The difference between EML and DML

Infiberone managerGVIP2018/2/25 14:15:29

The difference between EML and DML

Today we’d like briefly introduce the difference between EML and DML. We see it very often in our products. First, let’s see their definitions:

DML: Directly Modulated Laser

EML: Electric-absorption Modulated Laser

The electro absorption modulation laser (EML) is an integrated device of the electro absorption modulator (EAM) and the DFB laser (LD). It is better than the direct modulated laser (DML), and the power consumption is large and expensive.

In my understanding, the DFB laser is a typical DML. Let me draw a picture to make it more clearly.

On the left side, the lifting arm is "1", and the lower arm is "0". If the beauty on the right side sees clearly, that is normal business. If she cannot see it clearly, then it would be wrong and we called it “bit error”.

DML saves energy when she stays in”0”, but when it shift from “0” to “1”, the beauty on the right side cannot see it clearly (Large dispersion cost). And she needs time for shifting. Also the range is limited when shifting (extinction ratio is small)

EML, we assume it from another picture. We say she stays in lifting her arms, then added an “EA” in the middle.

EML = DFB+EA. Her arms has to be lifted up all the time, consuming energy. The little pineapple man lift a board to block the beauty on the right to see her, it is a”0”, if not, it is a “1”. So EML can transmitter longer and dispersion cost is small.

Let’s see the principle of EA:

The quantum confinement Stark effect (QCSE), when the external power plant is perpendicular to the quantum well, the square band structure inclines. The restriction of electrons and holes has also changed, and the energy level of the electrons can reduce the capacity of the hole. This allows the absorption peak to move towards a long wavelength direction. Therefore, the long wavelength side band optical absorption is greatly increased.

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