1. What is EML (Electro-absorption Modulated Laser)?
An Electro-absorption Modulated Laser (EML) is an integrated optoelectronic device that combines:
- A Distributed Feedback (DFB) laser or other laser source.
- An Electro-Absorption Modulator (EAM) in a single package.
EMLs are commonly used in high-speed optical communication systems, particularly in datacenter and telecom networks, because they provide high modulation speed, low chirp, and low power consumption.
2. What is EAM (Electro-absorption Modulator)?
An Electro-absorption Modulator (EAM) is a semiconductor-based optical modulator that controls the intensity of light by changing the absorption of an optical signal in response to an applied voltage.
- EAMs are typically made of Indium Phosphide (InP) or III-V compound semiconductors.
- When a negative voltage is applied, the absorption increases, reducing the transmitted optical power (attenuation).
- When no voltage is applied (floating), absorption is lower, allowing more light to pass through.
EAMs are commonly integrated with lasers like DFB lasers to form EMLs, where they act as high-speed external modulators.
3. Relationship Between EML and EAM
- An EML consists of a laser source + an EAM in a single package.
- EAM is responsible for modulating the laser output in an EML.
- The bias voltage on the EAM affects the output optical power.
4. Why Compare EAM Floating vs. Bias 0V?
- When EAM is floating, it is not actively controlled, which can lead to slightly higher or lower optical power depending on device behavior.
- When EAM is biased at 0V, its modulation characteristics change, possibly leading to different attenuation levels.
Conclusion
- EMLs are essential for high-speed optical communication, combining a laser and an EAM.
- The EAM inside an EML modulates light intensity by controlling absorption based on applied voltage.