Low phase noise frequency synthesizers are of paramount interest in many areas of micro-mm wave technology, encompassing for example advanced wireless communication, radar, radio-astronomy, and precision instrumentation. Although this broad research field is not bereft of methods for the generation of either low phase noise micro- or mm waves, no universal system applicable to low phase noise generation for micro and mm waves has yet been demonstrated. Here we propose a new photonic frequency discriminator based on a two wavelength delayed self-heterodyne interferometer which is compatible with such an objective. The photonic frequency discriminator can be a reference both for micro and mm waves to lower their phase noise. As a proof-of-concept, we demonstrate a low phase noise tunable OEO (6–18 GHz) and locking of a heterodyne beat between two cw lasers (10–400 GHz) with low relative phase noise. The required components for the photonic frequency discriminator are off-the-shelf and can be readily assembled. We believe this new type of photonic frequency discriminator will enable a new generation of universal precision tunable sources for the X, K, V, W and mm-bands and beyond.

/pdf/a-photonic-frequency-discriminator-based-on-a-two-wavelength-8s0tj7ijwo.pdf

A photonic frequency discriminator based on a two wavelength delayed self-heterodyne interferometer for low phase noise tunable micro/mm wave synthesis

We propose and experimentally demonstrate a spurious level and phase noise improved Fourier domain mode-locked optoelectronic oscillator (FDML-OEO) based on a self-injection-locking (SIL) technique. The scheme applies a dual-loop FDML-OEO structure, in which a long optical fiber delay loop is used to injection-lock the OEO with a short oscillating optical fiber delay loop. SIL is achieved so long as the delay of the long loop is tuned at the integral multiple of the oscillation loop. The spur suppression ratio of the wideband linear frequency modulated (LFM) signal generated by the FDML-OEO can be improved by 14 dB under SIL. Furthermore, the modification of the spur suppression ratio depending on the injection power is also demonstrated. The phase noise of the proposed OEO is -127.5 dBc/Hz at 10 kHz offset, which is much improved comparing with a free-running OEO.

Spurious level and phase noise improved Fourier domain mode-locked optoelectronic oscillator based on a self-injection-locking technique.

/pdf/optoelectronic-oscillator-for-5g-wireless-networks-and-5dfr23tdxh.pdf

Optoelectronic oscillator for 5G wireless networks and beyond

A novel optical feedback technique using self-injection locked and phase locked loop (SILPLL) is employed for phase noise reduction of free-running microwave oscillators. Phase noise reduction of 27 dB at 10-kHz offset has been demonstrated by applying this technique for a 10-GHz state of art dielectric resonator oscillator achieving −137 dBc/Hz at 10-kHz offset. A phase noise prediction of this feedback technique is also presented, which very closely corroborates with experimental results. Analysis of SILPLL using the modeling has shown that further phase noise reductions could be achieved, by reducing the flicker phase noise of the long delay lines and microwave amplifiers. Phase noise of −147 dBc/Hz at 10-kHz offset is predicted when the relative intensity noise (RIN) is reduced to the RIN of −170 dB/Hz for an optical power leading to a photocurrent of 5 mA and the $\text{b}_{\mathrm {\mathbf {-1}}}$ (flicker noise) levels of −125 dBc/Hz for RF amplifiers.

Limits in Timing Jitters of Forced Microwave Oscillator Using Optical Self-ILPLL

Low phase noise radio frequency (RF) sources generated by voltage controlled oscillators (VCOs) are described. Optical modulators driven by a VCO may be used to generate optical side-bands to cw lasers. The spectral extent of said side-bands can be increased via frequency broadening in highly nonlinear waveguides. Free running mode locked low phase noise comb oscillators can be used as reference oscillators to generate beat signals between those side-bands and individual comb modes at distal spectral regions, thereby creating an error signal used to reduce the phase noise of VCOs and the generation of low phase noise RF signals. VCO phase noise may be reduced by using free-running modelocked comb lasers phase locked to external frequency references, by omitting a reference comb and using a nonlinear interferometer for generating an error signal, or by locking a slave comb to the modulation frequency of an intra-cavity modulator driven by the VCO.

Systems and methods for low noise frequency multiplication, division, and synchronization

A very clean and low phase noise microwave oscillator is required for communication and high resolution imaging. A frequency stabilized and tunable opto-electronic oscillator (OEO) is realized as synthesizer using a long fiber optic delay line combined with a tunable narrowband microwave filter. Forced oscillation using both self-injection locking and self-phase lock loop, as SILPLL provides an ultra-low close-in and far away from carrier phase noise to achieve a record low phase noise. A YIG microwave filter combined with an optically tuned transversal filter is employed to implement frequency tuned OEO to realize highly stable synthesizer in X-band. Phase noise − 136dBc/Hz at offset frequency 10kHz is achieved for 9GHZ to 11GHz. Moreover, a synthesizer for K-band is demonstrated by adjusting the operation point of a dual drive MZM (DD-MZM) from quadrature point of Vpi/2 to Vpi, where the second harmonic in addition to fundamental is efficiently generated with −127dBc/Hz phase noise at offset frequency 10kHz for 18–22GHz.

Forced SILPLL oscillation of X- and K-band frequency synthesized opto-electronic oscillators

Ultra-low phase noise performance is required for frequency agile local oscillators, which are the core for high resolution imagers, spectrum analyzers, and high speed data communications. A forced opto-electronic oscillator (OEO) benefits from frequency stabilization techniques for realizing a clean and low phase noise source at microwave and millimeter wave frequencies. Forced oscillation techniques of self-injection locking and self-phase lock loop are combined to provide an ultra-low oscillator phase noise both close-in and far-away from the carrier frequency, while a tunable yttrium iron garnet microwave filter combined with a wavelength tuned transversal filter are employed to implement both coarse and fine frequency tuning for a tunable X-band OEO. A phase noise of −137 dBc/Hz at an offset frequency of 10 kHz is achieved covering the frequencies of 9 to 11 GHz with a fine frequency tuning resolution of 44 Hz/pm and coarse tuning of 25 MHz/mA. Moreover, the long term stability of the output signal is tested, and a maximum frequency drift of 2 kHz is measured within 60 min for the X-band synthesizer.

Frequency synthesis of forced opto-electronic oscillators at the X-band

A reduced phase noise of stable microwave oscillators is reported by forced oscillation using self-ILPLL technique fiber optical delayed feedback. Fiber optic links using single drive and dual drive MZM have been used to implement the optical feedback path. A phase noise reduction of 22 dB at 300 Hz offset is measured for a commercially available DRO at 10 GHz using dual drive MZM in long fiber optic delay lines. The measured −127 dBc/Hz at 14 kHz offset has been demonstrated by employing 4km and 8km fiber optic delay lines.

Oscillator phase noise reduction using optical feedback with dual drive Mach-Zehnder modulator

Low-noise local oscillators are very important in modern communication systems. To realize a stable solution with a limited size, symmetric multimode multi-section semiconductor laser pairs are reported in this article for building a chip-level RF synthesizer. The symmetric laser structure utilizes a shared distributed Bragg reflector (DBR) and counterpropagating laser output with the help of an external feedback circuit to achieve self-mode-locking. The achieved phase noise performance is −92 dBc/Hz at a 10 kHz offset frequency for intermodal operation at 26.4 GHz using 5 locked modes, which is a 57 dB improvement compared to the free-running case. Moreover, an RF synthesizer covering frequencies of 11–13 GHz is realized based on the achieved mode-locked system using current tuning. The related phase noise of the laser pair beat-note output is −100 dBc/Hz at a 10 kHz offset of carrier frequencies of 11–13 GHz, which is 58 dB better than the phase noise of the beat-note output without mode-locking over 11–13 GHz.

RF Frequency Synthesizer Based on Self-Mode-Locked Multimode Lasers

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