- 期刊
光通道效能監視技術中之Q值檢測
Q-factor Monitoring in Optical Channel Performance Monitoring Techniques
摘要
在高速光學網路／全光化網路趨勢的推動下，傳輸距離越來越遠。除了傳統電的節點逐漸減少，存在傳統電的節點的電網路性能監測器也隨著逐漸消除。因此，一個既可以存在全光化網路，又可以執行電網路性能監測器的方法就必須被發展出來。要偵測光訊號的品質可以藉由量測光訊號的功率、波長、光訊雜比等等。但是，為了更精確地監測信號品質，尤其是數位傳輸系統，一般有兩個參數用來評估性能：誤碼率(BER)及Q值。誤碼率量測相當費時，無法達到即時監測，而Q值量測迅速，又可以用來推估誤碼率，是最被應用在光通道性能量測的參數之一。 本文提出一種改進目前量測光訊號Q值的方法。一般量測Q-factor必須要先藉由取樣(sampling)的機制來重建出訊號的波形，再進一步得知光訊號1/0準位功率的變化，就可以進一步地推算Q值。而sampling的機制需要一個sampling pulse來trigger以便取樣。當訊號的傳輸速率越高時，這些sampling pulse的寬度就要越窄。以10Gbps的訊號為例，一個bit的duration是100ps，那sampling pulse的寬度就至少要小於100個ps，這樣才能取到位元中一個點的功率。要是太寬，就會取到好幾個bit的平均功率，就分不出1跟0來。要產生越窄的sampling pulse，不管在光或是電的domain上，這都是很複雜的事。所以我們提出一個Non-sampling-based的技術，可以避免這些sampling機制的問題，來量測Q-factor。我們的構想是藉由－Power-to-Wavelength Conversion Module，不同準位的輸入光功率變化會反映在不同輸出光波長上的變化，利用這樣的特性來取代sampling的機制。不同的光功率輸入power to wavelength conversion module，就會響應出不同顏色波長的光輸出。在這裡不同顏色光的出現比例，就代表了輸入訊號在不同光功率出現的比例。我們只要再利用－分光器，將不同顏色的光分開，再經過一低頻的photo detector，就可以統計不同顏色光的平均光功率。藉此來得知輸入訊號在準位1/0上光功率變化的情形，就可以來計算Q-factor。而除了光波長的變化以外，還可以轉換至其他各種領域，比如光極性、不同光輸出埠等等。
並列摘要
As the high speed/All Optical Networks develop, the transmission distance is pushing farther and farther. Following the reducing of electrical nodes, (the electrical performance monitoring) in the transitional nodes is also gradually disappearing. Thus, We should develop a performance monitoring technology which is suitable for all optical networks and traditional electrical networks. We can measure the optical power, wavelength and optical signal to noise ratio (OSNR) to monitor the quality of the optical signal. However, if we want to monitor the optical signal more accurately, we should use bit error rate (BER) and Q factor. Measuring the BER is very (time-consuming), while measuring Q factor is very convenient. Q factor can be used to estimate the BER so that Q factor is very commonly used in monitoring the optical signals quality of the optical channel. We propose an advanced Q factor measuring technology. For ordinary Q factor measuring technology, we should sample the received signal, and we can rebuild the waveform profile and then get the optical power variation of bit 1/0 so that we can calculate the Q factor. However, we need the sampling pulse to trigger the sampling. The higher the data rate, the narrower the sampling pulse. For example, if we want to monitor 10Gbps optical signal, we need sampling pulse smaller than 100ps. Thus, the sampling period showed not be so large as to get several bits per sample. To our best knowledge, no matter in optical or electrical domain, it is very difficult to generate very narrow sampling pulse. In this article, we propose a non-sampling-based technology to measure Q factor and avoid the drawback of sampling-based technology. The idea is using Power-to-Wavelength Conversion Module, which will map the variation of input optical power to variation of output wavelengths. In other words, different optical power will let Power-to-Wavelength Conversion Module generate different wavelengths. Different wavelengths stand for different optical power levels. Moreover, we can use an optical filter to separate the wavelengths and calculate the optical power of each wavelength. Finally, we can gather the power variation of input optical signal and figure out the Q factor. Besides the variation of wavelengths, we can also use optical polarization and different output ports.