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A novel and simple dual-band dual-sense circularly polarized (CP) metal-strip antenna is proposed. The antenna fed by a coplanar waveguide (CPW) with the advantages of uniplanar geometry and easier fabrication consists of a square slot and two split-ring elements. By appropriately introducing dual split-ring elements, the proposed dual-band CP design can easily be achieved. The two resonant frequencies are controlled by the size of the two split-ring elements. The proposed antenna prototype is fabricated and measured. Experimental results show that good CP radiation performances are obtained at both resonant frequencies. The proposed antenna has an impedance bandwidth (|S 11 | ≤ −10 dB) of 63.3% (2.0 ∼ 3.9 GHz), and the dual band circular polarization with left hand circular polarization (LHCP) at 2.2 GHz and the right hand circular polarization (RHCP) at 3.8 GHz are obtained. Also, the 3-dB axial ratio bandwidths are about 220 and 190 MHz at the lower and upper band, respectively.

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We demonstrate a mid-IR ZnGeP2 (ZGP) optical parametric oscillator (OPO) pumped by a dual-end-pumped actively acousto-optic Q-switched Ho:YAG ceramic laser. The maximum average output power of 35 W is obtained at a pulse repetition frequency of 20 kHz from the Ho:YAG ceramic laser. Under the maximum incident pump power of Ho:YAG ceramic laser, the maximum output power of 14 W is obtained from the ZGP OPO, corresponding to the slope efficiency of 49.6% with respect to the incident pump power. The wavelength can be tuned from 3.5 𝜇m to 4.2 𝜇m (signal), corresponding to 5.2-4.1 𝜇m (idler). The beam quality 𝑀 2 is less than 2.3 from the ZGP OPO.

We propose a 2.1 μm high energy dissipative soliton resonant (DSR) fiber laser system based on mode-locked seed laser and dual-stage amplifiers. In the seed laser, nonlinear amplifying loop mirror technique is employed to realize mode-locking. The utilization of in-band pump scheme and long gain fiber enables effective exciting 2.1 μm pulses. A section of ultra-high numerical aperture fiber (UHNAF) with normal dispersion and high nonlinearity and an output coupler with large coupling ratio are used to achieve high energy DSR. By optimizing the UHNAF length to 55 m, a 2103.7 nm, 88.1 nJ DSR with a 3-dB spectral bandwidth of 0.48 nm and a pulse width of 17.1 ns is obtained under proper intracavity polarization state and pump power. The output power and conversion efficiency are 0.233 W and 4.57 %, respectively, both an order of magnitude higher than previously reported holmium-doped DSR seed lasers. Thanks to the high output power and