Superluminescent diode interferometer using sinusoidal phase modulation for step-profile measurement

Area of Science:

• Optical physics
• Metrology
• Interferometry

Background:

• Accurate measurement of optical path difference (OPD) exceeding a wavelength is challenging.
• Traditional interferometry methods often struggle with phase ambiguity for longer OPDs.

Purpose of the Study:

• To develop a novel interferometric technique for measuring optical path difference (OPD) longer than a wavelength.
• To achieve high-accuracy measurements in the nanometer range.
• To demonstrate the method's applicability for surface profiling.

Main Methods:

• Utilized the relationship between the degree of coherence (DCH) and optical path difference (OPD).
• Employed a superluminescent diode as the light source.
• Implemented sinusoidal phase-modulating interferometry to detect DCH and interference signal phase.

Main Results:

• Successfully measured OPDs longer than a wavelength with high accuracy (a few nanometers).
• Combined DCH-derived OPD with interference phase for unambiguous long-range measurement.
• Experimental validation confirmed the interferometer's effectiveness for step-profile measurements.

Conclusions:

• The proposed interferometer effectively overcomes the limitations of traditional methods for measuring long OPDs.
• The technique offers a robust solution for high-accuracy metrology, particularly in surface characterization.
• This approach provides a valuable tool for applications requiring precise dimensional measurements beyond the single-wavelength limit.