Wavelength Switching Research Articles

Design of fiber-integrated tunable thermo-optic C-band filter based on coated silicon slab

BackgroundOptical filters are required to have narrow band-pass filtering in the spectral C-band for applications such as signal tracking, sub-band filtering or noise suppression. These requirements lead to a variety of filters that offer thermo-optic effect for optical switching, however, some of which without proper thermal and optical efficiency.MethodsIn this paper we propose a tunable thermo-optic filtering device based on a coated silicon slab resonator with an increased Q-factor to allow for an efficient thermo-optical switching in the C-band. The device can be designed either for long range wavelength tuning or for short range with increased wavelength resolution.ResultsTheoretical examination of the thermal parameters affecting the filtering process is shown together with experimental results. Proper channel isolation with an extinction ratio of 20 dB is achieved with a spectral bandpass width of 0.07 nm.ConclusionsThis Si slab based filter characteristics make it suitable for wavelength switching systems such as dense wavelength division multiplexing. In addition, the filter is fiber integrated in order for it to be more compatible with other optics communication devices.

Pulse-to-pulse wavelength switching of a nanosecond fiber laser by four-wave mixing seeded stimulated Raman amplification.

We report on a multi-color fiber laser based on four-wave mixing (FWM) and stimulated Raman scattering (SRS), delivering rapidly wavelength switchable narrowband output at 1064, 1122, and 1186nm. High-power pulses from a nanosecond pulsed fiber master oscillator power amplifier at 1064nm are combined with 1122nm of seed light for Raman amplification at the first Stokes order in a standard single-mode fiber. With increasing power, we observe a narrowband spectral component at 1186nm, without any additional seed or resonator at this wavelength. We analyze this occurrence of a narrowband second Stokes order both experimentally and theoretically and suggest it is a result of FWM seeding of the SRS amplification in the fiber. We demonstrate that the wavelength shifting can be controlled electronically within microseconds for very rapid and even pulse-to-pulse wavelength changes. This wavelength conversion method can extend the spectral coverage of single-wavelength fiber lasers for biomedical imaging.

Hybrid Wavelength Switched-TDMA High Port Count All-Optical Data Centre Switch

The physical layer data plane design of an all-optical network switch capable of scaling to 1024 ports at 25 Gb/s per port is presented and experimentally evaluated. Fast-tuning DSDBR lasers modulated with line-coded bipolar data allow combined wavelength switching and time-division multiple access to provide packet switch-like functionality with over 2 Tb/s of total switch bandwidth. A passive fiber star coupler core with high sensitivity DSP-free coherent receivers creates a low complexity easily upgradeable building block for data center networks.

Photoacoustic imaging of lymphatic pumping.

The lymphatic system is responsible for fluid homeostasis and immune cell trafficking and has been implicated in several diseases, including obesity, diabetes, and cancer metastasis. Despite its importance, the lack of suitable in vivo imaging techniques has hampered our understanding of the lymphatic system. This is, in part, due to the limited contrast of lymphatic fluids and structures. Photoacoustic imaging, in combination with optically absorbing dyes or nanoparticles, has great potential for noninvasively visualizing the lymphatic vessels deep in tissues. Multispectral photoacoustic imaging is capable of separating the components; however, the slow wavelength switching speed of most laser systems is inadequate for imaging lymphatic pumping without motion artifacts being introduced into the processed images. We investigate two approaches for visualizing lymphatic processes in vivo. First, single-wavelength differential photoacoustic imaging is used to visualize lymphatic pumping in the hindlimb of a mouse in real time. Second, a fast-switching multiwavelength photoacoustic imaging system was used to assess the propulsion profile of dyes through the lymphatics in real time. These approaches may have profound impacts in noninvasively characterizing and investigating the lymphatic system.

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.

Tunable narrow linewidth all-fiber thulium-doped fiber laser in a 2 µm-band using two Hi-Bi fiber optical loop mirrors

We propose an all-fiber Tm-doped fiber laser with a tunable and narrow laser line generated in a wavelength region of 2 µm. A single laser line with a linewidth below 0.05 nm, tunable in a wavelength range of 44.25 nm, is obtained. The laser linewidth and the discrete wavelength tuning range depend on the characteristics of the two fiber optical loop mirrors with high birefringence in the loop that forms the cavity. Dual-wavelength laser operation is also observed at tuning range limits with a wavelength separation of 47 nm. Alternate wavelength switching is also observed.

Optical Ethernet—Flexible Optical Metro Networks

Enhanced flexibility in optical transport networks is a key requirement to support dynamic traffic load in packet-based networks. Today, flexibility is achieved by packet switches linked by static point-to-point transport connections. Wide-stretched synchronization patterns, line coding schemes, and forward error correction (FEC) frames prohibit flexibility right at the transport layer. We introduce a new optical transport concept that combines packet aggregation with a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">multipoint-to-point</i> line coding and FEC processing. This concept avoids the quadratic full mesh scalability problem of other aggregated switching technologies such as, e.g., wavelength switching. It combines the flexibility of a distributed Ethernet switch and the performance of a leading edge optical transport system.

Construction of Nonblocking Wavelength/Space Switches with AWGs and WSSes

In this paper, we how to use two technologies, AWG (arrayed-waveguide grating) and WSS (wavelength selective switches), to design nonblocking wavelength/space optical cross connects. An AWG is a passive device and can route multiple wavelengths simultaneously. However, to apply AWGs, there are several issues to consider, including the wavelength conversion range, crosstalk, and switch size constraint. We show a decomposition technique for designing an AWG-based nonblocking wavelength/space switch. The decomposition is carried out in a transformed space network. The new technique is simpler in concept and more flexible in setting switch sizes. We also study another class of wavelength/space switches that are based on WSSes and compare the two approaches in terms of the scalability, switch size constraint, and number of WCs (wavelength converters) required.

Simultaneous Switching at Multiple Wavelengths Using Plasmon Induced Transparency and Fano Resonance

Plasmon-induced transparency, an effect analogous to electromagnetically induced transparency in atomic systems, is investigated theoretically in a plasmonic waveguide-coupled resonator device. Transmittance peak is induced through modulation of an external control beam, which alters the nonlinear optical response of a third-order Kerr medium incorporated within the structure. This induced transparency is utilized to achieve optical switching simultaneously at two wavelengths. At higher intensities, an induced peak exhibiting Fano resonant feature enables demonstration of simultaneous switching at three wavelengths. The performance of the switch is evaluated by determining the differential transmittance at the switching wavelengths.

Tunable all-optical switch/demultiplexer using nonlinear MMI waveguides

In this paper, a tunable optical switch/demultiplexer has been presented based on nonlinear multimode interference waveguides. The proposed structure can be utilized as a multi-wavelength optical switch or dynamic wavelength division demultiplexer. This dual application of the structure has been designed based on the cooperation of self-imaging and self-guiding phenomena of multimode waveguides. Simulation results show the mean value of insertion loss equal to −1.91 dB for the switching application of structure. Also, the wavelengths with 3 nm channel spacing and almost 3 nm full width at half power of outputs can be received in the multiplexing application. Two-dimensional beam propagation method has been utilized in order to simulate and verify the performance of proposed device.

A targeted illumination optical fiber probe for high resolution fluorescence imaging and optical switching

An optical imaging probe with targeted multispectral and spatiotemporal illumination features has applications in many diagnostic biomedical studies. However, these systems are mostly adapted in conventional microscopes, limiting their use for in vitro applications. We present a variable resolution imaging probe using a digital micromirror device (DMD) with an achievable maximum lateral resolution of 2.7 μm and an axial resolution of 5.5 μm, along with precise shape selective targeted illumination ability. We have demonstrated switching of different wavelengths to image multiple regions in the field of view. Moreover, the targeted illumination feature allows enhanced image contrast by time averaged imaging of selected regions with different optical exposure. The region specific multidirectional scanning feature of this probe has facilitated high speed targeted confocal imaging.

2 MHz multi-wavelength pulsed laser for functional photoacoustic microscopy.

Fast functional photoacoustic microscopy requires multi-wavelength pulsed laser sources with high pulse repetition rates, short wavelength switching time, and sufficient pulse energies. Here, we report the development of a stimulated-Raman-scattering-based multi-wavelength pulsed laser source for fast functional photoacoustic imaging. The new laser source is pumped with a 532 nm 1 MHz pulsed laser. The 532 nm laser beam is split into two: one pumps a 5 m optical fiber to excite a 558 nm wavelength via stimulated Raman scattering; the other goes through a 50 m optical fiber to delay the 532 nm pulse by 220 ns. The two beams are combined and coupled into an optical fiber for photoacoustic excitation. As a result, the new laser source can generate 2 million pulses per second, switch wavelengths in 220 ns, and provide hundreds of nanojoules pulse energy for each wavelength. Using this laser source, we demonstrate optical-resolution photoacoustic imaging of microvascular structures and oxygen saturation in the mouse ear. The ultrashort wavelength switching time enables oxygen saturation imaging of flowing red blood cells, which is valuable for high-resolution functional imaging.

OPSquare: A Flat DCN Architecture Based on Flow-Controlled Optical Packet Switches

Aiming at solving the scaling issues of bandwidth and latency in current hierarchical data center network (DCN) architectures, we propose and investigate a novel optical flat DCN architecture in which the number of interconnected ToRs scales as the square of the optical packet switches&#x2019; (OPS) port count (OPSquare). The proposed flat DCN architecture consists of two parallel inter- and intra-cluster networks that are built on a single-hop OPS with nanosecond time and wavelength switching for efficient statistical multiplexing operations. Fast optical flow control is implemented for solving packet contentions that may occur at the buffer-less optical switches. The performance of OPSquare DCN in terms of scalability, packet loss, latency, and throughput is assessed by a numerical simulation employing OMNeT++ under realistic data center (DC) traffic. The results report a server-to-server latency of less than 2 &#x03BC;s (including packet retransmission), a packet loss &lt;10&#x2212;5 at a load of 0.4, and a DC size of 10,240 servers with a ToR buffer size equal to 50 KB for all traffic patterns. Moreover, the cost and power consumption of the OPSquare DCN have been studied and compared with fat-tree DCN based on electrical switches and H-LION connected by an arrayed wave guide grating router (AWGR). The results indicate 23.8% and 39% cost and power savings, respectively, for the OPSquare DCN supporting 160,000 servers with respect to the fat-tree DCN. The OPSquare has a cost saving of 56% compared with H-LION for a 160,000-server DCN.

(Box-filling-model)-based ONU schedule algorithm and bandwidth-requirement-based ONU transfer mechanism for multi-subsystem-based VPONs’ management in metro-access optical network

Abstract ONU schedule algorithm and ONU transfer mechanism for multi-subsystem-based VPONs’ management is proposed in this paper. To avoid frequent wavelength switch and realize high system stability, ONU schedule algorithm is presented for wavelength allocation by introducing box-filling model. At the same time, judgement mechanism is designed to filter wavelength-increased request caused by slight bandwidth fluctuation of VPON. To share remained bandwidth among VPONs, ONU transfer mechanism is put forward according to flexible wavelength routing. To manage wavelength resource of entire network and wavelength requirement from VPONs, information-managed matrix model is constructed. Finally, the effectiveness of the proposed scheme is demonstrated by simulation and analysis.

Proposal and experimental demonstration of SDM node enabling path assignment to arbitrary wavelengths, cores, and directions.

We propose a novel simple space division multiplexing (SDM) node which is rearrangeble nonblocking, and effectively utilizes enhanced network resources through SDM. The proposed node can reduce a number of ports of wavelength selective switches (WSSs) and a number of WSS modules by modifying conventional multi-stage switches and employing integrated multiple arrayed WSSs. We experimentally actualized the newly proposed node, and demonstrate wavelength, core, and direction switching functions based on 127-Gbps Dual Polarization Quadrature Phase Shift Keying (DP-QPSK) signals. We also confirm the feasibility of the proposed SDM node through SDM transmission experiments using a 40-km multicore fiber and a multicore amplifier.

Unified Architecture of an Integrated SDM-WSS Employing a PLC-Based Spatial Beam Transformer Array for Various Types of SDM Fibers

There is no doubt that wavelength-division multiplexing will continuously play an important role in future space-division multiplexing (SDM) capable optical networks. In this paper, we propose a unified architecture for integrated wavelength selective switches (WSSs) that can be applied to various types of SDM fibers and reconfigurable optical add/drop multiplexer switching types. A recently reported planar lightwave circuit (PLC)-based spatial beam transformer (SBT) array is anticipated to be used as a key enabler for the architecture to integrate multiple WSSs on a single liquid crystal on silicon beam steering device. The architecture enables individual switching and power adjustment functionality of an SDM-WSS that supports an uncoupled single-mode multicore fiber (SM-MCF) in an economical manner. The same architecture provides fractional joint wavelength switching functionality in an SDM-WSS for a few-mode MCF (FM-MCF) and a grouped-coupled-core MCF (GCC-MCF) as well as joint wavelength switching in an SDM-WSS for multiple few-mode fibers with almost no additional hardware complexity. Preliminary scalability evaluation shows that a 1&#x00D7;24 individual switching SDM-WSS for a single-mode eight-core uncoupled MCF or a 1&#x00D7;7 fractional joint wavelength switching SDM-WSS for a three-mode eight-core FM-MCF or a three-coupled-core &#x00D7; eight-group GCC-MCF is feasible using the SBT array design reported in the literature. The evaluation also shows that compared to the traditional approach based on conventional WSSs, the proposed architecture is anticipated to reduce the hardware footprint requirement by parallelism factor mC, where m and C indicate the number of modes per core and the number of cores per fiber, respectively.

Software-defined control-plane for wavelength selective unicast and multicast of optical data in a silicon photonic platform.

We demonstrate a programmable control-plane based on field programmable gate array (FPGA) with a power-efficient algorithm for optical unicast, multicast, and broadcast functionalities in a silicon photonic platform. The platform includes a silicon photonic 1×8 microring array chip which in conjunction with a fast tunable laser over the C-band is capable of delivering software controlled wavelength selective functionality on top of spatial switching. We characterize the thermo-optic response of microring resonators and extract key parameters necessary for the development of the control-plane. The performance of the proposed architecture is tested with 10 Gb/s on-off keying (OOK) optical data and error-free operation is verified for various wavelength and spatial switching scenarios. Lastly, we evaluate electrical power and energy consumption required to reconfigure the silicon photonic device for all possible wavelength operations and output ports combinations and show that unicast, multicast of two, three, four, five, six, seven, and broadcast functions are achieved with energy overheads of 0.02, 0.07, 0.18, 0.49, 0.76, 1.01, 1.3, and 1.55 pJ/bit, respectively.

Application of artificial neural networks for optimal design of OADM for DWDM applications

For greater flexibility and connectivity, optical add/drop multiplexers (OADMs) with wavelength routing devices and switches play a crucial role in DWDM optical networks. OADM can act as access node (AN) in any DWDM network. They can add or drop signals as per our requirement. A DWDM system is modeled using different number of channels, data rates and spacing between channels in terms of bit error rate (BER), optical signal to noise ratio (OSNR), Jitter and Dispersion. These parameters are then optimized and classification of signals analyzed by using Artificial Neural Networks. Comparison was performed between FBG/OADM and OFDM in respect of transmitted and received signal powers.

Amplification of a nanosecond laser pulse chain via dynamic injection locking of a laser diode.

We report a novel optical pulse generation method for high-speed wavelength switching of amplified nanosecond (ns) laser pulses resonant to atomic transitions. Under free-running conditions, a slave laser diode is blue-detuned with tens of GHz relative to the master laser. A nanosecond pulse chain generated by modulating the continuous-wave master laser with a fiber-pigtailed electro-optical intensity modulator is injected into the slave laser diode to fast switch the slave laser's wavelength back and forth. The output beam of the slave laser is filtered by a temperature-controlled etalon to get the amplified pulse chain. Based on our dynamic injection locking scheme, we produce an ns-scale square pulse chain with an effective ON/OFF ratio ∼108, considering at least the 60 dB scattering suppression by tuning the light-atom interactions with far off-resonance detuning and the 26.7 dB suppression ratio of the etalon. By studying the dynamic processes of injection locking, we determine the dependence of injection locking on both the injection power and the frequency detuning.

Observation of wavelength-switchable solitons in an all-polarization-maintaining erbium-doped fiber cavity based on graphene saturable absorber reflector**Project supported by the Program for Changjiang Scholars and Innovative Research Team in University, China (Grant No. PCSIRT: 1212), the Key Grant Science and Technology Planning Project of Beijing, China (Grant Nos. PXM2013_014224_000077 and PXM2012_014224_000019), and the Science and Technology Planning Project of Beijing Municipal

We present the generation of wavelength-switchable single-polarization solitons in an all-polarization-maintaining erbium-doped fiber laser mode-locked by a graphene saturable absorber. Ultrashort pulses centered at the wavelength of 1531.6 nm with the duration of 816 fs and centered at the wavelength of 1557.8 nm with the duration of 402 fs are separately obtained from the same fiber laser cavity. The cavity loss adjusted by the gold reflector plays a crucial role in wavelength switching.