| 摘要: | 本文旨在研究產生量子壓縮光源，並致力於將光路積體化，不僅提供光路更高的擴展性在操作上也更加穩定。透過單通光參量放大器產生非古典光源-壓縮態，依照海森堡的不確定性原理，知道光學中最小擾動極限，透過壓縮光的正交項能夠達到比標準量子極限更小的擾動;而相對的其另一個正交項會大於標準量子極限，能夠在量子感測領域中提供更高的精準度。此外，為了要實現大型量子光路，使用絕熱耦合器做為分光器，能提供製程高容忍度和高工作寬頻的特性。
本研究藉由鈮酸鋰基板成功的將壓縮光源和波長分光器整合在同一晶片上，從受激拉曼絕熱過程的理論出發，設計絕熱耦合器，並使用光束傳播法模擬波導耦合條件，到一系列的製程過程，經由半導體製程技術使晶片具有準相位匹配的週期性晶疇反轉結構及鈦擴散式波導，其中包括黃光微影、薄膜、擴散、研磨拋光、蝕刻，最後量測晶片特性(1)絕熱耦合器的消光比，在波長 1550nm 有高達 23.4dB，消光比大於 20dB 和大於10dB 分別有 18、68nm 頻寬，(2)非線性光學-倍頻現象，歸一化轉換效率有 15.8%/W/cm2
，(3)透過平衡零差檢測方法量測壓縮光，我們預計此晶片可以產生壓縮光和反壓縮光分別為-0.67dB、0.72dB。
未來可以設計不同耦合器，或是採用其他波導種類，甚至可以更換基板材料，使得晶片非線性轉換效率更高、能承受更高泵浦光能量、傳播損耗更低，製備出品質更好的晶片式壓縮光源，量子光源是量子光路系統中的首要條件，藉由此研究可以將量子光源在晶片上產生，作為光量子發展的一部份，提供穩定壓縮光源的價值，有文獻做了定向耦合器當作 50:50 分光鏡[1]，不只能增加兩道光的模態疊合程度，也能進一步將光路積體化，完成整個量子積體光路系統。
;This research is aimed to produce squeezed vacuum state in single-pass optical parametric amplifier (OPA) in nonlinear optics. The process based on a single-spatial-mode periodically poled lithium niobate (PPLN) waveguide, also called on-chip squeezer. In this work, we provide more compact, robustness and scalability via integrated photonic circuits rather than conventional optical measurement scheme. According to Heisenberg ′s uncertainty principle,
there is minimum fluctuation in optical field, that is standard quantum limit (SQL). By utilizing squeezing light, we can obtain noise level below SQL in one quadrature (may in amplitude or phase), and another quadrature will be amplified higher than SQL. This characteristic can apply
in quantum sensing area providing extra precise metrology. Additionally, in order to realize large photonic quantum circuits (PQCs), we designed adiabatic coupler (AC) which has fabrication tolerant and broadband operation properties as a beam splitter to separate pump and signal wavelength.
We had developed squeezing light source and beam splitter integrated on Ti-diffused periodically poled lithium niobate (PPLN) waveguides. From stimulated Raman adiabatic passage (STIRAP) theory, we built up adiabatic coupler geometric structure and simulation through beam propagation method (BPM), to fabrication process flow with lithography, thin
film, diffusion, chemical-mechanical polishing, etch. Finally, measuring the chip characteristic (1)Extinction ratio of adiabatic coupler achieve up to 23.4dB at 1550nm. In addition, extinction ratio more than 20dB and 10dB has 18nm、68nmrespectively. (2)Nonlinear optics process second harmonic generation (SHG), the chip demonstrates normalize SHG conversion efficiency 15.8%/W/cm2. with 15mm quasi phase matching (QPM) length. (3)By balance homodyne detection (BHD) method to measure squeezing level, we estimated the squeezing and anti squeezing levels can be -0.67dB and 0.72dB, respectively.
In future work, we can design different coupler and even can change the waveguide type which enhance the nonlinear conversion efficiency, durability for high-power pump and low propagation loss. Due to above mentioned optimizations, we can fabricate more quality on-chip squeezer. The quantum light source is preliminary condition in quantum network system. By means of the thesis contribution, we can offer a stable nonclassical light which is squeezing light. In other group, they integrated directional coupler (DC) as 50:50 beam splitter (BS) on chip cascade OPA process [1]. Not only did it improve the spatial mode matching, but it minimizes optical setup. We believe that our work combine the DC can toward integrated quantum system further. |
