Yunxiang Wang

Intensity noise of erbium-doped fiber laser based on full quantum theory

Traditionally, by means of full quantum theory, we present the intensity noise transfer function of an Er-doped fiber laser, on the basis of which we analyze the spectrum of the intensity noise. Our theoretical results are in agreement with the existing experiment results. This model explains not only how the noise is produced, but also how the spontaneous emission and dipole fluctuations have an effect on the output noise, which cannot be explained via rate equation theory. We analyze the physical sources of various contributions to the noise spectrum as well. The simulation results show that the noise of the Er-doped fiber laser mainly consists of the vacuum noise resulting from the output coupling, dipole fluctuation noise, the pump source intensity noise, and the spontaneous emission from the upper level to the ground level, which provides the theoretical basis for noise suppression. Compared to the solid laser, the Er-doped fiber laser shows lower resonant relaxation oscillation frequency.

The effect of gravitational spin-orbit coupling on the circular photon orbit in the Schwarzschild geometry

The representation of the group SL(2, C) provides a six-component spinor equivalent to the electromagnetic field tensor. By means of the description, one can treat the photon field in curved spacetime via spin connection and the tetrad formalism, which is of great advantage to study the gravitational spin–orbit coupling of photons. Once the gravitational spin–orbit coupling is taken into account, the traditional radius of the circular photon orbit in the Schwarzschild geometry should be replaced with two different radiuses corresponding to the photons with the helicities of respectively. Owing to the splitting of energy levels induced by the spin–orbit coupling, photons (from Hawking radiations, say) escaping from a Schwarzschild black hole are partially polarized, provided that their initial velocities possess nonzero tangential components.

Plasmonic microcavity formed by the Möbius strip

We propose a Mobius-strip-type plasmonic cavity with a silver Mobius strip sandwiched between dielectric layers. By brief theoretical and simulation analyses, we obtain that the factor of the cavity remains about 40 and the mode volume is ultrasmall (less than 1 ) which is more compact than that of the cylindric cavity. This Mobius-strip-type plasmonic cavity supporting the propagation of surface plasmon polaritons owns some unusual properties such as more effective volume and the spatial separation. More potential applications based on this cavity remain to be explored in future nanophotonics.

Tracking performance of optical phase locking loop with frequency discrimination and control subloop

Abstract. Optical phase locking is a key technique in homodyne coherent optical communication, coherent optical detection, and active coherent laser beam combination. In these applications, environmental temperature variation and mechanical vibration would affect the accuracy of phase locking, or even cause losing lock. These disturbances are generally equivalent to introducing phase jitter, phase step, frequency ramp, and frequency step in the loop. A frequency discrimination and control subloop is introduced to improve the frequency acquisition, and the tracking performance is studied experimentally. The loop can track phase step in 0.2 ms, and precisely track ±π/2 sine phase jitter for jittering frequency lower than 1 kHz. For frequency ramp, the residual phase error is unaffected for ramping rates slower than 40  MHz/s. The frequency discrimination and control subloop makes the loop lock quickly under a frequency step larger than the pull-in frequency. The mean tracking time is 31 ms for a 1 MHz frequency step. The maximum trackable frequency step is around 160 MHz. Continuous or step variation of phase and frequency could be tracked by the loop with the frequency discrimination and control subloop.

Full quantum mechanical model for intensity noise of the composite-ring erbium-doped fiber laser with feedback control

We present a full quantum mechanical model for a composite-ring erbium-doped fiber laser with a feedback loop, with a view to predict the achievable intensity noise reduction. By adding an electronic feedback term to the noise transfer function of the free running composite-ring fiber laser, an analytical expression is developed for the intensity noise spectrum of the current system. For ring fiber lasers, the model shows that the subcavity can suppress the noise at the high frequency and reduce the cutoff frequency to the quantum noise limit, and the feedback loop has a significant impact on suppressing the intensity noise near the relaxation oscillation.