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We present a single transceiver based modal characterization method for estimating the channel impulse response of MDM systems. Good agreements are found between the measured and simulated DGDs of a RCF supporting 5 mode groups.

We demonstrate efficient four-wave mixing among different spatial modes in a 1-km long two-mode fiber at telecommunication wavelengths. Two pumps excite the LPsub01/suband LPsub11/submodes, respectively, while the probe signal excites the LPsub01/submode, and the phase conjugation (PC) and Bragg scattering (BS) idlers are generated in the LPsub11/submode. For these processes we experimentally characterize their phase matching efficiency and bandwidth and find that they depend critically on the wavelength separation of the two pumps, in good agreement with the numerical study we carried out. We also confirm experimentally that BS has a larger bandwidth than PC for the optimum choice of the pump wavelength separation.

We review the performances of few-mode in-line fiber amplifiers for mode division multiplexed transmission systems. We have experimentally demonstrated that differential modal gain (DMG) of 20 dB small signal gain for all the guided modes with a gain flatness of ≤4.0 dB over the full C-band. Numerical modelling suggests that the DMG can be reduced to

We report a novel compact all-fiber technique to control the beam propagation and beam pattern in free space. By coating an azo-polymer thin film layer on the optical fiber end surface, various surface relief grating (SRG) structures were inscribed over the film using a single step direct exposure of interference patterns to form a novel organic/inorganic composite fiber optics beam shape converter. The linear and concentric SRGs were experimental characterized along with numerical simulations.

We experimentally demonstrate all-solid 10 and 20 μm core diameter multi-trench fibers for UV and visible wavelengths. Measurements ensure an effective single-mode operation over a wide range of bend radii, which is suitable for applications such as beam delivery. Both fibers were fabricated by the conventional modified chemical vapor deposition process, which is suitable for mass production. Moreover, all-solid fiber design ensures easy cleaving and splicing.

We theoretically propose an air-core erbium doped fiber amplifier capable of providing relatively uniform gain for 12 orbital angular momentum (OAM) modes (vertical bar L vertical bar = 5, 6 and 7, where vertical bar L vertical bar is the OAM mode order) over the C-band. Amplifier performance under core pumping conditions for a uniformly doped core for each of the supported pump modes (110 in total) was separately assessed. The differential modal gain (DMG) was found to vary significantly depending on the pump mode used, and the minimum DMG was found to be 0.25 dB at 1550 nm provided by the OAM (8,1) pump mode. A tailored confined doping profile can help to reduce the pump mode dependency for core pumped operation and help to increase the number of pump modes that can support a DMG below 1 dB. For the more practical case of cladding-pumped operation, where the pump mode dependency is almost removed, a DMG of 0.25 dB and a small signal gain of >20 dB can be achieved for the 12 OAM modes across the full C-band. Refereed/Peer-reviewed

We demonstrate mode-multiplexed transmission over all-fiber optically amplified spans of 215 km and 179 km for 3 and 6 spatial modes, respectively. The spans were amplified using two cladding-pumped few-mode fiber amplifiers. Refereed/Peer-reviewed

An optical transmission loop experiment over hollow-core fiber is demonstrated with 1.25Gb/s OOK, 40G DP-QPSK, 100G DP-QPSK modulation schemes over distances of 31.0 km, 74.8 km, 55.8 km respectively, using two fiber spans with 2.7 km and 3.5 km length.

We investigated various types of optical fiber sensor based on novel structure of photonic crystal fibers (PCFs) including Ge-doped ring defect PCF and Suspended ring core PCF. Furthermore, a new type of fiber named C-type fiber is utilized as a fiberized sensor unit in/outlet. This configuration enabled to package the entire sensor unit in fiber form as well as could overcome prior limitations in PCF-based optical sensors such as too small holes for efficient measurand entry and sophisticated fabrication processes. The experiment and simulation results proved that the designed sensor can improve both sensitivity and response time compare to conventional PCF based sensors.

This paper reviews our recent work on novel large-mode area fibers for high power lasers and amplifiers. An ultra-low- NA fiber and single-trench fiber have been proposed for mode area scaling of the fundamental mode. In case of single-trench fiber design, resonant coupling of the higher order modes has been exploited to achieve effective single mode operation in fiber with large effective mode area. Our proposed fiber designs are easy to fabricate using conventional low-loss fiber fabrication techniques, and moreover, being all solid structure, they ensure easy cleaving and splicing. A monolithic and compact high power fiber laser/amplifier device with a good output beam quality can be achieved using Single-trench fiber design.

We propose a novel fiber design single-trench fiber (STF) for large mode area fiber laser and amplifier. Fiber offers cylindrical symmetry and also offer higher refractive index of core compared to cladding. This avoids the need of stack and draw process and refractive index compensation of core doped with index raising rare earth and co-dopants ions, which are an indispensable condition in most of other fiber designs. That is why, this fiber design can be fabricated with conventional modified chemical vapour deposition process in conjunction with solution doping process, which can dramatically reduce the fabrication cost, hence suitable for mass production. Fiber offers very high loss (>10dB/m) and low power fraction in core ( 80%) thanks to the resonant coupling between core and ring modes. We fabricated a preform for 30μm core STF using MCVD process in conjunction with solution doping process in a single step, without using any micro-structuration and pixilation of core. Experiments ensure the robust single mode behaviour irrespective of launching condition of input beam. Furthermore, this fiber used in three stages MOPA provides 80kW peak pulses with repetition rate of 500 kHz, average power up to 10W, with M 2 ~ 1.14. Moreover, all solid structure ensures easy cleaving and splicing. In nutshell, an ultra-low cost, monolithic, compact, and an effective single mode fiber amplifier device can be achieved using single-trench fiber.

We present a novel cascaded two-stage microoptical waveguide (MOW) on microactuating platform (MAP) structure for applications in high-power ultrawideband variable optical attenuator (VOA). The device consists of a fused biconical taper (FBT) fiber coupler, which acts as a MOW, mounted on an electromechanical system MAP, where an axial stress over the waist of FBT coupler is precisely controlled by a piezoelectric transducer actuator. Cascaded two stages with complementary spectral responses were employed to enhance the spectral flatness and optical extinction ratio, which allowed the maximum attenuation over 60 dB at 1450 nm and a low spectral tilt of < 1 dB over 100 nm for 20-dB attenuation, as well as low polarization-dependent loss of < 0.07 dB. These VOA characteristics were maintained for optical power over 1 W.

We experimentally demonstrate a new compact surrounding refractive-index sensor using a MMF-CSF-MMF (MCM) structure. The evanescent waves in the coreless silica fibre (CSF) region can directly interact with the surrounding medium. Due to its distinctive resonant spectral feature, the MCM sensor showed a high sensitivity of 4.37 × 10−4 for a refractive index range of 1.30 to 1.44, suggesting that the proposed device may be suitable for a wide range of biomedical and chemical sensor applications.

A novel silica index-guiding holey fibre (IGHF) design is proposed utilizing a new defect structure that is composed of a three-layered defect with a central air hole germanosilicate ring and silica clad, based on a hollow optical fibre (HOF). Effects of these parameters on birefringence were numerically analysed using the plane wave expansion method. The proposed IGHF showed unique modal properties such as uniform birefringence and differential group delay in 1.55 µm optical communication windows that have not been achieved in prior arts.

We present a novel variable optical attenuator (VOA) using a new micro-optical waveguide (MOW) on micro-actuating platform (MAP) structure. The device consists of a fused biconical taper (FBT) coupler mounted on an electromechanical system where the axial stress over the waist of FBT coupler is precisely controlled. Its operation is based on change of coupling constant by compressive stress induced photoelastic effects on the waist zone. Three different types of devices operating near 1450 nm were fabricated with different cross-sectional morphologies at the FBT waists. The device with a circular cross section showed the highest stress sensitivity, where π phase shifts in the coupling constant were observed at an axial displacement of 9.5 μm. The proposed device showed a monotonic and continuous attenuation control up to 34.45 dB, with a very low PDL of 0.06 dB and a relatively low operating voltage of 15.3 V.

A photonic integrated mode coupler based on silicon-on-insulator is employed for mode division multiplexing (MDM) over a 193 m 19-cell hollow-core photonic bandgap fibre (HC-PBGF) with a -3 dB bandwidth >120 nm. Robust MDM transmissions using LP01 and LP11 modes, and two degenerate LP11 modes (LP11a and LP11b) are both experimentally verified. © The Institution of Engineering and Technology 2014.

Spinning a fiber is the most viable and used technique to reduce polarization mode dispersion (PMD). Many papers have shown that by properly tuning the spin parameters, the differential group delay (DGD) of spun fibers can be greatly reduced. However, the precision with which these optimal profiles are practically implemented may be a problem. In this paper, we perform a statistical analysis of the effects that spin inaccuracy may have on fiber PMD, quantifying how the random uncertainty on spin parameters impairs the DGD. Some preliminary experimental results about spin-induced PMD reduction are also reported.

We propose a novel passive band-pass filtering scheme to obtain a net gain in a band-competing system using a W-type fiber waveguide, slicing a shorter wavelength gain band out of a given stimulated emission cross-section. By controlling the location of the LP mode cut-off wavelength and the accompanying bending loss are theoretically analyzed in terms of waveguide parameters.

A novel mode analysis method and differential mode delay measurement technique for a multimode optical fiber based on optical frequency domain reflectometry has been proposed for the first time. We have used a conventional OFDR with a tunable external cavity laser and a Michelson interferometer. A few-mode optical multimode fiber was prepared to test our proposed measurement technique. The differential mode delay (DMD) of the sample fiber was measured to be 16.58 ps/m with a resolution of 1.5 ps/m. We have also compared the OFDR measurement results with those obtained using a traditional time-domain measurement method.

We propose a three-layered W-type structure for laser fiber to facilitate the three-level radiative transition near 940 nm region of Nd ion, while suppressing the competing four-level transition near 1060 nm by introducing a novel highly wavelength selective loss mechanism. In order to achieve a net gain around 940 nm, requirements in fiber waveguide parameters for the LP01 mode cut-off and bending loss were theoretically investigated. The waveguide designs were experimentally confirmed generating stable CW single mode output power of 705 mW.

Novel photonic devices based on a new type of waveguide, hollow optical fibers (HOF), are described. Utilizing unique three layered structure of HOF, the central air hole, germanosilicate ring core, and silica cladding along with its adiabatic mode transformation capability we demonstrated versatile applications in short-haul, long-haul optical communications, and tunable wavelength selective devices. Detailed design parameters, fabrication arts of the fibers, and operation principles of the devices are discussed.

We propose and demonstrate a simple all-fiber spatial mode selective filter based on splicing a short segment of small-core SMF between two few-mode fibers. An 8dB MDL equalization range with less than 2dB IL is demonstrated for a 2-mode fiber device.

We report the first demonstration of silica-based thulium-doped fiber amplifier (TDFA) working in the 1.65 – 1.7 µm waveband. Up to 29 dB small signal gain and noise figure as low as 6.5dB are achieved.

We design and characterize a graded-index-ring-core fiber supporting 7 LP mode-groups (13 spatial modes) for mode multiplexed transmission with low MIMO processing complexity. Spatial and temporal modal properties are analyzed using an SLM-based mode multiplexer/demultiplexer.

We experimentally demonstrate a 9 LP-mode (15 spatial modes) fiber with low DMD, confirmed by both time of flight and S2 measurements. Low loss (∼0.2dB/km) is verified by OTDR measurement of the individual mode groups.

A review of recent progress on the implementation of in-line few mode EDFAs for SDM transmission is provided. Additionally, the design and construction of fully fiberised few-mode EDFAs will be discussed and the key technical challenges described.

We demonstrate an ultra-low-NA (~0.038) Yb-doped step-index-fiber fabricated using conventional MCVD and solution-doping process. The fiber ensures ~700µm2 Aeff for effective-single-mode operation and 81% laser efficiency with M2 ~1.1 at a bend diameter of 32cm.

We experimentally demonstrate a few-mode erbium doped fiber amplifier (FM-EDFA) supporting 6 spatial modes with a cladding pumped architecture. Average modal gains are measured to be >20dB between 1534nm-1565nm with a differential modal gain of similar to 3dB among the mode groups and noise figures of 6-7dB. The cladding pumped FM-EDFA offers a cost effective alternative to core-pumped variant as low cost, high power multimode pumps can be used, and offers performance, scalability and simplicity to FM-EDFA design. Refereed/Peer-reviewed

Hollow core photonic bandgap fibres (HC-PBGFs) are emerging as contenders in the race to identify the best solution for next-generation high capacity transmission systems, owing to their low nonlinearity, ultimate-low signal latency, an ideal match to thulium-doped fibre amplifiers and to the promise to deliver ultralow loss, potentially comparable or even below the level of state-of-the-art single mode fibres. Recently, substantial progress in the development of HC-PBGFs has been reported; however, for these fibres to stand a realistic chance of competing with solid transmission fibres, the key challenges of loss reduction over a sufficiently wide transmission bandwidth, as well as the ability to produce fibres in multi-hundred kilometre lengths must be addressed. A predicted route to reduce loss is by increasing the core size, e.g. from 19-cell to 37-cell. In this work we review recent progress in the development of HC-PBGFs based on a 37-cell core geometry, including the realization of fibres with low loss, wide bandwidth, low modal crosstalk and low bending loss, which have paved the way to data transmission experiments using mode division multiplexing. We also investigate the issue of longitudinal uniformity in HC-PBGFs and report a systematic study of defects observed in these fibres - a first step towards their removal and thus towards the demonstration of multi-kilometre lengths of defect free fibres.

We report the first demonstration of an inline two-mode group thulium-doped fiber amplifier (TMG-TDFA) operating at 2µm for mode-division multiplexed transmission. Similar gain and noise figure performance are obtained for both spatial modes under cladding-pumped operation.

We model and demonstrate a simple mode selective all-fiber coupler capable of exciting specific higher order modes in two- and few-mode fibres with high efficiency and purity. The coupler is based on inter-modally phase-matching the propagation constants in each arm of the asymmetric fused coupler, formed by dissimilar fibres. At a specific coupler diameter, the launched fundamental LP(01) mode is coupled into the higher order mode (LP(11), LP(21), LP(02)) in the other arm, over a broadband wave-length range around 1550 nm. Unlike other techniques, the demonstrated coupler is composed of a multimode fiber that is weakly fused with a phase matched conventional single mode telecom fiber (SMF-28). The beating between the supermodes at the coupler waist produces a periodic power transfer between the two arms, and therefore, by monitoring the beating while tapering, it is possible to obtain optimum selection for the desired mode. High coupling efficiencies in excess of 90% for all the higher order modes were recorded over 100 nm spectral range, while insertion losses remain as low as 0.5 dB. Coupling efficiency can be further enhanced by performing slow tapering at high temperature, in order to precisely control the coupler cross-section geometry.

In this letter, we propose a low-complexity adaptive channel state information (CSI) feedback scheme to maximize the throughput in IEEE 802.11ac systems. We analyze the two factors - the interference and the feedback overhead -and develop a method to attain an optimal CSI feedback quantization level with minimal additional complexity. Our numerical results and complexity comparisons verify the efficiency of the proposed scheme in terms of throughput and complexity.

We demonstrate a novel all-fiber gap-type tunable bandpass filter configuration that consists of a broadband hollow optical fiber (HOF) acoustooptic tunable filter (AOTF) concatenated with a narrowband single-mode fiber (SMF)-AOTF. Owing to the unique mode coupling properties of HOF-AOTF and SMF-AOTF, a narrow passband channel of a full-width at half-maximum (FWHM) of ~4 nm could be formed in a broad stopband platform of a 90-nm FWHM successfully. In this scheme, the center wavelength and rejection efficiency of both passband and stopband were found to be flexibly tunable by adjusting the frequency and the voltage of radio-frequency signals applied to individual acoustic transducers.

We review the progress towards multi-trench fibers for high power fiber laser applications. Such fiber designs address several challenges associated with power scaling of high power fiber laser.

A novel imaging technique that produces accurate amplitude and phase images of an optical fiber facet using only a phase-only liquid-crystal on silicon (LCOS) spatial light modulator (SLM) and a single-pixel detector is presented. The system can take images in two orthogonal polarizations and so provides a powerful tool for modal characterization of multimode fibers, which is of increasing importance due to their burgeoning use in telecommunications and medical applications. This technique first uses a simulated annealing algorithm to compute a hologram that collects light from a small region of the fiber facet. Next, the fiber facet is automatically brought into focus using adaptive aberration correction on the SLM. Finally, a common-path interferometer is created using the SLM, and the phase of the optical field at each pixel is determined. Finally, high-definition amplitude and phase images of a ring-core refractive index fiber are presented as a proof-of-principle demonstration of the technique. Refereed/Peer-reviewed

We report the first demonstration of an inline few-mode thulium doped fiber amplifier (TDFA) operating at 2μm for mode division multiplexed transmission. Similar gain and noise figure performance for both the LP(01) and LP(11) modes are obtained in a cladding pumped 2-mode group TDFA. A maximum gain of 18.3dB was measured at 1970nm with a 3dB gain bandwidth of 75nm while the average noise figure was measured to be between 7 and 8dB for wavelengths longer than 1970nm.

An optical chopper based re-circulating loop is presented for emulating long-haul transmission using few-mode fiber. A proper functioning of the loop is verified by transmission of 3 mode-division multiplexed × 128-Gb/s DP-QPSK over more than 1000 km of few-mode fiber.

We show transmission of 20 wavelength-division-multiplexed (WDM) × 960-Gb/s space-division-multiplexed 32QAM modulated channels (spectral efficiency (SE) of 15 bits/s/Hz) over 60 km of few-mode fiber (FMF) with inline few-mode EDFA (FM-EDFA). Soft-decision FEC was implemented and used to achieve error-free transmission.

We present a 2-mode group, switchable spatial mode erbium doped fiber laser incorporating a spatial light modulator. The laser wavelength can be tuned using an intra-cavity wavelength selective filter and provides >10dB extinction ratio between LP01/LP11 modes.

We present results of the first field trial ever to include a component of MDM. The demonstrated scenarios all confirm the possibility for a partial upgrade of legacy systems to few-mode technology.

We review the capacity records achieved using mode-division multiplexing in few-mode fiber and hollow-core photonic bandgap fibers. Currently the MDM-capacity record for both fiber types is 73.7 Tb/s, whereas per wavelength 960 Gb/s is achieved.

We report a tunable all-fiber bandpass filter based on a short hollow optical fiber serially concatenated between a pair of long-period fiber gratings. With novel core mode blocking in the hollow core fiber and its optimal design, the device showed a low insertion loss of 1.5 dB and broad-band passband tuning range of 84.3 nm covering both S- and C-band.

We demonstrate three possible scenarios for upgrading current single-mode transmission networks with high capacity few-mode fiber technology using mode-division multiplexing (MDM). The results were obtained from measurements over a number of field-deployed single-mode fiber links with an additional experimental in-line amplified few-mode fiber link. The results confirm the viability of employing MDM using few-mode fiber technology to gradually replace legacy optical systems.

We present the first in-band diode-pumped TDFAs operating in the 2 µm wavelength region and test their suitability as high performance amplifiers in potential future telecommunication networks. We demonstrate amplification over a 240 nm wide window in the range 1810 - 2050 nm with up to 36 dB gain and noise figure as low as 4.5 dB.

We experimentally demonstrate 2 × 2 and 3 × 3 fused fiber couplers made from dual mode fiber. A unique mode dependent power transfer characteristics as a function of pulling length is obtained that support various optical functionalities. Exploiting this we demonstrate several devices of interest for mode division multiplexed data transmission including LP11 mode filter, LP11 mode tap coupler, and 50:50 power splitter for both LP01 and LP11 modes.

Due to its unique non-diffracting and self-reconstructing nature, Bessel beams have been successfully adopted to trap multiple particles along the beam's axial direction. However, prior bulk-optic based Bessel beams have a fundamental form-factor limitation for in situ, in-vitro, and in-vivo applications. Here we present a novel implementation of Fourier optics along a single strand of hybrid optical fiber in a monolithic manner that can generate pseudo Bessel beam arrays in two-dimensional space. We successfully demonstrate unique optofluidic transport of the trapped dielectric particles along a curvilinear optical route by multiplexing the fiber optic pseudo Bessel beams. The proposed technique can form a new building block to realize reconfigurable optofluidic transportation of particulates that can break the limitations of both prior bulk-optic Bessel beam generation techniques and conventional microfluidic channels. (C) 2013 Optical Society of America

Cloud gaming service has recently received a lot of attention. However, there are still many technical challenges to be solved in order to provide the cloud-based commercial services for high-quality games. Latency is one of the most important issues to provide a good user experience. In this paper, we describe the implementation of cloud-based gaming service system for smart TV. And we show the latency comparison on game agents.

In cellular type of network, many attentions on transmission power have been paid to save energy as the growth of the telecommunication networks become remarkably large. In spite of concerns on transmission power, the multicast service still has to be provided with full of transmission power in order for even the worst channel user to be served. When the peak power that a transmitter can reach is limited, sometimes the transmitter is not able to provide service without transmission failure, namely, power-limited environment. In this paper, we analyzed the effects of the power limitation and the power deficiency. Our analysis presents the mathematical relationship between the transmission failure probability and given transmission power in the wireless multicast network, whereas the recent work shows the transmission failure probability only when the power is sufficiently supplied. The results are verified by numerical simulation. As an extension of the analysis, we also propose an algorithm for the given problem that a network suffers from the power-limited situation. This algorithm searches for the most proper transmission rate when the system operator has the outage policy, a guarantee of the minimum rate of successful transmission, in the power-limited situation. In case there is no policy, the algorithm contains an optimization problem which maximizes the Multicast Group Utility at given power. The group utility function is defined prior to the optimization problem. The simulation confirms that in the power-limited environment, the system operator can always find an adjusted transmission rate at which the group utility is maximized.

An in-line chemical gas sensor was proposed and experimentally demonstrated using a new C-type fiber and a Ge-doped ring defect photonic crystal fiber (PCF). The C-type fiber segment served as a compact gas inlet/outlet directly spliced to PCF, which overcame previous limitations in packaging and dynamic responses. C-type fiber was prepared by optimizing drawing process for a silica tube with an open slot. Splicing conditions for SMF/C-type fiber and PCF/C-type fiber were experimentally established to provide an all-fiber sensor unit. To enhance the sensitivity and light coupling efficiency we used a special PCF with Ge-doped ring defect to further enhance the sensitivity and gas flow rate. Sensing capability of the proposed sensor was investigated experimentally by detecting acetylene absorption lines. (C) 2013 Optical Society of America