Electronic integrated circuits (ICs), like those you have in your laptop or smart phone, work with electricity, i.e. by controlling the flow of electrons through the different elements of the circuit, like transistors, resistors and capacitors.

Can we also build ICs that work with photons instead of electrons? The answer is yes, they are called photonic integrated circuits (PICs), and are a fast growing technology which will have a huge impact in our everyday life. First developed during the decade of the 1990s¹, these photonic circuits use light, and compared to their electronic counterparts they are faster, generate less heat and are much more robust against interference.

In order to build a PIC one needs a source of light, in this case provided by a laser. PICs also use ‘waveguides’ which confine and route light inside the chip by total internal reflection, similar to the way metallic wires route electrons in an IC. Finally, several elements, like modulators, polarizers and couplers are used to manipulate the light.

There are several materials that can be used to fabricate a PIC, mainly silicon (Si), Indium Phosphide (InP) and silicon nitride (Si₃N₄), each one having their advantages. However, due to its scalability and amount of components available the most used is InP, which allows integration of all the elements (actives and passives) mentioned above into a single chip, making it more versatile and low-cost.

Moreover, one of the main challenges in developing a product based on a PIC is its packaging. If one needs to couple light in & out of the chip, active alignment is required, which makes packaging expensive and difficult to scale. By making use of InP one can instead generate and detect light electrically in the chip, by making use of an electrically driven laser and reading the electrical signals of a photodetector. This way one avoids the problem of active alignment and can use standard packaging process from the CMOS Industry.

PICs have been in use for several years, mainly in the telecommunications, sensing and biomedical markets. However new applications continue to emerge where PICs can be a useful solution, among them those related to quantum technologies.

At Quside we develop quantum-random number generators based on an InP PIC, which can produce high quality, Gbps random numbers required for high-performance computing, cryptography and QKD.