Monolithic integration of InGaAs/InAlGaAs-based semiconductor optical amplifiers and 10 Gb/s broadband electro-absorption modulators using quantum well intermixing technology

Mach-Zehnder phase modulators fabricated in LiNbO₃ (LN) dominate the market for data modulators at 10 Gb/s. Although LN modulators display a high-power handling capability with controlled chirp over a large optical bandwidth (i.e., full C-band), they are relatively large and expensive to manufacture when compared to semiconductor devices. By contrast, InP-based electro-absorption modulators (EAMs) are much more compact; however they have a limited bandwidth (5-10 nm) over which chirp is in the correct range to allow > 80 km reach. This paper presents the broadband electro-absorption modulator (BEAM) chip concept, which consists of monolithically integrating a series of EAMs using quantum well intermixing with each one tuned to give the correct chirp over a certain wavelength range. The total bandwidth of the device is thus extended to cover the whole C-band. In addition, a semiconductor optical amplifier (SOA) is serially integrated with the EAMs to recover the insertion loss due to fiber coupling and the series of EAMs. A unique quantum well intermixing (QWI) process is the method employed to achieve the monolithic integration of the multiple sections required for the BEAM chip. Key results reported here are open 10 Gb/s eye diagrams of the integrated EAMs along with data from the demo BEAM chips showing the achievement of >10 dB extinction ratio across the C-band, with >35 km reach.