200835182 九、發明說明： 【發明所屬之技術領域】 本發明係關於一種用於類比或數位信號之光學傳輸系 統，且更特定言之係關於一種使用外部調變之固態雷2 2 系統。此外，本發明係關於消除系統内由半導體雷射内諸 如電荷載流子之布朗運動之許多可能來源產生的白分量 (白雜訊）或由雷射之偏壓電流或熱環境中之波動產生 訊（其與頻率相反變化，且因此通常稱為” 1/f ”雜訊）。’、 【先前技術】 認為用電信號直接調變發光二級體（LED)或半導體雷射 之類比強度為此項技術中已知之用於於光纖上傳輸諸如語 音及視訊信號之類比信號的最簡單方法。儘管此類類比傳 輸技術之優點在於脈衝代碼調變或者類比或脈衝頻率調 變，但使用振幅調變通常對傳輸器之雜訊及失真特徵提 較為嚴格之要求。 一由於此等原目，在應用於採用具有零散射之光纖鏈路之 、傳輸鏈路之^況下’已經結合i 3 ! Q麵雷射使用直接調 夂技術。對於應用於城域及長距離光纖傳輸鏈路，鏈路低 損耗要求使用外部調變之155〇麵雷射，通常越過非常長 之距離（100 km)及高頻率（超過_ MHz)。此類鏈路之限制 因素可i為來自雷射之殘餘相位雜訊之轉換，該殘餘相位 _由光纖鏈路中存在之散射而轉換成振幅雜訊。本發 # j '主於提供用於與雷射之相位雜訊相關聯之雜訊消 除之間单且低成本系統的問冑，以便類比光學輸出可用於 127008.doc 200835182 城域及長距離光學網路，尤其用於寬頻RF信號之類比傳 輸。 雷射之直接電流調變亦已知用於數位光學傳輸系統，諸 如高密度分波多工(DWDM)系統。參看(例如)Kartalopoulos 之"DWDM NetW〇rkS，Devices，and Technology”（ieeeBACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical transmission system for analog or digital signals, and more particularly to a solid-state lightning 2 2 system using external modulation. Furthermore, the present invention relates to eliminating white components (white noise) generated by many possible sources of Brownian motion in a semiconductor laser such as charge carriers, or by bias currents in a laser or fluctuations in a thermal environment. Signal (which varies inversely with frequency and is therefore often referred to as "1/f" noise). 'Previous technique' It is believed that the analogy of the direct modulation of a light-emitting diode (LED) or semiconductor laser with an electrical signal is the most common analog signal known in the art for transmitting optical signals such as voice and video signals over optical fibers. Simple method. Although the advantages of such analog transmission techniques are pulse code modulation or analog or pulse frequency modulation, the use of amplitude modulation typically imposes stringent requirements on the noise and distortion characteristics of the transmitter. As a result of these, the direct modulation technique has been used in conjunction with i 3 ! Q-plane lasers in the case of transmission links using fiber links with zero scattering. For metro and long-haul fiber-optic transmission links, low link loss requires the use of externally modulated 155-plane lasers, typically over very long distances (100 km) and high frequencies (over _ MHz). The limiting factor for such a link may be the conversion of residual phase noise from the laser, which is converted into amplitude noise by the scattering present in the fiber link. This #j' is primarily intended to provide a single and low-cost system for noise cancellation associated with laser phase noise, so that analog optical output can be used for 127008.doc 200835182 metro and long-haul optics Network, especially for analog transmission of wideband RF signals. Direct current modulation of lasers is also known for use in digital optical transmission systems, such as high density wavelength division multiplexing (DWDM) systems. See, for example, Kartalopoulos "DWDM NetW〇rkS, Devices, and Technology" (ieee
Press，2003，第 154頁）。 除對於155〇 nm類比光學傳輸系統所要求之低雜訊特徵 以外’該系統必須為高度線性。特定類比傳輸器中固有之 失真阻止將線性電調變信號線性轉換為光學信號，而是致 使該信號變成失真。此等影響對於多通道視訊傳輸特別有 害’：多通道視訊傳輸要求極佳之線性以防通道彼此干 擾。兩度線性化之類比光學系統廣泛適用於商用類比系 統，諸如廣播TV傳輸、CATV、互動式TV及視訊電話傳 輸。 對光學及其它非線性傳輸器之線性化之研究已經持續一 段時間，但所提議之解決方案在實踐中具有缺點。上文論 述之大部分應用所具有之頻寬對於許多實際實施方案而言 過大。用於線性化之前饋技術需要複雜之系統組件，諸如 光功率組合器及多個光源。準光學前饋技術遭受類似之複 雜性問題’且進而需要匹配極佳之零件。然而，如下文論 述用於相位雜訊消除之前饋技術為可使用許多開發良好 之技術實施之實用技術。 如上文提到，已知在先前技術中與光學傳輸系統中使用 外部調變器。第5,699，179號美國專利描述—種用於降低光 127008.doc 200835182 纖誘發複合一次（cso)失真分量之外部調變且前饋線性化 類比光學傳輸器。 在本發明之前，尚未應用耦合至直接(電流)調變雷射之 相位調變器以用於消除由雷射之半導體結構中之各種雜訊 源產生之相位雜訊分量之用途。應注意，半導體雷射在其 振幅(通常稱為相對強度雜訊)及其相位中均展現雜訊。此 等雜。fl特性本貝上與雷射波長無關，但雜訊可在單模式光 纖傳輸中在不同波長處以不同方式出現。導致相位及振幅 雜訊之主要内部機制為雷射之活性區内之自發發射。由於 自發發射之光子與經由受激發射產生之彼等光子無特定相 位關係，因而所得光場之振幅及相位均受影響。自發發射 過紅為沾知的，且已經展不為由布朗運動過程描述，其中 雜訊頻譜於操作頻率内本質上恆定(白雜訊)。在雷射外 部’諸如微音效應、、溫度波動及偏麼電流雜訊之環境影響 亦可於光場中產生相位雜訊。此等事件通常導致光相位^ 其展現具有"1/f"相依性之雜訊頻譜。本發明設法藉由 前饋消除最小化來自半導體雷射之固有相位雜訊而不㈣ 訊之驅動機制如何。 【發明内容】 1.發明目的 本發明之目的在於提供一種使用直接調變雷 學傳輸系統。 良九 :發明之另一目的在於補償用於類比光學傳 射中之雜訊。 由 127008.doc 200835182 本發明之再一目的在於提供一種用於i55〇 類比光學 傳輸系統以改良相位雜訊降低的外部hnder調變 器。 本么月之又目的在於提供一種適用於長距離分散光纖 媒體且使用具有相位校正電路之直接調變雷射的高度線性 類比光學傳輸系統。 本發明之又一目的在於提供一種用於在適用於長距離分 散光纖媒體之類比光學傳輸系統中降低來自雷射之殘餘相 位雜訊的相移電路。 本卷明之目的亦在於提供一種寬頻類比光學傳輸系統中 之相位雜訊補償過程。 2·發明特徵 簡要且概括而言，本發明提供一種用於產生調變光學信 唬以經由分散光纖鏈路傳輸至遠端接收器之光學傳輸器， 其具有：輸入端，用於接收寬頻類比射頻信號輸入；半導 體田射，其用於產生具有相關聯相位雜訊之光學信號；以 及雜訊消除電路’其包括光學相位調變器，以用於降低光 ，傳輸器輸出中之相位雜訊，且進而降低光纖鏈路之接收 器端處所呈現的由於相位調變雜訊分量引起之信號失真。 另一態樣中，本發明提供一種用於經由分散光纖鏈路使 用之光學傳輸系統’其包括：具有類比信號輸入之光學傳 輸杰，半導體雷射；調變電路，用於直接調變該雷射；以 及相移電路，用於對於由半導體雷射產生之光學信號雜訊 消除與外部調變器相關聯之光學相位調變分量。 127008.doc 200835182 /另一態樣中，本發明進而提供一種低成本直接調變技 術，其較佳包括用於控制光學相位調變器之電路，該光學 相位調變器用於降低雷射所產生之相位雜訊分量。 予 本發明之另一態樣中，提供一種用於在類比信號傳輪中 降低相位雜訊之雜訊消除電路，其將來自半導體雷射之輸 出光予仏號为裂成兩個路徑，一個通往相位調變器且另一 個ι往頻率鑑別器。在振幅及相位上調整該相位調變消除 ，唬以匹配雷射產生之相位雜訊的頻率或相位相依性。該 等信號之相位藉由該等路徑之一者中之延遲或相位調整元 件予以同步。隨後藉由光學相位調變器重組主要及次要信 唬以產生僅具有振幅調變之單個光學信號。因此，相位 凋變态以最小化所得相位雜訊之方式調變來自半導體雷射 之主要信號’從而使得類比信號適於經由分散光纖鍵路傳 輸。 根據此揭不（包括以下詳細描述在内）以及藉由實踐本發 明，熟習此項技術者將容易瞭解本發明之額外目的、優點 及新穎特徵。當下文參看較佳實施例描述本發明時，應當 瞭解本發明並不限於此。能夠得到本文教示之普通熟習此 項技術者將認識到其它領域中之額外應用、修改及實施 例，該額外應用、修改及實施例屬於在本文中揭示及主張 之本發明範圍内，且本發明可相對於其具有顯著效用。 【實施方式】 現將描述本發明之細節，包括其例示性態樣及實施例。 參看附圖a以下描述，相同參考標號用於識別相同或功能 127008.doc 200835182 相似之-件’且希望以高度簡化之圖解方式說明例示性實 2的主要特徵。此外，不希望附圖騎實際實 :特徵或所描繪元件之相對尺寸，且附圖並非按比例： 表。 。。圖=為如第5,699,179號美國專利展現之利用外部調變 益的先前技術光學傳輸器之方塊圖。該傳輸器(通常用10 展示)經由光纖路徑30向接收器6〇傳輸光學信號。傳輸器 1〇包括半導體雷射12,其產生連續波(cw)輸出。此類雷射 之典型實例為分布式反饋（DFB)雷射及/或f一*⑽雷 身:’其以1，550 nm之波長產生輸出光束。來自雷射之未： 變光學信號藉由光纖14耦合至調變器16。調變器16可為諸 如Mach-Zehnder調變器之單個調變器、級聯]^2調變器或 諸如前饋線性化電路中之—個以上調變器。調變⑽亦經 由端子18及線路20接收寬頻RF信號，諸如振幅調變殘留邊 帶（AM-SDB)電纜電視（CATV)或視訊信號。此外，當使用 前饋線性化電路時，經由端子22及線路24向調變器16提供 去偏振信號。該去偏振信號用於在調變器丨6中將誤差校正 調變器（未圖示）之光學輸入去偏振。 攜載視訊資料之經調變光學信號藉由光纖鏈路％耦合至 放大器28。放大器28通常為铒摻雜光纖放大器（EDFA)。經 放大之光學#號耗合至通往接收器60的光纖傳輸線路3 〇。 該光纖傳輸線路30可為延伸經過若干千米之長距離鏈路。 在此情況下，可沿著該線路在其中以間隔距離提供諸如 EDFA 28之線路放大器，以便將該信號升壓至所需位準。 127008.doc -10- 200835182 在接收器60處，亦可提供放大器（未圖示）以升壓傳入光學 信號。隨後將經升壓之信號施加至光電檢測器且於接收器 60處解調變為電信號，該電信號代表線路5〇處之原始視訊 或資料信號。 圖1 (b)為利用雷射之直接電流調變之先前技術光學傳輸 器的方塊圖。將寬頻RF類比信號直接施加至雷射12。來自 雷射12之調變光學信號藉由光纖鏈路26耦合至放大器， 諸如EDFA。經放大之光學信號耦合至通往接收器⑼的光 纖傳輸線路30。在接收器處，將光學信號轉換成電信號， 該電信號代表線路50處之原始視訊或資料信號。 圖2為根據本發明之光學傳輸系統1〇〇之高度簡化方塊 圖。圖中展示類比RF信號輸入源101(諸如包括多個通道之 寬頻信號）及預失真電路1〇5。藉由使用預失真電路1〇5恰 當將施加至雷射1〇2之RF信號預失真，如先前技術中已 知，用於修改施加至雷射2RF信號以補償雷射之影響遠端 接收器處之信號的非線性響應。將預失真電路1〇5之輸出 施加至雷射102來將其調變。本發明中之雷射1〇2之調變可 為AM-VSB調變器或正交振幅調變器。將雷射之光學信號 輸出110分裂成兩個部分··一個部分施加至相位調變器 111 ;另一部分施加至頻率鑑別電路丨i 5。 圖2系統中所使用之邊緣發射半導體雷射較佳為分布式 反饋雷射（DFB)，但同樣可使用Fabry_Pert〇 (Fp)雷射。 DFB雷射為較佳途徑，因為其光學輸出主要包含於單個雷 射模式中，而FP雷射之光學能量在許多模式中散布。 127008.doc -11- 200835182 在車父佳實施例中，該雷射為雷射光輸出波長處於1530至 1 570 nm耗圍内之外腔雷射。此外，寬頻類比信號輸入具 有大於個倍頻程之頻寬且包括複數個相異資訊攜載通 道。 將頻率4皿別11 5之輸出施加至信號調節電路1 03，該信號 周節電路1 03由對於頻率鑑別器之輸出犯信號執行相異操 作之串聯連接序列電路組成。將灯信號施加至衰減器116 以恰畲調整該信號之振幅，以與雷射1〇2之相位雜訊特徵 所引入之相移分量的振幅相稱。 衰減器之輸出接著連接至相移電路i i 7。相移電路i i 7校 ::加至電路元件115、116、117之信號輸出與施加至調 k裔111之該信號相比的時滯。在所關注之視訊傳輸頻帶 (對於傳統CATV系統為中，半導體雷射 之相位雜巩為白”’即雜訊之頻譜功率密度與頻率無關。 在此情況T，相位校正路徑將需要具有恆定(可調整)增 益，其延遲恰好與主要路徑之延遲匹配。需要說明之一^ 態樣為頻率鑑別器’具體而言為相位校正路徑中之光學至 電予轉換過私。當光電二級體檢測到光學信號時，觀測到 稱為散射雜訊之現象。此雜訊由在光電二級體中吸收光子 以產生電子-電洞對之統計過程產生。此雜訊對於所有實 踐用途而言不可避免。因此’散射雜訊將對可實現之相位 雜訊消除量構成下限。Press, 2003, p. 154). In addition to the low noise characteristics required for 155 〇 nm analog optical transmission systems, the system must be highly linear. Distortion inherent in a particular analog transmitter prevents linear conversion of a linear electrical modulation signal into an optical signal, but causes the signal to become distorted. These effects are particularly harmful for multi-channel video transmissions: Multi-channel video transmission requires excellent linearity to prevent channels from interfering with each other. The analogy of two-degree linearization is widely used in commercial analog systems such as broadcast TV transmission, CATV, interactive TV and video telephony. Research on the linearization of optical and other non-linear transmitters has been going on for some time, but the proposed solution has drawbacks in practice. Most of the applications discussed above have bandwidths that are too large for many practical implementations. Forwarding techniques for linearization require complex system components such as optical power combiners and multiple light sources. Quasi-optical feedforward techniques suffer from similar complexities' and in turn require matching parts that are excellent. However, the forward-feeding technique for phase noise cancellation as described below is a practical technique that can be implemented using many well-developed techniques. As mentioned above, it is known to use external modulators in prior art with optical transmission systems. U.S. Patent No. 5,699,179 describes an externally modulated and feedforward linearized analog optical transmitter for reducing light 127008.doc 200835182 fiber induced composite primary (cso) distortion component. Prior to the present invention, phase modulators coupled to direct (current) modulated lasers have not been utilized for the purpose of eliminating phase noise components produced by various noise sources in laser semiconductor structures. It should be noted that a semiconductor laser exhibits noise in its amplitude (commonly referred to as relative intensity noise) and its phase. This is mixed. The fl characteristic is independent of the laser wavelength, but the noise can appear differently at different wavelengths in single mode fiber transmission. Leading to phase and amplitude The main internal mechanism of noise is the spontaneous emission in the active region of the laser. Since the spontaneously emitted photons have no specific phase relationship with their photons generated by stimulated emission, the amplitude and phase of the resulting light field are affected. Spontaneous emission of red is known and has not been described by the Brownian motion process, where the noise spectrum is essentially constant over the operating frequency (white noise). The environmental effects of external lasers such as microsonic effects, temperature fluctuations, and partial current noise can also produce phase noise in the light field. These events usually result in a phase of light that exhibits a noise spectrum with "1/f" dependencies. The present invention seeks to minimize the inherent phase noise from semiconductor lasers by feedforward cancellation without the driving mechanism of the (four) signal. SUMMARY OF THE INVENTION 1. Object of the Invention An object of the present invention is to provide a direct modulation lightning transmission system. Liang Ji: Another purpose of the invention is to compensate for the noise used in analog optical transmission. A further object of the present invention is to provide an external hnder modulator for use in an i55(R) analog optical transmission system to improve phase noise reduction. A further objective of this month is to provide a highly linear analog optical transmission system suitable for long-distance dispersion of optical fiber media using direct modulated lasers with phase correction circuitry. It is yet another object of the present invention to provide a phase shifting circuit for reducing residual phase noise from a laser in an analog optical transmission system suitable for long-distance distributed optical fiber media. The purpose of this disclosure is also to provide a phase noise compensation process in a broadband analog optical transmission system. 2. Inventive Features Briefly and in general terms, the present invention provides an optical transmitter for generating a modulated optical signal for transmission to a remote receiver via a distributed fiber optic link having an input for receiving a broadband analogy RF signal input; semiconductor field emission, which is used to generate an optical signal with associated phase noise; and noise cancellation circuit 'which includes an optical phase modulator for reducing light, phase noise in the transmitter output And further reducing signal distortion caused by phase modulated noise components present at the receiver end of the fiber optic link. In another aspect, the present invention provides an optical transmission system for use via a distributed optical fiber link, which includes: an optical transmission with analog signal input, a semiconductor laser; a modulation circuit for directly modulating the optical transmission system a laser; and a phase shifting circuit for canceling optical phase modulation components associated with the external modulator for optical signal noise generated by the semiconductor laser. 127008.doc 200835182 / In another aspect, the present invention further provides a low cost direct modulation technique, preferably comprising circuitry for controlling an optical phase modulator for reducing laser generation Phase noise component. In another aspect of the present invention, a noise cancellation circuit for reducing phase noise in an analog signal transmission wheel is provided, which outputs an output light from a semiconductor laser into two paths, one Go to the phase modulator and the other to the frequency discriminator. The phase modulation cancellation is adjusted in amplitude and phase to match the frequency or phase dependence of the phase noise generated by the laser. The phase of the signals is synchronized by a delay or phase adjustment element in one of the paths. The primary and secondary signals are then reconstructed by an optical phase modulator to produce a single optical signal having only amplitude modulation. Thus, the phase fade condition modulates the dominant signal from the semiconductor laser in a manner that minimizes the resulting phase noise so that the analog signal is suitable for transmission via the distributed fiber bond. Additional objects, advantages and novel features of the invention are apparent to those skilled in the <RTIgt; While the invention is described below with reference to the preferred embodiments, it should be understood that the invention is not limited thereto. Additional applications, modifications, and embodiments in other fields will be apparent to those skilled in the art, which are within the scope of the invention disclosed and claimed herein. It can have significant utility relative to it. [Embodiment] The details of the present invention, including its illustrative aspects and embodiments, will now be described. Referring to the following description of Figure a, the same reference numerals are used to identify the same or function 127008.doc 200835182 similar to the 'and' and it is intended to illustrate the main features of the exemplary embodiment 2 in a highly simplified schematic manner. In addition, the drawings are not intended to be an actual feature or the relative dimensions of the depicted elements, and the drawings are not to scale. . . Figure = is a block diagram of a prior art optical transmitter utilizing external modulation benefits as shown in U.S. Patent No. 5,699,179. The transmitter (usually shown at 10) transmits an optical signal to the receiver 6A via the fiber path 30. The transmitter 1 includes a semiconductor laser 12 that produces a continuous wave (cw) output. Typical examples of such lasers are distributed feedback (DFB) lasers and/or f-*(10) lightning bodies: 'which produces an output beam at a wavelength of 1,550 nm. From the laser: The optical signal is coupled to the modulator 16 by the optical fiber 14. The modulator 16 can be a single modulator such as a Mach-Zehnder modulator, a cascaded modulator, or more than one modulator such as in a feedforward linearization circuit. Modulation (10) also receives wideband RF signals, such as amplitude modulated vestigial sideband (AM-SDB) cable television (CATV) or video signals, via terminal 18 and line 20. In addition, when a feedforward linearization circuit is used, a depolarization signal is provided to the modulator 16 via terminal 22 and line 24. The depolarized signal is used to depolarize the optical input of the error correction modulator (not shown) in modulator 丨6. The modulated optical signal carrying the video material is coupled to amplifier 28 via a fiber optic link. Amplifier 28 is typically an erbium doped fiber amplifier (EDFA). The amplified optical ## is taken up to the optical fiber transmission line 3 to the receiver 60. The fiber optic transmission line 30 can be a long distance link that extends over several kilometers. In this case, a line amplifier such as EDFA 28 can be provided therein along the line at spaced distances to boost the signal to the desired level. 127008.doc -10- 200835182 At the receiver 60, an amplifier (not shown) may also be provided to boost the incoming optical signal. The boosted signal is then applied to the photodetector and demodulated at the receiver 60 to become an electrical signal representative of the original video or data signal at line 5〇. Figure 1 (b) is a block diagram of a prior art optical transmitter utilizing direct current modulation of a laser. The broadband RF analog signal is applied directly to the laser 12. The modulated optical signal from the laser 12 is coupled to an amplifier, such as an EDFA, via a fiber optic link 26. The amplified optical signal is coupled to a fiber optic transmission line 30 to a receiver (9). At the receiver, the optical signal is converted to an electrical signal that represents the original video or data signal at line 50. Figure 2 is a highly simplified block diagram of an optical transmission system 1 according to the present invention. The analog RF signal input source 101 (such as a wideband signal including a plurality of channels) and predistortion circuit 1〇5 are shown. The RF signal applied to the laser 1〇2 is suitably predistorted by using the predistortion circuit 1〇5, as is known in the prior art, for modifying the application to the laser 2RF signal to compensate for the effects of the laser. The nonlinear response of the signal. The output of the predistortion circuit 1〇5 is applied to the laser 102 to modulate it. The modulation of the laser 1 〇 2 in the present invention may be an AM-VSB modulator or a quadrature amplitude modulator. The laser optical signal output 110 is split into two parts. One portion is applied to the phase modulator 111; the other portion is applied to the frequency discrimination circuit 丨i5. The edge-emitting semiconductor laser used in the system of Figure 2 is preferably a distributed feedback laser (DFB), but a Fabry_Pert(Fp) laser can also be used. DFB lasers are the preferred approach because their optical output is primarily contained in a single laser mode, while the optical energy of the FP laser is spread across many modes. 127008.doc -11- 200835182 In the car parent embodiment, the laser is a laser beam with a laser light output wavelength in the range of 1530 to 1 570 nm. In addition, the wideband analog signal input has a bandwidth greater than one octave and includes a plurality of distinct information carrying channels. The output of the frequency band 11 is applied to the signal conditioning circuit 103, which consists of a series connected sequence circuit that performs a different operation on the output of the frequency discriminator. A lamp signal is applied to attenuator 116 to adjust the amplitude of the signal to match the amplitude of the phase shift component introduced by the phase noise characteristics of the laser 1〇2. The output of the attenuator is then connected to phase shift circuit i i 7 . The phase shift circuit i i 7: the time delay of the signal output to the circuit elements 115, 116, 117 compared to the signal applied to the chirp 111. In the video transmission frequency band of interest (for a conventional CATV system, the phase of the semiconductor laser is white), that is, the spectral power density of the noise is independent of the frequency. In this case, the phase correction path will need to be constant ( Adjustable) Gain, whose delay exactly matches the delay of the main path. One of the explanations is the frequency discriminator', specifically the optical-to-electrical pre-transformation in the phase-corrected path. When it comes to optical signals, a phenomenon called scattering noise is observed. This noise is generated by the statistical process of absorbing photons in the photodiode to generate electron-hole pairs. This noise is inevitable for all practical purposes. Therefore, 'scattering noise' will constitute the lower limit for the amount of phase noise cancellation that can be achieved.
Ik後將相移電路117之輪出施加到相位調變器⑴，以進 而將相位校正引入至光學信號中以進而校正或補償所產生 127008.doc -12- 200835182 之雜訊。 自光電二級體產生之光電流的頻譜雜訊密度給定為 <in2>=2elp 其中6為電子電荷且Ip為DC光電流。熟習此項技術者將立 即瞭解到此事實··雜訊功率對於所接收之光學功率具有線 I*生相依性’且因此受散射雜訊支配之過程之信號雜訊比隨 著所接收功率之增加而改良。此代表所提議發明中之基本 口又汁折衷。分接至相位校正路徑中之較多功率將以傳輸器 之光學輸出功率為代價而改良最終雜訊消除。 调變器111之輸出經由光纖112耦合至放大器113，該放 大為113隨後連接至光纖或鏈路114。在遠端處，光纖或鏈 路114連接至接收器，該接收器將所接收之光學信號轉換 為RF信號。 在不脫離本發明之精神及範圍之情況下，熟習此項技術 者將容易瞭解許多改變及修改。舉例而言，儘管在τν信 號調變雷射或發光二級體之上下文中作出描述及說明，但 諸如放大器之其它非線性裝置之固有失真可大量藉由此技 術消除。主要及次要路徑中之信號之相對相位之精密調整 在所說明之實施例中為在次要路徑中，但此亦可在具有粗 略調整之主要路徑中。次要路徑較佳，因為主要路徑中之 此類延遲可對於此路徑具有不恰當之阻抗。 本發明之技術及设備之各項態樣可在數位電路、或電腦 硬體、章刃體、軟體或其組合中實施。本發明之電路可於電 腦產品（其有形地實施於機器可讀存儲裝置中以由可程式 127008.doc 200835182 化處理器執行）中實施或在位於網路節點或網站處之軟體 (其可自動或根據需要下載至電腦產品)上實施。前述技術 。可由（例如）單個中央處理器、多處理器、__或多個數位信 號處理器、邏輯閘之閘陣列或硬連線邏輯電路執行，用於 執行一序列信號或指令程式以藉由操作輸入資料且產生輸 出而執订本發明之功能。該方法可有利地在可於可程式化 系統上執行之一或多個電腦程式中實施，該可程式化系統 包括至少-個經麵合以自資料存儲系統接收資料及指令且 向資料存儲系統傳輸資料及指令之可程式化處理器、至少 一個輸入/輸出裝置及至少一個輸出裝置。每一電腦程式 可視需要以高級程序或面向對象之程式化語言或以组合1 機器語言實施’·且在任何情況下’該語言可為編譯或翻譯 :言。舉例而言，適宜處理器包括通用微處理器及專用微 兩者―般而言’處理器將自只讀記憶體及/或隨 ^^己‘_接收指令及資料。適合於有形地實施電腦程 以曰令及:貝料之存儲裝置包括所有形式之非揮發性記憶 體’舉例而言包括：半導體裝置’諸如EpR⑽、E咖〇M =閃記憶體裝置；磁碟’諸如内部硬碟及抽取式 光碟，以及CD-ROM碟。任何前述裝置可由特 用積體電路（ASIC)補充或併入於ASI(：中。 寻 :瞭：，上述元件中之每—者或者兩者或兩者一 起^有效應詩與上㈣型不同之其它_之構造。 儘官已經將本發明說明且描述為實施於 中，但不教其限於所展示之纟 #輸糸、、先 U馮了在不以任何方 127008.doc -14- 200835182 式脫離本發明精神之情況下作出各種修改及結構變化。 二不作進一步分析之情況下，前述内容將如此全面揭露 本發明之要點，使得其他人可夢 精由應用當前知識而在不省 技術立場上完全構成本發明—般或料態樣之本 = 特徵之情況下容易將其調適以用於各種應用，且 意思及範圍内。 在乂下“專利範圍之均等 【圖式簡單說明】 藉由結合㈣參看以謂細描述，將更佳瞭解且更全面 理解本發明之此等及其它特徵及優點，其中： 圖1⑷為先前技術中已知之外部調變光學傳輸系統之高 度簡化方塊圖； ，1(b)為先前技術中已知之直接調變光學傳輪系統之高 度簡化方塊圖； 圖2為根據本發明之光學傳輸系統之高度簡化方塊圖。 於所附申請專利範圍中陳述本發明之新賴特徵及特性。 然而’可藉由結合附圖參看對具體實施例之詳細描述而最 佳瞭解本發明本身以及其其它特徵及優點。 【主要元件符號說明】 10 傳輸器 12 半導體雷射 14 光纖 16 調變器 18 端子 127008.doc -15- 200835182 20 22 24 26 28 30 ' 50 60 101 102 105 110 111 112 113 114 115 116 . 117 線路 端子 線路 光纖鏈路 放大器 光纖傳輸線路 線路 接收器 類比RF信號輸入源 雷射 預失真電路 光學信號輸出 相位調變器 光纖 放大器 光纖（鏈路） 頻率鑑別電路 衰減器 相移電路 127008.doc -16-Ik then applies the wheeling of phase shifting circuit 117 to phase modulator (1) to thereby introduce phase correction into the optical signal to thereby correct or compensate for the noise generated by 127008.doc -12-200835182. The spectral noise density of the photocurrent generated from the photodiode is given by <in2>=2elp where 6 is the electron charge and Ip is the DC photocurrent. Those skilled in the art will immediately understand the fact that the noise power has a line I* dependency on the received optical power' and therefore the signal-to-noise ratio of the process dominated by the scattered noise follows the received power. Increase and improve. This represents a fundamental compromise between the proposed inventions. More power tapped into the phase correction path will improve the final noise cancellation at the expense of the optical output power of the transmitter. The output of modulator 111 is coupled via fiber 112 to amplifier 113, which is then connected to fiber or link 114. At the far end, the fiber or link 114 is connected to a receiver that converts the received optical signal into an RF signal. Many variations and modifications will be readily apparent to those skilled in the art without departing from the scope of the invention. For example, although described and illustrated in the context of a τν signal modulated laser or illuminating diode, the inherent distortion of other non-linear devices such as amplifiers can be largely eliminated by this technique. The fine adjustment of the relative phase of the signals in the primary and secondary paths is in the secondary path in the illustrated embodiment, but this may also be in the primary path with coarse adjustments. The secondary path is preferred because such delays in the primary path can have an inappropriate impedance for this path. Aspects of the techniques and apparatus of the present invention can be implemented in digital circuits, or in computer hardware, in a blade, in a software, or in a combination thereof. The circuitry of the present invention can be implemented in a computer product (which is tangibly embodied in a machine readable storage device for execution by a programmable 127008.doc 200835182 processor) or in a software located at a network node or website (which can be automated) Or download it to the computer product as needed. The aforementioned technology. Executable by, for example, a single central processing unit, multiple processors, __ or multiple digital signal processors, logic gate arrays, or hardwired logic circuits for executing a sequence of signals or instruction programs for operation input The functions of the present invention are documented and produced. The method can advantageously be implemented in one or more computer programs executable on a programmable system, the programmable system including at least one surface to receive data and instructions from the data storage system and to the data storage system A programmable processor for transmitting data and instructions, at least one input/output device, and at least one output device. Each computer program can be implemented in a high-level program or an object-oriented stylized language or in a combined 1 machine language as needed. In any case, the language can be compiled or translated. For example, a suitable processor, including a general purpose microprocessor and a dedicated micro, will generally receive instructions and data from a read-only memory and/or as a result. Suitable for tangible implementation of computer programs and storage devices: the storage device for beryllium includes all forms of non-volatile memory 'for example: semiconductor devices such as EpR (10), E-Curry M = flash memory device; 'such as internal hard drives and removable discs, as well as CD-ROM discs. Any of the foregoing devices may be supplemented by an Integral Integrated Circuit (ASIC) or incorporated into ASI (:. Seeking:: each of the above elements, or both or both). The effect poem is different from the upper (four) type. The other embodiments have been described and described as being implemented in the present invention, but are not taught to be limited to the ones shown, and the first U von is not on any side 127008.doc -14- 200835182 Various modifications and structural changes can be made without departing from the spirit of the invention. In the case of no further analysis, the foregoing will fully disclose the gist of the present invention so that others can use the current knowledge without a technical standpoint. In the case of the present invention, it is easy to adapt it to various applications, and within the meaning and scope of the present invention. In the following, "the equality of patent scope [simple description of the schema] by combining (d) Referring to the detailed description, these and other features and advantages of the present invention will be better understood and more fully understood, wherein: Figure 1 (4) is the height of the externally modulated optical transmission system known in the prior art. Simplified block diagram; 1(b) is a highly simplified block diagram of a direct modulation optical transmission system known in the prior art; and Figure 2 is a highly simplified block diagram of an optical transmission system in accordance with the present invention. The present invention and its other features and advantages will be best understood from the following detailed description of the embodiments. 12 semiconductor laser 14 fiber 16 modulator 18 terminal 127008.doc -15- 200835182 20 22 24 26 28 30 ' 50 60 101 102 105 110 111 112 113 114 115 116 . 117 line terminal line fiber link amplifier fiber transmission line Line line receiver analog RF signal input source laser predistortion circuit optical signal output phase modulator fiber amplifier fiber (link) frequency discrimination circuit attenuator phase shift circuit 127008.doc -16-