Unruh Effect Simulations And Geodesic Lens Effect In Transformation Optical Waveguides

In order to control the propagation path of electromagnetic wave arbitrarily,a design method of transformation optics media has been proposed.In general,the transformation optical medium is used to control the electromagnetic wave by changing the electromagnetic parameters of material in the artificial metamaterials.At present,transformation optics has produced novel applications in the fields of invisibility cloak,illusion optics,perfect lens imaging and so on.However,this method of designing transformation optical devices by changing the electromagnetic parameters of materials faces great challenges in material preparation.Especially in the high-frequency visible light band,it is very difficult to prepare sub-wavelength structural units.In order to prepare transformation optics devices in the visible light band,people began to try to control the propagation constant of the waveguide by changing the geometrical parameters of the waveguide in the integrated optical waveguide,thereby regulating the propagation characteristics of photons.In recent years,the method of transformation optics has gradually been applied to the simulation of gravitational fields,scientists have begun to design optical waveguides to simulate some astronomical phenomena that cannot be directly observed,such as simulating photonic black holes,Einstein rings,and cosmic strings,etc.On the other hand,the Hawking radiation and Unruh effect caused by the quantum effect of gravity are also issues of general interest to scientists.The Unruh effect is a prediction that an accelerating observer will treat its surroundings as a thermal radiation bath,and the temperature is proportional to the acceleration.This effect plays an important role in verifying the excitation of accelerated detectors and atoms,the weak decay of noninertial protons,and the bremsstrahlung of accelerated particles.However,due to the high acceleration required for the Unruh temperature to reach a measurable value,it is difficult to directly detect the Unruh effect through experiments.Some theorists have proposed a method to simulate the Unruh effect through transformation optical waveguides,but the corresponding experimental verification has not been completed.Based on the theoretical model of transformation optics,we design and prepare a transformation optical fiber with gradient propagation constant to simulate the acceleration process of particles in the Unruh effect,by using the leaky radiation between the transformation optical fiber and the slab waveguide for the first time,we have successfully observed the leaky radiation caused by particle acceleration through microscopic fluorescence imaging.By accurately measuring the radiation angle,the Unruh temperature corresponding to different accelerated particles is obtained.This paper mainly studies the following aspects:1.We fabricate uniform micro-mano small-sized optical fibers,and successfully observed the optical fiber radiation phenomenon similar to Cherenkov radiation in experiments.According to the angle of Cherenkov radiation simulated by the leaky radiation of the uniform micro-nano fiber,the effective refractive index of the uniform micro-nano fiber can be calculated.By this method,a sensor for detecting the effective refractive index of a uniform micro-nano fiber can be fabricated.2.The accelerated motion of effective particles is simulated by the tapered micronano fiber.We use the hydrogen-oxygen flame to heat and stretch the fiber to prepare the tapered fiber with micro-nano size,and experimentally observe the radiation phenomenon of accelerated particles.The study found that different tapered micro-nano fibers can correspond well to particles with different accelerations,so as to obtain different Unruh temperatures.3.By using the conformal transformation method,we prove that the propagation of light in a flat thin film waveguide with gradient index is equivalent to that in a curved optical thin film waveguide with homogeneous medium.According to this equivalent relationship,we design a geodesic lens in a curved waveguide with uniform refractive index.This curved film waveguide has a focusing effect on light and can be used as an on-chip optical device.The transformation optical device studied in this paper can not only simulate the Unruh effect and geodesic effect in curved spacetime,but also provide a new design idea for integrated photonics devices,which has the potential to produce practical application value in the future.