Quantum cascade laser based, fiber coupled demultiplexed mid-infrared local oscillator for cryogenic applications

We have developed a fiber coupled demultiplexed local oscillator (LO) source for cryogenic applications based on a distributed feedback quantum cascade laser (QCL) at an operating wavelength of 10.6 μm. The coupling scheme relies on the combination of a phase grating generating multiple LO beams and a polycrystalline fiber delivering the demultiplexed LO signal to a superconducting mixer at 4 K in a closed-cycle cryostat. This scheme eases the use of a beam splitter in front of the mixer. Reflection phase grating generating 2 × 2 beams has been achieved with a total power efficiency of 64% based on a gold covered etched silicon nanostructure. The diffraction beam has been readily coupled into a 2 m long polycrystalline fiber, where a single-lobe circular beam has been delivered at the fiber output. By aligning the fiber core position to the center of a superconducting hot electron bolometer mixer at the rear side, we demonstrate the application of a fiber coupled demultiplexed QCL source for pumping the superconducting mixer with adequate LO power.We have developed a fiber coupled demultiplexed local oscillator (LO) source for cryogenic applications based on a distributed feedback quantum cascade laser (QCL) at an operating wavelength of 10.6 μm. The coupling scheme relies on the combination of a phase grating generating multiple LO beams and a polycrystalline fiber delivering the demultiplexed LO signal to a superconducting mixer at 4 K in a closed-cycle cryostat. This scheme eases the use of a beam splitter in front of the mixer. Reflection phase grating generating 2 × 2 beams has been achieved with a total power efficiency of 64% based on a gold covered etched silicon nanostructure. The diffraction beam has been readily coupled into a 2 m long polycrystalline fiber, where a single-lobe circular beam has been delivered at the fiber output. By aligning the fiber core position to the center of a superconducting hot electron bolometer mixer at the rear side, we demonstrate the application of a fiber coupled demultiplexed QCL source for pumping the s...