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Here we present a fully fiberized Bi-doped ring laser incorporating a fiber Bragg grating (FBG) operating at a wavelength of 1340nm, which provides 172mW of continuous-wave output power with a slope efficiency of 35%. In addition, we demonstrate a wavelength-tunable version of the laser, which can be tuned from 1320nm to 1370nm by employing a home-made mechanically tunable FBG. Within the whole 50nm tuning band the laser maintains the output power of more than 100mW and the slope efficiency of more than 25%. A maximum output power of ~165mW is achieved over the wavelength range of 1330-1340nm. The linewidth of tunable laser is 0.04nm.

We have studied second-harmonic generation (SHG) of a cw single-frequency ytterbium-doped fibre laser, using a periodically poled silica fibre as a nonlinear medium for frequency conversion. All-fibre external cavity SHG has been investigated for the first time. A twofold increase in second-harmonic power in a fibre ring cavity has been demonstrated and possibilities of further optimising the fibre scheme have been analysed.

We demonstrate a simple-to-fabricate refractometer based on the inscription of fiber Bragg gratings in a special C-shaped optical fiber. The C-shaped fiber was drawn into shape using a quarter cladding removed preform of a commercial standard single-mode fiber by simple machining. The sensor did not suffer from cross-sensitivity of the refractive index with ambient temperature fluctuations, commonly occurring with many optical fiber refractometers. A refractive index sensitivity of 1300 pm per refractive index unit (RIU) was achieved without employing any additional sensitization techniques such as tapering or etching. Published version

We present a tunable thulium-doped fiber laser (TDFL) incorporating a Tm/Ge co-doped fiber capable of accessing the U-band wavelength region (1620-1660nm). These results represents by far the shortest laser wavelengths so far for a TDFL.

Quantum sources that provide broadband biphotons entangled in both polarization and time-energy degrees of freedom are a rich quantum resource that finds many applications in quantum communication, sensing, and metrology. Creating such a source while maintaining high entanglement quality over a broad spectral range is a challenge, which conventionally requires various compensation steps to erase temporal, spectral, or spatial distinguishabilities. Here, we point out that in fact compensation is not always necessary. The key to generate broadband polarization-entangled biphotons via type-II spontaneous parametric downcoversion (SPDC) without compensation is to use nonlinear materials with sufficiently low group birefringence that the biphoton bandwidth becomes dispersion-limited. Most nonlinear crystals or waveguides cannot meet this condition, but it is easily met in fiber-based systems. We reveal the interplay of group birefringence and dispersion on SPDC bandwidth and polarization entanglement quality. We show that periodically poled silica fiber (PPSF) is an ideal medium to generate high-concurrence (>0.977) polarization-entangled photons over a broad spectral range (>77nm), directly and without compensation. This is the highest polarization-entanglement concurrence reported that is maintained over a broad spectral range from a compensation-free source.

In this paper we demonstrate a simple and new fibre optic technique for measuring detonation velocities using uniform fibre Bragg gratings. We compare this new system with chirped fibre Bragg grating diagnostics and show how coherent source illumination can yield spatial uncertainties below ±10 μm - a percentage error that is an order of magnitude lower than the broadband ASE methods we have tested.

The development of super continuum sources is driven by the requirements of a wide range of emerging applications. This paper points out how non-silica fibers are of benefit not only because their broad mid-IR transparency enables continuum generation in the 2–5µm region but also since the high intrinsic nonlinearity of the glasses reduces the power-threshold for devices at wavelengths below 2µm. For these glasses, the material zero-dispersion wavelength is typically shifted to long wavelengths compared to silica so dispersion tailoring is key to creating sources based on practical, near-IR, solid state pump lasers. We show how modeling work has produced fiber designs that provide flattened dispersion profiles with high nonlinearity coefficients and zero-dispersion wavelengths in the near-IR. Building on this flexibility, modeling of the pulse dynamics then demonstrates how coherent mid-IR supercontinuum sources could be developed. We also show the importance of the second zero-dispersion wavelength using bismuth fibers as an example. Nonlinear mode-coupling is shown to be a factor in larger core fibers for high-power applications. Demonstrations of supercontinuum in microstructured tellurite fibers, all-solid lead–silicate (SF57) fibers and in bismuth fibers and tapers are then reported to show what has been achieved experimentally using a range of materials and fiber geometries.

We investigate efficient broadband infrared supercontinuum generation in meter-length single-mode small-core tellurite holey fiber. The fiber is pumped by 1.06µm picosecond pulses in the normal dispersion region. The high Raman gain coefficient and the broad Raman gain bands of the tellurite glass are exploited to generate a cascade of Raman Stokes orders, which initiate in the highly normal dispersion region and quickly extend to longer wavelengths across the zero dispersion wavelength with increasing pump power. A broadband supercontinuum from 1.06µm to beyond 1.70µm is generated. The effects of the pump power and of the fiber length on the spectrum and on the power conversion efficiency from the pump to the supercontinuum are discussed. Power scaling indicates that using this viable normal dispersion pumping scheme, 9.5 W average output power of infrared supercontinuum and more than 60% conversion efficiency can be obtained from a 1 m long tellurite fiber with a large mode area of 500µm2.

An experimental demonstration of a two-channel OCDMA system with detection performed using standard linear detection or a TPA-based nonlinear detector is presented. These results show an improvement in the extinction ratio of the decoded signal by ∼5 dB using TPA detection. A simulation model of the TPA detector used during the experiments was created and used in a four-channel OCDMA system simulation using both linear and nonlinear detection methods. The simulation results show that error-free performance is achievable for a 4-user system using the nonlinear TPA detector while the OCDMA system employing linear detection is severely limited by the effects of noise generated by adjacent optical channels (multiple access interference).

In this paper, we analyze the optical conversion efficiency of a multimode pump source into a diffraction-limited beam in cladding-pumped Raman fiber lasers and amplifiers. We theoretically derive a relation of the cladding/core area ratio for efficient energy transfer from the pump into the first Stokes while avoiding the second Stokes generation that impedes the conversion efficiency of the first Stokes. In addition, we investigate experimentally the limits on the conversion efficiency in a pulse-pumped double-clad Raman fiber. We obtained a peak power conversion efficiency into the first Stokes in excess of 75% and a pulse energy conversion of 60%. We found that spatial pump mode depletion is the main limiting factor in this fiber, with concentric cladding and core. We discuss various solutions to overcome these limitations and improve on the current results.

In this talk we will review some of the latest advances in the use of fibre Bragg gratings and periodically poled fibre devices to access and generate high efficiency light sources in new wavelength bands.

We demonstrate the use of fiber Bragg grating based pulse-shaping technology to provide timing jitter tolerant data demultiplexing in an 80 Gb/s all-optical time division multiplexing (OTDM) system. Error-free demultiplexing operation is achieved with /spl sim/6 ps timing jitter tolerance using superstructured fiber Bragg grating based 1.7 ps soliton to 10 ps rectangular pulse conversion at the switching pulse input to a nonlinear optical loop mirror (NOLM) demultiplexer comprising highly nonlinear dispersion shifted fiber (HNLF). A 2-dB power-penalty improvement is obtained compared to demultiplexing without the pulse-shaping grating.

This paper presents a new enhanced design of fibre Bragg grating for flattening the gain profile of an erbium-doped fibre amplifier in transmission configuration. This grating has modulation of refractive index change and constant chirp rate, wherein both profiles of the parameters are properly apodized. The design utilizes an alternative approach to the renowned inverse scattering method, yet produces a similar spectral response quality and conceptually simpler. Moreover, it offers precise control over all parameters of the grating structure. It is shown that the design approach could produce gain-flattening filters of satisfactory quality through simulations using the accurate transfer matrix method.

We report a record multi-watt level and up to 45% efficient all-fiber frequency doubling in periodically poled silica fibers. Modulation instability is identified as the primary factor preventing further growth of the second-harmonic power.

We present a technique for the shaping of short pulses based on the use of superstructured fiber Bragg gratings (SSFBGs). We apply this technique to demonstrate the generation of 20-ps rectangular pulses by phase and amplitude profiling of 2.5-ps soliton pulses. Numerical calculations validate our experimental findings.

We experimentally demonstrate the use of saw-tooth optical pulses, generated using a superstructured fiber Bragg grating, to achieve high performance and efficient all-optical wavelength conversion in a scheme based on cross-phase modulation in a highly nonlinear fiber, with subsequent offset filtering. Compared to the use of more conventional waveforms, such as Gaussian pulses, the purpose-shaped saw-tooth pulses allow an improvement in the optical signal-to-noise ratio of the wavelength-converted signal of around 15 dB as well as a more than 6-dB improvement in receiver sensitivity.

We experimentally demonstrate the generation of picosecond triangular optical pulses using a superstructured fiber Bragg grating and show experimentally that use of this pulse shape can provide a three-fold improvement in conversion efficiency relative to the use of Gaussian pulses with similar pulse widths when used in a wavelength conversion scheme based on self-phase-modulation and subsequent offset filtering.

We demonstrate the capacity for fast dynamic reconfiguration of optical code-division multiple access (OCDMA) phase en/decoders based on fiber Bragg gratings and a thermal phase-tuning technique. The tuning time between two different phase codes is measured to be less than 2 s. An OCDMA system using tunable-phase decoders is compared with a system using fixed-phase decoders and, although the system using fixed-phase decoders exhibits a shorter output autocorrelation pulsewidth and lower sidelobes, the system using tunable-phase decoders has advantages of flexibility and a more relaxed requirement on the input pulsewidth.

We investigate experimentally and theoretically the linewidth of an Er-Yb-doped distributed feedback fiber laser. We find that two noise sources are mainly responsible for the observed behavior, fundamental thermal noise at low pump power levels and temperature fluctuations induced by pump intensity noise at higher powers. Potential techniques to overcome these limitations are discussed.

We experimentally demonstrate a novel all-optical all-fiberized pulse retiming scheme incorporating parabolic pulses generated in a linear fashion through pulse shaping in a superstructured fiber Bragg grating. The scheme relies on chirping the signal to be retimed using cross-phase modulation with the broader parabolic clock pulses, and subsequently retiming it through linear propagation in a dispersive medium. We demonstrate the cancellation of up to 4-ps root-mean-square timing jitter for /spl sim/2-ps data.

We report the first experimental demonstration of the optical pushbroom - a novel type of all-optical pulse compression. In the optical pushbroom high intensity pump pulses, tuned well away from the resonance of a Bragg grating, modify the transmission of a weak probe tuned near to the grating's photonic bandgap. The clarity of the experimental results and their close agreement with numerical simulations highlight the tremendous potential of the fiber environment for the detailed study and practical application of nonlinear Bragg grating effects.

We demonstrate an in-band-pumped continuous-wave single-frequency distributed-feedback (DFB) fiber laser emitting at a wavelength of 1836 nm with an output power of /spl sim/5 mW. The laser is subsequently amplified to 345 mW using a master-oscillator power amplifier configuration. To the best of the authors' knowledge, this is the first report of a Tm-co-doped single-frequency DFB fiber laser that is in-band pumped at 1565 nm. The laser is confirmed to operate in a single mode, using a scanning Fabry-Pe/spl acute/rot interferometer.

An experimental investigation of the anomalous linewidth behavior in a distributed feedback fiber laser is presented. It is found that not only does the linewidth deviate from the Schawlow-Townes linewidth formula by increasing with pump and laser power, but it also varies significantly with the pumping configuration. These observations have potentially important implications for the design and operation of such fiber lasers.

High power fibre laser sources in the 2 μm wavelength region with picosecond-scale pulse durations have attractive applications such as materials processing, eye-safe radar and nonlinear frequency conversion to mid-infrared wavelengths. Current implementations are typically based on the amplification of picosecond pulses obtained from a mode-locked oscillator, and pulse energies of several hundred nano-Joule and peak powers of the order of 10 kW have been achieved [1, 2].

Birefringence in poled fiber enables the direct (compensation-free) generation of broadband polarization-entangled photon pairs. However, birefringence and pump detuning also affect the entangled state, a subject we investigate in this work theoretically and experimentally.

We demonstrate a continuous-wave (CW) single-frequency narrow-linewidth laser at 1552 nm with an output power of 83 W using a master-oscillator power amplifier configuration. A seed from an all-fiber distributed feedback-laser with a linewidth of 13 kHz was polarization scrambled and boosted through a chain of amplifiers in an all-fiber configuration. The last amplification stage consisted of a highly efficient cladding-pumped large-core erbium-ytterbium co-doped fiber which helped increase nonlinear thresholds.

The authors report a widely tunable and highly efficient cladding-pumped erbium-ytterbium codoped large-core fiber laser, generating up to 43 W of output power at /spl sim/1.5 /spl mu/m with a narrow linewidth (0.16-nm full-width at half-maximum) and a good beam quality (M/sup 2/

A simple and precise method for tuning of localized phase shift in fiber Bragg grating (FBG) using mechanical micro-strain is proposed and experimentally verified. Positive and negative continuous phase shifts tuning between 0 and $+\pi/-\pi$ in a uniform FBG is experimentally demonstrated using confined micro-strain in a beam bending configuration. The magnitudes of the temporary phase shifts can be linearly controlled by changing the load displacement, with set-and-forget capability.

A 50-GHz grid fiber distributed feedback laser wavelength-division-multiplexing transmitter source is demonstrated pumped by a single continuous-wave Yb-fiber laser source at 977 nm. Up to 21 mW of output power is achieved per channel with maintenance of key operational parameters. The performance of this single Yb-fiber laser pump configuration is also compared with that of a semiconductor pump configuration which shows no degradation for all the important parameters.

We demonstrate the application of a uniform Bragg grating as a dynamically reconfigurable phase encoder-decoder for optical systems. Precise discrete phase modulation between chips is obtained simply by heating segments along the grating with fine resistive wires. Its reliability to generate and recognize various phase code sequences is demonstrated in a 16-chip 20-Gchip/s quaternary phase-shift keying coherent optical code-division multiple access experiment. The bit-error-rate response is also included to highlight its performance.

We demonstrate a tunable wavelength-division-multiplexing wavelength converter based on cross-phase modulation in just 5.8 m of highly nonlinear normal dispersion holey fiber (HF) and incorporating a precise compression-tuned apodized fiber-grating filter. We achieve both error-free and penalty-free 10-Gb/s wavelength conversion over a /spl sim/15-nm bandwidth. The short device length and correspondingly reduced pulse walkoff effect ensures a constant wavelength-converted signal pulsewidth across the full tuning range. The use of HF with normal dispersion eliminates the coherence-degradation related intensity noise previously observed in experiments employing anomalously dispersive HF.

Broadband polarization-entanglement over 100 nm is demonstrated in a poled fiber phase-matched for type-II downconversion in the 1.5- m telecom-band. Two-photon interference and Hong-Ou-Mandel interference are used experimentally to confirm the broadband nature of the entanglement.

In this letter, we demonstrate the use of a superstructured fiber Bragg grating to preshape optical pulses to obtain optimal operation of nonlinear all-optical switches. Specifically, we demonstrate the conversion of 2.5-ps soliton pulses into 20-ps rectangular pulses at the input to both fiber and semiconductor optical amplifier-based switches, and show that rectangular switching windows can be achieved thereby providing a 5-10-fold reduction in timing jitter sensitivity. Error free penalty free optical time-division-multiplexing switching was readily achieved over a /spl plusmn/7-ps timing mismatch range for the square pulse driven fiber nonlinear optical loop mirror switch versus a /spl plusmn/1-ps range for the switch driven directly with 2.5-ps laser pulses.

Up to 27-nm continuous tuning is demonstrated from Er/Yb all-fiber distributed-feedback (DFB) lasers using a simple tuning technique for axial extension and compression. The demonstrated devices operate with powers up to 10 dBm and remain operating in single mode over the full tuning range. Our results represents the broadest tuning-range previously reported in any DFB laser configuration and demonstrate that uniform compression tuning of long Bragg gratings is possible with high reliability.

We experimentally demonstrate the direct generation of polarization-entangled photon pairs in an optical fiber at room temperature by exploiting type-II phase-matched spontaneous parametric down-conversion. A second-order nonlinearity is artificially induced in the 17-cm-long weakly birefringent step-index fiber through the process of thermal poling, and quasi-phase-matching allows for the generation of entangled photons in the 1.5-micron telecom band when the fiber is pumped at 775 nm. A greater-than $80\ensuremath{\mathbin:}1$ coincidence-to-accidental ratio is achieved, limited mainly by multiphoton pair generation. Without the need to subtract accidentals or to compensate for walk-off, the raw two-photon interference visibility is found to be better than $95%$, and violation of Bell's inequality is observed by more than 18 standard deviations. This makes for a truly alignment-free, plug-and-play source of polarization-entangled photon pairs.

A simple technique for transverse mode selection in a large-mode-area (multimode) fiber laser is described. The technique exploits the different spectral responses of feedback elements based on a fiber Bragg grating and a volume Bragg grating to achieve wavelength-dependent mode filtering. This approach has been applied to a cladding-pumped thulium-doped fiber laser with a multimode core to achieve a single-spatial-mode output beam with a beam propagation factor (M2) of 1.05 at 1923 nm. Without mode selection the free-running fiber laser has a multimode output beam with an M2 parameter of 3.3. Selective excitation of higher order modes is also possible via the technique and preliminary results for laser oscillation on the LP11 mode are also discussed along with the prospects for scaling to higher power levels.

We propose and demonstrate error-free conversion of a 40 Gbit/s optical time division multiplexed signal to 4 × 10 Gbit/s wavelength division multiplexed channels based on cascaded second harmonic and difference frequency generation in a periodically poled lithium niobate waveguide. The technique relies on the generation of spectrally (and temporally) flat linearly chirped pulses which are then optically switched with short data pulses in the nonlinear waveguide. Error-free operation was obtained for all channels with a power penalty below 2dB.

Precise control of the bandwidth of quasi-phase-matched second-harmonic generation in silica fibers is realized through chirped-period poling. The bandwidth is expanded by a factor of 33 over a uniform-period poled fiber of the same interaction length.

We predict theoretically and demonstrate experimentally the ability to generate and control the strengths of various second-harmonic signals in birefringent poled fiber. This is done by simply twisting the fiber.

A novel method for selectively exciting a single-spatial-mode (fundamental or higher-order) in a high-power multi-mode fiber laser resonator is presented. Preliminary results for a cladding-pumped Tm-doped silica fiber laser are discussed.

We present and experimentally demonstrate simple relationships between the refractive index modulation, the chirp-rate or dispersion and the transmission loss through, and reflection of, chirped Bragg gratings, and apply them to the design of a new type of gain flattening filter with incorporated dispersion compensation.

The generation of 236 mW of second-harmonic power in a 32-cm-long periodically poled silica fiber, corresponding to an average conversion efficiency of 15.2+/-0.5%, is reported. This represents the highest normalized second-harmonic conversion and the highest average second-harmonic power ever reported for a periodically poled silica fiber, to our knowledge. The enhancement is attributed to an improved design of the specialty twin-hole fiber and the extension of the nonlinear interaction length.

This paper demonstrates a retiming system operating at rates of 40 and 160 Gbit/s, which incorporates a superstructured fiber Bragg grating (SSFBG) as a pulse shaping element. The original data pulses are shaped into flat-topped (rectangular) pulses to avoid conversion of their timing jitter into pulse amplitude noise at the output of a nonlinear fiber-based Kerr switch. Thus retiming is performed in a single step avoiding wavelength conversion. The benefits of using shaped rather than conventional pulse forms in terms of timing jitter reduction are confirmed by bit-error rate (BER) measurements.

Stable single frequency two-micron lasers are attractive sources for numerous application areas, including spectroscopy, gas sensing and nonlinear frequency conversion [1–2]. In this paper we report on a Tm-doped silica fibre laser, based on a short cavity distributed Bragg reflector (DBR) design, employed in a simple master-oscillator power-amplifier configuration to produce 2.8 W of stable, linearly-polarised single-frequency output at 1943 nm.

We review our recent progress in the area of reshaping of short optical pulses in both time and frequency domain produced using superstructured fibre Bragg gratings (SSFBGs). We mainly focus our discussion on the saw-tooth pulse shape as an interesting example of the powerful combination of nonlinear optical switches and tailored optical pulses.

Thulium-doped silica fiber lasers and amplifiers offer a route to very high average power in the two-micron wavelength regime. This presentation reviews recent progress and considers the prospects for further improvement in performance.

We review the operating principles and performance of optical pulse processing systems which exploit the powerful combination of Kerr-nonlinearity based optical switches and tailored optical pulses (e.g. square, triangular and parabolic) produced using superstructured fiber Bragg gratings.

We review the operating principles and performance of optical pulse processing systems exploiting the powerful combination of Kerr-nonlinearity based optical switches and tailored optical pulses (e.g. square, parabolic and saw-tooth) produced using superstructured fibre Bragg gratings.

We experimentally demonstrate the generation of picosecond saw-tooth optical pulses, which are shaped using a fiber Bragg grating, to provide timing jitter tolerant optical time-division multiplexing (OTDM) data demultiplexing in a scheme based on cross-phase modulation (XPM) in an optical fiber, with subsequent offset filtering. A power improvement of more than 5dB is obtained compared to demultiplexing with more conventional shapes, such as Gaussian, with a similar pulse width.

Saw-tooth pulses, shaped using a fiber Bragg grating, provide timing jitter tolerant OTDM data demultiplexing in a scheme based on cross-phase modulation in fibre, with subsequent offset filtering.