Solving Fresnel equation for refractive index using reflected optical power obtained from Bessel beam interferometry

Tissue characterization using axicon probe-assisted common-path optical coherence tomography

In this work, a common-path optical coherence tomography (OCT) system is demonstrated for characterizing the tissue in terms of some optical properties. A negative axicon structure chemically etched inside the fiber tip is employed as optical probe in the OCT. This probe generates a quality Bessel beam owning a large depth-of-field, ∼700 µm and small central spot size, ∼3 µm. The OCT system is probing the sample without using any microscopic lens. For experimental validation, the OCT imaging of chicken tissue has been obtained along with estimation of its refractive index and optical attenuation coefficient. Afterwards, the cancerous tissue is differentiated from the normal tissue based on the OCT imaging, refractive index, and optical attenuation coefficient. The respective tissue samples are collected from the human liver and pancreas. This probe could be a useful tool for endoscopic or minimal-invasive inspection of malignancy inside the tissue either at early-stage or during surgery.

A Superimposed QD-Based Optical Antenna for VLC: White LED Source

Visible light communication (VLC) is a versatile enabling technology for following high-speed wireless communication because of its broad unlicensed spectrum. In this perspective, white light-emitting diodes (LED) provide both illumination and data transmission simultaneously. To accomplish a VLC system, receiver antennas play a crucial role in receiving light signals and guiding them toward a photodetector to be converted into electrical signals. This paper demonstrates an optical receiver antenna based on luminescent solar concentrator (LSC) technology to exceed the conservation of etendue and reach a high signal-to-noise ratio. This optical antenna is compatible with all colors of LEDs and achieves an optical efficiency of 3.75%, which is considerably higher than the similar reported antenna. This antenna is fast due to the small attached photodetector—small enough that it can be adapted for electronic devices—which does not need any tracking system. Moreover, numerical simulation is performed using a Monte Carlo ray-tracing model, and results are extracted in the spectral domain. Finally, the fate of each photon and the chromaticity diagram of the collected photons’ spectra are specified.

Universal photonics tomography

3D imaging is essential for the study and analysis of a wide variety of structures in numerous applications. Coherent photonic systems such as optical coherence tomography (OCT) and light detection and ranging (LiDAR) are state-of-the-art approaches, and their current implementation can operate in regimes that range from under a few millimeters to over more than a kilometer. We introduce a general method, which we call universal photonics tomography (UPT), for analyzing coherent tomography systems, in which conventional methods such as OCT and LiDAR may be viewed as special cases. We demonstrate a novel approach (to our knowledge) based on the use of phase modulation combined with multirate signal processing to collect positional information of objects beyond the Nyquist limits.

A Proposal for Optical Antenna in VLC Communication Receiver System

Visible Light Communication (VLC) is an important emerging choice for high-speed wireless communication. In this perspective, light-emitting diodes as illuminators will be modulated to transmit data simultaneously. However, the receivers bring severe difficulties due to cost, response time, and sensitivity with a wide Field Of View (FOV). To avoid these problems, one approach is to apply a large area photodetector; however, this solution is slow and costly. Another method is to focus light on a fast photodetector by optical components, but the photodetector’s FOV decreases, resulting from the conservation of etendue. Another option is Luminescent Solar Concentrators (LSCs). This paper demonstrates a novel shape of LSC with advantages such as inexpensive, fast response time, small antenna area for VLC purposes with significant geometrical gain, FOV, and ultra-broad bandwidth. It does not require any complex tracking system and active pointing but, due to its tiny size, it can also be adapted in integrating and mobile devices. Numerical simulation is done using Monte-Carlo raytracing, and the results are demonstrated in the spectral domain. The optical efficiency of the proposed antenna is obtained at 1.058%, which is about 0.4% better than the efficiency levels reported in other works, and the geometric gain of the antenna is reported to be 44, which is significant.

Bessel beam with a micrometer-size central spot and interferometry for small volume bioliquid refractive index measurement

This work demonstrates an interferometric technique to measure the refractive index (RI) of microliter volume of biosample solutions with the help of an optical fiber negative axicon and Bessel beam with the micrometer-size central spot. The RI measuring device consists of a broadband superluminescent diode (SLD) source along with an optical circulator and spectrometer. The axicon optical fiber probe packaged with a glass slide is connected to a broadband SLD source through an optical circulator, and a drop of microliter bioliquid sample is placed on the packaged probe's head. The reflected light from the glass-liquid interface couples back to the axicon probe and interferes with the reference beam generated at the air-glass interface of the axicon. The interference spectrum is further analyzed by applying the fast Fourier transform to calculate power from the respective interface and solve the Fresnel equation for the RI measurement. The RI of small sample volume ∼2µl of glucose solutions and bovine serum albumin protein solutions are reported as an application of the proposed method. This sensing platform shows promising applications in biomedicine for monitoring small volume various biosample concentrations. We also demonstrate RI measurement of flowing liquid sample using the developed setup in case the design can be considered for microfluidic channel research.

All-fiber negative axicon probe with a Bessel beam for cellular-level low coherence phase microscopy and refractive index measurement

We demonstrate an all-fiber negative axicon probe with a Bessel beam for low coherence phase microscopy including refractive index measurement of a cellular level sample in reflection mode. The negative axicon chemically incised at the distal end of the optical fiber spawns the Bessel beam. The system provides a phase sensitivity of ∼0.28 mrad and optical path length sensitivity of ∼23 pm in air. The lateral resolution and working distance are found to be ∼3.91 µm and 650 µm to exhibit the performance of the system experimentally. The three-dimensional (3D) phase map of the cheek cell along with the refractive index is obtained from the reflected power spectrum. The combined low coherence phase microscopy and refractive index measurement provides the system with a potential for biological application. Also, the all-fiber probe can be easily integrated as an endoscopic probe.