3-D analysis of LiNbO3: Ti channel waveguides and directional couplers

An efficient method of calculation of effective refractive indexes and field distribution of guided optical modes in diffused channel waveguides and directional couplers is presented. Refractive index distribution which follows from the theory of two-dimensional anisotropic diffusion is considered. Experiments which relate the refractive index profile with fabrication parameters are described. Then the coupling length of a directional coupler can be calculated from the fabrication parameters. The results correspond well to recently published experimental data.     

A comparison of power requirements of traveling-wave LiNbO3optical couplers and inteferometric modulators

It is shown that a coupler and interferometer may be considered two extremes of a generalized two-guide coupler device in which electrode length is less than a coupling length. For electrode lengths less than half of a coupling length, the generalized device looks more like an interferometer than a coupler. The impedance and electrical loss of asymmetric-stripe and coplanar-waveguide transmission lines on LiNbO3for thick as well as thin electrodes are then presented. The effects of the electrical loss on the bandwidth and drive requirements of traveling-wave LiNbO3couplers and interferometric devices are discussed, and it is shown that electrical loss in the transmission line is more detrimental to a coupler than to an interferometer. These results are then used to compare the drive power requirements of coupler and interferometric devices, and it is shown that for the same bandwidth and same optical guide dimensions, an interferometric device with a coplanar transmission line can require a lower drive power than a coupler with an asymmetric-stripe line.     

Three-electrode Ti:LiNbO3optical switch

Modifications of the conventional electrode arrangement of electrooptic directional coupler switches are described. UniformDelta Betaelectrodes can be symmetrically shortened to ∼ 40 percent of their length without significant increase in electrical drive voltage. Based on this result, a new three-electrode switch is described which can be used to electrically adjust both the bar and the crossed states of the switch. It is also demonstrated that the three-electrode arrangement can be used to reduce or eliminate optical crosstalk in Ti : LiNbO3switches.     

An experimental study of in-plane light scattering in titanium diffused Y-cut LiNbO3optical waveguides

This paper describes experimental studies on in-plane scattering of TE-polarized light in titanium-diffused Y-cut LiNbO3optical waveguides as a function of the diffusion process parameters of time, temperature, and the initial film thickness. The dependence of surface roughness on the waveguide fabrication parameters is also described. It has been found that as diffusion time and temperature are increased, in-plane light scattering firstly decreases but then eventually increases. The eventual increase in in-plane scattering is, apparently, because of growth of subsurface waveguide defects. From these studies, a reasonably consistent interpretation for the dependence of the quality of the optical waveguide on the waveguide fabrication parameters has emerged.     

10 GHz bandwidth traveling-wave LiNbO3optical waveguide modulator

A broad-band traveling-wave electrooptic modulator of Ti-diffused LiNbO3optical waveguide was designed, constructed, and tested at 0.63 μm over a bandwidth of 10.5 GHz. Using a novel asymmetric electrode configuration as a microwave waveguide, practically smooth frequency response of the modulator was obtained. For 300 mW drive power, the phase modulation index was 1 rad at 2 GHz and 0.53 rad at 10 GHz, while the intensity modulation index was 64 and 34 percent, respectively.     

Control of birefringence in Ti:LiNbO3optical waveguides by proton exchange of lithium ions

The control of birefringence in Ti: LiNbO3optical waveguides by proton exchange is investigated in detail. It is shown that annealing of deep proton exchanged waveguides (7-8 mum) in an oxygen atmosphere allows precise control of the birefringence over a broad range of values. Even optically isotropic guides can be fabricated.     

Thermal annealing of He+implanted optical waveguides in LiNbO3

The annealing of He⁺implanted optical waveguides is required to reduce the damage in the guiding layer of the sample. Results of the effect of this process are presented together with the aging characteristics of these waveguides which are due to room temperature annealing. The effect of sample temperature during implantation is also presented which may be considered as an annealing process occurring during implantation.     

Electrooptic linear chirped grating lenses on planar optical Ti:LiNbO3waveguides

We report the experimental investigation of the first electrooptic chirped grating lenses (F/28 and F/56) on single-mode planar Ti-indiffused LiNbO3waveguides for TE and TM modes at 633 nm. These lenses perform simultaneously the basic functions of focusing, switching, and modulation of guided wave beams.     

Wavelength dependent properties of He+implanted optical waveguides in LiNbO3

The effects of wavelength on the attenuation and propagation constant of TE and TM modes in He+ implanted optical waveguides in LiNbO3are presented. It is shown that the TM mode properties are determined by the ion damage profile, while the TE mode properties are considerably influenced by lithium loss which occurs during implantation.     

Acoustooptic Bragg deflection in LiNbO3Ti-diffused waveguides

A LiNbO3acoustooptic Bragg deflector utilizing a Ti-diffused optical waveguide and acoustic surface waves, which requires only 50 mW of electrical drive power to obtain 70-percent deflection, has been demonstrated.     

C2F6reactive ion-beam etching of LiNbO3and Nb2O5and their application to optical waveguides

Properties of C2F6(freon 116) reactive ion-beam etching (RIBE) of LiNbO3, Ti-indiffused LiNbO3, and sputter-deposited Nb2O5film on LiNbO3are reported. A maximum differential etching ratio of approximately 5:1 has been measured for LiNbO3and the AZ 1350B Shipley photoresist. We have used this etching technique to fabricate diffraction gratings on both Ti-indiffused LiNbO3and Nb2O5- LiNbO3waveguides with measured throughput efficiencies in excess of 85 percent.     

High-Q micro-ring resonators and grating couplers for silicon-on-insulator integrated photonic circuits

An ultra-small integrated photonic circuit has been proposed,which incorporates a high-quality-factor passive micro-ring resonator(MR) linked to a vertical grating coupler on a standard silicon-on-insulator(SOI) substrate.The experimental results demonstrate that the MR propagation loss is 0.532 dB/cm with a 10μm radius ring resonator,the intrinsic quality factor is as high as 202.000,the waveguide grating wavelength response curve is a 1 dB bandwidth of 40 nm at 1540 nm telecommunication wavelengths,and the measured fiber-to-fiber coupling loss is 10 dB.Furthermore,the resonator wavelength temperature dependence of the 450 nm wide micro-ring resonator is 54.1 pm/℃.Such vertical grating coupler and low loss MR-integrated components greatly promote a key element in biosensors and high-speed interconnect communication applications.     

Length minimization in integrated optical circuits incorporatingdirectional couplers and curved sections

An analysis is presented that describes minimization of overall channel waveguide length in integrated optical circuits incorporating directional couplers and curved sections. Calculations are presented for LiNbO₃, GaAlAs, and SiO₂-Si based optical channel waveguides. The results demonstrate the presence of a minimum total length corresponding to a particular degree of field confinement. The value of overall length at the minimum is shown to be significantly lower than that for other values of field confinement allowing single-mode operation     

Anomalous attenuation and depolarization scattering in y-cut LiNbO3proton exchanged waveguides

A large anomalous attenuation and depolarization scattering have been observed iny-cut,x-direction propagating LiNbO3proton exchanged waveguides at 0.632 μm wavelength. We observe this phenomenon only when the mode effective index is smaller than the ordinary indexn_{0} (n_{0} = 2.286). The effect is caused by phase-match scattering into the substrate. Exchange solutions with various mole percentages of lithium benzoate have been used and the same phenomenon has been consistently observed.     

Optical branching effect in photorefractive sensitive Ti:LiNbO3slab waveguides

This paper describes splitting of a single optical beam into several beams (the branching effect) in photorefractive sensitive Ti:LiNbO3slab waveguides. The branching effect is studied as a function of time and optical input power.     

Strip waveguides in LiNbO3fabricated by combined metal diffusion and ion implantation

Embedded strip waveguides in LiNbO3are fabricated by a titanium in-diffusion followed by a masked implantation of helium ions which reduces the refractive index in the unmasked regions and confines the optical wave. This technique yields waveguides with well-defined lateral dimensions and strong optical confinement. The index profiles of helium implanted LiNbO3are determined with an index reduction of more than 1 percent up to about 1 μm depth for 350 keV He+ ions at a dosePhi simeq 10^{16}cm^-2. Electrooptic devices with self-aligned electrodes are fabricated by using the implantation mask as a lift-off mask, and Mach-Zehndet type interferometers are investigated.     

Low radiation loss branching/combining of optical circuits using high-silica channel waveguides

A new branching/combining optical circuit structure using high-silica channel waveguides was proposed to reduce radiation loss where branching occurs. In this structure, an additional low-refractive-index layer was formed at the junction surface between the main and branching channels. The loss in a conventional circuit could be successfully reduced by over 0.4 dB in the through channel and 0.1 dB in the reflecting channel. The allowable conditions for a low-refractive-index layer were obtained through experimental and theoretical studies.     

Optical properties of planar waveguides formed by He+implantation in LiNbO3

The variation in optical properties of He+ -implanted LiNbO3waveguides has been investigated as a function of ion energy and dose for both TE and TM polarizations. Results presented indicate the importance of implant temperature in determining waveguide properties. The effect of aging on optical attenuation is also reported. Although TM (ordinary) mode behavior is determined by the refractive-index profile caused by ion damage, TE-(extraordinary) mode properties are also affected by changes in stoichiometry.     

多模干涉耦合器及其在光通信系统中的应用

文章概述了多模干涉耦合器的结构、工作原理和目前常用的分析方法,重点阐述了多模干涉耦合器的光传输特性.最后,详细介绍了多模干涉耦合器在光纤通信系统的多种用途.