Page 179 - Optofluidics Fundamentals, Devices, and Applications

154 Cha pte r Se v e n

into the beam between two SMFs, generating an interferometric
response that is tunable in amplitude due to the inherent mobility of
the fluid plug. The capillary is treated using silanization chemistry to
manipulate the meniscus shape for optimal optical performance.
Figure 7-16 (top) shows a generic Mach-Zehnder interferometer.
The signal entering the device is split into two arms, one of which
induces a comparative delay resulting in a phase difference that
underlies the characteristic attenuation of the interferometers spectral
structure. Figure 7-16 (bottom) shows a schematic of the single-beam
interferometer in which the incident beam is split in two by an inter-
face, on either side of which is a material of differing refractive index,
effectively resulting in a Mach-Zehnder interferometer. As opposed
to what is usually found in a Mach-Zehnder interferometer, the

I 1 Delay δ

Input Output

I 2

A 0
SMF SMF
Fluid

a = 0
A = A /2 Meniscus
1
0
Input Output
A – A 1
0

Optical beam
a = 2 μm

Cut plane
Square capillary
FIGURE 7-16 (top) A schematic of a Mach-Zhender interferometer showing the
relative light paths and delay in one arm. (bottom) A schematic of the compact
single beam optofl uidic interferometer. (C. Grillet, P. Domachuk, V. Ta’eed, et al.,
“Compact tunable microfl uidic interferometer,” Opt. Express, 12, 5440–5447
(2004).)