We report on a 795 nm atomic filter consisting of a stimulated Raman gain amplifier together with normal Faraday anomalous dispersion optical filtering (FADOF) at the rubidium D1 line. The filter is operated with a single transmission peak. The gain of the filter's transmission light signal is enhanced up to 85-fold compared to case operating without a stimulated Raman transition. Based on atomic coherence, the filter's minimum transmission bandwidth is less than 22 MHz. In each filtering channel, the signal light's frequency can be tuned by changing the detuning of the coupling light. Such a filter with stimulated Raman gain is more efficient in extracting weak signals in the presence of a strong light background compared with the normal FADOF. This expands the range of potential applications in optical communications and lidar technology. This filtering method can also be extended to the lines of other atoms.
We report on a 795 nm atomic filter consisting of a stimulated Raman gain amplifier together with normal Faraday anomalous dispersion optical filtering (FADOF) at the rubidium D1 line. The filter is operated with a single transmission peak. The gain of the filter's transmission light signal is enhanced up to 85-fold compared to case operating without a stimulated Raman transition. Based on atomic coherence, the filter's minimum transmission bandwidth is less than 22 MHz. In each filtering channel, the signal light's frequency can be tuned by changing the detuning of the coupling light. Such a filter with stimulated Raman gain is more efficient in extracting weak signals in the presence of a strong light background compared with the normal FADOF. This expands the range of potential applications in optical communications and lidar technology. This filtering method can also be extended to the lines of other atoms.
Taking advantages of ultra-narrow bandwidth and high noise rejection performance of the Faraday anomalous dispersion optical filter (FADOF), simultaneously with the coherent amplification of atomic stimulated emission, we propose a stimulated amplified Faraday anomalous dispersion optical filter (SAFADOF) at cesium 1470 nm. The SAFADOF is able to significantly amplify very weak laser signals and reject noise in order to obtain clean signals in strong background. We show that for a weak signal of 50 pW, the gain factor can be larger than 25000 (44 dB) within a bandwidth as narrow as 13 MHz. Having the ability to amplify weak signals with low background contribution, the SAFADOF finds outstanding potential applications in weak signal detections.
The transmission characteristics of a Raman-amplified atomic filter that can be used to detect fairly weak signals in free-space quantum-key distribution or laser communications are analyzed and discussed in the coherent and incoherent pump fields respectively. The theoretical model for the calculation of the transmission characteristics of a ground-state Raman-amplified Faraday dispersion atomic optical filter based on Raman gain and Faraday rotation is presented. The results show that the filter in a coherent pump field can achieve higher transmission and larger tunability than that in an incoherent pump field due to elimination of pumping detuning. In addition, the filter has a large scale tunability over 3.5 GHz via the Faraday transmission peak adjusted while its bandwidth is only 66 MHz, which is useful for free-space laser communication and lidar systems.
Taking advantages of ultra-narrow bandwidth and high noise rejection performance of the Faraday anomalous dispersion optical filter (FADOF), simultaneously with the coherent amplification of atomic stimulated emission, a stimulated amplified Faraday anomalous dispersion optical filter (SAFADOF) at cesium 1470 nm is realized. The SAFADOF is able to significantly amplify very weak laser signals and reject noise in order to obtain clean signals in strong background. Experiment results show that, for a weak signal of 50 pW, the gain factor can be larger than 25000 (44 dB) within a bandwidth as narrow as 13 MHz. Having this ability to amplify weak signals with low background contribution, the SAFADOF finds outstanding potential applications in weak signal detections.
A Raman-amplified atomic filter is demonstrated experimentally. With a coupling light detuned from the D2 line of 85Rb, a weak signal light can be amplified by a factor of 55, and the bandwidth of the filter's transmission spectrum is narrowed to approximately 60 MHz. Moreover, the transmission wavelength is adjustable by changing the coupling-light frequency. Compared with a conventional dispersive atomic filter, this Raman-amplified atomic filter could be more efficient to suppress background noise in free-space quantum-key distribution or a laser-communication system.
To obtain the weak signal light detection from the high background noise,a study on ultra-narrow bandwidth Faraday anomalous dispersion optical filter(FADOF) at the 87Rb D1 line,5S1/2F=2→5P1/2 F′=1transmission(795 nm) is demonstrated experimentally.A sample cell filled with Rubidium atoms in which the proportion of 87Rb is greater than that of the nature rubidium is placed in a homogeneous magnetic field between two crossed Glan-Thompson polarizers.The incident probe light goes through the sample cell,and interacts with the atoms.Because of the Faraday rotation,the function of the filter can be realized.When the experiment condition changed,the result of transmission spectrum changed accordingly.With the temperature rising from 340 K to 360 K,the variation of the transmission spectrum is recorded particularly.And the reason for the variation is analyzed carefully.At a proper temperature and magnetic field,a transmission spectrum narrowed to ~220 MHz is obtained,and the peak transmission is about 48%.The performance of the87Rb D1 line is better than that of the 85Rb.