Steady-state analysis of a saturable nonlinear amplifying fibre loop resonator

Abstract

The steady-state response is analysed for a saturable nonlinear amplifying fibre loop resonator. With the amplification, the bistable region represented by the saturation coefficient of the nonlinear refractive index and by the feedback gain of the fibre loop is found to be highly enlarged when compared with the conventional passive loop resonator.     

High-birefringence fiber loop mirrors and their applications as sensors

The reflection and transmission characteristics of a high-birefringence fiber loop mirror (HiBi-FLM), which is composed of a standard fiber coupler and one-section or multisection high-birefringence fibers (HBFs), are analyzed and discussed in detail. Theoretical reflectivity and transmissivity expressions for HiBi-FLMs with one-, two-, and three-section HBFs were obtained. The procedure for calculating reflectivity and transmissivity for HiBi-FLMs with n-section HBFs is given. Experimental results have verified the theoretical model. The basic characteristics of the one-section HiBi-FLM when strain and high temperature are applied to HBFs were analyzed and investigated theoretically and experimentally. The experimental results are in good agreement with the theoretical analysis. Furthermore, a strain--temperature sensor that makes use of those characteristics, which is new for applications of HiBi-FLMs, has been proposed and demonstrated.     

Stable two-wavelength lasers by use of a double alpha-type fiber cavity with fiber grating mirrors

For high-frequency (20-200 GHz) modulated light sources, we developed and investigated two-wavelength lasers using the double alpha-type fiber cavities with fiber grating mirrors. For variations of polarization states and pump powers, parallel alpha-type coupled cavity lasers were found to be more stable than serial lasers.     

Properties of an optical time-division demultiplexing module using serialized nonlinear optical loop mirrors

Abstract

In this paper, the properties of the demultiplexing module using the serialized nonlinear optical loop mirrors have been investigated. The noise of the demultiplexing output has been discussed in detail. The influences of the switches' settings on the noise and the properties of the bit error rate of each demultiplexing channel have also been investigated. It is shown that the power penalty of the demultiplexing module in a serial structure using the nonlinear optical loop mirrors is much lower than that in the parallel structure and it will be very small if the settings of the loop mirrors are carefully chosen     

Linearly polarized er(3+)-doped fiber laser by use of a fiber loop polarizer and a wavelength-selective fiber loop reflector

We demonstrate a novel single-polarization Er(3+)-doped fiber Fabry-Perot laser. The all-fiber Fabry-Perot cavity is simple inasmuch as it is formed by only two fiber-based components, a fiber loop polarizer and a wavelength-selective fiber loop reflector. The threshold power is 6.5 mW, the slope efficiency is 12.2%, and the extinction ratio is approximately 25 dB.     

Broadband dispersion-compensating fiber for high-bit-rate transmission network use

The optimum refractive-index profile and drawing temperature were investigated so as to maximize the figure of merit for multicladding broadband dispersion-compensating fibers. Based on the results of the investigation, the authors have fabricated a highly bend-resistant fiber with a 92.6-ps/(nm dB) figure of merit using the modified chemical-vapor deposition method for dispersion compensation in the 1.5-1.6-μm wavelength region. The manufactured dispersion compensator does not suffer bend loss at 1.55 μm for curvatures of radia of 6.3 and 3.3 cm, and it has a 1.1-dB/km bend loss at a curvature of radius of 1.6 cm. Codoping the germanium silicate core with fluorine diminishes the optical loss down to 0.70 dB/km at a 1.55-μm wavelength.     

光孤子通信系统的色散控制研究

光纤色散特性是支撑光纤孤子通信的决定性因素。比较了目前的几种色散补偿方案后,着重对相位共轭控制的色散控制方式进行了分析研究,该方式利用光纤非线性四波混频产生与输入光脉冲信号相位共轭的输出光脉冲信号,光脉冲的频谱以泵浦光频为中心进行反转,构建成相位共轭器,实现了对放大自发辐射(ASE)噪声、孤子相互作用与色散波等的控制,达到提高系统传输速率、距离和通信容量的目的。     

Nonlinear soliton propagation by use of the split-step reconstruction technique

A split-step reconstruction technique is proposed to solve a nonlinear wave equation. A nonlinear wave equation can be segmented into a set of linear equations that can be solved in the time domain by use of the split-step reconstruction technique. With this technique, one can avoid the propagation errors that occur as a result of nonlinear wave equation splitting. We propose an adaptive mesh control to increase the speed with which nonlinear wave equations can be calculated.     

Enigmas of optical and matter-wave soliton nonlinear tunneling

The method of mathematical analogies opens the possibility to study optical and matter-wave solitons in parallel and, due to the evident complexity of experiments with matter wave solitons, offers remarkable possibilities in studies of the BEC systems by performing experiments in the nonlinear optical systems and vice versa. We discuss previous misinterpretations of the binding soliton energy and investigate all possible scenarios of nonlinear soliton tunneling of Schrödinger solitons including soliton splitting on a potential barrier, leading to partial reflection and partial transmission, sub-barrier soliton tunneling and over-barrier soliton reflection. We reveal the most significant modifications of soliton tunneling scenarios due to increasing the binding energy, and show that the self-compressing soliton resembles more the classical particle case than a quantum mechanical behavior. The enhancement of the soliton binding energy is of decisive importance in the testing of a long-standing theoretical result which predicts that an optical soliton can tunnel between two regions of anomalous dispersion across a forbidden region of normal dispersion (enhanced soliton spectral tunneling effect).     

Supraluminal velocity of a pulse envelope maximum in amplifying optical fiber

Frequency-modulated Gaussian pulse propagation in an amplifying fiber is described within the framework of a linear model with an allowance for the second-order dispersion effects. It is demonstrated that the presence of an imaginary part in the group velocity dispersion parameter of the single-mode optical fiber with luminous gain leads to the possibility of the pulse envelope at a supraluminal velocity.     

Picosecond nonlinear optical studies of unsymmetrical alkyl and alkoxy phthalocyanines

We present our results on picosecond nonlinearities in unsymmetrical alkyl and alkoxy phthalocyanines, studied using the Z-scan technique. Both open and closed aperture Z-scan curves were recorded and nonlinear coefficients were extracted. Solvent contribution to the nonlinearity was identified. We recorded large, off-resonant second hyperpolarizabilities (γ) at 800 nm with estimated values of ∼ 6.5 × 10⁻³¹ esu and ∼ 8.9 × 10⁻³¹ esu for unsymmetrical alkyl and alkoxy phthalocyanines, respectively. Evaluated figures of merit indicate that these are potential molecules for photonic applications.     

Reflection and transmission properties of holographic mirrors and holographic Fabry-Perot filters. I. Holographic mirrors with monochromatic light

The reflection and transmission coefficients of holographic mirrors (HM's) and holographic Fabry-Perot filters (HFPF's) are studied. The diffraction efficiencies, the angular selectivities, and the wavelength sensitivities of HM's and HFPF's and their effects on the spectrum and on the coherence properties of the incident light are investigated. The results show that holographic techniques can indeed be used to construct high-quality reflecting mirrors and Fabry-Perot filters. HM's illuminated by a monochromatic plane wave are investigated in detail. The reflection and transmission coefficients are first studied as functions of frequency (wavelength) of the incident light and also as functions of the angle of incidence. It is shown that HM's can be used as highly reflecting mirrors around their Bragg angle of incidences. Their reflectivity curves have fairly wide angular- and frequency-selectivity ranges.     

Generation of soliton and bound soliton pulses in mode-locked erbium-doped fiber laser using graphene film as saturable absorber

We report an observation of soliton and bound-state soliton in passive mode-locked fibre laser employing graphene film as a passive saturable absorber (SA). The SA was fabricated from the graphene flakes, which were obtained from electrochemical exfoliation process. The graphene flakes was mixed with polyethylene oxide solution to form a polymer composite, which was then dried at room temperature to produce a film. The film was then integrated in a laser cavity by attaching it to the end of a fibre ferrule with the aid of index matching gel. The fibre laser generated soliton pulses with a 20.7 MHz repetition rate, 0.88 ps pulse width, 0.0158 mW average output power, 0.175 pJ pulse energy and 18.72 W peak power at the wavelength of 1564 nm. A bound soliton with pulse duration of ~1.04 ps was also obtained at the pump power of 110.85 mW by carefully adjusting the polarization of the oscillating laser. The formation of bound soliton is due to the direct pulse to pulse interaction. The results show that the proposed graphene-based SA offers a simple and cost efficient approach of generating soliton and bound soliton in mode-locked EDFL set-up.     

Three-dimensional shape measurement of a diffusing surface by use of a femtosecond amplifying optical Kerr gate

We propose a system for three-dimensional (3D) shape measurement of a diffusing surface by use of a previously developed femtosecond amplifying optical Kerr gate (fs-amp OKG). The system has an opening time of 459 fs and a maximum transmittance of 185%. It also provides good 3D imaging performance: a transverse imaging resolution of 70 mum, a depth resolution of 100 mum, and a positioning accuracy of 5.9 mum in depth. It is found that the optical Kerr effect and the amplification process in the fs-amp OKG do not cause the quality of a time-resolved image to deteriorate. We prove the effectiveness of the proposed system by measuring the shapes of completely diffusing objects with stepped and spherical surfaces.     

Two-Dimensional Visualization of Fluorescence Lifetimes by use of a Picosecond Laser and a Streak Camera

Two-dimensional distributions of the effective lifetime of the fluorescence emission induced by short-pulsed laser radiation are obtained from two-dimensional images recorded with a streak camera and a charge-coupled device by means of a separation algorithm method (SAM). In theory, the best response with respect to noise is obtained for lifetimes corresponding to a range of pixels of 5-50 in the CCD, that is, 5-50 ps at the fastest streak speed. In experiments the SAM is compared with pure time-resolved measurements, and it is used for two-dimensional lifetime evaluation. The laser-pulse duration is 25 ps, and the lower limit of the lifetime resolution as used in the experiments is estimated to be 200-250 ps. The results demonstrate the possibility of performing pattern recognition independently of the relative distribution of emission intensity between regions of different fluorescence lifetimes. The technique is demonstrated for static objects but can in principle be extended to nonstationary objects if two detectors are used.     

Reflection and transmission properties of holographic mirrors and holographic Fabry-Perot filters. II. Holographic mirrors with partially coherent light

The reflection and transmission properties of holographic mirrors (HM's) under partially coherent illumination are investigated with emphasis on the properties of reflected light. The effects of a HM on the spectrum and on the coherence properties of partially coherent incident light are studied. We show that within angular and frequency-selectivity ranges of HM's (where their reflectivities are nearly uniform), the changes in the spectrum and in the coherence properties are negligible. Yet changes are expected when the spectrum of the incident light falls beyond frequency-selectivity ranges of the HM's or when the spectrum of the reflected light is observed beyond the angular-selectivity ranges of the mirrors. We illustrate the results by considering in detail the performance of HM's when the incident light is produced by planar secondary Gaussian Schell-model sources. Some computed curves are presented.     

Symmetric operating point for increasing the extinction ratio of semiconductor based optical loop mirrors

Terahertz optical asymmetric demultiplexors (TOADs) use a semiconductor optical amplifier in an interferometer to create an all-optical switch and have potential uses in many optical networking applications. Here we demonstrate and compare experimentally a novel and simple method of dramatically increasing the extinction ratio of the device using a symmetrical configuration as compared to a ‘traditional’ configuration. The new configuration is designed to suppress the occurrence of self-switching in the device thus allowing signal pulses to be used at higher power levels. Using the proposed configuration an increase in extinction ratio of 10 dB has been measured on the transmitted port whilst benefiting from an improved input signal power handling capability.     

Image transmission and radiation by truncated linearly polarized multimode fiber

We study the use of individual multimode fibers for the purposes of microendoscopy. We discuss the question of image decomposition in the several modes propagating over the fiber and their scattering at the truncated fiber end. We derive analytically the scattering matrix of the "fiber-to-air" interface, we quantify the extent of intermodal coupling, and we evaluate the radiation diagram from the fiber end. Results show that intermodal coupling is weak, so that it appears possible to "capture" an external image and transmit the same through the fiber, after appropriate phase correction, without excessive distortion.     

Co-sputtering of aluminum-silver alloy mirrors for use as solar reflectors

Reflective coatings for solar energy applications need to have a high reflectivity that does not degrade significantly on exposure to the atmosphere. In theory aluminum-silver alloys could have some of the desirable characteristics for possible use as solar reflectors. This work describes the parameters necessary to produce adherent aluminum-silver alloy films with continuous compositional gradients. The composition profiles of the films were obtained from microprobe and X-ray diffraction analyses. A metallographic examination showed the structure of the films.