Confocal microscopy offers enhanced image contrast and signal-to-noise ratio compared to wide-field illumination microscopy, achieved by effectively eliminating out-of-focus background noise. In our study, we initially showcase the functionality of a line-scanning confocal microscope aligned through the utilization of a Digital Light Projector (DLP) and a rolling shutter CMOS camera. In this technique, a sequence of illumination lines is projected onto a sample using a DLP and focusing objective (50X, NA=0.55). The reflected light is imaged with the camera. Line-scanning confocal imaging is accomplished by synchronizing the illumination lines with the rolling shutter of the sensor, leading to a substantial enhancement of approximately 50% in image contrast. Subsequently, this setup is employed to create a dataset comprising 500 pairs of images of paper tissue. This dataset is employed for training a Generative Adversarial Network (cGAN). Roughly 45% contrast improvement was measured in the test images for the trained network, in comparison to the ground-truth images.
In this work, in addition to the sensor application of coated optical microresonator, we show the phase transition of Pd-H system using WGMs. WGMs are propagating on a cylindrical microresonator which is based on a single mode optical fiber coated with a desired metal thickness and desired morphology. Light coupling is achieved by tapered fiber connected to a tunable laser working in the infrared wavelength. WGMs are observed and tracked by transmitted laser light. The sensor consisting of the resonator and a tapered fiber is placed in a metal chamber that is connected to the gas tanks. Desired concentration of the gas is achieved by mixing the carrier gas (nitrogen) and hydrogen. By increasing or decreasing of the hydrogen concentration in the sensing chamber, palladium layer expands or contracts. The change in the radius of the resonator translates in to shifts in spectral positions of the WGMs. However, these expansion or contractions rates are different for different phases of the Pd – H system. For instance, solid solution of hydrogen in palladium, represented by α has the lowest expansion or contraction. In contrast β phase has the highest rate. These phase transitions and intermediate phase are shown using the WGMs.
In this work, we present robust and easy-to-fabricate optical gas and vapor sensors based on optical fiber resonators (OFR) coated with palladium (Pd) thin films, Pd micro-particles and polymer brushes (PB). Pd based sensors are used for hydrogen (H2) gas detection in concentration range of 0% to 1% and polymer brush-coated OFR are used for detection of vapor in concentration range of 0 to 25%. Sensing mechanism of these sensors is based on spectral shift of resonance wavelength which are called whispering gallery modes (WGMs). This spectral shift is due to volume expansion of the sensing material. Tapered fiber is used in order to excite WGMs in coated OFRs. Good sensitivity and repeatability results are obtained for all three types of sensors.
Optical fiber resonator (OFR) sensor is presented for bulk liquid refractive index (RI) sensing. The sensing mechanism relies on the spectral shifts of whispering gallery modes (WGMs) of OFRs which are excited using a tapered fiber. OFR liquid RI sensor is fully characterized using water solutions of ethanol and ethylene glycol (EG). A good agreement is achieved between the analytical calculations and experimental results for both TE and TM polarizations. The detection limit for bulk RI is calculated to be between 2.7 – 4.7 × 10−5 refractive index unit (RIU). The OFR sensor provides a robust, easy-to-fabricate and sensitive liquid refractive index sensor which can be employed in lab-on-a-chip applications.
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