What is the full form of EML?

Introduction

Externally Modulated lasers (EML) are a certain kind of laser used in optical communications that transmits high−speed data across extremely huge distances. It was designed to have high optical power, a small linewidth, and fast modulation speeds.

Due to its capability to transfer data at fast rates over long distances with low signal distortion, EMLs are frequently utilized in optical communication systems, such as fibre−optic networks. EMLs' external modulation is an important component in modern communication systems since it allows for high data speeds by superimposing the data signal onto the laser beam. Also, EMLs can be used in microwave photonics, sensing, and other scientific uses that require highly effective laser sources of information.

Working Principle of Externally Modulated Laser

A Continuous−Wave (CW) laser beam is modulated using an external modulator as part of the operation of an Externally Modulated Laser (EML). The modulator, which may change the laser beam's intensity or phase using a high−speed electrical signal, is commonly an electro−optic modulator or a Mach−Zehnder interferometer. The modulated data stream is subsequently transferred by the modified laser beam over an optical cable.

High−speed data transmission is made possible by external modulation by applying the data signal to the carrier frequency of the laser beam. This method, called intensity modulation, allows the ability to transmit high−speed data throughout long distances without experiencing severe signal distortions. The EML's low linewidth further ensures that the transmitted signal is of good quality and is not dispersed.

Due to the flexibility of the External modulation method' modulation form, a range of modulation techniques, such as On−off keying (OOK), Amplitude shift keying (ASK), and Phase shift keying (PSK), may be employed. EMLs are appropriate for usage in DWDM systems, which allow the transmission of many signals over a single fiber, because of their high power consumption.

Advantages and Disadvantages of Externally Modulated Laser

Advantages of Externally Modulated Lasers (EML) consist of:

• High−speed Modulation − Because of their high−speed modulation capacity, EMLs are appropriate for use in optical communication systems that need high−speed data transport.

• Low dispersion − The narrow linewidth of EMLs ensures that dispersion−related signal distortion in transmitted transmissions is maintained to a minimum.

• Flexibility − EMLs are flexible to a range of communication applications since they offer a number of modulation modes.

• High output power − Due to their high power consumption, EMLs are suitable for use in Dense Wavelength−Division Multiplexing (DWDM) systems that call for high−power laser sources.

Disadvantages of EMLs (Externally Modulated Lasers) consist of:

• Complexity − EMLs are becoming increasingly complex and costly because they require external modulators.

• Low bandwidth − Directly modulated lasers (DMLs), which can transmit data through an increased frequency range, have a higher bandwidth than EMLs, which have a smaller bandwidth.

• Temperature sensitivity − EMLs are sensitive to temperature variations, which may have an effect on the way they work.

• Excessive energy consumption − EMLs have a high power consumption price in comparison to DMLs, which may additionally prevent their use in low−power systems.

Applications of Externally Modulated Laser

Compared to other fields, externally modulated lasers (EMLs) are utilized in a number of optical communication systems. EMLs can be used in the following ways:

• Fibre−optic communication − Due to its high−speed modulation capabilities, low dispersion, and adaptability, EMLs are often utilized in long−haul and local networks in fibre−optic communication systems.

• Microwave photonics − For microwave photonics applications including radio−over−fiber systems, sensing, and radar, EMLs provide high−power laser sources with powerful modulation capabilities.

• Coherent communication systems − coherent optical transmission and coherent signal detection, rely on high−quality, short−linewidth laser sources provided by EMLs.

• Instruments − High−power laser sources with outstanding modulation capabilities are provided by EMLs in scientific instruments such as spectroscopy, lidar, and laser interferometry.

• Applications in biomedicine − EMLs are utilised to offer high−quality laser sources with high−speed modulation capabilities in biomedical applications including Optical Coherence Tomography (OCT) and fluorescence microscopy.

• Test and Measurement − EMLs provide high−speed, steady laser sources with outstanding modulation capabilities for use in test and measurement applications such as bit−error−rate testing and optical power measurement.

Conclusion

In conclusion, it should be noted that Externally Modulated Lasers (EMLs) are essential components of contemporary optical communication systems and other scientific fields. They are useful for a variety of applications, including fibre−optic communication, microwave photonics, coherent communication, instrumentation, biomedical applications, test and measurement, because of their high−speed modulation capabilities, low dispersion, and versatility.

While complexity, limitations on bandwidth, temperature sensitivity, and high power consumption are some of the disadvantages of EMLs, ongoing research and development are addressing these issues and improving their performance. In the future, EMLs are expected to play an increasingly significant role in satisfying the increasing demand for high−speed, reliable, and effective communication systems.

Frequently Asked Questions

Q1. What is the difference between EMLs and DMLs?

Ans: DMLs directly modulate the laser's current, whereas EMLs utilize external modulation.

Q2. What modulation format are EMLs using?

Ans: The modulation formats that EMLs can use are OOK, ASK, and PSK.

Q3. What type of output power do EMLs typically have?

Ans: EMLs are capable of producing high−power outputs, which are generally in the few watt to a few mill watt range.