This paper examines the sensitivity improvements that have been achieved by making use of slow light in a variety of
fiber sensors. We show in particular that slow light can have dramatically different impacts depending on its nature
(material or structural) and on the parameter that is being sensed. In a fiber optic gyroscope measuring an absolute
rotation for example, structural slow light does not enhance the maximum sensitivity achievable for a given loss and
sensing area compared to a non-resonant structure such as a Sagnac-based fiber optic gyroscope. However, it does
reduce the length of fiber required to achieve this sensitivity. For fiber sensors relying on the measurement of absorption,
such as gas detectors, structural slow light improves the sensitivity because it increases the effective path length through
the absorber and therefore the level of absorption. Material slow light, on the other hand, has been measured to have no
impact on the sensitivity. For many other parameters besides rotation and absorption, the sensitivity is expected to be
enhanced by either type of slow light, by orders of magnitude with suitable configurations. We illustrate this enormous
potential with two configurations of strain sensors utilizing a fiber Bragg grating (FBG) as the sensing and slow-light
medium. In properly designed FBGs supporting light with a group index in the range of 50 to 130, we measured a
maximum sensitivity of 1.7-3.14 105 strain-1 and a record minimum detectable strain of 820-880 fε/√Hz. This value is
~730 lower than the previous record using conventional light in a passive FBG sensor, in accord with predictions.
Further enhancements are expected with straightforward improvements in FBG design.
We demonstrate through numerical simulations that a fiber Bragg grating operated in transmission can support much
slower light than previously anticipated. This is accomplished by increasing the grating's index modulation, reducing its
loss, optimizing its length, and apodizing its index profile. With current fiber Bragg grating loss and index modulation,
we predict that group velocities lower than c/1000 are attainable. We validate this concept with a record measured group
index of 130 in a strong apodized grating (index modulation of ~1.1 10-3) with a nearly optimized length of 1.2 cm and
an inferred loss coefficient of 1 m-1.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.