Single-mode Receiver Research Articles

Single-mode fiber coupling with a M-SPGD algorithm for long-range quantum communications.

Satellite-based quantum communication is a promising approach for realizing global-scale quantum networks. For free-space quantum channel, single-mode fiber coupling is particularly important for improving the signal-to-noise ratio of daylight quantum key distribution (QKD) and compatibility with standard fiber-based QKD. However, achieving a highly efficient and stable single-mode coupling efficiency under strong atmospheric turbulence remains experimentally challenging. Here, we develop a single-mode receiver with an adaptive optics (AO) system based on a modal version of the stochastic parallel gradient descent (M-SPGD) algorithm and test its performance over an 8 km urban terrestrial free-space channel. Under strong atmospheric turbulence, the M-SPGD AO system obtains an improvement of about 3.7 dB in the single-mode fiber coupling efficiency and a significant suppression of fluctuation, which can find its applications in free-space long-range quantum communications.

Dynamic light scattering with single-mode receivers: partial heterodyning regime

A frequent source of errors in dynamic light-scattering experiments is partial heterodyning caused by scattering on large particles or imperfections of the sample cell. With a conventional two-pinhole receiver it is impossible to distinguish its effect from the effects of a finite detector area and detector nonlinearity. However, an accurate data analysis is feasible when a single-mode light receiver is employed. We present formulas for single-mode autocorrelation and cross-correlation functions that include a local oscillator and an incoherent background of arbitrary strength and take into account detector nonlinearity (e.g., dead time) up to second order. A simple but accurate method for the determination of the nonlinearity parameters and the effective number of receiver modes is also provided. The success of the data-evaluation procedure is demonstrated by the measurement of the hydrodynamic radius of latex in the presence of deliberately added local-oscillator or incoherent-background contributions.

Dynamic light scattering with single-mode and multimode receivers

Single-mode optical fibers provide the ideal receiver optics for dynamic light-scattering measurements. Theoretical analysis shows that with a single-mode fiber one can achieve a theoretical limit of 1 for the coherence factor while maintaining a high light-collection efficiency. In fact, the sensitivity of the single-mode receiver surpasses that of a classical two-pinhole setup with a coherence factor of 0.8 by a factor of 4 and the advantage increases rapidly when a still higher coherence factor is desired. In addition, a single-mode fiber receiver offers the possibility of working with an arbitrary large scattering volume and with an arbitrary working distance. All these features are also demonstrated experimentally by a remarkably simple apparatus that consists, essentially, of a commercial laser beam delivery assembly.

Nonclassical states in optical communication to a remote receiver (Corresp.)

The relation between the density operators of the aperture fields of a single-mode optical transmitter and a single-mode receiver is simply expressed in terms of their quasiprobability distributions. This formulation indicates that when the receiver is so far away that it picks up only a small fraction of the transmitted energy, the state induced in its aperture field by a nonclassical transmitted state differs only slightly from what it would be were a certain equivalent classical state transmitted instead. The implications for remote communications are discussed.