ANALYSIS AND DESIGN OF HIGH-SPEED HIGH-EFFICIENCY GAAS-ALGAAS DOUBLE-HETEROSTRUCTURE WAVE-GUIDE PHASE MODULATOR

A P-p-i-n-N, GaAs-AlGaAs, TE-TM mode phase modulator, which has both the high phase shift efficiency of a p-n homojunction modulator and the high speed associated with a P-i-N modulator, is considered by incorporating p- and n-GaAs buffer layers and utilizing the higher order effects in these layers. The device structure is analyzed by considering the individual contributions of both the electrooptic [linear electrooptic (LEO) and quadratic electrooptic (QEO)] effects and the free carrier [plasma (PL) and bandgap shift (BS)] effects. These effects are studied in detail as a function of the reverse bias, operating wavelength, doping concentration, and intrinsic layer thickness. The results are in excellent agreement with the theoretical predictions. As predicted, the QEO coefficient R is shown to vary as exp (3/lambda-3) and the new value of 4.3(+/- 0.5) x 10(-16) and 1.3(+/- 0.5) x 10(-16) cm2/V2, respectively, have been determined. With the intrinsic layer thickness varied from zero to reasonably large value, viz., 0.35-mu-m, comparative studies between the p-n homojunction, P-i-N and P-p-i-n-N modulators are presented to demonstrate the superior performance of the P-p-i-n-N phase modulator. An efficient 82-degrees/V . mm phase modulator with an estimated bandwidth of 3.5 GHz and a power per bandwidth of 18 mW/GHz at 1.06-mu-m is demonstrated.