INFORMATION TECHNOLOGY

Chip long-range Besselauss beam generator


Bessel beams have significant large depth of field and self-healing characteristics, and have been widely used in quantum entanglement, underwater 3D imaging, optical micromanipulation, microscopy and other fields. However, traditional methods of generating Bezier beams (such as circular slits and lenses, conical prisms, spatial light modulators (SLMs), etc.) use bulky optics that make the system bulky and complex, hindering the practical application of Bezier beams.

Recently, several compact systems have been proposed, such as the generation of Bezier beams by using methods such as photonic integrated loops (PIC), metasurfaces, integrated waveguides, and 3D printed optical fibers. However, the short propagation distance of the Bezier beam produced by the above technique severely limits the application of the Bezier beam in the long propagation distance scene.

A research team led by Professor Song Junfeng from the State Key Laboratory of Integrated Optoelectronics and Pengcheng National Laboratory from the School of Electronic Science and Engineering of Jilin University proposed a circumferentially distributed grating array photonic chip structure based on silicon-on-insulator (SOI) process to generate a Betheselsian beam (BGb) with long propagation distance. Laser beams with the intensity distribution of the first type of Bessel function were emitted at wavelengths ranging from 1500 nm to 1630 nm, and they measured 10.24 m in the laboratory without any optics. Finally, they applied this photonic chip to the measurement of rotational speed and distance of rotating targets.

The results were published in Light: Science & Applications under the title “On-chip generation of Bessel–Gaussian beam via concentrically distributed grating arrays for long-range sensing.” This work was supported by the National Key Research and Development Program of China, the National Natural Science Foundation of China, the Major Science and Technology Program of Jilin Province and the Science and Technology Innovation Research Team Program of Jilin University.

They summarize the principle by which integrated silicon photonic chips produce long-range Bessel-Gaussian beams: “Bessels Gaussian beams can be obtained by superimposing a series of grating beams. Each grating beam can be approximated as a Gaussian beam, and due to the coherence between the Gaussian beams and the symmetry of the circumferential distribution, it forms a Beziergauss beam in the overlapping region. The emission and divergence angles of the Gaussian beam determine the spatial position of the overlapping zone, which can theoretically go to infinity. ”

“Next, in order to generate long-range BGb, the waveguide structure needs to be carefully designed, especially the grating array width and grating period. To do this, we did a lot of simulation work and finally determined their dimensions. As shown in Figure 1, 64 grating arrays are integrated on the SOI, and the entire ring structure is 870 μm in diameter and fabricated using a CMOS process on a 130 nm process. ”

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Figure 1: Integrated chip Besselduss beam generator. a Optical micrograph of integrated silicon photonic chip, and the sub-map in the lower left corner is the near-field pattern of the chip surface under working conditions. b Magnified view of local grating array of photonic chip, grating array diagram and grating size diagram under scanning electron microscope. c Simulated raster array far-field diagram. d Besselgauss beam profile measured at 5.91m from the chip surface. One-dimensional intercept profile of the Besseldus beam at e 5.91m.

“Rotation is a common phenomenon in nature, and methods of measuring rotational velocity are essential to reveal the properties of matter, accurately measure and analyze the composition of celestial bodies. The Besselgauss beam consists of two 1st order vortex beams that turn opposite, and the polarization characteristics of the Besselgosian beam are shown in Figure 2.

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Figure 2: Polarization characteristics of a Bethelgauss beam generated by an integrated photonic chip. a theoretical beam intensity distribution of the far field, b – e intensity distribution in different polarization states in theory. f Light field intensity distribution measured at 2.2 m on the chip surface, and light field intensity distribution measured at 2.2 m on the chip surface of g – j through polarizers at different angles.

The rotational Doppler effect of the vortex beam was used to detect the rotation speed of the rotating object (as shown in Figure 3), and the object distance was measured using the phase ranging principle. This provides an integrated solution for high-precision measurement of object rotation speed and distance information. ”

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Figure 3: Schematic diagram of the experimental setup for measuring the rotation speed of a rotating object using a Bethelgauss beam generated by a silicon photonic chip and the experimental results. a Diagram of experimental setup. b Measurement results at different rotational speeds (75 r/s – 100 r/s). c Speed resolution test, ten speeds are measured at equal intervals in the range of 99.7 r/s to 100 r/s, for b, the red dots are the measurement data, and the blue lines are the theoretical data.

“Since the reported integrated optical chip size is less than 1 square millimeter, the cost of a single chip will be reduced to less than 50 cents in mass production. This low-cost, high-quality, long-range BGb emitter is key for future Bezier beams in large-scale, miniaturized and highly stable applications,” they add. (Source: LightScience Applications WeChat public account)

Related paper information:https://doi.org/10.1038/s41377-023-01133-2

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