Optical gradient force for all-optical control in photonic circuits

Abstract

In this project, we apply the optical gradient force in a slot-waveguide structure for

all-optical control of a mechanically variable waveguide structure. The optical

gradient force is ideal for realising all-optical control since it offers immense design

flexibility, low power operation and direct tenability through the optical pump power.

The slot-waveguide also has great flexibility for design variation and optimisation

despite its simple and compact structure. The relationship between the

slot-waveguide dimensions and the generated optical force, waveguide mechanical

displacement and slot-waveguide delay is investigated and the design is optimised

for high performance and ease of fabrication. When used as a nano-optomechanical

actuator, the designed slot-waveguide produces a force of 1 pN/μm/mW, which is on

the same order as the force produced by existing electrostatic comb drives. However,

the optical actuator has additional advantages such as avoiding the problem of

side-instability and immunity to electromagnetic interference and mechanical shock.

We also simulate the performance of the designed slot-waveguide as a tunable optical

delay line and find that the slot-waveguide can produce a refractive index change

comparable to that of an optical fiber based delay line. However, the slot-waveguide

delay line is optically controlled, compact and requires lower pump power, enabling

its use in integrated optical signal processing components. An experimental

demonstration of the nano-optomechanical actuator is presented as proof of concept,

showing that the theoretical analysis is valid and setting the direction for future

exploration of the optical gradient force.