Strained silicon as a new electro-optic material.

For decades, silicon has been the material of choice for mass fabrication of electronics. This is in contrast to photonics, where passive optical components in silicon have only recently been realized. The slow progress within silicon optoelectronics, where electronic and optical functionalities can be integrated into monolithic components based on the versatile silicon platform, is due to the limited active optical properties of silicon. Recently, however, a continuous-wave Raman silicon laser was demonstrated; if an effective modulator could also be realized in silicon, data processing and transmission could potentially be performed by all-silicon electronic and optical components. Here we have discovered that a significant linear electro-optic effect is induced in silicon by breaking the crystal symmetry. The symmetry is broken by depositing a straining layer on top of a silicon waveguide, and the induced nonlinear coefficient, chi(2) approximately 15 pm V(-1), makes it possible to realize a silicon electro-optic modulator. The strain-induced linear electro-optic effect may be used to remove a bottleneck in modern computers by replacing the electronic bus with a much faster optical alternative.

Electrically tunable Yb-doped fiber laser based on a liquid crystal photonic bandgap fiber device.

We demonstrate electrical tunability of a fiber laser using a liquid crystal photonic bandgap fiber. Tuning of the laser is achieved by combining the wavelength filtering effect of a tunable liquid crystal photonic bandgap fiber device with an ytterbium-doped photonic crystal fiber. We fabricate an all-spliced laser cavity based on the liquid crystal photonic bandgap fiber mounted on a silicon assembly, a pump/signal combiner with single-mode signal feed-through and an ytterbium-doped photonic crystal fiber. The laser cavity produces a single-mode output and is tuned in the range 1040-1065 nm by applying an electric field to the silicon assembly.

Liquid crystal parameter analysis for tunable photonic bandgap fiber devices.

We investigate the tunability of splay-aligned liquid crystals for the use in solid core photonic crystal fibers. Finite element simulations are used to obtain the alignment of the liquid crystals subject to an external electric field. By means of the liquid crystal director field the optical permittivity is calculated and used in finite element mode simulations. The suitability of liquid crystal photonic bandgap fiber devices for filters, waveplates or sensors is highly dependent on the tunability of the transmission spectrum. In this contribution we investigate how the bandgap tenability is determined by the parameters of the liquid crystals. This enables us to identify suitable liquid crystals for tunable photonic bandgap fiber devices.

Electrically tunable bandpass filter using solid-core photonic crystal fibers filled with multiple liquid crystals.

An electrically tunable bandpass filter is designed and fabricated by integrating two solid-core photonic crystal fibers filled with different liquid crystals in a double silicon v-groove assembly. By separately controlling the driving voltage of each liquid-crystal-filled section, both the short-wavelength edge and the long-wavelength edge of the bandpass filter are tuned individually or simultaneously with the response time in the millisecond range.

Thermal tunability of photonic bandgaps in liquid crystal infiltrated microstructured polymer optical fibers.

We demonstrate the photonic bandgap effect and the thermal tunability of bandgaps in microstructured polymer optical fibers infiltrated with liquid crystal. Two liquid crystals with opposite sign of the temperature gradient of the ordinary refractive index (E7 and MDA-00-1444) are used to demonstrate that both signs of the thermal tunability of the bandgaps are possible. The useful bandgaps are ultimately bounded to the visible range by the transparency window of the polymer.

Biased liquid crystal infiltrated photonic bandgap fiber.

A simulation scheme for the transmission spectrum of a photonic crystal fiber infiltrated with a nematic liquid crystal and subject to an external bias is presented. The alignment of the biased liquid crystal is simulated using the finite element method to solve the relevant system of coupled partial differential equations. From the liquid crystal alignment the full tensorial dielectric permittivity in the capillaries is derived. The transmission spectrum for the photonic crystal fiber is obtained by solving the generalized eigenvalue problem deriving from Maxwell's equations using a vector element based finite element method. We demonstrate results for a splay aligned liquid crystal infiltrated into the capillaries of a four-ring photonic crystal fiber and compare them to corresponding experiments.

Frequency tunability of solid-core photonic crystal fibers filled with nanoparticle-doped liquid crystals.

We infiltrate liquid crystals doped with BaTiO3 nanoparticles in a photonic crystal fiber and compare the measured transmission spectrum with the one achieved without dopant. New interesting features, such as frequency modulation response of the device and a transmission spectrum with tunable attenuation on the short wavelength side of the widest bandgap, suggest a potential application of this device as a tunable all-in-fiber gain equalization filter with an adjustable slope. The tunability of the device is achieved by varying the amplitude and the frequency of the applied external electric field. The threshold voltage for doped and undoped liquid crystals in a silica capillary and in a glass cell are also measured as a function of the frequency of the external electric field and the achieved results are compared.

On-chip tunable long-period grating devices based on liquid crystal photonic bandgap fibers.

We design and fabricate an on-chip tunable long-period grating device by integrating a liquid crystal photonic bandgap fiber on silicon structures. The transmission axis of the device can be electrically rotated in steps of 45 degrees as well as switched on and off with the response time in the millisecond range. The strength of the loss peak is controlled electrically, and the spectral position of the loss peak is thermally tunable. This compact design results in a stable grating and permits this device to be more easily applied in practical systems.

Optically fed microwave true-time delay based on a compact liquid-crystal photonic-bandgap-fiber device.

An electrically tunable liquid-crystal, photonic-bandgap-fiber-device-based, optically fed microwave, true-time delay is demonstrated with the response time in the millisecond range. A maximum electrically controlled phase shift of around 70 degrees at 15 GHz and an averaged 12.9 ps true-time delay over the entire modulation frequency range of 1-15 GHz are obtained.

Continuously tunable all-in-fiber devices based on thermal and electrical control of negative dielectric anisotropy liquid crystal photonic bandgap fibers.

We infiltrate photonic crystal fibers with a negative dielectric anisotropy liquid crystal. A 396 nm bandgap shift is obtained in the temperature range of 22-80 degrees C, and a 67 nm shift of long-wavelength bandgap edge is achieved by applying a voltage of 200 Vrms. The polarization sensitivity and corresponding activation loss are measured using polarized light and a full broadband polarization control setup. The electrically induced phase shift on the Poincaré sphere and corresponding birefringence change are also measured. According to the results, tunable wave plates working in the wavelength range of 1520-1580 nm and a potential for realizing a polarimeter working at the 1310 nm region are experimentally demonstrated.

Noise filtering in a multi-channel system using a tunable liquid crystal photonic bandgap fiber.

This paper reports on the first application of a liquid crystal infiltrated photonic bandgap fiber used as a tunable filter in an optical transmission system. The device allows low-cost amplified spontaneous emission (ASE) noise filtering and gain equalization with low insertion loss and broad tunability. System experiments show that the use of this filter increases for times the distance over which the optical signal-to-noise ratio (OSNR) is sufficient for error-free transmission with respect to the case in which no filtering is used.

Tunable diffraction and self-defocusing in liquid-filled photonic crystal fibers.

We suggest and demonstrate a novel platform for the study of tunable nonlinear light propagation in two-dimensional discrete systems, based on photonic crystal fibers filled with high index nonlinear liquids. Using the infiltrated cladding region of a photonic crystal fiber as a nonlinear waveguide array, we experimentally demonstrate highly tunable beam diffraction and thermal self-defocusing, and realize a compact all-optical power limiter based on a tunable nonlinear response.

Soliton collision and Raman gain regimes in continuous-wave pumped supercontinuum generation.

We numerically investigate supercontinuum generation using continuous-wave pumping. It is found that energy transfer during collision of solitons plays an important role. The relative influence of Raman gain on spectral broadening is shown to depend on the width of the calculation time window. Our results indicate that increasing the spectral linewidth of the pump can decrease the supercontinuum spectral width. Using a fiber with smaller dispersion at the pump wavelength reduces the required fiber length by decreasing the temporal width of the solitons formed from modulation instability. This also reduces the sensitivity to the pump spectral linewidth.

Swept wavelength source in the 1 microm range.

We demonstrate scanning over 1.1 nm with a frequency shifting ring source using a Ytterbium doped fiber amplifier (YDFA). It is, to the best of our knowledge, the first time an YDFA has been used in this configuration, and operation in the 1-1.1 microm wavelength range is made possible. We demonstrate a novel timing scheme that suppresses unwanted Q-switching behavior. Finally, using a concatenated numerical amplifier model, we are able to accurately predict the behavior of the source.

Selective detection of antibodies in microstructured polymer optical fibers.

We demonstrate selective detection of fluorophore labeled antibodies from minute samples probed by a sensor layer of complementary biomolecules immobilized inside the air holes of microstructured Polymer Optical Fiber (mPOF). The fiber core is defined by a ring of 6 air holes and a simple procedure was applied to selectively capture either alpha-streptavidin or alpha-CRP antibodies inside these air holes. A sensitive and easy-to-use fluorescence method was used for the optical detection. Our results show that mPOF based biosensors can provide reliable and selective antibody detection in ultra small sample volumes.

Continuously tunable devices based on electrical control of dual-frequency liquid crystal filled photonic bandgap fibers.

We present an electrically controlled photonic bandgap fiber device obtained by infiltrating the air holes of a photonic crystal fiber (PCF) with a dual-frequency liquid crystal (LC) with pre-tilted molecules. Compared to previously demonstrated devices of this kind, the main new feature of this one is its continuous tunability due to the fact that the used LC does not exhibit reverse tilt domain defects and threshold effects. Furthermore, the dual-frequency features of the LC enables electrical control of the spectral position of the bandgaps towards both shorter and longer wavelengths in the same device. We investigate the dynamics of this device and demonstrate a birefringence controller based on this principle.

Optical devices based on liquid crystal photonic bandgap fibres.

Photonic Crystal Fibers (PCFs) have appeared as a new class of optical waveguides, which have attracted large scientific and commercial interest during the last years. PCFs are microstructured waveguides, usually in silica, with a large number of air holes located in the cladding region of the fiber. The size and location of these air holes opens up for a large degree of design freedom within optical waveguide design. Further, the existence of air holes in the PCF gives access close to the fiber core and by introducing new materials into the air holes, a high interaction between light and hole material can be obtained, while maintaining the microstructure of the waveguide. In this paper, we describe what we call Liquid Crystal Photonic Bandgap Fibers, which are PCFs infiltrated with Liquid Crystals (LCs) in order to obtain increased fiber functionality. We describe a thermo-optic fiber switch with an extinction ratio of 60dB and tunable PBGs using thermo-optic tuning of the LC. These devices operate by the PBG effect and are therefore highly sensitive to the refractive index distributions in the holes.

All-optical modulation in dye-doped nematic liquid crystal photonic bandgap fibers.

Photonic crystal fibers (PCFs) have attracted significant attention during the last years and much research has been devoted to develop fiber designs for various applications, hereunder tunable fiber devices. Recently, thermally and electrically tunable PCF devices based on liquid crystals (LCs) have been demonstrated. However, optical tuning of the LC PCF has until now not been demonstrated. Here we demonstrate an all-optical modulator, which utilizes a pulsed 532nm laser to modulate the spectral position of the bandgaps in a photonic crystal fiber infiltrated with a dye-doped nematic liquid crystal. We demonstrate a modulation frequency of 2kHz for a moderate pump power of 2-3mW and describe two pump pulse regimes in which there is an order of magnitude difference between the decay times.

Ultra-large bandwidth hollow-core guiding in all-silica Bragg fibers with nano-supports.

We demonstrate a new class of hollow-core Bragg fibers that are composed of concentric cylindrical silica rings separated by nanoscale support bridges. We theoretically predict and experimentally observe hollow-core confinement over an octave frequency range. The bandwidth of bandgap guiding in this new class of Bragg fibers exceeds that of other hollow-core fibers reported in the literature. With only three rings of silica cladding layers, these Bragg fibers achieve propagation loss of the order of 1 dB/m.

Broadband light generation at approximately 1300 nm through spectrally recoiled solitons and dispersive waves.

We experimentally study the generation of broadband light at approximately 1300 nm from an 810 nm Ti:sapphire femtosecond pump laser. We use two photonic crystal fibers with a second infrared zero-dispersion wavelength (lambda Z2) and compare the efficiency of two schemes: in one fiber lambda Z2=1400 nm and the light at 1300 nm is composed of spectrally recoiled solitons; in the other fiber lambda Z2=1200 nm and the light at 1300 nm is composed of dispersive waves.