White light interferometry (WLI) is the 3D imaging sensor based on interferometry to obtain depth information by acquiring constructive interference. It allows a deep scanning range in high resolution while there are still limitations that lead to a low imaging speed and vibration from the mechanical movement. In this study, we resolved the vibration problem by isolating the depth scanning part in the tunable-path-difference source (TPDS) with a fiber stretcher from the interferometric measurement part. We also applied line-field interferometry to improve scanning speed and to image not only flat surfaces but also curved objects in variable fields of view.

In this project, we demonstrate the fabrication of short, yet adiabatic 2- and 3-mode selective optical lanterns using double-clad fibers as input, replacing the newly demonstrated graded index fiber. Using three types of fibers with slightly different numerical apertures, we obtained very short components while retaining full adiabaticity. The resulting photonic lanterns are short and less fragile than components made with the current fabrication process, and they feature both low excess loss and high mode selectivity.

Total internal reflection fluorescence (TIRF) microscopy has been used to image the surface features of biological samples while minimizing background fluorescence. However, traditional single-spot TIRF illumination often contains regions of nonuniformity and shadow effects, which are undesirable for high-quality super-resolution imaging. Here we propose using a photonic lantern to generate high-intensity multi-spot TIRF illumination that is artifact-free, highly uniform, and suitable for single-molecule localization microscopy (SMLM). We characterize the beam profile, speckle contrast and transmission efficiency of the photonic lantern, and further demonstrate super-resolution imaging with lower excitation power than the traditional approach.

Spectrometers are used widely in scientific applications that require wavelength-resolved optical sensing and imaging. Recently, computational spectrometers that improve on the bandwidth, resolution, and size tradeoffs of traditional spectrometers have been demonstrated using novel custom optics that are expensive to fabricate. We present a computational spectrometer that uses an inexpensive off-the-shelf diffuser to create a speckle pattern on the image sensor. By computationally inverting this spectral-spatial multiplexed pattern, we are able to reconstruct the input spectrum at nanometer-level resolution. Our computational spectrometer design has the potential to be cost-effective for applications such as reflectance spectroscopy.

We present a novel hyperspectral imaging system working in the visible and in the short-wave infrared (SWIR) spectral region based on a Fourier-transform (FT) approach. The technology presents high light throughput and spatial resolution, a software adjustable spectral resolution, and a wide versatility of use. It employs a common-path interferometer, generating two replicas of the image with controllable delay and remarkable accuracy and stability. The monochromatic camera (CMOS, CCD, or InGaAs bidimensional sensor) does not require any relative movement with respect to the sample. The absence of gratings and slits guarantees an exceptional throughput that ensures high-quality data even at the lowest light dose, making this technology particularly suitable in fluorescence studies, or where low-illuminance conditions are recommended in order not to damage the samples. We will show several examples of the use in remote sensing and microscopy.

We report the hyperspectral imaging system for the measurement of anthocyanin accumulations in ‘bok choy’ grown in the different environmental conditions in the indoor farms. Wavelength bandwidth from 400nm to 700nm that covers chlorophyll A, B, and anthocyanin absorption peaks was three dimensionally (wavelength vs intensity in the area of 100cm2) measured by hyperspectral imaging instrument. Estimated anthocyanin accumulations by hyperspectral imaging technique were compared with those measured by chemical (destructive) analysis. Coinciding results between hyperspectral and destructive analysis suggest that hyperspectral imaging system can be a valuable photonic instrument to replace previously used destructive analysis in agricultural researches. (Supported by 421035-04)

In-situ, non-destructive chemical characterisation of visually identical samples, including those concealed in containers, is required in fields such as forensics, suspicious substance screening or product quality control. We present a variation of Raman spectroscopy which harnesses the fact that the Fourier transform of tightly-focussed Bessel beam is an annulus. This increases the collection of light originating beyond a container wall and simultaneously reduces the collection of light from the container, enabling non-contact, non-destructive detection of samples in sealed containers. Example measurements include alcoholic beverages in their original bottles and pharmaceuticals in opaque plastic containers.

FMCW LiDAR is an optical measurement technology that is drawing attention in various industries. For 3D FMCW imaging, a proper beam scanning process is required. Since conventional mechanical beam scanners have limits in automotive FMCW LiDAR, active researches on solid-state beam scanners are ongoing. Despite advantages of solid-state beam scanners, there is a disadvantage in field of view (FOV) with current solid-state scanners. In this study, we conducted studies on extending the FOV of the solid-state FMCW LiDAR system. By applying a relay optical system, we achieved an extension in FOV of our system and 3D FMCW images are obtained.

Conventional FMCW-LiDAR uses a high-performance ADC to obtain digitized signals and analyze bit frequencies through FFT to measure distance. High accuracy, SNR, and real-time operation in FMCW Lidar requires a high sampling rate ADC and many FFT points, which is a burden on hardware and signal processing. In this study, a frequency-mixed FMCW-LiDAR was designed to overcome the limitation of the conventional system. The local oscillator LO was supplied in the form of an electric chirp signal, and the resolution and measurable range of the signal are determined according to the range of sweep frequency. By mixing the sweeping LO and beat signals, the proposed system enables frequency analysis on the time axis, enabling efficient analysis in data acquisition.

In this work, we investigate the stability and limitations of two data processing technologies to enhance resolution and measurement range even further based on computational efforts. Therefore, the utilization of error-diffusion dithering for noise reduction and phase estimation was investigated in relation to different sample surface roughness values. It was shown that noise reduction of greater than 85% and measurement range extensions of up to 20% are achievable. Additionally, dithering approaches were combined with compressed sensing in order to achieve higher measurement speeds.

Frequency-modulated continuous wave (FMCW) light detection and ranging (LiDAR) is attractive as the next generation of LiDAR. Since FMCW LiDAR is an optical method of measuring a distance using light interference, the distance measurement range is limited according to the coherence length of laser light. For this reason, FMCW LiDAR is forced to use a special laser with a long coherence length. In this study, we propose to increase the measurable distance range through a novel frequency decoding method using a dual interferometer. Experimentally, we can increase the measurable distance over the full range of coherence length.

Coherent ranging is widely used as an optical method to measure a distance from a very fine area to a very wide area. Since distance measurement depends on light interference, a limitation occurs in the coherence length of a laser source light. We attempted to overcome this problem by creating multiple delay lines for each wavelength using a fiber Bragg grating (FBG) reflector in the interferometer. Using the proposed method, it is possible to measure the extended longer distance by using the conventional laser with a short coherence length.

We demonstrate a system for high-precision, high-resolution and long-range LiDAR measurements using dual optical frequency combs. The system uses a new type of single-cavity dual-comb solid-state laser combined with a fiber-based apparatus for detection of the light reflected by a target. The fiber setup implements heterodyne detection with the roles of the two combs interchanged, thereby using the Vernier effect to extend the ambiguity range beyond the inverse of the laser repetition rate. With this approach, we obtain sub-micron precision with >10 meter range (scalable to kilometers) using a time-of-flight based approach to analyze the digitized interferogram signal.