Breakthrough in long-range fiber optic communication First traveling wave amplifier built on a photonic chip
Scientists at EPFL have developed photonic integrated circuits that demonstrate a new principle of optical amplification on a silicon chip. It can be used for LIDAR, transoceanic fiber amplifiers or optical signals used in data center telecommunications [1].
01Quantum-limited amplification of optical signals in optical fibers
The ability to quantum-limited amplification of optical signals contained in optical fibers is arguably one of the most important technological advances at the foundation of the modern information society. In optical communications, the choice of the 1550 nm wavelength band is influenced not only by the minimum loss of silica fibers (a development recognized by the 2008 Nobel Prize in Physics), but equally by the method of amplifying these signals, which is essential to enable transoceanic fiber optic communications.
Optical amplification plays a key role in almost all laser-based technologies, such as optical communications, for example for data centers, communication between servers and between continents via transoceanic fiber links, and ranging applications such as coherent frequency modulated continuous wave (FMCW) lidar, and with greater accuracy than ever before. Today, optical amplifiers based on rare earth ions such as erbium and group III-V semiconductors are widely used in the real world.
These two methods are based on amplification by optical leapfrogging. But there is another example of optical signal amplification: the traveling wave parametric amplifier, which achieves signal amplification by changing a small system "parametric" quantity, such as the capacitance or nonlinearity of the transmission line.
02Optical Parametric Amplifiers
Since the 1980s, it has been known that the inherent nonlinearity of optical fibers can also be used to create a traveling wave optical parametric amplifier whose gain is independent of atomic or semiconductor jumps, meaning that it can be broadband and can cover virtually any wavelength.
Parametric amplifiers are also unaffected by the smallest input signal, which means they can be used to amplify the weakest signals and large input powers in a single setup. Finally, the gain spectrum can be customized through waveguide geometry optimization and dispersion engineering, which provides tremendous design flexibility for the target wavelength and application. Most interestingly, parametric gain can be derived in unusual wavelength bands that are unreachable by conventional semiconductors or rare-earth doped fibers. Parametric amplification is inherently quantum-limited and even noise-free amplification can be achieved.
03Limitations of silicon
Despite the attractive properties of optical parametric amplifiers in optical fibers, the pump power requirements of silicon dioxide are very high due to its weak Kerr nonlinearity. Advances in integrated photonic platforms over the last two decades have led to significant enhancements in effective Kerr nonlinearity, which is not possible in quartz fibers, but not in continuous-wave operational amplifiers.
Professor Tobias Kippenberg, head of the Photonics and Quantum Measurement Laboratory at EPFL, stated [2], "Working in continuous-wave mode is not just an 'academic achievement'. In fact, it is crucial for the practical operation of any amplifier, because it means that any input signal can be amplified - for example, optically encoded information, signals from lidars, sensors, etc. Time- and spectrum-continuous traveling wave amplification is critical to the successful implementation of amplifier technology in modern optical communication systems and the emerging applications of optical sensing and ranging."
04Breakthrough photonic chip
The principle of continuous traveling wave optical parametric amplifier based on photonic integrated circuit.
Photonic chip-based continuous traveling wave optical parametric amplifier and frequency conversion.
A new study led by Dr. Johann Riemensberger of Kippenberg's team has now solved this challenge by developing a traveling wave amplifier based on a continuously operating photonic integrated circuit.Riemensberger said, "Our research results are the result of more than a decade of integrated nonlinear photonics research and the quest for ever-lower waveguide losses."
The researchers used an ultra-low-loss silicon nitride photonic integrated circuit more than two meters long to build the first traveling wave amplifier on a photonic chip measuring 3x5 mm2. The chip operates in a continuous state and provides 7 dB net on-chip gain and 2 dB net inter-fiber gain in the telecom band.
In the future, the team can use precise photolithography control to optimize waveguide dispersion to obtain parametric gain bandwidths in excess of 200 nm. And because of the very low fundamental absorption loss of silicon nitride (about 0.15 dB/m), further fabrication optimization could result in a maximum parametric gain of more than 70 dB on a chip with a pump power of just 750 mW, exceeding the performance of the best fiber amplifiers.
The application areas for this amplifier are limitless," says Kippenberg. From optical communications that can extend signals beyond the typical telecom bands, to mid-infrared or visible lasers and signal amplification, to lidar or other applications where lasers are used to detect, sense and interrogate classical or quantum signals."
Reference link:
[1]https://www.nature.com/articles/s41586-022-05329-1
[2]https://actu.epfl.ch/news/photonics-chip-allows-light-amplification/
