Reconstruction of the characteristics and determination of the parameters of a statistical surface roughness from light scattering data in an integrated waveguide in the presence of noise

A computer simulation is used to obtain the solution to the direct and inverse problems of the waveguide scattering of laser radiation by a stationary statistical surface roughness of the substrate of an integrated optical waveguide in the presence of additive or multiplicative white noise. It is shown that the procedure developed for processing far-field scattering data is capable of providing the necessary information on the statistical properties of the surface roughness even when the signal-to-noise ratio is very low (SNR≈1). For a given additive or multiplicative noise with SNR≥1, the proposed method allows one, in the model calculations, to reconstruct the autocorrelation function with an error within 50–80% when the roughness correlation interval varies from λ/50 to 10λ (correspondingly). In this case, the correlation interval can be determined with an error no greater than 10–30%, and an rms height of the order of 1–500 Å, with an error less than 5–15%.     

Femtosecond pulse generation using stimulated Raman scattering in integrated silicon optical waveguide device

To generate ultrafast femtosecond optical pulses, we propose a model of an integrated device consisting of a Mach-Zehnder interferometer (MZI) with two symmetric 3 dB directional couplers and a straight waveguide based on the single-mode silicon-on-insulator (SOI) optical waveguide. The principle of pulse generation in the presented device is based on the strong stimulated Raman scattering (SRS) in silicon; the center wavelength of the pulse generated is tunable by changing the center wavelength of the co-propagating pump pulse. Numerical results show that, when a continuous wave (CW) with a weak power at 1670 nm wavelength and a pump pulse with a high peak power at 1550 nm wavelength are co-propagating, a narrow femtosecond pulse with a pulse width (full width at half maximum, FWHM) of ∼60 fs (FWHM of the pump pulse is 166.5 fs) can be achieved in the device proposed. In addition, when the waveguide length, pump peak power, and pump-pulse width are fixed, the properties of generated femtosecond pulse depend strongly on the incident chirp of the pump pulse and the CW power.     

Polarization modulation of light in an optical waveguide under lateral compression

It is shown that a lateral pressure applied to a circular single-mode optical waveguide changes the phase difference between two orthogonally polarized modes and thereby modulates the polarization state of light (elastooptic effect). The efficiency of polarization modulation is characterized by a strain-to-phase difference conversion factor as applied to polarization modes of the fiber. An expression relating the phase difference between the modes and the displacement of squeezing plates is obtained and checked in real experiments and numerically. The efficiency of conversion of lateral pressure to phase difference between the polarization modes is shown to be fairly high, on the order of 10⁴ rad/(μm m).     

Reduced quantum noise in waveguide coherent Raman scattering spectroscopy

Waveguide regimes of nonlinear-optical interactions allow a reduction of quantum noise in spectra of coherent Raman scattering (CRS). We will find the optimal waveguide length providing the maximum quantum limit for the signal-to-noise ratio in waveguide CRS and assess this ratio for laser intensities right below the optical breakdown threshold. This analysis shows that the quantum-limit signal-to-noise ratio of coherent femtosecond CRS spectroscopy of the gas phase can be increased in the waveguide regime by more than four orders of magnitude relative to the regime of tight focusing.     

Acousto-optic light deflection in an Al2O3 optical waveguide structure

The total deflection of an optical guided wave by a surface acoustic wave (SAW) in a silicon-based SiO₂/AL₂O₃/SiO₂ optical waveguide structure is reported. The SAW is generated by an interdigital transducer with piezoelectric ZnO deposited on top of the optical waveguide structure.     

Acousto-optic light deflection in an Al2O3 optical waveguide structure

The total deflection of an optical guided wave by a surface acoustic wave (SAW) in a silicon-based SiO₂/AL₂O₃/SiO₂ optical waveguide structure is reported. The SAW is generated by an interdigital transducer with piezoelectric ZnO deposited on top of the optical waveguide structure.     

Polymer optical waveguide based on integrated optics

The fabrication and characterization of refractive index profiles of multimode mode polymer optical waveguides is reported. Effect of annealing temperature on guided losses of polymer (polystyrene) thin film optical waveguide is also presented. Efficient coupling over a 110 nm spectral bandwidth was experimentally demonstrated with a prism-coupler designed to match the dispersion of a particular waveguide.     

纳米集成光路中的光源、光波导和光增强

使用近场光学显微术(scanning near-field optical microscopy, SNOM)研究了ZnO亚微米线端面出射性质,不同空间形貌Ⅱ-Ⅵ族半导体荧光器件光波导特性,二维光子晶体、准晶光子晶体对LED的出射增强作用以及表面等离激元(surface plasmon polariton, SPP)与半导体纳米荧光器件的相互作用,对纳米集成光路中的光源、光波导、光增强三个重要问题做了实验和理论上的分析.研究发现半导体微纳米线端面出射光束的质量与样品的直径有密切关系.通过合理地设计其直径和 关键词： 纳米集成光路 扫描近场光学显微术 光波导 光增强     

纳米集成光路中的光源、光波导和光增强

使用近场光学显微术(scanning near-field optical microscopy, SNOM)研究了ZnO亚微米线端面出射性质，不同空间形貌Ⅱ-Ⅵ族半导体荧光器件光波导特性，二维光子晶体、准晶光子晶体对LED的出射增强作用以及表面等离激元(surface plasmon polariton, SPP)与半导体纳米荧光器件的相互作用，对纳米集成光路中的光源、光波导、光增强三个重要问题做了实验和理论上的分析.研究发现半导体微纳米线端面出射光束的质量与样品的直径有密切关系.通过合理地设计其直径和     

Theory of noise in optical amplifiers

We show that the classical model of the amplifier noise can well describe the amplifier-noise characteristics and that the signalgain, the spontaneous emission factor, and the optical bandwidth are all the information necessary for analyzing the amplifier-noise characteristics. The accumulation of noise in the amplifier chain is also discussed in detail.     

利用受激布里渊散射在光纤中实现光存储

利用有限差分法在慢变包络近似下求解了耦合波方程组,并从理论上实现了短光脉冲的存储。研究了数据脉冲的读出效率随声子寿命、布里渊增益系数、数据脉冲强度和控制脉冲强度的变化规律。结果显示:在长声子寿命的条件下,可以获得高的读出效率和长的存储时间,而布里渊增益系数和数据脉冲强度对读出效率没有影响;增大布里渊增益系数可以降低所需控制脉冲的强度。这种方法对短脉冲可以实现有效存储,而对长脉冲不能实现存储。     

Theory of light scattering from rough surfaces and interfaces and from volume inhomogeneities in an optical layer stack

Abstract

A theoretical method is described for calculating the bidirectional scattering characteristic for any given thin-film multilayer geometry in which the surfaces and interfaces are assumed to be rough, and where statistical inhomogeneities in the optical permittivities may also exist in each layer. The light energy scattered in any direction depends on geometrical thickness, the permittivities of the ideal layer stack and also on the corresponding auto- and cross-correlation functions. The expressions that are obtained for the scattered field are completely general in the sense of the Born approximation of first order in the imperfections and the exciting fields. The contributions of interface and volume scattering can be assumed arbitrarily because both are derived in a unique way. The main new result consists in the occurrence of four different possibilities of coupling between the scattered and exciting waves due to the standing wave character of both light waves. It is easy to show that the case of a columnar structure reduces the theoretical effort and leads to a similarity of this volume case to that of normal interface scattering. The matrix formalism used in analogy to the normal calculations of reflection and transmission coefficients allows a simple physical interpretation of the light propagation through the layer system and straightforward numerical calculations.     

Theory of light scattering from rough surfaces and interfaces and from volume inhomogeneities in an optical layer stack

A theoretical method is described for calculating the bidirectional scattering characteristic for any given thin-film multilayer geometry in which the surfaces and interfaces are assumed to be rough, and where statistical inhomogeneities in the optical permittivities may also exist in each layer. The light energy scattered in any direction depends on geometrical thickness, the permittivities of the ideal layer stack and also on the corresponding auto- and cross-correlation functions. The expressions that are obtained for the scattered field are completely general in the sense of the Born approximation of first order in the imperfections and the exciting fields. The contributions of interface and volume scattering can be assumed arbitrarily because both are derived in a unique way. The main new result consists in the occurrence of four different possibilities of coupling between the scattered and exciting waves due to the standing wave character of both light waves. It is easy to show that the case of a columnar structure reduces the theoretical effort and leads to a similarity of this volume case to that of normal interface scattering. The matrix formalism used in analogy to the normal calculations of reflection and transmission coefficients allows a simple physical interpretation of the light propagation through the layer system and straightforward numerical calculations.     

利用受激布里渊散射在光纤中实现光存储

利用有限差分法在慢变包络近似下求解了耦合波方程组,并从理论上实现了短光脉冲的存储。研究了数据脉冲的读出效率随声子寿命、布里渊增益系数、数据脉冲强度和控制脉冲强度的变化规律。结果显示：在长声子寿命的条件下,可以获得高的读出效率和长的存储时间,而布里渊增益系数和数据脉冲强度对读出效率没有影响;增大布里渊增益系数可以降低所需控制脉冲的强度。这种方法对短脉冲可以实现有效存储,而对长脉冲不能实现存储。     

Effect of noise on characteristics of optical waveguide systems

Transient regimes of an optical waveguide system in the presence of additive and multiplicative noises are studied. The presence of noise is shown to result in a transformation of the spectrum of radiation modes. The effect of noise on the efficiency of input of electromagnetic energy into a waveguide system is studied.     

Rh-B doped polymeric optical waveguide for integrated optics

A systematic study of fabrication and characterization of rhodamine-blue (Rh-B) doped polystyrene waveguide is presented. Optical absorption and mode effective refractive index measurement was performed on the waveguides fabricated on glass substrate prepared by dip coating technique. It is observed that doping of dye increase the index of refraction of waveguides. The losses, however, decrease initially for dye concentration upto 0.1% and thereafter increase rapidly.     

Inverse problem of scattering of monochromatic light in a statistically irregular waveguide: Theory and numerical simulation

The inverse linear problem of the theory of waveguide scattering of monochromatic light for noisy and pure input data is studied. Under natural physical and mathematical constraints on the measured scattering diagram, a correct analytical solution of the formulated inverse problem in a statistically irregular waveguide is obtained for the case of integral and differential scattering. The results of numerical simulation are presented and discussed.     

Rayleigh backscatter noise in integrated optical resonance gyro

Rayleigh backscatter noise in integrated optical resonance gyroscope (IORG) is researched both in theoretically and experimentally. The characteristics of Rayleigh backscatter noise in the resonator of SiO₂ on Si substrate are formulized, and the static state and dynamic state models of IORG are constructed. The relationship between the optical signal and Rayleigh backscatter noise is simulated, and the affection between the interference signal of Rayleigh backscatter noise and reverse optical signal is also calculated. The degree of degrading the performance of resonator due to Rayleigh backscatter noise is analyzed, such as finesse and fundamental detection limit. The relationship between the line-width of the tunable laser and the intensity of transmit light and Rayleigh backscatter noise is simulated. Through the theory of modulation, the method of inflicting two different frequencies to the arm of integrated optical modulator is presented. The verified experiment result showed that the saw-tooth wave modulation could effectively restrain Rayleigh backscatter noise in IORG.     

Modulation instability of pulsed radiation in an optical waveguide in the presence of the traveling refractive index wave

The conditions for the onset of modulation instability of wave packets in an optical waveguide in the presence of the traveling refractive index wave are investigated. An expression governing the growth rate of a small harmonic perturbation at the early development stage of the modulation instability is obtained. Based on numerical analysis, the behavior of the wave packet at the developed modulation instability stage is studied for different parameters of the waveguide and the refractive index wave.