The material behaviour of sutured tendons is important in healing models as mechanical trauma to the tendon during
surgery can compromise the healing process. This work demonstrates the use of spectral domain optical coherence
tomography (SD-OCT) for the monitoring of normal and injured, and subsequently repaired flexor tendons and their
behaviour under load. Vertical crimp patterns in normal tendons were observed to be replaced by uniform scattering as
the load increases, but the crimp periods in sutured tendons were constrained at the suture site, with gap separation at the
suture joint tapering off at high loads. This information could be useful for surgeons who need to balance gap separation
in healing tendons and sustainable load.
This work investigates the use of optical coherence tomography (OCT) to identify virus infection in orchid plants. Besides revealing the cross-sectional structure of orchid leaves, highly scattering upper leaf epidermides are detected with OCT for virus-infected plants. This distinct feature is not observable under histological examination of the leaf samples. Furthermore, the leaf epidermides of stressed but healthy plants, which exhibit similar visual symptoms as virus-infected plants, are not highly scattering and are similar to those of healthy plants. The results suggest that virus-infected orchid plants can be accurately identified by imaging the epidermal layers of their leaves with OCT. The OCT modality is suitable for fast, nondestructive diagnosis of orchid virus infection, which may potentially lead to significant cost savings and better control of the spread of viruses in the orchid industry.
Applications involving fluorescence detection in point-of-care systems are both interesting and challenging in nature. The applications usually require a simple, compact, robust, highly sensitive yet affordable system. As a result, the system needs to be efficient in fluorescence detection by using practical and easily fabricated, hence inexpensive sensors. In this paper, a fluorescence sensor using an in-fiber microchannel has been developed and tested successfully. A blue LED, multimode PMMA or silica fiber, mini-PMT and fluorescein in PBS pH 7.4 buffer solution were used as the excitation source, light guide, fluorescence detector and sample, respectively. Microfluidic channels of 100μm width and 1cm length were fabricated in the optical fibers using a direct write CO2 laser system. The channels in the fibers were examined using a SEM and an optical microscope. Experimental results show that the sensor is highly sensitive, being able to detect 0.1 μg/L of fluorescein in the PBS buffer solution, with good signal to noise ratio and the results are reproducible. The data obtained using silica fibers as sensors when compared with the results from PMMA fibers show that the silica fiber sensor has better sensitivity than the PMMA fiber sensor. This could be due to the fouling effect created by the frosty layer at the bottom of the microchannel made within the PMMA fiber. Our future work will integrate the fiber sensor into microfluidic chips for lab-on-a-chip applications.
A long-period grating (LPG) coated with gelatin was developed as a high relative humidity (RH) sensor. The resonance dip or coupling intensity of the LPG spectrum varies with humidity while the resonance wavelength remains constant. The principle of operation of the sensor is based on the effect of an external medium, with higher refractive index than that of silica or cladding, on the LPG spectrum. Experimental investigations on the sensor yield a sensitivity of 1.2dB/%RH with an accuracy of ±0.25%RH, and a resolution of ±0.00833%RH. The LPG RH sensor also offers repeatability, hysteresis and stability errors of less than ±0.877%RH, ±0.203%RH and ±0.04%RH respectively. In addition to the characterization of the LPG RH sensor, further studies were conducted to determine the effect of grating periodicities on the sensitivity. Results show that higher-order cladding modes from smaller grating periods enable the sensor to achieve higher sensitivity to humidity. This method is proposed to be more cost effective as compared to more complex spectroscopic methods based on wavelength detection. This sensor can also help to solve problems in measuring high humidity with existing relative humidity measurement systems.
High resolution tunable optical filters are important in dense wavelength division multiplexing (DWDM) applications as channel spacing in optical communications systems can be as low as 0.4nm. The bandwidth of the filter must be narrow, to prevent filtering neighbouring channels. In this paper, a simple, low cost technique for the tuning of the Bragg wavelength of the FBG filter with high resolution and good repeatability is demonstrated. A FBG was embedded in a triangular carbon fiber composite package and aluminium plates were used to clamp the wider end of the package, leaving the thinner end free, like a cantilever beam. A micrometer was placed under the thinner end of the package and the vertical displacement of the micrometer will bend the carbon composite. This bending will produce compression and tension forces on the FBG depending on which side of the package is used, which will result in a shift of the Bragg wavelength. The total tuning range of the FBG filter is 2nm with a resolution of 1pm. The repeatability error was found to be 0.4% over the whole tuning range. The 3dB bandwidth of the reflected spectra from the FBG is 0.235nm, much less than channel spacing of 0.4nm.
The use of LPG embedded in carbon-fiber composite laminates (ELPG), in a 4-3 configuration, for bending measurement has been demonstrated. With increased bending curvatures on the 4 layers side, the coupling strength of the cladding mode decreases while the resonance wavelength remains relatively constant. A reduction in coupling strength leads to a reduction of the resonance amplitude depth. From the bending test covering the range of curvatures from 0m-1 to 2m-1, the ELPG yields a sensitivity of 5.065dB/m-1 and a repeatability of 98.1%. In another investigation, the ELPG ability to determine direction of bend has also been demonstrated by applying bending at the 3 layers side of the laminate. Despite having a short curvature range between 0m-1 and ~0.626m-1, the test demonstrates an increase of the cladding mode coupling strength with an increase in bending curvature, thus showing the ELPG ability to differentiate bending directions. By exploiting the unique characteristics of ELPG, two ELPGs can be exploited for 2-axis measurement of structures. Hence the overall cost and complexity of the bending sensor system can be greatly reduced.
For an embedded LPG bending sensor, in which the its resonance coupling strength changes with bending curvature, cross-talk issues between temperature and bending curvature arises if it is to be deployed in non-controlled environments. A 2 x 2 matrix method was thus employed for simultaneous measurement of bending curvature and temperature for the embedded LPG bending sensor. The matrix is made up of bending and temperature coefficients from 2 different fiber-types LPG; one is H2-loaded and the other is Bo/Ge co-doped. To find out the percentage error, a random test has to be carried out and the matrix was deployed for calculation. From the test results, the percentage error achieved for curvature measurement yields less than 6%. For temperature measurement, the percentage error fluctuates between 1.56% and 5.4%. The use of simultaneous measurement of both bending curvature and temperature enables researchers and engineers to measure bending of structures more accurately.
A low cost, low complexity fiber optic humidity sensor is very desirable because of the various advantages fiber optic sensors have over conventional electrical sensors. In this paper a simple, low cost plastic optical fiber (POF) sensor based on cobalt chloride (CoCl2) and gelatin coating on the curved sensing point with a humidity sensing range from 60% to 95%RH is presented. An investigation into the effect of bending radii of the fiber at the sensing point as well as fiber core diameter on sensitivity of the humidity sensor is conducted to find the best way to improve sensing performance. The sensing mechanism of the POF humidity sensor is the attenuation of the evanescent wave at the bent portion of the fiber by absorption due to CoCl2. The sensor has a sensing range from 60%RH to 95%RH. The hysteresis error is negligible and a resolution of 0.01%RH is achieved. The repeatability error can be as low as 1.1% for the whole sensing range. Investigation of the effect of fiber diameter shows that the sensitivity of the sensor improves with larger fiber diameters. The sensitivity of the sensor increases when the sensing portion of the fiber is bent to a small radius.