Mario Bolea

Optical UWB pulse generator using an N tap microwave photonic filter and phase inversion adaptable to different pulse modulation formats

We propose theoretically and demonstrate experimentally an optical architecture for flexible Ultra-Wideband pulse generation. It is based on an N-tap reconfigurable microwave photonic filter fed by a laser array by using phase inversion in a Mach-Zehnder modulator. Since a large number of positive and negative coefficients can be easily implemented, UWB pulses fitted to the FCC mask requirements can be generated. As an example, a four tap pulse generator is experimentally demonstrated which complies with the FCC regulation. The proposed pulse generator allows different pulse modulation formats since the amplitude, polarity and time delay of generated pulse is controlled.

Highly chirped single-bandpass microwave photonic filter with reconfiguration capabilities

We propose a novel photonic structure to implement a chirped single-bandpass microwave photonic filter based on the amplitude modulation of a broadband optical signal transmitted by a non-linear dispersive element and an interferometric system prior to balanced photodetection. A full reconfigurability of the filter is achieved since amplitude and phase responses can be independently controlled. We have experimentally demonstrated chirp values up to tens of ns/GHz, which is, as far as we know, one order of magnitude better than others achieved by electrical approaches and furthermore, without restrictions in terms of frequency tuning since a frequency operation range up to 40 GHz has been experimentally demonstrated.

Photonic arbitrary waveform generation applicable to multiband UWB communications.

A novel photonic structure for arbitrary waveform generation (AWG) is proposed based on the electrooptical intensity modulation of a broadband optical signal which is transmitted by a dispersive element and the optoelectrical processing is realized by combining an interferometric structure with balanced photodetection. The generated waveform can be fully reconfigured through the control of the optical source power spectrum and the interferometric structure. The use of balanced photodetection permits to remove the baseband component of the generated signal which is relevant in certain applications. We have theoretically described and experimentally demonstrated the feasibility of the system by means of the generation of different pulse shapes. Specifically, the proposed structure has been applicable to generate Multiband UWB signaling formats regarding to the FCC requirements in order to show the flexibility of the system.

Nonlinear dispersion-based incoherent photonic processing for microwave pulse generation with full reconfigurability.

A novel all-optical technique based on the incoherent processing of optical signals using high-order dispersive elements is analyzed for microwave arbitrary pulse generation. We show an approach which allows a full reconfigurability of a pulse in terms of chirp, envelope and central frequency by the proper control of the second-order dispersion and the incoherent optical source power distribution, achieving large values of time-bandwidth product.

Multiband-UWB Signals Generation Based on Incoherent Microwave Photonic Filters

A structure for multiband-UWB waveforms generation is proposed using an N tap microwave photonic filter with positive and negative taps. The system is based on phase inversion in electro-optical modulators and the sliced broadband source optical signal by means of a structure of AWGs, which permits us to obtain a high number of taps. System performance is experimentally shown by the generation of a uniform waveform. Capabilities as reconfigurability and frequency tuning have been also experimentally demonstrated. The flexibility of the system allows us to obtain multiband UWB waveforms, which fulfill the FCC spectral requirements.

High-order UWB pulses scheme to generate multilevel modulation formats based on incoherent optical sources

We present a high-order UWB pulses generator based on a microwave photonic filter which provides a set of positive and negative samples by using the slicing of an incoherent optical source and the phase inversion in a Mach-Zehnder modulator. The simple scalability and high reconfigurability of the system permit a better accomplishment of the FCC requirements. Moreover, the proposed scheme permits an easy adaptation to pulse amplitude modulation, bi phase modulation, pulse shape modulation and pulse position modulation. The flexibility of the scheme for being adaptable to multilevel modulation formats permits to increase the transmission bit rate by using hybrid modulation formats.

High-Performance Low Coherence Interferometry Using SSB Modulation

Low coherence interferometry (LCI) is an optical measurement technique that has attracted the interest for relevant fields like medicine or sensing. With the objective of improving LCI capabilities, microwave photonics (MWP) arises as an innovative technology to enhance LCI possibilities. In this letter, a novel MWP-LCI approach is proposed and experimentally demonstrated to measure the optical path difference (OPD) of a sample. The operation principle of the technique is based on the analysis of the interference pattern through a dispersive element to retrieve its visibility using a vector network analyzer. Different capabilities of the system in terms of sensitivity, resolution, and SNR have been proved. In this case, the proposal is able to avoid carrier-suppression effect leading to a sensitivity improvement of 20 dB in comparison with previous structures for certain values of the OPD. Moreover, the OPD range has been extended up to 10 mm achieving an invariant resolution over all operation range. Finally, the improvement of the SNR of the system has been experimentally demonstrated by controlling properly the RF resonance profile through the adjustment of the optical source power distribution. We have observed an improvement of the dynamic range close to 40 dB for a Gaussian profile.

High-order UWB pulse generation based on a microwave photonic filter using incoherent optical sources

We propose and experimentally demonstrate a photonic pulse generator for Ultra-Wideband application which is based on a microwave photonic filter whose coefficients are obtained by slicing of a broadband optical source and the polarity is controlled by phase inversion in electro-optical modulator. High-order UWB pulses have been experimentally obtained due to the number of taps which can be easily increased. Therefore, the adaptation of the waveforms to the FCC mask is improved considerably and the efficiency of the system is increased in terms of power spectral density.

Harmonic distortion in microwave photonic filters

We present a theoretical and experimental analysis of nonlinear microwave photonic filters. Far from the conventional condition of low modulation index commonly used to neglect high-order terms, we have analyzed the harmonic distortion involved in microwave photonic structures with periodic and non-periodic frequency responses. We show that it is possible to design microwave photonic filters with reduced harmonic distortion and high linearity even under large signal operation.

A novel MWP proposal for low-coherence interferometry applications

In this paper, by means of a well-established parallelism between MWP and LCI, a novel MWP-LCI technique is proposed and experimentally evaluated. This technique is based on the slicing of a broadband source which is transmitted through a dispersive element. The optical path differences (OPD) under test modifies the electrical transfer function of the MWP-LCI subsystem through a interferometric structure. The OPD range is increased due to the right allocation of the interferometric structure and extended close to zero for removing the basedband component due to the avoidance of the Carrier Suppression Effect (CSE) and the incorporation of a balanced detection, respectively. In this sense, an OPD range of more than 1.4 cm has been experimentally achieved. In the whole range, a considerable improvement of sensitivity has been achieved in comparison to previous contributions. For low OPD values, the improvement is around 6 dB, but more importantly, for high OPD values, a sensitivity improvement larger than 20 dB is achieved. On the other hand, it is also demonstrated that the proposed scheme maintains the resolution through the complete measurement range. These key parameters only depends on the operation bandwidth of the RF and electrooptical components.