A poled electrooptic fiber

A simple fabrication technique, readily extensible to volume manufacturing, is presented to produce an electrooptically active fiber segment that can be simply integrated into optoelectronic devices. The fabrication technique offers a dielectric isolation structure surrounding the fiber to allow high field poling, a pair of electrodes used both for poling and for inducing an electrooptic effect that can be lithographically defined for either velocity-matched, high speed RF modulation or quasiphasematched three-wave mixing interactions, and ends of the fiber unaffected by the fabrication and available for splicing with additional fiber sections. An electrooptic coefficient, including overlap between the nonlinearity and the fiber mode, as high as 0.3 pm/V was obtained by combined temperature/electric field poling.     

Growth and decay of the electrooptic effect in thermally poled B/Gecodoped fiber

Using an in situ technique for measuring the induced electrooptic effect during poling, we have studied the growth and decay characteristics of thermally poled twin hole B/Ge codoped fiber devices. The decay characteristic measured at elevated temperatures were best fitted with a stretched exponential function, indicating a distribution of relaxation times is present in this material. Using the Arrhenius relation, we calculate an activation energy for the stability of the electrooptic effect with this material and poling geometry in the range from 25 to 28 kJ/mol (0.28-0.31 eV), corresponding to a lifetime at 298 K of approximately 45 days     

热极化光纤中线性电光系数对调制频率的响应

热极化方法可在熔石英熊猫保偏光纤器件中产生线性电光效应,由此可制成热极化光纤器件.为获得热极化光纤器件的调制频率响应特性,进行了热极化保偏光纤的调制频率响应实验研究,并探讨了其机理.实验表明,已制成的热极化熊猫光纤,在其上所加调制频率小于1 kHz的范围内,会使极化产生的线性电光系数产生声频共振.当调制频率大于2 kHz后,电光效应基本不受调制频率的影响.机理分析表明,热极化使非晶态的熔石英光纤中形成了类晶体结构.极化光纤中产生的反压电效应会导致器件的线性电光系数产生声频共振.     

Optimum parameters for CO2 laser-assisted poling ofoptical fibers

CO₂ laser-assisted poling is a new technique that potentially allows rapid poling and spatially selective poling. The effect of scan-rate, multiple scans, and power fluctuations on CO₂ laser-assisted poling were investigated. For a beam irradiance of 52 W · cm^-2 the minimum necessary dwell time was 0.55 s; multiple scans have no effect unless the poling conditions are changed. CO₂ laser-assisted poling was found to be sensitive to perturbations such as laser power fluctuations, which were detrimental. Under optimized conditions the maximum electrooptic coefficient achieved was 0.4 pm/V. Fiber devices up to 90 cm in length have been poled     

Modification of thermal poling evolution using novel twin-holefibers

Thermal poling current and electrooptic evolution were studied for a standard twin-hole fiber and two novel design twin-hole fibers. The poling characteristics were modified in the novel fibers, which had a trap or donor region inside the anode hole. Modifications of the poling characteristics were observed in both the current evolution and the electrooptic evolution. The novel fiber designs can facilitate the tailoring of poled fiber device characteristics     

First demonstration of thermally poled electrooptically tunablefiber Bragg gratings

We demonstrate electrooptic tuning of a fiber Bragg grating (FBG) fabricated in a thermally poled fiber. 40 pm of tuning was demonstrated, corresponding to an electrooptic coefficient of 0.25 pm/V. Such electrooptic tunable FBG's have strong potential for numerous devices, including all-fiber amplitude modulators and high-speed tunable filters     

Modeling the electrooptic evolution in thermally poledgermanosilicate fibers

We formulate a simple quantitative three-species charge-carrier transport model, consisting of two distinct positive ions and a single negative ion, to describe the dynamics during thermal poling of a germanosilicate optical fiber. We numerically solved the equations and report one-dimensional space-time solutions for the electrooptic (EO) coefficient. In the two-cation model, our findings show the EO coefficient initially dips near the anode and then monotonically rises to a steady-state value, higher than that produced by the initial applied poling field. However, at the cathode, the electric field quickly dropped to zero where it remained zero for the poling duration. The introduction of a moving negative ion clearly shows the existence of a dead time characteristic appearing at the cathode, resulting in a gain in the initial EO coefficient. This model also reveals that the resulting EO evolution in a thermally poled germanium-boron codoped fiber can he attributed to the movement of just two ions of opposite polarity. To explain the increase in the EO coefficient in boron codoped germanosilicate fiber, we found it necessary to allow for an increase in the third-order susceptibility by a factor of ~3.4     

Evidence of space-charge effects in thermal poling

The in situ thermal poling processes in germanosilicate fibers for positive and negative poling voltages are significantly different. Thermal poling of silica fibers consists of two processes: the faster linear process of charge migration and the subsequent single exponential process of charge ionization. Both the shielding electrical field due to charge migration and the ionization electrical field due to charge ionization are able to be frozen-in at room temperature and lead to the residual linear electrooptic effects. The observations support that the mechanism of the induced electrooptic effects is based on space charge electrical fields instead of dipole/bond orientation     

Optical intensity modulator based on a novel electrooptic polymerincorporating high μβ chromophore

We have synthesized a novel electrooptic (EO) polymer based on a high μβ chromophore incorporating tricyanobutadiene acceptors. A crosslinked polyurethane network was also adopted to enhance its thermal stability. In order to find the optimum poling condition for the polymer, the influence of the electric poling profile on optical characteristics such as the EO effect, thermal stability, and damage was investigated. Then a high-speed intensity modulator using the EO polymer was designed and fabricated. The measured half-wave voltage V_π was 4.5 V at the wavelength of 1.31 μm. Accordingly, the achieved EO coefficient r₃₃ was as high as 25 pm/V, and the thermal stability of the poled polymer was as high as 95°C. Finally, the modulator was successfully operated up to 40 GHz     

Second-order optical nonlinearity in thermally poled phosphorus-doped silicon dioxide thin-film waveguides

A phosphorus-doped silicon dioxide nonlinear planar waveguide on a GE124 fused silica substrate using plasma-enhanced chemical vapour deposition and thermal poling technique is implemented. The stable second-order nonlinear susceptibility induced in the waveguide is estimated to be around 0.58 pm/V by means of hydrofluoric acid etching, Maker?s fringe measurement and grid search curve fitting using a double-step nonlinear profile. This nonlinear planar waveguide may be applied to fabricate an electrooptic device on the silicon photonic chip.     

Electrooptic ferroelectric Na/sub 0.5/K/sub 0.5/NbO/sub 3/ films

We report on waveguiding and electrooptic properties of epitaxial Na/sub 0.5/K/sub 0.5/NbO/sub 3/ films grown by radio-frequency magnetron sputtering on Al/sub 2/O/sub 3/(11_02) single crystal substrates. High optical waveguiding performance has been demonstrated in infrared and visible light. The in-plane electrooptic effect has been recorded in transmission using a transverse geometry. At dc fields, the effective linear electrooptic coefficient was determined to 28 pm/V, which is promising for modulator applications.     

A novel pulse-poling technique for EO polymer waveguide devicesusing device electrode poling

The authors describe a novel method for poling electrooptic polymer modulators using a pulse-poling technique. Device electrodes were used directly for poling, such that the poling field is selectively applied in a counter-aligned fashion while the single field is coaligned, thus requiring only a single-voltage source for poling and modulation. Channel waveguide losses caused by poling with the device electrodes were measured and compared to total waveguide poling. The technique was found to introduce less overall loss for devices with inactive waveguide regions of more than a few millimeters and simplifies fabrication requirements     

Electrooptic light modulation and second-harmonic generation in novel diazo-dye-substituted poled polymers

The nonlinear-optical susceptibilities, x/sup (2)/, of a diazo-dye-substituted polymer poled with high electric fields were determined experimentally and theoretically. The electrooptic modulation of He-Ne laser light in a traveling-wave channel-waveguide modulator using the diazo-dye-substituted poled polymer is reported, and the linear electrooptic coefficient of the poled polymer is estimated from a measured half-wave voltage. The polymer studied is a poly(methyl methacrylate) copolymerized with a methacrylate ester of the dicyanovinyl-terminated diazo dye derivative. This polymer is called 3RDCVXY. The corona-poled 3RDCVXY polymer exhibits a x/sup (2)/ value of 1*10/sup -6/ esu at 1.06 mu m. The thermal stability is excellent even at 80 degrees C. The poled 3RDCVXY polymer film shows a linear electrooptic coefficient as high as 40 pm/V at 0.633 mu m. An electrooptical light modulation in the channel 3RDCVXY polymer waveguides with a half-wave voltage as low as 5 V was obtained.<>     

Electrooptic polymer modulators operating in both TE and TM modes incorporating a vertically tapered cladding

We propose a modified electrooptic (EO) PMMA polymer waveguide structure supporting both TE and TM modes in spite of the large birefringence induced by the poling. A vertically tapered structure is employed to connect a single-mode rib waveguide and a confinement-enhanced rectangular buried waveguide. This waveguide structure can be easily fabricated by a two-step reactive ion etching (RIE) process with a shadow mask. To demonstrate TE/TM confinement and single-mode operation, Mach-Zehnder intensity modulators are fabricated by incorporating the proposed waveguide structure. The extinction ratio is better than -15 dB, which proves the single-mode operation. Half-wave voltages for TM and TE modes are 6 and 24 V, respectively.     

Integrated-optic focal-spot intensity modulator using electroopticpolymer waveguide

A novel integrated-optic focal-spot intensity modulator comprising an electrooptic (EO) phase-distribution modulator and a focusing grating coupler (FGC) in an EO polymer planar waveguide on a Si substrate is proposed and demonstrated. The integrated phase-distribution modulator is made up of three-finger top electrodes and a planar bottom electrode sandwiching the waveguide. The electrodes are used for both the poling process and the modulation of the phase distribution of the guided wave. The FGC couples the guided wave to a beam focused on a point in free space. The intensity distribution of the focused spot is modulated by altering the wavefront of the guided wave. The bottom metal electrode is extended to the place under the FGC and serves as a reflection film so that the output coupling occurs only into the direction of the air for increasing the efficiency. The device was designed and fabricated with an active polymer p-NAn-PVA (p-nitroaniline n-polyvinyl alcohol). An extinction ratio of the focal-spot intensity was higher than 3 dB at a modulation voltage of 30 V for 3-mm-long electrodes. The frequency response was measured to be flat over 2 MHz. The EO effect induced by poling showed no significant relaxation over 300 h in an unconditioned room (20-30°C)     

热极化保偏光纤电光相位调制器

对熊猫保偏光纤热极化 ,制成了一种新型保偏光纤电光相位调制器。在 2 80℃温度下 ,在磨抛并镀有微带电极的熊猫光纤两侧加 30 0 0V直流高电压进行极化 ,制成的电光相位调制器的电光系数为 0 47± 0 .0 5pm/V。此新型光纤电光相位调制器由保偏光纤制成 ,可用其构成偏振稳定的干涉型全光纤器件。     

Demonstration of thermal poling in holey fibres

A second-order nonlinearity is induced for the first time in a holey fibre by thermal poling. Non-phase matched second harmonic generation with a ~10^-8/W conversion efficiency is observed and the electro-optic coefficient is measured to be ~0.02 pm/V     

Efficient electrooptic modulator in InGaAlAs/InP optical waveguides

A single heterostructure InGaAlAs/InP phase modulator utilizing the quadratic electrooptic effect (QEO) is reported for the first time. The calculated value of the QEO coefficient from the measurements is 3.7×10^-19 m²/V² at 80 meV below the band edge. In addition, the linear electrooptic effect (LEO) coefficient is estimated to be 1.2×10^-12 m/V, which is comparable to that of GaAs. The propagation loss of a single mode ridge waveguide is in the range of 1.5-1.7 dB/cm, which is better than the previously reported value in this material system. The measured single mode phase shifts are 5.5 and 2.8°/V mm for TE and TM polarizations, respectively. These values are the largest reported so far in an InGaAlAs system     

Integrated optical waveguide polarizer based on photobleaching-induced birefringence in an electrooptic polymer

A TE-pass waveguide polarizer is fabricated by utilizing the photobleaching-induced birefringence at room temperature in an electrooptic polymer. The polarizer consists of the photobleached waveguide supporting only TE mode, which is integrated in the middle of the etched rib waveguide supporting both TE and TM modes. It has a simple structure and requires no high temperature process like poling. The measured polarization extinction ratio is about 21 dB at the wavelengths of 1.3 and 1.55 /spl mu/m, and the estimated excess loss is about 0.4 dB.     

TE-TM mode converter in a poled-polymer waveguide

A novel active TE-TM mode converter in a poled electrooptic polymer waveguide is demonstrated. The mode converter utilizes a 45°-off poling configuration, which can be obtained by arranging upper- and lower-stripe poling electrodes with a proper lateral displacement. The mode-conversion properties and electrooptic effect are demonstrated by using a vector-beam propagation method in a buried channel-type waveguide. Applications to integrated polymer-waveguide devices are also suggested