1,601 research outputs found
Generating mid-IR octave-spanning supercontinua and few-cycle pulses with solitons in phase-mismatched quadratic nonlinear crystals
We discuss a novel method for generating octave-spanning supercontinua and
few-cycle pulses in the important mid-IR wavelength range. The technique relies
on strongly phase-mismatched cascaded second-harmonic generation (SHG) in
mid-IR nonlinear frequency conversion crystals. Importantly we here investigate
the so-called noncritical SHG case, where no phase matching can be achieved but
as a compensation the largest quadratic nonlinearities are exploited. A
self-defocusing temporal soliton can be excited if the cascading nonlinearity
is larger than the competing material self-focusing nonlinearity, and we define
a suitable figure of merit to screen a wide range of mid-IR dielectric and
semiconductor materials with large effective second-order nonlinearities
. The best candidates have simultaneously a large bandgap and a
large . We show selected realistic numerical examples using one of
the promising crystals: in one case soliton pulse compression from 50 fs to 15
fs (1.5 cycles) at 3.0\mic is achieved, and at the same time a 3-cycle
dispersive wave at 5.0\mic is formed that can be isolated using a long-pass
filter. In another example we show that extremely broadband supercontinua can
form spanning the near-IR to the end of the mid-IR (nearly 4 octaves).Comment: submitted to Optics Materials Express special issue on mid-IR
photonic
The light filament as vector solitary wave
We present an analytical approach to the theory of nonlinear propagation of
femtosecond optical pulses with broad-band spectrum in gases. The vector
character of the nonlinear third-order polarization is investigated in details,
taking into account the carrier to envelope phase. The corresponding system of
vector amplitude equations is written by using left-hand and right-hand
circular components of the electrical field. We found that this system
nonlinear equations admits vector soliton solution with Lorentz shape.
The solution presents relatively stable propagation and rotation with GHz
frequency of the vector of the electrical field in plane, orthogonal to the
direction of propagation. The evolution of the intensity profile demonstrate
weak self-compression and week spherical wave in the first milliseconds of
propagation.Comment: 5 pages, 1 figur
A high-speed optical star network using TDMA and all-optical demultiplexing techniques
The authors demonstrate the use of time-division multiplexing (TDM) to realize a high capacity optical star network. The fundamental element of the demonstration network is a 10 ps, wavelength tunable, low jitter, pulse source. Electrical data is encoded onto three optical pulse trains, and the resultant low duty cycle optical data channels are multiplexed together using 25 ps fiber delay lines. This gives an overall network capacity of 40 Gb/s. A nonlinear optical loop mirror (NOLM) is used to carry out the demultiplexing at the station receiver. The channel to be switched out can be selected by adjusting the phase of the electrical signal used to generate the control pulses for the NOLM. By using external injection into a gain-switched distributed feedback (DFB) laser we are able to obtain very low jitter control pulses of 4-ps duration (RMS jitter <1 ps) after compression of the highly chirped gain switched pulses in a normal dispersive fiber. This enables us to achieve excellent eye openings for the three demultiplexed channels. The difficulty in obtaining complete switching of the signal pulses is presented. This is shown to be due to the deformation of the control pulse in the NOLM (caused by the soliton effect compression). The use of optical time-division multiplexing (OTDM) with all-optical switching devices is shown to be an excellent method to allow us to exploit as efficiently as possible the available fiber bandwidth, and to achieve very high bit-rate optical networks
Designing microstructured polymer optical fibers for cascaded quadratic soliton compression of femtosecond pulses
The dispersion of index-guiding microstructured polymer optical fibers is
calculated for second-harmonic generation. The quadratic nonlinearity is
assumed to come from poling of the polymer, which in this study is chosen to be
the cyclic olefin copolymer Topas. We found a very large phase mismatch between
the pump and the second-harmonic waves. Therefore the potential for cascaded
quadratic second-harmonic generation is investigated in particular for soliton
compression of fs pulses. We found that excitation of temporal solitons from
cascaded quadratic nonlinearities requires an effective quadratic nonlinearity
of 5 pm/V or more. This might be reduced if a polymer with a low Kerr nonlinear
refractive index is used. We also found that the group-velocity mismatch could
be minimized if the design parameters of the microstructured fiber are chosen
so the relative hole size is large and the hole pitch is on the order of the
pump wavelength. Almost all design-parameter combinations resulted in cascaded
effects in the stationary regime, where efficient and clean soliton compression
can be found. We therefore did not see any benefit from choosing a fiber design
where the group-velocity mismatch was minimized. Instead numerical simulations
showed excellent compression of nm 120 fs pulses with nJ pulse
energy to few-cycle duration using a standard endlessly single-mode design with
a relative hole size of 0.4.Comment: 11 pages, 8 figures, submitted to JOSA
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