Microresonator solitons for massively parallel coherent optical communications

Optical solitons are waveforms that preserve their shape while propagating, relying on a balance of dispersion and nonlinearity. 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. DKS are generated in an integrated silicon nitride microresonator by four-photon interactions mediated by Kerr nonlinearity, leading to low-noise, spectrally smooth and broadband optical frequency combs. In our experiments, we use two interleaved soliton Kerr combs to transmit a data stream of more than 50Tbit/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.Comment: 10 pages, 3 figure

Flexible terabit/s Nyquist-WDM super-channels using a gain-switched comb source

Terabit/s super-channels are likely to become the standard for next-generation optical networks and optical interconnects. A particularly promising approach exploits optical frequency combs for super-channel generation. We show that injection locking of a gain-switched laser diode can be used to generate frequency combs that are particularly well suited for terabit/s super-channel transmission. This approach stands out due to its extraordinary stability and flexibility in tuning both center wavelength and line spacing. We perform a series of transmission experiments using different comb line spacings and modulation formats. Using 9 comb lines and 16QAM signaling, an aggregate line rate (net data rate) of 1.296 Tbit/s (1.109 Tbit/s) is achieved for transmission over 150 km of standard single mode fiber (SSMF) using a spectral bandwidth of 166.5 GHz, which corresponds to a (net) spectral efficiency of 7.8 bit/s/Hz (6.7 bit/s/Hz). The line rate (net data rate) can be boosted to 2.112 Tbit/s (1.867 Tbit/s) for transmission over 300 km of SSMF by using a bandwidth of 300 GHz and QPSK modulation on the weaker carriers. For the reported net data rates and spectral efficiencies, we assume a variable overhead of either 7\% or 20\% for forward- error correction depending on the individual sub-channel quality after fiber transmission

Coherent terabit communications with microresonator Kerr frequency combs

Optical frequency combs enable coherent data transmission on hundreds of wavelength channels and have the potential to revolutionize terabit communications. Generation of Kerr combs in nonlinear integrated microcavities represents a particularly promising option enabling line spacings of tens of GHz, compliant with wavelength-division multiplexing (WDM) grids. However, Kerr combs may exhibit strong phase noise and multiplet spectral lines, and this has made high-speed data transmission impossible up to now. Recent work has shown that systematic adjustment of pump conditions enables low phase-noise Kerr combs with singlet spectral lines. Here we demonstrate that Kerr combs are suited for coherent data transmission with advanced modulation formats that pose stringent requirements on the spectral purity of the optical source. In a first experiment, we encode a data stream of 392 Gbit/s on subsequent lines of a Kerr comb using quadrature phase shift keying (QPSK) and 16-state quadrature amplitude modulation (16QAM). A second experiment shows feedback-stabilization of a Kerr comb and transmission of a 1.44 Tbit/s data stream over a distance of up to 300 km. The results demonstrate that Kerr combs can meet the highly demanding requirements of multi-terabit/s coherent communications and thus offer a solution towards chip-scale terabit/s transceivers

Multi-wavelength coherent transmission using an optical frequency comb as a local oscillator

Steadily increasing data rates of optical interfaces require spectrally efficient coherent transmission using higher-order modulation formats in combination with scalable wavelength-division multiplexing (WDM) schemes. At the transmitter, optical frequency combs (OFC) lend themselves to particularly precise multi-wavelength sources for WDM transmission. In this work we demonstrate that these advantages can also be leveraged at the receiver by using an OFC as a highly scalable multi-wavelength local oscillator (LO) for coherent detection. In our experiments, we use a pair of OFC that rely on gain switching of injection-locked semiconductor lasers both for WDM transmission and intradyne reception. We synchronize the center frequency and the free spectral range of the receiver comb to the transmitter, keeping the intradyne frequencies for all data channels below 15 MHz. Using 13 WDM channels, we transmit an aggregate line rate (net data rate) of 1.104 Tbit/s (1.032 Tbit/s) over a 10 km long standard single mode fiber at a spectral efficiency of 5.16 bit/s/Hz. To the best of our knowledge, this is the first demonstration of coherent WDM transmission using synchronized frequency combs as light source at the transmitter and as multi-wavelength LO at the receiver

Optimally Coherent Kerr Combs Generated with Crystalline Whispering Gallery Mode Resonators for Ultrahigh Capacity Fiber Communications

International audienceOptical Kerr frequency combs are known to be effective coherent multiwavelength sources for ultrahigh capacity fiber communications. These combs are the frequency-domain counterparts of a wide variety of spatiotemporal dissipative structures, such as cavity solitons, chaos, or Turing patterns (rolls). In this Letter, we demonstrate that Turing patterns, which correspond to the so-called primary combs in the spectral domain, are optimally coherent in the sense that for the same pump power they provide the most robust carriers for coherent data transmission in fiber communications using advanced modulation formats. Our model is based on a stochastic Lugiato-Lefever equation which accounts for laser pump frequency jitter and amplified spontaneous emission noise induced by the erbium-doped fiber amplifier. Using crystalline whispering-gallery-mode resonators with quality factor Q∼109 for the comb generation, we show that when the noise is accounted for, the coherence of a primary comb is significantly higher than the coherence of their solitonic or chaotic counterparts for the same pump power. In order to confirm this theoretical finding, we perform an optical fiber transmission experiment using advanced modulation formats, and we show that the coherence of the primary comb is high enough to enable data transmission of up to 144  Gbit/s per comb line, the highest value achieved with a Kerr comb so far. This performance evidences that compact crystalline photonic systems have the potential to play a key role in a new generation of coherent fiber communication networks, alongside fully integrated systems

Terabit/s communications using chip-scale frequency comb sources

High-speed optical interconnects rely on advanced wavelength-division multiplexing (WDM) schemes. However, while photonic-electronic interfaces can be efficiently realized on silicon-on-insulator chips, dense integration of the necessary light sources still represents a major challenge. Chip-scale frequency comb sources present an attractive alternative for providing a multitude of optical carriers for WDM transmission. In this paper, we give an overview of our recent progress towards terabit communications with chip-scale frequency comb sources. In a first set of experiments, we demonstrate frequency comb generation based on silicon-organic hybrid (SOH) electro-optic modulators, enabling line rates up to 1.152 Tbit/s. In a second set of experiments, we use injection locking of a gain-switched laser diode to generate frequency combs. This approach leads to line rates of more than 2 Tbit/s. A third set of experiments is finally dedicated to using Kerr nonlinearities in integrated nonlinear microcavities for frequency comb generation. We demonstrate coherent communication using Kerr frequency comb sources, thereby achieving line rates up to 1.44 Tbit/s. Our experiments show that frequency comb generation in chip-scale devices represents a viable approach to terabit communications