Optical amplifier series: Introduction to Semiconductor Optical Amplifier
Semiconductor optical amplifier (SOA) is an optical amplifier based on semiconductor gain media. It is essentially like a fiber coupled semiconductor laser tube, with the end mirror replaced by an anti reflective film; Tilted waveguides can be used to further reduce the end reflectivity. Signal light is usually transmitted through a semiconductor single-mode waveguide, with a lateral dimension of 1-2 μ m and a length of approximately 0.5-2mm. The waveguide mode significantly overlaps with the active (amplification) region, which is pumped by current. Injecting current generates a certain carrier density in the conduction band, allowing for optical transitions from the conduction band to the valence band. The maximum gain occurs at photon energies slightly above the bandgap energy.
Working principle of semiconductor optical amplifier
Semiconductor optical amplifiers(SOA) amplify incident light signals through stimulated emission, and their mechanism is the same as that of semiconductor lasers. SOA optical amplifier is just a semiconductor laser without feedback, and its core is to obtain optical gain by reversing the number of particles when the semiconductor optical amplifier is optically or electrically pumped.
Types of SOA Semiconductor optical amplifier
According to the role played by SOA in customer systems, they can be divided into four categories: serial, booster, switching SOA, and preamplifier.
1. Direct insertion: higher gain, moderate Psat; Lower NF and lower PDG, usually associated with polarization independent SOA·
2. Enhancer: Higher Psat, lower gain, usually dependent on polarization;
3. Switch: higher extinction ratio and faster rise/fall time;
4. Pre amplifier: suitable for longer transmission distances, lower NF, and higher gain.
Advantages of SOA Semiconductor optical amplifier
The optical gain provided by SOA within the bandwidth is relatively independent of the wavelength of the incident optical signal.
Inject current as an amplified pump signal, rather than optical pumping.
Due to its compact size, SOA can be integrated with multiple waveguide photonic devices on a single planar substrate.
4. They use the same technology as diode lasers.
SOA can operate in the communication spectral bands of 1300 nm and 1550 nm, with a wider bandwidth (up to 100 nm).
6. They can be configured and integrated to serve as preamplifiers at the optical receiver end.
SOA can be used as a simple logic gate in WDM optical networks.
Limitations of SOA Semiconductor optical amplifier
SOA can provide output optical power of up to tens of milliwatts (mW), which is typically sufficient for single channel operation in fiber optic communication links. However, WDM systems may require up to several mW of power per channel.
2. Due to the coupling of input optical fibers into and out of SOA integrated chips often causing signal loss, SOA must provide additional optical gain to minimize the impact of this loss on the input/output aspects of the active region.
SOA is highly sensitive to the polarization of input optical signals.
4. They generate higher levels of noise in active media than fiber amplifiers.
If multiple optical channels are amplified as needed in WDM applications, SOA will cause severe crosstalk.
Post time: Feb-24-2025