A 40 Gbit/s hybrid optical code-division multiplexing (OCDM)/ wavelength-division multiplexing (WDM) system is experimentally demonstrated and simultaneous multiwavelength optical encoding of a single supercontinuum source using superstructured fiber Bragg grating is achieved. The interchannel interference and noise of the OCDM/WDM system is suppressed apparently by incorporating a nonlinear amplifying loop mirror, both the sidelobe and the pedestal are reduced, the waveform quality of decoded signal is improved, and the original 8.2 ps autocorrelation peak of decoded pulse is compressed to 4.8 ps.
Based on the chirp-pulse compensation technique, a 40-GHz supercontinuum (SC) source generated in a highly nonlinear fiber (HNLF) with large normal dispersion is investigated. We show numerically and experimentally that the widest SC spectrum can be obtained by setting a two-stage all-fiber pulse compressor consisted of the HNLF and standard single-mode fiber (SMF) in front of the last-section HNLF for SC generation. The third dispersion of the fibers, especially the SMF used as chirp-compensating fiber, is found to greatly degrade the SC spectrum generated in this scheme.
A seven-chip, 280-Gchip/s OCDM system incorporating quaternary phase coding and decoding is experimentally demonstrated. The encoder and decoder, consisting of superstructured fiber Bragg gratings, are fabricated using the equivalent-phase-shift method; only ordinary phase masks and submicrometer precision in control are required. Interchannel interference noise is also considered and evaluated; 40-Gbit/s×2-channel multiplexing is demonstrated. In addition, a nonlinear amplifying loop mirror (NALM) within the receiver is introduced to improve the system performance under two-channel operation. Switching is obtained for peak signal power less than 10 mW. We show that the NALM can act as a nonlinear processing element capable of reducing both the pedestal associated with conventional matched filtering and the width of the associated code recognition pulse.
Effective utilization of highly nonlinear fiber (HNLF) with relative large normal dispersion to further broaden optical spectrum of 40-GHz, 1.2-ps optical pulse train is investigated, in which an optimized scheme is presented. In the scheme, the pulse is launched into the HNLF of the first section to generate the spectrum broadened linearly up-chirped pulse, and recompressed after propagating through a suitable length of conventional single-mode fiber (SMF) of the second section for the pulse chirp being compensated. At last, the pulse travels through the second HNLF of the third section for further optical spectrum broadening. This new scheme applies the chirp pulse compensation technique and has scalability to the peak power of seed pulse. The experimental results show that ~1.7 nm increment of 3dB spectrum bandwidth is obtained when the new scheme is implemented given the same HNLF length and input seed pluses, and the coherence properties of the original pulses are maintained. This scheme provides a more effective means of pulse spectrum broadening in the HNLF when the peak power of seed pulse is confined by the EDFA output power and the high repetition rate of pulse laser.
FTTH/FTTC systems will be soon used in both a broadcast service and a wavelength-addressed point-to-point communication service. Optical wavelength routers will be the key devices in these systems. In this paper, we propose a new method for high-density optical routing using arrayed- waveguide gratings (AWGs), present the transmission properties of the wavelength router, and analyze the channel crosstalks and the insertion losses of the 16-channel wavelength router. The results show that the channel crosstalks are less than -18 dB, and the insertion losses are less than -6 dB. Its advantages include small volume with miniatured structure, low insertion loss, low coupling loss to fiber, and compatible with the microelectronics technology. It can be used to construct photonic integrated circuits with the waveguide laser diodes and photodetectors.
KEYWORDS: Near field, Particles, Optical tweezers, Near field optics, Near field scanning optical microscopy, Dielectrics, Cladding, Numerical analysis, Electromagnetism, Optical microscopy
A new scheme for optical trapping is presented in this paper. The method is based on a tapered filter probe with a tip diameter less than a light wavelength. A three-dimension gradient optical field is formed within the optical near field of the filter probe, and a particle approaching the fiber probe tip will be trapped. The evanescent eletromagnetic field in the vicinity of the fiber tip is calculated by the multiple multipole method (MMP). The intensity distributions and the trapping potentioal of the near fields of the tip versus the longitudinal and transverse distances from the tip are analyzed respectively. The trapping force is obtained for a dielectric particle. The numerical calculating results show the availability of this method.
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