Surface-Relief Fiber Bragg Grating Fabrication

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1. Basic Process Overview

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2. Fiber Preparation

   1. Put purple nitrile gloves on.
   2. Cut approximately 1 meter of horizontal core D-fiber.

   3. Stripping

      1. Locate the middle of the fiber.
      2. Strip approximately 3 centimeters of the jacket from the center of the fiber. Strip 1 centimeter from both ends of the fiber.

      3. Fujikura High Strength Stripper

         1. 
         2. Turn on the power switch on the front of the stripper. The Power lamp should go on.
         3. Make sure the slide base has been moved toward the stripping blades. Check the blades for cleanliness and brush away any remaining coating, chips ect.
         4. Set the fiber you want to strip in the fiber holder.
         5. Close the auxiliary holding arm.
         6. Close the top cover the stripper. Depress the cover with your right hand. When the cover is closed and depressed, the red heater lamp will go on.
         7. Wait about three seconds for the heater lamp color to change to green.
         8. While depressing the top cover, slowly and smoothly slide the base to the left until the desired length has been stripped.
         9. Open top cover.
         10. Open auxiliary holding arm.
         11. Open fiber holder and remove fiber.
         12. Clean all jacket chips from the stripper.

      4. Red Luminos Stripper

         1. 
         2. Locate the middle of the fiber and hold it in a loop. Do not force the fiber into a tight loop. It will break.
         3. Lower the loop into dichloromethane. Keep it there for no longer than 10 seconds.
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         4. Place the edge of the dipped section of fiber between the blades as shown.
         5. Depress the blades, and slowly pull the fiber allowing the jacket to come off.
         6. Clean the blades.

   4. Place the Fiber in the Etch Boat

      1. 
      2. Remove the top magnets
      3. Place the fiber in the holder so that the stripped region is in the center with the flat side up. The flat side is the most shinny side.
      4. Replace one of the top magnets.
      5. Pull the fiber taut and replace the other magnet.
      6. Remove the other magnet and pull the fiber taught.
      7. Test to see that the fiber is centered by sliding the magnets together. The fiber should bend in a curve that goes straight down or straight up and the stripped edges should be level as shown___.

   5. Clean the fiber

      1. Place the etch boat over the ultrasonic cleaner.
      2. Slide the magnets together until the stripped section of the fiber is completely submersed in the isopropyl alcohol.
      3. Turn the cleaner on. The cleaner will turn off when it is done.
      4. Slide the magnets back.
      5. Place the etch boat over the beaker of DeContam.
      6. Slide together until the stripped section of the fiber is completely submersed.
      7. Leave the fiber in the DeContam for three minutes.
      8. Slide the magnets back and dry the fiber with the air.

3. HF Etch

   1. 
   2. Place the etch boat on the water beaker in the spill tray.
   3. Cleave the ends of the fiber.
   4. Be sure the polarizer is in place.
   5. Focus the laser into the fiber. Do not etch unless you have at least 20 microwatts of power. Add more here
   6. Suit up in the acid gear: apron, splash goggles, face shield, nitrile gloves.
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   7. CAREFULLY place the container of HF in the spill pan and remove the lid.
   8. Place the etch boat over the HF. Slide the magnets together until the stripped section of the fiber is submersed. Do not allow any part of the fiber jacket to touch the HF.
   9. Start the LabVIEW etchB program.
   10. After about 30 minutes the power will begin to oscillate. Remove the fiber from the acid after three complete oscillations as show in figue__.
   11. Leave fiber in the water until you have turned off the laser and have everything disconnected.

4. Sulfuric Acid Etch

   1. Take etch boat into the clean room.
   2. Suit up in the acid gear: apron, splash goggles, face shield, nitrile gloves.
   3. Place beaker of Sulfuric onto a hot plate. Heat the acid to 190°C.
   4. Place the etch boat onto the Sulfuric beaker. Slide the magnets together until the stripped section of the fiber is submersed. Do not allow any part of the fiber jacket to touch the Sulfuric acid.
   5. Leave the fiber in the acid for 5 minutes.
   6. Place the fiber into a beaker of water while you clean up and remove your acid gear.
   7. Rinse the fiber in water for 3 minutes.

5. RIE the Fiber

   1. Tape the fiber to the center of a wafer with the flat side up.
      1. 
   2. Check that it is flat side up with a microscope.
   3. Place the wafer into the RIE.
   4. Follow standard procedures to operate the RIE.
   5. Etch the fiber for 30 seconds at a Power of 250.

6. Photoresist

   1. Apply Surpass 4000 to the etched section of the fiber for one minute.
   2. Rinse the fiber in DI water.
   3. Dry the fiber with Nitrogen.
   4. Re-tape the fiber to the center of the wafer. Check the fiber under a microscope to ensure that it is flat side up.
   5. Once the fiber is flat side up, place the end of four 2-inch pieces of tape on the back of the wafer. Wrap the excess fiber around the wafer sticking it to these pieces of tape. Once wrapped, stick the tape down on the other side of the wafer. NOTE do not squeeze the tape loop together.
   6. Place the wafer on the spinner, turn on the vacuum pump.
   7. Apply thinned photoresist 700 to the etched area of the fiber.
   8. Spin it at 6000 rpm for 1 minute with an acceleration of 15.
      1. 
   9. Turn off the vacuum pump and place the wafer on a hot plate set to 90°C for 1 minute.
   10. Take the fiber off the hotplate and remove the tape using a razor blade. Be careful not to break the wafer or cut the fiber with the blade.
   11. Remount the fiber parallel to the flat edge of the wafer about 1 inch above the edge. Make sure the flat side is up. DO NOT use the microscope to check the fiber since it is not a yellow light.
   12. Place the wafer and fiber in a black wafer holder. Try to wrap the the ends of the fiber inside of the holder. If they do not stay, close the holder with the ends of the fiber coming out of the corners. Be careful not to break the ends when closing the holder.

7. Expose the fiber

   1. Turn on the “LASER IN USE” sign.
   2. Put safety goggles on.
   3. Turn on UV lamp.
   4. Measure the power at the mirror. To determine exposure time divide 21000 by the power (in microwatts), this will give you a time in seconds.
   5. Set the shutter to the appropriate time interval.
   6. Make sure only the yellow lights are on.
   7. Remove the fiber from the black wafer holder.
   8. Place the desired mask over the fiber and expose the fiber to the UV lamp for 30 seconds.
   9. Mount the wafer next to the mirror with the fiber in a horizontal position. The wafer and fiber should be mounted so that the edge of the etched region is at the edge of the mirror.
      1. 
   10. Turn off the yellow lights and open the shutter (the shutter will automatically close at the end of the preset time interval.)
   11. Place the wafer back into the black wafer holder.

8. Develop the fiber

   1. Take the fiber back into the clean room. DO NOT take it out of the black wafer holder until under yellow light.
   2. Place the wafer in the white dipper holder with the fiber at the bottom of the wafer.
   3. Immerse the wafer and the fiber in the developer, Shippley 1.2L, for 10 seconds. Move the wafer back and forth while in the developer.
   4. Remove the wafer from the developer and place it under running water to stop the process. Rinse the fiber and the wafer thoroughly.
   5. Dry the fiber and the wafer with nitrogen gas.
   6. Place the wafer on a hotplate set to 90°C for five minutes.
   7. After baking the fiber it is very likely not to be flat side up. Check the fiber under the microscope and remount it if necessary. Remount the fiber back in the middle of the wafer.
   8. Continue to use the black wafer holder to transport the wafer and fiber. This will help to keep the fiber clean.
   9. Test the fiber Bragg Grating

9. RIE the fiber

   1. Tape the fiber to the center of a wafer with the flat side up. Check that it is flat side up with a microscope.
   2. Place the wafer into the RIE.
   3. Follow standard procedures to operate the RIE.
   4. Etch the fiber for 1 minute at a Power of 250.

10. Clean Fiber

    1. Use a swab to clean the etched section of the fiber with Acetone and Isopropyl Alcohol.

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