Optical delay line (ODL) plays a crucial role in various detection techniques such as terahertz time-domain spectroscopy (THz-TDS), and optical pump detection. This article proposes a novel ...multi-mirror array optical delay line (MMAODL) structure suitable for THz-TDS systems, which consists of a laser collimator, a rotating disk, a multi mirror array, a pyramid prism, and a plane mirror. Based on the principle of ray tracing, a theoretical mathematical model of MMAODL was constructed. Combined with simulation, the working angle of MMAODL was obtained to be 13 deg, and the theoretical delay time was 228.71 ps. Using the THz TDS system, the actual time length of the 8-cycle MMAODL structure, calibrated by the FP standard, was tested and demonstrated to be 228.47 ps, and the time-domain error of the collected signal was found to be approximately 0.014 ps. When an 8-cycle MMAODL is combined with a 4000-rpm motor, the theoretical waveform reproduction rate can reach 533 Hz, which simultaneously meets the requirements of a THz-TDS system for long delay time and high scanning frequency.
Comparing with electronic beam forming, integrated optical beam forming is very promising for optical controlled phase array system, because much broader band beam steering can be achieved without ...the beam squint effect. The single channel optical true time delay lines based on the cascade microring resonators and switched optical delay waveguides have been extensively investigated. The optical beam forming chip based on multi-channel microring resonators have also been demonstrated, however only limited working bandwidth were obtained due to their inherent tradeoff between the delay and bandwidth. The bandwidth limitation can be overcome by using integrated optical beam forming chip composed of switched optical delay waveguides, which has not been demonstrated and evaluated. Here, a 1×4 optical beamforming chip with four integrated switchable delay lines units designed to control the Ka-band phased antenna arrays is proposed and demonstrated experimentally. The maximum delay of 96 ps with a delay increment about 3.02 ps/stage was obtained, which is in accordance with the design well. Based on the measured delay times, the directional diagrams of the optical beamforming network were simulated and beam angle coverage of 90° can be achieved. Furthermore, a magnitude response experiment was carried out to evaluate the performance of the optical beam forming chip, and a remarkable working bandwidth of 29 GHz was achieved.
•We proposed an integrated four channel OBFN chip designed for a 40 GHz PAA.•The OBFN chip was packaged and delay increaments of 3.06 ps were realized.•A maximum radiation angle deviation is about 3.32° from the design radiation angle.•The OBFN chip can work well within K and Ka band with a bandwidth of about 29 GHz.
The authors demonstrate a photonic link for stable radio frequency (RF) dissemination over fibre based on passive phase compensation with an active-assisted control method. A variable optical delay ...line is introduced in the transmitting link for active-assisted phase compensation. After active-assisted compensation, the residual jitter is <500 fs. Experimentally, an RF signal at a frequency of 5 GHz is successfully transmitted over a 20-km fibre link, with the stability of 2.49 × 10−14 at 1 s and 9.19 × 10−18 at 104 s.
The development of radio-frequency (RF) filters with bandwidth reconfigurability and frequency tunability in the MHz range is increasingly important to broadband wireless communication and radar ...systems. In this paper, we demonstrate a reconfigurable RF filter based on a silicon integrated optical true time delay line (OTTDL). The OTTDL is a four-path parallel structure with the reconfiguration enabled by thermo-optic Mach-Zehnder interferometer switches. By controlling the power splitting ratio of the switches, three different orders of finite impulse response filters with a variable bandwidth are realized. The bandwidth can be varied from 180.9 MHz to 662.0 MHz and the center frequency can be tuned in one free-spectral range up to 1 GHz.
In this paper, based on the double strip silicon nitride platform, we designed and fabricated a low loss continuously tunable broadband optical delay line, which contains a 5-bit optical switched ...delay line and a single tunable optical ring resonator working at "off-resonance". Optical double sideband modulation link measurement results show it can achieve continuous delay tuning of 395.5 ps and in-band delay fluctuations of about 4 ps and 1 ps were obtained in 8 GHz and 5 GHz working bandwidths, respectively. In addition, the proposed optical delay line has a low on-chip insertion loss of 3 dB and a very low optical loss delay ratio of 0.0022 dB/ps. Moreover, it's delay tuning range can be easily increased by cascading more thermo-optic switches. The delay bandwidth can be expanded by adopting the optical single sideband modulation or increasing the FSR of the optical ring resonator. This integrated tunable optical delay line with good overall performances and expand ability shows great potential for microwave photonic applications.
We report a broadband optical delay line programmable for delays up to 1 <inline-formula><tex-math notation="LaTeX">{{\bf \mu s}}</tex-math></inline-formula> with nanosecond resolution, while ...preserving an arbitrary and unknown polarization state of the original light. The delay line comprises bidirectional pass in cascaded segments of standard single-mode fibers, along with terminal reflection from Faraday mirrors (FMs) at both ends. Each segment contains either a short path or a long path, selected by an optical switch. The FMs auto-compensate for random polarization fluctuations introduced by the optical fibers, thereby restoring the initial polarization state. Broadband operation of the delay line was assessed by investigating dispersion of both the fiber and the FMs. Surprisingly, we found that the two-pass propagation in the fiber can mitigate dispersive distortion introduced by the FM. Numerical experiments demonstrated that the output polarization state of the delay line has a mean fidelity better than 99% over a range of 50-nm deviation from the central wavelength. Remarkably, the mean fidelity often surpasses that in the absence of the fiber itself.
In this article, a photonic technique is proposed for generating the microwave signal of multiple shapes. Furthermore, this is modified to give a microwave signal with frequency multiplying ...capability, which does not require an optical filter. The proposed methodology is relied on the polarization modulator (PM), the Mach-Zehnder modulator (MZM), and the variable optical delay line (VODL), where the transmission point of PM has been selected by static phase of polarizer controller and MZM by the dc bias voltage. An RF signal of 6-GHz frequency is applied at PM to modulate the optical carrier signal. Frequency-dependent VODL has been used to provide dynamic phase shifts in the harmonics of the modulated signal. Firstly, 12-GHz full-wave rectified (FWR) and 6-GHz half-wave rectified (HWR) sinusoidal signals have been generated using PM and VODL. For the generation of FWR and HWR, respective phase shifts of <inline-formula> <tex-math notation="LaTeX">- \pi /2 </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">\pi </tex-math></inline-formula> have been introduced by VODL. Then, a sextupled microwave signal of 36-GHz frequency has been generated which is further processed for the generation of triangular-shaped HWR of 6-GHz frequency. This has been achieved by modulating one of the split powers of PM with the help of an MZM. The generation of such multishape rectified waveforms has not been reported before. Also, the frequency sextupling capability of the proposed technique defines the multifunctionality of the system. Theoretical analysis of the considered approach has been given which is supported by simulated results and validated by the experimental results.
For simplification of mobile base station architecture, we present remote beamforming of an array antenna integrated with photodiode based on photonics. Variable optical delay lines (VDLs) and ...variable optical attenuators (VOAs) are utilized for tailoring the RF phases and amplitudes and radio-over-fiber (RoF) technique is adopted for RF signal transmission. First, we show a simple demonstration of 60-GHz antenna beamforming using VDLs and VOAs with the aim of simplification of RoF signal generation at a control site. Next, we present experimental results on 60-GHz band digital signal transmission at 7 and 14 Gbit/s with beamforming function, in which eight compact antenna modules are arrayed in a row. Finally, we investigate RoF signal generation at 40 GHz utilizing the 1.3-μ m band electroabsorption modulator-integrated laser diode, where an optical filter and an optical amplifier are used to boost the modulation component and the successful formation of various beam patterns by tuning VDL and VOA is shown.
The optical-frequency-comb-based (OFC-based) sampling method is of better efficiency than a heterodyne receiver when measuring non-cooperative signals over a large frequency range. However, ...under-sampling during the down-conversion process often results in missing frequency information, necessitating multiple OFCs for recovery. This article proposes a frequency-phase-mapping method with a single OFC is proposed to recover the missing frequency information. First, an asymmetric two-branch electro-optical-modulating structure is designed to acquire the phase difference caused by the time delay. Then, the acquired phase difference is mapped into the signal frequency by a complex unit circle without <inline-formula> <tex-math notation="LaTeX">2\pi </tex-math></inline-formula>-blur. A dimension-expanding procedure is proposed by introducing multimeasuring to enhance the robustness performance. The influence of frequency range, signal-to-noise ratio (SNR), and measuring times are analyzed in detail. The experiment indicates that the correct ratio of frequency recovery can reach 93.5% when the SNR is 20 dB, the frequency range is 1-12 GHz, and the measuring times are 2, demonstrating the proposed method's efficiency.
In this paper a theoretical derivation of unloaded and loaded Q-factor of delay-line cavities, such as optical fiber delay-lines, and delay-line based oscillators, such as optoelectronic oscillators ...(OEOs), is presented based on three approaches: (I) second-order resonator approximation, (II) linear time-invariant phase-space model and (III) energy approach. Theoretical expressions for unloaded and loaded Q-factor of delay-line based cavities and oscillators are derived. We show that the Q-factor of a delay-line based cavity is a function of its round-trip time that is not equal to the energy decay-time of usual microwave or optical resonators. Hence, the behavior of the Q-factor of a delay-line based cavity will not be the same as that of the usual resonators. We show that the loaded Q-factor of a delay-line cavity is greater than its unloaded Q-factor!, besides we show that the Q-factor of a lossy delay-line cavity is the same as that of the lossless one! (in contrast to the behavior of the usual resonators). We also show that the Q-factor of a delay-line based oscillator is proportional to the half of the round-trip time of its delay line while the Q-factor of an oscillator based on a usual resonator is proportional to the energy decay time of its resonator.
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