Measurement of intermodulation distortion in a unitraveling-carrier refracting-facet photodiode and a p-i-n refracting-facet photodiode

In this letter, we present an experimental characterization of third-order intermodulation distortion (IM3) at 5.8 GHz in a unitraveling-carrier refracting-facet photodiode (UTC-RFPD) and a p-i-n refracting-facet photodiode (pin-RFPD). The IM3 in the pin-RFPD is considerably reduced compared to the waveguide-type p-i-n photodiode. The third-order intercept point (IP3) of the UTC-RFPD does not decrease as the photocurrent increases, indicating that space-charge-induced nonlinearity is well suppressed in this photodiode. The two-tone IP3 of the UTC-RFPD estimated from the measurement reaches a very high level of 40.5 dBm.

I. Introduction

Optical Fiber distribution of microwave signal is promising for dedicated short-range communications (DSRC) in intelligent transportation systems. Recently, we have successfully demonstrated transmission of down-stream microwave signal through a fiber-radio link employing a highoutput-power photodiode [1]. When a photodiode is used under a high-input-power condition, a concern is that third-order intermodulation distortion (IM3) in the photodiode will limit the performance of the fiber-radio link. In this letter, we report an evaluation of IM3 in two high-speed and high-output-power photodiodes, i.e., a unitraveling-carrier refracting-facet photodiode (UTC-RFPD) [2], and a p-i-n refracting-facet photodiode (pin-RFPD) [3], in the 5.8-GHz band assigned for DSRC systems. In the measurements, three individually modulated laser diodes were used for light sources in order to evaluate IM3 down to very low levels.