Full-wave modal analysis of the rectangular waveguide grating

Dispersion characteristics of the rectangular waveguide grating for microwave amplifier applications are studied for the first time in the rigorous mathematical manner on the basis of the singular integral equation (SIE) method. In particular, the validity of the simplified approach is discussed by comparing the results obtained by both methods. Numerical results show that the dispersion curves obtained by the SIE method are in surprisingly good agreement with those obtained before. Additionally, it has been pointed out that there exists some regime where the differences between the SIE and simplified treatments become notable     

Dual resonance in a long-period waveguide grating

We fabricated a specially designed polymer long-periodwaveguide grating to demonstrate the phenomenon of dual resonance arising from light coupling between the core mode and a low-ordercladding mode of the waveguide. By varying the temperature of the grating, we observed the onset and the evolution of the dual-resonancewavelengths. The separation between the dual-resonancewavelengths was varied by ∼110 nm with a temperature variation of ∼10 °C. The experimental results are explained well by the simulation results. PACS 42.79.Dj; 42.79.Gn     

Multilayer resonances sharpened by grating waveguide resonance

A multilayer planar structure comprising a highly reflective multilayer dielectric mirror and a corrugated waveguide is proposed for use as a narrow passband optical filter. The proposed filter has a much narrower linewidth than a usual Fabry–Perot cavity with two multilayer dielectric mirrors. It is shown that the narrowing of the linewidth is due to the strong spectral dependence of the phase of the wave reflected from the waveguide grating mirror. The shape of the pass band can be made symmetrical by a proper choice of the grating groove profile.     

Design of a high-speed optical dark-soliton detector using a phase-shifted waveguide Bragg grating in reflection

A theoretical study of a new application of a simple pi-phase-shifted waveguide Bragg grating (PSWBG) in reflection mode as a high-speed optical dark-soliton detector is presented. The PSWBG consists of two concatenated identical uniform waveguide Bragg gratings with a pi phase shift between them. The reflective PSWBG, with grating reflectivities equal to 0.9, a free spectral range of 1.91 THz, and a nonlinear phase response, can convert a 40 Gbit/s noisy dark-soliton signal into a high-quality 40 Gbit/s return-to-zero signal with a peak power level of approximately 17.5 dB greater than that by the existing Mach-Zehnder interferometer with free spectral range of 1.91 THz and a linear phase response.     

A reflection interferometer with a noninverted response function based on a phase grating

It is shown that the inclusion of a simple phase grating in the optical scheme of a resonator provides the possibility of performing spectral investigations in reflected light with characteristics of a Fabry-Perot interferometer. The response function of the interferometer is examined, and experimental results are presented.     

Modelling of the surface plasmon resonance waveguide sensor with Bragg grating

The operation of a novel device – a waveguide surface plasmon resonance sensor with a UV-written Bragg grating – is theoretically analysed using two methods. In the simple perturbation approach, the metal/dielectric layer system supporting the resonance excitation of the surface plasma wave is considered to be a perturbation of the original dielectric waveguide with Bragg grating that is analysed using a coupled-mode theory. The second approach consists of the rigorous method of bi-directional mode expansion and propagation using the Floquet mode formalism developed recently for the analysis of waveguide grating structures. The results of both approaches are mutually compared, and the operation characteristics of this novel sensing device are briefly described.     

Electromagnetically induced phase grating controlled by spontaneous emission

Electromagnetically induced phase grating controlled by spontaneous emission is studied. The results show that the diffraction efficiency of phase grating is strikingly enhanced due to the existence of spontaneously generated coherence (SGC), and the diffraction efficiency of 35% can be obtained in optimal SGC parameter case. Furthermore, at large SGC parameter, the high efficiency of phase grating can be maintained by the application of weak coupled and relatively strong probe fields, and choosing the proper length of atomic sample. At the same time, in such an atomic system, the SGC effect depends on incoherent pump.     

Giant enhancement of two-photon fluorescence induced by resonant double grating waveguide structures

We report a 350-fold enhancement of ultra-short-pulse-excited two-photon fluorescence (TPF) using a resonant double grating waveguide structure (DGWS). These structures show vanishing transmission and maximum reflection under resonance conditions, i.e. specific wavelength, polarisation and angular orientation of the incident light. This guided mode phenomenon is characterised by a large field enhancement inducing an enormous TPF signal of fluorescent molecules at the waveguide surface, as compared to direct non-resonant excitation. We demonstrate that high spectral acceptance for ultra-short pulses with broad spectral bandwidths can be achieved by a specifically designed DGWS, and that neither beam focussing nor high laser power is necessary for TPF excitation. Due to the high enhancement of more than two orders of magnitude, DGWS can be considered as a powerful platform for TPF applications such as biosensing and microarray technology. PACS 42.62.Be; 42.79.Dj; 42.79.Gn     

Resonant modal conversion in a two-mode waveguide

We characterize a system consisting of a two-mode waveguide coupled to a single-mode microring resonator possibly presenting a nonlinear response of Kerr type. By using the scattering parameter formalism extended to the multimode domain, we show that in the linear regime and for an ideally transparent medium, each resonance of the system can be exploited to perform complete even-to-odd (respectively, odd-to-even) modal conversion. Moreover, when the Kerr nonlinearity is effective, the microring enables a power-dependent modal switching mediated by phase bistability. Thanks to its mode-processing capabilities, this configuration is suitable to find application as a functional building-block in mode-division multiplexing (MDM) photonic integrated circuits.     

Autocollimation reflection by a ribbon grating with a screen

Institute of Radiophysics and Electronics, Academy of Sciences of the Ukrainian SSR. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 33, No. 3, pp. 348–356, March, 1990.     

Experimental study of the resonance reflection of a plane electromagnetic wave from a wide-spaced strip grating

The resonance reflection of a plane electromagnetic wave from a diffraction grating consisting of wide-spaced, thin, tilted metal strips is confirmed and investigated experimentally. Good agreement is obtained between the experimental results and published theoretical data. Zh. Tekh. Fiz. 68, 138–140 (May 1998)     

Method for measuring the phase error distribution of a wideband arrayed waveguide grating in the frequency domain

We describe a method for measuring the phase error distribution of an arrayed waveguide grating (AWG) in the frequency domain when the free spectral range (FSR) of the AWG is so wide that it cannot be covered by one tunable laser source. Our method is to sweep the light frequency in the neighborhoods of two successive peaks in the AWG transmission spectrum by using two laser sources with different tuning ranges. The method was confirmed experimentally by applying it to a 160 GHz spaced AWG with a FSR of 11 THz. The variations in the derived phase error data were very small at +/-0.02 rad around the central arrayed waveguides.     

Loss in a rectangular optical waveguide induced by the crossover of a second waveguide

We calculate the loss induced in a single-mode rectangular optical waveguide by the presence of a second waveguide, perpendicular to the first, which crosses over the first waveguide at a variable distance d. Our calculation is applied to the analysis of several doped silica waveguides of practical importance for optical circuit design.     

Sound reflection by a resonator array in a multimode cylindrical waveguide

The paper considers the problem of scattering of the mth symmetric mode by an array of Q rings of identical, closely located Helmholtz resonators joined by necks to the walls of a wide circular pipe. The distance between rings is equal to half the wavelength of this mode at frequency ??, equal or close to the eigen-frequency of the resonator ring with allowance for the connected mass and interaction of neighboring rings via inhomogeneous modes. The coefficient of reflection of the mth mode from this grating array is calculated.     

Spectral interferometric technique to measure the relative phase change on reflection from a thin-film structure

A two-step white-light spectral interferometric technique to measure the relative phase change on reflection from a thin-film structure is presented. The technique is based on recording of the channeled spectra at the output of a Michelson interferometer and their processing by using a windowed Fourier transform to retrieve the phase functions. In the first step, the phase difference between the beams of the interferometer with a thin-film structure is retrieved. In the second step, the structure is replaced by a reference sample of known phase change on reflection and the corresponding phase difference is retrieved. From the two phase differences, the relative phase change on reflection from the thin-film structure is obtained. The feasibility of the simple method is confirmed in processing the experimental data for a SiO₂ thin film on a Si wafer of known optical constants. Four samples of the thin film are used and their thicknesses are determined. The thicknesses obtained are compared with those resulting from reflectometric measurements, and good agreement is confirmed.     

Analysis of a deep waveguide Bragg grating

Spectral properties of a very deep Bragg grating operating in a first diffraction order on a single-mode planar waveguide have been studied theoretically. It is shown that the scattering loss can be low (a few percent), the reflectivity very high (over 90%), the reflection band is shifted against the Bragg wavelength toward the shorter wavelengths, and its spectral shape is very different from that of a shallow grating. Inside a reflection band, a part of the input optical power penetrates through the grating even if it is infinitely long. These properties are predicted by modelling using two independent computer codes based on different modelling methods, namely the bi-directional mode expansion and propagation method (BEP), and a method of lines (MoL). The first method is discussed in some detail here. The work has been performed within the framework of European Action COST 240.     

Anomalous behaviour in a Bragg reflection waveguide

A novel asymmetric Bragg reflection waveguide (BRW) showing anomalous dispersion characteristic is presented. The abnormal behaviour of increase of modal effective index with wavelength is primarily caused by the changes taking place in the imaginary part of the Bloch wavevector, in the periodic stratified cladding. The phase velocity and the group velocity dispersion characteristics for the waveguide have also been analyzed. Such an anomalous behaviour can find applications in the design of integrated optical devices.     

System degradation due to phase error induced crosstalk in WDM optical networks employing arrayed waveguide grating multi/demultiplexer

The phase error induced crosstalk within arrayed waveguide gratings (AWG) have been investigated theoretically as well as simulation. For WDM system, a crosstalk level of −21.9 dB causes a power penalty of 1 dB for 64 channels and less than 0.5 dB for 16 channels and 32 channels, respectively. For crosstalk level of −30 dB and below, the power penalty is negligible. Crosstalk due to phase error also causes higher power penalty at higher bit rate. Bit rate of 10, 20 and 40 Gbits/s causes power penalty of 1 dB with crosstalk level of −41.5, −46.25 and −49 dB, respectively.     

Measurement of the nonlinear phase shift induced by cascaded interactions in a periodically poled lithium niobate waveguide

We report on the measurement of nonlinear phase shift phiNL induced by a strong pump at wavelength lamda p on a weak signal at lamda s through a cascade of two second-order interactions in a periodically poled lithium-niobate waveguide. The experiment is performed by use of an interferometric scheme especially designed to be insensitive to slow mechanical and thermal drift effects. The observed behavior of phiNL as a function of pump power and of wavelength difference lamda p - lamda s, is in good agreement with the theoretical predictions.     

Expected performance of waveguide grating routers in the presence of random phase and amplitude errors

The expected waveguide grating router response is calculated analytically in the presence of random, uncorrelated phase and amplitude errors. It is shown that the expected crosstalk, as well as the standard deviation of the crosstalk power, is indirectly proportional to the number of grating arms.