Thermally expanded core (TEC) technology is an effective method of high-power fiber lasers. Miniaturization is also a major challenge for high-power lasers. We have proposed a miniaturized mode-locker based on TEC fiber and M o T e 2 -polyvinyl alcohol (PVA) film. The proposed mode-locker is consisting of two TEC ferrules, a piece of M o T e 2 -PVA film and a ceramic sleeve. The length of the proposed device is about 20 mm, and its outer diameter is about 2 mm. The relations between heating time, heating temperature, and mode field diameter (MFD) have been numerically simulated. The bending loss with respect to MFD has also been analyzed. The simulation results have revealed the trade-off relation between maximal tolerable intensity and low cavity loss, which means that there is an optimal MFD corresponding to optimal heating time and heating temperature. The proposed mode-locker has been applied in an integrated fiber laser, which has emitted ultrafast soliton with 3 times intensity larger than that of conventional sandwiched-type saturable absorber. The proposed mode-locker and fiber laser will find important applications in laser processing, laser ranging, and optical communication.

We present the detailed numerical analysis and characterization of SiGe/Si heterojunction electro-optic modulator at 2 μm, 4.3 μm, and 5 μm wavelengths. We investigate the band, the refractive index, and the carrier injection efficiency of SiGe/Si heterojunction PIN electrical structure. Numerical investigations are carried out on the key geometrical parameters, doping concentration, Ge content. The results show that the modulated voltage of SiGe/Si PIN heterojunction modulator is lower 50% than that of Si modulator under the same modulation effect. In order to eliminate the absorption losses of SiO2 in mid-infrared, the punch Mach–Zehnder optical structure is established and researched. The research present that the modulator has the short 500 µm phase shifters and the low VπLπ of 0.042 Vcm under forward bias voltage, and the extinction ratio is greater than 12.81 dB. The high-speed transmission characteristics are shown to have clean eye diagrams up to 40 Gbps in mid-infrared.