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The effect of higher-order amplified spontaneous scattering in Raman amplification is investigated. With the effect, a structure of third-order distributed fiber Raman amplifier (DFRA) is introduced and its band-width is studied and optimized. A method of multiorder pumps with multi-wavelengths is adopted, which is different from that of multi-wavelength pumps for the conventional DFRA. Simulation results indicate that pumps in different orders have different functions: the first-order pump can improve the gain flatness and extend the bandwidth, the second-order pump can increase the gain value, whereas the third-order pump can provide powers for pumps in other orders and improve the noise figure (NF) together with them; a flat spectrum with the bandwidth of 80 nm, gain of 24 dB, ripple of less than 1 dB, and a low NF over a span of 120 km is achieved. All these results are beneficial to design a broadband higher-order Raman pumping DFRA in future experimental work. A modified genetic algorithm is also proposed in optimizing the bandwidth. [ABSTRACT FROM AUTHOR]

Raman effect brings the inevitable limitation of gain flatness in the fiber-optical parametric amplifier even if the phase-matched condition is well satisfied. Phase-matched gain is modulated by the real part of Raman susceptibility especially when it is on the anti-Stokes side. The real part mainly determines the gain profile and limits the flat-gain bandwidth to be less than 180 nm. An asymmetric modulated gain spectrum appears due to the assistance of the imaginary part on the Stokes side. Simulation results also show that the single- and dualpump configurations have different gain amplitude modulation factors induced by Raman. [ABSTRACT FROM AUTHOR]

A chemical sensor based on a Bragg grating in the multimode fiber has been demonstrated experimentally. Experimental results indicate that the reflection peak of high-order mode P2 exhibits a much higher concentration sensitivity of the chemical solution than the reflection peak P1 of the high-order mode. The sensor has been used to measure the concentrations of propylene glycol solutions and sugar solutions, which could detect 0.05% and 0.04% concentration change for them with the wavelength interrogation module of 1-pm resolution. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 1739–1741, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21761 [ABSTRACT FROM AUTHOR]

A new nonlinear evolution equation including the vector nature of the electromagnetic field and the frequency variation of the mode profile is derived. A kind of new nonlinearity is demonstrated. Its magnitude is strongly dependent on the waveguide geometrical parameters, which will lead to a suppression of the Raman soliton self-frequency shift in a photonic crystal fiber with a tellurite subwavelength core. Our results can be supported by the detailed numerical simulations. [ABSTRACT FROM AUTHOR]

Unique dispersion characteristics and enhanced nonlinearity make the small-core photonic crystal fiber (PCF) an ideal candidate for nonlinear optical devices to telecommunication applications. Some technical reasons behind great research interest of highly nonlinear PCFs in optical communication components are reviewed. Nonlinear effects in highly nonlinear PCFs and their research progress are presented. Several typical applications including WDM sources, optical amplification, optical switching, wavelength conversion, optical regeneration and all-optical demultiplexing etc are introduced, together with state-of-the art performances. Some new possible applications and future prospects are discussed. [ABSTRACT FROM AUTHOR]

We demonstrate an all-optical quantization scheme by slicing the supercontinuum (SC) generated in the normal dispersion region of a highly nonlinear fiber. The -20 dB bandwidth of the SC is broadened from 12.9 to 49.7 nm when input average power varies from 0.062 to 0.692 mW, which is used for realizing subsequent quantization. In addition, in order to evaluate the system performance, we have calculated the values of differential nonlinear error, integral nonlinear error, and effective number of bit from the experimental results as 0.471 least significant bit (LSB), 0.519 LSB, and 4.39 bit, respectively. [ABSTRACT FROM AUTHOR]

A scheme for real-time optical demultiplexing is proposed by utilizing the time-broadened and linearly chirped pulses instead of the conventional mode-locked pulses. The copies of the optical -time-division-multiplexed signal are acquired through a dual-pump parametric gate and used as the parametric multicast block. Simulation results show that the demultiplexing from 160 Gb/s down to sixteen 10 Gb/s tributaries can be achieved only by using a sampling source of 10 GHz. The proposed scheme can effectively reduce the complexity of parallel processing, and find important applications in the high-speed all-optical signal processing. [ABSTRACT FROM AUTHOR]

The all-optical differential equation solver has great potential in high-speed and wide-band signal processing, such as special waveform generation and description of the complex dynamics. We propose an all-optical differential equation solver in a silicon microring resonator with tunable constant coefficient k. Using inverse Raman scattering effect, k can be tunable by changing the power of the incident pump light. The influences of the pump power and signal pulse width on the tunable range of k are investigated. It is demonstrated that k is continuously tunable in the range of 0.035∕ps to 0.130∕ps with the error of <5%. [ABSTRACT FROM AUTHOR]

We propose an all-optical spectral quantization scheme based on soliton self-frequency shift (SSFS) and spectral compression (SC) in cascaded chalcogenide-silicon slot waveguides. The optical spectrum can be compressed to 13 nm after the process of SSFS. Simulation results show that the effective-number-of-bit of 4.966-bit can be improved by 2.076-bit compared with the scheme without SC. [ABSTRACT FROM AUTHOR]

The ultraviolet to visible continuum generations are experimentally demonstrated by coupling femtosecond pump pulses around 800 nm into the normal dispersion region close to the zero-dispersion wavelength in the fundamental mode of a silica photonic crystal fiber (PCF). The ultraviolet to visible continuum is generated through a combination of nonlinear effects including degenerate four-wave mixing, cross-phase modulation, and stimulated Raman scattering. When pump pulses with the wavelength of 800 nm and the input average power of 500 mW are used, more than 40% of the incident pump power is converted to the ultraviolet to visible spectral region. The evolution of the output spectra for different PCF lengths is studied to understand the nonlinear propagation dynamics during the process of the continuum generation. The ultraviolet to visible continuum generation will find important applications in the ultraviolet and visible-based biophotonics and spectroscopy. [ABSTRACT FROM AUTHOR]

A high sensitivity refractive index sensor based on a single mode-small diameter no core fiber structure is proposed. In this structure, a small diameter no core fiber (SDNCF) used as a sensor probe, was fusion spliced to the end face of a traditional single mode fiber (SMF) and the end face of the SDNCF was coated with a thin film of gold to provide reflective light. The influence of SDNCF diameter and length on the refractive index sensitivity of the sensor has been investigated by both simulations and experiments, where results show that the diameter of SDNCF has significant influence. However, SDNCF length has limited influence on the sensitivity. Experimental results show that a sensitivity of 327 nm/RIU (refractive index unit) has been achieved for refractive indices ranging from 1.33 to 1.38, which agrees well with the simulated results with a sensitivity of 349.5 nm/RIU at refractive indices ranging from 1.33 to 1.38. [ABSTRACT FROM AUTHOR]

We experimentally demonstrated the generation of dispersive waves (DWs) at the visible wavelength by coupling femtosecond pulses into the anomalous dispersion region of the second-order mode of a homemade photonic crystal fiber. When center wavelengths of the pump pulses are located at 800 and 850 nm and input average powers Pav are increased from 300, to 400, and to 500 mW, the blue-shifted DWs can be generated during the soliton dynamics and are tunable within the wavelength range of 614 to 561 nm. Moreover, the conversion efficiency ηDW of DWs is enhanced from 5% to 21%, and the corresponding bandwidth BDW is broadened from 17 to 30 nm. It is believed that the DWs can be used as the ultrashort pulse source for visible photonics and spectroscopy. [ABSTRACT FROM AUTHOR]

An alternative light source for coherent anti-Stokes Raman scattering (CARS) microspectroscopy based on red-shifted solitons in a polarization-maintaining photonic crystal fiber (PM-PCF) is experimentally demonstrated. By coupling femtosecond pulses into the anomalous dispersion region of the fundamental mode of a PM-PCF along the slow and fast axes, the red-shifted solitons generated can be used as the Stokes beams when the pump pulses are chosen as the pump beams. Through the process of red-shift, the frequency differences of the pump-Stokes beams are tunable in the ranges of 0 to 4068 cm-1 and 0 to 4594 cm-1, respectively. Moreover, because of the well maintained polarization states of the pump and Stokes beams and the high output powers of the solitons, CARS microspectroscopy using the proposed source will have a high signal-to-noise ratio and short data acquisition time. CARS microspectroscopy based on the proposed all-fiber light source can be used for studying a wide range of vibrational Raman spectra. [ABSTRACT FROM AUTHOR]

We optimize a proposed multicast parametric synchronous sampling scheme. Two segments of 1 cm high nonlinear spiral photonic crystal fiber are utilized as a nonlinear medium in parametric processors. Meanwhile, a segment of 1.8 km dispersion compensation fiber is used to obtain linear chirped sampling pulses instead of a 5 km single-mode fiber. The experimental results show that a 120 GSa/s equivalent sampling rate, high power of sampling copies, and low variance are obtained. [ABSTRACT FROM AUTHOR]

All-optical analog-to-digital converters based on the third-order nonlinear effects in silicon waveguide are a promising candidate to overcome the limitation of electronic devices and are suitable for photonic integration. In this paper, a 2-bit optical spectral quantization scheme for on-chip all-optical analog-to-digital conversion is proposed. The proposed scheme is realized by filtering the broadened and split spectrum induced by the self-phase modulation effect in a silicon horizontal slot waveguide filled with silicon-nanocrystal. Nonlinear coefficient as high as 8708 W-1/m is obtained because of the tight mode confinement of the horizontal slot waveguide and the high nonlinear refractive index of the silicon-nanocrystal, which provides the enhanced nonlinear interaction and accordingly low power threshold. The results show that a required input peak power level less than 0.4 W can be achieved, along with the 1.98-bit effective-number-of-bit and Gray code output. The proposed scheme can find important applications in on-chip all-optical digital signal processing systems. [ABSTRACT FROM AUTHOR]

Gain and Noise figure (NF) characteristics in dual-pump parametric amplifier based on silicon on insulator (SOI) Rib waveguides are numerically investigated in the presence of nonlinear losses. The impact of structure parameters of the silicon optical parametric amplifiers (SOPAs) on the gain and the NF are also analyzed. The results show that both the height and the width of the silicon on insulator (SOI) can affect the gain and the NF of SOPAs. 354nm bandwidth (3dB) and 8.135 maximum gain can be achieved by tailoring the structure parameters of the SOI rib waveguides. Moreover, the dispersion and the effective mode area of SOI are also analyzed. [ABSTRACT FROM AUTHOR]

We propose a scheme for the real-time optical sampling of a multicast signal based on the parametric process. The linearly chirped and time-broadened pulses are used instead of the traditional mode-locked sampling pulses. The amount of signal copies or the rate of sampling train can be efficiently reduced by the chirped pulses while keeping a high-equivalent sampling rate. Simulation results show that the equivalent sampling rate of 120 GSa/s can be obtained by using only a sampling source of 10 GHz together with three signal copies. This scheme can efficiently improve the sampling rate in the real-time optical sampling and reduce the requirement on electronic devices for signal processing. [ABSTRACT FROM AUTHOR]

The properties of an all-optical parametric amplifier (OPA) based on four-wave-mixing (FWM) in a silicon microring resonator (MR) side-coupled to a bus waveguide are investigated. The influences of microring structural parameters on amplification performance are analyzed in the presence of two-photon absorption (TPA) and free carrier absorption (FCA) caused by TPA. The simulation results show that, due to the field enhancement, an OPA inside an MR can achieve similar net gain with a much smaller waveguide and lower pump power compared with that based on a straight waveguide. [ABSTRACT FROM AUTHOR]

We have investigated the generation and transmission of optical millimeter (mm)-wave signal based on optical phase modulator (PM) and fiber Bragg grating (FBG) filter. With an optimized modulation depth of PM and a higher carrier suppression ratio via a notch filter, the generated optical mm-wave can be transmitted over a long-distance without fading. We have also theoretically analyzed the impact of time shift on the eye closure of optical and electrical signal due to the fiber dispersion, which is well in accord with the experimental results. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1787–1793, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22622 [ABSTRACT FROM AUTHOR]

Broadband supercontinuums (SC) are generated by soliton self-frequency shift (SSFS) of hollow-core photonic crystal fiber (HC-PCF) in our laboratory. With the pump works at 810nm when the pump power increase from 400 to 600mW, the Raman Soliton shifts from 2089 to 2215nm, the bandwidth of SC increases from 2213 to 2320nm. The ultra-violet part of SC is below 180nm, and the mid-infrared part of SC exceeds 2500nm. Moreover, the influence of pump power on SC is also analyzed. [ABSTRACT FROM AUTHOR]

A novel plasmonic polarization filter based on the diamond-shape photonic crystal fiber (PCF) is proposed. The resonant coupling characteristics of the PCF polarization filter are investigated by the full-vector finite-element method. By optimizing the geometric parameters of the PCF, when the fiber length is 5 mm, the polarization filter has a bandwidth of 990 nm and an extinction ratio (ER) of lower than –20 dB. Moreover, a single wavelength polarization filter can also be achieved, along with an ER of –279.78 dB at wavelength 1.55 μm. It is believed that the proposed PCF polarization filter will be very useful in laser and optical communication systems. [ABSTRACT FROM AUTHOR]

Anti-Stokes signals at the near-ultraviolet wavelength are efficiently generated based on degenerate four-wave mixing by coupling the femtosecond pulses into the fundamental mode of a photonic crystal fibre. When the pump pulses with the central wavelength of 840 nm and the average power of 300 mW are used, the conversion efficiency ηs of the anti-Stokes signal at 432 nm can be up to 40%, and the pulse width is measured to be 42 fs by the Talbot effect. [ABSTRACT FROM AUTHOR]

In this paper, we propose an integratable spectral quantization scheme for all-optical analog-to-digital conversion (AOADC) by slicing the supercontinuum, which is generated in a chalcogenide (As2S3) horizontal slot waveguide. The numerical simulation results show that a 4-bit quantization resolution is successfully achieved along with a signal-to-noise ratio of 23.96 dB and an effective number of bit (ENOB) of 3.98 bit. The required As2S3 waveguide length and input peak power are only 1.5 cm and 900 mW, respectively, owing to the high nonlinear coefficient of 115.8 W−1/m. It is believed that this proposed scheme can find important applications in the photonic integratable AOADC with low power consumption. [ABSTRACT FROM AUTHOR]