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Optical Amplifiers

The transmission loss of the light passing through the optical fiber is a very small value of less than 0.2 dB per km with a light wavelength in the 1,550 nm band. Therefore clearest optical fibers can transmit signals more than 100 kilometers without amplification-much farther than copper wires. When the signal must span a longer distance, it is passed through an optical amplifier, which multiplies the strength of the optical signal.

 

A device that receives some input signal and generates an output signal with higher optical power is known as an optical amplifier. Input and output signals are laser beams generally, that are propagating as Gaussian beams in free space or in a fiber.

 

Then, optical fiber amplifiers were invented in 1989 for high expanded transmission distance while operating over the C-band, with low cost and very low noise. Electronic repeaters were replaced by optical amplifiers, allowing to be the signal in the optical domain. The fourth generation of lightwave systems using optical amplifiers and the lithium niobate external modulator, transmission distances of nearly 1000 km could be reacted at 2.5 and 10 Gbps.

 

Optical amplification plays a key role in virtually all laser-based technologies such as optical communication, used for instance in data centers to communicate between servers and between continents through trans-oceanic fiber links, to ranging applications like coherent Frequency Modulated Continuous Wave (FMCW) LiDAR – an emerging technology that can detect and track objects farther, faster, and with greater precision than ever before.

 

Types of Optical Amplifiers

There exist several physical processes to achieve optical amplification, namely the action of enhancing or boosting the power of an electromagnetic (EM) light wave. These processes can be grouped into three fundamental categories: laserscattering (Raman and Brillouin) and parametric.  The major types of optical amplifiers include an EDFA, FRA, and SOA.

 

Difference between an OFA and SOA

There are 2 types of optical amplifiers; an OFA (Optical Fiber Amplifier) and SOA (Semiconductor Optical Amplifier). There are 2 further types of OFAs; an EDFA (Erbium-Doped Fiber Amplifier) and an FRA (Fiber Raman Amplifier).

 

EDFA (Erbium Doped Fiber Amplifier)

EDFA is 1 type of OFA and is an optical amplifier with erbium ions added to the core of the optical fiber and are most widely used optical amplifier.  It features high gain and low noise, is polarization independent, and can amplify optical signals in the 1.55 μm band or 1.58 μm band.

EDFA (Erbium Doped Fiber Amplifier) – Physics and Radio-Electronics

They comprise fibers doped with atoms of erbium, a rare-earth element that absorbs light energy from an external pump laser. The erbium atoms then release that energy to amplify weak optical signals across the entire band of wavelengths that the laser transmits. With careful control, a string of dozens of optical fiber amplifiers can transmit signals thousands of kilometers across the ocean.

Irradiating a coupling module with light at 1.48 µm enables the light to be internally stored as energy, and light in the 1.55 µm band causes optical amplification when it propagates, and obtains a gain of 20 to 30 dB.

 

FRA (Fiber Raman Amplifier)

An FRA is a type of OFA. It causes stimulated emission based on SRS when strong excitation light enters the optical fiber. The light is then amplified in a wavelength range about 100 nm longer than the excitation light wavelength. It has a wide amplification wavelength region, and can be freely set by the wavelength of the excitation light.

 

SOA (Semiconductor Optical Amplifier)

As suggested by the name, an SOA is a semiconductor element. By performing antireflective processing on the cleavage plane of a semiconductor laser and eliminating the resonator structure, light can enter from outside the semiconductor and amplify light via stimulated emission.

An SOA can be made in a compact size and its lower running costs compared to an EDFA mean it more economically efficient. Up until recent years, the input light of an SOA was highly polarization dependent, but research into low polarization dependency has proceeded in recent years. Furthermore, EDFAs are being replaced by SOAs at data centers, and their use is expected to expand in future optical communication.

 

Example SOA Applications

The SOA is used for embedding in 100G CFP/CFP2 ER4. Light sources for optical communication in the 1.3 μm band is used for 40 km transmission among data centers, and between mobile phone base stations and data centers. However, SOAs are required as pre-amplifiers to counter attenuation in the communication light when performing long-distance transmission. SOAs are embedded in 100 G CFP/CFP2 ER4 transceivers, and are now playing an important role in the market.

 

Optical parametric amplifiers

It has been known since the 80’s that the intrinsic nonlinearity of optical fibers can also be harnessed to create traveling-wave optical parametric amplifiers, whose gain is independent of atomic or semiconductor transitions, which means that it can be broad-band and virtually cover any wavelength.

Parametric amplifiers also do not suffer from a minimum input signal, which means that they can be used to amplify both the faintest signals and large input power in a single setting. And finally, the gain spectrum can be tailored by waveguide geometry optimization and dispersion engineering, which offers enormous design flexibility for target wavelengths and applications.

Most intriguingly, parametric gain can be derived in unusual wavelength bands that are out of reach of conventional semiconductors or rare-earth-doped fibers. Parametric amplification is inherently quantum-limited, and can even achieve noiseless amplification.

 

Silicon limitations

Despite their attractive features, optical parametric amplifiers in fibers are compounded by their very high pump power requirements resulting from the weak Kerr nonlinearity of silica. Over the past two decades, the advances in integrated photonic platforms have enabled significantly enhanced effective Kerr nonlinearity that cannot be achieved in silica fibers, but have not achieved continuous-wave-operated amplifiers.

“Operating in the continuous-wave regime is not a mere ‘academic achievement’,” says Professor Tobias Kippenberg, head of EPFL’s Laboratory of Photonics and Quantum Measurements at EPFL. “In fact, it is crucial to the practical operation of any amplifier, as it implies that any input signals can be amplified – for example, optically encoded information, signals from LiDAR, sensors, etc. Time- and spectrum-continuous, travelling-wave amplification is pivotal for successful implementation of amplifier technologies in modern optical communication systems and emerging applications for optical sensing and ranging.”

 

Breakthrough photonic chip

A new study led by Dr Johann Riemensberger in Kippenberg’s group has now addressed the challenge by developing a traveling-wave amplifier based on a photonic integrated circuit operating in the continuous regime. “Our results are a culmination of more than a decade of research effort in integrated nonlinear photonics and the pursuit of ever lower waveguide losses,” says Riemensberger.

The researchers used an ultralow-loss silicon nitride photonic integrated circuit more than two meters long to build the first traveling-wave amplifier on a photonic chip 3×5 mm2 in size. The chip operates in the continuous regime and provides 7 dB net gain on-chip and 2 dB net gain fiber-to-fiber in the telecommunication bands. On-chip net-gain parametric amplification in silicon nitride was also recently achieved by the groups of Victor Torres-Company and Peter Andrekson at Chalmers University.

In the future, the team can use precise lithographic control to optimize the waveguide dispersion for parametric gain bandwidth of more than 200 nm. And since the fundamental absorption loss of silicon nitride is very low (around 0.15 dB/meter), further fabrication optimizations can push the chip’s maximum parametric gain beyond 70 dB with only 750 mW of pump power, exceeding the performance of the best fiber-based amplifiers.

“The application areas of such amplifiers are unlimited,” says Kippenberg. “From optical communications where one could extend signals beyond the typical telecommunication bands, to mid-infrared or visible laser and signal amplification, to LiDAR or other applications where lasers are used to probe, sense and interrogate classical or quantum signals.”

 

Global Optical Amplifier Market

The global optical amplifier Market is estimated to surpass $935.23 mark by 2023 growing at an estimated CAGR of more than 6.7% during the forecast period 2018 to 2023. Fiber amplifiers hold the highest market share of 51% and estimated to grow at a CAGR of 7.8%. By region America hold the highest market share of 34%.

 

A number of factors such as the soaring infrastructural investments, rising technological advancements in wireless sensor, mounting number of data centers, burgeoning demand for data transmission without data losses for longer distances, and surging number of smart cities and smart homes will act as a growth driver for the optical amplifier market.

 

One of the key growth drivers of the market is the rapid advancements being made in the telecommunication sector. Optical networking or fiber optic has become a guided medium of choice in telecommunications. Optical amplifiers serve as a circuit enabling technology in optical communication networks. The adoption of optical amplifiers in this sector has enabled the transmission of huge volumes of data over a wide distance, ranging from 62 miles to transoceanic distances.

 

The global optical amplifiers market has increased due to the rapid growth of data centers, improved signal quality in transmission without any data loss among many other factors are demanding the growth of the market across wide range of industries in near future.

 

The optical amplifier market is categorized into data center, telecommunication, industrial, military and defense, healthcare, aerospace, and others, based on end user. The telecommunication category is expected to hold the largest market share during the forecast period, owing to the use of optical fiber and optoelectronic devices, such as optical amplifiers, as a prefered choice for communication medium.

 

The advent of new technologies, such as 5G and autonomous driving, is leading to the increased data traffic, which is driving the demand for optical amplifiers. This category is followed by the data center category, due to the increasing number of data centers that need multiple devices, servers, and systems, which require several optical amplifiers.

 

According to P&S Intelligence, Asia-Pacific (APAC) is expected to account for the largest share in the optical amplifier market in the coming years. This can be attributed to the increasing penetration of smartphones and expanding broadband user base in the region. For instance, according to the India Cellular & Electronics Association (ICEA), the number of smartphone users in India will rise from 500 million in 2019 to 829 million by 2022. ICEA also states that the average monthly data consumption of an individual will reach 18 GB by 2024.

 

Optical Amplifier Market Competitive Landscape

Due to the presence of various players, the optical amplifier market is highly competitive in nature, with the players rapidly launching new products to increase their presence. For instance, in 2020, Furukawa Electric Co. Ltd. developed new pump sources for forward Raman amplifiers, which will achieve higher data transfer speed and long-distance transmission in ultrahigh-speed optical fiber communication.

 

Currently, the optical amplifier market is witnessing the introduction of a large number of products by companies such as APE Angewandte Physik & Elektronik GmbH, Finisar Corporation, Accelink Technology Co. Ltd., Santec Corporation, Source Photonics, Viavi Solutions Inc., Broadcom Inc., NEC Corporation, Newport Corporation, Lumentum Operations LLC, Source Photonics, Furukawa Electric Co. Ltd., Emcore Corporation, Sumitomo Electric Industries Ltd., and Viavi Solutions Inc.

 

For example, in 2020, Furukawa Electric Co. Ltd. created new pump sources for forwarding Raman amplifiers to attain long-distance transmission and high data transfer speed in ultrahigh-high speed optical fiber communication.

 

 

 

References and Resources also include:

https://www.eurekalert.org/news-releases/972874

https://www.industryarc.com/Report/15345/optical-amplifiers-market.html

https://www.anritsu.com/en-au/sensing-devices/guide/optical-amplifier

 

About Rajesh Uppal

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