In-depth reveal centroids – this optical adjustment field of “black technology”

1．Application Background:

Centering mounting of lenses is the basis of optical system mounting and a key step in determining imaging quality. The traditional optical system configuration is simple, the number of lenses is small, the mounting tolerance is loose, the precision requirement is low, and the passive mounting method of machining tolerance fit is often used. However, as the complexity of the optical system increases and the imaging quality requirements improve, the traditional method is no longer adequate. Medium and high optical systems have adopted the active mounting method, through the centering instrument and other precision instruments to fine-tune the position of the lens to ensure that the overall optical axis of the lens coaxiality to reach the highest.

2．Classification:

Centrifuges are mainly classified into three categories according to the working principle: transmission type, dual optical path type and reflection type.

Transmission type centrifuge: analyze the eccentricity by measuring the movement trajectory of the image point after the beam passes through the lens, but can only measure the comprehensive effect of the whole lens, and cannot measure individually for each surface.

Dual optical path centroid: The upper and lower optical paths measure the center of curvature of the upper and lower surfaces of the lens and calculate the deviation of the optical axis, but it is only applicable to single lens, and the calibration of the upper and lower optical paths is prone to systematic errors.

Reflective centroid: Taking the rotary axis system as the reference, through the self-collimator and the front mirror, it measures the movement track of the image point after the light beam is reflected from the lens surface, with high sensitivity, but there are shortcomings such as weak light source and fewer number of test surfaces.

Highlight: Opto Alignment Lens Laser Alignment System (LAS)

Opto Alignment’s LAS™ system uses a laser light source and reflective measurement principle, solving the many shortcomings of traditional centering instruments, and is especially suitable for high-precision mounting of advanced lenses. The system not only has high measurement accuracy, but also can be equipped with various bands of infrared light sources to complete the inspection and mounting of infrared lenses, and the switching of light sources can be accomplished by software operation, which greatly improves work efficiency and flexibility.

3.Opto Alignment: The Pearl of the Optical Manufacturing Industry

Founded in 1992 and a member of SPIE, Opto Alignment provides complete solutions from design to performance testing for the optical manufacturing industry. Its business covers a wide range of industries with customers in aerospace, astronomy, military, medical and semiconductor sectors, including NASA, Honeywell, Boeing and other companies. The LAS™ system also has a wide range of application examples in major optical manufacturing centers in China.

4.LAS System Principles and Technical Highlights

Measurement principle:

The LAS™ system measures the eccentricity between the optical axis of the mirror to be measured and the geometric axis of the outer edge by precisely aligning the optical axis of the laser light source with the rotary axis of the air-bearing. When the mirror is rotated, the CCD captures the image of the center of curvature (or mirror vertex) and draws a circle simultaneously, and finally calculates the optical axis deviation from the diameter of the drawn circle.

Technical highlights:

Light source and detector system: single-wavelength laser light source, high energy density of light source, adjustable light intensity, can easily mount more than 25 pieces of optical components. It supports the switching of light sources from near infrared to far infrared in various wavelengths to meet the detection needs of different lenses.

Rotary table and tilt adjustment: Adopting high-precision air-floating rotary table and tilt adjustment table of spherical goniometer working principle to ensure the measurement accuracy and efficiency.

Component Thickness and Air Gap Measurement: Equipped with the world’s top short coherence interferometer module, with an accuracy of up to 0.1um, it can test a variety of parameters of the internal components of the lens.

Intelligent software: supports Zemax and CodeV import, automatically plans display ranges, and provides a variety of ways to display measurement results, making it easy for operators to make quick judgments and adjustments.