Shien-Kuei Liaw

Passive gain-equalized wide-band erbium-doped fiber amplifier using samarium-doped fiber

A passive gain-equalization technique of erbium-doped fiber amplifier (EDFA) using a samarium-doped fiber to obtain wide-band flattened gain operation is reported. In the wavelength range from 1529-1559-nm, small inter-channel gain variations can be achieved. This simple technique is suitable for multiwavelength wide-band in-line-amplifier cascaded transmission applications.

Dynamic power-equalized EDFA module based on strain tunable fiber Bragg gratings

An adaptive power-equalized erbium-doped fiber amplifier (EDFA) module is proposed and experimentally demonstrated by using strain tunable fiber Bragg gratings (FBGs). In a demonstration for a five-channel wavelength-division-multiplexed (WDM) system, the EDFA module can effectively reduce the power variation from 11 dB to 0.3 dB. Measured power penalty for 2.5-Gb/s data is less than 0.5 and 1.1 dB for 5 and 17 dB of signal attenuation by tunable FBGs, respectively. The power-equalized EDFA module can find wide applications in WDM lightwave transmission systems.An adaptive power-equalized erbium-doped fiber amplifier (EDFA) module is proposed and experimentally demonstrated by using strain tunable fiber Bragg gratings (FBGs). In a demonstration for a five-channel wavelength-division-multiplexed (WDM) system, the EDFA module can effectively reduce the power variation from 11 dB to 0.3 dB. Measured power penalty for 2.5-Gb/s data is less than 0.5 and 1.1 dB for 5 and 17 dB of signal attenuation by tunable FBGs, respectively. The power-equalized EDFA module can find wide applications in WDM lightwave transmission systems.

Hybrid wavelength-division-multiplexing systems for high-capacity digital and analog video trunking applications

A five-channel hybrid wavelength-division-multiplexing (WDM) system with one AM-VSB channel and four 2.5 Gb/s channels was demonstrated for video trunking and distribution applications. Two erbium doped fiber amplifiers (EDFAs) with saturated output power of +13 dBm were used for a standard single mode fiber span of 100 km. Error-free transmission for the digital channels and a carrier-to-noise ratio (CNR) higher than 50 dB for the AM-VSB channel could be achieved simultaneously.

Tunable Fiber Laser Using a Broad-Band Fiber Mirror and a Tunable FBG as Laser-Cavity Ends

By using a broad-band fiber mirror (BFM) and a tunable fiber-Bragg-grating at either end of laser cavity, a wavelength tunable erbium-doped fiber laser is demonstrated. In a forward pump scheme using 100 mW pump power at 1480 nm, stable lasing output power of 21.14-mW measured at 1544.8 nm is obtained with a threshold pump power of 4.7 mW. A side-mode suppression ratio as high as 57.9 dB, wavelength tuning range up to 30 nm with step resolution of 0.2 nm and power variation less than plusmn1.0 dB are achieved. For a backward pump scheme, the BFM acts as a broad-band reflector both for the lasing signal and pump source. The high performance, cost-effective BFM based tunable fiber laser may play an important role in fiber optics communication and fiber sensing applications.

Design and analysis of an angular-segmented full-mobility visible light communications receiver

This paper presents the concept, design and analysis for a visible light communications receiver utilising the angular and spatial diversity in order to achieve full mobility and protection from signal blocking in a typical home/office environment. The proposed receiver uses seven sub-receivers, each dedicated to an independent viewing angle and direction. Employing selection combining, the receiver with the strongest signal is used for the communications channel. Full performance evaluation and numerical analysis of the proposed system have been performed in MATLAB and compared to that of a single receiver. The received power, impulse response, corresponding signal-to-noise ratios and root-mean-square delay spread are also investigated. Copyright

Pump efficiency improvement of a C-band tunable fiber laser using optical circulator and tunable fiber gratings

We propose and demonstrate a tunable fiber laser based on an optical circulator (OC) and two tunable fiber Bragg gratings (TFBGs). The OC acts as a pump power router to improve the pumping efficiency, and a 4% increase in overall conversion efficiency has been observed. The combined tuning spectra range of two TFBGs could cover the entire C-band spectrum from 1530 to 1560 nm. Stable laser output power above 10 dBm is obtained using 1.9 m of erbium-doped fiber and TFBGs with 50% reflectivity. With power equalization by using variable optical attenuators, the power variation is less than 0.1 dB in the whole C band with narrow linewidth of 0.05 nm. A signal-to-noise ratio of 60 dB and a continuous tuning resolution of 0.5 nm have been achieved. The TFBG-based tunable fiber laser can be a promising light source for WDM transmission and fiber sensor applications.

Impact Response of a Wind Turbine Blade Measured by Distributed FBG Sensors

An impact monitoring system using an array of fibre Bragg grating (FBG) sensors has been established on a wind turbine blade. The effect of sensor layout on detection capability has been investigated. The possibility to identify the location of an impact is also discussed. This preliminary work may shed some light on how to establish an optimal monitoring system with a minimum number of sensors while achieving an acceptable sensitivity and coverage. With such a system, the corresponding strain history and occurrence of local damage can be monitored, thus helping to narrow down the scope for detailed examination during an overhaul and enabling the integrity of a wind turbine blade to be more reliably assessed.

Multichannel bidirectional transmission using a WDM MUX/DMUX pair and unidirectional in-line amplifiers

We propose a repeated bidirectional WDM transmission system using cascaded WDM MUX/DMUX pairs as narrow-bandpass filters and reflection attenuators. Fiber span is increased by inserting unidirectional EDFAs between WDM MUX/DMUX pair as in-line amplifiers. A three-channel hybrid system with one 10-Gb/s and two 2.5-Gb/s channels is also demonstrated In the 1550-nm region for transmission over 150 km of dispersion-shifted fiber. Negligible power penalty due to back reflection was observed.We propose a repeated bidirectional WDM transmission system using cascaded WDM MUX/DMUX pairs as narrow-bandpass filters and reflection attenuators. Fiber span is increased by inserting unidirectional EDFAs between WDM MUX/DMUX pair as in-line amplifiers. A three-channel hybrid system with one 10-Gb/s and two 2.5-Gb/s channels is also demonstrated In the 1550-nm region for transmission over 150 km of dispersion-shifted fiber. Negligible power penalty due to back reflection was observed.

Effects of aperture averaging and beam width on a partially coherent Gaussian beam over free-space optical links with turbulence and pointing errors

Joint effects of aperture averaging and beam width on the performance of free-space optical communication links, under the impairments of atmospheric loss, turbulence, and pointing errors (PEs), are investigated from an information theory perspective. The propagation of a spatially partially coherent Gaussian-beam wave through a random turbulent medium is characterized, taking into account the diverging and focusing properties of the optical beam as well as the scintillation and beam wander effects. Results show that a noticeable improvement in the average channel capacity can be achieved with an enlarged receiver aperture in the moderate-to-strong turbulence regime, even without knowledge of the channel state information. In particular, it is observed that the optimum beam width can be reduced to improve the channel capacity, albeit the presence of scintillation and PEs, given that either one or both of these adverse effects are least dominant. We show that, under strong turbulence conditions, the beam width increases linearly with the Rytov variance for a relatively smaller PE loss but changes exponentially with steeper increments for higher PE losses. Our findings conclude that the optimal beam width is dependent on the combined effects of turbulence and PEs, and this parameter should be adjusted according to the varying atmospheric channel conditions. Therefore, we demonstrate that the maximum channel capacity is best achieved through the introduction of a larger receiver aperture and a beam-width optimization technique.

Demultiplexer crosstalk rejection requirements for hybrid WDM system with analog and digital channels

Hybrid WDM systems with both analog and digital channels are a natural choice for the video transmission applications. The effects of crosstalk in a hybrid WDM system are measured and analyzed in this letter. The required crosstalk rejection ratio is also provided with the assumption that the differences in received optical power among various channels are the same as their differences in receiver sensitivities.