Browsing by Subject "Modulation depth"

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    All-fiber all-normal dispersion laser with a fiber-based Lyot filter
    (Optical Society of America, 2010-04-15) Özgören, K.; Ilday, F. Ö.
    We propose the use of a short section of polarization-maintaining fiber as a birefringent medium to construct an all-fiber Lyot filter inside the cavity of a fiber laser. This allows mode-locked operation of an all-fiber all-normal dispersion Yb-fiber oscillator without the use of a bulk bandpass filter and using standard components. Moreover, filter bandwidth and modulation depth is easily controlled by changing the length and splice angle of the polarization-maintaining-fiber section, leading to an adjustable filter. At mode-locked operation, the 30% output fiber port delivers 1nJ pulses that are dechirped to 230 fs duration.
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    Broadband terahertz modulators using self-gated graphene capacitors
    (Optical Society of America, 2015) Kakenov, N.; Balci, O.; Polat, E. O.; Altan, H.; Kocabas, C.
    We demonstrate a terahertz intensity modulator using a graphene supercapacitor which consists of two large-area graphene electrodes and an electrolyte medium. The mutual electrolyte gating between the graphene electrodes provides very efficient electrostatic doping with Fermi energies of 1 eV and a charge density of 8 × 1013 cm-2. We show that the graphene supercapacitor yields more than 50% modulation between 0.1 and 1.4 THz with operation voltages less than 3 V. The low insertion losses, high modulation depth over a broad spectrum, and the simplicity of the device structure are the key attributes of graphene supercapacitors for THz applications.
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    Generation of soliton molecules with independently evolving phase in a mode-locked fiber laser
    (Optical Society of America, 2010) Ortaç, Bülend; Zaviyalov, A.; Nielsen, C.K.; Egorov, O.; Iliew, R.; Limpert, J.; Lederer, F.; Tünnermann, A.
    We report the experimental generation of two-soliton molecules in an ytterbium-doped fiber laser. These molecules exhibit an independently evolving phase and are characterized by a regular spectral modulation pattern with a modulation depth of 80%. © 2010 Optical Society of America.
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    Graphene mode-locked Cr:LiSAF laser at 850 nm
    (OSA - The Optical Society, 2015) Canbaz F.; Kakenov, N.; Kocabas, C.; Demirbas, U.; Sennaroglu, A.
    We report, for the first time to our knowledge, a mode-locked femtosecond Cr:LiSAF laser initiated with a high-quality monolayer graphene saturable absorber (GSA), synthesized by chemical-vapor deposition. The tight-focusing resonator architecture made it possible to operate the Cr:LiSAF laser with only two 135 mW, 660 nm low-cost single-mode diode lasers. At a pump power of 270 mW, the laser produced nearly transform-limited 68 fs pulses with an average power of 11.5 mW at 850 nm. The repetition rate was around 132 MHz, corresponding to a pulse energy and peak power of 86 pJ and 1.26 kW, respectively. Once mode locking was initiated with the GSA, stable, uninterrupted femtosecond pulse generation could be sustained for hours. The saturation fluence and the modulation depth of the GSA were further determined to be 28 μJ/cm2 and 0.62%, respectively. 2015 Optical Society of America.
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    Observation of soliton molecules with independently evolving phase in a mode-locked fiber laser
    (2010) Ortaç, B.; Zaviyalov, A.; Nielsen, C.K.; Egorov O.; Iliew, R.; Limpert J.; Lederer F.; Tünnermann, A.
    We report the experimental generation of two-soliton molecules in an all-polarization-maintaining ytterbium-doped fiber laser operating in the normal dispersion regime. These molecules exhibit an independently evolving phase and are characterized by a regular spectral modulation pattern with a modulation depth of 80% measured as an averaged value. Moreover, the numerical modeling confirms that the limited modulation depth of the spectrum is caused by the evolution of the phase difference between the pulses. © 2010 Optical Society of America.
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    Properties of a microjoule-class fiber oscillator mode-locked with a SESAM
    (IEEE, 2011) Lecaplain, C.; Ortac, Bülend; MacHinet G.; Boullet J.; Baumgartl, M.; Schreiber, T.; Cormier, E.; Hideur, A.
    Energy scaling of ultrafast Yb-doped fiber oscillators has experienced rapid progress largely driven by many applications that require high average power femtosecond pulses. The fundamental challenge for ultrafast fiber lasers relies on the control of excessive nonlinearity, which limits pulse energy. The development of all-normal dispersion laser cavities based on large-mode-area photonic crystal fibers (PCFs) has enabled significant energy scaling [1-3]. In particular, up to microjoule energy levels have been achieved from rod-type fiber-based oscillators [2-3]. In such lasers, pulse shaping is dominated by the strength of the mode-locking mechanism which determines the pulse properties. In this contribution, we report the generation of high-energy sub-picosecond pulses from a highly normal dispersion fiber laser featuring an Yb-doped rod-type PCF and a large-mode-area PCF [Fig.1(a)]. Passive mode-locking is achieved using saturable absorber mirrors (SAMs). We study the influence of the SAM parameters on performances obtained in this new class of fiber oscillators. The structures exhibit 20 % modulation depths and 500 fs relaxation time with resonant and antiresonant designs. The antiresonant SAM structures ensure absorption bandwidths 45 nm while the resonant structures exhibit 20 nm bandwidths. Stable mode locking with average powers as high as 15 μW at 15 MHz repetition rate, corresponding to microjoule energy level are obtained with all the structures. However, pulse properties and pulse shaping mechanism distinguish between resonant and antiresonant designs. Using a broadband antiresonant SAM leads to generation of highly-chirped pulses with 30 ps duration and 10 nm spectral width [Fig.1(b)]. The output pulses are extra-cavity dechirped down to 550 fs duration. By increasing the strength of the mode-locking mechanism through the combination of the SAM with the NPE process, we obtain shorter pulses with slightly boarder spectra. Indeed, the output pulse duration is decreased from 30 ps to 13 ps by adjusting the wave-plates settings. The dechirped pulse duration is then shortened to 450 fs. We note that the current laser performances are limited to 1 J by the available pump power. Using a resonant SAM structure, the output pulse duration is decreased to 7 ps [Fig.1(b)]. This pulse shortening results from the spectral filtering induced by the limited SAM bandwidth. All these results are in good agreement with numerical simulations which will be discussed in this communication. © 2011 IEEE.