Environmentally protected photonic integrated circuit

An environmentally protected photonic integrated circuit, comprising:

• an indium phosphide, InP, -based substrate having a first surface that is at least partially provided with an InP-based optical waveguide;
• and
• a dielectric protective layer that is arranged to cover at least the first surface of the InP-based substrate and the InP-based optical waveguide, the dielectric protective layer being configured to:
• protect said photonic integrated circuit from environmental contaminants;
• enable confinement of optical radiation in the dielectric protective layer in at least one direction that is transverse to a direction of propagation of the optical radiation;
• and
• allow exchange of the optical radiation between the InP-based optical waveguide and the dielectric protective layer;
• wherein the InP-based optical waveguide and the dielectric protective layer provide said photonic integrated circuit with a multilevel optical waveguide assembly,
• wherein the InP-based optical waveguide has a dimension in a direction transverse to the first surface of the InP-based substrate, said dimension having a first value in a first part of said waveguide and a second value in a second part of said waveguide, the second value being smaller than the first value, said waveguide comprising a tapered section that is configured and arranged to interconnect the first part of said waveguide and the second part of said waveguide thereby allowing an optical mode field of the optical radiation upon passing the tapered section from the first part to the second part to be divided in a first portion that is present in said waveguide and a second portion that is present in the dielectric protective layer, and
• wherein the InP-based optical waveguide is a nonplanar optical waveguide, and wherein the dielectric protective layer is a conformal coating that provides the multilevel optical waveguide assembly with a nonplanar dielectric optical waveguide that is configured to allow confinement of the second portion of the optical mode of the optical radiation in the dielectric protective layer in two orthogonal directions that both are transverse to the direction of propagation of the optical radiation.