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    Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/68846

    Title: 應變量子井和波長偏移量對超高速(>40Gbit/sec) 850nm光波段的垂直共振腔面射型雷射之高溫和動態 特性的影響;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)
    Authors: 許毅軒;Hsu,Yi-Xuan
    Contributors: 電機工程學系
    Keywords: 垂直共振腔面射型雷設;光連接;應力量子井;波長偏移量;VCSELs;Optical interconnect;Strained quantum well;Detuning wavelength
    Date: 2015-07-28
    Issue Date: 2015-09-23 14:44:58 (UTC+8)
    Publisher: 國立中央大學
    Abstract: 下一個世代的光連結(optical interconnect,OI)技術的數據速率(data rate)將會是50Gb/s,為了達到這個目標垂直共振腔面射型雷射 (VCSELs)的3dB頻寬必須達到30GHz以上,而且此元件除了在常溫特性要好之外,且在85℃時的3dB頻寬也不能劣化太多。在論文裡會探討垂直共振腔面射型雷射主動層(active layer)的設計,藉由探討不同的應力量子井設計和波長偏移量對850nm VCSEL的靜態和動態特性有什麼影響。
    首先,我們比較GaAs/Al0.3Ga0.7As 和Al0.1In0.15Ga0.75As/Al0.3Ga0.7As兩種不同量子井結構的元件特性,而且此兩種元件都在相同水氧孔徑(5µm)以及相同波長偏移量(17nm)條件下做比較,結果顯示Al0.1In0.15Ga0.75As/Al0.3Ga0.7As量子井的元件3dB頻寬在室溫可以達到24GHz而85℃為 17GHz,另一方面GaAs/Al0.3Ga0.7As量子井的元件3dB頻寬在室溫只能達到20GHz而85℃為10 GHz,所以利用應力量子井可以增加垂直共振腔面射型雷射的3dB頻寬並且改善高溫特性。
    為了更進一步增加3dB頻寬,我們利用較多的增益峰值(gain peak wavelength)和共振腔共振波長( etalon wavelength)的波長偏移量(~20nm)。起初這個方法是用在分佈反饋半導體雷射(DFB Laser),但分佈反饋半導體雷射需要藍移的偏移量(blue-shift detuning),藍移的偏移量的定義為共振腔波長<增益峰值波長。
    然而VCSEL需要紅移的偏移量(red-shift detuning),這是因為VCSEL有比較大的熱阻,所以當電流增加時,元件熱效應會造成VCSEL有能隙窄化(bandgap narrowing)這個現象。
    利用較多的波長偏移量(~20nm)以及不同銦含量的應力量子井,我們發現In0.1Ga0.9As/Al0.3Ga0.7As和Al0.1In0.15Ga0.75As/Al0.3Ga0.7As兩種應力量子井的元件在水氧孔徑較小(3µm)時,3dB頻寬都接近30GHz。但當我們把元件的水氧孔徑做大(8µm)時,我們發現In0.1Ga0.9As/Al0.3Ga0.7As量子井的元件3dB頻寬只能到達20GHz並且需要較大的驅動電流(~17 kA/cm2),而Al0.1In0.15Ga0.75As/Al0.3Ga0.7As量子井的元件只需要較小的驅動電流(~8 kA/cm2)3dB頻寬就可以到達26GHz,而且因為我們把水氧孔徑做大,可以使元件電流密度降低,也因此我們元件的可靠度會提升,這也是目前高可靠度及超高速(>40Gb/s)VCSEL所需要的特性。
    ;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.
    Appears in Collections:[電機工程研究所] 博碩士論文

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