Mikhail N. Zervas

Generation of a 40-GHz pulse stream by pulse multiplication with a sampled fiber Bragg grating.

A sinc-sampled fiber Bragg grating is used to achieve multiplication of the repetition rate of a pulse stream from 10 to 40 GHz. The spectral characteristics of the grating ensure that the resultant pulses-solitons of 3.4-ps width-have the same individual pulse characteristics as those of the input.

A new design approach for fiber DFB lasers with improved efficiency

The standard distributed feedback (DFB) laser optimization method is critically investigated and a new design approach based on the effective cavity length is presented. By applying this method in an erbium-ytterbium co-doped fiber, the pump-to-signal conversion ratio is increased by 40% for the same total device length and pumping conditions. The laser with the proposed design is produced and the theoretical results are verified by the experimental work.

Design considerations in optical add/drop multiplexers based on grating-assisted null couplers

The performance of a fully optimized optical add/drop multiplexer (OADM), based on null couplers and tilted Bragg gratings, is studied in detail. It is shown that maximization of the device performance involves three main optimization steps. First, the waveguide asymmetry (V/sub 2//V/sub 1/ ratio) should be optimized in order to minimize the extinction ratio of the unwanted mode at the null coupler waist. Second, the coupler taper shape should he optimized in order to further minimize the aforementioned extinction ratio. Third, the grating tilt angle and relative width can be also optimized to give negligible backreflections at the input port and minimize radiation losses. The results show that the proposed high-performance OADM configuration can meet stringent telecom specifications.

321 W average power, 1 GHz, 20 ps, 1060 nm pulsed fiber MOPA source

Pulses from a gain-switched laser diode were amplified in a fiber MOPA system to produce in excess of 320 W of average power in 20 ps pulses at 1 GHz repetition rate at 1060 nm.

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.

Ultra-smooth lithium niobate photonic micro-structures by surface tension reshaping

Annealing of micro-structured lithium niobate substrates at temperatures close to, but below the melting point, allows surface tension to reshape preferentially melted surface zones of the crystal. The reshaped surface re-crystallizes upon cooling to form a single crystal again as it is seeded by the bulk which remains solid throughout the process. This procedure yields ultra-smooth single crystal superstructures suitable for the fabrication of photonic micro-components with low scattering loss.

Experimentally verified modeling of erbium-ytterbium co-doped DFB fiber lasers

For the first time, the simulation results of fiber distributed feedback (DFB) lasers are compared against experimental data in this paper. The pump source, active medium, and grating are all modeled and simulated to predict actual laser characteristics. Simple characterization methods are illustrated for the measurement of model parameters. Large loss at the pump wavelength is observed, attributed to the lifetime quenching of Yb ions, and included in the model as a critical parameter. DFB lasers with two different apodization profiles successfully simulated with the same set of model parameters.

Novel full-cycle-coupler-based optical add-drop multiplexer and performance characteristics at 40-Gb/s WDM networks

A novel configuration of an interferometric device, based on a full-cycle full (100%) coupler structure, loaded with a Bragg grating symmetrically placed into the uniform coupler waist, is proposed for use as an optical add-drop multiplexer (OADM) with simultaneously optimized add and drop actions. A general method for designing a suitable Bragg grating for optimal inscription in to the uniform coupler waist is also proposed for use in to the device design and development. The performance of the device is characterized at 40-Gb/s wavelength-division-multiplexing (WDM) networks using theoretical systems simulations and is compared directly with other alternative OADM architectures.

11.1 W average power, 20 ps pulses at 1 GHz repetition rate from a fiber-amplified gain-switched 1.06 /spl mu/m Fabry-Perot laser diode

20 ps pulses at 1 GHz repetition rate were obtained from a gain-switched 1.06 /spl mu/m semiconductor laser utilizing pulse compression with normally dispersive fiber. The pulses were amplified in fiber to give average output power 11.1 W.

Spectroscopy, Modeling, and Performance of Erbium-Doped Ta

The design, fabrication, spectroscopic characterization, and performance of an Er:Ta2O5 rib waveguide amplifier is described. Rib waveguides with low loss (<; 0.65 dB/cm at 1600 nm) were obtained. Their absorption spectrum was measured and McCumber theory was employed to obtain the emission spectrum, leading to the absorption and emission cross sections. Numerical modeling for gain optimization in Er:Ta2O5 waveguide amplifiers is presented, employing the experimentally determined parameters. Finally, net optical gain of 2.1 dB/cm at 1531.5 nm is demonstrated in a 2.3 cm long Er:Ta2O5 rib waveguide when pumped with 977 nm laser diode, and compared with simulations to deduce the extent of upconversion.