Measurement of reduction in SHG coefficient of LiNbO/sub 3/ by proton exchanging

The SHG coefficient of a proton-exchanged layer of LiNbO/sub 3/, relative to the bulk value, has been measured for the first time by non-phase-matched SHG using a grating sample. It was found that the d/sub 33/ coefficient is reduced to approximately 0.5 of the bulk value by proton exchanging in pure benzoic acid.<>     

Electrooptically wavelength-tunable polarization converter utilizing strain-optic effect on X-cut LiNbO/sub 3/

A new electrooptically wavelength-tunable polarization converter by strain-optic effect on LiNbO/sub 3/ is presented. The polarization conversion is achieved by the tilt of waveguide principal axis caused by the stress induced by the proton-exchanged region on the single side of the waveguide. Simply increasing the proton-exchange time can enlarge the stress-distributed region and its interaction with the input light, thus, the conversion efficiency can be enhanced. By electrooptic effect, the wavelength of maximum conversion can be tuned at a rate of 0.081 nm/V with a maximum conversion efficiency of 92.4%.     

Proton-exchanged optical waveguides in LiNbO/sub 3/ using octanoic acid

Low-loss proton-exchanged planar waveguides in z-cut LiNbO/sub 3/ were fabricated and characterized optically using octanoic acid as a proton source. The waveguide exhibited a step-index profile with an index change of 0.118 measured at 0.633 mu m. The lowest waveguide propagation loss measured was 1.2 dB/cm, and it was reduced further to 0.4 dB/cm after annealing. The diffusion rate and the activation energy using this acid were found to be lower than those reported using other acids.<>     

Measurement of the increase in the SHG coefficient of proton-exchanged LiNbO/sub 3/ after annealing using a grating diffraction technique

The effect of limited levels of annealing on the second harmonic generation (SHG) coefficient (d/sub 33/) of proton-exchanged LiNbO/sub 3/ has been determined by measuring nonphasematched SHG in a diffraction grating structure. The effect of annealing is to partially restore the intrinsic nonlinearity of the proton-exchanged layer.<>     

Optical gain in proton-exchanged Cr:LiNbO/sub 3/ waveguides

The authors report on a study of optical gain in chromium-doped LiNbO/sub 3/ waveguides formed by the proton-exchange process. Optical gain in proton-exchanged Cr:LiNbO/sub 3/ channel waveguides has been measured for the first time. These waveguides show potential for diode-laser pumping of an integrated, broadband tunable laser in the 750-1150 nm spectral range.<>     

Direct comparison of hydrogen depth distributions and refractive index profiles in annealed proton-exchanged Z-cut LiNbO/sub 3/ waveguides

For the first time, to the authors' knowledge, hydrogen distributions in weakly and strongly annealed proton-exchanged z-cut LiNbO/sub 3/ have been measured using modified secondary ion mass spectrometry and correlated with refractive index profiles determined by optical waveguide measurements.<>     

Index profile of proton-exchanged waveguides in LiNbO/sub 3/ using pyrophosphoric acid

A systematic study was carried out on proton-exchanged LiNbO/sub 3/ optical waveguides using pyrophosphoric acid. A maximum surface index increase of 0.145 was measured at 0.633 mu m for z-cut substrates. The index profile could be accurately modelled by a polynomial expression of simply by a 'truncated' step-index profile.<>     

A novel wet-etching method using joint proton source in LiNbO/sub 3/

By mixing benzoic and adipic acids as the source of proton exchange, wet etched ridge waveguides are fabricated in Z-cut LiNbO/sub 3/. Under appropriate adipic-benzoic acid concentration ratios, the joint proton source can suppress the proton diffusion in the lateral directions, and thus, the sidewalls are much more vertical than the usual. The etched depths are also enhanced for more than 30%. And meanwhile, the fabricated ridge waveguides possess smooth surfaces and the scattering losses are lower than that of the conventionally produced samples.     

Multilayer spatial angular filter with airgap tuners to suppress grating lobes of 4/spl times/1 array antenna

A multilayer spatial angular filter with airgap tuners to suppress the grating lobes of a 4/spl times/1 array antenna is proposed. By using the airgap tuner, a commercial standard substrate can be chosen for the filter, to achieve its resonance condition, instead of /spl lambda//sub g//4 substrate. The measured beam patterns of the 4/spl times/1 array with the filter show that the grating and sidelobes are effectively diminished by 15 to 30 dB in the region of interest.     

A 54-GHz distributed amplifier with 6-V/sub PP/ output for a 40-Gb/s LiNbO/sub 3/ modulator driver

We have developed a distributed amplifier for a LiNbO/sub 3/ modulator driver using double-doped AlGaAs-InGaAs-AlGaAs pseudomorphic high electron mobility transistors (p-HEMTs). By using a stabilization and negative resistance control technique with source inductance and grounded coplanar waveguided lines, we obtained a gain of 15 dB, a bandwidth of 54 GHz, and 6-V/sub PP/ output. These results indicate that our circuit is a leading candidate for use as a LiNbO/sub 3/ modulator driver in 40-Gb/s fiber-optic communication systems.     

High-speed and low-driving-Voltage thin-sheet X-cut LiNbO/sub 3/ Modulator with laminated low-dielectric-constant adhesive

We present a novel thin-sheet X-cut LiNbO/sub 3/ optical modulator structure which can be fabricated by precise polishing and lapping to obtain a thinner LiNbO/sub 3/ substrate for a lower driving voltage in addition to velocity matching and impedance matching. We demonstrated that the fabricated modulator had a driving voltage V/spl pi/ of 2 V and zero chirp for 40-Gb/s operation and had a high potential for suppressed dc drift, and long-term reliability.     

质子交换LiNbO3平板波导及其导波层的色散关系研究

本文实验研究了用于新型光子器件的质子交换ＬｉＮｂＯ３的平板波导,在各种条件下制备了质子交换波导,建立了波导制备交换条件与波导参数之间的联系,获得了导波层的色民得到的结论对波导中非线性光学过程提供了理论基础。     

Gamma-Ray Irradiation-Enhanced Wet-Etching of Proton-Exchanged Lithium Niobate

Gamma-ray irradiation-enhanced wet-etching of proton-exchanged Z-cut Y-propagating LiNbO₃ is presented. The etched ridge height of a sample with gamma-ray irradiation of intensity 650 krad/h on a LiNbO₃ substrate for 30 min is three times larger than that without. Moreover, experimental results show the propagation loss values of Ti-indiffused LiNbO₃ waveguides fabricated on the irradiated ridge structures are only slightly larger than those on the nonirradiated ones.     

A highly damage-resistant Zn:LiNbO/sub 3/ ridge waveguide and its application to a polarization-independent wavelength converter

We have fabricated a periodically poled ridge waveguide using a liquid phase epitaxy (LPE)-grown Zn:LiNbO/sub 3/ substrate. The waveguide can confine both the transverse electric and transverse magnetic mode. Its strong resistance to photorefractive damage enables stable parametric amplification. We demonstrate polarization-independent wavelength conversion using polarization diversity in a single waveguide.     

Proton-exchanged LiNbO/sub 3/ optical waveguides using stearic acid

Proton-exchanged optical waveguides have been fabricated in z-cut LiNbO/sub 3/ using a new proton source: stearic acid. These waveguides were characterized optically and were found to exhibit a step index profile with Delta n=0.118 measured at 0.633 mu m. The propagation losses were typically around 1.5 dB/cm, and the diffusion constant and the activation energy for the proton-exchange process were measured to be 5*10/sup 6/ mu m/sup 2//h and 69 kJ/mol, respectively.<>     

Enhancement of domain inversion in LiTaO3 using heattreatment with metal-oxide mask

The domain inversion depth is enhanced in proton-exchanged LiTaO ₃ using heat treatment with a metal-oxide mask. Since this method can lower the proton exchange rate to get the same domain inversion depth, the degradation of the crystal quality in the domain-inverted layer is reduced     

Measurement of piezoelectric constant of LiNbO/sub 3/ crystal using interferometric optical fibre sensor

The piezoelectric constant of LiNbO/sub 3/ crystal, d/sub 33/, which has been controversial, is measured with an optical fibre sensor using homodyne interferometry. The minimum detected displacement of the LiNbO/sub 3/ crystal is well under 0.3 AA and with this, d/sub 33/ is determined as 0.7*10/sup -11/ m/V.<>     

Widely tunable multichannel wavelength conversion using multiple wavelength quasi-phase-matched LiNbO/sub 3/ waveguide

Widely tunable multichannel wavelength conversion using a multiple wavelength quasi-phase-matched LiNbO/sub 3/ waveguide is proposed. Simultaneous conversion of four-channel signals with a tunable range of more than 35 nm is successfully demonstrate for the first time.     

40 GHz, low half-wave voltage Ti:LiNbO/sub 3/ intensity modulator

A 5 V half-wave voltage (V/sub pi /) electro-optic Ti:LiNbO/sub 3/ intensity modulator with a -7.5 dB (electrical) optical response at 40 GHz is demonstrated at 1.3 mu m. A thick electrode structure is used in conjunction with a thin substrate to achieve a near optical-microwave phase match and a broadband electrical response.<>     

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/.