A novel design of two-mode (DE)MUX based on multimode interference (MMI) couplers on InP substrate is proposed. A phase shifting section based on the thickness variation of the core layer is introduced in the (DE)MUX to realize a 100% mode conversion efficiency and multiplexing. The total length of the structure is only 549 μm, much shorter than other InP based mode (DE)MUXs. Simulations show that, the device crosstalk is below -20 dB and the insertion loss is lower than 1 dB for both of the fundamental mode and the first order mode within the whole C band. This new structure can be potentially integrated with other devices based on InP substrate to serve as a monolithic few-mode transmitter/receiver.
We have investigated 1.3-μm InGaAsP strained multi-quantum-well (MQW) lasers on InP substrate for direct
modulation applications using the commercial laser simulator PIC3D. The physical mechanisms affecting the laser
dynamic characteristics such as nonradiative recombination losses and vertical electron leakage effect are considered in
our simulation. The number of wells is optimized because increasing the number of QWs can decrease the nonradiative
recombination losses and increase the modal differential gain, nevertheless, the carrier distribution between wells
become more non-uniform with too many QWs numbers resulting in uneven simulated recombination rate and
increasing Auger recombination. The influence of barrier height is analyzed and a tradeoff has to be determined because
too high barriers results in more nonuniform carrier distribution in the active regions, increasing the Auger
recombination rate severely while the vertical current leakage outside the QWs will increase dramatically at lower barrier
height. The 1.3-μm FP laser with the MQWs of 6 wells, 1.15 Q barriers bandgap and 8 wells, 1.1 Q barrier bandgaps is
fabricated and characterized. The FP laser with MQWs structures composed of 8 compressive strain quantum wells and 9
barriers with the optimized bandgap 1.1 Q shows better properties. The threshold current is around 19 mA and the
resonance frequency of 9.5 GHz and 3-dB bandwidth in excess of 13.3 GHz at 120 mA injection current. This
modulation frequency is suitable for 10 Gbits/s optical data transmission.