Amplified double recirculating delay line using a 3×3 coupler

We propose the use of a 3×3 coupler as a signal divider to implement an amplified double recirculating delay line. We describe the circuit layout and provide a subsequent analysis leading to the computation of its transfer function under general arbitrary conditions. The different conditions in which the structure can be operated, their effect on the overall transfer function, and stability conditions are also addressed. The use of the amplified double recirculating delay line as a building block to implement more complex filters is also considered     

Analysis of four-port optical fiber ring and loop resonators usinga 3×3 fiber coupler and degenerate two-wave mixing

A theoretical analysis of four-port optical fiber ring and loop resonators using a 3×3 fiber directional coupler and degenerate two-wave mixing is presented. Expressions for the circulating (resonant) and output fields and intensities, as well as resonance conditions for two slightly different configurations of the loop resonator and for the ring resonator are obtained. It is found that the use of the degenerate two-wave mixing greatly improves the characteristics of these resonators. For example, the crosstalk of the ring or loop resonators when used as a wavelength division demultiplexer can be significantly deduced     

A Vernier fiber double-ring resonator with a 3×3 fibercoupler and degenerate two-wave mixing

A theoretical study of a new and simple Vernier fiber ring resonator is presented. The ring resonator consists of two fiber rings constructed from a single-mode 3×3 fiber directional coupler and two single-mode fiber delay lines. Degenerate two-wave mixing is used to achieve the Vernier operation, which significantly increases the free spectral range of the device. In addition, the input beam is also amplified. This device can be used as a wavelength division demultiplexer     

Performance parameters of a wavelength-division demultiplexer madewith a single 3×3 coupler optical fiber ring or loopresonator

The performance parameters of a two-channel demultiplexer made with a single 3×3 coupler fiber ring or loop resonator are evaluated theoretically. These parameters include crosstalk, output intensity of the selected channel, and channel separation. Their dependence on the parameters of the coupler and the fiber such as the coupling length of the coupler, kd, the phase change of the fiber delay line, &thetas;, and the round-trip amplitude transmission coefficient of the fiber ring or loop G, which is the product of the amplitude transmission coefficients of the coupler and the fiber delay line and the amplitude gain of the degenerate two-wave mixing, is investigated. It is found that the best performance can be obtained at G=1     

A single-mode optical fiber ring resonator using a planar 3×3fiber coupler and a Sagnac loop

We present the first theoretical analysis of an optical fiber ring resonator using a planar 3×3 fiber directional coupler and a fiber Sagnac loop. In the planar 3×3 fiber directional coupler, the three fibers inside the coupler lie in the same plane. Expressions for the circulating (resonant) and the output fields of the fiber ring resonator are obtained. It is found that this fiber ring resonator has a special property where there are two or more main resonance peaks or dips inside a period 2π of the phase change of the fiber ring resonator. This ring resonator may have applications as a sensor with high-phase sensitivity and a densely spaced two-channel wavelength division multi/demultiplexer     

Improved demodulation scheme for fiber optic interferometers usingan asymmetric 3×3 coupler

Problems associated with the demodulation of the signal produced by a fiber optic interferometer which employs a 3×3 fiber coupler are investigated both theoretically and experimentally. It is shown that existing demodulation methods do not work well, especially when the 3×3 coupler is asymmetric, as is often the case. Modifications to improve the performance of a previously proposed method are suggested. Furthermore, an alternative demodulation circuit is presented which is simple and which works well even when the 3×3 coupler is asymmetric     

Fabrication of wavelength-insensitive 8×8 star coupler

The fabrication and performance of a wavelength-insensitive 8×8 star coupler is described. The integrated-optic star coupler consists of two fan-shaped channel waveguide arrays facing each other and a slab waveguide region located in between. The wavelength-insensitive light splitting was realized by properly tailoring the mode coupling in the input array region. The coupler exhibits low-average excess losses of α=1.4 dB (standard deviation σ=0.40 dB) at λ=1.3 μm and α=1.7 dB (σ=0.44 dB) at λ= 1.55 μm, respectively     

Fiber Bragg grating interrogation and multiplexing with a 3×3coupler and a scanning filter

We present a new technique for fiber Bragg grating (FBG) sensor interrogation and multiplexing. The technique combines a scanning bandpass filter used to multiplex by wavelength multiple gratings in a single fiber, and an unbalanced Mach-Zehnder fiber interferometer made with a 3×3 coupler to detect strain-induced wavelength shifts. A demonstration system interrogates four gratings in a single fiber at a sampling rate up to 20 kHz, with a noise floor measured at less than 10 nϵ/√(Hz) above 0.1 Hz     

16×16 optical-fiber crossbar switch operating at 0.85 μm

An optical-fiber crossbar switch has been constructed using fully integrated GaAs optoelectronic receivers, custom monolithic GaAs laser drivers, and an electrical 32×32 silicon crossbar switch. 470 Mb/s operation has been achieved with a bit error rate of less than 10^-12. The approach uses a monolithic GaAs optoelectronic integrated receiver to convert optical signals into electrical signals that are fed into an Si 32×32 electronic crossbar switch. The switch outputs are used to drive laser transmitters consisting of a custom monolithic GaAs IC laser driver and a 0.85 μm GaAs/AlGaAs laser. The system could be reconfigured in 1 μm, limited by the control logic, with the switch chip capable of reconfiguration in 35 ns. No errors are induced by reconfiguration     

Fabrication of 2×2 tapered multimode interference coupler

The authors demonstrate a 3 dB 2×2 parabolically tapered multimode interference (MMI) coupler with a large cross-section and space between the different ports using silicon-on-insulator technology. The device exhibits a uniformity of <0.8 dB and can be used in the realisation of an MMI-based optical switch with a high extinction ratio     

Fabrication of 7×6 multimode optical fiber gratingdemultiplexer-star coupler using a single GRIN-rod lens

A multimode optical fiber grating demultiplexer-star coupler having seven demultiplexing channels and six fan-out channels is demonstrated. This device consists of an input-output fiber array, in which 42 output fibers are aligned radially around an input fiber, a single gradient-index (GRIN)-rod lens and a multifacet blazed reflection grating. In this device, the incident light beam is split into six beams, each of which is diffracted at the multifacet grating and couples to the output fibers. The device has a working band from 0.62 to 0.88 μm, channel separation from 36 to 45 nm and 3 dB bandwidth from 13 to 24 nm. We also evaluate the unevenness in the center wavelength and the minimum excess loss among the fan-out channels and discuss the relationship between the unevenness and the fabrication accuracy of the optical components in detail     

Miniaturization and harmonic suppression rat-race coupler using C-SCMRC resonators with distributive equivalent circuit

This letter describes a miniaturized spurious pass-band suppression rat-race coupler using compensated spiral compact microstrip resonant cell (C-SCMRC) resonators. A distributive equivalent circuit model is proposed for circuit synthesis. The C-SCMRC resonator has been simulated by the equivalent circuit and method of moments (MoM) method. The measured results have good agreement with the simulated ones. The circuit area of the proposed rat-race coupler is only 45% of the conventional coupler. Furthermore, experimental results show that the coupler suppressed the second and third harmonic signals, -32.5dB and -22.5dB.     

Fabrication of 4×4 tapered MMI coupler with large crosssection

MMI coupler with large cross section has low coupling loss between the device and fiber. However, large chip area is required. Recently proposed N×N tapered MMI coupler shows a substantial reduction in device geometry. No such kind of devices with N>2 has yet been realized up to now. The authors have demonstrated a 4×4 parabolically tapered MMI coupler with large cross section that can match the SM fiber in silicon-on-insulator (SOI) technology. The device exhibits a minimum uniformity of 0.36 dB and excess loss of 3.7 dB. It represents a key component for realization of MMI-based silicon integrated optical circuit technology     

Simultaneous measurement of two strain components using 3×3and 2×2 coupler-based passive demodulation of optical fibersensors

This paper uses 3-3 and 2-2 coupler passive demodulation of combined Michelson and polarimetric optical fiber sensors to simultaneously measure axial and transverse strain components in a single optical fiber sensor. The separated Michelson and polarimetric signals are used with isothermal Michelson and polarimetric phase strain models to provide two independent equations describing the strain in the fiber. These equations provide enough information to simultaneously calculate axial and transverse strains in surface mounted sensors. Experiments performed on vibrating cantilever beams show good agreement with measurements made with resistance strain gauges     

Integrated-optic double-ring resonators with a wide free spectralrange of 100 GHz

Integrated-optic double-ring resonators with a wide free spectral range (FSR) of 100 GHz are fabricated using GeO₂-doped silica waveguides with a high relative refractive index difference (Δ) of 1.5%. The resonators are composed of two ring resonators comprising small ring waveguides with radii of 1.75 and 2.0 mm. The double-ring resonator module exhibited a wide FSR of 98.0 GHz, a finesse of higher than 138, a low crosstalk of less than -11.7 dB, and a low insertion loss of 6.1 dB. The measured FSR of 98.0 GHz is wider than any previously reported ring resonator composed of optical waveguides     

Linear 0.20 GHz modulation with a 1×2 directional coupler

The design and performance of a traveling-wave 1×2 directional coupler modulator are described. A 0-20 GHz response (-4 dB _e) was achieved for Ti:LiNbO₃ devices at the 1.3-μm wavelength. From experimental determinations of coupling coefficient and interarm intrinsic phase-mismatch for several modulators, linear dynamic ranges of, on average, 78 dB and voltage sensitivities of down to 9 μV are determined (for 1-mW detector power, 3-kHz bandwidth, 50-Ω detector load). The dependence of sensitivity on the coupling coefficient is described, and the effect of the buffer layer thickness on the optical bandwidth and sensitivity is demonstrated     

4×4 polymer thermo-optic directional coupler switch at 1.55μm

An integrated 4×4 polymer thermo-optic switch at 1.55 μm is demonstrated for the first time. A fibre to fibre insertion loss of 10 dB, and extinction ratios of 17.5-19.5 dB were measured. The polarisation sensitivity was typically less then 0.5 dB and the response time was less then 1 ms. The electrical power consumption was found to be 70 mW per single switch     

New structure of optical homodyne receiver utilising a 4×4fibre directional coupler

A new structure of optical homodyne receiver based on a 4×4 fibre directional coupler is proposed. It has the characteristics of balanced detection, high receiving sensitivity, and the ability to tolerate wide laser linewidth     

Single-mode 1×3 equal-power divider using a substratemicroprism and two waveguide expanders

A new single-mode 1×3 equal-power divider using a substrate microprism and two waveguide expanders has been proposed and analyzed. Simulation results show that with appropriate phase-front tilt and field modification, equal power division and low insertion loss can be attained for a large branching angle. The effects of device parameters are also discussed to facilitate the design of the proposed equal-power divider. Because of not requiring extra regions of indices different from those of the waveguide and substrate, the proposed equal-power divider can be easily fabricated