Ultrafast electro-optic time-frequency fractional Fourier imaging at the single-photon level

Area of Science:

• Optics and Photonics
• Quantum Technologies
• Signal Processing

Background:

• The Fractional Fourier Transform (FRT) is a generalization of the Fourier Transform, crucial for time-frequency (TF) analysis.
• FRT finds applications in signal processing and quantum sensing, requiring low-noise TF operations.
• Existing FRT implementations often rely on noisy non-linear optical processes.

Purpose of the Study:

• To introduce a versatile, low-noise, single-photon-compatible optical implementation of the Fractional Fourier Transform.
• To demonstrate fast, all-electronic control over the FRT angle.
• To explore the trade-off between FRT angle and optical bandwidth.

Main Methods:

• Synthesized optical TF FRT using a sequence of spectral dispersers and an electro-optic modulator (EOM)-based time-lens.
• Employed state-of-the-art EOMs to avoid noise from non-linear optical interactions.
• Utilized precise radio-frequency signal control for fast, electronic adjustment of the FRT angle.

Main Results:

• Demonstrated FRT angles up to 1.63 radians for coherent, temporally separated pulses (11.5 ps width) at 800 nm.
• Achieved good agreement between simulated and measured spectra in both bright-light and single-photon regimes.
• Established a trade-off between maximal FRT angle and optical bandwidth, supporting up to 248 GHz.

Conclusions:

• The presented EOM-based FRT offers a low-noise, versatile, and electronically controllable platform for optical TF processing.
• The system shows excellent scalability potential with advancements in EOM integration.
• Envisages broad applications in classical and quantum all-optical TF processing, including sensing and filtering.