ToF Module Cover Glass Design Requirements

Scope: The values in this article are SGI integration design recommendations, not universal industry standards. Final selection should be verified against the module, working distance, FOV, installation position, and complete product performance.

Why Does Cover Glass Matter to a ToF System?

In a ToF module or depth camera, the cover glass is located in front of the emitter and receiver. Its material, thickness, surface treatment, and assembly tolerance influence the infrared optical path, signal strength, and the consistency of the final depth data. It should therefore be evaluated as an integration component rather than only as an enclosure or appearance part.

Material and Structural Requirements

Reinforced Glass

Reinforced glass is the preferred baseline material for the cover glass. Its optical and mechanical properties are easier to control during product validation and mass production.

Thickness

A recommended thickness range is 0.55–1.0 mm. The final value still needs to be checked with the optical stack, mechanical strength, installation method, and depth performance.

Planar Structure

A planar cover glass is preferred. A curved surface should not be introduced only for industrial design purposes because curvature, thickness variation, and assembly error can change the optical path. Ordinary structural parts also do not provide the same optical precision as a lens, increasing validation and production-consistency risks.

When Plastic or Acrylic Is Considered

Plastic and acrylic materials may yellow or experience reduced infrared transmission over time and temperature changes. If a non-glass material is used, it must be validated at the actual operating band and against the required depth performance.

Infrared Transmittance at 940 nm

Lower cover-glass transmittance generally reduces signal strength and may shorten the effective operating distance of a ToF system. The recommended evaluation band is 940 nm ± 7 nm.

Application level	Recommended transmittance
Conventional obstacle avoidance and pose recognition	T ≥ 91%
High-performance face recognition	T ≥ 95%

These values should be confirmed together with the target working distance and application performance. A single transmittance value cannot replace complete system validation.

Surface Treatment and CG Partition

AF Coating

An anti-fingerprint coating is recommended for the outer surface. A water droplet contact angle of >110° is a useful reference for evaluating water repellency and contamination resistance. Fingerprints, water droplets, and dust can interfere with the infrared path and reduce point-cloud quality.

CG Partition

If contamination cannot be sufficiently avoided, a CG partition can separate the optical window from surrounding areas. The recommended slot or window width is ≥1.3 mm; the final dimension must be confirmed with the FOV, installation position, and mechanical structure.

Recommended Design Principles

Item	Recommendation
Material	Reinforced glass
Thickness	0.55–1.0 mm
Structure	Planar
Operating band	940 nm ± 7 nm
Conventional transmittance	T ≥ 91%
High-performance transmittance	T ≥ 95%
Surface treatment	AF coating
AF reference	Water droplet contact angle >110°
CG slot or window	≥1.3 mm
Assembly	VHB double-sided adhesive tape

Engineering Validation Checklist

• Verify infrared transmittance at 940 nm ± 7 nm rather than relying only on visible-light transmittance.
• Measure depth accuracy, effective range, noise, and point-cloud stability with the cover glass installed.
• Check the effects of fingerprints, water droplets, dust, and cleaning cycles on depth output.
• Confirm optical alignment, FOV, adhesive thickness, flatness, and assembly tolerance in pilot production.
• Repeat validation after temperature and environmental reliability tests, especially when using non-glass materials.

FAQ

What thickness is recommended for a ToF cover glass?

A baseline range of 0.55–1.0 mm is recommended. The final thickness should be selected with the optical and mechanical stack.

Why is a planar cover glass preferred?

A planar structure reduces optical-path changes caused by curvature and makes system calibration and production consistency easier to control.

What infrared transmittance should be used?

For 940 nm ± 7 nm, the reference is T ≥ 91% for conventional obstacle avoidance and pose recognition, and T ≥ 95% for high-performance face recognition.

Is AF coating necessary?

It is recommended because fingerprints and water droplets can affect the infrared path and depth output. A water droplet contact angle above 110° is a useful reference.

SGI Perspective

For ToF modules, RGB-D cameras, and 3D vision systems, cover glass should be managed as an optical and integration component. SGI can evaluate a cover-glass solution together with the ToF module's working distance, FOV, installation position, and application target, and support the complete validation path.

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