Semiconductor lasers and optical amplifiers for optical communication

Semiconductor lasers are characterized by low volume, ease of use, high energy efficiency and low production costs. Thanks to these advantages, these lasers are taking an exclusive place in optical telecommunications.

Semiconductor optical amplifiers are the essential building blocks of a semiconductor laser, and at the same time perform functions such as optical amplification or wavelength conversion.

Most fiber-optic transmission systems require lasers emitting a single wavelength, known as single-mode lasers. Lasers are often used in direct modulation to encode the information to be transmitted. Distributed feedback lasers (DFB) are then developed for this type of application.

Most long-distance or metropolitan networks use Wavelength Division Multiplexing (WDM). Wavelength-tunable lasers have been developed for these applications. These are single-mode lasers whose wavelength can be precisely adjusted over the entire C-band (1.53 to 1.565 μm), for example. This greatly facilitates inventory management, since it is no longer necessary to have a spare laser for each wavelength. They are also a key component of Reconfigurable Optical Add and Drop Multiplexers (ROADMs), which route traffic and convert it to wavelength.

The growing need to increase component functionality, combined with the maturity of III-V semiconductor and silicon technology, is driving the rapid development of Photonic Integrated Circuits (PICs). This involves integrating several elements on the same semiconductor substrate to perform complex functions. Two techniques are currently being developed in parallel for the manufacture of PICs integrating active functions (emission, modulation and detection): monolithic integration on InP and hybrid III-V integration on silicon.

The aim of this article is to present semiconductor lasers and optical amplifiers for optical telecommunication applications. It describes the materials, structures and main characteristics of this type of laser. It then reviews distributed feedback lasers (DFB), tunable lasers, pulsed lasers and laser-integrated photonic circuits. Finally, the article concludes with a look at the development prospects for this type of semiconductor laser in the years to come.