The size and cost of astronomical instruments for extremely large telescopes (ELTs), are pushing the limits of what is feasible, requiring optical components at the very edge of achievable size and performance. Operating at the diffraction-limit, the realm of photonic technologies, allows for highly compact instruments to be realized. In particular, Integrated Photonic Spectrographs (IPSs) have the potential to replace an instrument the size of a car with one that can be held in the palm of a hand. This miniaturization in turn offers dramatic improvements in mechanical and thermal stability. Owing to the single-mode fiber feed, the performance of the spectrograph is decoupled from the telescope and the instruments point spread function can be calibrated with a much higher precision. These effects combined mean that an IPS can provide superior performance with respect to a classical bulk optic spectrograph. In this paper we provide a summary of efforts made to qualify IPSs for astronomical applications to date. These include the early characterization of arrayed waveguide gratings for multi-object injection and modifications to facilitate a continuous spectrum, to the integration of these devices into prototypical instruments and most recently the demonstration of a highly optimized instrument directly fed from an 8-m telescope. We will then outline development paths necessary for astronomy, currently underway, which include broadening operating bands, bandwidth, increasing resolution, implementing cross-dispersion on-chip and integrating these devices with other photonic technologies and detectors such as superconducting Microwave Kinetic Inductance Detector arrays. Although the focus of this work is on IPS applicability to astronomy, they may be even more ideally suited to Earth and planetary science applications.
Mazin Lab at UCSB is developing MKID instrument for astronomy at near infrared, optical and ultraviolet wavelength. We use MIKDs as single photon detectors by measuring the arrival time of incoming photons with an accuracy of a few microseconds and with a relatively high energy resolution (R~10 at 1um). We fabricate kilopixels array of MKIDs and we incorporate them in our own instruments for UVOIR astronomy with the main application being exoplanets direct imaging.
We present the work being made in our lab in the development and fabrication of 10 to 20k pixels arrays for the DARKNESS (Dark-speckle Near-IR Energy-resolved Superconducting Spectrophotometer) and MEC (MKID Exoplanet Camera) instruments, respectively. The 6-step fabrication process has been upgraded over the last months in order to improve the sensitivity of the arrays. The detectors are made of platinum silicide (PtSi) since MKIDs with very high internal quality factor have been successfully fabricated from this material. Furthermore, PtSi with very uniform superconducting properties over 4inch substrate are much more easier to deposit than the regular TiN used in most existing MKIDs technology. Among various upgrades, we coated the PtSi sensitive area with a SiO2/Ta2O5 bi-layer in order to reduce the reflection of optical photons hitting the detectors. The light absorption is increased by a factor of 2 in the instruments bandwidth. The DARKNESS instrument has been successfully commissioned last summer and MEC, the world largest superconducting camera, is installed at the Subaru telescope since the beginning of the year. Our effort leads to the fabrication of arrays of detectors with a median internal quality factor of 100 000 with an energy resolution of 10 at 1um and a pixel yield approaching 95%.
In addition, we will present new MKID design in which the conventional meander inductor and interdigitated capacitor are replaced by a square inductor and a large parallel plate capacitor made of two metal plates separated by a ~10-nm thick dielectric layer. This parallel plate design allows us to drive the MKIDs at a higher power, which in turns should increase the sensitivity of the detectors. Following promising results from our first design, second generation of parallel plate MKID devices have been made from Hf/HfO2/Nb tri-layers deposited in-sit. We obtained high quality factor from the parallel plate MKIDs and we were able to detect photons with this new MKIDs design. Another way to improve the sensitivity of MKIDs is to use a low Tc material, compared to Tc ~ 1K usually used. We fabricated MKIDs arrays with superconducting Hafnium, Tc = 450mK, and we demonstrated that resonators with very high internal quality factors Qi~300 000 and an energy resolution of 9 at 808nm can be achieved.
Excess phase noise has been observed in microwave kinetic inductance detectors (MKIDs) which prevents the
noise-equivalent power (NEP) of current detectors from reaching theoretical limits. One characteristic of this
excess noise is its dependence on the power of the readout signal: the phase noise decreases as the readout
power increases. We investigated this power dependence in a variety of devices, varying the substrate (silicon
and sapphire), superconductor (aluminum and niobium) and resonator parameters (resonant frequency, quality
factor and resonator geometry). We find that the phase noise has a power law dependence on the readout power,
and that the exponent is -1/2 in all our devices. We suggest that this phase noise is caused by coupling between
the high-Q microwave resonator that forms the sensitive element of the MKID and two-level systems associated
with disorder in the dielectric material of the resonator. The physical situation is analogous to the resonance
fluorescence in quantum optics, and we are investigating the application of resonance fluorescence theory to
MKID phase noise.