TY - JOUR
T1 - Ultrafast laser inscription in ZBLAN integrated optics chips for mid-IR beam combination in astronomical interferometry
AU - Tepper, Jan
AU - Labadie, Lucas
AU - Gross, Simon
AU - Arriola, Alexander
AU - Minardi, Stefano
AU - Diener, Romina
AU - Withford, Michael J.
PY - 2017/8/21
Y1 - 2017/8/21
N2 - Astronomical interferometry is a unique technique that allows observation with angular resolutions on the milliarcsec scale by combining the light of several apertures hundreds of meters apart. The PIONIER and GRAVITY instruments at the Very Large Telescope Interferometer have demonstrated that silica-based integrated optics (IO) provide a small-scale and highly stable solution for the interferometric beam combination process. Yet, important science cases such as exoplanet hunting or the spectroscopic characterization of exoplanetary atmospheres are favorable for observation in the mid-IR, namely the atmospheric windows L and L′ band (3-4 µm), a wavelength range that is not covered by conventional silica-based IO. Here, we propose laser-inscribed IO 2x2 couplers in ZBLAN and experimentally assess the critical properties of the component for broadband mid-IR interferometry. We measure the splitting ratio over the 2.5 to 5.0 µm range and find excellent broadband contrast over the L (3.1-3.6 µm) and L′ (3.6-4.0 µm) bands. Furthermore, we quantify the dispersion properties of the coupler and find a phase variation as low as 0.02 rad across the L and L′ band, respectively. By optimizing the NA of our injection beam, we measured a very high total throughput of 58% over the L band including Fresnel reflection and coupling losses. We also compare our findings to recent advances in mid-IR IO in GLS and discuss its advantages and disadvantages for the implementation in future mid-IR interferometers.
AB - Astronomical interferometry is a unique technique that allows observation with angular resolutions on the milliarcsec scale by combining the light of several apertures hundreds of meters apart. The PIONIER and GRAVITY instruments at the Very Large Telescope Interferometer have demonstrated that silica-based integrated optics (IO) provide a small-scale and highly stable solution for the interferometric beam combination process. Yet, important science cases such as exoplanet hunting or the spectroscopic characterization of exoplanetary atmospheres are favorable for observation in the mid-IR, namely the atmospheric windows L and L′ band (3-4 µm), a wavelength range that is not covered by conventional silica-based IO. Here, we propose laser-inscribed IO 2x2 couplers in ZBLAN and experimentally assess the critical properties of the component for broadband mid-IR interferometry. We measure the splitting ratio over the 2.5 to 5.0 µm range and find excellent broadband contrast over the L (3.1-3.6 µm) and L′ (3.6-4.0 µm) bands. Furthermore, we quantify the dispersion properties of the coupler and find a phase variation as low as 0.02 rad across the L and L′ band, respectively. By optimizing the NA of our injection beam, we measured a very high total throughput of 58% over the L band including Fresnel reflection and coupling losses. We also compare our findings to recent advances in mid-IR IO in GLS and discuss its advantages and disadvantages for the implementation in future mid-IR interferometers.
KW - Integrated optics devices
KW - Integrated optics materials
KW - Glass and other amorphous materials
KW - Microstructure fabrication
KW - Waveguides
KW - Fringe analysis
KW - Interferometry
KW - Phase measurement
UR - http://www.scopus.com/inward/record.url?scp=85027570028&partnerID=8YFLogxK
UR - http://purl.org/au-research/grants/arc/CE1101018
U2 - 10.1364/OE.25.020642
DO - 10.1364/OE.25.020642
M3 - Article
C2 - 29041743
AN - SCOPUS:85027570028
VL - 25
SP - 20642
EP - 20653
JO - Optics Express
JF - Optics Express
SN - 1094-4087
IS - 17
ER -