lithium niobate / 06 Devices / 6.6
6.6 Frequency combs and frequency shifters
L1 Phenomenon
A comb is light made of many evenly spaced colors. Drive a low-loss LN ring with a microwave at exactly its round-trip frequency and each pass adds sidebands, building hundreds of lines; pump a ring hard enough and the Kerr effect forms a soliton whose spectrum is a comb.
Resonant EO comb, through port, critical coupling, FSR 10 GHzmodel; 1201 lines computed (±6 THz)
lines above −60 dB 111span 8.8 nm
Dispersion
Model derived: lumped phase modulation β = πV/Vπ per round trip at exactly one FSR (round-trip recursion; with dispersion, coupled-mode sideband equations). FSR and D2 are templates. A stronger drive flattens the triangular envelope on the dB axis, so more lines clear −60 dB. Bracket: > 900 lines at about 10 GHz reported by Zhang 2019 reported, a reference, not a fit.
Lines within 60 dB
- Optical span
- 8.8 nm
Dispersion
A stronger drive flattens the triangular envelope on the dB axis, so more lines clear −60 dB. Model derived: through port, critical coupling, lumped phase modulation β = πV/Vπ per round trip at exactly one FSR (round-trip recursion; with dispersion, coupled-mode sideband equations); FSR 10 GHz and D2 are templates template. Bracket: > 900 lines at about 10 GHz reported by Zhang 2019 reported, a reference, not a fit. Lines at telecom wavelengths drawn in false color.
L2 Devices and values
| Device | Value | Source |
|---|---|---|
| Resonant EO comb, microring | > 900 lines at about 10 GHz, wider than the L band | reported |
| Coupled-ring EO comb | 30% efficiency, 132 nm span, 336 fs | reported |
| EO time-lens pulse source | 520 fs, 30 GHz, 0.54 pJ | reported |
| EO comb in TFLT (not LN) | > 450 nm (> 60 THz), > 2,000 lines, triply resonant | reported |
| EO frequency shifter (coupled rings) | up to 28 GHz at about 90% on-chip efficiency; cascaded 119.2 GHz from 29.8 GHz drive | reported |
| Acousto-optic frequency shifter | 3 GHz, > 30 dB carrier suppression | reported |
| First LN Kerr soliton | self-starting, bidirectional switching via photorefraction | reported |
| Near-octave soliton | 4/5 octave, 335 GHz repetition rate | reported |
| Octave-spanning soliton | octave, Raman suppressed | reported |
| Photorefraction-assisted soliton | single soliton > 13 h without feedback | reported |
L3 Model and open values
- EO comb line power falls off with line index at a slope set by round-trip loss relative to modulation index; dispersion limits the span. The figure uses the round-trip recursion of a ring phase-modulated at one FSR [Zhang et al. 2019].
- The n2 of LN tabulated in Zhu 2021 has no traced primary measurement; no n2 value is given.
Sources
| Ref | Title | Link |
|---|---|---|
| Gong et al. 2020 | Near-octave lithium niobate soliton microcomb | doi:10.1364/OPTICA.400994 |
| He et al. 2019 | Self-starting bi-chromatic LiNbO 3 soliton microcomb | doi:10.1364/OPTICA.6.001138 |
| Hu et al. 2021 | On-chip electro-optic frequency shifters and beam splitters | doi:10.1038/s41586-021-03999-x |
| Hu et al. 2022 | High-efficiency and broadband on-chip electro-optic frequency comb generators | doi:10.1038/s41566-022-01059-y |
| Shao et al. 2020 | Integrated microwave acousto-optic frequency shifter on thin-film lithium niobate | doi:10.1364/OE.397138 |
| Song et al. 2024 | Octave-spanning Kerr soliton frequency combs in dispersion- and dissipation-engineered lithium niobate microresonators | doi:10.1038/s41377-024-01546-7 |
| Wan et al. 2023 | Photorefraction‐Assisted Self‐Emergence of Dissipative Kerr Solitons | doi:10.1002/lpor.202300627 |
| Yu et al. 2022 | Integrated femtosecond pulse generator on thin-film lithium niobate | doi:10.1038/s41586-022-05345-1 |
| Zhang et al. 2019 | Broadband electro-optic frequency comb generation in a lithium niobate microring resonator | doi:10.1038/s41586-019-1008-7 |
| Zhang et al. 2025 | Ultrabroadband integrated electro-optic frequency comb in lithium tantalate | doi:10.1038/s41586-024-08354-4 |