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2026-09

Optical Grating Design: Pitch, Diffraction, Material, and Manufacturing Process

Introduction

An optical grating is a periodic structure that modifies the transmission, reflection, or diffraction of light. Depending on its geometry and operating principle, an optical grating may consist of parallel lines, transparent slots, reflective lands, circular tracks, or two-dimensional patterns.

Precision optical gratings are used in spectrometers, optical encoders, interferometers, image measurement equipment, laser systems, and industrial inspection instruments.

For product designers and optical engineers, the grating should be specified according to its optical function and manufacturing method. Pitch, line width, material thickness, surface reflectivity, flatness, and alignment accuracy all influence the final system performance.

Grating Pitch and Line Density

Grating pitch is the distance from one line or slot to the corresponding point on the next line. It is one of the most important parameters in optical grating design.

Common specification terms include:

Pitch
Line spacing
Line density
Grating period
Slot width
Land width
Duty cycle
Open-area ratio

For a grating with fine pitch, the line width and space width must be controlled consistently across the active area. A pitch error can result in nonuniform diffraction, phase error, optical distortion, or measurement instability.

In encoder applications, resolution may be expressed as approximately 100 to 5000+ lines per revolution. In linear optical applications, the design may instead be specified by pitch in micrometers or lines per millimeter.

One-Dimensional and Two-Dimensional Structures

Optical gratings can be designed as one-dimensional or two-dimensional structures.

A one-dimensional grating typically contains parallel lines or slots. It may be used for:

Diffraction
Position measurement
Linear scale systems
Optical modulation
Encoder sensing

A two-dimensional grating may contain crossed lines, square grids, rectangular apertures, or custom periodic structures. It may be used in:

Image calibration
Machine vision
Alignment systems
Optical inspection
Experimental photonics

The design should define the reference direction, active area, alignment marks, and orientation tolerance.

Material Selection

Stainless steel 301 and stainless steel 304 are commonly considered for precision metal optical gratings.

Stainless steel 301 may provide:

High strength in thin gauges
Good spring-back resistance
Suitable performance for lightweight structures
Compatibility with thin metal grating designs

Stainless steel 304 may provide:

General corrosion resistance
Good industrial durability
Stable performance in many environments
Broad material availability

The appropriate grade depends on the optical architecture and mechanical environment. For reflective optical systems, the surface condition and coating may be as important as the base metal.

Thickness and Aspect Ratio

The thickness range for a custom precision metal grating may be approximately 0.02–0.5 mm. The thickness-to-feature ratio has a direct influence on manufacturability.

When the material is thin compared with the pitch, chemical etching can produce fine repeated structures with relatively low mechanical stress. When the material becomes thicker, the following issues require more attention:

Lateral undercut
Sidewall profile
Etch factor
Minimum slot width
Residual stress
Cleaning difficulty
Pattern collapse or deformation

The designer should avoid specifying a slot width that is unnecessarily small relative to the material thickness unless the optical system requires it.

Chemical Etching Versus Laser Cutting

Chemical etching is often suitable for thin optical grating structures with repeated lines and complex patterns. It can process multiple parts on one sheet and does not require a dedicated hard stamping die.

Laser cutting may be considered for:

Prototypes
Low-volume production
Larger slots
Rapid design changes
Parts requiring localized cutting

However, the laser process may introduce heat-affected zones, taper, recast, or edge discoloration. These factors should be evaluated according to the optical path.

Stamping may be appropriate for high-volume designs after the tool has been validated. It can provide high productivity, but tool wear, burr formation, material deformation, and minimum feature size must be reviewed.

Surface Finish and Optical Behavior

The optical effect of a metal grating depends on whether the system uses transmission, reflection, or both.

A matte surface may help reduce uncontrolled reflection and glare. A polished or coated surface may be preferred for reflective optical structures. Surface finish requirements may include:

Roughness
Reflectivity
Color or appearance
Scratch limits
Residue limits
Coating compatibility
Cleanliness level

Surface finish should not be selected based only on visual appearance. It must be matched to wavelength, light source, sensor configuration, incidence angle, and optical working distance.

Dimensional Tolerance and Alignment

A precision optical grating may require tolerances in the range of approximately ±2–±10 μm, depending on the geometry and inspection method.

Critical tolerances may include:

Pitch variation
Line width variation
Active area position
Angular orientation
Flatness
Hole position
Concentricity
Reference mark location

For two-dimensional gratings, orthogonality and registration between the two pattern directions may also be important.

Conclusion

Optical grating design requires coordination between optical theory, mechanical structure, and manufacturing capability. Pitch, line density, duty cycle, thickness, surface condition, flatness, and alignment should be defined together.

Chemical etching can be an effective solution for custom stainless steel optical gratings, especially when the design includes fine repeated structures, thin metal, complex apertures, or moderate production volumes.

About NKEYTO

NKEYTO is the international brand of Shenzhen Xintu Precision Hardware Co., Ltd., a precision metal manufacturing supplier based in Shenzhen, China.

We provide one-stop precision metal manufacturing services, including chemical etching, precision laser cutting, stamping, CNC machining, electroplating, and other customized surface treatments. Our capabilities support the development and production of precision metal components for industries such as semiconductors, electronics, optics, medical devices, and industrial applications.

With engineering support and flexible manufacturing capabilities, we help customers develop customized metal parts from prototypes to small and medium-volume production.

For technical evaluation or quotation, please feel free to contact:

Luna
Head of International Trade & Pre-Sales Technical Consultant
Email: luna@nkeyto.com
WhatsApp: +1 213 221 9094
Phone / WeChat: +86 135 5470 8126

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