Miniaturized fiber taper reflective interferometer for high temperature measurement

Abstract

We present an ultra-small all-silica high temperature sensor based on a reflective Fabry-Perot modal interferometer (FPMI). Our FPMI is made of a micro-cavity (approximately 4.4 microm) directly fabricated into a fiber taper probe less than 10 mum in diameter. Its sensing head is a miniaturized single mode-multimode fiber configuration without splicing. The sensing mechanism of FPMI is the interference among reflected fundamental mode and excited high-order modes at the end-faces. Its temperature sensitivity is approximately 20 pm/degrees C near the wavelength of 1550 nm. This kind of sensor can work in harsh environments with ultra-large temperature gradient, but takes up little space because of its unique geometry and small size.

Miniature Engineered Tapered Fiber Tip Devices by Focused Ion Beam Micromachining

“…Microscope image of a typical TFT, five photographs separated by four dashed vertical lines are used to show the whole profile of the TFT. The black arrow indicates the milling location (Kou et al, 2010b). Reprinted with permission.…”

“…Thus the micromachining accuracy is limited and the size of the microcavity is large (tens of micrometers). The latest progress in FIB technique opens a new widow of opportunity for ultra-small size cavity (Kou et al, 2010a(Kou et al, , 2010b. Microcavities with nanometer-scale accuracy in a subwavelength microfiber could be fabricated by FIB, which is relatively difficult for fs laser approach.…”

“…The fundamental LP 01 mode can be coupled to high-order LP 0m mode in the taper transition or be excited to high-order LP 0m mode at the end-faces. I 1 or I 2 possibly includes LP 01 or LP 0m mode (Kou et al, 2010b). We also break the cavity and measure the reflection I 1 at end-face 1; flat reflective spectrum without obvious interference fringes is observed.…”

“…We also break the cavity and measure the reflection I 1 at end-face 1; flat reflective spectrum without obvious interference fringes is observed. Accordingly, a reasonable assumption is to consider only one dominated mode in I 1 (LP 01 mode) and I 2 (LP 01 or LP 0m mode excited when inputting I 2 into end-face 1) (Kou et al, 2010b). We call this kind of device as a hybrid FP modal interferometer (FPMI).…”

“…We call this kind of device as a hybrid FP modal interferometer (FPMI). The interference spectrum can be modelled using the following two-beam optical interference equation (Kou et al, 2010b):…”