Photonic chip-based soliton frequency combs covering the biological imaging window

Abstract

Dissipative Kerr solitons (DKS) in optical microresonators provide a highly miniaturised, chip-integrated frequency comb source with unprecedentedly high repetition rates and spectral bandwidth. To date, such frequency comb sources have been successfully applied in the optical telecommunication band for dual-comb spectroscopy, coherent telecommunications, counting of optical frequencies and distance measurements. Yet, the range of applications could be significantly extended by operating in the near-infrared spectral domain, which is a prerequisite for biomedical and Raman imaging applications, and hosts commonly used optical atomic transitions. Here we show the operation of photonic-chip-based soliton Kerr combs driven with 1 micron laser light. By engineering the dispersion properties of a Si3N4 microring resonator, octave-spanning soliton Kerr combs extending to 776 nm are attained, thereby covering the optical biological imaging window. Moreover, we show that soliton states can be generated in normal group–velocity dispersion regions when exploiting mode hybridisation with other mode families.

Influences of multiphoton absorption and free-carrier effects on frequency-comb generation in normal dispersion silicon microresonators

“…Such chip-level integratable microcavities with a high quality factor enable efficient nonlinear optical processes like cascaded four-wave mixing (FWM), which can lead to broadband frequency-comb generation from a continuous-wave laser. Kerr frequency combs have been observed in many platforms like MgF 2 resonators [5,6], diamond [7], silica disks [8,9], aluminum nitride [10,11], silicon nitride [12][13][14], and silicon [15,16], since it was first demonstrated in silica microtoroids [17]. Generally, frequency combs are generated in the anomalous dispersion region in these materials, which can be achieved by elaborate waveguide cross-section engineering.…”

“…Generally, frequency combs are generated in the anomalous dispersion region in these materials, which can be achieved by elaborate waveguide cross-section engineering. However, obtaining anomalous dispersion in an arbitrary central wavelength is still challenging, as material dispersion in the visible and near-infrared range is mostly normal due to ultraviolet absorption [12]. Moreover, materials like Si 3 N 4 have a strong absorption peak near 10 μm, which will strongly influence the optical properties at shorter wavelengths [18], that is, obtaining anomalous dispersion is challenging in the mid-infrared range (MIR).…”

Dissipative Kerr solitons in optical microresonators

“…Although Kerr combs have been known for more than one decade (7) [and have been reviewed in (6,(26)(27)(28)], the discovery of the DKS regime (9) has unlocked their full potential by providing a route to broadband and fully coherent microresonator-based frequency combs, overcoming earlier challenges of low coherence (29)(30)(31). Such soliton-based microcombs in chip-integrated microresonators have achieved low-power, octave-spanning frequency combs in various spectral windows that now encompass the near-infrared (32,33), telecommunication (34,35), and mid-infrared spectral window (18,36), with repetition rates from only a few gigahertz (37) to terahertz. The observation of DKS in microresonators yields a merging of soliton physics and high-precision frequency comb applications, stimulating a renaissance in dissipative soliton research and enabling many technological applications.…”

Chip-Based Frequency Combs for High-Resolution Optical Coherence Tomography

“…Si3N4 frequency combs have recently been recently generated using a reflective semiconductor amplifier as a pump source enabling a millimeter sized electrically pumped source 22 In order to enable a large imaging range using the optical comb as an OCT source of at least 2 mm (comparable with commercial OCT imaging range), we design the combs with a small spectral line spacing of 0.21 nm (corresponding to 38 GHz) using a large microresonator with a perimeter of 1.9 mm (see the Supplementary Materials). This perimeter is at least an order of magnitude larger than traditional high confinement micro-resonators 14,24,25 . In order to achieve sufficient optical power build up and enable comb generation in such a large cavity 8,26 , we rely on the extremely low loss platform recently demonstrated 27 .…”