Narrow-band acousto-optic tunable filtering in a two-mode fiber.

Area of Science:

• Photonics
• Optical Engineering
• Acousto-Optics

Background:

• Two-mode elliptical-core fibers support spatial modes crucial for advanced optical functions.
• Acousto-optic coupling offers a tunable mechanism for manipulating light propagation.
• Developing efficient optical filters is essential for wavelength-selective signal processing.

Purpose of the Study:

• To demonstrate a novel optical filter based on acousto-optic coupling.
• To characterize the performance of the filter in terms of bandwidth, polarization dependence, and insertion loss.
• To investigate the power requirements for achieving full acousto-optic mode conversion.

Main Methods:

• Utilized acousto-optic coupling between spatial modes in a two-mode elliptical-core fiber.
• Measured optical bandwidth, differential group delay, and polarization dependence.
• Quantified optical insertion loss and acousto-optic mode conversion efficiency.

Main Results:

• Achieved an optical bandwidth of 0.85 nm at 1090 nm, matching theoretical predictions.
• Observed a slight polarization dependence with a 0.28-nm passband peak difference.
• Demonstrated full acousto-optic mode conversion with only 8 mW of electrical input power.

Conclusions:

• The demonstrated acousto-optic filter in a two-mode fiber is effective for narrow-band optical filtering.
• The filter exhibits low insertion loss, dominated by bending losses, and negligible coupling losses.
• The low power requirement for mode conversion highlights the practical viability of this acousto-optic filtering approach.