Abstract
A stable dual-wavelength Tm3+:Ho3+ co-doped fiber laser operating above 2 μm based on cascaded single-mode-multimode-single-mode (SMS) fiber structures is proposed and experimentally demonstrated. Based on the theoretical analysis of the transmission properties of the SMS fiber structure, two cascaded SMS fiber devices with different multimode fiber (MMF) lengths were used in our laser system, where one acted as a long-pass filter to suppress the competitive laser below 2 μm, and the other worked as a band-pass filter to select the specific operating wavelengths of the laser. Dual-wavelength operation of the fiber laser at 2002.8 and 2016.1 nm has been achieved in the experiment with a signal to a noise ratio up to 50 dB.
Highlights
Fiber lasers around 2 μm, corresponding to characteristic absorption lines of liquid water, greenhouse gases and some other chemical compounds, have attracted intense attention over the past few years [1,2,3]
We present the investigation of the transmission spectrum of an SMS fiber device in the 2 μm wavelength region and the demonstration of a dual-wavelength fiber laser operating above 2 μm by using two cascaded SMS fiber structures
This short wavelength lasing usually cannot be suppressed by adjusting the transmission peak of the SMS2 with different MMF lengths because an SMS fiber device with a long multimode fiber length is associated with a relatively small transmission peak spacing and small loss differences between these peaks, which is essential for dual-wavelength or multi-wavelength operation
Summary
Fiber lasers around 2 μm, corresponding to characteristic absorption lines of liquid water, greenhouse gases and some other chemical compounds, have attracted intense attention over the past few years [1,2,3]. As defined in Ref. 15, an SMS fiber structure with a fixed MMF length has the best self-imaging quality at the highest transmission peak, where the quasi-reproduction of the input field occurs. As the wavelength deviates from the transmission peak, the phase differences between excited modes at the end of MMF increase and the self-imaging quality decreases [15], which induces increased transmission loss This can be understood intuitively by looking at the transmission spectrum of a 50 mm long MMF SMS device, where the loss increases with the wavelength decreasing from 2050 to 2000 nm. As illustrated by the spectra shown in Fig. (d), we can combine the two SMS devices with MMF lengths of 50 and 200 mm in a cascaded fashion in a Tm3+:Ho3= co-doped fiber laser to achieve dual-wavelength operation above 2 μm
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