Self-mixing interferometry is a promising technique for a variety of measurement applications. Using a laser diode with
an external cavity as interferometer, the technique offers several advantages over traditional interferometric
configurations. This research used a self-mixing interferometer built in our own laboratory. It is based on a blue emitting
GaN laser diode with a wavelength of 405 nm. Light is directed through an optical fiber from which a 1-cm section of
cladding has been removed, and a cuvette for holding the sample is fixed around this part. Interference patterns, created
in the laser cavity, are acquired with a computer-based data acquisition system and later processed using Matlab
software. Since samples with different refractive indices create interference patterns with different phases, even small
changes in sample concentrations can be measured. However, coupling light into a single-mode optical fiber is a very
challenging task, and the setup is very sensitive to external interference like airflows or vibrations. Experiments with the
device showed that, in stability measurements, the standard deviation of the recorded fringe pattern shifts was only 1.7
nm. In sample measurements, the refractive index change in the sample chamber varied from 1.0029 to 1.33,
corresponding to a fringe pattern shift of 297±4 nm.
This paper presents a label-free optical biosensor based on a Young's interferometer configuration that uses a vertically
integrated dual-slab waveguide interferometer as sensing element. In this element, linearly polarized light is coupled into
a dual-slab waveguide chip from the input end-face, and the in-coupled zeroth order mode propagates in separated upper
and lower waveguides. At the output end-face, the two closely spaced coherent beams diffract out and produce an
interference fringe pattern. An evanescent wave field, generated on the surface of the upper waveguide, probes changes
in the refractive index of the studied sample, causing a phase shift in the fringe pattern. Compared to a conventional
integrated Young's interferometer utilizing a Y-junction as the beam splitter, the dual-slab waveguide Young's
interferometer has the advantage of easy fabrication and large tolerance to the input-coupling beam. This paper builds a
measurement system to investigate sensor performance using glucose solutions with various concentrations. These
glucose concentration measurements are performed within the physiological range of 30mg/dl ~ 500mg/dl. The results
indicate that a dual-slab waveguide interferometer yields an average phase resolution of 0.002 rad, which corresponds to
an effective refractive index change of 4×10-8 with an interaction path length of 15 mm.
This paper presents a novel method for detecting a change in the refractive index of samples. One of its major
applications is sensing molecular interaction in biological samples. In our study a self-mixing interferometer (SMI) was
chosen as the instrument for measuring the refractive index in free -space. A GaN blue laser diode was used as a light-emitting
source. Compared with traditional interferometric configurations, self-mixing interferometry combined with
the laser diode package has the advantage of a compact setup and high sensitivity.
Long-term stability issue was first concerned in our research. The results showed that in 15 minutes the movement of
the fringe pattern formed by the self-interfered laser beam is 13.6 nm. The measurement of the refractive index was
performed by adding a heating element to the external cavity of the SMI. The refractive index of the air in the external
cavity was varied by the atmospheric temperature. The change in the refractive index of the air was calculated using
both a modified Edlén equation and the recorded self-interfered signals. The results showed that the change in the
refractive index observed from the shift in the fringe pattern is compatible with that calculated with the modified Edlén
equation, or about 1×10-6/°C with optical path length of 5 cm. Theoretically, the smallest movement of the fringe pattern
that can be detected with our measurement setup is 1.6 nm, corresponding to a 10-8 change in the refractive index in the
external cavity.
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.