Single-mode Optical Fiber Coupler Research Articles

Single-mode optical fiber couplers made of fluoride glass.

We demonstrate the first single-mode optical fiber couplers made with ZBLAN optical fiber. Couplers are fabricated using a controlled tapering procedure enabling high reproducibility while limiting glass crystallization. A coupling ratio of up to 41%/59% in cross/through ports with an excess loss of 2.5 dB is obtained at a wavelength of 2.73 μm. In addition, the stability of a coupler with traces of surface crystallization is tested at ambient atmosphere over a period of more than 90 days.

Single-Mode ZBLAN Fiber Couplers

We demonstrate single-mode ZBLAN optical fiber couplers. A controlled tapering procedure leads to coupling ratios of 5%/95% and 14%/86% at a wavelength of 2200 nm, with insertion losses of 1.6 dB and 1.8 dB, respectively.

All-chalcogenide single-mode optical fiber couplers.

We demonstrate the fabrication of all chalcogenide single-mode optical fiber couplers including broadband couplers, wavelength division multiplexers, and polarization beamsplitters. The functionality of each coupler is engineered with a careful design of geometry. As a result, broadband couplers can be set to any arbitrary coupling ratio. Wavelength division multiplexers provide a coupling extinction ratio up to 35dB, and polarization beamsplitters provide a polarization extinction ratio up to 18dB.

Chloroform Vapor Sensor Based on Air-Gap of the Mach-Zehnder Interferometer

The proposal of this study is demonstrating a simple vapor sensor for chloroform (CHCI3) utilitizing air gap region of the Mach-Zehnder interferometer (MZI) by using a single mode optical fiber coupler (3 dB) structure. In the last few decades, flammable liquids such as chloroform have been highly used. This chemical liquid has some degrees of carcinogenic effects in humans in addition to acute and chronic exposure results like blurred vision and nausea. The two arms of MZI contain a free space gap utilized to serve the sensing mechanism by adding chemical liquid volumes (0.2, 0.4, 0.6, 0.8, and 1) ml and to set the phase difference with air-gap distance 0.5 mm. The small variation in the effective refractive index of chloroform is due to changing the propagation of the transmitted light in the MZI’s gap that will further shift the optical phase of the signal. The experimental results indicate that the output power decreased when the air gap distance is 0.5 mm, and the shifting of wavelength will increase toward blue shift when increasing the chloroform liquid volumes. A maximum wavelength shift of chloroform is 0.0251 nm when the liquid volume is 1 ml and sensitivity of chloroform is 0.0223 nm/ml at air gap distance 0.5 mm for different chloroform liquid volumes.

The Possibility of a Simultaneous Transmission οf Ultrasound and Laser Radiation via Flexible Optical Silica Glass Fibre

Glass optical fibres are a promising medium for simultaneous laser-ultrasonic applications. The proposed application system is based on simultaneous transmission of laser radiation and ultrasounds in a flexible silica glass fibre. The optical fibre’s core was made of SiO2 (97%) and GeO2 (3%) and the cladding was 100% SiO2. The material the optical fibre is made of enables simultaneous transmission of laser radiation and ultrasonic wave. Experiments were performed using a Mach–Zehnder optical waveguide interferometer with single-mode optical fibre coupler. This paper presents measurement results for delivering ultrasonic waves to the optical fibre using longitudinal vibrations generated by a sandwich ultrasonic transducer with a velocity transformer. The study presents the relations concerning simultaneous operation of both types of waves and the possibilities of transmission of low frequency, high power ultrasonic wave in optical fibres using a sandwich type transducer.

Characterization of gradient-index lens-fiber spacing toward applications in two-photon fluorescence endoscopy

We report on the experimental investigation into the characterization of two-photon fluorescence microscopy based on the separation distance of a single-mode optical fiber coupler and a gradient-index (GRIN) rod lens. The collected two-photon fluorescence signal exhibits a maximum intensity at a defined separation distance (gap length) where the increasing effective excitation numerical aperture is balanced by the decreasing confocal emission collection. A maximum signal is found at gap lengths of approximately 2, 1.25, and 1.75 mm for GRIN lenses with pitches of 0.23, 0.25, and 0.29 wavelength at 830 nm. The maximum two-photon fluorescence signal collected corresponds to a threefold reduction of axial resolution (38.5 microm at 1.25 mm), compared with the maximum resolution (11.6 microm at 5.5 mm), as shown by the three-dimensional imaging of 10 microm beads. These results demonstrate an intrinsic trade-off between signal collection and axial resolution.

Two-photon fluorescence endoscopy with a micro-optic scanning head.

A major obstacle in the race to develop two-photon fluorescence endoscopy is the use of complicated bulk optics to transmit an ultrashort-pulsed laser beam and return the emitted fluorescence signal. We describe an all-fiber two-photon fluorescence microendoscope based on a single-mode optical fiber coupler, a microprism, and a gradient-index rod lens. It is found that the new endoscope exhibits an axial resolution of 3.2 microm and is capable of imaging transverse cross sections of internal cylindrical structures as small as approximately 3.0 mm in diameter. This device demonstrates the potential for developing a real-time diagnostic tool for biomedical research without the need for surgical biopsy and may find applications in photodynamic therapy, microsurgery, and early cancer detection.

Fibre-optic two-photon scanning fluorescence microscopy.

Two geometries of a novel two-photon fluorescence microscope incorporating single-mode fibre optics for the delivery of ultrashort-pulsed illumination to a remote sample are characterized. First, a 785 nm single-mode optical fibre is implemented in a scanning microscope, which demonstrates that an improvement in axial resolution is achieved due to the non-linear response of the fibre to intense ultrashort-pulsed light. Second, a 785 nm single-mode optical fibre coupler is adapted, in which case spectral broadening and blue shifting of the ultrashort-pulsed laser beam caused by the non-linear response of the fibre to ultrashort-pulsed illumination are experimentally characterized. An investigation into the impact of temporal broadening of the ultrashort-pulsed beam on the systems is also considered. The coupling efficiency of both geometries for various illumination wavelengths is also presented. The introduction of the fibre coupler to the system has significant advantages, including an improved optical sectioning effect and a reduction in the number of bulk optical components resulting in a low-cost, compact instrument. Sets of three-dimensional images of fluorescent polymer microspheres and biological material confirm these features.

Compact two-photon fluorescence microscope based on a single-mode fiber coupler

We present a two-photon fluorescence microscope based on a three-port single-mode optical fiber coupler. It is found that the coupler behaves as a low-pass filter that can deliver an ultrashort-pulsed laser beam of as much as 150 mW of power in the wavelength range from 770 to 870 nm as well as collect a two-photon fluorescence signal in the visible range. As a result of using the fiber coupler, the new two-photon imaging system exhibts a number of advantages, including a compact arrangement, freedom from vibration from lasers and electronic devices, self-alignment, reduction of multiple scattering, and an enhanced optical sectioning effect. The effectiveness of the new instrument is demonstrated with a set of three-dimensional images of biological samples. This instrument may make two-photon fluorescence endoscopy possible for in vivo medical applications.

FIBER OPTIC TECHNIQUE FOR SENSING TEMPERATURE, CONTAMINATION, AND LAYER THICKNESS OF IMMISCIBLE LIQUIDS

In accordance with the principle of the technique based on Fresnel reflection, reflectivity of a dielectric surface depends on the difference of refractive indices of the surface and the surrounding medium, and the reflection coefficient is defined as the ratio of the reflected light power to the incident light power. In the investigations reported, the amount of back reflected light at one of the output ports of a 2 × 2 single-mode optical-fiber coupler due to Fresnel reflection was monitored by means of a high sensitivity …

Experimental investigation of the influence of the refractive index of the intermediate planar layer on the properties of a polished type single-mode fibre coupler

We present a detailed experimental investigation of the influence of the refractive index and thickness of a waveguiding planar layer placed between two fibres in a polished type single-mode optical fibre coupler. Experiments were performed for different distances between the fibres. The investigation not only revealed some new possibilities for the practical use of such coupler, but provided a reliable quantitative database for future theoretical modelling of this complex waveguiding structure.

Properties of a polished type single-mode optical fibre coupler with an intermediate planar waveguide

One possible way to prepare a compact optical fibre coupler (OFC) with fixed coupling ratio for applications in different devices and systems is demonstrated. Experimental and theoretical results are presented concerning the properties of the glued OFC for three different thicknesses of the glue layer: < 0.1 μm; 0.8 μm and 1.6 μm. The couplers are compared with respect to their temperature and spectral characteristics.

Direct-coupling single-mode fiber ring resonator

A single-mode resonator is constructed by joining together the ends of the coupled fiber of a 2 × 2 directional single-mode optical fiber coupler. Analytical expressions are obtained for the resonance conditions. The effects of different kinds of losses are investigated. The variation of the phase at resonance and the problem of mismatch are discussed. A formula for the finesse of the resonator is also given. Unlike reentry fiber resonators, this kind of resonator needs a directional coupler with only a small coupling coefficient. It is possible to achieve a high finesse and symmetrical outputs. Applications of such a resonator are discussed.

Experiments in Optical Multiplex Operation Over Single-Mode Optical Fibers Using Commercial Single-Mode Optical Fiber Couplers

Article Experiments in Optical Multiplex Operation Over Single-Mode Optical Fibers Using Commercial Single-Mode Optical Fiber Couplers was published on March 1, 1987 in the journal Journal of Optical Communications (volume 8, issue 1).

Fused Single-Mode Optical Fibre Couplers (Invited Paper)

A tutorial introduction to the fused-tapered single-mode optical fibre coupler is presented. It is shown that the properties of the coupler can be deduced from fundamental physical arguments without reference to the detailed internal construction of the component. Some of the important experimental properties are discussed and a detailed theoretical model is discussed.

Fibre-optic vibration probe

A practical all-fibre laser vibrometer is described. The design has been optimised for hand-held use and incorporates a frequency-scanned laser diode and a single-mode optical fibre coupler. The vibration information is extracted by a pseudoheterodyne technique.

Analysis of a tunable single mode optical fiber coupler

We report the operation and the theoretical modeling of an efficient, tunable, and low-loss single mode fiber coupler. The coupler design follows a scheme previously reported, in which two optical fibers mounted in curved grooves in separate quartz substrates are polished until sufficient cladding material has been removed to permit optical coupling between the mated polished faces of the fibers. The results of a computer analysis of the distributed coupling taking place between the fibers are discussed, emphasizing the intuitive dependences of the coupling coefficient and effective interaction length of the device on its geometrical parameters. A detailed experimental analysis of fiber couplers follows in which we characterize two types of couplers made with different brands of single-mode fibers. Operation up to 100 percent coupling ratio and 50 dB extinction ratio between coupled and direct branch as well as operation in overcoupling regimes are demonstrated, both at visible and infrared signal wavelengths. Tuning curves are shown that emphasize the excellent tunability properties of such couplers in which the coupling ratio can be smoothly and continuously tuned between 0 and 100 percent. Experimental evidence of the relatively low loss level and very low polarization dependence of the fiber couplers are also presented. All experimental results, including an analysis of the influence of the refractive index of the intermediate layer of index-matching liquid between the polished faces of the fibers, are found to be very well predicted by our theoretical model.

A large-tolerant single-mode optical fiber coupler with a tapered structure

An efficient and large-tolerant single-mode optical fiber coupler with a tapered structure is fabricated and studied experimentally. The maximum coupling efficiency of 95 percent and the tolerance in the coupling length of 2.5 mm permitting the coupling efficiency of more than 90 percent are obtained experimentally. The approximate analysis based upon a coupled mode equation is developed using a step transition model in order to describe the basic principle of this coupler.