Abstract
We propose and demonstrate a high-performance wavelength-switchable erbium-doped fiber laser (EDFL), enabled by a figure-8 compound-ring-cavity (F8-CRC) filter for single-longitudinal-mode (SLM) selection and a polarization-managed four-channel filter (PM-FCF) for defining four lasing wavelengths. We introduce a novel methodology utilizing signal-flow graph combined with Mason's rule to analyze a CRC filter in general and apply it to obtain the important design parameters for the F8-CRC used in this paper. By combining the functions of the F8-CRC filter and the PM-FCF assisted by the enhanced polarization hole-burning and polarization dependent loss, we achieve the EDFL with fifteen lasing states, including four single-, six dual-, four tri- and one quad-wavelength lasing operations. In particular, all the four single-wavelength operations are in stable SLM oscillation, typically with a linewidth of <600 Hz, a RIN of ≤-154.58 dB/Hz@≥3 MHz and an output power fluctuation of ≤±3.45%. In addition, all the six dual-wavelength operations have very similar performances, with the performance parameters close to those of the four single-wavelength operations, superior to our previous work and others' similar work significantly. Finally, we achieve the wavelength-spacing tuning of dual-wavelength operations for photonic generation of tunable microwave signals, and successfully obtain a signal at 23.10 GHz as a demonstration.
Highlights
Single-longitudinal-mode (SLM) erbium-doped fiber laser (EDFL) in C-band (1530–1565 nm) has been adopted or anticipated as the preferred light source for many important applications, due to its outstanding inherent merits such as low intensity and phase noise, narrow linewidth, high beam quality, and excellent compatibility with fiber optical systems
2 showing the enlarged maximum transmission peak in the third channel in (b-2). (c-1) Simple ring erbiumdoped fiber laser (EDFL) model for verifying the capability of figure-8 compound-ring-cavity (F8-CRC) filter combining with the polarization-managed four-channel filter (PM-FCF) to select SLM theoretically; (c-2) Simulated laser oscillating for 20 loops for the model in (c-1) but without considering the gain saturation effect and mode competition in EDF induced by homogeneous broadening effect; Inset-3 showing the enlarged laser oscillating in the first channel in (c-2)
When the pump power of 980 nm LD was beyond the threshold, we achieved fifteen lasing states, including four single, six dual, four tri- and one quad-wavelength operations through adjusting the TL-polarization controller (PC) and drop-in pol7a0.r9i6z%ation controller (DI-PC) carefully to tune the polarization-axes of the coiled EDF and the state of polarization (SOP) of light inside the laser cavity
Summary
Single-longitudinal-mode (SLM) erbium-doped fiber laser (EDFL) in C-band (1530–1565 nm) has been adopted or anticipated as the preferred light source for many important applications, due to its outstanding inherent merits such as low intensity and phase noise, narrow linewidth, high beam quality, and excellent compatibility with fiber optical systems. The polarization control is an excellent way to achieve the switching among different operation states of MWEDFLs, especially combining it with a polarization-dependent multi-channel filter, such as a high-birefringence FBG (HB-FBG) [23]. In the previous work [24], we designed a four-channel superimposed HB-FBG (SI-HB-FBG) reflecting filter, and used it in a four-wavelength-switchable EDFL (4WS-EDFL) to obtain switching operation among 15 lasing states, including single-, dual-, tri- and quad-wavelength. There is only one report on a four-channel filter made of two cascaded HB-FBGs for achieving a switchable multi-wavelength fiber laser [51], the authors used a polarization controller (PC) between two HB-FBGs to rotate the polarization Their approach is complicated and unstable, and has the issue that the laser outputs are all not in SLM oscillation. The superiority for tri- and quad-wavelength switchable operations based on the PM-FCF is validated, in comparison with what is achieved with the SI-HB-FBG
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