Evgeny Myslivets

50-Gb/s Silicon Optical Modulator

Optical modulators formed in silicon are the keystone to many low cost optical applications. Increasing the data rate of the modulator benefits the efficiency of channel usage and decreases power consumption per bit of data. Silicon-based modulators which operate via carrier depletion have to the present been demonstrated at data rates up to 40 Gb/s; however, here we present for the first time optical modulation at 50 Gb/s with a 3.1-dB extinction ratio obtained from carrier depletion based phase shifter incorporated in a Mach-Zehnder interferometer. A corresponding optical insertion loss of approximately 7.4 dB is measured.

Generation of wideband frequency combs by continuous-wave seeding of multistage mixers with synthesized dispersion

We numerically and experimentally demonstrate efficient generation of an equalized optical comb with 150-nm bandwidth. The comb was generated by low-power, continuous-wave seeds, eliminating the need for pulsed laser sources. The new architecture relies on efficient creation of higher-order mixing tones in phase-matched nonlinear fiber stages separated by a linear compressor. Wideband generation was enabled by precise dispersion engineering of multiple-stage parametric mixers.

Overcoming Kerr-induced capacity limit in optical fiber transmission

Getting around the capacity crunch The growing appetite for an ever-faster Internet and enhanced long-haul communication requires the pumping of more light down optic fibers. However, light-induced nonlinearities limit how much light can be pumped into the fiber without compromising the signal. This limitation has led to the prospect of a “capacity crunch.” Temprana et al. eliminated the effects of nonlinearity by using digital back-propagation methods with mutually coherent laser pulses from a single frequency comb. Science, this issue p. 1445 Digital back-propagation is used to mitigate light-induced nonlinear effects in optic fiber. Nonlinear optical response of silica imposes a fundamental limit on the information transfer capacity in optical fibers. Communication beyond this limit requires higher signal power and suppression of nonlinear distortions to prevent irreversible information loss. The nonlinear interaction in silica is a deterministic phenomenon that can, in principle, be completely reversed. However, attempts to remove the effects of nonlinear propagation have led to only modest improvements, and the precise physical mechanism preventing nonlinear cancellation remains unknown. We demonstrate that optical carrier stability plays a critical role in canceling Kerr-induced distortions and that nonlinear wave interaction in silica can be substantially reverted if optical carriers possess a sufficient degree of mutual coherence. These measurements indicate that fiber information capacity can be notably increased over previous estimates.

Wavelength Multicasting via Frequency Comb Generation in a Bandwidth-Enhanced Fiber Optical Parametric Mixer

We demonstrate a self-seeded multicasting device capable of delivering a large number of signal integrity preserving spectrally-distinct copies. The new multicasting device relies on efficient higher-order mixing in a two-pump parametric mixer. Precise dispersion engineering was deployed to generate a frequency-comb spanning over a 140-nm band, and resulted in the creation of more than 60 spectral copies of the signal with conversion efficiencies higher than -3 dB. The fidelity of the multicasting device with respect to signal intensity and phase was characterized experimentally. The spectral replication process was found to induce low penalty with both ON-OFF and differential phase-shift keying signals, thereby indicating compatibility with arbitrary amplitude/phase signaling formats.

Spectral linewidth preservation in parametric frequency combs seeded by dual pumps

We demonstrate new technique for generation of programmable-pitch, wideband frequency combs with low phase noise. The comb generation was achieved using cavity-less, multistage mixer driven by two tunable continuous-wave pump seeds. The approach relies on phase-correlated continuous-wave pumps in order to cancel spectral linewidth broadening inherent to parametric comb generation. Parametric combs with over 200-nm bandwidth were obtained and characterized with respect to phase noise scaling to demonstrate linewidth preservation over 100 generated tones.

155-nm Continuous-Wave Two-Pump Parametric Amplification

We investigate the synthesis of flat parametric response of a dual-pumped device with a distant pump separation ranging from 130 to 180 nm. The Raman contribution to the nonlinear polarization introduced predictable gain ripple and dispersion fluctuation along the highly nonlinear fiber had to be precisely accounted for. A 3-dB equalized gain was observed over 100 nm using 130-nm separated pumps. Record gain bandwidth of 155 nm was also measured for the first time.

Spatial Equalization of Zero-Dispersion Wavelength Profiles in Nonlinear Fibers

Longitudinal zero-dispersion wavelength (ZDW) fluctuations in long waveguides impose a fundamental limit on the achievable parametric mixer bandwidth. We demonstrate for the first time that the precisely measured ZDW profile can be taken advantage of by applying spatially controlled tension along the fiber length for fluctuation reduction and synthesis of a wide mixer response. The technique was experimentally validated by measuring local dispersion and tension maps and synthesizing a 145-nm-wide fiber parametric amplifier.

Spectrally Equalized Frequency Comb Generation in Multistage Parametric Mixer With Nonlinear Pulse Shaping

A novel approach to improve the flatness of wide-band parametric frequency combs is presented. The method relies on nonlinear pulse shaping prior to parametric mixing in a comb-generating device. The parametric comb is generated in a cavity-less multistage shock-wave mixer, using continuous-wave (CW) laser as comb seed. The pulse shaping is accomplished in a regenerative stage incorporating nonlinear optical/amplifying loop mirror (NOLM/NALM) and provides near-ideal seeds for spectrally equalized frequency comb generation in the output mixing stage. The new technique was implemented separately on two comb generators with a coarse (100 GHz) and dense (10 GHz) tone spacing. A 4 dB flatness over 100 nm is achieved with wide-pitched comb, while the fine-pitched device yielded 1500 tones and possessed sub-2 dB spectral flatness over 120 nm bandwidth.

Scalable Multicasting in One-Pump Parametric Amplifier

We report the experimental demonstration of all-optical wavelength multicasting of OC-768 (40 Gbps) channel using a single-pass, pump modulated parametric amplifier. The performances of 1-to-20 and 1-to-40 multicasting with excellent signal fidelity were observed. The impairment mechanisms were identified from cascaded filtering, linear and nonlinear crosstalk. It is shown that the parametric amplifier offers a wide range of operation characterized by minimal multicast penalty. We show that all multicast channels have an error free performance with Q factors well above the forward error correction (FEC) limit within the designed operating range.

Wideband Parametric Frequency Comb as Coherent Optical Carrier

We report the first use of the CW-seeded parametric comb as a multiwavelength source for coherent channel transmitters. The new comb source relies on a multistage parametric mixer design seeded by a single kilohertz-linewidth master laser. The resultant frequency comb provides more than 120 tones in a 100-nm-wide continuous band, all possessing kilohertz-scale linewidth inherited from the master laser. The applicability of the new comb source as a coherent channel carrier was quantified by error-vector magnitude and bit-error rate metrics of individual spectral lines modulated by QPSK signaling. The performance of the new source exceeded that of the standard tunable coherent transmitter while providing a qualitatively lower frequency uncertainty and drift.