Low-Loss Cascaded Mach–Zehnder Multiplexer Integrated $25\hbox{-}{\rm Gbit}/{\rm s}\times 4\hbox{-}{\rm Lane}$ EADFB Laser Array for Future CFP4 100 GbE Transmitter

A 4 × 25-Gb/s electroabsorption modulator integrated with a distributed feedback (DFB) laser (EADFB laser) array monolithically integrated with a low-loss optical multiplexer (MUX) is developed for 100 GbE transmitters for the first time. A cascaded Mach-Zehnder (MZ) filter, which has no intrinsic loss, is used as the MUX. The design and fabrication of the MZ-MUX for 100 GbE are thoroughly described. The measured loss of fabricated MZ-MUX is 2-3 dB, which is improved by 4 dB compared with that of the conventional 1 × 4 multimode interference MUX. The MZ-MUX is monolithically integrated with a four-EADFB-laser array and the output power of the chip is increased by 3 dB compared with that of a conventional 4 × 25-Gb/s monolithically integrated chip. With the folded layout, the size of the chip is similar to that of the conventional chip. The fabricated chip is packaged into a very compact transmitter optical subassembly (TOSA). The system requirements are satisfied with semi-cooled operation, and very clear eye openings are obtained after 10-km single-mode-fiber transmission. The adjustment of filter spectra by current injection is also shown, and fine tuning is possible with very low injection current.

I. Introduction

To cope with the demand for huge data capacity in local area networks (LANs), the 100 GbE has recently been standardized [1]–[3]. In 100 GbE, a multi lane LAN-WDM system is employed, in which lane signals with 800-GHz wavelength spacing at around 1.3- are used. This means that four-lane, high-speed light sources are required [4]–[7], which increase the size and power consumption of the whole transmitter. Since there is a limitation on the size and the maximum power consumption of the transceiver, reducing its size is essential, and this requires large-scale-integration of discrete components. In addition, semi-cooled operation is highly desired for lowering electrical power consumption.