Method of making mosaic gratings by using a two-color heterodyne interferometer containing a reference grating

Area of Science:

• Optics and Photonics
• Metrology
• Nanotechnology

Background:

• Fabricating large gratings requires mosaicking smaller ones, which can introduce wavefront aberrations.
• Existing alignment methods lack precision, limiting the performance of large-area optical systems.

Purpose of the Study:

• To develop a precise method for mosaicking planar gratings without introducing wavefront aberrations.
• To enable the creation of large-area gratings from smaller subapertures.

Main Methods:

• A two-color heterodyne interferometric technique was proposed and demonstrated.
• Lateral and longitudinal phase errors were separated and eliminated using two wavelengths.
• The heterodyne scheme improved phase difference measurement accuracy.

Main Results:

• A perfect mosaic of two planar gratings was successfully fabricated.
• The method ensures the lateral gap is an integer multiple of the grating period.
• Experimental results showed a lateral alignment error below 1% for 0.72 micrometer period gratings.

Conclusions:

• The proposed two-color heterodyne interferometry is an effective method for high-precision grating mosaicking.
• This technique eliminates wavefront aberrations, allowing subaperture gratings to substitute for larger ones.
• The demonstrated accuracy paves the way for advanced large-area optical component fabrication.