Fiber Optical Parametric Amplifier Research Articles

Simple geometric interpretation of signal evolution in phase-sensitive fibre optic parametric amplifier.

Visualisation of complex nonlinear equation solutions is a useful analysis tool for various scientific and engineering applications. We have re-examined the geometrical interpretation of the classical nonlinear four-wave mixing equations for the specific scheme of a phase sensitive one-pump fiber optical parametric amplification, which has recently attracted revived interest in the optical communications due to potential low noise properties of such amplifiers. Analysis of the phase portraits of the corresponding dynamical systems provide valuable additional insight into field dynamics and properties of the amplifiers. Simple geometric approach has been proposed to describe evolution of the waves, involved in phase-sensitive fiber optical parametric amplification (PS-FOPA) process, using a Hamiltonian structure of the governing equations. We have demonstrated how the proposed approach can be applied to the optimization problems arising in the design of the specific PS-FOPA scheme. The method considered here is rather general and can be used in various applications.

Optimizing bandwidth of fiber optical parametric amplifier with different combinations of higher-order dispersion coefficient signs

This paper investigates the influence of different combinations of second-order (β2 ), fourth-order (β4 ) and sixth-order (β6 ) dispersion coefficient signs (negativity/positivity) to the fiber optical parametric amplifier gain performance. The numerical simulation has exploited the fourth-order Runge-Kutta method to solve the coupled amplitude equations which basically represent the parametric process of four-wave mixing. In the normal regime at which β2 is positive, the fiber optical parametric amplifier exhibits a poor gain spectrum and it is well performed once the pump is presumed to be in anomalous regime i.e. β2 is negative. The effect of β4 is significant when the signal wavelength is further from the pump wavelength and a wide amplification bandwidth is produced when the fiber have positive β4 in the anomalous regime. As for β6 , unfortunately in this simulation its influences are hardly can be seen probably because of its small value regardless its sign, but, from phase-mismatch equation it is shown that its impact is prominent when the signal is positioned way far from the pump. All in all, this shown that the signs combination of the higher-order dispersion coefficients are significant in order to optimize the FOPA amplification bandwidth.

Designing broadband fiber optic parametric amplifier based on near-zero single ZDW PCF with ultra-flat nature

We propose a broadband fiber optic parametric amplifier (FOPA) based on a near-zero ultra-flat dispersion profile with a single zero-dispersion wavelength (ZDW) by using a selective liquid infiltration technique. The amplifier gain and bandwidth is investigated for a variety of fiber lengths, pump power, and operating wavelengths. It is observed that sufficient peak gains and broader bandwidths can be achieved with a small negative anomalous dispersion (β2≤0) and a positive value of the 4th-order dispersion parameter (+ β4) around the pump. We can optimize an FOPA with a bandwidth of more than 220 nm around the communications wavelength.

Pulsed optical parametric amplification based on photonic crystal fibres

In this paper, we simulate pulsed one-pump fibre optical parametric amplifiers (1-P FOPAs) based on photonic crystal fibres in telecommunication region. At first, a PCF is designed such that its zero-dispersion wavelength is located at 1535 nm in order to fulfil the phase-matching condition for the parametric amplification in the telecommunication region. Then, the dispersion coefficients of the PCF including β2, β3, β4 and β5 as well as the nonlinear parameters are calculated at the pump, signal and idler wavelengths. Finally, the coupled nonlinear Schrödinger equations are numerically solved and the impacts of pump power and the pulse shape on the evolution of each pulse along the 1-P FOPA are investigated. The results show that the peak powers of the pump, signal and idler are periodically varied and each pulse is distorted and broadened as it propagates down the fibre optical parametric amplifiers. Also, the pulse distortion and broadening increase with the increase in both propagation distance and the input peak power.

FOPA Pump Phase Modulation and Polarization Impact on Generation of Idler Components

Fiber optical parametric amplifiers (FOPA) are well known for the variety of potential applications in all-optical signal processing. Many of these applications use the idler spectral components that are produced by the four wave mixing parametric process. The performance of parametric amplifiers and, therefore, also of generation of idler spectral components, is highly dependent on different factors, including stimulated Brillouin scattering (SBS) and polarization of the input signal. The aim of this article is to investigate the influence of pump phase modulation of parametric amplifiers, used for SBS mitigation, and the impact of mutual state of polarization mismatch of the input signal and the pump on the generation of idler spectral components. The obtained results have shown that it is crucial for systems with FOPAs to ensure that the input signal and the pump are co-polarised, as polarization dependant gain of 16.7 dB and 33.5 dB difference in idler generation was observed in the performed simulations. It was also found that applying the phase-modulation of the pump for SBS mitigation has caused 54 % idler spectral broadening. Therefore additional measures must be taken to avoid inter-channel crosstalk among the neighbour channels. DOI: http://dx.doi.org/10.5755/j01.eie.22.4.15924

Numerical analysis of broadband fiber optical parametric amplifiers pumped by two chirped pulses

An optical parametric amplifier pumped by two chirped pump pulses has been analytically and numerically investigated to predict the spectral gain bandwidth and its temporal distribution. We highlight that the properties of the amplifier depend strongly on the relative chirp values and a uniform spectrotemporal gain can be obtained when the two chirps have opposite signs. A chirped signal pulse owing a very broad bandwidth has also been injected and we demonstrate the amplification of ultrashort pulse with this type of amplifier.

Quantum information tapping using a fiber optical parametric amplifier with noise figure improved by correlated inputs.

One of the important functions in a communication network is the distribution of information. It is not a problem to accomplish this in a classical system since classical information can be copied at will. However, challenges arise in quantum system because extra quantum noise is often added when the information content of a quantum state is distributed to various users. Here, we experimentally demonstrate a quantum information tap by using a fiber optical parametric amplifier (FOPA) with correlated inputs, whose noise is reduced by the destructive quantum interference through quantum entanglement between the signal and the idler input fields. By measuring the noise figure of the FOPA and comparing with a regular FOPA, we observe an improvement of 0.7 ± 0.1 dB and 0.84 ± 0.09 dB from the signal and idler outputs, respectively. When the low noise FOPA functions as an information splitter, the device has a total information transfer coefficient of Ts+Ti = 1.5 ± 0.2, which is greater than the classical limit of 1. Moreover, this fiber based device works at the 1550 nm telecom band, so it is compatible with the current fiber-optical network for quantum information distribution.

Designing a photonic crystal fiber for an ultra-broadband parametric amplification in telecommunication region

A photonic crystal fiber (PCF) with a zero-dispersion wavelength (ZDW) in the telecommunication region is designed and an ultra-broadband fiber optical parametric amplifier (FOPA) based on such PCF is simulated. Results show that the PCF-based FOPA exhibits much higher gain with a very broad bandwidth (covering O- to U-band) in comparison with the highly nonlinear fiber (HNLF)-based FOPA. Also, the required fiber length and the input pump power are reduced for the PCF-based FOPA. The obtained results show the great potential of the PCF-based OPA for the telecommunication applications, e.g. amplification of wavelength-division multiplexing (WDM) signals.

Gain-saturated one-pump fiber optical parametric amplifiers in presence of longitudinal dispersion fluctuations

In this paper, we investigate the impact of longitudinal dispersion fluctuations of the optical fiber on the gain spectrum and the saturation behavior of one-pump fiber-optical parametric amplifiers (1-P FOPAs). The gain spectra and the saturation curves of 1-P FOPAs are simulated by solving the coupled amplitude equations numerically and taking into account the dispersion fluctuations as a stochastic process with a given standard deviation and correlation length. Results show that the shape and the level of the gain spectrum and also the saturation power of 1-P FOPAs are considerably changed in the presence of dispersion fluctuations in comparison with the case when dispersion fluctuations are ignored. This feature is also totally different compared with the small-signal gain spectrum of the FOPA in the presence of dispersion fluctuations. Moreover, the value of the change in the gain and the saturation power depends strongly on the fluctuation parameters, i.e., the standard deviation and the correlation length.

Broadband optical parametric amplifier formed by two pairs of adjacent four-wave mixing sidebands in a tellurite microstructured optical fibre

A broadband fibre-optical parametric amplifier (FOPA) operating at a novel wavelength region that is far from the pump wavelength has been demonstrated by exploiting two pairs of adjacent four-wave mixing (FWM) sidebands generated simultaneously in a tellurite microstructured optical fibre (TMOF). Owing to the large nonlinearity of the TMOF and the high pump peak power provided by a picosecond laser, a maximal average gain of 65.1 dB has been obtained. When the FOPA is operated in a saturated state, a flat-gain amplification from 1424 nm to 1459 nm can be achieved. This broadband and high-gain FOPA operating at new wavelength regions far from the pump offers the prospect of all-optical signal processing.

Raman-Enhanced Phase-Sensitive Fibre Optical Parametric Amplifier.

Phase-sensitive amplification is of great research interest owing to its potential in noiseless amplification. One key feature in a phase-sensitive amplifier is the gain extinction ratio defined as the ratio of the maximum to the minimum gains. It quantifies the capability of the amplifier in performing low-noise amplification for high phase-sensitive gain. Considering a phase-sensitive fibre optical parametric amplifier for linear amplification, the gain extinction ratio increases with the phase-insensitive parametric gain achieved from the same pump. In this work, we use backward Raman amplification to increase the phase-insensitive parametric gain, which in turn improves the phase-sensitive operation. Using a 955 mW Raman pump, the gain extinction ratio is increased by 9.2 dB. The improvement in the maximum phase-sensitive gain is 18.7 dB. This scheme can significantly boost the performance of phase-sensitive amplification in a spectral range where the parametric pump is not sufficiently strong but broadband Raman amplification is available.

Generation of continuous variable quantum entanglement using a fiber optical parametric amplifier.

We demonstrate the experimental generation of quadrature amplitude entanglement in the 1550 nm band by using a fiber optical parametric amplifier. The measured noise variances of the difference and sum of the quadrature amplitudes of the pulsed signal and idler twin beams fall below the shot noise limit by about 1 and 0.8 dB (4.2 and 3.6 dB after the correction for efficiency), respectively, showing that the inseparability criterion of Einstein-Podolsky-Rosen entanglement I<2 is satisfied. Our investigation reveals that the quality of the measured entanglement can be further improved by increasing the transmission efficiency of the twin beams and by optimizing the temporal mode matching of the two sets of homodyne detection systems.

Generation of multi-mode squeezed vacuum using pulse pumped fiber optical parametric amplifiers.

Multimode squeezed states are essential resources in quantum information processing and quantum metrology with continuous variables. Here we present the experimental generation of squeezed vacuum via the degenerate four wave mixing realized by pumping a piece of dispersion shifted fiber with mode-locked ultrafast pulse trains. The noise fluctuation is lower than the shot noise limit by 1.1 ± 0.08 dB (1.95 ± 0.17 dB after correction for detection losses). The detailed investigation illustrates that the results can be further improved by suppressing Raman scattering and by reshaping the spectrum of the local oscillator to achieve the required mode-matching of the homodyne detection system. Our study is useful for developing a compact fiber source of multi-mode squeezed vacuum.

Multi-order dispersion engineering in binary multi-clad microstructured fiber towards designing nonlinear devices

We report here a detailed investigation of multi-order dispersion engineering in soft-glass (SF6/SF57/LLF1) based binary multi-clad microstructured fiber (BMMF) in designing nonlinear fiber devices. A full-vector modal analysis is devised to obtain all six field components of the guided mode in order to procure the exact propagation characteristics in an N-layered fiber structure. Investigations for these SF6/LLF1 based BMMF reveal the presence of significant longitudinal field, typical electric field discontinuity and feeble ellipticity in the dominant magnetic field. Subsequently, we analysed in details the dependence of dispersion characteristics on the associated structural parameters. It is seen that the transverse design parameters (core-diameter, pitch and the low-index filling fraction) can be used as a key to widely tune the zero-dispersion-wavelength (ZDW). Various interesting dispersion profiles from the point of view of nonlinear application, namely, ultra-flat dispersion, all-normal dispersion, two-zero-dispersion, three-zero-dispersion are extracted by modifying the geometry. We then discuss an advanced aspect of dispersion engineering that involves minute control over the individual higher-order dispersion parameters. It is observed that this novel structure can yield fine-tuning of HOD’s while keeping the ZDW/maximum dispersion wavelength fixed at the desired operating wavelength. We mark our achievement in demonstrating an incredible control of dispersion through exact structural designing of soft-glass BMMF in the limit of practical realization. The effectiveness of this advanced dispersion tuning is readily implemented in designing a host BMMF that yields a two-octave spanning SC source, wideband fiber-optic parametric amplifier and narrow-band parametric sources in the near infrared to short-wave infrared (NIR–SWIR) region where efficient light sources, amplifiers presently do not exist.

Demonstration of Ultra Wideband Phase-Sensitive Fiber Optical Parametric Amplifier

This letter demonstrates the capability of fiber optical parametric amplifiers, in phase-sensitive mode, to provide low-noise amplification over a bandwidth in excess of 170 nm, with the cutoff set as minimum gain of 10 dB. We have measured both gain and noise figure for two different lengths of the gain medium offering diverse gain profiles. Noise figure measurements confirm ultra-low noise operation along the four telecom bands— namely $S$ -, $C$ -, $L$ -, and U-band. Electrical noise figures for a limited wavelength range were also measured to confirm the measured optical noise figures.

Phase-sensitive fiber-based parametric all-optical switch.

We experimentally demonstrate, for the first time, an all-optical switch in a phase-sensitive fiber optic parametric amplifier operated in saturation. We study the effect of phase variation of the signal and idler waves on the pump power depletion. By changing the phase of a 0.9 mW signal/idler pair wave by π/2 rad, a pump power extinction ratio of 30.4 dB is achieved. Static and dynamic characterizations are also performed and time domain results presented.

Tri-band spectroscopic optical coherence tomography based on optical parametric amplification for lipid and vessel visualization.

A tri-band spectroscopic optical coherence tomography (SOCT) system has been implemented for visualization of lipid and blood vessel distribution. The tri-band swept source, which covers output spectrum in 1.3, 1.5, and 1.6 μm wavelength windows, is based on a dual-band Fourier domain mode-locked laser and a fiber optical parametric amplifier. This tri-band SOCT can further differentiate materials, e.g., lipid and artery, qualitatively by contrasting attenuation coefficients difference within any two of these bands. Furthermore, ex vivo imaging of both porcine artery with artificial lipid plaque phantom and mice with coronary artery disease were demonstrated to showcase the capability of our SOCT.

Polarized fiber optical parametric amplification in randomly birefringent fibers.

A comprehensive theoretical model to investigate phase matching in degenerate polarized fiber optical parametric amplifiers (FOPAs) in randomly birefringent fibers is developed. We show that in the small signal region, simulation results from the proposed model agree well with the experimental results. It was also shown that four waves mixing (FWM) effect could compensate polarization mode dispersion (PMD) induced phase mismatch. Similar to counter-propagating fiber Raman amplifiers (FRAs), the degree of polarization of FOPAs approaches unity exponentially with the gain but at a larger rate 1/Γ. Thus larger polarization-pulling can be achieved in FOPAs than the counter-propagating FRAs for the same gain.

Investigation of Raman-Assisted Crosstalk Reduction in Multi-Wavelength Fiber Optical Parametric Amplification

Suppression of four-wave mixing (FWM) crosstalk during multi-wavelength amplification in a Raman-assisted fiber optical parametric amplifier (FOPA) is investigated theoretically and experimentally. The principle of crosstalk reduction by using a backward Raman pump is revealed by analytical expressions and verified by simulations. The crosstalk reduction is attributed to the unique power evolution of the signals caused by the monotonically increasing parametric pump power in the Raman-assisted FOPA. We obtain more than 7-dB reduction in FWM crosstalk initiated from both degenerate-FWM and nondegenerate-FWM processes in the Raman-assisted FOPA, as compared to a conventional FOPA with equivalent signal gain. The experimental results show excellent agreement with the simulations. We also discuss the effects of signal channel number and the powers of the parametric pump and the Raman pump on the FWM crosstalk. The simulation results indicate that under the same level of signal gain, the amount of crosstalk reduction can be increased by using a stronger Raman pump associated with a weaker parametric pump.

Complete temporal mode analysis in pulse-pumped fiber-optical parametric amplifier for continuous variable entanglement generation.

Mode matching plays an important role in measuring the continuous variable entanglement. For the signal and idler twin beams generated by a pulse pumped fiber optical parametric amplifier (FOPA), the spatial mode matching is automatically achieved in single mode fiber, but the temporal mode property is complicated because it is highly sensitive to the dispersion and the gain of the FOPA. We study the temporal mode structure and derive the input-output relation for each temporal mode of signal and idler beams after decomposing the joint spectral function of twin beams with the singular-value decomposition method. We analyze the measurement of the quadrature-amplitude entanglement, and find mode matching between the multi-mode twin beams and the local oscillators of homodyne detection systems is crucial to achieve a high degree of entanglement. The results show that the noise contributed by the temporal modes nonorthogonal to local oscillator may be much larger than the vacuum noise, so the mode mis-match can not be accounted for by merely introducing an effective loss. Our study will be useful for developing a source of high quality continuous variable entanglement by using the FOPA.