Engineering Arbitrarily Oriented Spatiotemporal Optical Vortices Using Transmission Nodal Lines

It has been recently demonstrated that optical pulses can hold transverse orbital angular momentum(OAM). Generation of such vortices typically requires bulky optics, and only OAMs that are fully longitudinal or transverse have been demonstrated until now. Here we investigate a general family of spatiotemporal vortices with arbitrarily oriented OAM and introduce a compact device for its generation. The device operates by having a transmission nodal line, which is a topological defect in the wavevector-frequency spectra of the transmission coefficient. We show that the position and dispersion of the transmission nodal line can be controlled by structural symmetry of the device. By transmitting a Gaussian pulse through the device, we can generate spatiotemporal vortices with its nodal line and OAM oriented along any arbitrary direction. This ability to generate a full family of spatiotemporal vortex pulses may find application in pulse shaping or sensing in the spatiotemporal domain. Our work also provides a novel approach of engineering topological response functions in photonic crystal slabs. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement