Nanotechnology-Enabled Sensors

72 Chapter 3: Transduction Platforms
Fig. 3.7 Two types of optical fiber as sensing platforms: (top) when cladding is
removed and the core is exposed to the target analyte or the sensitive layer is deposited
on this core (bottom) when a sensitive layer is deposited at the end of an
optical fiber.
3.3.4 Interferometric Optical Transducers
Interferometric optical transducers are measure the constructive and destructive
interference of optical waves. In general, waves traveling through
a waveguide is split into two or more beams of equal intensity. After splitting,
one of the beams travels unperturbed through the waveguide, whilst
the others travel through a waveguide that may be exposed to the sample
media. The light beams are then recombined either destructively or constructively,
and the optical properties of this recombined beam (e.g. intensity,
wavelength, phase, etc) are analyzed.
Interferometric optical sensors are ideal for realizing on-chip optical
sensors as they can be fabricated using standard microfabrication techniques.
They have a relatively simple input and output coupling, capability
for differential on-chip referencing with excellent stability. However, their