The % factor and frequency responses of electroabsorption-type optical-intensity modulators, especially InGaAs/ InAlAs MQW modulators, are described. A method of exactly estimating the value of the + factor is presented under the nonlinearity of extinction-ratio characteristics. For measuring the frequency response of modulators, the sideband strength of the modulated output light with an optical spectrum analyzer is analytically compared with the microwave power of photodiode direct detection with an electrical spectrum analyzer. Furthermore, % factors and modulation frequency responses are measured using InGaAs/InAlAs MQW modulators. As a result, the values of the + factor with the present method are found to be smaller than those with the conventional method under linear extinction-ratio characteristics, especially at a large signal modulation. The measurement method with sideband strength which does not need a fast photodiode is confirmed to be very effective for estimating the high-speed frequency response of an optical modulator having an % factor of less than 2. Moreover, the MQW modulators are found to have an + factor of less than 1.0 under actual driving voltages, and to be candidates for a high-speed optical modulator.

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