Modelling, manufacturing and characterization of two 4 and 8-pixel Fourier phase gratings operated at 1.4 THz are reported, mainly applicable as local oscillator multiplexers for heterodyne receivers. Comparing the measurements with full 3D simulations shows good agreements and provides good understanding. Power efficiency of around 70% is experimentally derived for both gratings. We demonstrate the application of both, as multiple beam local oscillators to simultaneously pump (or operate) an array of 4-pixel superconducting mixers.

This paper is a report on the demonstration and stabilization of a 2x4 NbN hot electron bolometer (HEB) array receiver for GUSTO based on a multiple beam local oscillator (LO). Through the combination of a FIR Gas laser and a Fourier phase grating we were able to generate a 8 beam pattern at 1.4 THz. For the array demonstration, it used a 2x2 HEB mixer array which was translated vertically to match the full 2x4 LO beam pattern. Here two lens with a 60 mm were applied to reduce the beam pattern divergence, allowing for a 12 mm spacing between the beams to be achieved at 130 mm from the grating. To stabilize the array receiver, we introduced a new stabilization method, requiring only a voice coil PID controlled loop between the beam originated from the gas laser and a given pumped pixel. The total power Allan time measurements indicate a five times improvement on a two-pixel system stability.