Michelson Interference Research Articles

Effective Michelson interference observed in fiber-optical analogue of Hawking radiation.

We experimentally observe the stimulated analogue of Hawking radiation produced in a photonic-crystal fiber, with a pulsed pump and a continuous-wave probe. In particular, we propose and demonstrate an innovative method to boost the efficiency and probe the coherence characteristics of the analogue Hawking effect relying on a double pump pulse with a controlled temporal delay. We show that the emitted analogue Hawking radiation corresponds to the coherently-added, interfering Hawking signals resulting from the probe interacting with each pump pulse. We introduce a simple effective Michelson interference model, and demonstrate excellent agreement between our experimental data and the predictions derived from this model. Importantly, while naively increasing the pump power in an attempt to boost the Hawking-radiation generation efficiency results in the distortion of the output signal, we show that at the maxima of the observed Hawking-signal interference pattern, the signal can be increased by a factor of >3 (up to 4 under ideal experimental conditions). This approach could be extended to the use of sequences of m pulses, resulting in a Hawking-signal enhancement of m2.

Optical fiber Michelson interference sensor for measuring refractive index

Optical fiber Michelson interference sensor for measuring refractive index

Measurement of glass thickness and refractive index based on spectral interference technology.

A non-contact glass thickness and refractive index measurement method based on spectral interferometry is proposed. The method uses the Michelson interference principle to calculate the interference signal obtained by the spectrometer using the Fourier transform algorithm to obtain the modulation period of the spectral interference fringes. The geometrical thickness and refractive index of a glass sample can be calculated from the optical path difference between the reflected light of the reference arm and that of the front and back surfaces of the glass sample before and after being placed in the measuring arm. The linear interpolation method is used to resample the interference pattern in the frequency domain to ensure uniform sampling. It also adopts an improved phase extraction algorithm in the Fourier domain, which improves the anti-interference ability of the measurement system, and it exhibits a fast detection speed and high signal-to-noise ratio. To verify the accuracy of the measurement results of this method, a high-precision coordinate measuring machine is used for comparative experiments, and the characteristics of the tested object are analyzed. The experimental results show that the measurement accuracy of the system is in good agreement with that of a high-precision coordinate measuring machine.

An intensity modulated fiber-optic carbon monoxide sensor based on Ag/Co-MOF in-situ coated thin-core fiber

Abstract An intensity modulated fiber-optic carbon monoxide (CO) sensor by integrating in-situ solvothermal-growth Ag/Co-MOF sensing film is fabricated and evaluated. The Michelson interference sensing structure is composed of single-mode fiber (SMF), enlarged taper, thin-core fiber (TCF), and Ag film as the reflector. Ag/Co-MOF was coated on the cladding of the TCF as the sensing material, and the enlarged taper is located between TCF and SMF as the coupler. The structure, morphology, compositions and thermal stability of the Ag/Co-MOF sensing film were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), etc. The sensitivity of the sensor is 0.04515 dB/ppm, and the fitting parameter of the CO concentration is 0.99876. In addition, the sensor has the advantages of good selectivity, good signal and temperature stability, and it has potential application in trace CO detection.

Research on Michelson interference refractive index sensing technique based on double-core microfiber*

Research on Michelson interference refractive index sensing technique based on double-core microfiber*

An Optical Fiber Sensor for Oriented Bending Based on Eccentric UV Exposure

The optical fiber sensor for oriented bending based on eccentric UV exposure is fabricated. With the eccentric UV exposure on the ready-made Michelson interference fiber structure, the optical sensor gives the oriented bending characteristics by changing the radial circular symmetry of fiber cladding refractive indexes. The principle of the asymmetric process of the eccentric exposure to cladding mode are analyzed. The bending loss of the excited cladding mode in different radial directions is detected. The experimental results show that the Michelson interference has some oriented bending characteristics in the eccentric UV exposure process. There are different bending sensitivity in different radial directions. Furthermore, the bending sensitivity is higher on the exposed side and the curvature sensitivity is 5.5 dB·m. On the opposite side, the bending sensitivity is lower and the curvature sensitivity is -1.31 dB·m. With these oriented bending characteristics, the optical sensor can be applied to oil and gas exploration and development and to oriented seismic wave vector detection.

Silver-coated three-core fiber Michelson interferometer for liquid-level measurement

Abstract The Michelson liquid-level sensor based on silver coated the end face of the three-core fiber reflection structure has been proposed to measure continuous or discrete liquid level. The Michelson interference structure can be obtained by the combination of the single-mode optical fiber and the three-core optical fiber with the silver film coated on the other end face of it. The inter-mode interference can be obtained by the fiber-core mismatch at the fusion joint. The liquid level can be measured by monitoring the dip wavelength shift of the interference spectrum. The results indicate that the sensitivity of the liquid-level sensor will decrease with the increasing sensing length. The sensing length of 30 mm is selected to investigate the performance of the sensor. The sensitivity of water level is reached as high as 392.83 pm/mm with an excellent linearity of 0.99946. Interestingly, the sensitivity of the sensor increases with the liquid refractive index and the sensitivity of the refractive index for NaCl solution is 4410.74 pm/mm/RIU. The performance of the sensor is very stable in the range of 20–90 °C. The maximum drift for temperature is 0.3001 nm. The sensor can be applied to the measurement of the liquid level in different environments.

Michelson liquid-level sensor based on cascaded no-core fiber and single-mode fiber structure

A novel Michelson sensor is proposed and applied to detect the liquid level. The sensor was fabricated by a section of no-core optical fiber (NCF) which is sandwiched between two single-mode fibers (SMFs). One single-mode fiber (SMF1) acts as light guide, and the tip of the other single mode fiber (SMF2) is coated with silver film as mirror. The high-order modes are excited when light travels from SMF1 to NCF and couple into the SMF2 at the NCF-SMF2 interface. The core and the cladding modes are reflected by the silver film of SMF2 and then couple twice at the NCF-SMF2 interface to form Michelson interference. Through simulation optimization and experimental verification, the optimized lengths of 15 mm and 30 mm are determined for NCF and SMF2, respectively. Interestingly, the NCF and SMF2 have the similar sensing responsivity in the liquid level sensing measurement. In the range of 15−90 °C, the sensor exhibits a temperature-insensitive characteristic. In the 0–44 mm liquid level range, the sensitivities of the deionized water, 5 % NaCl, 10 % NaCl and 15 % NaCl aqueous solutions are 216.16, 232.22, 253.41 and 276.87 pm/mm, respectively, and the refractive index sensitivity is 2223.5658 pm/mm/RIU. The sensor has clear interference fringes, simple structure, high liquid level sensitivity, good linearity and temperature insensitivity. It has the potential application in the field of small-scale liquid level monitoring.

Micro-Cap on 2-Core-Fiber Facet Hybrid Interferometer for Dual-Parameter Sensing

In this article, we demonstrate a “Fabry-Perot + Michelson” hybrid interferometer based on a polymer micro-cap located on asymmetric 2-core fiber (2CF) facet. Because the polymer micro-cap comprises a flat reflector and a concave reflector, the light propagating in the centric core will be reflected twice forming Fabry-Perot interference. Due to the bias angle between the eccentric core and the concave reflector, the light in the eccentric core reflects only once on the flat reflector and would interfere with the other reflected light in the 2CF. The experimental results show that Fabry-Perot and Michelson interference occur and are superimposed on the directly detected spectrum. Independent interferometric spectrums can be separated by Discrete Fourier Transform to achieve humidity-temperature simultaneous measurement based on coefficient matrix demodulation. Moreover, this new optical fiber sensing platform is all-solid, high-integration, and flexible, so it has potential in lab-on-fiber applications.

Surface profile measurement of doped silicon using near-infrared low-coherence light.

A scanning interferometry system based on near-infrared low-coherence interferometry by using a superluminescent diode (SLD) as the light source is presented. The system cannot only measure the surface profile of doped double-sided polished silicon but also measure its optical thickness and refractive index. The measurement system uses near-infrared CCD to detect interferometric light in the near infrared, based on the Michelson interference principle. SLD has low temporal and high spatial coherence and high penetration to doped silicon wafers; thus, higher visibility can be obtained when measuring the rear side. Meanwhile, the optical thickness measured by low coherent scanning interference is compared with the optical thickness obtained by spectrally resolved interferometry to verify the accuracy of the system. Due to the periodic characteristics of interference fringes, the coherence length of the narrowband light source is usually greater than the path length difference of the interferometer. It gives the measurement a phase ambiguity of 2π, which may severely limit the application of the measurement. However, the short coherent length SLD light source used in the project can avoid 2π phase ambiguity problems. Besides, this system can perform full scanning in a larger step and achieve rapid on-line measurement of the target surface.

A Non-Intrusive Electrical Discharge Localization Method for Gas Insulated Line Based on Phase-Sensitive OTDR and Michelson Interferometer

To overcome the high cost and low-spatial resolution of the electrical discharge localization systems for the gas insulated line (GIL), a non-intrusive distributed optical fiber sensing system based on the phase-sensitive optical time domain reflectometer (phi-OTDR) and the optical fiber Michelson interference is proposed. In the system, the Michelson interference provides a trigger signal since it has a better sensitivity and a higher frequency response, and the phi-OTDR localizes the ultrasonic vibration induced by a discharge. First, the principle of the proposed discharge localization system is introduced. Then, the bandwidth and multi-points distributed sensing performances of the system are investigated based on the ultrasonic signal induced by a piezoelectric transducer. Furthermore, the localization results of experiment using gas insulated switchgear spacer discharges indicate that the sensing distance of the sensing system can reach 1 km and the positioning accuracy of the discharge is smaller than 15 m. Thus, the system meets the requirement of the GIL discharge localization. Contrary to the traditional GIL discharge methods, the system has several advantages, such as non-intrusive, better spatial resolution, lower cost, and greatly simplified structure.

Oblique incidence dynamic phase-shifting interferometer based on inclination angle deflection

An oblique incidence dynamic phase-shifting interferometer based on inclination angle deflection is proposed to quickly obtain the surface distribution of optical surface with flatness of micron dimension. A 2×2 point source array is introduced into a Michelson interference system, and the incidence angle of each point source on the interferometer cavity is adjusted precisely to induce equal phase shift. Spatial separation is realized in combination with a lens array. The four phase-shifting interferograms are captured simultaneously on a single CCD, thereby realizing dynamic measurement. The flatness of a 35 mm aperture silicon wafer is measured at oblique incidence angle of 68°, the root mean square (RMS) is 1.631 μm and peak-to-valley (PV) is 9.082 μm. The experimental results indicate that the proposed interferometer overcomes the disturbance of vibration environment and extends the measurement range of interferometer with high precision by introducing the simultaneous phase-shifting interferometry based on inclination angle deflection into the oblique incidence interference system.

Arbitrary phase shifting method for fiber-optic fringe projection profilometry based on temporal sinusoidal phase modulation

A new arbitrary phase shifting method is proposed in this paper for fiber-optic fringe projection profilometry. By introducing a small temporal sinusoidal phase modulation to the phase shift and employing the phase-generated carrier (PGC) method, the time-varying interference phase α(t)can be demodulated from the Michelson interference signal, which is reflected by the fiber end faces and recorded concurrently with the recording of the fringe pattern. Integrate sin [α(t)] and cos [α(t)] respectively, and then the phase shifts between frames can be determined and consequently used to solve the phase map with least-squares PS algorithm. The noise model of this method is deduced from which the optimum modulation amplitude can be selected. In the experiment, four fringe patterns with uncalibrated phase shifts were recorded under strong environmental disturbance, and were analyzed by utilizing the Carre algorithm, the proposed method and the modified Fourier transform (MFT) method respectively. A visual criterion is used to evaluate the performances of these methods. Experimental results indicate that the proposed method is much more robust to phase shift miscalibration than the Carre algorithm, and its performance is comparable to that of the MFT method while its computational complexity is substantially lower. Therefore, the proposed method is suitable for real-time phase shift calibration.

Phase-shifting digital holography with vortex beam in one single exposure

Phase-shifting digital holography in one single exposure has the potential for observation of dynamic objects in the absence of multiple exposure which is very sensitive to environment. Here the vortex beam with different eccentricity and topological charge has been introduced into Michelson interference path and referred to as the vortex reference wave. Multi-copy images of the measured object can be simultaneously generated in the other beam path, and then interfere with the vortex reference wave in one single exposure. Unused parts of the reference wave can be used to remove zero-order term in the process of reconstruction. A proof-of-principle experiment was conducted to validate the feasibility and validity of our proposed phase-shifting digital holography in one single exposure.

Magnetostriction Measurement System of Magnetic Thin Films with Michelson Interference

Magnetostriction Measurement System of Magnetic Thin Films with Michelson Interference

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.

Generation of narrowband Lamb waves based on the Michelson interference technique**Project supported by the National Natural Science Foundation of China (Grant Nos. 11374230 and 11774264).

An optical method of generating narrowband Lamb waves is presented. It is carried out with a laser line array in a thermoelastic regime implemented by the Michelson interference technique, where the formed array element spacing can be flexibly and conveniently changed to achieve selective mode excitation. In order to simulate the displacement response generated by this array, its intensity distribution function is presented to build a theoretical analysis model and to derive the integral representation of the displacement response. The experimental device and measuring system are built to generate and detect the Lamb waves on a steel plate. Numerical calculation results of narrowband Lamb wave displacement signals based on the theoretical model show good agreement with experimental results.

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.

A method to improve the stability of the optical interference system

The measurement system based on optical interference has obvious advantages of high precision and high sensitivity. However, the signal is easy to be disturbed by vibration from environment, so the system needs to stay away from the vibration source. To use the optical interference method for real-time measurement, it has to im-prove the system’s stability. In this paper, we proposed an integrated Michelson interference device to measure the thicknesses of multiple layers of optical plate, which could improve the stability of the optical interference system in a new way. Through smart design and high precision processing technique, the light path of the structure was integrated into a whole, which could avoid disturbing successfully. Compared with fiber based interferometer, this device could bring obviously more stable signal. The thicknesses of the multiple layers of optical plate were measured to confirm its feasibility to do the real-time precision measurement.

Three-degree-of-freedom common-path laser measurement system

Common optical path arrangement was adopted to design a three-degree-of-freedom laser measurement system for measuring 1D displacement and 2D angles of a moving stage simultaneously on the basis of the principles of Michelson interference and laser auto-collimation. In the displacement measurement, the fine resolution of displacement measurement was achieved by using optical path difference doubling technique. Combined with polarization interference technology and signal differential processing, high-quality displacement output signal was obtained. In the angle measurement, changes in yaw and pitch of a moving stage caused the position change of the mirror which was mounted on the stage. The incident beam was reflected by the mirror and detected by a four-quadrant detector. According to the position change of the spot, yaw and pitch angles were obtained. The stability, resolution tests and the comparison experiments with the British Renishaw XL-80 laser interferometer were done. Experimental results show that the system has the resolution of 0.8 nm for displacement measurement and 0.2″ for angle measurement. Compared with the results of Renishaw XL-80 laser interferometer, the maximum deviation of displacement is less than 100 nm within the measurement range of 50 mm. The maximum deviations of yaw and pitch are 0.5″ and 0.4″.