Stokes Signal Research Articles

Spatial and frequency multimode in the dressing parametric amplified multiwave mixing process

The quantum multimode of correlated fields is essential for future quantum-correlated imaging. Here we investigate multimode properties theoretically and experimentally for the parametric amplified multiwave mixing process. The multimode behavior of the signals in our system stems from spatial phase mismatching caused by frequency resonant linewidth. In the spatial domain, we observe the emission rings with an uneven distribution of photon intensity in the parametric amplified four-wave mixing process, suggesting different spatial modes. The symmetrical distribution of spatial spots indicates the spatial correlation between the Stokes and anti-Stokes signals. While in the frequency domain, the multimode character is reflected as multiple peaks splitting in the signals’ spectrum. A novelty in our experiment, the number of multimodes both in the spatial and frequency domains can be controlled by dressing lasers by modifying the nonlinear susceptibility. Finally, we extend the multimode properties to the multiwave mixing process. The results can be applied in quantum imaging.

Tunable hybrid spectral filter and time-division multiplexing of second-order fluorescence controlled by phonon and dressing on Pr3+:YSO

Atom-like nonlinear responses of rare earth doped crystal Pr3+:Y2SiO5 (Pr3+: YSO) exhibit unique features compared with other nonlinear crystals. The responses become more interesting, while Pr3+: YSO is modulated simultaneously by temperature and multi-parameters related to dressed state. The generations of Stokes and fluorescence (FL) signals are demonstrated in both time and spectral domains. Here, we are presenting a new controlling strategy by interaction between dressing and phonon on Pr3+: YSO to manipulate the intensity of Stokes and FL signals. Interaction between dressing and phonon leads to more stable nonlinear response of the YSO crystal, which is very important for integrated quantum photonic device stability and multi-functionality. Also, we have realized tunable hybrid spectral filter (narrow-band pass notch filter (NBPNF), narrow-band stop notch filter (NBSNF)) and time-division multiplexing router on Pr3+: YSO by controlling the interaction between dressing and phonons. Tunable hybrid spectral filter and pure NBPNF are realized from dressing dip of Autler-Townes (AT) splitting and spectral intensity Stokes emission peak. Also, time-division multiplexing router is realized by time-domain adiabatic expansion. Furthermore, optical switch between tunable hybrid spectral filter to pure NBPNF is realized from dressing dip (AT splitting) to spectral intensity Stokes emission peak. Our experimental results suggests advanced technique for realizing tunable hybrid spectral filter with a contrast of about 98%, and optical time-division multiplexing router with channel equalization is about 85%.

Optical Polarimetric Detection for Dental Hard Tissue Diseases Characterization.

Dental enamel constitutes the outer layer of a crown of teeth and grows nearly parallel. This unique nanostructure makes enamel possess birefringence properties. Currently, there is still no appropriate clinical solution to examine dental hard tissue diseases. Therefore, we developed an optical polarization imaging system for diagnosing dental calculus, caries, and cracked tooth syndrome. By obtaining Stokes signals reflected from samples, Mueller images were constructed and analyzed using Lu-Chipman decomposition. The results showed that diattenuation and linear retardance images can distinguish abnormal tissues. Our result also aligns with previous studies assessed by other methods. Polarimetric imaging is promising for real-time diagnosing.

Temperature switch and router of two and three-mode noise correlation in Pr3+:YSO crystal

Rare earth doped crystal Pr3+:Y2SiO5 has unique features, whose nonlinear response is dynamically triggered and modulated by the interaction between dressing and phonon effect. In this article, we have demonstrated the switching from two-mode bunching to anti-bunching like phenomenon of noise intensity fluctuations used for noise correlation. Here, switching in bunching phenomenon is caused by relative nonlinear phase, which is induced by self- and cross-phase modulation. In contrast with two-mode bunching, three-mode bunching case hardly follows the switching mechanism attributed to the destructive interaction among the phases of Stokes, anti-Stokes and FL signals. We also have realized switching and routing application in two and three mode bunching. Both functions (switching and routing) are controlled by manipulating temperature of cryostat and gate delay. Our experimental results provide the novel technique for switching and channel equalization ratio of about 96%. The intensity switching speed is achieved about 17 ns.

Erbium gain effects on Stokes signal performance in a Fabry–Perot Brillouin Erbium fiber laser

The effect of the Erbium gain on the Stokes signal performance is experimentally presented in this paper. Linear Brilllouin Erbium fiber laser cavity is tested under different 1480 nm pump power ranges (0–125 mW). Different Brillouin pump (Bp) power values of 2, 4 and 6 dBm are used in this study. Stokes signal net gain and threshold power are recorded at all generated Stokes signals for these Bp powers values. 2 dBm Bp power shows higher net gain, low threshold, large Stokes numbers and low required 1480 nm pump power compared to 4 and 6 dBm. Up to 8.3 dB net gain, threshold of − 10.3 dBm, 24 Stokes signals and with a maximum 1480 nm pump power of 92.2 mW are recorded for 2 dBm Bp power. Stokes signal threshold is recorded at the near end of the single mode fiber at which Nth order Stokes is generated.

Influence of bidirectional cavity structure on the Brillouin Stokes signal characteristics in ring BFL

We experimentally demonstrate the effects of Brillouin amplifications on the stimulated Brillouin scattering threshold as well as the generated Stokes power. Brillouin fiber laser (BFL) ring cavity structure is used to show the effect of bidirectional signal propagation on threshold and Stokes power. The laser cavity is tested with conventional technique in which there is no signal circulation take place. Both structures are tested under the same experimental conditions using 5 km SMF length, threshold power for the 1 st Stokes signal is improved and reduced up to 90% in ring cavity structure compared to its value in conventional technique. The threshold is reduced, from the value of 16.2 mW in conventional structure to be 1.67 mW in ring laser cavity. Furthermore, different SMF lengths are tested and exhibits the same threshold reduction ratio. In addition, the 1 st and the 2nd Stokes signals within ring laser cavity are tested in terms of threshold and Stokes signals power. In addition, the induced Brillouin gain effect within a bidirectional ring cavity are studied on the maximum Brillouin Stokes signal power.

A tunable multi-wavelength Brillouin-erbium linear cavity fiber laser with higher optical signal to noise ratio

We experimentally demonstrated a widely tunable multi-wavelength Brillouin-erbium fiber laser by utilizing a double-pass pre-amplification Brillouin pump (BP) within a single-linear laser cavity. Owing to this pre-amplification technique, the laser can operate at low pump power and exhibit a low threshold operation of 35 mW pump power to create the first Stokes signal. By adjusting the polarization controller (PC), self-lasing cavity modes’ oscillation can be tuned over 10 nm from 1562 nm to 1572 nm. We experimentally showed that the proposed novel fiber laser structure can achieve up to ~33 output channels with a constant wavelength spacing of 0.088 nm at 7.4 dBm of BP power and 250 mW of the 980 nm pump power by varying the wavelength of the BP and adjusting the PC. In addition, an average of 32 stable output channels could all be tuned over 12 nm with an average optical signal to noise ratio of 25 dB.

Signatures of quiet Sun reconnection events in Ca ii, Hα, and Fe i

We use observations of quiet Sun (QS) regions in the H$\alpha$ 6563 \AA, Ca~{\sc ii} 8542 \AA\, and Fe~{\sc i} 6302 \AA\ lines. We observe brightenings in the wings of the H$\alpha$ and Ca~{\sc ii} combined with observations of the interacting magnetic concentrations observed in the Stokes signals of Fe~{\sc i}. These brightenings are similar to Ellerman bombs (EBs), i.e. impulsive bursts in the wings of the Balmer lines which leave the line cores unaffected. Such enhancements suggest that these events have similar formation mechanisms to the classical EBs found in active regions, with the reduced intensity enhancements found in the QS regions due to a weaker feeding magnetic flux. The observations also show that the quiet Sun Ellerman bombs (QSEBs) are formed at a higher height in the upper photosphere than the photospheric continuum level. Using simulations, we investigate the formation mechanism associated with the events and suggest that these events are driven by the interaction of magnetic field-lines in the upper photospheric regions. The results of the simulation are in agreement with observations when comparing the light-curves, and in most cases we found that the peak in the Ca~{\sc ii} 8542 \AA\ wing occurred before the peak in H$\alpha$ wing. Moreover, in some cases, the line profiles observed in Ca~{\sc ii} are asymmetrical with a raised core profile. The source of heating in these events is shown by the MURaM simulations and is suggested to occur 430 km above the photosphere.

Dominance of backward stimulated Raman scattering in gas-filled hollow-core photonic crystal fibers

Backward stimulated Raman scattering in gases provides a promising route to compression and amplification of a Stokes seed-pulse by counter-propagating against a pump-pulse, as has been already demonstrated in various platforms, mainly in free-space. However, the dynamics governing this process when seeded by noise has not yet been investigated in a fully controllable collinear environment. Here we report the first unambiguous observation of efficient noise-seeded backward stimulated Raman scattering in a hydrogen-filled hollow-core photonic crystal fiber. At high gas pressures, when the backward Raman gain is comparable with, but lower than, the forward gain, we report quantum conversion efficiencies exceeding 40% to the backward Stokes at 683 nm from a narrowband 532-nm-pump. The efficiency increases to 65% when the backward process is seeded by a small amount of back-reflected forward-generated Stokes light. At high pump powers the backward Stokes signal, emitted in a clean fundamental mode and spectrally pure, is unexpectedly always stronger than its forward-propagating counterpart. We attribute this striking observation to the unique temporal dynamics of the interacting fields, which cause the Raman coherence (which takes the form of a moving fine-period Bragg grating) to grow in strength towards the input end of the fiber. A good understanding of this process, together with the rapid development of novel anti-resonant-guiding hollow-core fibers, may lead to improved designs of efficient gas-based Raman lasers and amplifiers operating at wavelengths from the ultraviolet to the mid-infrared.

Spatiotemporal dynamics of Raman coherence in hollow-core fibers for a pump-probe setup

We present an experimental and theoretical study of the stimulated Raman emission in hollow-core kagome waveguides in a pump-probe arrangement. We perform an experimental investigation of the power of the Stokes signal from the probe, which is below the stimulated Raman scattering threshold, as a function the pump-probe delay time. The results show the Stokes power to increase with pump-probe delay, reaching a maximum at 10 ns, and to decrease afterward. In view of a coherence decay time of only 0.25 ns, we demonstrate a surprisingly slow reduction of Stokes signal with the characteristic time much longer than the coherence decay time by a factor of up to 40. The numerical investigations explain the observed phenomenon as a result of the spatiotemporal dynamics of the probe pulse and Raman coherence. We show that the increase of the characteristic time can be related to the spatial position of the intense sideband generation event and its dependence on the pump-probe delay.

Particle Filtering for Stochastic Navier--Stokes Signal Observed with Linear Additive Noise

We consider a nonlinear filtering problem whereby the signal obeys the stochastic Navier--Stokes equations and is observed through a linear mapping with additive noise. The setup is relevant to dat...

Fiber bragg grating assisted cavity loss reduction in the generation of multiwavelength brillouin fiber laser

This work investigates two types of multiwavelength Brillouin fiber laser configurations. These configurations are ring-cavity multi-wavelength Brillouin fiber laser employs fiber Bragg grating and S-shaped multiwavelength Brillouin fiber laser. The two arrangements comprise of 10km long single mode fiber as a gain medium and operate in the C-band region. Replacing the S-Shaped with Bragg grating fiber has led to a loss reduction in the ring-cavity multiwavelength Brillouin fiber laser and subsequently generated higher number Brillouin Stokes (BS) signals. The maximum of 33 BS signals with ∼0.08nm (∼10GHz) spacing is obtained. Optical signal to noise ratio of about 15dB is observed at output coupling ratio of 70%, when 1550nm of Brillouin pump is launched into the ring-cavity multiwavelength Brillouin fiber laser employs fiber Bragg grating. In contrast, due to the limitation of high cavity losses, only 17 BS signals with ∼0.16 (20GHz) spacing are generated from the S-shaped multi-wavelength Brillouin fiber laser. These findings contribute new insights and profiles of the multi-wavelength Brillouin fiber laser employs fiber Bragg grating that has the capability to reduce cavity losses while generating a high number of Brillouin Stokes signals.

Instantaneous Area Based Online Detection of Bend Generated Error in a Raman Optical Fiber Distributed Temperature Sensor

Error-free temperature measurement by Raman scattering based optical fiber distributed temperature sensor (OFDTS) is possible if the sensing fiber has no sharp bend. However, in real life applications, the sensing fiber might have sharp bend that may cause discontinuity in the profiles of Raman anti-Stokes (AS) and Stokes (St) signals resulting in erroneous distributed temperature measurement by OFDTS. In such a case, it is necessary to detect the presence and location of the bend. For a human operator using OFDTS, it is difficult to detect the presence of bend and locate it by visually observing AS and St signals. In this article, an online automated technique based on measurement of a new parameter called the instantaneous area of analytic intrinsic mode functions (IMFs) of St signals is presented to serve the purpose. The proposed technique is more automation friendly than earlier reported technique where area corresponding to IMF of complete duration of St signal was considered. The instantaneous area parameter alone is able to detect both the bend induced malfunctioning of OFDTS and the location of bend.

40 GHz narrow linewidth frequency-switched microwave signal generation based on a single-longitudinal-mode double-Brillouin-frequency spaced Brillouin fiber laser.

A novel approach to generating 40 GHz narrow linewidth frequency-switched microwave signals is proposed and demonstrated. In this scheme, a single-longitudinal-mode (SLM) double-Brillouin-frequency spaced Brillouin fiber laser with dual-ring configuration and unpumped erbium-doped fiber (EDF) is used to generate dual-wavelength lasers, and a fiber Bragg grating is used to select the laser for different Brillouin frequency spacings. Dual-ring configuration and unpumped EDF are designed to select the mode for the SLM laser. Dual-wavelength lasers are inserted into a photodetector, and microwave signals at 10.66, 21.39, 32.12, or 42.85 GHz can be obtained. The linewidth of the generated microwave signals is less than 69 kHz. The frequency drift at each frequency is less than 0.83 MHz. The frequency noise and linewidth of Stokes signals are measured, and the linewidth broadening effect of microwave signals is analyzed.

Fluctuation initiation of Stokes signal and its effect on stimulated Brillouin scattering pulse compression.

In this paper, a theoretical model is developed to demonstrate that fluctuations in the Stokes signal and occurrence position contribute to the final compression ratio in stimulated Brillouin scattering (SBS). This theoretical analysis can be applied to the investigation of the temporal characteristics of SBS pulse compression. This model agrees well with the experimental results in a two-stage SBS compressor.

Quantum Optics Model of Surface-Enhanced Raman Spectroscopy for Arbitrarily Shaped Plasmonic Resonators

We present a self-consistent quantum optics approach to calculating the surface enhanced Raman spectrum of molecules coupled to arbitrarily shaped plasmonic systems. Our treatment is intuitive to use and provides fresh analytical insight into the physics of the Raman scattering near metallic surfaces and can be applied to a wide range of geometries including resonators, waveguides, as well as hybrid photonic-plasmonic systems. Our general theory demonstrates that the detected Raman spectrum originates from an interplay between nonlinear light generation and propagation. Counter intuitively, at the nonlinear generation stage, we show that the Stokes (anti-Stokes) signal at the molecule location depends on the plasmonic enhancements, through the local density of photon states (LDOS), at the anti-Stokes (Stokes) frequency. However, when propagating from the vibrating molecule to the far field, the Stokes (anti-Stokes) emission experiences a plasmonic enhancement at the Stokes (anti-Stokes) frequency, as expected. We identify the limits of the commonly known E^4 electric-field rule for Raman signal enhancement near plasmonic surfaces at low pump powers, as well as a different E^8 rule at high pump powers, and we clarify the role of the LDOS. Our theory uses a generalized quantum master equation where the plasmonic system is treated as an environmental bath that is described through the photonic Green function of the medium. Therefore, any electrodynamics related physics, such as quenching and propagation, are self-consistently included in the model. The presented formalism is also capable of spatially describing the full Raman response in a simple analytical way, which is typically not possible using simpler coupled mode theories, even if one adopts a quantum picture.

Adaptive phase matching probe-injection technique for enhancement of Brillouin scattering signal

We report on a simple and efficient method for enhancing Brillouin scattering signal, i.e., adaptive phase matching (APM) probe-injection technique. In this technique, a low-polarization broad-spectrum probe wave is injected opposite to the pump, which can enhance any stokes signal in its APM range instantly by selective stimulated Brillouin amplification. With advantages of simple scheme, real-time multi-signal enhancement and sweep-free measurement, this technique has a great potential for improving the signal-to-noise ratio of Brillouin gain spectrum in the Brillouin scattering application systems.

Multiple lasing Brillouin Fiber Laser with the implementation of reflective Fiber Bragg Grating in a ring cavity configuration

A multi-wavelength Brillouin fiber laser with the implementation of reflective fiber Bragg grating is developed. In this ring cavity architecture, the fiber laser system is performed by the stimulated Brillouin scattering effect and four-wave mixing process. An improvement in the number Brillouin Stokes signal and average of the optical signal to noise ratio were generated through the reflection process of fiber Bragg grating. Due to the optimization of output coupling ratio from 10% to 60%, the highest Brillouin Stokes signal of 17 and average optical signal to noise ratio of 14.7 dB were recorded at 60% of the output coupling ratio. The amplified Brillouin pump power of 16.5 dBm at 1550 nm of Brillouin pump wavelength was injected into the laser system. A constant line spacing of 0.08 nm at each of the Brillouin Stokes signals was also recorded.

Lasing characteristics of 10 GHz signal spacing in a ring cavity multi-wavelength Brillouin fiber laser employing fiber Bragg grating

This paper experimentally demonstrated a ring cavity multi-wavelength Brillouin fiber laser employing fiber Bragg grating (FBG) that operated in the C-band region. The FBG plays a significant role to reflect signals and filter selected wavelengths. A number of generated Brillouin Stokes (BS) signals and tuning range ability were investigated. A 9[Formula: see text]km length of single mode fiber was utilized to provide a Brillouin gain medium for generating stimulated Brillouin scattering effect. In this work, at optimum output coupling ratio of 90% and Brillouin pump (BP) wavelength of 1550[Formula: see text]nm, up to a maximum of 26 BS signals were recorded by injecting 63.1[Formula: see text]mW of amplified BP powers. The BS signals were also tunable within the ranges of 1544–1556[Formula: see text]nm in accordance with the FBG properties at 3[Formula: see text]dBm bandwidth of 5[Formula: see text]nm.

An L-band multi-wavelength Brillouin–erbium fiber laser with switchable frequency spacing

In this paper, a novel L-band multi-wavelength Brillouin–erbium fiber laser consisting of two ring cavities is proposed and demonstrated. The frequency spacing can be switched, corresponding to the single and double Brillouin frequency shifts, by toggling the optical switch. Under a 980 nm pump power of 600 mw, and a Brillouin pump power of 4 mW and wavelength of 1599.4 nm, up to 16 Stokes signals with a frequency spacing of 0.089 nm and 5 Stokes signals with double spacing of 0.178 nm are generated. A wavelength tunability of 15 nm (1593 nm − 1608 nm) is realized for both frequency spacings. The fluctuation of Stokes signals for both single and double Brillouin spacing regimes in the proposed setup is less than 1.5 dB throughout a 30 min time span.