A diode-cladding-pumped mid-infrared passively Q-switched Ho 3+ -doped fluoride fiber laser using a reverse designed broad band semiconductor saturable mirror (SESAM) was demonstrated. Nonlinear reflectivity of the SESAM was measured using an in-house Yb 3+ -doped mode-locked fiber laser at 1062 nm. Stable pulse train was produced at a slope efficient of 12.1% with respect to the launched pump power. Maximum pulse energy of 6.65 µJ with a pulse width of 1.68 µs and signal to noise ratio (SNR) of ~50 dB was achieved at a repetition rate of 47.6 kHz and center wavelength of 2.971 µm. To the best of our knowledge, this is the first 3 μm region SESAM based Q-switched fiber laser with the highest average power and pulse energy, as well as the longest wavelength from mid-infrared passively Q-switched fluoride fiber lasers.

A diode-cladding-pumped mid-infrared passively Q-switched Ho 3+-doped fluoride fiber laser using a reverse designed broad band semiconductor saturable mirror (SESAM) was demonstrated. Nonlinear reflectivity of the SESAM was measured using an in-house Yb 3+-doped mode-locked fiber laser at 1062 nm. Stable pulse train was produced at a slope efficient of 12.1% with respect to the launched pump power. Maximum pulse energy of 6.65 µJ with a pulse width of 1.68 µs and signal to noise ratio (SNR) of ~50 dB was achieved at a repetition rate of 47.6 kHz and center wavelength of 2.971 µm. To the best of our knowledge, this is the first 3 μm region SESAM based Q-switched fiber laser with the highest average power and pulse energy, as well as the longest wavelength from mid-infrared passively Q-switched fluoride fiber lasers.

A nonlinear polarization rotation based all-fiber passively mode-locked Tm³⁺-doped fiber laser is demonstrated by using a 45° tilted fiber grating (TFG) as an in-line polarizer. The 45° TFG centered at 2000 nm with polarization dependent loss (PDL) of >12 dB at 1850 nm~2150 nm range was UV inscribed for the first time in SM28 fiber using a 244 nm Ar⁺ continuous wave laser and a phase mask with 25 mm long uniform pitch and titled period pattern of 33.7° with respect to the fiber axis. Stable soliton pulses centered at 1992.7 nm with 2.02 nm FWHM bandwidth were produced at a repetition rate of 1.902 MHz with pulse duration of 2.2 ps and pulse energy of 74.6 pJ. As increased pump power, the laser also can operate at noise-like regime with 18.1 nm FWHM bandwidth and pulse energy of up to 250.1 nJ. Using the same 45° TFG, both stable soliton and noise-like mode-locking centered at ~1970 nm and ~2050 nm, were also achieved by shortening and extending the length of Tm³⁺-doped fiber, respectively, exhibiting advantages of broadband and low insertion loss at 2 µm band.

Reconfigurable conductive pattern created by photoexcitation of high‐resistivity semiconductor provides a powerful approach to realize broadband spatial terahertz modulators (STM), which are highly demanded for constructing cost‐effective and compact terahertz (THz) system. Here a high performance all‐optical STM is proposed and realized based on silicon micropyramid arrays (Si‐MPA), which not only enhances the light harvesting across a broad wavelength range, but also greatly increases the active area for THz modulation. Upon illuminating the Si‐MPA by light with various wavelengths, modulation depth (MD) of four times larger than that of bare silicon is achieved. A maximum MD of 93.8% is obtained under 638 nm laser with a low power density of 1 W cm−2. Reconfigurable THz imaging system based on the Si‐MPA modulator and a single‐element detector is constructed, with which precise THz beam mapping and fast real‐time imaging with 225 pixels are demonstrated. This Si‐MPA‐based STM with large MD at low illumination power density is promising for many THz applications including imaging, beam shaping, holographic projection, etc.