利用液晶元件之可調式光解多工器╱濾波器╱增益等化器之研究

Abstract

在本論文中，我們發展出利用液晶元件之可調光解多工器/濾波器。它是由準直鏡、削角入射光柵、成像透鏡、穿透式之液晶空間光調制器及作為輪出用的光纖陣列所組成。其光柵一階繞射光經過透鏡聚焦在液晶空間調制器與光纖陣列上。選取適當的液晶空間調制器像素使得想要的波長穿透並由光纖陣列所接收。在初步實驗中，12頻道波長解多工已展示。每一頻道中心波長針對國際電信聯盟所訂定頻道間距100GHz波長所設計。頻道串音小於-30 dB。平均1/3/30 dB 穿透頻寬分別是0.06/0.11/1.09 nm。頻道切換比最高可以達到22dB。不同之間的頻道可以交互切換，其上升下降時間分別大概是12及88ms。各頻道中心波長精確到 0.02 nm (儀器極限)。 我們可以利用可調光濾波器補償各頻道間功率光功率差，我們選擇兩個像素所其對應波長間峰值功率差原是17.9 dB，經獨立控制兩像素電壓，使得兩頻道波長功率差等化至0.3 dB以內(儀器極限)。

We have developed a liquid-crystal-based tunable optical demultiplexer/filter. It consists of a collimating lens, grazing-incident grating, image lens, a transmission-type liquid crystal spatial light modulator (LC-SLM), and fiber array for output. In this device, first-order diffracted signal light by the grating is directed to the image lens and focused on to the LC-SLM and fiber array. Selecting the appropriate LC-SLM pixels allows light of the desired wavelength to transmit into the fiber array. Demultiplexing into 12 channels is demonstrated in the initial experiment. The channels are designed according to the International Telecommunication Union (ITU) grid with channel spacing of 100 GHz. Channel crosstalk is less than –30 dB. The average 1dB, 3dB, and 30dB passbands of the demultiplexer/filter are 0.06 nm, 0.11 nm, and 1.09 nm, respectively. The extinction ratio can be as high as 22dB. Different channels can be switched with a rise and fall times of ~12 ms and 88 ms, respectively. The center wavelength of each channel is accurate to 0.02 nm (Instrument limited). Liquid-crystal-based tunable optical filters can compensate for power difference between the channels. We selected two pixels corresponding to two wavelengths with peak-power difference of 17.9 dB. By independently controlling the voltage driving the two pixels, the output of the two channels can be equalized to within 0.3 dB (Instrument limited).