GHz Channel Spacing Research Articles

Simultaneous four-channel thermal adaptation of polarization insensitive silicon photonics WDM receiver.

We propose a novel approach to demonstrate simultaneous multi-wavelength locking during temperature changes in a silicon photonic polarization insensitive microring-based wavelength division multiplexing (WDM) receiver. The DC component of a single monitoring photodetector at the through port of the microring filter array is exploited as a feedback signal with no additional power consumption. This feedback signal is used in control circuitry to properly tune the microring filters using ohmic heating, thus creating a feedback loop for thermal adaptation. We describe the necessary information, specifically each microring filter's room temperature resonant wavelength and tunability, which can be used to calibrate and achieve proper wavelength configurability and locking. In addition, we describe a simple control algorithm based on an adaptive gradient method often used in machine learning, allowing the receiver to endlessly demultiplex at different temperatures. We successfully achieve thermal adaptation over a temperature range >37°C and demultiplex a 4 × 25 Gb/s on-off-keying signal of 150 GHz channel spacing, all while the polarization is scrambling.

Low-Cost WDM Fronthaul Enabled by Partitioned Asymmetric AWGR With Simultaneous Flexible Transceiver Assignment and Chirp Management

The explosion of mobile traffic requires fronthaul networks to provide huge data capacity. One straightforward solution is to use wavelength division multiplexing (WDM) technologies with a sufficient number of transceivers, but the massive deployment of fronthaul networks inevitably adds transceiver cost. In this paper, we propose and demonstrate a low-cost scheme using a asymmetric arrayed waveguide grating router (AWGR) and distributed feedback Bragg (DFB) directly modulated lasers (DMLs) for WDM fronthaul. First, the centralization feature of a cloud radio access network (C-RAN) puts the transceivers together by nature, offering the potential to reduce the number of deployed transceivers based on optical switching fabric. We design what we believe is a novel asymmetric N × M AWGR-based switching fabric featuring a partitioned cyclic routing property that (i) enables flexible contention-free transceiver assignment; (ii) relaxes the requirement of tuning range, which allows the use of DFB lasers with moderate tuning range; and (iii) changes the diversity of the tuning range from N types to N∕M types. We also investigate the scalability of the scheme and show its rearrangeable contention-free assignment feature. Second, to adopt cost-effective DMLs, the intrinsic Gaussian-shape AWGR's edge filtering is employed to manage the frequency chirp of DFB DMLs, avoiding additional optical or electrical processing modules. Experiments are conducted to demonstrate the robustness of this scheme. In particular, we report that the allowable optical signal's frequency deviation ranges from −7.5 GHz to 7 GHz, and the induced additional crosstalk to AWGR’s adjacent port due to a deliberate frequency offset is far below the system design limit. In addition, the scheme is compatible with common 50 GHz, 100 GHz, and 200 GHz channel spacing AWGRs

Kerr effect based spectrum sliced wavelength division multiplexing for free space optical communication

The super-continuum spectrum sliced WDM FSO system is evaluated at 2.5Gbps data rate up to link distance of 5Km. A Highly Nonlinear Fiber (HNLF) is channel for the generation of high power broad spectrum for spectrum slicing. A dense SS-WDM is investigated at 75GHz channel spacing among 4 channels to make system bandwidth efficient. Performance of SC-SS-WDM and WDM is scrutinized for FSO system under rain, fog, haze etc. Wavelength division free space optical system exhibits more error at 5Km as compared to spectrum sliced WDM FSO system. Also, the demonstrated architecture is accommodative, flexible and low cost system that can perform well under atmospheric turbulences.

Tunable V-Cavity Laser with Butt-Joint Passive Tuning Section for Fast Wavelength Switching

We report on the fast carrier-induced wavelength switching in V-cavity laser using butt-joint passive tuning section. Using the carrier plasma based tuning effect in combination with temperature induced gain spectrum shift, over 25-nm wavelength tuning with 100 GHz channel spacing is obtained with side-mode suppression ratio up to 40 dB. Sixteen channels can be switched by using a single electrode control on the long cavity electrode and seven channels on the short cavity electrode. Mode competition is observed during the transient and the switching delay time varies from 1 to 11 ns for different switching paths.

Temperature-Tolerant Wavelength-Setting and -Stabilization in a Polymer-Based Tunable DBR Laser

In this paper, we present a method of self-detection of mode hops in a distributed Bragg reflector tunable laser using the voltage drop in the active section as a monitoring signal. Based on this method, a wavelength setting and stabilization algorithm that is tolerant to temperature variations is proposed. Wavelength locking for a period of more than seven days with an accuracy better than ±1.25 GHz has been achieved, meeting the ITU-T standard for 25 GHz channel spacing. Under forced changes in the operation temperature from 15° to 60°, with variations of 0.1°/s, the maximum allowed deviation of ±2.5 GHz for the ITU-T standard with 50 GHz channel spacing was kept.

Cascaded chirped narrow bandpass filter with flat-top based on two-dimensional photonic crystals.

We propose a structure of a cascaded chirped narrow bandpass filter with a flat-top based on two-dimensional (2D) photonic crystals (PhCs). The filter discussed here consists of three filter units, each with a resonator and two reflectors. Coupled mode theory and transfer matrix method are methodologies applied in the analysis of the features. The calculations show that the bandwidth of the filter can be adjusted by changing the distances between resonators and reflectors, and based on this, a flat-top response can be achieved by chirped-cascading the filter units. According to the theoretical model, we design a narrow bandpass filter based on 2D PhCs with a triangular lattice of air holes, the parameters of which are calculated using the finite element method. The simulation results show that the filter has a center frequency of 193.40THz, an insertion loss of 0.18dB, a flat bandwidth of 40GHz, and ripples of about 0.2dB in the passband. The filter is suitable for dense-wavelength-division-multiplexed optical communication systems with 100GHz channel spacing.

Design and optimization of photonic crystal based eight channel dense wavelength division multiplexing demultiplexer using conjugate radiant neural network

In this paper, two dimensional photonic crystal, based eight-channel demultiplexer is proposed and designed for DWDM applications. The performance parameters of the demultiplexer such as transmission efficiency, channel spacing, spectral line width, Q factor, and crosstalk have been evaluated. The proposed demultiplexer comprises of bus waveguide, drop waveguide and parellogram resonant cavity (PRC). The bus waveguide transmits light to the PRC and exits through respective drop waveguide. The PRC consists of a parellogram resonator with a nano ring cavity that is used for dropping eight specific wavelength for ITU-T G 694.1 standard with 50 GHz channel spacing. The circular ring resonator is placed above the PRC wherein a resonant air hole (Cr) is positioned for desired channel selection. The channel selection is done by altering the radius of the air hole. In addition, a conjugate radiant neural network is implemented for optimizing the radii of resonant air holes to select the required channel wavelength. The proposed device is very compact and it could be considered for implementing the photonic integrated circuits.

Hundred gigahertz spacing Si arrayed‐waveguide grating using rib‐waveguide multimode interference coupler at slab–array interface

Silicon arrayed-waveguide grating using rib-waveguide multimode interference coupler at the array and slab waveguide interface is reported. A 100 GHz channel spacing 8ch device showing 2.8 dB insertion loss is obtained. The insertion loss was improved compared with a device using simple width taper.

Demonstration of 4 lanes of 4 × 100 Gbps DMT transmission with channel spacing of 50-GHz compatible with DWDM

Abstract We experimentally demonstrate 4 lanes of 416-Gb/s discrete multi-tone (DMT) transmission with 50-GHz channel spacing. This is the first demonstration of 4 × 100 G transmission with less than 100-GHz channel spacing and it can be compatible with dense wavelength division multiplexing (DWDM).

Rapidly reconfigurable high-fidelity optical arbitrary waveform generation in heterogeneous photonic integrated circuits.

This paper demonstrates rapidly reconfigurable, high-fidelity optical arbitrary waveform generation (OAWG) in a heterogeneous photonic integrated circuit (PIC). The heterogeneous PIC combines advantages of high-speed indium phosphide (InP) modulators and low-loss, high-contrast silicon nitride (Si3N4) arrayed waveguide gratings (AWGs) so that high-fidelity optical waveform syntheses with rapid waveform updates are possible. The generated optical waveforms spanned a 160 GHz spectral bandwidth starting from an optical frequency comb consisting of eight comb lines separated by 20 GHz channel spacing. The Error Vector Magnitude (EVM) values of the generated waveforms were approximately 16.4%. The OAWG module can rapidly and arbitrarily reconfigure waveforms upon every pulse arriving at 2 ns repetition time. The result of this work indicates the feasibility of truly dynamic optical arbitrary waveform generation where the reconfiguration rate or the modulator bandwidth must exceed the channel spacing of the AWG and the optical frequency comb.

$16\times 100$ GHz Echelle Grating-Based Wavelength Multiplexer on Silicon-on-Insulator Platform

This letter reports on an Echelle grating demultiplexer for dense wavelength-division-multiplexing applications with 16 channels and 100 GHz channel spacing. The Echelle grating is designed and fabricated on a silicon-on-insulator platform with a silicon guiding layer of 300 nm. The measured insertion losses of the Echelle grating are lower than 2 dB for all channels and the crosstalk is below 15 dB. Error free transmission was obtained for all channels with negligible penalty.

Performance Evaluation and Nonlinear Mitigation through DQPSK Modulation in 32 × 40 Gbps Long-Haul DWDM Systems

AbstractHigher spectral efficiency and greater data rate per channel are the most cost-effective strategies to meet the exponential demand of data traffic in the optical core network. Multilevel modulation formats being spectrally efficient enhance the transmission capacity by coding information in the amplitude, phase, polarization or a combination of all. This paper presents the design architecture of a 32-channel dense wavelength division multiplexed (DWDM) system, where each channel operates with multi-level phase modulation formats at 40 Gbps. The proposed design has been simulated for 50 GHz channel spacing to numerically compute the performance of both differential phase-shift keying (DPSK) and differential quadrature phase-shift keying (DQPSK) modulation formats in such high-speed DWDM system. The transmission link is analyzed with perfect dispersion compensation and also with under-compensation scheme. The link performance in terms of quality factor (

Reconfigurable high-speed optical fibre networks: Optical wavelength conversion and switching using VCSELs to eliminate channel collisions

Abstract We experimentally provide an alternative solution to channel collisions through up-wavelength conversion and switching by using vertical cavity surface-emitting lasers (VCSELs). This has been achieved by utilizing purely optical wavelength conversion on VCSELs at the low attenuation, 1550 nm transmission window. The corresponding transmission and bit error-rate (BER) performance evaluation is also presented. In this paper, two 1550 nm VCSELs with 50–150 GHz channel spacing are modulated with a 10 Gb/s NRZ PRBS 2 7 -1 data and their interferences investigated. A channel interference penalty range of 0.15–1.63 dB is incurred for 150–50 GHz channel spacing without transmission. To avoid channel collisions and to minimize high interference penalties, the transmitting VCSEL with data is injected into the side-mode of a slave VCSEL to obtain a new up converted wavelength. A 16 dB extinction ratio of the incoming wavelength is achieved when a 15 dBm transmitting beam is injected into the side-mode of a −4.5 dBm slave VCSEL. At 8.5 Gb/s, a 1.1 dB conversion and a 0.5 dB transmission penalties are realized when the converted wavelength is transmitted over a 24.7 km G.655 fibre. This work offers a low-cost, effective wavelength conversion and channel switching to reduce channel collision probability by reconfiguring channels at the node of networks.

Performance analysis of 112 Gb/s\xd74-channel WDM PDM-DQPSK optical label switching system with spectral amplitude code labels

We present the performance analysis of 112 Gb/s×4 wavelength division multiplexing (WDM) 100 GHz channel spacing polarization division multiplexed-differential quadrature phase shift keying (PDM-DQPSK) optical label switching system with frequency swept coherent detected spectral amplitude code labels. Direct detection is chosen to demodulate the payload by applying a polarization tracker, while 4-bits of 156 Mb/s spectral amplitude code label is coherently detected with a scheme of frequently-swept coherent detection. We optimize the payload laser linewidth as well as the frequency spacing between the payload and label. The label and payload signal performances are assessed by the eye-diagram opening factor (EOF) and bit-error rate (BER) at 10–9 as a function of the received optical power (ROP) and the optical signal to noise ratio (OSNR). The payload could well be demodulated after 900 km at a bit error rate of 10‒3 using forward error correction (FEC).

Integrated line-by-line optical pulse shaper for high-fidelity and rapidly reconfigurable RF-filtering

We present a 32 channel indium phosphide integrated pulse shaper with 25 GHz channel spacing, where each channel is equipped with a semiconductor optical amplifier allowing for programmable line-by-line gain control with submicrosecond reconfigurability. We critically test the integrated pulse shaper by using it in comb-based RF-photonic filtering experiments where the precise gain control is leveraged to synthesize high-fidelity RF filters which we reconfigure on a microsecond time scale. Our on-chip pulse shaping demonstration is unmatched in its combination of speed, fidelity, and flexibility, and will likely open new avenues in the field of advanced broadband signal generation and processing.

Low loss 100 GHz spacing Si arrayed‐waveguide grating using minimal terrace at slab–array interface

Si wire arrayed-waveguide grating is reported using local rib waveguide generating multimode interference at the array and slab waveguide interface. An 8ch device with 100 GHz channel spacing showing 1.2 dB insertion loss is obtained. A loss improvement near the theory was attained using minimum terrace area compared with a device using simple width taper.

Long reach DWDM-PON with 12.5 GHz channel spacing based on comb source seeding

A long reach dense wavelength division multiplexing passive optical network (DWDM-PON) with 12.5 GHz channel spacing is proposed and experimentally demonstrated. An optical frequency comb source is used to provide the multiwavelength seeding light, while reflective semiconductor optical amplifiers (RSOAs) are installed in both optical line terminal (OLT) and optical network units (ONUs) as colorless transmitter. The experimental results show that the bidirectional transmission for 1.2 Gbit/s data rate is achieved over 80 km single mode fiber (SMF).

Generation and Transmission of Optical Solitons in Ultrahigh Speed Long-Haul Systems

High bit rates optical communication systems pose the challenge of their tolerance to linear and nonlinear fiber impairments.The techniques processing of linear and nonlinear impairments involve which balance between linear and nonlinear impairments. Optical Solitons are the special breed of wave packets which can propagate over long distance without changing in their shape and velocity. Effective transmission distance could be increased by proper circuit designing and balancing Group velocity dispersion (GVD) with its counterpart Self phase modulation (SPM. The comparison between the results of single channel soliton source and CW laser 33% RZ_DPSK modulatiom formats shows that the soliton source has the better performance than the CW. Soliton source which has a Q factor of 98.4 at distance of 60Km, while the CW laser with 33% RZ-DPSK has 70.01 at distance at 60Km, when power lunch is (10) dBm. On other hand the BER is (-11.2) when SNR (5) dB at 60km, while CW laser with 33% RZ-DPSK has BER (-20) at SNR (5) dB at distance 60Km.The soliton system at multichannel (8x40Gb/s) with 50 GHz channel spacing has BER (-15) while 33%RZ-DPSK has BER (-9) at SNR (6.87) dB at 60Km distance.

Next-generation 400 Gb/s Ethernet PMD over SMF at 1310 nm via DD-OFDM with electro-absorption modulator-based transmitters

The technical feasibility of an unamplified 4 x 100 Gb/s wavelength division multiplexed direct-detection optical OFDM system that uses electro-absorption modulators (EAM) as transmitters is numerically demonstrated for up to 10-km reach of single-mode fiber (SMF) in O-band and 800 GHz-channel spacing. Based on the use of currently available optical components, most of which were developed for the current long-reach Ethernet standard, operating around 1300 nm, error-free operation (pre-FEC BER less than 3.8E-5) is achieved. The architecture here put forward represents a backward compatibility alternative that can be used to define next-generation 2- and 10-km 400 Gb/s Ethernet standard.

Analysis of the four-wave mixing impact on the most heavily affected channels of dense and ultra-dense wavelength division multiplexing systems using non-zero dispersion shifted fibers

In this paper, the impact of four-wave mixing (FWM) phenomenon on the system performance has been analyzed via focusing on effects of FWM products falling into the center channels, i.e. the most heavily affected ones among all, of equally spaced 9-, 11-, 13- and 15-channel DWDM systems having channel spacing values of 12.5GHz, 25GHz, 50GHz and 100GHz, and UDWDM systems having 6.25GHz channel spacing value. DWDM and UDWDM systems using four different single-span commercially available NZDSFs, i.e. TeraLight™, LEAF®, TrueWave®-Reach and TrueWave®-RS, have been considered in simulations. Results show that for all NZDSF types, input powers even as low as 1mW do not satisfy a minimum 23dB signal-to-crosstalk ratio (SXR) criterion in UDWDM and DWDM systems using 6.25GHz and 12.5GHz channel spacing values, respectively. Furthermore, for all DWDM and UDWDM systems, the lowest and the highest FWM crosstalk values belong to the TeraLight and the TrueWave-RS fibers, respectively, at all input powers, channel numbers and channel wavelengths while the minimum and the maximum SXR variations with varying channel wavelengths are obtained in the TrueWave-Reach and the LEAF fibers, respectively.