Temporal Interference Pattern Research Articles

Phase‐Modulated Interferometry, Spectroscopy, and Refractometry using Entangled Photon Pairs

AbstractThe authors demonstrate a form of two‐photon‐counting interferometry by measuring the coincidence counts between single‐photon‐counting detectors at an output port of a Mach–Zehnder Interferometer (MZI) following injection of broad‐band time‐frequency‐entangled photon pairs (EPP) generated from collinear spontaneous parametric down conversion into a single input port. Spectroscopy and refractometry are performed on a sample inserted in one internal path of the MZI by scanning the other path in length, which acquires phase and amplitude information about the sample's linear response. Phase modulation and lock‐in detection are introduced to increase detection signal‐to‐noise ratio and implement a “down‐sampling” technique for scanning the interferometer delay, which reduces the sampling requirements needed to reproduce fully the temporal interference pattern. The phase‐modulation technique also allows the contributions of various quantum‐state pathways leading to the final detection outcomes to be extracted individually. Feynman diagrams frequently used in the context of molecular spectroscopy are used to describe the interferences resulting from the coherence properties of time‐frequency EPPs passing through the MZI. These results are an important step toward the implementation of a proposed method for molecular spectroscopy—quantum‐light‐enhanced 2D spectroscopy.

Interference properties of two-component matter wave solitons

Wave properties of solitons in a two-component Bose–Einstein condensate are investigated in detail. We demonstrate that dark solitons in one of components admit interference and tunneling behavior, in sharp contrast to the scalar dark solitons and vector dark solitons. Analytic analyses of interference properties show that spatial interference patterns are determined by the relative velocity of solitons, while temporal interference patterns depend on the velocities and widths of two solitons, differing from the interference properties of scalar bright solitons. Especially, for an attractive interactions system, we show that interference effects between the two dark solitons can induce some short-time density humps (whose densities are higher than background density). Moreover, the maximum hump value is remarkably sensitive to the variation of the solitons’ parameters. For a repulsive interactions system, the temporal-spatial interference periods of dark–bright solitons have lower limits. Numerical simulation results suggest that interference patterns for the dark–bright solitons are more robust against noises than bright–dark solitons. These explicit interference properties can be used to measure the velocities and widths of solitons. It is expected that these interference behaviors can be observed experimentally and can be used to design matter wave soliton interferometer in vector systems.

Ultrafast quantum interferometry with energy-time entangled photons

Many quantum advantages in metrology and communication arise from interferometric phenomena. Such phenomena can occur on ultrafast time scales, particularly when energy-time entangled photons are employed. These have been relatively unexplored as their observation necessitates time resolution much shorter than conventional photon counters. Integrating nonlinear optical gating with conventional photon counters can overcome this limitation and enable subpicosecond time resolution. Here, using this technique and a Franson interferometer, we demonstrate high-visibility quantum interference with two entangled photons, where the one- and two-photon coherence times are both subpicosecond. We directly observe the spectral and temporal interference patterns, measure a visibility in the two-photon coincidence rate of $(85.3\pm0.4)\%$, and report a CHSH-Bell parameter of $2.42\pm0.02$, violating the local-hidden variable bound by 21 standard deviations. The demonstration of energy-time entanglement with ultrafast interferometry provides opportunities for examining and exploiting entanglement in previously inaccessible regimes.

Generation of an arbitrary chirped microwave waveform with high time-bandwidth product for increasing range resolution of RADAR by using photonic technique

An approach for photonic generation of an arbitrary chirped microwave waveform with an increased time-bandwidth product (TBWP) is proposed and experimentally demonstrated. In the proposed model, light from the mode locked laser is splitted into two parts by using 1 × 2 power splitter: one is sent to linearly chirped fiber Bragg grating (LCFBG) through circulator and the other is time delayed by fiber delay line. The optical pulse in upper arm is time stretched by the LCFBG. Meanwhile, the optical pulse in lower arm experiences a time delay and then stretched by the dispersive single mode fiber. Temporal interference pattern is generated with an increasing or decreasing free spectral range by combination of two time-stretched optical pulses. Finally, the temporal interference pattern which is obtained at the output of optical coupler is transformed into an arbitrary chirped microwave waveform by using a photo-detector. The main advantage of this proposed model is high TBWP in the range of 750–1000 which ultimately results in an increased range resolution of radio detection and ranging.

Ionization of atoms by few-cycle laser pulses: spatial and temporal interference effects

SynopsisThe intra-pulse interference effects appearing during the ionization of atoms by few-cycle laser pulses is studied. These are the result of coherent superposition of electronic wave packets, which follow different spatio-temporal paths. With the help of a wave function analysis tool, the spatial and temporal interference patterns are disentangled and studied separately.

Second-order interference of two independent and tunable single-mode continuous-wave lasers**Project supported by the National Natural Science Foundation of China (Grant No. 11404255) and the Doctor Foundation of Education Ministry of China (Grant No. 20130201120013).

The second-order temporal interference of two independent single-mode continuous-wave lasers is discussed by employing two-photon interference in Feynman’s path integral theory. It is concluded that whether the second-order temporal interference pattern can or cannot be retrieved via two-photon coincidence counting rate is dependent on the resolution time of the detection system and the frequency difference between these two lasers. Two identical and tunable single-mode continuous-wave diode lasers are employed to verify the predictions. These studies are helpful to understand the physics of two-photon interference with photons of different spectra.

Two-photon interference with non-identical photons

Two-photon interference with non-identical photons is studied based on the superposition principle in Feynman's path integral theory. The second-order temporal interference pattern is observed by superposing laser and pseudothermal light beams with different spectra. The reason why there is two-photon interference for photons of different spectra is that non-identical photons can be indistinguishable for the detection system when Heisenberg's uncertainty principle is taken into account. These studies are helpful to understand the second-order interference of light in the language of photons.

The first- and second-order temporal interference between thermal and laser light.

The first- and second-order temporal interference between two independent thermal and laser light beams is discussed by employing the superposition principle in Feynman's path integral theory. It is concluded that the first-order temporal interference pattern can not be observed by superposing two independent thermal and laser light beams, while the second-order temporal interference pattern can be observed in the same condition. These predictions are experimentally verified by employing pseudothermal light to simulate thermal light. The relationship between the indistinguishability of alternatives and photons is analyzed. The conclusions are helpful to understand the interference of different kinds of light and the difference between the coherence properties of thermal and laser light.

The second-order interference of two independent single-mode He–Ne lasers

The second-order spatial and temporal interference patterns with two independent single-mode continuous-wave He–Ne lasers are observed when these two lasers are incident to two adjacent input ports of a 1:1 non-polarizing beam splitter, respectively. Two-photon interference based on the superposition principle in Feynman's path integral theory is employed to interpret the experimental results. The conditions to observe the second-order interference pattern with two independent single-mode continuous-wave lasers are discussed. It is concluded that frequency stability is important to observe the second-order interference pattern with two independent light beams.

Photonic Generation of Continuously Tunable Chirped Microwave Waveforms Based on a Temporal Interferometer Incorporating an Optically Pumped Linearly Chirped Fiber Bragg Grating

A novel approach to generating a chirped microwave waveform with continuously tunable chirp rate based on a temporal interferometer incorporating an optically pumped linearly chirped fiber Bragg grating (LCFBG) is proposed and demonstrated. The temporal interferometer is realized using a Mach-Zehnder interferometer (MZI) that incorporates an LCFBG and a dispersion compensating fiber to generate a temporal interference pattern with an instantaneous frequency that is linearly proportional to time. A linearly chirped microwave waveform with its shape that is identical to the temporal interference pattern is generated at the output of a photodetector. The tuning of the chirp rate of the generated waveform is realized by optically pumping the LCFBG that is written in an erbium-ytterbium co-doped fiber with different pumping powers. The key advantage of using optical pumping over external thermal tuning or mechanical tuning to tune the dispersion of the LCFBG is that the dispersion can be tuned at a high speed and controlled remotely. Moreover, the undesirable birefringence effects existing in the mechanical tuning technique can also be avoided. A theoretical analysis is performed that is verified by numerical simulations and an experiment. A linearly chirped microwave waveform with a tunable chirp rate from 79 to 64 GHz/ns by changing the injection current to the pumping laser diode from 0 to 100 mA is generated. The experimental results also show that the central frequency of the generated chirped microwave waveform can be changed by tuning the longitudinal offset of the MZI.

Ultrafast and Ultrahigh-Resolution Interrogation of a Fiber Bragg Grating Sensor Based on Interferometric Temporal Spectroscopy

A novel technique to achieve ultrafast and ultra-high-resolution interrogation of a fiber Bragg grating (FBG) sensor based on interferometric temporal spectroscopy is proposed and experimentally demonstrated. In the proposed system, two FBGs with one serving as the sensor grating and the other serving as the reference grating are connected at two arms of an interferometer. An ultrashort optical pulse from a pulsed laser is sent to the interferometer. Two pulses will be obtained due to the reflection of the two FBGs and then both are sent to a dispersive element to map the sensor grating wavelength shift to a temporal spacing change between the two dispersed pulses due to the dispersion-induced wavelength-to-time mapping. A temporal interference pattern is generated between the temporal pulses. The temporal spacing change is further mapped to the interference pattern frequency change, leading to a greatly improved interrogation resolution due to the inherently high sensitivity of a temporal interferometer. The proposed technique overcomes the fundamental tradeoff between the interrogation speed and resolution in a temporal-spectroscopy-based FBG interrogation system and that between the measurement resolution and dynamic range in a dual-wavelength heterodyne-based interrogation system. An ultrafast real-time interrogation of an FBG strain sensor with a sampling rate of 48.6 MHz and an interrogation resolution as high as 0.61 pm are experimentally demonstrated.

Complete Characterization of an Optical Pulse Based on Temporal Interferometry Using an Unbalanced Temporal Pulse Shaping System

We propose and demonstrate a simple method for the full characterization of an ultrashort optical pulse based on temporal interferometry, using an unbalanced temporal pulse shaping (UB-TPS) system. The UB-TPS system consists of a Mach-Zehnder modulator and two dispersive elements (DEs) having opposite dispersion, but nonidentical in magnitude. The entire system can be considered as a typical balanced TPS system for a real-time Fourier transformation to generate two time-delayed replicas of the input optical pulse, followed by a residual DE to perform a second real-time Fourier transformation to convert the two time-delayed pulse replicas to two frequency-sheared optical spectra. The spectral interferometry is performed in the time domain. The spectral magnitude and phase information of the input optical pulse is accurately and unambiguously reconstructed from the recorded temporal interference pattern based on a Fourier transform algorithm. Compared with a conventional pulse characterization system based on linear interferometric measurement using an optical interferometer implemented by using discrete components, the proposed system features better stability, higher adaptability, and single-shot measurement. The use of the proposed system for the characterization of a femtosecond pulse before and after passing through a 60-m-long single-mode fiber is experimentally demonstrated.

Performance investigation of an integrated Young interferometer sensor using a novel prism-chamber assembly

A novel prism-chamber assembly was prepared for application in optical waveguide based chemical and biological sensors, making the sensor easily and reproducibly operate. By using the prism-chamber assembly, the performance of a composite waveguide based integrated Young interferometer sensor was investigated. The temporal interference pattern detected with a single-slit photodetector heavily relies on the slit width, and regular high-contrast patterns can be obtained under the condition that the slit width is smaller than the spatial periodicity of the sensor. Increasing the temperature of water in the chamber leads to a quasi-linear variation in the phase difference with Deltaphi/DeltaT approximately -9.1 degrees/degrees C. Significant dependence of the sensor's sensitivity on the polarization state of the guided mode was also observed. The sensor is stable and reliable, capable of real-time detection of very slow bioreactions at the interface.

Repetitive excitation of charge oscillations in semiconductor heterostructures

We create forced excitonic charge oscillations in semiconductor heterostructures by excitation with periodic optical pulse sequences. The far-infrared radiation that accompanies the charge oscillations shows temporal interference patterns for pulse sequences with different optical phase profiles, providing evidence for phase induced population transfers between exciton levels in a semiconductor.