用於光無線通信和傳感高亮度、高速垂直共振腔面射型雷射陣列;High-Brightness, High-Speed VCSEL Arrays for Optical Wireless Communication and Sensing

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Title:	用於光無線通信和傳感高亮度、高速垂直共振腔面射型雷射陣列;High-Brightness, High-Speed VCSEL Arrays for Optical Wireless Communication and Sensing
Authors:	蘇坎;Khan, Zuhaib
Contributors:	電機工程學系
Keywords:	光無線通信;導致空間燒孔效應;垂直腔面發射激光器;Optical wireless communication;Spatial hole burning effect;Vertical Cavity surface emitting lasers (VCSEL)
Date:	2023-03-31
Issue Date:	2024-09-19 16:48:06 (UTC+8)
Publisher:	國立中央大學
Abstract:	摘要高速、高亮度的垂直共振腔面射型雷射(VCSELs)在當今的許多應用中都有使用，例如用於自動駕駛汽車、機器人和無人機的雷達光源、光學互連(OI)市場、3維(3D)感測和光學無線通信(OWC)通道，並對於發展 5G、6G 和衛星通信的下一代無線通信系統，具有相當大的潛力。高 CW 功率(大約幾百毫瓦)、高亮度、高速光源在上述應用中為關鍵因素。因此與邊射型雷射相比，VCSEL 在抗輻射性方面具有優勢，並且透過足夠的散熱，VCSEL 陣列的輸出功率可以隨二維尺寸成比例地增加。為了實現高亮度輸出，VCSEL 陣列需要具有高輸出功率、窄發散角和微小的主動區，可以通過使用鋅擴散、表面浮雕、光子晶體或抗導腔體結構來製造出符合上述條件的單膜(SM)VCSEL陣列。然而，為了抑制這些 VCSEL 結構中的高階模態雷射，必須引入額外的腔內損耗，這通常會導致閾值電流增加(Ith)和雷射的量子效率降低。此外，在不同的偏壓電流下，這些單膜(SM)或多膜(MM) VCSEL輸出的偏振態通常不穩定。利用X光雙晶測量結果驗證電鍍銅基板引起的拉伸應變，可以獲得高度單膜(SM) 和單偏振輸出光束的 VCSEL 陣列，並且具有最小的腔內損耗和更小的閾值電流。然而，由於高度單膜(SM) VCSEL陣列的高光功率密度，導致空間燒孔(SHB)效應，致使高速數據傳輸出現顯著的低頻roll-of和眼圖質量下降。此外，單膜(SM)VCSEL 通常具有較低的阻尼係數，這會導致EO和頻率響應中出現明顯的共振，導使眼圖質量顯著下降。為了進一步提高最大光功率，同時保持高亮度和提高長距離OWC應用所需的眼圖質量，想出了一種新穎的VCSEL陣列結構，設計的Mesa擁有交叉-並聯多個獨立VCSEL腔體。這種陣列在光功率、窄發散角、更低的 RIN 和傳輸眼圖，以上這些方面能得到改善。這些增強的靜態/動態性能是由於VCSEL的Mesa和腔體擴展產生之每個單元VCSEL的單膜(SM)輸出光子密度減弱。此外，如果我們進一步希望將光無線通信(OWC)和數據中心市場中各種微型或奈米衛星之間的鏈接距離增加到幾公里，並提高數據傳輸速率，那麼VCSEL 光源則必須具有高連續波(CW)功率和更寬且平穩的EO 頻率響應圖。另外，透過不均勻的電流注入雙電極，導致相鄰 VCSEL 單元之間的光耦合較弱，我們得以證明，超緊密陣列佈局和光孔之間具有小間距尺寸的Pad電極具有高光功率輸出。由於我們陣列中的這種弱耦合，使得頻率響應(EO)更加平穩，從而導致眼圖質量進一步改善。這種新型陣列很有可能進一步提高下一代 OWC 通道的傳輸性能。 ;Abstract High-speed and high-brightness vertical-cavity surface emitting lasers (VCSELs) are utilized in numerous applications nowadays such as light source in development of lidar for use in autonomous cars, robots, and unmanned aerial vehicles, optical interconnect (OI) markets, 3-dimensional (3-D) sensing and optical wireless communication (OWC) channels which is one potential solution for development of the next generation of wireless communication systems for 5G, 6G and satellite communications. A high CW power (hundreds of mW), high-brightness, high-speed light source is critical in the aforementioned applications. In comparison to their counterparts, edge-Emitting Lasers (EELs), VCSELs have an advantage in terms of radiation resistance and by providing adequate heat dissipation, the output power of a VCSEL array can be increased proportionally with size of 2-D VCSEL array. To achieve high-brightness output, a VCSEL array with a high output power, narrow divergence angle and small active area is highly desirable which can be achieved by fabricating VCSEL array of single-mode (SM) VCSEL units either by using zinc (Zn)-diffusion, surface relief, photonic crystal or anti-guide (leaky) cavity structures. However, to suppress higher-order mode lasing in these VCSEL structures, additional intra cavity loss must be introduced, which generally leads to an increase in the threshold current (Ith) and a decrease in quantum efficiency of the laser. In addition, under different bias currents, the polarization states of the output from these SM or MM VCSELs are usually not stable. VCSEL array structure capable of producing highly SM and single-polarized output beams with minimum intra-cavity loss and less threshold current can be obtained using tensile strain induced by the integration of the electroplated copper substrate verified by the double-crystal x-ray measurement results. However, due to high optical power density of highly SM VCSEL arrays, it will result in spatial hole burning (SHB) effect that leads to significant lower frequency roll-off and degradation of eye-pattern quality for high-speed data transmission. Additionally, SM VCSELs typically have a reduced damping factor (γ), which causes noticeable resonances in the E-O and (RIN) frequency responses, resulting in significant deterioration of the eye pattern quality. In order to further improve the maximum optical power while maintaining high brightness and enhancing the eye pattern quality that are required for long-reach OWC applications, a novel VCSEL array structure is designed in which several independent single VCSEL cavities are connected in parallel and having criss-cross mesas connecting each VCSEL cavity. The performance of these arrays improves in terms of optical power, narrow divergence angle, lower RIN, and better eye-opening quality for high-speed data transmission. These enhanced static/dynamic performance is due to weakening of photon density in the SM output from each VCSEL unit produced by the extension of mesas as well as cavity of VCSEL. Moreover, if we further want to increase linking distance between various micro or nanosatellites in optical wireless communication (OWC) and data center market up to several kilometers with increased data transmission rate, then VCSEL light sources having high continuous wave (CW) power with wider and dampened E-O frequency response is highly desired. A novel design in both ultra-compact array layout and pad electrodes with a small pitch size (20 μm) between the light emission apertures has been demonstrated that possess high (CW) optical output power, results in weak optical coupling between neighboring VCSEL units by the non-uniform current injection from dual electrodes. Due to such such weak coupling in our array, the electrical-optical (E-O) frequency response is dampened more that substantially leads to further improvement in eye-pattern quality. Such novel array has high possibility to further improve transmission performance in the next generation OWC channel.
Appears in Collections:	[Graduate Institute of Electrical Engineering] Electronic Thesis & Dissertation

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