Fabrication of silicon-tipped fiber-optic temperature sensors using aerogel-assisted glass soldering with precise laser heating.

We demonstrate the fabrication of fiber-optic Fabry-Perot interferometer (FPI) temperature sensors by bonding a small silicon diaphragm to the tip of an optical fiber using low melting point glass powders heated by a 980 nm laser on an aerogel substrate. The heating laser is delivered to the silicon FPI using an optical fiber, while the silicon temperature is being monitored using a 1550 nm white-light system, providing localized heating with precise temperature control. The use of an aerogel substrate greatly improves the heating efficiency by reducing the thermal loss of the bonding parts to the ambient environment.

Analysis of single-mode fiber-optic extrinsic Fabry-Perot interferometric sensors with planar metal mirrors.

We theoretically study the spectral characteristics and noise performance of wavelength-interrogated fiber-optic sensors based on an extrinsic Fabry-Perot (FP) interferometer (EFPI) formed by thin metal mirrors. We develop a model and use it to analyze the effect of key sensor parameters on the visibility and spectral width of the sensors, including the beam width of the incident light, metal coating film thickness, FP cavity length, and wedge angle of the two mirrors. Through Monte Carlo simulations, we obtain an empirical equation that can be used to estimate the wavelength resolution from the visibility and spectral width, which can be used as a figure-of-merit that is inherent to the sensor and independent on the system noises.

Fiber-optic silicon Fabry-Perot interferometric bolometer with improved detection limit for magnetic confinement fusion.

Fiber-optic bolometers (FOBs) intended for plasma radiation measurement in magnetically confined fusion have been previously developed using a silicon pillar that functions as both a Fabry-Perot interferometer (FPI) for temperature measurement and an absorber for the radiation. We report an FOB design that can significantly improve the detection sensitivity over earlier designs by engineering the absorber of the FOB. Our design uses the fact that, compared with a silicon pillar, a gold film with the same x-ray absorption thickness will show a much higher temperature rise from a given power density of the radiation.

High resolution, fast response fiber-optic temperature sensor with reduced end conduction effect.

We report a fiber-optic silicon Fabry-Perot temperature sensor with high speed by considering the end conduction effect, which refers to the unwanted heat transfer between the sensing element and the fiber stub delaying the sensor from reaching thermal equilibrium with the ambient environment. The sensor is constructed by connecting the narrow edge surface of a thin silicon plate to the edge of the microtube attached to the fiber tip. Compared to the traditional design where the silicon plate is attached to the fiber end face on its large plate surface, the new sensor design minimizes the heat transfer path to the fiber stub for improved sensor speed.

Polarization-insensitive, omnidirectional fiber-optic ultrasonic sensor with quadrature demodulation.

We report an ultrasonic sensor system based on a low-finesse Fabry-Perot interferometer (FPI) formed by two weak chirped fiber Bragg gratings (CFBGs) on a coiled single-mode fiber. The sensor system has several desirable features for practical applications in detecting ultrasound on a solid surface. By controlling the birefringence of the fiber coil during the sensor fabrication, the sensor is made insensitive to the polarization variations of the laser source.

Constant temperature operation of fiber-optic hot-wire anemometers.

We demonstrate the constant temperature (CT) operation of a fiber-optic anemometer based on a laser-heated silicon Fabry-Perot interferometer (FPI), where the temperature of the FPI is kept constant by adjusting the heating laser power through a feedback control loop and the output signal is the heating laser power. We show that the CT operation can dramatically improve the frequency response over the commonly used constant power (CP) operation, where the laser heating power is kept constant and the output signal is the temperature of the FPI. For demonstration, we used a 100-μm-diameter, 200-μm-thick silicon FPI attached to the tip of a single-mode fiber as the anemometer.

A Silicon-tipped Fiber-optic Sensing Platform with High Resolution and Fast Response.

In this article, we introduce an innovative and practically promising fiber-optic sensing platform (FOSP) that we proposed and demonstrated recently. This FOSP relies on a silicon Fabry-Perot interferometer (FPI) attached to the fiber end, referred to as Si-FOSP in this work. The Si-FOSP generates an interferogram determined by the optical path length (OPL) of the silicon cavity.

A fiber-optic bolometer based on a high-finesse silicon Fabry-Pérot interferometer.

We report a fiber-optic bolometer based on a high-finesse silicon Fabry-Perot interferometer (FPI). The silicon FPI absorbs and converts the incident radiation into temperature variations, which are interrogated by the shift of the reflection spectrum of the FPI. The FPI is a silicon pillar with one side coated with a high-reflectivity dielectric mirror and the other side coated with a gold mirror.

Self-gauged fiber-optic micro-heater with an operation temperature above 1000°C.

We report a fiber-optic micro-heater based on a miniature crystalline silicon Fabry-Perot interferometer (FPI) fusion spliced to the endface of a single-mode fiber. The silicon FPI, having a diameter of 100 μm and a length of 10 or 200 μm, is heated by a 980 nm laser diode guided through the lead-in fiber, leading to a localized hot spot with a temperature that can be conveniently tuned from the ambient temperature to >1000°C in air. In the meantime, using a white light system operating in the 1550 nm wavelength window where the silicon is transparent, the silicon FPI itself also serves as a thermometer with high resolution and high speed for convenient monitoring and precise control of the heater temperature.

Optical fiber vector flow sensor based on a silicon Fabry-Perot interferometer array.

We report a miniature fiber-optic water vector flow sensor based on an array of silicon Fabry-Perot interferometers (FPIs). The flow sensor is composed of four silicon FPIs, one in the center with the other three equally distributed around it. The center FPI is heated by a cw laser at 980 nm, which is guided through the lead-in single mode fiber.

Influence of fiber bending on wavelength demodulation of fiber-optic Fabry-Perot interferometric sensors.

In practical applications of fiber optic sensors based on Fabry-Perot interferometers (FPIs), the lead-in optical fiber often experiences dynamic or static bending due to environmental perturbations or limited installation space. Bending introduces wavelength-dependent losses to the sensors, which can cause erroneous readings for sensors based on wavelength demodulation interrogation. Here, we investigate the bending-induced wavelength shift (BIWS) to sensors based on FPIs.

High-resolution, large dynamic range fiber-optic thermometer with cascaded Fabry-Perot cavities.

The paradox between a large dynamic range and a high resolution commonly exists in nearly all kinds of sensors. Here, we propose a fiber-optic thermometer based on dual Fabry-Perot interferometers (FPIs) made from the same material (silicon), but with different cavity lengths, which enables unambiguous recognition of the dense fringes associated with the thick FPI over the free-spectral range determined by the thin FPI. Therefore, the sensor combines the large dynamic range of the thin FPI and the high resolution of the thick FPI.

Flexible graphene saturable absorber on two-layer structure for tunable mode-locked soliton fiber laser.

Using a two-layer structure consisting of polyethylene terephthalate (PET) and polydimethylsiloxane (PDMS) to support graphene grown by chemical vapor deposition (CVD), we demonstrate a flexible integrated graphene saturable absorber (SA) on microfiber for passive mode-locked soliton fiber laser. This method can optimize the light-graphene interaction by using evanescent field in the integration structure. Moreover, the fiber laser with the in-line microfiber-to-graphene SA can realize the tunabilities of both the 3dB bandwidth of output optical spectrum and the pulse width of soliton.

Manipulation of dark photonic angular momentum states via magneto-optical effect for tunable slow-light performance.

We propose a novel scheme in realizing tunable slow-light performance by manipulating dark photonic angular momentum states (PAMSs) in metamaterials via the magneto-optical effect. We show that by applying a static magnetic field B, some pairs of sharp transmission dips can be observed in the background transparency window of a complex metamaterial design. Each pair of transmission dips are related to the excitation of dark PAMSs with opposite topological charges -m and +m, with a lifted degeneracy due to the classic analogue of Zeeman effect.

Actively manipulation of operation states in passively pulsed fiber lasers by using graphene saturable absorber on microfiber.

We experimentally demonstrate an operation switchable Erbium-doped fiber laser by employing graphene saturable absorber (GSA) on microfiber. With the introducing of a polydimethylsiloxane layer, a graphene can be considered as a parallel plate on microfiber and induces different propagation losses to TE and TM modes. By the use of such polarization sensitive GSA on microfiber, Erbium doped fiber laser with switchable operation states such as continuous wave, stable Q-switching, Q-switched mode-locking, and continuous-wave mode-locking, can be achieved by simply tuning the polarization states in the laser cavity.