Note: Optical fiber milled by focused ion beam and its application for Fabry-Pérot refractive index sensor

Abstract

We introduce a highly compact fiber-optic Fabry-Pérot refractive index sensor integrated with a fluid channel that is fabricated directly near the tip of a 32 μm in diameter single-mode fiber taper. The focused ion beam technique is used to efficiently mill the microcavity from the fiber side and finely polish the end facets of the cavity with a high spatial resolution. It is found that a fringe visibility of over 15 dB can be achieved and that the sensor has a sensitivity of ∼1731 nm/RIU (refractive index units) and a detection limit of ∼5.78 × 10−6 RIU. This miniature integrated all-in-fiber optofludic sensor may find use in minimal-invasive biomedical applications.

Simultaneous measurement of temperature and refractive index using focused ion beam milled Fabry-Perot cavities in optical fiber micro-tips

“…The advantage of FIB is the superior surface quality of the reflecting surfaces obtained with FIB compared to that produced with a fs-laser [16]. Preliminary work on microcavities milled with FIB has been presented, where cavities have been fabricated in tapered fiber tips for either temperature [18] or refractive index sensing [19,23]. Cavities in microwires for temperature and vibration sensing have been shown [20] as well as focused ion beam milled cavities in polished optical fibers [21].…”

“…Micromachining is a more recent technique that allows for the creation of very small cavities or microcavities. The two prominent techniques for optical fiber micromachining are femtosecond laser micromachining [11][12][13][14][15][16][17] and focused ion beam (FIB) milling [18][19][20][21][22][23]. Femtosecond (fs) laser micromachining has been used to create cavities in several ways.…”

Temperature-insensitive refractive index sensing by use of micro Fabry–Pérot cavity based on simplified hollow-core photonic crystal fiber

“…Recently, the micro FP cavity has received increased research attention because of its low temperature cross-sensitivity, high RI and/or strain sensitivities, and convenient reflection mode of detection. The FP cavity fabricated by focused ion beam milling has been used to measure the RI around 1.30 with a high sensitivity of 1731 nm∕RIU [14] however; the temperature crosssensitivity of the device was not reported. By employing a femtosecond laser, micro FP cavity can be fabricated in single mode fiber (SMF) [15,16] and PCF [17], with a temperature sensitivity of larger than 2 pm∕°C, corresponding to a temperature cross-sensitivity of greater than 2 × 10 −6 RIU∕°C.…”

Selective filling of photonic crystal fibers using focused ion beam milled microchannels

“…A Helios EBS3 FIB with Ga + ion source is used here to mill microchannels for the lateral access in the following liquid infiltration. FIB has been used in a number of fiber-based applications, including fabrication of a Fabry-Pérot microcavity [11] and long period gratings [12], micromachining of fiber tips [13], and the milling of side access holes in structured optical fibers [10]. As a consequence of its applications in semiconductor technology, the FIB technique is mature and more flexible than the femtosecond laser processing, and dual-beam instruments combining a scanning electron microscope (SEM) and FIB are commercially available nowadays.…”