Shuo Yen Tseng

Engineering of fast mode conversion in multimode waveguides

We propose fast and robust mode conversion in multimode waveguides based on Lewis-Riesenfeld invariant theory. The design of mode converters using the multimode driving for dynamical invariant is discussed. Computer-generated planar holograms are used to mimic the shaped pulses driving the states in three-level quantum systems. We show that the invariant-based inverse engineering scheme reduces mode converter length as compared to the common adiabatic scheme.

Variable splitting ratio 2×2 MMI couplers using multimode waveguide holograms

Variable power splitting ratio 2x2 MMI couplers using multimode waveguide holograms are analyzed. Theoretical analysis shows that variable splitting ratios can be obtained with surface relief holograms on MMI couplers with fixed dimensions. Devices with paired-imaging lengths are designed on a silicon-on-insulator (SOI) platform. Beam propagation simulations are used to verify a matrix theory analysis and to investigate proposed device performance. Fabrication tolerance of the proposed device is also analyzed.

Implementation of discrete unitary transformations by multimode waveguide holograms.

Integration of holograms into multimode waveguides allows the implementation of arbitrary unitary mode transformations and unitary matrix-vector multiplication. Theoretical analysis is used to justify a design approach to implement specific functions in these devices. Based on this approach, a compact mode-order converter, a Hadamard transformer, and a spatial pattern generator-correlator are proposed and analyzed. Beam propagation simulations are used to verify the theoretical calculations and to address bandwidth, scalability, and fabrication criteria. Optical pattern generators were successfully fabricated using standard photolithographic techniques to demonstrate the feasibility of the devices.

Mode conversion using optical analogy of shortcut to adiabatic passage in engineered multimode waveguides

A shortcut to adiabatic mode conversion in multimode waveguides using optical analogy of stimulated Raman adiabatic passage is investigated. The design of mode converters using the shortcut scheme is discussed. Computer-generated planar holograms are used to mimic the shaped pulses used to speed up adiabatic passage in quantum systems based on the transitionless quantum driving algorithm. The mode coupling properties are analyzed using the coupled mode theory and beam propagation simulations. We show reduced device length using the shortcut scheme as compared to the common adiabatic scheme. Modal evolution in the shortened device indeed follows the adiabatic eigenmode exactly amid the violation of adiabatic criterion.

Compact and high conversion efficiency mode-sorting asymmetric Y junction using shortcuts to adiabaticity.

We propose a compact and high conversion efficiency asymmetric Y junction mode multiplexer/demultiplexer for applications in on-chip mode-division multiplexing. Traditionally, mode sorting is achieved by adiabatically separating the arms of a Y junction. We shorten the device length using invariant-based inverse engineering and achieve better conversion efficiency than the adiabatic device.

Short and robust directional couplers designed by shortcuts to adiabaticity

We propose short and robust directional couplers designed by shortcuts to adiabaticity, based on Lewis-Riesenfeld invariant theory. The design of directional couplers is discussed by combining invariant-based inverse engineering and perturbation theory. The error sensitivity of the coupler is minimized by optimizing the evolution of dynamical invariant with respect to coupling coefficient/input wavelength variations. The proposed robust coupler devices are verified with beam propagation simulations.

Mode Conversion/Splitting by Optical Analogy of Multistate Stimulated Raman Adiabatic Passage in Multimode Waveguides

We propose and describe mode converter/splitter based on optical analogy of multistate stimulated Raman adiabatic passage in multimode waveguides. Computer-generated planar holograms are used to implement the coupling coefficients that mimic the optical pulses used in the transfer among quantum states of atoms and molecules. The mode coupling properties in multimode waveguides are analyzed using the coupled-mode theory and shown to resemble the multistate stimulated Raman adiabatic passage process. Key features of multistate systems are illustrated with theoretical calculations and numerical examples. Mode converter and splitter are designed based on the theoretical analysis and verified using beam propagation simulations.

Short and robust silicon mode (de)multiplexers using shortcuts to adiabaticity

Compact silicon mode (de)multiplexers based on asymmetrical directional couplers are designed using shortcuts to adiabaticity. The coupling coefficient and propagation constants mismatch are engineered to optimize the device robustness. Simulations show that the devices are broadband and have large fabrication tolerance.

Measurement of complex χ(3) using degenerate four-wave mixing with an imaged 2-D phase grating

We present a simple optical arrangement for phase sensitive detection of degenerate four-wave mixing (DFWM) to characterize the real and imaginary parts of Chi((3)) using an imaged 2-D phase grating. Phase sensitive coherent detection of DFWM signal is demonstrated. Phase stabilization of the interferometric arms is obtained passively with the 2-D grating. A processable polyacetylene sample is characterized at a wavelength of 1.5 microm using this technique. The observed nonlinearity is determined to be a fast (<250 fs) effect using a simple test.

Robust coupled-waveguide devices using shortcuts to adiabaticity

Shortcuts to adiabaticity, originally developed in the context of quantum control, are powerful tools for the design of high coupling efficiency, robust, and short coupled-waveguide devices. The counterdiabatic protocol cancels the unwanted coupling in system evolution by the addition of a counterdiabatic term. The invariant-based inverse-engineering approach designs system evolution using the decoupled eigenstates of the Lewis-Riesenfeld invariant. The single-shot shaped-pulse technique directly parameterizes the solution of the coupled-mode equation. Starting from the counterdiabatic protocol, we show that these seemingly very different shortcuts to adiabaticity techniques are equivalent in the framework of coupled-waveguide systems. When combined with perturbation treatment of the coupled-mode equation, robust coupled-waveguide devices against errors can be obtained.