Study On Wavelength Tuning Property Of MEMS-Tunable Vertical-Cavity SOAs

With the development of VCSEL technologies, vertical-cavity semiconductor optical amplifiers (VCSOA) have become to attract people's increasing interest. There have been some research results which indicate that VCSOA have the inherent advantages of high-fiber coupling efficiency, polarization insensitivity, and low noise figure, etc. Furthermore, they can be a low-cost alternative to in-plane SOA. So they have potential applied prospects in the domain of optical modulations, optical switches, optical detections, as well as wavelength conversion.Limited to the linewidth of the Fabry-Perot (F-P) structure, the bandwidth of VCSOA is commonly narrow. In order to make VCSOA more flexible for modern fiber-optic networks, tunable devices must be developed. It is therefore of great interest to make tunable VCSOA that can cover a wider wavelength range and can be precisely adjusted to match the wavelength of the signal. Previously, temperature-tuning of long wavelength VCSOA has been investigated, but a more promising approach is micro-electromechanical (MEMS) tuning. Here, mechanical alteration of the effective cavity length gives rise to tuning ranges greater than those that can be achieved by refractive index modulation.In this paper, unlike the previous coupling cavity way, we propose a method which using transfer matrix method to study the gain and bandwidth property of the MT-VCSOA, and mainly bases on the structure of the MT-VCSOA comprised of different material layers. According to the similar method dealing with the DBR, the characteristic matrices of the layers in the active region, quantum well of different thickness, substrate are built up. Then after multiplying the characteristic matrices of all the layers in the DBR, quantum well, air-gap, and substrate orderly, the transfer matrix of the MT-VCASOA is obtained. Combing the refractive index of the substrate, the gain property of the MT-VCSOA can be studied. It avoids to calculate the effective cavity length and the gain enhancement factor by this way, and the results responding to the structure of the MT-VCSOA.Using the obtained transfer matrix, the characteristics of gain and bandwidth of the semi-conductor coupled cavity (SCC) and extended-cavity (EC) structure MT-VCSOA are studied respectively. The influence of the the carrier density and DBR numbers to the peak gain and bandwidth are obtained. The results are same to the published papers, and show the validity of the method. At the same time, the different bandwidth and gain properties between the SCC and EC are compared.