Photonic chirped radio-frequency generator with ultra-fast sweeping rate and ultra-wide sweeping range

Abstract

A high-performance photonic sweeping-frequency (chirped) radio-frequency (RF) generator has been demonstrated. By use of a novel wavelength sweeping distributed-feedback (DFB) laser, which is operated based on the linewidth enhancement effect, a fixed wavelength narrow-linewidth DFB laser, and a wideband (dc to 50 GHz) photodiode module for the hetero-dyne beating RF signal generation, a very clear chirped RF waveform can be captured by a fast real-time scope. A very-high frequency sweeping rate (10.3 GHz/μs) with an ultra-wide RF frequency sweeping range (~40 GHz) have been demonstrated. The high-repeatability (~97%) in sweeping frequency has been verified by analyzing tens of repetitive chirped waveforms.

External Modulation Method for Generating Accurate Linear Optical FMCW

“…This shows that the jitter rates largely maintain the same level even though the sweep speed changes from 0.005 GHz/μs to 2.5GHz/μs. This is a significant improvement compared to the previous study [9] and demonstrates that the inference between the jitter rate and the sweep speed is substantially alleviated by employing the external modulation method. The result also implies that the relaxation oscillation in a laser cavity dominates and significantly affects the final accuracy of the optical FMCWs generated by internal modulation techniques.…”

“…several GHz/μs). This can be seen in Wun's system [9] in which the frequency jitter rate increased by a factor of 6 when the sweep speed was increased by a factor of 6.5. This can mainly be attributed to the intrinsic relaxation oscillations present in lasers, especially unavoidable when they are modulated directly for generation of different linear sweep speeds.…”

“…There has been extensive efforts made to update the characteristics of linear FMCWs, including enlarging sweep spans, increasing sweep speed or slope, reducing jitter rates, and improving linearity. Several methods based on intracavity modulation techniques have been reported for generating FMCWs, including Fourier Domain Mode Locking [6], semiconductor laser with a hybrid optoelectronic feedback loop [7][8], phase locking between two independent lasers [9], electronic-photonic heterogeneous integration [10], and optical heterodyne detection [11]. However, many of these suffer a common problem in terms of frequency jitter rates when the chirp rates reach several GHz/μs.…”

Photonic generation of linearly chirped millimeter wave based on comb-spacing tunable optical frequency comb

“…6,7 The radar pulses, for example, are usually frequency chirped to improve the time-bandwidth product (compression ratio), thus to promote the range resolution under the same radar detection distance. Photonic generation methods, such as direct frequency-to-time mapping technique 8,9 and heterodyne-beating technique, 10,11 have been proposed and achieved. As a promising alternative, photonic generation of linear frequency-chirped signal can meet the requirements of high center frequency and broad chirp range.…”

Photonic Synthesis of Spread Spectrum Radio Frequency Waveforms With Arbitrarily Long Time Apertures

“…These restrictions are incompatible with established applications such as chirped radar [15], which typically employs waveforms with time apertures in the microsecond to millisecond range and much larger TBPs. Waveforms with fast chirp rates and time apertures in the microsecond range have been generated by heterodyne mixing of a fixed frequency and a rapidly frequency swept laser, e.g., [13], but the repeatability of the generated waveforms is a challenge. Another approach [10], [11], [16], which does provide a high degree of repeatability, is based on switching between multiple basis waveforms obtained via line-by-line pulse shaping of optoelectronically generated frequency combs [17].…”