Abstract

Over the last 15 years, a new photosensitive glass called photo-thermo-refractive (PTR) glass has been developed for the recording of volume holographic elements such as volume Bragg gratings. Main advantage of such elements is that they allow obtaining narrowband filters in both spectral and angular spaces [1]. However, the further decrease of the spectral bandwidth of volume Bragg gratings represents a technological issue and is thus limited to values between 50 and 100 pm depending on their central wavelength. For some applications such as LIDARS or the longitudinal mode selection of Nd:YAG lasers [2], bandwidth in the range of a few picometers or tens of picometers would be required. Hence, new technology must be developed in order to achieve ultra-narrowband selectivity. In this paper we present the fabrication of so-called Moiré reflecting Bragg gratings (Moiré RBG), resulting from the recording of two reflecting Bragg gratings with shifted periods (figure 1). Such structure was widely investigated in the past in germanium doped silica fibers [3]. However, due to the unavailability of bulk photosensitive materials, no experimental demonstration of Moire RBG was performed. PTR glass allows recording of high efficiency reflecting Bragg gratings in a few millimeters glass samples and losses can be kept low below 1%. Hence, PTR glass makes an ideal candidate for the recording of Moiré RBG with very high transmission at resonance.

© 2009 IEEE