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     

Theoretical modeling of optical amplification in Er-doped Ti:LiNbO3 waveguides

An accurate theoretical analysis is presented describing optical amplification in Er-diffused Ti:LiNbO₃ channel waveguides. It follows as far as possible the theory already developed for Er-doped fibers. As optical pumping around λ_p≈1.48 μm is considered, a quasi-two-level model for the Er³⁺ ions is used with wavelength-dependent cross sections. The optical gain in the 1.53 μm<λ<1.64-μm wavelength range is evaluated. The characteristic parameters, as Er concentration profile, cross sections, pump, and signal mode distributions and waveguide (scattering) losses are taken from experiments. Examples of numerically calculated pump-, small-signal-gain-, and ASE-evolutions are presented. The model has been tested by comparing computed and experimentally observed gain characteristics for Xˆ- and Yˆ-cut LiNbO₃; an almost quantitative agreement has been obtained     

Fabrication tolerance of Ti:LiNbO3 waveguides

A simulation program based on the three-dimensional beam propagation method (BPM) is used to study the fabrication conditions of single-mode Ti:LiNbO₃ waveguides. The calculated cutoff wavelengths are in good agreement with experimental data. The thickness of titanium needed to support the fundamental and first-order modes for three Ti strip widths (6, 7, and 8 μm) is calculated. The two-dimensional BPM is used to calculate the coupling length from the fabrication conditions. Results are consistent with measured data. The fabrication tolerances of the coupling length of directional couplers are also presented     

High-speed shielded velocity-matched Ti:LiNbO3 opticalmodulator

A shielded velocity-matched Ti:LiNbO₃ optical modulator is investigated, focusing on the characteristics of the traveling-wave (TW) electrode and the optical waveguide. The optical waveguide is analyzed and its parameters are determined using the newly developed modified-step-segment method (MSSM). The TW electrode is analyzed using the second-order triangular element quasi-TEM finite element method (FEM). By taking the thickness of the coplanar waveguide (CPW) traveling-wave (TW) electrode into consideration, it is confirmed that there is an optimum overlaid layer thickness for a given electrode thickness. It is also shown that very wide modulation bandwidth can be attained by using the optimum CPW TW electrode thickness and overlaid layer thickness     

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。     

Performance and modeling of broadband LiNbO3 travelingwave optical intensity modulators

The design, fabrication and characterization of a traveling wave Ti:LiNbO₃ Mach-Zehnder interferometric modulator are discussed. The dependence of the velocity match condition on electrode thickness and wall angle is demonstrated experimentally and with finite element calculations. A set of test electrode structures is fabricated to study electrical losses in the modulator electrode. Loss coefficients are assigned to different sections of the device, and dielectric and radiative losses are shown to play an important role at high frequencies. This information is used in conjunction with finite-element calculations to develop accurate models for both the electrical and optical responses. The frequency dependence of the half-wave voltage is measured and shown to be in good agreement with a model     

Erbium-doped single- and double-pass Ti:LiNbO3 waveguideamplifiers

Single-pass and double-pass Er-diffused Z- and X-cut Ti:LiNbO₃ waveguide amplifiers, optically pumped at λ _p≈1484 nm, have been investigated. With a 48 mm long Z-cut amplifier device, Er-diffusion doped at 1100°C, 6.7 dB (coupled pump power P_p,c=170 mW) and 14.7 dB (P_p,c=90 mW) net small-signal gain have been achieved with a single-pass and a double-pass configuration, respectively, at the signal wavelength λ_s=1531 nm. A Z-cut sample doped at 1135°C showed a considerably improved behavior. 11.3 dB single-pass net small-signal gain has been obtained (P_p,c=170 mW; sample length 5.7 cm). Theoretical calculations predict gain figures up to 20 dB in single-pass and 40 dB in double-pass Er:Ti:LiNbO₃ amplifiers with increased (realistic) lengths of 10 cm     

Modeling of Ti:LiNbO3 waveguide directional couplers

A simple and accurate method is presented for studying the coupling characteristics of 3D diffused channel waveguide directional couplers. The method is based on the scalar variational principle and differs from other methods as it does not require any assumption for the functional form of the trial field. The authors also propose an equivalent 2D directional coupler that also gives accurate results and, hence, saves considerable computational time, Comparison with experimental and other theoretical results is also presented     

Ti:LiNbO3 stripe waveguide Bragg reflector gratings

The first demonstration of Bragg reflector grating filters in Ti:LiNbO₃ single-mode channel guides is reported. Filter bandwidths as narrow as 0.14 nm centred at 1.476 μm have been achieved for TE polarisation in Y-cut (X-propagating) material     

Fluctuational crosstalk in Ti:LiNbO3 directional couplerswitches

It has been found that the fluctuations in the Ti concentration along waveguides of Ti:LiNbO₃ directional coupler switches degrade the switch extinction ratio and introduce an unwanted crosstalk between both channels. We discuss analytically the effect of effective optical index fluctuations on the transfer matrix of the optical switch. We demonstrate the sensitivity of the mismatch to the statistics of the fluctuations of the Ti concentration     

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     

Suppression of crosstalk drift in Ti:LiNbO3 waveguideswitches

The authors report on DC drift characteristics with short relaxation times (typically 20-30 s) of LiNbO₃-based electrooptic switches for use at the wavelength of 1.3 μm. They evaluated the switch elements without oxide buffer layers to focus on the substrate. Sputter-etching of more than 20 nm of the substrate surface after waveguide fabrication results in a remarkable suppression of the drift: drift-induced crosstalk of below -25 dB has been achieved. The sputtering process also reduces the range of scatter of voltage drift among four switches fabricated on a single substrate. With data on the capacitance and resistance between a pair of electrodes, the above effects are attributed to the removal of the surface layer by sputtering     

Ti:Er:LiNbO3 waveguide laser of optimized efficiency

The development of a Fabry-Perot-type Ti,Er:LiNbO₃ waveguide laser of optimized CW output power up to 63 mW (λ_s =1561 nm) at a pump power level of 210 mW (λ_p=1480 nm) and a slope efficiency of up to 37% is reported. The theoretical model for the waveguide laser is presented and applied to determine the optimum resonator configuration using waveguide parameters obtained from a detailed characterization of the laser sample. With pulsed pumping, waveguide laser pulses of up to 6.2 W peak power were observed. Apart from residual relaxation oscillations, the laser emission proved to be shot-noise limited     

Ti扩散LiNbO_3单模波导参数的测量

对Ti扩散LiNbO_3波导分别采用双曲正割和抛物线分布来近似其折射率的高斯分布,在两个波长下由相应的两种近似本征值方程分别推得了单模波导参数的计算公式,并在4880(?)和6328(?)激光波长下利用棱镜耦合器测量了单模波导参数,对测量结果给出必要的理论分析。     

Simulations of Ti:LiNbO3 waveguide modulators-acomparison of simulation techniques

The modulation characteristics of several Ti:LiNbO₃ waveguide devices were simulated. For the electrooptic effect, both a spatially dependent and a uniform modulation field were considered. Both the three-dimensional beam propagation method and the two-dimensional beam propagation method with effective index were used in the simulations. The results of simulations and measured device performance are compared     

Ti:LiNbO3 interferometric activated X-switch forhigh-speed applications: IAX

High-speed switching is accomplished by using a balanced bridge interferometric switch with X-switches as electro-optic tunable 3 dB couplers. A device with a 3-dB bandwidth of 6·5 GHz at a switching voltage of 7·0 V and an insertion loss of 4 dB has been realised for λ=1·3 μm     

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     

Analysis of end-pumped Nd:Ti:LiNbO3 microchip waveguideFabry-Perot lasers

A self-consistent analysis of end-pumped Nd:Ti:LiNbO₃ microchip waveguide lasers based on the fast Fourier transform beam propagation method (FFT-BPM) has been proposed. The algorithm of the model allows one to describe the laser gain and pump absorption in terms of the complex atomic susceptibility for the case of the Nd³⁺ ions. Considering the interference effects between the forward and backward light waves, the population inversion longitudinal and transversal spatial effects can be simulated. The laser characteristics of the Nd:Ti:LiNbO₃ waveguide laser correlate well with the experimental data and theoretical results. The design rules for the optimized microchip laser are also developed by using the proposed model     

90° reflecting mirrors in Ti:LiNbO3 waveguidestructures

The first integrable 90° reflecting mirrors in LiNbO₃ waveguide structures are reported. Mirror power efficiencies (⩽28%) have been measured experimentally and are compared with theoretical values obtained by mode overlap integration     

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