Photonic integrated circuit with encapsulated reference arm

A photonic integrated circuit (PIC) for interferometric sensor comprising:

• a bottom layer called substrate;
• a first coupling means suitable for coupling an incident light radiation (Lin) to the photonic integrated circuit (PIC);
• a directional splitter linked to the first coupling means and configured to split the light radiation (Lin) coupled by the first coupling means to at least one pair of waveguides included in the photonic integrated circuit, each pair of waveguides comprising:
• a first waveguide called sensitive arm wherein a first portion of the light radiation is propagated, said sensitive arm being exposed to a first ambient medium (M1) and to at least one compound to be detected (C) inducing a modification of the local refractive index perceived by the evanescent part of the electromagnetic field of the first portion of the light radiation, and
• a second waveguide called reference arm wherein a second portion of the light radiation is propagated,
• an encapsulation layer encapsulating the reference arm, said encapsulation layer being impermeable to the compound or compounds to be detected (C), so that the reference arm is exposed only to a second ambient medium (M2), substantially of the same nature as the first ambient medium (M1) and without said compound to be detected,
• a directional combiner combining the first portion of the light radiation from said reference arm, called first transmitted portion, and the second portion of the light radiation from said sensitive arm, called second transmitted portion, to form a transmitted radiation;
• a second coupling means suitable for coupling said transmitted radiation to a medium external to the photonic integrated circuit (PIC);
• a top layer called superstrate covering at least the first and the second coupling means, the directional splitter and the directional combiner and not covering the sensitive arm and the reference arm, said encapsulation layer being deposited on top of the superstrate.