Fig. 1: Enabling fine control of waveguide cross-section shape and sizes by SPIM-WGs. | Light: Science & Applications

Fig. 1: Enabling fine control of waveguide cross-section shape and sizes by SPIM-WGs.

From: On-chip beam rotators, adiabatic mode converters, and waveplates through low-loss waveguides with variable cross-sections

Fig. 1

All images (LED, laser, simulation) excluding the phase pattern have the same frame size of 30 × 30 µm. Scale bars are 10 µm. a Classic multiscan laser fabrication technique has a large z step resolution (8 µm in this case). The red arrow marks laser propagation direction. Distances of core spacing along x axis (Δx), and z axis (Δz) are presented beside the diagram. b Three proposed fabrication schemes and the corresponding fabricated waveguides. In experimental demonstrations, Scheme I had Δx = Δz = 0.4 µm, with 20 horizontal and 6 vertical scans. Scheme II had Δx = 0.4 µm, Δz = 1.5 µm, with 20 horizontal and 2 vertical scans. Scheme III had Δx = Δz = 1.5 µm, with six horizontal and two vertical scans for the x-aligned rectangular waveguide, two horizontal and six vertical scans for the z-aligned rectangular waveguide. Labels: “LED”—images obtained with LED-illuminated microscope; “Laser”—785 nm laser transmission mode profile imaged at the waveguide output facet; “Z11”—manually induced primary spherical aberration61 (corresponding to Zernike mode 11 phase aberration) applied to spatial light modulator (SLM). “x-a.”—x-aligned rectangular waveguides. “z-a.”—z-aligned rectangular waveguides. c Simplified diagram of laser fabrication system with phase control. SLM is imaged to objective pupil with a 4 f telescope system. SLM spatial light modulator, Objective objective lens. d Manually induced additional spherical beam-shaping phases to SLM and their effects on laser focus and single-scan waveguides. Note that these phases are not used to correct spherical aberration caused by refractive index mismatch between air and sample, which was pre-corrected in all our experiments (please refer to “Phase pattern for SLM” section for details). Left: beam-shaping phase applied to SLM in addition to aberration corrections. Middle: simulated focal intensity distribution (enlarged images in Supplementary Fig. S1). Right: LED illumined microscopic image of single-scan waveguides. e Scheme III fabrication with negative spherical beam-shaping phase (Z11 = −1), demonstrating significant improvement of cross-section control

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