Current status and trends in various sectors of photonics industry in Mainland China are reviewed, which includes
optical fiber communication, optical preform, fiber and cable, photonic devices and chips, LED illumination and display,
and photovoltaics. Then, from the challenges and risks they are facing, critical importance of innovation is discussed. In
the evolving Innovation Economy, the core competence of a company, an industry or a country is its innovation power
and the capability to grab (and manage) talented people.
A transfer matrix of an arbitrary period in a long-period fiber grating (LPFG) is derived. Cascade of such matrices can be used easily to calculate the overall performance of LPFG with fast variation in parameters (which is common practice in LPFGs) such as period length, strength, etc. more precisely. Results show that the difference in transmittivity between our work and traditional coupled-mode theory becomes obvious when abrupt change such as (pi) phase-shift occurs. This method can be used in the mask design aiming at overall performance optimization through period-by-period pattern adjustment. Finally, a genetic algorithm is used to optimize the LPFG period by period.
Analytical expressions of transient phenomena in discrete fiber Raman amplifiers (FRAs) are presented in this paper. It is found that the recovery time in gain-saturated backward-pumped FRAs equals to the round-trip time of optical wave in the FRA, and is typically in the order of 10-1 ms. The power excursion amplitude and recovery time will increase dramatically in cascaded FRAs, leading to severe system performance degradation. Characteristics of transience in cascaded and gain-clamped FRAs and some design guidelines are also discussed based on these analytical expressions.
Based on the weak intensity/phase modulation transfer matrix H, a matrix V for intensity noise (IN) and phase noise (PN) evolution along nonlinear, dispersive and lossy fiber is derived, while matrix description makes it especially useful in noise evolution analysis in systems with chained optical amplifiers. Evolution of two noise sources, laser phase noise and ASE of EDFA, is examined in detail through V. IN, PN and optical field noise spectral densities are studied uniformly. Correspondingly, electrical signal-to-noise ratio (SNRe), equivalent linewidth ((Delta) (upsilon) eq and optical signal-to-noise ratio (SNRo) are used to characterize system performance. It is found that for IM systems, an optimal P0 corresponding to minimum SNRe exists in positive dispersion fibers, and input optical power cannot be arbitrarily increased to improve SNRe even though only noise is considered. On the contrary, in negative dispersion fibers, SNRe is improved with increasing P0 monotonously. For PM systems with negligible laser phase noise and regardless of the sign of fiber dispersion, an optimal optical power also exists to ensure minimum phase noise. SNRo, a combined contribution from intensity and phase noise, is better in fibers with negative dispersion than that in fibers with positive dispersion under the same P0.
Analytical expressions of equivalent noise figure and other noise characteristics of distributed fiber Raman amplifier (DFRA) are derived, for the first time to the knowledge of the authors, including difference in polarization state and attenuation coefficients between pump and signal light(s) as well as multiple-wavelength pumping. Accordingly, their impact on DFRA performance and optical signal-to-noise ratio improvement ((Delta) OSNR) of a cascaded DFRA+EDFA is investigated. With increasing DFRA on-off gain, (Delta) OSNR increases first linearly and then logarithmically, leading to saturation. Results of this work agree well with existing work. Based on these results, some guidelines on DFRA design is proposed.
A semi-analytical expression of double backward Rayleigh scattering (DRB) noise in a backward-pumped distributed fiber Raman amplifier (B-DFRA) is derived. A receiver is assumed to follow the B-DFRA, and various electrical noise terms in the receiver are compared with the DRB noise term which is shown dominating under elevated Raman on-off gain. An equivalent receiver sensitivity is introduced as a comprehensive measure of B-DFRA performance.
Dispersion Compensation has to be performed when 32x10Gbs long haul signals transmission in G.652 fiber. Optimum system transmission performance depends on the amount and distribution of dispersion compensation, laser performance and the nonlinear effects of fiber transmission, etc. System performance calculation under dispersion compensation is given, and system performance influenced by various factors under complete and residual compensation conditions is analyzed in this paper, with 6x22dB as an example.
A rigorous analytical transmission matrix H for optical wave with weak modulation, including intensity modulation (IM) and phase modulation (PM), is derived considering the fiber nonlinearity, dispersion and loss based on the physical process. Four elements of matrix H correspond to conversions of IM->IM, PM->IM, IM->PM and PM->PM, respectively and the nonlinear components are extensively investigated. Physical insight of transmission effects is obtained explicitly. Matrix description makes it especially useful in the design and analysis of chained optical amplifier systems.
The proper combination of source linewidth enhancement factor (alpha) through electro-absorption modulator (EAM) and fiber dispersion coefficient D in wavelength division multiplexed (WDM) optical transmission systems can greatly extend the dispersion-limited system regeneration length Lreg (up to 70% for a 16 X 10 Gb/s X 400 km system). Four-wave-mixing-induced power penalty will only slightly increase due to the none-zero fiber dispersion, although more Erbium-doped fiber amplifiers are needed to compensate for the fiber attenuation. This scheme can also effectively suppress the modulation instability and self-phase modulation, etc. In general, when dispersion management or dispersion compensation measures are adopted for WDM systems using EAM with positive (alpha) , slightly over-compensation the fiber dispersion for all channels can effectively extend Lreg or reduce the dispersion-induced eye opening penalty if fiber nonlinearities remain tolerable.
The high density wavelength division multiplexing (HD-WDM) system presented here has 8 channels in 1.55 micrometers optical band with wavelength spacing of 100 GHz. Each channel operates at 622 Mb/s by using directly modulated DFB-LD. Accurate temperature control and current control methods have been taken to ensure the wavelength stability of 200 MHz in standard deviation. Three high-quality EDFA's are used in the 420 km optical fiber transmission to compensate the loss of fiber, star couplers and F-P optical filter. An F-P filter with 0.3 nm bandwidth and 1.2 dB insertion loss is used as a demultiplexer in front of the receiver to select every channel and reduce amplified spontaneous emission noise. An optical receiver with PIN-FET front-end has been used, which has sensitivity of -31 dBm BER equals 10-10. Good SNR characteristic is obtained for all channels after the transmission. In this paper we describe an 8 X 622 Mb/s HD-WDM experiment system and its 420 km optical fiber transmission. Some critical problems in long distance HD-WDM transmission also have been studied in this paper.
A performance analysis method of WDM optical fiber transmission system is proposed in this paper based on a semi-analytic approach. Here signal distortion caused by combined effects of fiber chromatic dispersion, SPM and XPM is obtained from computer simulation, while ASE noise and crosstalk due to fiber FWM are treated as additive Gaussian noise in the optical domain. An analytic formula for FWM noise power in a dispersion-managed system is also proposed. As an example, non-zero positive dispersion fiber and large negative dispersion fiber is used as transmission and dispersion compensating fiber respectively in a wide-real WDM network. Our results of performance analysis show that appropriate design of dispersion management scheme for the WDM network may achieve 4 X 10 Gb/s transmission over 2000 km with 6 dB power margin.
A new dispersion compensation method for high-speed wavelength-division-multiplexing terrestrial systems with cascaded EDFAs was proposed. Specially designed dispersion-shifted fiber (SDDSF), generating -2 approximately -4 ps/km/nm dispersion around 1.55 micrometers is used to avoid severe four-wave mixing, while CCITT G.652 non-dispersion shifted fiber is used to compensate for the negative dispersion of SDDSF over the entire EDFA bandwidth. The eye opening penalty of dispersion in systems of bitrate as high as 10 Gb/s per channel after 1000 km fiber transmission could still be less than 1 dB. It is a cheaper, more simple and reliable scheme.
Using a comprehensive model proposed by the author, it is found that the amplified spontaneous emission (ASE) propagating opposite to the pump beam causes depression to pump and signal evolution near to the pump input end of a high-gain erbium-doped fiber amplifier (EDFA). In a m-stage cascaded EDFA chain, the S/N ratio is inversely proportional to m, and the gain may decrease with increasing m if the signal wavelength markedly deviates from the ASE peak wavelength.
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