Fig. 1. Schematic of the dual-cavity vapor cell.

Fig. 2. Schematic of the principle of anodic bonding.

Fig. 3. Schematic of the DRIE of the silicon wafer of a vapor cell.

Fig. 4. (a) and (b) SEM images of a vapor cell with different shapes. (c) Schematic of the simulated etching effect. (d) and (e) Etching depth during the etching process.

Fig. 5. Schematic of the anodic-bonding process. (a) and (b) First anodic bonding. (c) Filled alkali-metal compounds. (d) and (e) Second anodic bonding. (f) Completed vapor cell.

Fig. 6. Current–voltage curves during the anodic-bonding process.

Fig. 7. (a) Image of the etched silicon wafer. (b) Image of the fabricated bonded silicon wafer.

Fig. 8. Vapor cells of different optical cavity lengths compared with a dime: (a) 4 mm long and (b) 1 mm long.

Fig. 9. (a) Test platform for D2 absorption spectroscopy. (b) D2 absorption spectra at different temperatures.

Fig. 10. Helium leak rate measurement of vapor cells with different optical cavity lengths.

Fig. 11. SEM images of the anodic-bonding surface.