Guillermo E. Villanueva

Single Bandpass Photonic Microwave Filter Based on a Notch Ring Resonator

A novel tunable single bandpass photonic microwave filter is proposed. It is based on optically filtering one of the sidebands of a phase-modulated optical carrier by means of the notch response of a silicon-on-insulator ring resonator. The filter response can be tuned by changing the laser wavelength. Experimental results to prove the concept are provided.

Dual-Wavelength DFB Erbium-Doped Fiber Laser With Tunable Wavelength Spacing

A novel tunable dual-wavelength distributed-feedback fiber laser is presented. It is based on the optical resonances induced by two local phase shifts introduced in the periodic structure of an erbium-doped fiber Bragg grating. A dynamic control of the phase shifts, which are generated by piezoelectric transducers, permits the tunability of the wavelength spacing between the optical harmonics of the laser signal. The wavelength spacing is continuously tuned from 0.128 to 7 GHz. Moreover, a microwave carrier is created within such frequency tuning range by the heterodyne photodetection of the dual-wavelength laser signal.

Phase and Amplitude Stability of EHF-Band Radar Carriers Generated From an Active Mode-Locked Laser

We study the phase and amplitude stability of RF signals, generated at different frequencies by heterodyning pairs of modes from the optical spectrum of an active mode-locked laser, and we focus on the dependence of noise on the RF frequency. A specific theoretical model is derived, and the amplitude and timing jitter behaviour of the RF signals are analyzed and experimentally validated. The timing jitter reveals to be constant at any RF generated frequency, making the considered RF generation method suitable for the realization of flexible and highly stable micro- and millimeter-wave coherent radar transceivers. The performance of the considered RF generation architecture are compared with a state-of-the-art RF synthesizer, proving that the optically generated RF signals meet the high stability requirements of the new generation of coherent radar systems, even at extremely high frequencies (EHF).

Linear and nonlinear optical properties of carbon nanotube-coated single-mode optical fiber gratings

Single-wall carbon nanotube deposition on the cladding of optical fibers has been carried out to fabricate an all-fiber nonlinear device. Two different nanotube deposition techniques were studied. The first consisted of repeatedly immersing the optical fiber into a nanotube supension, increasing the thickness of the coating in each step. The second deposition involved wrapping a thin film of nanotubes around the optical fiber. For both cases, interaction of transmitted light through the fiber core with the external coating was assisted by the cladding mode resonances of a tilted fiber Bragg grating. Ultrafast nonlinear effects of the nanotube-coated fiber were measured by means of a pump-probe pulses experiment.

Tunable Photonic Microwave Filter With Single Bandpass Based on a Phase-Shifted Fiber Bragg Grating

A novel tunable photonic microwave single bandpass filter based on the optical resonance originated by a local phase shift introduced in the periodic structure of a fiber Bragg grating is proposed. Dynamic control of the phase shift is obtained employing a piezoelectric transducer in order to stretch the grating, thus changing the resonance wavelength. A photonic microwave filter is obtained by using an optical single-sideband modulation. Experimental results are provided in order to prove the concept.

Active and Passive Mode-Locked Fiber Lasers for High-Speed High-Resolution Photonic Analog-to-Digital Conversion

We present a complete set of mode-locked fiber lasers designed for photonic analog-to-digital conversion. Design, simulation, fabrication, and characterization of Er-doped fiber lasers are carried out through optimizing their performance to suit the requirements of high-speed and high-resolution photonic-assisted analog-to-digital converters. The required properties are achieved by active mode-locking on the basis of amplitude modulation of the cavity losses through a Mach-Zehnder modulator, and passive mode-locking on the basis of fast semiconductor saturable absorbers and intracavity polarizing fibers. The use of an intracavity polarizing fiber in combination with a fast saturable absorber allows dynamic control of the operation regimes through polarization control. Besides these oscillators designed with ring cavity structure, a short linear cavity with fundamental repetition frequency at the order of 1 GHz is studied, and an effective continuous tunability of the repetition frequency is obtained by an electromechanical transducer. Pulsed repetition rates up to 20 GHz, pulsewidths down to 500 fs, and time jitters below 180 fs are obtained. Fiber lasers based on standard and commercially available telecom devices are demonstrated to be a low-cost, compact, and versatile optical source for photonic-assisted analog-to-digital conversion.

Dynamic control of the operation regimes of a mode-locked fiber laser based on intracavity polarizing fibers: experimental and theoretical validation.

An intracavity polarizing fiber is proposed to control the emission regime of a passively mode-locked fiber laser. Stable operation in self-starting high and low dispersion soliton mode-locking and 100 GHz multiwavelength regimes is demonstrated through numerical simulations and experimental validation. Mode-locking stability is ensured by a saturable absorber in the ring cavity. The effective selection of operation regime is dynamically carried out by controlling the intracavity polarization state.

Stable optically generated RF signals from a fibre mode-locked laser

Phase stability of RF signals obtained by two-mode filtering of a fibre mode-locked laser is analyzed. Time jitter is shown to be constant with selected mode spacing, confirming the scheme capability for generating stable RF signals up to extremely-high frequency.

Comprehensive Theoretical and Experimental Study of Short- and Long-Term Stability in a Passively Mode-Locked Solitonic Fiber Laser

We demonstrate the short- and long-term stable operation of an all-polarization-maintained Fabry-Pérot cavity passively mode-locked fiber laser. The laser operates in an all-anomalous-dispersion solitonic regime. Laser stability is studied by a variety of measurements, which confirm the high stability of the laser in the temporal and spectral-both optical and electrical-domains. Pulse durations of 540 fs, period-relative time jitters of ~0.0150/00, and long-term uninterrumped operation with 0.4% variation (standard deviation) in the average output power are obtained. The highly stable operation of the laser oscillator was maintained after amplifying the laser output with a conventional EDFA. Pulse durations of ~244 fs, period-relative time jitters of ~0.0190/00, and an average output power of 20 mW were obtained after amplification, while maintaining the 100-dB signal-to-noise ratio of the laser oscillator measured at 500-Hz offset from the fundamental harmonic frequency. The theoretical validation of our experimental results is based on solutions of the Nonlinear Schrödinger Equation. We demonstrate that wavelength and z -position dependences of the active medium gain must be taken into account for an accurate correspondence with the experimental properties of the laser.

Short-and-long-term highly stable oscillation and amplification of linearly polarized passively mode-locked solitonic fiber laser resonators

In this work, we present a short- and long-term operation and environmentally-stable, all-polarization-mantained, Fabry-Pérot resonator, passively mode-locked fiber laser operating in an all-anomalous-dispersion solitonic regime. Our results confirm that the highly stable operation of the laser oscillator is maintained after amplifying the laser output with a conventional EDFA. Such stability has been studied by a variety of measurements in the temporal and spectral -both optical and electrical- domains before and after amplification. Pulse durations of 540 fs, period-relative time jitters of ~0.015‰, and long-term uninterrumped operation with <1.8% variation of the individually photodetected pulse peak powers are obtained for the laser oscillator. After amplification, dispersion-induced pulse durations of ~244 fs, period-relative time jitters of ~0.019‰ and an average output power of 20mW are obtained, while maintaining the 100 dB signal-to-noise ratio (SNR) measured at 500 Hz offset from the fundamental harmonic frequency of the photodetected signal. We have also carried out a theoretical validation of the emission properties of our laser oscillator based on solutions of the Nonlinear Schröedinger Equation that take into account wavelength and z-position dependence of the active medium gain.