High-power widely tunable Raman fiber laser

Tunable Raman fiber lasers have attracted great interest owing to their high efficiency and reliability important for applications, such as optical fiber communications and sensing, spectroscopy, and instrument testing. Their tuning range is defined by the Raman gain bandwidth amounting to about 40 nm in telecom spectral range (∼1550 nm) for conventional silica single mode fibers (SMF). To increase the range, highly nonlinear fibers which broaden pump spectrum may be incorporated in the cavity of Raman fiber lasers, see e.g. [1]. Another approach is to involve Rayleigh scattering forming random distributed feedback in a relatively long fiber resulting in prominent flattening of the tuning curve [2]. In this paper we report on combination of these two techniques in tunable Raman fiber lasers thus providing great improvement of their output characteristics. © 2013 IEEE.

Simultaneous measurement for liquid level and refractive index based on all-fiber modal interferometer

A simple fiber sensor capable of simultaneous measurement of liquid level and refractive index (RI) is proposed and experimentally demonstrated. The sensing head is an all-fiber modal interferometer manufactured by splicing an uncoated single-mode fiber with two short sections of multimode fiber. The interference pattern experiences blue shift along with an increase of axial strain and surrounding RI. Owing to the participation of multiple cladding modes with different sensitivities, the height and RI of the liquid could be simultaneously measured by monitoring two dips of the transmission spectrum. Experimental results show that the liquid level and RI sensitivities of the two dips are 245.7 pm/mm, -38 nm/RI unit (RIU), and 223.7 pm/mm, -62 nm/RIU, respectively. The approach has distinctive advantages of easy fabrication, low cost, and high sensitivity for liquid level detection with the capability of distinguishing the RI variation simultaneously. © 2013 Copyright Taylor and Francis Group, LLC.

45°-TFG based in-fiber polarizer at 800nm by UV inscription

We show in-fiber polarizers at 800nm range with polarization extinction ratio (PER) up to 37dB, fabricated by UV-inscribing grating structures tilted at 45° in standard single mode fiber. The results show that the PER of such polarizers increases linearly with the grating length. © OSA 2012.

Two cascaded SOAs used as intensity modulators for adaptively modulated optical OFDM signals in optical access networks

Detailed theoretical and numerical investigations of the transmission performance of adaptively modulated optical orthogonal frequency division multiplexed (AMOOFDM) signals are undertaken, for the first time, in optical amplification and chromatic dispersion (CD) compensation free single mode fiber (SMF) intensity-modulated and directdetection (IMDD) systems using two cascaded semiconductor optical amplifiers in a counterpropagating configuration as an intensity modulator (TC-SOA-CC-IM). A theoretical model describing the characteristics of this configuration is developed. Extensive performance comparisons are also made between the TC-SOA-CC and the single SOA intensity modulators. It is shown that, the TC-SOA-CC reaches its strongly saturated region using a lower input optical power much faster than the single SOA resulting in significantly reduced effective carrier lifetime and thus wide TC-SOA-CC bandwidths. It is shown that at low input optical power, we can increase the signal line rate almost 115% which will be more than twice the transmission performance offered by single SOA. In addition, the TCSOA-CC-IM is capable of supporting signal line rates higher than corresponding to the SOA-IM by using 10dB lower input optical powers. For long transmission distance, the TC-SOA-CC-IM has much stronger CD compensation capability compared to the SOA-IM. In addition the use of TC-SOA-CC-IM is more effective regarding the capability to benefit from the CD compensation for shorter distances starting at 60km SMF, whilst for the SOA-IM starting at 90km. © 2014 Optical Society of America.

Eigenvalue communications in nonlinear fiber channels

Continuous progress in optical communication technology and corresponding increasing data rates in core fiber communication systems are stimulated by the evergrowing capacity demand due to constantly emerging new bandwidth-hungry services like cloud computing, ultra-high-definition video streams, etc. This demand is pushing the required capacity of optical communication lines close to the theoretical limit of a standard single-mode fiber, which is imposed by Kerr nonlinearity [1–4]. In recent years, there have been extensive efforts in mitigating the detrimental impact of fiber nonlinearity on signal transmission, through various compensation techniques. However, there are still many challenges in applying these methods, because a majority of technologies utilized in the inherently nonlinear fiber communication systems had been originally developed for linear communication channels. Thereby, the application of ”linear techniques” in a fiber communication systems is inevitably limited by the nonlinear properties of the fiber medium. The quest for the optimal design of a nonlinear transmission channels, development of nonlinear communication technqiues and the usage of nonlinearity in a“constructive” way have occupied researchers for quite a long time.

Ultra-long range distributed fibre sensing using virtually transparent propagation

Distributed fibre sensors provide unique capabilities for monitoring large infrastructures with high resolution. Practically, all these sensors are based on some kind of backscattering interaction. A pulsed activating signal is launched on one side of the sensing fibre and the backscattered signal is read as a function of the time of flight of the pulse along the fibre. A key limitation in the measurement range of all these sensors is introduced by fibre attenuation. As the pulse travels along the fibre, the losses in the fibre cause a drop of signal contrast and consequently a growth in the measurement uncertainty. In typical single-mode fibres, attenuation imposes a range limit of less than 30km, for resolutions in the order of 1-2 meters. An interesting improvement in this performance can be considered by using distributed amplification along the fibre [1]. Distributed amplification allows having a more homogeneous signal power along the sensing fibre, which also enables reducing the signal power at the input and therefore avoiding nonlinearities. However, in long structures (≥ 50 km), plain distributed amplification does not perfectly compensate the losses and significant power variations along the fibre are to be expected, leading to inevitable limitations in the measurements. From this perspective, it is simple to understand intuitively that the best possible solution for distributed sensors would be offered by a virtually transparent fibre, i.e. a fibre exhibiting effectively zero attenuation in the spectral region of the pulse. In addition, it can be shown that lossless transmission is the working point that allows the minimization of the amplified spontaneous emission (ASE) noise build-up. © 2011 IEEE.

Optical communications : past, present and future trends

In this talk we will review some of the key enabling technologies of optical communications and potential future bottlenecks. Single mode fibre (SMF) has long been the preferred waveguide for long distance communication. This is largely due to low loss, low cost and relative linearity over a wide bandwidth. As capacity demands have grown SMF has largely been able to keep pace with demand. Several groups have been identifying the possibility of exhausting the bandwidth provided by SMF [1,2,3]. This so called “capacity-crunch” has potentially vast economic and social consequences and will be discussed in detail. As demand grows optical power launched into the fibre has the potential to cause nonlinearities that can be detrimental to transmission. There has been considerable work done on identifying this nonlinear limit [4, 5] with a strong re- search interest currently on the topic of nonlinear compensation [6, 7]. Embracing and compensating for nonlinear transmission is one potential solution that may extend the lifetime of the current waveguide technology. However, at sufficiently high powers the waveguide will fail due to heat-induced mechanical failure. Moving forward it be- comes necessary to address the waveguide itself with several promising contenders discussed, including few-mode fibre and multi-core fibre.

Humidity sensitivity of topas optical fibre bragg grating

Fibre Bragg gratings at 1568nm have been inscribed in single mode TOPAS microstructured polymer optical fibre to characterise thermal and humidity sensitivity of the fibres in the 1550nm spectral region. Results demonstrate a temperature sensitivity of approximately -36 pm/°C and a humidity sensitivity of no more than - 0.59 pm/%RH. The fibre material appears to be very attractive for long term monitoring of high strains because of its insensitivity to humidity.

A compact polymer optical fibre ultrasound detector

Polymer optical fibre (POF) is a relatively new and novel technology that presents an innovative approach for ultrasonic endoscopic applications. Currently, piezo electric transducers are the typical detectors of choice, albeit possessing a limited bandwidth due to their resonant nature and a sensitivity that decreases proportionally to their size. Optical fibres provide immunity from electromagnetic interference and POF in particular boasts more suitable physical characteristics than silica optical fibre. The most important of these are lower acoustic impedance, a reduced Young's Modulus and a higher acoustic sensitivity than single-mode silica fibre at both 1 MHz and 10 MHz. POF therefore offers an interesting alternative to existing technology. Intrinsic fibre structures such as Bragg gratings and Fabry-Perot cavities may be inscribed into the fibre core using UV lasers. These gratings are a modulation of the refractive index of the fibre core and provide the advantages of high reflectivity, customisable bandwidth and point detection. We present a compact in fibre ultrasonic point detector based upon a POF Bragg grating (POFBG) sensor. We demonstrate that the detector is capable of leaving a laboratory environment by using connectorised fibre sensors and make a case for endoscopic ultrasonic detection through use of a mounting structure that better mimics the environment of an endoscopic probe. We measure the effects of water immersion upon POFBGs and analyse the ultrasonic response for 1, 5 and 10 MHz.

Thermal effects on the photoelastic coefficient of polymer optical fibers

We measure the radial profile of the photoelastic coefficient C(r) in single-mode polymer optical fibers (POFs), and we determine the evolution of C(r) after annealing the fibers at temperatures from 40°C to 80°C. We demonstrate that C(r) in the fibers drawn from a preform without specific thermal pre-treatment changes and converges to values between 1.2 and 1.6×10-12 Pa-1 following annealing at 80°C. The annealed fibers display a smoothened radial profile of C(r) and a lowered residual birefringence. In contrast, the mean value of C(r) of the fiber drawn from a preform that has been pre-annealed remains constant after our annealing process and is significantly higher, i.e., 4×10-12 Pa-1. The annealing process decreases the residual birefringence to a lower extent as well. These measurements indicate the impact of annealing on the thermal stability of the photoelastic coefficient of POFs, which is an essential characteristic in view of developing POF-based thermomechanical sensors.

Label-free immunoassay for porcine circovirus type 2 based on excessively tilted fiber grating modified with staphylococcal protein A

Using excessively tilted fiber grating (Ex-TFG) inscribed in standard single mode fiber, we developed a novel label-free immunoassay for specific detection of porcine circovirus type 2 (PCV2), which is a minim animal virus. Staphylococcal protein A (SPA) was used to modify the silanized fiber surface thus forming a SPA layer, which would greatly enhance the proportion of anti-PCV2 monoclonal antibody (MAb) bioactivity, thus improving the effectiveness of specific adsorption and binding events between anti-PCV2 MAbs and PCV2 antigens. Immunoassay experiments were carried out by monitoring the resonance wavelength shift of the proposed sensor under different PCV2 titer levels. Anti-PCV2 MAbs were thoroughly dissociated from the SPA layer by treatment with urea, and recombined to the SPA layer on the sensor surface for repeated immunoassay of PCV2. The specificity of the immunosensor was inspected by detecting porcine reproductive and respiratory syndrome virus (PRRSV) first, and PCV2 subsequently. The results showed a limit of detection (LOD) for the PCV2 immunosensor of ~9.371TCID50/mL, for a saturation value of ~4.801×103TCID50/mL, with good repeatability and excellent specificity.

The effect of high optical power on modern fibre at 1.5 μm

Here we study the impact of high optical power, within the C-band, on the reliability of modern single mode fibre. Our experiments show that modern fibre demonstrates >10 dB higher power handling performance beyond what has previously been reported.

Polarimetric sensitivity to hydrostatic pressure and temperature in birefringent dual-core microstructured polymer fiber

We experimentally characterized a birefringent microstructured polymer fiber of specific construction, which allows for single mode propagation in two cores separated by a pair of large holes. The fiber exhibits high birefringence in each of the cores as well as relatively weak coupling between the cores. Spectral dependence of the group and the phase modal birefringence was measured using an interferometric method. We have also measured the sensing characteristics of the fiber such as the polarimetric sensitivity to hydrostatic pressure and temperature. © 2010 SPIE.

56 Gb/s multi-band CAP for data center interconnects up to an 80 km SMF

We present the first (to the best of our knowledge) experimental demonstration of a 56 Gb/s multi-band carrierless amplitude and phase modulation (CAP) signal transmission over an 80-km single-mode fiber link with zero overhead pre-FEC signal recovery and enhanced timing jitter tolerance for optical data center interconnects.

Switchable dual-wavelength erbium-doped fibre laser utilizing two-channel fibre Bragg grating fabricated by femtosecond laser

We propose and demonstrate a switchable dual-wavelength erbium-doped fibre ring laser. Competition between the lasing wavelengths in erbium-doped fibre laser at room temperature is suppressed by incorporating a two-channel fibre Bragg grating (TC-FBG), which consists of two highly localized sub-gratings fabricated by femtosecond laser in single mode fibre. Wavelengths and polarization states of the lasing lines are selected by the TC-FBG. Laser output can be switched between single- and dual-wavelength operations by simply adjusting the polarization controller. Stable dual-wavelength output is verified at room temperature with a power fluctuation less than 0.27 dB, and wavelength fluctuation less than 0.004 nm.