F. Abdullah

Characteristics of multiwavelength L-band Brillouin–Raman fiber laser under forward and backward pumped environment

We experimentally investigate the performance of L-band multiwavelength Brillouin-Raman fiber laser (MBRFL) under forward and backward pumped environments utilizing a linear cavity. A short length of 1.18 km dispersion compensating fiber is used as a nonlinear gain medium for both Brillouin and Raman gain. Experimental results indicate that the gain in the copumped laser configuration is higher than the gain in the counterpumped configuration. A stable and constant number of Brillouin Stokes lines up to 23 Stokes, with channel spacing of 0.08 nm and more than 20 dB of optical signal to noise ratio, can be generated as well as tuning over 20 nm in the L-band region from 1570 to 1590 nm. The laser generating the Brillouin Stokes lines exhibits flat amplitude bandwidth and high average output power of 0.8 and 1.6 dBm for the copropagation and counterpropagation pumps, respectively. Moreover, the tuning range bandwidth of the MBRFL can be predicted from the oscillated Brillouin pump gain profile.

Pressure sensing utilizing linear cavity erbium-doped fiber laser

In this paper, we report a fiber laser pressure sensor based on linear cavity erbium-doped fiber laser. The fiber laser structure comprises of an erbium-doped fiber amplifier, a circulator, an optical coupler and a fiber Bragg grating (FBG) which acts simultaneously as a lasing wavelength selecting components as well as a pressure sensor. The FBG is fitted to the shock tube where the pressure is applied. The fiber laser pressure sensor has a low threshold power of 7 mW, an output power of 2.28 mW and an optical signal to noise ratio over 55 dB. The proposed fiber laser sensor is expected to be an attractive choice for long-distance pressure monitoring.

High gain double-pass L-band EDFA with dispersion compensation as feedback loop

We demonstrate an efficient double-pass L-band erbium-doped fiber amplifier (EDFA) incorporating chirped fiber Bragg grating (CFBG). The amplifier structure exploits the characteristics of CFBG to reflect the amplified signal back into the gain medium, filter out the recycled forward amplified spontaneous emission and block the residual 1480 nm pump power. The amplifier configuration has high gain and low noise figures as compared to double-pass EDFA using broadband mirror. The demonstrated amplifier has gain of more than 48 dB and low noise figure of less than 4 dB at low input signal power of −40 dBm.

Live Monitoring System for Ethernet Passive Optical Network health using Fiber Bragg Grating

This paper presented a Live Monitoring System (LMS) for Ethernet Passive Optical Network (EPON) condition. Fiber Bragg Gratings (FBG) with different center frequencies is used as the monitoring devices. Different bit rates, of 2.5 Gbps and 10 Gbps are used as transmission speed. The performance of downstream signal with the monitoring signal propagating in the same fiber is observed. The simulation result shows that the performance of EPON system with 8 users is in acceptable range where transmission distance at bit error rate (BER) 10-9 is 47 km for 2.5 Gbps and 27 km for 10 Gbps system.

L-Band Multi-Wavelength Brillouin–Raman Fiber Laser with 20-GHz Channel Spacing

Abstract A tunable multi-wavelength L-band Brillouin–Raman fiber laser with a 20-GHz channel spacing utilizing bidirectional ring cavity is proposed and experimentally investigated. The laser employs a co-pumped dispersion compensating fiber as a gain medium for both Brillouin and Raman gains. With a Raman pump of 425 mW, the laser system can generate up to 12 double-spaced Brillouin Stokes signals. This simple laser configuration provides stable Brillouin Stokes signals in the absence of self-lasing cavity modes with a tuning range exceeding 35 nm without using any filtering mechanism. The Stokes signals have more than 20 dB of optical signal-to-noise ratio.

Four-wave mixing crosstalk suppression based on the pairing combinations of differently linear-polarized optical signals.

A new approach to suppressing the four-wave mixing (FWM) crosstalk by using the pairing combinations of differently linear-polarized optical signals was investigated. The simulation was conducted using a four-channel system, and the total data rate was 40 Gb/s. A comparative study on the suppression of FWM for existing and suggested techniques was conducted by varying the input power from 2 dBm to 14 dBm. The robustness of the proposed technique was examined with two types of optical fiber, namely, single-mode fiber (SMF) and dispersion-shifted fiber (DSF). The FWM power drastically reduced to less than −68 and −25 dBm at an input power of 14 dBm, when the polarization technique was conducted for SMF and DSF, respectively. With the conventional method, the FWM powers were, respectively, −56 and −20 dBm. The system performance greatly improved with the proposed polarization approach, where the bit error rates (BERs) at the first channel were 2.57 × 10−40 and 3.47 × 10−29 at received powers of −4.90 and −13.84 dBm for SMF and DSF, respectively.

Mitigation of FWM crosstalk in WDM system using polarization interleaving technique

In long-haul transmission systems, optical transmission characteristics are degraded by four-wave mixing (FWM) generated in optical fibers. This paper presents a new approach to reduce the four wave mixing crosstalk based on polarization interleaving is presented. The FWM behavior and the performance of WDM systems were analyzed using the proposed technique. The simulation was performed using different power values with 100 GHz channel spacing, and at a data rate of 60Gb\s. It was found that the FWM power was drastically reduced to -64 dBm when the polarization technique was used. In addition, the WDM system performance showed that at the sixth channel (192 THz), the suggested approach incurred a BER of 4.86×10-21, in comparison with the absence of the approach where the BER was 4.3×10-10 at the same received power. The results prove that the proposed system is superior in mitigating FWM crosstalk.

Raman amplification effects on stimulated Brillouin scattering threshold in multiwavelength Brillouin-Raman fiber laser

We report experimental results demonstrating the stimulated Brillouin scattering threshold (SBSTH) features in multiwavelength Brillouin-Raman fiber laser against Raman pump power (RPP) variation. The reduction of SBSTH is attributed to the Raman amplification on each of oscillated Brillouin pump power (OBP) and generated Stokes signals. The saturation in SBSTH is owing to the RPP depletion, this saturation is coincides with the appearance of Raman peak gain. In addition, the red shift effect became significant at RPP beyond 650mW and led to degradation of the Raman amplification. This degradation appeared as an increase in SBSTH after the saturation region. Moreover, the Brillouin Stokes comb can be generated only at the saturation region of the Raman amplification between 350 to 600 mW of Raman pump.

Evolution of Surface Acoustic Waves in an Optical Microfiber

This paper reports stimulated Brillouin scattering characterization in a tapered optical fiber using full-vectorial finite element-based numerical methods. Numerical simulations of both optical and acoustic waves’ propagation through a tapered microfiber have been carried out. Acoustic modes over a range of wavenumber for different fiber core radii are obtained and nature of their both dominant and non-dominant displacement vector profiles are studied and discussed. Acoustic mode profiles show confinement of the acoustic wave predominantly at the core cladding interface. In addition, the acoustooptical overlap factors at different fiber radii are also presented.

Determining the inhibitor content of transformer insulating oil using UV-Vis spectroscopy

Monitoring and inspection of inhibitor content in transformer insulating oil has been a routine test for power utilities. Although new uninhibited transformer insulating oil contains naturally occurring inhibitors, these inhibitors could deplete over time during operation. Once the inhibitor depleted completely, the oil would start to deteriorate at a faster rate and eventually could lead to faults in transformer. The common method of determining the weight percentage of inhibitor in transformer oil is through Fourier Transform Infrared (FTIR) spectroscopy. However, this method is laboratory-based, which means oil sampling at site is necessary and the oil samples need to be transported to the laboratory. The necessity for oil sampling, coupled with the high cost of FTIR equipment have led to high maintenance cost. Therefore, this work investigated the possibility of using single wavelength or waveband optical detection for the determination of weight percentage of inhibitor in transformer oil using ultraviolet-visible-near infrared (UV-VIS-NIR) spectroscopy. Result of the work shows that the samples with inhibitor produced an absorbance peak at 1403nm. The peak absorbance of the spectral response is proportional to the weight percentage of inhibitor content that was measured using the conventional method, which is IEC 60666. An equation was derived to model the peak absorbance and weight percent of inhibitor content (%IC) of the oil and it was verified with additional oil sample with a known weight percent of Inhibitor content.