688 research outputs found
Applications of nonlinear four-wave mixing in optical communication
In this paper I will briefly review some applications of nonlinear four-wave-mixing in optical fibers and silicon-nitride waveguides. This includes ultrafast all-optical waveform sampling and ‘noiseless’ phase-sensitive optical amplification which have been demonstrated to enable signal recovery at very low optical powers
Electro-optic dual-comb interferometry over 40-nm bandwidth
Dual-comb interferometry is a measurement technique that uses two laser
frequency combs to retrieve complex spectra in a line-by-line basis. This
technique can be implemented with electro-optic frequency combs, offering
intrinsic mutual coherence, high acquisition speed and flexible repetition-rate
operation. A challenge with the operation of this kind of frequency comb in
dual-comb interferometry is its limited optical bandwidth. Here, we use
coherent spectral broadening and demonstrate electro-optic dual-comb
interferometry over the entire telecommunications C band (200 lines covering ~
40 nm, measured within 10 microseconds at 100 signal-to-noise ratio per
spectral line). These results offer new prospects for electro-optic dual-comb
interferometry as a suitable technology for high-speed broadband metrology, for
example in optical coherence tomography or coherent Raman microscopy
Phase-sensitive fiber-optic parametric amplifiers and their applications
The basics and recent progress in nonlinear fiber-based phase-sensitive parametric amplifiers is discussed. In addition, their potential use as in-line amplifiers, resulting in significant link performance improvement potential, is highlighted
Tunable superlattice p-i-n photodetectors: characteristics, theory, and application
Extended measurements and theory on the recently developed monolithic wavelength demultiplexer consisting of voltage-tunable superlattice p-i-n photodetectors in a waveguide confirmation are discussed. It is shown that the device is able to demultiplex and detect two optical signals with a wavelength separation of 20 nm directly into different electrical channels at a data rate of 1 Gb/s and with a crosstalk attenuation varying between 20 and 28 dB, depending on the polarization. The minimum acceptable crosstalk attenuation at a data rate of 100 Mb/s is determined to be 10 dB. The feasibility of using the device as a polarization angle sensor for linearly polarized light is also demonstrated. A theory for the emission of photogenerated carriers out of the quantum wells is included, since this is potentially a speed limiting mechanism in these detectors. It is shown that a theory of thermally assisted tunneling by polar optical phonon interaction is able to predict emission times consistent with the observed temporal response
Fiber-based phase-sensitive optical amplifiers and their applications
Optical parametric amplifiers rely on second-order susceptibility (three-wave mixing) or third-order susceptibility (four-wave mixing) in a nonlinear process where the energy of incoming photons is not changed (elastic scattering). In the latter case, two pump photons are converted to a signal and to an idler photon. Under certain conditions, related to the phase evolution of the waves involved, this conversion can be very effi-cient, resulting in large amplification of an input signal. As the nonlinear process can be very fast, all-optical applications aside from pure amplification are also possible. If the amplifier is implemented in an optical input-phase-sensitive manner, it is possible to amplify a signal wave without excess noise, i.e., with a noise figure of 0 dB. In this paper, we will provide the fundamental concepts and theory of such amplifiers, with a focus on their implementation in highly nonlinear optical fibers relying on four-wave mixing. We will discuss the distinctions between phase-insensitive and phase-sensitive operation and include several experimental results to illustrate their capability. Different applications of parametric amplifiers are also discussed, including their use in optical communication links
Impact of 4D channel distribution on the achievable rates in coherent optical communication experiments
We experimentally investigate mutual information and generalized mutual
information for coherent optical transmission systems. The impact of the
assumed channel distribution on the achievable rate is investigated for
distributions in up to four dimensions. Single channel and wavelength division
multiplexing (WDM) transmission over transmission links with and without inline
dispersion compensation are studied. We show that for conventional WDM systems
without inline dispersion compensation, a circularly symmetric complex Gaussian
distribution is a good approximation of the channel. For other channels, such
as with inline dispersion compensation, this is no longer true and gains in the
achievable information rate are obtained by considering more sophisticated
four-dimensional (4D) distributions. We also show that for nonlinear channels,
gains in the achievable information rate can also be achieved by estimating the
mean values of the received constellation in four dimensions. The highest gain
for such channels is seen for a 4D correlated Gaussian distribution
Optical bandgap engineering in nonlinear silicon nitride waveguides
Silicon nitride is awell-established material for photonic devices and
integrated circuits. It displays a broad transparency window spanning from the
visible to the mid-IR and waveguides can be manufactured with low losses. An
absence of nonlinear multi-photon absorption in the erbium lightwave
communications band has enabled various nonlinear optic applications in the
past decade. Silicon nitride is a dielectric material whose optical and
mechanical properties strongly depend on the deposition conditions. In
particular, the optical bandgap can be modified with the gas flow ratio during
low-pressure chemical vapor deposition (LPCVD). Here we show that this
parameter can be controlled in a highly reproducible manner, providing an
approach to synthesize the nonlinear Kerr coefficient of the material. This
holistic empirical study provides relevant guidelines to optimize the
properties of LPCVD silicon nitride waveguides for nonlinear optics
applications that rely on the Kerr effect
Low-Power 400-Gbps Soft-Decision LDPC FEC for Optical Transport Networks
We present forward error correction systems based on soft-decision low-density parity check (LDPC) codes for applications in 100–400-Gbps optical transport networks. These systems are based on the low-complexity “adaptive degeneration” decoding algorithm, which we introduce in this paper, along with randomly-structured LDPC codes with block lengths from 30 000 to 60 000 bits and overhead (OH) from 6.7% to 33%. We also construct a 3600-bit prototype LDPC code with 20% overhead, and experimentally show that it has no error floor above a bit error rate (BER) of 10−15 using a field-programmable gate array (FPGA)-based hardware emulator. The projected net coding gain at a BER of 10−15 ranges from 9.6 dB at 6.7% OH to 11.2 dB at 33% OH. We also present application-specific integrated circuit synthesis results for these decoders in 28 nm fully depleted silicon on insulator technology, which show that they are capable of 400-Gbps operation with energy consumption of under 3 pJ per information bit
Comparison between Coherent Superposition in DSP and PSA for Mitigation of Nonlinearities in a Single-span Link
An experimental comparison is made between nonlinearity mitigation through coherent superposition optically in a phase-sensitive amplifier and electrically in DSP. The improved nonlinear tolerance is quantified in terms of EVM with high received power and sensitivity with high launch power
One photon-per-bit receiver using near-noiseless phase-sensitive amplification
Space communication for deep-space missions, inter-satellite data transfer and Earth monitoring requires high-speed data connectivity. The reach is fundamentally dictated by the available transmission power, the aperture size, and the receiver sensitivity. A transition from radio-frequency links to optical links is now seriously being considered, as this greatly reduces the channel loss caused by diffraction. A widely studied approach uses power-efficient formats along with nanowire-based photon-counting receivers cooled to a few Kelvins operating at speeds below 1 Gb/s. However, to achieve the multi-Gb/s data rates that will be required in the future, systems relying on pre-amplified receivers together with advanced signal generation and processing techniques from fibre communications are also considered. The sensitivity of such systems is largely determined by the noise figure (NF) of the pre-amplifier, which is theoretically 3 dB for almost all amplifiers. Phase-sensitive optical amplifiers (PSAs) with their uniquely low NF of 0 dB promise to provide the best possible sensitivity for Gb/s-rate long-haul free-space links. Here, we demonstrate a novel approach using a PSA-based receiver in a free-space transmission experiment with an unprecedented bit-error-free, black-box sensitivity of 1 photon-per-information-bit (PPB) at an information rate of 10.5 Gb/s. The system adopts a simple modulation format (quadrature-phase-shift keying, QPSK), standard digital signal processing for signal recovery and forward-error correction and is straightforwardly scalable to higher data rates. Space communication: Opening optical links Communication links for deep-space exploration spacecraft and satellites could become more efficient using an optical system which can reduce signal losses during transmission and delivers one bit of data per each received photon at a rate of 10 gigabits per second. Peter Andrekson and colleagues at Chalmers University of Technology in Sweden developed the system and demonstrated its potential in laboratory scale experiments. It relies on a technology known as phase-sensitive optical amplification. The researchers transmitted signals across only a one meter, but they believe their work proves the validity of a process that could readily be scaled up for communication across space. Replacing current radio-frequency technology with more effective optical systems could meet the demands of future space communications systems, which will need to operate at higher data rates and across greater distances
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