The Influence of Strained Multiple Quantum Wells and Wavelength Detuning on the Dynamic Performances of Ultra-High Speed (>40 Gbit/sec) 850 nm Vertical-Cavity Surface-Emitting Lasers (VCSELs)

• Main Authors: Yi-Xuan Hsu, 許毅軒
• Other Authors: Jin-Wei Hsu
• Format: Others
• Language: zh-TW
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/tgq5cs

碩士 === 國立中央大學 === 電機工程學系 === 103 === To meet the application of next generation optical interconnect (OI) with data rate as high as 50 Gbit/sec, a high-speed vertical-cavity surface-emitting laser (VCSEL) with a 3-dB electrical-to-optical (E-O) bandwidth over 30 GHz and can be operated from room-temperature (RT) to 85℃ is highly desired. In this thesis, the influence of active layer design, which includes wavelength detuning and strained multiple quantum wells (MQWs), on the static/dynamic performances of high-speed 850 nm VCSEL have been investigated in detail. Compared with the reference device with the lattice-matched GaAs/Al0.3Ga0.7As MQWs design, the studied device with a highly strained Al0.1In0.15Ga0.75As/Al0.3Ga0.7As MQWs design exhibits a faster speed performance (23 vs. 20 GHz) and an improved high-temperature performances under the case of same oxide-aperture (~5 µm) and the same wavelength detuning (+15 nm). Furthermore, in order further boost the speed performance of these VCSELs with highly strained active layers design, a strong wavelength detuning (> +20 nm; etalon wavelength > material gain peak wavelength) was adopted in our studied devices. Such positive wavelength detuning design for VCSEL bandwidth enhancement is conflict with that of the typical reported distributed-feedback (DFB) laser, which usually needs a blue-shift detuning for speed enhancement. This is because that the VCESL devices usually have a larger thermal resistance and suffered from more serious device-heating induced bandgap narrowing during operation than those of DFB lasers. With such a strong detuning design, it is found that both In0.1Ga0.9As/Al0.3Ga0.7As and Al0.1In0.15Ga0.75As/Al0.3Ga0.7As MQWs design can attain nearly 30 GHz O-E bandwidth and (quasi-) single-mode performances with a diameter of oxide-relief apertures less than 5µm. On the other hand, when the oxide-relief aperture reaches ~8µm, the devices with Al0.1In0.15Ga0.75As/Al0.3Ga0.7As well exhibits a much better speed performance (>24 vs. 20 GHz) than that of In0.1Ga0.9As one due to its larger compressive strain in active layers. This thus results in a much lower driving-current density (~8 vs. ~17 kA/cm2) of devices with Al0.1In0.15Ga0.75As well for the same desired high-speed performance (~27 GHz). By use of these newly demonstrated low-driving current density VCSELs with strong positive wavelength detuning (+ 20 nm), high-speed performance, excellent transmission performance, which includes an extremely low energy-to-data rate ratio (EDR: 228 fJ/bit) and record-low driving-current density (8 kA/cm2; 3.5mA) have been successfully achieved for 41Gbit/sec error-free transmission over 100 meter OM4 multi-mode fiber.