Generation of a squeezed state at 1.55 μ with periodically poled LiNbO3

We report on the generation of a squeezing vacuum at 1.55 μm using an optical parametric amplifier based on periodically poled LiNbO₃. Using three specifically designed narrow linewidth mode cleaners as the spatial mode and noise filter of the laser at 1.55 μm and 775 nm, the squeezed vacuum of up to 3.0 dB below the shot noise level at 1.55 μm is experimentally obtained. This system is compatible with standard telecommunication optical fibers, and will be useful for continuous variable long-distance quantum communication and distributed quantum computing.     

Generation of a continuous-wave squeezed vacuum state at 1.3 μm by employing a home-made all-solid-state laser as pump source

We present a continuous-wave squeezed vacuum generation system at a telecommunication wavelength of 1.3 μm. By employing a home-made single-frequency Nd:YVO4 laser with dual wavelength outputs as the pump source, via an optical parameter oscillator based on periodically poled KTP, a squeezed vacuum of 6.1 dB±0.1 dB below the shot noise limit at 1342 nm is experimentally measured. This system could be utilized for demonstrating practical quantum information networks.     

Generation of a squeezed state at 1.55 μm with periodically poled LiNbO3

We report on the generation of a squeezing vacuum at 1.55 μm using an optical parametric amplifier based on periodically poled LiNbO 3.Using three specifically designed narrow linewidth mode cleaners as the spatial mode and noise filter of the laser at 1.55 μm and 775 nm,the squeezed vacuum of up to 3.0 dB below the shot noise level at 1.55 μm is experimentally obtained.This system is compatible with standard telecommunication optical fibers,and will be useful for continuous variable long-distance quantum communication and distributed quantum computing.     

Generation of squeezed TEM01 modes with periodically poled KTiOPO4 crystal

Spatial quantum optics and quantum information based on the high order transverse mode are of importance for the super-resolution measurement beyond the quantum noise level. We demonstrated experimentally the transverse plane TEM01 Hermite-Gauss quantum squeezing. The squeezed TEM01 mode is generated in a degenerate optical parametric amplifier with the nonlinear crystal of periodically poled KTiOPO4. The level of 2.2-dB squeezing is measured using a spatial balance homodyne detection system.     

Generation of intensity difference squeezed state at a wavelength of 1.34 μm

The intensity difference squeezed state, which means that the fluctuation of the intensity difference between signal and idler beams is less than that of the corresponding shot noise level(SNL), plays an important role in high sensitivity measurement, quantum imaging, and quantum random numbers generation. When an optical parametric oscillator consisting of a type-Ⅱ phase-matching periodically poled KTiOPO_4 crystal operates above the threshold, an intensity difference squeezed state at a telecommunication wavelength can be obtained. The squeezing of 7.7 ± 0.5 dB below the SNL is achieved in an analysis frequency region of 2.4–5.0 MHz.     

Phasematching properties of congruent MgO-doped and undoped periodically poled LiNbO<Subscript>3</Subscript> for optical parametric oscillation with ultrafast excitation at 1 µm

A detailed theoretical analysis of the optical properties of periodically poled crystals of lithium niobate for optical parametric oscillation with excitation at 1 μm is presented. Crystals of congruent lithium niobate with and without MgO-doping are considered. The choice of materials, their basic optical properties, quasi-phasematching and wavelength tuning ranges, as well as dispersive effects are discussed. These results provide a useful roadmap for the construction of optical parametric oscillators and generators operating in the ultrashort pulse regime with excitation at 1 μm.     

Analysis of the laser performance of Tm3+, Tb3+(Ho3+):YVO4 crystals at ～1.5μm wavelength

The absorption spectra of Tb,Tm:YVO_4 and Ho,Tm:YVO_4 are measured. The radiant and non-radiant transition probabilities from higher level to lower level, A_{i,j} and ω_{i,j}, and the cross-elaxation probability are calculated in virtue of Judd－Ofelt and Dexter theories. The fluorescence lifetime of Tm^{3+} in the Tb^{3+} (or Ho^{3+}) co-doped crystal is calculated. It indicates that the lifetime of initial level {}^3H_4 of the laser transition can be shorter than that of terminal level {}^3F_4 of the transition if the atomic percentage of Tb^{3+} (or Ho^{3+}) ions is bigger than about 1 at%: namely, by means of the co-doping Tb^{3+} (or Ho^{3+}) ions the self-termination phenomenon of laser light can be eliminated. Inserting the optic parameters to the formula deduced here on the laser threshold power P^{(4)}_{th} and the slope efficiency η^{(4)}_s of the four-energy-level system, we obtain the relationship of threshold power P^{(4)}_{th} to the concentration of Tm^{3+} ions and discuss the effect of Tb^{3+} (or Ho^{3+}) ion concentration on the laser threshold power P^{(4)}_{th} around 1.5μm wavelength. The result shows that Tb,Tm:YVO_4 crystal is a better choice to make the laser at ～1.5μm wavelength than Ho,Tm:YVO_4 crystal. We give the appropriate composition of (1－2) at% Tb, (1－2) at% Tm:YVO_4, just for reference.     

Directly LD-pumped passively Q-switched YVO<Subscript>4</Subscript>-Nd:YVO<Subscript>4</Subscript> laser at 1.34 μm with a V<Superscript>3+</Superscript>: YAG saturable absorber

The performance of a directly LD-pumped passively Q-switched YVO₄-Nd:YVO₄ laser at 1.34 μm with a V³⁺:YAG saturable absorber was demonstrated for the first time to the best of our knowledge. The average output power of 580 mW was obtained at the pump power of 8.8 W, corresponding to the optical conversion efficiency of 6.6% and slope efficiency of 11%. The minimum pulse width was 280 ns with the pulse repetition rate of 230 kHz, which was attained with a T = 5.6% output coupler at the pump power of 8.8 W.     

Passively Q-switched laser performance of Nd:Lu<Subscript>0.15</Subscript>Y<Subscript>0.85</Subscript>VO<Subscript>4</Subscript> operating at 1.34 μm with a V:YAG saturable absorber

A diode-pumped passively Q-switched Nd:Lu_0.15Y_0.85VO₄ crystal laser at 1.34 μm with V:YAG employed as the saturable absorber was demonstrated for the first time to our best knowledge. The maximum average output power of 0.529 W was achieved under the pump power of 5.6 W, corresponding to an opticaloptical conversion efficiency of over 9.4% and slope efficiency of over 16%. The pulse width was shortened to 85.6 ns, corresponding to the maximum pulse repetition rate of 250 kHz. The largest single pulse energy and peak power were 5.57 μJ and 58.74 W, respectively.     

Diode-pumped passively Q-switched and mode-locked Nd:GGG laser at 1.3 μm with V<Superscript>3+</Superscript>:YAG saturable absorber

Using V³⁺:YAG crystal as the saturable absorber, a diode-pumped passively Q-switched and mode-locked Nd:GGG laser operating at 1.3 μm is realized for the first time. The mode-locking modulation depth of nearly 100% has been achieved. The maximum output power and the single Q-switched pulse energy are 410 mW and 8.3 μJ. The mode-locked pulse inside the Q-switched pulse has a repetition rate of 349 MHz, and its average pulse width is estimated to be about 750 ps.     

Pulse width compression and enhancement of peak power in a diode-pumped doubly Q-switched Nd:GdVO<Subscript>4</Subscript> 1.34 μm laser with AO and V<Superscript>3+</Superscript>:YAG saturable absorber

By using both acousto-optic (AO) modulator and V³⁺:YAG saturable absorber, a diode-pumped doubly Q-switched a-cut Nd:GdVO₄ laser at 1.34 μm is realized. The average output power and the pulse width for different AO repetition rate f have been measured. The experimental results show that the doubly Q-switched laser can compress the pulse width and improve the pulsed peak power in comparison to the singly Q-switched laser with AO or V³⁺:YAG saturable absorber. At the pump power 10.34 W and f = 10 kHz, the greatest pulse width compression ratio 72% and the highest peak power improvement 8.8 times have been obtained, respectively.