Michael Kevan Durkin

Sinc-sampled fiber Bragg gratings for identical multiple wavelength operation

Through a periodic sine modulation of the refractive index-profile in fiber Bragg gratings (FBGs), we demonstrate gratings with multiple equally spaced and identical wavelength channels. We show 10-cm-long gratings with 4, 8, and 16 identical uniform wavelength channels separated by the ITU spacing of 100 GHz and a 22.5-cm-long grating with four identical dispersion compensating channels with a 200-GHz separation designed to dispersion compensate 80-km data transmission through standard fiber at 1.55 /spl mu/m.

Influence of nonideal chirped fiber grating characteristics on dispersion cancellation

The effect of nonideal dispersion and reflection characteristics of chirped fiber gratings on the performance of 10-Gb/s nonreturn-to-zero-transmission systems operating over standard fiber is investigated. The system penalty for different amplitude and period ripples are quantified. Analyses of an experimental grating confirm that current fabrication technology can meet the requirements for <1-dB-penalty operation.

Custom design of long chirped Bragg gratings: application to gain-flattening filter with incorporated dispersion compensation

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.

Chirped moire fiber gratings operating on two-wavelength channels for use as dual-channel dispersion compensators

Long continuously chirped moire fiber gratings are demonstrated. Clean, dual-channel operation with dispersion equivalent to 100 and 200 km of standard fiber is shown from gratings of lengths 35.1 cm and 1 m. The gratings show reflection and time-delay characteristics of the same high quality as previously reported in single-channel chirped gratings.

Latest development of high-power fiber lasers in SPI

High Power Fiber Lasers (HPFLs) and High Power Fiber Amplifiers (HPFAs) promise a number of benefits in terms of their high optical efficiency, degree of integration, beam quality, reliability, spatial compactness and thermal management. These benefits are driving the rapid adoption of HPFLs in an increasingly wide range of applications and power levels ranging from a few Watts, in for example analytical applications, to high-power >1kW materials processing (machining and welding) applications. This paper describes SPI’s innovative technologies, HPFL products and their performance capabilities. The paper highlights key aspects of the design basis and provides an overview of the applications space in both the industrial and aerospace domains. Single-fiber CW lasers delivering 1kW output power at 1080nm have been demonstrated and are being commercialized for aerospace and industrial applications with wall-plug efficiencies in the range 20 to 25%, and with beam parameter products in the range 0.5 to 100 mm.mrad (corresponding to M2 = 1.5 to 300) tailored to application requirements. At power levels in the 1 - 200 W range, SPI’s proprietary cladding-pumping technology, GTWaveTM, has been employed to produce completely fiber-integrated systems using single-emitter broad-stripe multimode pump diodes. This modular construction enables an agile and flexible approach to the configuration of a range of fiber laser / amplifier systems for operation in the 1080nm and 1550nm wavelength ranges. Reliability modeling is applied to determine Systems martins such that performance specifications are robustly met throughout the designed product lifetime. An extensive Qualification and Reliability-proving programme is underway to qualify the technology building blocks that are utilized for the fiber laser cavity, pump modules, pump-driver systems and thermo-mechanical management. In addition to the CW products, pulsed fiber lasers with pulse energies exceeding 1mJ with peak pulse powers of up to 50kW have been developed and are being commercialized. In all cases reducing the total “cost of ownership” for customers and end users is our primary objective.

High-peak-power, high-energy, high-average-power pulsed fiber laser system with versatile pulse duration and shape

The rapid development of commercial multi-kW continuous-wave fibre lasers and high-peak power fibre lasers leads to a natural convergence toward high-average power high-peak power pulsed fibre lasers whose applications include marking, trimming, micromachining, precision drilling, welding and cutting while retaining the characteristics advantage of the fibre laser such as compactness, high-efficiency, reliability and maintenance-free operation.

Distribution of photodarkening-induced loss in Yb-doped fiber amplifiers

Photodarkening-induced output power degradations and long-term stability in high power pulsed and CW fiber laser MOPA systems are discussed. The studied laser systems are based on aluminosilicate single-mode Yb-doped fibers and use the GTWave fiber technology for cladding pumping. The active fiber lengths are between 10-30m. We have tested Yb-doped fiber amplifiers operated under both pulsed and CW mode. Using OTDR background-loss measurements we show, for the first time, that the photodarkening-induced loss is non-uniformly distributed along the length of the active fiber. By calculating the average inversion along the fiber length, we show that the induced loss follows closely an Yb-inversion dependence to the power of 2. In addition we have studied the temperature dependence of the output power variation. It is shown that increasing (decreasing) operating temperature results in decrease (increase) of the laser output power, reaching the new equilibria over time scales of ~200hours. We also present data on the non-photodarkening SPI fiber which is used in all SPI products.

High peak power, high rep-rate pulsed fiber laser for marking applications

Fibre pulsed lasers are increasingly being adopted as the laser of choice in a number of industrial applications, such as micromachining, drilling and marking. In peak-power-driven applications, such as marking, it is essential to retain high peak powers (in excess of 2.5 to 5 kW) at high repetition rates in order to achieve faster character marking and increased throughput.

Power penalties due to in-band and out-of-band dispersion in FBG cascades

We measure the in-band dispersion penalty in a cascade of five 50-GHz low-dispersion linear-phase fiber Bragg gratings (FBGs) and compare the results with conventional apodised FBGs. At the 0.5-dB power penalty level, the usable bandwidth of a single linear-phase FBG (40 GHz) is twice as wide as that of a conventional apodised FBG (19 GHz). The bandwidth-utilization factor of a single linear-dispersion grating is 89%, while for the five-grating cascade, it is 76%. To our knowledge, these are the highest values reported to date for cascaded optical devices. The corresponding factors for the conventional gratings are 53% and 31%. We also measure the additional penalty on a dropped channel caused by a cascade of five adjacent-channel gratings. The bandwidth narrowing due to the adjacent-channel FBGs is 6 GHz both for linear-phase and conventional FBGs, giving a usable bandwidth of 34 GHz (linear-phase) and 13 GHz (conventional).

Advanced fibre Bragg gratings for high performance dispersion compensation in DWDM systems

We present experimental results of fiber Bragg gratings designed by inverse-scattering for dispersion compensating 80 km of standard fiber on a 50 GHz grid the device offers significantly improved bandwidth utilisation and dispersion linearity over conventional designs.