Phase Sensitivities of Optical Fibre Ring and Loop Resonators Using a Non-planar or Planar 3 × 3

Abstract

A comparison is made between computed phase sensitivities of the output intensities of twelve different types of optical fibre single-loop resonators using a non-planar or planar (collinear) 3 × 3 fibre coupler. The dependence of the phase sensitivities on major parameters of the fibre and the 3 × 3 fibre coupler is investigated. It is found that four types of fibre resonators (the PFPOFR1, PFPOFL5, TFPOFR and PFPOFR3) have high phase sensitivities (they are the highest phase sensitivities among many passive fibre ring and loop resonators with one to two 2 × 2 or 3 × 3 fibre couplers), while those of the rest are relatively small. These four types of fibre resonators may therefore be used as optical sensors.     

Output Characteristics of an Optical Fibre Ring Resonator Using a Planar or Nonplanar 3 × 3 Fibre Coupler: A Comparison

Abstract

A comparison is made between the output characteristics of type 1 optical fibre ring resonators with a different type of 3 × 3 fibre coupler, that is a planar or a nonplanar coupler. Three different nonplanar couplers are formed when the central fibre 1 of a loosely coupled planar 3 × 3 fibre coupler is displaced normally from the common plane. Such a 3 × 3 fibre coupler can be identified by the value of its relative coupling ratio m ₃. The dependence of the output intensities of the ring resonator on the coupling length kd and the relative coupling ratio m ₃ of the 3 × 3 fibre coupler is investigated. The former dependence can be used as a guide to obtain suitable output characteristics of a fibre ring resonator for a specific application, while the latter can be used to choose the right type of 3 × 3 fibre coupler to build a fibre ring resonator. It is found that the output characteristics of a fibre ring resonator with a 3 × 3 planar (m ₃ = 0) or an equilateral triangular (m ₃ = 1) fibre coupler are usually better than those of the others.     

Analysis and Comparison of Birefringent Fibre Ring Resonator Types

Abstract

We present a theoretical model that can be used to determine the output of fibre ring resonators made with birefringent fibre, and with different types of polarization-selective or polarization-insensitive couplers. We derive tolerances for the coupler polarization crosstalk, splice alignment, and input polarization mode purity necessary for optimum operation of each type.     

Design of a compact dual-mode ring resonator bandpass filter with harmonic suppression

Abstract

An approach to suppress the harmonic responses in a dual-mode circular ring resonator bandpass filter is presented. Feed lines with one-sided coupling arms are suitably relocated around the ring resonator to introduce phase interference between two degenerate modes for simultaneously suppressing the second and third harmonics. Three open loop resonators at the rim of the ring are adopted to further suppress the second harmonic. By fabricating on a FR4 glass-epoxy base, this approach is demonstrated to have effectiveness in broadening the filter's rejection band in both simulations and measurements without affecting the fundamental response or increasing the device size.     

Transfer characteristics and propagation effects of a multi-resonance ring resonator-based optical device

Abstract

We describe the linear and nonlinear optical transfer characteristics of a multi-resonance device consisting of two optical ring resonators coupled one to the other and to an optical waveguide. The propagation effects displayed by the device are compared with those of a sequence of fundamental ring resonators coupled to a waveguide.     

Coherence phenomena in coupled pptical resonators

Abstract

We predict a variety of photonic coherence phenomena in passive and active coupled ring resonators. Specifically, the effective dispersive and absorptive steady-state response of coupled resonators is derived, and used to determine the conditions for coupled-resonator-induced transparency and absorption, lasing without gain, and cooperative cavity emission. These effects rely on coherent photon trapping, in direct analogy with coherent population trapping phenomena in atomic systems. We also demonstrate that the coupled-mode equations are formally identical to the two-level atom Schrödinger equation in the rotating-wave approximation, and use this result for the analysis of coupled-resonator photon dynamics. Notably, because these effects are predicted directly from coupled-mode theory, they are not unique to atoms, but rather are fundamental to systems of coherently coupled resonators.     

Analysis of a Fibre-optic Ring Resonator with Polarization Effects: Application to Polarization Sensing with Improved Sensitivity

Abstract

A theoretical analysis for a fibre-optic ring resonator is given by assuming a polarization modulation in the loop fibre. If the change in polarization angle θ in the loop is large, the output intensity has two resonance dips separated in phase by an angle equal to 2θ, when the loop phase is scanned from 0 to 2π. When θ is small, the resonator output produces only one resonance dip and the amplitude of this resonance dip is a measure of θ. By placing a polarizer at the resonator output, a resonance peak in the intensity is produced with an amplitude that increases with increasing θ. Such a system has potential applications, for example, in Faraday current sensing, with an increased sensitivity. The effects of birefringence in the loop and the angle of polarization of the input light are also analysed.     

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.     

Transmission performance of one waveguide and double micro-ring resonator using 3×3 optical fiber coupler

Abstract

This paper investigates theoretically the transmission characteristics of one waveguide and double micro-ring resonator using 3 × 3 optical fibre coupler. Our analytical solution of transmittance is suitable for either linearly distributed coupler or circularly symmetric distributed coupler. The all-optical analogue to electromagnetic inducted transparency spectrum of one waveguide and double micro-ring resonators can be controlled by changing the coupling strength between waveguide and micro-rings, the absorption coefficient around micro-rings, as well as the asymmetric coupling coefficients between non-adjacent waveguides. The curves show that the transitions of transmission spectra sensitively depend on asymmetric coupling coefficients.     

Spectral Filtering Effect of Fused Fibre Couplers in Femtosecond Fibre Soliton Lasers

Abstract

A fused fibre coupler has been used as a spectral filter in a femtosecond fibre soliton laser to eliminate the spectral sideband structure associated with periodic amplification of solitons in the regime where the characteristic soliton period of the generated pulses approaches that of the overall fibre laser loop length.     

Towards cost effective manufacturing of Ti/SiC fibre composites and components

Abstract

Titanium/silicon carbide fibre composites offer an excellent combination of weight specific properties and are ideal for many components in gas and steam turbine engines. However, potential industrial applications are hampered by the relatively high cost of the materials. This paper critically examines the characteristics of various manufacturing or processing routes for such composites, including well developed processes, such as foil–fibre–foil, physical vapour deposition, and vacuum plasma spraying, and new slurry powder metallurgy processes currently being developed. For a given manufacturing route, composite properties are enhanced if the material possesses uniform fibre distribution and a low oxygen content and is free from fibre/matrix interface reactions, residual voids, and fibre damage. The capabilities of the above processes in satisfying these requirements are compared and discussed. Possibilities of reducing product costs are analysed. Several ways of improving the cost effectiveness of mamifacturing such composites are outlined.     

Quantum Cryptography Using Polarization Feedback

Abstract

A system for quantum cryptography using polarization-preserving optical fibre and a feedback loop to compensate for time-dependent changes in the state of polarization has been implemented. Error rates of less than 0·5% have been demonstrated and much lower error rates can be expected in the future. An improved system that does not require the use of polarization-preserving fibre, and with expected data transmission rates of 100 kHz, is under construction.     

Dual wavelength demultiplexer based on metal–insulator–metal plasmonic circular ring resonators

Abstract

In this paper, we investigated a plasmonic demultiplexer structure based on Metal–Insulator–Metal (MIM) waveguides and circular ring resonators. In order to achieve the structure of demultiplexer, two improved ring resonators have been used, which input and outputs MIM waveguides coupled by the ring resonators. To improve the transmission efficiency, a reflector was introduced at the right end of the input and output waveguides. By substituting the ring core with dielectric, the possibility of tuning the resonance wavelength of the proposed structure is illustrated, and the effect of various parameters such as radius and refractive index in transmission efficiency is studied in detail. This is useful for the design of integrated circuits in which it is not possible to extend the dimension of the ring resonator to attain a longer resonance wavelength. Transmission efficiency and quality factor of the single ring are 84% and 110, respectively. The simulation results using finite difference time domain method shows that in the proposed demultiplexer, which is composed of two rings with different core refractive indexes, the average power efficiency, bandwidth for each output channel, and the mean value of crosstalk are estimated 80%, 17 nm, and ?26.95 dB, respectively. It is revealed that the significant features of the device are high transmission efficiency, low crosstalk, high-quality factor, and tunability for desired wavelengths. Therefore, the proposed structure has the potential to be applied in plasmonic integrated circuits.     

Analysis of optical-fiber loop resonators with a collinear 3 × 3 fiber coupler

A theoretical analysis is presented of an optical-fiber loop resonator with a collinear (planar) 3 × 3 fiber coupler in which the cores of the three fibers inside the coupler lie in the same plane. Six different types of the fiber loop resonator (types 1-6) can be constructed in conjunction with different inputs. Expressions for the circulating (resonant) and output intensities and resonance conditions of the six types are derived. Performance parameters such as finesse, cross talk, and maximum output intensity are evaluated when these fiber loop resonators are used as spectral filters and as closely spaced two-channel wavelength-division multiplexerdemultiplexers. Computed results indicate that full resonances cannot be reached simultaneously for both output intensities and that, in general, the output characteristics of the type 5 loop resonator are the best, followed by those of type 6.     

Smart piezoelectric Fibre composites

Abstract

Piezoelectric materials are capable of actuation and sensing and have found uses in applications including ultrasonic transducers, hydrophones, micropositioning devices, accelerometers, and structural actuators. A composite configuration for structural actuation having significant advantages over conventional piezoelectric actuators has been conceived, and the recent development of piezoelectric ceramic fibres < 100 μ m in diameter has enabled this concept to be realised. It is envisaged that these composites will find uses in contour control, non-destructive testing, vibration suppression, and noise control. The possibility of computer control using closed loop systems has led to these composites emerging as potential 'smart' materials and structures. Since their conception, less than a decade ago, significant advances have been made in many areas concerned with composite performance, such as fibre and matrix technology and configuration optimisation. These advances are charted, the fibre, matrix, and electrode technologies are reviewed, and the manufacture, modelling, and applications of these new piezoelectric composites, known as active fibre composites, are discussed.     

One-dimensional chain of maps with unidirectional threshold coupling

A study is made of a loop of logical transformations, semi-infinite or closed in a ring, with a fundamentally new type of coupling, which we call unidirectional threshold coupling. The chain is a unidirectional series-coupled union of bistable elements, whose switching from one state to the other requires a finite time. Pis’ma Zh. Tekh. Fiz. 23, 61–66 (March 26, 1997)     

Multiplexed Fibre-optic Sensors Using Ring Interferometers

Abstract

We describe a number of multiplexing techniques which may be used for fibre-optic sensors in which the sensing element is a ring resonator. The basic optical unit comprises a sensing ring resonator connected to a second interrogating ring resonator of nearly equal length, and illuminated by a source of short coherence length. A number of such units may be combined to form an array, using coherence multiplexing techniques. Using such an arrangement, the high finesse of the ring resonator may be exploited to yield a sensor of increased sensitivity over that obtainable with a two-beam interferometer. When a high-coherence source is used, then multiplexing may be accomplished using frequency-division techniques. However, in this case, the resonators must have low finesse, in order to avoid cross-talk. We also show that when a source of moderate coherence length is used, it is possible to use both frequency division and coherence multiplexing simultaneously, with the potential of realizing a large sensor array.     

Planar HTS structures for high-power applications in communication systems

The use of rotational symmetric modes of superconductive disk (ring) resonators in order to increase the power handling capability of planar filters has been proposed. Several YBCO disk resonators on LaAlO₃ and sapphire substrates have been measured as one- and two ports. The unloaded Q-factor of the resonators has been measured to be greater than 10⁵ up to the oscillating power of 50 kW. Experimental results obtained show that a disk resonator can be used as a building block for low insertion loss, sharp skirt high-power planar filters at low GHz frequency range and temperatures of around 60 K.     

Study of Periodic Intensity Profiles by Fourier Transform of the Time-interval Probability Measurement: Application to Lifetime Measurements

Abstract

In this paper a general study is made to find out the possibility of obtaining information about a periodic intensity profile from the measurement of the Fourier transform of the time-interval probability (FT-TIP). It is found that information can be obtained for small intensities. FT-TIP is then applied to fluorescence decay spectroscopy and it is shown, by a computer simulation method, that lifetimes can be measured with small errors for very small intensities.     

Drift of an Optical Fibre Gyroscope Caused by the Faraday Effect and Its Reduction by Use of a Polarizing Fibre

The drift of fibre gyroscopes caused by a magnetic field via the Faraday effect is formulated in a simple model with a polarizing fibre as a sensing loop. It is found that polarizing fibre, which has a extremely large loss difference between two polarization modes, can make the drift less than that with polarization-maintaining fibre. In this case, the drift is inversely proportional to the square of the loss difference. Although currently available polarizing fibre must be improved to have a larger loss difference, by using such a polarizing fibre or an absolute single-polarization fibre, we can reduce the requirement for shielding the magnetic field and/or the way of winding the sensing loop. The use of these fibres is attractive for applications that demand ultra-low drift, for example, geophysical applications.