Fig. 1: Compact Kerr comb package based on FFPR. | Nature Communications

Fig. 1: Compact Kerr comb package based on FFPR.

From: Low-noise frequency synthesis and terahertz wireless communication driven by compact turnkey Kerr combs

Fig. 1: Compact Kerr comb package based on FFPR.The alternative text for this image may have been generated using AI.

a Frequency synthesizer driven by a compact Kerr comb source. b Transmission spectrum around 1550 nm of FFPR. Inset: picture of FFPR and microscope photo of the end face. c Ring-down trace of FFPR. Inset: fitted trace in logarithmic scale. d Quantum noise (QN) limit, pump noise (PN) limit, and thermorefractive noise (TN) limit of FFPR. The parameters used in the calculation are as follows: QLD = 4 × 103, β = 0.1, and αg = 2.529,30,31. n2 = 3 × 10−20 m2/W, effective mode field area Aeff = 112 μm2, group velocity dispersion (GVD) β2 = − 27 fs2/mm, Pin = 100 mW, λ = 1545 nm, n = 1.45. e Frequency noise spectral densities of the DFB laser with free-running state (red curve) and injection-locked to the FFPR (blue curve). 1 km of delay fiber is used. The dashed lines label the fundamental linewidth levels, indicating a noise reduction factor of over 105. f Schematic of our Kerr comb setup. Inset: picture of the package with a size of 85 × 90 × 25 mm. g Picture of the Kerr comb setup inside the package. ①, DFB laser diode (chip-on-carrier); ②, collimating lens; ③, a set of half-wave plates (HWP), Faraday rotator (FR), and polarizing beam splitter (PBS); ④, HWPs; ⑤, reflective mirrors; ⑥, FFPR; ⑦, silicon phase sheet; ⑧, beam splitter; ⑨, monitor photodetector. The solid blue, solid red, and dashed red curves represent for pump beam from the DFB laser diode, the comb beam from the FFPR, and the feedback beam to the DFB laser diode, respectively.

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