Abstract
Reconfigurable photonic devices capable of routing the flow of light enable flexible integrated-optic circuits that are not hard-wired but can be externally controlled. Analogous to free-space spatial light modulators, we demonstrate all-optical wavefront shaping in integrated silicon-on-insulator photonic devices by modifying the spatial refractive index profile of the device employing ultraviolet pulsed laser excitation. Applying appropriate excitation patterns grants us full control over the optical transfer function of telecommunication-wavelength light travelling through the device, thus allowing us to redefine its functionalities. As a proof-of-concept, we experimentally demonstrate routing of light between the ports of a multimode interference power splitter with more than 97% total efficiency and negligible losses. Wavefront shaping in integrated photonic circuits provides a conceptually new approach toward achieving highly adaptable and field-programmable photonic circuits with applications in optical testing and data communication.
Highlights
With optical links replacing electrical connections on ever shorter length scales, all-optical control of optical signals becomes ever more desirable to circumvent the electronic speed limit and avoid transformation losses between optical and electrical domains
Wavefront shaping has been demonstrated as a powerful tool in both characterizing and controlling the optical modes in threedimensional complex media [17,18,19]. Translating these capabilities to an integrated platform opens up significant opportunities for freeform shaping of optical signals in integrated photonic circuits. We demonstrate this general technique on the example of shaping wavefronts in SOI multimode interference (MMI) regions effectively and with negligible loss
We experimentally realized dynamic routing of light in a 1x2 MMI power splitter to any output port with better than 97% efficiency, cross talk below -27 dB, and negligible losses
Summary
With optical links replacing electrical connections on ever shorter length scales, all-optical control of optical signals becomes ever more desirable to circumvent the electronic speed limit and avoid transformation losses between optical and electrical domains. We show that spatial refractive index profiles can be controlled all-optically, allowing us to dynamically route light between outputs of a SOI multimode interference (MMI) device. Tuning of the refractive index using thermal or electro-optic elements positioned at these specific intermediate cross-sectional planes allows controlling the asymmetry of the self-images at the output using a single control parameter. While such multimode interference power splitters (MIPSs) are of technological interest, they provide only a limited range of tuning capabilities while requiring relatively large device footprints of several hundreds of micrometres in length [21,22,23,24,25]. The MMIdevice (220 nm thick silicon slab of size 6 μm x 31.87 μm) under investigation is a standard component in state-of-the-art silicon photonics and was experimentally verified to have insertion losses below 1 dB [26]
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