Vertical-cavity surface-emitting lasers(VCSEL) have many advantages such as low threshold current and single mode operation

as well as easy to be fabricated in high-density arrays and low cost in manufacturing.VCSELs are used in many areas

for example

optical communications

optical interconnections

and optical signal processing.But in some applications

the polarization orientation is sensitive

such as optic recording and laser frequency doubling.It is necessary to control the polarization characteristics of VCSEL effectively.In fact

the reliable control of the polarization orientation of single devices with small emission window is realized through many methods

in which the most popular one is the sub-wavelength surface grating technique.But due to the existence of multi-transverse modes in high power VCSEL devices with large emission window

the polarization orientation changes from one basic state to the other orthogonal one depending on the input current and temperature.The temperature dependence of the polarization characteristics of a 980 nm bottom-emitting laser with 500 μm emitting aperture is investigated.The temperature changes from 298 K to 368 K with a increasing step of 5 K.It is not easy to directly measure the temperature of the active region

so the temperature of the heatsink is used to characterize the temperature of the active region.Apolari-zation beam splitter(PBS) element is used to split the two orthogonal polarization states into transmission wave and reflection wave

respectively.The output powers and center-wavelengths of these two orthogonal polarizations states are measured by using a semiconductor laser parameters test system.The temperature dependence of the output power of each polarization state is the same as that of the total output power of the device without the PBS.The center-wavelength difference between the two polarization states increases slowly with increasing temperature.When comparing the polarization behavior of both states

we find that the reflection state reaches threshold of lasing before the transmission state when the device is kept at a temperature below 328 K.But the output power in the transmission state rises quickly than that in the reflection state.At every temperature

there is a certain current where the powers in the two states are equal with increasing the current.With increasing the current further

the power in the transmission state is higher than that in the reflection state.And when the device is kept at a temperature above 328 K

there is no obvious alternation point between the two states

and the power in the transmission state is higher than that in the reflection state all the time.The reason may be that at low temperature and low current

the heat effect is not serious

the red shifts of the reflection wave and transmission wave are both small

but reflection one is a little more

so the reflection wave is closer to the center-wavelength of DBR.With increasing the current

the internal temperature of the device increases seriously

the red shift of reflection state increase faster than that of transmission state

so the transmission wave is closer to the center-wavelength of DBR.At high temperature the heat effect is serious

whatever at low current and high current

both of the red shifts are big

so the transmission wave is closer to DBRcenter-wavelength all the time.According to the detailed investigation on the polarization characteristics of large diameter VCSEL device

a method with an external resonator was proposed to realize a stable polarization orientation with a resonance length of about 0.45 mm.