A method for performing noninvasive blood glucose measurements was developed. The method is based on mid-infrared absorption spectroscopy and uses only a few wavenumbers to measure blood glucose levels unconditionally. We found that the regression of blood glucose levels using only three wavenumbers, which were selected using a series cross-validation technique, realized accuracies comparable to those of cases in which a greater number of wavenumbers are used. In addition, we demonstrated the performance of this model through correlations among different types of data.

A ball lens mounted hollow optical fiber Raman probe (BHRP) consisting of a single hollow optical fiber (HOF) and a micro-ball lens was developed for performing a high axial resolution and high-sensitivity remote Raman analysis of biomedical tissues. The total diameter of the probe head is 640 microm. The BHRP is useful in the measurement of thin-layered tissues that are in contact with the probe's surface because the probe has a limited depth-of-field optical property. An optical calculation study suggested that it is possible to vary the probe's working distance by selecting different materials and diameters for the ball lens. Empirical studies revealed that this probe has a higher axial resolution and a higher sensitivity than an HOF Raman probe without the ball lens. The spectrum of a mouse stomach measured with the BHRP had better quality and considerably lower noise than that measured with a conventional Raman microscope. These results strongly suggest that the BHRP can be used effectively in biomedical applications.

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Hollow glass waveguides with a 250-µm i.d. have been fabricated with a liquid-phase deposition technique that uses silica tubing as a base material. The losses of the 250-µm-bore guide measured at CO(2) laser wavelengths are as low as 2.0 dB/m. The straight losses for the hollow guides are in good agreement with theoretically predicted losses as a result of the nearly ideal structure of the guides. It is also shown that the guides have low bending losses, a nearly pure-mode delivery, and good high-power laser transmission. By proper design of the dielectric thickness, the guide is also able to deliver Er:YAG laser energy with a low loss of 1.2 dB/m for the 320-µm-bore waveguide. Because the hollow glass waveguide is very flexible and robust, it is quite suitable for medical applications.