## 3 Experimental Results and Discussion  
The fabrication process for proposed apodized sampled grating is shown in Figure 10. First, a 2.5-\(\upmu\)m thin film of 25% FSU-8-doped material FBPA-PC EP was spin coated with the speed of 3000 rpm for 20 s on the SiO\({}_{2}\) lower cladding. Next, a 40 nm-thickness Al film was evaporated on the FBPA-PC EP film with a low vacuum of \(5.0\times 10^{-3}\) Pa. After Al film was evaporated, the positive  
Figure 8: Reflection spectrum of (**a**) traditional sampled grating; (**b**) the proposed apodized sampled grating when \(N=5\) and \(t=0.5\). Figure 9: (**a**) Cross-sectional thermal field distribution of the metal-printing heater. (**b**) Simulated reflection spectrum of proposed sampled grating when \(\Delta T=0\)\({}^{\circ}\)C, 10 \({}^{\circ}\)C and 20 \({}^{\circ}\)C, respectively. photoresist BP212 was spin coated on the Al film and should be baked at 85 \({}^{\circ}\)C for 20 min. Then the wafer was exposed to a 200 mW Hg UV lamp power through a positive lithography plate and the exposure time was 4.0 s. Finally, this device was immersed in the concentration of 5%o NaOH solution for 20 s and flashed by deionized water to remove BP212 photoresist and unexposed Al film. This device was composed of two Al metal strips. Figure 11a shows the top view of the electrode measured by optical microscope (\(\times\)100) and Figure 11b shows the morphology of apodized sampled grating in one sampling period using optical microscope (\(\times\)200). Figure 11c,d shows the appearance of the device at the beginning and center position of the grating, respectively. The length of grating in one sample period was 400 \(\upmu\)m. The width between two strips could be observed as 5.1 \(\upmu\)m and the ridge width was approximately 5.6 \(\upmu\)m. The duty cycle could be estimated at 0.8. The lateral shift \(\Delta S\) at the beginning and the end of the grating is almost zero in Figure 11c and \(\Delta S_{0}\) is close to \(\Lambda\)/2 in Figure 11d. Figure 11: (**a**) Top view of the electrode measured by optical microscope (\(\times\)100); (**b**) morphology of grating region (\(\times\)200); (**c**) Appearance of the grating at the beginning (\(\times\)500); (**d**) Appearance of the grating at the center (\(\times\)500). Figure 10: Fabrication process for the proposed apodized sampled grating. Figure 12a presents the schematic diagrams of the measurement system. The apodized sampled tunable waveguide grating was characterized by signal wavelengths in a range from 1530 to 1570 nm by an amplified spontaneous emission (ASE) (SC-5) laser. The electrical modulating power from a signal generator was loaded on the electrodes of the gratings by needle probes. The optical spectrum analyzer (OSA) (MS9740A) was used to detect the reflected power of the grating. The output light signal was divided into two parts by the splitter. One part entered into optical power meter to evaluate the insertion loss and the other part launched into photo detector and oscilloscope (DS4024). The light power entering into the oscilloscope was converted to electrical signals. The propagation loss of the straight waveguide was measured by the cutback method. It was found to be 0.15 dB/cm at 1550-nm wavelength. The insertion loss of the device was directly measured to be about 6.5 dB. Figure 12b shows the signal produced by the signal generator and the signal generated by the broad spectrum ASE laser. The TO switching response of the apodized sampled grating was observed by applying square-wave voltage with amplitude as 1.015 V at a frequency of 300 Hz. The rise and fall switch times were measured as 1.508 ms and 630.5 \(\upmu\)s, respectively. The difference between rise and fall switch times can be explained as the fall time mainly depends on the heat dissipation rate. The silica bottom-cladding has a thermal conductivity of 1.2 Wm\({}^{-1}\)\({}^{\circ}\)C\({}^{-1}\), which is much larger than that of 25% doped FBPA-PC EP material (0.25 Wm\({}^{-1}\)\({}^{\circ}\)C\({}^{-1}\)).