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Abstract. This paper reviews recent progress on ultrashort pulse generation with erbium-doped fiber ring lasers. The passive mode-locking technique of polarization additive pulse mode-locking (P-APM) is used to generate stable, selfstarting, sub-500 fs pulses at the fundamental repetition rate from a unidirectional fiber ring laser operating in the soliton regime. Saturation of the APM, spectral sideband generation, and intracavity filtering are discussed. Harmonic modelocking of fiber ring lasers with soliton pulse compression is addressed, and stability regions for the solitons are mapped and compared with theoretical predictions. The stretchedpulse laser, which incorporates segments of positive-and negative-dispersion fiber into the P-APM fiber ring, generates shorter (sub-100 fs) pulses with broader bandwidths (> 65 nm) and higher pulse energies (up to 2.7 nJ). We discuss optimization of the net dispersion of the stretched-pulse laser, use of the APM rejection port as the laser output port, and frequency doubling for amplifier seed applications. We also review the analytical theory of the stretched-pulse laser as well as discuss the excellent noise characteristics of both the soliton and stretched-pulse lasers. 42.60F; 42.65; 42.80 Fiber lasers were made possible in the 1960s by the incorporation of trivalent rare-earth ions such as neodymium, erbium, and thulium into glass hosts [1]. Soon thereafter neodymium was incorporated into the cores of fiber waveguides [2,3]. Due to the high efficiency of the Nd +3 ion as a laser, early work focused on Nd +3 -doped silica fiber lasers operating at 1.06 µm [4]. Doping of silica fibers with Er +3 ions was not achieved until the 1980s [5,6]. Since that time Er +3 -doped fiber lasers have received much attention, because the lasing wavelength at 1.55 µm falls within the low-loss window of optical fibers and thus is suitable for optical fiber communications. Rare-earth ions such as Ho +3 [7,8], Tm +3 [9-11], and * Current address: Lucent Technologies/Bell Labs, 791 Holmdel-Keyport Road, Holmdel, NJ, USA * * Current address: NTT Access Network Systems Laboratory, Tokai-mura, Naka-gun, Ibaraki-ken 319-11, Japan Yb +3 [12,13] have also been used as dopants or co-dopants in silica or fluoride fibers, allowing new lasing or pumping wavelengths, and Pr +3 has been incorporated into fluoride fiber, providing emission at 1.3 µm [14,15]. PACS:Among the numerous advantages of fiber lasers are simple doping procedures, low loss, and the possibility of pumping with compact, efficient diodes. The fiber itself provides the waveguide, and the availability of various fiber components minimizes the need for bulk optics and mechanical alignment. Many different cavity configurations can be easily built with fibers and fused-fiber couplers, including linear FabryPerot, ring, and combinations of the two. Enhancement of the fiber nonlinearity due to large signal intensities and long interaction lengths is an additional advantage of fiber lasers that is particularly important for mode-locki...

Two small GTPase Rabs, Rab32 and Rab38, have recently been proposed to regulate trafficking of melanogenic enzymes to melanosomes in mammalian epidermal melanocytes; however, the exact molecular mechanism of Rab32/38-mediated transport of melanogenic enzymes has never been clarified, because no Rab32/38-specific effector has ever been identified. In this study, we screened for a Rab32/38-specific effector by a yeast two-hybrid assay using a guanosine triphosphate (GTP)-locked Rab32/38 as bait and found that VPS9-ankyrin-repeat protein (Varp)/Ankrd27, characterized previously as a guanine nucleotide exchange factor (GEF) for Rab21, functions as a specific Rab32/38-binding protein in mouse melanocyte cell line melan-a. Deletion analysis showed that the first ankyrin-repeat (ANKR1) domain functions as a GTP-dependent Rab32/38-binding domain, but that the N-terminal VPS9 domain (i.e., Rab21-GEF domain) does not. Small interfering RNA-mediated knockdown of endogenous Varp in melan-a cells caused a dramatic reduction in Tyrp1 (tyrosinase-related protein 1) signals from melanosomes but did not cause any reduction in Pmel17 signals. Furthermore, expression of the ANKR1 domain in melan-a cells also caused a dramatic reduction of Tyrp1 signals, whereas the VPS9 domain had no effect. Based on these findings, we propose that Varp functions as the Rab32/38 effector that controls trafficking of Tyrp1 in melanocytes.

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additive pulse mode-locking uses segments of fiber of large positive and large negative group velocity dispersion (GVD) in the cavity. The changes in pulse width per pass due to the varying GVD can be an order of magnitude or more. A theory is developed based on the master equation that covers this case of large pulse changes in one transit. The general predictions of the theory are verified by experimental results.