experimentally demonstrated. The probe single stranded DNA (ssDNA) was bound with the surface of the optofluidic channel through the Poly-l-lysine layer, and the hybridization between a short 22-mer probe ssDNA and a complementary target ssDNA was carried out and detected by interrogating the fringe visibility of the reflection spectrum. Then, the DNA methylation was also detected through the binding between the methylated DNA and the 5-methylcytosine (5-mC) monoclonal antibody. The experiments results demonstrate that the limit of detection of 5nM is achieved, establishing the tunable mode coupler as a sensitive and versatile biosensor. The sensitive optical fiber optofluidic biosensor possesses high specificity and low temperature cross-sensitivity.

Observation of fundamental thermal noise in optical fibers down to infrasonic frequencies

The intrinsic thermal noise in optical fibers represents the ultimate limit for fiber-based systems. However, at infrasonic frequencies, the spectral behavior of the intrinsic thermal noise is still unclear. In this letter, we present measurements of the fundamental thermal noise in optical fibers that are obtained using a balanced fiber Michelson interferometer. When an ultra-stable laser is used as the laser source and other noise sources are carefully controlled, the 1/f spectral density of the thermal noise is observed down to infrasonic frequencies, and the measured magnitude is consistent with the results of theoretical predictions at frequencies over the range from 0.2 Hz to 20 kHz. Moreover, as observed experimentally, the level of the 1/f thermal noise can be reduced by changing the coatings of the optical fibers. This therefore indicates one possible way to reduce thermal noise in optical fibers at low Fourier frequencies. Finally, the inconsistency between the experimental data and the existing theory for thermomechanical noise is discussed.