Wavelength-selective Modulator Research Articles

Dual-Function Wearable Hydrogel Optical Fiber for Monitoring Posture and Sweat pH.

In recent years, wearable devices have been widely used for human health monitoring. Such monitoring predominantly relies on the principles of optics and electronics. However, electronic detection is susceptible to electromagnetic interference, and traditional optical fiber detection is limited in functionality and unable to simultaneously detect both physical and chemical signals. Hence, a wearable, embedded asymmetric color-blocked optical fiber sensor based on a hydrogel has been developed. Its sensing principle is grounded in the total internal reflection within the optical fiber. The method for posture sensing involves changes in the light path due to fiber bending with color blocks providing wavelength-selective modulation by absorption changes. Sweat pH sensing is facilitated by variations in fluorescence intensity triggered by sweat-induced conformational changes in Rhodamine B. With just one fiber, it achieves both physical and chemical signal detection. Fabricated using a molding technique, this fiber boasts excellent biocompatibility and can accurately discern single and multiple bending points, with a recognition range of 0-90° for a single segment, a detection limit of 0.02 mm-1 and a sweat pH sensing linear regression R2 of 0.993, alongside great light propagation properties (-0.6 dB·cm-1). With its extensive capabilities, it holds promise for applications in medical monitoring.

An (adjustable RN)-based multi-OLT PON and the dynamic programming algorithm for downstream channel

In this paper, a multiple optical line terminal (OLT) passive optical network (PON) and the dynamic programming algorithm for downstream channel is proposed. By wavelength-selectable module, the adjustable remote node (RN) is constructed. By this adjustable RN, a simple and efficient multi-OLT PON is designed. By the way of first-plan and then-load, optical network unit (ONU) groups are established in order to realize the fast loading of ONUs. Specially, by introducing dynamic programming algorithm, the wavelength bandwidth utilization is maximized. Finally, by the simulation and analysis, the effectiveness of the proposed scheme is demonstrated.

Proposal of in-line wavelength-selective modulator based on waveguide interferometer

Proposal of in-line wavelength-selective modulator based on waveguide interferometer

High-speed coherent CW terahertz spectrometer

In-fibre wavelength selective modulation of the optical phase enables the electro-optic control of the terahertz phase in continuous-wave photomixing terahertz systems without any free-space optics. Using a fully fibre-coupled terahertz setup, a coherent scan of a frequency range of 1.5 THz with 100 MHz resolution in less than 24 s is demonstrated. This sample rate of 1.6 ms/sample is more than 20 times faster than any previous broadband scans reported.

In-Fiber Wavelength-Selective Modulation of WDM Channels With Performance Analysis

An in-fiber wavelength-selective optical intensity modulator has been developed to superimpose low-rate overhead (OH) data on the transit high-speed payload signals. The tunable fiber Bragg grating, as the heart of a wavelength-selective modulator (WSM), is designed and properly biased to implement the desired modulation specification. Potential performance limitations of WSM are investigated and described in terms of eye opening penalty and crosstalk between wavelength-division-multiplexing channels. A simple OH/label erasing technique is also provided and used for modifying the labels through cascaded WSMs. The performance of such cascaded systems is calculated both with and without considering the optical loss compensation. The results confirm the ability of WSMs for low-speed applications such as QoS management and service level agreement for differentiated services.

Rapid timescale processes and the role of electronic surface coupling in the photolysis of diatomic ligands from heme proteins.

We have observed coherent oscillations of the heme protein myoglobin (Mb) following femtosecond laser excitation and photodissociation of the CO, O2, and NO bound ligands. Use of a novel methodology, involving "wavelength selective modulation" of the pump and/or probe laser pulse train, allows us to discriminate between coherences created by pump fields of differing wavelength within the laser pulse versus signals that arise from the decay of either vibrational or electronic populations. The population driven signals appear when pump field interactions having the same optical frequency are allowed to contribute to the signal detection channel. One surprising result, which will be stressed in the discussion, is the observation of a distinct product state vibrational coherence (the iron-histidine stretching vibration of deoxy Mb at 220 cm(-1)) that depends upon the presence of pump field interactions having a wavelength mismatch that is equal to the 220 cm(-1) vibrational frequency. This observation is surprising because the iron-histidine mode is not observed in the resonance Raman measurements on the six-coordinate reactant species. Thus, the pump-pulse laser excitation between the ground and excited state, which leads to the ligand dissociation, is evidently able to create a "field driven" vibrational coherence of a resonance Raman inactive mode that extends into non-vertical regions of the reactive excited state potential energy surface. Non-radiative electronic surface crossing, followed by the rapid development of new electronic forces on the nuclei, appears to be ruled out as a source of the coherent signals (the random phase of the optically uncoupled modes is one possible explanation for this observation). The extremely rapid timescale (<< 150 fs) for the development of the (S = 2) high-spin product state of the iron atom from the initial unphotolyzed state (S = 0) is worthy of further theoretical discussion because of the spin forbidden nature of such a transition. Excited state admixtures of the iron spin states are presumably involved, and the mixing of these states, along with the unpaired electron on NO, may help to explain the ultrafast time scales and large amplitudes that characterize the NO geminate recombination in comparison to CO.

Wavelength selective modulation in femtosecond pump–probe spectroscopy and its application to heme proteins

We demonstrate novel lock-in detection techniques, using wavelength selective modulation of ultrafast pump and probe laser pulses, to discriminate between vibrational coherence and electronic population decay signals. The technique is particularly useful in extracting low frequency oscillations from the monotonically decaying background, which often dominates the signal in resonant samples. The central idea behind the technique involves modulating the red and/or blue wings of the laser light spectrum at different frequencies, ΩR and ΩB, followed by a lock-in detection at the sum or difference frequency, ΩR±ΩB. The wavelength selective modulation and detection discriminates against contributions to the pump–probe signal that arise from degenerate electric field interventions (i.e., only field interactions involving different optical frequencies are detected). This technique can be applied to either the pump or the probe pulse to enhance the off-diagonal terms of the pump induced density matrix, or to select the coherent components of the two-frequency polarizability. We apply this technique to a variety of heme-protein samples to reveal the presence of very low-frequency modes (∼20 cm−1). Such low-frequency modes are not observed in standard pump–probe experiments due to the dominant signals from electronic population decay associated with resonant conditions. Studies of the diatomic dissociation reaction of myoglobin (MbNO→Mb+NO), using wavelength selective modulation of the pump pulse, reveal the presence of an oscillatory signal corresponding to the 220 cm−1 Fe–His mode. This observation suggests that the spin selection rules involving the ferrous iron atom of the heme group may be relaxed in the NO complex. Mixed iron spin states associated with adiabatic coupling in the MbNO sample could explain the fast time scales and large amplitude that characterize the NO geminate recombination.