Optical Phase Conjugation Research Articles

Phase Conjugation Using Four‐Wave Mixing in Fast Green FCF Dye‐Doped Gelatin Film

We present optical phase conjugation based on the degenerate four‐wave mixing (DFWM) arrangement in gelatin films doped with acid blue 3 dye (FAST GREEN FCF) using He‐Ne laser of total power 50 mW. Various parameters which influence the phase‐conjugate (PC) signal during the DFWM process were studied (angle of between the forward pump and the probe beam, transition of gelatin film, reflectivity as a function of forward and backward beam). A maximum phase‐conjugate beam reflectivity of about 0.02% has been observed in these dye‐doped gelatin films. PACS: 42.65.‐k, 42.65.Hw.

Reduction of Parametric Amplified Noise in Nonlinear Fiber Channels by Use of Wiener Filtering

As a parametric amplified noise, nonlinear phase noise limits the channel capacity in multispan fiber-optics transmissions. In this paper, the reduction of nonlinear phase noise by use of Wiener filtering is studied. Extracting signal from time-domain concepts, parametric amplified noise covering signal spectrum in frequency domain can be suppressed considerably. Timing jitter and ghost pulses due to intrachannel nonlinearities can also be compensated. Nonparametric Wiener filtering is used at the end of six configurations of dispersion compensation (DC) transmission lines: pre- and postlumped DC, distributed DC without optical phase conjugation (OPC), dispersion inversion (DI) about midlink OPC with, respectively, one-for-multispan, single type span and alternate type span on each side of OPC. It is found that single-DI and alternate-DI schemes have higher input power capacity than one-for-multi-DI scheme. Further reductions in the nonlinear phase noise accumulation for all these DC maps are obtained with Wiener filtering, and higher absolute dispersion can decrease signal fluctuation due to nonlinear phase noise, as well.

Stimulated Rayleigh–Bragg Scattering From a Two-Photon Absorbing CdSe–CdS–ZnS Quantum-Rods System: Optical Power Limiting and Phase-Conjugation

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This work reports the properties of stimulated Rayleigh–Bragg scattering (SRBS) from a two-photon absorbing CdSe–Cds–ZnS quantum-rods (QRs) solution in chloroform, excited by 1064-nm and <formula formulatype="inline"> <tex>$\sim$</tex></formula>13-ns laser pulses. The two-photon absorbing capability of the scattering medium, as well as the pump threshold, spectral structure, and pulse waveforms of the backward stimulated scattering were measured. Comparing to a pure solvent or an organic dye-solution, the semiconductor QR system has many advantages such as the lower pump threshold, higher energy transfer efficiency, and better photo-physical and photo-chemical stability. The measured output/input characteristic curve shows that the backward SRBS can enhance the optical power limiting performance that is based on two-photon absorption, backward stimulated scattering, and other nonlinear absorption mechanisms. In addition, the backward SRBS beam from our sample medium exhibits a fairly good optical phase-conjugation capability, so that the distortion influence from an inserted aberrator can be automatically removed. </para>

Dependence on geometry of coherent Raman-scattered Stokes mode in weakly polar magnetized semiconductors

Abstract Using electromagnetic treatment, a detailed analytical investigation is made of the coherent Raman scattering (CRS) of the Stokes component of scattered wave in an obliquely magnetized (with respect to the direction of propagation) weakly polar III–V semiconductor. The origin of the CRS process lies in the third-order nonlinear optical susceptibility arising from the induced nonlinear current density (due to finiteness of Szigeti effective charge and differential polarizability) and interaction of pump wave with the density fluctuation generated within the medium. The agreement in magnitude of the third-order Raman susceptibility between our calculated values and experimental as well as other theoretical values is found to be good. Using the coupled mode theory of plasmas the steady-state Raman gain coefficient is determined via the effective susceptibility. The results suggest that magnetic field enhances the CRS gain coefficient by a factor of three when cyclotron frequency is tuned to optical phonon frequency under moderate pump field strengths. For field strengths E0>108 V m−1, the contribution of effective charge is nearly wiped off and the Raman gain spectrum becomes dependent on differential polarizability only. The CRS gain coefficient increases with increasing scattering angle and results in a maximum value for the backscattered mode. The backward Raman gain is found to be nearly 104 times larger than forward gain. The analysis also suggests the possibility of observing optical phase conjugation via CRS in weakly polar III–V semiconductors subjected to an external magnetic field.

SUPPRESSION OF SOLITON TIMING JITTERS BY PERIODIC OPTICAL PHASE CONJUGATIONS AND OPTICAL FILTERS

We propose a new method for suppressing the timing jitters of soliton pulses by using periodic phase conjugations and optical spectral filters in a high bit-rate transmission system. It is proven that the tolerable transmission distance limited by timing jitters can be increased through modulating frequency shifts by optical phase conjugators and eliminating the interaction between dispersive waves and the central pulses by optical filters. Our results also show that the optical-phase-conjugated soliton with spectral filters is superior to the common soliton in suppressing polarization mode dispersion induced by random birefringence. The physical mechanisms of soliton timing jitters are analyzed.

Trends in stimulated Brillouin scattering and optical phase conjugation

AbstractAn overview on current trends in stimulated Brillouin scattering and optical phase conjugation is given. This report is based on the results of the “Second International Workshop on stimulated Brillouin scattering and phase conjugation” held in Potsdam/Germany in September 2007. The properties of stimulated Brillouin scattering are presented for the compensation of phase distortions in combination with novel laser technology like ceramics materials but also for e.g., phase stabilization, beam combination, and slow light. Photorefractive nonlinear mirrors and resonant refractive index gratings are addressed as phase conjugating mirrors in addition.

Control of polarization signal distortion by frequency domain phase conjugation in optical fiber systems

Optical frequency domain phase conjugation (FDPC) is based on phase conjugation of spectrum of an input signal. It is equivalent to the phase conjugation and the time reversal of the temporal envelope of an input signal. The use of FDPC to control polarization signal distortion in birefringent optical fiber systems is proposed. Evolution of polarization signals in the system using midway FDPC is analyzed theoretically and simulated numerically. It is shown that the distortion of polarization signals can be controlled effectively by FDPC. The impairments due to dispersion and nonlinear effects can be suppressed simultaneously.

Analytical Design of SPM-Limited Systems With Optical Phase Conjugation

Optical phase conjugation (OPC) is a promising technique to compensate the nonlinear impairment in optical fiber communications. However, the compensation for nonlinearity by use of OPC is limited by the asymmetry of signal power. Thus, the optimization of a link taking advantage of OPC is demanded. In this letter, an analytical model is proposed to optimize the design of self-phase-modulation (SPM)-limited systems in which the nonlinearity is compensated by OPC. Using the model, the optimal location of the phase conjugator can be evaluated, and an analytical expression of optimal net residual dispersion is obtained. Moreover, the SPM-compensation efficiency of OPC can be estimated conveniently.

Phase conjugation in weakly piezoelectric magnetized semiconductor-plasmas

The occurrence of optical phase conjugation via stimulated Brillouin scattering (OPC-SBS) in weakly piezoelectric III–V semiconductor plasmas subjected to a large magnetostatic field under off-resonant transition regime has been explored theoretically. The reflectivity of the phase conjugate wave is dependent upon the Brillouin susceptibility and can be significantly enhanced through n-type doping of the crystal and the simultaneous application of a magnetostatic field. Moreover, the threshold pump intensity required for the occurrence of SBS in the crystal with finite optical attenuation can be considerably diminished through proper selection of the doping concentration and magnetostatic field. Consequently, OPC-SBS becomes a possible tool in phase-conjugate optics even under not-too-high power laser excitation by using doped n-type semiconductors kept under the influence of a large magnetostatic field. Numerical estimates made for n-InSb crystal at 77 K duly irradiated by a nanosecond pulsed 10.6 µm CO2 laser reveal that high OPC-SBS reflectivity can be achieved at excitation intensities below the optical damage threshold if the semiconductor crystal is used as an optical waveguide with an interaction length of a few millimetres.

Modulated optical phase conjugation in rhodamine 110 doped boric acid glass saturable absorber thin films

The optical phase conjugation signal in nearly nondegenerate four wave mixing was studied using a rhodamine 110 doped boric acid glass saturable absorber nonlinear medium. We have demonstrated a narrow band optical filter (2.56±0.15Hz) using an optical phase conjugation signal in the frequency modulation of a weak probe beam in the presence of two strong counterpropagating pump beams in rhodamine 110 doped boric acid glass thin films (10−4m). Both the pump beams and the probe beam are at a wavelength of 488nm (continuous-wave Ar+ laser). The probe beam frequency was detuned with a ramp signal using a piezoelectric transducer mirror.

Narrow band optical filter in fluorescein doped boric acid glass saturable absorber thin films

We demonstrate narrow band optical filter like frequency response with full width half maximum (FWHM) of nearly (1.75 ± 0.25) Hz in fluorescein doped boric acid glass films [10 −4 M], using modulated optical phase conjugation and a nearly non-degenerate four wave mixing technique. Modulated optical phase conjugation signals are described in the limit of a weak probe and relatively strong pump beams. Both pump beams are of nearly equal intensity at a wavelength of 514.5 nm from a continuous-wave Ar + laser. The probe beam frequency has been detuned with a ramp signal using a piezo electric mirror.

Retracing random paths

Diffuse scattering can prevent high-resolution imaging in thick biological media. Researchers have now shown that such scattering can be completely cancelled by optical phase conjugation, opening the path to a new generation of medical imaging techniques.

Optical phase conjugation for turbidity suppression in biological samples

Elastic optical scattering, the dominant light interaction process in biological tissues, prevents tissues from being transparent. While scattering may appear stochastic, it is in fact deterministic in nature. We show that, despite experimental imperfections, optical phase conjugation (lambda = 532 nm) can force a transmitted light field to retrace its trajectory through a biological target and recover the original light field. For a 0.69 mm thick chicken breast tissue section, we can enhance point source light return by approximately 5x10(3) times and achieve a light transmission enhancement factor of 3.8 within a collection angle of 29 degrees . Additionally, we find that the reconstruction's quality, measured by the width of the reconstructed point source, is independent of tissue thickness (up to 0.69 mm thick). This phenomenon may be used to enhance light transmission through tissue, enable measurement of small tissue movements, and form the basis of new tissue imaging techniques.

Dynamic properties and optical phase conjugation of two-photon pumped ultrashort blue stimulated emission in a chromophore solution

The dynamic properties of two-photon pumped blue lasing $(\ensuremath{\sim}470\phantom{\rule{0.3em}{0ex}}\mathrm{nm})$ in the solution of an organic chromophore [2-acetyl-6-(dimethylamino)naphthalene], excited by $\ensuremath{\sim}160\text{\ensuremath{-}}\mathrm{fs}$ laser pulses at $\ensuremath{\sim}775\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$, have been studied. Both the forward and backward stimulated emission are enhanced by feedback from the reflection at the two optical windows of the solution filled cuvette. Under current experimental conditions, the lasing wavelengths in the forward and backward directions were almost the same, but both blueshifted compared to the fluorescence peak wavelength of the sample solution. The temporal behavior of the lasing output was recorded by a high-speed streak camera system. The multipulse structure and spectral properties of the output lasing are semiquantitatively explained. In addition, excellent optical phase-conjugation properties of the backward stimulated emission were observed; the aberration influences from an aberrator on the backward lasing beam were automatically removed.

Characteristics of Optical Interconnection for Power Transmission Based on Phase Conjugation Generation by a Ring-Resonator

To establish an interconnection for power transmission between two moving objects, optical phase conjugation is applied for non-mechanical, all-optical tracking and compensation of atmospheric distortions. The installation of the connection starts in sending a coherent pilot signal by the power receiver towards the transmitter. There, the incident light is collected and directed into a nonlinear medium placed inside a ring cavity. Scattered light enters the resonator and initiates a dynamic hologram writing with the incident pilot signal. Hence, a stable oscillation is generated by diffracted light of the pilot signal. Out-coupling is performed by a combination of an in-cavity half-wave plate and a polarizing beam splitter. This beam is reflected back into the nonlinear medium to generate the phase conjugated beam by four-wave mixing. Phase and direction of this beam can be manipulated without affecting the dynamic hologram thanks to the previous performed out-coupling. The final power transmission is realized by amplification of the phase conjugated beam. In this paper, we present initial results of the described setup. The angular range of generating the phase conjugated beam and its fidelity is analyzed.

Mechanism of phase conjugation via stimulated Brillouin scattering in narrow band gap semiconductors

We develop a theoretical model to study optical phase conjugation via stimulated Brillouin scattering (OPC-SBS) in narrow band gap transversely magnetized semiconductors. Threshold value of pump electric field and reflectivity of the image radiation for the onset of OPC-SBS are estimated. The analysis is applied to both cases viz. centrosymmetric (CS) and non-centrosymmetric (NCS) crystals. Numerical estimates made for n-type InSb crystal at liquid nitrogen temperature duly irradiated by nanosecond pulsed 10.6μm CO2 laser shows that high OPC-SBS reflectivity (90%) can be achieved in NCS crystals at moderate pump electric fields if the crystal is used as an optical waveguide with relatively large interaction length (L=5mm) which proves its potential in practical applications such as fabrication of phase conjugate mirrors.

2-D PSTD Simulation of optical phase conjugation for turbidity suppression

Turbidity Suppression via Optical Phase Conjugation (TS-OPC) is an optical phenomenon that uses the back propagation nature of optical phase conjugate light field to undo the effect of tissue scattering. We use the computationally efficient and accurate pseudospectral time-domain (PSTD) simulation method to study this phenomenon; a key adaptation is the volumetric inversion of the optical wavefront E-field as a means for simulating a phase conjugate mirror. We simulate a number of scenarios and demonstrate that TS-OPC deteriorates with increased scattering in the medium, or increased mismatch between the random medium and the phase conjugate wave during reconstruction.

Simultaneous Cancellation of Fiber Loss, Dispersion, and Kerr Effect in Ultralong-Haul Optical Fiber Transmission by Midway Optical Phase Conjugation Incorporated With Distributed Raman Amplification

An alternative application of distributed Raman amplification (DRA) for ultralong-haul optical fiber transmission is proposed. In our study, the DRA is employed in a transmission system using midway optical phase conjugation (OPC) for amplifying an optical signal and, at the same time, for constructing signal power evolution, which is symmetrical with respect to the midpoint of the system where the OPC is performed. Then, the nonlinear signal waveform distortions that are caused by the Kerr effect, as well as fiber dispersion, are almost completely compensated by the OPC, whereas the fiber loss is compensated by the DRA. Three possible symmetrical signal power maps - a power map that has a reverse sign of the power map that is caused by lump amplification, a flat signal power map, and an arbitrary symmetrical signal power map - are numerically designed by using appropriate Raman pump powers. We show that the flat power map exhibits smaller difference from the target and a higher optical signal-to-noise ratio and requires lower pump power than the other two power maps. Numerical simulation results demonstrate that, by employing the flat power maps with a span of 40 km, a single-wavelength signal whose data rate is 160 Gb/s can be successfully transmitted over 5000 km, and the Kerr effect is sufficiently suppressed near limitation due to the nonlinear accumulation of noise. Finally, we study the feasibility of expanding our method to wavelength-division-multiplexed signal transmission by designing a DRA gain with multiple-wavelength pumping to simultaneously obtain a flat power map and a wide-and-flat gain bandwidth. By using four-wavelength Raman pumps while carefully choosing pump wavelengths and their powers, we achieve the DRA gain that simultaneously gives a fluctuation of the signal power of only 3.5%, a gain ripple of only 5.3%, and, at the same time, a gain bandwidth of as wide as 46 nm.

Multichannel dispersion compensation using a silicon waveguide-based optical phase conjugator

We experimentally demonstrate dispersion compensation using a silicon-based optical phase conjugator. We achieve simultaneous transmission of four dense wavelength division multiplexing (DWDM) channels spaced at 100 GHz and operating at 10 Gbits/s over 320 km of standard fiber. The measured power penalty at bit error rate of 10(-9) is less than 0.3 dB.

Dispersion-Compensation Schemes for 160-Gb/s 1200-km Transmission by Optical Phase Conjugation

Appropriate dispersion management possesses the superiority to relax the limitation of nonlinearities in high-speed transmission systems employing optical phase conjugation (OPC). In this paper, several dispersion-compensation schemes have been analytically and numerically investigated in a 160-Gb/s OPC system. A comprehensive performance comparison of these schemes over 1200-km transmissions has been carried out to present a reference for future OPC system designs. The scheme with a gradient dispersion map is recommended, particularly for G.655 fiber with a relatively low local dispersion.