A continuously tunable multi-tap complex-coefficient microwave photonic filter based on a tilted fiber Bragg grating

Area of Science:

• Photonics
• Optical Engineering
• Signal Processing

Background:

• Tilted fiber Bragg gratings (TFBGs) exhibit unique coupling coefficient properties.
• Kramers-Kronig relations link coupling coefficients and phase shifts in optical systems.
• Microwave photonic filters are crucial for high-frequency signal manipulation.

Purpose of the Study:

• To implement a multi-tap continuously tunable microwave photonic filter with complex coefficients.
• To leverage the linear phase shift property of TFBGs for filter applications.
• To demonstrate a novel method for generating complex coefficients in photonic systems.

Main Methods:

• Utilizing the linearly increasing coupling coefficients of TFBG cladding-mode resonances.
• Introducing linearly increasing phase shifts to optical carriers via TFBG.
• Translating phase shifts to microwave signals by optical carrier beating.
• Achieving tunability through optical pumping of an Er/Yb co-doped TFBG.

Main Results:

• Successfully generated complex coefficients with linearly increasing phase shifts.
• Demonstrated a proof-of-concept multi-tap microwave photonic filter.
• Achieved frequency tunable ranges of 150 MHz for a three-tap filter and 120 MHz for a four-tap filter.

Conclusions:

• The TFBG-based approach enables the first implementation of a continuously tunable microwave photonic filter with complex coefficients.
• The method effectively translates optical phase shifts into microwave signal complex coefficients.
• This work presents a promising technique for advanced tunable photonic filter design.