Ultra-sensitive all-optical comagnetometer with laser heating

Ultra-sensitive comagnetometers, which are designed to detect nuclear-and electron-spin-dependent interaction, have important applications ranging from basic research to inertial navigation systems (INSs). Unfortunately, electric heating, which is typically used in comagnetometers, introduces systematic errors because of the unavoidable generation of a modulated magnetic field. In this study, we investigate and introduce K-Rb-21Ne comagnetometer that uses laser heating for the first time, when operated in the spin-exchange relaxation free (SERF) regime. The performance of the comagnetometer, which is equipped with both laser heating and electric heating, is investigated, and the two heating modes are compared. The temperature characteristics of the comagnetometer are studied theoretically and experimentally. By optimizing the operating temperature and power density of the pump-light, an equivalent rotation sensitivity of 2.5×10^(-7) rad/s/√Hz@1Hz is achieved in laser heating mode. The improvement of laser-heating technology could prove essential to reduce electron relaxation and increase the low-frequency sensitivity of comagnetometers. Our results indicate that laser heating can make comagnetometers more suitable for applications in basic research (fifth force, dark matter, etc.), INSs, and other accurate measurements of electronic and nuclear precession.

Orientation and Ellipticity Dependence of High-order Harmonic Generation in Nanowires

It has been predicted that high-order harmonic generation (HHG) in nanowires has the potential to scale up photon energy and harmonic yield. However, studies on HHG in nanowires are still theoretical and no relevant experimental results have been reported as yet. Our experimental observation of the high-order harmonic in cadmium sulfide nanowires (CdS NWs) excited by a mid-infrared laser is, to our knowledge, the first such study, and it verifies some of the theoretical results. Our experimental results show that the observed harmonics are strongest when a pump laser is parallel to the nanowires. Therefore, the theoretical prediction that harmonics are strongest under the nanowires parallel to the laser field is confirmed experimentally; this can be used to determine the orientation of the nanowire. In addition, harmonics are sensitive to the variation of pump light ellipticities. This orientation dependence opens new opportunities to access ultrafast and strong-field physics of nanowires.

Graphene-Assisted Polymer Waveguide Optically Controlled Switch Using First-Order Mode

All-optical devices have a great potential in optical communication systems. As a new material, graphene has attracted great attention in the field of optics due to its unique properties. We propose a graphene-assisted polymer optically controlled thermo-optic switch, based on the Ex01 mode, which can reduce the absorption loss of graphene. Graphene absorbs 980 nm pump light, and uses the heat generated by ohmic heating to switch on and off the signal light at 1550 nm. The simulation results show that, when the graphene is in the right position, we can obtain the power consumption of 9.5 mW, the propagation loss of 0.01 dB/cm, and the switching time of 127 μs (rise)/125 μs (fall). The switching time can be improved to 106 μs (rise) and 102 μs (fall) with silicon substrate. Compared with an all-fiber switch, our model has lower power consumption and lower propagation loss. The proposed switch is suitable for optically controlled fields with low loss and full polarization. Due to the low cost and easy integration of polymer materials, the device will play an important role in the fields of all-optical signal processing and silicon-based hybrid integrated photonic devices.

Observation of frequency-uncorrelated photon pairs generated by counter-propagating spontaneous parametric down-conversion

We report the generation of frequency-uncorrelated photon pairs from counter-propagating spontaneous parametric down-conversion in a periodically-poled KTP waveguide. The joint spectral intensity of photon pairs is characterized by measuring the corresponding stimulated process, namely, the difference frequency generation process. The experimental result shows a clear uncorrelated joint spectrum, where the backward-propagating photon has a narrow bandwidth of 7.46 GHz and the forward-propagating one has a bandwidth of 0.23 THz like the pump light. The heralded single-photon purity estimated through Schmidt decomposition is as high as 0.996, showing a perspective for ultra-purity and narrow-band single-photon generation. Such unique feature results from the backward-wave quasi-phase-matching condition and does not has a strict limitation on the material and working wavelength, thus fascinating its application in photonic quantum technologies.

All-Chalcogenide Ring Fiber Laser

We demonstrate the first all-chalcogenide Brillouin fiber laser as well as the first all-chalcogenide ring cavity laser. The compact device comprises two engineered components: an As2Se3 optical fiber coupler combined to an As2S3 amplifying fiber. While the coupler simultaneously enables insertion of pump light, extraction of laser light, and the formation of a ring cavity, the amplifying fiber provides nonlinear gain to ensure laser oscillation. Thanks to the strong Brillouin gain of As2S3, only 3 m of amplifying fiber is required, thus making a resonant cavity with a free spectral range significantly larger than the Brillouin gain spectrum. The laser therefore naturally enables single longitudinal mode operation without additional filtering device. Acting as a coherence enhancing component, the resulting Brillouin laser benefits of a linewidth reduction factor of 7 with respect to the pump laser. Finally, this laser design is compatible with a broad range of wavelengths that spreads from 1.55 µm up to 8 µm, thanks to its all-chalcogenide structure.

Theoretical and Experimental Investigation of the Effect of Pump Laser Frequency Fluctuations on Signal-to-Noise Ratio of Brillouin Dynamic Grating Measurement with Coherent FMCW Reflectometry

Signal-dependent speckle-like noise has constituted a serious factor in Brillouin-grating based frequency-modulated continuous-wave (FMCW) reflectometry and it has been indispensable for improving the signal-to-noise ratio (S/N) of the Brillouin dynamic grating measurement to clarify the noise generation mechanism. In this paper we show theoretically and experimentally that the noise is generated by the frequency fluctuations of the pump light from a laser diode (LD). We could increase the S/N from 36 to 190 merely by driving the LD using a current source with reduced technical noise. On the basis of our experimental result, we derived the theoretical formula for S/N as a function of distance, which contained the second and fourth-order moments of the frequency fluctuations, by assuming that the pump light frequency was modulated by the technical noise. We calculated S/N along the 1.35 m long optical fiber numerically using the measured power spectral density of the frequency fluctuations, and the resulting distributions agreed with the measured values in the 10 to 190 range. Since higher performance levels are required if the pump light source is to maintain the S/N as the fiber length increases, we can use the formula to calculate the light source specifications including the spectral width and rms value of the frequency fluctuations to achieve a high S/N while testing a fiber of a given length.

Contactless Determination of Electric Field in Metal–Insulator–Semiconductor Interfaces by Using Constant DC-Reflectivity Photoreflectance

We applied photoreflectance (PR) spectroscopy for contactless determination of the electric field strength at buried interfaces in metal–insulator–semiconductor (MIS) structures. The PR is an all-optical version of an electromodulated reflectance spectroscopy. The tradeoff of this adoption is that this requires an additional feedback system to eliminate background problems induced by scattered pump light and/or photoluminescence. A microcomputer-based feedback system has been developed for this elimination. Despite the very tiny signal intensity, we successfully attained a sufficiently good signal–noise ratio to determine the electric field strength in oxide-based MIS interfaces that exhibits a large, unwanted photoluminescence signal. The field strength was evaluated to be ca. 0.25 kV/cm.

An optical regenerative wavelength conversion scheme for satellite based on SPM of SOA and offset filter

An optical regenerative wavelength conversion scheme without separated pump laser is put forward to promote the wavelength utilization ratio in distributed satellite network. The scheme adopts the self-phase modulation(SPM) in semiconductor optical amplifier(SOA) to broaden the signal spectrum toward both higher and lower frequency owing to the property that the time of carrier recover is less than pulsewidth. Then the signal light and pump light are extracted by a high-pass filter and a low-pass filter respectively. Finally, the wavelength conversion is realized based on the four-wave mixing(FWM), where the signal light and pump light are passing through another SOA. The simulation results demonstrate that the conversion efficiency can be more than 15dB, and the Q factor improvement can reach to 4dB when input power is small than -22dBm.

Методы возбуждения параметрического резонанса в схеме оптического магнитометрического датчика

An experimental comparison of the methods for modulating the parameters of resonant transverse to the external magnetic field pumping radiation in a two-beam optical magnetometric sensor (so called Bell-Bloom scheme) is carried out, as well as a comparison of these methods with the standard method of radio-frequency excitation of magnetic resonance under conditions of strong laser pumping. It is shown that although the standard method allows one to achieve a greater suppression of the spin-exchange broadening of the magnetic resonance line by pumping light, the Bell-Bloom scheme has advantages that make it possible to obtain similar sensitivity values upon modulation of both the intensity and polarization of the pump light; at the same time, the Bell-Bloom scheme is potentially characterized by higher speed, which is essential for the problems of magnetoencephalography and ultra-low field magnetic resonance imaging.