1269067 (1) 玫、發明說明 【發明所屬之技術領域】 本發明乃關於採用雙折射晶圓之光學低通濾波器。 【先前技術】 光學低通濾波器爲，爲了抑制攝像元件於受光之際所 產生之虛擬信號，而將光線的影像頻率數之高頻成分消除 者，其特性乃藉由分離光線的分離模式來決定。 關於以往的光學低通濾波器，例如有日本特開20 GO-56268 號公 報所示 之光學 低通濾 波器。 此光學低通濾波器是由，光學軸互爲相異之3片的雙 折射晶圓所疊合而成。所疊合的3片雙折射晶圓被分割， 並形成多數個光學低通濾波器。 具體而言，3片的雙折射晶圓均是對水晶錠的光學軸 爲4 4 · 8度來切割上述水晶錠而形成。此3片的雙折射晶 圓是由，分離入射光爲水平方向之水平方向雙折射晶圓， 及分離入射光爲對水平方向雙折射晶圓的分離方向之+4 5 度方向之+45度方向雙折射晶圓，及分離入射光爲對水平 方向雙折射晶圓的分離方向之-45度方向之-45度方向雙 折射晶圓所組成，並依序疊合這些水平方向雙折射板、 + 45度方向雙折射板、-45度方向雙折射板，來形成光學 低通濾波器。 入射於此光學低通濾波器的光線，經由水平方向雙折 射板分離爲一般光線及異常光線，而分離成一般光線及異 -4- 1269067 (2) 常光線，分離後的一般光線及異常光線，各自藉由+/-45 度方向雙折射板（圖中省略）而分離成4點。 藉由採用此光學低通濾波器以將入射光分離爲4點， 來分離對CCD等攝像元件之輸入光，並使模糊影像且引 發疊紋的虛擬信號降低。 目前，攝像元件的格間距（Cell Pitch )有變小的趨 勢。亦即，於近年來所製造出的CCD當中，與以往的尺 寸相同的設計下，將其格間距縮小以增加像素數（例如， 從2 00萬像素增加至3 0 0萬像素的情況等）。因此，伴隨 著C CD 8的格間距的縮短，有必要縮短光學低通濾波器中 之光線的分離寬度。 然而，爲了縮短光學低通濾波器中之光線的分離寬 度，有必要將構成光學低通濾波器的各個雙折射板的厚度 變薄。再者，有必要將+/ - 4 5度方向雙折射板的厚度變爲 水平方向雙折射晶圓的1/，2。因此，於+/-45度方向雙 折射晶圓當中，更需要具有較薄的厚度，而使硏磨加工變 得困難，並導致成本的上升。 此外，於雙折射晶圓的組合中，由於實際上水晶錠的 成長並不大，因此難以得到大型的+/-45度方向雙折射晶 圓。此外，一般而言，+/-45度方向雙折射晶圓的形狀 爲’於沿著對光學軸呈45度方向的邊之矩形形狀上欠缺 了 1個大角者。於此情況下，從雙折射晶圓當中分割多數 個矩形形狀的光學低通濾波器之切割工程當中，會產生材 料的損失並造成效率的惡化。 1269067 (3) 因此，爲了解決上述課題，本發明的目的在於提供， 容易進行雙折射晶圓的硏磨加工之光學低通濾波器，此 外，本發明的目的在於提供，可使欠缺的部分對雙折射晶 圓全體的比例爲零或是降低，並於一次生產可生產多數 個，因而降低生產成本的光學低通濾波器。 【發明內容】 爲了達成上述目的，本發明之光學低通濾波器，乃藉 由對水晶錠的光學軸具有角度來切割水晶錠而形成之雙折 射晶圓所構成，並分離入射光，其特徵爲上述雙折射晶圓 是由，對水晶錠的光學軸以大於44.8度的角度來切割上 述水晶錠而形成。 根據本發明，因爲雙折射晶圓是藉由對水晶錠的光學 軸以大於 44.8度的角度來切割上述水晶錠而形成，因 此，爲了得到與以往的切割角度爲44.8度者相同的分離 寬度，而使雙折射晶圓的厚度變厚，因而於硏磨雙折射晶 圓之際，可以不需在意雙折射晶圓產生破損等材料的損 失，而容易進行加工作業，並降低生產成本。此外，由於 雙折射晶圓是藉由對水晶錠的光學軸以大於44.8度的角 度來切割上述水晶錠而形成，即使水晶錠的成長幅度不 大，亦可增大雙折射晶圓的面積，其結果爲，即使雙折射 晶圓欠缺1個角，由於欠缺的部分對雙折射晶圓全體的比 例亦較小，因此可以抑制於分割多數個光學低通濾波器之 際所形成之具有缺陷之光學低通濾、波器的數量，因而可並 -6 - 1269067 (4) 降低生產成本。 此外’根據本發明，因爲雙折射晶圓是藉由對水晶錠 的光學軸以大於4 4 · 8度的角度來切割上述水晶錠而形 成’因此可使雙折射晶圓的厚度變厚，並容易調整厚度於 預先所設定的厚度。例如，以往之將用於數位相機（攝像 裝置）之CCD的像素數從200萬像素增加至300萬像素 的情況下’必須進行光學低通濾波器的厚度之變更，並藉 由該變更來改變數位相機中之光路徑長等之數位相機本身 之設計變更’而根據本發明之光學低通濾波器，因爲可調 整雙折射晶圓的切割角度，並使其厚度與以往者相同，因 此只要設定雙折射晶圓的尺寸，則不需改變數位相機中之 光路徑長，而降低生產成本。 再者’如上述般之在將光學低通濾波器用於具有 C CD之數位相機等攝像裝置之情況下，爲了防止攝像裝 置本身的設計變更所造成之生產成本的增加，因此預先設 定光學低通濾波器的厚度。在此，若是將本發明的光學低 通濾波器用於攝像裝置的話，則因爲雙折射晶圓是藉由對 水晶錠的光學軸以大於4 4.8度的角度來切割上述水晶錠 而形成，因此不需改變光學低通濾波器的厚度而可降低其 分離寬度，因而可對應C C D的像素數的增加。 具體而言，於上述的構成中，上述雙折射晶圓不僅可 由多數枚疊合來形成，亦可加以分割而形成多數個，而多 數枚當中的至少1枚上述雙折射晶圓是由，對水晶錠的光 學軸以大於44.8度的角度來切割上述水晶錠而形成。或 -7- 1269067 (5) 者是，於上述的構成中，上述雙折射晶圓不僅可由 疊合來形成，亦可由，分割這些多數枚的雙折射晶 成各個多數枚的雙折射板，並將由各個雙折射晶圓 之多數枚的雙折射板加以疊合而形成，而多數枚當 少1枚上述雙折射晶圓是由，對水晶錠的光學軸 4 4.8度的角度來切割上述水晶錠而形成。 此外，於上述的構成中，亦可於所疊合的多數 述雙折射晶圓當中，至少包含，對水晶錠的光學軸 44 · 8度的角度來切割上述水晶錠而形成，並分離入 水平方向或是垂直方向之第1雙折射晶圓；及對水 光學軸以大於44.8度的角度來切割上述水晶錠而 並分離入射光爲對水平方向或是垂直方向呈45度 第2雙折射晶圓。 於此情況下，因爲使分離入射光爲對水平方向 直方向呈45度方向之第2雙折射晶圓的厚度變厚 使一般而言其厚度較第1雙折射晶圓爲薄的第2雙 圓的厚度增加，於硏磨第2雙折射晶圓之際，可以 意雙折射晶圓產生破損等材料的損失，而容易進行 業。 於上述的構成中，所疊合的多數枚的上述雙 圓，是由1枚的第1雙折射晶圓及2枚的第2雙折 所構成’上述第1雙折射晶圓是以，1個互爲對向 與光學軸呈平行之矩形狀來形成，並且，上述第2 晶圓爲5角形狀’當中所鄰接的3個角以略爲直 多數枚 圓來形 所形成 中的至 以大於 枚的上 以大於 射光爲 晶鏡的 形成， 方向之 或是垂 ，因而 折射晶 不需在 加工作 折射晶 射晶圓 的兩邊 雙折射 角來形 1269067 (6) $ ’ 且與此3個角當中的中央的角對向並與光學軸正交 的邊來形成。 此外，於上述的構成中，上述之對水晶錠的光學軸大 Μ 44·8度的角度，最好設定於對該光學軸小於80度以 Τ ’尤其是若是設定在69度的話，則更容易形成光學低 通濾波器。 【實施方式】 以下參照圖面來說明本發明的實施型態。 如第1圖所示般，本發明的實施型態之光學.低通濾波 器1是由，切割水晶錠2而形成之雙折射晶圓3 1、3 2、 3 3所構成。 雙折射晶圓3 1爲本發明之所謂的第1雙折射晶圓， 爲分離入射光爲水平方向之晶圓。此雙折射晶圓3 1是由 對水晶錠的光學軸以大於44.8度的角度來切割上述水晶 錠而形成，如第2圖（a )所示般，是以1個互爲對向的 兩邊4與光學軸A呈平行之矩形狀來形成。 雙折射晶圓32爲分離入射光爲對水平方向呈+4 5度 方向之晶圓。此雙折射晶圓3 2是由對水晶錠的光學軸69 度來切割上述水晶錠而形成，如第2圖（b )所示般，爲 5角形狀，當中所鄰接的3個角5以直角來形成，並且與 此3個角5當中的中央的角5對向並與光學軸A正交的 邊6來形成。 雙折射晶圓33爲分離入射光爲對水平方向呈-45度 -9- 1269067 (7) 方向之晶圓。此雙折射晶圓33是由對水晶錠的光學軸69 度來切割上述水晶錠而形成，如第2圖（c )所示般，爲 5角形狀，當中所鄰接的3個角5以直角來形成，並且與 此3個角5當中的中央的角5對向並與光學軸A正交的 邊6來形成。 此雙折射晶圓3 2、3 3爲本發明之所謂的第2雙折射 晶圓，在此設定用於形成此雙折射晶圓3 2、3 3之對光學 軸A的切割角度爲6 9度，此6 9度乃藉由以下的數學式1 所算出。此外，由此數學式所算出之切割角度的特性，則 顯示於第3〜5圖。第3圖爲顯示切割角度及d = 5 8 9.3 (nm )之際的係數（參照第4圖）之間的關係之表，其 圖示則顯示於第4圖。此外，第5圖爲顯示切割角度、及 切割角度爲44.8度之際之與雙折射晶圓32、33的厚度比 之間的關係之圖式。 <數學式1> d ~ (ne2~no2) sin Θ cos Θ f ne2sin2 Θ +no2cos2 Θ (d :分離寬度、ne = 1.5 5 3 4 :異常光線的折射率、 η ο = 1 · 5 4 4 3 : —般光線的折射率、0 :切割角度、t :雙折 射晶圓的厚度） 從數學式1當中，可得知雙折射晶圓3 1、3 2、3 3的 分離寬度d (參照第7圖），與切割角度0及雙折射晶圓 的厚度t相關。於本發明的實施型態中，因爲設定用於形 -10- 1269067 (8) 成雙折射晶圓3 2、3 3之對光學軸 A的切割角度爲6 9 度’因此相較於以44 · 8度來切割的情況，其分離寬度d 較短。 接下來，採用第2圖來詳細說明光學低通濾波器1的 生產製程。 水晶錠2以對其光學軸 A呈44.8度的角度被切割 (參照第1圖（a ))，並形成第2圖（a )所示之雙折射 晶圓3 1。接下來，水晶錠2以對其光學軸A呈6 9度的角 度被切割（參照第1圖（b ))，並形成第2圖（b )、第 2圖（c )所示之雙折射晶圓3 2、3 3。如此形成的雙折射 晶圓3 1、3 2、3 3，乃依據雙折射晶圓3 1、雙折射晶圓 3 2、雙折射晶圓3 3的順序來疊合。而所疊合的雙折射晶 圓3 1、3 2、3 3，乃藉由切割機器之晶圓切割機，於形成9 個矩陣狀的方式，在分割線（參照第2圖（d ))上來分 割，並形成可正常動作之7個光學低通濾波器1。 入射於所形成的光學低通濾波器1之光線，藉由以雙 折射晶圓3 1所形成之水平方向雙折射板（圖中省略）， 而分離成一般光線及異常光線，分離後的一般光線及異常 光線，各自藉由以雙折射晶圓32、33所形成之+/-45度方 向的雙折射板（圖中省略）而分離成4點。 經由上述生產製程所生產之光學低通濾波器1，用於 例如第6圖（a )所示之數位相機等攝像裝置中。 如第6圖（a )所示般，於此攝像裝置中設置了，將 攝影之際所接收的光線加以集光之透鏡7、及在多數個攝 -11 - 1269067 (9) 像元件（圖中省略）中接收藉由透鏡7加以集光之光線， 並將其光線資訊轉換爲數位資料之CCD8。然後，光學低 通濾波器1設置於這些透鏡7及CCD8之間的光路徑（長 度1 )中。於此光學低通濾波器1的光線的入射面1 a及射 出面1 b上，形成用於防止光漫射之抗反射塗裝（圖中省 略）。 於攝像裝置中，光線從外部入射於透鏡7，並藉由透 鏡7加以集光。經由集光後的光線，則經由光學低通濾波 器1來分離，並入射於CCD8的各個受光元件。 目前，CCD8的格間距（Cell Pitch )有變小的趨勢。 亦即，例如於近年來所製造出的CCD8當中，與以往的尺 寸相同的設計下，將其格間距縮小以增加像素數（例如， 從2 0 0萬像素增加至3 0 0萬像素的情況等）。因此，伴隨 著CCD8的格間距的縮短，有必要縮短光學低通濾波器中 之光線的分離寬度d，從上述數學式1亦可得知，可藉由 採用本發明的實施型態之雙折射晶圓3 2、3 3，來縮短分 離寬度d。 此外，於以往的光學低通濾波器1當中，爲了增加 C C D 8的像素數，而採用使分離寬度d縮短之雙折射板。 因此，光學低通濾波器的厚度變薄，其結果爲，第6圖 (a )所示之光路徑長1爲可變。因此，於以往的光學低 通濾波器1當中，將通過玻璃等疊合於雙折射板上來調整 光學低通濾波器的厚度。然而，根據本發明的實施型態之 光學低通濾波器1，因爲+/-45度方向的雙折射板32a、 -12- 1269067 (10) 3 3b的厚度較厚，因此將這些+/-45度方向的雙折射板 3 2 a、3 3 b的厚度調整爲預先設定的厚度。因此，可以不 需改變光路徑長1而縮短分離寬度d，因而可對應CCD 8 的像素數的增加，再者，亦可不需採用雙折射板以外的通 過玻璃等其他媒體，而可降低生產成本。亦即，例如，將 CCD8的像素數從200萬像素增加至3 00萬像素的情況 下，必須改變數位相機中之光路徑長等之數位相機本身之 設計變更，但是根據此光學低通濾波器1，因爲僅僅需要 將這些+/-45度方向的雙折射板32a、33b的厚度調整爲預 先設定的厚度，因此可降低生產成本。 如上述般，根據此光學低通濾波器1，因爲分離入射 光爲對水平方向呈+/-45度方向之雙折射晶圓32、33，乃 對水晶錠2的光學軸A爲6 9度的角度來切割水晶錠而形 成，因此爲了爲了得到與以往的切割角度爲4 4 · 8度者相 同的分離寬度d (參照第7圖），一般乃使雙折射晶圓 3 2、3 3的厚度變厚，因而於硏磨雙折射晶圓3 2、3 3之 際，可以不需在意雙折射晶圓3 2、3 3產生破損等材料的 損失，而容易進行加工作業，並降低生產成本。 此外，於本發明的實施型態中’因爲雙折射晶圓 3 2、3 3乃對水晶錠2的光學軸A爲ό 9度的角度來切割水 晶錠而形成，因此可使由種水晶2 1所培育而成的水晶變 薄。例如，將形成本發明的實施型態所示之雙折射晶圓 3 2、3 3之水晶錠2的厚度，設定爲從種水晶2 1開始算起 爲t。接下來，如以往的情況相同般，在將雙折射晶圓 -13- 1269067 (11) 32、33以對水晶錠的光學軸爲44.8度的角度來切割上述 水晶錠而形成的情況下，如第8圖（b )所示般，將水晶 錠2’的厚崖，設定爲從種水晶21’開始算起爲t’。從第8 圖（b )可得知，於以往的情況之以44.8度來切割的情況 下，水晶錠2’的厚度必須從t變厚爲t’。因此，將本發明 的實施型態所示之從厚度t的水晶錠2來形成雙折射晶圓 3 2、3 3的情況，與從以往的水晶錠2 1 ’來形成雙折射晶圓 3 2、3 3的情況相較，可縮短水晶錠2的培育時間，並可 降低生產成本。此外，如第8圖所示般，水晶錠2、2 ’隨 著水晶的培育，其有效長度Y、Y’的長度變短。因此，由 本發明的實施型態之水晶錠2所形成之雙折射晶圓3 2、 3 3的片數較多，就生產成本面而言較爲理想。而以厚度t 的水晶錠2的光學軸A爲44.8度來切割厚度t的水晶錠2 來形成雙折射晶圓3 4的情況下，如第8圖（a )所示般， 不僅其面積變小，並且若是雙折射晶圓3 4的1個角切割 的較大的話，則無法從雙折射晶圓3 4形成較多數的雙折 射板，就生產效率而言較不理想。 此外，藉由將雙折射晶圓3 2、3 3的切割角度設定爲 對水晶錠的光學軸A爲69度，即使水晶錠2的成長幅度 不大，亦可增大雙折射晶圓3 2、3 3的面積，不僅如此， 即使雙折射晶圓3 2、3 3欠缺1個角，由於欠缺的部分對 雙折射晶圓3 2、3 3全體的比例亦較小，因此可以抑制於 分割9個光學低通濾波器1之際所形成之具有缺陷之光學 低通濾波器1 1的數量至2個爲止（參照第2圖（d ))， -14- 1269067 (12) 因而可並降低生產成本。 此外，雙折射晶圓3 2、3 3是以對水晶錠2的光學軸 A爲69度的來切割而形成，因此從第3〜5圖中亦可得 知，若是切割角度爲 6 9度的話，則相較於切割角度爲 4 4.8度之際，可將雙折射晶圓的厚度t變厚約1.501倍。 此外，即使爲6 9度以外者，只要超過44.8度，並在第5 圖所示般之產生急劇變化的臨界値之8 0度以下的話，則 可任意設定切電角度，並與本發明的實施型態相同，相較 於切割角度爲44.8度，可將雙折射晶圓的厚度t變厚， 並得到本發明的實施型態的效果。 本發明的實施型態之光學低通濾波器1乃以矩形形狀 形成，但是並不限定於此，可配合所要求的形狀來形成任 意形狀。 此外，於本發明的實施型態中，乃依據雙折射晶圓 3 1、雙折射晶圓3 2、雙折射晶圓3 3的順序來疊合，但是 並不限定於此，例如依據雙折射晶圓3 2、雙折射晶圓 3 3、雙折射晶圓3 1的順序，或是依據雙折射晶圓3 1、雙 折射晶圓3 3、雙折射晶圓3 2的順序來疊合均可。 此外’於本發明的實施型態中，乃採用3片的雙折射 晶圓，但是片數並不限定於此，例如，配合5片的用途來 改變其片數’並改變光的分離點數。此外，雙折射晶圓 3 2、3 3乃將光線分離爲+/ - 4 5度方向，但是並不限定於 此’例如，配合將光線分離爲+/- 3 0度方向的用途來改變 角度。如此’藉由採用從1片至多數片之片數來將光線分 -15- 1269067 (13) 離爲任意的方向上，可任意將光線的分離點從2點變更爲 多數點的任意點，而其分離模式可例如第9圖（a )〜 (d )所示之各種模式來形成。 此外’本發明的實施型態之雙折射晶圓3 2、3 3爲5 角形，但是其形狀亦可爲多角形等之任意形狀。 此外’爲了容易形成雙折射晶圓，亦可將所有的雙折 射晶圓以對水晶錠的光學軸A爲6 9度的角度來切割水晶 錠而形成。 此外’於本發明的實施型態中，由疊合而成的雙折射 晶圓3 1、雙折射晶圓3 2、雙折射晶圓3 3來形成9個光學 低通濾波器1，但亦可配合所要求的尺寸來任意設定光學 低通濾波器1的個數。 此外’本發明的實施型態之光學低通濾波器i的生產 製程亦可爲以下所說明之生產製程。而從此生產製程所生 產出的光學低通濾波器1，與上述生產製程所生產出的光 學低通濾波器1具有相同作用效果。 水晶錠2以對其光學軸A爲4 4 · 8度的角度來切割 (參照第1圓（a ))，並形成第2圖（a )所示之雙折射 晶圓3 1 °接下來，水晶錠2以對其光學軸a爲6 9度的角 度來切割（參照第丨圖（b ))，並形成第2圖（b )及第 2圖（c )所示之雙折射晶圓3 2、3 3。這些所形成的雙折 射晶圓3 1、3 2、3 3，藉由晶圓切割機各自在分割線上來 分割，並從雙折射晶圓3 1、3 2、3 3，各自形成9個雙折 射板（圖中省略）。之後，從各個雙折射晶圓3 1、3 2、 -16- 1269067 (14) 3 3所形成之每一片雙折射板，依序加以疊合’並形 個光學低通濾波器1。同樣的，由剩下的雙折射晶圓 3 2、3 3所形成之雙折射板’亦形成可正常動作之光 通濾波器1。 此外，於本發明的實施型態中，乃採用光學低通 器1於數位相機等攝像裝置上，但是其配置並不限定 6圖（a )所示者’例如，亦可如第6圖（b )所示者 於第6圖（b )所示之光學低通濾波器1當中 度方向雙折射板33a設置於鄰接CCD8的光線入射面 水平方向雙折射板3 1 a與+4 5度方向雙折射板3 2 a則 於C C D 8與透鏡 7的光路徑（長度1 )中之中間的 上。而於-45度方向雙折射板33a的入射面33a，及 方向雙折射板31a的入射面31b與+45度方向雙折 3 2 a的射出面3 2 c上，均形成抗反射塗裝（圖中省略） 如此，如第6圖（b )所示，以具有間隔的方式 成做爲光學低通濾波器1的構成之多數的雙折射板， 此，可縮短分離寬度d。 而於第6圖（b )所示之光學低通濾波器1當中 度方向雙折射板33a設置於鄰接CCD8的光線入射面 水平方向雙折射板3 la與+45度方向雙折射板32a則 於CCD8與透鏡7的光路徑中之中間的位置上，但是 限定於此，只要在光路徑上，可配合用途，於任何的 上設置任意片數之分離光線爲任意方向之雙折射板。 成1 3 1、 學低 濾波 於第 ，-45 ’而 設置 位置 水平 射板 〇 來構 藉由 ，45 ，而 設置 並不 位置 1269067 (15) 〔產業上之可利用性〕 如以上所說明般，根據本發明之光學低通濾波器，可 容易進行雙折射晶圓的硏磨加工，並且使欠缺的部分對雙 折射晶圓全體的比例爲零或是降低，一次生產可生產多數 個，因而降低生產成本。 亦即，根據本發明，因爲雙折射晶圓是藉由對水晶錠 的光學軸以大於44 · 8度的角度來切割上述水晶錠而形 成，因此，爲了得到與以往的切割角度爲44.8度者相同 的分離寬度，而使雙折射晶圓的厚度變厚，因而於硏磨雙 折射晶圓之際，可以不需在意雙折射晶圓產生破損等材料 的損失，而容易進行加工作業，並降低生產成本。此外， 由於雙折射晶圓是藉由對水晶錠的光學軸以大於44 · 8度 的角度來切割上述水晶錠而形成，即使水晶錠的成長幅度 不大，亦可增大雙折射晶圓的面積，其結果爲，即使雙折 射晶圓欠缺1個角，由於欠缺的部分對雙折射晶圓全體的 比例亦較小，因此可以抑制於分割多數個光學低通濾波器 之際所形成之具有缺陷之光學低通濾波器的數量，因而可 並降低生產成本。 此外，根據本發明，因爲雙折射晶圓是藉由對水晶錠 的光學軸以大於44.8度的角度來切割上述水晶錠而形 成，因此可使雙折射晶圓的厚度變厚，並容易調整厚度於 預先所設定的厚度。例如，以往將用於數位相機（攝像裝 置）之CCD的像素數從200萬像素增加至3 00萬像素的 情況下，必須進行光學低通濾波器的厚度之變更，並藉由 -18- 1269067 (16) 該變更來改變數位相機中之光路徑長等之數位相機本身之 設計變更，而根據本發明之光學低通濾波器，因爲可調整 雙折射晶圓的切割角度，並使其厚度與以往者相同，因此 只要設定雙折射晶圓的尺寸，則不需改變數位相機中之光 路徑長，而降低生產成本。 再者，如上述般之在將光學低通濾波器用於具有 C CD之數位相機等攝像裝置之情況下，爲了防止攝像裝 置本身的設計變更所造成之生產成本的增加，因此預先設 定光學低通濾波器的厚度。在此，若是將本發明的光學低 通濾波器用於攝像裝置的話，則因爲雙折射晶圓是藉由對 水晶錠的光學軸以大於4 4.8度的角度來切割上述水晶錠 而形成，因此不需改變光學低通濾波器的厚度而可降低其 分離寬度，因而可對應C C D的像素數的增加。 【圖式簡單說明】 第1圖（a )係顯示本發明的實施型態之，對光學軸 之用於形成雙折射晶圓的切割角度爲4 4 · 8度之水晶錠的 槪略圖，第1圖（b )係顯示，對光學軸之用於形成雙折 射的切割角度爲6 9度之水晶錠的槪略圖。 第2圖（a )係顯示本發明的實施型態之，分離入射 光爲水平方向之雙折射晶圓的平面圖，第2圖（b )係顯 示本發明的實施型態之，分離入射光爲對水平方向呈+4 5 度之雙折射晶圓的平面圖，第2圖（c )係顯示本發明的 實施型態之，分離入射光爲對水平方向呈-4 5度之雙折射 -19- 1269067 (17) 晶圓的平面圖，第2圖（d )係顯示本發明的實施型態 之，疊合3枚雙折射晶圓的平面圖。 第3圖係顯示，本發明的實施型態之切割角度及 d = 5 8 9.3 ( nm )之際的係數（參照第4圖）之間的關係之 表。 第4圖係顯示，本發明的實施型態之切割角度及 d = 5 8 9 · 3 ( nm )之際的係數之間的關係之圖式。 第5圖係顯示，本發明的實施型態之切割角度、及切 割角度爲44.8度之際之與雙折射晶圓3 2、3 3的厚度比之 間的關係之圖式。 第6圖（a )係顯示，設置了本發明的實施型態的光 學低通濾波器之攝像裝置之，光路徑中之構成元件的配置 圖，第6圖（b )係顯示，其他實施型態的光學低通濾波 器之攝像裝置之，光路徑中之構成元件的配置圖。 第7圖係顯示，通過本發明的實施型態的光學低通濾 波器之光線的分離模式之圖式。 第8圖（a ) 、 （ b )係顯示，爲了比較本發明的實施 型態的光學低通濾波器及以往的實施型態的光學低通濾波 器，而形成了各個光學低通濾波器之水晶錠的厚度及有效 長度之圖式。 第9圖係顯示，通過與第7圖所示之分離模式不同之 本發明的實施型態的光學低通濾波器之，其他分離模式之 圖式。 -20- 1269067 (18) 【符號說明】 I'll 光學低通濾波器 1 a、3 1 b 光線入射面 1 b、3 2 c 光線射出面 2、2 ’ 水晶銳 2 1、2 1 ’ 種水晶 3 1、3 2、3 3 雙折射晶圓1269067 (1) FIELD OF THE INVENTION The present invention relates to an optical low-pass filter using a birefringent wafer. [Prior Art] The optical low-pass filter is used to suppress the high-frequency component of the image frequency of the light in order to suppress the virtual signal generated by the image sensor when it is received by light, and its characteristics are separated by the separation mode of the light. Decide. For the optical low-pass filter of the prior art, for example, an optical low-pass filter disclosed in Japanese Laid-Open Patent Publication No. 20-56268. The optical low-pass filter is formed by laminating three birefringent wafers whose optical axes are different from each other. The stacked three birefringent wafers are divided and a plurality of optical low pass filters are formed. Specifically, each of the three birefringent wafers is formed by cutting the crystal ingot with an optical axis of 4 4 · 8 degrees. The three birefringent wafers are horizontally birefringent wafers in which the incident light is separated horizontally, and the incident light is separated by +45 degrees in the direction of the separation direction of the horizontal birefringent wafer by +45 degrees. The direction birefringent wafer and the separated incident light are composed of a 45-degree birefringent wafer in a direction of -45 degrees in the direction of separation of the horizontal birefringent wafer, and the horizontal birefringent plates are sequentially stacked, + 45 degree birefringent plate, -45 degree birefringent plate to form an optical low pass filter. The light incident on the optical low-pass filter is separated into general light and abnormal light through the horizontal birefringent plate, and is separated into general light and different -4- 1269067 (2) constant light, and the separated general light and abnormal light are separated. Each is separated into 4 points by a +/- 45 degree birefringent plate (omitted from the figure). By using this optical low-pass filter to separate the incident light into four points, the input light to the image pickup element such as the CCD is separated, and the virtual image which blurs the image and causes the moiré is lowered. At present, the cell pitch of the image pickup element (Cell Pitch) tends to be small. In other words, in the CCDs manufactured in recent years, the grid spacing is reduced to increase the number of pixels (for example, from 200,000 pixels to 300,000 pixels, etc.). . Therefore, with the shortening of the lattice spacing of C CD 8, it is necessary to shorten the separation width of the light in the optical low-pass filter. However, in order to shorten the separation width of the light in the optical low-pass filter, it is necessary to thin the thickness of each of the birefringent plates constituting the optical low-pass filter. Furthermore, it is necessary to change the thickness of the birefringent plate in the +/ - 45 degree direction to 1/2 of the horizontal birefringent wafer. Therefore, among the birefringent wafers of +/- 45 degrees, it is more desirable to have a thinner thickness, which makes the honing process difficult and causes an increase in cost. Further, in the combination of birefringent wafers, since the growth of the crystal ingot is not large, it is difficult to obtain a large +/- 45-degree direction birefringent crystal. Further, in general, the shape of the +/- 45-degree birefringent wafer is such that one large corner is missing from the rectangular shape along the side of the optical axis at 45 degrees. In this case, in the cutting process of dividing a plurality of rectangular optical low-pass filters from among the birefringent wafers, material loss occurs and efficiency is deteriorated. 1269067 (3) Therefore, in order to solve the above problems, an object of the present invention is to provide an optical low-pass filter which is easy to perform honing processing of a birefringent wafer, and an object of the present invention is to provide a defective portion. The ratio of the total number of birefringent wafers is zero or is reduced, and an optical low-pass filter that can produce a plurality of productions at a time, thereby reducing production costs. SUMMARY OF THE INVENTION In order to achieve the above object, an optical low-pass filter of the present invention is constituted by a birefringent wafer formed by cutting a crystal ingot with an angle of an optical axis of a crystal ingot, and separating incident light. The birefringent wafer is formed by cutting the crystal ingot at an angle of more than 44.8 degrees to the optical axis of the crystal ingot. According to the present invention, since the birefringent wafer is formed by cutting the crystal ingot at an angle of more than 44.8 degrees to the optical axis of the crystal ingot, in order to obtain the same separation width as the conventional cutting angle of 44.8 degrees, Further, since the thickness of the birefringent wafer is increased, it is possible to perform processing operations and reduce the production cost without damaging the loss of materials such as breakage of the birefringent wafer when the birefringent wafer is honed. In addition, since the birefringent wafer is formed by cutting the crystal ingot at an angle of more than 44.8 degrees to the optical axis of the crystal ingot, even if the growth rate of the crystal ingot is not large, the area of the birefringent wafer can be increased. As a result, even if the birefringent wafer lacks one corner, the proportion of the missing portion to the entire birefringent wafer is small, so that it is possible to suppress the defects formed when dividing a plurality of optical low-pass filters. The number of optical low-pass filters and filters can be reduced to -6 - 1269067 (4) to reduce production costs. Furthermore, according to the present invention, since the birefringent wafer is formed by cutting the crystal ingot at an angle of more than 44.8 degrees to the optical axis of the crystal ingot, the thickness of the birefringent wafer can be made thicker, and It is easy to adjust the thickness to the thickness set in advance. For example, when the number of pixels of a CCD used for a digital camera (camera) is increased from 2 million pixels to 3 million pixels, the thickness of the optical low-pass filter must be changed and changed by the change. In the digital camera, the design of the digital camera itself is long, and the optical low-pass filter according to the present invention can adjust the cutting angle of the birefringent wafer and make the thickness the same as in the past. The size of the birefringent wafer eliminates the need to change the optical path length in the digital camera and reduces production costs. In the case where the optical low-pass filter is used for an image pickup device such as a digital camera having a C CD as described above, in order to prevent an increase in production cost due to design change of the image pickup device itself, the optical low pass is preset. The thickness of the filter. Here, if the optical low-pass filter of the present invention is used for an image pickup apparatus, since the birefringent wafer is formed by cutting the crystal ingot at an angle of more than 4 4.8 degrees to the optical axis of the crystal ingot, It is necessary to change the thickness of the optical low-pass filter to reduce the separation width, and thus it is possible to correspond to an increase in the number of pixels of the CCD. Specifically, in the above configuration, the birefringent wafer may be formed not only by a plurality of laminations but also by a plurality of divisions, and at least one of the plurality of birefringent wafers may be The optical axis of the crystal ingot is formed by cutting the above crystal ingot at an angle greater than 44.8 degrees. Or, in the above configuration, the birefringent wafer may be formed not only by lamination, but also by dividing a plurality of birefringent crystals into a plurality of birefringent plates, and A plurality of birefringent plates of each birefringent wafer are superposed, and a plurality of the above birefringent wafers are cut by the angle of 4.8 degrees to the optical axis 4 of the crystal ingot. And formed. Further, in the above configuration, at least the plurality of stacked birefringent wafers may be formed by cutting the crystal ingot at an angle of 44. 8 degrees from the optical axis of the crystal ingot, and may be separated into horizontal layers. a first birefringent wafer in a direction or a vertical direction; and cutting the crystal ingot at an angle of more than 44.8 degrees to the water optical axis and separating the incident light into a second birefringent crystal of 45 degrees in a horizontal direction or a vertical direction circle. In this case, the thickness of the second birefringent wafer in which the incident light is separated in the direction of 45 degrees in the horizontal direction is increased, so that the thickness is generally smaller than that of the first birefringent wafer. The thickness of the circle is increased, and when the second birefringent wafer is honed, the loss of materials such as breakage of the birefringent wafer can be caused, and it is easy to carry out the business. In the above configuration, the plurality of superposed double circles are composed of one first birefringent wafer and two second birefringents. The first birefringent wafer is 1 The two wafers are formed in a rectangular shape parallel to the optical axis, and the second wafer has a shape in which the three corners adjacent to the five-corner shape are formed by a slightly straight majority. The larger than the upper part is formed by the larger than the illuminating lens, and the direction is either vertical. Therefore, the refracting crystal does not need to be birefringent angle on both sides of the working refractive refracting wafer to form 1269067 (6) $ ' and 3 The central corners of the corners are formed opposite to each other and to the side orthogonal to the optical axis. Further, in the above configuration, the angle of the optical axis of the crystal ingot is greater than 44. 8 degrees, preferably set to be less than 80 degrees to the optical axis, especially if it is set at 69 degrees. It is easy to form an optical low pass filter. [Embodiment] Hereinafter, embodiments of the present invention will be described with reference to the drawings. As shown in Fig. 1, the optical low-pass filter 1 of the embodiment of the present invention is constituted by birefringent wafers 3 1 , 3 2 , 3 3 formed by cutting the crystal ingot 2 . The birefringent wafer 31 is a so-called first birefringent wafer of the present invention, and is a wafer in which incident light is separated in a horizontal direction. The birefringent wafer 31 is formed by cutting the crystal ingot at an angle of more than 44.8 degrees to the optical axis of the crystal ingot. As shown in Fig. 2(a), the two sides are opposite each other. 4 is formed in a rectangular shape parallel to the optical axis A. The birefringent wafer 32 is a wafer in which incident light is separated in a direction of +45 degrees in the horizontal direction. The birefringent wafer 3 2 is formed by cutting the crystal ingot by 69 degrees to the optical axis of the crystal ingot, and as shown in FIG. 2(b), has a 5-corner shape, and the adjacent three corners 5 are It is formed at a right angle and is formed by a side 6 that is opposite to the central axis 5 of the three corners 5 and orthogonal to the optical axis A. The birefringent wafer 33 is a wafer in which incident light is separated in a direction of -45 degrees -9 to 1269067 (7) in the horizontal direction. The birefringent wafer 33 is formed by cutting the crystal ingot by 69 degrees to the optical axis of the crystal ingot, and has a 5-angle shape as shown in FIG. 2(c), wherein the adjacent three corners 5 are at right angles. It is formed and formed by the side 6 which is opposite to the central axis 5 of the three corners 5 and orthogonal to the optical axis A. The birefringent wafers 3 2, 3 3 are the so-called second birefringent wafers of the present invention, and the cutting angle for the optical axis A for forming the birefringent wafers 3 2, 3 3 is set to 6 9 The degree is calculated by the following mathematical formula 1. Further, the characteristics of the cutting angle calculated by the mathematical expression are shown in Figs. 3 to 5. Fig. 3 is a table showing the relationship between the cutting angle and the coefficient (see Fig. 4) at d = 5 8 9.3 (nm), and the illustration is shown in Fig. 4. Further, Fig. 5 is a view showing the relationship between the cutting angle and the thickness ratio of the birefringent wafers 32, 33 at the cutting angle of 44.8 degrees. <Mathematical Formula 1> d ~ (ne2~no2) sin Θ cos Θ f ne2sin2 Θ +no2cos2 Θ (d : separation width, ne = 1.5 5 3 4 : refractive index of abnormal light, η ο = 1 · 5 4 4 3: refractive index of general light, 0: cutting angle, t: thickness of birefringent wafer) From the mathematical formula 1, the separation width d of the birefringent wafers 3 1 , 3 2, and 3 3 is known (refer to Figure 7) is related to the cutting angle 0 and the thickness t of the birefringent wafer. In the embodiment of the present invention, since the cutting angle for the optical axis A of the birefringent wafers 3 2, 3 3 is set to be 6 9 degrees, it is set as compared with 44 · In the case of cutting at 8 degrees, the separation width d is short. Next, the production process of the optical low-pass filter 1 will be described in detail using FIG. The crystal ingot 2 is cut at an angle of 44.8 degrees with respect to its optical axis A (see Fig. 1(a)), and the birefringent wafer 31 shown in Fig. 2(a) is formed. Next, the crystal ingot 2 is cut at an angle of 69 degrees with respect to its optical axis A (refer to FIG. 1(b)), and birefringences shown in FIGS. 2(b) and 2(c) are formed. Wafers 3 2, 3 3 . The thus formed birefringent wafers 3 1 , 3 2, and 3 3 are laminated in the order of the birefringent wafer 31, the birefringent wafer 3, and the birefringent wafer 33. The stacked birefringent wafers 3 1 , 3 2 , and 3 3 are formed by dividing the line by a wafer cutting machine of a cutting machine in a matrix form (see FIG. 2( d )). It is divided up and forms seven optical low-pass filters 1 that can operate normally. The light incident on the formed optical low-pass filter 1 is separated into general light and abnormal light by a horizontal birefringent plate (not shown) formed by the birefringent wafer 31, and is generally separated. The light and the extraordinary light are each separated into four points by a birefringent plate (not shown) formed in the +/- 45-degree direction formed by the birefringent wafers 32, 33. The optical low-pass filter 1 produced by the above production process is used in an image pickup apparatus such as a digital camera shown in Fig. 6(a). As shown in Fig. 6(a), the image pickup apparatus is provided with a lens 7 for collecting light received at the time of photographing, and a plurality of photographing elements 11 to 1269067 (9). In the middle omitted, the light received by the lens 7 is received, and the light information is converted into the CCD 8 of the digital data. Then, the optical low pass filter 1 is disposed in the optical path (length 1) between these lenses 7 and CCD 8. On the incident surface 1 a and the exit surface 1 b of the light of the optical low-pass filter 1, an anti-reflective coating for preventing light diffusion (not shown) is formed. In the image pickup apparatus, light is incident on the lens 7 from the outside, and is collected by the lens 7. The light collected by the light is separated by the optical low-pass filter 1 and incident on the respective light receiving elements of the CCD 8. At present, the cell pitch of the CCD 8 has a tendency to become smaller. In other words, for example, in the CCD 8 manufactured in recent years, the grid size is reduced to increase the number of pixels (for example, from 200,000 pixels to 3,000,000 pixels) in the same design as the conventional one. Wait). Therefore, as the lattice spacing of the CCD 8 is shortened, it is necessary to shorten the separation width d of the light in the optical low-pass filter. It is also known from the above mathematical expression 1 that the birefringence of the embodiment of the present invention can be employed. Wafers 3 2, 3 3 to shorten the separation width d. Further, in the conventional optical low-pass filter 1, in order to increase the number of pixels of C C D 8, a birefringent plate having a reduced separation width d is used. Therefore, the thickness of the optical low-pass filter is reduced, and as a result, the optical path length 1 shown in Fig. 6(a) is variable. Therefore, in the conventional optical low-pass filter 1, the thickness of the optical low-pass filter is adjusted by superposing on a birefringent plate by glass or the like. However, according to the optical low-pass filter 1 of the embodiment of the present invention, since the thickness of the birefringent plate 32a, -12-1269067 (10) 3 3b in the +/- 45-degree direction is thick, these +/- The thickness of the birefringent plates 3 2 a, 3 3 b in the 45-degree direction is adjusted to a predetermined thickness. Therefore, the separation width d can be shortened without changing the optical path length of one, so that the number of pixels of the CCD 8 can be increased, and further, other media such as glass can be used without using a birefringent plate, and the production cost can be reduced. . That is, for example, when the number of pixels of the CCD 8 is increased from 2 million pixels to 300 million pixels, it is necessary to change the design change of the digital camera itself such as the optical path length in the digital camera, but according to the optical low pass filter 1. Since it is only necessary to adjust the thicknesses of these +/- 45-degree directions of the birefringent plates 32a, 33b to a predetermined thickness, the production cost can be reduced. As described above, according to the optical low-pass filter 1, since the incident light is separated into birefringent wafers 32, 33 having a direction of +/- 45 degrees in the horizontal direction, the optical axis A of the crystal ingot 2 is 6 9 degrees. Since the angle is formed by cutting the crystal ingot, in order to obtain the same separation width d as that of the conventional cutting angle of 4 4 · 8 degrees (refer to Fig. 7), the birefringent wafers 3 2, 3 3 are generally used. The thickness becomes thicker, so that when the birefringent wafers 3 2, 3 3 are honed, the loss of materials such as breakage of the birefringent wafers 3 2, 3 3 can be avoided, and the processing operation can be easily performed and the production cost can be reduced. . Further, in the embodiment of the present invention, since the birefringent wafers 3 2, 3 3 are formed by cutting the crystal ingot at an angle of ό 9 degrees to the optical axis A of the crystal ingot 2, it is possible to use the crystal 2 The crystal grown in 1 is thin. For example, the thickness of the crystal ingot 2 forming the birefringent wafers 3 2, 3 3 shown in the embodiment of the present invention is set to be t from the seed crystal 2 1 . Next, as in the case of the prior art, when the birefringent wafers-13-1269067 (11) 32, 33 are formed by cutting the crystal ingot at an angle of 44.8 degrees to the optical axis of the crystal ingot, As shown in Fig. 8(b), the thick cliff of the crystal ingot 2' is set to be t' from the seed crystal 21'. As can be seen from Fig. 8(b), in the case where the conventional case is cut at 44.8 degrees, the thickness of the crystal ingot 2' must be increased from t to t'. Therefore, when the birefringent wafers 3 2 and 3 3 are formed from the crystal ingot 2 having the thickness t as shown in the embodiment of the present invention, the birefringent wafer 3 2 is formed from the conventional crystal ingot 2 1 '. Compared with the case of 3 3, the cultivation time of the crystal ingot 2 can be shortened, and the production cost can be reduced. Further, as shown in Fig. 8, the crystal ingots 2, 2' have a shorter length of the effective lengths Y and Y' as the crystal is cultivated. Therefore, the number of the birefringent wafers 3 2, 3 3 formed by the crystal ingot 2 of the embodiment of the present invention is large, and it is preferable in terms of production cost. On the other hand, when the crystal ingot 2 of the thickness t is cut by the optical axis A of the crystal ingot 2 having a thickness t of 44.8 degrees to form the birefringent wafer 34, as shown in Fig. 8(a), not only the area thereof is changed. If the angle of one corner of the birefringent wafer 34 is large, a large number of birefringent plates cannot be formed from the birefringent wafer 34, which is less preferable in terms of production efficiency. Further, by setting the cutting angle of the birefringent wafers 3 2, 3 3 to 69 degrees to the optical axis A of the crystal ingot, the birefringent wafer 3 2 can be increased even if the growth rate of the crystal ingot 2 is not large. The area of 3 3 is not limited to this. Even if the birefringent wafers 3 2 and 3 3 lack one corner, the proportion of the missing portions to the total of the birefringent wafers 3 2 and 3 3 is small, so that the division can be suppressed. The number of optical low-pass filters 11 having defects formed by the nine optical low-pass filters 1 is up to two (refer to FIG. 2(d)), and -14-1269067 (12) can be reduced Cost of production. Further, since the birefringent wafers 3 2, 3 3 are formed by cutting the optical axis A of the crystal ingot 2 by 69 degrees, it is also known from the third to fifth figures that the cutting angle is 6 9 degrees. In this case, the thickness t of the birefringent wafer can be increased by about 1.501 times as compared with the cutting angle of 4 4.8 degrees. In addition, even if it is more than 6 degrees, as long as it exceeds 44.8 degrees, and it is 80 degrees or less of the critical 値 which changes rapidly as shown in FIG. 5, the cutting angle can be set arbitrarily, and it is set with the this invention. The embodiment is the same, and the thickness t of the birefringent wafer can be made thicker than the cutting angle of 44.8 degrees, and the effect of the embodiment of the present invention can be obtained. The optical low-pass filter 1 of the embodiment of the present invention is formed in a rectangular shape, but is not limited thereto, and can be formed into any shape in accordance with a desired shape. In addition, in the embodiment of the present invention, the birefringent wafer 31, the birefringent wafer 3, and the birefringent wafer 3 are stacked in the order of the birefringent wafer 31, but are not limited thereto, for example, according to birefringence. The order of the wafer 3, the birefringent wafer 3 3, the birefringent wafer 31, or the order of the birefringent wafer 31, the birefringent wafer 33, and the birefringent wafer 32 is superimposed. can. Further, in the embodiment of the present invention, three sheets of birefringent wafers are used, but the number of sheets is not limited thereto. For example, the number of sheets is changed by the use of five sheets and the number of separation points of light is changed. . In addition, the birefringent wafers 3 2, 3 3 separate the light into a +/ - 45 degree direction, but are not limited thereto. For example, the angle is changed to match the separation of the light into a +/- 30 degree direction. . Thus, by separating the light from -15 to 1269067 (13) in any direction from the number of slices to the majority, the separation point of the light can be arbitrarily changed from 2 to any point of the majority. The separation mode can be formed, for example, in various modes shown in Figs. 9(a) to (d). Further, the birefringent wafers 3 2, 3 3 of the embodiment of the present invention have a rectangular shape, but the shape thereof may be any shape such as a polygonal shape. Further, in order to easily form a birefringent wafer, all of the birefringent wafers may be formed by cutting a crystal ingot at an angle of 69 degrees to the optical axis A of the crystal ingot. In addition, in the embodiment of the present invention, nine optical low-pass filters 1 are formed by laminating birefringent wafers 31, birefringent wafers 3, and birefringent wafers 3, but The number of optical low-pass filters 1 can be arbitrarily set in accordance with the required size. Further, the production process of the optical low-pass filter i of the embodiment of the present invention may be the production process described below. The optical low-pass filter 1 produced by the production process has the same effects as the optical low-pass filter 1 produced by the above production process. The crystal ingot 2 is cut at an angle of 4 4 · 8 degrees with respect to its optical axis A (refer to the first circle (a )), and the birefringent wafer 3 shown in Fig. 2 (a) is formed. The crystal ingot 2 is cut at an angle of 69 degrees with respect to its optical axis a (refer to Fig. (b)), and the birefringent wafer 3 shown in Figs. 2(b) and 2(c) is formed. 2, 3 3. The formed birefringent wafers 3 1 , 3 2 , and 3 3 are respectively divided by the wafer dicing machine on the dividing line, and 9 doubles are formed from the birefringent wafers 3 1 , 3 2 , and 3 3 , respectively. Refraction plate (omitted in the figure). Thereafter, each of the birefringent plates formed from the respective birefringent wafers 3 1 , 3 2 , -16 - 1269067 (14) 3 3 is sequentially laminated and an optical low-pass filter 1 is formed. Similarly, the birefringent plate ' formed by the remaining birefringent wafers 3 2, 3 3 also forms a normally operable light-passing filter 1. Further, in the embodiment of the present invention, the optical low-pass device 1 is used in an image pickup device such as a digital camera, but the configuration thereof is not limited to the one shown in FIG. (a). For example, it may be as shown in FIG. b) The optical low-pass filter 1 shown in Fig. 6(b) is provided with a birefringent plate 33a in the direction of the light incident surface of the adjacent CCD 8 in the horizontal direction of the birefringent plate 3 1 a and +4 5 degrees. The birefringent plate 3 2 a is in the middle of the light path (length 1) of the CCD 8 and the lens 7. On the other hand, the incident surface 33a of the birefringent plate 33a in the -45-degree direction, and the incident surface 31b of the direction birefringent plate 31a and the exit surface 3 2 c of the double-folded 3 2 a in the +45-degree direction are formed into an anti-reflective coating ( In the figure, as shown in Fig. 6(b), a plurality of birefringent plates having a configuration of the optical low-pass filter 1 are formed at intervals, whereby the separation width d can be shortened. In the optical low-pass filter 1 shown in FIG. 6(b), the intermediate-direction birefringent plate 33a is disposed on the light incident surface of the CCD 8 adjacent to the horizontal direction of the birefringent plate 3 la and the +45-degree direction birefringent plate 32a. The position between the CCD 8 and the light path of the lens 7 is limited to this, and any number of separated light rays may be provided in any direction as long as it is used in the light path. Into 1 3 1 , learn to filter at the first, -45 ' and set the position horizontal plate 〇 to construct, 45, and the position is not set 1269067 (15) [industrial availability] as explained above According to the optical low-pass filter of the present invention, the honing processing of the birefringent wafer can be easily performed, and the ratio of the missing portion to the entire birefringent wafer is zero or reduced, and a plurality of productions can be produced in a single production. reduce manufacturing cost. That is, according to the present invention, since the birefringent wafer is formed by cutting the crystal ingot at an angle of more than 44. 8 degrees to the optical axis of the crystal ingot, in order to obtain a cutting angle of 44.8 degrees from the conventional one. The same separation width makes the thickness of the birefringent wafer thicker. Therefore, when the birefringent wafer is honed, it is possible to easily perform processing operations and reduce the loss of materials such as breakage of the birefringent wafer. Cost of production. In addition, since the birefringent wafer is formed by cutting the crystal ingot at an angle of more than 44. 8 degrees to the optical axis of the crystal ingot, even if the growth of the crystal ingot is not large, the birefringent wafer can be increased. As a result, even if the birefringent wafer lacks one corner, since the proportion of the missing portion to the entire birefringent wafer is small, it can be suppressed from being formed when a plurality of optical low-pass filters are divided. The number of defective optical low-pass filters can thus reduce production costs. Further, according to the present invention, since the birefringent wafer is formed by cutting the crystal ingot at an angle of more than 44.8 degrees to the optical axis of the crystal ingot, the thickness of the birefringent wafer can be made thick, and the thickness can be easily adjusted. The thickness is set in advance. For example, when the number of pixels of a CCD used for a digital camera (imaging device) is increased from 2 million pixels to 300 million pixels, the thickness of the optical low-pass filter must be changed, and by -18-1269067 (16) The change is to change the design change of the digital camera itself such as the optical path length in the digital camera, and the optical low-pass filter according to the present invention can adjust the cutting angle of the birefringent wafer and make the thickness thereof The former is the same, so as long as the size of the birefringent wafer is set, the optical path length in the digital camera does not need to be changed, and the production cost is reduced. Further, in the case where an optical low-pass filter is used for an image pickup device such as a digital camera having a C CD as described above, in order to prevent an increase in production cost due to design change of the image pickup device itself, an optical low pass is set in advance. The thickness of the filter. Here, if the optical low-pass filter of the present invention is used for an image pickup apparatus, since the birefringent wafer is formed by cutting the crystal ingot at an angle of more than 4 4.8 degrees to the optical axis of the crystal ingot, It is necessary to change the thickness of the optical low-pass filter to reduce the separation width, and thus it is possible to correspond to an increase in the number of pixels of the CCD. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1(a) is a schematic view showing a crystal ingot for forming a birefringent wafer having a cutting angle of 4 4 · 8 degrees, in an embodiment of the present invention, 1 (b) shows a schematic diagram of a crystal ingot for a cutting angle of 6 9 degrees for forming an optical axis. Fig. 2(a) is a plan view showing a birefringent wafer in which incident light is separated in a horizontal direction, and Fig. 2(b) shows an embodiment of the present invention, in which incident light is separated. A plan view of a birefringent wafer having a height of +45 degrees in the horizontal direction, and Fig. 2(c) shows an embodiment of the present invention, and the incident light is separated into a birefringence of -45 degrees in the horizontal direction - 19 - 1269067 (17) Plan view of wafer, and Fig. 2(d) shows a plan view of three birefringent wafers stacked in an embodiment of the present invention. Fig. 3 is a table showing the relationship between the cutting angle of the embodiment of the present invention and the coefficient (refer to Fig. 4) at the time of d = 5 8 9.3 (nm). Fig. 4 is a view showing the relationship between the cutting angle of the embodiment of the present invention and the coefficient at the time of d = 5 8 9 · 3 (nm). Fig. 5 is a view showing the relationship between the cutting angle of the embodiment of the present invention and the thickness ratio of the birefringent wafers 3 2, 3 3 when the cutting angle is 44.8 degrees. Fig. 6(a) is a view showing the arrangement of constituent elements in the optical path of the image pickup apparatus of the optical low-pass filter of the embodiment of the present invention, and Fig. 6(b) shows another embodiment. A configuration diagram of constituent elements in the optical path of the optical low-pass filter of the state. Fig. 7 is a view showing a mode of separation of light rays passing through an optical low-pass filter of an embodiment of the present invention. Fig. 8(a) and (b) show the optical low-pass filter formed in order to compare the optical low-pass filter of the embodiment of the present invention with the optical low-pass filter of the conventional embodiment. A pattern of the thickness and effective length of the crystal ingot. Fig. 9 is a view showing the other separation modes of the optical low-pass filter of the embodiment of the present invention which is different from the separation mode shown in Fig. 7. -20- 1269067 (18) [Description of symbols] I'll optical low-pass filter 1 a, 3 1 b light incident surface 1 b, 3 2 c light exit surface 2, 2 ' crystal sharp 2 1 , 2 1 ' Crystal 3 1, 3 2, 3 3 birefringent wafer
31a、32a、33a、33b 雙折射板 4 兩邊 5 角 6 邊 7 透鏡31a, 32a, 33a, 33b birefringent plate 4 on both sides 5 angles 6 sides 7 lenses
8 CCD A 光學軸 L 長度8 CCD A optical axis L length
t、t’ 厚度 Y、Y， 有效長度 -21 -t, t' thickness Y, Y, effective length -21 -