Abstract
Optical frequency combs (OFCs) generated in microresonators with whispering gallery modes are demanded for different applications including telecommunications. Extending operating spectral ranges is an important problem for wavelength-division multiplexing systems based on microresonators. We demonstrate experimentally three spectrally separated OFCs in the C-, U-, and E-bands in silica microspheres which, in principle, can be used for telecommunication applications. For qualitative explanation of the OFC generation in the sidebands, we calculated gain coefficients and gain bandwidths for degenerate four-wave mixing (FWM) processes. We also attained a regime when the pump frequency was in the normal dispersion range and only two OFCs were generated. The first OFC was near the pump frequency and the second Raman-assisted OFC with a soliton-like spectrum was in the U-band. Numerical simulation based on the Lugiato–Lefever equation was performed to support this result and demonstrate that the Raman-assisted OFC may be a soliton.
Highlights
Microresonators with whispering gallery modes (WGMs) are attractive for various applications, including classical and non-classical ones [1,2]
The first Optical frequency combs (OFCs) was near the pump frequency and the second Raman-assisted OFC with a soliton-like spectrum was in the U-band
We have obtained the first OFC near the pump frequency in the C-band, the second Stokes OFC in the U-band and beyond, and the third anti-Stokes OFC in the E-band
Summary
Microresonators with whispering gallery modes (WGMs) are attractive for various applications, including classical and non-classical ones [1,2]. The OFC generation in microresonators, demonstrated for the first time in 2007 [14], has greatly expanded the application range of such photonic devices [1]. They are used in coherent communication [15,16], dual-comb spectroscopy [17], optical atomic clock [18], ultrafast optical ranging [19], and in many more areas. On-chip microresonators belong to one of the most actively developing areas [20], silica microresonators are of great interest, since they are a very convenient platform for the development of micro-photonic devices. To protect silica microresonators from air flows, dust, and high humidity, they are portably and robustly packaged [22]
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