A polarization independent GaAs-AlGaAs electrooptic modulator

Two designs for polarization independent GaAs-AlGaAs interferometric electrooptic modulators are described. One design uses the linear electrooptic effect to couple degenerate TE/TM eigenmodes of a single-mode waveguide. In the other design the eigenmodes need only be near degenerate. The design using the coupling between near degenerate TE/TM modes utilizes a novel biasing scheme. A novel polarization independent GaAs-AlGaAs interferometric optical modulator based on this design has been fabricated and characterized at 1.3 μm. This modulator is fabricated as a traveling wave modulator incorporating 50 Ω, phase velocity matched, low microwave loss electrodes for maximum electrical bandwidth     

Wavelength-tunable electrooptic polarization conversion inbirefringent waveguides

Wavelength-tunable, electrooptic polarization conversion in a birefringent waveguide accomplished with a multiple cascade of alternating TE←→TM mode converter and TE/TM phase shifter sections is analyzed. Such polarization converters have been demonstrated in LiNbO₃ and have been used as electrooptically tunable narrowband (Δλ⩽λ₀/1000) wavelength filters with tuning ranges of at least λ₀/200. It is shown that the polarization converter requires only two independent drive voltages and provides arbitrary polarization transformations from any general input polarization to any desired output polarization with simultaneous wavelength tunability. The device is characterized by its overall transfer matrix and the optical bandwidths and tuning ranges for various electrode geometries     

AlGaAs-GaAs quantum-well electrooptic phase modulator with disorderdelineated optical confinement

Waveguide phase modulators, with 0.5- and 1-μm quantum-well (QW) active regions which are defined by impurity induced disordering are investigated theoretically. By controlling the extent of the interdiffusion in the lateral claddings, the refractive index difference between the core and claddings is used to provide single-mode operation. Strong optical confinement, which is required to produce single-mode high-efficiency modulation, requires the peak impurity concentration to be at the center of the QW active region. Moreover, the annealing time needs to be optimized so that single mode can be maintained at the desired bias field. A low dopant concentration is also expected to minimize the destruction of the modulator structure. The results show that since the core/cladding interface is graded, the width of the metal contact is important. A comparison of modulation efficiency for active layer thicknesses of 0.5 and 1.0 μm shows that the 0.5-μm one is a more efficient structure and its absorption loss can be reduced by increasing the applied field from 50 to 100 kV/cm     

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     

Coupled GaAs multiple-quantum-well channel waveguides includingquadratic electrooptic effect

Two coupled channel waveguides using GaAs multiple quantum wells are investigated using an improved coupled-mode theory for anisotropic waveguides and the effective index method. The quadratic electrooptic effect in the multiquantum-well structures is taken into consideration. It is shown that only a moderate electric field for multiquantum-well waveguides is necessary to achieve the optical power switching compared with that required for a bulk GaAs waveguide     

A high-frequency GaAs optical guided-wave electrooptic interferometric modulator

The characteristics and frequency response of a GaAs monolithic guided-wave interferometric modulator operating at 1.3 μm are presented. The interfetometer consists of three-guide coupler input and output sections and single-mode p+-n--n+ slab-coupled rib-waveguide active arms. The measured electrical bandwidth of an interferometer with 2 mm long active arms was 2.2 GHz and limited by parasitics. This corresponds to a small signal optical bandwidth of ≈ 3.0 GHz when the interferometer is biased in a linear portion of the optical output versus voltage characteristics. Reduction of parasitics should result in a substantial increase in the bandwidth of these devices.     

Optical pulse generation using guided-wave electrooptic modulator with resonant electrodes and polarization reversal

This paper reports on optical pulse generation using a new guided-wave electrooptic (EO) phase modulator with long resonant electrodes and polarization reversal. Adopting polarization-reversal structure to a guided-wave EO modulator with long standing-wave resonant electrodes, high-efficiency optical modulation is obtained by the compensation of the transit-time effect. By operating a fabricated EO phase modulator with a large amplitude modulation signal, optical sidebands over 100 GHz were obtained. Furthermore, optical pulse trains of an /spl sim/ 25-ps pulsewidth and a 15.28-GHz repetition frequency were successfully obtained by controlling the generated optical sidebands by use of an optical synthesizer.     

Laser-power stabilization using a quantum-well modulator

A novel method for laser-power stabilization using a multiple quantum-well reflection electroabsorption modulator with a Fabry-Perot cavity is demonstrated. Stable operation of the modulator produces a linear relationship between control current and optical absorption which permits the realization of noninterferometric optical subtraction and the implementation of a negative feedback architecture. Using this stabilization technique and a modulator with a 70% reflectivity change, intensity noise as large as ±75% of the incident level can be eliminated from a noisy laser beam     

0-1 GHz waveguide 10.6 μm GaAs electrooptic modulator

A GaAs electrooptic modulator for use in 10.6-μm laser frequency shifting applications is described. High-beam-quality output signals with a frequency tunability of 0.1-1.0 GHz were demonstrated. Thick epitaxial GaAs-AlGaAs waveguide structures were successfully fabricated into single-mode channel waveguides with excellent optical and electrooptic properties. A lumped-element modulator, with electrical and electrooptic characteristics in good agreement with theory, was operated at RF drive power levels up to the reverse breakdown voltage limit. The insertion loss of the modulator was quite high, due to absorption losses in the epitaxial material     

Demonstration of wavelength-insensitive biasing using an electrooptic polymer modulator

Wavelength-insensitive biasing (WIB) of an optical intensity modulator was demonstrated using the photobleaching technique to control the initial phase difference of the electrooptic polymer modulator. The WIB technique reduced the wavelength sensitivity of the bias point at 1550 nm by a factor of 17.     

Electroabsorption and electrooptic modulation in single crystalZnSe-ZnSSe waveguides grown by OMVPE on GaAs

Electroabsorption and the electrooptical effect were used to modulate argon laser light in ZnSe single crystal waveguides. The electrical contacts were Schottky barriers that created a nonuniform electric field in the samples. The nonuniform electric fields are modeled, and the experimental results are matched to this model. The electroabsorption experiments showed a modulation depth of 9.2 dB at an applied voltage of 255 V and a wavelength of 476 nm. With the same applied voltage at λ=488 nm the modulation depth was only 0.53 dB. Electrooptic phase modulation was also investigated. A phase shift of π was found at 60 V for a sample of 3 mm length. The half wave voltage was independent of wavelength for wavelengths from 488 to 515 nm     

GaAs/AlGaAs electro-optic modulator with bandwidth >40 GHz

A high speed GaAs/AlGaAs travelling wave Mach-Zehnder electro-optic modulator has been fabricated. The device uses a novel slow wave electrode design to achieve phase velocity matching and has a measured electrical bandwidth >40 GHz     

16-arrayed electrooptic polymer modulator

A 16-arrayed polymeric optical modulator is fabricated using an electrooptic (EO) polymer with a large EO coefficient and good thermal stability. The 16-arrayed modulator has lumped-type electrodes with a response time of less than 1 ns. The 16-arrayed modulator has good uniform modulation characteristics between the individual modulators. The deviation of half-wave voltages is 0.2 V and that of insertion losses about 1 dB. Crosstalks range from -28 to -36 dB and extinction ratios are more than 21 dB.     

Analysis of a microwave amplifier using the electrooptic junction modulator

Analysis of a proposed amplifier using the electro-optic junction modulator combined with an efficient photodetector shows that gain can be expected at microwave frequencies. The power gain-band product is found to increase linearly with light source power. Calculated gain-band productsG_{p}^{1/2}f, for a light power of one watt at the modulator input, a modulator length of one cm and a width of 10 microns are: for a GaAs modulator-2.6 GHz and for a GaP modulator-710 MHz. A traveling wave design shows gain proportional to the number of segments. For the same conditions as above, and using one thousand segments each 10 microns long, calculated gain-frequency products are: GaAs-820 GHz and GaP-130 GHz. An elementary noise calculation for the traveling wave design indicates that the amplifier is potentially capable of low noise operation.     

Light modulator using piezoelectric films with waveguides

A light modulator using piezoelectric films based on optical interference of the Mach-Zehnder type has been proposed and demonstrated. The modulator is constructed with two optical waveguides joined to each other at both ends to divide the incident light and to recombine them, and each waveguide is fabricated on a polyvinylidene fluoride (PVDF) film to serve as a voltage-driven phase-shifter.     

非线性液晶聚合物电光调制器

文章描述了透明非线性液晶聚合物的合成，准直和非线性光学性质，给出了液晶事物电光调制器的制作和测试方法及应用。     

PLZT film waveguide Mach-Zehnder electrooptic modulator

We report the numerical analysis and the fabrication of a reversed-ridge PLZT film waveguide. It is single-mode, has low transmission loss, and has large transverse cross-section suitable for efficient coupling to single-mode optical fibers. We used this structure to fabricate Mach-Zehnder (MZ) waveguide modulators. The field distribution in the channel and Y branch waveguides was calculated using a beam propagation method to analyze the modal profiles and the propagation loss. The reversed-ridge waveguides and the MZ structures were fabricated on r-sapphire substrates with a patterned ITO spacer film by sol-gel deposition. At 1.55 μm the propagation loss was 2.7 dB/cm. In the MZ, the half-wave modulation voltage was 8.5 V using 1.55 μm light and electrode length of 3.5 mm     

Extinction ratio of electrooptic light modulator

The dependence of the extinction ratio on the angle of inclination between the end surfaces of electrooptic crystals with natural birefringence and on the light spot size is described in the electrooptic light modulators.     

High-speed electrooptic phase modulators using InGaAs/InAlAsmultiple quantum well waveguides

High-speed phase modulation of waveguided InGaAs/InAlAs multiple-quantum-well optical modulators operating at 1.55 μm is described. The modulator requires a low voltage for π-phase-shift ( V_π=2.5 V) as well as a small intensity modulation depth of 1 dB. The measured electrical 3-dB bandwidth is 10 GHz, giving a bandwidth-to-voltage ratio of 4 GHz/V