La Lumière et son utilisation

Photonics

1. What is photonics?

“Photonics”, coming from the Greek word “phos” which means light, appeared in the late 1960s. It is a domain of study based on light and more precisely on the small particles within it: photons. The aim of this science is to manipulate those particles in order to generate, detect or transmit information. Photonics’ principles depend on the two aspects of photons: photons as a wave or as corpuscles.

Photonics is considered as a true field with the invention of the laser in 1960. Later, it has provided lots of telecommunications technologies that are now used in Internet.

For a better comprehension of this science, a focus on photons is necessary.

1. Photons

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        Originally called “light quanta” by Albert Einstein, the term “photon” first appeared in 1926. It came from the Greek word phos which means light.

        In physics, the photons are symbolized by the Greek letter gamma ɣ. The choice of this letter is based on the discovery of the gamma rays. According to Rutherford and Edward Andrade, those rays are shape of light. 

1. Quanta of light

Throughout the centuries, many speculations have been done on the description given to light. Two different schools of thought were facing each other. On the one hand, some scientists had a corpuscular vision of the light. On the other hand, other believed that the light acted like a wave. Until the 18th century, the corpuscular theory dominated despite the existence of theories affirming the opposite.

With the highlight of the interference and diffraction phenomena by Thomas Young and Augustin Fresnel, huge changes happened. The corpuscular theory is left in favor of the wavelike theory of light.

However, the wavelike theory had some flaws. According to the theory, there is a dependency between the light wave energy and its amplitude. But some researches showed that it was totally wrong: light wave energy depends only on its frequency.

It was not until 1905 that the mystery was solved. Thanks to Albert Einstein, the quantification of light’s energy is recognized as a property of light. In addition to that, he also affirmed that emission of electrons from a material can be explained by the movement of quanta in a continuous space. Furthermore, he added that the energy generated during the electron’s emission is linearly dependent on the wave frequency.

1. Physical properties

1. Electric Charge

With an electric charge smaller than 1×10-37 e, photons are considered as non-charged particles. It is described by the parameters of its wave vector. Therefrom, their wavelength λ (lambda) and their direction of propagation can be determined.

        The emission of photon can be caused by many things such as:

• The acceleration of a charge
• An atom or a nucleus going from a level of energy to a small one
• The annihilation between a particle and its antiparticle

1. Mass, moving speed and spin

The photon is a massless element. Experiences have proven that its mass was close to 10-54 kg. Thus, scientists to neglect it.

        Photon moves to the speed of celerity: 3×108 meters per second.

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