Elsevier

Optics & Laser Technology

Volume 40, Issue 6, September 2008, Pages 785-789
Optics & Laser Technology

Scaling effects on the dynamic characteristics of long-wavelength vertical-cavity surface-emitting lasers (VCSELs)

https://doi.org/10.1016/j.optlastec.2007.12.006Get rights and content

Abstract

The influence of the oxide aperture radius on the characteristics of a long-wavelength vertical-cavity surface-emitting laser (VCSEL) lasing at 1550 nm is presented in this paper. While previous works in the literature mostly investigate the scaling effects of short-wavelength VCSELs. The importance of studying the effects of long-wavelength operation should not be underestimated, as it could be used in fiber optics communication to mitigate dispersion and attenuation of the channel. Using the oxide-confined VCSEL model, the dynamic operations were examined taking into account the carrier-noise, photon-noise and phase-noise, including feedback of the external cavity. Our simulations show that by reducing the oxide aperture up to a given optimal radius, an improvement in the device's characteristics can be demonstrated. Below this value, performance degradation is expected due to increased diffraction losses, reduced confinement factor and enhanced spontaneous emission.

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 outputdN(t)dt=-N(t)τN-vgg0kN(t)-Ntr1+εSk(t)Sk(t)+ηinjI(t)qVa,dSk(t)dt=-Sk(t)τS-Γvgg0N(t)-Ntr1+εSk(t)Sk(t)+βN(t)τN,whereVa=nwdwπRox2.

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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