Optical Module Background and Basic Principle

In the introduction of product parameters of optical modules, we often mention the modulation mode as a key indicator, DML (Directly Modulation Laser) and EML (External Modulation Laser) are two major modulation technologies for optical modules. The basic function of an optical module is to achieve optoelectronic conversion, i.e., the mutual conversion of electrical and optical signals, in order to transmit data in an optical fibre.

DML Modulation Technology

The basic principle of DML modulation technology is to directly control the current through the laser to emit light of different intensities. When the modulating signal is high, the modulating current flows through the laser diode (LD) and the laser emits light normally, while when the modulating signal is low, the modulating current does not flow through the LD and the laser does not emit light.DML modulation is simple and direct, but the laser is always in an unstable state during the modulation process, which may result in the quality of the output signal being affected by the non-linear effect.

EML Modulation Technology

Unlike DML, the EML modulation technique passes a constant current through the laser, while the intensity of the optical signal is varied by an external modulator. When the modulation signal is high, the electrical absorber does not absorb the light emitted by the LD, and most of the light passes through the electrical absorber; while when the modulation signal is low, the electrical absorber absorbs most of the light, and most of the light can not pass through the electrical absorber. This modulation allows the laser to maintain a stable light-emitting state, thereby improving the quality of the output signal.EML modulation technology is generally used for rate of 10Gbps or more, long distance 40KM and above the optical module.

DML and EML modulation technology selection

The core difference between DML and EML lies in how they respond to the specific needs of customers: DML demonstrates greater price competitiveness, while EML is more suitable for application scenarios that require higher margins. In ETU-LINK's optical module product line, we provide a choice of optical modules based on DML and EML modulation technologies according to customers' diverse needs and application scenarios.

ETU-LINK 100G QSFP28 series:

ETU-LINK 100G BIDI series products:

In summary, DML and EML, as two important modulation technologies for optical modules, play an important role in their respective application scenarios. ETU-LINK will continue to devote itself to the R&D and innovation of optical module technology, and provide customers with more high-quality and efficient optical module products.