Jesús Palací

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).

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.

Reconfigurable Photonic Microwave Filter Based on Four-Wave Mixing

A simple technique to reshape the response of tapped delay line photonic microwave filters is demonstrated. The technique is based on the generation and control of a set of optical carriers by means of four-wave mixing. Experimental results show reconfiguration from 2 to 5 taps with uniform and apodized amplitude distributions.

Terahertz transceiver concept

We present a photoconductive terahertz transceiver based on a modulation of the optical pulses used for generation and detection at different rates. External modulation of the THz pulses is not required as opposed to previously reported approaches. Devices from fiber-optic technology are used, providing flexibility and stability to the system. Imaging and thickness measurement experiments are carried out to demonstrate the performance of the transceiver.

Biconical Tapered Fibers Manipulation for Refractive Index and Strain Sensing Applications

Tapered fibers are used in multitude of applications due to its great versatility and functionality. In particular, this type of fibers is especially useful for sensing applications. For this purpose, tapered fibers must be adequately manipulated to avoid disturbances in the sensors response. In this paper, a guideline for the correct handling of biconical tapered fibers during refractive index and strain measurements is presented and analyzed considering several manipulation scenarios and its corresponding influence in the performance of the system.

Control of terahertz emission in photoconductive antennas through an additional optical continuous wave

The manipulation of the operating conditions of photoconductive antennas by means of an additional continuous wave (CW) is reported. It is used to control a fiber-based terahertz (THz) time-domain-spectroscopy system at telecom wavelengths. The injection of an optical CW into the transmitter allows the control of the THz amplitude without causing major degradation to the system performance. This, for instance, can be exploited to perform modulation of the THz signal.

All-fiber processing of terahertz-bandwidth signals based on cascaded tapered fibers.

Tapered single-mode fibers are employed to perform dynamic pulse shaping in a bandwidth of several terahertz. The transfer function of cascaded biconical tapers is controlled by introducing a phase shift into one of them through mechanical stretching. It is a simple and low-cost technique with potential to process signals with bandwidths as large as those allocated by standard optical fiber while introducing little degradation. Femtosecond pulses are shaped to prove the concept.

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.