Optical injection of a 1.3μm wavelength VCSEL with intracavity patterning

Abstract

Summary form only given. We present the optical injection response of wafer-fused long wavelength VCSELs with and without intracavity patterning. Nonlinear responses such as limit cycle oscillations and four wave mixing are seen, and results summarized on dynamics maps.The dynamics of a solitary semiconductor laser are rather simple, with perturbations in photon or carrier number leading to damped oscillations on at the relaxation frequency. However, when we inject external light into the laser we can modify the coupling between the laser field and the carrier population, changing the dynamics, including undamping the oscillations, changing their frequency, and even leading to chaotic oscillations [1]. The laser response depends on the frequency and power level of the external light, as well as intrinsic characteristics of the laser itself, such as the photon and carrier lifetimes, laser gain, linewidth enhancement parameter, and so on. Usually, the only parameters of the laser that can be changed are its current and temperature bias [2], but here we present the dynamic responses of two VCSELs: a standard waferfused VCSEL, and one with two shallow arcs etched inside the cavity region, that aim to suppress a polarization switch by introducing anisotropy to the two polarization modes [3]. We select typical examples of a standard (unpatterned) VCSEL with a threshold of 1.3 mA and a polarization switch at 3.5 mA, and a nearby patterned VCSEL with a threshold of 1.2 mA and switch at 5.6 mA. They emit at 1311.9 nm wavelength when biased at 2 mA at room temperature and have similar polarization mode splittings of 19.5 and 16 GHz, respectively. The VCSELs are biased at 1.5xIth and then injected with light from a commercially available fiber-pigtailed DFB laser, which is temperature-tuned to match the resonant wavelength of the VCSEL. Its bias current is used to set the fine frequency detuning from the VCSEL. External optical attenuation sets the amount of light incident on the VCSEL surface. At each detuning and input power level for the DFB laser, the VCSEL injection response is recorded using an rf or optical spectrum analyzer. As an example, the response of the standard VCSEL to input light polarized parallel to the operating mode and detuned by +2 GHz is shown in Fig. 1(left). The VCSEL demonstrates four-wave-mixing, subharmonic excitation, and then period doubling as the incident light level is increased. At higher input power levels, the VCSEL operates in a limit cycle with unbounded phase dynamic state [1], where the VCSEL mode becomes strongly red shifted in relation to the input light. The dynamic behavior for both VCSELs is summarized in the maps shown in Fig. 1. The standard VCSEL (center) is excited into limit cycle behavior for a wide range of detuning frequencies and only shows stable injection locking when the orthogonal polarization mode is unintentionally injected. Near zero detuning there is a large area that shows four-wave mixing. The patterned VCSEL shows weaker response to injected light, with a narrower bandwidth and no four-wave mixing region. On the other hand, the device does show a region of stable injection for small negative detuning. Cavity patterning thus offers a method to vary the injection response of a diode laser and possibly engineer its behavior for specific applications. Schematic of the patterned VCSEL.