Single-longitudinal-mode (SLM) lasers have attracted much interest due to applications in an optical fiber sensor system[
Chinese Optics Letters, Volume. 15, Issue 10, 100601(2017)
Tunable single-longitudinal-mode SOA-based fiber laser based on the spectral narrowing effect in a dispersion-shifted fiber
A tunable single-longitudinal-mode (SLM) semiconductor optical amplifier (SOA)-based fiber laser based on a dispersion-shifted fiber (DSF) is proposed and successfully demonstrated. SLM operation is obtained due to the spectral narrowing effect resulting from inverse four-wave mixing in a DSF. A tunable optical filter performs wavelength selection function. By inserting a length of DSF in the laser cavity, SLM lasing can possibly be obtained when laser oscillation is stably established after traveling through the DSF many roundtrips. Stable tunable SLM oscillation with a signal-to-noise ratio as high as 65 dB over a wavelength range of about 35 nm is achieved experimentally, and each spectral linewidth is less than 6.5 kHz.
Single-longitudinal-mode (SLM) lasers have attracted much interest due to applications in an optical fiber sensor system[
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The configuration of the proposed SLM SOA-based fiber laser is shown schematically in Fig.
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Figure 1.Schematic configuration of the proposed SLM SOA-based fiber laser.
The DSF is the key component in the laser cavity, which is used to ensure SLM lasing. As presented in Ref. [
In the experiment, by the adjustment of the PCs and the TOF, tunable single frequency output with a wavelength ranging from 1534.96 to 1570.02 nm has been achieved. Figure
Figure 2.(Color online) Spectra of the laser output with wavelength ranging from 1534.96 to 1570.02 nm.
Figure 3.(a) Optical spectrum and (b) RF spectrum of the laser output.
The output spectrum linewidth was measured using the self-heterodyne method with a length of 40 km delayed single mode fiber (SMF) and an acoustic optical modulator (AOM) of 210 MHz frequency shifting. A typical delayed self-heterodyne RF spectrum (the black line) and the corresponding Lorentz curve fitting (the red line) are shown in Fig.
Figure 4.(Color online) Delayed self-heterodyne RF spectrum of the laser output.
As a comparison, we also measured the RF spectrum at the output of the SOA-based fiber laser when the DSF in the laser cavity was replaced by an SMF with the same length. As can be seen in Fig.
Figure 5.Beat notes observed by measuring the RF spectrum at the output of the laser when DSF was replaced with SMF.
Note that in the experiment, we used three different lengths of DSF (1.3, 3.6, and 5 km DSF), and the 5 km DSF gave the best result. This could be explained from the inverse FWM effect as discussed in Ref. [
Another point we have to note is that an SOA instead of an EDF amplifier (EDFA) is used as the gain medium, since it can greatly shorten the laser cavity and, consequently, increase the longitudinal-mode spacing, which makes it easier to obtain the SLM operation.
In conclusion, a tunable SLM SOA-based fiber laser based on a DSF is proposed and successfully demonstrated. The spectral narrowing effect that results from an inverse FWM in the DSF is verified experimentally. The use of the DSF in a fiber ring laser to achieve SLM lasing is then demonstrated. The results show stable SLM oscillation with an SNR as high as 65 dB and a spectral linewidth of less than 7 kHz over a tuning wavelength range of about 35 nm. The proposed SOA-based fiber laser may offer potential applications in optical measurement and optical telecommunications due to its simple configuration and wide tunability.
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Zhenkun Shen, Lin Wang, Yuan Cao, Xudong Wang, Xinhuan Feng, Bai-Ou Guan, "Tunable single-longitudinal-mode SOA-based fiber laser based on the spectral narrowing effect in a dispersion-shifted fiber," Chin. Opt. Lett. 15, 100601 (2017)
Category: Fiber Optics and Optical Communications
Received: May. 2, 2017
Accepted: Jun. 16, 2017
Published Online: Jul. 19, 2018
The Author Email: Xinhuan Feng (eexhfeng@gmail.com)