Baryon Acoustic Oscillations from Integrated Neutral Gas Observations: an instrument to observe the 21cm hydrogen line in the redshift range 0.13 < z < 0.45 - status update.

BINGO (BAO from Integrated Neutral Gas Observations) is a unique radio telescope designed to map the intensity of neutral hydrogen distribution at cosmological distances, making the first detection of Baryon Acoustic Oscillations (BAO) in the frequency band 980 MHz - 1260 MHz, corresponding to a redshift range 0.127 < z < 0.449. BAO is one of the most powerful probes of cosmological parameters and BINGO was designed to detect the BAO signal to a level that makes it possible to put new constraints on the equation of state of dark energy. The telescope will be built in Paraíba, Brazil and consists of two \thicksim 40m mirrors, a feedhorn array of 50 horns, and no moving parts, working as a drift-scan instrument. It will cover a 15 ^{\circ} ∘ declination strip centered at \sim \delta ∼ δ =-15 ^{\circ} ∘ , mapping \sim ∼ 5400 square degrees in the sky. The BINGO consortium is led by University of São Paulo with co-leadership at National Institute for Space Research and Campina Grande Federal University (Brazil). Telescope subsystems have already been fabricated and tested, and the dish and structure fabrication are expected to start in late 2020, as well as the road and terrain preparation.

Optical fiber Fabry-Perot interferometer based on phase-shifting technique and birefringence crystals.

In this paper, the optical fiber Fabry-Perot (F-P) interferometer based on phase-shifting technique and birefringence crystals is proposed and demonstrated. We use the characteristics of birefringence and four birefringence crystals with different thicknesses to obtain the quadrature phase-shifted signals, which are demodulated by phase-shifting technique. Two types of sensing interferometers are used in the experiment. One is the optical fiber F-P sensor and the other is composed of the fiber end face and the glass surface fixed on the nanopositioning stage. The experimental results show that the normalized standard deviation (SD) of the calibration microphone centerline is 1.97 and 2.63 times larger than the optical fiber F-P interferometer under the sinusoidal sonic signals of 21 kHz and 40 kHz, and the interferometer is effective in avoiding phase ambiguity. The proposed interferometer has high stability and can adapt to a larger measurement range.