第三章 全場相對相位與絕對相位之量測
3.5 絕對相位量測方法之比較與量測誤差
3.5.3 理論誤差之比較
在3.3 節的方法中，量測相位時可能會受到以下幾種誤差的影響，茲分 述如下：
(1) 特徵相位誤差：V 與 Vπ 的誤差會直接對特徵相位
0 引入一個系統誤差 Δ
0，由電源供應器可得輸出電壓V 之解析度為 ΔV1 = 0.016 V；此外，Vπ 可 經由量測得到[29]，且可估計其誤差為 ΔV2 = 0.015 V。因此
0的最大估計誤差可表示成
2 2
122 1 max
0 ( ) ( / )
V V V V
≈ 0.03°，其中
max估計為最大可能相位值
max = 180°。(2) 取樣誤差與偏極混合誤差：此兩項誤差詳細描述於 2.4 節裡，不再贅述，
分別為取樣誤差 = 0.036°以及偏極混合誤差
s = 0.03°。
p綜合上述，
之量測理論誤差∆
可估計為
=
0 +
s + ∆
p = 0.096°。而在3.4 節的方法中，並不存在特徵相位誤差
0，因此其絕對相位
之 量測理論誤差∆
與2.4 節之全場外差干涉術的誤差估算相同，為
=
s +∆
p = 0.066°。3.6 小結
本章的內容主要是利用外差干涉術進行二維相位延遲的量測，藉以實現全場 相對相位與絕對相位之量測。所謂「相對相位」是指測試訊號二維平面內的所有 像素的相位，相對於平面上某個指定像素相位的差值，也就是使用該指定像素的 干涉訊號做為參考訊號；而「絕對相位」指的是以測試訊號以外的其他干涉或電 子訊號做為參考訊號，所求得測試訊號的相位。本研究的待測樣本為圓形的四分 之一波片，首先在3.2 節說明利用光束未通過樣本的部分做為參考訊號，以相對 相位的量測方法完成二維相位延遲的量測；在3.3 節中提出以振幅低於半波電壓 的鋸齒波驅動EO 的方法，可實現絕對相位之量測；在 3.4 節中提出另一種對 3.3 節的改進方法，利用振幅等於半波電壓的非對稱三角波驅動 EO，可簡化 3.3 節 的步驟，並降低絕對相位的量測誤差；最後在3.5 節中，比較了利用 3.3 節與 3.4 節的方法量測四分之一波片相位延遲分佈的結果、訊號處理以及理論誤差。
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