Keang-Po Ho

Fiber-fault identification for branched access networks using a wavelength-sweeping monitoring source

We propose and experimentally demonstrate a new fiber-fault identification scheme for optically amplified branched networks. The scheme makes use of fiber Bragg gratings and an internally generated light source from erbium-doped fiber amplifiers through an optical feedback loop, and no additional dedicated monitoring source is required. The monitoring technique invokes both frequency and time domain by sweeping the wavelength of the monitoring source. By combining with a conventional optical time-domain reflectometer technique, exact location in fiber cut in branched network can be identified readily.

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.

Exact analysis of homodyne crosstalk induced penalty in WDM networks

We present an exact analytical probability density function and a closed-form bit-error-rate (BER) formula for wavelength-division multiplexing (WDM) networks with homodyne crosstalk from a single dominant channel. The derived crosstalk penalties are in excellent agreement with that obtained from experiments.

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.

Performance analysis of optical transmission system with polarization-mode dispersion and forward error correction

This letter shows that sufficient interleaving is essential for forward error correction to provide average bit-error-rate (BER) improvement in a high polarization-mode-dispersion (PMD) system. While error correction improves the outrage probability, in term of average BER, error correction cannot extend the tolerable PMD level and provides no performance improvement when PMD is larger than 0.2-bit interval.

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.

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.

Power equalized wavelength-selective fiber lasers using fiber Bragg gratings

Abstract A fiber Bragg grating (FBG) based multi-wavelength ring laser is experimentally investigated in this paper. The lasing wavelengths can be dynamically selected by using a 1× N optical switch. Micro-bender between FBGs is used as variable attenuator to equalize the output power for each lasing wavelength. By using passive multi-ring cavities (MRC) method, single- or dual-wavelength laser of equal output power is demonstrated for a signal-to-noise ratio (SNR) of 63 dB and a narrow linewidth of 3 kHz.

Performance of an eight-wavelength bidirectional WDM add/drop multiplexer with 80-Gbit/s capacity

Reconfigurable wavelength-division multiplexed (WDM) networks can be employed to provide cost-effective, flexible capacity growth. Each WDM channel is transparent to signal format, bit-rate, and protocol. One important element in optical networks is the WDM add/drop multiplexer (WADM), especially in a ring topology. To date, most WADMs are unidirectional in which the optical signal must add/drop in the same direction. The purpose of this work is to demonstrate a bidirectional WADM. Because the signal can be added/dropped in both directions, only a single fiber is required for bidirectional transmission, as in the case of single fiber for a bidirectional ring. For a unidirectional ring, a signal must pass through all fiber nodes to reach the upstream node. A bidirectional ring can increase the throughput because the signal can pass through a smaller number of hops to reach some of the fiber nodes.

Efficient photonic mixer with frequency doubling

A photonic mixer can upconvert/downconvert the signal in a fiber link to replace a conventional electronic mixer. We demonstrate a photonic mixer with frequency doubling that can be driven by half the intermediate frequency with low-cost microwave and optical components. The photonic mixer has a conversion loss of about 3.2 dB, which is the lowest conversion loss ever reported.