A small and low cost extrinsic Fabry-Perot (FP) fiber low-frequency acoustic pressure sensor (EFPAS) based on polydimethylsiloxane (PDMS) diaphragm is proposed. The EFPAS is fabricated by fusion splicing a single mode fiber (SMF) with a hollow-core fiber (HCF), which embed a PDMS diaphragm by the capillary effect, to form an air micro-cavity. The structural strength of the whole thin diaphragm based sensing probe is improved by the ingenious design, and a high precision optical fiber cutting system can be used to control the length of air micro-cavity. Simulation proves that the PDMS diaphragm with large radius and small thickness will help to improve the sensitivity, but there is a tradeoff between sensitivity and the mechanical strength. Experimental results show that the sensor has the acoustic pressure sensitivity of 0.427 mV/mPa with a high linear pressure response in the range of 5 mPa–720 mPa. A stable signal-to-noise ratio (SNR) about 80 dB with a noise floor at 0 dB can be realized at 30 Hz and a 0.5 Hz resolution can be observed ranging from 10 to 50 Hz of low-frequency acoustic wave (The relative error of measured frequency is lower than 1%). Its high precision of low-frequency acoustic measurement and simple fabrication process make it an attractive tool for acoustic sensing and photo-acoustic spectroscopy.

Small in-fiber Fabry-Perot low-frequency acoustic pressure sensor with PDMS diaphragm embedded in hollow-core fiber

An ultra-wideband fiber optic acoustic sensor based on graphene diaphragm with a thickness of 10nm has been proposed and experimentally demonstrated. The two reflectors of the extrinsic Fabry-Perot interferometer is consist of fiber endface and graphene diaphragm, and the cavity is like a horn-shape. The radius of the effective area of the ultrathin graphene diaphragm is 1mm. Attributed to the strong van der Waals force between the diaphragm and the ceramic ferrule, the sensor head can be applied not only in the air but also underwater. Experimental results illustrate that ultra-wideband frequency response is from 5Hz to 0.8MHz, covering the range from infrasound to ultrasound. The noise-limited minimum detectable pressure level of 0.77Pa/Hz1/2@5Hz and 33.97μPa/Hz1/2@10kHz can be achieved, and the applied sound pressure is 114dB and 65.8dB, respectively. The fiber optic acoustic sensor may have a great potential in seismic wave monitoring, photoacoustic spectroscopy and photoacoustic imaging application due to its compact structure, simple manufacturing, and low cost.

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Ultrathin graphene diaphragm-based extrinsic Fabry-Perot interferometer for ultra-wideband fiber optic acoustic sensing.

We demonstrate a highly sensitive and stable fiber-optic Fabry–Perot cantilever microphone based on fast demodulated white-light interferometry. The cavity length of the low-finesse Fabry–Perot interferometry is absolutely measured by realizing a high-speed demodulation method utilizing a full spectrum, with the advantages of both high resolution and large dynamic range. An acoustic test demonstrates high sensitivities and linear responsivities at frequencies below 2 kHz. The pressure responsivity and the noise-limited minimum detectable acoustic pressure level are measured to be 211.2 nm/Pa and 5  μPa/Hz1/2, respectively, at the frequency of 1 kHz. Comparative experimental results show that the signal-to-noise ratio is over 10 times higher than a reference condenser microphone.

Fast demodulated white-light interferometry-based fiber-optic Fabry-Perot cantilever microphone.

We demonstrate a fiber-optic Fabry-Perot acoustic sensor based on a Parylene-C diaphragm of 500 nm in thickness. The excellent diaphragm forming ability and good adhesion of Parylene-C make the sensor fabricate up to 9 mm in diameter. Acoustic testing demonstrates a high dynamic pressure sensitivity of 2239 nm/Pa and a noise limited equivalent acoustic signal level of 22.1 μPa/Hz1/2 at the frequency of 20 Hz. The frequency response exhibits an obvious peak at the frequency of 13 Hz. The sensor can be used for low-frequency acoustic pressure detections, which is necessary in surveillance and security systems.

High-Sensitivity Fabry-Perot Interferometric Acoustic Sensor for Low-Frequency Acoustic Pressure Detections

Basilar membrane-inspired self-powered acoustic sensor enabled by highly sensitive multi tunable frequency band

A fiber-optic acoustic pressure sensor based on a large-area nanolayer silver diaphragm is demonstrated with a high dynamic pressure sensitivity of 160  nm/Pa at 4 kHz frequency. The sensor exhibits a noise limited detectable pressure level of 14.5  μPa/Hz(1/2). Its high dynamic pressure sensitivity and simple fabrication process make it an attractive tool for acoustic sensing and photo-acoustic spectroscopy.

https://kuscholarworks.ku.edu/bitstream/handle/1808/18736/Xu-accoustic_pressure_sensor2014.pdf;sequence=1

Fiber-optic acoustic pressure sensor based on large-area nanolayer silver diaghragm

The invention discloses a membrane-type minitype photoacoustic cell and an application thereof. The membrane-type minitype photoacoustic cell and the application thereof are characterized in that the membrane-type minitype photoacoustic cell is provided with a cylinder body, a vibration sensing thin film is arranged at one end of the cylinder body, an optical fiber is plugged into the other end of the cylinder body, and a cylindrical photoacoustic cavity is formed. An airflow through-hole is arranged on the lateral wall of the cylinder body, the detection light and the exciting light modulated by audio frequency signals are transmitted through the optical fiber. The membrane-type minitype photoacoustic cell has a miniaturized volume, the detection sensitivity is high, the photoacoustic detection is in an all-optical structure, and the membrane-type minitype photoacoustic cell can be used for gas concentration detection under inflammable and explosive circumstances.

Membrane-type minitype photoacoustic cell and application thereof

The invention discloses a long-period fiber bragg grating manufacturing method based on the ink-jet printing technology. The long-period fiber bragg grating manufacturing method based on the ink-jet printing technology is characterized in that firstly, a fiber coating of an optical grating writing zone is stripped off, so that a fiber cladding is exposed and a fiber is fixed on a fiber clamp; the ink-jet printing technology is adopted, photoresist coatings with periodical intervals cover the fiber cladding and the photoresist coatings are dried; an argon ion ultraviolet laser with the wavelength of 248nm is adopted and the exposed fiber cladding is scanned and exposed. The fiber cladding which is not covered by the photoresist coatings and a fiber core located in the fiber cladding sense light and variation of the photoinduced refractive indexes is generated through the light-sensing fiber core; the photoresist coatings are removed to manufacture a long-period fiber bragg grating. By means of the ink-jet printing technology, an image structure with the grating period can be rapidly printed on the surface of the fiber cladding. The long-period fiber bragg grating manufacturing method is simple and rapid in manufacturing process, suitable for being manufactured in batches and good in consistency.

Long-period fiber bragg grating manufacturing method based on ink-jet printing technology

The invention discloses a method for manufacturing an embedded fiber grating filter. The method for manufacturing the embedded fiber grating filter is characterized by comprising the steps that a fiber bragg grating is written into a grating writing-in area of a long-period fiber grating through a phase mask method by means of an argon ion ultraviolet laser with the wavelength of 248 nm, so that the embedded fiber grating filter is obtained. The method for manufacturing the embedded fiber grating filter is simple in technology, the extinction ratio of the obtained embedded fiber grating filter is higher than 40 dB, the filtering bandwidth of the obtained embedded fiber grating filter is smaller than 1 nm, and the filtering central wavelength can be accurately controlled; when fiber bragg gratings with different refection central wavelengths are written into the grating writing-in area of the long-period fiber grating in a segmented mode, an embedded fiber grating multi-wavelength filter compact in structure can be obtained.

Gong Kui

Papers

Fiber-optic acoustic pressure sensor based on large-area nanolayer silver diaghragm

Membrane-type minitype photoacoustic cell and application thereof

Long-period fiber bragg grating manufacturing method based on ink-jet printing technology

Method for manufacturing embedded fiber grating filter