In the optical industry, the collimator serves as the core device for calibrating and testing optical systems, known as the “ruler of light”. It converts diverging light into strictly parallel beams and establishes reference standards for precision measurement. From basic laboratory testing to extreme challenges in space exploration, five mainstream configurations solve precision problems for diverse scenarios with distinctive designs, acting as a vital link between scientific research and engineering applications.

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1.Transmissive Collimator: Wide-Field Reference for Visible Light

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Working Principle: A double cemented or double separated lens group converges the light source, and a reticle carries reference scales to generate parallel beams within the visible light band (380-780 nm).

Wide Range of Applications: The transmissive collimator is designed to deliver large-aperture parallel beams with versatile functions. Equipped with interchangeable reticles, dedicated accessories, viewing microscopes and auxiliary telescopes, it can fulfill various testing and calibration tasks.

Chromatic Aberration Optimization: Combinations of different optical glasses eliminate chromatic aberration, keeping the wavelength deviation Δλ below 5 nm in the visible spectrum and ensuring superior image quality.

Application Limitations: Self-weight of large-aperture lenses (＞200 mm) tends to cause optical axis offset. Special materials such as germanium single crystal and fused silica are required for infrared and ultraviolet bands.

Typical Scenarios: Assembly and alignment of optical instruments; measurement of back focal length and focal length for lenses and objectives; resolution testing and image quality evaluation of lenses, prisms, plane mirrors and various optical objectives.

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2.On-Axis Reflective Collimator: Classic Choice for Industrial Calibration

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Optical Design: A parabolic primary mirror collimates light, while a planar or hyperbolic secondary mirror folds the optical path. All optical axes are strictly coaxial, and the reflective structure completely eliminates chromatic aberration.

Technical Advantages: Compact design for long focal lengths. With an F/10 long focal ratio, an effective focal length of 10 meters is realized within a 1-meter barrel, ideal for production line integration and space-constrained environments.

Easy Alignment: Coaxial symmetry simplifies assembly and adjustment. The optical axis deviation can be controlled within 10 μrad, meeting the requirements for rapid industrial calibration.

Performance Deficiency: Central obscuration causes 20%~30% luminous flux loss, which reduces the signal-to-noise ratio (SNR) in low-illumination environments.

Industrial Applications: Light distribution curve testing for automotive LED lamps (parallelism error ＜1.5°); beam collimation calibration for laser cutting machines (divergence angle ＜0.5 mrad at 2 meters), guaranteeing precision in industrial manufacturing.

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3.On-Axis Cassegrain Collimator: Folded Optical Core for Aerospace Remote Sensing

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Core Structure: Adopting a Cassegrain dual-reflection system, light exits through the central aperture of the primary mirror after two reflections. Its effective focal length can reach more than 15 times the aperture diameter.

Precision Breakthrough: Ultra-high resolution inherited from Hubble Telescope design, reaching 0.05 arcseconds (the resolution limit of human eyes is 60 arcseconds). It can identify text on a coin 30 kilometers away, supporting 0.5-meter ground sampling distance for high-resolution satellites.

Space Efficiency: The folded optical path reduces barrel length by 60%. For instance, a 1.2-meter-aperture unit achieves an effective focal length of 18 meters for satellite payloads, simulating long-distance targets in deep space exploration.

Engineering Challenges: Diffraction caused by the secondary mirror support is suppressed by carbon fiber trusses. The assembly and alignment precision is required up to λ/50 (approximately 12.6 nm).

Cutting-edge Applications: Modulation Transfer Function (MTF) calibration for satellite remote sensing payloads, anti-glare testing for rover navigation cameras, ensuring clear imaging in extreme environments.

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4.Off-Axis Reflective Collimator: Unobstructed Beam for High-Precision Scenarios

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Design Innovation: The mirror group is placed off the optical axis to completely eliminate central obscuration. Aspherical or freeform primary mirrors generate fully unobstructed parallel beams.

Performance Advantages: High contrast output with edge field illumination uniformity above 95%. It meets the 1:10000 contrast requirement of 193 nm light sources for ASML lithography tools and ensures lithography accuracy for 22 nm linewidth.

Full-Spectral Compatibility: Covers deep ultraviolet (193 nm) to mid-infrared (10.6 μm) without material replacement, serving as core equipment for semiconductor wafer inspection (50 nm defect detection).

Manufacturing Threshold: The surface figure error of mirrors must be within 6.3 nm (λ/100), which relies on nano-precision magnetorheological polishing (surface roughness Ra ＜ 1 nm).

Key Scenarios: Wavefront aberration testing (＜λ/10) for AR/VR optical modules, field curvature correction for EUV lithography objectives, advancing nano-scale precision in consumer electronics and chip manufacturing.

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5.Off-Axis Cassegrain Collimator: Alignment Specialist for Extreme Environments

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Technology Integration: Off-axis Cassegrain configuration with freeform optimized primary and secondary mirrors, combined with an active optical compensation system to break traditional performance limits.

Disruptive Advantages: Ultra-wide distortion-free field of view, equivalent to projecting a uniform light spot at a distance of 1 kilometer, suitable for testing large-field optical systems.

Extreme Environment Adaptability: Zerodur primary mirror (coefficient of thermal expansion ≤ 1×10⁻⁶/℃) with an 18-point flexible support structure maintains wavefront error below λ/20 under temperature variation from -40℃ to +80℃, adapting to space vacuum and extreme temperature conditions.

Engineering Excellence: The rear support structure of the primary mirror limits gravitational deformation within 5 nm (roughly 1/20 of a human hair’s diameter). It supports thousand-kilometer-level beam alignment for satellites (accuracy ≤ 5 μrad) and ensures efficient reception of single-photon signals in quantum communication.

Cutting-edge Applications: Exoplanet imaging (stellar glare suppression ratio up to 10⁹:1) and calibration for deep space exploration payloads, setting the precision limits for space communication and astronomical observation.