This page describes in detail the method for producing chemically sharpened fiber optic implants as used in Hanks and Kopec et al. Nature 2015. Questions about this protocol can be directed to Charles Kopec ( http://brodywiki.princeton.edu/wiki/index.php/Charles_Kopec ). Please cite Hanks and Kopec et al. if you use this method in your work:

Hanks TD, Kopec CD, Brunton BW, Duan CA, Erlich JC, Brody CD. Distinct relationships of parietal and prefrontal cortices to evidence accumulation. Nature. 2015 Apr 9;520(7546):220-3

Newest Motoried Etching Protocol 2017

What you need

FC fibers: 1m FC-FC duplex fiber (50um code, 125um cladding) from fibercables.com (item #FCC2433)
Pliers
Fiber optic stripper
Razor blade (to cut whole fiber)
One stereotax arm with fine AP control arms
HF acid (1ml HF capped with mineral oil in 1.5ml eppendorf), volcanoes,platforms
Eppendorf rack with support "volcano" (made from Sugru, make volcano on the small eppendorf side so the 1.5ml eppendorf sits above the rack, this is why you need the volcano for extra support)
Motor control unit
- Laser cutting diagram for control unit housing (cut from 1/8" thick acrylic sheet) download [1] We cut our parts in house but they can be ordered from a company like https://www.pololu.com/product/749
  - Tap 10-32 threads into the 4 holes in the base place
  - Snap the electronic pieces into the top plate and connect all wires.
  - Assemble the unit (it's a little bit of a puzzle to get them all to snap together) and secure it with 2" 10-32 screws (you'll need to add a few washers to take up a bit of the screw length)
  - The motor attaches to the back plate with metric 4-M3 screws.
  - Press fit the small gear onto the motor and the large gear onto the Nirishige
- Motor [Amazon part B01MZWPBXU]
- Power control electronics [Amazon part B00QLYO7XU]
- DC power adapter [Amazon part B00J8CG86G ]
- DC power connector [Amazon part B00CUKHN0S]
Narishige MO-10 One-axis Oil Hydraulic Micromanipulator (press fit the large gear onto the control unit)

Preparing the fiber optic

Begin with a FC-FC duplex fiber

Cut the four ends off.

Use the Dremel to remove the outer collar. Wear eye protection because the Dremel bit may shatter. Make two cuts on the two opposite sides of it (it's too strong to be bent after one cut).

The two halves of the outer collar will fall after the cuts are made, exposing the inside parts.

Unscrew the internal metal protection. To unscrew hold onto the two rings in the picture. Because there is glue where the two parts are screwed together, you need pliers to unscrew them.

Once the metal parts are unscrewed and removed the fiber still contains 2 plastic jackets. The outer one is opaque (white, orange, and yellow are typical colors). The inner plastic jacket is typically clear. The metal part that is still left is glued to the fiber, so it cannot be removed.

Cut the fiber to the desired length and strip away both plastic jackets for the length that will be inserted into the brain (strip away a little more than what will be inserted since some fiber will be completely lost in the etching process).

Motorized Etching

Set up the etching station as shown below

Close up view of the fiber optic and HF acid

Set up the motor control station as shown. Ensure the Narishige control unit is oriented properly such that when the motor spins the drive unit withdraws the fiber from the acid.

Disengage the gears and lower the Narishige control unit to the 10mm mark. Turn on the motor (green button) and set the speed to 5. Turn off the motor (green button) and reengage the gears.

Using the microscope, lower the fiber through the mineral oil until it contacts the acid surface.

Using the stereotax arm, lower the fiber 2.5mm into the acid. Turn on the motor (green button) and start a timer counting up. The fiber will be slowly withdrawn from the acid. This results in a short taper through the cladding of the fiber optic (where no light travels).

After 17 minutes increase the speed to 100. This will quickly remove the remaining fiber from the acid resulting in a long taper through the fiber's core (where the light travels).

At ~29 minutes the Nirishige should have withdrawn 2.5mm. Turn the motor off (green button) and raise the fiber tip through the mineral oil and above the eppendorf. Inspect it under the microscope. The two different etch angles should be apparent. The protocol reliably results in a fiber etched tip of 1.8-2mm.

Fibers of different dimensions will require different speeds, durations, or both. We have successfully etched large diameter fibers (200-400um core) using just the slow speed of 5 for the entire etch. Larger fibers will result in a longer taper and therefore one will have to begin by inserting more fiber into the acid.

Older Etching Method

Fiber Preparation

For plastic LC fibers see note at the end of this page. http://brodywiki.princeton.edu/wiki/index.php/Etching_Fiber_Optics#Plasic_LC_Connectors

Begin with a 1m FC-FC duplex fiber (50um code, 125um cladding) from fibercables.com (item #FCC2433).

Cut the four ends off.

Make a cut in the outer plastic collar and remove it.

With a pair of pliers remove the remainder of the plastic collar.

The outer metal collar holds the orange outer plastic jacket in place.

Remove it by gently squeezing it with pliers until it deforms slightly from circular. Then rotate 90 degrees and bend it back to circular. Repeat this process until the metal fatigues and breaks off.

Some fiber optics have an inner metal collar

Remove it the same way you did the outer metal collar by gently squeezing the metal until it fatigues and breaks.

The fiber should now look like this

Fold the strengthening fibers back and cut them as close to the metal connector as possible. The clearer the opening the easier a later step will be.

The fiber should now look like this.

Cut the fiber using a new sharp razor to a length typically 5mm longer than the depth you plan to insert the fiber.

Strip away the inner plastic jacket. To avoid breaking the fiber, strip off the jacket in segments no longer than 7mm each.

At each point where you cut the inner plastic jacket for stripping, you will likely nick the innermost clear plastic jacket. This is okay as long as no nicks occur within 3mm of the fiber tip.

Etching the fiber

Mark a point 2mm from the tip of the fiber using a paint pen. It is critical that you get NO paint in the first 2mm as the etching will not occur symmetrically

Lower the fiber tip 2mm into 48% hydrofluoric acid capped with a layer of mineral oil. The red paint dot should be entirely in the oil, right at the oil/acid interface, thus ensuring 2mm of fiber is in the acid. Let stand for 85 minutes. During the etching a bubble may appear at the tip of the fiber, this is normal.

Remove the fiber from the acid and immediately submerge 5mm in deionized water for 5 minutes. Then remove from the water and submerge in acetone for at most 30 seconds. This will soften the clear plastic jacket making it easier to remove. Submerge 2mm more than the depth you plan to insert the fiber to and remove all of that plastic in the next step. Watch the fiber tip closely while in the acetone. If the tip begins to bend remove it immediately.

Position the fiber tip flat along a raised smooth surface.

With a fresh sharp utility razor gently make a small nick in the plastic jacket. Use very little downward force to avoid damaging the glass fiber. The plastic has been softened and should easily cut. Once you are through the plastic jacket with the blade resting on the glass fiber, gently push sideways towards the fiber tip. The plastic jacket should tear at the nick completely around. Continue pushing the jacket until you've opened a 0.5mm gap.

With a pair of sharp forceps grab the plastic jacket at the tip (where there is no glass fiber now) and carefully remove it by pulling it straight off. You should now have exposed the chemically sharpened glass fiber optic.

If you need to remove more of the plastic jacket you can peel it off with the razor by holding the blade at a 45 degree angle relative to the glass fiber and cutting towards the metal connector. Remove the pealed portion of jacket with forceps and repeat with the other half of the jacket.

Prepare a tiny batch of 5 minute 2-part epoxy and load into the back of a 3ml syringe with straight metal tip.

With the fiber tip pointing up, fill the cavity inside the FC connector with epoxy. This step is made easier if the yellow strengthening fibers were cleanly removed. It is essential that that fiber is surrounded by epoxy and immobilized.

Test the fiber by connecting it to a laser. The illumination should be broad and uniform.

Plasic LC Connectors

Essentially the instructions for preparing and etching a fiber attached to a plastic LC connector are the same, however we've noticed that regardless of the duration in the acid we cannot get some batches of fibers to etch to a point. The following steps have been found to achieve high quality etched LC fibers:

Initial fiber.

Cut the two pairs of ends off.

Separate the two fibers in each pair

With a pair of pliers remove the plastic collar. Sometimes the external plastic and the kevlar will come off with the collar (see bottom one). Other times it is necessary to gently squeeze the metal until it fatigues to remove these parts

The fibers should look like this now

Take fiber optic stripper, and use middle hole to strip the plastic (don't strip more than 7mm at a time!)

Mark with paint 2mm away from tip of the fiber

Soak 2mm of plastic coated fiber in concentrated HF for 48 minutes.

Soak in water, then acetone, and remove the clear plastic jacket as described above.
This should reveal a partially etched fiber. Most of the outer glass cladding will be etched away but the fiber will not taper to a point.
Re-submerge the tip (only 100um or so) in the acid. Under a microscope your should be able to see the acid pull up the sides of the fiber in creating a tiny meniscus.
Allow the tip of the fiber to soak in the acid until it is completely dissolved (the meniscus will disappear), approximately 20 minutes.
Remove the fiber from the oil and inspect. Under 6x magnification you should be able to notice the tip of the tapered fiber now has a point. Epoxy and test the fiber as described above.

Etching Fiber Optics

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