Novel optical add-drop multiplexer for wavelength-division-multiplexing networks

Two novel optical add-drop multiplexer (OADM) with different self-healing functionalities for reliable wavelength-division-multiplexing networks are presented and demonstrated. Single or multiple failure-link traffics can be bi-directionally restored without the need for wavelength conversion or extra backup fiber links. To evaluate the performances of the proposed structures, a 77-channel CATV signal is experimentally transmitted with a favorable carrier-to-noise ratio (CNR), composite second-order (CSO) and composite triple beat (CTB) performances.     

Fully reconfigurable optical add-drop multiplexer based on parallel configuration using Mach-Zehnder module

Reconfigurable optical add-drop multiplexer (ROADM) with the ability of dynamic configuration will be one of the core equipment for the future optical transport networks. This paper proposes an effective scheme for fully ROADM with parallel modularized structure and ability of upgrading. Each module consists of a Mach-Zehnder interferometer based on fiber Bragg grating (FBG), a 1 × 2 optical switch and a Y-model combiner. Optical signal with single wavelength or multiwavelength could be dropped or added at one drop port or add port by configuring the optical switch in each module. The proposed ROADM with four-stage parallel connection is designed and experimentally investigated to prove its performance and advantage in dynamic selection of the wavelengths and upgrading. It is also showed that this ROADM can also reduce the ununiformity of power at output port and drop port to improve the optical signal to noise ration (OSNR) of the whole system.     

Tunable optical add-drop multiplexer based on long-period fiber gratings for coarse wavelength division multiplexing systems

We propose and experimentally demonstrate a voltage-controllable add-drop multiplexer with a tunable coupler based on long-period fiber gratings (LPFGs). The tunable coupler is based on cladding mode coupling between two parallel LPFGs with divided coil heaters, which controls the resonant wavelength positions of the two LPFGs. The wavelength tunability of the tunable coupler is measured to be -0.45 nm/degrees C in the temperature range from 20 to 120 degrees C. The large tuning range of optical signals (approximately 50.54 nm) from 1502.32 to 1552.86 nm, which covers both the short (S) and the conventional (C) bands, is achieved. The channel isolation is as high as approximately 40 dB. It has several advantages, including a broad tuning range of wavelength in both the S- and C-bands, high channel isolation, no backreflection, and so on.     

All-fiber add-drop filters based on microfiber knot resonators

We demonstrate an all-fiber add-drop filter composed of a microfiber knot (working as a resonator) and a fiber taper (working as a dropping fiber). The dropping taper can be either parallel or perpendicular to the input port of the filter. A quality factor (Q factor) of 13,000 is obtained from a parallel-coupling 308 microm diameter microknot add-drop filter with a free spectral range (FSR) of 1.8 nm. A Q factor of approximately 3300 is obtained from a cross-coupling 65 microm diameter microknot add-drop filter with a FSR of 8.1 nm. This device is particularly easy to fabricate and to connect to fiber systems.     

Compact four-channel reconfigurable optical add-drop multiplexer using silicon photonic wire

We designed and fabricated a four-channel reconfigurable optical add-drop multiplexer based on silicon photonic wire waveguide, which is controlled through the thermo-optic effect. The effective footprint of the device is about 1000 × 500 μm². The minimum insertion loss including the transmission loss and coupling loss is about 10.7 dB. The tuning bandwidth is about 17 nm, the average tuning efficiency about 6.11 mW/nm and the tuning speed about 24.5 kHz.     

Promising compact wavelength-tunable optical add-drop multiplexer in dense wavelength-division multiplexing systems

We design and model a highly compact and tunable optical add-drop multiplexer (OADM) device that consists of long-period gratings and piezoelectric ceramic fiber stretchers. The proposed OADM shows that 50 dense wavelength-division multiplexing channel signals can be selected in the wavelength range from 1526.25 to 1563.75 nm with 0.75-nm channel spacing, which covers the whole C-band gain spectrum of an erbium-doped fiber amplifier. The cross talk between channels is less than -39 dB, and the total insertion loss of the device is approximately 0.24 dB, which includes the splicing losses, the mode mismatching loss, and the expected losses in the two side-by-side coupled fibers.     

An integrated reconfigurable optical add-drop multiplexer based on using an opto-VLSI processor and a 4-f imaging system

A novel integrated reconfigurable optical add-drop multiplexer (ROADM) structure is proposed and demonstrated experimentally. The ROADM employs an interface substrate that enables the integration of a fiber-lens collimator array and an Opto-VLSI processor to realise a 4-f imaging system through optical beam steering. Phase hologram optimization of the Opto-VLSI processor is investigated, for maximizing the number of wavelength channels while keeping adequate insertion loss and crosstalk levels. Experimental results are shown, which demonstrate a broadband operation and the principle of the ROADM with crosstalk of less than −30.5 dB and insertion loss of less than 6 dB for the drop and through operation modes.     

Variable bandwidth of dynamic add-drop filters based on coupling-controlled microdisk resonators

Dynamic add-drop filters with variable bandwidth are demonstrated on microelectromechanical-system (MEMS)-actuated microdisk resonators for what is believed to be the first time. The tuning mechanism is based on a variable power coupling ratio that is controlled by varying the gap spacing between the waveguide and the microdisk through MEMS actuators. The results show wavelength switching with an extinction ratio of 20 dB and a tunable bandwidth ranging from 12 to 27 GHz. These dual functions were realized using the device with the operation voltage varying between 0 and 35 V.     

Sub-nanosecond optical switch based on silicon racetrack resonator

<正>We experimentally demonstrate a small-size and high-speed silicon optical switch based on the free carrier plasma dispersion in silicon.Using an embedded racetrack resonator with a quality factor of 7400,the optical switch shows an extinction ratio exceeding 13 dB with a footprint of only 2.2×10~(-3)mm~2.Moreover,a novel pre-emphasis technique is introduced to improve the optical response performance and the rise and the fall times are reduced down to 0.24 ns and 0.42 ns respectively,which are 25%and 44%lower than those without the pre-emphasis.     

一种新颖的由分插复用器构成的双向WDM网络

提出了一种新颖的双向波分复用网络结构,由多个分插复用器通过单模光纤连接而成。其中,分插复用器是基于声光效应和光纤布拉格光栅的反射特性制成的。由理论分析和实验得到的结果表明,该器件可实现一定数量信道的光信号的双向分插复用。这种双向波分复用光网络可按要求进行设计,使具有某种特征波长的光信号在设定位置的分插复用器中实现分插复用,使其按所设计的光路在波分复用网络中传输。     

Polarization-independent rapidly tunable optical add-drop multiplexer utilizing non-polarizing beam splitters in Ti:LiNbO3

A polarization-independent four-port wavelength-tunable optical add drop multiplexer (OADM) that utilizes non-polarizing relaxed beam splitters has been analyzed and demonstrated in Ti:LiNbO₃ at the 1530 nm wavelength regime. The design utilizes an asymmetric interferometer configuration with strain induced index grating for polarization coupling along its arms that are shifted in position relative to each other. Experimental results of the filter response agree with theoretical predictions. Electrooptic tuning over a range of 15.7 nm at a rate of 0.08 nm/V has been measured. A temporal response < 46 ns to a 20 V step change in tuning voltage has been demonstrated. Fiber-to-fiber insertion loss is ~ 6.5 dB.     

Ultracompact plasmonic racetrack resonators in metal-insulator-metal waveguides

Among various plasmonic waveguides, the metal-insulator-metal (MIM) type is the most promising for true subwavelength photonic integration. To date, many photonic devices based on MIM waveguides have been investigated, including resonators. However, most of the reported MIM ring resonators suffer from low extinction ratios and the reasons are unexplored in the literature. In this paper, we present a comprehensive analysis of the underlying causes of the low performance of MIM ring resonators, and give the analytical transmission relation for a universal all-pass ring resonator with coupling loss. Based on the analysis we propose plasmonic racetrack resonators in MIM waveguides and show that the performance can be greatly improved.     

Long-period-grating-assisted optical add-drop filter based on mismatched twin-core photosensitive-cladding fiber

A noninterferometric optical fiber add-drop channel filter based on a mismatched twin-core photosensitive-cladding fiber and long-period fiber grating is demonstrated. With assistance from the fiber grating, co-directional spectrally selective cross coupling between the two cores can be realized with an efficiency of 90%.     

Ring fiber resonators based on fused-fiber grating add-drop filters:application to resonator coupling

We introduce a fiber ring optical resonator based on adiabatic fused-fiber grating couplers. The coupling of a through fiber to the resonator is controlled by the strength of the fiber Bragg gratings. By using two of these couplers and incorporating erbium-doped (ED) fiber in the ring, we control the internal loss of the ring by pumping the ED fiber. The transmission spectra of the through port and the drop port of a four-port configuration, a ring coupled to two waveguides, are measured. We show that the loss/coupling ratio of the ring-fiber system can be changed and thus that the transmission properties of the fiber can be controlled.     

Reconfigurable optical multiplexer based on liquid crystals for polymer optical fiber networks

In this work, different novel 3×1 multiplexer structures for being used in polymer optical fiber networks are proposed. Designs are compact, scalable, and of low consumption, capable of operating in a large wavelength range simultaneously 660, 850, and 1300 nm, due to the use of nematic liquid crystal cells. Light that comes from each input port is handled independently and eight operation modes are possible. Control electronics has been made using a programmable integrated circuit. Electronic system makes available the managing of the optical stage using a computer. An additional four optical sensors have been included for allowing the optical status checking. Finally, a polarization independent multiplexer has been implemented and tested. Insertion losses less than 4 dB and isolation better than 23 dB have been measured. In addition, 30-ms and 15-ms setup and rise times have been obtained. The proposed multiplexer can be used in any polymer optical fiber network, even in perfluorinated graded index one, and it can be specially useful in optical sensor networks, or in coarse wavelength division multiplexing networks.     

Experimental investigation on submicron rib waveguide microring/racetrack resonators in silicon-on-insulator

In experiment, characteristics of silicon microring/racetrack resonators in submicron rib waveguides have been systematically investigated. It is demonstrated that only a transverse-electric mode is guided for a ratio of slab height to rib height h/H = 0.5. Thus, these microring/racetrack resonators can only function for quasi-transverse-electric mode, while they get rid of transverse-magnetic polarization. Electron beam lithography and inductively coupled plasma etching were employed and improved to reduce sidewall roughness for low propagation loss and high performance resonators. Then, the effects of waveguide dimensions, coupling region design, waveguide roughness, and oxide cladding for the resonators have been considered and analyzed.     

Experimental demonstration of plasmonic racetrack resonators with a trench structure

We fabricated and investigated a plasmonic racetrack resonator with a trench structure. Trench channel plasmon polaritons excited by end-fire coupling at a wavelength of 633 nm are observed in the fabricated racetrack resonator. The racetrack resonator also worked as a plasmonic racetrack resonator. The experimental and simulation results of the electric field distributions are in good agreement.     

Two-dimensional optical ring resonators based on radial Bragg resonance

A Bragg-reflection-based ring resonator is proposed and analyzed. Closed-form expressions for the field and dispersion curves for radial Bragg gratings and photonic bandgap crystals are derived. The required gratings exhibit a chirped period and a varying index profile. Small bending radii and strong control over the resonator dispersion are possible by the Bragg confinement. Large free spectral range and low radiation loss are predicted theoretically.     

Novel waveguide components based on complementary electrically small resonators

In this paper, we present a new class of waveguide components based on the use of complementary electrically small resonators etched on metallic sheets. We first show a rectangular-to-circular waveguide transition that allows to effectively match waveguides with different cross-sections and to transform the linearly polarized TE₁₀-mode of a rectangular waveguide into a circularly polarized TE₁₁-mode of a circular waveguide. Then, using similar structures, we present the design and the numerical results of two power dividers and of an orthomode transducer. All these components, employing only thin metallic sheets with properly shaped slits, can be integrated in waveguide transmission systems without increasing their space occupancy. A proper set of full-wave numerical simulations proves the validity of the proposed approach.