Abstract
We analyze the influence of thermal effects on the polarization-resolved light-current (LI) characteristics of verticalcavity surface-emitting lasers (VCSELs). We use a model that is an extension of the spin-flip model incorporating material gain that is frequency and temperature dependent, and a rate equation for the temperature of the active region, which takes into account decay to a fixed substrate temperature, Joule heating and nonradiative recombination heating. The model also incorporates the red shift for increasing temperature of the gain curve and of the cavity resonance. The temperature sensitivity of the lasing threshold current is found to be in good qualitative agreement with observations and with previous reports based on detailed microscopic models. The temperature dependence of the polarization switching point, when the dominant polarization turn off and the orthogonal polarization emerges, is characterized in terms of various model parameters, such as the room-temperature gain-cavity offset, the subtracte temperature, and the size of the active region.
Highlights
Vertical-cavity surface-emitting lasers (VCSELs) have great potential as inexpensive light sources for high-speed fiber-optical communication systems because they allow direct fiber coupling and provide high beam quality with longitudinal single-mode output power at wavelengths of interest for data links and optical fiber technologies [1, 2].Much effort has been done towards the development of long-wavelength VCSELs (λ ≥ 1.3 μm), to meet the requirements for communication standards such as 10 Gigabit Ethernet
In contrast to 850 nm VCSELs, that are designed such that the gain peak and the cavity resonance are nearly aligned at room temperature, long-wavelength VCSELs have a relatively large spectral detuning between the gain and the cavity resonance at room temperature
We proposed a modification of the spin-flip model, which incorporates thermal effects in a simple and computationally efficient way, allowing for a dynamic description of temperature variations
Summary
Vertical-cavity surface-emitting lasers (VCSELs) have great potential as inexpensive light sources for high-speed fiber-optical communication systems because they allow direct fiber coupling and provide high beam quality with longitudinal single-mode output power at wavelengths of interest for data links and optical fiber technologies [1, 2]. VCSELs often present polarization instabilities that can be related to variations of the active region temperature with increasing injection current. A main conclusion of our study is that the dependence of the polarization switching point, IPS, on the substrate temperature, Ts, and on the RT gain-cavity offset, δ0, is as that of the threshold current, Ith, having both a parabolic-like variation. A limitation of the model proposed here is that it does not take into account spatial effects, because it assumes that the orthogonal linear polarizations are emitted on the fundamental transverse mode This is important well above threshold, where laser output is emitted in several high-order transverse modes, and Joule heating has been shown to be a dominant mechanism in determining the transverse mode formation [19, 22].
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