We demonstrated tunable Q-switched and mode-locked Ho3+/Pr3+-codoped ZBLAN fiber laser in mid-infrared region using single-walled carbon nanotubes. Both stable Q-switched pulses from 2837.6 to 2892.6 nm and modelocked pulses from 2836.2 to 2872.6 nm were achieved.
An optically tunable radio frequency (RF) downconversion scheme is proposed based on an optoelectronic oscillator (OEO) incorporating a tunable microwave photonic filter. The local oscillation (LO) is generated in the OEO, whose frequency is varied through simply tuning the frequency difference between the optical carrier and the reflection notch of a phase-shifted fiber Bragg grating (PS-FBG). The LO and the input RF signal are combined and added to the OEO loop by a single phase modulator. The RF modulation sidebands and one of the LO modulation sidebands are extracted out of the OEO loop by the PS-FBG and sent to a photo-detector to achieve RF downconversion. In the experiment, optically tunable LOs in the frequency range of 6 GHz to 15 GHz are generated, and RF signals in the frequency range of 7 GHz to 16 GHz are successfully down-converted to intermediate frequency band around 1 GHz. The proposed scheme has the potential to cover a frequency range beyond 40 GHz.
We propose and demonstrate a self-calibrating approach to measure the magnitude response of a broadband electro-optic intensity modulator based on photonic downconversion sampling. A low-repetition-rate mode-locked laser is employed to sample a swept-frequency microwave signal via the modulator under test, where the magnitude response of the modulator is calculated from the relative intensity of the Fourier frequency components in the first Nyquist frequency range and the direct current. In the experiment, magnitude response and half-wave voltage versus frequency of a commercial Mach-Zehnder electro-optic modulator within a frequency range of 0-40 GHz is successfully measured using the proposed method.