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比较注重物理性的文章，看看思路，之前有翻译摘要
文章的思路很清晰，就是为了说明散斑降低的机制在激光背投显示中。提出假设实验验证。
Speckle reduction mechanism in laser rear projection displays using a small moving diffuser
1. INTRODUCTION | 1.简介
Rear projection displays that use laser light sources at- | 背投显示 that 使用激光光源吸引了
tract a great deal of interest because of their wide color | a great deal of interest because of their 宽广的色域，
gamut, smaller and lighter optical systems, and lower | 更小更轻的光学系统，and 更低的
power consumption. The recent development of green la- | 功率消耗。The recent development of 绿色
ser diodes [1] will further enhance laser rear projection | 激光二极管will 更增强激光背投的
developments. However, a severe problem hinders the | 发展。 However，一个严重的问题阻碍 the
implementation of laser rear projection displays. When | 实现 of 激光背投显示。When
laser light is diffused at a diffuser, such as a screen, an | 激光 is 散射 在一个散射板，such as a 屏幕，an
interference pattern called a speckle pattern is generated | 干涉图样 called 散斑图样 is 产生
[2–6].
Generally, a speckle pattern is observed as a high- | 一般的，散斑图样 is 观察 as a 高对比度
contrast ?ne-granular pattern. The degradation of image | 细腻粒状的图样。The degradation of 图像
quality on the screen by speckle patterns is a severe prob- | 质量 on the 屏幕 by 散斑图样 is a 严重的问题
lem, and an urgent need exists to reduce speckle for the | and an 紧急的需要存在 to 降低散斑 of the
realization of laser rear projection displays. Necessity for | 实现 of 激光背投显示。必要性 for
its reduction was recognized and discussed especially in | its 降低 was 确认 and 讨论 特别的 in
microinterferometry in early times. Several authors have | 显微干涉 in 早些时候。Several 作者 have
described methods of improving image quality [7–14]. | 描述方法 of 提高像质[7-14]。
These techniques for reducing the speckle effects can be | These techniques for 降低散斑效应 can be
viewed as producing an incoherent superposition of sev- | viewed as 产生 一个 不相干的 叠加 of 几个
eral images with different speckle patterns. | 图像 with 不同散斑图样[OK,这里介绍了一个方法，几个互补的图样相加，则成为均匀的]
Although these have revealed essential speckle reduc- | 虽然 these have revealed 本质的散斑降低
tion techniques, reduction methods for rear projection dis- | 技术，降低方法 for 背投显示
plays require relatively a simple optical system; as optical | 需要相对简单的光学系统，as 光学
systems project a small image on a micro-display from | 系统投射 a 小图像 on a 微型显示 from
?fty to one hundred times larger, high power laser light | 50-100 倍大小，高功率激光
sources must be used; the effective use of the power also | 光源 must be used，the 效率 use of the 功率也是
demands a system with a large numerical aperture or a | 需要 a 系统 with a 大的数值孔径 or a
simple lens composition. In this regard, several methods | 简单镜头组成。在这方面，几种方法
for speckle reduction in displays have been proposed | of 散斑降低 in 显示 have been 建议
[15–19], and the method recognized as the most effective | [15-19]，and the 方法 recongnized as the most 有效
is the moving diffuser (screen) method [15]. Figure 1(a) | is the 移动散射屏方法[15].图1(a)
shows an optical system that uses the moving diffuser | 展示了一个光学系统 that uses the 移动散射屏
method. The principle of the method is essentially the | 方法.The principle of the method is essentially 相同
same technique used for holographic microinterferometry | 技术 used for 显微干涉全息
that produces a superposition of different speckle | that 产生一个叠加 of 不同的散斑
patterns—generation of various speckle patterns over | 图样-----产生 of 不同的散斑图样 over
such short periods of time that the human eye cannot rec- | such 短周期 of 时间 that the 人眼 cannot 意识到
ognize each pattern. The eye perceives temporally aver- | 每个图样。the eye 感知暂时 平均的
aged patterns and hence the speckle is considered to be | 图样 and hence the 散斑 is considered to be
effectively reduced. The moving diffuser method uses two | 有效的降低了。The 移动散射屏方法 uses 两个
diffusive screens placed close together, one ?xed and one | 散射屏 放置相近的，一个固定 and 一个
moving. However, despite its high effectiveness at speckle | 移动。However，不管 its 高效率 at 散斑
reduction, some problems make it dif?cult to use the | 降低，some problems make it 困难 to use the
method in ?nished products. The mechanical system | 方法 in 最终产品。the 机械系统
needed to move the large diffusive screen is cumbersome, | 需要移动大的散射屏 is 笨重，
and the dif?culty in reducing the back-scattering of am- | and the 难度 in 降低 the 后向散射 of 环境
bient light in bright rooms results in a low screen con- | 光 in 明亮的房间 导致 in a 低的屏幕对比度
trast.
2. TARGET SYSTEM | 2.目标系统
To solve these problems, a method that uses a small mov- | 要解决这些问题，a method that uses 一个小移动
ing diffuser plate in the optical projecting system [20] has | 散射片 in the 光学投影系统[20] has been 建议
been proposed (hereafter we call this the “small diffuser | (因此我们称之为“小散射物方法”)
method”). Figure 1(b) shows a schematic of an optical sys- | 图1(b) 显示了原理 of 光学
tem that uses the small diffuser method. In this method, | 系统 that uses 小散射物方法。In this 方法，
laser light is diffused by a small plate before it passes | 激光 is 散射 by a 小片 before it 通过
through a micro-display and is projected onto the screen. | 微显示 and 被投影到屏幕上
The effect of the small moving diffuser is expected to be | the 效果 of 小移动散射物 is 期望达到
equivalent to that of the conventional moving diffusive | 和传统的移动屏的效果一样
screen in terms of the relative motions of the two diffus- |
ers. Because this method does not require the complex | 由于 这个方法不需要 复杂
screens required by the moving diffuser method, it is ex- | 的屏幕 需要 by 移动散射屏方法，it is
pected to be a practical solution for the actual products. | 期望 to be a 实际的解决方案 for 实际产品
Optimization of the small diffuser systems requires a | 优化 of the 小散射物 系统 需要 一个
deep understanding of the speckle reduction mechanism | 很深的理解 of the 散斑降低机制
in the method. One common model treats speckle genera- | in the 方法。一个通用的模型 对待 散斑的产生
tion and reduction using some assumed statistical prop- | and 降低 using some 假设 的统计
erties of speckle patterns [3,21], in which speckle is as- | 属性 of 散斑图样[3,21]，in which 散斑 is 假设
sumed as the interference of light consisting of random | as the 干涉 of 光包含随机的
amplitudes and phases. Random-walk theory is applied to | 振幅和相位。随机漫步理论 is 用来
describe these randomly distributed diffusive elements. | 描述 this 随机的分布的 散射元件
Although statistically consistent equations can be derived | 虽然统计连贯 方程 can be 导出
from this model, the physical processes of speckle genera- | 从 这个模型，the 物理过程 of 散斑产生
tion by diffusers and speckle reduction by rotation do not | by 散射屏 and 散斑降低 by 旋转 do not
appear explicitly in it. The assumption of randomness in | 明确的 in it。the 假设 of 随机性 in
the model without a physical basis makes it dif?cult to | the 模型 without a 物理的基础 makes it 困难
apply it to real speckle generation to reduce speckles in | 应用它到实际的散斑产生和降低散斑 in
speci?c systems. Besides, as we mention in this paper, the | 特定的系统。除此之外，as we mention in this paper，the
signi?cant speckle property on projection displays is the | 重要的散斑属性 on 投影显示 is the
existence of an independent speckle generated at the | 存在 of an 独立的散斑产生 at the
screen that must be suppressed in addition to the speckle | 屏幕 that must be 抑制 除了 the 散斑在
in the optical system. An appropriate model describing | 光学系统。一个合理的模型描述
the physical process of speckle generation is needed to | the 物理过程 of 散斑产生 is 必要的 to
clarify these phenomena and speckle reduction mecha- | 清晰的解释 these 现象 and 散斑降低机制
nisms. More speci?cally, physical effects by the rotation of | 更具体的，物理效应 by the 旋转 of
the small diffuser and the resultant mechanism of speckle | the 小散射物 and the 由此而来的 机制 of 散斑
reduction on the screen must be explained based on the | 降低 on the 屏幕 must be 解释 base on the
model. | 模型
Our approach was to consider the physical aspects of | 我们的方法 was to 考虑 the 物理方面 of
speckle effects in the small diffuser method based on ex- | 散斑效应 in the 小散射物 方法 based on
perimental results to obtain a model with which we can | 实验的结果 to obtain a model with which 我们可以
directly analyze speckle reduction mechanisms. Although | 直接的分析散斑降低机制。 虽然
we focused on the small diffuser method in this paper, the | 我们关注 小散射物方法 in this paper， the
results must be effective on analyses for other time- | 结果must be 有效 on 分析 for other 时间平均
averaging speckle reduction methods as well. | 散斑降低方法 as well.
3. SPECKLE GENERATION MODEL FOR THE | 3.散斑产生模型 for 小散射屏方法
SMALL DIFFUSER METHOD |
The fundamental model for speckle generation used in | 散斑产生的基础模型 used in
this paper is shown in Fig. 2. To simplify the interference | this paper is 示出 in 图2. to 简化 干涉
of diffused light at the diffuser, only two pairs of light | of 散射的光线 at the 散射屏，只有2对光线
sources are illustrated. From each source, diffused laser | 被绘画出。从每个光源，被散射了的激光
light spreads into space. Interference of the diffused light | 扩展到空间。干涉 of the 散射光
from these sources generates many bright regions in | from these 光源 产生许多明亮区域 in
which the constructive interference condition is met. | which the 结构的 干涉条件 is 达到
When human eyes or detectors such as CCD cameras are | 档人眼 or 探测器 such as CCD 相机 are
placed in front of the diffuser, bright dots due to the in- | 放置 在散射屏前面。 由于干涉产生的明亮点
terference should be observed at anterior focal points | should be 观察到在前焦点
(hereafter we use “focal plane” in this sense). Many light | （所以在这一的意义下我们用“焦平面”），许多光源
sources are on the diffuser, and the interference of these | 被散射 on the 散射屏，and the 干涉 of these 光源
sources makes the complex speckle pattern. The bright | makes the 复杂散斑图样。the 明亮
dots of the pattern should be in the space between the dif- | 点 of the 图样 should be 空间中 介于
fuser and the detector, where the focal plane of the detec- | 散射屏和探测器之间。 where the 焦平面 of the 探测器
tor is set, as shown in Fig. 2. Furthermore, if the focal | is set ，如图2，更进一步，if the 焦平面
plane is set to the far side of the diffuser, the bright dots | is set to the 远端 of the 散射屏，the 亮点
should be seen in the air at the back of the diffuser. | should be seen 在空气中 at the 后面 of 散射屏
The experimental setup is shown in Fig. 3. In the be- | the 实验设置是图3 ，开始的时候
ginning, we conducted experiments in this section with- | 我们进行实验 in this 段 没有旋转 the 小的散射屏
out rotating the small diffuser. The wavelength of the la- | 激光波长是
ser diode was 532 nm. Emitted laser light was passed to | 530nm，出射激光 was 进行到
the small diffuser, and the diffused light was projected to | 小的散射屏，and the 散射光 投射到
a screen 1 m away. The speckle patterns on the screen | 1m外的屏幕，the 散斑图样 on the 屏幕
were measured with a CCD camera placed 1 m from the | were 测量 with a CCD 相机放置在1m距离
screen. In the actual small diffuser system, other optical | 屏幕。在实际的小散射屏系统，另外的光学
components such as a homogenizer and a micro-display | 元件 例如 均质 和 微型显示器
are also used (Fig. 1), but only those components illus- | are 也是用 图1，but 只有 those 元件
trated in Fig. 3 are essential to speckle reduction. The | 绘画出在图3 are 本质 to 散斑降低。the
photo in Fig. 4 shows a speckle pattern that appeared on | 照片在图4 表示一个散斑图样 that 出现在
the screen of the system. A coarse granular pattern can be | 系统的屏幕.一个粗糙的颗粒图样可以
seen. In addition, a ?ne granular pattern appears to be | 看到。附加的，一个细颗粒度的图样出现
superimposed on the coarse pattern. The graph in Fig. 5 | 叠加在粗粒度图样上。图5
shows the intensity distribution of the pixels along the | 示出强度分布 of 像素 沿着白虚线
white dotted line indicated in the speckle pattern. The | 表示的散斑图样
gradual bumps correspond to the coarse pattern, and the | 缓变的起伏对应粗图样
steep bumps correspond to the ?ne pattern. As the gen- | 陡变的起伏对因细图样
eration of this speckle pattern with two different super- | 产生的散斑图样有两个不同的叠加
imposed granular patterns is a unique characteristic of | 是系统的特点
the system, we analyzed the process that caused it. | 我们分析了过程 that 导致这个样子
Because the speckle is generated by diffusive media, | 因为散斑 is 产生 by 散射媒质
two components in this system could possibly generate it: | 两个元件 in this system 可以可能产生它：
the small diffuser and the screen. If the speckle shown in | 小的散射屏 和 屏幕，如果散斑 shown in
Fig. 4 were generated at the screen, it should have been | 图4产生在屏幕，它应该有被观察
observed even if the CCD camera were defocused from the | 就算 CCD相机离焦 from
screen, because the interference pattern should have ex- | 屏幕，因为干涉图样应该连续
isted continuously in the space between the screen and | 的存在于空间 between 屏幕和相机
the camera. If the speckle were generated at the small dif- | 如果散斑产生在小的散射屏
fuser, the pattern should have been affected by the | 图样应该被影响 by the
change in optical parameters of the projection lens, such | 改变 in 光学参数 of the 投影镜头，比如
as the F-number. Thus, by examining both cases, we were | F数，所以，by 考察两种情况，我们可以
able to clarify the speckle generation in the system. | 搞清楚 the 散斑的产生 in the 系统。
Speckle patterns in the mid-space can be observed by | 散斑图样 in the 中间空间 can be 观察到 by
changing the focal length of the CCD camera. We defo- | 改变焦距 of CCD相机(镜头的)，我们离焦
cused the focal plane of the camera by 500 mm from the | 那个焦平面 of 相机 by 500 mm 从屏幕算起
screen and compared the obtained patterns with the origi- | and 对比获得的图样 with 原始
nal ones. The resultant photos are shown in Fig. 6: the | 那个，结果图片如图6所示，左右
left and right photos show the no-defocusing and defocus- | 图像 表明 无离焦和离焦的情况
ing cases, respectively. The coarse aspect of the speckle | 分别的，粗糙的部分 of 散斑图样
pattern obviously disappeared after defocusing, and only | 明显消失 after 离焦，and 只有
the ?ne pattern remained. The persistence of the ?ne pat- | 细腻的图样留下，细图样的坚持
tern implied that it was generated at the screen, while | 暗示 that it was 产生在屏幕，当
the disappearance of the coarse pattern implied that it | 粗图样消失 暗示 that it
was generated at the small diffuser. | was 产生在小屏.
After resetting the focal plane of the camera to the | after 重设置 相机的焦平面 to the
screen, we changed the F-number of the projection lens to | 屏幕，我们改变f数of the 投影镜头 to
observe the effect of the optical condition change. The | 观察光学条件的影响，the
photos in Fig. 7 show the pattern change that occurred | 图是图7，示出图样改变 that 发生在
when we decreased the F-number from F/11 to F/4. The | 当我们降低f数从F/11到F/4。the
change in the granularity of the coarse pattern was con- | 改变 in 粒度 of the 粗糙图样 was 确定
?rmed, and the pattern was determined to have been gen- | and the 图样 was 确定 to have been 产生在
erated at the small diffuser. | 小屏
To determine whether the coarse pattern generated at | 要确定 是否 粗图样产生 at
the small diffuser was actually another speckle or just a | the 小屏 was 实际上另外一个 散斑 或者 只是一个
projected real image of the diffuser, we conducted another | 被投影的实像 of the 散射屏，我们构造了另外
experiment. Because the speckle was caused by the inter- | 一个实验，因为散斑 was 造成 by the 干涉 of
ference of diffused light, granular patterns should not | 散射光，粒度图样 应该不
have appeared if incoherent light were used. If the pat- | 出现 如果非相干光 were used.如果图样
tern had been a real image, it would have appeared re- | 是实像，it 将无论如何都会出现
gardless of the coherency of the light source. To con?rm | 而跟光源的相关性无关。to 确定这个
this, we changed the light source from a laser diode to an | 我们改变光源从LD到LED
LED (an incoherent light source) and measured the pat- | and 测量图样
terns at the screen directly. Figure 8 shows the experi- | 在屏幕上。图8示出
mental setup. As shown in the schematic, we removed the | 实验设置，表示的是原理，我们移除
screen and placed a CCD panel (without detector lens) at | 屏幕 and 将CCD探测面（没有镜头）放在
the position of the screen. The results are shown in Fig. 9. | 原来屏幕的地方。结果如图9
The pattern on the right was obtained with laser light | 图样在右边是LD的
and that on the left was obtained with an LED light | 左边的是LED的，粒度
source. The granular pattern appeared only when the la- | 粒度的图样之当使用LD时候出现
ser was used. The results clearly showed that the granu- | 结果清晰的表明 that the粒度图样
lar pattern generated at the small diffuser was actually | 产生 在小屏 was 实际上
another speckle. | 另外一个散斑
The speckle generation model that we obtained based | 散斑产生模型 that we 得到 基于
on these experiments is illustrated in Fig. 10. Two inde- | 这些实验 绘画在图10中，两个
pendent speckles exist in this system: a coarse speckle | 独立的散斑存在在系统里：一个粗糙散斑
generated at the small diffuser and a ?ne speckle gener- | 产生在小散射屏，一个细散斑产生在屏幕
ated at the screen. We call the former the primary speckle | 我们称前者为主要散斑后者为
and the latter the secondary speckle in this paper. | 次要散斑在文章里。
4. PHYSICAL ASPECTS OF THE | 4.物理方面 of the 粒度of 散斑图样
GRANULARITY OF SPECKLE PATTERNS
The small diffuser method reduces speckle on the screen | 小屏方法降低散斑在屏幕上
by rotating the small diffuser. Rotation of the diffuser cor- | by 旋转小屏。旋转of 小屏
responds to rotation of the primary speckle patterns pro- | 对应于旋转投射到屏幕的主散斑图样
jected on the screen. This means that speckle reduction is | 这意思就是，散斑降低 is
achieved by the movement of the primary speckle pat- | 达到by the 运动 of 主要散斑图样
terns on the screen. | 在屏幕上。
Although speckle patterns have a variety of complex | 虽然散斑图样有一个变化 of 复杂的
granular forms, they are fundamentally interference pat- | 粒度形式，他们基本的干涉图样
terns of diffused light. Bright regions of the patterns ap- | of 散射光。亮区域 of 图样出现
pear where light interferes constructively, and dark re- | 在光干涉加强，and 暗区域
gions appear where light interferes destructively. | 出现在光减弱
Constructive interference occurs when the light is in | 加强的相干出现在 光线 in
phase and destructive interference occurs when it is out of | 相位(同相) and 减弱的出现在反相
phase. Thus, speckle patterns can be considered an indi- | 所以，散斑图样可以考虑为一个指示器
cator of the underlying phase difference. From this point | of 底层 的相位差。从这个观点出发，
of view, the granularity of the speckle patterns indicates | 散斑图样的粒度指示了
how steeply the underlying phase difference is distrib- | 相位差的分布有多陡峭
uted. For example, a coarse speckle pattern should have a | 例如，粗糙的散斑图样应该有一个
relatively moderate phase difference change in a unit | 相对中等的相位差变化 in a 单位面积。
area.
Figure 11 shows the experimental setup that we used | 图11示出实验的设置 that 我们用来
to verify this hypothesis. A mask sheet with two pinholes | 验证这个假定。一个掩膜片 with 两个针孔
was placed at the screen position. Each pinhole had a di- | was 放置在屏的位置。每一个针孔 had a 直径
ameter of 70um, and they were separated by 300um. A | of 70um，and they were 分离了300um，一个
CCD camera was placed in front of the sheet. Light pass- | CCD相机 was放置于 掩膜片的前面。光线穿过
ing through these pinholes spread and formed an interfer- | 这些针孔扩散 and 形成一个干涉图样
ence pattern with a sine curve intensity shape on the | with a 正弦曲线的强度形状在CCD平面。
CCD panel. The change in the phase difference between | the 变化 in the 相位差 between
the holes shifted the position of the interference pattern | 孔便宜 the 位置 of 干涉图样 on the 平面。
on the panel. If the change in the phase difference was | 如果改变在相位上是1/2波长，
one-half of a wavelength, the pattern shifted its shape by | 图样偏移它的形状by 半个波长，
half a wavelength. Thus, if the speckle pattern re?ected | 那么，如果散斑图样反应了
the phase difference distribution, the resultant interfer- | 相位差的分布，the 结果的干涉图样
ence pattern should have shifted along with the primary | 应该和主散斑图样一样偏移。
speckle pattern.
The experimental results are shown in Fig. 12. We con- | 实验结果在图12中，我们构造
ducted experiments with two speckle patterns of different | 实验 with 两个散斑图样 of 不同
granularity by changing the F-number of the projection | 粒度 by 改变f数 of the 投影镜头。
lens. Results for the ?rst case, F/8, are shown in Figs. (a)– | 结果是第一个情况，F/8图a-d
(d) in the left column. The photo in (a) shows the speckle | 在左边的列，图片in a 表示散斑图样
pattern projected onto the pinholes (the photo was taken | 投射到针孔上（the 图片 was 取得
without the mask sheet of the double pinholes). The two | 没有掩膜片 of 双孔）。the 两个圆
circles indicate the relative sizes of the pinhole diameters | 表示相对尺寸 of 针孔直径
and gap against the pattern. As the speckle pattern | 和他们的间隙相对于图样，当散斑图样
moved across the pinholes, the interference pattern also | 移动通过针孔时，干涉图样也平移
shifted. Movement of the speckle pattern by 560um | 移动 of the散斑图样 by 560um
made the interference pattern shift by one wavelength. | 让干涉图样移动by 一个波长
This meant that the phase difference between the holes | 这表明 相位差 between the 孔
changed approximately with the wavelength of the laser | 改变大约with th 激光波长。
light. The second case, F/16, shown in (e)–(h) in the right | the 第二个情况，F/16，e-h图，右边的列
column, shows a coarser primary speckle pattern. The re- | 表示一个更粗糙的主要散斑图样。
sultant interference pattern barely shifted its position. | 结果干涉图样很少变化它的位置。
This meant that with the coarser primary speckle pat- | 这表明 更粗糙的主要散斑图样，
tern, the phase difference between the holes changed a | 相位差 between 两孔改变一点点。
little. These experimental results indicate that the pri- | 这个实验结果表明，主要
mary speckle pattern re?ects its phase difference distri- | 散斑图样反应它的相位差分布
bution and that the increment of the granularity of the | and that the 增量 of 粒度 of the
pattern decreases the phase difference in a unit area. | 图样 降低相位差在一个单位区域内
De?ning the degree of granularity of the speckle pat- | 定义粒度的度量 of 散斑图样
tern is convenient for further analysis. We de?ned this | is 方便 for 更进一步的分析。我们定义这个
from the intensity spectrum of the pattern in the spatial | 从强度谱 of the 图样 in the 空间域
frequency domain. Figure 13 is the Fourier transform of a | 图13 是傅立叶变换 of a
speckle pattern. We de?ned the degree of granularity as | 散斑图样。我们定义粒度的度量，as
the reciprocal number of the frequency, the intensity of | 倒数 of the 频率（空间频率单位lp/mm），
which is the half value of that of the lowest frequency in | 强度对应是半值 of the 最低频率在频谱上
the spectrum, excluding the DC component at the fre- | 不包括直流分量 在频域=0
quency equal to zero.
Because the speckle pattern represents its phase differ- | 因为散斑图样代表它的相位差分布
ence distribution, the physical effects of shifting the pat- | the 物理效应 of 移动图样 by
tern by rotation of the small diffuser can be deduced. As | 旋转小散射屏 就可以被推导。
shown in Fig. 14, when the speckle pattern on the sheet is | 如图14，当散斑图样 on the 薄片 is
rotated continuously, the phase difference between the | 连续的旋转，相位差 between
two pinholes also changes, and the resultant interference | 双针孔 也在变化。and the 结果干涉图样
pattern shifts. Consequently, the pattern measured by the | 移动了。所以，图样测量by
CCD camera is temporally averaged in intensity, and its | CCD相机 is 暂时的强度上平均，and 它的
contrast is reduced. The contrast of the averaged pattern | 对比度就降低了。对比度 of the 平均图样
depends on the change in the phase difference. As the dif- | 取决于相位差的变化。相位差
ference of the phases is larger when the granularity of the | 变大 当 粒度变小。更细的主要散斑
speckles is smaller, ?ner primary speckle patterns should | 图样应该产生更
result in ?atter interference patterns on the CCD. | 平的干涉图样在CCD上
Experimental results are shown in Fig. 15. As we | 实验结果如图15，
showed in the previous section, the granularity of the pri- | 正如之前展示的，粒度of 主要
mary speckle increased with the increment of the | 散斑增加 with F数增加 of
F-number of the projection lens. The degree of granularity | 投影镜头。the 粒度的度量
of the primary speckle patterns corresponding to each | of 主要散斑图样对应每个
F-number is also plotted. The solid horizontal line in the | F数也绘画出了。水平实线在图中
graph indicates the distance between the two pinholes. | 表示两个针孔的距离。
When the degree of granularity was smaller than the dis- | 当粒度的度量小于针孔间距
tance, the resultant interference pattern in (b) showed no | 产生的干涉图样是b，表示没有干涉
interference. This meant that when the small diffuser | 这表明当小散射屏旋转
was rotated, the phase difference change was large | 时，相位差变化 was 足够大
enough to reduce the temporally averaged coherency be- | 到降低暂时平均干涉性 在
tween the two pinholes. The middle pattern (c) is the case | 两针孔之间。中间的图样c情况是
when the degree of granularity was almost the same size | 当粒度的度量 几乎相同尺寸
as the distance between the pinholes. The resultant inter- | as 针孔间距。结果干涉
ference pattern showed little interference. The rightmost | 图样 表示一点干涉。最右边
pattern (d) shows the case for a much larger degree of | 的图样d表示大得多的粒度度量
granularity. In this case, interference can obviously be | 这样的情况下，干涉显然被辨认。
recognized.
These experimental results showed that the degree of | 这些实验结果说明，粒度的度量
granularity of the primary speckle corresponded to the | of 主要散斑 对应于 the
size of coherent region for the secondary speckle of the | 尺寸 of 干涉区域 for 次要散斑 of
screen, when the small diffuser was rotated. | 屏幕，当小散射屏旋转。
5. SPECKLE REDUCTION BY ROTATION OF | 5.散斑降低 by 旋转 of the 小散射屏
THE SMALL DIFFUSER
The results of the previous section explain the mechanism | 之前的结果解释了
of speckle reduction in the small diffuser system. When | 散斑降低机制 in 小散射板系统，当
the small diffuser was stationary, the secondary speckle | 小的散射板静止，次要散斑
generated at the screen was unaffected because no change | 产生在屏幕 was 不影因为没有变化
occurred in the interference conditions there. When the | 发生在干涉条件这里。当
small diffuser was rotated continuously, the movement of | 小散射板 was 持续旋转，移动 of
the primary speckle changed the interference condition | 主要散斑的干涉条件变化
on the screen. This affected the generation of the second- | 在屏幕上。这影响产生 of 次要散斑
ary speckle. Because the degree of granularity of the pri- | 因为粒度的度量 of 主要
mary speckle on the screen represented the size of the co- | 散斑在屏幕上代表干涉区域的尺寸
herent region, the contrast of the secondary speckle | 。对比度 of 次要散斑降低 as
decreased as the degree of granularity declined. | the 粒度的度量下降。
We con?rmed that the speckle reduction depended on | 我们确定 that the 散斑降低 依赖于
the degree of granularity as follows. We measured the | 粒度的度量如下：我们测量散斑
speckle contrasts on the screen by changing the degree of | 对比度在屏幕上 by 改变粒度的度量
granularity of the primary speckle. The speckle contrast | of 主要散斑。散斑的对比度
was calculated by dividing the standard deviation of the | 被计算 by 除以 标准差 of the
intensity distribution of the obtained speckle pattern by | 强度分布 of the 取得的散斑图样 by
its mean intensity. To improve its validity, we changed not | 它的平均强度。要提高它的置信度，我们改变
only the F-number of the projection lens but also its mag- | 不只是投影镜头F数，也改变了放大率和
ni?cation and the diffusing angle range of the small dif- | 散射角范围 of 小散射屏。
fuser. Figure 16 shows the result. As the degree of granu- | 图16示出结果。当粒度度量增加
larity increased, the corresponding speckle contrast also | 对应的散斑对比度也增加
increased. In every case when the granularity was | 在每一个情况下，当粒度改变，
changed, the resultant values lay on the same approxi- | 结果值坐落在同样的近似曲线上。
mate curve. This clearly showed that the degree of granu- | 这清晰的表明粒度的度量
larity of the primary speckle was the key parameter in | of 主要散斑是关键参数 in
speckle generation on the screen. | 屏幕上的散斑产生。
6. CONCLUSIONS | 6.结论
We have established a speckle generation model for the | 我们建立了一个散斑产生的模型 for
small diffuser method and found two speckles in the sys- | 小散射屏方法 and 找到两个散斑在系统：
tem: a coarse speckle generated at the small diffuser and | 一个粗糙散斑 产生在小散射屏 and
a ?ne speckle generated at the screen. These two speckles | 一个细的散斑产生在屏幕。这两个散斑
must be treated separately. | 必须区别对待。
From experiments using a mask sheet with double pin- | 从实验用掩膜片 with 双针孔，
holes, we con?rmed that the granular pattern of the | 我们确定粒度图样 of
speckles represented the underlying phase difference dis- | 散斑代表底层的相位差分布。
tribution. This meant that the ?ner speckle pattern had a | 这表明 细微散斑图样有
steeper phase difference change. When the primary | 更剧烈的相位差改变。当主要
speckle pattern moved as a result of the rotation of the | 散斑图样移动 as a result of the 旋转of
small diffuser, the granularity of the pattern determined | 小散射屏，图样的粒度 确定了
the coherency within a unit area on the screen, and the | 干涉性 在一个单位面积之内在屏幕上。
degree of granularity corresponded to the coherent area | and the 粒度的度量对应干涉区域尺寸
size.
The dependency of the coherency on the degree of | 干涉性对粒度的度量的依赖
granularity determined the speckle contrast on the screen | 确定了散斑对比度 在屏幕上
when the diffuser was rotated. The speckle contrast in- | 当散射屏旋转 。散斑对比度增加
creased with the degree of granularity. Hence the degree | with 粒度的度量增加。所以粒度的度量
of granularity can be used as a uni?ed index when dis- | 可以用做一个统一的指数 当
cussing speckle reduction effects. | 讨论散斑降低效应。
From these results, we have obtained a valid speckle | 从这些结果出发，我们获得了可用的散斑
generation model and clari?ed the mechanism of speckle | 产生模型 and 澄清了散斑降低的机制
reduction in the small diffuser method. | in 小散射屏方法。
论文原文
https://m.sciencenet.cn/blog-408189-353004.html
上一篇：第17篇摘要学习
下一篇：摘要翻译，OCT相关
文章的思路很清晰，就是为了说明散斑降低的机制在激光背投显示中。提出假设实验验证。
Speckle reduction mechanism in laser rear projection displays using a small moving diffuser
1. INTRODUCTION | 1.简介
Rear projection displays that use laser light sources at- | 背投显示 that 使用激光光源吸引了
tract a great deal of interest because of their wide color | a great deal of interest because of their 宽广的色域，
gamut, smaller and lighter optical systems, and lower | 更小更轻的光学系统，and 更低的
power consumption. The recent development of green la- | 功率消耗。The recent development of 绿色
ser diodes [1] will further enhance laser rear projection | 激光二极管will 更增强激光背投的
developments. However, a severe problem hinders the | 发展。 However，一个严重的问题阻碍 the
implementation of laser rear projection displays. When | 实现 of 激光背投显示。When
laser light is diffused at a diffuser, such as a screen, an | 激光 is 散射 在一个散射板，such as a 屏幕，an
interference pattern called a speckle pattern is generated | 干涉图样 called 散斑图样 is 产生
[2–6].
Generally, a speckle pattern is observed as a high- | 一般的，散斑图样 is 观察 as a 高对比度
contrast ?ne-granular pattern. The degradation of image | 细腻粒状的图样。The degradation of 图像
quality on the screen by speckle patterns is a severe prob- | 质量 on the 屏幕 by 散斑图样 is a 严重的问题
lem, and an urgent need exists to reduce speckle for the | and an 紧急的需要存在 to 降低散斑 of the
realization of laser rear projection displays. Necessity for | 实现 of 激光背投显示。必要性 for
its reduction was recognized and discussed especially in | its 降低 was 确认 and 讨论 特别的 in
microinterferometry in early times. Several authors have | 显微干涉 in 早些时候。Several 作者 have
described methods of improving image quality [7–14]. | 描述方法 of 提高像质[7-14]。
These techniques for reducing the speckle effects can be | These techniques for 降低散斑效应 can be
viewed as producing an incoherent superposition of sev- | viewed as 产生 一个 不相干的 叠加 of 几个
eral images with different speckle patterns. | 图像 with 不同散斑图样[OK,这里介绍了一个方法，几个互补的图样相加，则成为均匀的]
Although these have revealed essential speckle reduc- | 虽然 these have revealed 本质的散斑降低
tion techniques, reduction methods for rear projection dis- | 技术，降低方法 for 背投显示
plays require relatively a simple optical system; as optical | 需要相对简单的光学系统，as 光学
systems project a small image on a micro-display from | 系统投射 a 小图像 on a 微型显示 from
?fty to one hundred times larger, high power laser light | 50-100 倍大小，高功率激光
sources must be used; the effective use of the power also | 光源 must be used，the 效率 use of the 功率也是
demands a system with a large numerical aperture or a | 需要 a 系统 with a 大的数值孔径 or a
simple lens composition. In this regard, several methods | 简单镜头组成。在这方面，几种方法
for speckle reduction in displays have been proposed | of 散斑降低 in 显示 have been 建议
[15–19], and the method recognized as the most effective | [15-19]，and the 方法 recongnized as the most 有效
is the moving diffuser (screen) method [15]. Figure 1(a) | is the 移动散射屏方法[15].图1(a)
shows an optical system that uses the moving diffuser | 展示了一个光学系统 that uses the 移动散射屏
method. The principle of the method is essentially the | 方法.The principle of the method is essentially 相同
same technique used for holographic microinterferometry | 技术 used for 显微干涉全息
that produces a superposition of different speckle | that 产生一个叠加 of 不同的散斑
patterns—generation of various speckle patterns over | 图样-----产生 of 不同的散斑图样 over
such short periods of time that the human eye cannot rec- | such 短周期 of 时间 that the 人眼 cannot 意识到
ognize each pattern. The eye perceives temporally aver- | 每个图样。the eye 感知暂时 平均的
aged patterns and hence the speckle is considered to be | 图样 and hence the 散斑 is considered to be
effectively reduced. The moving diffuser method uses two | 有效的降低了。The 移动散射屏方法 uses 两个
diffusive screens placed close together, one ?xed and one | 散射屏 放置相近的，一个固定 and 一个
moving. However, despite its high effectiveness at speckle | 移动。However，不管 its 高效率 at 散斑
reduction, some problems make it dif?cult to use the | 降低，some problems make it 困难 to use the
method in ?nished products. The mechanical system | 方法 in 最终产品。the 机械系统
needed to move the large diffusive screen is cumbersome, | 需要移动大的散射屏 is 笨重，
and the dif?culty in reducing the back-scattering of am- | and the 难度 in 降低 the 后向散射 of 环境
bient light in bright rooms results in a low screen con- | 光 in 明亮的房间 导致 in a 低的屏幕对比度
trast.
2. TARGET SYSTEM | 2.目标系统
To solve these problems, a method that uses a small mov- | 要解决这些问题，a method that uses 一个小移动
ing diffuser plate in the optical projecting system [20] has | 散射片 in the 光学投影系统[20] has been 建议
been proposed (hereafter we call this the “small diffuser | (因此我们称之为“小散射物方法”)
method”). Figure 1(b) shows a schematic of an optical sys- | 图1(b) 显示了原理 of 光学
tem that uses the small diffuser method. In this method, | 系统 that uses 小散射物方法。In this 方法，
laser light is diffused by a small plate before it passes | 激光 is 散射 by a 小片 before it 通过
through a micro-display and is projected onto the screen. | 微显示 and 被投影到屏幕上
The effect of the small moving diffuser is expected to be | the 效果 of 小移动散射物 is 期望达到
equivalent to that of the conventional moving diffusive | 和传统的移动屏的效果一样
screen in terms of the relative motions of the two diffus- |
ers. Because this method does not require the complex | 由于 这个方法不需要 复杂
screens required by the moving diffuser method, it is ex- | 的屏幕 需要 by 移动散射屏方法，it is
pected to be a practical solution for the actual products. | 期望 to be a 实际的解决方案 for 实际产品
Optimization of the small diffuser systems requires a | 优化 of the 小散射物 系统 需要 一个
deep understanding of the speckle reduction mechanism | 很深的理解 of the 散斑降低机制
in the method. One common model treats speckle genera- | in the 方法。一个通用的模型 对待 散斑的产生
tion and reduction using some assumed statistical prop- | and 降低 using some 假设 的统计
erties of speckle patterns [3,21], in which speckle is as- | 属性 of 散斑图样[3,21]，in which 散斑 is 假设
sumed as the interference of light consisting of random | as the 干涉 of 光包含随机的
amplitudes and phases. Random-walk theory is applied to | 振幅和相位。随机漫步理论 is 用来
describe these randomly distributed diffusive elements. | 描述 this 随机的分布的 散射元件
Although statistically consistent equations can be derived | 虽然统计连贯 方程 can be 导出
from this model, the physical processes of speckle genera- | 从 这个模型，the 物理过程 of 散斑产生
tion by diffusers and speckle reduction by rotation do not | by 散射屏 and 散斑降低 by 旋转 do not
appear explicitly in it. The assumption of randomness in | 明确的 in it。the 假设 of 随机性 in
the model without a physical basis makes it dif?cult to | the 模型 without a 物理的基础 makes it 困难
apply it to real speckle generation to reduce speckles in | 应用它到实际的散斑产生和降低散斑 in
speci?c systems. Besides, as we mention in this paper, the | 特定的系统。除此之外，as we mention in this paper，the
signi?cant speckle property on projection displays is the | 重要的散斑属性 on 投影显示 is the
existence of an independent speckle generated at the | 存在 of an 独立的散斑产生 at the
screen that must be suppressed in addition to the speckle | 屏幕 that must be 抑制 除了 the 散斑在
in the optical system. An appropriate model describing | 光学系统。一个合理的模型描述
the physical process of speckle generation is needed to | the 物理过程 of 散斑产生 is 必要的 to
clarify these phenomena and speckle reduction mecha- | 清晰的解释 these 现象 and 散斑降低机制
nisms. More speci?cally, physical effects by the rotation of | 更具体的，物理效应 by the 旋转 of
the small diffuser and the resultant mechanism of speckle | the 小散射物 and the 由此而来的 机制 of 散斑
reduction on the screen must be explained based on the | 降低 on the 屏幕 must be 解释 base on the
model. | 模型
Our approach was to consider the physical aspects of | 我们的方法 was to 考虑 the 物理方面 of
speckle effects in the small diffuser method based on ex- | 散斑效应 in the 小散射物 方法 based on
perimental results to obtain a model with which we can | 实验的结果 to obtain a model with which 我们可以
directly analyze speckle reduction mechanisms. Although | 直接的分析散斑降低机制。 虽然
we focused on the small diffuser method in this paper, the | 我们关注 小散射物方法 in this paper， the
results must be effective on analyses for other time- | 结果must be 有效 on 分析 for other 时间平均
averaging speckle reduction methods as well. | 散斑降低方法 as well.
3. SPECKLE GENERATION MODEL FOR THE | 3.散斑产生模型 for 小散射屏方法
SMALL DIFFUSER METHOD |
The fundamental model for speckle generation used in | 散斑产生的基础模型 used in
this paper is shown in Fig. 2. To simplify the interference | this paper is 示出 in 图2. to 简化 干涉
of diffused light at the diffuser, only two pairs of light | of 散射的光线 at the 散射屏，只有2对光线
sources are illustrated. From each source, diffused laser | 被绘画出。从每个光源，被散射了的激光
light spreads into space. Interference of the diffused light | 扩展到空间。干涉 of the 散射光
from these sources generates many bright regions in | from these 光源 产生许多明亮区域 in
which the constructive interference condition is met. | which the 结构的 干涉条件 is 达到
When human eyes or detectors such as CCD cameras are | 档人眼 or 探测器 such as CCD 相机 are
placed in front of the diffuser, bright dots due to the in- | 放置 在散射屏前面。 由于干涉产生的明亮点
terference should be observed at anterior focal points | should be 观察到在前焦点
(hereafter we use “focal plane” in this sense). Many light | （所以在这一的意义下我们用“焦平面”），许多光源
sources are on the diffuser, and the interference of these | 被散射 on the 散射屏，and the 干涉 of these 光源
sources makes the complex speckle pattern. The bright | makes the 复杂散斑图样。the 明亮
dots of the pattern should be in the space between the dif- | 点 of the 图样 should be 空间中 介于
fuser and the detector, where the focal plane of the detec- | 散射屏和探测器之间。 where the 焦平面 of the 探测器
tor is set, as shown in Fig. 2. Furthermore, if the focal | is set ，如图2，更进一步，if the 焦平面
plane is set to the far side of the diffuser, the bright dots | is set to the 远端 of the 散射屏，the 亮点
should be seen in the air at the back of the diffuser. | should be seen 在空气中 at the 后面 of 散射屏
The experimental setup is shown in Fig. 3. In the be- | the 实验设置是图3 ，开始的时候
ginning, we conducted experiments in this section with- | 我们进行实验 in this 段 没有旋转 the 小的散射屏
out rotating the small diffuser. The wavelength of the la- | 激光波长是
ser diode was 532 nm. Emitted laser light was passed to | 530nm，出射激光 was 进行到
the small diffuser, and the diffused light was projected to | 小的散射屏，and the 散射光 投射到
a screen 1 m away. The speckle patterns on the screen | 1m外的屏幕，the 散斑图样 on the 屏幕
were measured with a CCD camera placed 1 m from the | were 测量 with a CCD 相机放置在1m距离
screen. In the actual small diffuser system, other optical | 屏幕。在实际的小散射屏系统，另外的光学
components such as a homogenizer and a micro-display | 元件 例如 均质 和 微型显示器
are also used (Fig. 1), but only those components illus- | are 也是用 图1，but 只有 those 元件
trated in Fig. 3 are essential to speckle reduction. The | 绘画出在图3 are 本质 to 散斑降低。the
photo in Fig. 4 shows a speckle pattern that appeared on | 照片在图4 表示一个散斑图样 that 出现在
the screen of the system. A coarse granular pattern can be | 系统的屏幕.一个粗糙的颗粒图样可以
seen. In addition, a ?ne granular pattern appears to be | 看到。附加的，一个细颗粒度的图样出现
superimposed on the coarse pattern. The graph in Fig. 5 | 叠加在粗粒度图样上。图5
shows the intensity distribution of the pixels along the | 示出强度分布 of 像素 沿着白虚线
white dotted line indicated in the speckle pattern. The | 表示的散斑图样
gradual bumps correspond to the coarse pattern, and the | 缓变的起伏对应粗图样
steep bumps correspond to the ?ne pattern. As the gen- | 陡变的起伏对因细图样
eration of this speckle pattern with two different super- | 产生的散斑图样有两个不同的叠加
imposed granular patterns is a unique characteristic of | 是系统的特点
the system, we analyzed the process that caused it. | 我们分析了过程 that 导致这个样子
Because the speckle is generated by diffusive media, | 因为散斑 is 产生 by 散射媒质
two components in this system could possibly generate it: | 两个元件 in this system 可以可能产生它：
the small diffuser and the screen. If the speckle shown in | 小的散射屏 和 屏幕，如果散斑 shown in
Fig. 4 were generated at the screen, it should have been | 图4产生在屏幕，它应该有被观察
observed even if the CCD camera were defocused from the | 就算 CCD相机离焦 from
screen, because the interference pattern should have ex- | 屏幕，因为干涉图样应该连续
isted continuously in the space between the screen and | 的存在于空间 between 屏幕和相机
the camera. If the speckle were generated at the small dif- | 如果散斑产生在小的散射屏
fuser, the pattern should have been affected by the | 图样应该被影响 by the
change in optical parameters of the projection lens, such | 改变 in 光学参数 of the 投影镜头，比如
as the F-number. Thus, by examining both cases, we were | F数，所以，by 考察两种情况，我们可以
able to clarify the speckle generation in the system. | 搞清楚 the 散斑的产生 in the 系统。
Speckle patterns in the mid-space can be observed by | 散斑图样 in the 中间空间 can be 观察到 by
changing the focal length of the CCD camera. We defo- | 改变焦距 of CCD相机(镜头的)，我们离焦
cused the focal plane of the camera by 500 mm from the | 那个焦平面 of 相机 by 500 mm 从屏幕算起
screen and compared the obtained patterns with the origi- | and 对比获得的图样 with 原始
nal ones. The resultant photos are shown in Fig. 6: the | 那个，结果图片如图6所示，左右
left and right photos show the no-defocusing and defocus- | 图像 表明 无离焦和离焦的情况
ing cases, respectively. The coarse aspect of the speckle | 分别的，粗糙的部分 of 散斑图样
pattern obviously disappeared after defocusing, and only | 明显消失 after 离焦，and 只有
the ?ne pattern remained. The persistence of the ?ne pat- | 细腻的图样留下，细图样的坚持
tern implied that it was generated at the screen, while | 暗示 that it was 产生在屏幕，当
the disappearance of the coarse pattern implied that it | 粗图样消失 暗示 that it
was generated at the small diffuser. | was 产生在小屏.
After resetting the focal plane of the camera to the | after 重设置 相机的焦平面 to the
screen, we changed the F-number of the projection lens to | 屏幕，我们改变f数of the 投影镜头 to
observe the effect of the optical condition change. The | 观察光学条件的影响，the
photos in Fig. 7 show the pattern change that occurred | 图是图7，示出图样改变 that 发生在
when we decreased the F-number from F/11 to F/4. The | 当我们降低f数从F/11到F/4。the
change in the granularity of the coarse pattern was con- | 改变 in 粒度 of the 粗糙图样 was 确定
?rmed, and the pattern was determined to have been gen- | and the 图样 was 确定 to have been 产生在
erated at the small diffuser. | 小屏
To determine whether the coarse pattern generated at | 要确定 是否 粗图样产生 at
the small diffuser was actually another speckle or just a | the 小屏 was 实际上另外一个 散斑 或者 只是一个
projected real image of the diffuser, we conducted another | 被投影的实像 of the 散射屏，我们构造了另外
experiment. Because the speckle was caused by the inter- | 一个实验，因为散斑 was 造成 by the 干涉 of
ference of diffused light, granular patterns should not | 散射光，粒度图样 应该不
have appeared if incoherent light were used. If the pat- | 出现 如果非相干光 were used.如果图样
tern had been a real image, it would have appeared re- | 是实像，it 将无论如何都会出现
gardless of the coherency of the light source. To con?rm | 而跟光源的相关性无关。to 确定这个
this, we changed the light source from a laser diode to an | 我们改变光源从LD到LED
LED (an incoherent light source) and measured the pat- | and 测量图样
terns at the screen directly. Figure 8 shows the experi- | 在屏幕上。图8示出
mental setup. As shown in the schematic, we removed the | 实验设置，表示的是原理，我们移除
screen and placed a CCD panel (without detector lens) at | 屏幕 and 将CCD探测面（没有镜头）放在
the position of the screen. The results are shown in Fig. 9. | 原来屏幕的地方。结果如图9
The pattern on the right was obtained with laser light | 图样在右边是LD的
and that on the left was obtained with an LED light | 左边的是LED的，粒度
source. The granular pattern appeared only when the la- | 粒度的图样之当使用LD时候出现
ser was used. The results clearly showed that the granu- | 结果清晰的表明 that the粒度图样
lar pattern generated at the small diffuser was actually | 产生 在小屏 was 实际上
another speckle. | 另外一个散斑
The speckle generation model that we obtained based | 散斑产生模型 that we 得到 基于
on these experiments is illustrated in Fig. 10. Two inde- | 这些实验 绘画在图10中，两个
pendent speckles exist in this system: a coarse speckle | 独立的散斑存在在系统里：一个粗糙散斑
generated at the small diffuser and a ?ne speckle gener- | 产生在小散射屏，一个细散斑产生在屏幕
ated at the screen. We call the former the primary speckle | 我们称前者为主要散斑后者为
and the latter the secondary speckle in this paper. | 次要散斑在文章里。
4. PHYSICAL ASPECTS OF THE | 4.物理方面 of the 粒度of 散斑图样
GRANULARITY OF SPECKLE PATTERNS
The small diffuser method reduces speckle on the screen | 小屏方法降低散斑在屏幕上
by rotating the small diffuser. Rotation of the diffuser cor- | by 旋转小屏。旋转of 小屏
responds to rotation of the primary speckle patterns pro- | 对应于旋转投射到屏幕的主散斑图样
jected on the screen. This means that speckle reduction is | 这意思就是，散斑降低 is
achieved by the movement of the primary speckle pat- | 达到by the 运动 of 主要散斑图样
terns on the screen. | 在屏幕上。
Although speckle patterns have a variety of complex | 虽然散斑图样有一个变化 of 复杂的
granular forms, they are fundamentally interference pat- | 粒度形式，他们基本的干涉图样
terns of diffused light. Bright regions of the patterns ap- | of 散射光。亮区域 of 图样出现
pear where light interferes constructively, and dark re- | 在光干涉加强，and 暗区域
gions appear where light interferes destructively. | 出现在光减弱
Constructive interference occurs when the light is in | 加强的相干出现在 光线 in
phase and destructive interference occurs when it is out of | 相位(同相) and 减弱的出现在反相
phase. Thus, speckle patterns can be considered an indi- | 所以，散斑图样可以考虑为一个指示器
cator of the underlying phase difference. From this point | of 底层 的相位差。从这个观点出发，
of view, the granularity of the speckle patterns indicates | 散斑图样的粒度指示了
how steeply the underlying phase difference is distrib- | 相位差的分布有多陡峭
uted. For example, a coarse speckle pattern should have a | 例如，粗糙的散斑图样应该有一个
relatively moderate phase difference change in a unit | 相对中等的相位差变化 in a 单位面积。
area.
Figure 11 shows the experimental setup that we used | 图11示出实验的设置 that 我们用来
to verify this hypothesis. A mask sheet with two pinholes | 验证这个假定。一个掩膜片 with 两个针孔
was placed at the screen position. Each pinhole had a di- | was 放置在屏的位置。每一个针孔 had a 直径
ameter of 70um, and they were separated by 300um. A | of 70um，and they were 分离了300um，一个
CCD camera was placed in front of the sheet. Light pass- | CCD相机 was放置于 掩膜片的前面。光线穿过
ing through these pinholes spread and formed an interfer- | 这些针孔扩散 and 形成一个干涉图样
ence pattern with a sine curve intensity shape on the | with a 正弦曲线的强度形状在CCD平面。
CCD panel. The change in the phase difference between | the 变化 in the 相位差 between
the holes shifted the position of the interference pattern | 孔便宜 the 位置 of 干涉图样 on the 平面。
on the panel. If the change in the phase difference was | 如果改变在相位上是1/2波长，
one-half of a wavelength, the pattern shifted its shape by | 图样偏移它的形状by 半个波长，
half a wavelength. Thus, if the speckle pattern re?ected | 那么，如果散斑图样反应了
the phase difference distribution, the resultant interfer- | 相位差的分布，the 结果的干涉图样
ence pattern should have shifted along with the primary | 应该和主散斑图样一样偏移。
speckle pattern.
The experimental results are shown in Fig. 12. We con- | 实验结果在图12中，我们构造
ducted experiments with two speckle patterns of different | 实验 with 两个散斑图样 of 不同
granularity by changing the F-number of the projection | 粒度 by 改变f数 of the 投影镜头。
lens. Results for the ?rst case, F/8, are shown in Figs. (a)– | 结果是第一个情况，F/8图a-d
(d) in the left column. The photo in (a) shows the speckle | 在左边的列，图片in a 表示散斑图样
pattern projected onto the pinholes (the photo was taken | 投射到针孔上（the 图片 was 取得
without the mask sheet of the double pinholes). The two | 没有掩膜片 of 双孔）。the 两个圆
circles indicate the relative sizes of the pinhole diameters | 表示相对尺寸 of 针孔直径
and gap against the pattern. As the speckle pattern | 和他们的间隙相对于图样，当散斑图样
moved across the pinholes, the interference pattern also | 移动通过针孔时，干涉图样也平移
shifted. Movement of the speckle pattern by 560um | 移动 of the散斑图样 by 560um
made the interference pattern shift by one wavelength. | 让干涉图样移动by 一个波长
This meant that the phase difference between the holes | 这表明 相位差 between the 孔
changed approximately with the wavelength of the laser | 改变大约with th 激光波长。
light. The second case, F/16, shown in (e)–(h) in the right | the 第二个情况，F/16，e-h图，右边的列
column, shows a coarser primary speckle pattern. The re- | 表示一个更粗糙的主要散斑图样。
sultant interference pattern barely shifted its position. | 结果干涉图样很少变化它的位置。
This meant that with the coarser primary speckle pat- | 这表明 更粗糙的主要散斑图样，
tern, the phase difference between the holes changed a | 相位差 between 两孔改变一点点。
little. These experimental results indicate that the pri- | 这个实验结果表明，主要
mary speckle pattern re?ects its phase difference distri- | 散斑图样反应它的相位差分布
bution and that the increment of the granularity of the | and that the 增量 of 粒度 of the
pattern decreases the phase difference in a unit area. | 图样 降低相位差在一个单位区域内
De?ning the degree of granularity of the speckle pat- | 定义粒度的度量 of 散斑图样
tern is convenient for further analysis. We de?ned this | is 方便 for 更进一步的分析。我们定义这个
from the intensity spectrum of the pattern in the spatial | 从强度谱 of the 图样 in the 空间域
frequency domain. Figure 13 is the Fourier transform of a | 图13 是傅立叶变换 of a
speckle pattern. We de?ned the degree of granularity as | 散斑图样。我们定义粒度的度量，as
the reciprocal number of the frequency, the intensity of | 倒数 of the 频率（空间频率单位lp/mm），
which is the half value of that of the lowest frequency in | 强度对应是半值 of the 最低频率在频谱上
the spectrum, excluding the DC component at the fre- | 不包括直流分量 在频域=0
quency equal to zero.
Because the speckle pattern represents its phase differ- | 因为散斑图样代表它的相位差分布
ence distribution, the physical effects of shifting the pat- | the 物理效应 of 移动图样 by
tern by rotation of the small diffuser can be deduced. As | 旋转小散射屏 就可以被推导。
shown in Fig. 14, when the speckle pattern on the sheet is | 如图14，当散斑图样 on the 薄片 is
rotated continuously, the phase difference between the | 连续的旋转，相位差 between
two pinholes also changes, and the resultant interference | 双针孔 也在变化。and the 结果干涉图样
pattern shifts. Consequently, the pattern measured by the | 移动了。所以，图样测量by
CCD camera is temporally averaged in intensity, and its | CCD相机 is 暂时的强度上平均，and 它的
contrast is reduced. The contrast of the averaged pattern | 对比度就降低了。对比度 of the 平均图样
depends on the change in the phase difference. As the dif- | 取决于相位差的变化。相位差
ference of the phases is larger when the granularity of the | 变大 当 粒度变小。更细的主要散斑
speckles is smaller, ?ner primary speckle patterns should | 图样应该产生更
result in ?atter interference patterns on the CCD. | 平的干涉图样在CCD上
Experimental results are shown in Fig. 15. As we | 实验结果如图15，
showed in the previous section, the granularity of the pri- | 正如之前展示的，粒度of 主要
mary speckle increased with the increment of the | 散斑增加 with F数增加 of
F-number of the projection lens. The degree of granularity | 投影镜头。the 粒度的度量
of the primary speckle patterns corresponding to each | of 主要散斑图样对应每个
F-number is also plotted. The solid horizontal line in the | F数也绘画出了。水平实线在图中
graph indicates the distance between the two pinholes. | 表示两个针孔的距离。
When the degree of granularity was smaller than the dis- | 当粒度的度量小于针孔间距
tance, the resultant interference pattern in (b) showed no | 产生的干涉图样是b，表示没有干涉
interference. This meant that when the small diffuser | 这表明当小散射屏旋转
was rotated, the phase difference change was large | 时，相位差变化 was 足够大
enough to reduce the temporally averaged coherency be- | 到降低暂时平均干涉性 在
tween the two pinholes. The middle pattern (c) is the case | 两针孔之间。中间的图样c情况是
when the degree of granularity was almost the same size | 当粒度的度量 几乎相同尺寸
as the distance between the pinholes. The resultant inter- | as 针孔间距。结果干涉
ference pattern showed little interference. The rightmost | 图样 表示一点干涉。最右边
pattern (d) shows the case for a much larger degree of | 的图样d表示大得多的粒度度量
granularity. In this case, interference can obviously be | 这样的情况下，干涉显然被辨认。
recognized.
These experimental results showed that the degree of | 这些实验结果说明，粒度的度量
granularity of the primary speckle corresponded to the | of 主要散斑 对应于 the
size of coherent region for the secondary speckle of the | 尺寸 of 干涉区域 for 次要散斑 of
screen, when the small diffuser was rotated. | 屏幕，当小散射屏旋转。
5. SPECKLE REDUCTION BY ROTATION OF | 5.散斑降低 by 旋转 of the 小散射屏
THE SMALL DIFFUSER
The results of the previous section explain the mechanism | 之前的结果解释了
of speckle reduction in the small diffuser system. When | 散斑降低机制 in 小散射板系统，当
the small diffuser was stationary, the secondary speckle | 小的散射板静止，次要散斑
generated at the screen was unaffected because no change | 产生在屏幕 was 不影因为没有变化
occurred in the interference conditions there. When the | 发生在干涉条件这里。当
small diffuser was rotated continuously, the movement of | 小散射板 was 持续旋转，移动 of
the primary speckle changed the interference condition | 主要散斑的干涉条件变化
on the screen. This affected the generation of the second- | 在屏幕上。这影响产生 of 次要散斑
ary speckle. Because the degree of granularity of the pri- | 因为粒度的度量 of 主要
mary speckle on the screen represented the size of the co- | 散斑在屏幕上代表干涉区域的尺寸
herent region, the contrast of the secondary speckle | 。对比度 of 次要散斑降低 as
decreased as the degree of granularity declined. | the 粒度的度量下降。
We con?rmed that the speckle reduction depended on | 我们确定 that the 散斑降低 依赖于
the degree of granularity as follows. We measured the | 粒度的度量如下：我们测量散斑
speckle contrasts on the screen by changing the degree of | 对比度在屏幕上 by 改变粒度的度量
granularity of the primary speckle. The speckle contrast | of 主要散斑。散斑的对比度
was calculated by dividing the standard deviation of the | 被计算 by 除以 标准差 of the
intensity distribution of the obtained speckle pattern by | 强度分布 of the 取得的散斑图样 by
its mean intensity. To improve its validity, we changed not | 它的平均强度。要提高它的置信度，我们改变
only the F-number of the projection lens but also its mag- | 不只是投影镜头F数，也改变了放大率和
ni?cation and the diffusing angle range of the small dif- | 散射角范围 of 小散射屏。
fuser. Figure 16 shows the result. As the degree of granu- | 图16示出结果。当粒度度量增加
larity increased, the corresponding speckle contrast also | 对应的散斑对比度也增加
increased. In every case when the granularity was | 在每一个情况下，当粒度改变，
changed, the resultant values lay on the same approxi- | 结果值坐落在同样的近似曲线上。
mate curve. This clearly showed that the degree of granu- | 这清晰的表明粒度的度量
larity of the primary speckle was the key parameter in | of 主要散斑是关键参数 in
speckle generation on the screen. | 屏幕上的散斑产生。
6. CONCLUSIONS | 6.结论
We have established a speckle generation model for the | 我们建立了一个散斑产生的模型 for
small diffuser method and found two speckles in the sys- | 小散射屏方法 and 找到两个散斑在系统：
tem: a coarse speckle generated at the small diffuser and | 一个粗糙散斑 产生在小散射屏 and
a ?ne speckle generated at the screen. These two speckles | 一个细的散斑产生在屏幕。这两个散斑
must be treated separately. | 必须区别对待。
From experiments using a mask sheet with double pin- | 从实验用掩膜片 with 双针孔，
holes, we con?rmed that the granular pattern of the | 我们确定粒度图样 of
speckles represented the underlying phase difference dis- | 散斑代表底层的相位差分布。
tribution. This meant that the ?ner speckle pattern had a | 这表明 细微散斑图样有
steeper phase difference change. When the primary | 更剧烈的相位差改变。当主要
speckle pattern moved as a result of the rotation of the | 散斑图样移动 as a result of the 旋转of
small diffuser, the granularity of the pattern determined | 小散射屏，图样的粒度 确定了
the coherency within a unit area on the screen, and the | 干涉性 在一个单位面积之内在屏幕上。
degree of granularity corresponded to the coherent area | and the 粒度的度量对应干涉区域尺寸
size.
The dependency of the coherency on the degree of | 干涉性对粒度的度量的依赖
granularity determined the speckle contrast on the screen | 确定了散斑对比度 在屏幕上
when the diffuser was rotated. The speckle contrast in- | 当散射屏旋转 。散斑对比度增加
creased with the degree of granularity. Hence the degree | with 粒度的度量增加。所以粒度的度量
of granularity can be used as a uni?ed index when dis- | 可以用做一个统一的指数 当
cussing speckle reduction effects. | 讨论散斑降低效应。
From these results, we have obtained a valid speckle | 从这些结果出发，我们获得了可用的散斑
generation model and clari?ed the mechanism of speckle | 产生模型 and 澄清了散斑降低的机制
reduction in the small diffuser method. | in 小散射屏方法。
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