Abstract
Photonic technologies will be at the heart of future terrestrial planet hunting interferometers. In particular the mid-infrared spectral region between 3.5 - 4.2 μm is the ideal window for hunting for young extra-solar planets, since the planet is still hot from its formation and thus offers a favorable contrast with respect to the parent star compared to other spectral regions. This paper demonstrates two basic photonic building blocks of such an instrument, namely single-mode waveguides with propagation losses as low as 0.29±0.03 dB/cm at a wavelength of 4 μm as well as directional couplers with a constant splitting ratio across a broad wavelength band of 500 nm. The devices are based on depressed cladding waveguides inscribed into ZBLAN glass using the femtosecond laser direct-write technique. This demonstration is the first stepping stone towards the realization of a high transmission mid-infrared nulling interferometer.
Highlights
The mid-infrared (MIR) spectral region between 3.5 − 4.2 μm, known as the astronomical L’ band, is the ideal window to hunt for young extra-solar planets
This paper demonstrates two basic photonic building blocks of such an instrument, namely single-mode waveguides with propagation losses as low as 0.29±0.03 dB/cm at a wavelength of 4 μm as well as directional couplers with a constant splitting ratio across a broad wavelength band of 500 nm
Stellar interferometry relies on combining beams of light from a single target collected by multiple apertures
Summary
The mid-infrared (MIR) spectral region between 3.5 − 4.2 μm, known as the astronomical L’ band, is the ideal window to hunt for young extra-solar planets. The same group demonstrated improved propagation losses as low as 0.33 dB/cm for As2S3 chalcogenide glass guides by using photolithography and dry-etching techniques [15]. As only negative index contrast tracks were realized, waveguides were constructed by stitching multiple tracks together to form a depressed cladding This approach allows for waveguides of arbitrary core size and cladding thickness by adding more tracks making it amenable to longer wavelength operation and allowing full control over the span of the single-mode region. By using the direct-write technique as opposed to lithographic techniques for instance, it is possible to fabricate 3D structures [25,26] For these reasons it would be interesting to investigate ZBLAN as a platform for MIR applications, such as the one outlined here as well as for MIR waveguide lasers for chemical sensing applications.
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