Lightweight Low‐Noise Linear Isolator Integrating Phase‐ and Amplitude‐Engineered Temporal Loops

Abstract

The quest for efficient and versatile microwave and optical isolators has recently led to spawn space–time‐modulated isolator structures. However, such space‐time isolators suffer from a large profile and complex architecture that is required for a progressive nonreciprocal space–time coupling. To overcome these limitations, here a nonmagnetic phase‐engineered temporal loop‐based isolator featuring large isolation levels, suppressed undesired time harmonics while exhibiting a low profile is proposed. The proposed isolator is composed of two temporal loops that provide desired constructive and destructive interferences of different time harmonics. Furthermore, these two loops are designed in a way to assure that the circulation and reflection of different time harmonics strengthen a unidirectional signal transmission with low insertion loss. An experimental demonstration of the proposed time‐modulated isolator is provided at microwave frequencies, featuring strong unidirectional wave transmission through the isolator with more than 27 dB contrast between the forward and backward waves, across a fractional bandwidth of 14.3%. The proposed technique outperforms alternative approaches, that is, space–time modulation, ferrite magnets, nonlinearity, and HBT/CMOS transistors. It features a highly linear response with OP1dB of higher than 31 dBm, high power rating of more than 47 dBm, and a low noise figure of 3.4 dB.

4D Wave Transformations Enabled by Space–Time Metasurfaces: Foundations and illustrative examples

“…ST metasurfaces may take advantage of ST modulation capabilities, including nonreciprocal frequency generation [12], [16], [22], [23], parametric wave amplification [9], [24]- [26], asymmetric dispersion [27]- [29], and energy accumulation [30]. Frequency generation and nonreciprocity are of particular interest in ST-modulated (STM) slabs [16], [21], [22], [27], [29], [31]- [33], which are endowed by asymmetric periodic electromagnetic transitions in their dispersion diagram [13], [27], [28], [31], [34]. In practice, the ST modulation is achieved through pumping external energy into the medium [6], [11], [12], [22], [27], [35].…”