An InP-Based Optical Equalizer Monolithically Integrated With a Semiconductor Optical Amplifier

We present the first optical equalizer realized on Indium Phosphide material that is also monolithically integrated with a semiconductor optical amplifier. We show that the device can mitigate inter-symbol interference arising from narrowband optical filtering of 40-Gb/s non-return-to-zero data. Significant improvement in the measured bit-error rates after optical equalization of the filtered signal is reported. It is shown that the device can also mitigate the impairments arising from residual chirp and electrical filtering in the transmitter and receiver.

I. Introduction

With data rates increasing beyond 40 Gb/s, it is becoming more challenging to achieve the required bandwidths in optical communication systems. Optical equalizers [1] have been shown to compensate the inter-symbol interference (ISI) resulting from fiber dispersion, insufficient bandwidth in a system [2], [3], or nonlinear impairments from a semiconductor optical amplifier (SOA) [4]. The transmitter may be limited by both the electrical bandwidth of its modulator and driver, and by the bandwidth of the optical multiplexing system. An optical equalizer can play a critical role in achieving higher data rates and it would be advantageous to have a device that is sufficiently compact to allow packaging in the transmitter module or ultimately to be monolithically integrated with the laser and modulator. Since optical equalizers introduce loss as part of the equalization process, the capability to integrate a gain element would allow the transmitter power to be maintained. This makes the integration of an equalizer on an Indium Phosphide (InP)-based platform, which has a smaller bend radius and can provide optical amplification and ultimately integration with the rest of the transmitter, an attractive option.