FM and AM responses of a three-electrode DBR laser diode

Abstract

Tunable narrow linewidth semiconductor lasers are very attractive for a variety of applications in future communications, such as dense WDM, local oscillator tuning in coherent systems, and optical switching in local area networks. For such systems, FSK is an attractive modulation scheme since the transmitter laser frequency can be modulated through direct current modulation. The frequency modulation is due to change in the refractive index of the laser medium induced by the modulated injection current. This change is a consequence of both the temperature modulation effect (dominant at low frequency) and the active region carrier density modulation effect (dominant at high rates). The laser FM response is determined by the simultaneous action of these two effects. Continuous wavelength tuning is necessary for FSK, and also desirable for WDM applications. Recent studies have been focused on the development of wavelength tunable lasers using multielectrode distributed feedback (DFB) and distributed Bragg reflector (DBR) structures [ 11. Although the theory of such lasers i s developed, some phenomena limiting the laser ultimate performance have not yet been completely understood. One of the most important devices among multielectrode lasers is the three-electrode DBR laser (see Fig. l), which has an active Fabry-Perot section, and two passive sections, one for phase control and one with a built-corrugation for frequency control. The passives waveguides are usually made of materials with a higher bandgap than that of the active layer in order to make them transparent. Hence, there is only spontaneous and no stimulated recombination in these sections. Fig. 2. represent FM response of the three-electrode DBR laser with fixed value of I , = 40mA and I , = 21, = 50mA. When the modulation current is applied to the active region, the FM response is similar to those of a conventional laser case (amplitude modulation with frequency chirping). In contrast, when the modulation current is applied to one of the passive regions, the FM response presents a flat region for low frequencies, dips and then peaks in the vicinity of IIGHz.The FM efficiency and the bandwidth depend on the modulation current into one of the passive sections or both sections.

Time-Domain Large Signal Investigation on Dynamic Responses of the GDCC Quarterly Wavelength Shifted Distributed Feedback Semiconductor Laser

“…For the phase-shifted distributed feedback semiconductor laser diode, the electric field in the laser cavity is given by [8]:…”

“…The fields and can be derived from the Maxwell's equations using the slowly varying amplitude approximation. Time-dependent coupled equation can be written as [8] [11]:…”

“…is the spontaneous emission term contributed to the forward and backward propagation components, the stochastic property of the noise term ( ) is described by a random process with zero mean value and correlation function as described in [8][9] [10] satisfying the correlation:…”

“…Where is the group velocity, is the optical confinement factor, ( ) is the coupling coefficient between the forward and backward propagation waves, is the waveguide loss (includes the absorption in both the active and cladding layer as well as any scattering), ( ) is the phase shift at position, is the gain compression coefficient (non-linear coefficient to take into account saturation effects) and is the spontaneous emission term contributed to the forward and backward propagation components, the stochastic property of the noise term ( ) is described by a random process with zero mean value and correlation function as described in [8][9] [10] satisfying the correlation:…”