TABLE OF CONTENTS Electrical characterisation through the measurement of current-voltage ( I ? V) derivatives was used as an early method to understand current paths in the injection laser and its lasing behaviour [ [28] [29] [30]]. For the stripe-geometry laser, the circuit equivalent below threshold is just an ideal diode with a series resistance R. The I ? V characteristics of the diode can be expressed by the Shockley equation [ [31]]:
where I s is the saturation current, k is the Boltzmann constant, T is the absolute temperature, V d is the voltage across the diode, and ? is the ideality factor. Above threshold, the voltage across the laser diode saturates, and the measured voltage across the laser diode is simply given as:
The threshold point can be identified by observation of a "kink" in the I(dV/dI) versus I characteristics [ [30]].
In practice, a DC shunt path exists diverting the current away from the active region, which can be approximated as a simple shunt resistor [ [28]]. During high-speed modulation, however, frequency-dependent shunt paths exist, which are more complicated than just a simple shunt resistor. These shunt paths also depend on the type of the laser structure used (including geometry and doping density) [ [32]]. They are known as the electrical parasitics of the laser, which limit the extrinsic modulation bandwidth [ [33] [34]].
To illustrate the...
