A zonal decoupling algorithm used to control a dual deformable mirror (DM) is proposed. One of the two DMs is characterized with a large stroke (woofer), while the other one is characterized by a high spatial frequency (tweeter). A numerical model is used to compare the zonal decoupling algorithm with some traditional zonal decoupling algorithms. The simulation results indicate that the algorithm presented in this Letter improves the performance in suppressing the coupling error. An experimental system is built to prove the effectiveness of this algorithm. The experiments demonstrate that the phase aberrations could be effectively compensated and that the coupling error could also be suppressed.

A new two-stage carrier-phase recovery scheme using a combination of an optical pilot-aided algorithm with the crossed constellation transformation algorithm for either square-framed or non-square-framed M-level-quadrature amplitude modulation (QAM) Nyquist systems is proposed. It is verified in 32- and 128-QAM systems that it can provide high linewidth tolerance with little complexity.

An optical fiber extrinsic Fabry–Perot interferometer (EFPI) is designed and fabricated for refractive index (RI) sensing. To test the RI of liquid, the following two different methods are adopted: the wavelength tracking method and the Fourier-transform white-light interferometry (FTWLI). The sensitivities of sensors with cavity lengths of 288.1 and 358.5 μm are 702.312 nm/RIU and 396.362 μm/RIU, respectively, by the two methods. Our work provides a new kind of RI sensor with the advantages of high sensitivity, mechanical robustness, and low cross sensitivity to temperature. Also, we provide a new method to deal with gold film with a femtosecond laser.

For the development of mid-infrared fiber-optical elements, one needs light-stable, flexible materials that are transparent within this spectral band. Solid solutions of silver and monadic thallium halides prove to be the most suitable crystalline media for these needs. We study the light stability variation of high-purity AgCl1 xBrx (0≤x≤1) and Ag1 xTlxBr1 xIx (0≤x≤0.05) crystals by measuring the optical transmission change as functions of the composition and UV exposure time. The former is executed in a broad spectral range from 6500 350 cm 1, within which we choose three wavelengths to trace the transmission change. For thallium-monoiodide-containing samples, an effect is observed that we assumed to be translucence.

Streak tube imaging lidar (STIL) is an active imaging system that has a high range accuracy with the use of a pulsed laser transmitter and streak tube receiver to produce 3D range images. This work investigates the effect of the time bin size on the range accuracy of STIL systems based on the peak detection algorithm. The numerical simulation indicates that the time bin size has a significant effect on the range accuracy, resulting in a modified analytical estimate of the range error. An indoor experiment with a planar target is carried out to validate the theory that shows the linear relationship between the range error and the time bin size. Finer 3D depth images of a fist model are acquired by using a smaller time bin size and the best range error of 0.003 m is achieved with the optimal time bin size of 0.07 ns.

Based on a single-channel laser self-mixing interferometer, we present a new simultaneous measurement of the vibration amplitude and the rotation angle of objects that both affect the power spectrum containing two peaks of the interferometer signals. The fitted results indicate that the curve of the peak frequency versus the vibration amplitude follows a linear distribution, and the curve of the difference of the two-peak power values versus the angle follows a Gaussian distribution. A vibration amplitude with an error less than 3.0% and a rotation angle with an error less than 11.7% are calculated from the fitted results.

A system of an add-drop microring resonator integrated with a sampled grating distributed feedback (SG-DFB) is investigated via modeling and simulation with the time-domain traveling wave (TDTW) method. The proposed microring resonator comprises a SiO2 waveguide integrated with an InGaAsP/InP SG-DFB, and the SiO2 waveguide consists of a silicon core having a refractive index of 3.48 and Kerr coefficient of 4.5×10 18 m2/W. The SG-DFB consists of a series of grating bursts that are constructed using a periodic apodization function with a burst spacing in the grating of 45 μm, a burst length of 5 μm, and 10 bursts across the total length of the SG-DBR. Transmission results of the through and drop port of the microring resonator show the significant capacity enhancement of the generated center wavelengths. The Q-factor of the microring resonator system, defined as the center wavelength (λ0) divided by 3 dB FWHM, without and with integration with the SG-DFB is calculated as 1.93×105 and 2.87×105, respectively. Analysis of the dispersion of the system reveals that increasing the wavelength results in a decrease of the dispersion. The higher capacity and efficiency are the advantages of integrating the microring resonator and the InGaAsP/InP SG-DFB.

Polarization switching (PS) characteristics in a 1550 nm vertical-cavity surface-emitting laser (VCSEL) subject to circularly polarized optical injection (CPOI) are experimentally investigated. The results show that, under different biased current, a solitary 1550 nm VCSEL can oscillate at y polarization mode (y mode), two polarization components (PCs) coexistence or x polarization mode (x mode). The PS characteristics induced by CPOI for the VCSEL operating at y mode and x mode are analyzed and the evolutions of dynamical states with the injected power are discussed. Additionally, the mappings of nonlinear dynamical states are given in the parameters space of the injected power and frequency detuning.

It is demonstrated that high-Q (Q～108) bottle microresonators can be fabricated by using a CO2 laser to heat a vertical single-mode fiber with a small weight attached to its lower end. A tunable continuous-wave laser is used to excite whispering-gallery modes in a bottle microresonator through a fiber taper, and a ringing phenomenon is observed. The observed ringing phenomenon is well explained through the numerical solution of a dynamic equation. In addition, an explicit function is given to describe the light field in the resonator, and the theoretical transmission based on the function also agrees very well with the experimental ringing phenomenon.

A laser diode array side-pumped Nd:glass square rod amplifier of the dimensions 12 mm×12 mm is designed. The fluorescence is evenly distributed in the Nd:glass amplifier. When the pump power is 66.32 kW, the small signal gain increases by 3.23 times. Under the condition of a 1 Hz repetition frequency, 50 mJ of injected seed-light energy, and a 10 mm×10 mm aperture, the output energy of the laser beam can reach 1.62 J during the four-pass amplification. The output energy stability of the laser pulse is 2.94% (RMS), and the square pulse distortion is smaller than 2. The energy amplification of the injected laser beam from millijoules to joules is realized.

We demonstrate wavelength-selectable visible emissions from a miniature crystalline laser that combines the stimulated Raman scattering (SRS) effect in an Nd:YVO4 crystal with intracavity frequency mixing in an angle-tuned beta barium borate (BBO) crystal. The presented laser is operating on demand at any one of three wavelengths in the green-yellow spectral region. Up to 600, 560, and 200 mW output powers at 559, 532, and 588 nm, respectively, are obtained from the continuous wave (CW) laser having a 18 mm long resonator and a 3.8 W laser diode end pumping. The pump threshold for each visible wavelength is less than 0.4 W.

The continuous wave (CW) and passively Q-switched (PQS) performances of diode-pumped Nd:(LaxGd1 x)3Gd5O12 (Nd:LaGGG) at 1.33 μm are achieved for the first time to our knowledge. The maximum CW output power of 5.1 W is obtained with the optical-optical conversion efficiency of 25.3% and the slope efficiency of 26.6%. In the PQS operation, by using the V3+:YAG crystal as the saturable absorber, the maximum average output power, shortest pulse width, largest pulse energy, and highest peak power are measured to be 1.1 W, 27.54 ns, 75.78 μJ, and 2.44 kW, respectively.

In this Letter, we demonstrate the anisotropy of laser emission in disordered Nd:ScYSiO5 (Nd:SYSO) crystals cut along the optical indicatrix axes. High-powered lasers with different oscillation wavelengths and polarizations are realized by using different oriented crystals as gain media. For Y-cut crystals, the dual-wavelength laser vibration direction is found to be along the X axis and a maximum output power of 9.43 W is obtained, giving an optical-to-optical conversion efficiency of 48.8% and a slope efficiency of 51.3%. For X- and Z-cut crystals, 1075 and 1078 nm lasers operating orthogonally polarize oscillate with total output powers of 7.07 and 8.43 W, respectively. The experimental results reveal that the intrinsic anisotropy for the monoclinic disordered laser crystals could make laser design flexible and controllable.

A method for fabricating deep grating structures on a silicon carbide (SiC) surface by a femtosecond laser and chemical-selective etching is developed. Periodic lines corresponding to laser-induced structure change (LISC) are formed by femtosecond laser irradiation, and then the SiC material in the LISC zone is removed by a mixed solution of hydrofluoric acid and nitric acid to form grating grooves. Grating grooves with a high-aspect ratio of approximately 25 are obtained. To obtain a small grating period, femtosecond laser exposure through a phase mask was used to fabricate grating structures with a 1.07 μm period on the surface of the SiC.

The use of red light or near-infrared radiation as a luminescent probe for in vivo bio imaging is crucial in order to restrict the strong absorption of short-wavelength light below 600 nm in tissue. It is demonstrated that the emission color of Yb/Ho codoped NaYF4 nanoparticles can be tuned from green to red by incorporating Ce3+ ions. However, compared with that of the NaYF4:Yb/Ho nanoparticles, the photoluminescence intensity of the Ce3+-tridoped NaYF4:Yb/Ho nanoparticles is drastically reduced. In this work, Ce3+-incorporated core/shell NaYF4:Yb3+50%@NaYF4:Ho3+0.5% nanoparticles are prepared. A strong red emission and a high-intensity ratio between the red emission and green emission are obtained in these upconversion nanoparticles. The emission intensity increases by a factor higher than 120 when compared with that of the NaYF4:Yb/Ho/Ce nanoparticles. This result indicates that the Ce3+ incorporation into the 160.2540 Fluorescent and luminescent materials 160.4760 Optical properties