Fiber Bragg grating sensing system with wavelength-swept-laser distribution and self-synchronization.

Fiber Bragg gratings (FBGs) with various interrogation schemes to estimate the FBG's spectrum shift have been widely used in fiber sensing systems. Wavelength swept laser (WSL) based interrogation architectures have been proposed to offer rapid and high-quality sensing performance. However, for getting higher sensing accuracy, the demands for high-performance WSL may push the system cost. Under these considerations, a WSL distribution architecture allowing multiple sensing processing units (SPUs) to share the WSL is studied in this Letter. A self-synchronization scheme is proposed to enable flexible SPU deployment with no concerns for the clock calibration. The proposed system is experimentally studied. Temperature estimation error of ∼2.5∘C and ∼0.5∘C with sensitivities of 0.13°C/ms and 0.14°C/ms, respectively, for the high and small temperature ranges are demonstrated.

Multi-point temperature sensing using a linear-cavity lasing system.

A multi-point fiber sensing system formed from a linear cavity laser is proposed. Various optical sensing systems have been investigated, for example, using fiber Bragg grating (FBG) and Brillouin scattering for multi-point sensing. This paper focuses on a simple sensing system by using multi-wavelength lasing with parallel cavities and a semiconductor optical amplifier (SOA). First, optical nonlinearity in amplification of the SOA is discussed to clarify the effects of gain saturation and four-wave mixing on the proposed multi-channel sensing system. And then lasing conditions in the linear cavity laser consisting of an SOA, an arrayed waveguide grating (AWG), and FBGs are theoretically investigated. The multi-wavelength lasing power is found to be limited mainly by gain saturation in the SOA. The lasing power for the eight-channel system is evaluated to be -8.5 dBm when the total loss in the linear cavity is 10 dB. The lasing power can be increased by 3 dB when the channel number is decreased to four. Next, multi-wavelength lasing in the cavity consisting of an SOA, an AWG, a loop mirror, and fiber mirror reflectors is experimentally demonstrated up to eight channels. Finally, two-channel temperature sensing ranging from 13°C to 76°C is experimentally confirmed by using two FBGs as the sensing elements with an AWG having 100-GHz bandwidth.

Noise tolerance in wavelength-selective switching of optical differential quadrature-phase-shift-keying pulse train by collinear acousto-optic devices.

Optical switching of high-bit-rate quadrature-phase-shift-keying (QPSK) pulse trains using collinear acousto-optic (AO) devices is theoretically discussed. Since the collinear AO devices have wavelength selectivity, the switched optical pulse trains suffer from distortion when the bandwidth of the pulse train is comparable to the pass bandwidth of the AO device. As the AO device, a sidelobe-suppressed device with a tapered surface-acoustic-wave (SAW) waveguide and a Butterworth-type filter device with a lossy SAW directional coupler are considered. Phase distortion of optical pulse trains at 40 to 100 Gsymbols/s in QPSK format is numerically analyzed. Bit-error-rate performance with additive Gaussian noise is also evaluated by the Monte Carlo method.

All-optical switch consisting of two-stage interferometers controlled by using saturable absorption of monolayer graphene.

At routing nodes in future photonic networks, pico-second switching will be a key function. We propose an all-optical switch consisting of two-stage Mach-Zehnder interferometers, whose arms contain graphene saturable absorption films. Optical amplitudes along the interferometers are controlled to perform switching between two output ports instead of phase control used in conventional switches. Since only absorption is used for realizing complete switching, insertion loss of 10.2 dB is accompanied in switching. Picosecond response can be expected because of the fast response of saturable absorption of graphene. The switching characteristics are theoretically analyzed and numerically simulated by the finite-difference beam propagation method (FD-BPM).

Comparison of rat mandible bone characteristics in F344 substrains, F344/Du and F344/N.

The characteristics of the mandible bone were compared through DXA methods between two major substrains of F344 rats, F344/DuCrlCrlj and F344/NSlc at around 60 days of age. Since these two substrains are clearly different in survival and mandible morphology, some genetic differences are supposed to exist. In contrast to a previous microsatellite analysis, clear and significant differences were detected in the body and mandible weights, the mandible bone mineral contents (BMC), bone area (AREA), bone mineral density (BMD) and bone mineral ratio (BMR), between F344/DuCrlCrlj and F344/NSlc, with the mandible molar teeth intact in the bone. Thus, care is needed in the experimental use of these substrains, as results may differ between them. The newly proposed parameter, BMR, may especially contribute to the comparison of bone characteristics among species.

Morphometric comparison of the rat mandible in F344 substrains, F344/Du and F344/N.

The shape of the mandible was compared by morphometric methods to ascertain the genetic differences between two substrains of F344 rats, F344/DuCrlCrlj and F344/NSlc. Since these two substrains are clearly different in survival and the incidence of age associated disorders; thus, some genetic differences are suggested to be present between them. Although previous microsatellite analysis did not detect any differences between the two F344 substrains, the present study clearly detected interesting differences in the mandible morphology. At 2 months of age, the F344/Du mandible was characterized by a larger size, especially in length, than the F344/N mandible. The shape of the mandible seemed to be more variable in F344/N. This clear substrain difference suggests the importance of the substrain recognition in F344 rats, especially in experimental usage.