Fig. 1. Design scheme and simulation of PLLW. (a) Schematic diagram of PLLW. Insert: ring-shape output. (b) Simulated mode field of input side. (c) Simulated mode field of output side.

Fig. 2. (a) Processing parameter window of the FLDW single track in PG. Top-view of different regional tracks consistent with window (b) I, (c) II, and (d) III in (a), respectively. All of the tracks are written with depths of 200 µm.

Fig. 3. Dependence of the width and length of densified tracks on FLDW depth. Inserts: microscopic cross-section images of tracks in different depths. Scale bar: 1 µm. All of the tracks are written with scanning speed of 40 µm/s in PG.

Fig. 4. Microscopic cross-section images of the PLLW (a) input and (b) output with a ring radius of 4 µm. The PLLW is written with scanning speed of 40 µm/s and pulse energy of 175 nJ. Microscopic cross-section images of the PLLW (c) input and (d) output with a ring radius of 8 µm. The PLLW is written with scanning speed of 40 µm/s and pulse energy of 165 nJ. The near-field distributions of PLLWs with a ring radius of (e) 4 µm and (f) 8 µm. Inserts: mode images of input and output sides.