Wavelength-selective directional couplers as ultrafast optical differentiators

Area of Science:

• Photonics and Optical Engineering
• Integrated Optics
• Ultrafast Signal Processing

Background:

• Ultrafast optical differentiation is crucial for high-speed signal processing.
• Existing methods face limitations in speed and integration.
• Directional couplers offer a promising platform for integrated photonic devices.

Purpose of the Study:

• To design and theoretically propose wavelength-selective directional couplers for ultrafast optical differentiation.
• To achieve differentiation in the femtosecond regime (> 10 THz bandwidth).
• To enable both 1st-order and 2nd-order differentiation using a single coupler design.

Main Methods:

• Designing directional couplers with dissimilar waveguides.
• Achieving wavelength matching of propagation constants at the center wavelength.
• Tuning the product of coupling coefficient and coupling length for desired differentiation order.
• Numerical simulations to evaluate performance.

Main Results:

• The proposed differentiators achieve wavelength-selective operation.
• A single coupler can be configured for 1st-order or 2nd-order differentiation.
• Numerical simulations show low differentiation errors (~2%).
• Energetic efficiency for 1st-order differentiation is approximately 11%.

Conclusions:

• The designed optical differentiators are suitable for ultrafast signal processing.
• The proposed design offers a feasible integrated differentiation unit.
• This work advances the development of high-performance optical signal processing circuits.