Graded index single crystal active waveguide in glass
In one aspect the invention provides a graded refractive index single crystal waveguide having a glass block containing at least one crystal core, the crystal core having a central portion extending along an axis from a first end to a second end; an interface defining a peripheral boundary of the crystal core at a junction of the crystal core and an adjacent portion of the glass block, and a continuous, radially symmetric misorientation transverse to the central portion; wherein the misorientation has a misorientation angle that increases with increasing distance from the central portion towards the interface.
1. A method of making a graded refractive index single crystal waveguide, the method comprising:
a) providing a block of glass;
b) focusing a plurality of femtosecond (fs) laser pulses having a power density on a focal point within the block of glass, thereby heating the glass and inducing crystallization;
c) translating the focal point through the glass along an axis at a scanning speed, thereby generating a single crystal within the glass, the crystal comprising a lattice oriented along the axis,
wherein the single crystal comprises a central portion extending along the axis, an interface defining a peripheral boundary of the crystal core at a junction of the crystal core and an adjacent portion of the glass block and a continuous, radially symmetric misorientation transverse to the central portion;
wherein the misorientation has a misorientation angle that increases with increasing distance from the central portion towards the interface.
2. The method according to claim 1 , wherein the misorientation angle reaches a maximum of about 15° at the interface of the crystal core.
3. The method according to claim 1 , wherein the glass comprises 35Li 2 O-35Nb 2 O 5 -30SiO 2 glass.
4. The method according to claim 1 , wherein the crystal core comprises LiNbO 3 .
5. The method according to claim 1 , wherein the power density is between about 151 GW/m 2 and about 243 GW/m 2 .
6. The method according to claim 1 , wherein the laser scanning speed is between about 15 and about 75 μm/s.
7. The method according to claim 1 , wherein the power density and scanning speed are 243 GW/m 2 and 15 μm/s; 243 GW/m 2 and 25 μm/s; or 209 GW/m 2 and 15 μm/s, respectively.
8. The method according to claim 1 , wherein the plurality of pulses has a frequency of about 200 kHz.