We know that since the 1990s, WDM wavelength division multiplexing technology has been used for long-distance fiber optic links spanning hundreds or even thousands of kilometers. For most countries and regions, fiber optic infrastructure is their most expensive asset, while the cost of transceiver components is relatively low.
However, with the explosive growth of network data transmission rates such as 5G, WDM technology has become increasingly important in short distance links, and the deployment volume of short links is much larger, making the cost and size of transceiver components more sensitive.
At present, these networks still rely on thousands of single-mode optical fibers for parallel transmission through space division multiplexing channels, and the data rate of each channel is relatively low, at most only a few hundred Gbit/s (800G). T-level may have limited applications.
But in the foreseeable future, the concept of ordinary spatial parallelization will soon reach its scalability limit, and must be supplemented by spectrum parallelization of data streams in each fiber to maintain further improvements in data rates. This may open up a whole new application space for wavelength division multiplexing technology, where the maximum scalability of channel number and data rate is crucial.
In this case, the frequency comb generator (FCG), as a compact and fixed multi wavelength light source, can provide a large number of well-defined optical carriers, thus playing a crucial role. In addition, a particularly important advantage of optical frequency comb is that the comb lines are essentially equidistant in frequency, which can relax the requirements for inter channel guard bands and avoid the frequency control required for single lines in traditional schemes using DFB laser arrays.
It should be noted that these advantages are not only applicable to the transmitter of wavelength division multiplexing, but also to its receiver, where the discrete local oscillator (LO) array can be replaced by a single comb generator. The use of LO comb generators can further facilitate digital signal processing in wavelength division multiplexing channels, thereby reducing receiver complexity and improving phase noise tolerance.
In addition, using LO comb signals with phase-locked function for parallel coherent reception can even reconstruct the time-domain waveform of the entire wavelength division multiplexing signal, thereby compensating for the damage caused by the optical nonlinearity of the transmission fiber. In addition to the conceptual advantages based on comb signal transmission, smaller size and economically efficient large-scale production are also key factors for future wavelength division multiplexing transceivers.
Therefore, among various comb signal generator concepts, chip level devices are particularly noteworthy. When combined with highly scalable photonic integrated circuits for data signal modulation, multiplexing, routing, and reception, such devices may become key to compact and efficient wavelength division multiplexing transceivers that can be manufactured in large quantities at low cost, with transmission capacity of tens of Tbit/s per fiber.
At the output of the sending end, each channel is recombined through a multiplexer (MUX), and the wavelength division multiplexing signal is transmitted through single-mode fiber. At the receiving end, the wavelength division multiplexing receiver (WDM Rx) uses the LO local oscillator of the second FCG for multi wavelength interference detection. The channel of the input wavelength division multiplexing signal is separated by a demultiplexer and then sent to a coherent receiver array (Coh. Rx). Among them, the demultiplexing frequency of the local oscillator LO is used as the phase reference for each coherent receiver. The performance of this wavelength division multiplexing link obviously depends largely on the basic comb signal generator, especially the width of the light and the optical power of each comb line.
Of course, optical frequency comb technology is still in the development stage, and its application scenarios and market size are relatively small. If it can overcome technological bottlenecks, reduce costs, and improve reliability, it may achieve scale level applications in optical transmission.
Post time: Dec-19-2024