Lei Yuan

Clemson University | CU · Department of Electrical and Computer Engineering

In this paper, we demonstrate the feasibility of an innovative method to fabricate flexibly embedded microchannels in bulk ceramics of complex geometries. This innovative method is an integration of extrusion freeforming (EFF) and picosecond (PS) laser machining. The bulk ceramic green body of complex geometries was fabricated using the extrusion m...

We report an open cavity, cantilever-based fiber optic Fabry–Perot interferometer hydrophone. The hydrophone is made of fused silica material, and its micro-cantilever beam is directly fabricated by femtosecond (fs) laser micromachining. The theoretical analyses and experimental verifications of the frequency response of the sensor are presented.

We present our recent progress in fiber optic acoustic sensors formed by using a Fabry–Perot (FP) interferometer with a silica diaphragm/cantilever on the tip of a single-mode fiber, fabricated by the femtosecond (fs) laser ablation technique. The directivity of an acoustic sensor with a silica diaphragm was improved by packaging the sensor head in...

In this work, we demonstrated the fabrication of crack-free luminescent Er-doped silica coatings sintered using a CO2 laser. The silica sol-gel precursor with controllable rheology was developed using tetraethyl orthosilicate (TEOS) and hexamethyldisiloxane (HMDS). Luminescence activation was achieved through doping with Er ions. Coatings sintered...

A ferrofluid filled coaxial cable Fabry-Perot interferometer is proposed for magnetic field sensing. Both the interferogram shift and the reflection intensity change of the sensor response are studied when external magnetic field is applied. The sensor is tested to work from 0 Gauss to 160 Gauss, and has a highly linear response above 50 Gauss, wit...

We present a coaxial cable interferometer based distributed sensing system for 3D beam shape estimation. By making a series of reflectors on a coaxial cable, multiple Fabry-Perot cavities are created on it. Two cables are mounted on the beam at proper locations, and a vector network analyzer (VNA) is connected to them to obtain the complex reflecti...

This work focuses on demonstrating the fabrication of miniaturized scintillators based on rare earth activated YAG ceramics using the direct inkjet printing method. Erbium was chosen as the activator, and YAG sol-gel precursor inks were prepared under precise hydrolysis and polycondensation reactions. The precursors showed excellent control over rh...

We report an integrated whispering gallery mode microresonator-based sensor probe for refractive index sensing. The probe was made by sealing a borosilicate glass microsphere into a thin-wall glass capillary pigtailed with a multimode optical fiber. The intensities of the resonant peaks were found decreasing exponentially (linearly in a log scale)...

We report a new distributed fiber optic sensing technique using optical carrier based microwave interferometry. The concept has been demonstrated using different types of optical fibers including singlemode fiber, multimode fiber, single crystal sapphire fiber and polymer fiber. Using the microwave-photonic technique, many fiber interferometers wit...

A non-destructive technique for inspection of a Bismaleimide (BMI) composite is presented using an optical fiber sensor. High performance BMI composites are used for Aerospace application for their mechanical strength. They are also used as an alternative to toughened epoxy resins. A femtosecond-laser-inscribed Intrinsic Fabry-Perot Interferometer...

In this paper, we present a pure silica micro-cantilever based optical fiber sensor for acoustic wave detection. The cantilever is directly fabricated by fs laser micromachining on an optical fiber tip functioning as an inline Fabry-Perot interferometer (FPI). The applied acoustic wave pressurizes the micro-cantilever beam and the corresponding dyn...

In this paper, we summarize our recent research progresses on the understanding, design, fabrication, characterization of various photonic sensors for energy, defense, environmental, biomedical and industry applications. Femtosecond laser processing/ablation of various glass materials (fused silica, doped silica, sapphire, etc.) will be discussed t...

This paper reports the stress-induced birefringence generated in an optical fiber using femtosecond laser (fs) irradiations and the fabrication of in-fiber waveplates and polarizers. Optical birefringence was created in a single-mode fiber by introducing a series of symmetric cuboid stress rods on both sides of the fiber core and along the fiber ax...

A type of extrinsic Fabry-Perot interferometer (EFPI) fiber optic sensor, i.e., the microcavity strain sensor, is demonstrated for embedded, high-temperature applications. The sensor is fabricated using a femtosecond (fs) laser. The fs-laser-based fabrication makes the sensor thermally stable to sustain operating temperatures as high as 800°C. The...

Optofluid system has been more and more attractive in optical sensing applications such as chemical and biological analysis as it incorporates the unique features from both integrated optics and microfluidics. In recent years, various optofluid based structures have been investigated in/on an optical fiber platform which is referred to as “lab in/o...

We report a two-axis fiber inclinometer fabricated using an ultraweak terahertz-range fiber Bragg grating. Three sensing grating structures were inscribed along a single-mode optical fiber using a femtosecond laser, bound together into a sensing array using thermoformed plastic, and fixed to a two-axis rotational stage. Inclination tests were perfo...

Optical birefringence was created in a single-mode fiber by introducing a series of symmetric cuboid stress rods on both sides of the fiber core along the fiber axis using a femtosecond laser. The stress-induced birefringence was estimated to be 2.4 × 10⁻⁴ at the wavelength of 1550 nm. By adding the desired numbers of stressed rods, an in-fiber qua...

Research and development in advanced sensors with embedded monitoring capability have experienced significant growth in recent years, fueled by their broad applications in real-time measurement of a wide variety of physical, chemical, and biological quantities. Compared with conventional sensors with bulky assemblies, recent progress in 3D manufact...

This paper demonstrates fiber-based intrinsic Fabry-Perot interferometer fabricated by femtosecond laser micromachining with a modified method based on the index matching oil, to enhance the spectral uniformity with 7.27 dB. Its temperature sensing property is also investigated in the range of 0–100 °C, with a sensitivity of 11.68 pm/°C.

This letter reports a fiber Bragg grating (FBG) for distributed sensing applications fabricated using single-mode optical fiber and a femtosecond laser and interrogated in the terahertz (THz) range. A theoretical model of device behavior was derived, which agreed well with experimentally observed device behavior. In order to investigate the utility...

A miniaturized chemical vapor sensor probe was developed using a porous glass microsphere (PGM) as the alignment-free optical microresonator. The porous microsphere was placed inside a thin wall silica capillary tube that was fusion-spliced to an optical fiber. The whispering gallery modes (WGMs) of the microsphere were excited by the evanescent fi...

This Letter reports on an ultraweak intrinsic Fabry–Perot interferometer (IFPI) array fabricated by a femtosecond (fs) laser for distributed sensing applications. Ultralow reflectors ( < − 60 dB ) were obtained. IFPIs with different physical lengths showed identical temperature sensitivity ( − 1.5 GHz / ° C ). A distributed temperature sensing test...

Research and development in photonic micro/nanodevices and structures have experienced a significant growth in recent years, fueled by their broad applications as sensors for in situ measurement of a wide variety of physical, chemical and biological quantities. Recent advancement in ultrafast and ultra-intense pulsed laser technology has opened a n...

Optical fiber interferometers (OFIs) have been extensively utilized for precise measurements of various physical/chemical quantities (e.g., temperature, strain, pressure, rotation, refractive index, etc.). However, the random change of polarization states along the optical fibers and the strong dependence on the materials and geometries of the opti...

This paper presents an approach for simultaneous measurement of temperature and pressure using miniaturized fiber inline sensors. The approach utilizes the cascaded optical fiber inline intrinsic Fabry-Perot interferometer and extrinsic Fabry-Perot interferometer as temperature and pressure sensing elements, respectively. A CO2 laser was used to cr...

An all-in-fiber prototype optofluidic device was fabricated by femtosecond laser irradiation and subsequent selective chemical wet etching. Horizontal and vertical microchannels can be flexibly created into an optical fiber to form a fluidic cavity with inlets/outlets. The fluidic cavity also functions as an optical Fabry–Perot cavity in which the...

A U-shaped optical fiber inline microchannel was fabricated by femtosecond laser irradiation and subsequent selective chemical wet etching. A high quality micro-cavity embedded inside the channel was obtained to construct a Fabry-Perot interferometer (FPI). A fringe visibility of 20 dB in spectrum domain was achieved. High temperature survivability...

A compact Michelson interferometer (MI) in a single-mode fiber (SMF) is successfully formed by CO2 laser irradiation to measure refractive index (RI) values. The fiber inline MI mainly consists of two parts: one is the waist region in fiber formed by CO2 laser irradiation and the other one is the fiber tip end facet with pure gold sputter coating....

We report a method to fabricate SERS fiber probe by femtosecond laser micromachining on a microfiber tip. Multimode optical fibers are tapered to outer diameter of 4 to 20 μm. Femtosecond laser pulses are used to form nanostructures on the cleaved endface of the microfiber tip. This endface is then activated by silver sputter coating. To confine th...

Reflectivity spectrum of beam propagation method (BPM), for the first time to the best of our knowledge, is realized and utilized to model all-optical fiber interferometric sensor formed by a U-shape microcavity embedded in a single mode optical fiber and illustrate the principle of sensor structures varied by the length and the depth of U-shape mi...

A microcavity extrinsic Fabry–Perot interferometric (EFPI) fiber-optic sensor is presented for meas- urement of strain. The EFPI sensor is fabricated by micromachining a cavity on the tip of a standard single-mode fiber with a femtosecond (fs) laser and is then self-enclosed by fusion splicing another piece of single-mode fiber. The fs-laser-based...

Figure 2 in a previous Letter [ Opt. Lett. 38, 4609 (2013)] was incorrect and is modified here.

A fiber inline Michelson interferometer fiber optic sensor was presented for sensing applications, including high temperature performance and refractive index change. The sensor was fabricated using one-step femtosecond (fs) laser micromachining technique. A step structure at the tip of a single mode optical fiber was formed during the micromachini...

In this Letter, we report on a fiber-optic Fabry–Perot interferometric pressure sensor with its external diaphragm surface thinned and roughened by a femtosecond laser. The laser-roughened surface helps to eliminate outer reflections from the external diaphragm surface and makes the sensor immune to variations in the ambient refractive index. The s...

This study investigates the resonant effects on nonlinear photoionization of Li4 cluster under femtosecond laser irradiation. The real-time and real-space time-dependent density functional theory is applied to describe the optical linear response and nonlinear electron dynamics during the laser-material interactions. The calculations describe well...

Spinel MgAl2O4 thin films have been coated on phi 75-mu m single crystal sapphire fibers and sapphire wafers by low-temperature (700 degrees C) firing of (Mg2+, Al3+)-chelated polymeric precursor films. The MgAl2O4 coating was demonstrated to be chemically stable on sapphire substrate at temperatures as high as 1200 degrees C. No evidences of solid...

In this paper, we demonstrate a fiber pigtailed thin wall capillary coupler for excitation of Whispering Gallery Modes (WGMs) of microsphere resonators. The coupler is made by fusion-splicing an optical fiber with a capillary tube and consequently etching the capillary wall to a thickness of a few microns. Light is coupled through the peripheral co...

A quantum model with the consideration of laser wave-particle duality based on the plasma model is employed for the femtosecond laser pulse train processing of fused silica. Effects of the key pulse train parameters, such as the pulse separation time and the number of pulses per train on the distributions of free electron are discussed. The calcula...

An extrinsic Fabry-Perot interferometric (EFPI) fiber optic sensor is presented for measurement of strain at high ambient temperatures. The sensor is fabricated using a femto-second (fs) laser. The EFPI sensor is fabricated by micromachining a cavity on the tip of a standard single-mode fiber and is then self-enclosed by fusion splicing another pie...

We report a reflection-based phase-shifted long period fiber grating (PS-LPFG) and demonstrate its capability for simultaneous measurement of temperature and external reflective index (RI). The sensor device comprises a grating directly written by CO2 laser and silver-coated end face. A π-shifted LPFG is presented with two attenuation bands through...

A fiber inline Michelson interferometer was fabricated by micromachining a step structure at the tip of a single-mode optical fiber using a femtosecond laser. The step structure splits the fiber core into two reflection paths and produces an interference signal. A fringe visibility of 18 dB was achieved. Temperature sensing up to 1000°C was demonst...

This Letter reports a polymer optical fiber (POF) based large strain sensor based on the multimode interference (MMI) theory for the application of structural health monitoring. A section of POFs is sandwiched between two silica single mode fibers to construct a single-mode-multimode-single-mode structure that produces a MMI spectrum. The strain se...

An approach to the simultaneous measurement of refractive-index (RI) and temperature changes using optical ring resonators is proposed and theoretically demonstrated. With a liquid-core silica ring resonator as an example, two different-order whispering gallery modes (WGMs) might differ in not only RI but also temperature sensitivities. Thus, a sec...

Optical microresonators have been proven effective for developing sensitive chemical and biological sensors by monitoring the changes in refractive index or mass near the resonator surface. The rotationally symmetric structures support high quality (Q) whispering gallery modes (WGMs) that interact with the local environment through the evanescent f...

A porous-wall hollow glass microsphere (PW-HGM) was investigated as an optical resonator for chemical vapor sensing. A single mode optical fiber taper was used to interrogate the microresonator. Adsorption of chemical molecules into the nanosized pores induced a refractive index change of the thin wall and thus a shift in its resonance spectrum. Th...

An optical microresonator based upon a hollow sphere with a porous wall has been proposed for use as a refractive index sensor. The sensor structure was created by coupling a Porous Wall Hollow Glass Microsphere (PW-HGM) to a single mode fiber taper (Corning SMF-28). The experimental results showed that the PW-HGM can be effectively stimulated by e...

We propose a highly sensitive chemical sensor by functionally coating a zeolite film on the external surface of an optical microsphere. Using the perturbation theory, a model is developed to calculate sensor sensitivity and analyze the impact of the zeolite film thickness. The quality factor and detection limit are also investigated by using an app...