A Semiconductor Optical Amplifier (SOA) is essentially a laser diode (LD) with no feedback from its input and output ports and hence is also referred to as a Traveling-Wave Amplifier (TWA). Semiconductor optical amplifiers (SOAs) have proven to be versatile and multifunctional devices that are key building blocks for optical networks.
There are five parameters used to characterize a Semiconductor Optical Amplifier (SOA): (1) Gain (Gs); (2) Gain Bandwidth; (3) Saturation Output Power (PSAT); (4) Noise Figure (NF); (5) Polarization Dependent Gain (PDG).
A Semiconductor Optical Amplifier (SOA) should have the highest gain appropriate to the application. A wide optical bandwidth is also desirable so that the Semiconductor Optical Amplifier (SOA) can amplify a wide range of signal wavelengths. Gain saturation effects introduce undesirable distortion to the output so an ideal SOA should have very high saturation output power to achieve good linearity and to maximize its dynamic range with minimum distortion. An ideal Semiconductor Optical Amplifier (SOA) should also have a very low noise figure (the physical limit is 3dB) to minimize the amplified spontaneous emission (ASE) power at the output. Finally, an ideal Semiconductor Optical Amplifier (SOA) should have very low polarization sensitivity to minimize the gain difference between the transverse-electric (TE) and transverse-magnetic (TM) polarization states. However, an ideal Semiconductor Optical Amplifier (SOA) is impossible to realize because of the physical limitations of the various processes taking place within it.
InPhenix’s 1310nm Semiconductor Optical Amplifiers (SOAs) are ideal O-Band Optical Amplifiers. Inphenix also offers SOAs for E-band, S-band, C-band, L-band, and U-band wavelengths.
· Saturated power > 10dB
· Small signal gain > 10dB over the entire O-band (1270 to 1340nm)
· Ripple < 1 dB
· Compact + Low Cost
· 100GBASE-LR4 Transceiver test and measurement
· Passive component testing
· Splitting/tap loss compensation
· Reach extension (increase link budget): booster amplifier and per-amplifier
|Typical Spectral Width(nm)
|Max. Noise Figure
|Polarization Dependent or Independent||Package||Part Number|
|Peak Wavelength(nm)||Category||Typical Gain(dB)||Typcial Psat(dBm)||Typical Spectral Width(nm)||Max. Noise Figure(dB)||Typical Current(mA)||Polarization Dependent
A Semiconductor Optical Amplifier (SOA) is an optoelectronic device that can amplify an input optical signal under appropriate operating conditions. A schematic diagram of a basic SOA is presented in Fig.1 (below).
Fig.1-SOA simplified diagram.
An electric current externally applied to the Semiconductor Optical Amplifier excites electrons in the active region of forward biased pn-junction. When photons travel through the active area they can cause these electrons to lose some of their extra energy and generate more photons that match the wavelength of the initial ones, so called stimulated photon emission.The embedded waveguide is used to confine the propagating signal wave to the active area. Therefore, an optical signal passing through the active region is amplified and is said to have experienced optical gain.
Inphenix’s SOAs come in different form factors starting as small as a 6-pin mini butterfly that can be mounted in a CFP/CFP2 transceiver to a desktop that can be integrated with drivers and custom ordered passive components.
Inphenix SOA’s have been tested to meet Telcordia GR-468-CORE for extremely high reliability, as well as the RoHS directive.
Inphenix’s semiconductor optical amplifiers have proven to be versatile and multifunctional devices that are key building blocks for optical networks.There are five main parameters used to characterize a Semiconductor Optical Amplifier (SOA):
A Semiconductor Optical Amplifier should have the highest gain appropriate to the application. A wide optical bandwidth is also desirable so that the SOA can amplify a wide range of signal wavelengths. Gain saturation effects introduce undesirable distortion to the output so an ideal SOA should have very high saturation output power to achieve good linearity and to maximize its dynamic range with minimum distortion. An ideal SOA should also have a very low noise figure (the physical limit is 3dB) to minimize the amplified spontaneous emission (ASE) power at the output. Finally, an ideal SOA should have very low polarization sensitivity to minimize the gain difference between the transverse-electric (TE) and transverse-magnetic (TM) polarization states. However, an ideal SOA is impossible to realize because of the physical limitations of the various processes taking place within it.
Fig. 2- SOA interrelated parameters.
SOA parameters are strongly interrelated, and in order to achieve the best value of one parameter, the other specification(s) should be compromised and/or spectral operation area should be controlled, as it is schematically shown on Fig.2.
Depending on the role SOAs play in the customer’s system, they can be classified into four categories: in-line,booster; switch SOA and preamplifier;
In addition, PDG can determine polarity of an SOA. For instance, if the PDG is less than 1.5dB, the SOA is Polar Independent (P-I) and if the PDG is up to 10 dB, the SOA is Polar Dependent (P-D).
Amplification is a basic principle application of SOAs in optical communication system. SOAsarea highly versatile component that can be used for various amplifications and routing functions in telecommunications. Commercialized SOAs are now widely available in the market and are fast-becoming a cost-effective solution to optical amplification in advanced optical systems for core, metro, and ultimately access applications. SOA can be employed in any optical communication network to regenerate signals at various points in the link by operating either as a booster amplifier (post-amplifier), in-line amplifier.
SOAs are in use by a wide variety of industries. One of the most important industries is telecoms, where they are valued for routing and switching. In addition, SOAs are used to boost or amplify signal output for long-distance fiber-optic communications. In this application, telecom firms employ fiber-optic lines from headquarters to the data centers. These transmission lines can exceed 10km or more, requiring the use of SOAs to boost/amplify the signal from the usual light sources.
Fig. 3-SOAs in photonic carriers (top) can be used in Photonic Integrated Circuit (PIC) (bottom-left).
SOAs can also be used to perform functions that are, and will be, useful in future optically transparent networks. These all-optical functions can help to overcome the so called ‘electronic bottleneck’ which is presently a major limiting factor in the deployment of high-speed optical communication networks, like, for example, optical wavelength converter. Invariably, SOA functional applications are based on SOA nonlinearities. These nonlinearities are principally caused by carrier density changes induced by the amplifier input signals. The four main types of nonlinearity commonly exploited in SOAs arecross-gain modulation (XGM), cross-phase modulation (XPM), self-phase modulation (SPM) and four-wave mixing (FWM).
Sensing is another important industry utilizing SOAs in many applications. One important use of SOAs in sensors is the Fiber-Bragg Interrogators. In this setup, either an SLD or DFB is used as the input light-source. An SOA boosts the optical signal to a fiber-Bragg grating (FBG), often through a circulator to control direction of the optical signals. Changes in temperature or strain change the wavelength or timing of the optical signals to a PD/sensor. This can alert the user to possible malfunctions.
Fig. 4- Fiber-Bragg Grating with SOA in-line amplifier
Another important use of SOAs in sensing is with Light Detection and Ranging (LiDAR). LiDAR devices can be small, for only Doppler-ranging or appear as an array capable for mapping.An example of LiDAR application uses Frequency Modulated Continuous Wave (FMCW) to detect the Doppler effect of movement, such as with autonomous cars and drones. In addition, FMCW can be used for cartography and inspection. SOAs used in narrowband, usually with DFBs, can have high output power >20mW, for longer range.
Fig. 5- LiDAR chip with integrated SOAs. An array of these chips gives a wide-area scan.
Fig.6- Frequency Modulated Continuous Wave (FMCW) LiDAR. SOAs in green.
The previously highlighted features of small size, good integration capability and high potential for cost reduction through scaled manufacturing processes will continue to ensure that the SOA plays an increasingly important role in future advanced optical networks. Coarse wavelength division multiplexing (CWDM) is an economic route for giving connection flexibility and increased throughput for metro and enterprise network layers. Extending the capacity and distance of CWDM systems (>100 km) requires a low cost optical amplifier operating across the entire optical bandwidth (from 1260 nm to 1620 nm). The SOA is the only viable technology available today that can be deployed to meet these expanding applications.
An expanded role for SOAs in telecoms is in their use in Wavelength Division Multiplexing-Passive Optical Networks (WDM-PON). Cable companies utilizing fiber-optic lines from the home office to the customer receiving the data, often have nodes, or distribution centers, to assist in switching and routing data. This setup allows the efficient distribution of data to a large customer base. SOAs are an early application of WDM-PON but may see growth in the future.
There are several other attractive applications of SOA, such as intensity and phase modulation, SOA logic for the use of optical signal processing, SOA add/drop multiplexer for optical time division multiplexed network, SOA pulse generator to generate pulse easily at high frequencies (> 10 GHz), SOA clock recovery required in optical receivers and 3R generators, SOA dispersion compensator to overcome the chromatic dispersion which limits the transmission distance, and SOA detector to detect optical signal. SOAs can also be used for gating optical signals, i.e. signals can be either amplified or absorbed by SOAs. The blocking properties of SOAs at low bias currents are extremely useful because they enable channel routing functions, such as reconfigurable add/drop multiplexers (ROADM), to be produced with off channel isolation better than 50 dB.