High-precision wavelength-flexible frequency division for metrology

Abstract

We realize and investigate a wavelength-flexible phase-coherent all-optical frequency-by-2 divider. Frequency division is obtained via self-phase locking in a degenerate continuous-wave (cw) optical parametric oscillator (OPO). The wavelength flexibility of the divider is based on the use of quasiphase matching (QPM) with perpendicular polarizations of the OPO output waves (type II). Mutual injection of the subharmonic waves is achieved by using an intracavity quarter-wave plate. A locking range of up to 160 MHz is observed experimentally, and a stable, self-phase-locked operation of the OPO is achieved over typically 15 minutes. For the first time, we measure the frequency stability of the divider by recording the relative phases of the subharmonic waves as a function of time. For a measurement time interval of 40 s, we measure a residual frequency instability of the divider of 8 · 10 −18 . We demonstrate a full control of the OPO's output waves' phase difference and observe the related change in power ratio of the subharmonic waves in agreement with the theoretically expected behavior. We propose that this possibility to monitor the divider's drift within the locking range via the power ratio can be used for stabilizing that drift in order to achieve a significant improvement of the long-term stability of the frequency-by-2 divider.

Generation of two-color polarization-entangled optical beams with a self-phase-locked two-crystal Optical Parametric Oscillator

“…In this paper, we will focus on the regime of lower threshold. These equations are similar to that obtained in a onecrystal self-phase locked OPO, which has been studied in detail in [18,19,25]. For a given input pump intensity, the phase-locked operation can be obtained only for a given range of the relevant parameters (i.e cavity length and crystal temperature) which defines a so-called "locking zone".…”

“…Such systems have recently attracted a lot of attention as efficient sources of non-classical light [21,22,23]. Stable operation has been demonstrated experimentally even with very small coupling [17,24,25] and their non-classical properties are very encouraging…”

Generation of 8.3 dB continuous variable quantum entanglement at a telecommunication wavelength of 1550 nm

“…To realise the triply resonant condition in an optical cavity, the temperature of the nonlinear crystal should first be controlled. An extra optical element was inserted in the cavity to compensate the dispersion of the optical modes [19,20], but the inserted element increased the intracavity loss. A wedged nonlinear crystal was used to compensate the dispersion by adjusting the crystal interaction length [15,21].…”

Experimental generation of 8.4 dB entangled state with an optical cavity involving a wedged type-II nonlinear crystal

“…In this case the operating model of triple-resonance of signal, idler and pump modes should be a favorable choice. For completing three-mode resonance, two physical parameters of NOPA need to be adjusted at least [21][22][23][24][25][26][27][28]. By adjusting the temperature of KTP around the phase-match point, the doubleresonance of the signal and idler modes can be demonstrated [8,17].…”

“…By adjusting the temperature of KTP around the phase-match point, the doubleresonance of the signal and idler modes can be demonstrated [8,17]. In [21,25,26], an extra optical element is inserted in the optical cavity to compensate the dispersion between the pump and the subharmonic modes. However, because the inserted element must increase the intracavity loss of the NOPA, the high entanglement is not obtained [21].…”