200840362 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信號之光學傳輸系統，且特 疋言之係關於一種直接調變或外部調變固態雷射器。此 外，本發明係關於消除由半導體雷射器内諸如電荷載流子 之布朗運動之諸多可能來源產生之白雜訊分量（白雜訊）或 由雷射器之偏壓電流或熱環境中之波動產生之雜訊（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極體（LED)或半導體雷射 态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^類比 傳輸技術之優點在於與諸如數位脈衝代碼調變或者類比或 脈衝頻率調變之數位傳輸相比具有顯著較小之頻寬要求<， 但使用振幅調變通常對傳輸器之雜訊及失真特徵提出較為 嚴格之要求。 由於此等原目，在應用於採用$有零散射之光纖鍵路之 短傳輸鏈路之情況下，已經結合1310 nm雷射器使用直接 調變技術。對於應用於城域及長距離光纖傳輸鏈路，鏈路 2損耗要求使用外部調變之1550 nm雷射器，通常越過非 *長之距離（100 km)及高頻率（超過900 MHz)。此類鏈路之 限制因素可能為來自雷射器之殘餘相位雜訊之轉換，該殘 餘相位雜訊經由光纖鏈路中存在之散“轉換成振幅雜 訊。本發明因此專注於提供用於與雷射器之相位雜訊相關 127009.doc 200840362 聯之雜訊消除之簡單且低成本系統的問題，以便類比光學 輸出可用於城域及長距離光學網路，尤其用於寬頻RF信號 之類比傳輸。 雷射器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，and200840362 IX. Description of the Invention: [Technical Field] The present invention relates to an optical transmission system for analog signals, and in particular to a direct modulation or external modulation solid state laser. Furthermore, the present invention relates to the elimination of white noise components (white noise) generated by many possible sources of Brownian motion in a semiconductor laser, such as charge carriers, or in a bias current or thermal environment by a laser. Noise generated by fluctuations (which change in opposite frequency, and is therefore often referred to as "1/f" noise). [Prior Art] It is believed that the use of electrical signals to directly modulate the analog intensity of a light-emitting diode (LED) or semiconductor laser state is the simplest known in the art for transmitting analog signals such as voice and video signals over optical fibers. method. Although the advantage of this analog transmission technique is that it has significantly smaller bandwidth requirements than digital transmissions such as digital pulse code modulation or analog or pulse frequency modulation, the use of amplitude modulation is often miscellaneous to the transmitter. The signal and distortion characteristics impose stricter requirements. For these purposes, direct modulation techniques have been used in conjunction with 1310 nm lasers in the case of short transmission links using fiber-optic links with zero-scatter. For metro and long-haul fiber-optic transmission links, link 2 loss requires the use of an externally modulated 1550 nm laser, typically over a long distance (100 km) and a high frequency (over 900 MHz). A limiting factor for such links may be the conversion of residual phase noise from the laser, which is "converted into amplitude noise" via the presence of the fiber link. The present invention therefore focuses on providing Laser phase noise related 127009.doc 200840362 The problem of simple and low-cost systems for noise cancellation, so that analog optical output can be used for metro and long-haul optical networks, especially for analog transmission of wideband RF signals. Direct current modulation of lasers is also known for digital optical transmission systems, such as high density wavelength division multiplexing (DWDM) systems. See, for example, "DWDM Netw〇rks, Devices, and Kartalopoulos".
TeChn〇l〇gy”（lEEE Press，2003，第 154 頁）。 除對於1550 nm類比光學傳輸系統所要求之低雜訊特徵 以外，该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 σ "亥夕通道視訊傳輸要求極佳之線性以防通道彼此干 擾。高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…及視訊電話傳 輸。 作為對於直接電流調變之替代方式，已知於先前技術中 =光學傳輸系統中㈣連續波（cw)雷射器之外部調變器。 第5,699，179#u美國專利描述—種外部調變之前饋線性化類 比光學傳輸器’其用於減少光纖誘發之複合二次（cs⑺失 真分量。 對光學及其它非線性傳輪器之線性化之研究已經持續_ 段時間，但所提議之解決方案在實踐中具有缺點。上文論 述之大部分應賴具有之頻寬對於許多實際實施方案^ 過大。用於線性化之前饋技術f要複雜之系統組件，諸如 127009.doc 200840362 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。 在本發明之前，尚未應用耦合至外部調變雷射器之相位 調變器以用於消除由雷射器之半導體結構中之各種雜訊源 產生之相位雜汛分量之目的。應注意，半導體雷射器在其 振幅（通常稱為相對強度雜訊）及其相位中均展現雜訊。此 等雜訊特性本質上與雷射波長無關，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λ之主要内部機制為雷射器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 射過耘為热知的，且已經展示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）。在雷射器 外部，諸如微音效應、溫度波動及偏壓電流雜訊之環境影 響亦可於光場中產生相位雜訊。此等事件通常導致光相位 雜訊，其展現具有”l/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器之固 有相位雜訊而不論雜訊之驅動機制如何。 【發明内容】 i 發明目的 本發明之目的在於提供一種使用外部調變雷射器之改良 光學傳輸系統。 127009.doc 200840362 本發明之另一目的在於補償用於光學傳輸系統之雷射器 中之雜訊。 本叙明之再一目的在於提供一種用於外部調變丨55〇 nm 類比光學傳輸系統以改良相位雜訊降低之外部相位調變 器。 、 本發明之又一目的在於提供一種適用於遠距離分散光纖 媒體且使用外部調變雷射器連同耦合至光學信號之相位校 (、 正電路及相位調變器之高度線性光學傳輸系統。 本t月之又目的在於提供一種用於在適用於遠距離分 政光纖媒體之類比光學傳輸系統中降低來自外部調變雷射 器之殘餘相位雜訊之相移電路。 本發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 簡單且概括而言，本發明提供一種用於產生調變光學信 〇 唬以經由光纖鏈路傳輸至遠端接收器之光學傳輸器，其包 括·雷射器；調變器，其用於用RF信號外部調變該雷射 、 器，以產生包括含有調變資訊分量之光學信號；以及相位 凋文器，其耦合至該調變器之輸出端，以用於消除該雷射 • 裔中產生之雜訊信號。 另恶樣中’本發明提供一種用於產生調變光學信號以 經由分散光學鏈路傳輸至遠端接收器之光學傳輸器，其具 有·半導體雷射器，其用於產生具有相關聯相位雜訊之光 子L唬，雜訊消除電路，其耦合至該雷射器之輸出端，且 127009.doc 200840362 :括用於降低雷射器中產生之相位雜訊之光學相位調變 态，以及外部調變1立 ° ，、輕合至該相位調變器之輸出端且 用於=寬頻類比射頻信號輸人且調變該光學信號。 另心樣中，本發明提供一種用於經由分散光纖鏈路使 用之光學傳m其包括：具有類比或數位職號輸入 之光學傳輸器；半導體雷射器；調變電路，其用於外部調TeChn〇l〇gy” (lEEE Press, 2003, p. 154). In addition to the low noise characteristics required for the 1550 nm analog optical transmission system, the system must be highly linear. Distortion prevention inherent in specific analog transmitters The linear electrical modulation signal is linearly converted into an optical signal, which causes the signal to become distorted. These effects are particularly σ" for multi-channel video transmission, which requires excellent linearity to prevent channels from interfering with each other. Linearization analog optical systems are widely used in commercial analog systems, such as broadcast TV transmission, CATV, interactive... and video telephony transmission. As an alternative to direct current modulation, it is known in the prior art = optical transmission system (4) External modulating device for continuous wave (cw) lasers. 5, 699, 179 #u US Patent Description - Externally modulated pre-feed linearized analog optical transmitter 'which is used to reduce fiber-induced composite quadratic (cs(7) distortion) The research on the linearization of optical and other nonlinear wheel-passers has been going on for a while, but the proposed solution is There are disadvantages in the above. Most of the above discussion should have a bandwidth that is too large for many practical implementations. It is used to linearize the system components before the feed technology f, such as 127009.doc 200840362 optical power combiner and multiple Light source. Quasi-optical feedforward technology suffers from similar complexity problems and, in turn, needs to be matched to excellent parts. However, as discussed below, the feedforward technique for phase noise cancellation is a practical technique that can be implemented using many well-developed techniques. Prior to the present invention, phase modulators coupled to externally modulated lasers have not been utilized for the purpose of eliminating phase noise components produced by various sources of noise in the semiconductor structure of the laser. It should be noted that Semiconductor lasers exhibit noise in their amplitude (commonly referred to as relative intensity noise) and their phase. These noise characteristics are essentially independent of the laser wavelength, but the noise can be different in single mode fiber transmission. The wavelength appears in different ways. The main internal mechanism that causes the phase and amplitude λ is the spontaneous emission in the active region of the laser. The photons have no specific phase relationship with their photons generated by stimulated emission, and thus the amplitude and phase of the resulting light field are affected. Spontaneous emission is known to be well known and has been shown to be described by the Brownian motion process. The spectrum is essentially constant over the operating frequency (white noise). Outside the laser, environmental influences such as microsonic effects, temperature fluctuations, and bias current noise can also produce phase noise in the light field. Events typically result in optical phase noise, which exhibits a noise spectrum with "l/f" dependence. The present invention seeks to minimize the inherent phase noise from the semiconductor laser by feedforward cancellation regardless of the driving mechanism of the noise. SUMMARY OF THE INVENTION i OBJECT OF THE INVENTION It is an object of the present invention to provide an improved optical transmission system using an externally modulated laser. 127009.doc 200840362 Another object of the invention is to compensate for noise in a laser for an optical transmission system. A further object of the present description is to provide an external phase modulator for externally modulated 丨55〇 nm analog optical transmission systems to improve phase noise reduction. It is still another object of the present invention to provide a highly linear optical transmission system suitable for remotely dispersing optical fiber media and using an externally modulated laser with phase correction (positive circuit and phase modulator) coupled to the optical signal. A further object of the present invention is to provide a phase shifting circuit for reducing residual phase noise from an externally modulated laser in an analog optical transmission system suitable for long-range optical fiber media. The object of the present invention is also to provide A phase noise compensation process in a broadband analog optical transmission system. 2 · Inventive Features Simple and general, the present invention provides an optical for generating a modulated optical signal for transmission to a remote receiver via a fiber optic link a transmitter comprising: a laser; a modulator for externally modulating the laser with an RF signal to produce an optical signal comprising a modulated information component; and a phase sigma coupled to The output of the modulator is used to eliminate the noise signal generated in the laser. In addition, the present invention provides a method for generating modulation The optical signal is transmitted to the optical receiver via the decentralized optical link to the remote receiver, which has a semiconductor laser for generating a photon L唬 with associated phase noise, a noise cancellation circuit coupled to The output of the laser, and 127009.doc 200840362: includes an optical phase modulation for reducing phase noise generated in the laser, and an external modulation of 1 deg, and light coupling to the phase modulation The output of the device is used for = broadband analog RF signal input and modulation of the optical signal. In addition, the present invention provides an optical transmission for use via a distributed optical fiber link including: analogy or digital position Optical transmitter; semiconductor laser; modulation circuit for external adjustment
丈該田射…以及用於消除與半導體雷射器所產生之雜訊 相關聯之光學相位調變分量之電路。 本發月之另_悲樣中，提供_種用於在類比信號傳輸中 降低相位雜訊之雜訊消除電路，其將來自半導體雷射器之 外部調變器之輸出光學信號***成兩個路徑，—個通往相 位调變器且另-個通往頻率鑑別器。於振幅及相位上調整 該相位調變消除信號，以匹配雷射器產生之相位雜訊之頻 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同步。接著藉由相位調變器重組主 要及次要信號，以產生僅具有振幅調變之單個光學信號。 因此相位调變器以最小化所得相位雜訊之方式調變來自 半導體雷射器之主要信號，從而使得類比信號適於經由分 散光纖鏈路傳輸。 根據此揭示（包括以下詳細描述在内）以及藉由實踐本發 明’熟習此項技術者將易於瞭解本發明之額外目的、優點 及新穎特徵。儘管下文參看較佳實施例描述本發明，但應 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内之額外應用、修改及實施 127009.doc 200840362 例，該等額外應用、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㈣樣及實施例。 參看附圖及以下描述，4目同參考標號用於識別相同或功能 相似之元件’且希望以高度簡化之圖解方式說明例示性實 施例之主要特徵。此外，不希望附圖描繪實際實施例之每 個特徵或所描繪元件之相對尺寸，且附圖並非按比例繪 製。 囷為如第5,699，179號美國專利中展現之利用外部調變 為之先則技術光學傳輸器之方塊圖。該傳輸器（通常用ι〇 展不）經由光纖路徑30向遠端接收器6〇發射光學信號。傳 輸：ίο包括半導體雷射器12，其產生連續波(cw)輸出。此 類語射w之典型實例為分布式反饋（dfb)雷射器及/或 雷射11，其通常以1550 nm之波長產生輸出光 束來自雷射器之未調變光學信號藉由光纖14耦合至調變 σσ 16凋變器16可為諸如Mach-Zehnder調變器之單個調變 裔、級聯MZ調變器或諸如前饋線性化電路中之一個以上 凋支裔。调變器16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_sd⑴有線電視或The field... and the circuit used to eliminate the optical phase modulation component associated with the noise generated by the semiconductor laser. In another _ sad sample of this month, a noise cancellation circuit for reducing phase noise in analog signal transmission is provided, which splits the output optical signal of the external modulator from the semiconductor laser into two The path, one to the phase modulator and the other to the frequency discriminator. The phase modulation cancellation signal is adjusted in amplitude and phase to match the frequency or phase dependence of the phase noise generated by the laser. The phases of the signals are synchronized by delay or phase adjustment elements in one of the paths. The primary and secondary signals are then recombined by a phase modulator to produce a single optical signal having only amplitude modulation. The phase modulator therefore modulates the dominant signal from the semiconductor laser in a manner that minimizes the resulting phase noise, thereby making the analog signal suitable for transmission via a split fiber link. Additional objects, advantages and novel features of the invention are apparent from the <RTIgt; </ RTI> <RTIgt; </ RTI> <RTIgt; Although the invention is described below with reference to the preferred embodiments, it should be understood that the invention is not limited thereto. Those of ordinary skill in the art will be able to recognize additional applications, modifications, and implementations in other fields. The additional applications, modifications, and embodiments are within the scope of the invention disclosed and claimed herein. The invention can be used with respect to it. [Embodiment] The details of the present invention, including the exemplary (four) and examples thereof, will now be described. The reference numerals are used to identify the same or functionally similar elements, and the main features of the exemplary embodiments are illustrated in a highly simplified schematic manner. In addition, the drawings are not intended to depict the particular features of the various embodiments of the embodiments. A block diagram of a prior art optical transmitter using external modulation as shown in U.S. Patent No. 5,699,179. The transmitter (usually unabling) transmits optical signals to the remote receiver 6A via the fiber path 30. Transmission: ίο includes a semiconductor laser 12 that produces a continuous wave (cw) output. A typical example of such a speech w is a distributed feedback (dfb) laser and/or laser 11, which typically produces an output beam at a wavelength of 1550 nm. The unmodulated optical signal from the laser is coupled by fiber 14 to The modulated σσ 16 fader 16 can be a single modulation, such as a Mach-Zehnder modulator, a cascaded MZ modulator, or one or more of the feeders, such as a feedforward linearization circuit. The modulator 16 also receives a wideband rf signal such as an amplitude modulated vestigial sideband (am_sd(1) cable or via terminal 18 and line 20.
視訊仏唬。此外，當使用前饋線性化電路時，經由端子U 及線路24向調變器16提供去偏振信號。該去偏振信號用於 於凋、文斋16中將到達誤差校正調變器（未圖示）之光學輸入 去偏振。 127009.doc 200840362Video video. In addition, when a feedforward linearization circuit is used, a depolarization signal is provided to the modulator 16 via terminal U and line 24. The depolarized signal is used to depolarize the optical input of the error correction modulator (not shown) in the withering and texting 16 . 127009.doc 200840362
攜載視訊資料之經調變光學信號藉由光纖鏈路26耦合至 放大器28。放大器28通常為铒摻雜光纖放大器（EDFA)。經 放大之光學信號耦合至通往接收器60之光纖傳輸線路30。 該光纖傳輸線路3 0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。 在接收器60處，亦可提供放大器（未圖示）以升壓傳入之光 學h號。隨後將經升壓之信號施加至光電偵測器且於接收 器60處解調變以產生電信號，該電信號代表線路5〇處之原 始視訊或資料信號。 圖2為根據本發明第一實施例利用外部調變器之光學傳 輸器之方塊圖。該傳輸器（通常用100展示）將光學信號經由 光纖路徑30傳輸至遠端接收器。傳輸器ι〇〇包括半導體雷 射器101，其產生連續波（CW)輸出。此類雷射器之典型實 例為分布式反饋（DFB)雷射器及/或Fabry-per0t雷射器，其 通常以155〇 nm之波長產生輸出光束。 圖2系統中使用之邊緣發射半導體雷射器較佳為分布式 反饋雷射器（DFB)，但同樣可使用Fabry_Per〇t(Fp)雷射 器。DFB雷射器為較佳途徑，因為其光學輪出主要包含於 單個雷射模式中，而FP雷射器之光學能量於許多模式中散 布。在較佳實施例中，該雷射器為雷射器光輸出波長在 1530至1570 nm範圍内之外腔雷射器。 來自雷射器之未調變光學信號***成兩個部分；第一部 分藉由光纖103耦合至調變器1〇2。調變器 ° Z可為诸如 127009.doc -11 - 200840362The modulated optical signal carrying the video material is coupled to amplifier 28 via fiber optic link 26. Amplifier 28 is typically an erbium doped fiber amplifier (EDFA). The amplified optical signal is coupled to fiber optic transmission line 30 to 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. At the receiver 60, an amplifier (not shown) may also be provided to boost the incoming optical h-number. The boosted signal is then applied to the photodetector and demodulated at the receiver 60 to produce an electrical signal representative of the original video or data signal at line 5〇. Figure 2 is a block diagram of an optical transmitter utilizing an external modulator in accordance with a first embodiment of the present invention. The transmitter (generally shown at 100) transmits the optical signal to the remote receiver via fiber path 30. The transmitter ι includes a semiconductor laser 101 that produces a continuous wave (CW) output. Typical examples of such lasers are distributed feedback (DFB) lasers and/or Fabry-per0t lasers, which typically produce an output beam at a wavelength of 155 〇 nm. The edge-emitting semiconductor laser used in the system of Figure 2 is preferably a distributed feedback laser (DFB), but a Fabry_Per〇t (Fp) laser can also be used. DFB lasers are the preferred approach because their optical wheeling is primarily contained in a single laser mode, while the optical energy of the FP laser is spread in many modes. In a preferred embodiment, the laser is an external cavity laser having a laser light output wavelength in the range of 1530 to 1570 nm. The unmodulated optical signal from the laser is split into two parts; the first part is coupled to the modulator 1〇2 by the optical fiber 103. The modulator ° Z can be such as 127009.doc -11 - 200840362
Mach-Zehnder調變器之單個調變器、級聯MZ調變器或諸 如前饋線性化電路中之一個以上調變器。調變器1〇2經由 端子104及線路1〇5接收諸如振幅調變殘留邊帶（AM-SDB) 有線電視（CATV)或視訊信號之寬頻RF信號或者數位信 號。類比信號可具有大於一個倍頻程之頻寬且攜載複數個 通道。此外，當使用前饋線性化電路時，類似於圖丨之配 置向调變器提供去偏振信號。該去偏振信號用於於調變器 102中將到達誤差校正調變器（未圖示）之光學輸入去偏振。 如上文提到的，雷射器之光學信號輸出***成兩個部 分：一個部分施加至調變器102;另一部分藉由光纖1〇6耦 合至頻率鑑別器107。 將頻率鑑別器107之輸出施加至衰減器i 〇8以恰當地調整 該信號之振幅，以與雷射器101之相位雜訊特徵所引入之 相位調變分量之振幅相稱。 衰減器108之輸出隨後連接至相位偏移電路1〇9。電路 109校正施加至電路元件107、1〇8之信號輸出與直接施加 至調變器102之該信號相比之時滯。在所關注之視訊傳輸 頻帶（對於傳統CATV系統為5〇 MHz-1000 MHz)中，半導體 雷射器101之相位雜訊為”白”，即雜訊之頻譜功率密度與 頻率無關。在此情況下，相位校正路徑1〇6、1〇7、1〇8、 1〇9將需要具有恆定（可調整）增益，其延遲恰好與主要路徑 1〇3、102及110之延遲匹配。需要說明之一項態樣為頻率 鑑別器107對信號之作用，具體而言為相位校正路徑中之 光學至電學轉換過程的結果。當光電二極體檢測到光學信 127009.doc •12- 200840362 遽％ ’觀测到稱為散射雜訊之現象。此雜訊由在光電二極 體中吸收光子以產生電子-電洞對之統計過程產生。此雜 汛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。 隨後將相位偏移電路109之輸出施加至相位調變器110， 以進而藉由其相位調變將相位校正引入至光學信號中以進 而才父正或補償雷射器所產生之雜訊。 自光電二極體產生之光電流之頻譜雜訊密度給定為 <in2>=2elp 其中e是電子電荷且。是DC光電流。熟習此項技術者將立 即瞭解此事實：雜訊功率對於所接收之光學功率具有線性 相依〖生’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得以改良。此代表所提議發明中之基 本設計折衷。分接至相位校正路徑1〇6、ι〇7、ι〇8、ι〇9··. 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 終相位雜訊消除。 相位調變器110之輸出經由光纖U1耦合至放大器112， 該放大器112隨後連接至光纖或鏈路3〇。在遠端處，光纖 或鏈路30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，類似於圖1中展現的。 圖3為根據本發明第二實施例利用外部調變器之光學傳 輸器之方塊圖。邊傳輸器（通常用2〇〇展示）將光學信號經由 光纖路徑30傳輸至遠端接收器。傳輸器2〇〇包括半導體雷 射器101，其產生連續波（cw)輸出。此類雷射器之典型實 127009.doc -13- 200840362 例為分布式反饋（DFB)雷射器及/或Fabry-Perot雷射器，其 通常以1550 nm之波長產生輸出光束。來自雷射器之未調 變光學信號***成兩個部分；一個部分藉由光纖1 〇3耦合 至相位調變器110。相位調變器11〇將相位校正引入至光學 信號中’以進而校正或補償雷射器所產生之雜訊。相位調 變為110之CW輸出搞合至調變器1〇2，以產生含有調變資 訊之光學信號。 调變器102可為諸如Mach-Zehnder調變器之單個調變 裔、級聯MZ调變器或諸如前饋線性化電路中之一個以上 調變器。調變器102經由端子1〇4及線路105接收諸如振幅 調變殘留邊帶（AM-SDB)有線電視（CATV)或視訊信號之寬 頻RF信號或者數位信號。此外，當使用前饋線性化電路 時，類似於圖1之配置向調變器提供去偏振信號。該去偏 振信號用於對調變器1〇2中之誤差校正調變器（未圖示）之光 學輸入去偏振。 如上文提到的，雷射器之光學信號輸出***成兩個部 分：一個部分施加至相位調變器丨1〇 ;另一部分藉由光纖 106麵合至頻率鑑別電路1〇7。 將頻率鑑別器107之輸出施加至衰減器108以恰當調整該 4吕號之振幅，以與雷射器1 〇 1之相位雜訊特徵所引入之相 位調變分量之振幅相稱。 衰減器108之輸出隨後連接至相位偏移電路1〇9。電路 109校正施加至電路元件1〇7、108之信號輸出與施加至相 位調變器110之該信號相比之時滞。在所關注之視訊傳輸 127009.doc -14- 200840362 頻帶（對於傳統CATV系統為50 MHz-1000 MHz)中，半導體 田射器101之相位雜訊為，,白”，即雜訊之頻譜功率密度與 頻率無關。在此情況下，相位校正路徑1〇6、1〇7、1〇8、 109將需要具有恆定（可調整）增益，其延遲精確匹配於主要 路徑103、102及110之延遲。需要說明之一項態樣為頻率 鑑別器107，具體而言為相位校正路徑中之光學至電學轉 換過程。f光電二極體檢測到光學信號時，觀測到稱為散 射雜訊之現象。此雜訊係由在光電二極體中吸收光子以產 生電子-電洞對之統計過程所產生。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。 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，儘管在視訊或 夕通道TV信號調變雷射器或發光二極體之上下文中作出 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☆此路徑具有不恰當之阻 抗。 本發明之技術及㈣之各項態樣可在數位電路、或電腦 硬體、㈣、軟體或其組合中實施。本發明之電路可^ 腦產品（其有形地實施於機器可讀存儲裝置中以由可程 化處理器執行)中實施或在位於網路節點或網站處之軟體 127009.doc -15- 200840362 (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 ^ ^ w m ^A 、—或多個數位信 執:、邏輯閉之間陣列或硬連線邏輯電路執行，用於 =2!號或指令程式以藉由操作輪入資料且產生輸 出而執仃本發明之功能。該方 ^, ^ y j有利地在可於可程式化 …執…或多個電腦程式中實施，該可程式化系統 個'_合以自資料存儲系統接《料及指令且 向-貝料存儲系統傳輸資料及指令 j %式化處理器、至少 一個輸入/輸出裝置及至少一 ^目不高 滅置。母一電腦程式 了視萬要以高級程序或面向對象 嫌哭&山虫 心柱式化浯g或以組合或 機时彡口吕μ施’·且在任何情況 士五^ 血， 成^ a可為編譯或翻譯 口口 s。舉例而言，適宜處理器 卢g匕括通用微處理器及專用微 处里恣兩者。一般而言，處 德六& 益將自只讀記憶體及/或隨 機存取記憶體接收指令及資料。 斗、此人 ^ σ於有形地實施電腦程 式“及資料之存儲裝置包括所有形式之非揮發性記憶 體，舉例:言包括··半導體褒置，諸如epr〇m、㈣汉⑽ =閃記憶體裝置；磁碟’諸如内部硬碟及抽取式碟；磁 _’·以及CD_R〇_。任何前述裝置可由特別設計之專 用積體電路（ASIC)補充或併入於ASIC中。 將瞭解，上述元件中之每一者或者兩者或兩者以上在一 起亦:有效應用於與上述類型不同之其它類型之構造。 儘管已經將本發明說明日ρ 兄月且七田迷為實施於光學傳輸系統 ’旦不希望其限於所展示之細節，因為可在不以任何方 式脫離本發明精神之情況下作出各種修改及結構變化。 127009.doc •16- 200840362 在不作進一步分析之情二 本發明之^你 則述内容將如此全面展現 4呶Θ之要點，使得其 了精由應用當前知識而在不省 ⑨在先則技術立場上 曾牲& 兀王構成本發明一般或特定態樣之本 夤特〖生之特徵之情況下容 ra L, lL ^ 肝其_適以用於各種應用，且 口此此頒調適應當且希望包 音田 匕3在以下申請專利範圍之均等 w心及乾圍内。 【圖式簡單說明】A single modulator of a Mach-Zehnder modulator, a cascaded MZ modulator or one or more modulators such as a feedforward linearization circuit. The modulator 1〇2 receives a wideband RF signal or a digital signal such as an amplitude modulated vestigial sideband (AM-SDB) cable television (CATV) or video signal via terminal 104 and line 1〇5. The analog signal can have a bandwidth greater than one octave and carry a plurality of channels. In addition, when a feedforward linearization circuit is used, a depolarization signal is provided to the modulator similar to the configuration of the diagram. The depolarized signal is used in the modulator 102 to depolarize the optical input to the error correction modulator (not shown). As mentioned above, the optical signal output of the laser is split into two parts: one part applied to the modulator 102; the other part is coupled to the frequency discriminator 107 by the fiber 1〇6. The output of frequency discriminator 107 is applied to attenuator i 〇 8 to properly adjust the amplitude of the signal to be commensurate with the amplitude of the phase modulation component introduced by the phase noise characteristics of laser 101. The output of the attenuator 108 is then connected to a phase shift circuit 1〇9. The circuit 109 corrects the time lag of the signal output applied to the circuit elements 107, 1 〇 8 compared to the signal applied directly to the modulator 102. In the video transmission band of interest (5 〇 MHz-1000 MHz for conventional CATV systems), the phase noise of the semiconductor laser 101 is "white", that is, the spectral power density of the noise is independent of the frequency. In this case, the phase correction paths 1〇6, 1〇7, 1〇8, 1〇9 would need to have a constant (adjustable) gain with a delay that exactly matches the delay of the primary paths 1〇3, 102 and 110. One aspect that needs to be explained is the effect of the frequency discriminator 107 on the signal, specifically the result of the optical to electrical conversion process in the phase correction path. When the photodiode detects an optical signal 127009.doc •12- 200840362 遽% ', a phenomenon called scattering noise is observed. This noise is produced by a statistical process that absorbs photons in the photodiode to produce an electron-hole pair. This miscellaneous is inevitable for all practical uses. Therefore, the scattered noise will form a lower limit on the amount of phase noise cancellation that can be achieved. The output of phase shifting circuit 109 is then applied to phase modulator 110 to thereby introduce phase correction into the optical signal by its phase modulation to thereby positively or compensate for the noise generated by the laser. The spectral noise density of the photocurrent generated from the photodiode is given by <in2>=2elp where e is an electron charge. It is a DC photocurrent. Those skilled in the art will immediately understand the fact that the noise power has a linear dependence on the received optical power and thus the signal-to-noise ratio of the process dominated by the scattered noise is improved as the received power increases. . This represents a fundamental design compromise in the proposed invention. The more power tapped into the phase correction paths 1〇6, ι〇7, ι〇8, ι〇9··. will improve the final phase noise cancellation at the expense of the optical output power of the transmitter. The output of phase modulator 110 is coupled via fiber U1 to amplifier 112, which is then coupled to the fiber or link. At the far end, fiber optic or link 30 is coupled to a receiver that converts the received optical signal to an RF signal, similar to that shown in FIG. Figure 3 is a block diagram of an optical transmitter utilizing an external modulator in accordance with a second embodiment of the present invention. An edge transmitter (usually shown in Figure 2) transmits the optical signal to the remote receiver via fiber path 30. Transmitter 2A includes a semiconductor laser 101 that produces a continuous wave (cw) output. Typical examples of such lasers are the Distributed Feedback (DFB) lasers and/or Fabry-Perot lasers, which typically produce an output beam at a wavelength of 1550 nm. The unmodulated optical signal from the laser is split into two parts; a portion is coupled to phase modulator 110 by fiber 1 〇3. The phase modulator 11 引入 introduces phase correction into the optical signal' to thereby correct or compensate for the noise generated by the laser. The CW output whose phase is changed to 110 is coupled to the modulator 1〇2 to generate an optical signal containing the modulated information. The modulator 102 can be a single modulation, such as a Mach-Zehnder modulator, a cascaded MZ modulator, or more than one of the feedforward linearization circuits. The modulator 102 receives a wideband RF signal or a digital signal such as an amplitude modulated vestigial sideband (AM-SDB) cable television (CATV) or video signal via terminal 1〇4 and line 105. Moreover, when a feedforward linearization circuit is used, a depolarization signal is provided to the modulator similar to the configuration of FIG. The depolarization signal is used to depolarize the optical input of an error correction modulator (not shown) in modulator 〇2. As mentioned above, the optical signal output of the laser is split into two parts: one part applied to the phase modulator 丨1〇; the other part is affixed to the frequency discrimination circuit 1〇7 by the optical fiber 106. The output of the frequency discriminator 107 is applied to the attenuator 108 to properly adjust the amplitude of the signal to match the amplitude of the phase modulation component introduced by the phase noise characteristics of the laser 1 〇 1. The output of the attenuator 108 is then connected to a phase shift circuit 1〇9. The circuit 109 corrects the time lag of the signal output applied to the circuit elements 1 〇 7, 108 compared to the signal applied to the phase modulator 110. In the video transmission of the 127009.doc -14-200840362 frequency band (50 MHz-1000 MHz for the conventional CATV system), the phase noise of the semiconductor field 101 is "white", that is, the spectral power density of the noise. Regardless of frequency, in this case, the phase correction paths 1〇6, 1〇7, 1〇8, 109 would need to have a constant (adjustable) gain whose delay exactly matches the delay of the primary paths 103, 102 and 110. One aspect to be explained is the frequency discriminator 107, specifically the optical to electrical conversion process in the phase correction path. When the photodiode detects an optical signal, a phenomenon called scattering noise is observed. The noise is generated by the statistical process of absorbing photons in the photodiode to produce an electron-hole pair. This noise is inevitable for all practical uses. Therefore, the scattering noise will be achievable for phase noise. The elimination amount constitutes a lower limit. Many changes and modifications will be readily apparent to those skilled in the art without departing from the spirit and scope of the invention. For example, although the video signal is modulated in the video or eve channel The description and description are made in the context of a illuminator or illuminating diode, but the inherent distortion of other non-linear devices such as amplifiers can be largely eliminated by this technique. The precise adjustment of the relative phase of the signals in the primary and secondary paths is illustrated. In the embodiment, it is in the secondary path, but this can also be in the main path with coarse adjustment. The secondary path is preferred because such delay in the main path can have an inappropriate impedance to the path. The invention and the aspects of (4) may be implemented in digital circuits, or computer hardware, (4), software, or a combination thereof. The circuit of the present invention may be tangibly embodied in a machine readable storage device. Implemented in a programmable processor or implemented on software at a network node or website, 127009.doc -15- 200840362 (which can be downloaded to a computer product automatically or on demand). The foregoing techniques can be performed, for example, by a single CPU, multiple ^ ^ wm ^A, - or multiple digits:: Logic closed array or hardwired logic execution, for =2! or instruction program to operate The function of the present invention is performed by wheeling in the data and generating an output. The party ^, ^ yj is advantageously implemented in a programmable program or a plurality of computer programs, the programmable system is ' The data storage system is connected to the materials and instructions and transmits data and instructions to the -beware storage system, the at least one input/output device and at least one of the devices are not high-definition. Advanced program or object-oriented crying & mountain worm heart column 浯g or combination or machine when 彡口吕μ施'· and in any situation Shi Wu ^ blood, into ^ a can be compiled or translated mouth s For example, a suitable processor includes both a general purpose microprocessor and a dedicated microprocessor. In general, Deutsche & Co. will receive instructions and data from read-only memory and/or random access memory.斗, this person ^ σ in the tangible implementation of computer programs "and data storage devices include all forms of non-volatile memory, for example: words including · semiconductor devices, such as epr〇m, (four) Han (10) = flash memory Device; disk 'such as internal hard disk and removable disk; magnetic _' and CD_R 〇 _. Any of the foregoing devices may be supplemented or incorporated in an ASIC by a specially designed dedicated integrated circuit (ASIC). Each of them, or two or more of them, is also effective: it is applied to other types of constructions different from the above types. Although the present invention has been described as the day of the month and the seven fields are implemented in the optical transmission system. It is not intended to be limited to the details shown, as various modifications and changes can be made without departing from the spirit of the invention. 127009.doc •16- 200840362 Without further analysis, the present invention is The content will be so comprehensively presented as the main point of the 4th, so that it is based on the application of current knowledge and in the absence of 9 prior technical positions. In the case of the specific characteristics of the characteristics of the characteristics of the characteristics of the characteristics of the production of la L, lL ^ liver _ suitable for a variety of applications, and this is the tone of adaptation and hope that Bao Yin Tian 3 in the following patent scope Equally w heart and dry circumference. [Simple diagram]
圖1為先前技術中已知之外 十 卜4调變光學傳輸系統之高度 簡化方塊圖； 圖2為根據本發明之光學傳輪系統之第—實施例之高度 簡化方塊圖；及 圖3為根據本發明之光學傳輸系統之第二實施例之高度 簡化方塊圖。 在隨附中請專利範圍中陳述本發明之新穎特徵及特性。 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 半導體雷射器 14 光纖 16 調變器 18 端子 20 線路 22 端子 127009.doc -17- 200840362 24 26 28 30 30 50 60 100 c 101 102 103 104 105 106 107 ί 1〇8 109 110 111 ' 112 200 線路 光纖鏈路 放大器 光纖傳輸線路 光纖（鍵路） 線路 接收器 傳輸器 半導體雷射器 調變器 光纖 端子 線路 光纖 頻率鑑別器 衰減器 相位偏移電路 相位調變器 光纖 放大器 傳輸器 127009.doc -18 -1 is a highly simplified block diagram of a ten-modulation optical transmission system known in the prior art; FIG. 2 is a highly simplified block diagram of a first embodiment of an optical transmission system in accordance with the present invention; and FIG. A highly simplified block diagram of a second embodiment of the optical transmission system of the present invention. The novel features and characteristics of the present invention are set forth in the appended claims. The invention itself, as well as other features and advantages thereof, may be best understood by referring to the detailed description of the embodiments. [Main component symbol description] 10 Transmitter 12 Semiconductor laser 14 Fiber 16 Modulator 18 Terminal 20 Line 22 Terminal 127009.doc -17- 200840362 24 26 28 30 30 50 60 100 c 101 102 103 104 105 106 107 ί 1〇8 109 110 111 ' 112 200 line fiber link amplifier fiber transmission line fiber (keyway) line receiver transmitter semiconductor laser modulator fiber terminal line fiber frequency discriminator attenuator phase shift circuit phase modulation Optical fiber amplifier transmitter 127009.doc -18 -