Many people have confusion about how to choose the right spatial light modulator (SLM) product for their technical needs. This article shares some perspectives to elicit more valuable opinions and help everyone select their desired product!

Spatial light modulators can control different light wave parameters. As shown in the schematic below, the incident beam is manipulated by the control signal acting on the modulation unit, causing changes in the spatial distribution of the amplitude, phase, or polarization state of the outgoing beam.

Schematic Diagram of Spatial Light Modulator

Therefore, when selecting a suitable spatial light modulator, the first step is to clarify which parameter needs to be controlled: amplitude, phase, or polarization state. Then design the experimental scheme to determine the product model selection.

For liquid crystal spatial light modulators (LC-SLMs), the numbers in the HDSLM product model represent the pixel size. R represents the phase type, RA represents the amplitude type liquid crystal spatial light modulator. -NIR represents the near-infrared band, -TELCO represents the communication band, and -G represents the green light band.

· When the product coating is for the near-infrared band, -NIR is added after the letter R in the product model, e.g., HDSLM80R-NIR.

· When the product coating is for the communication band, -TELCO is added after the letter R in the product model, e.g., HDSLM80R-TELCO.

· When the product coating is for the green light band, -G is added after the letter R in the product model, e.g., HDSLM80R-G.

· When the modulation type is amplitude type, the letter A is added after the letter R in the product model, e.g., the basic amplitude type product model is HDSLM80RA.

For DMD-type spatial light modulators, the numbers in the HDSLM product model represent the pixel size. D represents the DMD type SLM. The number after D represents the diagonal size of the micromirror array. UV represents the 363-420nm ultraviolet band, NIR represents the 800-2000nm band. DDR represents the high-speed memory version, SSD represents the large-capacity onboard SSD storage version.

01 Phase-Type Spatial Light Modulator

Phase-type spatial light modulators are primarily based on liquid crystal chips. Although scientific papers discuss methods for implementing phase modulation using DMD chips, utilizing complex amplitude transformation principles to theoretically prove phase modulation, the DMD itself cannot directly modulate phase. Algorithmic conversion is required to achieve phase modulation through amplitude changes. Before delving deeper, you can search for the industry standard "Phase-Type Liquid Crystal Spatial Light Modulator" on the Enterprise Standard Website to understand the indicator definitions for SLMs. Below is an illustration of the weight and value that different indicators represent for various applications, making it easier to select the appropriate product accordingly.

Relationship between Pixel Size and Diffraction Angle

Figure adapted from SID

Evaluation Weights of SLM Metrics for Different Applications

Explanation: The meaning of the evaluation weight is that a higher score indicates a greater impact of that metric on the application. Simply put, this metric will directly affect the final achievable outcome of the research topic.

For example, the pixel size directly impacts the diffraction field of view in holographic displays, theoretically limiting the maximum achievable field of view for holographic research. Therefore, purely from the perspective of pixel size, the HDSLM36R is clearly more suitable for holographic display research. In WSS (Wavelength Selective Switch) applications, phase stability and accuracy directly affect the final system's insertion loss. The HDSLM80R-TELCO spatial light modulator can outperform other domestic and international models by over 10dB in terms of system insertion loss, making it the preferred choice for large-scale industrial equipment. Recommended selections for HDSLM phase products include:

· HDSLM80R: Suitable for high-precision holographic measurement, light field control, and beam shaping fields; excellent performance in the infrared band, highly recommended.

· HDSLM36R: Popular 4K resolution product, integrates RGB collimated light sources and 3-color sequential Gamma; especially suitable for micro-nano DOE simulation, color holographic display research, holographic AR imaging technology, etc.

· HDSLM45R/HDSLM64R: Suitable for light field control and other applications; very good cost-performance ratio among 2K HD products.

· HDSLM80R-NIR/HDSLM80R-TEC: Suitable for infrared applications, including laser parallel processing, laser stealth dicing (axial multifocal).

· HDSLM80R-TELCO: The essential choice for 1550nm band applications such as WSS, TOF, and optical communication. Major domestic and international manufacturers are adopting this chip and driver to develop products. We provide custom FPC cable and interface services to facilitate the optimization of WSS equipment optical paths.

02 Amplitude-Type Spatial Light Modulator

Spatial light modulators are divided into two main categories: liquid crystal LCoS elements and DMD elements. The differences between them are as follows:

· LCoS chips have analog signal-controlled units (8bit/10bit) or digital signal-controlled units; DMD chips are digital signal-controlled units (1bit-16bit). This results in different amplitude control precision.

· DMD uses a time-integrated grayscale mode, meaning amplitude changes are time-integrated, using duty cycle to correspond to grayscale information, which can lead to signal discontinuity during high-speed exposure. LCoS provides absolute grayscale, relatively more stable.

· DMD involves electrostatically controlled micromirror mechanical movement, which can be polarization-independent, leading to high light utilization efficiency. LCoS chips are polarization-dependent, requiring linearly polarized light for incidence, resulting in lower light energy efficiency.

· DMD has microsecond-level response time, up to a maximum of 20KHz; LC liquid crystal material has a millisecond-level response time.

· DMD chips are exclusively supplied by the US company TI, restricting some sensitive customers. LCoS chip sources are abundant, with suppliers in South Korea, Japan, and Taiwan/Hong Kong regions. Furthermore, the LCoS chip industry supply chain offers greater autonomy in choices, from wafer procurement or self-development, coating to liquid crystal encapsulation, liquid crystal materials, etc., with multiple domestic and international suppliers available.

· DMD chips cover the UV band and have a relatively higher power damage threshold. LCoS chips, due to factors related to the liquid crystal PA layer, experience a sharp decline in lifespan in the UV band, limiting their application.

Therefore, choosing between a DMD chip and an LCoS chip mainly depends on factors such as energy utilization efficiency, response time, autonomy/controllability, grayscale characteristics, damage threshold, and wavelength range. Then, based on project requirements, refine the selection from perspectives such as cost-performance ratio, pixel size, and optical path simplicity.

The HDSLM D-series DMD-type spatial light modulators are suitable for different applications depending on pixel size, frame rate, and version type. Customers can select according to their usage needs.

· HDSLM80RA: Suitable for star simulators, infrared target simulators, etc., with good stability.

· HDSLM45RA: Suitable for developing high-speed structured light projectors.

Summary:
The selection of a phase-type spatial light modulator is highly dependent on the goals of the research project itself. Different applications place significantly different emphasis on various metrics. This relies on users having fundamental research literacy and sufficient experimental data to truly select the "suitable" model. Every ruler has its shortcoming, every inch has its strength; "suitability" is the most crucial criterion. Simply comparing parameter indicators is no longer meaningful.