Vector vortex beam radiator in photon integrated chip and application thereof
Technical Field
The invention relates to a technology in the optical field, in particular to a vector vortex beam radiator and a method for generating and transmitting vector vortex rotation in a waveguide of a photon integrated chip.
Background
Light is capable of carrying both spin and orbital angular momentum. In recent years, there has been great interest in researchers by vector vortex beams whose spin varies spatially and whose center has a singular point. Vector eddy currents provide additional new degrees of freedom and new resources for classical and quantum information, its inherent infinite dimensions and field structure characteristics make it useful for increasing the information capacity of classical information, high-dimensional quantum state generation, precision measurement, and quantum communication and quantum computation in Gao Weixi erbet space. Because vector vortex rotation is applied in the fields of classical information and quantum information on a large scale, an integrated device and equipment need to be developed, so that vector vortex light generation, transmission and control processing are integrated, the problems of connection errors, access loss, interface noise and the like in a macroscopic light path can be avoided, and the stability, reliability and robustness of a system are improved. Currently, researchers have achieved the radiation of vector eddy currents from the surface of an integrated device to free space using micro-ring resonators (Integrated compact optical vortex beam emitters), but the generation and manipulation and handling of vector eddy currents inside an integrated chip remains to be addressed. In addition, the femtosecond laser processing can selectively modify the interior of the material without damaging the surface of the material, thereby manufacturing a three-dimensional structure with any shape.
Disclosure of Invention
According to the defects and the shortcomings of the prior art and combining the characteristic of high flexibility of femtosecond laser processing, the invention provides a vector vortex beam radiator and application thereof, the modulated femtosecond laser is used for processing an asymmetric coupler structure consisting of an annular waveguide capable of transmitting vortex rotation and a single-mode waveguide, and the phase matching condition is regulated and controlled by regulating and controlling the size of the annular waveguide, so that the first-order and second-order vortex rotation can be efficiently generated; meanwhile, vortex light transmission, generation and control inside the integrated chip are realized, and the degree of freedom of processing on the integrated chip is increased.
The invention is realized by the following technical scheme:
the invention relates to a preparation method of an asymmetric coupler, which is characterized in that femtosecond laser is focused below the surface of glass by a femtosecond laser direct writing technology, the radius of an annular waveguide capable of transmitting vector vortex rotation is scanned to achieve a phase matching condition with a single-mode waveguide, and the processed asymmetric coupler can be used for generating a multi-order vortex rotation mode.
The femtosecond laser direct writing refers to: the femtosecond laser pulse was set to have a center at 513nm, a pulse duration of 290fs, a repetition rate of 1MHz, and a lens with a numerical aperture of 0.7 was used with a write-through speed of 5mm/s.
The multiple scans include: first-order annular waveguide direct writing and second-order annular waveguide direct writing, wherein: the direct write power of the single-mode waveguide is 154mw, and the power of the first-order annular waveguide is 136-144mw; the second-order annular waveguide power is 142-150mw.
The glass is preferably borosilicate at 170 μm below the surface of the glass.
The number of times of the annular waveguide scanning is 12.
The radius of the first-order annular waveguide is about 3.7 mu m, and the radius of the second-order annular waveguide is about 5 mu m.
The condition of phase matching with the single-mode waveguide is as follows: the propagation constant of the single-mode waveguide and the propagation constant of the annular waveguide are equal.
The invention relates to a coupler prepared by the method, which is of an asymmetric structure and is positioned 170 mu m below the surface of glass on average, and comprises the following components: annular waveguide and single mode waveguide, wherein single mode waveguide is oval.
The invention relates to the use of the asymmetric coupler described above for generating vector eddy currents inside a photonic integrated chip.
The invention relates to a chip for realizing the application, which comprises the asymmetric coupler prepared by the method.
Technical effects
Compared with the prior art, the invention adopts the femtosecond laser direct-writing technology to manufacture the transparent hard material and can efficiently generate vortex rotation, the chip of the invention can stably generate first-order and second-order vortex rotation, when the direct-writing pulse energy is lower, vector vortex rotation is generated, and when the direct-writing pulse energy is higher, scalar vortex rotation is generated, namely pure state is efficiently generated, and the generation efficiency is as high as 74 percent. The quantum optical chip technology is perfected, the quantum optical chip technology has the function of vortex optical fiber in macroscopic optics, the miniaturization and the integrability of vortex light generation, transmission and control are realized, the problems of connection error, access loss, interface noise and the like of the quantum optical chip in a macroscopic optical path are avoided, and the stability, the reliability and the robustness of the system are improved.
Drawings
FIG. 1 is a schematic diagram of first-order and second-order vortex rotation generation in an embodiment;
in fig. 1: a wavefront of the Gaussian light which is driven in 1, a wavefront of the second-order vector vortex rotation which is emitted from the waveguide by the single-mode waveguide 2, the annular waveguide 3, the wavefront of the second-order vector vortex rotation which is emitted from the waveguide by the annular waveguide 4, a wavefront of the reference Gaussian light which is used for interference by the beam splitter 5, and an interference pattern of the vortex rotation 7 and the Gaussian light interference;
FIG. 2 is a schematic diagram of first order vector vortex light generation in an embodiment;
FIG. 3 is a graph showing the variation of first-order vortex light with write-through pulse energy according to an embodiment;
in fig. 3: (a) the generated first-order vortex rotation mode and the change of conversion efficiency along with the energy of the direct writing pulse, (B) the polarization analysis of the typical B, D and F modes in (a), (c) the generated second-order vortex rotation mode and the change of conversion efficiency along with the energy of the direct writing pulse, and (D) the polarization analysis of the typical R, S and T modes in (c);
FIG. 4 is a schematic representation of the results of a vortex beam array;
in fig. 4: (a) is a schematic diagram of an array type asymmetric directional coupler, (b) is an intensity pattern and an interference pattern generated by a first-order vortex beam array, (c) is an intensity pattern and an interference pattern generated by a second-order vortex beam array, (d) is an intensity distribution of a first-order vector vortex rotation extracted and outputted from (b) along a radial direction, and (e) is an intensity distribution of a second-order vector vortex rotation extracted and outputted from (c) along a radial direction.
Detailed Description
As shown in fig. 1, the asymmetric coupler and the chip thereof according to the present embodiment include: a coupler comprising a single mode waveguide 2 and a ring waveguide 3, wherein: the wave front 1 of the incident Gaussian light is coupled with the annular waveguide 3 through the single-mode waveguide 2 by evanescent waves, reaches a phase matching condition under a certain condition to generate a second-order vector eddy current wave front 4, and enters the beam splitter 5 together with the wave front 6 of the reference Gaussian light for interference to obtain an interference pattern 7 of the eddy current and Gaussian light interference.
As shown in fig. 2, gaussian light of different polarizations is incident on a single mode waveguide of a directional coupler, and coupled to an adjacent annular waveguide via evanescent waves to produce vector eddy currents of different spatial distributions.
The first row H of the figure is a horizontally polarized gaussian beam incident on a single-mode waveguide of an asymmetric coupler, the intensity distribution of the obtained eddy currents and the intensity distribution obtained by performing polarization projection analysis on the intensity distribution, and the last row refers to the spatial polarization distribution of the vector eddy currents as radial polarization.
The second row V is the intensity distribution of the vortex induced rotation obtained by the incidence of the vertically polarized gaussian beam and the intensity distribution obtained by the polarization projection analysis thereof, and the last column refers to the spatial polarization distribution characteristic of the vector vortex induced rotation at this time.
The third row D is the intensity distribution of the eddy current generated by the incident coupling of the diagonally polarized gaussian beam to the adjacent annular waveguide and the intensity distribution obtained by the polarization projection analysis thereof, and the last column refers to the spatial polarization distribution characteristic of the vector eddy current at this time.
The fourth row R is the intensity distribution of the eddy current generated by the incident coupling of the Gaussian beam with right hand circular polarization to the adjacent annular waveguide and the intensity distribution obtained by carrying out polarization projection analysis on the intensity distribution, and the last row refers to the spatial polarization distribution characteristic of vector eddy current; the coupling lens used therein was 16 times, its numerical aperture was 0.25, and the focal length was 11mm.
As shown in FIG. 3, by simulating the phase matching condition, the radius of the annular waveguide generating the first-order (second-order) vortex rotation is estimated to be 3.5 μm (4.9 μm), and considering the complexity of femtosecond laser processing and two different waveguide structures, in implementation, we scan the radius of the annular waveguide near the estimated value to obtain better mode matching, and finally implementation obtains that the radius of the first-order (second-order) waveguide is respectively 3.7 μm (5.0 μm). Implementation finds that when the direct write pulse energy is small, vector vortex rotation is generated; it is clear from fig. 3 (b) that vector vortex rotation is generated when the direct write pulse energy is small; when the direct writing pulse energy is large, scalar eddy current rotation, namely a pure state, is generated, and the conversion efficiency is as high as 74%; at the same time, both first order and second order eddy currents have a better power fill where both first order and second order modes generated are better (see fig. 3 (a) and (c)).
As shown in fig. 4, the present embodiment relates to a method of generating a vortex beam array, comprising the steps of:
step 1) obtaining a plurality of vortex beam arrays in the power filling area through femtosecond laser processing direct writing.
Step 2) the orders of the generated vector vortex rotation are verified by generating clockwise and counterclockwise spiral interference fringes by interfering the generated vortex beam with the gaussian beam (see fig. 4 (b) and (c)), and simultaneously, the generated vector vortex beam is found to have better circular symmetry along the radial intensity analysis (see fig. 4 (d) and (e)).
The asymmetric directional coupler array in fig. 4 can generate a vortex beam array, and the intensity distribution of the vortex beam is analyzed along the radial direction, so that the light spot symmetry is better, and the vortex beam array can be used for quantum information processing.
Compared with the prior art, the invention not only perfects the quantum optical chip technology and ensures that the quantum optical chip technology has the function of vortex optical fiber in macroscopic optics, but also realizes the microminiaturization and integration of vortex light generation, transmission and control, avoids the problems of connection error, access loss, interface noise and the like in a macroscopic light path, and improves the stability, reliability and robustness of the system. Most importantly, the degree of freedom of processing on the photon integrated chip is increased, and the high-dimensional quantum state space on the photon integrated chip is greatly increased, so that quantum computing capacity can be greatly improved in a mode of on-chip control and superentanglement and the like.
The foregoing embodiments may be partially modified in numerous ways by those skilled in the art without departing from the principles and spirit of the invention, the scope of which is defined in the claims and not by the foregoing embodiments, and all such implementations are within the scope of the invention.