projection systems for commercial and consumer applications. The DMD is also an
attractive Spatial Light Modulator for applications that may use monochromatic and/or
coherent light sources both inside and outside of the visible spectrum.
The DLP
The DMD presents some unique advantages and considerations that must be
understood for these applications particularly when using coherent or semi-coherent
sources with the DMD. When used with such sources the fact that the DMD is a 2D
array of periodically spaced mirrors cannot be ignored, rather the diffractive effects can
be understood and even exploited.
The purpose of this paper is to present an intuitive understanding of the 2D
diffraction properties of the DMD and the advantages and challenges that result.
Understanding Diffraction – an intuitive view
Single Slit Diffraction.
To begin our journey lets consider diffraction from a single slit. We will assume
that the length of the slit is much larger than the height “a” of the slit so that the
dimension along the slit is not considered. We will also assume that the distance “D” to
the “screen” is very much larger than the slit width. If the incident light is a
monochromatic plane wave then there will be some angles in which the overall light from
the slit will constructively interfere and others that will destructively interfere giving rise
to light and dark bands on the screen.* The following link has a great illustration: Single-
Slit Diffraction.
Now let us replace the flat screen with a cylindrical screen centered on the slit and
let the distance to the screen be “R”, the radius of the semicircle. Then for every angle to
the screen we can project back to the plane of the slit such that we can now map every
* If we take the normal to the plane of the slit opening (also normal to the screen) as 0 degrees and the
center of the slit as the origin, then the intensity at the screen will be proportional to
2
sin( )
sin sin( )
U
U
[the “Sinc” function where the argument is in (U sin())]. Derivation of the intensity
can be found in numerous texts on slit diffraction
May not be reproduced without the permission of Texas Instruments Incorporated
Copyright 2008 Texas Instruments Incorporated
ZHCA614
激光器和 DLP®
TI DN 2509927
2008 年 9 月
采用激光器和 DLP® DMD 技术
目的
DLP® 数字微镜器件 [DMD] 一直在面向商业和消费应用的视频投影系统中使用。对于那些有可能采用位于可
见光谱之内和/或之外的单色或相干光源的应用而言，DMD 也是一种富有吸引力的空间光调制器。
针对此类应用，必须了解 DMD 带来的一些独特优势与考虑因素，特别是在把相干或半相干光源与 DMD 一
起使用的时候。当与这些光源一起使用时，不可忽视DMD 是一种规则重复空间排列的反射镜二维阵列这一
事实，同时要充分理解乃至利用其衍射效应。
本文旨在帮助读者直观地了解 DMD 的二维衍射特性，以及由此带来的优点和挑战。
spatial light modulator for use with coherent
light applications. The reflective nature of our device allows large amounts of light
energy to be modulated with a modicum absorbed by the device.
另外，在使用 DMD 和相干光时还有一些源于衍射本质的特殊考虑因素：
• 对于给定的波长和像素间距，衍射级仅由入射角固定于方向空间（反射镜的开关切换不会使其移动）。
• 衍射级的光强包络由反射镜的形状（对于 DMD 而言是正方形）决定，因而无法在不影响所有其他衍射
级的情况下任意地对个别衍射级进行消光。
结论
DLP® DMD 是一种富有
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