Wavelength Switching Research Articles

Asymmetric Optical Wavelength Switch Based on LCoS-SLM for Edge Node of Optical Access Network

A novel design of optical wavelength switch, based on an asymmetric switching architecture for edge node implementation, is presented in this paper. Compared to previous research for optical core transport network applications, the proposed work has a unique aspect to build dynamic multicasting and spectral equalization, vital functionalities for optical wavelength switch in the edge of optical access networks. An optical wavelength switch was experimentally implemented and evaluated in a 4 × 16 switching architecture to demonstrate the concept. This dynamic multicasting and spectral equalization were achieved by utilizing liquid crystal on a silicon spatial light modulator (LCoS-SLM) device. An optimal design of computer-generated holograms (CGHs) through an improved GS algorithm was used to perform the beam steering and wavelength switching. A variety of wavelength switching scenarios has been experimentally evaluated. The measurement results showed an average insertion loss of around -12.5 dB, and the calculated crosstalks were all less than -28 dB. Its applications in digital data transmissions were evaluated to achieve a transmission speed larger than 2.5 Gbps. The eye diagram measurement results showed that most wavelength switching scenarios have nearly bit-error-free transmission. The scenario includes the multicasting with spectral equalization within the proposed asymmetrical switching architecture.

Optical links on silicon photonic chips using ultralow-power consumption photonic-crystal lasers.

Ultrashort-distance optical interconnects are becoming increasingly important due to continuous improvements in servers and high-performance computers. As light sources in such interconnects, directly modulated semiconductor lasers with an ultrasmall active region are promising. In addition, using Si waveguides is important to provide low loss optical links with functions such as wavelength filtering and switching. In this paper, we demonstrate a wafer-scale heterogeneous integration of lambda-scale embedded active-region photonic-crystal (LEAP) lasers and Si waveguides, achieved through precise alignment. We numerically and experimentally demonstrated the coupling design between the LEAP lasers and Si waveguides; it is important to match propagation constants of Si waveguides and wavenumber of the optical cavity modes. The LEAP lasers exhibit an ultralow threshold current of 13.2-μA and 10-Gbit/s direct modulation. We also achieved the first data transmission using an optical link consisting of a LEAP laser, Si waveguide, and photodetector and obtained an averaged eye diagram at a bit rate of 10 Gbit/s with a bias current of 150 μA.

High-sensitivity frequency modulation CARS with a compact and fast tunable fiber-based light source.

Frequency modulation (FM) coherent anti-Stokes Raman scattering (CARS) is presented, using a compact as well as fast and widely tunable fiber-based light source. With this light source, Raman resonances between 700cm-1 and 3200cm-1 can be addressed via wavelength tuning within only 5 ms, which allows for FM CARS measurements with frame-to-frame wavelength switching. Moreover, the functionality for high-sensitivity FM CARS measurements was integrated by means of fiber optics to keep a stable and reliable operation. The light source accomplished FM CARS measurements with a 40 times enhanced sensitivity at a lock-in amplifier (LIA) bandwidth of 1 Hz. For fast imaging with frame-to-frame wavelength switching at a LIA bandwidth of 1 MHz, an 18-fold contrast enhancement could be verified, making this light source ideal for routine and out-of-lab FM CARS measurements for medical diagnostics or environmental sensing.

Molecular Spin State Switching and Photochromism in the Red and Near Infrared with Ni(II) Chlorin and Ni(II) Bacteriochlorin.

Molecules or ions are either paramagnetic (unpaired electrons) or diamagnetic (all electrons are paired). Switching between the two states under ambient conditions was considered a typical solid state phenomenon and has been termed spin crossover. The first single-molecule spin state switches operated with light in solution were developed a decade ago and offer a number of technical applications that are not accessible to solid state systems. Magnetic switching in biological environments, however, requires water solubility, and for in vivo applications, switching wavelengths within the bio-optical window (650-950 nm) are needed. We now present molecular spin state switches that are water-soluble and switchable in the far-red and near-infrared region. At the same time, they are photochromic compounds with excellent photophysical properties. trans-cis isomerization is induced with 505 nm radiation, and cis-trans conversion with 620 or 720 nm radiation. The metastable cis isomers are stable at room temperature for at least several weeks. The detailed mechanism of this surprising and unprecedented long wavelength photoisomerization of azobenzenes is still under investigation.

Sleep-aware wavelength and bandwidth assignment scheme for TWDM PON

The energy efficiency and delay performance of PON are two inversely related phenomena. Higher sleep time of the Optical Network Units (ONUs) results in higher upstream (US) delays due to increased traffic queues during the ONU Asleep state. Although an efficient dynamic bandwidth and wavelength assignment (DWBA) scheme can decrease US delays by minimizing the bandwidth waste and improving the fairness of bandwidth distribution among the ONUs. However, the conventional DWBA schemes are not designed to work with cyclic sleep mode (CSM) and they keep on assigning bandwidth to ONUs even if the ONU is in Asleep state leading to wastage of bandwidth and degraded CSM performance. Therefore, in this work a sleep aware DWBA scheme for TWDM PON is presented to coordinate with CSM mode. It only assign bandwidth to Active ONUs during the guaranteed phase, surplus phase and excess phase allocation phases which minimizes the bandwidth waste and the bandwidth lost at the ONU end. The wavelength switching process is also improved by only considering the Active state ONUs to balance the traffic load on all the wavelengths. The simulation results support our claim as the SA-DWBA scheme on average achieves DWBA schemes due to up to 50% to 65% higher energy savings compared to other due to longer ONU Asleep times. However, the increased upstream delays of all the traffic classes in SA-DWBA scheme remain within the set delay limit of 50 ms.

High Contrast All-Optical Dual Wavelength Switching of Femtosecond Pulses in Soft Glass Dual-Core Optical Fiber

All-optical switching of 75 fs pulses centered at 1560 nm, driven by 270 fs, 1030 nm pulses in a dual-core optical fiber exhibiting high index contrast is presented. The fiber is made of a thermally matched pair of lead silicate and borosilicate glasses used as core and cladding material, respectively. The novel switching approach is based on nonlinear balancing of dual-core asymmetry, by control pulse intensity induced group velocity reduction of the fast fiber channel. Due to the fiber core made of soft glass with high nonlinearity high switching contrast exceeding 20 dB is reached by using control pulses of only few nanojoule energy. The optimum fiber length is 14 mm, which closely match the calculated coupling length at the signal wavelength. The results express significant progress in comparison to similar studies based on self-switching of solitonic pulses in dual-core fibers and represent high application potential.

Multicascade-linked synthetic-wavelength digital holography using a line-by-line spectral-shaped optical frequency comb.

Phase imaging without a phase wrapping ambiguity is required for wide-axial-range 3D imaging in the fields of surface topography measurement and biomedical imaging. Although multicascade-linked synthetic-wavelength digital holography (MCL-SW-DH) using an optical frequency synthesizer (OFS) is a promising method to meet this requirement, the slow switching of multiple optical wavelengths in the OFS prevents rapid imaging. In the work described in this article, a line-by-line spectral-shaped electro-optics-modulator-based optical frequency comb (EOM-OFC) is used as a light source in MCL-SW-DH to achieve rapid image acquisition. While MCL-SW-DH enables surface topography measurement with millimeter-order axial range and micrometer-order axial resolution, the line-by-line spectral-shaped EOM-OFC extracts a single narrow-linewidth OFC mode from the 10 GHz-spacing EOM-OFC at a center wavelength of 1545 nm within a spectral range of 30 nm at an interval of 500 ms. The effectiveness of the proposed MCL-SW-DH was highlighted by performing surface topography measurement with four step differences of sub-millimeter to millimeter size with an axial uncertainty of 2.08 µm in the image acquisition time of several seconds. The proposed MCL-SW-DH will be a powerful tool for 3D imaging with a wide axial range and high axial resolution.

A Programmable ROADM System for SDM/WDM Networks

This paper proposed and evaluated a programmable ROADM system for MCF-based SDM/WDM networks. The proposed ROADM system employing both bypass connection and Route-and-Select wavelength switching enables adaptable virtual topology in optical networks by dynamically configuring bypass connection cores. The simulation results confirmed this ROADM system could provide acceptable performance with an around 10–20% reduction in the total cost including the number of ports and WSSs by comparing with a fully flexible SDM/WDM ROADM system, which cannot be implemented due to the required extremely high-port-count WSSs.

Passively Q-switched fiber laser with single and double wavelength switching based on parallel FBGs

We proposed a passively Q-switched fiber laser with switchable wavelength based on two parallel fiber Bragg gratings. By increasing the input power, a single wavelength with a center wavelength of 1545.63 nm and dual wavelengths with a center wavelength of 1545.63 nm and 1553.60 nm can be obtained respectively. The wavelength spacing of the dual wavelengths is 8.17 nm, and the maximum repetition frequency of Q-switching is 24.27 kHz, and the narrowest pulse width is 5.48 ms. The combination of parallel fiber grating and erbium-ytterbium co-doped fiber (EYDF) saturable absorber provides a simple and feasible method to obtain stable (single and double wavelength switching) passively Q-switched pulses.

ICES: an innovative crosstalk-efficient 2 × 2 photonic-crystal switch

Crosstalk and insertion loss are the crucial determinants of ring resonated routers. A novel 2 × 2 optical switch is proposed through a combination of broadband waveguide crossing and X-shape photonic crystal ring resonators. The main goal of the proposed design is to demonstrate the switching wavelengths based on changing the refractive index and reduce the level of the crosstalk and insertion loss. The performance of the proposed structure is analyzed using two-dimensional finite difference time domain and plane-wave expansion methods. Results show that crosstalk noise and insertion loss can be significantly reduced by using optimized crossbar waveguide and novel structure with bending elimination, thereby allowing higher network scalability and better performance and utility for future many-core architectures. Maximum crosstalk and insertion loss of −37.41 and 0.3 dB are obtained at 1570.5 nm, respectively. The size of the proposed structure is 18.69 × 19.6 μm2, which can be used for photonic integrated circuits design due to its compactness.

All-fiber Mach–Zehnder interferometric comb filter based on macrobend single-mode optical fiber for selecting lasing performance in 1-micron region

We report on a new method to select between tunable single- and multi-wavelength switchable lasing performances in continuous-wave (CW) ytterbium-doped fiber laser (YDFL). The wavelength selection and switching techniques are based on the whispering gallery mode (WGM) effect in a Mach–Zehnder interferometric comb-filter formed by bending a standard single-mode fiber (SMF) into a balloon like shape. By incorporating the proposed comb-filter into the laser ring cavity and adjusting the SMF’s bending diameter to control the spectral cavity losses, the single-wavelength lasing was tuned from 1065.26 to 1048.6 nm. Furthermore, by appropriately rotating the polarization controller (PC) cascaded with the filter, the laser can be switched between the dual-and triple-wavelength lasing operations. Two sets of switchable triple-wavelength lasing operations around 1045 nm were obtained with a side-mode suppression ratio (SMSR) of 26.9 dB and 22.4 dB, respectively. To the best of our knowledge, this is the first demonstration of a balloon-like interferometer based comb-filter using a bare bending SMF. The experimental results indicate that the proposed filter provides a promising method to achieve tunable single- or switchable multi-wavelength YDFL.

AI-optimised tuneable sources for bandwidth-scalable, sub-nanosecond wavelength switching.

Wavelength routed optical switching promises low power and latency networking for data centres, but requires a wideband wavelength tuneable source (WTS) capable of sub-nanosecond switching at every node. We propose a hybrid WTS that uses time-interleaved tuneable lasers, each gated by a semiconductor optical amplifier, where the performance of each device is optimised using artificial intelligence. Through simulation and experiment we demonstrate record wavelength switch times below 900 ps across 6.05 THz (122×50 GHz) of continuously tuneable optical bandwidth. A method for further bandwidth scaling is evaluated and compared to alternative designs.

Full‐range wavelength switching at tunable distributed amplification‐DFB laser with high‐accuracy feedforward control

Full‐range wavelength switching at tunable distributed amplification‐DFB laser with high‐accuracy feedforward control

Bin-Packing-Based Online Dynamic Bandwidth and Wavelength Allocation Algorithm in Super-PON

Super passive optical network (Super-PON) is a next-generation Ethernet PON (NG-EPON) candidate that is envisaged to provide high data rate and low latency. For NG-EPON, there are two types of algorithms that manages bandwidth and wavelength scheduling, namely offline and online. The latter method is more scalable and efficient than the former method. Several online algorithms exist that propose schemes to manage wavelength and bandwidth scheduling. However, these algorithms lack in efficient wavelength utilization and switching. In this work, we propose a novel online bin-packing based dynamic bandwidth and wavelength allocation (DBWA) algorithm for Super-PON, namely updated best fit bin-packing (UBF-BP). This algorithm limits the wavelength switching per cycle, and uses the modified version of best fit bin-packing (BF-BP) technique for optimal wavelength allocation. Simulation results show that the proposed DBWA algorithm has a low complexity and overcomes the inefficiencies of wavelength utilization and switching. This results in lower network delay and higher channel utilization than the state-of-the-art DBWA. Furthermore, to verify the correctness of the proposed algorithm, we propose an analytical model and validate these simulation results with the analytical results.

SOA-MZI based 4 × 4 interconnected crossbar photonic wavelength switching for datacenter load balancing

Our paper is focused on an extremely efficient structure for photonic crossbar switch using a fundamental building element, a semiconductor optical amplifier (SOA) in a Mach–Zehnder interferometer configuration. The switch is designed with a 10 Gbps rate and a high Q-factor of 30; a bit error rate ranging between ∼e − 122 and ∼e − 184 is achieved. In addition, the designed photonic switch model is reliable in terms of having an extinction ratio of 16 dB on average. High optical signal-to-noise ratio values, ranging between 101 and 104 dB, provide the low interference of noise in the required signals. It is observed that the proposed configuration is fast enough to provide a switching time ranging between 0.146 and 0.227 ns and is feasible in scaling the ports with an increase in the number of users to maintain a good quality factor. Hence, the proposed architecture can be taken as a solution for challenges in future datacenter network switching.

Confocal visible/NIR photoacoustic microscopy of tumors with structural, functional, and nanoprobe contrasts

Distinguishing early-stage tumors from normal tissues is of great importance in cancer diagnosis. We report fiber-based confocal visible/near-infrared (NIR) optical-resolution photoacoustic microscopy that can image tumor microvasculature, oxygen saturation, and nanoprobes in a single scanning. We develop a cost-efficient single laser source that provides 532, 558, and 1064 nm pulsed light with sub-microseconds wavelength switching time. Via dual-fiber illumination, we can focus the three beams to the same point. The optical and acoustic foci are confocally aligned to optimize the sensitivity. The visible and NIR wavelengths enable simultaneous tumor imaging with three different contrast modes. Results show obvious angiogenesis, significantly elevated oxygen saturation, and accumulated nanoparticles in the tumor regions, which offer comprehensive information to detect the tumor. This approach also allows us to identify feeding and draining vessels of the tumor and thus to determine local oxygen extraction fraction. In the tumor region, the oxygen extraction fraction significantly decreases along with tumor growth, which can also assist in tumor detection and staging. Fiber-based confocal visible/NIR photoacoustic microscopy offers a new tool for early detection of cancer.

Broadly and finely tunable hybrid silicon laser with nanosecond-scale switching speed.

We demonstrate a hybrid silicon tunable laser with wide tunability and rapid switching speed for applications in sensing and optical networks. By implementing an optimized carrier injection phase shifter design, the filters of the silicon laser cavity may be efficiently controlled, enabling both fine and broad wavelength tuning across a 56 nm range, in addition to a rapid 10 ns switching time. The laser emits up to 10 dBm output power, and the linewidth is near 200 kHz. The fast wavelength switching demonstrated here may be employed in data center and access networks, while the potential for rapid wavelength sweeping is attractive for optical sensing and imaging applications.

High-Speed Wavelength Switching at TDA-DFB Laser Based on a Nonlinear Model

In order to realize a high-speed optical switch for optical packet switching (OPS), we have been focused on a wavelength routing optical switch consisting of tunable lasers and an arrayed waveguide grating (AWG), and have studied high-speed wavelength switching of a tunable distributed amplification (TDA)-distributed feedback (DFB) laser. Previously, we achieved high-speed wavelength switching by feedforward control based on linear control theory. In this article, to realize higher-speed wavelength switching, we proposed a more accurate control model based on the nonlinearity of the TDA-DFB laser. We applied our nonlinear model to 400-GHz-wide and 600-GHz-wide wavelength switching and realized high-speed wavelength switching times of 33 ns and 39 ns, respectively.

Transmission spectra of single ring coupled-waveguide resonator configuration by finite difference time domain method

Development of optical waveguide resonators have greatly expanded and continues to grow since they have kinds potential applications such as wavelength filtering, switching, coupling and multiplexing. One of resonators, coupled waveguides, ring resonators are designed and operated using various coupling configurations. Ring resonators can be particularly used as wavelength filter if the wavelength can fit a whole multiple time in the circumference of the ring. This article proposes to investigate the transmission spectra from the power source and amplify it in linearized ring resonator configurations and varies the input amplitude on five different wavelengths. With finite difference time domain method, the geometry and power source are simulated to obtain the better result and configuration. The results show the intensity phenomena of filtering in optical circuit.

Wavelength Switchable Multi-Wavelength Erbium-Doped Fiber Laser Based on Polarization-Dependent Loss Modulation

We propose and demonstrate a novel and simple wavelength switchable multi-wavelength erbium-doped fiber (EDF) laser based on polarization-dependent loss (PDL) modulation with cascaded fiber Bragg gratings (FBGs) as the wavelength comb filter. PDL is generated and controlled by different polarization angles between the polarization state of each lasing line and the optical fiber polarizer in the laser cavity. The PDL modulation balances the difference between the total loss and the wavelength-dependent lasing gain. The relations among gain, loss, and laser output power under different PDL conditions are numerically analyzed on the basis of a simplified Giles model in an EDF laser system. Results show that multi-wavelength lasing lines can be built up by properly tuning the PDLs in different wavelengths. The amount of lasing lines can be switched by changing the PDL intensity in a certain wavelength. In an experiment, the PDL in that certain wavelength is modulated by utilizing four polarization controllable elements, each of which includes an FBG and a corresponding polarization controller (PC). One PC is used to control the polarization state of the reflected lasing line on the center wavelength of the FBG. A four-wavelength individually switchable EDF laser system is demonstrated by utilizing this wavelength switchable method, in which the switching operation for the single-, dual-, triple-, and four-wavelength laser output is verified. The experimental results are consistent with the theoretical results. All wavelength switching operations are conveniently controlled by merely adjusting the PCs. This simple structure and flexible wavelength switchable operations show that this multi-wavelength EDF laser has great potential in practical applications.