Simultaneous broadband microwave downconversion and programmable complex filtering by optical frequency comb shaping

Abstract

High-repetition-rate optical frequency combs can act as broadband photonic mixers and downconvert a microwave signal to an intermediate frequency (IF) band so that it becomes accessible with high-speed electronics. In this Letter, we show that with line-by-line pulse shaping and dispersive propagation, the photonic mixer can simultaneously perform programmable multitap complex-coefficient-filtering within the IF band. This solution opens new possibilities for microwave signal processing by combining the flexibility of optoelectronic frequency comb technology with high-speed analog-to-digital converters.

Comb-Based RF Photonic Filters Based on Interferometric Configuration and Balanced Detection

“…The estimated shot noise is −155.4 dBm/Hz at the total output photocurrent of 18.2 mA. Using (17) and (20), the calculated total output noise and excess noise are −150.3 and −152 dBm/Hz, respectively. Above 2 GHz, the measured output noise levels are flat and their average values are very close to the simulated value.…”

“…In [16] and [18], reconfigurable phase filters were implemented and applied for compression of wideband RF chirp signals. Using a similar comb-based RF filter configuration but without the interferometer, rapid (ß20 ns) bandwidth reconfiguration was demonstrated in [19], and simultaneous tunable bandpass filtering and downconversion was reported in [20]. Thus, such comb-based RF photonic filters offer a degree of reconfigurability far beyond what is currently available from other technologies, as well potential for extremely fast tuning and reconfigurability.…”

“…However, it is not easy to implement these schemes with large number of filter taps. Other approaches utilize multi-wavelength sources [6]- [20]. In these schemes, RF-modulated multi-wavelength signals are transmitted through a single dispersive fiber or chirped fiber Bragg grating.…”

“…Thus, this scheme also possesses a finite impulse response filter response and allows easy scaling of the filter taps by using various multi-wavelength sources. The above mentioned multi-channel sources have been realized in various ways, including an array of continuous-wave laser sources [7], [8], spectrally sliced broadband light sources [9], [10], and optical frequency combs such as mode-locked lasers [11] and electro-optically (EO) generated combs [12]- [20]. Among these sources, the EO-generated combs are very attractive for RF photonic filtering and other RF photonic signal processing due to their spectral flatness, high coherence, tunable repetition rate, and good stability [21], [22].…”

Interference suppression and tunability enhancement for OFC-based simultaneous microwave down-conversion and filtering

“…In traditional methods [2][3][4][5], narrowband optical filters was widely adopted to combine with optical signal mixing for simultaneous RFphotonics filter and down-converters, which brings simplification for structure but raises the requirement of high resolution and broadband tunability for optical filters. Recently, a novel method based on optical frequency comb (OFC) was proposed as an alternative [6]. OFC is considered as a promising multi-wavelength source to build microwave photonics filter (MPF) for large number of coherent spectral lines [7][8][9][10].…”