Scaling effects on the dynamic characteristics of long-wavelength vertical-cavity surface-emitting lasers (VCSELs)
Introduction
The vertical-cavity surface-emitting laser (VCSEL) was first proposed and fabricated in the late 1970s. VCSELs have a long list of advantages over edge-emitting lasers, such as low-threshold currents and small power consumption, thermally stable operation, high-speed modulation capability, ease of testing and mass production with high yield [1].
Long-wavelength (1300–1550 nm) VCSELs have begun to spark great interest among researchers as a suitable candidate for long-haul-fiber-based links. In addition, true single mode devices with stable polarization may be achieved, even for large diameters of 5–7 μm. This corresponds to minimum dispersion and minimum loss in standard optical fiber at 1.3 and 1.55 μm, respectively [2].
In this paper, an analysis and simulation of a long-wavelength VCSEL based on InGaAsP/InP quantum well (QW) lasers operating at a wavelength of 1550 nm wavelength is carried out. In the simulation, the carrier-noise, photon-noise and phase-noise, including feedback from the external cavity, are taken into account. However, the thermal effects, electrical parasitics and longitudinal transport in the QWs are omitted in this study.
Section snippets
Device structure
The oxide aperture VCSEL device used for simulation was designed for emission at 1550 nm wavelength. It consists of three strained InGaAsP wells as shown in Fig. 1. The top-emitting VCSEL contains p-type AlGaInAs/InP distributed Bragg reflectors (DBRs) for the top layer and n-type AlGaInAs/InP DBRs for the bottom layer. The effective cavity length of the active layer is set to 1λ.
Top reflectivity of the p-DBRs, Rt, is set at 0.97, while bottom reflectivity for n-DBRs, Rb, is set to 0.999 [3].
Small-signal analysis
By linearizing the rate equations in the time domain and then Fourier-transforming to obtain the spectral fluctuations as a function of frequency, the small-signal analysis may be carried out [9], [10].
Assuming that the laser rate equations in Eq. (3) have a time-dependent drive current as the input, and providing the photon density in the active region as the outputwhere
By
Conclusions
The dynamic characteristics of a long-wavelength VCSEL and the effect of scaling the oxide aperture on the device performance have been reviewed in this paper. The results were consistent and optimal performance was achieved when Rox was between 2.5 and 3.0 μm. From our simulation, a high D-factor value was observed at Rox=3.0 μm. This means that at moderate optical power levels, it is possible to obtain high-modulation bandwidths. The simulated device achieved a high ROF at modulation bandwidth
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Cited by (1)
Comparing long wavelength and short wavelength vertical-cavity surface-emitting lasers
2008, Proceedings of IEEE 2008 6th National Conference on Telecommunication Technologies and IEEE 2008 2nd Malaysia Conference on Photonics, NCTT-MCP 2008