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Radio over fiber (RoF) has emerged as one of the most economical, high-bandwidth and low loss transmission for microwave signals [1]. In a simple RoF system, the optical carrier is modulated by an RF signal resulting in an optical carrier with sidebands also referred as Double Side Band (DSB) scheme. Though simple, the distribution of power in multiple sidebands make it power inefficient and susceptible...
There is significant interest in high power laser sources that can work outside the Yb emission band, for example, near 1.5um wavelength, for many applications like eye safe material processing, free space light transmission, pump sources for other lasers and LIDAR. Raman fiber lasers offer an excellent method to achieve high powers in a variety of wavelength regions [1]. In its conventional implementation,...
Continuous-wave (CW) super-continua have found applications in various domains such as sensing, spectroscopy, test and measurement and generation of broadly tunable lasers. CW supercontinua are implemented by high power pumping of a fiber in the anomalous dispersion regime, close to its zero-dispersion [1-3]. Pumped by Ytterbium doped fiber lasers, photonic crystal fibers are necessary since conventional...
We propose a new, all-passive architecture for high-efficiency cascaded Raman conversion. We demonstrate this with a high-power, fifth-order cascaded Raman converter (from 1117nm to 1480nm) with output power of 64W and conversion efficiency of 60%.
Stimulated Raman Scattering is one of the primary nonlinearities limiting power scaling of high power fiber lasers and amplifiers. Conversion of signal light into the Raman generated Stokes component can result in several undesirable consequences such as temporal instabilities, spurious pulsing, beam quality degradation, focusing errors etc. most of which are catastrophic for the laser system. In...
We demonstrate significant thermo-optic degradation of single-modedness in active large mode area fibers due to heat generation in the fiber. We propose and demonstrate through simulations, simple compensation mechanisms using custom length dependent fiber coiling.
We introduce and provide experimental verification for a new model and representation of pump absorption in rare-earth-doped double-clad fibers based on underlying physics. The model allows for simple evaluation of wavelength resolved, length dependent absorption.
We report on recent development of core- and cladding-pumped multicore fiber amplifiers suitable for amplifying space division multiplexed signals. Amplification, noise properties of these amplifiers are shown, and scopes for further development will be discussed.
We demonstrate record power and efficiency for 1.5micron fiber lasers using a cascaded Raman laser based on a new architecture with output power of 301W at 1480nm and optical to optical conversion efficiency of 42%.
Continuous wave and nanosecond pulse amplification in a higher-order-mode, Er-doped-fiber amplifier with 6000 μm2 effective area is demonstrated. Both 1480nm pump and 1560nm signal propagate in the LP0, 14 mode.
A CW Erbium-doped fiber laser with >100W at 1554nm is demonstrated. The laser is core-pumped in-band by a Raman fiber laser with record power of >140W at 1480nm. The total conversion efficiency is ∼75%.
We demonstrate programmable control of a pulse shaper that achieves both fine resolution and broad bandwidth operation by dispersing light into two dimensions. We show line-by-line pulse shaping at 5 GHz in a closed-loop configuration.
We discuss research at Purdue University in which ultrafast optical signal processing approaches are adapted for generation, processing, and compression of ultrabroadband RF electrical signals.
We report on a 4-channel radio-frequency arbitrary waveform generator, capable to switch within a clock period among synthesized radio-frequency arbitrary waveforms. The system works by combining an original switching scheme of time-multiplexed multi-wavelength optical frequency combs with a two-dimensional line-by-line pulse shaper featuring broad bandwidth operation over large temporal windows....
Microwave photonic filters utilizing optical frequency comb have shown programmable passband, high stopband attenuation, and easy tunability. We demonstrate flat top bandpass filter. To obtain high stopband attenuation, smooth apodization of comb spectrum to specific profile is necessary. Stopband attenuation is significantly enhanced by utilizing comb which achieves the necessary shape directly from...
We demonstrate a reconfigurable all-diffractive setup for spectral synthesis. It is based on a spatially patterned diffractive lens implemented using a phase-only two-dimensional liquid-crystal on-silicon spatial light modulator. Experimental results show good agreement with the theory.
Using electro-optic modulators, we generate a 41-line 10-GHz spaced Gaussian-shaped optical comb. We use this comb to demonstrate apodized microwave photonic filters with greater than 43-dB sidelobe suppression, without the need for a pulse shaper.
We demonstrate a scheme to scale the bandwidth by several times while enhancing spectral flatness of frequency combs generated by intensity and phase modulation of CW lasers using cascaded four-wave mixing in highly nonlinear fiber.
We demonstrate a scheme to scale the bandwidth by several times while enhancing spectral flatness of frequency combs generated by intensity and phase modulation of CW lasers using cascaded four-wave mixing in highly nonlinear fiber.
We present flat-top microwave photonic filters through amplitude and phase shaping of optical frequency combs. Flat-topped filters with greater than 27-dB stopband loss are demonstrated using 32 taps with both positive and negative tap coefficients.
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