||Optical Devices for Collimating and Guiding Edge-Emitting Laser Diodes Via Multiphoton Microfabrication
||Department of Engineering Science
vertical-cavity surface-emitting laser
近年來，藉由多光子激發技術 (multiphoton excitation, MPE) 所製造的眾多微製程光學元件的應用在半導體領域獲得了極大的進步。但是對於具有準直與導引功能，並直接製程於半導體雷射的光學元件組合並沒有太多的實驗和研究。在此論文中，三甲基丙烷三丙烯酸酯 (Trimethylolpropane triacrylate, TMPTA) 的三維 (3 dimension, 3D) 結構是藉由多光子激發技術的聚合效應來製程。因為多光子激發技術因吸收範圍侷限於極小體積之中，因此相比於傳統的單光子激發 (single photon excitation)，多光子激發擁有更佳的切片特性，所以可製造出高空間解析度的任意形狀結構並精確的置於雷射二極體上。在製程的過程中，使用製程溶液包含了當為反應性單體 (reactive monomer) 的三甲基丙烷三丙烯酸酯，孟加拉玫瑰紅素(rose Bengal, RB) 為光活化劑 (photoinitiator)，也稱為光敏劑。而三乙胺(Triethylamine, TEA) 為共同起始劑 (co-initiator)，在製程過程中，藉由飛秒雷射 (femtosecond laser)，光活化劑被雙光子效應 (two-photon absorption, TPA) 所激發。而自由基在過程中產生，並和三甲基丙烷三丙烯酸酯溶合產生聚合物鏈。在雷射加工方面，為了避免雷射光所造成的熱效應來破壞結構，並使最大化雷射之效率，所以雷射波長會選擇可使玫瑰紅素產生更佳的雙光子吸收波段。同時調控最佳的雷射製程參數來製作二維與三維的微結構。在製程完成後透過一般光學顯微鏡或是雙光子激發螢光影像和掃描式電子顯微鏡來觀察和檢視結構之形態。
此論文之目的是在於使用雙光子激發，在邊設型雷射二極體(edge-emitting laser, EEL) 表面上直接製程具有準直和導引的光學元件之組合。用於導引平行於地面邊設型雷射產生的雷射光，與準直具有發散角之雷射。
As of currently, many optical application in microstructures are being made via multiphoton excitation (MPE) attached on semiconductors. However, there is a lack of research regarding direct fabrication on semiconductor lasers with combination of optical structures that consists of both the abilities to guide and collimate the laser beam. In this thesis, MPE technique is utilized to create three dimensional (3D) structures via polymerization in trimethylolpropane triacrylate (TMPTA) solution. Due to the fact that the precision of MPE is in focal volume, the sectioning effect is significantly better than single-photon excitation. With this technique, the high spatial resolution of the 3D waveguide devices has the ability to collimate and redirect laser beam can be directly fabricated on specific location of laser diodes. The main mechanism of the multiphoton-induced fabrication technique was done in TMPTA solutions, the solution contains TMPTA as the reactive monomer, rose Bengal (RB) as the photoactivator, and trimethylamine (TEA) as co-initiator. In this process, the photoactivator is activated through two-photon absorption (TPA) of femtosecond laser to produce the two-photon polymerization (TPP). In addition, femtosecond laser can generate enough photon energy density within focal volume. Hence, the free radicals are produced from the reaction and the energy is then transferred to the monomers. After having the energy transferred, the TMPTA monomers attach with each other through covalent bonding and form a precise, delicate, transparent and rigid structure on selected area in micron-scale that standard fabrication methods could find difficult to work with.
The objective of this thesis is to use TPP to fabricate a combination of photonics devices directly on edge-emitting laser diode (EEL). Through guiding the laser in the direction similar to vertical-cavity surface-emitting laser diode (VCSEL) then collimate the divergent laser beam by a lens. VCSEL is the trend of laser diode technology since it is economical to manufacture, easier to couple with optical fiber. And the circular-like laser beam from VCSEL can be collimated more efficiently. However, due to the fact that VCSEL has a short cavity, it is difficult to generate higher power output. On the other hand, EEL have long cavity to generate stronger laser. By attaching the optical devices to EEL, this semiconductor laser will then be able to have much greater value of power output and the direction is relatively close to VCSEL for better versatility and flexibility in potential electric device applications.
In conclusion, this thesis has concluded that it is possible to have direct fabrication through MPE to construct optical devices on specific location on a semiconductor laser with designate functions and properties. Though there are some defects exist, it could be improved with adjustment on design and process, and the future potential continues.
Table of Contents VII
List of Figures IX
List of Abbreviations XII
Chapter 1 Introduction 1
1.1 Background 1
1.2 Literature review 2
1.3 Motivation and goal 3
1.4 Outline 3
Chapter 2 Ultrafast Laser System and Multiphoton Microfabrication Mechanism 5
2.1 Optical setup and Ultrafast laser system 5
2.1.1 Ultrafast laser system 6
2.1.2 Optical setup and electronic control system 6
2.1.3 3D freeform modeling and design-transformation 11
2.2 Multiphoton microfabrication mechanism 12
2.2.1 Nonlinear optical effects 12
2.2.2 Multiphoton absorption and excitation 13
2.1.3 Multiphoton-induced photochemistry 16
Chapter 3 Three-dimensional Microstructures of Polymers and Proteins 21
3.1 Fabrication materials 21
3.2 Sample preparation 22
3.3 Fabrication process 25
3.4 3D polymer and protein microstructures 29
3.4.1 BSA microstructures 29
3.4.2 NOA81 microstructures 30
3.4.3 TMPTA microstructures 30
Chapter 4 TMPTA optical devices fabricated on semiconductor laser diode 32
4.1 Semiconductor laser diodes and laser path 32
4.2 Optical devices design and 3D transformation 35
4.3 Fabrication outcome observation 40
4.4 Direct fabrication on EEL diode and a noval software program on z-coordinate detection. 42
Chapter 5 Conclusions and Future Work 47
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