Fig. 1. PL spectra of ErxY2−xSiO5 crystalline thin films prepared by sol–gel and PLD methods at 17 K.

Fig. 2. TEM image of highly oriented Er2SiO5 crystal.

Fig. 3. XRD patterns of ErxY2−xSiO5 PLD thin films as a function of Er content x [24].

Fig. 4. XRD patterns of ErxY2−xSiO5 and ErxYbyY2−x−ySiO5 PLD thin films (x=0.33, y=0.33).

Fig. 5. XRD patterns of ErxY2−xSiO5 RAS thin films annealed at 1200°C and 1250°C.

Fig. 6. PL emission of ErxY2−xSiO5 and ErxYbyY2−x−ySiO5 thin films excited by 654.5 nm light at room temperature. They show (a) I413/2→I415/2 transitions of Er3+ and (b) PL emission in the range from 950 to 1100 nm.

Fig. 7. PL intensity ratio of ErxYbyY2−x−ySiO5 and ErxY2−xSiO5 crystalline thin films at 1.53 μm, as a function of the excitation wavelength. The dashed lines show PL spectra of both samples for comparison.

Fig. 8. 1.53 μm emission decay rate as a function of the Er concentration. The solid lines show the fitting curves by Eq. (5).

Fig. 9. Schematic diagram of the spherical grain model. Density plots show distribution of the excited Er ions at the steady state.

Fig. 10. CUC emission spectra of the sol–gel sample. The energy diagram and CUC energy transfer process are also shown.

Fig. 11. CUC process modeling of the ErxY2−xSiO5 crystal.

Fig. 12. CUC emission intensity as a function of excitation power. The solid line is a calculation result using the rate equation [Eq. (6)] with Cup=1×10−17  cm3 s−1.

Fig. 13. Summary plots of the CUC coefficients as a function of Er concentration for various host materials [13,29,3436" target="_self" style="display: inline;">–36]. The dashed line shows the linear dependence expected from the Förster energy transfer.

Fig. 14. Schematic diagram of the waveguide with buried Si guide layer.

Fig. 15. Top views of the ErxY2−xSiO5 (x=0.45) waveguide prepared by DSA (top). CUC emission image along the waveguide (middle) and the CUC emission intensity profile (bottom) are also shown.

Fig. 16. Decay coefficient as a function of Er concentration. The solid line is the linear approximation of a series of the sol–gel samples.

Fig. 17. Schematic diagram of ErxY2−xSiO5 waveguide slotted into Si PhC. (a) SEM photograph of a top view of the PhC before the sol–gel process, (b) cross-sectional view of the waveguide device, and (c) SEM image after the crystallization. The light propagation direction is perpendicular to the diagram.

Fig. 18. Top views of the Si PhC–S Er0.4Y1.6SiO5 waveguide. Infrared camera (middle) and CUC emission image along the waveguide (bottom) are also shown.

Fig. 19. (a) PL spectra and the edge emission intensity versus (b) exposed length from the Si PhC–S Er0.4Y1.6SiO5 waveguide.

Fig. 20. Gain characteristics of Si PhC–S Er0.4Y1.6SiO5 waveguide estimated by VSL method.