Analysis of polarization dependence for OTDM demultiplexers based on four-wavelength mixing in semiconductor optical amplifier

In optical time-division multiplexing (OTDM) systems using the four-wave mixing (FWM) in a semiconductor optical amplifier (SOA) for time demultiplexing, the polarization states of control pulse and OTDM data lights are an important factor in the optical time demultiplexing process, which can influence the bit error rate (BER) of OTDM systems. In this paper, we analyze the effect of light polarization states on the FWM of a SOA, and use a simulation approach to study the BER performance of 100 Gbit/s OTDM systems that use the FWM in a SOA for optical time demultiplexing. It reveals that the BER or Q factor of OTDM systems is dependent on the misalignment θ between the polarization states of OTDM data and control lights. With increasing θ, both the optical power of resulting FWM component and the BER performance (or Q factor) of OTDM systems is degraded. For linearly polarized lights, our results show that the increase of BER and the reduction in Q factor are made smoothly when θ changes its value from 0° to 75°, whereas the degradation of BER and Q factor becomes rapid when θ exceeds 75°. Although the best system BER is obtained for θ = 0°, the BER performance can still tolerate some misalignment θ (e.g., up to 20° in our simulation). This is useful for the engineering design and applications of SOA-based optical time demultiplexers.     

FDTD simulation of wavelength conversion of ultrashort pulses utilizing intersubband absorption in AlGaN/GaN quantum wells

The four-wave mixing (FWM) characteristics of 500-fs pulses in nonlinear optical waveguides utilizing the saturation of the intersubband absorption at 1.55 μm in nitride multiple quantum wells are calculated by a one-dimensional finite-difference time-domain (FDTD) method combined with three-level rate equations describing the intersubband carrier dynamics. Efficiency for a 100-nm wavelength conversion in a 160-μm waveguide is predicted to be higher than 3% both for up- and down-conversions. The extinction ratio is higher than 20 dB. As for the short-pulse application, however, the conversion efficiency is strongly dependent on the phase difference between the pump and signal pulses, especially when the efficiency is high. This causes ambiguity in the output power. Therefore, the cross-loss-modulation (XLM) converter is preferable to the FWM converter for OTDM application. The FWM converters are considered to be applicable to simultaneous conversion of WDM signals.     

分布反馈激光器中剩余法布里-珀罗腔模对非简并四波混频特性的影响

基于四波混频(FWM)的全光波长转换技术是未来多波长通信系统的核心技术之一。除半导体光放大器(SOA)外,半导体激光器也是进行波长变换的器件。实验研究了小频率失谐到大频率失谐下分布反馈(DFB)激光器中剩余法布里珀罗腔模对非简并四波混频(NDFWM)的影响,并对其四波混频转换效率进行了分析。结果表明:当探测光波长与法布里珀罗腔的某一谐振波长一致时,分布反馈激光器中的四波混频转换效率将得到显著的增强;当频率失谐为太赫兹时,仍可得到较高的四波混频转换效率。     

Control of four-wave mixing phase-matching condition using the Brillouin slow-light effect in fibers

All-optical control of the phase-matching condition in four-wave mixing (FWM) processes is demonstrated using the Brillouin slow-light effect in optical fibers. A counterpropagating stimulated Brillouin scattering (SBS) pump has been used to control the phase velocity of the FWM pump in a wavelength conversion scheme. Both experimental results and theoretical simulations show an SBS-controlled 20 dB difference on the wavelength conversion efficiency.     

Investigation of in-plane orientation characteristics for Bi-2212/MgO thin films fabricated by the MOD method

We investigated the characteristics of in-plane orientation for c-axis-oriented Bi-2212 thin films on MgO substrates, fabricated by the metal–organic decomposition (MOD) method. Bi-2212/MgO films were annealed using a 2-step heat treatment. The dominant rotation angle of the Bi-2212 film was 45° ([1 0 0] of Bi-2212 // [1 1 0] of MgO) for a precursor film fabricated at 500 °C and fired at 840 °C for 0 min or 30 min. However, after firing for 1 h the ?-scanning signal indicating the 45° angle became smaller and the signal representing an angle of about ±12° ([1 0 0] of Bi-2212 // [5 1 0] of MgO) became larger. After firing for 3 h, this ±12° signal became dominant. The extent of the 45° angle’s shift to ±12° increased with increasing firing time. On the other hand, when the precursor film was fabricated at 430 °C, signals indicating angles of 0°, ∼±12°, and 45° were observed after firing for 30 min. The rotation angle depended on the precursor-fabrication temperature when the precursor film was fired at 840 °C for 0 min or 30 min.     

Efficient four-wave mixing of a coupled double quantum-well nanostructure

We propose an efficient four-wave mixing (FWM) scheme in an asymmetric semiconductor double quantum-well (SDQW) structure based on intersubband transitions, and obtain the corresponding explicit analytical expressions for the input probe and generated FWM pulsed fields by use of the coupled Schrödinger-Maxwell approach. Under the resonant and phase-matched conditions, the FWM efficiency versus several variables is also discussed in details and the maximum FWM efficiency of the system under study is greater than 25%. Such a semiconductor system is much more practical than its atomic counterpart because of its flexible design and the controllable interference strength. This nonlinear optical process in the SDQW solid-state material can be used for efficiently generating coherent short-wavelength radiation.     

Simultaneous four channel wavelength conversion of 50Gbps CSRZ–DPSK signals in S and C bands using HNLF without additional pump signals

Optical wavelength conversion is expected to be an important technique for future advanced dense wavelength division multiplexing systems. It enhances wavelength routing capabilities, improves network reconfigurability and eliminating the problem associated with wavelength reuse in network. Here, simultaneous 50Gbps four channel wavelength conversion is established in S and C bands of ITU grid using four wave mixing (FWM) technique in high nonlinear fiber (HNLF) without additional pump signals. Since the four channel wavelength conversion is to be performed, the frequency spacing between the pairs of signal in S and C bands should be maintained in order to avoid the signal degradation by the effect of higher order FWM. Thereby the best frequency spacing between the pairs of signals in S and C bands is estimated to maintain good BER over the wavelength converted signals of both bands. So the selected frequency spacing between the pairs fulfills the freedom of selecting any frequency spacing within a pair of wavelengths in S and C band signals. It is also shown that CSRZ–DPSK modulated input signal enhances the BER of wavelength converted signals over the RZ–DPSK. In addition to this, uniform wavelength conversion over a wide bandwidth with a reduced length of HNLF is achieved and also the best power range is estimated to obtain good conversion efficiency.     

Mid-infrared efficient generation by resonant four-wave mixing in a three-coupled-quantum-well nanostructure

We present a cascade configuration for the realization of highly efficient four-wave mixing (FWM) process in an asymmetric semiconductor three-coupled-quantum-well (TCQW) structure based on intersubband transitions (ISBTs). In the proposed TCQW scheme, the efficiency of the generated FWM mid-infrared (MIR) signal is significantly enhanced and the obtained maximum efficiency is greater than 50%. The corresponding explicit analytical expressions for the input probe and generated FWM pulsed fields are derived by use of the coupled Schrödinger-Maxwell approach and the FWM efficiency versus several variables is also discussed in details. Such a semiconductor system is much more practical than its atomic counterpart because of its flexible design and the wide adjustable parameters. This nonlinear optical process in the TCQW solid-state material can be used for efficiently generating coherent short-wavelength radiation.     

Numerical analysis for four-wave mixing based wavelength conversion of differential phase-shift keying signals

We numerically investigate the main constrains for high efficiency wavelength conversion of differential phase-shift keying （DPSK） signals based on four-wave mixing （FWM） in highly nonlinear fiber （HNLF）. Using multi-tone pump phase modulation techniques, high efficiency wavelength conversion of DPSK signals is achieved with the stimulated BriIlouin scattering （SBS） effects effectively suppressed. Our analysis shows that there is a compromise between conversion efficiency and converted idler degradation. By optimizing the pump phase modulation configuration, the converted DPSK idler＇s degradation can be dramatically decreased through balancing SBS suppression and pump phase modulation degradation. Our simulation results also show that these multi-tone pump phase modulation techniques are more appropriate for the future high bit rate systems.     

Polarization insensitive wavelength multicasting of DPSK signal using four-wave mixing in a birefringent photonic crystal fiber

We demonstrate polarization-insensitive wavelength multicasting of differential phase-shift keying (DPSK) signal based on four-wave mixing (FWM) in a highly nonlinear, birefringent photonic crystal fiber (PCF). The 10-Gbit/s RZ-DPSK input signal is copied to 8 wavelength channels through FWM with three optical pumps. The pump wavelengths are unequally spaced to avoid undesirable crosstalk from pump-to-pump beatings. The dependence of conversion efficiency on input signal polarization is suppressed by exploiting the PCF birefringence together with control of the pump polarizations. All pump polarizations are aligned at 45 degrees to the principal axes of the PCF. Open eyes and error-free results are obtained in all the 8 multicast channels for polarization-scrambled RZ-DPSK input signal.     

High Efficiency Four-Wave Mixing with Relaxation Coupling of Longitude-Optical Phonons in Semiconductor Quantum Wells

The time-dependent analysis of four-wave mixing(FWM) has been performed in four-level double semiconductor quantum wells(SQWs) considering the cross-coupling of the longitude-optical phonons(LOP) relaxation. It is shown that both the amplitude and the conversion efficiency of the FWM field enhance greatly with the increasing strength of cross-coupling of LOP relaxation. Interestingly, a double peak value of the conversion efficiency is obtained under a relatively weak single-photon detuning considering the LOP coupling. When the detuning becomes stronger,the double peaks turn into one peak appearing at the line respect to the about equality two control fields. The results can be interpreted by the effect of electromagnetically induced transparency and the indirect transition. Such controlled high efficiency FWM based on the cross-coupling LOP may have potential applications in quantum control and communications.     

All-optical wavelength conversion for 10-Gb/s NRZ payload and 2.5-Gb/s OFDM label in optical-packet-switched network

Simultaneous wavelength conversion based on four-wave mixing (FWM) for 10-Gb/s NRZ payload and 2.5-Gb/s OFDM label signals in optical switching network is experimentally demonstrated. The dual-pump scheme based on FWM in semiconductor optical amplifier (SOA) is employed and simultaneous wavelength conversion for optical packet with one optical payload of 10-Gb/s non-return-to-zero (NRZ) on-off keying (OOK) signals and one optical label of 2.5-Gb/s OFDM signals are realized. The bit-error-rate performance is evaluated for both payload and label after wavelength conversion.     

Experimental demonstration on 40 Gbit/s all-optical multicasting logic XOR gate for NRZ-DPSK signals using four-wave mixing in highly nonlinear fiber

We propose and demonstrate all-optical multicasting logic XOR gate for non-return-to-zero differential phase-shift keying (NRZ-DPSK) signals by using non-degenerate four-wave mixing (FWM) in a highly nonlinear fiber (HNLF). Theoretical analysis regarding the operation principle of NRZ-DPSK logic XOR gate is clearly described by deriving an analytical solution under the non-depletion approximation. The NRZ-DPSK logic XOR operation is attributed to the linear relationship of complex amplitudes between converted idlers and input NRZ-DPSK signals. By using three non-degenerate FWM processes in an HNLF, 40 Gbit/s all-optical multicasting logic XOR gate for NRZ-DPSK signals are successfully demonstrated in the experiment.     

A Novel Method for Wavelength Conversion with Dual-pump Four-wave Mixing in a Semiconductor Optical Amplifier

Using a semiconductor-fiber ring laser, a novel method for the all optical wavelength conversion based on dual-pump four-wave mixing (FWM) in a semiconductor optical amplifier (SOA) is demonstrated. For the input signal with different wavelengths, only one external pump is needed. This scheme can simplify the dual-pump FWM in SOA and has nearly constant conversion efficiency and signal-to-noise ratio (SNR) over 50nm range of wavelength shifts.     

A Novel Method for Wavelength Conversion with Dual-pump Four-wave Mixing in a Semiconductor Optical Amplifier

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Four-wave mixing in dual wavelength fiber laser utilizing SOA for wavelength conversion

In this paper, a novel configuration of a wavelength converter is set forth by utilizing a semiconductor optical amplifier (SOA) as a nonlinear gain medium to generate a four-wave mixing (FWM) effect by using a dual wavelength bi-erbium-doped fiber laser that uses an Arrayed Waveguide Grating (AWG) together with two optical channel selector (OSC) as selective elements to function as a dual wavelength switchable pump power. The four-wave mixing (FWM) is produced with a wavelength detuning of 7 nm from the pump and signal which used is as the converted signal at wavelength 1532.8 nm or 1534.5 nm for transferring data from the input signal at wavelength 1547.0 nm. Thus, even though the conversion efficiency is as low as −43 dB, it is still possible for applications as a wavelength converter.     

Intra-cavity second harmonic generation with Nd:YVO4/BIBO laser at 542 nm

We report, for the first time, an efficient intra-cavity second-harmonic generation (SHG) at 1084 nm in a nonlinear optical crystal, BiB₃O₆(BIBO) at the direction of (θ, ?) = (170.1°, 90°), performed with a LD end-pumped cw Nd:YVO₄ laser. With 590 mW diode pump power, a continuous-wave (cw) SHG output power of 19 mW at 542 nm yellow-green color has been obtained using a 1.5 mm-thick BIBO crystal. The optical conversion efficiency was 3.22%. It was found that the output wavelength could be 532 nm, 537 nm or 542 nm according to regulating the angle of BIBO.     

Inhibiting the onset of the three-photon destructive interference in ultraslow propagation-enhanced four-wave mixing with dual induced transparency

We propose a dual electromagnetically induced transparency (EIT) based multiwave mixing scheme that retains the significantly enhanced conversion efficiency enabled by ultraslow propagation of pump waves, yet is also capable of inhibiting and delaying the onset of the detrimental three-photon destructive interference that limits the further growth of the four-wave mixing (FWM) field. We show that the new scheme exhibits a wave-matching condition that is fundamentally different from the conventional FWM without EIT, and the efficient generation of the mixing wave is not critically dependent upon the FWM detuning to achieve constructive interference as required in the conventional FWM. These are significant steps forward in enabling applications of ultraslow wave nonlinear optics.     

Baking impact on photoelectrochemical cells performance of electrodeposited CdSe films

Cadmium selenide (CdSe) nanocrystalline thin films in the form of upright nanocones, perpendicular to substrate surface, are grown electrochemically onto a conducting and transparent indium-tin-oxide substrate at room temperature and impact of baking under oxygen flow on their structure, morphology, optical absorbance and dark-light photoelectrochemical cell performance is explored. Crystallinity improvement followed by enhancement in the surface roughness 11-19 nm and reduction in water contact angle from 60° to 22° (±0.2)° due to baking impact showed increase in crystallite size from 25 to 100 Å. Increase in current density from 0.07 to 5.61 mA/cm² after baking under oxygen flow has promoted the conversion efficiency to 0.5% from 0.007%.     

Amplitude Regenerative Characteristics of RZ-DPSK Wavelength Converter Based on Four-Wave Mixing in SOA

We investigate the phase-preserving amplitude regenerative characteristics of the return-to-zero （RZ） differential- phase-shift-keying （DPSK） wavelength conversion based on four-wave m/xing （FWM） in a semiconductor optical amplifier （SOA）. The Q-factor and the optical signal-to-noise ratio （OSNR） before and after conversion are experimentally obtained and analysed in different input noise power levels. In both the continuous-wave and synchronous clock pumping cases, we find that there is amplitude clamping in the FWM conversion due to the gain saturation of SOA, which can suppress the amplitude fluctuation of the converted DPSK signal before and after demodulation. We have achieved 2-dB Q penalty improvement in our experiment demonstration of lOGbit/s RZ-DPSK signal with OSNR lower than 19dB.