A fiber-optic Fabry-Perot interferometer was constructed by splicing a short length of photonic crystal fiber to a standard single-mode fiber. The photonic crystal fiber functions as a Fabry-Perot cavity and serves as a direct sensing probe without any additional components. Its pressure and temperature responses in the range of 0-40 MPa and 25°C-700°C were experimentally studied. The proposed sensor is easy to fabricate, potentially lowcost, and compact in size, which makes it very attractive for high-pressure and high-temperature sensing applications. . These advantages make them very suitable for deployment in space-limited harsh environments such as turbine engines and power plants and in the oil and gas industry, where pressure and temperature are the two most common measurands [3][4][5][6][7]. Many methods have been developed to fabricate fiberoptic FPIs. These include using conventional hollow-core fiber [3][4][5], chemical etching [7,8], and laser micromachining [9,10]. Recently, FPIs made from hollow-core photonic bandgap fiber [11] and solid-core photonic crystal fiber (PCF) [12] by simply cleaving and splicing have been demonstrated as strain and temperature sensors. The former needs a coating film onto the fiber endface, thereby increasing the complexity of the fabrication process. The latter as a temperature sensor is not stable, because the air holes are exposed to external environment [13].In this Letter, we report a fiber-optic FPI constructed by splicing a solid-core PCF to a standard single-mode fiber (SMF), and the other end of the PCF was collapsed with arc discharge using a fusion splicer. The entire fabrication process was performed using a commercially available fusion splicer. The principle of the FPI sensor is also presented here. We experimentally investigated the high-pressure and high-temperature characteristics of the proposed FPI sensor. Measurements of pressure up to 40 MPa and temperature up to 700°C were carried out. The pressure and temperature coefficients of the FPI sensor were measured to be −5:8 pm=MPa and ∼13 pm=°C, respectively. The experimental results agree well with the theoretical analysis. Figure 1(a) illustrates the experimental setup of our measurement. A broadband source (BBS) centered at 1530 nm is used to illuminate the FPI through an optical circulator. The reflection spectrum of the FPI is observed by an optical spectrum analyzer (OSA). Figures 1(b) and 1(c) show the schematic diagram and photograph of the fabricated FPI. A short length of a solid-core PCF (PM-1550-01 by Blaze Photonics) was first spliced to a standard SMF using the technique reported in [14]. Because of the small difference in refractive index between the SMF and the PCF, a mirror with relatively low reflectivity was formed at the fiber interface. The PCF was then cleaved to a length of several millimeters. A second lowreflection mirror at the end of the solid core was formed due to Frésnel reflection. As a result, a relatively weak FPI was constructed with an intensity contrast of ∼6 dB as sh...

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Khurram Karim Qureshi would like to acknowledge the support provided by the deanship of research at King Fahd University of Petroleum and Minerals (KFUPM) through project no. SB181022.

A novel all-optical bit-error monitoring system is demonstrated by cascading two all-optical logic gates: an inverted wavelength converter and an optical NOR gate which are realized using injection-locked laser diodes operating at different thresholds. Real-time optical monitoring signal is generated which indicates the positions and duration of both bit and burst errors in 10-Gb/s nonreturn-to-zero signals.

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