Note: the thermo-optic resistor is an alternative to the standard electro-optic modulator in the AOEO cascade.

The basic premise behind thermo-optic modulation is that heat will slightly change the index of refraction of the substrate and will introduce phase information into the light. This is different from electro-optic modulation which relies on voltage inducing a mechanical change in the crystal due to its piezoelectric properties. This mechanical change adjusts the index of refraction and introduces phase information into the light.

1. Evaporate 200nm of aluminum on a 1mm thick x-cut lithium niobate wafer.

2. Di-saw cut the wafer in 10x15mm sections.

3. Prep the wafer for writing on the Heidelberg.

4. Write file 4000x100_Mask1_Etch_Inverted_RSpads.dxf. As noted in the filename, this is to be written inverted and auto-centered on the device.

5. After development, wet etch the aluminum.

6. Make sure the device is clean. Use nanostrip, acetone and IPA as necessary.

7. Proton exchange and anneal as per current specifications. Metricon if desired to check for modes.

8. Make sure the device is clean. Prep the sample for writing on the Heidelberg.

9. Write file 4000x100_Mask2_Etch_Inverted_buffer.dxf. As noted in the filename, this is to be written inverted but not auto-centered. Use the manual offset feature to align to the + mark remaining from mask 1. Try to get the sample as straight as possible on the chuck and use the measure rotation feature before writing.

10. After development, wet etch the aluminum.

11. Make sure the device is clean. Prep the sample for writing on the Heidelberg.

12. Write file 4000x100_Mask3_Liftoff_SiO2_Strips.dxf. As noted in the filename, this is a direct write (non-inverted) for a liftoff process. Use the manual offset feature to align to the + mark remaining from mask 1. Try to get the sample as straight as possible on the chuck and use the measure rotation feature before writing.

13. After development, evaporate 200nm of SiO2 on the sample. Use the generic crucible stored near the EBEAM that says “Quartz.” Note that SiO2 has a tooling factor of 168.6.

14. Perform liftoff by placing the sample in an Acetone bath for a few minutes. Use a pipette to water-jet any remaining SiO2 that is not in the channel.

15. Make sure the device is clean. Prep the sample for writing on the Heidelberg.

16. Write file 4000x1000_Mask4_Liftoff_NonInverted_ResistiveStrips.dxf. As noted in the filename, this is a direct write (non-inverted) for a liftoff process. Use the manual offset feature to align to the + mark remaining from mask 1. Try to get the sample as straight as possible on the chuck and use the measure rotation feature before writing.

17. After development, evaporate 75nm of NiCr on the sample. Note that NiCr has a tooling factor of 99.2.

18. Perform liftoff by placing the sample in an Acetone bath for a few minutes. Use a pipette to water-jet any remaining NiCr that is not desired. Be especially careful to look for electrical shorts across the aluminum pads.

19. Make sure the device is clean. Prep the sample for writing on the Heidelberg.

20. Write file 4000x100_Mask5_Etch_Inverted_AO_Transducer.dxf. As noted in the filename, this is to be inverted. Use the manual offset feature to align to the + mark remaining from mask 1. Try to get the sample as straight as possible on the chuck and use the measure rotation feature before writing.

21. After development, wet etch the aluminum.

22. Polish the 10mm sample edge closest to the transducers. Make sure that there is no aluminum on top of the sample between the transducers and the light exit edge or you can get absorption effects.

23. Make sure the device is clean. Ensure that the area reserved for prism coupling is clear of debris.

24. Wirebond the device to the proper AOEO breakout board. Note that the transducers will be wired to receive an RF signal while the thermo-optic pads will be wired to DC voltages on a power supply. Ensure that the breakout board is elevated above the lithium niobate chip so that it does not block the light from the exit edge.

25. Check the functionality of the transducers by connecting them to the S11 port of the calibrated network analyzer.

26. Prism couple the device and check for a wet spot. Mount the device onto the testing apparatus. Ensure that the laser is coupled into the device by checking for the characteristic streak and mode lines.

27. Connect the DC voltage lines from the power supply to the breakout board for the line you want to test. Connect the RF signal line from the signal generator to the breakout board for the line you want to test.

28. Test the transducers first. Attach a polarizing sheet to eliminate all light except TM. Find the diffracted dot that you can steer by adjusting the frequency.

29. Once you have the dot in an easily viewable location, test the thermo-optic stage. Turn up the current so that the device is solely voltage limited. Slowly adjust the voltage and watch for the AO modulated dot to shift vertically. To keep the resistor from burning out, stay below 17 volts.

30. As soon as the full AO/TO cascade is functional, draw a picture! Consider using an Arduino driver to control TO output voltages and AO RF signals. If you wanted to go a step further, you could attach a joystick to directly control the positioning of the dot.