Semiconductor Lasers and Photonic Integrated Circuits

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Applications
Overview

Voltage-Controlled Integrated Laser Mach-Zehnder Modulator

Description

The integration of laser source and Mach-Zehnder (MZ) modulator offers benefits arising from cost effective packaging and wavelength independent behavior making it an ideal transmitter concept for WDM systems. Design tolerances such as the residual optical feedback from the modulator output facet need to be studied carefully as they introduce frequency chirp and relaxation oscillation, and thus, limit the modulation performance in high bit-rate systems.
This application illustrates a model of a voltage-controlled InP MZ modulator that accounts for the carrier dynamics inside the modulated InP region. Internal loss and gain are changed dynamically according to [1]. With this approach it is possible to modulate voltage, current and phase simultaneously.

Typical Results

The schematic for the integrated laser MZ modulator is shown in Figure 1.A MQW-DFB laser acts as CW source; its optical spectrum is represented in Figure 2. Two Y-splitters are used to form the two branches of the MZ modulator. At each branch, a voltage-control module sets the values of two chosen parameters (internal loss and gain) according to the applied voltage [1]. The injection current passes through the module with no changes. The phase control module determines the dependence of phase shift on the input electrical signal. Figure 3 shows the voltage drive signal as well as the optical power and chirp of the modulated output signal. The carrier density variation inside the quantum wells is shown in Figure 4.

Keywords

Integrated Laser Mach-Zehnder Modulator, Carrier Dynamics, MQM-DFB Laser