Abstract
In the last few decades, various solutions have been proposed to increase the modulation bandwidth and, consequently, the transmission bit-rate of semiconductor lasers. In this manuscript, we discuss a design procedure for a recently proposed laser cavity realized with the monolithic integration of two distributed Bragg reflector (DBR) lasers allowing one to extend the modulation bandwidth. Such an extension is obtained introducing in the dynamic response a photon-photon resonance (PPR) at a frequency higher than the modulation bandwidth of the corresponding single-section laser. Design guidelines will be proposed, and dynamic small and large signal simulations results, calculated using a finite difference traveling wave (FDTW) numerical simulator, will be discussed to confirm the design results. The effectiveness of the design procedure is verified in a structure with PPR frequency at 35 GHz allowing one to obtain an open eye diagram for a non-return-to-zero (NRZ) digital signal up to 80 GHz . Furthermore, the investigation of the rich dynamics of this structure shows that with proper bias conditions, it is possible to obtain also a tunable self-pulsating signal in a frequency range related to the PPR design.
Highlights
Semiconductor laser diodes with a wide direct modulation bandwidth represent an important element to fulfill the continuously increasing request for low-cost optical communications systems with a high bit-rate
Since the photon-photon resonance (PPR) usually occurs at a frequency that is much higher than the CPR frequency, the request for an almost flat modulation response implies the need for a proper cavity design to have the PPR at the correct frequency, allowing one to fill the gap between the PPR and CPR peaks of the modulation response
For the composite distributed Bragg reflector (DBR) cavity under consideration (Figure 1a), as well as for the other cases of laser cavity referenced in Section 1, a proper choice of the cavity parameters is the essence for the exploitation of the PPR mechanism between the lasing mode and the nearest neighbor with the requested frequency separation
Summary
Semiconductor laser diodes with a wide direct modulation bandwidth represent an important element to fulfill the continuously increasing request for low-cost optical communications systems with a high bit-rate (see, e.g., [1]). A second approach used to extend the lasers dynamic properties is to take advantage, in a properly designed cavity, of the interaction between the lasing mode and an adjacent longitudinal cavity mode This interaction is made possible by the carrier pulsation introduced by the current modulation applied at the gain section electrode [6,7,10,11,12]. Since the PPR usually occurs at a frequency that is much higher than the CPR frequency, the request for an almost flat modulation response implies the need for a proper cavity design to have the PPR at the correct frequency, allowing one to fill the gap between the PPR and CPR peaks of the modulation response In this condition of modulation bandwidth extension, it is possible to obtain an open eye diagram of an NRZ signal at a greater bit-rate than in the corresponding single-section.
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