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七郎 / Seven Liu

科学与艺术,恰如人生中的红颜知己。 本博内容保留所有权利.

 
 
 

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4.13 Photo diodes & data signal sources 光电二极管和数字信号源  

2012-06-30 19:16:58|  分类: 读点英文 |  标签: |举报 |字号 订阅

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Disc drives extract information from the optical disc in several ways. The most obvious information is the user data, but to make everything work many other types of information have to be acquired from the disc.

光驱通过几种方式从光盘提取数据,其中最显而易见的数据就是用户数据,但要让一切运行起来,还需要从盘片上取得其他各种类型的信息。

The source of the information is the light modulations (variations). This is generated by the interaction between the microscopic structures in the disc and the coherent light and is projected by the drive optics on the 4-quadrant photo detector. The 4-quadrant photo detector is a chip with for photo diodes arranged in a two by two pattern.

信息的来源是经过调制的光(光的变化)。这通过盘片上的微观结构、相干光以及通过光学器件将光投影到四象限光电探测器上。四象限光电探测器是含有四个以2×2方式排列的光电管的芯片。

Each photo diode generate an individual signal, denoted by A, B, C and D. different combinations of the signals are used to generate different types of information. On ROM-discs, the only digital information is stored in the spiral of pits in the mirror surface. From the pits, the HF-signal is generated. On RE-discs and R discs, corresponding information is written into the information layer, the dye or the phase change stack, as marks and spaces.

每个光电二极管各生成一个单独的信号,分别是A、B、C和D。不同类型的信息由四个信号以不同方式组合形成。在只读(ROM)盘片上,只有数字信息存储于镜面上的坑形螺旋轨道。从坑形中生成高频(HF)信号。在可擦写(RE)和可录(R)盘片上,相关信息是写在记录层上的,记录层可以层染料层或相变材料层,信息被记录成标记(mark)和间隔(space)的形式。

The HF-signal is the main information channel, carrying all the user data. The signal is generated by adding the four photo diodes signals.

高频(HF)信号时主通道信息,承载所有的用户信息。信号由四个光电二极管的信号累加构成。

A + B + C + D = HF

The optical source of the HF-signal is the main beam, the 0th order in the diffraction pattern. The signal is generated two optical phenomena, interference, by which the disc generates changes between destructive and constructive interference, and scattering of the incoming beam.

高频信号的光源是主光束、即衍射图中的0级光。该信号生成两种光学现象:干涉,即盘片反射光形成建设性干涉和摧毁性干涉的交替变化,以及入射光束的散射。

An optimal destructive interference is achieved when the pit depth is 1/4 of the wave-length λ and the energy reflected from the pit equals the energy reflected outside the pit.

最理想的摧毁性干涉在坑深为1/4波长时形成,此时从坑底反射回来的能量与坑外反射回来的能量相等。

The pit depth of 1/4 λ makes the total travel distance difference 1/2 after reflection, for half of the light intensity.

坑深为1/4波长时,使反射后的总光程差相差1/2波长,为光强的一半。

The scattering happens as the slopes and the edges of the pit structure do not reflect all of the light back into the focus lens. It results in a general loss of light, which is determined by the slope of the pit edges.

散射发生于坑形结构的斜坡和边缘,此处未能将光全部反射回聚焦镜头。光的损失通常取决于斜坡和坑的边缘。

Even if the information carried by the HF-signal is digital, the signal is analog as the pits are smaller than the spot. On RE-discs and R-discs, instead of pits, there is a spiraled modulated groove, the pre-groove. The pre-groove serves several purposes and the signals and information it carries are available even if the disc is not written.

尽管通过HF信号是用数字化方式承载信息,但因为坑形比光斑小,HF信号仍然是模拟的。在RE盘片和R盘片上,螺旋调制沟槽取代了坑形,称为预制沟槽(pre-groove)。预制沟槽有多重功能,即使盘片未刻录的时候,轨道也承载着信号和信息。

The groove is used for tracking and indicating where the user-data can be written. It has a sinusoidal wobble used for track speed control. The pre-groove also carries the position and control data used by the drive for correct operation. The fundamental of the wobble is modulated to carry the digital information.

沟槽用于激光头进行轨道跟踪并指出用户数据可写在何处。轨道按正弦曲线方式摆动,用于控制跟踪速度。预制沟槽还载有位置信息和用于驱动器进行正确操作的控制数据。沟槽的摆动原则是通过调制承载数字化信息。

The laser beam interacts with the groove to generate the RPP-signal, (Radial Push-Pull-signal). The RPP-signal carries the information of the difference between the right and left side of the 1st order beams in the diffraction pattern. The intensity ratio in the two diffraction beams varies by the spot position relative to the track.

激光束与沟槽相互作用,生成RPP信号(径向推挽信号)。RPP信号中承载的信息是衍射图中左右两个1级衍射光的差异信息。两个衍射光束的光强比随着光斑在轨道上的相对位置变化而发生变化。

(A+B) – (C+D) =RPP

The RPP-signal is generated by the difference between signals from the photo diode pairs on the left and right side edge of the groove projects the light on one side of the groove on the other side of the detector. When the spot is symmetrically positioned on the groove, the intensity on the left and right side of the detector are equal.

RPP信号由四只光电二极管左边两个和右边两个之间的信号差异而生成。当光斑对称定位于沟槽上时,左右两侧探测器接受到的光强是相等的。

The information in the RPP-signal is extracted with the tracing servo activated with the spot position as in position Ⅱ, following the groove. The tracking servo keeps the spot on the groove, resulting in an average RPP-signal (close to) of zero. The frequency of the wobble and modulation of the pre-groove is much higher than it is possible for the servo to follow. This results in the wobble modulation being available in the RPP-channel. The RPP-signal can sometimes be used for tracking of ROM-discs too, but in that case, the signal carries no digital information.

RPP信号中的信息通过被例如处于位置Ⅱ的光斑激活的跟踪伺服系统提取,实现轨道跟踪。跟踪伺服系统保持光斑位于沟槽上,得到的平均RPP信号是(接近)零。预制沟槽摆动和调制的频率远远高于伺服系统可觉察的范围,因此在RPP通道中可进行摆动调制。RPP信号有时也可用于ROM盘片的轨道跟踪,但在那种情况下,RPP信号中不包含数字信息。

Note: The sharpness of the spot edges is to improve visibility only. An optimal realistic spot has an intensity distribution as an airy pattern without any sharp edges.

备注:光斑边缘的清晰度只对提高可见度有用。可实现的最好光斑的光强分布状况应是没有尖锐边缘的艾里斑。

 

 

 

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Key Words:

·microscopic 微观的

·wobble 摆动

·sinusoidal 正弦曲线的

·symmetrically 对称的

 

 

 

以下资料来自维基百科:

The principle of superposition of waves states that when two or more waves are incident on the same point, the total displacement at that point is equal to the vector sum of the displacements of the individual waves. If a crest of a wave meets a crest of another wave of the same frequency at the same point, then the magnitude of the displacement is the sum of the individual magnitudes – this is constructive interference. If a crest of one wave meets a trough of another wave then the magnitude of the displacements is equal to the difference in the individual magnitudes – this is known as destructive interference.

两列波在同一介质中传播发生重叠时,重叠范围内介质的质点同时受到两个波的作用。若波的振幅不大,此时重叠范围内介质质点的振动位移等于各别波动所造成位移的矢量和,这称为波的叠加原理。若两波的波峰(或波谷)同时抵达同一地点,称两波在该点同相,干涉波会产生最大的振幅,称为相长干涉(建设性干涉);若两波之一的波峰与另一波的波谷同时抵达同一地点,称两波在该点反相,干涉波会产生最小的振幅,称为(destructive diffraction)相消干涉(摧毁性干涉)。

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