A short-cavity fibre laser oscillator emitting 12 ps-long pulses at the fundamental cavity frequency of 550 MHz is reported. The simple, stable and ultra-compact laser cavity consists of a short active fibre section which is spliced to a narrowband fibre Bragg grating, and a butt-coupled semiconductor saturable absorber mirror. Only 8 cm of the heavily Er/Yb co-doped phosphate-glass active fibre is sufficient to produce as much as 775 mW of average Output power at 1.5 mu m directly from the oscillator.

We report using short, heavily-doped active phosphate fiber for generation of picosecond pulses at 1.5 mum, with the peak power of 19 kW which results in a record-high aerial power density of 24 GW/cm 2 in the fiber core.

We report an all-fiber passively mode-locked fem-tosecond laser oscillator based on the heavily doped Er-Yb phosphate-glass active fiber. Only 20 cm of the gain fiber is sufficient to produce as much as 1.1 W of average output power at 1.5 mu m directly from the oscillator. The laser can be harmonically mode-locked at repetition rates ranging from 1.7 to 7.2 GHz by adjusting the polarization bias in the cavity. The pulsewidth varies from 300 to 570 fs at the lowest and the highest repetition rate, respectively, and the maximum peak pulse power exceeds 1 kW.

We report on a passively mode-locked all-fiber laser oscillator at 1.5 microm based on heavily doped phosphate-glass active fiber. An active fiber only 20 cm long is sufficient to produce as much as 2.4 W of average output power directly from the oscillator. The width of the mode-locked pulses varies from 8 ps at the lowest output power in the mode-locked state to 44 ps at the highest power. Our picosecond laser oscillator features a high repetition rate of 95 MHz and high peak pulse power of approximately 540 W. The oscillator combines the convenience of all-fiber construction with power performance that was previously achievable only with mode-locked bulk-optic laser oscillators or more complex systems involving fiber amplifiers.

We describe a novel method for subpicosecond pulse shaping based on longitudinal spectral decomposition in dispersive media. The entire system is created with standard telecommunications equipment allowing for integration with optical communication networks. The technique has the potential for time–bandwidth products ⩾104 due to exclusive reliance on time-domain processing. We introduce the principle of operation and subsequently support it with results from our experimental system. Both theory and experiments suggest third-order dispersion as the principle limitation to realizing a large number of resolvable spots. Chirped fiber Bragg gratings offer a route to increase the time–bandwidth product for high-speed signal processing applications.

Summary form only given. Microstructured fibers and fiber lasers are providing new approaches for achieving single transverse mode guiding in large core fibers. We have successfully fabricated microstructured fibers from phosphate glass that allows the same high doping levels as in our step index fibers. We developed a two step draw-stack-redraw process that enables the realization of various microstructured cladding and multiple core designs. With our first active microstructured fibers we obtained the following important results. We fabricated and tested the first phosphate glass microstructured fiber lasers with large Er-Yb-codoped cores. For an 11-cm-long cladding-pumped fiber laser, more than 3 W continuous wave output powers has been demonstrated and single-mode beam quality was obtained for an active core area larger than 400 /spl mu/m/sup 2/. We performed, to the best of our knowledge, the first systematic study on how a negative core-cladding index difference influences microstructured optical fiber's modal behavior. Single-mode lasing has been realized for short-length cladding-pumped phosphate glass fibers with large depressed-index Er-Yb-codoped cores. Large core microstructured fibers allowed us to construct even shorter fiber lasers at Watt level output power. A 3.5 cm short microstructured fiber laser produced 5 W cw output power at a pump-to-signal conversion efficiency of 20%. To scale the output power of compact fiber lasers systems to even higher levels, we are working on phase-locked arrays of single mode fiber lasers. This work was initiated through theoretical modeling. Only recently, we were able to use the flexibility of our two-step fiber drawing process to fabricate fibers with multiple cores that can be used to test phase-locking techniques. Initial experiments in this direction has been started. As an example, a microscope image of our microstructured fiber with 12 active cores is shown. Another image demonstrates the lasing action of all 12 cores just above threshold indicating quality and homogeneity of the multi-core fiber. To avoid thermal issues, the first 2 fibers feature a 4 times lower (2 wt%) Yb/sub 2/O/sub 3/ doping level compared to our record breaking step index fibers leading to reduced pump absorption and efficiency. However, even with these test fibers we achieved more than 2 W of combined output power with more than 10% conversion efficiency in a 10 cm fiber laser.

We demonstrate tunable, single-pulse spectral phase measurement of broadband ultrafast signals by linear spectral interferometry. The approach is based on a coherently coupled pair of optical parametric amplifiers (OPAs). The first amplifier is the source of a signal pulse that is coupled into a nonlinear medium, where the pulse generates a broadband signal by nonlinear interactions; the second OPA provides a phase-correlated reference pulse that can be tuned across the broad spectral range and used for complete characterization of the broadband signal generated by the first OPA. An experimental demonstration of the technique for a nonlinearly modulated femtosecond pulse with a bandwidth of >200 nm occupying the range 1.13-1.36 µm is given.

This research aims to extend the number of resolvable spots by utilizing a novel pulse shaping technique based solely on time domain processing through the use of linear chromatic dispersion for spectral decomposition. A potential advantage of this technique over conventional time-space approaches to pulse shaping is the large number of resolvable spots possible when using a dispersed-pulse time window.

Applications of ultrashort pulse laser technology in information processing, imaging and communication security are discussed in the paper.

This paper presents applications of nonlinear optics and ultrafast pulse lasers for optical information processing. Nonlinear wave mixing process based on three- and four- wave mixing in a second order nonlinear crystal inside the spectral processing device (SPD) is utilized. Signal processing is performed in the temporal frequency domain by spatially dispersing the frequency components in a SPD and performing operations on the spectrally decomposed wave (SDW) using its unique time-domain properties. These techniques enable femtosecond rate space-to-time conversion for multiplexing an ultrahigh bandwidth serial temporal channel onto slower parallel channels.

We investigate two-photon absorption in a silicon CCD for single-shot correlation of femtosecond pulses with nanojoule energy levels. The approach is dem’onstrated by detecting the interferometric correlation of 180 fs pulses from a parametric oscillator at 1.54 pm.

We demonstrate a novel method for spectral analysis of microwave signals that employs time-domain processing in fiber. We use anomalous dispersion in single-mode fiber to perform a Fresnel transform followed by a matched amount of dispersion-compensating fiber to perform an inverse Fresnel transform of an ultrashort pulse. After the Fresnel-transformed waveform is modulated by the microwave signal, the waveform at the output of the dispersion-compensating fiber represents the ultrashort pulse convolved with the microwave spectrum. An experimental system for spectral analysis of microwave signals in the range 6-21 GHz is demonstrated.

We describe several concepts for real time shaping and detection of femtosecond laser pulses using optical nonlinearities. Cascaded second order wave mixing is used for-real-time conversion of spatial-domain images to ultrafast time-domain optical waveforms. We experimentally demonstrate a cascaded nonlinearity arrangement allowing generation of complex amplitude femtosecond waveforms with high fidelity and good conversion efficiency. Single-shot, phase-sensitive detection of femtosecond pulses is demonstrated using both nonlinear wave-mixing and 2-photon absorption in semiconductor detector arrays. Using commercial silicon charge-coupled device (CCD), the latter approach allows detection of broadband ultrashort signals in the important wavelength range around 1.5 microns without phase-matching limitations. Finally We describe an approach to characterization of the multimode fiber using ultrashort pulse interferometry.

Linear dispersion in optical fiber, while seen as a principle hindrance to high data rate optical communications, can be experimentally exploited to map the spectral components of a propagating optical waveform in time. The process is an analog to Fresnel or Fraunhofer diffraction fields in space and results in a similar transformation of a time-domain optical pulse after extended propagation in fiber (e.g., equivalent to the approximate Fourier transform realized under the Fraunhofer approximation) [1]. Recently, dispersion in single mode fiber has been reported as a means to assist in arbitrary RF-waveform generation [2]. We seek to extend the utility of dispersive fiber by performing RF signal analysis through manipulation of RF-modulated optical pulses.

We describe various optical techniques for processing and detection of femtosecond laser pulses. Photorefractive and cascaded second order nonlinear wave mixing are used for space-to-time conversion, transforming space domain information into ultrafast temporal waveforms. An inverse operation that transforms a femtosecond pulse sequence into a quasi-stationary spatial image is performed with spectral domain three wave-mixing. We also demonstrate single-shot phase sensitive femtosecond pulse detection with two-photon absorption in a conventional silicon detector array. This approach allows efficient detection of wide-bandwidth ultrafast signals in the wavelength range of 1-2mum.

Summary form only given. We report a single-shot approach for generating the sonogram of an ultrashort pulse using two-photon absorption in a standard CCD camera. In the experimental apparatus a laser pulse is introduced into a spectral decomposition setup consisting of a diffraction grating and a cylindrical lens telescope, imaging the surface of the grating onto the CCD array.

We present an experimental technique capable of single-shot recording of an ultrashort laser pulse sonogram by use of two-photon absorption in a conventional silicon CCD camera. The quadratic spectral phase, introduced into a 100-fs pulse by a grating stretcher, was measured and found to be in good agreement with the analytically calculated value. The nonlinear response of silicon allows sonogram characterization in a wavelength range from 1 to 2 mum .

An experimental technique for single-shot generation of the sonogram of an ultrashort laser pulse is demonstrated. The method is based on the time gating of a spectrally decomposed test signal, transferring its spectral phase into a spatial phase, and the spatial filtering of the signal to produce a sonogram. The technique is evaluated experimentally, producing sonograms for linearly and nonlinearly chirped femtosecond laser pulses. The single-shot technique permits reconstruction of ultrashort pulse complex amplitude profiles and is useful for showing the signal in real time.

We present an experimental setup capable of performing a single-shot interferometric correlation of femtosecond pulses using two-photon conductivity in a standard silicon CCD camera. The method is demonstrated with 100-fs pulses at 1.4 microm.

We demonstrate several nonlinear optical techniques that allow spatial-temporal processing of femtosecond laser pulses. Photorefractive and cascaded second order nonlinear wave mixing is used to convert space domain information into ultrafast temporal waveforms. Spectral domain three wave mixing allows time imaging of femtosecond signals as well as characterization of the signal complex amplitude. Femtosecond pulse iriterferometry is applied for spatial and temporal characterization of the multimode optical fiber.