Algorithm-Driven Light Field Revolution: SLM Technology Leads to a New Era of Smart Optics
Spatial light modulator (SLM) is essentially a dynamic optical device capable of spatially distributed modulation of the amplitude, phase or polarization state of light waves. Our self-developed SLM products use silicon-based liquid crystal technology to control the arrangement of liquid crystal molecules through electrical signals to achieve precise regulation of incident light waves. This precise control capability makes the Spatial Light Modulator (SLM) an "intelligent canvas" within optical systems. It is capable of generating a wide variety of complex light field distributions within the optical path.
Principle of spatial light modulator
Amplitude-Type Spatial Light Modulator TSLM023-A
The Amplitude Spatial Light Modulator (SLM) achieves amplitude modulation through the optical rotation effect of liquid crystals and the extinction effect of the polarizer.
Phase-Type Spatial Light Modulator FSLM-2K73-P03HR
The phase-type Spatial Light Modulator (SLM) utilizes voltage to alter the alignment direction of liquid crystal molecules, thereby adjusting their refractive index to generate a programmable phase delay. The power of a Spatial Light Modulator (SLM) lies in its programmability, and the realization of this programmability relies on various phase diagram generation algorithms. These algorithms calculate the phase patterns that need to be loaded onto the SLM according to the distribution of the target light field. They serve as a bridge connecting digital computation and optical modulation.
Amplitude-Type Spatial Light Modulator: Algorithm-Driven Precise Modulation of Light Intensity
Amplitude-type spatial light modulator requires linearly polarized light to be incident. It achieves the control of the light field by manipulating the amplitude distribution of the light wave. When the polarization direction of the incident linearly polarized light is consistent with that of the polarizer, the optical rotation effect of the liquid crystal molecules will change the polarization state of the light. After passing through the analyzer, amplitude modulation is formed. This type of spatial light modulator serves as an important tool in fields such as optical information processing and image projection.
1.Graphical Method
For the amplitude-type spatial light modulator (SLM), direct encoding is carried out. The target light intensity distribution is linearly mapped to the grayscale values ofthe SLM, generating various simple and complex patterns, and implementing programmable amplitude masking. By updating the SLM patterns in real time, different optical experiment requirements can be met. For example, it can be applied to the single-slit, double-slit, circular aperture, and other shapes (such as triangle, five-pointed star, rectangle, hexagon, etc.) in the interference and diffraction experiment module of our company's teaching system. It can satisfy various educational and teaching experimental requirements related to interference and diffraction.
Single/Double-Slit Experiment
Circular-Aperture Diffraction
Rectangular-Aperture Diffraction
2.In terms ofimage filtering, intricate reticle patterns are generated through high-precision grayscale manipulation on the Fourier frequency spectrum plane of the optical system. For example, one-dimensional gratings, two-dimensional gratings, etc., can disperse the information of light waves and are widely applied in spectral analysis within the industry and in fiber optic communication system applications. Filtering is carried out on the focal plane behind the lens, blocking frequencies in different directions (such as high frequency, low frequency, x-direction, y-direction, etc.). The SLM operating in the amplitude modulation state can achieve filtering such as low-pass filtering, high-pass filtering, and slit filtering.
One/Two-Dimensional Grating
Aperture-Shaped Filtering
2.Optical Expression Method
Amplitude-type Fresnel zone plate: Based on the required parameters of the zone plate, a corresponding two-dimensional grayscale image or binary image is generated in the computer using the theory of Fresnel zone plates. Its structure is composed of a series of alternating transparent and opaque annular zones. By utilizing a spatial light modulator in combination with a Fresnel zone plate, a specific light intensity distribution pattern can be formed, thereby achieving the amplitude modulation of the incident light. Meanwhile, leveraging the Fresnel zone plate enables the precise control of the spatial distribution of light intensity. When applied in laser processing, it can cause the laser to generate a specific light intensity distribution within the processing area, fulfilling the requirements of different parts of the material for light intensity during the processing.
3.Amplitude Hologram Method
The amplitude hologram is a technology that mainly records and reconstructs the object light field information by modulating the amplitude distribution of light. Different from the phase hologram, the amplitude hologram encodes the light field information only by changing the transmittance or reflectance of light. It utilizes the amplitude-modulated fringes to reconstruct the original object light wave through the diffraction effect, and it has important applications in holographic display and projection, optical data storage, anti-counterfeiting technology, and optical interferometry.
Phase-Type Modulator: The Algorithmic Art of Wavefront Modulation
Phase-type spatial light modulators also require linearly polarized light to be incident, and the polarization direction should be consistent with the long axis of the liquid crystal molecules. When a voltage is applied to change the orientation of the liquid crystal molecules, the refractive index changes accordingly, resulting in a programmable phase delay. In this way, the phase distribution of the light wave can be altered to achieve more complex light field modulation. It has irreplaceable advantages in fields such as holographic display, optical tweezers, and adaptive optics.
- Phase Retrieval Algorithm
- GS Algorithm
The most classic phase recovery algorithm, the Gerchberg-Saxton (GS) algorithm, uses Fourier transform to iteratively operate between the spatial domain and the frequency domain, gradually approaching the target light field. It has a simple principle and fast computation speed, making it highly suitable for application scenarios with high real-time requirements. Our company has developed a color holographic system, which applies the GS algorithm to load the calculated three-color holograms on the SLM, modulate the light field in a certain rate sequence, and realize the color information display through the cumulative effect of the persistence of vision of the human eye.
GS Algorithm-Color Holographic System
- GSW Algorithm
Considering that the GS algorithm is simple and prone to getting trapped in local optima, the GSW algorithm introduces a weighted algorithm mechanism on the basis of the GS algorithm. During the iteration process, different weights are assigned to different frequency components, thereby improving the reconstruction quality. Based on this, the GSW algorithm is adopted to generate multiple beam arrays with specific arrangements, which is applied in parallel processing and multi-focus imaging.
Laser Bam Splitting Processing for 2x2, 3x3 Arrays
- Hybrid hologram algorithm
The principle of using the hybrid hologram algorithm for flat-top beam shaping is to design a hybrid hologram based on the diffraction characteristics of the liquid crystal grating and the modulation characteristics of the spatial light modulator (SLM). The hybrid hologram consists of two parts: a binary grating and a geometric mask. The binary grating includes two different gray levels, which can be set according to the phase conversion requirements. The geometric mask is the beam-shaping area, which can be of any shape. By using this hologram for shaping, a beam with an approximately flat-top energy distribution in the Gaussian central region can be obtained. Meanwhile, a binary gray-level grating can be further designed according to the beam intensity distribution of the SLM to control the shape and intensity distribution of the shaped beam.
The Principle of Hybrid Hologram Shaping
- Stationary Phase Method
The stationary phase method is an important mathematical tool in the flat-top shaping of laser beams. It achieves the conversion of the laser beam from a Gaussian distribution to a flat-top distribution by modulating the beam phase to redistribute the incident Gaussian light spot into a flat-top beam with uniform intensity. Meanwhile, combining with iterative optimization algorithms such as the GS algorithm and simulated annealing can further improve the uniformity of the flat-top beam. Additionally, when combined with our company's phase-type spatial light modulator, it has a wide range of applications in laser material processing (cutting, welding), photolithography systems, optical inspection systems, etc.
The Simulation Effect of Shaping By The Stationary Phase Method
- Random Mask Phase Matching Algorithm
Axial multi-focal points have important applications in the field of industrial processing. By adopting the random mask phase matching algorithm, the phase diagrams at different axial positions are obtained through calculation. Random mask plates with the corresponding quantity are designed. The phase information at the corresponding positions is randomly extracted and summed up to obtain a phase diagram, which is loaded onto the SLM for modulation, thus realizing the axial multi-focal points. This significantly improves the energy consistency of the axial multi-focal points, enabling the SLM to be more widely applied in the field of industrial processing.
Simulation of 1×3 Axial Multi-Focal Points
- Optical Expression Method
In response to the diverse demands for special beams in the fields of teaching, scientific research, and industrial processing, our company, relying on the spatial light modulator (SLM) technology, has developed customized calculation methods and solutions based on structured light fields such as vortex beam, Bessel beams Laguerre-Gaussian beam, etc. These can precisely meet the core technical requirements of scenarios such as precision micro-nano processing, optical manipulation, and quantum communication.
1.Vortex Beam
By utilizing the electro-optic effect of liquid crystals, the SLM was realized to modulate the amplitude and phase of the incident light wave, enabling the wavefront transformation of the light wave, and the vortex light was formed by loading holograms using the spatial light modulator, which realized a wide range of applications in the field of optical communication and particle manipulation.
Vortex Beams Corresponding to Different Topological Charge Numbers
Vortex Beams Realize Particle Manipulation In The Optical Tweezers System
- Bessel Beam
Bessel beam is a special form of non-diffracting beam. The distribution of its electric field intensity in the cross-section follows the Bessel function. Moreover, during the propagation process, the Bessel beam can maintain the transverse light intensity distribution unchanged and has an infinite non-diffraction distance. It has important applications in the fields of optical manipulation, laser precision machining, microscopic imaging, and optical communication.
Phase Diagram And Intensity Diagram of The Bessel Beam (M = -10)
- Laguerre-Gaussian Beam
The Laguerre-Gaussian beam (LG beam) is a special high-order laser mode, and its transverse electric field distribution is jointly described by the Laguerre polynomial and the Gaussian function. The LG beam has a helical phase wavefront and orbital angular momentum, and it has important applications in fields such as optical manipulation, communication, and quantum optics.
Phase Diagram And Intensity Diagram of The Laguerre-Gaussian (LG) Beam (M = -10, P = 2)
- Hermite-Gaussian Beam
The Hermite-Gaussian beam (HG beam) is one of the common high-order transverse modes in the laser resonator, and its transverse electric field distribution is jointly described by the Hermite polynomial and the Gaussian function. The HG beam is one of the fundamental modes in laser physics. By virtue of its orthogonality and controllability, it has a wide range of applications in fields such as laser technology, communication, imaging, and quantum optics.
Phase Diagram and Intensity Diagram of The Hermite-Gaussian (HG) Beam (M = 2, P = 2)
- Phase-Type Fresnel Zone Plate
The Fresnel zone plate (FZP) is an optical element based on diffraction focusing. Traditionally, it is used to control the amplitude. However, the optical path difference between each zone and its adjacent zone is an odd multiple of a half-wavelength, which makes the light passing through different zones have the same phase at the focal point, thus realizing the modulation of the phase of the incident light. This phase modulation characteristic has important applications in fields such as optical imaging, optical communication, and biomedical imaging.
AI Algorithms Meet Spatial Light Modulators: Ushering in a New Era of Intelligent Optics!
The deep integration of artificial intelligence (AI) and spatial light modulators SLM is driving a revolution in optical technology. Machine learning empowers SLM to achieve real-time wavefront correction and holographic projection optimization, significantly enhancing the imaging quality and the display effects in AR/VR systems. The combination of neural networks and SLM fully exploits the parallel advantages of optical computing. It not only constructs new architectures such as optical convolutional networks but also enables real-time dynamic holographic control through spiking neural networks. Deep learning further breaks through the limits of optics, making cutting-edge technologies like lensless imaging and super-resolution microscopy possible, while also optimizing application scenarios such as optical communication. This collaborative innovation not only improves the performance of existing systems but also gives rise to numerous breakthrough applications. With the continuous advancement of algorithms and hardware, the AI+SLM technology will demonstrate greater potential in fields such as intelligent imaging, optical computing, and quantum optics. It will propel optical systems towards a more intelligent and precise direction of development.
Summarize
In the present era of rapid development of optoelectronic technology, the spatial light modulator (SLM) has become a core device in fields such as optical computing, laser processing, and holographic imaging. Whether in traditional optical computing or cutting-edge photonic neural networks, the SLM has demonstrated remarkable potential. Currently, through its deep integration with deep learning algorithms, the SLM is facilitating the transition of intelligent light field Modulation from a theoretical paradigm to an engineering realization. In the future, with the industrialization of optical computing chips and the continuous optimization of AI algorithms, the SLM will play a more pivotal role in areas such as communication, computing, imaging, and quantum technology.
References:
Wang Yutao. Control of Beam Morphology and Quality Based on Hybrid Hologram [D]. Hubei University of Technology, 2018.
Liu KX, Wu JC, He ZH, Cao LC. 4K-DMDNet: diffraction model-driven network for 4K computer-generated holography. Opto-Electron Adv 6, 220135 (2023).