200832046 九、發明說明： 【發明所屬之技術領域】 本發明係關於一種顯示系統及其光導管，特別關於一 種投影系統及其光導管。 【先前技術】 由於大顯示面積、小型化以及輕量化系統的多重需求 下，影像投影系統成為目前光電產業中最熱門的分項之 ——" 〇 請參閱圖1所示，影像投影系統在此簡稱為投影系統 1，其係具有一光源10、一色輪組件11、一光導管（Light Tunnel) 12、一透鏡組件13、一數位微鏡元件（Digital Micro-mirror Device，DMD) 14 及一投射單元 15。光源 10係發射光線至色輪組件11後進入光導管12，再經由透 鏡組件13聚焦至數位微鏡元件14上，藉由驅動電極控制 數位微鏡元件14上複數微反射鏡（圖中未示）之傾斜角 度及偏轉時間，切換光的反射方向，再經由投射單元15 投射至一螢幕16上而成像。 請同時參閱圖1及圖2,習知之光導管12主要係由四 片光學元件121所組成，組裝時利用治具來固定四片光學 元件121後，再以一黏著劑122塗佈於兩兩光學元件121 之交接處，使該等光學元件121相互接合。由於，光導管 12之内表面係具有一反射層，因此當光源10所發射之光 束經由一入口端123進入光導管12後，經由反射層多次 200832046 反射後由出口端124輸出，可使光線亮度變得均勻化。 然而，於實際組裝光導管12時，光學元件121與光 學元件121間必須藉由黏著劑122黏合。當使用過多的黏 著劑122時，於固化後，黏著劑122之厚度容易影響該等 光學元件121之對位精準，進而影響光線的均勻度。此外， 於組裝光導管12時，黏著劑122也可能溢入光導管12之 内表面，進而影響光導管12之出光品質，確實有待改進。 【發明内容】 有鑑於上述課題，本發明之目的為提供一種投影系統 及其光導管，具有對位精準、組裝容易及不易溢膠之優點。 緣是，為達上述目的，依本發明之光導管包含複數光 學元件與一黏著劑，至少其中之一光學元件之一端係具有 一第一凹部，黏著劑係黏合光學元件而形成一光通道，至 少一部分之黏著劑係位於第一凹部中。 為達上述目的，依本發明之投影系統包含一光源、一 色輪組件及一光導管。其中，色輪組件係設置於光源之一 側。光導管具有複數光學元件與一黏著劑，至少其中之一 光學元件之一端係具有一第一凹部，黏著劑係黏合光學元 件而形成一光通道，至少一部分之黏著劑係位於第一凹部 中0 承上所述，本發明之投影系統及其光導管係具有凹 部，相較習用結構而言，黏著劑之至少一部分係位於凹部 之中。藉由凹部之設置，可使得黏著劑不易溢入該等光學 200832046 元件面對光通道之一面，故可確保光導管之出光品質。另 外，於組裝該等光學元件時，可避免因為黏著劑使用過 量，進而影響該等光學元件於組裝對位時的精準度。 【實施方式】 以下將參照相關圖式，說明依本發明較佳實施例之投 影系統及其光導管。 請參閱圖3，係為本發明第一實施例之光導管2，包 含複數光學元件21、22、23、24及一黏著劑G。 於本實施例中，該等光學元件21、22、23、24係分 別為一第一光學元件21、一第二光學元件22、一第三光 學元件23及一第四光學元件24。其中，該等光學元件21、 22、23、24之排列方式，係以第一光學元件21與第二光 學元件22係呈錯位設置，而第三光學元件23係與第四光 學元件24係呈錯位設置為例。 另外，至少其中之一光學元件之一端係具有一第一凹 部211。於本實施例中，第一凹部211係設置於第一光學 元件21之一端，而第一凹部211係為一凹槽，當然，第 一凹部211亦可為一凹窩或一凹坑，此外，第一凹部211 之長度係約等於第一光學元件21之長度設置。 當然，第一凹部211之數量與長度係可不受限制。如 圖4所示，第一光學元件21之一端係可具有二第一凹部 21Γ，該等第一凹部21Γ之長度亦可小於第一光學元件21 之長度，而該等第一凹部21Γ係分別設置於第一光學元件 200832046 21之前後區域。 請再參閱圖3，於本實施例中，光導管2係以各光學 元件分別具有一凹部為例，第二光學元件22具有一第二 凹部221，第三光學元件23具有一第三凹部231，而第四 光學元件24具有一第四凹部241。其中，第一光學元件 21之第一凹部211係鄰設於第三光學元件23 ;第二光學 元件22之第二凹部221係鄰設於第四光學元件24 ;第三 光學元件23之第三凹部231係鄰設於第二光學元件22 ; 而第四光學元件24之第四凹部241係鄰設於第一光學元 件21。當然，第二凹部221、第三凹部231及第四凹部241 之數量及設置位置係可配合實際需要而改變。 如圖3所示，黏著劑G係黏合該等光學元件21、22、 23、24而形成一光通道L。於黏合接著面時，過多的黏著 劑G係可流入於第一凹部211中，以避免固化後黏著劑G 的厚度會影響了該等光學元件21、22、23、24之對位。 當然，於黏合時也可直接將第一凹部211填滿。於本實施 例中，部分黏著劑G也同樣位於第二凹部221、第三凹部 231及第四凹部241中。 由於，部分黏著劑G係位於該等凹部211、22卜231、 241之中，故於組裝該等光學元件21、22、23、24時，黏 著劑G之厚度便不會影響該等光學元件21、22、23、24 之對位，進而能提升該等光學元件21、22、23、24之組 裝精準度。此外，由於該等凹部211、221、231、241之 設置，使得黏著劑G不易溢入該等光學元件21、22、23、 200832046 24面對光通道L之一面，而不易影響光通道L之出光品質。 另外，光導管21之該等光學元件21、22、23、24亦 可具有其他不同結構形狀之變化。 如圖5所示，第一光學元件21之一端21a具有一第一 嵌槽212 ;第二光學元件22之一端22a具有一第二嵌槽 222 ;第三光學元件23之一端23a具有一第三嵌槽232 ; 第四光學元件24之一端24a具有一第四嵌槽242。如此一 來，第一光學元件21之另一端21b係設置於第三嵌槽232 中；第二光學元件22之另一端22b係設置於第四嵌槽242 中；第三光學元件23之另一端23b係設置於第二嵌槽222 中；第四光學元件24之另一端24b係設置於第一嵌槽212 中。 於本實施例中，第一嵌槽212與第一凹部211係分別 位於第一光學元件21之二端21a、21b ;第二嵌槽222與 第二凹部221係分別位於第二光學元件22之二端22a、 22b ;第三嵌槽232與第三凹部231係分別位於第三光學 元件23之二端23a、23b ;而第四嵌槽242與第四凹部241 係分別位於第四光學元件24之二端24a、24b。當然，亦 可將該等嵌槽212、222、232、242與該等凹部211、221、 231、241分別設置於該等光學元件21、22、23、24之同 一端。 接著，請參閱圖6，係為本發明第二實施例之光導管 3，包含複數光學元件31、32、33、34及一黏著劑G。 於本實施例中，該等光學元件31、32、33、34係分 200832046 別為第一光學元件31、第二光學元件32、第三光學元件 ' 、 33及第四光學元件34。其中，第一光學元件31係與第二 •、 光學元件32相對而設，第三光學元件33係與第四光學元 ， 件34相對而設。 另外，至少其中之一光學元件之一端係具有一第一凹 部311。於本實施例中，第一凹部311係位於第一光學元 件31之一端，而第一光學元件31之另一端更具有另一第 一凹部312，且該等第一凹部311、312係分別位於第一光 f 學元件31相對之二表面。此外，該等第一凹部311、312 係分別鄰設於第三光學元件33及第四光學元件34。 第二光學元件32係具有二第二凹部321、322，該等 第二凹部321、322係分別位於第二光學元件32之二端， 且位於第二光學元件32相對之二表面。此外，該等第二 凹部321、322係分別鄰設於第三光學元件33及第四光學 元件34。 於實際組裝光導管3時，係利用治具由兩兩光學元件 % 交接處進行點膠，過多的黏著劑G則會流入該等凹部 311、312、321、322。待固化後，黏著劑G係黏合該等光 學元件31、32、33、34而形成一光通道L，且部分黏著劑 G係位於該等凹部311、312、321、322之中。 由於該等凹部311、312、321、322之設置，使得該 等光學元件31、32、33、34於對位時，不會因為黏著劑G 之用量而影響了對位的精度。相較習用結構而言，黏著劑 G也不容易溢入該等光學元件31、32、33、34面對光通道 200832046 L之一面，使得影響光導管3之出光品質。 於本發明第二實施例之光導管3中，該等凹部311、 312、32卜322係分別位於光學元件31、32之二端，且位 於光學元件31、32相對之二表面，當然，亦可將改變該 等凹部311、312、321、322之設置位置。 如圖7所示，該等第一凹部313、314係位於第一光 學元件31之同一表面，該等第二凹部323、324係位於第 —光學元件32之同一表面。如此一來，第一凹部313與 第二凹部323係分別面對第三光學元件33之二端，而第 一凹部314與第二凹部324係分別面對第四光學元件34 之二端，使得位於該等凹部313、314、323、324之黏著 劑G係可黏合該等光學元件31、32、33、从。 隶後，請參閱圖8，以說明本發明較佳實施例之投影 系統4。 投影糸統4具有一光源40、一色輪組件41、一光導 管42、一透鏡組件43、一數位微鏡元件44及一投射單元 45。其中，色輪組件41係鄰設於光源4〇之一側，而光導 管42係可設置於光源40與色輪組件41之間或是設置於 色輪組件41相對於光源40的一側。 當光源40之光線經過色輪組件41、光導管42、透鏡 組件43、數位微鏡元件44及投射單元45而於一螢幕46 成像之方式係為習知技術，在此容不贅述。 另外，本實施例中之光導管42結構，係可與第一實 施例中之光導管2或第二實施例中之光導管3相同，在此 11 200832046 亦容不贅述。 承上所述，本發明之投影系統及其光導管係具有凹 部，相較習用結構而言，黏著劑之至少一部分係位於凹部 之中。藉由凹部之設置，可使得黏著劑不易溢入該等光學 元件面對光通道之一面，故可確保光導管之出光品質。另 外，於組裝該等光學元件時，可避免因為黏著劑使用過 量，進而影響該等光學元件於組裝對位時的精準度。 以上所述僅為舉例性，而非為限制性者。任何未脫離 本發明之精神與範轉，而對其進行之等效修改或變更，均 應包含於後附之申請專利範圍中。 【圖式簡單說明】 圖1係為習知之一投影系統之一示意圖； 圖2係為習知之一光導管之一示意圖； 圖3係為本發明第一實施例之光導管之一示意圖； 圖4係為本發明第一實施例之光導管之一示意圖，係 顯示第一光學元件具有二第一凹部之態樣； 圖5係為本發明第一實施例之光導管之一示意圖，係 顯示該等光學元件分別具有嵌槽之態樣； 圖6係為本發明第二實施例之光導管之一示意圖； 圖7係為本發明第二實施例之光導管之一示意圖，係 顯示凹部位於光學元件同一表面之態樣；以及 圖8係為本發明較佳實施例之投影系統之一示意圖。 12 200832046 元件符號說明： 1 投影系統 10 光源 11 色輪組件 12 光導管 121 光學元件 122 黏著劑 123 入口端 124 出口端 13 透鏡組件 14 數位微鏡元件 15 投射單元 16 螢幕 2 光導管 21 第一光學元件 21a 第一光學元件之一端 21b 第一光學元件之另一端 211 第一凹部 211， 第一凹部 212 第一嵌槽 22 第二光學元件 22a 第二光學元件之一端 22b 第二光學元件之另一端 221 第二凹部 13 200832046 222 第二嵌槽 23 第三光學元件 23a 第三光學元件之一端 23b 第三光學元件之另一端 231 第三凹部 232 第三嵌槽 24 第四光學元件 24a 第四光學元件之一端 24b 第四光學元件之另一端 241 第四凹部 242 第四嵌槽 3 光導管 31 第一光學元件 311 第一凹部 312 第一凹部 313 第一凹部 314 第一凹部 32 第二光學元件 321 第二凹部 322 第二凹部 323 第二凹部 324 第二凹部 33 第三光學元件 34 第四光學元件 14 200832046 4 投影系統 40 光源 41 色輪組件 42 光導管 43 透鏡組件 44 數位微鏡元件 45 投射單元 46 螢幕 G 黏著劑 L 光通道200832046 IX. DESCRIPTION OF THE INVENTION: TECHNICAL FIELD The present invention relates to a display system and a light pipe therefor, and more particularly to a projection system and a light pipe therefor. [Prior Art] Due to the large display area, miniaturization and multiple requirements of lightweight systems, image projection systems have become the most popular sub-items in the optoelectronic industry - " Please refer to Figure 1, the image projection system is This is simply referred to as a projection system 1 having a light source 10, a color wheel assembly 11, a light tunnel 12, a lens assembly 13, a digital micro-mirror device (DMD) 14 and a Projection unit 15. The light source 10 emits light to the color wheel assembly 11 and enters the light pipe 12, and then is focused onto the digital micromirror device 14 via the lens assembly 13, and the plurality of micromirrors on the digital micromirror device 14 are controlled by the driving electrodes (not shown) The tilting angle and the yaw time are switched, and the direction of reflection of the light is switched, and then projected onto a screen 16 via the projection unit 15 for imaging. Referring to FIG. 1 and FIG. 2 simultaneously, the conventional light guide 12 is mainly composed of four optical elements 121. After assembling, four optical elements 121 are fixed by using a fixture, and then coated with an adhesive 122. The intersection of the optical elements 121 causes the optical elements 121 to engage each other. Since the inner surface of the light pipe 12 has a reflective layer, when the light beam emitted by the light source 10 enters the light pipe 12 via an inlet end 123, it is reflected by the reflection layer multiple times 200832046 and then outputted by the outlet end 124, so that the light can be made. The brightness becomes uniform. However, when the light guide 12 is actually assembled, the optical member 121 and the optical member 121 must be bonded by the adhesive 122. When too much adhesive 122 is used, the thickness of the adhesive 122 tends to affect the alignment accuracy of the optical elements 121 after curing, thereby affecting the uniformity of light. In addition, when the light pipe 12 is assembled, the adhesive 122 may also overflow into the inner surface of the light pipe 12, thereby affecting the light quality of the light pipe 12, which is indeed to be improved. SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide a projection system and a light guide thereof, which have the advantages of accurate alignment, easy assembly, and difficulty in overflowing. In order to achieve the above object, the light guide according to the present invention comprises a plurality of optical elements and an adhesive, at least one of the optical elements has a first recess at one end, and the adhesive adheres the optical element to form an optical passage. At least a portion of the adhesive is located in the first recess. To achieve the above object, a projection system according to the present invention comprises a light source, a color wheel assembly and a light guide. Wherein, the color wheel assembly is disposed on one side of the light source. The light guide has a plurality of optical elements and an adhesive, and at least one of the optical elements has a first recess at one end, the adhesive bonding the optical element to form a light passage, and at least a part of the adhesive is located in the first recess. As described above, the projection system of the present invention and its light guide have recesses in which at least a portion of the adhesive is located in the recess as compared to conventional structures. By the arrangement of the recesses, the adhesive is not easily spilled into the optics. 200832046 The component faces one side of the optical channel, thus ensuring the light quality of the light guide. In addition, when the optical components are assembled, the use of the adhesive can be avoided, which in turn affects the accuracy of the optical components when they are assembled. [Embodiment] A projection system and a light guide thereof according to a preferred embodiment of the present invention will be described below with reference to the related drawings. Referring to Fig. 3, a light guide 2 according to a first embodiment of the present invention comprises a plurality of optical elements 21, 22, 23, 24 and an adhesive G. In the present embodiment, the optical elements 21, 22, 23, and 24 are a first optical element 21, a second optical element 22, a third optical element 23, and a fourth optical element 24, respectively. The optical elements 21, 22, 23, and 24 are arranged such that the first optical element 21 and the second optical element 22 are misaligned, and the third optical element 23 and the fourth optical element 24 are arranged. The misalignment is set as an example. Further, at least one of the optical elements has a first recess 211 at one end. In this embodiment, the first recess 211 is disposed at one end of the first optical component 21, and the first recess 211 is a recess. Of course, the first recess 211 can also be a dimple or a dimple. The length of the first recess 211 is approximately equal to the length of the first optical element 21. Of course, the number and length of the first recesses 211 are not limited. As shown in FIG. 4, one end of the first optical element 21 may have two first recesses 21, and the length of the first recesses 21Γ may be smaller than the length of the first optical element 21, and the first recesses 21 are respectively The front region is disposed before the first optical element 200832046 21 . Referring to FIG. 3 again, in the embodiment, the light guide 2 is exemplified by each of the optical elements having a concave portion, the second optical element 22 has a second concave portion 221, and the third optical element 23 has a third concave portion 231. And the fourth optical element 24 has a fourth recess 241. The first concave portion 211 of the first optical element 21 is disposed adjacent to the third optical element 23; the second concave portion 221 of the second optical element 22 is disposed adjacent to the fourth optical element 24; and the third of the third optical element 23 The concave portion 231 is adjacent to the second optical element 22; and the fourth concave portion 241 of the fourth optical element 24 is adjacent to the first optical element 21. Of course, the number and arrangement positions of the second recess 221, the third recess 231, and the fourth recess 241 can be changed according to actual needs. As shown in FIG. 3, the adhesive G bonds the optical elements 21, 22, 23, and 24 to form an optical path L. When the adhesive is applied to the face, an excessive amount of the adhesive G can flow into the first recess 211 to prevent the thickness of the adhesive G from affecting the alignment of the optical members 21, 22, 23, 24 after curing. Of course, the first recess 211 can also be filled directly when bonding. In the present embodiment, the partial adhesive G is also located in the second recess 221, the third recess 231, and the fourth recess 241. Since the partial adhesive G is located in the recesses 211, 22, 231, and 241, the thickness of the adhesive G does not affect the optical components 21, 22, 23, and 24 when the optical components 21, 22, 23, and 24 are assembled. The alignment of 21, 22, 23, and 24 can further improve the assembly accuracy of the optical components 21, 22, 23, and 24. In addition, due to the arrangement of the concave portions 211, 221, 231, and 241, the adhesive G does not easily overflow into one of the optical elements 21, 22, 23, 200832046 24, and does not easily affect the optical channel L. Light quality. In addition, the optical elements 21, 22, 23, 24 of the light pipe 21 may also have variations in other different structural shapes. As shown in FIG. 5, one end 21a of the first optical element 21 has a first recess 212; one end 22a of the second optical element 22 has a second recess 222; and one end 23a of the third optical element 23 has a third end. The slot 232; one end 24a of the fourth optical component 24 has a fourth slot 242. In this way, the other end 21b of the first optical component 21 is disposed in the third recess 232; the other end 22b of the second optical component 22 is disposed in the fourth recess 242; the other end of the third optical component 23 23b is disposed in the second recess 222; the other end 24b of the fourth optical component 24 is disposed in the first recess 212. In this embodiment, the first recess 212 and the first recess 211 are respectively located at the two ends 21a, 21b of the first optical component 21; the second recess 222 and the second recess 221 are respectively located in the second optical component 22. The second end 22a, 22b; the third recess 232 and the third recess 231 are respectively located at the two ends 23a, 23b of the third optical element 23; and the fourth recess 242 and the fourth recess 241 are respectively located at the fourth optical element 24 The two ends 24a, 24b. Of course, the cavities 212, 222, 232, 242 and the recesses 211, 221, 231, 241 may be disposed at the same end of the optical elements 21, 22, 23, 24, respectively. Next, referring to Fig. 6, a light guide 3 according to a second embodiment of the present invention includes a plurality of optical elements 31, 32, 33, 34 and an adhesive G. In the present embodiment, the optical elements 31, 32, 33, 34 are divided into the first optical element 31, the second optical element 32, the third optical element ', 33, and the fourth optical element 34, respectively. The first optical element 31 is provided opposite to the second optical element 32, and the third optical element 33 is provided opposite to the fourth optical element and the element 34. Further, at least one of the optical elements has a first recess 311 at one end. In this embodiment, the first recess 311 is located at one end of the first optical element 31, and the other end of the first optical element 31 has another first recess 312, and the first recesses 311, 312 are respectively located. The first optical element 31 is opposite the two surfaces. Further, the first concave portions 311 and 312 are respectively disposed adjacent to the third optical element 33 and the fourth optical element 34. The second optical element 32 has two second recesses 321 and 322 respectively located at two ends of the second optical element 32 and on opposite surfaces of the second optical element 32. Further, the second concave portions 321, 322 are adjacent to the third optical element 33 and the fourth optical element 34, respectively. When the light pipe 3 is actually assembled, the jig is dispensed by the junction of the two optical elements, and the excess adhesive G flows into the recesses 311, 312, 321, and 322. After being cured, the adhesive G bonds the optical elements 31, 32, 33, 34 to form a light path L, and a portion of the adhesive G is located in the concave portions 311, 312, 321, 322. Due to the arrangement of the recesses 311, 312, 321, 322, when the optical elements 31, 32, 33, 34 are aligned, the accuracy of the alignment is not affected by the amount of the adhesive G. Compared with the conventional structure, the adhesive G does not easily overflow into the optical elements 31, 32, 33, 34 facing one side of the optical channel 200832046 L, so that the light quality of the light guide 3 is affected. In the light pipe 3 of the second embodiment of the present invention, the recesses 311, 312, and 32 are respectively located at two ends of the optical elements 31 and 32, and are located on opposite surfaces of the optical elements 31 and 32, of course, The set positions of the recesses 311, 312, 321, 322 can be changed. As shown in Fig. 7, the first recesses 313, 314 are located on the same surface of the first optical component 31, and the second recesses 323, 324 are located on the same surface of the first optical component 32. In this way, the first concave portion 313 and the second concave portion 323 respectively face the two ends of the third optical element 33, and the first concave portion 314 and the second concave portion 324 respectively face the two ends of the fourth optical element 34, so that Adhesives G located in the recesses 313, 314, 323, 324 can bond the optical elements 31, 32, 33, and. Referring now to Figure 8, a projection system 4 in accordance with a preferred embodiment of the present invention is illustrated. The projection system 4 has a light source 40, a color wheel assembly 41, a light pipe 42, a lens assembly 43, a digital micromirror device 44, and a projection unit 45. The color wheel assembly 41 is disposed adjacent to one side of the light source 4, and the light pipe 42 can be disposed between the light source 40 and the color wheel assembly 41 or on the side of the color wheel assembly 41 with respect to the light source 40. The manner in which the light of the light source 40 is imaged on the screen 46 through the color wheel assembly 41, the light guide 42, the lens assembly 43, the digital micromirror device 44, and the projection unit 45 is a conventional technique, and is not described herein. In addition, the structure of the light pipe 42 in this embodiment can be the same as that of the light pipe 2 in the first embodiment or the light pipe 3 in the second embodiment, and is not described here. As described above, the projection system of the present invention and its light guide have recesses in which at least a portion of the adhesive is located in the recess as compared to conventional structures. By the arrangement of the recesses, the adhesive can be prevented from overflowing into the surface of the optical element, so that the light quality of the light guide can be ensured. In addition, when the optical components are assembled, the use of the adhesive can be avoided, which in turn affects the accuracy of the optical components when they are assembled. The above is intended to be illustrative only and not limiting. Any equivalent modifications or alterations of the present invention are intended to be included within the scope of the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of one of the conventional projection systems; FIG. 2 is a schematic view of one of the light pipes of the prior art; FIG. 3 is a schematic view of a light pipe according to the first embodiment of the present invention; 4 is a schematic view of a light pipe according to a first embodiment of the present invention, showing a first optical element having two first concave portions; FIG. 5 is a schematic view showing a light guide of the first embodiment of the present invention; Figure 6 is a schematic view of a light pipe according to a second embodiment of the present invention; Figure 7 is a schematic view of a light pipe according to a second embodiment of the present invention, showing a concave portion A view of the same surface of the optical component; and Figure 8 is a schematic illustration of a projection system in accordance with a preferred embodiment of the present invention. 12 200832046 Symbol Description: 1 Projection System 10 Light Source 11 Color Wheel Assembly 12 Light Pipe 121 Optical Element 122 Adhesive 123 Inlet End 124 Outlet End 13 Lens Assembly 14 Digital Micromirror Element 15 Projection Unit 16 Screen 2 Light Guide 21 First Optics Element 21a One end of the first optical element 21b The other end of the first optical element 211 First recess 211, First recess 212 First slot 22 Second optical element 22a One end of the second optical element 22b The other end of the second optical element 221 second recess 13 200832046 222 second recess 23 third optical element 23a one end of the third optical element 23b the other end of the third optical element 231 third recess 232 third recess 24 fourth optical element 24a fourth optical element One end 24b The other end of the fourth optical element 241 Fourth recess 242 Fourth slot 3 Light guide 31 First optical element 311 First recess 312 First recess 313 First recess 314 First recess 32 Second optical element 321 Two recesses 322 second recesses 323 second recesses 324 second recesses 33 third light The fourth element 34 of the optical element of the projection system 40 142008320464 color wheel assembly 42 light source 41 light guide 43 of the lens assembly 44 digital micromirror element 45 projecting unit 46 screen G adhesive optical path L