James J. Morikuni

A simple rate-equation-based thermal VCSEL model

Motivated by the potentially large number of devices and simulations involved in optoelectronic system design, and the associated need for compact optoelectronic device models, we present a simple thermal model of vertical-cavity surface-emitting laser (VCSEL) light-current (LI) characteristics based on the laser rate equations and a thermal offset current. The model was implemented in conventional SPICE-like circuit simulators, including HSPICE, and used to simulate key features of VCSEL LI curves, namely, thermally dependent threshold current and output-power roll-over for a range of ambient temperatures. The use of the rate equations also allows simulation in other non-dc operating regimes. Our results compare favorably to experimental data from three devices reported in the literature.

A comprehensive circuit-level model of vertical-cavity surface-emitting lasers

The increasing interest in vertical-cavity surface-emitting lasers (VCSELs) requires the corresponding development of circuit-level VCSEL models for use in the design and simulation of optoelectronic applications. Unfortunately, existing models lack either the computational efficiency or the comprehensiveness warranted by circuit-level simulation. Thus, in this paper we present a comprehensive circuit-level model that accounts for the thermal and spatial dependence of a VCSELs behavior. The model is based on multimode rate equations and empirical expressions for the thermal dependence of the active-layer gain and carrier leakage, thereby facilitating the simulation of VCSELs in the context of an optoelectronic system. To confirm that our model is valid, we present sample simulations that demonstrate its ability to replicate typical dc, small-signal, and transient operation, including temperature-dependent light-current (LI) curves and modulation responses, multimode behavior, and diffusive turn-off transients. Furthermore, we verify our model against experimental data from four devices reported in the literature. As the results will show, we obtained excellent agreement between simulation and experiment.

Spatially independent VCSEL models for the simulation of diffusive turn-off transients

Carrier diffusion and spatial hole burning can have a severe impact on vertical cavity surface emitting laser (VCSEL) performance. In particular, these phenomena can produce secondary pulses, bumps, and optical tails in the VCSEL turn-off transient which limit both the system bit rate and the bit error rate (BER). To study these effects, laser rate equation models that include both spatial and temporal dependence are often employed; however, simulations which require discretization of both space and time, while accurate, typically consume vast amounts of computational power. In this paper, we demonstrate that models based on well-accepted spatially independent rate equations can be used to simulate these effects. These models exhibit the advantages of the full spatio-temporal approach but execute much more quickly. We also integrate these models into electronic computer-aided design (CAD) tools which will enable circuit and system designers to simultaneously simulate electrical and optical performance.

Compact representations of mode overlap for circuit-level VCSEL models

The compact representations for mode overlap presented simplify the implementation, simulation, and extraction of circuit-level VCSEL models by eliminating the need for numerically evaluating these models overlap integrals whenever the degree of overlap between transverse mode and carrier profiles changes. By adopting either analytical fits for the integrals, or linearly-interpolated tables of pre-calculated integral values, it becomes possible for the user of these models to interactively alter the overlap without impacting the simulation time.

Optoelectronic computer-aided design

The success of the modern silicon electronics industry can be attributed, in part, to the availability of advanced modeling and simulation computer-aided design (CAD) tools. This modeling and simulation infrastructure is crucial for product design; without these tools, multiple design and fabrication iterations are required in order to optimize design and system parameters, a process which severely impacts cycle time and end-product cost. Because the field of optoelectronics has not yet reached the same level of product proliferation as the electronics industry, a corresponding CAD infrastructure does not yet exist for the modeling and simulation of optoelectronic devices, circuits, and systems. We address this issue.

Circuit-level model of semiconductor photodetectors

In this paper, we present a circuit-level model of semiconductor photodetectors which accounts for photocurrent, dark current, junction capacitance, and other parasitic effects. We have implemented the model within a standard circuit-level simulation environment While parasitic elements will typically place the ultimate limit on high-speed device performance, in some cases the transit-time limited impulse response of the photocurrent can also be important. In order to properly account for this effect, prior circuit-level modeling efforts have been based on the modification of existing simulation code to account for the numerical convolution of an optical input signal with the impulse response. We, on the other hand, will demonstrate how existing linear component models can be used to describe the impulse response, thereby greatly simplifying the implementation of our model by circumventing the need to modify the simulator. Additional linear and nonlinear elements are added to account for dc and parasitic effects. These include the intrinsic current-voltage characteristics of the device, series resistance, and junction capacitance. After discussing the theory and implementation of our model, we demonstrate its ability to simulate device behavior during dc, small-signal, and transient operation.