All-fiber Michelson Interferometer Research Articles

All-Fiber Michelson Interferometer for Heart Rate and Breath Monitoring

All-Fiber Michelson Interferometer for Heart Rate and Breath Monitoring

A high resolution dilatometer using optical fiber interferometer.

We introduce a high-performance differential dilatometer based on an all-fiber Michelson interferometer at cryogenic temperature with 10-10 resolution in δL/L. It resolves the linear thermal expansion coefficient by measuring the oscillating changes of sample thickness and sample temperature with the interferometer and in situ thermometer, respectively. By measuring the linear thermal expansion coefficient α near the antiferromagnetic transition region of BaFe2As2 as a demonstration, we show that our dilatometer is able to measure thin samples with sub-pm-level length change resolution and mK-level temperature resolution. Despite the residual background thermal expansion of a few nm/K in the measurement results, our new dilatometer is still a powerful tool for the study of phase transition in condensed matter physics, especially has significant advantages in fragile materials with sub-100 μm thickness and being integrated with multiple synchronous measurements and tuning thanks to its extremely high resolution and contactless nature. The prototype design of this setup can be further improved in many aspects for specific applications.

Characterization of a thin-film metal-coated fiber optical phase modulator based on thermal effect with a nonlinear control interferometer

In this work, an optical fiber was coated by a thin-film metal layer to work as a fiber optical phase modulator based on thermal effect. This device was assembled in one of the arms of an all-fiber Michelson interferometer stabilized by a nonlinear control system based on variable structure and sliding modes. The frequency response reached 200 Hz, which can be considered high for a device based on the thermal effect. Compared with a fiber optical phase modulator based on the piezoelectric effect, the thermal modulator presented a higher scale factor per meter of optical fiber, showing the potential to work as a simple, low-cost, small-sized, short length, lightweight, and low-voltage fiber optical phase modulator.

Analysis and elimination the vibration disturbance in all-fiber distributed polarization coupling measurement

Michelson interferometer (MI) is used to measure distributed polarization coupling signal in high-birefringence polarization-maintaining fibers. Compared with space-light MI, the direct current (DC) components of interferograms of all-fiber MI fluctuate more intensely. Based on the analysis of the structure of all-fiber MI, the fluctuation is mainly induced by the disturbance of motorized delay line (MDL) in motion, as proven by the corresponding simulations and experiments. The signal processing method of group averages is proposed to eliminate the low-frequency vibration disturbance in the DC component of interferograms and prove such elimination by experiments. The frequency of vibration disturbance and interference principle maximum increases with increasing scanning speed of MDL. The initial position of MDL affects the frequency components and intensity. Additionally, the group average method can be used for other interferometers.

Active and passive phase stabilization for the all-fiber Michelson interferometer

We put forward two methods for phase stabilization in the all-fiber Michelson interferometer. To perform passive phase stabilization, we use a heat bath for all fibers and electro-optical components, and put the interferometer in a hermetic case. To perform active phase stabilization, we monitor output power of the interferometer and develop an electronic feedback control. The phase stabilization methods enable stable interference pattern for several minutes, and can be helpful for the development of the optimal quantum receiver for coherent signals.

A CNT-coated refractive index sensor based on Michelson interferometer with thin-core fiber

Abstract A refractive index sensor, which is based on Michelson interferometer (MI) with a thin core fiber (TCF) coated by CNT (Carbon Nanotube), is proposed and experimentally demonstrated. This sensor is fabricated by the splice of a sectioned single mode fiber (SMF) on one end of TCF, and the other end is turned into a circular arc by fusion discharge. Such an all-fiber MI incorporates an intermodal interference between the core mode and the cladding modes. CNT is coated on the surface of the TCF. With the variations inside the environmental refractive index (RI), the shift of the wavelength and intensity of the interference pattern have been brought about. Experimentally, sensitivity of 178.88 dB/RIU (refractive index unit), 165.77 nm/RIU, as well as a resolution of 5.59 × 10−4 RIU and 1.21 × 10−4 RIU, are achieved respectively within a field ranging from 1.334 to 1.371 RIU. Moreover, CNT is better than silicon materials in compatibility, and it will not be washed away after its being adsorbed to the surface of optical fibers. In addition, its application could be better implemented in actual measurements, due to its insensitivity to temperature.

Reduction of Laser Frequency Noise and Intensity Noise in Phase-Shifted Fiber Bragg Grating Acoustic-Emission Sensor System

The noise performance of a fiber-optic acoustic-emission (AE) sensor system is often limited by the laser intensity noise and the laser frequency noise. Here, we report a novel low-cost, high-performance noise reduction method for fiber-optic AE sensor system based on a $\pi$ -phase-shifted fiber Bragg grating. This method uses a reference channel built by an all-fiber Michelson interferometer formed by a $3\times3$ fiber-optic coupler and two Faraday mirrors. The reference channel has two outputs whose spectra are two sinusoidal fringes with a relative phase shift of $2\pi$ /3. A novel signal processing method is developed to extract both the laser intensity noise and the laser frequency noise from the outputs of the reference channel, which are subsequently removed from the output of the sensing channel. The results show that, for an AE sensor system using a distributed-feedback semiconductor laser as the laser source, this method achieves a noise reduction ratio of more than 20 dB. The reference channel possesses a broad operating spectral width and has the potential to be used in a multiplexed AE sensor system.

Homodyne digital interferometry for a sensitive fiber frequency reference.

Digitally enhanced homodyne interferometry enables robust interferometric sensitivity to be achieved in an optically simple configuration by shifting optical complexity into the digital signal processing regime. We use digitally enhanced homodyne interferometry in a simple, all-fiber Michelson interferometer to achieve a frequency reference stability of better than 20 Hz/√Hz from 10 mHz to 1 Hz, satisfying, for the first time in an all fiber system, the stability requirements for the Gravity Recovery and Climate Experiment Follow On mission. In addition, we have demonstrated stability that satisfies the future mission objectives at frequencies down to 1 mHz. This frequency domain stability translates into a fractional Allan deviation of 3.3 × 10(-17) for an integration time of 55 seconds.

Low-Coherence Interferometry for Measurement of Properties of Optical Components

We present a modification of the interferometric method for the measurement of refractive index or thickness of optical devices using an easily aligned, almost all-fiber Michelson interferometer. Applicability of the method is demonstrated by the chromatic dispersion measurement of photonic crystal fiber sample. The birefringence of the optical device based on LiNbO3 obtained from the measurement of refractive indices is demonstrated and its value is determined for two different crystal samples. It is also shown that when the thickness of, for example, photopolymer material is known the refractive index of the device can be determined. The described method can be a practical tool for laboratories with the need of inexpensive and easily built setup for measurement of refractive index or thickness of optical devices even in a broad spectral range.

Short-Scan Fiber Interferometer for High-Resolution Bragg Grating Array Interrogation

This paper reports on the application of a technique for high-resolution interrogation of a fiber Bragg grating array using an all-fiber Michelson interferometer where the method of scanning the interferometric delay is fiber stretching using a piezoelectric fiber stretcher. Compensation for the performance degrading effects associated with temporally scanned interferometers is achieved using Hilbert transform processing techniques. In contrast to measurement using Fourier transform spectroscopy, experimental data shows that a measurement accuracy of ±0.5 pm is attainable using the Hilbert transform technique from delay scans (~6 mm) which are shorter than the coherence length of the grating.

Complete characterization of optical pulses using a chirped fiber Bragg grating

A simple method for complete characterization of periodic optical pulses based on time domain interferometry is demonstrated. The method does not require the use of an interferometer. A chirped fiber Bragg grating is used for stretching the pulses to be characterized. The interference between the stretched overlapped pulses is recorded by a photodiode and a sampling oscilloscope. The phase response of the chirped fiber Bragg grating is measured by an all-fiber Michelson interferometer. A fast-Fourier-transform method is used for processing of interference patterns in both the time and spectral domain.

Continuous Non-contact Corneal Pachymetry with a High Speed Reflectometer

We developed an instrument that permits non-contact, continuous, high speed and high precision monitoring of corneal thickness and tested the stability and reproducibility of measurements made over extended time periods and under various conditions of low surface reflectivity encountered during protracted exposure of the unmoistened corneal surface to ambient air. The optical pachymeter (basic component of a broad-band, all-fiber Michelson interferometer) was used to monitor changes in the central corneal thickness of enucleated porcine eyes. Measurements were performed on three groups of eight eyes, each with different surface characteristics: intact epithelium, mechanically abraded epithelium, and 90 microm excimer laser keratectomy. Corneal thickness was monitored continuously with values recorded every 2 to 3 minutes for periods up to 1 hour in the absence of surface rinsing. The thicknesses of all unmoistened corneas could be monitored with a precision of 1 microm (ascertained using a calibration glass plate and a living human cornea) over the entire observation period. Under ambient air conditions, deturgescence occurred in each case, and ranged from 1 to 5 microm/min. The rate of corneal thinning was fairly constant during the first 15 minutes of monitoring, but was nonlinear thereafter. Corneas with an intact epithelium had the lowest thinning rate with only 10% of the original thickness lost during the course of 1 hour. Deturgescence increased to 25% in corneas that had mechanical removal of the epithelium and to 28.5% in those that had an anterior excimer laser keratectomy, during a similar time-period. With this new interferometric method, continuous, non-contact measurement of corneal thickness is possible to within a precision of 1 microm for periods up to 1 hour, even under the modified surface conditions after photoablative keratectomy. This device may be useful for on-line monitoring of ablation depths during such procedures.

Electronic speckle-pattern interferometry using single-mode fibers and active fringe stabilization

Optical fibers are used to provide object and reference illumination in the context of the electronic speckle-pattern interferometry technique. An all-fiber Michelson interferometer is used, with an electronic servo and a piezoelectric phase modulator, to obtain compensation for environmentally induced phase coupling into the fiber arms.

A fiber-optic interferometric flex disk accelerometer

A push-pull fiber-optic accelerometer, using an all-fiber Michelson interferometer will be described. The accelerometer consists of two “clamped” disks (4.6 cm in diameter, 1.0 mm thick, aluminum 6061-T6) that are joined at the outer boundary to a rigid cylinder and at the disk center by a rigid “spindle” that acts as a seismic mass. Flat spiral-wound coils attached to the inner surface of each disk detect the acceleration-induced strain in a manner similar to flexural disk hydrophone designs [Brown et al., Fiber & Int. Opt. 8(3), 169–191 (1989)]. The sensitivity below the disk's fundamental resonance of 2.8 kHz is 49 rad/g. The fractional phase change per unit force (1/φ) (δφ/δF) below the resonance is 56 × 10−12/N. A noteworthy feature of this sensor is that the sensing coils comprising the legs of the interferometer and the fiber coupler are totally internal to the sensor structure and thus are not exposed, making the sensor robust for industrial or shipboard applications. [Work supported by the Naval Postgraduate School Direct Funded Research Program and the Naval Sea Systems Command.]

High-sensitivity, fiber-optic, flexural disk hydrophone with reduced acceleration response

Abstract A hydrophone consisting of a hollow cylinder whose flexible, circular end plates are bonded to pairs of pat, spiral wound coils of optical fiber is described. When the end plate/disk is deformed due to a pressure difference, the outer and inner fiber coils experience opposite strains resulting in a “push—pull” optical path length difference which is detected in an all-fiber Michelson interferometer. The close proximity of the interferometric fiber coils, separated by the thin thermally conducting end plate, rejects thermal gradient-induced signals. The addition of a second identical end plate and fiber coil pair at the opposite end of the cylinder will double the acoustic sensitivity while canceling acceleration induced signals. The calculated and measured optical strain of a single simply supported plate, single-coil sensor (8.0 cm diameter, 3.0 mm thickness) using static pressure, acoustic pressure, and acceleration are in good agreement and yield a sensitivity of 0.21 rad/Pa (ΔΦ/ΦΔP = -301 dB ...

High-sensitive all-fiber michelson interferometer by use of differential output configuration

An all-fiber Michelson-type interferometer consisting of a multimode optical fiber directional coupler has been constructed and used to measure the vibrational displacements of a reflecting mirror. The smallest displacement of the order of 10 -1 μm is detected with high sensitivity by use of a polarizing beam splitter in conjunction with a differential amplifier for two photodiodes.