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<P class=MsoNormal style="LINE-HEIGHT: 17.25pt; TEXT-ALIGN: center" align=center><B><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">1. </SPAN></B><B><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">前言</SPAN></B><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana"> </SPAN></P>- f8 w0 v, m& ~) i
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<P class=MsoNormal style="LINE-HEIGHT: 17.25pt; TEXT-ALIGN: left" align=left><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体"> 自从</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">1982</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">年直径</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">12cm</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">的数字音频光盘</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">CD</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">问世以来,数字视频光盘</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">DVD</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">(</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">digital video disk</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">)一直是新一代光盘的一个梦想,虽然在几年前出现了</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">VCD</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">,但是对于光盘来讲,技术上没有改变,只是对数据进行了压缩,画质也只是</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">VHS</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">水准,不过是过渡性产品,在国外没有形成市场。</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana"><BR></SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体"> 数字图象信号具有在被编辑时画质不劣化,容易被计算机处理等优点,所以能记录</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">2</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">小时以上高画质的数字图象的光盘,已经让人盼望已久。最近几年,短波长的半导体激光器技术,薄型化光盘基板技术,对物透镜的高数值孔径</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">NA</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">化技术等的进步,使光盘的记录密度高密度化成为可能,同时数字连续可变画面压缩技术也有很大的进步,使长时间高画质的连续可变画面收录在一张光盘里成为可能。</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana"><BR></SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体"> 在以上这些技术基础被奠定之后,世界上的十家大企业共同制定了新世代数字视频光盘</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">DVD</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">(</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">digital video disk</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">)的标准,既在和原有</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">CD</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">同样尺寸下,记录容量为原来光盘</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">7.5</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">倍</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">4.7G</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">,并采用高画质的</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">MPEG2</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">数字信号压缩方式,使之能够存储</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">135</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">分的电影。</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana"><BR></SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体"> </SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">DVD</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">播放机主要是由光学头和</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">MPEG2</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">解码器两个关键技术组成的,其中</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">MPEG2</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">解码器由于是通用标准,目前开发出芯片的厂商不下十几家,而光学头的技术还主要掌握在日本厂商手中。</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana"><BR></SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体"> 光盘技术就是一束被聚焦到回折界限的最小激光束照射到盘面,由于记录着信息的盘面的凹凸对光的反射不同,就可以读出盘上的信息。</SPAN></P>) l. u' ?6 S1 l+ x) Y- o: i
3 j( ?5 r3 ~* \/ O: T<P class=MsoNormal style="LINE-HEIGHT: 17.25pt; TEXT-ALIGN: center" align=center><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana"><IMG height=227 src="http://www.33tt.com/upload/images/06/06071901.gif" width=379></SPAN></P>
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<P class=MsoNormal style="LINE-HEIGHT: 17.25pt; TEXT-ALIGN: left" align=left><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana"><BR></SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体"> 对于光学头来讲,它特有的技术有如下几个:</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana"><BR></SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体"> </SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">a. </SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">通过利用被聚焦到回折界限的最小激光束,穿过</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">0.6mm</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">的透明塑料层,从凹凸信息面取出信号。</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana"><BR></SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体"> </SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">b. </SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">使用半导体激光二极管,使用数值孔径</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">NA</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">为</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">0.6</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">的对物透镜,把激光束聚焦为由波长决定的回折界限为止的最小光束。</SPAN></P>3 d$ z5 ^; O* z6 y
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<P class=MsoNormal style="LINE-HEIGHT: 17.25pt; TEXT-ALIGN: center" align=center><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana"><IMG height=209 src="http://www.33tt.com/upload/images/06/06071902.gif" width=520></SPAN></P>. X* C0 i$ m+ s/ H+ C
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<P class=MsoNormal style="LINE-HEIGHT: 17.25pt; TEXT-ALIGN: center" align=center><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana"><BR></SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体"> </SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">c.</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">光盘外形的误差和不同光盘交换时带来的对物透镜的焦点位置在光盘信息记录面的位置变化,还有光盘回转时光盘面上下振动也会引起焦点位置变化,为了对焦点位置变化进行自动补正,必须把能够以精度为正负</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">1μm</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">对焦点位置控制的误差检出机能和控制用的伺服机构内藏在光学头里。</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana"><BR></SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体"> </SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">d.</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">光盘的形状中心和光盘的回转中心之间的偏心补正,还有对于在轨道间距为</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">0.74μm</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">的轨道上,精度正负</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">0.1μm</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">控制激光束对轨道的追迹控制用误差检出机能和控制用的伺服机构内藏在光学头里。</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana"><BR></SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体"> 在这里对于光盘装置系统,能满足以上要求的光学头的基本光学系,对物透镜</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">OL(object lens)</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">,作为光源的半导体激光二极管</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">LD(laser diode),</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">准直透镜</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">CL,</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">和其他一些光学头用的光学部品的原理及设计进行说明。</SPAN></P>
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<P class=MsoNormal style="LINE-HEIGHT: 17.25pt; TEXT-ALIGN: center" align=center><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">2. </SPAN><B><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">光学头基本原理</SPAN></B></P>
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<P class=MsoNormal style="LINE-HEIGHT: 17.25pt; TEXT-ALIGN: left" align=left><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体"> </SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">2.1.</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">光学头的基本光学系和光学部品的收差</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana"><BR></SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体"> 光学头是</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">DVD</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">系统的最大关键部件之一,它的基本原理图如下</SPAN></P>
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9 h* a/ N6 ]! \, `& U* [<P class=MsoNormal style="LINE-HEIGHT: 17.25pt; TEXT-ALIGN: left" align=left><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体"> 光学头是由</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">1.</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">对物透镜,</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">2.</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">准直透镜,</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">3. </SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">偏光分光棱镜,</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">4.</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">分光棱镜,</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">5.</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">反射镜,</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">6.1/4</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">波长板,</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">7.</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">焦点误差检出光学系,</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">8.</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">寻轨误差检出光学系等光学部品和光学系,</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">9.</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">焦点控制伺服机构(</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">F-ACT</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">)</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">,10.</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">寻轨控制伺服机构</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">(T-ACT)</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">等伺服机械控制部品,还有</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">11.</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">半导体激光二极管,</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">12.</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">多分割光电二极管</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">PD(photo diode)</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">等光电部件构成的。</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana"><BR></SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体"> 光学头能够读出光盘上的信号的原理是从激光二极管射出的发散</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">P</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">线性偏振激光通过准直透镜,成为平行光,再通过</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">1/4</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">波长片时,偏振方向旋转</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">45</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">度,变为圆偏光,这束平行的圆偏光被对物透镜聚焦到光盘的信息面,再反射回来(根据盘面的凸凹对光的反射不同),通过</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">1/4</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">波长片时,再一次偏振方向被旋转</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">45</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">度,成为</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">S</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">线性偏振光,在偏光分光棱镜</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">PBS</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">处被反射到误差检出系和信号系,反射光再一次被分为两路,误差系的一路通过凸透镜、圆柱透镜,投影到四分割的光电二极管上,根据各象限光量的大小,进行运算,对聚焦和寻轨伺服机构控制,使之读出正确的信号,另一路信号系的光束由凸透镜会聚到光电二极管,把光信号变为电信号。</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana"><BR></SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体"> 要想把激光聚焦成由波长决定的最小光束,必须把从</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">LD</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">发出的球面波的波面尽量无缺陷的传到光盘的情报记录面。也就是说,从</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">LD</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">发光开始到光盘为止,光学头成像系各部品全体的</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">RMS</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">波面收差必须限制在</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">0.07λ</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">以下,不然不能把激光光束聚焦为由干涉极限决定的最小光束。构成光头的各光学部品,光盘盘面,其中也包括对物透镜设置时的调整误差,以上这些合计的成像光学系全体的波面收差,必须限制在由</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">Warechal Criteron(δω)MC</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">给出的允许最大波面收差</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">0.07λ</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">以下。光盘已经由光盘标准规定,</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">(δω</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">)</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">DISK=0.05λ</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">,一般对物透镜的象差</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">(δω</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">)</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">ADJT=0.025λ</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">,要使全体</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">(δω)MC</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">小于</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">0.07λ</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">,对于其他的光学部品的收差必须严格控制。从</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">LD</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">开始到光盘为止,光头各光学部品的最大允许波面收差各用</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">(δω</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">)</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">LD</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">,</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">(δω</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">)</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">CL</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">,</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">(δω</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">)</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">PBS</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">,</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">(δω</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">)</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">QWP</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">,</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">(δω</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">)</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">MR,(δω</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">)</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">OL</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">表示,</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">Warechal Criteron</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">给出我们如下公式;</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana"><BR><BR></SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体"> </SPAN><B><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">(δω)MC≤λ/14</SPAN></B><B><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana"><BR></SPAN></B><B><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体"> </SPAN></B><B><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">(δω) 2MC=(δω</SPAN></B><B><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">)</SPAN></B><B><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">2LD (δω</SPAN></B><B><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">)</SPAN></B><B><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">2CL (δω</SPAN></B><B><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">)</SPAN></B><B><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">2PBS (δω</SPAN></B><B><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">)</SPAN></B><B><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">2QWP</SPAN></B><B><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana"><BR></SPAN></B><B><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体"> </SPAN></B><B><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana"> (δω</SPAN></B><B><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">)</SPAN></B><B><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">2MR (δω</SPAN></B><B><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">)</SPAN></B><B><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">2OL (δω</SPAN></B><B><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">)</SPAN></B><B><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">2DISK</SPAN></B><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana"><BR><BR></SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体"> 下面具体</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">DVD</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">的数值带入来试算一下。半导体激光二极管激光射出侧有平面玻璃窗,此外由于半导体激光器自身的特点,不可克服的有非点间隔,比理想波面要差,普通</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">(δω</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">)</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">LD</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">约为</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">0.013λ</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">。棱镜,反射镜等平面光学部品比较容易的以波面收差</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">0.01</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">~</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">0.015λ</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">制造出来。但是准直透镜和对物透镜等非平面光学部品,波面收差要想抑制在</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">0.03λ</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">之内,比较困难,分别定为准直透镜</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">0.025λ</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">和对物透镜</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">0.035λ</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">,这样根据式(</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">2</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">)得出全体</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">(δω)MC</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">的波面收差为</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">0.0694λ</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">,满足要求。即使对物透镜的波面收差被抑制在</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">0.035</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">以下,如果准直透镜的波面收差大于</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">0.025</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">,那样被聚焦光束的直径就会变大,从信息面读出数据错误频度就会变高。由于以上的理由,准直透镜的波面收差必须小于</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">0.025</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">,但球面单透镜要想达到这个值非常困难,一般采用球面玻璃组合透镜。</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana"><BR></SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体"> 从</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">DVD</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">光头的对物透镜射出的激光光束,需要一直跟踪光盘信息面上的轨道间距为</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">0.74μm</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">,最短凹坑长为</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">0.4μm</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">的轨迹,并正确读出凹坑信息。光强为光束中心强度</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">1/e2</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">的位置的光束直径被称为光束径</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">ω</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">,激光波长</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">λ=650nm</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">,对物透镜的数值孔径</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">NA=0.6,<BR></SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体"> </SPAN><B><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">ω=k×</SPAN></B><B><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">(</SPAN></B><B><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">λ/NA</SPAN></B><B><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">)</SPAN></B><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana"><BR></SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体"> 当对物透镜的入射光束的光强能量分布为均等分布时,系数</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">k</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">是</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">0.96</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">,光强能量分布为高斯分布时为</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">1.34</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">。从上式可以看出,光束径正比例于</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">λ/NA</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">,既要想提高光盘记录密度,缩小光束径,就需要使激光短波长化,并且提高对物透镜的</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">NA</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">。</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana"><BR></SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体"> 还有对物透镜的焦点深度</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 黑体">△</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">z</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">正比例于</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">λ/NA</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">的平方,</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">DVD</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">焦点深度与</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">CD</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">相比变窄</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">56%</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">,焦点误差的允许值变小。</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana"><BR></SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体"> </SPAN><B><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 黑体">△</SPAN></B><B><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana"> z</SPAN></B><B><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">~</SPAN></B><B><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">λ/NA2</SPAN></B><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana"><BR></SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体"> 光盘的倾斜引起的象差也会增加。对于焦点误差的允许值的减少,就需要提高焦点控制精度,</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">DVD</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">为了减少光盘的倾斜引起的收差,光盘的厚度减为</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">CD</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">的一半</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">0.6mm</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">。</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana"><BR></SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体"> </SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">2.2.</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">成像光学系</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana"><BR></SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体"> </SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">2.2.1.</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">激光二极管</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana"><BR></SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体"> 一般</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">LD</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">发出的光为与</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">PN</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">结合面平行的线性偏振光,但短波长的</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">LD</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">中大多发出与</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">PN</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">结合面垂直的线性偏振光,</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">DVD</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">要求</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">LD</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">在光盘面上的能量为</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">0.3mW</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">左右,这就需要</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">LD</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">发出的激光能量是</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">3</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">~</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">5mW</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">。</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana"><BR></SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体"> </SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">2.2.2.LD</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">的射出角特性和准直透镜</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana"><BR></SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体"> </SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">LD</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">射出的激光是发散光,从发光点离开一段观测到的光束断面强度分布,被称为远视野象</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">FFP(far field pattern)</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">,</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">FFP</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">垂直结合面方向宽,平行结合面方向窄,象下面图示的一样,是纵长的椭圆形。</SPAN></P>
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4 m% D) c O& T2 F3 b: K<P class=MsoNormal style="LINE-HEIGHT: 17.25pt; TEXT-ALIGN: left" align=left><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana"><BR></SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体"> </SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana"> LD</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">垂直结合面的放射角和平行结合面的放射角分别是</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">θ</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 黑体">⊥</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">,</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">θ</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 黑体">∥</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">。根据</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">LD</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">的放射角和对物透镜对光束强度的分布要求,确定准直透镜的焦点距离。</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana"><BR></SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体"> </SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">2.2.3.LD</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">的噪音特性和高频叠加</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana"><BR></SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体"> </SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">LD</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">有单模发光和多模发光两种激光发振方式。单模发光的最大问题是从光盘反射回来的光进入激光共振器,形成干涉,成为噪音,影响</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">SN,</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">为了消除噪音,需要对驱动电流进行高频叠加。而多模的</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">LD</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">抗干扰能力强,不需要高频叠加。</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana"><BR></SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体"> </SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">2.2.4.</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">偏光分光棱镜和</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">1/4</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">波长板的作用</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana"><BR></SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体"> 激光二极管射出的发散</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">P</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">线性偏振激光通过准直透镜,成为平行光,无反射折射的通过</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">PBS,.</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">再通过</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">1/4</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">波长片时,偏振方向旋转</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">45</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">度,变为圆偏光,这束平行的圆偏光被对物透镜聚焦到光盘的信息面,携带信息再反射回来,通过</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">1/4</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">波长片时,再一次偏振方向被旋转</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">45</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">度,成为</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">S</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">线性偏振光,在偏光分光棱镜</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">PBS</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">处被反射到误差检出系和信号系,使入射光和带有信号的反射光分离。</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana"><BR></SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体"> </SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">2.2.5.</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">对物透镜</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana"><BR></SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体"> </SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">DVD</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">光头要求对物透镜一定要象差小,特性优良,能够把光束聚焦到回折界限,也就是能够补正各种收差,使点象的大小完全由回折界限来决定。一般使用非球面光学树脂透镜。</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana"><BR></SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体"> </SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">2.3</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">误差检出系</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana"><BR></SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体"> 非点收差法</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana"><BR></SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体"> 焦点误差检出方式一般采用非点收差法,非点收差法就是根据光盘反射面位置的变化,反射光的聚焦位置移动,通过圆柱面透镜对投影光形状进行变化,用</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">4</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">分割</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">PD</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">差动检出。</SPAN></P>- a# F) s& @1 y4 O6 D
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# u/ J- `3 y- m5 u* @<P class=MsoNormal><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana"><BR></SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体"> 聚焦误差检出信号</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">=</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">(</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">A C</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">)</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">-(B D)/(A B C D)<BR></SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体"> 寻轨误差检出信号</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">=</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">(</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">A B</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">)</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">-(C D)/(A B C D)<BR></SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体"> </SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">PD</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">把光信号转变成电信号,前置放大,模拟运算,再经过相位补偿,把信号输入驱动放大器,驱动透镜驱动线圈,完成聚焦和寻轨控制。</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana"><BR><IMG height=245 src="http://www.33tt.com/upload/images/06/06071906.gif" width=653><BR><BR><BR><IMG height=232 src="http://www.33tt.com/upload/images/06/06071907.gif" width=645><BR><BR></SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体"> </SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">2.4.</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">信号系</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana"><BR></SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体"> 从</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">PBS</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">分离的含有信息的反射光,除一部分进入伺服机构的控制系,大部分进入信号系,由</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">PD</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">变成电信号,前置放大,成为</SPAN><SPAN lang=EN-US style="FONT-SIZE: 9pt; FONT-FAMILY: Verdana">RF</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">信号。</SPAN></P> |
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