Frequent glucose monitoring is a fundamental part of diabetes management, and good glucose control is important for long-term health outcomes. New types of electrochemical sensors that allow for continuous glucose monitoring (CGM) have become an important tool for diabetes management, although they still have drawbacks such as short lifetime and a need for frequent calibration. Other technologies are still being researched for CGM, in an attempt to replace the electrochemical sensors. Optical methods have several advantages for CGM, including potentially long sensor lifetimes and short measurement times, and many developments have been made over the last decades. This paper will review optical measurement methods for CGM, their challenges, and the current research status. The different methods will be compared, and the future prospects for optical methods will be discussed.

Abstract:A heterodyne interferometer has been built in order to characterize vibrations on micro-and nanostructures. The interferometer offers the possibility of both absolute phase and high resolution absolute amplitude vibrational measurements. By using two acousto-optic modulators (AOMs) in one of the interferometer arms and varying the frequency inputs of both, the setup is designed to measure vibrations in the entire frequency range 0 -1.2GHz. The system is here demonstrated on Capacitor Micromachined Ultrasonic Transducers (CMUTs) and a PZT transducer to show measurements from 5kHz up to 35MHz. We have measured absolute amplitudes with picometer resolution.

Vulnerable plaques constitute a risk for serious heart problems, and are difficult to identify using existing methods. Hyperspectral imaging combines spectral- and spatial information, providing new possibilities for precise optical characterization of atherosclerotic lesions. Hyperspectral data were collected from excised aorta samples (n = 11) using both white-light and ultraviolet illumination. Single lesions (n = 42) were chosen for further investigation, and classified according to histological findings. The corresponding hyperspectral images were characterized using statistical image analysis tools (minimum noise fraction, K-means clustering, principal component analysis) and evaluation of reflectance/fluorescence spectra. Image analysis combined with histology revealed the complexity and heterogeneity of aortic plaques. Plaque features such as lipids and calcifications could be identified from the hyperspectral images. Most of the advanced lesions had a central region surrounded by an outer rim or shoulder-region of the plaque, which is considered a weak spot in vulnerable lesions. These features could be identified in both the white-light and fluorescence data. Hyperspectral imaging was shown to be a promising tool for detection and characterization of advanced atherosclerotic plaques in vitro. Hyperspectral imaging provides more diagnostic information about the heterogeneity of the lesions than conventional single point spectroscopic measurements.

A heterodyne interferometer for highly sensitive vibration measurements in the range 100 kHz - 1.3GHz is presented. The interferometer measures absolute amplitude and phase. The signal processing of the setup is analyzed and described in detail to optimize noise suppression. A noise floor of 7.1 fm/Hz(1/2) at 21 MHz was achieved experimentally where the bandwidth is the inverse of all time needed for filter settling and signal sampling. To demonstrate the interferometer, measurements up to 220 MHz were performed on arrays of capacitive micromachined ultrasonic transducers (CMUTs). The measurements provided detailed information e.g. about the frequency response, vibration patterns and array uniformity. Such measurements are highly valuable in the design process of ultrasonic transducers.

Speckle and the compound speckle can be reduced by angle diversity. In laser projection displays, simple, low cost and efficient speckle reduction techniques require smart optical design. Using a MEMS scanner together with a condenser lens, laser beams with different illumination angles are obtained on the diffuser surface with low speckle contrast ratio (CR). After homogenizing within a rod integrator, the speckle field illuminates a display panel, and is projected onto the screen which forms the compound speckle. Characterization method to evaluate the compound speckle reduction efficiency is analyzed and discussed in a simplified optical system. The preliminary speckle reduction is demonstrated in a commercial projector where a 600 mW green laser has been used as the illumination source, and the compound speckle CR is brought down from 0.38 to 0.14.