Fourier Spectrometer based on Wide-range and Phase-locked Michelson Interferometer with Femtosecond Laser Excitation

A wide-range and phase-locked Michelson interferometer technique is described. This technique combined with femtosecond laser is used to measure the spectrum of the rare-earth ion Nd：YVO4, which presents very high signal to noise ratio of interferometric intensity output and higher spectral resolution than traditional grating spectrophotometer.

Phase-Sensitive Optical Time-Domain Reflectometer Based on a 120°-Phase-Difference Michelson Interferometer

A phase-sensitive optical time domain reflectometer （φ-OTDR） based on a 120°-phase-difference Michelson in- terferometer is proposed. The Michelson interferometer with arm difference of 4m is used to test the phase difference between the Rayleigh scattering from two sections of the fiber. A new demodulation method called the inverse transmission matrix demodulation scheme is utilized to demodulate the distributed phase from the backward scattering along the long fiber, The experimental results show that the 120°-phase-difference inter- ferometer φ-OTDR can detect the phase along the 3km fiber, and the acoustic signal within the whole human hearing range of 20 Hz-20 kHz is reproduced accurately and quickly.

LIGO Experiments Cannot Detect Gravitational Waves by Using Laser Michelson Interferometers—Light’s Wavelength and Speed Change Simultaneously When Gravitational Waves Exist Which Make the Detections of Gravitational Waves Impossible for LIGO Experiments

It is proved strictly based on general relativity that two important factors are neglected in LIGO experiments by using Michelson interferometers so that fatal mistakes were caused. One is that the gravitational wave changes the wavelength of light. Another is that light’s speed is not a constant when gravitational waves exist. According to general relativity, gravitational wave affects spatial distance, so it also affects the wavelength of light synchronously. By considering this fact, the phase differences of lasers were invariable when gravitational waves passed through Michelson interferometers. In addition, when gravitational waves exist, the spatial part of metric changes but the time part of metric is unchanged. In this way, light’s speed is not a constant. When the calculation method of time difference is used in LIGO experiments, the phase shift of interference fringes is still zero. So the design principle of LIGO experiment is wrong. It was impossible for LIGO to detect gravitational wave by using Michelson interferometers. Because light’s speed is not a constant, the signals of LIGO experiments become mismatching. It means that these signals are noises actually, caused by occasional reasons, no gravitational waves are detected really. In fact, in the history of physics, Michelson and Morley tried to find the absolute motion of the earth by using Michelson interferometers but failed at last. The basic principle of LIGO experiment is the same as that of Michelson-Morley experiment in which the phases of lights were invariable. Only zero result can be obtained, so LIGO experiments are destined failed to find gravitational waves.

Optical Fiber Bragg Grating Michelson Interferometer

A new Michelson interferometer based on fiber Bragg grating（FBG） is demonstrated. FBCs are used as reflectors, and the laser is replaced by a broadband source as input light in this interferometer. To demodulate the signals, a 3 × 3 coupler is used as a splitter. By combining with software demodulation, the outer interference can be obtained from the outputs of the interferometer. This kind of interferometer can also be wavelength-multiplexed easily by composing a series Michelson interferometer. The experiment results show that the clear interference fringe can be obtained by adjusting the path difference to make it less than interference length of FBG. The signals are also demodulated.

Analog Processing Based Vibration Measurement Technique Using Michelson Interferometer

A Michelson interferometer based sensor, to monitor the displacement and vibration of a surface, is presented. The interference signals detected in quadrature are processed using analog electronics to find the direction of the motion of a vibrating surface in real-time. The complete instrumentation and signal processing are implemented for the interpretation of the amplitude as well as positive and negative excursion of the vibration cycles. This new technique is simpler as compared to the techniques commonly used in the interferometer based vibration sensors. Using this technique, we have measured mechanical vibrations having a magnitude of the order of nanometers and frequency in the range of 50Hz to 500Hz. By making small changes in the electronic circuit, the technique can be implemented for the extended range of the vibration frequencies and amplitude.

Michelson interferometer composite cavity fiber laser sensor with radio frequency interrogation

A Michelson interferometer(MI) composite cavity fiber laser sensing system based on radio frequency(RF) interrogation is proposed and experimentally demonstrated. The system down-converts the traditional MI light frequency detection to RF detection, which improves the stability of the system. The optic fiber MI is placed in the laser resonator to form a composite cavity structure, which greatly improves the sensitivity of beat frequency signal demodulation.

Design and analysis of flexible colorless remote node using RSOA-assisted Michelson interferometer

A scheme of flexible colorless remote note with reflective semiconductor optical amplifier （RSOA） assisted Michelson interferometer is proposed. This is capable of generating an optical carrier suppressed signal at a specific radio frequency to suppress the penalty brought about by Rayleigh backscattering and reflection in a full-duplex single fiber transmission network. Simulations are conducted, and the validation of the proposal is discussed by observing the penalty eye opening factor. The results are useful for designing cost-effective multi-wavelength passive optical network （PON） or radio-over-fiber （RoF） systems.

Strain measurement using frequency modulation fiber optic interferometer

The method for measuring the strain of an object using an optical fiber and a frequency modulation(FM) coupled cavity semiconductor laser is proposed.This method uses the coherent FM heterodyne principle of the Michelson interferometer and can avoid the π/2 nonreciprocal phase bias and phase shifting problem existing in general fiber optic interferential sensors, the maximum detection range is limited by the coherent length of the semiconductor laser and its relative factor.

Combined optical fiber interferometric sensors for the detection of acoustic emission

A type of combined optical fiber interferometric acoustic emission sensor is proposed. The sensor can be independent on the laser source and make light interference by matching the lengths of two arms,so it can be used to monitor the health of large structure. Theoretical analyses indicate that the system can be equivalent to the Michelson interferometer with two optical fiber loop reflectors,and its sensitivity has been remarkably increased because of the decrease of the losses of light energy. PZT is powered by DC regulator to control the operating point of the system,so the system can accurately detect feeble vibration which is generated by ultrasonic waves propagating on the surface of solid. The amplitude and the frequency of feeble vibration signal are obtained by detecting the output light intensity of interferometer and using Fourier transform technique. The results indicate that the system can be used to detect the acoustic emission signals by the frequency characteristics.

Measurement of Refractive Index of Liquid-state Alloy SCN-Eth by Laser Interference

The method to measure the refractive index of the liquid-state metal is introduced. By inserting a wedge sample cell to the optical path of the Michelson interferometer, the refractive index of the liquid-state alloy SCN-Eth is measured at different temperatures and densities. The results show that this method can be applied to measure the refractive index of various liquids, especially at different temperatures.

Novel Micro Fourier Transform Spectrometers

The miniaturization of spectrometer opens a new application area with real-time and on-site measurements.The Fourier transform spectrometer(FTS)is much attractive considering its particular advantages among the approaches.This paper reviews the current status of micro FTS in worldwide and describes its developments;In addition,analyzed are the key problems in designing and fabricating FTS to be settled during the miniaturization.Finally,a novel model of micro FTS with no moving parts is proposed and analyzed,which may provide new concepts for the design of spectrometers.

迈克耳孙干涉仪分析的一种新方法

从多谱勒频移的方法,利用伽里略变换,对迈克耳孙干涉仪进行了全新的分析,从频率变化的角度对迈克耳孙干涉仪进行了新的认识,为我们利用该干涉仪提供了更为广阔的思维空间。

Long Period Fiber Grating Based Refractive Index Sensor With Enhanced Sensitivity Using Michelson Interferometric Arrangement

The long period fiber grating （LPFG） is widely used as a sensor due to its high sensitivity and resolution. However, the broad bandwidth of the attenuation bands formed by the mode coupling between the fundamental core mode and the cladding modes constitutes a difficulty when the device is used as a conventional sensor. To overcome this limitation, a Michelson interferometer-type sensor configuration has been developed, using an LPFG grating pair formed by coating a mirror at the distal end of the LPFG. This sensor configuration is more convenient to use and is able to overcome the limitations of the single LPFG based sensor as the shifts in the attenuation bands being more easily detectable due to the formation of the sharp spectral fringe pattern in the LPFG based Michelson interferometer. In this work, I studied the LPFG based Michelson interferometer as the refractive index sensor and discussed the sensitivity enhancement of the LPFG based Michelson interferometer as a refractive index sensor by employing higher order cladding modes and by reducing the cladding radius. The results demonstrated the HE17 mode with a cladding radius of 62.5 μm, in the range of surrounding refractive index （SRI） of 1 - 1.45, and its resonant peak showed a wavelength shift of 26.99nm/RIU. When the cladding region was further reduced to 24μm, the resonant peak showed a wavelength shift of 569.88 nm/RIU, resulting in a sensitivity enhancement of nearly 21 times. However, as the cladding region was etched further, then the HE17 order cladding mode and higher mode would be cut off. Therefore, the implementation of high sensitivity for SRI sensing with the reduced cladding in the LPFG based Michelson interferometer is dependent on the proper combination of the cladding radius and cladding mode order.

Phase noise characteristics of narrow-linewidth fiber laser and laser diode in unbalanced interferometers

The phase noises of two narrow-linewidth fiber laser and laser diode are measured by using unbalanced Michelson interferometers with various optical path differences （OPDs）. The measured results indicate that the phase noises of the two lasers do not change linearly with the OPD over the range from 1 to 100 m. The laser diode exhibits phase noise levels higher than that of the fiber laser at OPDs longer than 10 m. However, the laser diode outperforms the fiber laser at OPDs shorter than 10 m. The results obtained can assess laser performance and determine the suitable laser for use in a particular application.

Measurement of Martian atmospheric winds by the O_(2) 1.27 μm airglow observations using Doppler Michelson Interferometry: A concept study

China’s Mars exploration mission has stimulated tremendous interest in planetary science exploration recently.To propose potential scientific research projects,this study presents a concept simulation for the measurement of Martian atmospheric winds using the Doppler Michelson interferometry technique.The simulation is based on the satellite instrument initially designed for the Dynamic Atmosphere Mars Observer(DYNAMO)project to measure vertical profiles of winds from the 1.27μm airglow observations in the Martian atmosphere.A comprehensive DYNAMO measurement simulation forward model based on an orbit submodel,an atmospheric background field submodel,and an instrument submodel is developed using the Michelson equation.The simulated interferogram signal over the field of view(FOV)calculated by the forward model is associated with the filter transmittance function,column emission rate of airglow,wind velocity,temperature,and the Michelson phase.The agreement between the derived atmospheric signals from the simulated interferogram without altitude inversion and the input parameters used to initiate the forward model confirms the validity of the forward model.

A compact interferometer insensitive to scanning speed variations

A compact moving optical-wedge interferometer （CMOWI） is presented. This device consists of a moving optical wedge （MOW）, a fixed optical wedge （FOW）, a fixed compensating plate, and a beam-splitting cube. The optical path difference （OPD） is calculated and analyzed. The factor between the OPD and the displacement of the MOW is less than 1 if the refractive index and wedge angle of the MOW and FOW are chosen properly. Therefore, the CMOWI is insensitive to scanning speed variations compared with the traditional Michelson interferometer. The CMOWI is compact, small-sized, and suitable for low-resolution Fourier transform spectroscopy.

Low-loss high-extinction-ratio single-drive push-pull silicon Michelson interferometric modulator

We demonstrate a high-speed silicon carrier-depletion Michelson interferometric（MI）modulator with a low onchip insertion loss of 3 dB.The modulator features a compact size of 〈1 mm2 and a static high extinction ratio of 〉30 dB.The Vπ·Lπ of the MI modulator is 0.95–1.26 V·cm under a reverse bias of -1 to-8 V,indicating a high modulation efficiency.Experimental results show that a 4-level pulse amplitude modulation up to 20 Gbaud is achieved with a bit error rate of 6×10-3,and a 30 Gb/s binary phase-shift-keying modulation is realized with an error vector magnitude of 25.8%.

Compact fiber optic accelerometer

A compact fiber optic accelerometer based on a Michelson interferometer is proposed and demonstrated. In the proposed system, the sensing element consists of two single-mode fibers glued together by epoxy, which then act as a simple supported beam. By demodulating the optical phase shift, the acceleration is determined as proportional to the force applied on the central position of the two single-mode fibers. This simple model is able to calculate the sensitivity and the resonant frequency of the compact accelerometer. The experimental results show that the sensitivity and the resonant frequency of the accelerometer are 0.42 rad/g and 600 Hz, respectively.

Fiber-Optic Microstructure Sensors:A Review

This paper reviews a wide variety of fiber-optic microstructure(FOM)sensors,such as fiber Bragg grating(FBG)sensors,long-period fiber grating(LPFG)sensors,Fabry-Perot interferometer(FPI)sensors,Mach-Zchnder interferometer(MZI)sensors,Michelson interferometer(MI)sensors,and Sagnac interferometer(SI)sensors.Each FOM sensor has been introduced in the terms of structure types,fabrication methods,and their sensing applications.In addition,the sensing characteristics of different structures under the same type of FOM sensor are compared,and the sensing characteristics of the all FOM sensors,including advantages,disadvantages,and main sensing parameters,are summarized.We also discuss the future development of FOM sensors.

Experimental study of Fourier transform spectrometer based on MEMS micro-mirror

We propose a new Fourier transform spectrometer based on programmable microelectromechanical systems （MEMS） micro-mirror and an improved Michelson interferometer. The principle of the spectrometer is theoretically analyzed. A signal acquisition unit and an experimental set-up are designed. The spectrum of the polychromatie light source is obtained at a slantwise reflector angle of O.238°. The spectrum is analyzed by this system within the near infrared. The experimental results show that the spectral accuracy is less than 3 nm, and the signal-to-noise ratio （SNR） is 18 dB. The spectral resolution is less than 16 nm.