Making a 'Photonics cuddly toy' is a workshop that can be executed in Fab Labs.

Properties of this workshop:

Timeplanning: Total: 3h

1. Understanding the concept of 'Total Internal Reflection': 15 minutes
2. Implementing the optical fibres and bringing light to the surface: 1 hour
3. Controlling and implementing electronics: 1 hour 15 minutes
4. Finishing the bear: 30 minutes

This is the timeplanning of the basic workshop. If you also do the extensions, the time needed can be longer.

Target audience: Young students (10-14 years old)

Estimated cost: €...

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This instruction is published under the Creative Commons licence CC-BY-NC.

Step 1: Total Internal Reflection?

Bringing light to several places in the cuddly toy is based on total internal reflection.

Reflection is a property that you find very often in nature. For example, objects in the air can be reflected on a water surface. But this principle works vice versa as well, objects in water will also be reflected on the water surface.

Photo 1

Total internal reflection is the phenomena where light gets reflected inside a particular material over and over again. The angle of incidence is larger than a particular critical angle (θc) with respect to the normal to the surface.

Photo 2

You can demonstrate this phenomena. Take a glass with long, straight sides or something similar and fill it with water. Mix a very small amount (ca. one drop) of milk into the water, and direct the laser beam into the glass, as shown in the picture.

Photo 3 & 4

The water surface is another kind of mirror, which only works if the light hits the surface under a large angle of incidence (the smaller the angle of incidence, the more the light gets lost through the surface). In order to demonstrate that this reflection obeys the same law as the reflection on a metal mirror, please increase the angle of incidence and show that it is the same as the angle of reflection.

The laser beam will not leave the glass until it hits the bottom. You can see that the light beam becomes weaker and weaker. We can reduce this problem by having no milk in the water, however, without milk it would be much harder to see the beam. In order to make the light beam visible, some of the light has to be scattered by the milk droplet, what makes the beam weaker. Some light is also lost in reflections, if the angle of incidence is not large enough.

This effect is exactly the same in optical fibres as in the water glass, only the optical fibre is very long and thin and made out of plastic, which makes it flexible.

Photo 5,6 & 7

So, now you know all this, you can image what you need to give your cuddly toy bright eyes.

Step 2: Part List

Photonics parts:

  • Optical fibre
  • 1 RGB led (common cathode)

Electronic parts:

  • 3 resistors (1 of 220Ω, 2 of 330Ω)
  • 3 toggle switches
  • heat shrink sleeves
  • electric wire
  • 9V battery

Other parts:

  • Cuddly toy
  • Buttons
  • Wood
  • Cutter knive
  • Superglue
  • Sewing supplies
  • Fabric in the same colour as your bear

Tools (for example in Fab Labs):

  • Laser cutter
  • Drill
  • Sewing machine
  • Soldering iron

The photonics parts can be bought by EYESTvzw.
The electronic parts can be bought by Fablabfactory.

Step 3: Implementing Optical Fibers


Open up (be careful!) the cuddly toy to insert the optical fibres. You can cut along the seams of the fabric of the cuddly toy with a cutter knife in order to not make a lot of damage.

Take out some of the stuffing.

PHOTO 1,2 & 3

The control box and battery will also go in this opening at the end of the workshop. In order to replace the battery when necessary, the battery should be easily accessible.

So the bear should be reopened again and again. We are going to sew (sewing supplies) some extra pieces of fabric with Velcro to the ends of the fur of the bear. (The extra piece of fabric is necessary to fully close the bear again.)

Measure the length of the two pieces of fabric to the ends of the fur.

PHOTO 4,5 & 6

Measure also the length of the two pieces of Velcro. Sew one piece of the Velcro to one piece of fabric and sew the other one on the other piece of fabric.

PHOTO 7,8 & 9

Attach the fabric with pins to the bear. And stitch the fabric to the fur of the bear. Note that you should be able to stick the two pieces of Velcro together. Remove the unnecessary wires.

PHOTO 10 - 15

Use buttons to bring light to other parts of the bear. If you want some light in the belly of the bear, you should sew first a button, with preferably 4 holes on the preferred place.

PHOTO 16,17 & 18

Once you have the button where you want it to be, you can put an optical fibre through a hole of the button, through the fabric of the bear to the opening at his back. Attach a piece of tape around the end of the optical fibre, make sure the optical fibre cannot move anymore while working on the bear.

PHOTO 19, 20 & 21


If you have a lot of time, you can put several buttons on the bear, on each place you want to have light.

PHOTO 22, 23 & 24

If you want to give your cuddly toy a lightning eye, you can drill a hole in the plastic eye. Use a drill head with the same diameter as the optical fibre you will use. (Note the safety precautions of this drill.)

PHOTO 25, 26 & 27

Pull the optical fibre through the drilled hole to the opening of the bear. Attach the optical fibre with superglue to the plastic eye. Make sure the optical fibre cannot move anymore while working on the bear.

Step 4: Side Glow


If you send light at one side of an optical fiber, the light is only coming out at the other side of the optical fiber. But it is also possible to have light coming out of the optical fiber at the side. Herefor you need to give the light the acces to come out, by making notches (that are deep enough) in a part of the fibre.

PHOTO 1 & 2

We would like to make its hand glow in the dark. So we will attach a fibre with side glow effect on top of his hand.

The first step is to make notches in the optical fibre. For this side glow effect, we used optical fibres with a diameter of 2mm.

Make several notches next to each other, which are equally deep, over a certain distance. (Don’t choose this distance too long, otherwise the intensity of the light will decrease.) You can do this with a cutter knive, although this is not easy at all! If you are in a Fab Lab, use a laser cutter to make these notches.

The fibre gets weak after making notches in it, so it might break a lot easier when bending it. For this reason we already bend the fibre in the right angle and attach it like that on a wooden shelve.

Make an .svg file to put in the laser cutter, of use ours (which you can find on the website www.PHABLABS.eu).

PHOTO 3, 4 & 5

When removing the optical fibre from the shelve, make sure it stays curved, this to reduce the change of breaking the fibre.

Make holes on each side of the bear's hand. Put the fibre through it, and remove the scotch tape. (The ends of the fibre should go to the end of bear.

Sew the fibre on the top of his hand in order to fix the fibre.

PHOTO 6 - 11

If you now send light through the optical fiber, you can see light coming through on top of the bear's hand.


You can use this principle to make a mouth for the bear, or to decorate his ears. Put the ends of the optical fibre through the fabric and bring the ends to the opening. Give a stitching on the underside of the arch of the mouth.

PHOTO 12-17

Step 5: Controlling & Implementing LEDs


The only thing that is missing inside your bear is the light source. We are going to make a small box with the LED and the control system. We are going to use a white RGB LED, which can be controlled with three switches. (One for each colour).

We have soldered the components to each other like on the drawing on Photo 1 & 2.

PHOTO 1 & 2

The RGB LED has 4 legs. The longest one is the one that needs to be connected to the ground (GND). The leg at the left side of the longest leg, is for the red colour. The two at the right side are respectively for the green and the blue colour.

The legs for the colours need to be connected first to a resistor. Use a resistor of 220 Ω for the red colour and resistors of 330 Ω for green and blue.


Start with soldering a resistor of 220 Ω to the leg for the red colour of the LED. Then solder a coloured electric wire (more or less 10cm) to the other side of the resistor. Put a heat shrink sleeve on top of the resistor, make sure the total length of the resistor and all soldering is covered. Heaten up the shrink sleeve until it shrinks. Do the same with the other two colours (green and blue) of the white LED.

Solder a black electric wire (more or less 15 cm) to the longest leg of the LED. Cover the soldering with a heat shrink sleeve.

PHOTO 4 - 9

The ends of the three coloured electric wires (red, green and blue) now needs to be connected to a switch.

First cut small ends of heat shrink sleeves and slide them over the coloured electric wires. Weave the ends through a connector (the left or the right side) of the switch. Then solder these connections and cover the soldering with the heat shrink sleeve.

PHOTO 10, 11 & 12

The next step is to interconnect the switches in series and connect them with the positive pole of the battery. Here for you need one red electric wire of about 15 cm and two shorter red electric wires of about 6 cm.

I started to solder one end of a short red electric wire and one end of the longer red electric wire together to the middle connector of the switch of the blue colour. Before weaving and soldering those electric wires to the middle connector, make sure you first add a short piece of heat shrink sleeve on top of both wires. After soldering the ends to the connector, cover it with the sleeve and heat it up.

Then solder the other end of the short red wire (starting at the switch for the blue colour), together with an end of the second short red wire to the middle connector of the switch for the green colour. (Don’t forget the heat shrink sleeve!)

Finally solder the last end of the short wire to the middle connector of the switch for the red colour. (Don’t forget the heat shrink sleeve!)

PHOTO 13, 14 & 15

Use the laser cutter to make the wooden box. Provide in this box holes for the switches, holes for the connection of the battery and holes for the optical fibers. The unfolding drawing can be made in http://www.makercase.com/

Or you can use our .svg file.

PHOTO 16, 17 & 18

In order to prepare the fibres to put into the wooden box, stick all fibres in the bear together and cut them to the same length.

PHOTO 19, 20 & 21

Assembling the box and all components requires patience and attention.

Start with the battery connector. Insert the wires of the connector through the foreseen holes in the wooden box. Make a knot in the wires. Strip the ends of the wires and solder them to the ends of the red and black wires on the LED. (Don’t forget the heat shrink sleeve.)

PHOTO 22, 23 & 24

Insert the switches into the holes in the box. Secure the switches with nuts to the wooden box.

PHOTO 25, 26 & 27

Now glue five sides of the box together.

PHOTO 28, 29 & 30

The connection between the LED and the fibres in the bear is made with a heat shrink sleeve. Use such a sleeve that just fits around the fibres. Make sure the LED and the fibres are closely to each other. Then heat up the heat shrink sleeve.

PHOTO 31, 32 & 33

Next put all fibres into the wooden box and glue everything together.

PHOTO 34, 35 & 36

Make three holes in the back of the bear and put the switches through those holes. Secure the switches with nuts to the fur of the bear.

PHOTO 37, 38 & 39

Add a battery to the connector and put the box into the bear. Put some stuffing back into the bear as well.

Close him with the Velcro.

PHOTO 40, 41 & 42

Almost there :)

The final step is to secure the optical fibres to the button. Use super glue for this. After letting it dry a little, cut the fibres so they don’t stick out of the button anymore.

PHOTO 43, 44 & 45

Now the Photonics Cuddly Bear is finished.

Play with the switches and make all colours you want.

PHOTO 46 & 47


You can also make use of a second LED. Then you can split your bundle of fibres in two, one for each LED. The soldering is similar as above. But attach the red wires of both the LEDs together and eventually to the battery, and do the same for the black wires.

Step 6: End Result & Conclusions

What we learned?
You learned to use your creativity to approach complex challenges. You learned how to solder simple electric components.

If you are giving this workshop to a group of youngster, you can invite the parents over and organise a public showing. This to involve the parents, so they can engage the youngsters to come more often to the fablabs.

Concluding thoughts

Thanks to the invention of the optical fiber, it is possible to send light signals over hundreds of kilometers. The email from a friend in Australia and the internet blog with party pictures from Hawaii - they all travel around the globe as light flashes.

Light is fast. In fact, no object can move faster than light.

Light travels straight, unless it hits an object.

Sending light signals over many mirrors is very difficult. It is much easier to use flexible optical fibers to guide the light by total internal reflection.

Light highways on the ocean floor.

When you look up a website on the internet, it is very possible that the information you see has been sent to you as short light flashes through optical fibres over thousands of kilometres. The technique is the same as the one you used in the bear. But instead of red, green, and blue light signals, modern systems send and receive very short light flashes in 80 different colours in parallel. By packing several fibres together to an optical cable, such systems can send tremendous amounts of information all over the globe extremely fast. For instance, a single cable lying on the ground of the Mediterranean Sea between Egypt and France can send 10 TB (1012 byte) data per second – the equivalent of 16,000 CD ROMs, or everyone living in France having two phone conversations simultaneously! Similar cables connect all the continents of the globe (except Antarctica). Without this international network of light signals, the internet as we know it would simply not exist. Can you imagine all these light flashes rushing around the globe? In principle, it is just the same as you might have proposed for the villages in the Andes – just on a larger scale.


PHABLABS 4.0 is a European project where two major trends are combined into
one powerful and ambitious innovation pathway for digitization of European industry:

On the one hand the growing awareness of photonics as an important innovation driver and a key enabling technology towards a better society, and on the other hand the exploding network of vibrant Fab Labs where next-generation practical skills-based learning using KETs is core but where photonics is currently lacking.


This workshop was set up by the Brussels Photonics Team, Vrije Universiteit Brussels in close collaboration with Fablabfactory.

<p>This is really cute and would be great for kids that are afraid of the dark :)</p>

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