We demonstrate the optical measurements of heart-beat pulse rate and also elasticity of a polymeric tube, using a tapered fiber Mach-Zehnder interferometer. This device has two abrupt tapers in the Er/Yb codoped fiber and thus fractional amount of core mode is converted into cladding modes at the first abrupt taper. The core and cladding modes propagate through different optical paths and meet again at the second abrupt taper to produce interferences. The mechanical vibration signals generated by the blood vessels and by an inflated polymeric tube can perturb the optical paths of resonant modes to move around the resonant wavelengths. Thus, the cw laser signal is modulated to become pulses to reflect the heart-beat pulse rate and the elasticity of a polymeric tube, respectively.

No abstract

No abstract

We demonstrate an ultracompact and robust micro Sagnac loop interferometer by splicing the end-sphered hollow-core fiber against single mode fiber. The device length is less than 450Pm and the extinction ratio can be above 29dB. INTRODUCTIONSagnac loop interferometer (SLI) has been extensively used in gyroscopes, sensors, filters, and fiber lasers [1][2][3]. In contrast to the linear-optical-path interferometers like Mach-Zehnder, Michelson, and Fabry Perot, the Sagnac interferometer is based on a loop mirror in which the two light beams propagating in a common-path ring trajectory through a clockwise (cw) and a counterclockwise (ccw) direction. The phase difference coming from the birefringence between the cw and ccw lights give rise to the interferences. Conventionally, the all-fiber SLI comprises a 3 dB coupler with its two output ends are connected to become a loop mirror. The input light is split into two parts propagating along the loop mirror and recombined at the 3 dB coupler to produce interferences. However, this device is bulky and is not suitable for a space-limited situation like in the human body. In this work, we demonstrate the micro SLI using a sphered-end hollow-core optical fiber (HOF) which is splicing to the end of a singlemode fiber. The air core of the HOF near splicing point is intentionally tapered through an asymmetric arc discharging. The other end of the HOF is collapsed and sphered by arc discharging again to serve as a loop mirror to guide the light beam going backward. The core mode in the singlemode fiber is split into two parts to respectively propagate along the cladding of HOF and turn around at the sphere. Since the optical path for cw and ccw lights can not exactly overlap due to the birefringence, the induced optical path length difference (OPLD) leads to interference. A longer length of the HOF can lead to a smaller free spectral range (FSR) and a smaller angle of the tapered air core near the splicing point can help convert the core mode into cladding modes smoothly for good extinction ratios. The length of the HOF in this work is 450 Pm and the extinction ration can be above 29 dB. The FSR between two interfering wavelengths is about 150 nm which is in accordance with 5 Pm OPLD between the cw and ccw lights. This micro SLI is highly promising for special applications in a space-limited situation.

This paper describes the design of Mach Zehnder Interferometer and reviews its applications in emerging optical communication networks. Mach Zehnder Interferometer is basically used to measure relative phase shift between two collimated beams from a coherent light source. Using this basic principle a number of devices can be designed, few of these such as optical sensors, all-optical switches, optical add-drop multiplexer and modulator are discussed in this paper.