Silicon nitride chirped spiral Bragg grating with large group delay

Du, Z.; Xiang, Chao; Fu, Tingzhao; Chen, Minghua; Shen, Yang; Bowers, John E.; Chen, Hongwei

doi:10.1063/5.0022963

Cited by 36 publications

(16 citation statements)

References 36 publications

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“…One solution for on-chip dispersion management, required for pulse compression, is to replace long fiber with an integrated chirped Bragg grating 39 . Figure 4a shows the experimental set up, where we send the output of the cascaded EO modulators chip into the Bragg grating device via a circulator and characterize the pulse duration after reflection from the grating.…”

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confidence: 99%

Integrated femtosecond pulse generator on thin-film lithium niobate

Barton

Cheng

et al. 2022

Nature

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Integrated femtosecond pulse and frequency comb sources are critical components for a wide range of applications, including optical atomic clocks 1 , microwave photonics 2 , spectroscopy 3 , optical wave synthesis 4 , frequency conversion 5 , communications 6 , lidar 7 , optical computing 8 , and astronomy 9 . The leading approaches for on-chip pulse generation rely on mode locking inside microresonator with either third-order nonlinearity 10 or with semiconductor gain 11,12 . These approaches, however, are limited in noise performance, wavelength tunability and repetition rates 10,13 . Alternatively, sub-picosecond pulses can be synthesized without modelocking, by modulating a continuous-wave (CW) single-frequency laser using a cascade of electro-optic (EO) modulators 1,[14][15][16][17] . This method is particularly attractive due to its simplicity, robustness, and frequency-agility but has been realized only on a tabletop using multiple discrete EO modulators and requiring optical amplifiers (to overcome large insertion losses), microwave amplifiers, and phase shifters. Here we demonstrate a chip-scale femtosecond pulse source implemented on an integrated lithium niobate (LN) photonic platform 18 , using cascaded low-loss electro-optic amplitude and phase modulators and chirped Bragg grating, forming a time-lens system 19 . The device is driven by a CW distributed feedback (DFB) chip laser and controlled by a single CW microwave source without the need for any stabilization or locking. We measure femtosecond pulse trains (520 fs duration) with a 30-GHz repetition rate, flat-top optical spectra with a 10-dB optical bandwidth of 12.6 nm, individual comb-line powers above 0.1 milliwatt, and pulse energies of 0.54 picojoule. Our results represent a tunable, robust and low-cost integrated pulsed light source with CW-to-pulse conversion efficiencies an order of magnitude higher than achieved with previous integrated sources. Our pulse generator can find applications from ultrafast optical measurement 19,20 to networks of distributed quantum computers 21,22 .The ability to generate ultrashort, broadband and high-peak-power optical pulses on-chip has been a long-sought-after goal. The rapid advancement of low-loss nanophotonic waveguides has reduced the pulse energy for achieving nonlinear spectral broadening across octaves of bandwidth to sub-picojoules via supercontinuum generation 23 . However, all demonstrations to date rely on a table-top pulse laser source which increases the system complexity, size, and cost, and thus hinders practical applications. In addition, optical pulses can be generated via microresonator frequency comb sources (for short, microcombs) through coupling a continuous-wave laser into a highquality-factor microresonator 10 . However, microcombs are limited by their low efficiencies (ususally < 2%), comb-line power and high repetition rates, resulting in only tens of femtojoule pulse energies 10,24,25 . An alternative approach, based on compact and electrically pumped on-chip semiconductor mode...

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confidence: 99%

Integrated femtosecond pulse generator on thin-film lithium niobate

Barton

Cheng

et al. 2022

Nature

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“…The phase-modulation based design framework described in this paper has been recently adopted to synthesize on-chip discrete phase filters for dispersion compensation of both periodic 60 and aperiodic (e.g., telecom data) signals 61 using waveguide Bragg gratings (WBGs) in a silicon on insulator (SOI) platform. By implementing the phase-only filter using WBGs designed in a spiral geometry 62 , several orders of magnitude reduction in the overall device footprint, i.e., from few cm 2 to sub-mm 2 , could be realized. Towards circulator-free operation of reflective devices, a myriad of alternative solutions have been proposed to collect the reflected signal from Bragg gratings, such as contra-directional couplers 63 , asymmetric Y-splitters 64 , mode-converters assisted coupling elements 65 , etc.…”

Section: Discussionmentioning

confidence: 99%

All-fibre phase filters with 1-GHz resolution for high-speed passive optical logic processing

et al. 2023

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Photonic-based implementation of advanced computing tasks is a potential alternative to mitigate the bandwidth limitations of electronics. Despite the inherent advantage of a large bandwidth, photonic systems are generally bulky and power-hungry. In this respect, all-pass spectral phase filters enable simultaneous ultrahigh speed operation and minimal power consumption for a wide range of signal processing functionalities. Yet, phase filters offering GHz to sub-GHz frequency resolution in practical, integrated platforms have remained elusive. We report a fibre Bragg grating-based phase filter with a record frequency resolution of 1 GHz, at least 10× improvement compared to a conventional optical waveshaper. The all-fibre phase filter is employed to experimentally realize high-speed fully passive NOT and XNOR logic operations. We demonstrate inversion of a 45-Gbps 127-bit random sequence with an energy consumption of ~34 fJ/bit, and XNOR logic at a bit rate of 10.25 Gbps consuming ~425 fJ/bit. The scalable implementation of phase filters provides a promising path towards widespread deployment of compact, low-energy-consuming signal processors.

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“…Chirped Bragg grating waveguides exhibit low propagation loss, wide operation bandwidth, continuous delay tuning, and compact footprints [ 16 , 17 ]. Their tuning speed depends on the tunable laser and can reach the MHz level.…”

Section: Introductionmentioning

confidence: 99%

Integrated contra-directionally coupled chirped Bragg grating waveguide with a linear group delay spectrum

Gao¹,

Xu²,

Zhu³

et al. 2023

Front. Optoelectron.

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Due to the advantages of low propagation loss, wide operation bandwidth, continuous delay tuning, fast tuning speed, and compact footprints, chirped Bragg grating waveguide has great application potential in wideband phased array beamforming systems. However, the disadvantage of large group delay error hinders their practical applications. The nonlinear group delay spectrum is one of the main factors causing large group delay errors. To solve this problem, waveguides with nonlinear gradient widths are adopted in this study to compensate for the nonlinear effect of the grating apodization on the mode effective index. As a result, a linear group delay spectrum is obtained in the experiment, and the group delay error is halved. Graphical Abstract

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Silicon nitride chirped spiral Bragg grating with large group delay

Cited by 36 publications

References 36 publications

Integrated femtosecond pulse generator on thin-film lithium niobate

Integrated femtosecond pulse generator on thin-film lithium niobate

All-fibre phase filters with 1-GHz resolution for high-speed passive optical logic processing

Integrated contra-directionally coupled chirped Bragg grating waveguide with a linear group delay spectrum

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