Due to the limitation of the lens effect of the optical fibre and the inhomogeneity of the laser fluence on different cores, it is still challenging to controllably inscribe different fibre Bragg gratings (FBGs) in multicore fibres. In this article, we reported the FBG inscription in four core fibres (FCFs), whose cores are arranged in the corners of a square lattice. By investigating the influence of different inscription conditions during inscription, different results, such as simultaneous inscription of all cores, selectively inscription of individual or two cores, and even double scanning in perpendicular core couples by diagonal, are achieved. The phase mask scanning method, consisting of a 244nm Argon-ion frequencydoubled laser, air-bearing linear transfer stage and cylindrical lens and mirror setup, is used to precisely control the grating inscription in FCFs. The influence of three factors is systematically investigated to overcome the limitations, and they are the defocusing length between the cylindrical lens and the bare fibre, the rotation geometry of the fibre to the irritation beam, and the relative position of the fibre in the vertical direction of the laser beam.
Fiber optic sensors are fabricated for detecting static magnetic fields. The sensors consist of a UV inscribed long period grating with two 50 micron long microslots. The microslots are fabricated using the femtosecond laser based inscribe and etch technique. The microslots and the fiber surface are coated with a magnetostrictive material Terfenol-D. A spectral sensitivity of 1.15 pm/mT was measured in transmission with a working resolution of ±0.2 mT for a static magnetic field strength below 10 mT. These devices also present a different response when the spatial orientation of the fiber was adjusted relative to the magnetic field lines.
High resolution wavelength-tunable lasers are essential to sensing applications. For sensing applications,
high resolution is needed to improve the spatial resolution and/or measurement accuracy, and fast tuning
(sweeping) is required to enhance the measurement speed for dynamic sensing. However the demand of
high resolution conflicts with the requirement of fast continuous wavelength tuning. The solution to this
issue is tuning the wavelength of the output in a quasi-continuous way in which the length of each step is
dependent on the frequency of a RF generator which is used to drive a single-sideband (SSB) modulator in
the wavelength-swept optical system. In this paper, a principle of the step-tunable wavelength-swept
optical system is proposed and demonstrated. The two optical features of narrow bandwidth and fairly high
optical output power make the system unique for improving the accuracy of the measurement of the
center-wavelength of a fiber Bragg grating (FBG) sensor. In addition, changing the tuning-step by
adjusting the frequency of a RF generator electrically is user-friendly compared to the conventional
wavelength swept systems by tuning optical elements mechanically.
We demonstrate an ultra-long cavity all-fiber Erbium-doped fiber laser that is passively mode-locked by nonlinear
polarization rotation. The length of the resonant cavity amounts to 4.046 km, which is achieved by incorporating a 4 km
single mode fiber. The laser generates stable mode-locked pulses with a 50.90 kHz fundamental repetition rate. The
maximum average power of output pulses is 2.73 mW, which corresponds to per-pulse energy of 53.63 nJ.
In this paper, a novel soliton compressor based on dispersion decreasing fiber (DDF) assistant by Raman gain is studied.
The influence of Raman gain on compression quality is analyzed. The compressor is optimized by choosing proper gain.
An optimization of the linear decreasing DDF compression method is made through distributed optical fiber Raman
amplification with gain coefficient of 4.5dB/km. The pulse with width of 10ps is compressed down to 878.7fs, and the
compression factor is 11.38. Our research results show that distributed Raman amplification in DDF not only increases
the compression factor, but also improves the quality of compressed pulse.
In this paper, a novel WDM-to-OTDM conversion system which has a simple setup is proposed. The
system is a type of fiber loop consisting of an optical single-side-band (SSB) modulator that is driven by a
RF signal source at 10 GHz, a fiber circulator, a single mode fiber coupler, a fiber amplifier and an
ultra-narrowband high reflectivity fiber Bragg grating (FBG). The multi-wavelength WDM signals with
the spectral sampling interval of 10 GHz (0.08 nm at 1550 nm) is inputted into the system and can be
transformed to an OTDM signal carried by one wavelength. The advantages of this multi-wavelength
conversion system are that the requirement for the input optical power is low, the wavelength conversion is
fast due to the optic-electro effect in a nonlinear optical crystal and the system configuration is compact
without need of time delay lines.
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