Second-harmonic generation in ion-implanted KTiOPO/sub 4/ planar waveguides

The first example of second harmonic generation (SHG) in an ion implanted KTiOPO/sub 4/ waveguide is reported. This was formed by helium implantation, and SHG was achieved using zero order mode phase matching at lambda approximately=1.07 mu m. The results indicate that the high nonlinearity remains in the guiding region after implantation. The conversion efficiency in the guide is estimated to be >10% for approximately 1 mu J 20 ns pulsed excitation.<>     

Quasi-phase-matched second harmonic generation in a LiTaO3 waveguide

The authors report third-order quasi-matched (QPM) second harmonic generation (SHG) in a LiTaO₃ channel waveguide. A deep domain-inverted region is first fabricated by a proton-exchange and heat treatment technique. Then a uniform and low-pass channel waveguide is fabricated by pyrophosphoric acid proton exchange. Consequently, 12 mW of blue light is obtained at 424 nm wavelength with a conversion efficiency of 6%. The observed FWHM (full-width half maximum) temperature acceptance width for SHG power is 3.2°C and FWHM wavelength acceptance bandwidth for that is 0.2 nm. It is also shown that diffraction limited focusing of the generated blue light may be obtained     

Integrated optical device with second-harmonic generator,electrooptic lens, and electrooptic scanner in LiTaO3

This paper reports the first demonstration of an integrated optical device in z-cut LiTaO₃ that contains the following three functional parts: a quasiphase-matched second-harmonic generation (SHG) grating, an electrooptic (EO) lens, and an electrooptic scanner. The SHG device consists of channel waveguides passing through periodic domain-inverted gratings. The frequency of the input infrared (IR) light at 864 nm was doubled into blue light at 432 nm. A stack of EO lenses was used to collimate the light from the channel waveguide. The measured beam size at the output facet for various applied voltages to the lenses agreed with simulation. After collimation, light passes through an EO scanner that controls the angle of the output beam. A scanning sensitivity of 17 mrad/kV was measured for the scanner, compared to the calculated value of 15 mrad/kV     

LiNbO3 waveguide quasi-phase-matching second harmonicgeneration devices with ferroelectric-domain-inverted gratings formed byelectron-beam scanning

The characteristics of the formation of LiNbO₃ ferroelectric-domain-inverted gratings using electron-beam scanning are examined and discussed for application to waveguide quasi-phase-matching second-harmonic-generation (SHG) devices. It is found that the domain inversion tends to occur in segmented regions, and the inversion width is thinner near the crystal surface than inside the crystal. The dependence of the SHG efficiency on the grating structure is examined theoretically. Prototype devices for green and blue light generation have been fabricated and the device performance examined. Normalized SHG efficiencies as high as 50%/W and 70%/W, respectively, are obtained in green and blue light generation devices of 3.3-mm length. The experimental results are compared with the theoretical results     

Optimized second-harmonic generation in quantum cascade lasers

Optimized second-harmonic generation (SHG) in quantum cascade (QC) lasers with specially designed active regions is reported. Nonlinear optical cascades of resonantly coupled intersubband transitions with giant second-order nonlinearities were integrated with each QC-laser active region. QC lasers with three-coupled quantum-well (QW) active regions showed up to 2 /spl mu/W of SHG light at 3.75 /spl mu/m wavelength at a fundamental peak power and wavelength of 1 W and 7.5 /spl mu/m, respectively. These lasers resulted in an external linear-to-nonlinear conversion efficiency of up to 1 /spl mu/W/W/sup 2/. An improved 2-QW active region design at fundamental and SHG wavelengths of 9.1 and 4.55 /spl mu/m, respectively, resulted in a 100-fold improved external linear-to-nonlinear power conversion efficiency, i.e. up to 100 /spl mu/W/W/sup 2/. Full theoretical treatment of nonlinear light generation in QC lasers is given, and excellent agreement with the experimental results is obtained. For the best structure, a second-order nonlinear susceptibility of 4.7/spl times/10/sup -5/ esu (2/spl times/10/sup 4/pm/V) is calculated, about two orders of magnitude above conventional nonlinear optical materials and bulk III-V semiconductors.     

Harmonic blue light generation in periodically poled bulk near-stoichiometric MgO:LiNbO/sub 3/

A periodically poled structure with 6.95 /spl mu/m period and 10 mm interaction length was fabricated in a 1 mm-thick 1.8 mol% MgO doped near-stoichiometric LiNbO/sub 3/ (MgSLN) by using a multi-pulse poling technique. Blue SHG characteristics of this periodically poled MgSLN were investigated, in comparison with a periodically poled 5 mol% MgO doped congruent LiNbO/sub 3/.     

利用二次谐波产生研究Al2O3/Al(111)表面的动力学变化

主要介绍了当激光入射到单晶金属Al2O3／Al(111)表面时将发生二次谐波产生(SHG)现象的实验装置和实验方法,利用该装置可以研究SHG和从Al2O3／Al(111)表面反射的SHG在空间各向异性的变化情况,从而可以探测Al2O3／Al(111)表面结构对称性。实验中发现,当脉冲激光功率在2×106 W／cm2-9．6×106W／cm2范围内变化时,没有检测到SHG信号的各向异性变化;当使用P-极化泵浦激光时,发现Al2O3／Al(111)样品绕法线旋转360度时,P-极化的SHG信号在空间三个方向上呈现最大值相等;当使用脉冲强度为12×100 W／cm2的1064 nm P-极化泵浦激光时, Al2O3／Al(111)表面被损坏,损坏后的表面其SHG信号并不呈现对称的各向异性变化,当使用脉冲强度为11×106W／cm2的1064 nm P-极化泵浦激光时产生表面退火现象,从退火表面所产生的反射532 nm P-极化SHG信号中发现,SHG信号呈现衰减的各向异性成分。     

Spectroscopic analysis and diode-pumped laser results of Nd:BaY/sub 2/F/sub 8/

Single crystals of monoclinic BaY/sub 2/F/sub 8/, doped with different Nd/sup 3+/ concentrations, were successfully grown by means of the Czochralski method. Here, we present a polarized infrared (IR) spectroscopic investigation and diode-pumped continuous-wave laser results in the 1 /spl mu/m wavelength region. Moreover for the first time 1.3 /spl mu/m laser emission has been characterized. Q-switching results in the 1-/spl mu/m region are also presented.     

35-dB gain Tm-doped ZBLYAN fiber amplifier operating at 1.65 /spl mu/m

We demonstrate the first high gain rare-earth-doped fiber amplifier operating at 1.65 /spl mu/m. It consists of ZBLYAN fiber with a Tm/sup 3+/-doped core and Tb/sup 3+/-doped cladding, pumped by 1.22 /spl mu/m laser diodes. It is possible to achieve efficient amplification with Tm/sup 3+/ ions if their amplified spontaneous emission (ASE) in the 1.75 to 2.0 /spl mu/m wavelength region is suppressed by doping Tb/sup 3+/ ions in the cladding. A two-stage-type fiber amplifier is constructed and a signal gain of 35 dB is achieved for a pump power of 140 mW. A gain over 25 dB is realized in the 1.65 /spl mu/m to 1.67 /spl mu/m wavelength region.     

Continuous-wave erbium-diffused LiNbO/sub 3/ waveguide laser

The first integrated optical laser in LiNbO/sub 3/, doped by an indiffusion of Er/sup 3+/ prior to channel-guide fabrication by Ti diffusion is reported. Pumped by a colour centre ( lambda /sub p/=1.477 mu m), CW operation at lambda =1.532 mu m ( Delta lambda approximately 0.3 nm) with a threshold of approximately 8 mW absorbed power was achieved.<>     

Second harmonic generation phase-matching locus for 7.5 mol% Nb:KTPcrystals at near-infrared wavelengths

Both the type-II second harmonic generation (SHG) phase-matching locus in the three principal planes of 7.5 mol% Nb:KTiOPO₄ (KTP) crystals for wavelengths less than 1.8 μm and the type-II SHG phase-matching locus for 7.5 mol% Nb:KTP crystals for wavelengths of 970, 980, 1064.2, and 1311.4 nm are calculated on the basis of the Sellmeier equations. When compared with those in KTP crystals, the shapes of these curves are almost the same in the two crystals. These imply that Nb doping does not significantly change the phase-matching properties of KTP crystals, even though it does largely change the phase-matching parameter of KTP crystals. These make Nb:KTP crystals more attractive in direct SHG of semiconductor laser radiation to produce blue coherent light     

Ce:KTP晶体的生长及其相干和频蓝光的产生

采用熔盐法生长了光学质量的 Ce:KTP晶体。透过曲线表明 ,Ce:KTP在紫外截止波段附近的吸收比普通 KTP低约 10 %。采用 KTP晶体的倍频以及 Ce:KTP和频的组合 ,利用 Nd:YAG激光器的 1.32μm单一输出线束作抽运 ,实现了 0 .4 4μm相干蓝光的有效发生 ,其总效率约为2 .5%。     

Blue, green and yellow upconversion lasing in Er:YLiF/sub 4/ using 1.5 mu m pumping

The authors report blue, green and yellow upconversion laser action in Er/sup 3+/:YLiF/sub 4/ following pumping at 1.500 mu m below 80 K. For the blue transition the ratio of the output frequency to the input frequency is 3.3, the highest yet reported for an upconversion laser. In spite of the multiple upconversion steps, the thresholds for laser action were less than 80 mW. It is proposed that the nonlinear upconversion pumping proceeds via a sequence of several pairwise cross-relaxation steps.<>     

Pr/sup 3+/-doped fluoride single-mode fiber laser

Laser oscillation at 1.312 mu m was achieved using a Pr/sup 3+/-doped fluoride single-mode fiber laser pumped at 1.017 mu m. The operation of a rare-earth-doped fiber laser at 1.31 mu m, which is one of the central wavelengths in conventional optical telecommunication trunk line systems, was demonstrated for the first time using Pr/sup 3+/ ion as an active ion. The laser cavity consists of a mirror and a cleaved fiber facet used as an output mirror. The maximum output power, threshold pump, and slope efficiency are 26 mW, 370 mW, and 9.86%, respectively.<>     

AlF/sub 3/-based glass fibres with enhanced optical transmission

A significant reduction in the optical losses of AlF/sub 3/-based, infrared transmitting fibres has been achieved for the first time. A minimum loss of 0.05 dB/m at 2.65 mu m coupled with extended transparency beyond 4 mu m and excellent chemical durability makes these fibres excellent candidates for infrared sensing, remote spectroscopy, laser power delivery and active fibre research.<>     

Non-photorefractive CW Tm-indiffused Ti:LiNbO/sub 3/ waveguide laser operating at room temperature

We report laser operation at 1.81 /spl mu/m and 1.85 /spl mu/m in a Tm/sup 3+/:LiNbO/sub 3/ Ti-diffused waveguide doped by thermal indiffusion at high temperature. We believe this is the first time lasing has been seen in Tm:LiNbO/sub 3/ at room temperature. Continuous-wave operation was achieved at room temperature with a threshold of 42 mW launched pump power. The output power was observed to be stable, without any sign of photorefractive damage.     

GaAs/GaAlAs asymmetric Mach-Zehnder demultiplexer with reduced polarization dependence

A two-channel GaAs/AlGaAs asymmetric Mach-Zehnder wavelength demultiplexer with reduced polarization dependence was demonstrated. The device was fabricated on a single heterostructure comprising a 1.45- mu m-thick layer of GaAs on a 6.0- mu m-thick Ga/sub 0.85/Al/sub 0.15/As buffer layer. The epitaxial layers were grown by MOCVD (metalorganic chemical vapor deposition) on an n/sup +/ GaAs substrate. The single-mode rib waveguides, 3 mu m wide and 0.29 mu m high, were fabricated using standard photolithographic techniques followed by chemical etch and removal of the resist mask. Extinction ratios of 24.1 dB for transverse electric (TE) and 22.5 dB for transverse magnetic (TM) polarized light were measured on a device with an anti-reflection coating on its input and output facets. The active length of the device is approximately 6.5 mm and total loss of 1.1 dB was obtained in a 16-mm-long chip.<>     

Highly efficient and tunable Nd/sup 3+/ doped fluoride fibre laser operating in 1-3 mu m band

A highly efficient and tunable Nd/sup 3+/ doped fluoride fibre laser operating in the 1.3 mu m band pumped at 0.8 mu m is demonstrated. The pump laser is a titanium sapphire laser and the tuning element is a dielectric multicoated bandpass filter inserted in the cavity. The oscillation wavelength was successfully tuned from 1.315 to 1.348 mu m for the first time.<>     

GaAs/GaAlAs multiquantum well waveguides for all-optical switching at 1.55 mu m

The first measurements of selfphase modulation and nonlinear absorption in a GaAs/GaAlAs multiquantum well (MQW) waveguide near the half-bandgap resonance are reported. An intensity-dependent refractive index coefficient n/sub 2/ of 9*10/sup -14/ cm/sup 2//W and a two-photon absorption coefficient of 0.15 cm/Gw at 1.55 mu m wavelength for TM light were obtained. This corresponds to an intensity-independent figure of merit of 24 rad phase change in one nonlinear absorption length, high enough to allow the implementation of subpicosecond all-optical switches at 1.55 mu m wavelength.<>     

High-performance 1.06-/spl mu/m selectively oxidized vertical-cavity surface-emitting lasers with InGaAs-GaAsP strain-compensated quantum wells

We present the first room-temperature continuous-wave operation of high-performance 1.06-/spl mu/m selectively oxidized vertical-cavity surface-emitting lasers (VCSEL's). The lasers contain strain-compensated InGaAs-GaAsP quantum wells (QW's) in the active region grown by metalorganic vapor phase epitaxy. The threshold current is 190 /spl mu/A for a 2.5/spl times/2.5 /spl mu/m/sup 2/ device, and the threshold voltage is as low as 1.255 V for a 6/spl times/6 /spl mu/m/sup 2/ device. Lasing at a wavelength as long as 1.1 /spl mu/m was also achieved. We discuss the wavelength limit for lasers using the strain-compensated QW's on GaAs substrates.