LiteBIRD is a next generation satellite aiming for the detection of the Cosmic Microwave Background (CMB) B-mode polarization imprinted by the primordial gravitational waves generated in the era of the inflationary universe. The science goal of LiteBIRD is to measure the tensor-to-scaler ratio r with a precision of δr < 10<sup>-3</sup>♦, oﬀering us a crucial test of the major large-single-field slow-roll inflation models. LiteBIRD is planned to conduct an all sky survey at the sun-earth second Lagrange point (L2) with an angular resolution of about 0.5 degrees to cover the multipole moment range of 2 ≤ ℓ ≤ 200. We use focal plane detector arrays consisting of 2276 superconducting detectors to measure the frequency range from 40 to 400 GHz with the sensitivity of
3.2 μK·arcmin. including the ongoing studies.
We demonstrate a design of octave-band circular waveguide coupled planar ortho-mode transducer (OMT)
with Microwave Kinetic Inductance Detector (MKID) for LiteBIRD mission, a small-size satellite for cosmic
microwave background (CMB) polarization signal full-sky mapping. In our 4-pixel prototype design, each single
pixel is sensitive to two frequency bands (90 GHz and 150 GHz) corresponding to atmospheric window. Silicon
on insulator (SOI) has been selected for OMT structure and a broadband coplanar waveguide (CPW) 180-degree
hybrid is designed to cancel higher modes of a circular waveguide and add two signals from the fundamental
mode together. After a microstrip bandpass diplexer, a microstrip line to coplanar waveguide transition structure
couples signal to MKID. MKIDs are designed with Nb ground plane and Al/Ti bilayer center strip line to achieve
low frequency response and high sensitivity. A 4-pixel module is under test and we plan to deploy these multi-
chroic polarimeters on Nobeyama 45m telescope.
A focal plane based on MKID has been designed for cosmic microwave background (CMB) B-mode
polarization experiments. We are designing and developing a focal plane with broadband corrugated
horn array, planar OMT, 180 degree hybrid, bandpass filters, and MKIDs. The focal plane consists of 3
octave bands (55 - 108 GHz, 80 - 160 GHz, 160 - 320 GHz), 10 hexagonal modules. Broadband corrugated
horn-array has been directly machined from an Al block and measured to have a good beam shape which
is consistent with electromagnetic field simulations in octave bands. The horn array is designed to be low
standing-wave, light weight, and electromagnetic shield. The broadband 4 probes ortho-mode transducer
(OMT) is fabricated on Si membrane of an SOI wafer. A broadband 180 degree hybrid made with
coplanar waveguide (CPW) is used to reduce higher modes of the circular waveguide. Two bandpass
filters of each polarization are patterned with Nb microstrip. A prototype of the broadband corrugated
horn coupled MKIDs has been fabricated and tested.
Wide field cryogenic optics and millimeter-wave Microwave Kinetic Inductance Detector (MKID) cameras with Si lens array have been developed. MKID is a Cooper-pair breaking photon detector and consists of supercon- ducting resonators which enable microwave (~GHz) frequency multiplexing. Antenna-coupled Aluminum CPW resonators are put in a line on a Si substrate to be read by a pair of coaxial cables. A 220 GHz - 600 pixels MKID camera with anti-reflection (AR) coated Si lens has been demonstrated in an 0.1 K cryostat. A compact cryogenic system with high refractive index materials has been developed for the MKID camera.