Second-harmonic generation efficiency in periodically poled LiNbO3 waveguides

Quasi-phase-matched second-harmonic generation efficiency in periodically poled LiNbO₃ using titanium indiffusion, has been theoretically investigated. This permits clarifying how the involved guided modes convert the triangle-shaped form of the ferroelectric polarization in the crystal, via the overlap integral between this form and these modes, into an effective periodic nonlinear coefficient. As a consequence, the periodic function that really permits the quasi-phase-matching operation is the modulation of this effective nonlinear coefficient, the shape of which can be far from a triangular shape, as shown using different cases of mode profiles     

Nanosecond response of Bragg deflectors in periodically poled LiNbO3

For the first time, transients are measured for a bulk-optical Bragg-deflector based on an electrooptically (EO) induced grating in periodically poled LiNbO₃ (PPLN). Optical pulse risetimes of 1.2 ns are reported with a first-order diffraction efficiency of 76% for circular Gaussian beams. The fast risetime is accounted for by a substantially suppressed excitation of acoustic thickness modes and careful electrode design. For many applications, the device could replace both acoustooptical Bragg-deflectors and conventional EO amplitude modulators due to a fivefold reduction in risetime and fourfold reduction in drive power, respectively     

Widely and continuously tunable optical parametric generator based on MgO-doped periodically poled LiNbO3 crystal

Pulsed optical parametric generators(OPGs)and op-tical parametric oscillators(OPOs)have beenextensive-ly studied and developedfor generatingtunable coherentsources[1-5]that cover the wide spectral range fromthenear UVto the mid IR.In this letter we report…     

CW diode-pumped optical parametric oscillator in bulk periodicallypoled LiNbO3

The authors report a 1.96 μm doubly resonant optical parametric oscillator using bulk periodically poled LiNbO₃ directly pumped by a commercial 980 nm CW diode laser     

LiNbO3 optical intensity modulator packaged with monitorphotodiode

The assembly technique to simply install a monitor photodiode (PD) with a LiNbO₃ (LN) Mach-Zehnder modulator in the same package is proposed. A light radiated from the Mach-Zehnder Y-branch toward the LN output facet is lead into a glass bead, which is bonded to the LN facet as a fixture of the optical fiber. The end of the glass bead is cut to have an angled face, and the radiated light is reflected normal to the LN waveguide axis and toward the PD fixed on the side of package. The curved surface of the glass bead is effective to roughly focus the light onto the PD. We demonstrate that such monitor PD outputs an intensity modulation exactly reverse to the LN output modulation with a sensitivity higher than 0.03 A/W per optical output power of LN, indicating a usability of the PD output to monitor the drift of LN modulator     

Millimeter-wave Ti:LiNbO3 optical modulators

The design, fabrication, and characteristics of ridged Ti:LiNbO ₃ optical modulators that work in the millimeter-wave region are presented. A new concept of design under velocity matching is demonstrated for the proposed modulator. It has been shown by calculation that impedance matching is achieved and conductor loss is greatly reduced under velocity matching with wider gaps and a thicker coplanar waveguide electrode in conjunction with a ridge structure. Two types of Mach-Zehnder optical intensity modulators for the wavelength of 1.5 μm are developed. A fully packaged module for 40 Gb/s transmission with a half-wave voltage of 3.5 V and a broadband modulator responsible up to 100 GHz with a half-wave voltage of 5.1 V     

PPSLT皮秒中波红外光参量发生器

3~5 m 中红外激光在光电对抗领域有着重要的应用前景。如果中红外激光进入皮秒量级,将使其具有更高的峰值功率和作战效能。文中采用1.06 m 皮秒激光器泵浦单周期极化化学计量比钽酸锂晶体（周期为29.5 m）光参量产生器的方案,来获得皮秒中红外激光输出。其中皮秒泵浦源为自制的侧面泵浦结构1.06 m 皮秒再生放大器。该激光器在1 kHz 重复频率下,输出功率最高为2.02W,脉冲宽度为13.6 ps。光参量发生器采用温度调谐方式,获得了3.98~3.68 m（晶体从40~200℃）皮秒中波红外可调谐激光输出。在最高泵浦功率泵浦,晶体温度为120℃时,获得最大中红外激光输出（闲频光）190 mW,光光转换效率达9.4%,充分验证了采用OPG 的方式获得瓦级皮秒中红外激光输出的可行性。     

LiNbO3 optical waveguide fabrication by high-temperatureproton exchange

An efficient method, the high-temperature proton exchange (HTPE), to fabricate high-quality LiNbO₃ optical waveguides is studied. The new proton exchange source, the stearic acid diluted by lithium stearate, is proposed for HTPE process. The known soft proton exchange (SPE) process can be realized by HTPE. There are no phase transitions when the α-phase waveguides are fabricated by SPE. This phase presents the same crystalline structure as that of LiNbO₃ and, as expected, maintains the excellent nonlinear and electrooptical properties of the bulk material. The kinetics of HTPE is studied     

Cutoff wavelength of periodically segmented waveguides in Ti:LiNbO3

The cutoff wavelength for Ti:LiNbO₃ periodic segmented waveguides (PSWs) with different duty-cycles and of continuous waveguides has been measured for both polarizations, PSWs are described by an equivalent continuous waveguide and, using this model, a universal relationship between the cutoff wavelength of PSWs with different duty-cycles is proposed and verified experimentally     

CW Nd:MgO:LiNbO3 self-frequency-doubling laser at roomtemperature

A CW Nd:MgO:LiNbO₃ self-frequency-doubling laser has been demonstrated at room temperature for the first time. The second-harmonic output at λ=547 nm up to 18 mW was achieved in a simple resonator     

Ti:LiNbO_3质子交换光波导

本文研究了在Ti扩散LiNbO_3衬底上用苯甲酸质子交换制备光波导的方法,以及单模条件、折射率分布、交换系数、表面状态和热稳定性等问题。     

利用Fe:LiNbO_3晶体进行实时相关运算

本文介绍一种利用Fe:LiNbO_3晶体进行实时相关运算的方法。给出了与理论相一致的实验结果。     

LiNbO3晶体纳秒级光开关的研究

LiNbO3晶体由于其透光范围广,响应速度快,不易潮解等特点而广泛用于高精度和高速光开关快门。为了将LiNbO3光开关曝光时间拓宽到纳秒领域从而弥补现有的高速光开关的不足,文章阐述了LiNbO3作为光开关理论原理,对多波段通光的晶体长宽比进行了优化设计,并对LiNbO3纳秒级光开关的可行性进行了实验验证。实验半波电压与理论符合很好,实验光信号和电信号在纳秒级范围内能实现同步响应。研究结果证实了LiNbO3光开关在纳秒级范围内的可行性,并为LiNbO3纳秒级光开关的制作提供了理论和实验依据。     

Some optical properties of KTP, LiIO3, and LiNbO3

Measurements of the absorption coefficient for KTP, LiIO₃ , and LiNbO₃ are discussed. The variation of the refractive index with temperature has been measured for KTP and LiIO₃. It is necessary to know both the absorption coefficient β and the variation in the indexes of refraction with temperature change dn/dT to determine the average power limit of a nonlinear interaction. With the dn/dT information, it is also possible to estimate the temperature half width of any nonlinear interaction by calculating the variation of the phase-matching condition with temperature     

Investigations on short-path-length high-speed optical modulatorsin LiNbO3 with resonant-type electrodes

Short-path-length resonant-type high-speed optical modulators are presented. To reduce the active electrode length and enhance modulation efficiencies, different types of resonant electrode structures were investigated using computer simulation tools. Electrical power coupling into the resonators was optimized with a variety of power-feeding circuits. Their resulting optical and electrical behaviors are compared with measurements on modulators fabricated in Ti:LiNbO₃. As a result, resonant-type optical modulators are presented that achieve a low voltage-length product of 25 V mm at 30 GHz in the 1.55-μm wavelength range. Fiber-to-fiber loss of a fully packaged phase modulator with an active optical path length as short as 0.7 mm was 2.3 dB     

A broadband Ti:LiNbO3 optical modulator with a ridgestructure

We describe the design, fabrication, and characteristics of a Ti:LiNbO₃ optical modulator with a ridge structure. The structure keeps microwave propagation loss low and enables a large interaction between microwaves and optical waves under the conditions of velocity-matching and impedance matching, resulting in a large modulation bandwidth and low driving voltage. Using this structure, we have developed an optical intensity modulator with an optical 3-dB bandwidth of 75 GHz and a driving voltage of 5.0 V at a wavelength of 1.5 μm     

75 GHz broadband Ti:LiNbO3 optical modulator with ridgestructure

The authors propose a Ti:LiNbO₃ optical modulator employing a ridge structure with a thick electrode. The structure offers a low microwave propagation loss and strong interaction between microwaves and optical waves under conditions of velocity matching and impedance matching, resulting in a large modulation bandwidth and low driving voltage. Using this device, the authors have developed an optical intensity modulator with a 3 dB optical bandwidth of 75 GHz and a driving voltage of 5.0 V at 1.5 μm     

新型二阶非线性材料PPLN在光纤通信技术中的应用

周期性畴反转铌酸锂(PPLN)作为一种采用准相位匹配技术的新型光学二阶非线性材料,因其可以具有较高的光学非线性,从而使一批新型非线性全光处理技术在光通信系统中的应用成为可能,并成为当前全光网络研究中的热点之一.基于此,文章综述了近年来利用PPLN材料实现全光波长转换、色散补偿等技术的新方法和其发展趋势.     

LiNbO3 optical waveguides formed in a new proton source

Proton-exchanged planar waveguides have been fabricated on Z-cut and X-cut lithium niobate crystals by using a new proton source formed by a mixture of benzoic and adipic acids. Waveguide index profiles and optical characteristics have been obtained at different values of the adipic-benzoic acid concentration ratio. The samples have been structurally characterized by Raman and infrared (IR) absorption spectroscopy and double-crystal X-ray diffraction. Good quality samples have been fabricated by using 30 mol% ratio dilution, showing very low scattering levels (<0.1 dB/cm), relatively high electrooptic coefficient (r₃₃=0.88 pm/V), and low relative percentage of interstitial protons (26%). The main factor limiting the waveguide optical properties is the substitutional-interstitial proton ratio, which can be easily controlled to produce good quality waveguides. A demonstration of the repeatability of the exchange process in the acid mixture is also provided     

Integrated optical Ti:Er:LiNbO3 soliton source

Efficient diode-pumped and harmonically mode-locked operation of a fully packaged Ti:Er:LiNbO₃ waveguide laser at 1562- (TE) and 1575-nm (TM) wavelength has been demonstrated. The mode-locked pulses have been characterized in terms of time-bandwidth product, fine tuning, and stability. Noise suppression of 42 dB at the relaxation oscillation frequency has been achieved by feedback-controlled pumping. An external amplitude modulator has been used for encoding of the mode-locked pulse train with different bit sequences. Bit error rates of 10^-10 for a 1-0-1-0-bit sequence has been observed for more than half an hour