Optical phase conjugation (OPC) is an all-optical signal processing technique for mitigating fiber nonlinearity and is promising for building cost-efficient fiber networks with few optic-electric-optic conversions and long amplification spacing. In lumped amplified systems, OPC has a little nonlinearity mitigation efficiency for nonlinear distortion induced by cross-phase modulation (XPM) due to the asymmetry of power and chromatic dispersion (CD) maps during propagation in transmission fiber. In addition, the walk-off of XPM-induced noise becomes small due to the CD compensation effect of OPC, so the deterministic nonlinear distortion increases. Therefore, lumped amplified transmission systems with OPC are more sensitive to channel spacing than conventional systems. In this paper, we show the channel spacing dependence of NZ-DSF transmission using amplification repeater with OPC. Numerical simulations show comprehensive characteristics between channel spacing and CD in a 100-Gbps/λ WDM signal. An experimental verification using periodically poled LiNbO3-based OPC is also performed. These results suggest that channel spacing design is more important in OPC-assisted systems than in conventional dispersion-unmanaged systems.

We developed a polarization-independent and reserved-band-less complementary spectral inverted optical phase conjugation (CSI-OPC) device using dual-band difference frequency generation based on highly efficient periodically poled LiNbO3 waveguide technologies. To examine the nonlinearity mitigation in a long-haul transmission using a large number of OPCs, we installed a CSI-OPC device in the middle of a pure silica core fiber-based recirculating loop transmission line with a length of 320km. First, we examined the fiber-input power tolerance after 5,120-km and 6,400-km transmission using 22.5-Gbaud PDM-16QAM 10-channel DWDM signals and found a Q-factor improvement of over 1.3dB along with enhanced power tolerance thanks to mitigating the fiber nonlinearity. We then demonstrated transmission distance extension using the CSI-OPC device. The use of multiple CSI-OPCs enables an obvious performance improvements attained by extending the transmission distance from 6,400km to 8,960km, which corresponds to applying the CSI-OPC device 28 times. Moreover, there was no Q-factor degradation for the link in a linear regime after applying the CSI-OPC device more than 16 times. These results demonstrate that the CSI-OPC device can improve the nonlinear tolerance of PDM-16QAM signals without an excess penalty.

A two-dimensional (2D) wireless power transmission (WPT) system that handles a wide range of transmitted and received power is proposed and evaluated. A transmitter outputs the power to an arbitrary position on a 2D waveguide sheet by using a beam-forming technique. The 2D waveguide sheet does not require an absorber on its edge. The minimum propagation power on the sheet is increased 18 times by using the beam-forming technique. Power amplifier (PA) efficiency was improved from 19% to 46% when the output power was 10dB smaller than peak power due to the use of a PA supply-voltage and input power control method. Peak PA efficiency was 60%. A receiver inputs a wide range of power levels and drives various load impedances with a parallel rectifier. This rectifier enables a number of rectifying units to be tuned dynamically. The rectifier efficiency was improved 1.5 times while input power range was expanded by 6dB and the load-impedance range was expanded fourfold. The rectifier efficiency was 66-73% over an input power range of 18-36dBm at load impedances of 100 and 400Ω.

The effect of wavefront compensation in beam transmission is estimated for ground to satellite laser communications. A numerical analysis is performed using the combination of the isoplanatic angle, the atmospheric coherence length and the point-ahead angle to find the aperture size of the beam transmission with which the wavefront compensation effect appears most strongly.

We demonstrate the wide-band (> 25-nm) long-distance (> 1000-km) chromatic dispersion compensation by midway spectral inversion (MSI) using a periodically-polled LiNbO3 device. In order to achieve a flat zero net dispersion, the fourth order dispersion of the single-mode fibers is canceled by MSI, while the third order dispersion is compensated for by the negative slope dispersion compensation fiber (NS-DCF). The second order dispersion is canceled out by both. The long distance propagation is realized by a double recirculation-loop system. A very flat zero dispersion is measured for the first time for over 1000-km single-mode fiber propagation with MSI dispersion compensation.

An 80 Gbit/s conventional and carrier-suppressed return-to-zero optical time-division multiplexing signal transmission over a 208 km standard single-mode fiber was experimentally demonstrated. This was achieved by using mid-span optical phase conjugation based on four-wave mixing in semiconductor optical amplifiers. In addition, it was confirmed that the transmitted carrier-suppressed return-to-zero optical signal's carrier phase-relation was held.

Fiber four-wave mixing (FWM) based parametric wavelength conversion experiment is demonstrated. Over 91nm multi-channel simultaneous conversion is achieved. The bandwidth is to our knowledge, the broadest value of the published results. We shall argue that the method to realize the broadband wavelength conversion. Efficiency and/or bandwidth of the wavelength conversion is degraded mainly by the following obstacles, (a) inhomogeneity of the chromatic dispersion distribution along the fiber, (b) mismatch of the states of polarization (SOP) between pump and signals and (c) bandwidth limitation from coherence length. We discuss that an extremely short high-nonlinear fiber should overcome the above three obstacles. Furthermore we comment on the higher-order dispersion and also the influence of the stimulated Brillouin scattering (SBS). High-nonlinearity dispersion-shifted fiber (HNL-DSF) is a promising solution to generate the FWM efficiently in spite of the short length usage. We develop and fabricate HNL-DSF by the vapor-phase axial deposition method. Nonlinear coefficient of the fiber is 13.8 W-1km-1. We measure the conversion efficiency spectra of the four HNL-DSFs with different lengths. Length of each fiber is 24.5 km, 1.2 km, 200 m and 100 m respectively. It is shown that conversion bandwidth increases monotonically as the fiber length decreases. The result apparently proves the advantage of the extremely short fiber.

Research in radar polarimetry is hampered by shortcomings of the conventional formulation of polarimetric backscatter concepts. In particular the correct form of the Sinclair backscatter matrix under changes of polarization bases is derived from the antenna voltage (energy transfer) equation yielding the erroneous impression that radar polarimetry is a mongrel between scattering behavior and network performance. The present contribution restores logical consistency in a natural way by introducing the concept of an antilinear backscatter operator. This approach decouples scattering process and network performance, illuminates matrix analytical properties of the radar backscatter matrix and highlights characteristic states of polarization.

Fourier holographic image storage and reconstruction using BaTiO3 photorefractive crystal waveguide is investigated. The phase conjugation technique, which compensates image distortion caused by modal phase dispersion, successfully retores images stored in a test BaTiO3 crystal waveguide.