201039573 六、發明說明： 【發明所屬之技術領域】 本發明「直接偵測之全雙工光纖微波傳輸系統」是一整合式 光纖通訊系統，所使用的光源為單模態，可藉由所使用之鎖模光 源來鎖定特定之模態，各所選之模態可用不同調變方式來做傳 送，達到同時傳輸射頻訊號與基頻訊號，更可用於區域網路訊號、 智慧型傳輸系統訊號’光纖到家傳輸系統訊號與結合無線傳輸等。 ❹【先刚技術】 近年來高速接取網路（High Speed Access Network)技術就^光纖/微波 (Radio-Over-Fiber; ROF)傳輸系統’光纖/微波傳輸系統係將無線寬 頻通與光纖系統整合在一起；光纖/微波傳輸系統具有高速接取 網路之容量(Capacity)提昇及成本(Cost)下降之優點。而光纖/微波 傳輸系統在中心機房(Central Station; CS)將微波訊號(Micr〇wave201039573 VI. Description of the Invention: [Technical Field of the Invention] The "direct-detection full-duplex optical fiber microwave transmission system" of the present invention is an integrated optical fiber communication system, and the light source used is single mode, which can be used by The mode-locked light source is used to lock a specific mode, and each selected mode can be transmitted by using different modulation modes to simultaneously transmit the RF signal and the baseband signal, and can also be used for the regional network signal and the intelligent transmission system signal. Fiber-to-the-home transmission system signals combined with wireless transmission. ❹【First Technology】 In recent years, high-speed access network technology has been adopted. ^Radio-Over-Fiber (ROF) transmission system' fiber/microwave transmission system will be wireless broadband communication and fiber-optic system. Integrated; fiber/microwave transmission system has the advantages of high-speed access network capacity and cost reduction. The fiber/microwave transmission system transmits the microwave signal (Micr〇wave) in the central station (CS).
Signal)轉換成光訊號(Optical Signal)，然後分送到遠端的基地台 〇 (Base Stati〇ns; BS)，這種技術可提供寬頻及低損耗之特性。 在傳統的光纖/微波傳輸系統中，系統的頻寬被微波訊號裝置 所限制，而昂貴的微波訊號裝置，則會增加系統的成本。而在傳 統的雙側模系統架構中，光纖色散會導致射頻功率的大量降低。 有鑑於此，直接侧之全雙工光纖微波傳輸系統的發明，也孕育 而生。 在本發明之架構，接收端能只截取一個側模，也因為如此， 數位的基舰號可以直接從單-麵獲得，而光驗在傳輸一百 3 201039573 一十里後，光纖色散所引起的射頻功率之降低可以被避免，而 70MbpS的資料量在上行或下行傳輸時，經過單模光纖，仍然可以 得到低的誤碼率值。 本篇發明之傳輸光源部份運用雷射鎖模注入技術 (Injection-lockedtechnique) ’雷射鎖模注入技術不但能大幅提昇雷 射二極體既有之頻寬、且可以降低雷射擾頻效應及抑制側模達到 良好的側模抑制比來改善光傳輸品質，本發明在主雷射以及副雷 ^ 射部伤都是用分佈反饋式(Distributed Feedback, DFB)雷射。注入 鎖模不僅可以提高正一模的功率，也可以抑制光載波以及負一 模，而使用此種光源注入技術時，系統存在著一個相當重要的課 題，那就是注入光源波長的選擇，大抵而言會符合下式： dA{t) 1 r , —=2 g } ^ ] m - kA^ cos φ(ί) ^ = ^N(〇~Nlh]-k^s^(t)-2nAf 冲）：場振幅 #):相位差 外）：載波數 g:增益係數 :臨界的載波數 :注入到副雷射的場振幅 K、α:注入場和雷射場的耦合係數 4 201039573Signal) is converted into an Optical Signal and then distributed to the remote Base Station (Base Stati〇ns; BS), which provides broadband and low loss. In a conventional fiber/microwave transmission system, the bandwidth of the system is limited by the microwave signal device, and the expensive microwave signal device increases the cost of the system. In a traditional two-sided mode system architecture, fiber dispersion can result in a significant reduction in RF power. In view of this, the invention of the direct-side full-duplex fiber-optic microwave transmission system has also emerged. In the architecture of the present invention, the receiving end can only intercept one side mode, and because of this, the digital base ship number can be obtained directly from the single-sided surface, and the optical inspection is caused by the optical fiber dispersion after transmitting one hundred three 201039573 one ten miles. The reduction of the RF power can be avoided, and the amount of data of 70 MbpS can still obtain a low bit error rate value when passing through the single mode fiber in the uplink or downlink transmission. The invention relates to the transmission source part of the laser injection molding technique (Injection-lockedtechnique) 'Laser mode-locking injection technology can not only greatly increase the bandwidth of the laser diode, but also reduce the laser scrambling effect And suppressing the side mode to achieve a good side mode suppression ratio to improve the optical transmission quality. In the present invention, distributed laser (Distributed Feedback, DFB) laser is used in both the main laser and the secondary lightning damage. Injecting the mode-locking can not only improve the power of the positive mode, but also suppress the optical carrier and the negative mode. When using this kind of light source injection technology, the system has a very important issue, that is, the choice of the wavelength of the injected light source is large. The speech will meet the following formula: dA{t) 1 r , —=2 g } ^ ] m - kA^ cos φ(ί) ^ = ^N(〇~Nlh]-k^s^(t)-2nAf 冲) : Field amplitude #): Out of phase difference): Number of carriers g: Gain coefficient: Critical number of carriers: Field amplitude K, α injected into the sub-laser: Coupling coefficient of the injection field and the laser field 4 201039573
Af:主雷射和副雷射的頻率差 J:注入電流 心：載波延遲率 :光子延遲率 有鑑於傳統的雙侧模系統牟 大量降低。本創作，乃提供1光載=纖色散會導致射頻功率的 可降低由雄色散解致的_功率衰側織除技術， 缺點〇 讀减，而有效_決傳統之 令剃升叼王要目的，在於 :，使得光纖色散起的射頻；之== 比起傳統之方案，更具有創作性與實用性。 本發明「直接侧之全雙工光纖微波傳輪系統」，系統架構為 ❹中心_(centraiStatiGn，cs)、光塞取多K〇ADM)、_百二十 公里標準單模光纖傳輸鏈路與遠端的基地台(Base s她加咖)所 構成。中心機房又可分為上行部分與下行部分。在中心機房之下 行部分由一微波訊號產生器，一個電訊號分歧器，一個光耦合器， 四個刀佈反饋式雷射，兩個光循環器與一個掺錦光纖放大琴所構 成；在中心機房之上行部分由一光帶通濾波器，一個可調式光衰 減器’一個檢光器及一個數位示波器所構成。 光塞取多工器(OADM)，由一個光纖光柵，兩個光循環器所構成。 5 201039573 遠端的基地台部份，則是由一個可調式光衰減器，一個可調式光 • 帶通濾波器，一個檢光器，—個數位示波器所構成。其傳輸鏈由 三個四十公里單模光纖，兩個掺铒光纖放大器所構成。 本發明係直接偵測之全雙工光纖微波傳輸系統設計為先將一 含有數位及類比的訊號經由一對二之電訊號分歧器(RF SpHtter)分 出一路，載入到二個不同中心波長之分佈反饋式雷射，而主雷射 部份也是由兩個不同中心波長之分佈反饋式雷射所構成，經過 循環器(Optical Circulator)後，注入到副雷射，達到鎖模注入的效 果而在光循環器之輸出端再結合成一路且連接一個掺餌光纖放 大器。在一百二十公里的單模光纖上，有光塞取多工器，提供能 選擇j·生的載入或取出一個波長至遠端基地台。在上行至中心機房 部份，經由光轉電之流程後，依據訊號種類不同作不同的處理， 例如射頻魏需㈣㈣之處理，，此發明便_構成直接 偵測之全雙工光纖微波傳輸系統。Af: Frequency difference between main laser and sub-laser J: Injection current Center: Carrier delay rate: Photon delay rate In view of the large reduction in the traditional double-sided mode system. This creation is to provide 1 light load = fiber dispersion will lead to the reduction of RF power can be reduced by the male color dispersion caused by the _ power attenuation side weaving technology, the shortcomings read and subtract, and effective _ the traditional order to shave the king, It is: the radio frequency that makes the fiber disperse; == is more creative and practical than the traditional solution. The invention relates to a "direct-side full-duplex fiber-optic microwave transmission system", and the system architecture is ❹ center _ (centraiStatiGn, cs), optical plug-in multi-K 〇 ADM), _ hundred and twenty-kilometer standard single-mode optical fiber transmission link and The remote base station (Base s she plus coffee) is composed. The central computer room can be divided into an uplink part and a downlink part. The lower part of the central computer room consists of a microwave signal generator, an electric signal splitter, an optical coupler, four knife feedback lasers, two optical circulators and a fused fiber amplifying piano; The upper part of the equipment room consists of an optical bandpass filter, an adjustable optical attenuator 'a light detector and a digital oscilloscope. The optical plug multiplexer (OADM) consists of a fiber grating and two optical circulators. 5 201039573 The remote base station section consists of an adjustable optical attenuator, an adjustable light bandpass filter, a light detector, and a digital oscilloscope. The transmission chain consists of three forty kilometers of single-mode fiber and two erbium-doped fiber amplifiers. The present invention is a direct-detecting full-duplex optical fiber microwave transmission system designed to first divide a signal containing digital and analog signals through a pair of two electrical signal splitters (RF SpHtter) and load them into two different center wavelengths. The distributed laser is distributed, and the main laser portion is also composed of two distributed feedback lasers with different center wavelengths. After the optical Circulator, it is injected into the sub-laser to achieve the effect of mode-locking injection. At the output end of the optical circulator, they are combined into one way and connected to a doped fiber amplifier. On a single-mode fiber of 120 kilometers, there is a light-plugging multiplexer that provides the ability to select or load a wavelength to the remote base station. In the uplink to the central computer room, after the process of optical power transmission, different processing according to different types of signals, such as radio processing (4) (4), this invention constitutes a full-duplex optical fiber microwave transmission system that directly detects .
Ci 【實施方式】 本發明汉计了一個架構如圖一所示的實施範例。首先對於系 、、^構所使用之元件作其特性描述，於源頭部份為微波訊號產生 01特(·生為產生一類比訊號；一對二之電訊號分歧器102的功 能為將電訊—分為二；所使狀錢為分佈反饋式雷射 3a/103Wl03c/103d之特性為具有單一賴之光譜；光循環器1〇4 ^特性為有三端分別為編號1、編號2與編號3，當絲由編號！ 端輸入’貝’J會由編號2端輸出，若從編號2端輸入，則會由編號3 201039573 端輸出’若由編號3輯人，齡從編號㈤輸出。 • 一#光輕合器⑽的特性為單端的輸人光會以預先設計好的功 率比例由另-侧的多端輸出，由多端之—輸人的細僅由另一側 的單端輸出。掺铒光纖放大器1〇6可提升光功率，三個四十公里 的單模光纖傳輸鏈路1()7則將光訊號傳送出去。再來針對圖二架 構做描述’光塞取1G8的特性為能選擇性的載人或取出一 個波長’此在資料傳輸相同方向與波長上，放入不同資料内容； 〇光纖光柵1H其特性為具有針對特定之波長有極高之反射率，因 此所輸入至光纖光栅之光源中’符合光纖光栅之特定波長將會被 反射，而其餘之波長便會隨之通過。中心機房與遠端基地台端皆 有的元件為光帶通舰H 11G可_歸定之_，使所輸入之 光源僅有屬於該光帶通濾波器所調整之特定頻帶才可以輸出；可 調式光衰減n 111可調整光功率之衰減；檢光器112能將輸入之 光訊號進行光電轉換，因而輸出電訊號，數位示波器113可檢視 ❹傳輸品質，根據所測得之眼圖(Eye Diagram)與誤碼率(Bit Error Rate，BER)作檢視分析之用。 本發明之系統實施為使用一具有寬頻光源即分佈反饋式雷 射，且因分佈反饋式雷射亦有單縱模態之特性，便可藉由鎖模注 入技術選取其一模態作鎖模注入，有極佳之側模抑制比(Side_m〇de suppression ratio, SMSR)而利於傳輸，因此本發明利用二個分佈反 饋式雷射作為鎖模注入光源。 首先本發明系統實施方式為含有數位10GHz及類比70Mbps 7 201039573 的訊號合成後’經過—對二之電訊號分歧器再載入至反饋式雷射 作直接調變，圖3(a)中看到的就是已調變的光譜圖。 於路線a之部分’已直接調變的分佈反饋式雷射光源廳連接至 光循環器1G4之編號2端，且其波長&為1551 55nm ;光循環器 104之編號1端接一分佈反饋式f射娜，且其中心波長^為 1551.62nm’再將波長為λ2的光源鎖模注人分佈反饋式雷射職， 鎖模注入的光譜圖即為圖3(b)所示，圖中之正-模，就是λ2的波 Ο長。於路線b之部分’已直接賴的分佈反饋式雷射光源臟連 接至光循環H 104之編號2端，且其波長μ 155635nm ;光循 %器104之編號1端接一分佈反饋式雷射1〇3d，且其中心波長μ 為1556.42nm ’再將波長為心的光源鎖模注入分佈反饋式雷射 103c。其後再銜接一個能將線路^與d合二為一光耦合器1〇5與 一個接铒光纖放大器106 ’利用單模光纖把光纖微波鏈路將光信號 下行至遠端基地台109(a)與遠端基地台109(b)。 〇 已偶合之光訊號下行部分透過三個四十公里的標準單模光纖1〇7 以及二個摻斜光纖放大器106傳送，而傳輸鏈路上有光塞取多工 器108來上傳λ2(λ4)或下載λ2(λ4)特定波長至遠端的基地台端。而 遠端的基地台含有光帶通濾波器η〇則是用來濾除光載波以及負 一模’其濾除過後則由圖3(c)中可以看到，其後之光衰減器111 目的為了降低光功率，檢光器U2進行光轉電過程作解調之動作， 最後輸送於數位示波器113檢測眼圖及誤碼率。圖四⑻即是量測 下行訊號在10GHz/70MbpS頻道時的誤碼率圖，由圖可知，在相 8 201039573 同誤碼率1〇-9時，單一側模的功率靈敏度大於DSB 15 2dB ;圖五 ⑻與圖五(b)則分別是數位示波器所量測在DSB系統上之基頻訊 號眼圖與數位示波器所量測在SSB系統上之基頻訊號眼圖，比較 兩圖後可以知道，圖五(b)所量測在SSB系統上之基頻訊號眼圖 中’抖動(Jitter)及振幅(ampHtude)的波動程度遠遠低於圖五⑻。經 過圖四⑻（b)與圖五(a) (b)的說明後，更可以了解此發明的重要 性。而經過-百二十公里之上傳部分同樣也是由光帶通遽波器滤 Ο 除光之載波以及負一模，此特性也可以從圖3(c)中觀察到，光衰 減器目的為了降低光功率，檢光器進行光轉電過程作解調之動 作，最後輸送於數位示波器作檢視誤碼率如圖四❻)所示。 本發明之直接偵測之全雙工光纖微波傳輸系統，充分地證實 其優異之效能，且所使用之光源成本效應上亦具有經濟效應著 實為一架構簡潔且具低成本之架構，再者於本發明直接偵測之全 雙工光纖微波傳輸系統，從其檢測之誤碼率可以明顯發現在誤碼 〇率為10-9以下時，仍然具有相當高之靈敏度。光在進入數位示波 器之前的光帶通濾波器有效濾除光之載波以及負一模，則可大大 降低電訊號轉所造朗光纖色散問題。而電喊裝置的極高成 本，在本發明則不再被考慮，使得此架構，在經濟效應與應用程 度上’都更上層樓。 因此本發明「直接偵測之全雙工光纖微波傳輸系統」除了可 以達到良好之誤碼率與整合式傳輸系統外，更相當具有潛力與適 口於長距離傳輸’再者纟於本發明之祕其架制潔與具有極高 9 201039573 之成本效益，更為大幅提升佈署運用此發明之吸引力。 【圖式簡單說明】 =二係根據本發明之利用直接偵測之全雙工光纖微波傳輸系統之 永構圖。 圖=係根據本發明之光篩取多工器和基地台之配置架構圖。 圖二(a)係根據本發明之分佈反饋式雷射經直接調變後之光頻譜 圖。 〇，二⑼係根據本發明之毅長為^的光賴似人分佈反饋式雷 射。 圖一(C)係根據本發明之直接偵測SSB之光頻譜圖。 ，四(a)係根據本發明之量測下行訊號在1〇GHz/7〇Mbps頻道時的 备碼率圖。 ，四(b)係根據本發明之量測上行訊號在1〇GHz/7〇Mbps頻道時 誤碼率圖。 =丑⑷係根據本發明之數位示波器所量測在DSB系統上之基頻訊 就眼圖。 ^(b)係根據本發明之數麵波ϋ所制在SSB系統上之基頻訊 ^ 就眼圖。 【主要元件符號說明】 100 中心機房 1〇1 微波訊號產生器 102 電訊號分歧器 103(a)分佈反饋式雷射，中心波長為1551 55nm 103(b)分佈反饋式雷射，中心波長為1551 62nm 103(c)分佈反饋式雷射，中心波長為155635nm 103(d)分佈反饋式雷射，中心波長為155642nm 201039573 104 光循環器 105 一對二光搞合器 106 掺铒光纖放大器 107 單模態光纖 108 光塞取多工器 109 基地台 109(a) 基地台1 109(b)基地台2 110 可調式光帶通濾波器 111 可調式光衰減器 112 檢光器 113 數位示波器 114 光纖光柵 ❹ 11Ci [Embodiment] The present invention has an embodiment of an architecture as shown in FIG. Firstly, the characteristics of the components used in the system and the structure are described. In the source part, the microwave signal generates 01 special (the raw signal is generated to generate an analog signal; the function of the one-to-two electrical signal splitter 102 is to transmit the telecommunication). Divided into two; the characteristics of the distributed feedback laser 3a/103Wl03c/103d is characterized by a single spectrum; the optical circulator 1〇4 ^ characteristics are three ends are number 1, number 2 and number 3, When the wire is numbered! The input 'Bei' J will be output by the number 2 end. If it is input from the number 2 end, it will be output by the number 3 201039573. If it is numbered 3, the age is output from the number (5). The characteristics of the light-light combiner (10) is that the single-ended input light is output from the other-side multi-terminal at a pre-designed power ratio, and the multi-end-input is only output from the other side of the single-ended output. The amplifier 1〇6 can boost the optical power, and the three 40-kilometer single-mode fiber transmission link 1()7 transmits the optical signal. Then, the description of the structure of the second structure is made. Sexual manned or removed a wavelength 'this is in the same direction as the data transmission Long, put different data content; 〇 fiber grating 1H is characterized by a very high reflectivity for a specific wavelength, so the specific wavelength of the fiber grating input into the fiber grating will be reflected, and The remaining wavelengths will pass through. The components of both the central computer room and the remote base station are light-passing ships H 11G can be _ _ _, so that the input light source only belongs to the optical band pass filter The specific frequency band can be output; the adjustable optical attenuation n 111 can adjust the attenuation of the optical power; the optical detector 112 can photoelectrically convert the input optical signal, thereby outputting the electrical signal, and the digital oscilloscope 113 can check the transmission quality according to the measured The Eye Diagram and the Bit Error Rate (BER) are used for the inspection analysis. The system of the present invention is implemented by using a distributed feedback laser having a broadband source, and distributed feedback laser. There is also a single longitudinal mode characteristic, which can be selected by mode-locking injection technique as a mode-locking injection. It has an excellent side-mode suppression ratio (SID) and is advantageous for transmission. Therefore, the present invention utilizes two distributed feedback lasers as a mode-locked injection source. First, the system embodiment of the present invention is a signal synthesis including a digital 10 GHz and an analog 70 Mbps 7 201039573. To the feedback type of laser for direct modulation, see Figure 3 (a) is the modulated spectrum. In the part of the route a 'directed modulation of the distributed feedback laser source Hall connected to the optical circulator 1G4 is numbered 2, and its wavelength & is 1551 55nm; the number 1 of the optical circulator 104 is terminated with a distributed feedback type F-Nina, and its center wavelength is 1551.62 nm', and the light source with the wavelength λ2 is mode-locked. Injecting the feedback type of the laser, the spectrum of the mode-locked injection is shown in Figure 3(b). The positive-mode in the figure is the wavelength of λ2. The portion of the route b is directly distributed to the feedback laser source, which is connected to the number 2 end of the light cycle H 104 and has a wavelength μ 155635 nm; the number 1 of the optical circulator 104 is terminated with a distributed feedback laser. 1〇3d, and its center wavelength μ is 1554.42nm', and then the source of the wavelength is locked into the distributed feedback laser 103c. Then, one can connect the circuit ^ and d into an optical coupler 1〇5 and an interface fiber amplifier 106' to use the single-mode fiber to lower the optical signal to the remote base station 109 (a). ) with the remote base station 109 (b). The downlink portion of the coupled optical signal is transmitted through three forty kilometers of standard single mode fiber 1〇7 and two doped fiber amplifiers 106, and the optical link multiplexer 108 is transmitted on the transmission link to upload λ2(λ4). Or download λ2 (λ4) specific wavelength to the remote base station. The remote base station contains an optical bandpass filter η〇 for filtering out the optical carrier and a negative mode. After filtering, it can be seen in Figure 3(c), and then the optical attenuator 111 In order to reduce the optical power, the photodetector U2 performs a demodulation operation on the optical power conversion process, and finally transmits it to the digital oscilloscope 113 to detect the eye diagram and the bit error rate. Figure 4 (8) is the error rate chart when measuring the downlink signal at 10GHz/70MbpS channel. It can be seen from the figure that the power sensitivity of the single side mode is greater than DSB 15 2dB when the phase 8 201039573 has the same bit error rate of 1〇-9. Figure 5 (8) and Figure 5 (b) are the fundamental frequency signal eye diagram measured by the digital oscilloscope on the DSB system and the digital frequency signal on the SSB system measured by the digital oscilloscope. After comparing the two figures, you can know Figure 5(b) measures the jitter of the Jitter and amplitude (ampHtude) in the fundamental frequency signal on the SSB system, which is much lower than that in Figure 5 (8). The significance of this invention can be better understood after the description of Figures 4(8)(b) and 5(a)(b). After the transmission of -120 kilometers, the carrier is also removed by the optical bandpass chopper filter and the negative mode. This characteristic can also be observed from Figure 3(c). The purpose of the optical attenuator is to reduce The optical power, the optical detector performs the demodulation action of the optical power conversion process, and finally is transmitted to the digital oscilloscope for viewing error rate as shown in Fig. 4). The direct-detection full-duplex optical fiber microwave transmission system of the present invention fully proves its excellent performance, and the cost effect of the light source used also has an economic effect, which is a simple and low-cost architecture, and The full-duplex fiber-optic microwave transmission system directly detected by the invention can obviously find that the error rate of the detection is still relatively high when the error rate is 10-9 or less. The optical bandpass filter before the light enters the digital oscilloscope effectively filters out the carrier of the light and the negative mode, which can greatly reduce the problem of fiber dispersion caused by the conversion of the electrical signal. The extremely high cost of the electric shouting device is no longer considered in the present invention, so that the architecture is more up-to-date in terms of economic effects and application. Therefore, the "direct-detection full-duplex fiber-optic microwave transmission system" of the present invention has a potential and a long-term transmission in addition to a good bit error rate and an integrated transmission system. Its cost-effectiveness and high cost of 9 201039573 have greatly increased the appeal of deploying this invention. [Simple Description of the Drawings] = The second embodiment of the full-duplex fiber-optic microwave transmission system using direct detection according to the present invention. Figure = is a configuration diagram of a light screening multiplexer and a base station according to the present invention. Figure 2 (a) is a light spectrum diagram of a distributed feedback laser according to the present invention after direct modulation. 〇, 二(9) is a light-like distribution feedback laser according to the present invention. Figure 1 (C) is a light spectrum diagram of the direct detection SSB according to the present invention. (4) is a spare rate map of the downlink signal at 1 〇 GHz / 7 Mbps Mbps according to the measurement of the present invention. And (b) is a bit error rate diagram of the uplink signal measured at 1 〇 GHz / 7 〇 Mbps according to the measurement of the present invention. = Ugly (4) is a baseband analog eye diagram measured on a DSB system in accordance with the digital oscilloscope of the present invention. ^(b) is a fundamental image of the SSB system based on the surface wave of the present invention. [Main component symbol description] 100 Center room 1〇1 Microwave signal generator 102 Telecommunications signal divider 103(a) Distributed feedback laser with center wavelength of 1551 55nm 103(b) Distributed feedback laser with center wavelength of 1551 62nm 103(c) distributed feedback laser with a center wavelength of 155635nm 103(d) distributed feedback laser with a center wavelength of 155642nm 201039573 104 optical circulator 105 pair of two-light combiner 106 erbium-doped fiber amplifier 107 single mode Optical fiber 108 optical plug multiplexer 109 base station 109 (a) base station 1 109 (b) base station 2 110 adjustable optical band pass filter 111 adjustable optical attenuator 112 photodetector 113 digital oscilloscope 114 fiber grating ❹ 11