Generation of optical frequency combs in fibres

We numerically investigated the possibility of generating high-quality ultra-short optical pulses with broad frequencycombs spectra in a system consisting of three optical fibres. In this system, the first fibre is a conventional single-mode fibre, the second one is erbium-doped, and the last one is a low-dispersion fibre. The system is pumped with a modulated sine-wave generated by two equally intense lasers with the wavelengths λ ;1and λ2 such that their central wavelength is at λc = (λ1 + λ2)/2 = 1531 nm. The modelling was performed using the generalised nonlinear Schrödinger equation which includes the Kerr and Raman effects, as well as the higher-order dispersion and gain. We took a close look at the pulse evolution in the first two stages and studied the pulse behaviour depending on the group-velocity dispersion and the nonlinear parameter of first fibre, as well as the initial laser frequency separation. For these parameters, the optimum lengths of fibre 1 and 2 were found that provide low-noise pulses. To characterise the pulse energy content, we introduced a figure of merit that was dependent on the group-velocity dispersion, the nonlinearity of fibre 1, and the laser separation

Ultra-flat wideband single-pump Raman-enhanced parametric amplification

We experimentally optimize a single pump fiber optical parametric amplifier in terms of gain spectral bandwidth and gain variation (GV). We find that optimal performance is achieved with the pump tuned to the zero-dispersion wavelength of dispersion stable highly nonlinear fiber (HNLF). We demonstrate further improvement of parametric gain bandwidth and GV by decreasing the HNLF length. We discover that Raman and parametric gain spectra produced by the same pump may be merged together to enhance overall gain bandwidth, while keeping GV low. Consequently, we report an ultra-flat gain of 9.6±0.5 dB over a range of 111 nm (12.8 THz) on one side of the pump. Additionally, we demonstrate amplification of a 60 Gbit/s QPSK signal tuned over a portion of the available bandwidth with OSNR penalty less than 1 dB for Q2 below 14 dB

Astronomical optical frequency comb generation and test in a fiber-fed MUSE spectrograph

We here report on recent progress on astronomical optical frequency comb generation at innoFSPEC-Potsdam and present preliminary test results using the fiber-fed Multi Unit Spectroscopic Explorer (MUSE) spectrograph. The frequency comb is generated by propagating two free-running lasers at 1554.3 and 1558.9 nm through two dispersionoptimized nonlinear fibers. The generated comb is centered at 1590 nm and comprises more than one hundred lines with an optical-signal-to-noise ratio larger than 30 dB. A nonlinear crystal is used to frequency double the whole comb spectrum, which is efficiently converted into the 800 nm spectral band. We evaluate first the wavelength stability using an optical spectrum analyzer with 0.02 nm resolution and wavelength grid of 0.01 nm. After confirming the stability within 0.01 nm, we compare the spectra of the astro-comb and the Ne and Hg calibration lamps: the astro-comb exhibits a much larger number of lines than lamp calibration sources. A series of preliminary tests using a fiber-fed MUSE spectrograph are subsequently carried out with the main goal of assessing the equidistancy of the comb lines. Using a P3d data reduction software we determine the centroid and the width of each comb line (for each of the 400 fibers feeding the spectrograph): equidistancy is confirmed with an absolute accuracy of 0.4 pm

Mid-infrared optical parametric amplifier using silicon nanophotonic waveguides

All-optical signal processing is envisioned as an approach to dramatically decrease power consumption and speed up performance of next-generation optical telecommunications networks. Nonlinear optical effects, such as four-wave mixing (FWM) and parametric gain, have long been explored to realize all-optical functions in glass fibers. An alternative approach is to employ nanoscale engineering of silicon waveguides to enhance the optical nonlinearities by up to five orders of magnitude, enabling integrated chip-scale all-optical signal processing. Previously, strong two-photon absorption (TPA) of the telecom-band pump has been a fundamental and unavoidable obstacle, limiting parametric gain to values on the order of a few dB. Here we demonstrate a silicon nanophotonic optical parametric amplifier exhibiting gain as large as 25.4 dB, by operating the pump in the mid-IR near one-half the band-gap energy (E~0.55eV, lambda~2200nm), at which parasitic TPA-related absorption vanishes. This gain is high enough to compensate all insertion losses, resulting in 13 dB net off-chip amplification. Furthermore, dispersion engineering dramatically increases the gain bandwidth to more than 220 nm, all realized using an ultra-compact 4 mm silicon chip. Beyond its significant relevance to all-optical signal processing, the broadband parametric gain also facilitates the simultaneous generation of multiple on-chip mid-IR sources through cascaded FWM, covering a 500 nm spectral range. Together, these results provide a foundation for the construction of silicon-based room-temperature mid-IR light sources including tunable chip-scale parametric oscillators, optical frequency combs, and supercontinuum generators

Nonlinear Mixing In Silicon Waveguides For Swir And Mid-Ir Applications

We present results on four-photon mixing in silicon waveguides beyond 2μm using signals derived from ultra-compact telecom sources. This widely tunable parametric silicon source can combine narrow linewidth and complex modulation offering great potential for Mid-IR applications. © 2009 Optical Society of America

Optical Demultiplexing with Extinction Ratio Enhancement Based on Higher Order Parametric Interaction

We present the experimental demonstration of an all-optical demultiplexer for high speed OTDM data with optical regeneration capability. It is shown that higher order parametric interactions provide optical sampling with high extinction ratio

Two-Pump Four-Wave Mixing In Silicon Waveguides

We report dual-pump four wave mixing in silicon waveguides and demonstrate generation of up to 10 sidebands with self-seeded higher order pumps. A conversion efficiency of -8.38dB was measured between the signal and phase-conjugated idler. © 2009 Optical Society of America

Mid-Infrared Four-Wave Mixing In Silicon Waveguides Using Telecom-Compatible Light Sources

We report four-wave mixing in silicon waveguides in the spectral region beyond 2μm using infrared signals derived from telecom-compatible fiber-optic sources. We measure a high value of the nonlinear parameter γ = 103 (Wm)-1. © 2009 Optical Society of America

Efficient Kerr soliton comb generation in micro-resonator with interferometric back-coupling

Nonlinear Kerr micro-resonators have enabled fundamental breakthroughs in the understanding of dissipative solitons, as well as in their application to optical frequency comb generation. However, the conversion efficiency of the pump power into a soliton frequency comb typically remains below a few percent. We fabricate and characterize a hybrid Mach-Zehnder ring resonator geometry, consisting of a micro-ring resonator embedded in an additional cavity with twice the optical path length of the ring. The resulting interferometric back coupling enables to achieve an unprecedented control of the pump depletion: pump-to-frequency comb conversion efficiencies of up to 55% of the input pump power is experimentally demonstrated with a soliton crystal comb. We assess the robustness of the proposed on-chip geometry by generating a large variety of dissipative Kerr soliton combs, which require a lower amount of pump power to be accessed, when compared with an isolated micro-ring resonator with identical parameters. Micro-resonators with feedback enable accessing new regimes of coherent soliton comb generation, and are well suited for comb applications in astronomy, spectroscopy and telecommunications. Increasing the conversion efficiency of soliton crystals will enable further application of optical frequency comb. Here the authors engineer an hybrid Mach-Zehnder micro-ring resonator to achieve 80% pump-to-comb conversion efficiency based on dissipative Kerr solitons.Funding Agencies|BMBF (Federal Ministry of Education and Research)Federal Ministry of Education &amp; Research (BMBF) [03Z2AN11, 03Z2AN12]; European Research Council (ERC) under the European UnionEuropean Research Council (ERC) [740355, 874596]; Swedish Research Council (Vetenskapsradet)Swedish Research Council [2017-05309]</p