16383twf.doc/g 九、發明說明： 【發明所屬之技術領域】 本發明是有關於一種背投影顯示裝置（Rear pr〇jecti〇n Apparatus)，且特別是有關於一種利用反射式之弗瑞涅爾 反射鏡片（Fresnelmirror)的背投影顯示裝置。 【先前技術】 由於光學技術的快速發展，許多顯示裝置已經被開發 出來並應用到日常生活中。其中，背投影顯示裝置具有大 尺寸顯示以及高對比度等優點，因此其被視為顯示器中的 一重要發展趨勢。一般而言，背投影顯示裝置是觀察者與 投影機分別位在螢幕的兩側’觀察者藉由投影機從螢幕上 透射出來的投影光線而觀看圖像。 圖1繪示為習知的背投影顯示裝置的結構示意圖。請 參照圖1 ’習知的背投影顯示裝置100包括光學引擎H0、 投影鏡頭120、反射鏡130以及一螢幕140。其中，光學引 擎110包括光源112以及顯示元件114。光源112會發出 一光束150 ’且在光源112的前方設置一透鏡ina以匯聚 光束150。|貞示元件114位於光束150之傳遞路徑上，此 光束150經由顯示元件114之作用而形成影像光束16〇。 投影鏡頭120位於顯示元件114之後的影像光束160之傳 遞路徑上。反射鏡130位於投影鏡頭120之後的影像光束 160之傳遞路徑上’且影像光束16〇經由反射鏡13〇之反 射而到達螢幕140。此螢幕14〇位於反射鏡130之後的影 像光束160之傳遞路徑上，此影像光束16〇投影在螢幕140 1323789 16383twf.doc/g 上而形成影像。 習知的螢幕140結構中具有一弗瑞淫爾透鏡i42 (F_d iens)，且此弗瑞涅爾透鏡142為穿透式透鏡系 統。也就是說，影像光束16〇會入射到弗瑞埋爾透鏡⑷ 内進行折射而調整其行進方向後，再料幕⑽上形成影 像。圖2繪示為弗瑞;圼爾透鏡的局部放大示意圖。請參昭、 圖2’弗瑞淫爾透鏡142具有多個凹槽角他。影像光束、 160會自凹槽角142a進入弗瑞㈣透鏡142中，並在弗瑞 朗透鏡142中進行折射而改變其行進方向。—般而言， 凹槽角142a之間會有一螺距·(pitch)，利用螺距⑽ 的調整而可以改變影像光束_之行進方向 光束160更加平行化。 于〜像 由於衫像光束16G是透過折射的方式行進，所以 光束160會受到弗瑞淫爾透鏡142之臨界角（她㈣&响） 的限制。當影像光束16G之人射角度太大時，會使得影 光束160無法在弗瑞_透鏡142中產生折射，所以影像 光束⑽將無法形成平行光。因此，螢幕140的功效便無 另夕卜，右要使折射順利進行’則必須使弗瑞淫爾 透’兄 H定的厚度d’且需—併考慮其 之空間位置的設置。 千几1干 更詳、，’田而5，為了使背投影顯示裝置100之厚度縮 減’而調整其他光學元件之設置的作法，將產生下述的問 題丄圖3繪示為習知背投影顯示裝置中之影像光束的行進 不意圖。請參照圖3，如圖3巾所示之A位置為影像光克 160所預定到達的位置，一般而言’欲使背投影顯示裝置 7 16383twf.doc/g 100的厚度減小時，反射鏡13〇會相對移動到反射鏡13〇, 的位置’因此’根據光學的反射定律，此時影像光=160 將反射到B位置，而未能到達所預定的A位置。所以背 投影顯示裝置100將面臨到無法使影像光束16〇的反射g 度增大到所需要的反射角度之問題。 ^ 承上述’習知的作法會將反射鏡13〇傾斜一角度θ， 而使得影像光束160得到所需要的反射角度。圖4^示\ 傾斜反射鏡的示意圖❹請共同參照圖3與圖4，當所 需要的出射角度Θ2，則可利用θρ=90 —〇.5 (θ2—之公 式，調整傾斜反射鏡130的角度θρ，其中θι為影1像光^ 160的入射角度。因此，如圖3中反射到之Β位置的影像 光束160b ’即可經由傾斜之反射鏡130的作用，而形成到 達A位置的影像光束160a。但是，此傾斜反射鏡13〇的作 法，將會使得反射鏡130所佔用的空間增大，所以，如背 投影顯示裝置100也無法因此而做得更薄。 【發明内容】 有鑑於此，本發明的目的就是在提供一種背投影顯示 裝置，其可β更容易地改變影像光束的行進方向，並進而 降低背投影顯示裝置的厚度。 基於上述目的或其他目的，本發明提出一種背投影顯 示裝置，包括一光學引擎、一投影鏡頭、一弗瑞淫爾反射 鏡片以及一螢幕。其中，光學引擎包括一光源以及一顯示 元件。光源發出一光束。而顯示元件位於光束之傳遞路徑 上，此光束經由顯示元件之作用而形成一影像光束。投影 鏡頭位於顯示元件之後的影像光束之傳遞路徑上。弗瑞涅</ RTI> </ RTI> </ RTI> </ RTI> </ RTI> </ RTI> </ RTI> </ RTI> </ RTI> </ RTI> </ RTI> </ RTI> </ RTI> </ RTI> </ RTI> < Desc/Clms Page number> Rear projection display device of Fresnel mirror. [Prior Art] Due to the rapid development of optical technology, many display devices have been developed and applied to daily life. Among them, the rear projection display device has the advantages of large-size display and high contrast, and thus it is regarded as an important development trend in the display. In general, the rear projection display device is such that the viewer and the projector are positioned on both sides of the screen, respectively, and the viewer views the projected light transmitted from the screen by the projector. FIG. 1 is a schematic structural view of a conventional rear projection display device. Referring to FIG. 1 'The conventional rear projection display device 100 includes an optical engine H0, a projection lens 120, a mirror 130, and a screen 140. The optical engine 110 includes a light source 112 and a display element 114. Light source 112 emits a beam 150' and a lens ina is placed in front of source 112 to concentrate beam 150. The display element 114 is located on the transmission path of the beam 150, and the beam 150 forms an image beam 16〇 via the action of the display element 114. Projection lens 120 is located on the path of the image beam 160 behind display element 114. The mirror 130 is located on the transmission path of the image beam 160 after the projection lens 120 and the image beam 16 is reflected by the mirror 13 to reach the screen 140. The screen 14 is located on the transmission path of the image beam 160 behind the mirror 130. The image beam 16 is projected onto the screen 140 1323789 16383 twf.doc/g to form an image. The conventional screen 140 structure has a Fresnel lens i42 (F_d iens), and this Fresnel lens 142 is a transmissive lens system. That is to say, the image beam 16〇 is incident into the Freire lens (4) to refract and adjust its traveling direction, and then the image is formed on the rewinding screen (10). 2 is a partially enlarged schematic view of a Furui lens. Please refer to Figure 2, where the Frey sinus lens 142 has a plurality of groove angles. The image beam, 160, enters the Frey (four) lens 142 from the groove angle 142a and is refracted in the Frelang lens 142 to change its direction of travel. In general, there is a pitch between the groove angles 142a, and the direction of the image beam _ can be changed by the adjustment of the pitch (10). The beam 160 is more parallelized. Since the shirt image beam 16G travels through refraction, the beam 160 is limited by the critical angle of the Frei lens 142 (her (four) & ringing). When the angle of incidence of the image beam 16G is too large, the shadow beam 160 cannot be refracted in the Fresnel lens 142, so the image beam (10) will not be able to form parallel light. Therefore, the effect of the screen 140 is no longer necessary, and the right is to make the refraction smoothly.] The Fury must be made to have a thickness d' and need to be considered - and consider the spatial position setting. A thousand and a few more detailed, 'Tian 5, in order to reduce the thickness of the rear projection display device 100' and adjust the arrangement of other optical components, will produce the following problems. Figure 3 shows a conventional rear projection The travel of the image beam in the display device is not intended. Referring to FIG. 3, the position A shown in FIG. 3 is the position where the image light gram 160 is scheduled to arrive. Generally, when the thickness of the rear projection display device 7 16383 twf.doc/g 100 is reduced, the mirror 13 is reduced. 〇 will move relative to the mirror 13〇, the position 'so' according to the optical law of reflection, at this time the image light = 160 will be reflected to the B position, but failed to reach the predetermined A position. Therefore, the rear projection display device 100 will face the problem that the reflection g of the image beam 16 无法 cannot be increased to the required reflection angle. ^ The conventional practice described above tilts the mirror 13 一 by an angle θ such that the image beam 160 achieves the desired angle of reflection. 4 is a schematic view of the tilting mirror. Referring to FIG. 3 and FIG. 4 together, when the required exit angle Θ2, the tilt mirror 130 can be adjusted by using the formula θρ=90 —〇.5 (θ2−). The angle θρ, where θι is the incident angle of the image 1 image 160. Therefore, the image beam 160b' reflected to the position of the image in FIG. 3 can form an image reaching the A position via the action of the tilting mirror 130. The light beam 160a. However, the practice of tilting the mirror 13A will increase the space occupied by the mirror 130, so that the rear projection display device 100 cannot be made thinner as a result. Accordingly, it is an object of the present invention to provide a rear projection display device which can more easily change the traveling direction of an image beam and thereby reduce the thickness of the rear projection display device. Based on the above object or other objects, the present invention provides a back. The projection display device comprises an optical engine, a projection lens, a Fresnel reflection lens and a screen, wherein the optical engine comprises a light source and a display element. Out of a light beam, while the display element is located on the transmission path of the light beam, this light beam passing through the active element of the display light beam to form an image. After the transfer of the image beam path of the projection lens element located on the display. Fu Ruinie