平衡式零差偵測器是由兩個規格相同的光電二極體加上電流放大器及電壓放大器所組成的光子偵測裝置.當兩道頻率相同且強度相等的光照射在這兩個光電二極體時,由於它們在電路上的組態,所產生的光電流會互相抵消,電路裡的熱雜訊也會一同消失,最後只剩下散粒雜訊,這就是所謂的真空態.
評量平衡式零差偵測器的好壞,有兩個指標：第一個指標是光電二極體的量子效率,就是光轉換成電流的能力.另一個是共模拒斥比(CMRR),這是雜訊能被消除多少程度的指標.
這篇論文裡的內容,主要是借由量測兩種不同規格的光電二極體的量子效率與整體電路的CMRR值,再進一步地探討如何使這兩項指標能夠被實現最佳化的量測方式與實驗技術.這些最佳化的結果將有助於光壓縮態的偵測.

Balanced Homodyne Detector is a device which made of two identical photodiodes and Op.amplifiers.As two identical laser light (frequency and intensity) incident into the photodiodes, due to the circuit arrangement, the photocurrent from the two photodiodes would be canceled out.Even thermal noise also, and only shot noise (vacuum state) leaves.
Two indexes could evaluate the performance of Balanced Homodyne Detector: one is quantum efficiency of the photodiode, that indicates the ability of converting light energy into electrical current. The other one is CMRR (Common Mode Reject Ratio),that tells the efficiency of cancelling noise.
The main job of this thesis is to investigate the two indexes by comparing two different kind of photodiodes and circuits,and developing a electrical measuremental method for promoting the performance of the indexes.Based on the above, the measurement of the squeezed states of light may be achieved.

1. Introduction
1.1 The main goal of this thesis ...............................................2
1.2 The structure of this thesis ...............................................3
2. Theory background
2.1 What is the balanced homodyne detector ........................4
2.2 How does the BHD work ...................................................5
2.3 The concept of squeezed light .........................................9
3. Experimental setup
3.1 Electrical circuit and layout ...............................................15
3.2 The linear response of the photodiodes ...........................20
4. Summary and Future work
4.1 Quantum Efficiency ...........................................................23
4.2 CMRR ................................................................................26
4.3 Application ........................................................................29
4.3 Future work .......................................................................30
Appendix .................................................................................32 References...............................................................................36

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