Optimization of lens layout for THz signal free-space delivery

We investigate how to extend the air-space distance for Terahertz (THz) signal by using optimized lens layout. After a delivery over 129.6 cm air-space we realize the BER of 10 Gb/s QPSK signal at 450 GHz smaller than 1×10−4 with this optimized lens layout. If only two lenses are employed, the BER is higher than forward error correction (FEC) threshold at the input power of 15 dBm into the photodiode.