High-Current Backside-Illuminated Photodiode Array Module for Optical Analog Links

We have developed a high-current photodiode (PD) array module that consists of a beam splitter, which splits a light beam from a single-mode fiber into four beams with identical powers, a backside-illuminated InGaAs p-i-n PD array, and a two-stage Wilkinson RF power combiner. To obtain a linear PD response, the PD is equipped with a partially depleted absorber, which reduces the bias voltage. To prevent thermal failure, the backside-illuminated PD structure is used, which reduces the thermal resistivity. The beam splitter is fabricated using optical contacts at the SiO₂ interfaces between a coating film and a neighboring prism to prevent degradation of the adhesive glue at the prism interfaces along the optical path; therefore, light with a power of a watt level can be used. The two-stage Wilkinson combiner combines four RF outputs of the PD array into a single-RF output through a K connector; the combiner also works as an impedance-matching circuit. Experimental results reveal that an RF power output of 29.0 dBm can be obtained at a frequency of 5 GHz, and good intermodulation distortion characteristics with a third-order intercept point of 32.5 dBm can be achieved.