Fig. 1. Structure diagrams of devices. (a) VOA; (b) Bessel curve MMI

Fig. 2. Simulated spectra of normal MMI and Bessel curve MMI. (a) Loss for each channel; (b) excess loss of devices

Fig. 3. Simulated spectra of VOA

Fig. 4. Microscope images of devices. (a) Modulate arms of VOA; (b) (c) Bessel curve MMI.

Fig. 5. Measured insertion loss of Bessel curve MMI. (a) 1310 nm; (b) 1550 nm

Fig. 6. Voltametric characteristics and photodetection curves of device. (a) (b) At wavelength of 1310 nm; (c) (d) at wavelength of 1550 nm

Fig. 7. Measured spectra of VOA

Fig. 8. VOA response time. (a) At wavelength of 1310 nm; (b) at wavelength of 1550 nm