462751 s?4fltwf.doc/〇〇8 A7 B7 經濟部智慧財產局員工消費合作社印製 五、發明説明（丨） 本發明是有關於一種光纖通訊傳輸系統。且特別是有 關於一種設計用於同時抑制（1)刺激布里諾(Brillouin)散 射（stimulated Brillouin scattering，SBS)效應，及（2)由 一長距離傳送系統中之自我相位調變及外部相位調變誘-導 產生之調變二階失真（composite second-order’ CSO)之光 波來源。 最近分散式廣播多重頻道振幅調變（AM)有線電視 訊號之傳輸有超過約50公里(km)之距離之趨勢且通常是 使用一種操作在1550奈米(nm)波長範圍之光纖傳輸系統。 這些系統通常使用一種光發射機，此光發射機係由高功率 1550奈米雷射二極體，一以鈮酸鋰（LiNb03)爲基礎之外部 調變器’及—摻餌光纖放大器（erbium-doPed fiber amplifier，EDFA)，而其輸出功率可以超過20 dBm。雖 然此種發射機之光纖功率可以藉由使用一高功率摻餌光纖 放大器（EDFA)被增加此乃爲習知，但可被發射至一單模光 纖之最大光功率仍受限於SBS。此SBS效應導致輸入光波 藉由非線性光學折射-指標格柵(refractive-index grating)之 反射，其係由聲波以6km/SeC速度在光纖上移動所形成。 當入射光很強時，此指標格柵與輸入光波共鳴，結果產生 更多反射。目前已經有一些發明被建議以解決此問題。例 如，美國專利第5，420，828，美國專利第5，566，381 及美國專利第5，828，477等有建議一些解法，其中此美 國專利第5，828，477允許一 17 d.Bm之光功率被發射至 一寬頻光纖分散式系統。無論如何，此傳送距離最多只能 ____ 4 本紙張適用巾關家料·（ CNS > ( 21GX：297公釐) ' ' ^^1 ^^^1 ^^^1 - -- i m » . _..tf^^^^1 ^^^1 m ^^^1 ^^^1 、-" (請先閱讀背面之注意事項再填寫本頁) 經濟部智慧財產局S工消費合作社印製 4 62151 Α7 _ 5248twf.doc/008 B7 五、發明説明（"V ) 到50 km。在目前階段，並沒有商業化光發射機可以被用 來接收超過65 km之多頻道(multi-channel)振幅調變（AM) 有線電視（cable TV，CATV)訊號。理想上，一個發射功率 爲17 dBm之發射機具有一靈敏度爲〇 dBm之典型光接收 器及光纖傳送損失爲〇.2-0.22dB/km，此最大傳送距離必 須爲（17-0)/0.22 〜77km 或（17-0)/0.2 〜85km。不幸地，現有 之商業產品之最大傳輸距離只有50km。 在一光傳送系統中一個無中繼器(repeaterless)的系統 代表只有一個大功率Post-EDFA被使用於遠距離傳送。一 般地，一個無中繼器的系統因爲自我相位調變（self-phase modulation，SPM)及外部相位調變（external-phase modulation，EPM)之組合效應只可以傳送50-65 km。此SPM 效應係由發射功率相依-折射索引（lunched power dependent-refractive index)所造成，此效應導致光場之相 位變成距離的函數。此EPM效應係由光束經過一外部相 位調變器所造成，此SPM及EPM合成效應在一長距離1550 nm AM-CATV系統中通常導致調變二階(composite second-order，CSO)失真。此SPM、EPM與光纖色散之合成效應 導致相位調變轉換成振幅調變（PM_t〇-AM)，但因此所得之 AM成分不但不是所要求的’反而是一種非線性失真。結 果，大的CS0失真會在長距離傳送之後發生。當EPM調 變深度變得較高時此負面效應會變的更嚴重。462751 s? 4fltwf.doc / 〇〇8 A7 B7 Printed by the Consumer Cooperatives of the Intellectual Property Bureau of the Ministry of Economic Affairs. 5. Description of the Invention (丨) The present invention relates to a fiber-optic communication transmission system. In particular, it relates to a method designed to simultaneously suppress (1) the stimulated Brillouin scattering (SBS) effect, and (2) the self-phase modulation and the external phase in a long-distance transmission system The source of light waves for modulation second-order 'CSO generated by modulation inducement. Recently, decentralized broadcast multi-channel amplitude modulation (AM) cable signals have a tendency to transmit distances of more than about 50 kilometers (km) and usually use an optical fiber transmission system operating in the 1550 nanometer (nm) wavelength range. These systems usually use an optical transmitter consisting of a high-power 1550 nm laser diode, an external modulator based on lithium niobate (LiNb03), and an erbium-doped fiber amplifier (erbium -doPed fiber amplifier (EDFA), and its output power can exceed 20 dBm. Although the fiber power of such transmitters can be increased by using a high power bait-doped fiber amplifier (EDFA), it is common practice that the maximum optical power that can be transmitted to a single-mode fiber is still limited by SBS. This SBS effect causes the reflection of the input light wave by a non-linear optical-refractive-index grating, which is formed by the sound wave moving on the optical fiber at a speed of 6 km / SeC. When the incident light is strong, this indicator grid resonates with the input light wave, resulting in more reflections. Several inventions have been proposed to solve this problem. For example, U.S. Patent No. 5,420,828, U.S. Patent No. 5,566,381 and U.S. Patent No. 5,828,477 have suggested some solutions, among which U.S. Patent No. 5,828,477 allows a 17 d.Bm The optical power is transmitted to a broadband optical fiber distributed system. In any case, this conveying distance can only be up to ____ 4 papers suitable for household materials · (CNS > (21GX: 297 mm) '' ^^ 1 ^^^ 1 ^^^ 1--im ». _ .. tf ^^^^ 1 ^^^ 1 m ^^^ 1 ^^^ 1 、-" (Please read the precautions on the back before filling this page) Printed by S Industrial Consumer Cooperative, Intellectual Property Bureau, Ministry of Economic Affairs 4 62151 Α7 _ 5248twf.doc / 008 B7 V. Description of invention (" V) to 50 km. At the current stage, no commercial optical transmitter can be used to receive multi-channels over 65 km (multi-channel) Amplitude Modulation (AM) Cable TV (CATV) signal. Ideally, a transmitter with a transmission power of 17 dBm has a typical optical receiver with a sensitivity of 0 dBm and a transmission loss of 0.22 dB. / km, the maximum transmission distance must be (17-0) /0.22~77km or (17-0) /0.2~85km. Unfortunately, the maximum transmission distance of existing commercial products is only 50km. One in an optical transmission system A repeaterless system means that only one high-power Post-EDFA is used for long-distance transmission. Generally, a repeaterless system The combined effect of self-phase modulation (SPM) and external phase modulation (EPM) can only transmit 50-65 km. This SPM effect is determined by the transmitted power dependent-refractive index (lunched power dependent) -refractive index), this effect causes the phase of the light field to become a function of distance. This EPM effect is caused by the beam passing through an external phase modulator. The combined effect of SPM and EPM is a long distance of 1550 nm AM-CATV The system usually results in composite second-order (CSO) distortion. This combined effect of SPM, EPM, and fiber dispersion causes phase modulation to be converted to amplitude modulation (PM_t〇-AM), but the resulting AM component not only Rather than the required ', it is a kind of non-linear distortion. As a result, large CS0 distortion will occur after long distance transmission. This negative effect will become more serious when the EPM modulation depth becomes higher.
在此光纖傳輸系統中，上述SB.S及非線性光纖效應所 造成的CS0是兩個需要被解決的主要問題。通常地’此SBS 5 本紙張尺度逋用中两Η家輕準（CNS ) A4規格（210X297公釐） ---------------ir------iw— (請先閲讀背面之注$項再填寫本頁) 462151 經濟部智慧財產局Μ工消費合作社印製 A7 __5 2 4 8 twf . doc/ 008_B7____ 五、發明説明（乃） 效應藉由盡量打散光譜而被抑制* 一般並沒有考慮因爲大 的微波驅動功率造成對外部調變器所帶來的負面影響。此 通常方法只有抑制SBS效應但是並沒有抑制大於大約 65krti長距離PM-to-AM轉換所造成的CSO失真。 本發明之目的至少提供一光纖發射機藉由在最佳條件 下抑制SBS及EPM/SPM-induced CSO以達到一傳送距離 大於75 km，而此最佳條件是依所要求的傳送距離而調整 的。 本發明提供一光纖發射機，其包括一具有頻率fl之 第一合成微波信號（synthesized microwave signal)產生器稱 接至一分散式回饋（Distributed Feedback，DFB)雷射源， 一具有頻率f2之第二合成微波信號產生器耦接至外部相 位調變器，因此可打散調變光譜，以及一馬赫真德調變器。 此具有頻率fl之第一合成微波被設定成大約大於調變訊 號最高頻率之2至3倍。此具有頻率f2之第二合成微波 被設計成接近fl的諧波(harmonic)頻率且接近於fl的3 倍。此具有頻率Π及f2之微波信號分別被輸入至兩個功 率放大器（amplifier)，且之後分別被輸入至一雷射源及一 相位調變器。這兩個功率放大器藉由一微處理器控制以自 動調整在無中繼器設計時之光纖發射機在相位指標（phase index)爲1.4,或達到在一具有中繼器(repeater)設計中傳送 距離所要求之最佳索引。在無中繼器設計中此外部相位調 變器被耦接至一對光纖放大器或在具有中繼器設計中好幾 個光纖放大器被串列地耦接。最後的光纖放大器被耦接至 6 >紙浪尺^適用中國81家標ϋβ ) Λ4规格（210X297公Ϊ ) 一 ~ (請先閱讀背面之注意事項再填寫本頁) 訂 ^ 1 5 f A7 5248twf.doc/008 B7 五、發明説明（u,) 光接收器。 必須了解的是前述兩種一般描述及以下詳細描述是示 範性的，且在申請專利範圍中將提供更進一步的解釋。 爲讓本發明之上述目的、特徵、和優點能更明顯易懂， 下文特舉較佳實施例，並配合所附圖式，作詳細說明如下： 圖式之簡單說明： 第1A及1B圖繪示一方塊圖，其繪示本發明之較佳 實施例分別在無中繼器設計及具有中繼器設計中之光纖發 射機之結構圖； 第2A圖繪示本發明之較佳實施例由FM-PM或當 f2~3fl且兩個相位調變指標大約爲1.4時之兩個微波調變 所產生之理論的光譜；以及 第2B圖繪示本發明之較佳實施例對應於第2A圖之 理論的光譜之一測量光譜； 經濟部智慧財產局員工消費合作社印製 ^^^1 ^^^1 ^^^1 ^^^1 nn m I n^i ^^^1 ^^^1 ί *. (請先閱讀背面之注意事項再填寫本頁) 第3圖繪示本發明之較佳實施例所測得之SPM/EPM-induced CSO數値，其中#爲相位調變指標，在多級中繼 器AM-CATV系統之第78頻道以等長之全部光纖長度爲 函數所預期之數値計算及分析，其中光纖長度爲60km， 從每一 EDFA所發射之功率爲12dBm，頻率爲1.9GHz之 單音調相位調變，及每一 78 AM頻道之調變深度是3% ; 第4圖繪示本發明之較佳實施例所測得之SPM/EPM-induced CSO數値，在多級中繼器AM-CATV系統之第18 頻道以等長之全部光纖長度爲函數所預期之數値計算及分 析，其中所有的PM調變合成頻率之相位調變指標是2.5 , 1 本紙張尺度適用中國國家標準（CMS ) A4規格（210 X 297公釐〉 4 6 2 15 1 7 Α7 5248twf.doc/008 B7 五、發明説明（匕） 不同之數據差別在於第二微波信號頻率的大小，其餘參數 同圖3 : 第5圖繪示導因於SPM及EPM(開路)調變效應所產 生之CSO失真所造成之傳送距離限制，及在具有相同相 位調變指標之兩個微波皆爲相位調變所造成因SBS限制的 傳送距離；以及 第6圖繪示導因於SPM及EPM(開路）調變效應所產 生之CSO失真所造成之傳送距離限制，及在FM-PM技術 中藉由PM指標相關SBS臨界値，其中FM調變指標固定 爲 1.4。 標號說明： 36第一合成微波產生器裝置 38第二合成微波產生器裝置 40微處理器 42功率放大器 44光源 46相位調變器 48馬赫-真德光強度調變器 經濟部智慧財產局Μ工消費合作社印製 ^^^1 ^^^^1 ^^^^1 B^iJ— m *m ^^^^1 ^^^^1 ^^^^1 ^^^^1 m^i mf .-¾ (請先閲讀背面之注意事項再填寫本頁) 5〇方向耦合器 52外部相位調變器 54摻餌光纖放大器(EDFA) 56光接收器 本發明之光纖發射機包括在一最佳條件下同時抑制 SBS效應及SPM/EPM-induced CSO效應之能力，因此傳 8 本紙張尺度適用中國國家橾準（CNS > A4規格（2ίΟΧ 297公釐> A7 5248twf.doc/008 B7 五、發明説明（4 ) 送距離可有效增加。發明者已經發表此解決方法在June 1999 5 M.C. Wu et al. > Photonics Technologies Letters > Vol.ll ’ No.6，June 1999，p_718-720。藉由使用傳送 PM 及/或FM 1550nm的光可有效抑制SBS效應以打散光譜， 但是當傳送距離很長時將付出增加CSO的代價。因此， 在SBS及CSO抑制程度(levels)上必須取得妥協。本發明 藉由適當調整EPM調變深度限制頻譜的打散。此EPM調 變深度當光傳送距離變得較長時必須降低。要降低多少調 變功率依實際傳送距離而定。在一極端例子中，當傳送距 離必須最長，此時最小的SPM/EPM-induced CSO失真變 成最高優先，則不再需要SBS抑制。 如上所討論，此PM及/或FM調變深度必須被適當調 整特別是對一無中繼器系統。對一具有許多線上（in-line) 摻餌光纖放大器（EDFA)及沒有傳播補償（dispersion compensation)裝置的傳送系統，此PM及/或FM調變深度 可能必須被降低至0。 經濟部智慧財產局員工消費合作社印製 - - - ^^^^1 ^^^^1 ^^^^1 ^^^^1 ^^^^1 ^^^^1 J ϋκ t·^^— -¾ lvs (請先閔讀背面之注意事項再填寫本頁) 爲了增加傳送距離，此類比AM CATV訊號在未來必 須被數位的垂直振幅調變（quadrature-amplitude-moduUted，QAM)所取代。在此情形中，此系統結合許多 摻餌光纖放大器（EDFA)因此其傳送距離可到達近千公里。 本發明之光纖發射機至少適用於類比AM CATV訊號或數 位的垂直振幅調變（quadrature-amplitude-modulated，QAM) 訊號。爲了最小化SPM/EPM所導致的CSO非線性失真， 光纖發射機之相位調變指標必須被遞減。 ____ 9 本紐尺度逋用中固ϋ家操率（CNS > M規格（210X297公董> ' 4 6 2 1 5 1 A7 5248twf.doc/008 B7 五、發明説明（7) 第一實施例 經濟部智慧財產局員工消費合作社印製 ^—^1 - Ϊ - am 1^1- HI ^^—^1 I ^^^1 ^^^1 nn ^^^^1 ^1.^1 、-* (讀先閲讀背面之注意事項再填寫本頁) 請參照第1A及1B圖，其繪示本發明之較佳實施例 分別在無中繼器設計及具有中繼器設計中之光纖發射機之 結構圖。根據本發明的解決方法，在設計相對應的光纖發 射機時包括兩個步驟。第一個步驟是產生多頻光波源以抑 制SBS。在第1A圖中，此光纖發射機基本上包括一光源 44，例如是一雷射二極體或一高功率DFB雷射，一外部 相位調變器52，一馬赫真德光強度調變器48，一對依序 耦接在一起的摻餌光纖放大器(EDFA)。此對摻餌光纖放大 器（EDFA)的輸出被傳送至光接收器56。爲了達到要求的 調變指標，本發明更包括一第一微波合成產生器裝置36， 以產生一具有頻率fl之第一合成微波。及第二微波合成 產生器裝置38，以產生一具有頻率f2之第二合成微波合 成。此具有頻率Π之第一合成微波及具有頻率f2之第二 合成微波分別被耦接至兩個功率放大器42。這兩個合成微 波可包括，例如，一單頻微波，一氈抖（dithering)微波， 或一調變/編碼微波。此功率放大器42被耦接至雷射二極 體44及外部相位調變器52之相位調變器46，因此具有頻 率fl之第一音調微波驅動雷射二極體44及具有頻率f2之 第二音調微波驅動相位調變器46。 外部相位調變器52更包括，例如，一 AM光強度調 變器用以接收相位調變器46的輸出及一方向耦合器50以 接收馬赫-真德光強度調變器48的輸出及輸出至摻餌光纖 放大器（EDFA)54。此外部相位調變器52可爲以鈮酸鋰 __ 10 本紙張尺度適用中國國家標準（CNS ) A4规格（210X297公釐） 4 62 1 5 1 A7 5248twf.doc/008 37 五、發明説明（叉） (請先閲讀背面之注意事項再填寫本頁) (LiNb03)爲基礎或以半導體（如光電吸收調變器，Electro-Absorption Modulator)爲基礎。此相位調變器46被耦接至 馬赫-真德光強度調變器48，如此一馬赫-真德光強度調變 器被寬頻類比AM或數位QAM訊號所驅動。此馬赫-鼻德 光強度調變器48可能有一或兩個輸出埠，或更多。每一 個輸出埠可以被耦接至方向耦合器50再被耦接至摻餌光 纖放大器（EDFA)54。通常如果此方向耦合器50有兩個輸 出則此摻餌光纖放大器（EDFA)54成對地耦接。 經濟部智慧財產局員工消費合作社印製 此功率放大器42可藉由微處理器4〇控制，因此功率 放大器42的振幅是可程式(programmable)調整的。此要求 的調變指標因此可在兩個頻率fl及f2間自動調整。此具 有頻率fl之第一合成微波被設定爲系統中最高頻率的大 約2-3倍。例如，一個fl = l.72GHZ之FM調變器去調變高 功率DFB雷射光，其中1.72GHz大約是HFC系統頻寬 (860MHz)的兩倍。此具有頻率f2之第二音調微波大約是fl 的3倍，即f2大約是5.16 GHz。此具有頻率f2之第二合 成微波外部調變最好是使用PM的方法。此具有頻率fl之 FM第一合成微波在距離主要光載波1.72GHz處產生兩個 旁波帶因此我們可得到三個頻率光源。此具有頻率f2之PM 第二合成微波在距離先前所產生之三個頻率載波各 5.16GHz處分別產生兩個旁波帶。因此，此光源包括一擁 有9個頻率之光譜。當多頻道CATV訊號依序調變此9個 頻率光波源，此光譜的理論結果如_ 2A所示。圖2A繪 示本發明之較佳實施例由FM-PM或當f2〜3fl且兩個調變 _\ 1 本紙張尺度適用中標準（CNS ) A4規格（2彳0X 297公釐Ί" 4 β2 ? 5 t A7 5248twf.doc/008 B7 五、發明説明（q ) 指標大約爲1.4之兩個PM技術所產生之理論的光譜。此 實際的測量如圖2B所示，其繪示本發明之較佳實施例對 應於第2A圖之理論的光譜之一測量光譜。藉由本發明所 提供的方法可以達到足夠的SBS抑制是非常淸楚的。一個 已實驗用來驗證當1550nm光功率在到達18dBm，在一FM 調變指標爲1.35且PM調變指標爲2.4時可以發射至一 74km等長距離之標準通訊單模態光纖中。 經濟部智慧財產局員工消費合作杜印製 - -«^^1 m n ^^1 HI*R, l^i n ^^1 (請先聞讀背面之注意事項再填寫本頁) 在設計光發射機時之第二步驟爲降低在第一步驟中所 使用的FM及PM調變指標。此降低FM及PM調變指標 程度根據不同的傳送距離而定。第3圖繪示本發明之較佳 實施例所測得之CSO數値，在多級中繼器AM-CATV系統 之第78頻道以光纖長度爲函數所得之數値計算及實際量 測結果，其中光纖長度爲60km，從每一摻餌光纖放大器 (EDFA)所發射之功率爲12dBm，頻率爲1.9GHz之單音調 相位調變’及每一 78 AM頻道之調變深度是3%。參數p 代表相位調變指標。在圖3中，實線代表只有SPM效應 所導致的CSO失真。此測量結果顯示CSO失真是由SPM 效應及EPM效應兩者所組合而成。對一典型CSO需求爲-65dBc時，一個較大的相位調變指標會得到較短的傳送距 離。如此顯示光譜的打散必須被控制在最佳條件下。當PM 調變音調頻率增加時類似的特徵也顯示在第4圖中。第4 圖繪示本發明之較佳實施例所測得之CSO數値，在多級 中繼器AM-CATV系統之第78頻璋以光纖長度爲函數所 預期之數値計算及實際量測結果，其中所有的PM調變音 1 2 本紙張尺度適闲中國國家標準（CNS > A4規格（210x^7公釐> — ^62151 ‘ A7 5 2 4 8 twf.doc/ 0 0 8 B7 五、發明説明（〔p ) 調頻率之相位調變指標是2.5，且其他的參數如圖3。 在一最長無中繼器之光纖系統中爲了要找出最佳 PM/FM調變指標，一些針對光纖長度的理論曲線及在SBS 及CSO效應下以調變指標爲函數的複數個曲線被顯示在 圖5及圖6中。第5圖繪示導因於SPM及EPM(開路)調 變效應所產生之CSO失真所造成之傳送距離限制，及在 具有相同指標之兩個音調pM情形中SBS所造成之距離限 制。第6圖繪示導因於SPM及EPM(開路)調變效應所產 生之CSO失真所造成之傳送距離限制，及在FM-PM技術 中SBS所造成之傳送距離限制。其中FM指標固定爲1.4。 經濟部智慧財產局員工消費合作社印製 Λί * 0¾-3 (請先閲讀背面之注意事項再填寫本頁) 在第5圖及第6圖兩種情形中，當每一音調的調變指 標大約是1.4時最大無中繼器距離最長可達84km。藉由調 變指標被調整至1.4，本發明已經實驗證明可達到此傳送 距離。這與一般習知方法有很大的不同，一般習知方法設 定PM調變指標每音調爲2.4(請參考美國專利第5，828， 477號專利）。在本發明中，如圖1A或圖1B所示具有頻 率fl之第一合成微波及具有頻率f2之第二合成微波係由 微處理器40所控制，因此使用者可容易得到要求的調變 指標，而不需要額外知識去從具有頻率fl之第一合成微 波及具有頻率f2之第二合成微波之組合中去調整調變指 標。 第二實施例 以第1A圖及第1B圖所示之結構爲基礎，至少還有 兩種不同結構。例如，取而代之，將第一頻率調變器36 本紙張尺度適用中國國家標牟（CMS ) A4規格（210x297公董) 5 2 4 8 t w f . /008 A7 B7 五、發明説明（u ) 及第二頻率調變器38兩者皆耦接至光源44或將第一頻率 調變器36及第二頻率調變器38兩者皆耦接至相位調變器 46 ° 本發明提供一種光纖發射機在最佳條件下以同時抑制 SBS效應及CSO效應，因此針對無中繼器設計之大約84km 的傳送距離可以達到。本發明使用兩種控制下的音調頻率 以抑制SBS效應。此無中繼器設計被發現之最佳調變指標 爲1.4因此由SPM及EPM效應所導致的CSO失真可以被 有效降低，可達到最大傳送距離之結果。此最佳調變指標 的調整可以藉由具有控制程式之微處理器自動完成。 綜上所述，雖然本發明已以較佳實施例揭露如上’然 其並非用以限定本發明，任何熟習此技藝者，在不脫離本： 發明之精神和範圍內，當可作各種之更動與潤飾，因此本 發明之保護範圍當視後附之申請專利範圍所界定者爲準° ---------裝-- (請先閱讀背面之注意事項再填寫本頁) 經濟部智慧財產局員工消費合作社印製 本紙張尺度適用中國國家標準（CNS > Μ規格（2ί〇Χ297公釐）In this optical fiber transmission system, CS0 caused by the above-mentioned SB.S and nonlinear optical fiber effects are two main problems that need to be solved. Normally 'this SBS 5 paper size is used in both domestic and international standards (CNS) A4 specification (210X297 mm) --------------- ir ------ iw — (Please read the note on the back before filling in this page) 462151 Printed by the Intellectual Property Bureau of the Ministry of Economic Affairs, M Industrial Consumer Cooperative A7 __5 2 4 8 twf. Doc / 008_B7____ 5. Explanation of the Invention Spectral suppression * In general, the negative impact on external modulators due to large microwave drive power is not considered. This general method only suppresses the SBS effect but does not suppress the CSO distortion caused by long-distance PM-to-AM conversions greater than about 65krti. The object of the present invention is to provide at least one optical fiber transmitter by suppressing SBS and EPM / SPM-induced CSO under the optimal conditions to achieve a transmission distance greater than 75 km, and this optimal condition is adjusted according to the required transmission distance. . The present invention provides a fiber optic transmitter, which includes a first synthetic microwave signal generator having a frequency fl and is connected to a distributed feedback (DFB) laser source, and a first having a frequency f2 The two-combined microwave signal generator is coupled to an external phase modulator, so it can disperse the modulation spectrum and a Mach-Zehnder modulator. This first synthetic microwave having a frequency fl is set to be approximately two to three times greater than the highest frequency of the modulation signal. This second synthetic microwave having a frequency f2 is designed to be close to the harmonic frequency of fl and close to three times that of fl. The microwave signals with frequencies Π and f2 are input to two power amplifiers, respectively, and then input to a laser source and a phase modulator, respectively. These two power amplifiers are controlled by a microprocessor to automatically adjust the fiber optic transmitter's phase index at the repeater-less design to 1.4, or to achieve transmission in a repeater design The best index required for the distance. This external phase modulator is coupled to a pair of fiber amplifiers in a repeaterless design or several fiber amplifiers are coupled in series in a repeater design. The final fiber amplifier is coupled to 6 > Paper Wave Ruler ^ Applicable to 81 Chinese Standards ϋ β) 44 size (210X297 male Ϊ) 1 ~ (Please read the precautions on the back before filling this page) Order ^ 1 5 f A7 5248twf.doc / 008 B7 V. Description of the invention (u,) Optical receiver. It must be understood that the foregoing two general descriptions and the following detailed descriptions are exemplary and further explanations will be provided in the scope of the patent application. In order to make the above-mentioned objects, features, and advantages of the present invention more comprehensible, the following exemplifies preferred embodiments and the accompanying drawings for detailed description as follows: Brief description of the drawings: Figures 1A and 1B FIG. 2A shows a block diagram of a fiber optic transmitter in a repeater-less design and a repeater design of a preferred embodiment of the present invention; FIG. 2A shows a preferred embodiment of the present invention. FM-PM or theoretical spectrum produced by two microwave modulations when f2 ~ 3fl and two phase modulation indexes are about 1.4; and FIG. 2B shows a preferred embodiment of the present invention corresponding to FIG. 2A One of the theoretical spectra of the measurement spectrum; printed by the Consumer Cooperative of the Intellectual Property Bureau of the Ministry of Economic Affairs ^^^ 1 ^^^ 1 ^^^ 1 ^^^ 1 nn m I n ^ i ^^^ 1 ^^^ 1 ί *. (Please read the precautions on the back before filling out this page) Figure 3 shows the SPM / EPM-induced CSO number measured by the preferred embodiment of the present invention, where # is the phase modulation index. Channel 78 of the multi-stage repeater AM-CATV system calculates and analyzes the expected number of optical fibers with the same length as the function. It is 60km, the single-tone phase modulation of the power transmitted from each EDFA is 12dBm, the frequency is 1.9GHz, and the modulation depth of each 78 AM channel is 3%; FIG. 4 illustrates a preferred implementation of the present invention The SPM / EPM-induced CSO number measured in the example is calculated and analyzed on the 18th channel of the multi-stage repeater AM-CATV system with the same length of the entire fiber length as a function of the expected number. All of the PM The phase modulation index of the modulation synthesis frequency is 2.5, 1 This paper size applies the Chinese National Standard (CMS) A4 specification (210 X 297 mm> 4 6 2 15 1 7 Α7 5248twf.doc / 008 B7 V. Description of the invention ( (D) The difference between different data lies in the frequency of the second microwave signal. The remaining parameters are the same as in Figure 3: Figure 5 shows the transmission distance limitation caused by the CSO distortion caused by the SPM and EPM (open circuit) modulation effects. And the two microwaves with the same phase modulation index are the transmission distance restricted by SBS due to phase modulation; and Figure 6 shows the CSO distortion caused by SPM and EPM (open circuit) modulation effects Transmission distance limitation caused by PM and PM in FM-PM technology The relevant SBS critical threshold, where the FM modulation index is fixed at 1.4. Description of the symbols: 36 first synthetic microwave generator device 38 second synthetic microwave generator device 40 microprocessor 42 power amplifier 44 light source 46 phase modulator 48 Mach -Printed by Zhende Light Intensity Modulator, Intellectual Property Bureau, Ministry of Economic Affairs, M Industrial Consumer Cooperative, ^^^ 1 ^^^^ 1 ^^^^ 1 B ^ iJ— m * m ^^^^ 1 ^^^^ 1 ^^^^ 1 ^^^^ 1 m ^ i mf .-¾ (Please read the precautions on the back before filling out this page) 5〇 Directional coupler 52 External phase modulator 54 Alien-doped fiber amplifier (EDFA) 56 Optical receiver The optical fiber transmitter of the present invention includes the ability to simultaneously suppress the SBS effect and the SPM / EPM-induced CSO effect under an optimal condition. Therefore, it is said that this paper standard is applicable to China National Standards (CNS > A4 Specification (2ίΟχ 297 mm > A7 5248twf.doc / 008 B7 5. Description of the invention (4) The sending distance can be effectively increased. The inventors have published this solution in June 1999 5 M.C. Wu et al. ≫ Photonics Technologies Letters > Vol.ll 'No. 6, June 1999, p_718-720. By using PM and / or FM 1550nm light transmission, the SBS effect can be effectively suppressed to spread the spectrum, but when the transmission distance is long, the cost of increasing CSO will be paid. Therefore, compromises must be made in SBS and CSO suppression levels. The present invention limits the dispersion of the spectrum by appropriately adjusting the EPM modulation depth. This EPM modulation depth must be reduced as the light transmission distance becomes longer. The amount of modulation power to be reduced depends on the actual transmission distance. In an extreme example, when the transmission distance must be the longest and the smallest SPM / EPM-induced CSO distortion becomes the highest priority, SBS suppression is no longer needed. As discussed above, this PM and / or FM modulation depth must be appropriately adjusted, especially for a repeaterless system. For a transmission system with many in-line EDFAs and no dispersion compensation device, the PM and / or FM modulation depth may have to be reduced to zero. Printed by the Consumer Cooperative of the Intellectual Property Bureau of the Ministry of Economic Affairs---^^^^ 1 ^^^^ 1 ^^^^ 1 ^^^^ 1 ^^^^ 1 ^^^^ 1 J ϋκ t · ^^ — -¾ lvs (please read the notes on the back before filling this page) In order to increase the transmission distance, such analog AM CATV signals must be replaced by digital vertical-amplitude-moduUted (QAM) in the future. In this case, this system incorporates many EDFAs so that its transmission distance can reach nearly thousands of kilometers. The optical fiber transmitter of the present invention is at least suitable for analog AM CATV signals or digital vertical-amplitude-modulated (QAM) signals. In order to minimize the CSO non-linear distortion caused by SPM / EPM, the phase modulation index of the optical fiber transmitter must be decremented. ____ 9 The standard of homework in this New Zealand standard (CNS > M specification (210X297) > '4 6 2 1 5 1 A7 5248twf.doc / 008 B7 V. Description of the invention (7) First embodiment Printed by the Consumer Cooperative of the Intellectual Property Bureau of the Ministry of Economic Affairs ^ — ^ 1-Ϊ-am 1 ^ 1- HI ^^ — ^ 1 I ^^^ 1 ^^^ 1 nn ^^^^ 1 ^ 1. ^ 1,- * (Read the precautions on the back before filling this page) Please refer to Figures 1A and 1B, which show the preferred embodiments of the present invention in a repeater-less design and a fiber-optic transmitter in a repeater design Structure diagram. According to the solution of the present invention, there are two steps in designing the corresponding fiber transmitter. The first step is to generate a multi-frequency optical wave source to suppress SBS. In Figure 1A, this fiber transmitter is basically It includes a light source 44 such as a laser diode or a high power DFB laser, an external phase modulator 52, a Mach Zend light intensity modulator 48, and a pair of sequentially coupled EDFA. The output of this pair of EDFA is transmitted to the optical receiver 56. In order to achieve the required modulation index, the present invention more A first microwave synthesis generator device 36 is included to generate a first synthetic microwave having a frequency fl. And a second microwave synthesis generator device 38 is used to generate a second synthetic microwave synthesis having a frequency f2. This has a frequency Π The first synthetic microwave and the second synthetic microwave having a frequency f2 are respectively coupled to two power amplifiers 42. The two synthetic microwaves may include, for example, a single-frequency microwave, a dithering microwave, or a Modulate / encode microwave. This power amplifier 42 is coupled to the laser diode 44 and the phase modulator 46 of the external phase modulator 52, so the first tone microwave with the frequency fl drives the laser diode 44 And a second tone microwave-driven phase modulator 46 having a frequency f2. The external phase modulator 52 further includes, for example, an AM light intensity modulator for receiving the output of the phase modulator 46 and a directional coupler 50 for Receive the output of Mach-Zende light intensity modulator 48 and output to EDFA 54. This external phase modulator 52 can be lithium niobate __ 10 This paper standard is applicable to Chinese national standards (CNS ) A4 Regulation Grid (210X297 mm) 4 62 1 5 1 A7 5248twf.doc / 008 37 V. Description of the invention (fork) (Please read the notes on the back before filling this page) (LiNb03) based on semiconductor (such as photoelectric absorption Modulator, Electro-Absorption Modulator). This phase modulator 46 is coupled to the Mach-Zehnder light intensity modulator 48, so that a Mach-Zehnder light intensity modulator is broad-band analog AM or digital QAM signal driven. The Mach-Nude light intensity modulator 48 may have one or two output ports, or more. Each output port can be coupled to a directional coupler 50 and then to a bait-doped fiber amplifier (EDFA) 54. Generally, if the directional coupler 50 has two outputs, the EDFA 54 is coupled in pairs. Printed by the Consumer Cooperative of the Intellectual Property Bureau of the Ministry of Economic Affairs. This power amplifier 42 can be controlled by the microprocessor 40, so the amplitude of the power amplifier 42 is programmable. The required modulation index can therefore be adjusted automatically between the two frequencies fl and f2. This first synthetic microwave with frequency fl is set to about 2-3 times the highest frequency in the system. For example, a fl = 1.72GHZ FM modulator to modulate high power DFB laser light, of which 1.72GHz is about twice the bandwidth of the HFC system (860MHz). This second tone microwave with frequency f2 is about three times fl, that is, f2 is about 5.16 GHz. The external modulation of the second synthetic microwave having the frequency f2 is preferably a method using PM. This FM first synthetic microwave with frequency fl generates two sidebands at 1.72GHz from the main optical carrier, so we can get three frequency light sources. This PM second synthetic microwave with frequency f2 generates two sidebands at 5.16GHz each from the three frequency carriers previously generated. Therefore, this light source includes a spectrum with 9 frequencies. When the multi-channel CATV signal sequentially modulates these 9 frequency light sources, the theoretical result of this spectrum is shown in Figure 2A. Figure 2A shows a preferred embodiment of the present invention by FM-PM or when f2 ~ 3fl and two modulations _ 1 This paper size is applicable to the standard (CNS) A4 specification (2 彳 0X 297 mmΊ " 4 β2 5 t A7 5248twf.doc / 008 B7 V. Description of the invention (q) The theoretical spectrum produced by two PM technologies with an index of about 1.4. This actual measurement is shown in Figure 2B, which shows a comparison of the present invention. The preferred embodiment corresponds to one of the theoretical spectra measured in Figure 2A. The measured spectrum is very clear by the method provided by the present invention. One experiment has been used to verify that when the 1550nm optical power reaches 18dBm, In a FM modulation index of 1.35 and PM modulation index of 2.4, it can be transmitted to a standard single-mode optical fiber with a long distance of 74km. Printed by the consumer cooperation of the Intellectual Property Bureau of the Ministry of Economic Affairs--"^^ 1 mn ^^ 1 HI * R, l ^ in ^^ 1 (Please read the notes on the back before filling out this page) The second step when designing the optical transmitter is to reduce the FM and FM used in the first step. PM modulation index. The degree of reduction of FM and PM modulation index depends on different transmission distances. Figure 3 Draw the CSO number measured in the preferred embodiment of the present invention. The calculation and actual measurement results of the fiber length as a function of the 78th channel of the multi-stage repeater AM-CATV system, where the fiber length It is 60km, the power transmitted from each EDFA is 12dBm, the frequency of single tone phase modulation is 1.9GHz and the modulation depth of each 78 AM channel is 3%. The parameter p represents the phase modulation In Figure 3, the solid line represents the CSO distortion caused by the SPM effect only. This measurement shows that the CSO distortion is a combination of the SPM effect and the EPM effect. When a typical CSO demand is -65dBc, A larger phase modulation index will result in a shorter transmission distance. This shows that the dispersion of the spectrum must be controlled under optimal conditions. Similar characteristics are also shown in Figure 4 when the PM modulation tone frequency increases. Figure 4 shows the CSO data measured in the preferred embodiment of the present invention. The 78th frequency of the multi-stage repeater AM-CATV system is calculated and measured with the fiber length as a function of the expected data. As a result, all of the PM tunings were in 1 2 sheets of paper Standards in China (CNS > A4 specifications (210x ^ 7 mm > — ^ 62151 'A7 5 2 4 8 twf.doc / 0 0 8 B7) V. Description of the invention ((p) Phase adjustment of frequency adjustment The variation index is 2.5, and other parameters are shown in Figure 3. In order to find the best PM / FM modulation index in a longest repeater-free fiber system, some theoretical curves for fiber length and effects in SBS and CSO The plurality of curves below using the modulation index as a function are shown in FIG. 5 and FIG. 6. Figure 5 shows the transmission distance limitation caused by the CSO distortion caused by the SPM and EPM (open circuit) modulation effects, and the distance limitation caused by SBS in the case of two tone pMs with the same index. Figure 6 shows the transmission distance limitation caused by the CSO distortion caused by SPM and EPM (open circuit) modulation effects, and the transmission distance limitation caused by SBS in FM-PM technology. The FM index is fixed at 1.4. Printed by the Intellectual Property Bureau's Consumer Cooperatives of the Ministry of Economic Affairs Λί * 0¾-3 (Please read the precautions on the back before filling out this page) In the two cases shown in Figure 5 and Figure 6, when the modulation index of each tone is approximately When it is 1.4, the maximum repeater-free distance is up to 84km. By adjusting the modulation index to 1.4, the present invention has experimentally proven that this transmission distance can be achieved. This is very different from the conventional method, which sets the PM modulation index to 2.4 for each tone (refer to U.S. Patent No. 5,828,477). In the present invention, as shown in FIG. 1A or FIG. 1B, the first synthetic microwave having the frequency fl and the second synthetic microwave having the frequency f2 are controlled by the microprocessor 40, so the user can easily obtain the required modulation index. No additional knowledge is needed to adjust the modulation index from the combination of the first synthetic microwave with frequency fl and the second synthetic microwave with frequency f2. The second embodiment is based on the structures shown in Figs. 1A and 1B, and there are at least two different structures. For example, instead, apply the first frequency modulator 36 paper size to the Chinese national standard (CMS) A4 specification (210x297 public director) 5 2 4 8 twf. / 008 A7 B7 5. Description of the invention (u) and the second The frequency modulator 38 is both coupled to the light source 44 or both the first frequency modulator 36 and the second frequency modulator 38 are coupled to the phase modulator 46 ° The present invention provides an optical fiber transmitter in Under the best conditions, the SBS effect and the CSO effect are suppressed at the same time, so the transmission distance of about 84km designed for repeater-free can be achieved. The present invention uses two controlled tone frequencies to suppress the SBS effect. The best modulation index found for this repeaterless design is 1.4, so the CSO distortion caused by the SPM and EPM effects can be effectively reduced, and the result of the maximum transmission distance can be achieved. The adjustment of the best modulation index can be done automatically by a microprocessor with a control program. In summary, although the present invention has been disclosed in the preferred embodiment as above, it is not intended to limit the present invention. Any person skilled in the art can make various changes without departing from the spirit and scope of the invention. And retouching, so the scope of protection of the present invention shall be determined by the scope of the attached patent application ° --------- install-(Please read the precautions on the back before filling this page) Ministry of Economic Affairs The paper size printed by the Intellectual Property Bureau's employee consumer cooperatives applies Chinese national standards (CNS > Μ specifications (2ί〇 × 297 mm)