The monolithic integration of a wavelength-demultiplexer with evanescently coupled uni-traveling-carrier photodiodes

In this letter, we discuss a novel integration of a wavelength demultiplexer with a pair of uni-traveling-carrier photodiodes (UTC-PDs). With this integrated module, we could separate incoming wavelengths of 1530 and 1550 nm, which are near the wavelengths utilized for digital and analog signal transmission in coarse wavelength-division multiplexing (CWDM) systems. The integrated UTC-PDs exhibited the following advantages: a wide 3-dB bandwidth (25 GHz), a reasonable responsivity (0.35 A/W), and a high-saturation-current (>17 mA). A low level of radio frequency crosstalk between the two photodiodes (less than -15 dB) could also be achieved for a wide frequency range (near DC to 40 GHz). This is low enough for the multichannel receivers in a WDM broadcast system. In addition, by use of our module, we demonstrated digital/analog signals co-transmission and demultiplexing with speeds of 2.5 Gb/s at optical wavelengths of 1530 and 1550 nm.