During the last two decades, PT‐based relaxor ferroelectric crystals such as (1− x )Pb(Zn 1/3 Nb 2/3 )O 3 – x PbTiO 3 (PZN–PT), (1− x )Pb(Mg 1/3 Nb 2/3 )O 3 – x PbTiO 3 (PMN–PT), and (1− x − y )Pb(In 1/2 Nb 1/2 )O 3 – y Pb(Mg 1/3 Nb 2/3 )O 3 – x PbTiO 3 (PIN–PMN–PT or PIMNT) crystals, are widely studied due to their huge piezoelectric properties and super‐high electro‐mechanical coupling factors. They have excellent properties with compositions around the morphotropic phase boundary (MPB). It is gratifying that the PT‐based relaxor crystals are replacing traditional PZT piezo‐ceramics in many application fields. Most ferroelectrics with oxygen‐octahedral structure, which show outstanding electro‐mechanical properties, also have excellent optical performances. Ferroelectric single crystals with large electro‐optic (EO) modulation are widely applied in laser communication devices. For the practical applications, the knowledge of detailed optical parameters is desirable. This paper tries to show a global review on the optical properties of PT‐based relaxor ferroelectric crystals. In the present review, optical properties of the crystals are systematically summarized, including refractive index dispersion, transmittance, band gap, EO, acousto‐optic, and photorefractive properties. These properties change with the crystal composition, orientation, and poling condition. The purpose of the review is to provide a resource for the researchers who are concerned with basic physical investigation or optical device applications of the PT‐based relaxor ferroelectric crystals.

Chromium-doped CaMgSi2O6 ([Formula: see text]: CMS) fluorescent ceramics with various concentrations were fabricated using solid-state reaction technique. All the samples were sintered at 1250[Formula: see text]C for 3 h. Analysis of microstructure of the Cr[Formula: see text]: CMS ceramics shows homogeneous structure with grain size distributions between 0.86 nm and 2.26 nm. Luminescent spectra of the ceramics show two emission peaks, a strong peak at 872 nm and a weak peak at 960 nm because of [Formula: see text] transition of the Cr[Formula: see text] ions. Intensity of the emission peaks increases with Cr[Formula: see text] concentration, reaches maximum with 0.1 at.% Cr[Formula: see text], then decreases with higher Cr[Formula: see text] concentration. Owing to the differences in crystal field strength, the luminescent properties of the Cr[Formula: see text]: CMS fluorescent ceramics and powder are quite different.

In the field of laser technology, fiber lasers have developed rapidly because of its high power or energy. Q-switching technique has been widely used in fiber lasers to produce laser pulse. Here we demonstrate a passively Q-switched erbiumdoped fiber laser using a single-walled carbon nanotubes (SWCNTs) saturable absorber. The SWCNTs were fabricated by a new sol-gel method and placed onto the tip of a fiber ferrule. A TIWDM device replaced wavelength division multiplexer, isolation and tap to reduce the loss of the laser. Since only the evanescent field of the propagating light interacts with SWCNTs in saturable absorber, the fiber laser can maintain a relatively high intra-cavity power. As the pump power increasing, the output performance of the laser continues to improve. Laser center wavelength is 1560nm. An output pulse with energy of 70.9nJ is obtained with a repetition rate of 15.4 kHz and pulse width of 3.6 μs.

Passively Q-switched fiber laser (PQFL) has great potential applications in remote sensing, ranging, and optical communications. However, the PQFLs were seldom studied in view of both theory and experiment. This paper is dedicated to make up for this shortcoming. On the one hand, by describing the coupling rate equations of the PQFL system, the Q-switched pulse output with a modulation frequency of 17.61 kHz and a modulation period of 56.8 μs was obtained at 140 mW pump power. On the other hand, an erbium-doped PQFL whose performance is tunable by controlling the pump power and polarization state was constructed by using a single-walled carbon nanotube (SWCNT) as the saturable absorber (SA). The Q-switched pulse with a repetition rate of 17.61 kHz and a signal-to-noise ratio of 50.2 dB was output at a pump power of 140 mW. The theoretical simulation results were in good agreement with the experimental results. It was also verified from such two aspects that the repetition rate of the output pulse of PQFL was approximately proportional to the pump power. This research promotes the theory and design of PQFL.