Traveling-wave Electrooptic Modulator Research Articles

Comprehensive MoL analysis of a class of semiconductor-based transmission lines suitable for microwave and optoelectronic application

A comprehensive analysis procedure is presented to investigate mode propagation in a class of semiconductor-based transmission lines suitable for application in microwave or optoelectronic circuits. The method of lines (MoL) has been used to investigate single or multiconductor planar transmission line structures printed on a combination of insulating and semiconducting substrate. Homogeneous as well as inhomogeneous doping areas in the semiconductor are included in the theoretical formulation. Numerical results are presented for III–V semiconductor travelling wave electro-optic modulators in double-rib, multilayer strip waveguide configuration, microslabTM transmission lines with partial and full strip cover and slow-wave MIS microstrip/coplanar transmission lines on thick and thin film semiconductor substrate with gradually inhomogeneous doping layer.

Microwave characteristics of high-speed traveling-wave electrooptic modulators on III-V semiconductors

Microwave characteristics of III-V semiconductor traveling wave electrooptic modulators were studied rigorously by using the method of lines. This approach makes it possible to construct a complete computer model of double-rib, multilayer strip waveguide modulators which are out of reach of the classical methods. Both p-i-n junction and Schottky-barrier junction controlled devices have been investigated. The fringing microwave field has been found to play an important role in improving the modulator bandwidth. For the first time, a nonperfect electrode of finite thickness has been modeled. The method of lines algorithm has proved to be a valuable CAD tool for design and optimization of high-speed modulators. >

Analysis of a new microwave low-loss and velocity-matched III-V transmission line for traveling-wave electrooptic modulators

A new microwave transmission line with low loss and velocity matched to a lightwave for a III-V traveling-wave electrooptic modulator has been analyzed using the spectral domain technique. A bandwidth of >40 GHz and a half-wave voltage V/sub pi / of >

Waveguide electrooptic microwave modulator with a low control power

Characteristics of a traveling-wave electrooptic light modulator, controlled by a microwave power amplifier, were investigated. The input control power was 7.5 mW in the modulation frequency range 4–5 GHz. Optimization of the modulator characteristics made it possible to reduce the control power to 2–3 mW at 4–5 GHz and to less than 10 mW at 9–11 GHz.

100 GHz traveling-wave electro-optic phase modulator

Dramatic bandwidth enhancement has been achieved in a GaAs traveling-wave electro-optic phase modulator by the addition of a GaAs superstrate to suppress both velocity mismatch and electrical dispersion.

GaAs traveling-wave polarization electro-optic waveguide modulator with bandwidth in excess of 20 GHz at 1.3 μm

We report a 1.3-μm GaAs traveling-wave electro-optic waveguide modulator with a 3-dB optical bandwidth in excess of 20 GHz. The bandwidth was determined by directly detecting the modulated optical signal with a high-speed InP/GaInAs photodiode. The modulator has a coplanar strip electrode configuration with a double heterojunction Al0.032Ga0.968As/GaAs/Al0.032Ga0.968As optical guide grown by low-pressure organometallic vapor phase epitaxy.

Transmission line aspects of the design of broad-band electrooptic traveling-wave modulators

This paper proposes a two-layer traveling-wave type electrooptic modulator structure to maximize modulation bandwidth from transmission line aspects. This structure can be designed to satisfy the velocity matching and impedance matching condition simultaneously. A design method for this structure is discussed.

Traveling-wave electro-optic modulator with maximum bandwidth-length product

A traveling-wave Ti-indiffused LiNbO3 guided-wave Mach–Zehnder interferometric modulator has been fabricated and characterized at λ=0.85 μm. The modulator achieves the theoretical 3-dB linear small-signal bandwidth limit of 16 GHz for a 4-mm-long interaction length. With a ±2.25-V drive signal, an extinction ratio of 22 dB is achieved. Linear small-signal measurements made with a swept-frequency technique are compared to previously reported measurements.

Electrooptic gigahertz light-pipe modulator for CO<inf>2</inf>laser wavelength

We have built a traveling-wave electrooptic modulator for 10.6 μm where the optical beam propagates in a highly oversized waveguide. Three CdTe-crystals measuring 35 \times 0.8 \times 0.8 mm3each are cascaded to yield an aspect ratio of 131. Velocity matching between optical and modulating waves and a line impedance of 100 Ω are achieved by proper choice of dielectric embedding and of electrode width. Measured characteristics are: optical transmission 96 percent, maximum input VSWR 1.25:1, half-wave voltage 450 V, and frequency response ±1.1 dB over a 0.006-1 GHz range.

Measurement of velocity mismatch in traveling-wave electrooptic modulators

For traveling-wave electrooptic modulators, we describe an experimental method to determine the sign and magnitude of velocity mismatch between electrical and optical wave. To this end the waves are counterpropagated and frequencies yielding modulation nulls are determined. Such a measurement does also reveal dispersion of the modulator structure.

Some Experiments on Design Principle of Broadband Electrooptic Modulators (Technical Notes)

An experimental modulator was fabricated to test a design principle of broadband traveling-wave electrooptic light modulators proposed in a previous paper. The measured value of modulation bandwidth, 10 GHz, appears to confirm the design principle.

10 GHz bandwidth traveling-wave LiNbO3optical waveguide modulator

A broad-band traveling-wave electrooptic modulator of Ti-diffused LiNbO 3 optical 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.

Broad-band traveling-wave modulator using a LiNbO<inf>3</inf>optical waveguide

A traveling-wave electrooptic phase modulator using a Ti-in-diffused LiNbO 3 optical waveguide was designed and constructed with emphasis placed on broad-band operation. As a microwave waveguide, a coplanar parallel stripline of aluminum with characteristic impedance of 48 Ω was fabricated on the crystal surface. The electrodes are 1.5 μm thick, 1 cm long, and 60 μm apart. The modulator was tested at 0.63 μm over a bandwidth of 7.5 GHz. For 250-mW drive power, the measured phase-modulation index was 1 rad up to about 3 GHz and reduced to 0.5 tad at 7.5 GHz.

Travelling wave electro-optic modulators

The performance of travelling wave electro-optic modulators is considered. Analyses are made of the characteristics of these modulators in both the time and frequency domains. These analyses are used in the design of a 1.5 GHz modulator for high speed optical modulation. It is shown that even at these high bandwidths it is not necessary to resort to velocity compensation of the electrical and light signals.

0 to 3 GHz traveling-wave electrooptic modulator

A report is given on the construction and testing of a traveling-wave electrooptic modulator that requires a nominal 5-watt drive power to obtain 30 percent amplitude modulation from 0 to 3-GHz. The modulator employs potassium-dihydrogen-arsenate crystals and has been tested at 6328 Å with CW drive power.

Broadband Electro-Optic Traveling-Wave Light Modulators

A detailed analysis has been carried out of a broadband traveling-wave electro-optic light modulator using single crystals of currently available materials. The structure analyzed is that first proposed by Rigrod and Kaminow in which a light beam is reflected back and forth across a microwave transmission line with the angle between optical and microwave phase velocity vectors chosen so that the component of the optical phase velocity vector in the direction of microwave propagation is equal to the microwave phase velocity. For generality both amplitude and phase modulation are considered in single crystals belonging to three different symmetry groups, T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</inf> and D <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2d</inf> (V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</inf> ), (linear electro-optic effect) and O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">h</inf> (quadratic effect), for two different orientations of the modulating field. The inclusion of such practical factors as microwave and optical loss results in an optimum design in which the modulator dimensions and operating temperature are uniquely determined by the optical and microwave dielectric properties of the modulating medium. The main conclusions of the analysis are: (i) Either cuprous chloride or suitably biased strontium titanate may be used to produce 50 per cent linear modulation over a bandwidth of 10 gc with less than 5 watts of modulating power, using structures a few centimeters long that have practical manufacturing and operating tolerances. (ii) The upper modulation frequency limit is set by a cutoff frequency which arises from the finite width of the optical beam. (iii) The presence of appreciable crystalline strain in the modulating medium requires that the modulating system consist of a simple phase modulator followed by some form of frequency-selective discriminator. Such a system requires monochromatic but not necessarily coherent light.