Length Of Microcavity Research Articles

Optical fiber Fabry-Perot silica-microprobe for a gas pressure sensor

An all-fiber Fabry-Perot microprobe gas pressure sensor based on the femtosecond (fs) laser micromachining technology is proposed and demonstrated. The protruding-shaped silica-microprobe is spliced on the tip of the single mode fiber (SMF), and the gas microcavity is fabricated by the fs laser to form the Fabry-Perot interferometer (FPI), and the machining accuracy of the gas microcavity is better than 2 μm. The length of silicon-microprobe is less than 150 μm and its diameter is less than 30 μm, and the length of gas microcavity in microprobe is about 52 μm. The third reflective surface is formed at the junction between the microprobe and the SMF, the vernier effect can be cleverly utilized to improve the sensitivity of gas pressure. The experiment results indicate that the microprobe FPI gas pressure sensor has a sensitivity of 16.3536 nm/MPa with the increase of gas pressure, and a sensitivity of temperature is only 0.0043 nm/°C from 30 °C to 100 °C. The gas pressure sensor has the advantages of small size, high gas pressure sensitivity and low cross-sensitivity of temperature, and is expected to be applied in the special field, such as detection of gas pressure in alveoli.

Spherical microcavity-based membrane-free Fizeau interferometric acoustic sensor.

The monitoring of acoustic waves is essential for a variety of applications, ranging from photoacoustic imaging to industrial non-destructive evaluation and monitoring. Optical acoustic sensors have many advantages over electrical counterparts such as passivity and immunity to electromagnetic interference, and can be quite compact with all-fiber structures. A common approach is to optically detect the acoustically induced mechanical movement of a cantilever or a reflective membrane. However, sensors based on moving mechanical parts have limitations, because they are influenced by the mechanical properties of the structures involved that behave as a coupled spring-mass system. Here a new type of optical acoustic sensing concept based on a spherical microcavity fiber Fizeau interferometer is described. The sensor is fabricated by inserting a section of single-mode fiber into a spherical microcavity to form a Fizeau interferometer. Thanks to the elasto-optic effect, the sound pressure modifies the refractive index of the microcavity; then a corresponding change in the interferometric spectrum can be observed. The sensor was successfully used to detect acoustic waves under the whole audible region, from 20Hz to 20kHz. The experimental results show that the sensitivity can be improved via altering the length of microcavity. The structure is membrane-free, and the sensitivity will not be limited by these size restrictions which makes the technology an interesting alternative to conventional transducers for acoustic wave measurement.

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

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.

Simulation of microcavity organic light emitting device with two kinds of resonant cavity lengths

The resonant cavity length of microcavity influences the light emitting characteristics of microcavity organic light emitting device (MOLED) directly. According to the related calculation formula of microcavity device, when the lengths of microcavity are lambda/2 and lambda, the authors use transfer matrix method to simulate and compare with the functions of composite light emitting EL when exciton is in different positions of microcavity. The authors found that when the length of microcavity is lambda/2, the peaks of luminous spectrum are all at the 520 nm, and the width of half-peaks are all 17 nm. The peak intensity and integral intensity are biggest when exciton is in the central area of microcavity. When the length of microcavity is lambda and exciton is at different positions of microcavity, the peaks of luminous spectrum are all at the 520 nm of designed center wavelength, and the widths of half-peaks are all 12 nm. The peak intensity and integral intensity are smallest when exciton is in the central area of microcavity. After analyzing, The authors found that the light emitting characteristics is best when the exciton is at the maximum position of the electric field. This is because the electric field's intensities in the microcavity with two kinds of lengths are distributed differently. It illustrates that one should distinguish different resonant cavity length and exciton at the maximum position of the electric field within microcavity if one wants to create an efficient MOLED.