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J. Eur. Opt. Society-Rapid Publ. 21, 2( 2025)
Figure 4. Schematic diagram of optical beamforming scheme.
Figure 5. Schematic diagram of a 1 4 OBFN phased array antenna system based on adjustable optical true time delay lines or microwave photon phase shifters [ 23 ].
using electronic phase shifters. Figure 5 shows a 1 4 OBFN phased array antenna system based on adjustable optical delay lines or microwave photon phase shifters.
In Figure 5, the laser( LD) generates an optical carrier, and the RF signal is loaded onto the optical carrier through modulation and conversion to achieve electro-optical conversion. The OBFN consists of Optical True Time Delay Line( OTTDL) and Microwave Photon Phase Shifter( MWPPS). It should be pointed out that the MWPPS controls the phase of the output RF signal by changing the carrier phase. OTTDL delay signals by introducing different transmission times in the signal path, ensuring that signals of all frequencies have the same delay time during transmission. OTTDL is linear and independent of the frequency of the signal. Main function of the OBFN is to operate the OTDD and MWPPS in the optical domain, allocate and transmit them to each antenna element through the distribution network. Finally, use optical detectors to demodulate and recover RF or microwave signals in order to achieve signal transmission in antenna units and beam scanning.
Thanks to the inherent advantages of photonics such as ultra wideband optoelectronic devices, low transmission loss of optical fibers, and resistance to electromagnetic interference, it has great potential for applications in the generation, reception, and processing of high-frequency broadband microwave signals. In recent years, scholars at home and abroad have conducted in-depth research on optical beamforming networks and technologies. Outstanding achievements have been made in areas such as optical true delay lines, microwave photon phase shifters, optically controlled beamforming networks, and their miniaturization.
4 OTTD technology and its research status
OTTD technology is the most direct technical means to achieve phase delay of optical carrier signals, and it is also the most basic technical means to implement optical controlled beamforming systems. There are four common phase delay methods, including three time-domain processing methods and one spectral domain processing method.
It had been summarized that the relationship between the time delay caused by signal transmission in optical fibers and fiber length or refractive index in Reference [ 25 ].
sðL; kÞ ¼ L m g ðkÞ þ L c nðkÞþLDðkÞk ð25Þ
In formula( 25), Ds( L, k) is the delay time of an optical signal with a wavelength of k in a path of length L. cisthe propagation speed of light and m g( k) represents the group velocity of the transmitted optical signal. Dn( k) is the relative refractive index of the medium material in the path. D( k) is the dispersion coefficient of the medium in the path