Demonstration of a passive subpicostrain fiber strain sensor

Abstract

Abstract-We demonstrate a fiber Fabry-Perot (FFP) sensor capable of detecting sub-picostrain signals, from 100 Hz and extending beyond 100 kHz, using the Pound-Drever-Hall frequency locking technique. A low power diode laser at 1550 nm is locked to a free-space reference cavity to suppress its free-running frequency noise, thereby stabilizing the laser. The stabilized laser is then used to interrogate a FFP where the PDH error signal yields the instantaneous fiber strain.Index Terms-fiber sensor, modulation, interferometry, strain sensing, fiber resonator. , and seismic sensors for geophysical surveys [6]. The benefits over the piezo-electric strain sensors currently employed include their smaller cross-sectional area and their scalability to large arrays. In addition, the detector arrays could be remotely interrogated and optically multiplexed using standard telecommunications equipment.The Pound-Drever-Hall (PDH) frequency locking technique uses RF phase modulation of a laser beam incident on a FabryPerot interferometer. By detecting and demodulating the beam reflected off the Fabry-Perot cavity, a high signal-to-noise error signal is derived, yielding the instantaneous frequency difference between the laser frequency and the cavity resonance [7], [8]. This scheme has found many applications in areas involving laser stabilization and signal extraction [9], [10]. The most demanding application of the PDH technique is in the detection schemes for gravitational waves, which require strain sensitivities approaching ∆L/L = 10, where ε is a dimensionless unit of strain.In this paper, the PDH technique is applied to a simple fiber Fabry-Perot interferometer (FFP) formed by a Bragg grating pair. We present a fiber sensing system with, to our knowledge, an unprecedented strain sensitivity of better than 10 −12 ε/ √ Hz, in a band extending down to 100 Hz. The power of the PDH technique lies in its shot noise limited closed-loop spectral density of frequency noise, which is given by [9] S f,clmin (Hz/ √ Hz) = ∆ν c J 0 (β)

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

“…In many fiber-based systems, such as interferometric fiber-optic sensors [1][2][3][4] , fiber lasers [5][6][7] , and fiber-delay-line stabilized lasers 8 , the fundamental resolution or frequency stability is limited by the intrinsic thermal noise inside optical fibers. Thus, an experimental and theoretical understanding of the thermal noise in optical fibers is important.…”

Analytic Formulation of Transmission Light Intensity of Hole Blockers in Intensity-based Polymer Optical Fiber Sensors

“…This result leads us to conlcude that the cross sectional area of a POF is equal with the intensity of that POF. That is, the light energy distribution is 1 Il-Bum Kwon 1 Chi-Yeop Kim Chan-Wook Shim Dusun Hwang Yungjoo Chung homogenous over the cross sectional area of the POF. We can calculate the transmission light intensity by determining the area of the light beam passing through the blocker.…”

“…Compared with conventional electrical strain gages, fiber optic strain sensors have many advantages, such as electro-magnetic immunity and resistance to chemical corrosion. Therefore, in the past few years, there has been intense works on the development of fiber optic strain sensors [1][2][3][4]. These most of the developed sensors are very sensitive in measuring strain.…”

An Embeddable Strain Sensor with 30 Nano-Strain Resolution Based on Optical Interferometry

“…A number of high-resolution FBG strain sensors based on complex structures have been developed, including Fabry-Perot configuration [8,9], π-phase shifted gratings [10,11] chirped gratings [12], and sampled structures [13]. For instance, Gagliardi et al demonstrated a strain measurement at the 10 −13 ε·Hz −1/2 scale using an FBG resonator with a diode-laser source which is stabilized against quartz-disciplined optical frequency comb [1]; Huang et al proposed a static-strain sensor with a resolution of 1.0 nε based on a π-phase-shifted Bragg grating, combined with a wavelet threshold denoising algorithm [11].…”