Eccentric fiber Bragg gratings (EFGBs) in standard single-mode optical fiber by using point-by-point direct writing technique with 800 nm femtosecond laser. The experimental results show that the transmission spectrum amplitude is coupled by Bragg and cladding mode resonance over a wide spectrum range. Meanwhile, the spectral characteristics of EFBGs were studied by adjusting grating period, grating length, laser power and eccentric distance. The eccentric distance is the most essential parameter in terms of inscribing gratings. It can break up the original structural symmetry of the fiber by changing the offset of grating in the fiber core. This change will bring great opportunities and breakthroughs to the application of EFGBs.
The effects of pulse power, filling ratio, number of period and period on the long-period fiber gratings (LPFGs) by using radiation of femtosecond laser. The results show that the strong resonance peaks of LPFGs can be induced and the resonant peaks have different degrees of offset. When the parameters of the LPFG are set to be number of grating period of 70, filling ratio of 0.5, pulse power of 2.0 mW and period of 500 μm, the first resonance peak of LPFG has a blue-shift of 147.3 nm. Furthermore, the size of first resonance peak of LPFG is -19.4 dB. These characteristics of LPFGs provide a favorable opportunity for in-depth research of late-model sensing devices.
A scheme named “spoof” four wave mixing (SFWM) is proposed, where a dynamic refractive
index grating induced by the beating of the co-propagating pump and signal is able to modulate a Bragg
grating (BG) to create additional reflective peaks (ARPs) at either side of the unperturbed BG bandgap. When
a probe wave located at the wavelength of ARPs is counter-propagating, it is reflected from the induced
ARPS while tracking the signal data information but at the new wavelength. In contrast to the well-known
FWM, where the induced dynamic refractive index grating modulates photons to create a wave at a new
frequency, the SFWM is different in that the dynamic refractive index grating is generated in a nonlinear BG
to excite ARPS at either side of the original BG bandgap in reflection spectrum. This fundamental difference
enable the SFWM to avoid the intrinsic shortcoming of stringent phase matching required in the conventional
FWM, and allows novel all-optical wavelength conversion with modulation format transparency and
ultrabroad conversion range, which represents a major advantage for next generation of all-optical networks.
A hexangular lattice dual-concentric-core photonic crystal fiber is proposed, which is composed of an inner core to be
formed by missing a central air-hole, an outer ring core to be produced by reducing the size of the air-holes of the third
ring and the double cladding circle air-holes along the direction of fiber length. Based on the full vector finite element
method with anisotropic perfectly matched layers, its dispersion, leakage loss and mode field area are numerically
investigated. Numerical results indicate that the proposed fiber shows large negative dispersion, strong confinement
ability of guide mode, large effective mode area and low leakage loss and low sensitivity to the structure parameters.
And the wavelength of high negative dispersion value can be adjusted by artificially choosing the parameters of the
proposed PCF, such as Λ, d1 and f. The optimal design parameters with Λ=1.2μm, f=0.92, d1=0.52μm for proposed PCF
are obtained to achieve ultra-narrowband negative dispersion value for dispersion compensation. For the optimal design,
the dispersion value reaches as high as -3400 ps·km-1 nm-1 and the dispersion slope value is between -1000~ -6000
ps·km-1 nm-2 over C band (1.53-1.565μm). At wavelength of 1.55μm, the leakage loss is closed to 10-2 dB·m-1 and the
corresponding area of effective mode is 36μm2.
Light-emitting diode (LED) based endoscopic illumination devices have been shown to have several benefits over arclamp
systems. LEDs are energy-efficient, small, durable, and inexpensive, however their use in endoscopy has been
limited by the difficulty in efficiently coupling enough light into the endoscopic light cable. We have demonstrated a
highly homogenised lightpipe LED light source that combines the light from four Luminus LEDs emitting in the red,
green, blue and violet using innovative dichroics that maximise light throughput. The light source spectrally combines
light from highly divergent incoherent sources that have a Lambertian intensity profile to provide illumination matched
to the acceptance numerical aperture of a liquid light guide or fibre bundle. The LED light source was coupled to a
standard laparoscope and performance parameters (power, luminance, colour temperature) compared to a xenon lamp.
Although the total illuminance from the endoscope was lower, adjustment of the LEDs' relative intensities enabled
contrast enhancement in biological tissue imaging. The LED light engine was also evaluated in a minimally invasive
surgery (MIS) box trainer and in vivo during a porcine MIS procedure where it was used to generate 'narrowband'
images. Future work using the violet LED could enable photodynamic diagnosis of bladder cancer.
A mode hop free tunable blue laser at 465 nm based on an external cavity system is investigated. The single longitudinal
mode second-harmonic generation (SHG) blue laser was generated using quasi-phase matching (QPM) based MgO:
PPLN pumped by infrared diode laser at 930 nm with one lasing longitudinal mode. The wide turning rang in excess of
100 GHz is achieved by using combination the etalon, silica glass plate and narrow band filter into the external cavity,
which only allow one longitudinal mode running and operating wavelength tuning. 30 mw blue light was obtained at
wavelength of 465 nm with beam quality better then M2 =1.3.
Intra-cavity frequency doubling (ICFD) of an extended cavity 49-emitters edge-emitting laser bar has been demonstrated
in a quasi-phase matching MgO-doped periodically poled lithium niobate (MgO: PPLN) bulk crystal. A maximum of 1
W of second-harmonic light at 465 nm is generated at an operating injection current of 45 A with the optimal phase-matching
MgO:PPLN temperature of 50.4 °C. To increase the efficiency further, careful design of the lens used on the
fast and slow axis beam waists and use of lower-temperature MgO:PPLN planar-waveguide array can be considered.
Using the amplification transfer function of type1BaAlBO3F2 (BABF) crystal, the parametric fluorescence properties of
new BABF crystal have been investigated in the different quasi-phase matched modes. The parametric fluorescence
signal lifetime study is presented based on amplification gain obtained in the quasi-phase matched modes. This analysis
of parametric fluorescence signal lifetime is shown to be equal to the results obtained from the amplification transfer
Intra-cavity frequency doubling (ICFD) of electrically and optically surface emitting diode lasers in the near IR region
become more interesting [1-3] and will have an enormous impact in the display market. In this paper, Watts-level green
laser is generated by ICFD of multi-emitters laser bar using a MgO-doped periodically poled lithium niobate (MgO:
PPLN) bulk crystal, which has the potential to be scalable to high production volumes and low costs with immense
implication for laser-based projection displays.
Very fast current transients (10 A, 5 GHz) have been measured using the Faraday rotation in CdMnTe sample. RF magnetic fields with an amplitude of < 10 G have been measured, despite the laser intensity noise (at these bandwidths) and the noisy environments. This paper describes a technique whereby the insertion loss is minimized and the effect of the laser intensity noise reduced, enabling these small RF fields to be measured for the first time.