Broadband two‐thirds photonic microwave frequency divider

Abstract

A broadband two-thirds frequency divider based on two cascaded carrier-suppressed double sideband (CS-DSB) modulators is proposed and experimentally demonstrated. The first CS-DSB modulator is aimed to introduce an RF signal under frequency division to the system, and the second one is employed in an optoelectronic oscillator (OEO) loop to avoid the OEO from free running. By mixing the injection frequency and the oscillation frequency in the OEO loop, oscillation of a signal with its frequency equal to two-thirds of the injection frequency is established. An experiment is carried out, RF signals with frequencies from 12.3 to 17.7 GHz are successfully divided into 8.2 to 11.8 GHz. The maximum power ripple is 2.79 dB and the harmonic components suppression ratio is larger than 36.13 dB. Introduction: Frequency dividers play a significant role in optical communication systems and microwave photonic areas for agile frequency manipulation and signal processing [1-3]. Traditionally, frequency dividers are realised in the electrical domain with purely electronic active components [1]. Nevertheless, the active electrical components would introduce additional noise and deteriorate the signal-to-noise ratio of the systems. Also, electrical frequency dividers would also suffer from limited operational bandwidth and poor harmonic components suppression ratio. To deal with these problems, frequency dividers realised using photonic techniques are highly desired, thanks to the intrinsic characteristics brought by photonic techniques such as large bandwidth, high frequency, and electromagnetic interference immunity. Optical frequency division could be implemented based on the non-linear dynamics of a semiconductor laser [4], a non-linear fibre loop mirror [5], or an injection-locked optoelectronic oscillator (OEO) [6]. Such approaches, however, are lacking flexibility for the division of different frequencies due to the mechanism of narrowband filtering. Recently, we proposed a wideband frequency divider with a division factor of two by an OEO-based divider [7]; however, the harmonic components suppression is poor. In this Letter, a two-thirds frequency divider with large frequency tuning range and good harmonic suppression is proposed and experimentally demonstrated based on cascaded carrier-suppressed double sideband (CS-DSB) modulations, realised by two Mach-Zehnder modulators (MZMs) biased at the minimum transmission point (MITP). When an RF signal with a frequency of f 1 is applied to the first MZM (MZM1), two sidebands that are separated by 2f 1 would be generated, which is then sent to an OEO containing the second MZM (MZM2). Assume the frequency of the oscillation signal is f 2 , at the output of MZM2 four sidebands with offset frequencies to the optical carrier of −f 1 −f 2 , −f 1 + f 2 , f 1 −f 2 , f 1 + f 2 would be generated. To maintain the oscillation of the OEO, the beating frequencies of − f 1 + f 2 and f 1 − f 2 should equal to f 2 , leading to f 2 = 2/3f 1. As a result, two-thirds frequency division can be real...

Photonic‐assisted one‐third microwave frequency divider

“…A very high harmonic suppression ratio of over 71.5 dB can be seen in Figure 4(b). This is 50.2 dB and 35.4 dB higher than those reported in [4] and [6], respectively. Figure 4 shows that the system noise floor is around −55 dBm, which is measured using an ESA resolution bandwidth of 100 kHz and attenuation setting of 40 dB.…”

“…Therefore, the main MZM bias voltage V b3 is used to control the roundtrip phase of the frequency divided signal to satisfy the phase condition given in (7). This is different from the previously reported injection locking and regenerative photonic microwave frequency dividers [3][4][5][6][7], which use an EPS or an OVDL to control the round-trip signal phase to satisfy the phase condition. Using V b3 to control the microwave signal phase has a number of advantages over the conventional electrical approaches.…”

“…It can be seen from Figure 1 that the frequency divider is implemented by a DPMZM and an MZM connected in series. To our knowledge, three microwave frequency dividers based on cascaded modulators have been reported [6,7,9], but all require using an EPS to control the round-trip phase for generating a frequency-divided signal.…”

“…Several photonics-based microwave frequency divider structures have recently been reported. Most of them use an optoelectronic oscillator (OEO) to realise frequency division through injection locking [2,3] or based on regenerative technique [4][5][6][7]. Both techniques require a precise control of the gain and phase, a condition needed for frequency division at a given input frequency.…”

Photonics-Assisted Bandwidth-Doubling Dual-Chirp Microwave Signal Generation With Freely-Tunable Central Frequency

“…The high-pass filter (HPF) after the photodetector is used to filter out the generated baseband signal through beating between the two modulation sidebands of the optical signal from the upper branch. Mathematically, in the upper branch, the output optical field from the MZM working in CS-DSB modulation state can be written as [19] ( ) ( )…”