Integrated optics eight-port 90° hybrid on LiNbO3

The design, fabrication, and characterization of an integrated optical eight-port 90° hybrid in LiNbO₃ are discussed. The hybrid is realized as a bridge circuit comprising four directional couplers and two phase shifters, each of the devices being electrooptically tunable. The electrodes are fabricated as combined indium-tin-oxide/gold multilayers. The component provides the desired phase pattern of the intermediate frequency. Measurements on the phase stability of the integrated bridge show phase fluctuations of <±5° and a temperature drift of ≈15°/°C. Both may be eliminated by a phase control loop     

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     

Integrated optics in LiNbO3: recent developments indevices for telecommunications

Recent progress in lithium niobate based integrated optics is reviewed, emphasizing applications in the telecommunications area. Prospects for systems applications are discussed     

Temperature-tuned 90° phase-matching properties of LiB3O5

A single LiB₃O₅ crystal cut normal to x(=a) and z(=b) can be used for the 90° phase-matched SHG at 0.475-0.875 μm by heating the crystal from ~20 to 320°C. The improved Sellmeier's equations and new formula of the temperature variation of the refractive indexes are presented     

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     

高芯片偏振消光比铌酸锂多功能集成光学器件

分析了铌酸锂多功能集成光学器件的偏振消光机理,设计和制作了高芯片偏振消光比的铌酸锂多功能集成光学器件。器件采用切断部分输入直波导后在切断端面选择性镀阻光膜的结构以截断射入衬底的辐射光,与芯片耦合后实现了高于85dB的芯片偏振消光比。制作的器件插入损耗小于3.5dB,分光比为48/52~52/48,半波电压Vπ小于3.5V,尾纤偏振串音小于-33dB;在-55~+85℃全温范围内,损耗变化量小于0.2dB,分光比变化小于1%,尾纤偏振串音小于-27dB,能够满足工程化应用需要。     

Integrated optical high-voltage sensor using a Z-cut LiNbO3 cutoff modulator

An integrated optical AC high-voltage sensor based on a Z-cut LiNbO₃ cutoff modulator is fabricated by the proton diffusion method. It is a passive sensor that does not require any electrical bias or any voltage divider. Its sensing voltage range is extended by using the following method. First, its inherent linear range is extended, both by utilizing a novel electrode structure with dummy electrodes and by shortening the electrode length. The dummy electrodes reduce the magnitude of the Z-component electric field applied to the cutoff modulator. Second, a sensor configuration is designed to adjust its operating bias point optically by annealing and thus to utilize the whole extended linear range. The sensing voltage range of the cutoff modulator sensor exceeds AC 1000 V peak to peak     

Interdigital transducer for acousto-optic tunable filter on LiNbO3

Interdigital transducers on X-cut Y-propagating lithium niobate generate parasitic Bleustein-Gulyaev waves which reduce the acoustic efficiency. An increased number of electrode pairs improves the efficiency and an AOTF driven by an RF electric power of only 6 mW can be realised     

Adiabatic 2×2 polarization splitter on LiNbO3

The authors have demonstrated a passive 2×2 polarization splitter in x-cut LiNbO₃, using a hybrid Ti-indiffusion/proton-exchange technology. At a wavelength of 1530 nm, all paths exhibited an extinction ratio of better than 20 dB, with an average excess loss of 1 dB. This component can be integrated with optical filters, switches, and beam combiners to achieve polarization-independent operations     

UV-induced surface-relief gratings on LiNbO3 channelwaveguides

We report a new technique for fabricating Bragg gratings in LiNbO ₃ channel waveguides. This technique involves the irradiation of the waveguide by means of an ultraviolet beam. We also demonstrate the applications of these gratings as tunable input couplers and as Bragg reflectors     

Proton exchange in Y-cut LiNbO3

In the present work, planar waveguides in Y-cut LiNbO₃ were obtained using modified proton exchange (PE) conditions of: PE and subsequent annealing (APE), PE in buffered melts (BMPE), APE followed by PE (APE+PE), and PE in vapours (VPE). Benzoic acid was used as the proton source in the PE, BMPE, and (APE+PE) experiments. Cinnamic acid was used for obtaining VPE-waveguides. The main aim was to prevent surface damage of Y-cut crystals due to the strains introduced by proton exchange. The investigations performed showed that the surface etching is probably due to lattice deformation anisotropy leading to higher strains in PE Y-cut samples. Most encouraging results were observed, when an optimized (APE+PE)-procedure was used for waveguide formation. This method is very attractive for the fast preparation of deep high-index and low-loss waveguides in Y-cut LiNbO₃. This procedure allows passive and active elements to be produced in one and the same Y-cut substrate of LiNbO₃. Similar preliminary results were obtained under VPE conditions.     

Electro-optic effect in proton exchanged LiNbO3 andLiTaO3 waveguides

Electro-optic properties of proton-exchanged (PE) waveguide layers in LiTaO₃ and LiNbO₃ are studied and related to their optical characteristics. The proton-exchange process induces a degradation of the electro-optic activity in both types of waveguides, PE LiNbO₃ and PE LiTaO₃. The measured electro-optic effect is close to the detection sensitivity even when the exchange regime is performed at low temperatures for short periods of time. The PE samples have been annealed (APE waveguides) and the changes of their r₃₃ electro-optic coefficient has been followed at successively higher temperatures and periods of time. Subjected to annealing at temperatures between 265-420°C, the LiTaO₃ layers show a partially recovered r₃₃ coefficient, the recovering being different for quick and slow cooling of the samples. In thin APE LiNbO₃ waveguiding layers a restoration of r₃₃ up to 75% of the bulk value is observed due to the annealing at temperatures between 200-340°C     

Examination of LiNbO3/nitride heterostructures

Oxides such as LiNbO₃, PbTiO₃, etc. have large polarization effects arising from the ferroelectric and piezoelectric effects. Recent work on nitride heterostructures has shown that polar charge can be used to substitute for dopant charge and controlled to create a two-dimensional electron (and hole) gas, resulting in ohmic contacts and diode like current–voltage characteristics. In this paper, we examine the potential of using ferroelectrics with traditional semiconductors for applications in novel electronic devices. In particular, we examine their use in creating very high sheet charge densities of mobile charge and tailorable current–voltage characteristics. It is seen that owing to hysteresis based effects in the ferroelectric layer, the direction of variation of voltage has a marked effect on the charge induced as well as the variation of that charge with voltage.     

Broad-band reflection traveling-wave LiNbO3 modulator

A velocity matched traveling-wave Mach-Zehnder interferometer (MZI) in LiNbO₃ operating in reflection, is reported and drive voltages are compared to those for single-pass devices of the same length. The device achieves double-pass operation by simultaneously reflecting the optical and RF waves, Broad-band operation to 20 GHz with drive voltages from 0.5 to 1 V (<0.5 GHz) to ~4.5 V (at 20 GHz) is observed with the reflection device. This performance is superior to that of the single-pass device, which has drive voltages of 2.1 V (dc) to ~4.5 V (at 20 GHz)     

An LiNbO3 integrated coherence modulator

The authors describe the principle of operation and the performance of a newly integrated LiNbO₃ modulator specially designed to generate optical delays of several millimeters. This is achieved by using the simultaneous propagation of the TE and TM modes in a waveguide and by taking benefit of the high natural birefringence of LiNbO₃. This modulator is well-suited to coherence modulation of light in fiber-optic transmissions. When powered by a short coherence source, the large optical delays induced by a cascade of such modulators can be used as information carriers to transmit several signals simultaneously. A demonstration is reported using a single source and two modulators in cascade to transmit signals simultaneously     

Polarisation-independent LiNbO3 4×4 matrix switch

The first polarisation independent LiNbO₃ strictly non-blocking 4×4 matrix switch has been developed. This matrix switch has a 4-6 dB insertion loss at any incident polarisation with 1.3 μm wavelength and about 30 V switching voltage     

钛扩散LiNbO_3波导干涉仪调制器

研制成Ti扩散LiNbO_3波导干涉仪调制器。在0.6328微米的光波长下加1千赫方波信号。50千赫的脉冲信号和100千赫～30兆赫的正弦波信号进行了调制实验。实验样品的最大调制深度87％,半波电压V_π=45伏,电容8微微法,3分贝带宽可达800兆赫。     

Ferroelectric-domain-inverted gratings by electron beam on LiNbO3

In the field of integrated optics for WDM networks, periodically poled Ti:LiNbO₃ seems to be an attractive candidate as it allows to build polarization-independent devices. A preliminary study about LiNbO₃ without any Ti-indiffusion is presented here. Hence, a ferroelectric-inverted grating is achieved using electron beam (EB) on LiNbO₃. In this study, the EB irradiation is performed with a scanning electron microscope (SEM) featuring a maximum accelerating voltage of 30 kV. A specific computer-aided design (CAD) application driving the SEM allows to write different structures such as periodic gratings. The EB domain-reversal method seems to be promising because of the accurate control and resolution of the reversed domains it can create. A pertinent choice of the irradiation conditions (accelerating voltage, probe current, scanning velocity, etc.) permits to generate gratings with 6.6, 20 and 30 μm wide periods. The inversion patterns have been revealed by HF-etching: domain walls are perpendicular to the surface in the first microns beneath the surface and their depth is almost the whole thickness of the wafer.     

Polarization selective phase modulator in LiNbO3

An integrated optical phase modulator which selectively modulates only one mode of polarization is discussed. Selectivity is accomplished by controlling the ratio between the voltages applied to two different electrode sections. A method for determining the correct ratio and evaluating the polarization selectivity of the phase modulation Γ has been developed. Experimentally, a Γ of 46 dB for selective modulation in the TM direction and a corresponding value of 40 dB for the TE direction have been obtained. It is also shown that the concept is a possible alternative or complement to polarizers and polarization preserving components in optical sensors     

Polarization independent LiNbO3 8×8 matrix switch

A polarization-independent LiNbO₃ strictly blocking 8×8 matrix switch has been developed. A relatively low insertion loss, below 12 dB, has been obtained by a reduction in bending loss, using a wide bent waveguide width. The switch has less than -18.7-dB crosstalk and about 85-V switching voltage at any incident polarization with 1.3-μ wavelength light