Metamaterial-enabled arbitrary on-chip spatial mode manipulation

Asymmetric metamaterial sandwich structure with NIM characteristics for THz imaging application

This study presented a unique, miniaturised asymmetric interconnected vertical stripe (IVS) design for terahertz (THz) frequency applications. Therefore, this research aimed to achieve a frequency response of 0 to 10 THz using a 5 × 5 µm2 Silicon (Si) substrate material. Meanwhile, various parametric examinations were conducted to investigate variations in the performance. For example, the unit cell selection process was carefully examined by using various design structures and modifying the structure by adding split gaps and connecting bars between vertical stripes. Furthermore, the proposed sandwich structure design was used to compute the absorbance and reflectance properties. All the analytical examinations were executed utilising the Computer Simulation Technology (CST) 2019 software. The introduced IVS metamaterial exhibits negative index behaviour and has a single resonance frequency of 5.23 THz with an acceptable magnitude of - 24.38 dB. Additionally, the quadruple-layer IVS structure exhibits optimised transmission coefficient behaviour between 3 and 6 THz and 7 to 9 THz, respectively. However, the magnitude of the transmission coefficient increased with the number of material layers. Besides that, the absorbance study shows that using a quadruple-layer structure obtains unique and promising results. Overall, the proposed asymmetric IVS metamaterial design achieves the required performance by using a compact structure rather than extending the dimensions of the design.

Compact mode converter on SOI based on a polygonal subwavelength grating structure

In this Letter, we design and experimentally demonstrate compact mode converters with a lightning-like and arrow-like polygonal subwavelength grating (SWG) structure on a silicon-on-insulator (SOI) platform, which can convert the TE0 mode to the TE1 and TE2 modes, respectively. The footprints of the proposed TE0-1 and TE0-2 mode converters are only 4.44 × 1.3 and 5.89 × 1.8 µm2, respectively. The experimental results show the mode converters have a low insertion loss (<1 dB) and a broad bandwidth (>50 nm). The measured cross talks of the TE0-1 and TE0-2 mode converters are -7.2 dB and -10.3 dB, respectively. In addition, the proposed mode converters with the SWG structure have the advantage in fabrication, since only a one-step full-etching process is required.

Emulating the Deutsch-Josza algorithm with an inverse-designed terahertz gradient-index lens

An all-dielectric photonic metastructure is investigated for application as a quantum algorithm emulator (QAE) in the terahertz frequency regime; specifically, we show implementation of the Deustsh-Josza algorithm. The design for the QAE consists of a gradient-index (GRIN) lens as the Fourier transform subblock and patterned silicon as the oracle subblock. First, we detail optimization of the GRIN lens through numerical analysis. Then, we employed inverse design through a machine learning approach to further optimize the structural geometry. Through this optimization, we enhance the interaction of the incident light with the metamaterial via spectral improvements of the outgoing wave.

Ultra-compact and ultra-broadband arbitrary-order silicon photonic multi-mode converter designed by an intelligent algorithm

Multi-mode converters, which can achieve spatial mode conversion in multimode waveguide, play a key role in multi-mode photonics and mode-division multiplexing (MDM). However, rapid design of high-performance mode converters with ultra-compact footprint and ultra-broadband operation bandwidth is still a challenge. In this work, through combining adaptive genetic algorithm (AGA) and finite element simulations, we present an intelligent inverse design algorithm and successfully designed a set of arbitrary-order mode converters with low excess losses (ELs) and low crosstalk (CT). At the communication wavelength of 1550 nm, the footprint of designed TE_0-n (n = 1, 2, 3, 4) and TE_2-n (n = 0, 1, 3, 4) mode converters are only 1.8 × 2.2 µm². The maximum and minimum conversion efficiency (CE) is 94.5% and 64.2%, and the maximum and minimum ELs/CT are 1.92/-10.9 dB and 0.24/-20 dB, respectively. Theoretically, the smallest bandwidth for simultaneously achieving ELs ≤ 3 dB and CT ≤ -10 dB exceeds 70 nm, which can be as large as 400 nm for the case of low-order mode conversion. Moreover, the mode converter in conjunction with a waveguide bend allows for mode-conversion in ultra-sharp waveguide bends, significantly increasing the density of on-chip photonic integration. This work provides a general platform for the realization of mode converters and has good prospect in application of multimode silicon photonics and MDM.

Three-dimensional on-chip mode converter

The implementation of transverse mode, polarization, frequency, and other degrees of freedom (d.o.f.s) of photons is an important way to improve the capability of photonic circuits. Here, a three-dimensional (3D) linear polarized (LP) LP₁₁ mode converter was designed and fabricated using a femtosecond laser direct writing (FsLDW) technique. The converter included multi-mode waveguides, symmetric Y splitters, and phase delaying waveguides, which were constructed as different numbers and arrangements of circular cross section waveguides. Finally, the modes (LP_11a and LP_11b) were generated on-chip with a relatively low insertion loss (IL). The mode converter lays a foundation for on-chip high-order mode generation and conversion between different modes, and will play a significant role in mode coding and decoding of 3D photonic circuits.

Metasurface-Based Quantum Searcher on a Silicon-On-Insulator Chip

Optical analog computing has natural advantages of parallel computation, high speed and low energy consumption over traditional digital computing. To date, research in the field of on-chip optical analog computing has mainly focused on classical mathematical operations. Despite the advantages of quantum computing, on-chip quantum analog devices based on metasurfaces have not been demonstrated so far. In this work, based on a silicon-on-insulator (SOI) platform, we illustrated an on-chip quantum searcher with a characteristic size of 60 × 20 μm². We applied classical waves to simulate the quantum search algorithm based on the superposition principle and interference effect, while combining it with an on-chip metasurface to realize modulation capability. The marked items are found when the incident waves are focused on the marked positions, which is precisely the same as the efficiency of the quantum search algorithm. The proposed on-chip quantum searcher facilitates the miniaturization and integration of wave-based signal processing systems.

Extensible on-chip mode manipulations based on metamaterials

An extensible framework is proposed for on-chip spatial-mode manipulations based on metamaterial building blocks, which enables the excitation of arbitrarily high-order spatial modes in silicon waveguides. It makes a significant step towards the comprehensive and on-chip manipulations of spatial lights, and may provide promising opportunities for complex photonic functionalities.