Figure 1
From: Hybrid external-cavity lasers (ECL) using photonic wire bonds as coupling elements
Concept and realization of a hybrid ECL with a photonic wirebond (PWB) as intra-cavity coupling element. (a) Concept: The device consists of an InP-based reflective semiconductor optical amplifier (RSOA) that is connected to a thermally tunable feedback circuit on a silicon photonic (SiP) chip. A photonic wire bond (PWB, see Inset) connects the facet of the RSOA to the SiP external-cavity feedback circuit. The assembly is built on a metal submount that simultaneously acts as an efficient heat sink. (b) Building blocks of the device realized for our proof-of-concept demonstration. The 600 µm-long RSOA is equipped with a high-reflectivity (HR) coating at the back facet. The front facet is angled (tilt angle 9°) and anti-reflection-(AR)-coated with respect to polymer (refractive index n = 1.56). The SiP external-cavity circuit (framed in light blue) comprises a 350 µm-long spiral-shaped phase shifter for adjusting the intra-cavity phase (cavity phase tuner) and a tunable frequency-selective feedback structure. Frequency selectivity is provided by two symmetrically coupled Vernier ring resonators R1 and R2 in add-drop configuration with diameters D1 = 62 µm (R1) and D2 = 67 µm (R2) and with coupling gaps of 180 nm. Note that the cascaded Vernier rings can be assumed to be reciprocal, such that the feedback circuit behaves similarly to a Sagnac loop mirror. The lower left-hand input port of the 2 × 2 MMI can thus in principle be left unconnected, and the associated grating coupler shown in Subfigure (a) was omitted here for simplicity. (c) Microscope image of the assembled device. Left-hand side: InP RSOA; right-hand side: SiP chip (framed light blue). The relevant part of the external-cavity circuit is marked by a red bounding box.
