Subwavelength grating enabled on-chip ultra-compact optical true time delay line.

Junjia Wang,Lawrence R Chen,José Capmany,Ivan Glesk,Rhys Adams,Ivana Gasulla,Reza Ashrafi

doi:10.1038/srep30235

Abstract

An optical true time delay line (OTTDL) is a basic photonic building block that enables many microwave photonic and optical processing operations. The conventional design for an integrated OTTDL that is based on spatial diversity uses a length-variable waveguide array to create the optical time delays, which can introduce complexities in the integrated circuit design. Here we report the first ever demonstration of an integrated index-variable OTTDL that exploits spatial diversity in an equal length waveguide array. The approach uses subwavelength grating waveguides in silicon-on-insulator (SOI), which enables the realization of OTTDLs having a simple geometry and that occupy a compact chip area. Moreover, compared to conventional wavelength-variable delay lines with a few THz operation bandwidth, our index-variable OTTDL has an extremely broad operation bandwidth practically exceeding several tens of THz, which supports operation for various input optical signals with broad ranges of central wavelength and bandwidth.

Highlights

One approach for minimizing or reducing complexities associated with the length-variable optical true time delay line (OTTDL) is to develop an index-variable OTTDL where true time delay control can be realized through varying the group index/ propagation velocity in the waveguides
Our novel design provides a practical solution for achieving a small footprint and high degree of integration for this basic photonic building block, and increasing the performance of the photonic chip implementation of the above mentioned applications based on optical delay line (ODL)
Crosswise subwavelength grating (SWG) structures have been employed in various integrated photonic components such as fiber-chip grating couplers[32], wavelength demultiplexers[33], and devices incorporating high index-contrast structures[34,35,36,37,38,39], such as high quality factor cavities[36], hollow-core waveguides with very low propagation loss[37], single-layer lenses and focusing reflectors with high focusing power[38], and vertical-cavity surface-emitting lasers (VCSELs) with broadband operation range[39]

Summary

Introduction

The pulses need to be carried on different optical wavelengths (or carrier frequencies), e.g., λ1, λ2, etc., to experience different propagation velocities and correspondingly, different propagation time delays Our novel design provides a practical solution for achieving a small footprint and high degree of integration for this basic photonic building block, and increasing the performance of the photonic chip implementation of the above mentioned applications based on ODLs

Methods

Results

Discussion

Conclusion