A Faster, More Accurate Way of Characterizing Cube Beamsplitters

Significance of the Topic

Cube beamsplitters are fundamental components in optical systems, enabling beam splitting for imaging, polarization control, interferometry and telecommunications. Accurate characterization of their transmission, reflection and absorptance spectra is vital both at the design stage and in quality control of volume production.

Objectives and Study Overview

This application note demonstrates an in situ, fully automated approach to measure transmission (T), reflection (R) and calculate absorptance (A) of a dielectric cube beamsplitter without moving the sample. The goal is to eliminate measurement artifacts related to angle of incidence variations and coating nonuniformity, and to achieve high throughput for routine QA/QC workflows.

Methodology and Instrumentation

The study employed a 25 mm cubic beamsplitter coated with alternating titanium dioxide and silicon dioxide layers and bonded with optical adhesive. Measurements were performed on an Agilent Cary 7000 Universal Measurement Spectrophotometer (UMS). Independent motorized control of the sample orientation and detector position allowed:

• Transmission scans at 0° angle of incidence,
• Reflection scans with the detector rotated 90° about the sample,
• Spectral range from 500 nm to 720 nm with 1 nm intervals, 5 nm bandwidth and 0.5 s averaging time.

Used Instrumentation

• Agilent Cary 7000 UMS variable-angle absolute reflectance and transmittance spectrophotometer

Main Results and Discussion

The system provided self-consistent T and R data at the same sample location, yielding reliable absorptance profiles. Key findings at the design wavelength of 632.8 nm are:

• s-polarization: Transmission = 0.04 %, Reflection = 99.34 %
• p-polarization: Transmission = 98.19 %, Reflection = 0.11 %
• Absorptance remains below 0.30 % across the measured spectrum

This performance meets the specified targets (<0.2 % T for s-polarized light and >98 % T for p-polarized) and highlights the benefit of measuring T and R without sample movement.

Benefits and Practical Applications of the Method

The automated Cary 7000 UMS workflow delivers:

• High reproducibility by avoiding angle and positioning artifacts,
• Increased productivity through unattended batch measurements,
• Detailed spectral insight for both substrate and coating performance.

These advantages support both optical design teams and QA/QC laboratories in ensuring consistent quality of beamsplitter components.

Future Trends and Potential Uses

Advancements may include real-time inline QC integration, expansion to broader UV–NIR wavelength ranges, application to other optical thin-film architectures, and coupling with predictive modeling or AI-driven analysis to further streamline component qualification.

Conclusion

The Agilent Cary 7000 UMS offers a robust, accurate and efficient solution for characterizing cube beamsplitters. By enabling simultaneous transmission and reflection measurements at a fixed sample position, it overcomes common sources of error and supports high-volume, high-precision optical component testing.

Reference

1. Amotchkina T. V. et al. Oscillations in Spectral Behavior of Total Losses (1 − R − T) in Thin Dielectric Films. Optics Express 2012, 20(14), 16129–16144.