Psychometrics of the Korean Version of the screen for adult anxiety related disorders (SCAARED).

BACKGROUND: For enhanced management of anxiety disorders, early screening and accurate diagnostic differentiation are essential. The Screen for Adult Anxiety Related Disorders (SCAARED) has been developed to identify and categorize anxiety disorders, thereby facilitating timely and appropriate interventions. In line with this, we aimed to translate and validate the Korean version of the SCAARED questionnaire for the Korean population. METHODS: The original SCAARED was translated into Korean and administered to community adult population (N = 119) ages 18-45 years old in South Korea. The internal consistency and test-retest reliability of the SCAARED were evaluated. In addition, its factor structure was examined using confirmatory and exploratory factor analysis. Concurrent validity was evaluated by comparing SCAARED with the Depression, Anxiety and Stress Scale-21 (DASS), the Beck's Anxiety Inventory (BAI) and the State-Trait Anxiety Inventory (STAI). Test-retest reliability was evaluated one week after the first assessment. RESULTS: The SCAARED showed good internal consistency (Cronbach's α = 0.945) and test-retest reliability (γ = 0.883). The SCAARED had significant correlation with DASS-21 subscales (γ = 0.655-0.701), BAI (γ = 0.788) and STAI subscales (γ = 0.548-0.736), confirming good concurrent validity. The results of the Exploratory Factor Analysis showed four factors comparable to the original SCAARED (Generalized anxiety, Somatic/Panic/Agoraphobia, Social anxiety, and Separation anxiety). The area under the curve of the receiver operating characteristic of total and each of the factor scores ranged from 0.724 to 0.942. CONCLUSIONS: The Korean version of the SCAARED is a reliable and valid instrument to screen for anxiety disorders in the Korean adult populations.

An Artificial Neural Network to Eliminate the Detrimental Spectral Shift on Mid-Infrared Gas Spectroscopy.

We demonstrate the successful implementation of an artificial neural network (ANN) to eliminate detrimental spectral shifts imposed in the measurement of laser absorption spectrometers (LASs). Since LASs rely on the analysis of the spectral characteristics of biological and chemical molecules, their accuracy and precision is especially prone to the presence of unwanted spectral shift in the measured molecular absorption spectrum over the reference spectrum. In this paper, an ANN was applied to a scanning grating-based mid-infrared trace gas sensing system, which suffers from temperature-induced spectral shifts. Using the HITRAN database, we generated synthetic gas absorbance spectra with random spectral shifts for training and validation. The ANN was trained with these synthetic spectra to identify the occurrence of spectral shifts. Our experimental verification unambiguously proves that such an ANN can be an excellent tool to accurately retrieve the gas concentration from imprecise or distorted spectra of gas absorption. Due to the global shift of the measured gas absorption spectrum, the accuracy of the retrieved gas concentration using a typical least-mean-squares fitting algorithm was considerably degraded by 40.3%. However, when the gas concentration of the same measurement dataset was predicted by the proposed multilayer perceptron network, the sensing accuracy significantly improved by reducing the error to less than ±1% while preserving the sensing sensitivity.

Digital OPLL-based distributed Brillouin sensing system in optical fibers.

A digital optical phase-locked loop (OPLL) has been implemented to develop a distributed Brillouin sensing system in optical fibers. In our experiment, two commercial semiconductor lasers are phase-locked to each other with a highly flexible offset frequency using field programmable gate array (FPGA)-based electronics. Then, the difference frequency between the two lasers is highly stabilized and scanned by a desired step frequency in the vicinity of the Brillouin frequency of standard single-mode optical fibers. Consequently, the distribution of Brillouin frequency shift over a 50 km-long sensing fiber has been successfully measured by a very simple and low-cost Brillouin optical time-domain reflectometry (BOTDR) sensing system without any penalty in the sensing performance. The measurement repeatability at 50 km position of sensing fiber with a 5 m spatial resolution was measured be 4.5 MHz under fast measurement conditions: the number of trace averaging of 2000 and the frequency scan step of 12.8 MHz, showing the figure-of-merit of 3.0.

All-optical signal processing using dynamic Brillouin gratings.

The manipulation of dynamic Brillouin gratings in optical fibers is demonstrated to be an extremely flexible technique to achieve, with a single experimental setup, several all-optical signal processing functions. In particular, all-optical time differentiation, time integration and true time reversal are theoretically predicted, and then numerically and experimentally demonstrated. The technique can be exploited to process both photonic and ultra-wide band microwave signals, so enabling many applications in photonics and in radio science.

Time-frequency analysis of long fiber Bragg gratings with low reflectivity.

A new technique to investigate the spatial distribution of the reflection spectrum along fabricated long weak fiber Bragg gratings (FBG) is experimentally demonstrated, together with its potential applications for distributed fiber sensing and broadband signal processing. A short pulsed coherent light signal is launched into a FBG and the signal frequency is scanned through the FBG reflection spectrum. When the pulse duration is set much shorter than the transit time through the grating a time-resolved reflected signal can be obtained for each signal frequency. It informs about the distribution of the refractive index periodic perturbation along the entire FBG length, hence the uniformity or frequency chirp information of the fabricated FBG. This technique has been implemented to demonstrate a distributed temperature sensing system with high spatial resolution and to also realize a robust all-fiber tunable delay line for broadband signals.

Dual-pump push-pull polarization control using stimulated Brillouin scattering.

Stimulated Brillouin scattering (SBS) amplification of probe signals is highly polarization dependent. Maximum and minimum gain values are associated with a pair of orthogonal states of polarization (SOP), which are related to the pump SOP. Since the maximum gain is much higher than the minimum, the SOP of the output probe is pulled towards that of the maximum amplification. Polarization pulling is restricted, however, by pump depletion. In this work, a new method is proposed, analyzed and demonstrated for enhanced SBS polarization pulling, using two orthogonal pumps. Here, one pump amplifies one polarization component of the probe wave, and at the same time the other pump attenuates the corresponding orthogonal component, resulting in a push-pull effect. In the undepleted regime and for equal total power, the same degree of pulling is achieved as in the single pump case, but at a significantly less signal gain. Thus, the dual pump technique can provide high pulling efficiency for stronger input signals, deferring the onset of depletion.

Broadband true time delay for microwave signal processing, using slow light based on stimulated Brillouin scattering in optical fibers.

We experimentally demonstrate a novel technique to process broadband microwave signals, using all-optically tunable true time delay in optical fibers. The configuration to achieve true time delay basically consists of two main stages: photonic RF phase shifter and slow light, based on stimulated Brillouin scattering in fibers. Dispersion properties of fibers are controlled, separately at optical carrier frequency and in the vicinity of microwave signal bandwidth. This way time delay induced within the signal bandwidth can be manipulated to correctly act as true time delay with a proper phase compensation introduced to the optical carrier. We completely analyzed the generated true time delay as a promising solution to feed phased array antenna for radar systems and to develop dynamically reconfigurable microwave photonic filters.

Polarization-induced distortion in stimulated Brillouin scattering slow-light systems.

The vector analysis of stimulated Brillouin scattering amplification in birefringent fibers is extended to include signal pulses. The analysis finds that the different slow-light delays experienced by the states of polarization corresponding to maximum and minimum gain may result in severe pulse distortion. Thus, a generally polarized pulse, experiencing only a moderate gain, can become broader than a pulse aligned for maximum gain and delay. The effect is demonstrated in both numerical simulations and experiments.

Optimized shaping of isolated pulses in Brillouin fiber slow-light systems.

The effect of a proper shaping of the temporal envelope of isolated pulses in slow-light systems based on stimulated Brillouin scattering in optical fibers is studied and experimentally demonstrated. The pulse shape can be optimized to lead to a substantial enhancement of the delaying effect. The spectrum of the optical pulses is engineered so that the spectral width of the pulse is minimized while preserving the pulse duration, making possible to match at best the Brillouin spectrum. Exponentially shaped pulses show the minimal FWHM spectral width and experience the largest time delay when compared to Gaussian or rectangular pulses.

Self-advanced fast light propagation in an optical fiber based on Brillouin scattering.

We experimentally demonstrate an extremely simple technique to achieve pulse advancements in optical fibers by using both spontaneous amplified and stimulated Brillouin scattering. It is shown that the group velocity of a light signal is all-optically controlled by its average power while it propagates through an optical fiber. The signal generates an intense back-propagating Stokes emission that causes a loss on the signal through depletion. This narrowband loss gives rise to a fast light propagation at the exact signal frequency. The Stokes emission self-adapts in real time to the Brillouin properties of the fiber and to a wide extent to the signal bandwidth.

Simple technique to achieve fast light in gain regime using Brillouin scattering.

We describe a novel technique based on stimulated Brillouin scattering for propagating fast light (signal advancement) with low distortion in optical fibers. The essence of the technique relies on the presence of two separate gain resonances in the Brillouin gain spectrum generated by cascading two different fiber segments showing distinct Brillouin shifts. It can be shown that in between these two gain spectra, a reduced group index can be obtained. To further optimize our results, we broadened the pump spectrum by introducing a modulation of the current driving the pump laser to achieve a delay-bandwidth product close to the optimum conditions. This scheme eliminates the need of an external optical modulator and offers the advantage of a much reduced signal distortion.

Zero-gain slow & fast light propagation in an optical fiber.

Slow & fast light with null amplification or loss of a light signal is experimentally demonstrated. This novel method for producing zero-gain slow & fast light takes advantage of the great flexibility of stimulated Brillouin scattering in optical fibers to generate synthesized gain spectra. Generation of optical delays and advancements with minor amplitude change is realized through the superposition of gain and loss profiles showing very different spectral widths, resulting in a synthesized spectral profile identical to an ideal electromagnetically-induced transparency.