Bryan Park

Highly Sensitive Monolithic Silicon Photonic Crystal Fiber Tip Sensor for Simultaneous Measurement of Refractive Index and Temperature

Fiber optic sensors have applications in the measurement of a wide range of physical properties such as temperature, pressure, and refractive index. These sensors are immune to electromagnetic interference, made of high temperature dielectric materials and hence can be deployed in harsh environments where conventional electronics would fail. Photonic crystal (PC) fiber tip sensors are highly sensitive to changes in the refractive index and temperature while remaining compact and robust. In comparison to conventional fiber sensors such as fiber Bragg gratings (FBG) or long period fiber gratings (LPFG), they are attractive in several aspects. PC fiber tip sensors have better sensitivity to refractive index and temperature than FBG sensors and are have much smaller sensing volumes than FBGs and LPFGs. Their small size allows them to combine high sensitivity and structural robustness. The most attractive feature may be that PC fiber tip sensors also return a spectrally rich signal with independently shifting resonances that can be used to extract multiple physical properties of the measurand and distinguish between them. In this paper, we show that the PC fiber tip sensor is highly sensitive to the refractive index and temperature of the environment and that both parameters can be simultaneously determined using multiple wavelengths.

Photonic Crystal Fiber Tip Sensor for High-Temperature Measurement

We demonstrate a temperature sensor consisting of a 2-D, Silicon (Si), Photonic Crystal (PC) attached to the facet of a standard single-mode optical fiber. The 2-D PC sensors are fabricated on standard Si wafers, using a single mask and a combination of isotropic and anisotropic etching, and microassembled onto the facets of the optical fibers by Si-welding. The temperature of the Si-PC sensor is monitored by measuring its reflectance spectrum in the 1250 to 1650 nm wavelength range. The measured reflectivity peak shift is 0.11 nm°C in the 100°C to 700°C temperature range. The observed spectral shift and temperature sensitivity are significantly higher than high-temperature fiber Bragg grating sensors, and comparable to long-period fiber gratings sensors. The high sensitivity, combined with compactness and robust structure, give these sensors strong potential for use in harsh environments.

Photonic crystal fiber tip sensor for precision temperature sensing

We demonstrate that monolithic 2-dimensional photonic crystals (PCs) confined to the facet, or tip, of single-mode optical fibers can be designed as highly sensitive temperature sensors. Monolithic 2-D photonic-crystals are fabricated on silicon wafers and subsequently released and micro-assembled onto the tip of optical fibers. The PCs reflection spectrum is modulated by the temperature of the sensor and its environment and shows sensitivity comparable to Fiber Bragg Gratings (FBGs). In contrast to FBGs, the compact sensing element is localized at the tip of the fiber and the active sensor element is a disk of 10 mum diameter and 480 nm thickness. The sensor system is made of robust, high-temperature dielectric materials and therefore has the potential to be used for many applications including measurements in harsh environments.

Monolithic silicon photonic crystal slab fiber tip sensor

We demonstrate that monolithic photonic crystals (PCs) confined to the facet, or tip, of single-mode optical fibers can be designed as highly sensitive refractive index point sensors. Monolithic photonic-crystal slabs are fabricated on silicon wafers and subsequently released and micro-assembled on the tip of optical fibers. The PC slabs reflection spectrum is modulated by the refractive index of the environment and shows sensitivity comparable to Fiber Bragg Gratings (FBGs). The compact sensing element is located at the tip of a fiber and hence is a highly localized sensor. The sensor is made of robust, high-temperature dielectric materials and therefore has the potential to be used for many applications including measurements in harsh environments.

Double-Layer Silicon Photonic Crystal Fiber-Tip Temperature Sensors

This letter describes the manufacture and performance of a monolithic double-layer silicon photonic crystal temperature sensor. The sensor is fabricated on standard silicon wafers using oxide passivation and a combination of isotropic and anisotropic etching, and mounted on the facet of a standard single-mode optical fiber using template-assisted epoxy bonding. The double-layer configuration leads to coupling of the guided resonances in the two photonic crystals and enables sharper resonances and consequently higher temperature sensitivity and better detection limit (0.011 °C) than the single-layer counterpart. We experimentally demonstrate that the sensor has a twofold increased temperature sensitivity in terms of reflectivity change at a fixed wavelength (-0.00576/°C), and report on electromagnetic simulations explaining the enhanced sensor operation. The photonic crystal fabrication method and template-assisted bonding enable batch-fabrication of the sensors. Their small size, robust construction, and fiber interface make the sensors promising for numerous applications, including sensing in harsh environments.

Two-Axis MEMS scanner with transfer-printed high-reflectivity, broadband monolithic silicon photonic crystal mirrors

We present a two-axis electrostatic MEMS scanner with high-reflectivity monolithic single-crystal-silicon photonic crystal (PC) mirrors suitable for applications in harsh environments. The reflective surfaces of the MEMS scanner are transfer-printed PC mirrors with low polarization dependence, low angular dependence, and reflectivity over 85% in the wavelength range of 1490nm~1505nm and above 90% over the wavelength band of 1550~1570nm. In static mode, the scanner has total scan range of 10.2° on one rotation axis and 7.8° on the other. Dynamic operation on resonance increase the scan range to 21° at 608Hz around the outer rotation axis and 9.5° at 1.73kHz about the inner rotation axis.

High temperature photonic crystal fiber tip sensor

We demonstrate a temperature sensor consisting of a 2-dimensional, Silicon (Si), Photonic Crystal (PC) attached to the facet of a standard single-mode optical fiber. The 2-D PC sensors are fabricated on standard Si wafers, using a single mask and a combination of isotropic and anisotropic etching, and micro-assembled onto the facets of the optical fibers by Si-welding. The temperature of the Si-PC sensor is monitored by measuring its reflectance spectrum in the 1250 nm to 1650 nm wavelength range. The measured reflectivity peak shifts from 100°C to 700°C is 0.1036 nm/°C. The observed spectral shift and temperature sensitivity are significantly higher than other high-temperature fiber Bragg grating sensors, and comparable to long-period fiber gratings sensors. The high sensitivity along with the compactness and robustness gives these sensors the strong potential for use in harsh environments.

Double-layer silicon photonic crystal fiber tip sensor

We describe a double-layer monolithic silicon photonic crystal (PC) fiber tip sensor. The PC is fabricated using wafer-scale Si processing and epoxy bonding to the fiber. The sensor has sharper resonances and higher sensitivity to refractive index than previously-reported single-layer PC fiber tip sensors. The bonding technique enables batch production.

Monolithic Silicon Photonic Crystal Fiber Tip Sensors

Photonic Crystals (PC) enable sensitive and robust sensors for a large number of measurands, including temperature, refractive index, displacement, pressure, acceleration, and rotation. The small volumes of two-dimensional PC sensors also make them ideal for integration onto the facet of optical fibers. In this chapter, we describe the operation, design, and fabrication of Si PC sensors for refractive index and temperature, and the process technology used to integrate the sensors onto the facets of standard single-mode fibers (SMFs). The PC sensors are fabricated on standard Si wafers, using a single photolithography mask and a combination of isotropic and anisotropic etching. Once the sensor fabrication is completed, the miniaturized sensors (50 μm × 50 μm × 0.5 μm) are assembled onto SMF facets. The results are highly-sensitive, robust sensors with submicron sensing layers that are well suited for deployment in harsh environments, including temperatures up to 700 °C.

High-reflectivity, broadband monolithic silicon photonic crystal mirrors on two-axis MEMS scanner by transfer-printing

We demonstrate a two-axis electrostatic MEMS scanner integrated with high-reflectivity monolithic silicon photonic crystal (PC) mirrors by transfer printing. The PC mirrors show low polarization dependence and reflectivity over 85% in the wavelength range of 1490nm~1505nm and above 90% over the wavelength band of 1550~1570nm. The integration of nanophotonic devices on a MEMS platform with transfer printing enables novel devices with more flexible design and new functionality.