In this paper we describe the first realization of a combined radar and lidar system based on integrated photonic technology, developed within the project “RODI-RF/OPTICAL Combined coherent Transceiver for RADAR/LIDAR and RF/Optical communications in space” funded by the Italian Space Agency for the technological validation of photonic systems for space applications.
We report the design and implementation of a beam-forming network based on packaged integrated photonic circuits. Each of the four PICs emulating a phased-array antenna is optically fed by the 13GHz signal, and is able to adjust the phase exceeding 360° with a precision <1°. Experiments demonstrate an ultrafast antenna reconfiguration in less than 5ns
The phase response of a commercial saturable absorber based on semiconductor quantum wells embedded in a resonant
cavity is investigated. The nonlinear absorption change is accompanied by a variation of the spectral phase characteristic.
Also, a nonlinear change in the refractive index of the material, induced by the modified carrier density, produces a weak
shift in the resonant wavelength of the cavity. These effects can be exploited to realize an optically-controllable phase
shifter. Simulations based on a nonlinear model are also carried out in order to investigate the effect of the various cavity
parameters and phase response of the device under different operating conditions. The results from this characterization
and numerical analysis show that such device can have the potential for practical applications in telecom systems,
including dynamic dispersion compensation, tunable nonlinear effects compensation, and nonlinear signal processing
and all-optical regeneration of phase-modulated optical signals.
A 2x2 cross/bar optically-driven switch is implemented with a single semiconductor optical amplifier. The switch
exploits nonlinear polarization rotation experienced by two input signals in the amplifier in presence of a control pump
light. The two input data signals travel in opposite directions inside the amplifier. In absence of the control light, the lowpower
input signals do not experience nonlinear effects inside the amplifier; when the pump light is applied, both the
input data signals experience cross-phase modulation, which reflects in nonlinear polarization rotation for the output
signals due to polarization-dependent carriers modulation in the semiconductor amplifier. Polarizes are then used in the
output paths in order to discriminate the output packets for the two possible cases of control pump signal in the ON and
OFF state. Bit error rate measurements demonstrate error-free operation for both the possible switch configurations. By
letting the input signals to travel the amplifier in opposite directions this architecture enables operation with data packets
at the same wavelength. The switch speed is limited by the carriers recombination time in the amplifier, in the order of
few hundreds of ps. Semiconductor technology allows implementation of compact, cost-effective, and low-power
operating all-optical devices.
Wavelength conversion with high contrast ratio and low OSNR penalty has been achieved by using a resonant vertical-cavity all-optical switch based on saturable absorption in multiple-quantum-wells. The device was grown by MBE on InP substrate. It comprised a 19.5 pairs n+-Ga0.47In0.53As/InP bottom DBR, 28 Ga0.47In0.53As QWs, and a 50% reflective top dielectric mirror. We carried out conversion experiments between a wavelength-tunable modulated pump signal and a CW beam with a wavelength matching the Fabry-Perot resonance of the switch. Using a 622 Mb/s modulated pump with an average power of only 6-dBm we have demonstrated a 15 dB extinction ratio for the converted signal. The wavelength conversion process exhibited a weak dependence on the pump signal wavelength; we have achieved wavelength conversion in a range of 20 nm. BER/OSNR measurements on the wavelength converted data signal indicated a maximum OSNR penalty (at a BER=10-9) of about 2.5 dB, with respect to the input pump data, over the entire conversion range. Error free operation was observed up to 2 Gb/s when device performance degraded due to its long absorption recovery time. However, with further optimization, the device recovery time could be reduced to the picosecond range, extending its application to much higher date rates.
We report on a simple self-starting diode-pumped passively mode-locked Er-doped fibre laser based on two semiconductor saturable absorber mirrors (SESAMs), generating sub-picosecond stable optical pulses. Pulses duration between 350 and 650 fs (FWHM) was observed for pulses central wavelengths ranging between 1540 nm and 1570 nm. The cavity basic frequency was 3.7 MHz, and stable operation up to the third harmonic (11.1 MHz) was observed when the output power of the 980 nm diode pump was increased to its maximum value of ~300 mW. The maximum average output power was 19.45 mW, which corresponded to a pulse energy of ~4 nJ. Noise characterization of the mode-locked laser source was performed, in order to estimate the phase noise of the output pulses in terms of timing jitter. All the fiber components in the cavity were polarization maintaining in order to increase long-term stability of the laser operation.
Wavelength conversion with high contrast ratio and low OSNR penalty has been achieved by using a resonant vertical-cavity all-optical switch based on saturable absorption in multiple-quantum-wells. The device was grown by MBE on InP substrate. It comprised a 19.5 pairs n+-Ga0.47In0.53As/InP bottom DBR, 28 Ga0.47In0.53As QWs, and a 50% reflective top dielectric mirror. We carried out conversion experiments between a wavelength-tunable modulated pump signal and a CW beam with a wavelength matching the Fabry-Perot resonance of the switch. Using a 622 Mb/s modulated pump with an average power of only 6-dBm we have demonstrated a 15 dB extinction ratio for the converted signal. The wavelength conversion process exhibited a weak dependence on the pump signal wavelength; we have achieved wavelength conversion in a range of 20 nm. BER/OSNR measurements on the wavelength converted data signal indicated a maximum OSNR penalty (at a BER=10-9) of about 2.5 dB, with respect to the input pump data, over the entire conversion range. Error free operation was observed up to 2 Gb/s when device performance degraded due to its long absorption recovery time. However, with further optimization, the device recovery time could be reduced to the picosecond range, extending its application to much higher date rates.
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