MMIC Based InP/InGaAsP Intensity Optical Modulator

Abstract

The research presented in this paper concerns the development of a MMIC InPhGaAsP intensity optical modulator, suitable for chip level integration of photonic devices and MMICs. In the proposed codigluration the microwave field induces EL periodic structure via doping and electro-optic effects. The: interaction of light with the induced grating yields a modulated optical signal. The paper discusses the structure design anti the expected device performance. I -INTRODUCTIONThe merging of photonic and microwave devices on a MMIC chip will bring benefits to many applications: phased-array radar, antenna remoting, optical processing of microwave signal, and CATV signal distributioin. MMIC based optical detectors, such as InP based pseudomorphic HEMTs with cutoff frequencies well in the GHz range, has been reported, Martin [ 11. Inl-xGaxAsyP1-y quaternary is a suitable material for optoelectronic devices since it can be lattice matched grown on InP. The lattice-matching relation between the compositions x and y can be expressed as:Conventional photonic modulators are based on the linear electro-optic effect which is a y small in semiconductors, thus, requiring devices with long interaction length or large voltage, or both. A significant change in the refractive index and absorption can be achieved via the Franz-Keldysh effect which leads to the electrorefraction or quadratic electro-optic effect and electroabsorption. For photon energies far from de material band-gap energy the electrorefraction and electroabsorptiiori are weak , however as the photon energy approaches the band-gap energy both effects increase significantly. Thus in relation to the operation wavelength the semiconductor band-gap wavelength can be tailored to maximize the effects. In addition, a significant change in the refractive index can be obtained by the use of doping. Three effects contribute to the alterauion of the refractive index: the plasma, the band filling, and the band-gap shrinkage. These effects may be exploited in the fabrication of phase and intensity type modulators.It has been shown that InP/InC;aAsP intensity modulator based on electroabsorption, Lin [2], and phase modulator based on doping effects, Vinchant 131, offer small size and potentially large bandwidth, but suffer of high insertion loss or high drive voltage, or both. Recently, it has been reported, Lee [4],, that GaAs/GaAlAs phase modulator based on doping and electro-optic effects presents excellent performance in relation to size, bandwidth, and insertion loss. These results show thilt the combination of doping and electro-optic effects is a key element in the design of modulators with superior performance.It is the objective of this paper to propose an intensity optical modulator based on doping and electro-optic effects to be integ,rated with InP based MMICs.. The device design and expected performance are also presented. I1 -InGaAsP -REFRACTIVE INDEX ALTERATIONThe refractive index is function of the carrier concentration which can be changed by doping or depletion of...