Photonic crystal fibers have been a source of colorful and intriguing optical images from the time they were first developed. The images are all the more captivating because they often transmit information about the basic optical properties of the fiber—sometimes in a visually spectacular way. Some of the more significant effects that are apparent in this way are demonstrated, along with an interpretation of their meaning.

An all-fiber waveplate made by a piece of birefringent photonic crystal fiber (PCF) is proposed and studied in this paper. The characteristics of the proposed waveplate, including the wavelength dependent phase difference between the orthogonal polarized propagation mode in the waveplate, and temperature stability of the waveplate, were investigated theoretically and experimentally for the first time to our knowledge. Compared with the fiber waveplate made by the stress induced or the conventional geometrical shape formed (such as the elliptical core fiber) birefringent fiber, the waveplate based on the birefringent PCF has distinguishable advantages including high temperature stability and large bandwidth. A prototype quarter-waveplate is fabricated by cutting and splicing a segment of birefringent PCF with conventional single mode fiber. The measurement showed that the fluctuation of the ellipticity of the output light from the waveplate can be kept within±0.23° for temperatures varying from 25°C to 200°C, and the bandwidth for ellipticity larger than 43° can be as large as 70 nm.

Optical fiber sensors based on stimulated Brillouin scattering have now clearly demonstrated their excellent capability for long-range distributed strain and temperature measurements. The fiber is used as sensing element, and a value for temperature and/or strain can be obtained from any point along the fiber. After explaining the principle and presenting the standard implementation, the latest developments in this class of sensors will be introduced, such as the possibility to measure with a spatial resolution of 10 cm and below while preserving the full accuracy on the determination of temperature and strain.

We show from analytical analysis of the basic stimulated Brillouin scattering (SBS) equations in the time domain that the SBS amplification process does not amplify an external Stokes pulse and therefore cannot induce group delay of the Stokes pulse as claimed in the literature. Rather, the delayed output Stokes pulse is the pump radiation reflected by the induced acoustic wave, the amplitude of which determines the rate of the amplification process and time delay of the pulse. The latter is predominantly a consequence of the SBS buildup process determined by the inertia of the acoustic wave excitation. Analytical solutions of the SBS equations in the frequency domain show that spectral broadening of the pump radiation leads to only negligible broadening of the SBS spectral bandwidth and so does not provide an effective means to achieve broadband pulse delay.

A review of the main physical processes important for frequency doubling of fiber lasers and the results of development by the Novosibirsk group of the fiber lasers operating from blue-green to yellow-red spectral ranges with a potential of the broad continuous tuning are presented. These lasers with ~100 mW power are treated to be attractive light sources for applications in medicine, especially in confocal microscopy and flow cytometry.

There are many kinds of fiber lasers in the 1.5 mm band using erbium-doped fiber amplifiers. Our group has been studying and developing advanced fiber lasers, such as 1) 10–40 GHz harmonically mode-locked fiber lasers, 2) femtosecond fiber lasers that use single-wall carbon nanotube (CNT)-doped polymers as a saturable absorber, and 3) frequency-stabilized fiber lasers that employ acetylene C₂H₂. We will describe recent progress on these fiber lasers and their applications in this article.

Conjugated luminescent polymers and oligomers, exhibiting stimulated emission (SE), are dispersed in polymethylmethacrylate (PMMA), films and optical fibers, either by blending or upon copolymerisation. With this PMMA doping, we aim to achieve gain and ultrafast optical switching. The modification of the dopant’s chemical structure allows the tuning of the SE spectral region. Furthermore, we aim to achieve dopant chain isolation while maximising their concentration. In this paper, we present an overview of the research done in this area in the context of the European Union (EU)-funded research project “plastic optical fibers with embedded active polymers for data communications — POLYCOM”.

When its diameter goes close to or below the wavelength of the guided light, an optical microfiber/nanofiber (MNF) exhibits favorable properties such as tight optical confinement, strong near-field interaction, and excellent mechanical strength, which offers plenty of choices for combining a variety of functionalized materials ranging from semiconductors and metals to laser dyes; opens up plenty of opportunities for developing microphotonic or nanophotonic devices; and inspires new opportunities for near-field optics, nonlinear optics, and quantum optics.

The modified “flame brushing” technique has been used to manufacture microwires and nanowires from both silica and compound glasses. In this paper, the properties of the wires manufactured by this technique are presented. Applications fabricated from microwires are also discussed.

Circular birefringence is a property of chiral materials. In this work, we consider the use of chiral materials in optical fibres to produce circularly birefringent optical fibres and in fibres where a contrast in circular birefringence contributes to forming the waveguide. (−)-menthyl methacrylate is also investigated as a possible material for the fabrication of such fibres.

An efficient scheme to change the chirp rate of a fiber Bragg grating (FBG) has been developed based on a specially-designed cantilever beam with the beam-bending method. It allows, to date, the largest tuning range of 36 nm in reflection bandwidth of a chirped-FBG (CFBG) while keeping the center wavelength nearly fixed during the tuning process. Using this method, bandwidth-tunable fiber grating filters with tunable chromatic dispersion or differential group delay have been demonstrated. Channel spacing-tunable multi-wavelength filters based on both sampled- and superimposed-CFBGs have also been realized. Moreover, tuning of the bandwidth and channel spacing is continuous with this scheme that makes the achieved devices more flexible.

This paper presents a smart fiber Bragg grating (FBG) sensor system with an unobtrusive and easy-to-use FBG sensor bed, which automatically monitors the behavior of bedridden patients and their vital signs based on indicative spatio-temporal signature for adaptive intervention triggering and activity planning. We present the subtle design, fabrication, calibration, implementation and deployment issues of the FBG pressure sensors to be used in hospitals or nursing homes to prevent bedsore generation, patient falling out of the bed, and life-threatening situations such as patient’s heart rate weakening, breathing pattern change, etc. Through trials conducted in the laboratory for respiratory rate monitoring with a sample group of 10 subjects, the system showed maximum error of±€1 breaths per minute as compared to manual counting.

This paper describes progress in characterizing the distribution and localization of the second-order nonlinearity induced in thermally poled silicate glasses and optical waveguides, in particular, optical fibers. It starts by describing the basics of the poling technique, especially the most commonly used “thermal poling” technique. Then results of systematic investigation of the distribution of the second-order nonlinearity in poled glass and special fibers using second-harmonic microscopy are presented. Interesting issues such as the effectiveness of the poling technique for waveguides formed by ultrafast laser pulses are also discussed.

We propose a new hole-assisted polymer optical fiber design to eliminate the influence of dopant diffusion and to increase the ultra violet (UV) writing efficiency in fiber Bragg grating inscription. The optical waveguide is formed inside a solid core polymethyl methacrylate (PMMA) doped with photosensitive trans-4-stilbenemethanol, surrounded by a ring of three large air holes with double cladding. We determined a map of the single-mode and multi-mode phase transitions using a finite-element-based vectorial optical mode solver. A wide range of geometrical configurations for the single-transverse-mode (HE11) propagation in the visible was obtained. The design is optimized to operate at the low optical loss wavelengths of 580 and 770nm.

Polymer optical fibres (POFs) have historically been regarded as a poor relation to their silica counterparts because of their higher attenuation, but they also have a number of advantages, particularly when coupled with a range of properties that can be produced using microstructures. In terms of their mechanical properties, they are lighter, remain flexible at large core sizes and can be stretched well beyond 30% without breakage. They are also biocompatible, they do not produce dangerous shards, and their low processing temperatures allow functionalized organic materials to be incorporated without decomposition. Other advantages for specific applications include better transmission properties (in the THz region) and the possibility of refractive indices that are close to that of water.

We developed new optical switches based on nematic and ferroelectric liquid crystal (LC) cells for photonics applications. Certain new LC switches based on the effect of total internal reflection in nematic LC and deformed helix ferroelectric effect ferroelectric LC with very fast response time were developed. Fast bistable optical switches of the light polarization based on ferroelectric liquid crystal cells were proposed. The switches are characterized by 100μs switching time and 26dB crosstalk at the wavelength of 632.8nm and bistable, i.e., required zero power consumption in the switch state.
High frequency hysteretic free electrically controlled 0–2π phase modulation of light has been proposed using a very short helix pitch (less than 400nm) deformed helix ferroelectric liquid crystal. The electrically controlled 0–2π hysteretic free phase modulation was achieved at the driving voltage frequency up to 4kHz and the voltage amplitude of 32V. The application of fast V-shaped deformed helix ferroelectric ferroelectric LC (DHF-FLC) for new active-matrix liquid crystal display (LCD) and optical data processing devices is envisaged.
Photoalignment technology can be very useful for the new generation of liquid crystal devices as well as in new photovoltaic, optoelectronic and photonic devices based on highly ordered thin organic layers. We have investigated the LC photoalignment in superthin tubes, which are basic elements of switchable photonic crystal/liquid crystal structures and obtained the order parameter comparable with usual homogeneous nematic LC cells. We studied LC alignment on silicon surfaces with submicrometer-sized straight and curved waveguide profiles. The liquid crystal cladding refractive index was then varied according to the applied voltage, and subsequently the microresonator resonance wavelengths were tuned. Based on our initial measurements, the free spectral range (FSR) wavelength shift within the range of 20nm was obtained, which is comparable with a thermooptic effect. The new voltage controllable Si-based add drop filters are envisaged based on this principle.