Multi-channel WDM Research Articles

Analysis of proposed hybrid amplifier model for single to multi-channel WDM optical system at 10 Gbp/s with 100 GHz of channel spacing

In this paper, we have investigated a possible single to multi-channel upgrade employing different amplification (Booster, EDFA amplifier and Raman amplifier). A 10 GB/s single channel signal is launched onto a fiber (D = 3 ps/nm/km) link of 140 km. The system works at the sensitivity limit. To upgrade the system, the power-budget at the receiver must increase employing an optical preamplifier. Two alternatives are explored: an EDFA or a RA. Two 10-channels WDM systems are shown employing respectively an EDFA and a Raman amplifier. EDFA gain and Rama amplifier counter propagating pump are determined to obtain the same optical gain for both the system configurations. A multiple run has been carried on to search the optimum RA configuration.

Photonic Integrated Multichannel WDM Modulators for Data Read-Out Units

This study presents the recently developed monolithic photonic-integrated circuits that provide efficient amplitude modulation for wavelength division multiplexed optical channels. The circuits were designed for application as a read-out unit in a high-energy physics experiment, and are sufficiently general to be applied in various types of high-speed photonic transmitters. They were constructed using basic building blocks provided in an indium phosphide-based generic integration technology process and fabricated in a multi-project wafer run. Two variants of the circuits, utilizing modulators in Mach-Zehnder and Michelson interferometer configuration, are discussed. A modulation bandwidth of 18.6 GHz was measured and error-free transmission of a 10-Gb/s signal through 85 km of optical fiber was achieved.

Coupled atomic coherences induced by a standing wave

Atomic coherence effects with a strong standing-wave coupling field on a four-level system of hot Rb atoms are investigated. Amplitude modulation and phase modulation of the strong standing-wave field are coherently coupled in linear and nonlinear atomic polarizations in various multi-wave mixing processes. Such coupled atomic coherence effect leads to one-photon triple-bandpass filters in an electromagnetically induced transparency structure and two-photon bandgaps at two different wavelengths under two-photon resonance in the hot four-level Rb atoms. Such system can be useful for dispersion compensation in multi-channel WDM systems, all-optical switching and optical filters at multiple wavelengths.

Theoretical Modeling and Simulation of Higher Order FWM Crosstalks in Multichannel WDM Optical Communication Systems

In this paper, we derive a theoretical model for the higher order FWM power in WDM networks with NZDSF fibers for the first time. We have investigated the higher order FWM power theoretically and by numerical simulations. Dividing the fiber into finite number of elements and applying the boundary conditions, allow us derive an expression for second order power penalty. At the end of each element we derive the first order FWM power for all wavelengths and use these values to calculate the second order FWM power in the next element. Consequently, for each channel we can compute the total second order FWM power penalty at the end of the fiber.

Improved multi-channel multi-carrier generation using gain-independent multi-channel frequency shifting recirculating loop

We propose and experimentally demonstrate an improved scheme to generate optical frequency-locked multi-channel multi-carriers (MCMC), using a gain-independent multi-channel recirculating frequency shifter (MC-RFS) loop based on single sideband (SSB) modulation. We re-build the RFS structure with better performance. By using MC-RFS loop, we can generate N-channel subcarriers each round trip without interference. These subcarriers of each channel are stable and frequency-locked, which can be used for multi-channel WDM source. The dual-channel RFS loop is carried out for demonstration in our experiment with dual-carrier source. Using this scheme, we successfully generate 62 frequency-locked subcarriers with 25-GHz frequency spacing in 2 channels and each channel has 31 tones.

Multichannel optical frequency-locked multicarrier source generation based on multichannel recirculation frequency shifter loop

We propose and experimentally demonstrate a novel scheme to generate multichannel optical frequency-locked multicarrier by using multichannel recirculating frequency shifter (MC-RFS) loop. By using MC-RFS loop, we can generate N channels subcarriers each round trip without interference. These subcarriers of each channel are stable and frequency-locked, which can be used for a multichannel WDM source. Finally, the double channels RFS loop is carried out for demonstration in our experiment with double-carriers source. Using this scheme, we successfully generate 54 frequency-locked subcarriers with 25 GHz frequency spacing in two channels and each channel has 27 tones.

WDM-Coherent OCDMA over one single device based on short chip Super structured fiber Bragg gratings

We theoretically propose and demonstrate experimentally a Coherent Direct Sequence OCDMA en/decoder for multi-channel WDM operation based on a single device. It presents a broadband spectral envelope and a periodic spectral pattern that can be employed for en/decoding multiple sub-bands simultaneously. Multi-channel operation is verified experimentally by means of Multi-Band Super Structured Fiber Bragg Gratings with binary phase encoded chips fabricated with 1mm inter-chip separation that provides 4x100 GHz ITU sub-band separation at 1.25 Gbps. The WDM-OCDMA system verification was carried out employing simultaneous encoding of four adjacent sub-bands and two different OCDMA codes.

Analysis of polarization-independent tunable optical comb filter by cascading MZI and phase modulating Sagnac loop

A novel scheme of tunable optical comb filter constructed by cascading a polarization-swapping MZI and a phase modulating Sagnac loop is proposed. The key features of this comb filter design are its polarization-independence and high speed in wavelength tuning. The wavelength tunability can be readily achieved by incorporating an electro-optic phase modulator into the Sagnac loop. In addition, the filter can be made amplitude adjustable as well. The filter will be desirable for multi-wavelength fiber lasers, multi-channel optical signal processing and optical WDM systems.

Multi-channel WDM RZ-to-NRZ format conversion at 50 Gbit/s based on single silicon microring resonator

We comprehensively analyze multiple WDM channels RZ-to-NRZ format conversion using a single microring resonator. The scheme relies on simultaneous suppression of the first order harmonic components in the spectra of all the RZ channels. An optimized silicon microring resonator with free spectral range of 100 GHz and Q value of 7900 is designed and fabricated for this purpose. Multi-channel RZ-to-NRZ format conversion is demonstrated experimentally at 50 Gbit/s for WDM channels with 200 GHz channel spacing using the fabricated device. Bit error rate (BER) measurements show very good conversion performances for the scheme.

Simultaneous demodulation and demultiplexing of multi-rate WDM DPSK signals using a programmable wavelength-selective switch

We show demodulation and demultiplexing of multi-channel WDM differential phase-shift-keying (DPSK) signals operating simultaneously at 10 Gb/s and 40 Gb/s using a 1x4 wavelength selective switch. We achieve error-free performance for four channels equally spaced by 100 GHz propagated over an 85 km dispersion-compensated link. We study the advantages and limitations of this new DPSK demodulator compared with the conventional delay-line interferometer.

Analysis and minimization of cross phase modulation in semiconductor optical amplifiers for multichannel WDM optical communication systems

A theoretical model for crosstalk in multichannel wavelength division multiplexing communication systems due to cross phase saturation in semiconductor optical amplifier structure is developed. This theoretical model is used to analyze the impact of the cross phase noise on the performance of semiconductor optical amplifiers in saturation region for WDM communication system by using differential phase shift modulation format. It is shown that by increasing the carrier life time, width and thickness while reducing the confinement factor, differential gain and bias current in the SOA structure mitigates the cross talk due to cross phase saturation. The impact of penalty and cross phase noise imposed on multichannel WDM links have been investigated for different parameters of the SOA with the variation in transmission distance. With the slight increase in differential gain of 200.2 × 10 −18 cm 2 and confinement factor 0.41, the maximum transmission distance observed is 5220 km with good quality and nil power penalty for 10 × 40 Gb/s soliton RZ-DPSK WDM signals for the first time.

Efficient numerical simulation of multichannel WDM transmission systems limited by XPM

For numerical simulation of wavelength-division-multiplexed transmission lines including group-velocity dispersion, self-phase modulation, and cross-phase modulation, the computation time is reduced by almost one order of magnitude. This is done by taking into account the channel walkoff within one split step.

FBG-based multi-channel low dispersion WDM filters

Multi-channel FBGs for use as low dispersion WDM filters are reported. The filters are realised in a single section of optical fibre using superposition techniques and are designed for use in high-speed networks (10–40 Gbit/s) where they may be employed in OADM applications.

Emerging Trends in Fiber Optic Networks

In the last few vears, optical technology has shown how huge information traffic can be transmitted over a long distance. This success has permitted the commercialization of several high capacity point-to-point systems in terms of 10 Gbit/s single channel and Nx 2.5 Gbit/s multichannel WDM systems. As far as the impact of optical technology in telecommunication networks is concerned, it is not yet clear how the high bit-rate signal can be used to optimize the telecommunication traffic. It is evident that the use of optical technology strongly depends on the type and requirements of an optical network. As an example, the operating conditions are much different for access and transport networks since the distance involved in the former is very short (0.1-10 km), whereas in the latter it is quite long (100-1000 km). In this paper, the status of optical transmission technology for telecommunication networks has been reviewed, showing problems and possible solutions for optical networks.

Model of temperature dependence for gain shape of erbium-doped fiber amplifier

The problem of modeling the temperature dependence of erbium-doped fiber amplifier (EDFAs) is important for multichannel optical WDM systems. A physical model is presented in this paper, which could be used to predict the gain change under temperature variations for such systems. Some of the input parameters for the model are the erbium energy sublevel density, excitation coefficients from lower sublevels to upper sublevels of erbium ions, and electron distribution over energy levels. It is difficult to measure these parameters. In order to use the model for gain shape calculations, some simplifications are demonstrated. These simplifications lead to two numerical models, which are shown to be consistent with experimental data with reasonable accuracy, and are based only on two spectral measurements for different temperatures. Both numerical models were tested for the signal band and the 980 nm pump band of a typical erbium-doped fiber.

Broadband lossless DCF using Raman amplificationpumped by multichannel WDM laser diodes

Broadband Raman amplification is demonstrated in a dispersion compensating fibre (DCF). A polarisation combined four channel wavelength division multiplexing 14 xxnm laser diode unit is used for the pumping light source. Losses in the DCF are completely compensated for by means of the Raman gain over 50 nm bandwidth within /spl plusmn/0.5 dB variation.

Er 3+ doped fibre pre-amplifier with subsidiaryEDF for application in WDM systems using two separate wavelength bands of 1.53and 1.55 µm

An economical optical amplifier circuit for a pre-amplifier of multi-channel WDM systems, using two separate wavelength bands of 1.53 and 1.55 µm, is proposed. The optical sensitivity of the receiver between the two bands is balanced by installing a subsidiary Er3+ doped fibre (EDF) in the 1.55 µm path. Curves of bit error rates at 10 Gbit/s for a six-channel receiver, two channels in the 1.53 µm band and four channels in the 1.55 µm band, form a bunch of similar lines without any error floor.

Eight-channel p-i-n/HBT monolithic receiver array at 2.5 Gb/s per channel for WDM applications

We report a monolithic chip incorporating an eight channel p-i-n/HBT photoreceiver array designed for multichannel WDM applications. The p-i-n photodetectors are edge illuminated and centered at a 250 μm pitch for mating with either ribbon fiber connectors or waveguide demultiplexers. Each channel operates at 2.5 Gb/s with an electrical crosstalk of -20 dB between adjacent channels. The average sensitivity of each receiver in the array was measured to be (-20/spl plusmn/1) dBm for a bit error rate of 10/sup -9/ at a wavelength of 1.5 μm.

Demonstration of an integrated multichannel gratingcavity laserfor WDM applications

A novel semiconductor laser source suitable for wavelength division multiplexing applications is reported. The device is formed by monolithically integrating an array of reflector and output amplifier waveguides with a low loss transmission grating and focusing mirrors in a very compact manner. A prototype device generates signals at two wavelengths simultaneously with a channel separation of 21 nm.

IM-DD long-distance multichannel WDM transmission experiments using Er-doped fiber amplifiers

We have demonstrated multichannel wavelength-division multiplexed optical signal transmission experiments employing Er-doped fiber amplifiers. Four-channel transmission of 459 km and 1500 km experiments and two-channel transmission of 4550 km experiment are described, and the transmission penalty is analyzed. We also discuss the effect of four-wave mixing. The difference of the transmission fiber clearly shows the difference of the optical spectrum due to four-wave mixing after long-distance transmission. The results show the possibility of long-distance multidestination optical communication systems with wavelength-division multiplexed signals combined with Er-doped fiber amplifiers. >