Coarse Wavelength Division Multiplexing Systems Research Articles

Monolithically integrated four-channel laser array based on high-order surface gratings for O-band CWDM systems

An O-band monolithically integrated four-channel laser array based on high-order surface gratings is demonstrated. The fabricated laser array exhibits a wide bandwidth of up to 60 nm, with threshold currents ranging from 17 to 25 mA and slope efficiencies between 0.22 and 0.29 W/A. At an injection current of 200 mA, all side-mode suppression ratios (SMSRs) are above 40 dB, and the output power exceeds 36 mW. The high-order surface gratings are fabricated by standard lithography, which avoids high-precision lithography and a complex regrowth technique. A potentially cost-effective light source for coarse wavelength division multiplexing (CWDM) systems is provided.

Anti-reflection grating-assisted contra-directional coupler with large corrugation width

The grating-assisted contra-directional coupler (contra-DC) is one of the commonly used add-drop filters serving for coarse wavelength-division-multiplexing (CWDM) systems due to its flat-top and wide-band response. However, the free-spectral-range (FSR) of contra-DC is limited by the back reflection to the input port caused by the intra-waveguide coupling. In this paper we propose an anti-reflection grating-assisted contra-DC by simply increasing the sidewall corrugation width. The intra-waveguide coupling coefficient can be decreased to 0 when the corrugation width is increased to a certain value. The simulation result shows that the transmission at drop port is −0.42 dB, while the back reflection to the input port is only −22.0 dB. The 4-channel cascaded contra-DCs with wavelength range of ∼60 nm are also simulated, all the channels are not affected by the intra-waveguide coupling. We believe the proposed contra-DC with large corrugation width can be applied to the CWDM system requiring a broad spectrum range.

Design and Analysis of an O+E-Band Hybrid Optical Amplifier for CWDM Systems.

Broadband amplification in the O+E-band is very desirable nowadays as a way of coping with increasing bandwidth demands. The main issue with doped fiber amplifiers working in this band such as the bismuth-doped fiber amplifier is that they are costly and not widely available. Therefore, a wideband and flat-gain hybrid optical amplifier (HOA) covering the O+E-band based on a parallel combination of a praseodymium-doped fiber amplifier (PDFA) and a semiconductor optical amplifier (SOA) is proposed and demonstrated through numerical simulations. The praseodymium-doped fiber (PDF) core is pumped using a laser diode with a power of 500 mW that is centered at a wavelength of 1030 nm. The SOA is driven by an injection current of 60 mA. The performance of the HOA is analyzed by the optimization of various parameters such as the PDF length, Pr3+ concentration, pump wavelength, and injection current. A flat average gain of 24 dB with a flatness of 1 dB and an output power of 9.6 dBm is observed over a wavelength range of 1270-1450 nm. The noise figure (NF) varies from a minimum of 4 dB to a maximum of 5.9 dB for a signal power of 0 dBm. A gain reduction of around 4 dB is observed for an O-band signal at a wavelength of 1290 nm by considering the up-conversion effect. The transmission performance of the designed HOA as a pre-amplifier is evaluated based on the bit-error rate (BER) analysis for a coarse wavelength-division multiplexing (CWDM) system of eight on-off keying (OOK)-modulated channels, each having a data rate of 10 Gbps. An error-free transmission over 60 km of standard single-mode fiber (SMF) is achieved for different data rates of 5 Gbps, 7.5 Gbps, and 10 Gbps.

Investigation on Ultra-Compact 2DPC Coarse Wavelength Division Demultiplexer

A two dimensional Photonic Crystal (2DPC) based eight-channel wavelength division de-multiplexer is proposed and designed for Coarse Wavelength Division Multiplexing (CWDM) applications. The circular ring resonator, channel selector, circulator rod, L bend waveguide and linear bus waveguide are essential parts of the proposed system. The system’s functional parameters such as Transmission efficiency, resonant wavelength, spectral width, channel spacing, Quality factor and crosstalk investigated this paper. The eight different wavelengths of channels are filtered out by altering the size of channel selector rod, setting the radius of the circle shaped cavity and relative refractive index of circulator rod. Initially the Photonic Band gap (PBG) is manipulated by applying Plane Wave Expansion (PWE) method of the 2DPC structure. The functional parameters are analysed by Finite Difference Time Domain (FDTD) method in periodic and non-periodic structure of the proposed system to arrive normalized transmission spectrum. The resonant wavelengths of designed eight paths of the device are varying from 1420nm to 1460nm with average spectral width and channel spacing are 5.8nm, 5.6nm respectively. The footprint of the device is 286.84μm2. Hence, this small device can be implemented for CWDM systems in Photonic Integrated Circuits (PIC)

CWDM communication system based inline erbium-doped fiber amplifiers with the linear geometrical polarization model

Abstract Optical fiber coarse wavelength division multiplexing (CWDM) with erbium-doped fiber inline-amplifiers for the linear polarization geometrical model is studied in this paper for fiber system optimization by using the Optisystem simulation software. Signal gain (SG), noise figure (NF), and signal/noise are measured against CWDM optical fiber variations. The erbium-doped fiber amplifier (EDFA) is based on the Giles model which solves the steady-state rate equations for SG and signal absorption parameters with the cross-section area of the amplifier itself. The signal is optimized at EDFA length of 6 m, 10 Gb/s data rates (DRs) transmission and 10 km CWDM fiber optic length (FOL). Max. Q factor is degraded and min. BER is upgraded with both CWDM optical FLs and higher DRs transmission increase.

Mechanically-Induced Long-Period Fiber Gratings Using Laminated Plates.

This work presents a formation method of mechanically-induced long-period fiber gratings using laminated plates. The mechanically-induced long-period fiber grating is temporarily inscribed by compressing the optical fiber between a flat plate and the proposed laminated plate. In turn, the new laminated plate consists of a parallel assembling of single-edged utility blades. We present the experimental characterization of mechanically-induced long-period fiber gratings while employing three laminated plates with a period of 480 ± 20 µm and low duty cycles. These mechanically-induced long-period fiber gratings display a leading rejection band (>15 dB) with a couple of shallow rejection bands (<2 dB) in the range of 1100–1700 nm. This spectral behavior is due to the new mechanical fabrication process that is based on laminated plates that we have proposed, which consists of piling multiple blades with trapezoidal edges that are polished with different levels to obtain different duty-cycles. With the proposed method, we can obtain values of duty-cycles around 10%, much lower than those obtained using traditional methods. Additionally, with this new method, the required mechanical pressure to form the grating is remarkably reduced, which minimizes the probability of the optical fiber failure in the mechanically-induced long-period fiber gratings (MI-LPFGs). Moreover, the proposed mechanically-induced long-period fiber gratings with a single rejection band open the feasibility to implement coarse wavelength division multiplexing systems that are based on long-period fiber gratings.

Design of 4-channel AWG Multiplexer/demultiplexer for CWDM system

Arrayed Waveguide Grating (AWG) for Coarse wavelength division multiplexing (CWDM) system is a key component of above 100Gb/s high-speed optical transmission module in telecommunication and interconnects for data center. Based on the theory of light transmission, the relationships between structure parameters and optical performance of AWG chip are analyzed. Four-channel AWG MUX/DEMUX chips for CWDM system at O-band are designed and simulated according to the relationships. The simulation results show that the insertion loss of the MUX is below 0.8 dB with non-uniformity of 0.07 dB. The bandwidths at 1 dB and 3 dB are more than 10 nm and 17 nm, respectively. For DEMUX, multi-mode interference (MMI) couplers are introduced at the start of output waveguides to produce flat-top spectral response with 1 dB bandwidth of 12 nm. The lowest insertion loss and adjacent crosstalk are 2.78 dB and below −20 dB, respectively.

Compact photonic crystal multichannel drop filter for CWDM systems

A novel photonic crystal channel drop filter (PCCDF) is proposed to drop four coarse wavelength division multiplexing (CWDM) channels at 1490 nm, 1510 nm, 1530 nm and 1550 nm. A special coupled dual-loop design was used for multichannel forward/backward dropping for the first time. Due to the reduced number of the dropping resonators with this design, the proposed multichannel PCCDF has a very compact size (338 μ m2). High transmission efficiencies at the four ITU wavelengths (87.87%, 93.99%, 85.40% and 84.24%) can be obtained simultaneously. Furthermore, the same dimension parameters (lattice constant and rod radius) of the dual-loop resonators are helpful for easy fabrication. The proposed device could be used in future photonic integrated circuit-based CWDM communication systems.

Tunable broadband filter based on lithium-niobate asymmetric Mach–Zehnder interferometer for coarse wavelength-division multiplexing applications

Channel-select filtering technology is a very promising solution for realizing reconfigurable demultiplexing components required in a flexible coarse wavelength-division multiplexing system. Here, we propose and demonstrate an electro-optic tunable broadband filter based on an asymmetric Mach–Zehnder interferometer formed on lithium niobate for this application. The counter-tapered directional coupler is introduced to replace the conventional one formed with uniform waveguides so that a splitting ratio of 50%:50% is much easier to be realized over a wide wavelength range and, hence, increase bandwidth of the filter. In addition, to reduce the bending loss in the long-wavelength region, the waveguide width and the height of the involved S-bend waveguides are optimized experimentally. Our fabricated filter, which has a total length of ∼30 mm, exhibits an extinction ratio of ∼15 dB and a wide tuning range of >40 nm with an electrical wavelength tuning sensitivity of ∼4.5 nm / V.

Comparative Analysis of Erbium Doped Fiber Amplifier (EDFA) and Raman Optical Amplifier (ROA) in Nonlinear-CWDM System

The massive demands for high-rate application drove the telecommunication service to use large bandwidth capacity. The Coarse Wavelength Division Multiplexing (CWDM), a common use in Metro-WDM, can be a solution to provide large bandwidth in optical communications. In a communications system, there are attenuation and nonlinear effect decreasing the system performance. In order to overcome the limitation imposed by electrical regeneration to maintain system performance, a means of optical amplification was sought. In this paper presents the comparison of two competing technologies emerged: Erbium Doped Fiber Amplifier (EDFA) and Raman Optical Amplifier (ROA) to overcome the attenuation in the nonlinear system. We designed the CWDM system using 8 channels with 20 nm channel spacing and 60 km length. The result was conducted by varying the CW Laser power using -8, -6, -4, -2, 0, 2, 4, and 6 dBm. Based on the result of the research, raman amplification can maintain the BER and the Q-factor of the CWDM system better than EDFA. In addition, the received power in raman amplification larger than that received in EDFA. In conclusion,a CWDM system using ROA amplifier has better performance for the system than using EDFA amplifier.

Two-dimensional photonic crystal ring resonator-based channel drop filter for CWDM application

In this paper, a channel drop filter based on two-dimensional photonic crystal ring resonator (PCRR) is proposed. The proposed structure consists of bus waveguide, dropping waveguide and a ring resonator. We have focused on improving the dropping efficiency and quality factor of the structure by applying different optimization techniques. Optimized channel drop filter using PCRR is designed, and it is extended to drop three different channels by changing the inner rods radius in each ring resonator that act as a demultiplexer. As designed structure drops three different channels such as 1524, 1544 and 1565 nm, the band gap for the structure is calculated and observed by plane-wave expansion method. The normalized transmission spectra and resonance wavelengths for different radius are obtained using two-dimensional finite-difference time-domain method. The proposed PCRR-based demultiplexer has the channel spacing of about 20 nm which fulfils the requirements of coarse wavelength-division multiplexing systems. The size of the demultiplexer is small; hence, it can be utilized for photonic integrated circuits.

Multi‐channel photonic crystal drop filter with cascaded stubs

An eight-channel drop filter based on two-dimensional photonic crystal is proposed. A five-cascaded stub is used to receive 100% reflection feedback. The geometric parameters on the transmission spectra of the bus waveguide output port are investigated. The Fabry–Perot fibre grating theory is used to explain the influences. On the basis of the 100% reflector, a channel drop filter is designed according to the wavelength spacing in the coarse wavelength division multiplexing system. Numerical simulations demonstrate that each channel exhibits over 93% transfer efficiency.

Performance study on the effect of filter curve in CWDM System for the access network

This paper presents the study on the effect of filter variation on the coarse wavelength division multiplexing (CWDM) system. The filter curve will affect the performance of the CWDM system due to changes of received power lever and isolation of the signal. The significant impact on the received power level and isolation can be found when the required signal is isolated from unwanted signal by the steep curve of filter. As a result, BER of 1.0x 10-12 was obtained corresponding to receive power level of -24.27 dBm with isolation of 23.22 dB. When the wavelength spacing is reduced to 1nm, the isolation is only 11.30 dB and BER increased to 5.49x10-7 with a received power of -15.39 dBm.

Implementation of CWDM technique in access network

The Coarse Wavelength Division Multiplexing (CWDM) system presented in this paper has several distinct characteristics from the standard CWDM system. One of them is the channel spacing whereby it uses smaller channel spacing compared to the standard system. The other is that, the system uses a broad spectrum laser source. The source is filtered by using ‘Bragg Grating’ before being transmitted. The filtration gives higher OSNR compared to standard CWDM setup. It was found that the system can transmit through each channel up to 2.5 Gbps with the probability of error of 10-12 . The maximum distance that can be supported by this system is about 27 km, for the data rate of 155 Mbps.

Link Power Level Improvements in an Amplified 8-Channel CWDM System with Hybrid EDFA-SOA Pre-Amplifier

The link power improvement in a coarse wavelength division multiplexing (CWDM) system which is transmitted using a hybrid erbium-doped fiber amplifier (EDFA) and semiconductor optical amplifier (SOA) scheme as a pre-amplifier, is discussed. The network is designed for amplifying 8 CWDM channels ranging from 1471 nm to 1611 nm. The hybrid amplifiers’ gain measurement is obtained from experimental work with gain peak at 22 dB which is observed at 1531 nm. The amplifiers also caused power increment of 5.06 dB in the transmission link before the signal is split individually at the receiving end. Based on the higher gain peaks and power spectrum at 1531 nm and 1551 nm wavelengths, the proposed amplified link would be useful for the transmission of video applications.

Gain performance of cascaded and hybrid semiconductor optical amplifier in CWDM system

The incorporation of cascaded and hybrid-type optical amplifiers into the optical fiber link is advantageous for the purpose of achieving wide gain bandwidth of multi-wavelength coarse wavelength division multiplexing (CWDM) systems. Different amplifiers whose operating gain region differ from each other are connected in cascade, thus providing better gain performance as the overall gain is combined and flattened over a larger spectrum. In this paper, the effect of the crossover of the uniform gain of the semiconductor optical amplifier (SOA) and the nonuniform gain of erbium-doped fiber amplifier (EDFA) is analyzed using an in-line cascaded SOA-SOA and an in-line hybrid SOA-EDFA configuration in the amplification of an 8-channels CWDM system obtained from the simulation using Optisystem software. It was observed that the cascaded SOA-SOA produces higher gain of 25 dB and wider gain bandwidth of 60 nm compared to the hybrid SOA-EDFA configuration with maximum gain of only 24 dB and 40 nm bandwidth. In addition, better bit-error-rate (BER) performance which is within the typical values in optical fiber communication is also achieved from the cascaded SOA topology. Wider gain bandwidth obtained with the SOA-SOA configuration would permit the transmission of video application at 1551 nm in the proposed Ethernet CWDM system transmitted at 100 Mb/s data rates.

Photorefractive long-period waveguide grating filter in lithium niobate strip waveguide

To fabricate a long-period waveguide grating (LPWG) filter in a simple, reliable and low-cost way, a novel LPWG scheme based on photorefractive grating is designed and theoretically analyzed in a Ti-diffused strip waveguide embedded in a Ti-diffused planar \(\hbox {LiNbO}_{3}\) waveguide. By means of effective index method and coupled-mode theory, the processing conditions of the planar and the strip waveguide have been calculated. The minimum 100 % filtering length \(L=1.40\) cm and the coupling coefficient \(\kappa =112.23\,\hbox {m}^{-1}\) are obtained. The photorefractive LPWG filter can be used in coarse wavelength division multiplexing system.

Flat gain, wide bandwidth of in-line semiconductor optical amplifier in CWDM Systems

Semiconductor optical amplifier (SOA) is one of the commonly used amplifiers in optical networks. This paper reviews the SOA implementation in coarse wavelength division multiplexing (CWDM) systems, which includes the explanation of the fundamental concepts such as the configuration, principle of operation as amplifiers, and the performance in different CWDM topologies. Simulation using OptiSystem software was carried out to determine the gain saturation at high input power and longer wavelengths. It shows that SOA implementation in CWDM networks is capable of providing flat gain for 40 nm wavelength span.

Integration of both dense wavelength-division multiplexing and coarse wavelength-division multiplexing demultiplexer on one photonic crystal chip

An integrated model of photonic crystal (PC) demultiplexer that can be used to combine dense wavelength-division multiplexing (DWDM) and coarse wavelength-division multiplexing (CWDM) systems is first proposed. By applying the PC demultiplexer, dense channel spacing 0.8 nm and coarse channel spacing 20 nm are obtained at the same time. The transmission can be improved to nearly 90%, and the crosstalk can be decreased to less than −18 dB by enlarging the width of the bus waveguide. The total size of the device is 21×42 μm 2 . Four channels on one side of the demultiplexer can achieve DWDM in the wavelength range between 1575 and 1578 nm, and the other four channels on the other side can achieve CWDM in the wavelength range between 1490 and 1565 nm, respectively. The demonstrated demultiplexer can be applied in the future CWDM and DWDM system, and the architecture costs can be significantly reduced.

Tunable broadband light coupler based on two parallel all-fiber acousto-optic tunable filters

Based on the evanescent-field coupling between the cladding modes of two adjacent and parallel all-fiber acousto-optic tunable filters, tunable broadband light coupling with relatively uniform insertion loss of trapping spectrum was achieved. In the experiments, a wide spectral tuning range from 1490 nm to 1610 nm, covering the whole C- and L-band and parts of S-bands, was demonstrated with a wavelength tunability slope of -0.72 nm/kHz. The insertion loss of the trapping spectrum was uniform (around -5.0 dB, which can be improved with a longer evanescent-field coupling length) within the whole tuning spectral range. Such a light coupling structure would be useful in tunable broadband light coupler and broadband optical fiber add/drop multiplexer for applications in coarse wavelength division multiplexing systems.