According to the DNA encryption algorithm and the double-chaotic system which contains the optical chaos and the coupled map lattice chaotic system, a novel image encryption-then-transmission system is proposed. In the system, with identical chaotic injection from a master laser with two optical feedbacks, two slave lasers (SL1 and SL2) can output similar chaotic signals served as chaotic carrier to transmit image and used to generate the core part of the encryption scheme. A 128bit key is selected to generate the original value of the double-chaotic system, which decides the DNA complementary rule. The security analysis demonstrates the effectiveness of the proposed encryption system. The simulation results verify that the cryptosystem is enough to against the traditional attacks such as statistical attack, differential attack, brute force attack and entropy attack. Moreover, the encrypted image can be the optical message and transmitted in 10 km single mode fiber channel from SL1 to SL2. In order to ensure the security, we use the chaos masking technique to modulate and demodulate the optical message. Through numerical simulations of the cross-correlation function, the chaos synchronization between SL1 and SL2 is desired. The Q-factor is 9.559 and the bit error rate is 5.771$\times$10$^{-22}$.

The stable multipulse emission from an erbium-doped mode-locked fiber laser in dissipative soliton resonance (DSR) regime is numerically and experimentally investigated. It shows that in the multipulse operation of DSR, all pulses have identical characteristics. The number of these pulses is determined by the initial conditions, and keeps constant with the growth of pump power. Experimental results match well with the theoretical simulations. In the experiment, we obtain as high as 86 dual-wavelength DSR pulses, which have the same characteristics and are equally spaced in the cavity. Since the pulses behave similarly to harmonic mode-locking (HML), we call this phenomenon HML under DSR. By properly adjusting the polarization controllers, other numbers of multipulse emission in DSR region can be observed, which confirms that the number of DSR pulses depends on the initial conditions.

The pulse dynamics of harmonic mode-locking in a dissipative soliton resonance (DSR) region in an erbium-doped fiber ring laser is investigated at different values of anomalous dispersion. The fiber laser is mode-locked by a nonlinear polarization rotation technique. By inserting 0–200 m anomalous dispersion single-mode fiber in the laser cavity, the cavity length is changed from 17.3 to 217.3 m, and the corresponding dispersion of the cavity ranges from $-0.27$ to $-4.67{\mathrm{ps}}^2$. The observed results show that the tuning range of repetition rate under a harmonic DSR condition is highly influenced by the cavity dispersion. Furthermore, it is found that, by automatically adjusting their harmonic orders, the lasers can work at certain values of repetition rate, which are independent of the cavity length and dispersion. The pulses at the same repetition rate in different laser configurations have similar properties, demonstrating that each achievable repetition rate represents an operation regime of harmonic DSR lasers.

In this article, we demonstrate great potential of lightly-erbium(Er ³⁺ )-doped ZrF ₄ fiber in efficient power scaling at ∼2.8 μm, when excited at ∼1.7 μm. Core-pumped by a random Raman fiber laser at 1.69 μm, the 1.5 mol.% Er ³⁺ -doped ZrF ₄ fiber in a F-P cavity has experimentally yielded an output power of >6 W at 2.783 μm with a slope efficiency of up to 58.4% (with respect to the absorbed pump), close to its Stokes limit of 60.7% (1.69/2.783). To our knowledge, this is the highest efficiency of Er ³⁺ -doped ZrF ₄ fiber lasers in the mid-infrared. Further power scaling is only limited by the current pump power. Based on the validated numerical model, the dominant role of the excited state absorption (ESA) process (i.e., $^4{\mathrm{I}}_{13/2}{ \to }^4{\mathrm{I}}_{9/2}$ ) in exciting efficient ∼2.8 μm laser has been highlighted, and the resonant ground state absorption process (i.e., $^4{\mathrm{I}}_{15/2}{ \to }^4{\mathrm{I}}_{13/2}$ ) is also essential. The simulation results indicate that the pump wavelength closer to the ESA peak can yield a higher slope efficiency. In addition, heat load analyses via numerical modeling reveals that the $^4{\mathrm{I}}_{9/2}{ \to }^4{\mathrm{I}}_{11/2}$ multiphonon relaxation is the main heat source of the system. By taking fiber optical damage limit into account simultaneously, a high-power lightly-Er ³⁺ -doped ZrF ₄ fiber laser arrangement has been proposed, which theoretically enables 100-W-class output under a slope efficiency of >50% and a relatively low heat load.

The 3.92 μm laser pumped by 888 nm and 962 nm sources in a high concentration holmium-doped InF3 fiber is predicted and verified by simulation for the first time. Most parameters involved in the numerical model are taken from published results about the fundamental properties of holmium in fluoroindate glasses. The remaining unknown parameters are estimated from published 888 nm single-wavelength pumping experimental data. Simulated results indicate that the dual-wavelength pumping system can give a more powerful output than the single-wavelength pumping system when the total launched power is at the same level. The laser output as a function of the power of each source, as well as several macro factors such as fiber length and output coupler reflectivity, are investigated to find the best condition for higher output. To evaluate the importance and influence of the known interionic energy transfer processes, we analyze the corresponding laser output and changes of population densities of laser upper and lower levels by isolating each process. This investigation gives a preliminary insight into the 3.92 μm laser performance and interionic dynamics of the dual-wavelength pumping system in holmium-doped InF3 fibers.