Fig. 1. Schematic diagram of a 3D integrated multichannel WG filter: (a) 1:1 planar beam splitter. (b) 1:1 3D beam splitter. (c) WGs arranged in parallel with different periods. (d) Schematic of the filter attached to the ruler.

Fig. 2. Images of the 3D waveguide beam splitter cross-section under a microscope, mode energy distribution map, and mode energy extraction curve. (a) Microscope image of the polished cross-section of the waveguide splitter with four waveguides. (b) Energy distribution map of the optical mode field for the one-to-four beam splitter. (c) Lateral and longitudinal intensity extraction curves of the mode field in figure (b).

Fig. 3. Relationships between different laser exposure parameters and exposure point sizes. (a) Optical microscope images are shown after single-point exposure with varying laser single-pulse energy and exposure time at a depth of 170 μm inside the material. (b) The extracted exposure spot profiles are plotted concerning the change in laser exposure time. (c) The extracted exposure spot profiles are plotted concerning the change in laser single-pulse energy.

Fig. 4. Optical microscope images of the WG under various laser writing conditions, intensity extraction curves of the grating images, and the Fourier transform frequency spectrum curves of the intensity curves. The red lines on the left depict a partial microscopic view of the WG and its intensity extraction curve. The blue lines on the right depict the spectrum curve after performing a Fourier transformation on the intensity curve. (a) Single straight waveguide without grating. (b) Third-order grating with single-pulse energy of 480 nJ and exposure time of 1 ms. (c) Third-order grating with single-pulse energy of 480 nJ and exposure time of 25 ms. (d) Third-order grating with single-pulse energy of 300 nJ and exposure time of 1 ms. (e) Third-order grating with single-pulse energy of 540 nJ and exposure time of 1 ms.

Fig. 5. Effects of different parameters on the optical properties of the gratings: (a) laser exposure time, (b) single-pulse energy, and (c) grating order on the reflectivity and 3dB-bandwidth of the BG reflection spectrum.

Fig. 6. Reflectance spectrum of the 3D integrated multi-channel WG filter. (a) Experimental and (b) Simulation result. The center wavelength of four magnified views was 1450, 1500, 1550, and 1600 nm, respectively.