Add/drop applications in fiber ring networks based on a reconfigurable optical add/drop multiplexer in a re-circulating loop

A periodic add/drop system in a fiber ring network was investigated using a reconfigurable optical add/drop multiplexer (ROADM) in a re-circulating fiber loop. After seven cascaded add/drop nodes at every 150 km along the transmission, at bit error ratio (BER) equals to 10⁻⁹ and data rate of 10 Gbps, we observed a 2.5 dB power penalty for the passing through channels with 1050 km transmission distance, and 0.3 dB sensitivity penalty variation for the periodic add/drop channels at every 150 km, respectively.     

Flexible broadcasting and multicasting in 4λ × 10 Gb/s AOPR TWDM PON system

In this letter, we propose a new architecture of Time Wavelength Division Multiplexing Passive Optical Network (TWDM PON) system to support dynamic multi wavelength allocation (DMWA) in both upstream and downstream directions using an integrated semiconductor optical amplifier (SOA) and arrayed waveguide grating (AWG) with multi wavelength select continuous wave (CW) pump probe signal module. The significance of this architecture is the flexible routing function with the capability of multicasting and broadcasting between multiple optical line terminal (OLT) PON port with multiple optical distribution network (ODN) link using a new wavelength tuning free (WTF) OLT transmitter module to eliminate wavelength tuning delay in downstream signal utilizing multicasting Cross Gain Modulation (XGM) wavelength conversion. The experimental results show that 4λ × 10-Gb/s TWDM PON system can be used to connect 4096 users with the conventional fixed wavelength OLT transceivers with 36 dB link loss.     

Optical implementation of (3, 3, 2) regular rectangular CC-Banyan optical network

CC-Banyan network plays an important role in the optical interconnection network. Based on previous reports of (2, 2, 3) the CC-Banyan network, another rectangular-Banyan network, i.e. (3, 3, 2) rectangular CC-Banyan network, has been discussed. First, according to its construction principle, the topological graph and the routing rule of (3, 3, 2) rectangular CC-Banyan network have been proposed. Then, the optically experimental setup of (3, 3, 2) rectangular CC-Banyan network has been designed and achieved. Each stage of node switch consists of phase spatial light modulator (PSLM) and polarizing beam-splitter (PBS), and fiber has been used to perform connection between adjacent stages. PBS features that s-component (perpendicular to the incident plane) of the incident light beam is reflected, and p-component (parallel to the incident plane) passes through it. According to switching logic, under the control of external electrical signals, PSLM functions to control routing paths of the signal beams, i.e. the polarization of each optical signal is rotated or not rotated 90° by a programmable PSLM. Finally, the discussion and analysis show that the experimental setup designed here can realize many functions such as optical signal switch and permutation. It has advantages of large number of input/output-ports, compact in structure, and low energy loss. Hence, the experimental setup can be used in optical communication and optical information processing.     

Hybrid buffering architecture for packet contention resolution of an optical packet switch

Packet contention is a major issue in optical packet switching network and it is not a trivial task to resolve due to lack of optical RAM technology. In order to resolve contention optical buffering approach is used using fiber delay lines (FDLs). Yet there is a heavy packet loss rate due to unavailability of output port and free FDLs. This paper proposes a hybrid buffering architecture using feed-forward and feedback shared FLDs to resolve packet contention resolution of an optical packet switch. Feed-forward FDLs are used as primary buffer and feedback FDLs are implemented as supplementary buffer. Simulation result shows that proposed hybrid buffering switch achieves packet loss rate between 10⁻¹ and 10⁻² at heavy traffic load (ρ = 0.9) for a 32 × 32 switch using different FDL length.     

Optical 3R regeneration of 40 Gbit/s degraded data signals

A 40 Gbit/s optical 3R regenerator is proposed and demonstrated. The 3R regenerator consists of a dual-ring injection mode-locked fiber ring laser as the clock recovery module and an electroabsorption modulator (EAM) as the decision gate. The clock recovery module extracts the optical short pulse clock with low timing jitter from degraded 40 Gbit/s optical data streams, while the decision gate restores their signal quality. A numerical model describing the cross-absorption modulation effect in a bulk EAM is developed to explore the operating conditions, such as bias voltage, pump signal power. The timing jitter tolerance for the EAM optical gate is also investigated. Significantly improvement of BER is obtained from 40 Gbit/s RZ signals which are degraded by polarization mode dispersion or chromatic dispersion.     

Improvement of switching properties and cascadability of an ultra-fast reconfigurable optical crosspoint switch matrix using DPSK payloads

In this paper, we demonstrate mitigation of pattern-induced degradation in an optical crosspoint switch (OXS) matrix by utilizing differential phase shift keying (DPSK) modulation format. We experimentally demonstrate 4 × 4 unicast optical packet switching and dynamic reconfiguration for 4-channel, 200 GHz spacing of RZ-DPSK payloads. Reconfigurable time as fast as 2 ns is achieved owing to the optimized control circuit and device fabrication. The power and wavelength dependence are obtained for the RZ-DPSK payload. We also investigate the cascadability of the OXS based on re-circulating loops. Due to the great suppression of the pattern effect in OXS, DPSK has shown dramatical improvement of switching properties compared to conventional ON-OFF keying (OOK) signal. The DPSK payload can outperform OOK for 3.2 dB after 9 hops optical switching.     

Demonstration of an all-optical switching operation using an optical fiber grating coupler

An optical fiber grating coupler (FGC) is a fused optical fiber coupler with a tapered region in which refractive index-modulated gratings are written. In the FGC, the light with specific wavelength satisfying the Bragg condition of the grating can be dropped to one output port and other lights are transmitted to another output port when lights with various wavelengths are launched into the input port. The FGC can operate as an all-optical switch by controlling the Bragg wavelength of the grating using a third order nonlinear optical effect caused by a control light that are launched with a signal light. In this paper, an all-optical switching operation due to a third order nonlinear optical effect in an FGC is first demonstrated for a signal light with 1.55 μm-wavelength to be changed from one port of the FGC to another one by the 720 W peak of a control light from a Nd:YAG laser with 1.06 μm-wavelength. The switching efficiency obtained was 7%. It was clarified that a longer pulse length of the control light compared to the grating length is required to obtain a large Bragg wavelength shift for the switching. It was also clarified that the Bragg wavelength shift is caused by a third order nonlinear effect and a photothermal effect. A contribution of the photothermal effect was estimated. We also estimated the switching efficiency for pump power in the FGC switch.     

Design and optimization of novel ultra-compact SOI multimode interference optical switch

In this paper, an ultra-compact 3 × 3 SOI multimode interference optical switch is presented. There is only one hyperbolic multimode waveguide in the switch. By changing the refractive index of one or two parts within the hyperbolic multimode waveguide, the switch can realize on and off functions between any pair of input and output ports. The various states of the switch were simulated and analyzed using the finite difference beam propagation method (FD-BPM), the structure parameters of the switch were also designed and optimized. The optimized switch has excellent properties and the whole size of the switch is less than 4 mm.     

Multi-degree ROADM based on wavelength selective switches: Architectures and scalability

Multi-degree implementations of the reconfigurable optical add-drop multiplexer (ROADM) are analyzed in terms of in-band crosstalk performance with an emphasis on the reduction in the number of wavelength selective switches used in the module. It is shown experimentally that an 8-degree ROADM using the wavelength selective switches for channel adding and optical splitters for channel dropping performs closely to one that uses switches for both operations. A new modular architecture based on the wavelength selective switches is proposed for implementations applicable to large degree nodes. Performance analysis of this architecture indicates node scalability to 256 degree with crosstalk-induced power penalties below 0.5 dB.     

Design of full-bandwidth ROADM based on MMI and MRRs

In this paper, we propose a full-bandwidth reconfigurable optical add/drop multiplexer (ROADM) equipped with multiplexer/demultiplexer (MUX/DEMUX) and switch array. Based on the pairwise multimode interference (MMI) and side-ported MMI, the full-bandwidth MUX/DEMUX is achieved. The switch array based on microring resonators (MRRs) can achieve the function of the wavelength selective switches. By designing the second-order series-coupled MRR structure, using thermo-optic effect, the switch is able to get a switching ratio above 16 dB. The proposed ROADM system shows good performance for application in dynamic optical networks.     

Simultaneous implementation of all-optical OR and AND logic gates for NRZ/RZ/CSRZ ON-OFF-keying signals

An all-optical scheme for simultaneously realizing OR and AND logic gates based on three-input four-wave mixing (FWM) arising in a single semiconductor optical amplifier (SOA) is proposed and demonstrated. It has the ability to process not only conventional non-return-to-zero-ON-OFF-keying (NRZ-OOK) and return-to-zero-OOK (RZ-OOK) formats but also carrier-suppressed return-to-zero-OOK (CSRZ-OOK) format signals. Firstly, the performance of 40 Gb/s logic operation is numerically evaluated by a comprehensive dynamic SOA model considering three input signal induced FWM effect. Then, 10 Gb/s experimental demonstrations with clear waveforms and high extinction ratios (ERs) further verify the logic integrity of this scheme. Thus, the OR and AND logic gates simultaneously achieved within a single logic unit is compact and cost-effective for future optical signal processing applications.     

Investigation of wavelength division multiplexing ring network topology to enhance the system capacity

In this paper, we have investigated the wavelength division multiplexed (WDM) system using ring network topology. This network is used to increase the capacity with eight optical add/drop multiplexers (OADMs) by using dispersion compensating fiber and semiconductor optical amplifier (SOA) to achieve a distance up to 1600 km. It is observed that network shows the acceptable results at 15 Gbps data rate with 100 GHz channel spacing. The OADM nodes are also varied to investigate the network performance in the term of BER and Q-factor.     

Optical alignment tolerances in double-side irradiated self-written waveguide-induced fiber arrays packages

In this paper, we present our experimental study on the optical alignment tolerance between the couplings of single-mode fibers (SMFs) connected with a double-side irradiation-induced self-written waveguide (SWW). The study firstly focuses on the coupling of two SMFs and then on the two fiber arrays (FAs) for parallel optical communication. The SWW was formed in dye-dispersed epoxy materials by the photopolymerization technique. Rhodamine 6G dye was dispersed in epoxy, which is commonly used in the photonic packaging industry as a bonding adhesive. Using double-side irradiated SWW, we found the alignment tolerance for such optical interconnect to relax significantly. All the formed SWWs were evaluated in terms of optical loss. In our study, up to 4 µm misalignment tolerance was allowed for only 1 dB loss penalty. In addition, the optical interconnect formed by this technique was also able to tolerate up to ± 10 µm lateral shift with only 1 dB extra loss. The wavelength-dependent loss (from 1520 to 1610 nm) and polarization-dependent loss were less than 0.4 dB. The double-side irradiated SWW-induced couplings between two FAs also provided low optical loss. They were found to be less sensitive to temperature changes, and no significant distortion in the digital signal transmission test was observed. We believe that the findings are useful and applicable to other dye-dispersed epoxy material systems for relaxing the alignment tolerance of the optical interconnects in various photonic packaging situations.     

Study on dense multi-fiber backplane for a large-scale switching system

Dense multi-fiber backplane has great prospect in large-scale multi-rack connection system and optical Routers next generation as connecting equipment. The operation principle of multi-fiber backplane is presented in this paper. In order to conquer the difficulties in producing and upgrading the backplane with dense multi-fibers, starting from the traditional crossbar structure in switching backplane, an original method for optimizing the configuration of fiber circuit on backplane is adopted, and applied to the preparation of backplanes. An experimental setup and flow of producing are also proposed to predigest the process of producing. The advantage of this proposed method in maintaining and upgrading the backplane is proved through the achievement of two sample backplanes with 8(×8) × 8(×8) and 12(×8) × 8(×12) configuration and their testing results.     

A 1 × 2 optical switch using one multimode interference region

A 1 × 2 optical switch using only one multimode interference (MMI) region is designed and demonstrated in GaAs/AlGaAs. This design makes a single MMI region works as MMI coupler using paired interference at “off” state and symmetric interference at “on” state. By injecting a current of 110 mA, the measured on/off ratio and crosstalk are 23 dB and 33 dB, respectively in the demonstrated device with GaAs/GaAlAs.     

Performance enhanced down-stream signalling for next generation long-reach 10 Gbit/s passive optical networks

In this paper, we have analyzed the signal processing methods both in digital and optical domain to enhance the transmission performance of downstream signalling in long reach passive optical networks (LR-PONs). The impact of non-linear (NL) equalization through signal processing, i.e. Volterra Equalization (VE), Digital Backpropagation (BP) and Optical Phase Conjugation with Non-linearity Module (OPC-NM) is investigated, in 10 Gbit/s (XG) DP-QPSK long-reach wavelength division multiplexed (WDM) PONs without midspan repeaters over 120 km standard single mode fibre (SMF) link for down-stream signals. Due to the compensation of optical Kerr effects, the sensitivity penalty is reduced to 2 dB by BP algorithm, 1.5 dB by VE algorithm and 2.69 dB by OPC-NM. Moreover, with the implementation of NL equalization technique we are able to get the transmission distance of 126.6 km SMF for the 1:1024 split-ratio at 5 GHz channel spacing in the non-linear region. Furthermore, the concept of super passive optical network (S-PON) is also evaluated, which involves a repeater stage consisting of optical amplifiers, to study the feasibility for receiver side signal processing and simplification.     

Research on OCDMA-based PON monitoring technologies

An optical fiber fault location method based on OCDMA coding is proposed, which may locate branch optical fiber fault at local side. The method expands dynamic range through coding gain without influencing event distinction degree. Through simulation, it indicates that dynamic range of the method may support optical fiber fault detection in PON with branching ratio of 1:16 and transmission distance of 20 km, while the distinction degree is about 10 cm.     

Fabrication of the slanted electrode matrix on tilting 4.5° (1 1 1) silicon

The slanted low electrode matrix is designed and fabricated on one tilting 4.5° (1 1 1) silicon wafer to reduce the actuating voltage of 8×8 micro-electromechanical systems (MEMS) optical switch matrix. Due to compact size of the upper electrode chip and (1 1 1) silicon anisotropic etching in KOH solution, photomask is designed which is to fabricate the slanted low electrode matrix that can be matched with the upper electrode chip and every slanted low electrode has enough space for actuating cantilever. The experimental results show that all of the applied voltages for the full range of actuating micromirrors of 8×8 MEMS optical switch matrix are in the range of 67.2±0.5 V. It is demonstrated that the fabricated slanted low electrode matrix has good consistency and every slanted low electrode can be precisely aligned with one-to-one corresponding upper electrodes.     

Dynamic-channel-equalizer using in-line channel power monitor and electronic variable optical attenuator

We propose and demonstrate a polarization-insensitive dynamic-channel-equalizer (DCE) for compensating erbium-doped-fiber-amplifier (EDFA) amplified signals after dynamic optical add/drop. The DCE can be monolithically integrated on silicon-on-insulator (SOI) platform and is potentially low cost and compact. The DCE can compensate complicated gain slope shape, which may be generated in cascaded EDFAs or deliberate channel add/drop, based on individual channel equalization. Fifteen-decibel receiver sensitivity improvement at 10 Gb/s bit-error-rate (BER) measurement of 10⁻⁹ was achieved in the compensated channel by removing cross-gain-modulation generated by neighboring channel add/drop.     

A novel frequency sextupling scheme for optical mm-wave generation utilizing an integrated dual-parallel Mach-Zehnder modulator

A novel scheme is proposed for frequency sextupling mm-wave generation based on a laser and an integrated dual-parallel Mach-Zehnder modulator (MZM) without optical filter. Theoretical analysis is presented to suppress the undesired optical sidebands for the high quality generation of frequency sextupling mm-wave signal. The performance of the proposed scheme is evaluated by simulations. Utilizing the integrated MZM consisted of two sub-MZMs with extinction ratio of 30 dB, the optical sideband suppression ratio (OSSR) is as high as 29.9 dB and the radio frequency spurious suppression ratio (RFSSR) exceeds 24 dB without any optical or electrical filter. The impact of the nonideal RF driven voltage and phase difference of RF driven signal applied to two sub-MZMs of the integrated MZM on OSSR and RFSSR is discussed and analyzed. After transmission over fiber, the generated optical mm-wave signal demonstrates good performance. Furthermore, the performance of two cases for the proposed scheme is also compared.