With the development of innovative manufacturing techniques, next-generation fiber Bragg grating (FBG) components can now be produced with the level of performances and reliability that allow mass deployment of these devices for high-end applications. Gain flattening filters (GFF) with low-error function, low-dispersion WDM filters suitable for operation at 40 Gb/s and low group delay ripples multichannel chromatic dispersion compensators are among these high-end applications. Moreover, since FBG is an all-fiber technology, tunability can be easily implemented opening the door for applications such as tunable chromatic dispersion compensator. In this paper, we will present an overview of those high-end applications and show that FBG technology is well suited to overcome the challenges imposed by future optical networks.
One of the biggest challenges of silicon photonics is the efficient coupling of light between the sub-micron SiP waveguides and a standard optical fiber (SMF-28). We recently proposed a novel approach based on a spot-size converter (SSC) that fulfills this need. The SSC integrates a tapered silicon waveguide and a superimposed structure made of a plurality of rods of high index material, disposed in an array-like configuration and embedded in a cladding of lower index material. This superimposed structure defines a waveguide designed to provide an efficient adiabatic transfer, through evanescent coupling, to a 220 nm thick Si waveguide tapered down to a narrow tip on one side, while providing a large mode overlap to the optical fiber on the other side. An initial demonstration was made using a SSC fabricated with post-processing steps. Great coupling to a SMF-28 fiber with a loss of 0.6 dB was obtained for TEpolarized light at 1550 nm with minimum wavelength dependence. In this paper, SSCs designed for operation at 1310 and 1550 nm for TE/TM polarizations and entirely fabricated in a CMOS fab are presented.
TeraXion started silicon photonics activities aiming at developing building blocks for new products and customized
solutions. Passive and active devices have been developed including MMI couplers, power splitters, Bragg grating
filters, high responsivity photodetectors, high speed modulators and variable optical attenuators. Packaging solutions
including fiber attachment and hybrid integration using flip-chip were also developed. More specifically, a compact
packaged integrated coherent receiver has been realized. Good performances were obtained as demonstrated by our
system tests results showing transmission up to 4800 km with BER below hard FEC threshold. The package size is small
but still limited by the electrical interface. Migrating to more compact RF interface would allow realizing the full benefit
of this technology.
We review the improved performances of a narrow linewidth laser using negative electrical feedback obtained through
advances on narrowband FBG filters. Noteworthy, the tolerance of the laser to vibrations is significantly improved. As
an extension of this work, these narrow filters are proposed for filtering optical signals in RF photonics systems.
Chromatic dispersion (CD) in single-mode optical fiber distorts pulses and is a big obstacle against the upgrading of long-haul, dynamically routed wavelength division multiplexed (WDM) transmission systems at 10 Gbit/s and beyond. High-performance adaptive dispersion compensators are required as well as reliable low-cost hardware for the detection of residual CD. Targeting high-capacity metro systems, full-band 1.6-Tb/s (40x40Gbit/s) adaptive CD compensation is demonstrated in this experiment, using CSRZ-ASK and NRZ-DPSK modulation formats. A multichannel dispersion compensator, tunable in the range -700 to -1500 ps/nm, is automatically controlled by arrival time detection in one of the 40 transmitted WDM channels. Dispersion and its slope are tuned simultaneously by a thermal gradient of the grating-based compensator to match the parameters of standard single-mode fiber (SSMF) with lengths between 44 and 94 km.
Hongbin Zhang, A. Fauzi Abas, Ariya Hidayat, David Sandel, Suhas Bhandare, Frank Wüst, Biljana Milivojevic, Reinhold Noé, Martin Lapointe, Yves Painchaud, Martin Guy
The capacity limit of a thermally controlled fiber Bragg grating-based chromatic dispersion compensator, which was initially designed for 10 Gb/s operation, was investigated in a 40 Gb/s system. A CS-RZ DQPSK polarization division multiplex (PolDM) system was used as a testbed. An equivalent quasi error-free 5.94 Tb/s capacity was demonstrated when dispersion of up to 73.8 km of SSMF was compensated. The dispersion slope compensation was satisfactory for C-band operation. Additionally, it was found that the compensator introduced band-pass filtering behaviour, which reduced the compensator bandwidth as the dispersion setting was increased. It was also found that even after 41.5 km, there was around 2 dB penalty introduced to DQPSK system while 5 dB penalty to DQPDK-PolDM, referring to BER of 10-5.
Chromatic dispersion accumulated over a link of optical fiber causes transmission degradation for data rates of 10 Gbit/s and higher. The different technologies for compensating this effect are reviewed. They are compared based on their suitability for different applications. Characteristics such as system performance, tunability, insertion loss, bandwidth and size are discussed. Tunability is of increasing importance as the future networks become more and more agile and reconfigurable. Fine tuning is also a requirement at data rates of 40 Gbit/s and higher. In the context of WDM systems, operations in both single-channel and multi-channel regimes are discussed. Recent developments are presented and future trends are discussed.
In this paper, we show that Bragg gratings can greatly contribute to enhance the performances of today's optical amplifiers.
some of the applications of Bragg gratings in optical amplifiers such as gain equalization, gain stabilization and dispersion
compensation will thus be reviewed.
Broadband discrete and continuous tuning of erbium-doped fiber lasers is demonstrated in this paper. First, an exact
multiple of 100 GHz frequency step-tunable L band erbium-doped fiber ring laser is presented. Precise multiple of
100 GHz step-tunability is obtain by proper angle positioning of a 100 GHz Fabry-Perot micro etalon in the laser
cavity. Secondly, continuous tuning over 90 nm is shown in a laser using gain-band switching between C and L band
EDFAs. Lastly, a tunable laser design that uses a single gain medium to obtain 100 nm of tuning in the C and L
bands is demonstrated.
Gain equalization of an amplifier is performed by introducing spectrally designed Bragg gratings in the
mid-stage of a dual-stage erbium-doped fiber amplifier. The long-haul performances of the amplifier are
evaluated using a 50 km recirculating loop. The results show a clear improvement of the transmission
quality when equalizing the gain.
Gain equalization of an EDFA is performed by introducing spectrally designed all-fiber filters in the mid-stage of a dual-stage fiber amplifier. Two types of filters are studied: a cascade of narrow-band Bragg gratings for discrete equalization of a finite number of channels and a wide-band Bragg grating performing equalization over the whole 1539 nm to 1557 nm range. In future work, it is planned to use the discrete Bragg grating configuration to simultaneously perform Dispersion compensation (D), Equalization (E) and Stabilization of gain (S) and Channel dropping (C) in a dual-stage EDFA. Integration of these functions will result in a high performance amplifier called the DESC-EDFA.
We have undertaken a research directed to the realization of frequency-stabilized lasers for multifrequency optical communications in the 375 THz, 229 THz, and 193 THz (0.8, 1.3, and 1.55 micrometers ) bands. In this paper, we present an overview of our latest results in the 1.55 micrometers band. We compare the performance of optical frequency references based on lasers frequency-locked to acetylene molecules and rubidium atoms. The absolute vales and the frequency stability improvements are discussed. We also present techniques to transfer those performance to multiple frequencies for multifrequency communication systems. We study the use of an absolutely calibrated multimode Fabry-Perot optical resonator with transmission peals set at exact multiples of 100 GHz. We also study the use of a calibrated wavemeter based on a sum-frequency surface emitting multilayered nonlinear crystal to allow the precise tuning at any frequency in the vicinity of an absolute optical frequency standard.
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