Forced frequency stabilization techniques of self-injection locking (SIL) and self-phase locked loop (SPLL) have been demonstrated to be effective for phase noise reduction. In SIL scheme, a portion of the oscillator output is directly injected back to the oscillator after passing through a long delay while in SPLL, the delayed signal is used to compare against a non-delayed signal to generate an error signal which will be used to control the oscillator frequency. The published literature and reported patent investigations has revealed that SIL and SPLL are only being used independently, whereas in this thesis SILPLL is introduced for the first time by simultaneously combining of SIL and SPLL; the control theory based modeling of SIL, SPLL, and SILPLL techniques are developed and the simulation results have indicated that phase noise of the oscillation signal is enhanced as injection locking removes phase noise in far-out offset frequency, while phase locking effectively reduces the close-in to carrier phase noise. Optimum delay length and delay parameters are identified for the most effective performance. Both SIL and SPLL techniques require a low noise figure and long fiber optic delay lines to provide substantial phase noise reduction, but the long delay generates undesirable sidemodes that are seen within 20kHz to 200kHz offset to carrier for fiber optic delays from 10km to 1km and are difficult to be filtered out by electrical filters. Therefore, forced oscillation technique employing short and long delay is proposed to suppress these sidemodes. In this dissertation, experimental results of a dual self-injection locking (DSIL) and dual self-phase locked loop (DSPLL) employing short and long delays have been proposed for this sidemode suppression, while maintaining same amount of phase noise reduction provided by the long delay. As an example of DSIL, sidemode suppression of more than 20dB for fiber delay links of 1km and 5km have been experimentally achieved compared to a single 5km long SIL with a phase noise reduction of 40dB (in reference to free running oscillator) at 10kHz offset from carrier for both standard OEO and a self-seeded structure with electrical 3 port oscillator at 10GHz; for a DSPLL fiber delay lines of 3km and 5km, a sidemode suppression of 29dB have also been experimentally achieved compared to SPLL of 5km with a phase noise reduction of 30dB (in reference to free running oscillator) at 10kHz offset from carrier. For the case of SPLL, phase locking performance of a 10GHz oscillation signal are experimentally evaluated as various methods of phase locking are compared. Experiment results that demonstrate the benefit of SILPLL incorporating dual delays have been reported for the first time corroborating analytical predictions. A dual SILPLL (DSILPLL) system with 3km and 5km fiber delay has been implemented, and measured phase noise reduction of 40dB provided by DSILPLL is the same as DSIL at 10kHz offset. However, at 1kHz offset, DSILPLL provides a phase noise reduction of 52dB which is 11dB…

Optoelectronic Frequency Stabilization Techniques in Forced Oscillators

We report on the stabilization of the beatnote of a 1.5 mum dual-frequency laser using optical frequency locked loops (OFLLs). The principle of these OFLLs is based on an electro-optical frequency discriminator which contains one or two fiber-optic delay lines. The lowest phase noise, -107 dBrad2/Hz at 10 kHz for frequencies ranging from 2 to 6 GHz, has been obtained by combining two delays of 5 mus and 0.5 mus.

Self-stabilization of the beatnote of a 1.5 μm dual-frequency laser. Applications to optoelectronic microwave oscillators.

Dispersion impact on electrical signal generation at 54.8 GHz of a quantum dash (QDs) mode-locked Fabry-Perot (FP) lasers emitting at 1.55 mum has been measured. Optimum fibre length values that correspond to dispersion compensation have been found. For these optimal conditions a pulse width of 480 fs has been measured. These optimum fibre length values have been applied to the integration of two architectures of phase noise reduction schemes: a coupled opto-electronic oscillator (COEO) with a single self-injection loop associated to a self-phase-locked loop (PLL) and a dual loop COEO. A phase noise reduction of more than 30 dB at an offset frequency of 20 kHz has been obtained for the second architecture.

Optimization of a 54.8 GHz coupled opto-electronic oscillator through dispersion compensation of a mode-locked semiconductor laser

Oscillators in the gigahertz frequency range are key building blocks for telecommunication and positioning applications. Operating directly in the gigahertz while keeping high frequency stability and compactness is still an up-to-date challenge. Optomechanical crystals have demonstrated gigahertz frequency modes, thus gathering prerequisite features for using them as oscillators. Here, we report on the demonstration, in ambient atmospheric conditions, of an optomechanical crystal based on the concept of bichromatic lattice. It is made of InGaP, a low loss and TPA-free piezoelectric material, which makes it valuable for optomechanics. Self-sustained oscillations directly at 3 GHz are routinely achieved with a low optical power threshold of 40 μW and a short-term linewidth narrowed down to 100 Hz in agreement with phase noise measurements (−110 dBc/Hz at 1 MHz from the carrier) for free running optomechanical oscillators.

Optomechanical gigahertz oscillator made of a two photon absorption free piezoelectric III/V semiconductor

This paper reports on the stabilization of the beatnote of a dual-frequency laser on an optical fiber delay line, in a similar way as the one used for the stabilization of a microwave oscillator This study paves the way to the realization of widely tunable, low phase noise sources of optically carried microwave signals

Stabilization of the beatnote of a 1.5 μm dual-frequency laser using a fiber-optic delay line

Summary form only given. Heterodyning of optical modes of a diode-pumped solid-state dual-frequency laser (DFL) is an efficient way to generate optically carried microwave signals [1], that can be used for the distribution of radar local oscillator, coherent or direct detection lidar or the implementation of stable and tunable optoelectronic oscillators. However, the free-running frequency stability of a DFL might be too low for the most demanding applications. We present here the stabilization of the beatnote of an Er, Yb:glass DFL at 1.53 μm with an optical frequency locked loop (OFLL) [2,3].The oscillator is schematized Fig. 1. Used as a voltage controlled oscillator (VCO), the DFL generates a widely tunable microwave signal from 0 to 14 GHz by heterodyning its two orthogonally polarized optical modes. The optical beatnote is detected on two different high-speed photodiodes, the first one directly at the laser output, the second one after an optical fiber coil inducing a delay τ. These two microwave signals are mixed together; we then obtain an error signal which is injected, through a baseband filter, to the DFL frequency control input. This results in the stabilization of the beatnote frequency on a multiple of 1/ τ. 100 m Phase Noise (dBc/Hz)With a 100 m optical fiber delay line, the beatnote phase noise is improved by 60dB leading to a level of -20 dBc/Hz, at 10 Hz from the carrier (Fig. 2), a fairly good result for such a short delay. The beatnote linewidth is then reduced from few hundreds of hertz to few hertz. Since this architecture does not require an RF filter, this oscillator is tunable from 2.5 to 5.5 GHz, actually limited by the RF components of our frequency discriminator. Such an oscillator could be used in a radar, communication or electronic warfare system requiring widely tunable microwave frequency references distributed via photonic links. Moreover, it could find applications in the laser radar area, either by using the wide tunability of the emitted signal to obtain a high range resolution in a direct detection system [4], or by providing a widely tunable local oscillator in a coherent detection lidar.

Widely tunable optoelectronic oscillator based on a dual-frequency laser

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Stabilization of the beatnote of a 1.5 μm dual-frequency laser using a fiber-optic delay line

Widely tunable optoelectronic oscillator based on a dual-frequency laser