Multimode interference (MMI) laser diode devices have been developed for a large number of optoelectronic applications. Frequency domain methods have been widely used to simulate the behavior of this class of device at fixed operating wavelengths. However time domain models are becoming more popular in photonic simulations as they are able to more accurately model the nonlinear optical gain media such as that present in the saturable absorber section used in the MMI laser diode. A detailed understanding of the electrodynamic behavior of this kind of device is most easily accessed using a time domain method. Therefore we have developed a time domain simulator: employing a full band (FB) time-domain beam propagation method (TD-BPM) for modeling laser devices. By making physically consistent approximations, the proposed method can obtain accurate results for the broadband electromagnetic response with a much larger time step size than those required by other conventional numerical techniques. In order to approximate saturable gain media used in laser device, we have extended the FB-TDBPM algorithm to include frequency-dependent saturable gain by using a Z transform technique. In this paper we will present this approach and its application to the time domain modeling of laser devices.
Multimode interference (MMI) devices have been developed for a large number of optoelectronic applications. Frequency domain methods have been widely used to simulate the behavior of this class of device at fixed operating wavelengths. However time domain models are becoming more popular in photonic simulation as bandwidths increase and account needs to be taken of material properties such as nonlinearity. By making physically consistent approximations, the time-domain beam propagation method provides simulation without incurring the large memory and computational penalties of other time domain numerical methods. In this paper we will compare these various approaches in the context of simulating MMI devices, provide guidelines for the selection of one approach in preference to the other and discuss the limitations and errors introduced by some of the common approximations made.
Simulation has become central to the successful development of integrated optoelectronic components and devices. Due to its flexibility and ease of use, the Beam Propagation Method, BPM, has established itself as one of the most popular and useful modeling techniques currently available. Many versions of BPM have been explored and presented in the literature with various schemes used to discretize the transverse operator. Vector and wide angled formulations as well as bi-directional schemes have been shown to overcome the inherent scalar, paraxial and one-way propagation assumptions associated with the simpler schemes, consequently expanding the range of practical problems for which BPM is suitable. However, there remain many significant practical scenarios to which BPM currently has limited applicability, for example it struggles to cope with structures in which there are many reflections or with physically large geometries where stringent performance specifications for new designs demand highly accurate 3D simulations. We assess these limitations in comparison with other simulation techniques and consider the major improvements required in the near future.