What is the principle of Tik Tok love glasses?

It is the microstructure in the small circle that brings the halo of the shape of love, while the ordinary area of the lens without the small circle lights up normally, and the passing light images normally, so that we can still see the original object clearly.

Simply put, the "split pupil" is realized on the glasses-some light is still imaged in the original way, while the other part is scattered into the shape of love. (Of course, the light of the original light path can also pass through the diffraction area of the small circle, and the zero-order diffraction must exist, and the original object can also be imaged.

Simplify the model of the problem, and the street lamps in the distance will regard it as the incidence of parallel light from a point light source at infinity. The diffraction area on the glasses can add a wavefront modulation to the incident plane wavefront, and the human eye (or mobile phone camera) will be regarded as an ideal imaging lens.

The diffractive region on the spectacle lens can easily delay (modulate) the phase of each incident light with a certain material pattern. For example, if you want to delay the phase between the top layer and the light by π/2, you only need to stick a layer of material with a thickness of λ/4(n- 1) on the top layer of the light contact glasses.

For ordinary spectacle lenses, the plane wavefront is incident and the plane wavefront is emergent. However, for glasses with diffractive surface (phase modulation), the exit wavefront can be modified into various strange shapes. In Zemax, the lens position is changed to the binary 2-phase plane to simulate the additional phase and the final wavefront shape.

Note that the red dotted line is the approximate phase distribution after wavefront modulation here, that is, wavefront. We know that the propagation direction of light can be obtained by differentiating the wavefront, so we can also see that the light on the image plane is scattered.

This pair of glasses also uses the same principle, and through special phase modulation, a designed wavefront is obtained, which corresponds to the image plane and becomes the shape of love.

So how to design the pattern of the phase modulation surface according to the love pattern that you finally want to form? This can be achieved by an algorithm called IFTA (Iterative Fourier Transform Algorithm) or Gershberg-saxton algorithm. Now that the basic principles are finished, it should be easy to understand.