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Future space based observatories for the far infrared and sub-millimeter, such as SPICA and the origins space telescope (OST), will need ultra-sensitive background limited detectors at frequencies above 1 THz. We have developed a kinetic inductance detector (KID) coupled to dual polarization, broad band antenna. The detector combines high optical efficiency in two polarizations and broad band radiation detection from 1.4 to 2.8 THz.
The detector consists of a hybrid niobium titanium nitride/aluminum (NbTiN/Al) Kinetic Inductance Detector, fabricated on a silicon (Si) substrate. Radiation coupling is achieved using a so-called leaky lens antenna fabricated on a suspended silicon nitride (SiN) membrane. The radiation is coupled to the leaky wave antenna using a Si lens placed on top of it at a distance of 6 μm. The radiation absorbing section of the KID is fabricated entirely from aluminum, and integrated with the antenna to absorb power from both polarizations directly in the detector. We measured the device sensitivity in a 100 GHz band around 1.55 THz using a black body calibration source. The device shows photon noise limited performance with a noise-equivalent power below 3x10$^{-19}$ W/Hz$^{1/2}$ and good agreement between the measured and expected optical efficiency. The fractional power ratio between the powers received by the dual polarized detector and by the single polarized counterpart is measured to be a factor 2. This shows that the dual polarized device receives all power from an incoherent source. Additionally, we have measured the antenna beam pattern at the same frequency band and find a good agreement between the measured beam and simulations, which are done in reception. Standard transmission simulations, relying on reciprocity, were found to be not fully correct due of the intrinsic multi-moded nature of the antenna. To verify the frequency coverage, we have measured the detector frequency response using a Michelson interferometer and found broad band coupling in agreement with simulations.
The presented design can be upgraded to frequencies up to 10 THz using electron beam lithography. These results indicate that broad band, dual polarization radiation coupling above 1 THz is feasible using antenna coupled KIDs.
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