Optical solitons are waveforms that preserve their shape while propagating, relying on a balance of dispersion and nonlinearity [1,2]. Soliton-based data transmission schemes were investigated in the 1980s, promising to overcome the limitations imposed by dispersion of optical fibers. These approaches, however, were eventually abandoned in favor of wavelength-division multiplexing (WDM) schemes that are easier to implement and offer improved scalability to higher data rates. Here, we show that solitons may experience a comeback in optical communications, this time not as a competitor, but as a key element of massively parallel WDM. Instead of encoding data on the soliton itself, we exploit continuously circulating dissipative Kerr solitons (DKS) in a microresonator [3,4]. DKS are generated in an integrated silicon nitride microresonator [5] by four-photon interactions mediated by Kerr nonlinearity, leading to low-noise, spectrally smooth and broadband optical frequency combs [6]. In our experiments, we use two interleaved soliton Kerr combs to trans-mit a data stream of more than 50 Tbit/s on a total of 179 individual optical carriers that span the entire telecommunication C and L bands. Equally important, we demonstrate coherent detection of a WDM data stream by using a pair of microresonator Kerr soliton combs one as a multi-wavelength light source at the transmitter, and another one as a corresponding local oscillator (LO) at the receiver. This approach exploits the scalability advantages of microresonator soliton comb sources for massively parallel optical communications both at the transmitter and receiver side. Taken together, the results prove the significant potential of these sources to replace arrays of continuous-wave lasers in high-speed communications. In combination with advanced spatial multiplexing schemes [7,8] and highly integrated silicon photonic circuits [9], DKS combs may bring chip-scale petabit/s transceivers into reach.The first observation of solitons in optical fibers [2] in 1980 was immediately followed by major research efforts to harness such waveforms for long-haul communications [1]. In these schemes, data was encoded on soliton pulses by simple amplitude modulation using on-off-keying (OOK). However, even though the viability of the approach was experimentally demonstrated by transmission over one million kilometres [10], the vision of soliton-based communications was ultimately hindered by difficulties in achieving shape-preserving propagation in real transmission systems [1] and by the fact that nonlinear interactions intrinsically prevent dense packing of soliton pulses in either the time or frequency domain. Moreover, with the advent of wavelength-division multiplexing (WDM), line rates in long-haul communication systems could be increased by rather simple parallel transmission of data streams with lower symbol rates, which are less dispersion sensitive. Consequently, soliton-based communication schemes have moved out of focus over the last two decades. More recently, frequ...
Lasers are often used to characterize samples in a non-destructive manner and retrieve sensing information transduced in changes in amplitude and phase. In swept wavelength interferometry, a wavelength-tunable laser is used to measure the complex response (i.e. in amplitude and phase) of an optical sample. This technique leverages continuous advances in rapidly tunable lasers and is widely used for sensing, bioimaging and testing of photonic integrated components. However, the tunable laser requires an additional calibration step because, in practice, it does not tune at a constant rate. In this work, we use a self-referenced frequency comb as an optical ruler to calibrate the laser used in swept-wavelength interferometry and optical frequency domain reflectometry. This allows for realizing high-resolution complex spectroscopy over a bandwidth exceeding 10 THz. We apply the technique to the characterization of low-loss integrated photonic devices and demonstrate that the phase information can disentangle intrinsic from coupling losses in the characterization of high-Q microresonators. We also demonstrate the technique in reflection mode, where it can resolve attenuation and dispersion characteristics in integrated long spiral waveguides.
We experimentally demonstrate high-cardinality, low-complexity Voronoi constellations based on the E8 lattice over multiple time slots with OSNR and launch power gains of up to 1.7 and 2.4 dB for back-to-back and 80 km fiber transmission, respectively, compared to QAM formats.
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