教育部顧問室光通訊系統教育改進計畫台科大 師大 淡江 東南 萬能 教育部顧問室光通訊系統教育改進計畫 台科大 師大 淡江 東南 萬能 3. 光調變器之性能量測 (Modulation Measurements) Modulation measurement is essential in characterizing optical transmitters and receivers. To carry information on the optical signals,one may modulate the optical field by a phase modulator or an electroptic(EO) modulator. One way also modulate the light by an electroabsorption (EA) modulator or a Mach- Zehnder (MZ) modulator.

教育部顧問室光通訊系統教育改進計畫台科大 師大 淡江 東南 萬能 教育部顧問室光通訊系統教育改進計畫 台科大 師大 淡江 東南 萬能 3.1 Mach-Zehnder Modulator The Mach-Zehnder (MZ) modulator consists of two optical paths on an electro optic material. Electro optic materials have an index of refraction that can be changed by external voltage. By interference of two optical beams, the output light can be modulated.

教育部顧問室光通訊系統教育改進計畫台科大 師大 淡江 東南 萬能 教育部顧問室光通訊系統教育改進計畫 台科大 師大 淡江 東南 萬能 3.1 Mach-Zehnder Modulator When light from the two paths is combined at the output,the two signals will have slightly different phases. The velocity of propagation in each arm of the interferometer is different when a voltage applied to an electrode. Fig 3.1 Mach-Zehnder modulator

教育部顧問室光通訊系統教育改進計畫台科大 師大 淡江 東南 萬能 教育部顧問室光通訊系統教育改進計畫 台科大 師大 淡江 東南 萬能 3.2 EA Modulator An electro absorption (EA) modulator can use the effect that the band gap of a semicon- ductor can be adjusted as a function of reverse-bias voltage. The modulator’s absorption edge is adjusted to a high-loss or low-loss condition depending on the modulation voltage.

教育部顧問室光通訊系統教育改進計畫台科大 師大 淡江 東南 萬能 教育部顧問室光通訊系統教育改進計畫 台科大 師大 淡江 東南 萬能 3.3 DFB with EA Modulator The advantage of electro absorption modulators is that they are integrated on the same chip as the DFB laser. ( from “Fiber Optic Test and Measurement”, edited by D. Derickson) Fig 3.2 DFB laser followed by An integrated electro absorption External modulator.

教育部顧問室光通訊系統教育改進計畫台科大 師大 淡江 東南 萬能 教育部顧問室光通訊系統教育改進計畫 台科大 師大 淡江 東南 萬能 3.4 Modulation Measurements To measure the modulation characteristics of light wave components, one way use techniques in time or frequency domain: Time Domain Frequency Domain (from “Fiber Optic Test and Measurement”, edited by D. Derickson)

教育部顧問室光通訊系統教育改進計畫台科大 師大 淡江 東南 萬能 教育部顧問室光通訊系統教育改進計畫 台科大 師大 淡江 東南 萬能 Time Domain The modulating signal can be analog or digital. Digital modulation is essential in fiber optic applications. The time evolution of optical power can be characterized by detecting the light wave signal and applying the electrical signal to an oscilloscope. Fig 3.3 Time-Domain Analysis of the optical modulation

教育部顧問室光通訊系統教育改進計畫台科大 師大 淡江 東南 萬能 教育部顧問室光通訊系統教育改進計畫 台科大 師大 淡江 東南 萬能 Time Domain The clock signal used in the data generation is applied to the trigger input of the oscilloscope. The data signal is applied to the oscilloscope input through a calibrated optical receiver. High speed sampling oscilloscopes must be used for high data rates involved in telecommunication or data communication systems.

教育部顧問室光通訊系統教育改進計畫台科大 師大 淡江 東南 萬能 教育部顧問室光通訊系統教育改進計畫 台科大 師大 淡江 東南 萬能 Frequency Domain The frequency dependence of the device under test can be characterized by detecting the light wave signal and applying the electrical signal to an spectrum analyzer The electrical spectrum analyzer displays the spectral content of the modulation on the light wave signal Fig 3.4 Frequency domain analysis of the optical modulation The modulation frequency response of the optical receiver, amplifier, and the electrical spectrum analyzer must be calibrated.

教育部顧問室光通訊系統教育改進計畫台科大 師大 淡江 東南 萬能 教育部顧問室光通訊系統教育改進計畫 台科大 師大 淡江 東南 萬能 Frequency Domain The Fig. shows the power of the modulation signal as a function of the modulation frequency. Several characteristics of the modulation can be obtained ： 1.Depth of optical modulation 2.Intensity noise 3.Distortion Fig.3.5 DFB laser measurement Example showing modulation depth,distortion,and intensity noise parameters