Nyquist Pulse Generation and Optical Signal Processing

Nyquist pulse generation underpins modern high-speed optical communications by producing sinc-shaped waveforms that occupy the minimum spectral bandwidth for a given data rate. These pulses, characterised by zero intersymbol interference when spaced at the Nyquist rate, enable transmission at rates approaching theoretical limits of spectral efficiency. Optical signal processing techniques—ranging from time-domain multiplexing and coherent detection to all-optical sampling and time-lens operations—exploit the properties of these pulses to manipulate, demultiplex and analyse ultrafast signals. Advances in photonic integration, frequency comb sources and low-power modulators have streamlined the generation and handling of Nyquist pulses, yielding compact and energy-efficient platforms. Together, these developments support applications in data-centre interconnects, analogue-to-digital conversion, high-resolution sensing and beyond, where maximising data throughput and minimising footprint are paramount.

Research from Nature Portfolio

Recent studies have demonstrated that frequency-time coherence between modulators can replace bulky pulse sources to achieve all-optical sampling. By driving two coupled modulators with an electrical tone, optical waveforms are convolved in frequency and time, enabling electrically tuneable bandwidth, repetition rate and time-shift control without mode-locked lasers. This approach paves the way for integration on silicon photonic platforms.

Innovations in integrated time lenses have eliminated the need for dispersion or nonlinear media. A high-Q silicon nitride microring resonator acts as a time magnifier, stretching signals up to a hundredfold. Coupled with frequency-time coherent sampling, the device captures amplitudes and phases of signals with bandwidths exceeding 100 GHz using low-bandwidth electronics, offering a route to compact, cost-effective ultrafast measurement systems.

Research from all publishers

A low-bandwidth electronic approach leverages orthogonal sampling with sinc-pulse sequences distributed over parallel branches to synthesise wide-band signals. This method reduces sampling rate and bandwidth requirements while enhancing effective number of bits, demonstrating generation of Nyquist-shaped data at tens of gigahertz with modest electronics.

Parallel optical sampling has also been applied to high-bandwidth signal detection. By dividing an optical input into multiple low-bandwidth channels via sinc-pulse sequences generated by a Mach-Zehnder modulator, the technique down-converts signals with minimal error, boosting measurement precision and increasing achievable effective bits with standard detectors.

In data-centre interconnects, a two-channel optical time-division multiplexed system using wide Nyquist pulses offers cost-effective >100 Gb/s links. The use of phase-alternating pulses enhances tolerance to chromatic dispersion, enabling 200 Gb/s, four-level PAM transmission over kilometres of standard fibre and facilitating monolithic photonic integration.

Nyquist Pulse Generation and Optical Signal Processing publication trend

The graph below shows the total number of articles in nyquist pulse generation and optical signal processing across all publications each year (not limited to Nature Index journals).

Technical terms

Nyquist pulse: A sinc-shaped waveform whose zero crossings align with symbol intervals, eliminating intersymbol interference at the Nyquist rate.

Spectral efficiency: The ratio of data rate to occupied bandwidth, expressed in bits per second per hertz.

Time lens: An optical device that imparts a quadratic phase modulation in time, analogous to a spatial lens, for temporal magnification or compression.

All-optical sampling: Measurement of an optical waveform’s amplitude and phase via interaction with a reference optical pulse train, avoiding electronic conversion at high bandwidths.

Optical time-division multiplexing (OTDM): A technique that interleaves multiple pulse-based data streams in time to increase aggregate symbol rate on a single wavelength.

Mach-Zehnder modulator: An interferometric device that imprints amplitude or phase information onto an optical carrier using an applied electrical signal.

References

1. Orthogonal Sampling-Based Broad-Band Signal Generation With Low-Bandwidth Electronics. IEEE Open Journal of the Communications Society (2023).
2. Two-Channel OTDM System for Data-Center Interconnects: A Review. Sensors (2023).
3. Frequency-time coherence for all-optical sampling without optical pulse source. Scientific Reports (2016).
4. Nonlinearity- and dispersion- less integrated optical time magnifier based on a high-Q SiN microring resonator. Scientific Reports (2019).
5. High-Bandwidth Arbitrary Signal Detection Using Low-Speed Electronics. IEEE Photonics Journal (2022).