Editorial Feature

What to Know About Reflective Semiconductor Optical Amplifiers

Reflective Semiconductor Optical Amplifiers, also known as RSOAs, are high-performance, low-cost transceivers used for data amplification and modulation in radio over fiber systems, full-duplex optic access networks, and microwave photonics.

RSOA, RSOA, semiconductor, optical amplifiers, Reflective Semiconductor Optical Amplifiers, birefringent fiber

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These applications benefit from the desirable characteristics of RSOAs, which include wavelength-agility, high gain at low driving currents, excellent modulation linearity, bidirectional signals propagation within the same active cavity, remote seeding capability, and a variable fiber interface.

RSOA Functions

The RSOAs' dual functionality of downstream amplification and upstream modulation is combined with their ability to provide higher gain with less polarization dependency, lower injection currents, lower noise figure, higher modulation linearity, and lower temperature sensitivity than traditional amplifiers.   

These qualities have made these components indispensable for the sudden realization of modern connectivity applications that rely heavily on the modification of bidirectionally flowing DC currents.

What Are RSOAs Made Of?

Reflective Semiconductor Optical Amplifiers (RSOAs) are variations of semiconductor optical amplifiers (SOAs) with an anti-reflective coating on the front facet and high reflectivity on the rear facet. SOAs are semiconductor gain medium-based optical amplifiers.

RSOAs are fundamentally identical to a fiber-coupled laser diode with anti-reflection coatings on the end mirrors; a slanted waveguide may be utilized to further minimize the end reflectivities.

The RSOA's modification to the active medium cavity enables an optical signal to travel in one direction (ahead) to have its intensity boosted, while its information content is changed as it departs in the opposite direction (backward) without requiring extra fiber hardware and connections.

RSOA Characteristics

RSOAs are critical components in the construction of next-generation networks that depend on the convergence of optical and radio communications.

RSOAs' electro-optic responsiveness is limited by their finite bandwidth, which prevents them from being used for signal amplification and modulation at the connection speeds required by the target applications, notwithstanding their proven potential for direct modulation.

Reflective Semiconductor Optical Amplifiers provide a cost-effective wavelength-independent transmitter for use in passive optical networks, obviating the requirement for tuneable or stationary laser sources on the client premises.

The RSOA, supplied with a single continuous-wave source at the Optical Network Unit, may be shared across several users and can concurrently amplify and modify that seed in order to allow a wavelength-independent WDM overlay.

RSOA Limitations

The transmission rate that RSOAs potentially support in some applications is hampered by their sluggish direct (electrical) modulation speed, which itself is bound by the RSOA's finite modulation bandwidth.

This can be as low as a few GHz according to experimental measurements and numerical calculations.  A viable option that has garnered widespread acceptance in the scientific community due to its simple idea, effective application, and passive nature is to use frequency equalization and discrimination.

The objective is to suitably tune the data encoded signal's spectrally widened components at the RSOA output, which emerge as a result of dynamic modulation of both the RSOA bias current and consequent perturbation of the RSOA gain.

New Research Using Birefringent Fiber Loop

The Birefringent Fiber Loop (BFL) has been developed to improve the performance of RSOAs as intensity modulators. To model the RSOA reaction in the time domain and connect it with the BFL response within the frequency domain, a theoretically and computationally simplified model was used in research in the journal Photonics.

A thorough comparison of simulation and experimental findings validates the model's prediction. The use of the model as a framework for understanding electrically driven RSOA function and its improvement via optical notch filtering is justified based on reasonable theoretical conclusions.

The scheme's performance was also analyzed and quantified, as well as the possible range of RSOA direct modulation potential extensions offered by the BFL, which is consistent with experimental trends.

The findings of this comprehensive investigation demonstrate the importance of BFL in enabling RSOAs to directly modulate at data rates higher than those believed conceivable by their nominal modulation bandwidth.

New Findings Using Nanotechnology

A method for simulating a quantum dot reflective semiconductor optical amplifier (RSOA) with wideband optical gain has been proposed. This model is generated by superimposing several quantum dot groups with varying radii, utilizing solution process nanotechnology which is both feasible and cost-effective.

In addition, there have been few studies that have superimposed QD groups in RSOAs. Coupled rate equations were solved using a numerical approach. Because analytical answers are not accessible to further examine the model, this methodology is a perfect approximation for comprehending this technology.

A broad optical gain of roughly 30 dB was achieved using this strategy. This technology advances the construction of high-speed spectrum WDM passive optical networks by one step. Furthermore, multiple bands in the lightwave spectrum can be used, and all that is required is the selection of appropriate materials for QD synthesis at the desired wavelengths.

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References and Further Reading

Karadimoglou, F., et al. (2022). On Directly Modulated Reflective Semiconductor Optical Amplifier with Assistance of Birefringent Fiber Loop. Photonics. Online Published: 2 March 2022 https://www.mdpi.com/2304-6732/9/3/147

Zhou, P., et al. (2017). Reflective semiconductor optical amplifier with segmented electrodes for high-speed self-seeded colorless transmitter. Optics Express. https://opg.optica.org/oe/fulltext.cfm?uri=oe-25-23-28547&id=376599

Zoiros, K., et al. (2020). Reflective semiconductor optical amplifier pattern effect compensation with birefringent fiber loop. Optical and Quantum Electronics. Online Published: 28 July 2020  https://link.springer.com/article/10.1007/s11082-020-02485-4

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Akhlaqul Karomah

Written by

Akhlaqul Karomah

Akhlaqul has a passion for engineering, renewable energy, science, and business development.


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