Optical Packet Switching System Research Articles

Electronically Tunable Distributed Feedback (DFB) Laser on Silicon

AbstractAn electronically tunable distributed feedback (DFB) laser heterogeneously integrated on a silicon photonics platform is experimentally demonstrated. Tuning is achieved through carrier injection into the tuning layer of a tunable twin‐guide III–V membrane on silicon. A 2 nm continuous tuning range is achieved with a single tuning current. Continuous‐wave single‐mode laser operation with a side‐mode suppression ratio larger than 44 dB across the tuning range is obtained. Measured wavelength switching times are on the order of 3 ns and non‐return‐to‐zero on‐off keying direct modulation at 12.5 Gbit s−1 is readily achieved. This work can be a major advance toward the realization of optical burst or packet switching systems for future data center networks.

12.5 Gbit/s discretely tunable InP-on-silicon filtered feedback laser with sub-nanosecond wavelength switching times.

A heterogeneously integrated InP-on-silicon fast tunable filtered feedback laser is demonstrated. The laser device consists of a main Fabry-Pérot cavity connected to an integrated arrayed waveguide grating of which the outputs form external cavities in which semiconductor optical amplifiers can be switched to provide single-mode operation and tunability. The laser can operate at four different wavelengths whereby switching between each wavelength channel is done within one nanosecond. For each wavelength channel 12.5 Gbit/s NRZ-OOK direct modulation is demonstrated. The combination of fast wavelength switching with straightforward wavelength control and high-speed direct modulation characteristics make the demonstrated laser structure very attractive for use in optical packet or burst switching systems.

Review of contemporary literature on burst assembling and routing strategies in OBS networks

In the course of recent years, a lot of research has been directed in the ranges of optical packet switching and optical burst switching (OBS). This examination has been inspired by the requirement for procedures that are equipped for supporting the requesting prerequisites of developing dynamic high-transfer speed applications in an adaptable and effective way. In this paper we have undertaken the critical and mandatory factors of OBS such as (1) assembling the bursts, (2) routing (3) resource (such as transmission channels) scheduling and (4) burst segmenting for optimal transmission). Consequently the current research is focusing on these both of dissimilar variables of OBS and putting endeavors to contribute ideal ways to assemble, route, schedule or segment. This manuscript reviewed the nomenclature of the Optical Burst Switching Networks where fundamental ideas are examined and the aim is to identify the difficulties and strengths for optical packet and burst switching systems. This audit has been inspired by the requirement for methods that are equipped for supporting the future data transmission necessity of cutting edge applications and administrations of Internet Protocol systems. The authors have examined the fundamental ideas of OBS worldview and laid out issues identified with OBS systems. The future challenges that are still limiting the performance of the present contributions are told subsequently evincing the scope for future research.

Packets Buffering Enhancement with Hybrid Coding Labels for Virtual Optical Memory

For the practical deployment of optical packet switching (OPS) system, realizing all-optical buffering is a critical issue. In this paper, we present a hybrid labelling scheme based on optical code-division multiplexing (OCDM) over generalized multi-protocol label switching (GMPLS) network. The virtual optical memory is implemented by assigning queuing packets with different coded-WDM labels. The proposed hybrid labels combine the advantages of wavelength-division multiplexing (WDM) with spectral-amplitude-coding (SAC) OCDM. Due to the cyclic-shift property of arrayed-waveguide grating (AWG) and maximal-length sequence (M-sequence) codes, blocks of label generating and processing in node organization can be built in low complexity. Furthermore, utilizing hybrid coding technique in the buffering node increases the efficiency of label generating and processing. Derivation of the probability of packet missing is done to quantify the buffering performance of virtual optical memory. Simulation results show that the hybrid-coded labels, as compared to the conventional OCDM labels, are able to buffer the data packets with a relatively low probability of packet missing under similar label length.

Research of optical short pulse source with tunable repetition rate and ultra-low timing jitter

The highly stable optical short-pulse generator with high repetition rate is widely applied in many fields of optical communications, such as optical packet switching systems, high-speed analog-to-digital converter systems, wavelength division multiplexing networks, high-speed optical sampling systems and optical time division multiplexing networks. The optical short-pulse generator which is adopted in such systems mentioned above should possess high stability, low timing jitter, the tunability of the repetition-rate, and narrow pulse width. So far, most of the optical short pulses have been generated from the actively mode-locked lasers and the phase-modulated continuous wave lasers. However, both of the two methods require an additional microwave signal source. Consequently, the stability of such an optical short-pulse generator is strictly limited by the phase noise and stability of the additional microwave signal source. Since the concept of an optoelectronic oscillator which includes the generation of low noise optical pulses together with an ultra-low phase noise microwave signal was proposed by Yao in 1996, the optical short-pulse generator based on the optoelectronic oscillator has attracted much attention in recent years. According to this approach, Lasri demonstrated a novel, self-starting optoelectronic oscillator based on an electro-absorption modulator in a fiber-extended cavity for generating an optical pulse stream with high-rate and ultra-low jitter capabilities in 2003. In the scheme, the repetition rate of the generated optical pulses is 10 GHz, and the phase noise is-115 dBc/Hz at 10 kHz. Devgan demonstrated an optoelectronic oscillator by using a gain-switched vertical-cavity surface-emitting laser in a fiber-feedback configuration in 2006. The structure can generate a 2-GHz optical pulse stream with 750-fs timing jitter (over 100 Hz-10 MHz range). In the present paper, a novel optical short-pulse generator with tunable repetition rate and ultra-low timing jitter based on optoelectronic oscillator is demonstrated. The optoelectronic oscillator system can generate the microwave signal with ultra-low phase noise. The continuous wave light directly modulated by this microwave signal is phase modulated twice, and then the optical pulses with remarkable chirping rate are achieved. By optimizing the length of the dispersion compensating fiber, the optical pulses are further compressed. In this experiment, by utilizing a YIG tunable filter, the high-quality and tunable microwave signal within 8-12 GHz is achieved, which demonstrates the tunability of the repetition rate of the optical pulses. When the frequency of the microwave signal (i.e., the repetition rate of the optical pulses) is 9.6 GHz, the measured pulse width and the phase noise are 3.7 ps and-130.1 dBc/Hz at 10 kHz, respectively. Therefore, the timing jitter of the short optical pulse is calculated to be 60.1 fs (over 100 Hz to 1 MHz).

Application of a novel SSFBG-based single-input multiple-output encoder/decoder to optical packet switching

We propose a novel superstructured fiber Bragg grating (SSFBG) based single-input multiple-output (SIMO) en/decoder, which can simultaneously process a group of independent optical codes with a specific permutation and combination of code patterns and spatially separate encoded and decoded signals into different optical paths. The number of optical codes processed by the SIMO en/decoder can be flexibly changed. We theoretically and experimentally investigate the coding performance of the SIMO en/decoder and discuss the unique features of the proposed device. In the experiment, we employ the SIMO en/decoder for optical label processing in an optical-code based optical packet switching system with the data rate of 10 Gbit/s and the packet rate of 312.5 MHz. The four-SSFBG based SIMO en/decoder are capable of simultaneously generating/recognizing four 31-chip 640 Gchip/s optical code based labels and distribute the labels into four designated destinations.

Dimensioning shared-per-node recirculating fiber delay line buffers in an optical packet switch

Optical buffering based on fiber delay lines (FDLs) has been proposed as a means for contention resolution in an optical packet switch. In this article, we propose a queuing model for feedback-type shared-per-node recirculating FDL optical buffers in asynchronous optical switching nodes. In this model, optical packets are allowed to recirculate over FDLs as long as the total number of recirculations is less than a pre-determined limit to meet signal loss requirements. Markov Modulated Poisson Process (MMPP)-based overflow traffic models and fixed-point iterations are employed to provide an approximate analysis procedure to obtain blocking probabilities as a function of various buffer parameters in the system when the packet arrival process at the optical switch is Poisson. The proposed algorithm is numerically efficient and accurate especially in a certain regime identified with relatively long and variably-sized FDLs, making it possible to dimension optical buffers in next-generation optical packet switching systems.

Number of tunable wavelength converters and internal wavelengths needed for cost‐effective design of asynchronous optical packet switching system with shared or output fibre delay line buffer

Optical packet switching (OPS) is being considered as one of the switching technologies for a future optical internet. For contention resolution in an optical packet switching (OPS) system, the wavelength dimension is generally used in combination with a fibre delay line (FDL) buffer. In this study, the authors propose to reduce the number of tunable wavelength converters (TWCs) by sharing TWCs for cost-effective design of an asynchronous OPS system with a shared or an output FDL buffer. Asynchronous and variable-length packets are considered in the OPS system design. To investigate the number of TWCs needed for the OPS system, an algorithm is proposed, which searches for an available TWC and an unused internal wavelength, as well as an outgoing channel. This algorithm is applied to an OPS system with a shared or an output FDL buffer. Also, the number of internal wavelengths (i.e. the conversion range of the TWC) needed for an asynchronous OPS system is presented for cost reduction of the OPS system.

FPGA-Based Label Processor for Low Latency and Large Port Count Optical Packet Switches

We present a field-programmable gate array (FPGA)-based label processor for in-band optical labels with a processing time independent of the number of label bits. This allows for implementing an optical packet switching architecture that scales to a large port count without compromising the latency. As a proof of concept, we have employed an FPGA board with 100 MHz clock to validate the operation of the label processor in a 160 Gb/s optical packet switching system. Experimental results show successful three label bits processing and 160 Gb/s packets switching with 1 dB power penalty and 470 ns of latency. Projections on the label processor performance by using more powerful FPGAs indicate that 60 label bits ( optical addresses) can be processed within 31 ns.

Nonlinear Optical Signal Processing in Optical Packet Switching Systems

This paper discusses nonlinear optical signal processing employed in optical packet switching systems. Nonlinear optical signal processing provides optical label (header) recognition, optical switching, wavelength conversion, and time buffering with typically higher capacity, lower latency, and lower power consumption than electronic counterparts. In order to provide diverse signal processing functions, large-scale integration of nonlinear optical signal processing devices is essential. We discuss possible future directions in optical packet switching involving nonlinear optical signal processing of optical packets with advanced data and label modulation formats.

Huge capacity optical packet switching and buffering

We demonstrate 2.56 Tbit/s/port dual-polarization DWDM/DQPSK variable-length optical packet (20 Gbit/s × 64 wavelengths × 2 polarizations) switching and buffering by using a 2×2 optical packet switch (OPS) system. The optical data plane of the OPS system was constructed of multi-connected electro-optical switches and fiber delay lines. The accumulated polarization dependent loss of each optical path in the data plane was less than 5 dB. This low-polarization-dependence OPS system enabled us to handle DWDM/DQPSK optical packets (1.28 Tbit/s/port) with time-varying polarization after transmission through 100 km fiber in the field.

Retrial Queuing Models of Multi-Wavelength FDL Feedback Optical Buffers

Optical buffers based on Fiber Delay Lines (FDL) have been proposed for contention resolution in optical packet/burst switching systems. In this article, we propose a retrial queuing model for FDL optical buffers in asynchronous optical switching nodes. In the considered system, the reservation model employed is of post-reservation type and optical packets are allowed to re-circulate over the FDLs in a probabilistic manner. We combine the MMPP-based overflow traffic models of the classical circuit switching literature and fixed-point iterations to devise an algorithmic procedure to accurately estimate blocking probabilities as a function of various buffer parameters in the system when packet arrivals are Poisson and packet lengths are exponentially distributed. The proposed algorithm is both accurate and fast, allowing one to use the procedure to dimension optical buffers in next-generation optical packet switching systems.

All-optical recognition method of double two-dimensional optical orthogonal codes-based labels using four-wave mixing

A novel all-optical label recognition method is proposed and demonstrated experimentally which is based on fiber Bragg gratings (FBGs)-based encoder/decoder and semiconductor optical amplifier (SOA). In this scheme, the optical label is firstly decoded properly, the decoded signal then generates the 1st and the 2nd order four-wave mixing (FWM) effect in different SOA, any of the frequencies achieved by the 2nd order FWM is extracted to recognize the optical label. The proposed solution can favor hardware simplicity over bandwidth efficiency in order to achieve the double two-dimensional optical orthogonal codes (2D-OOCs)-based optical label recognition in an optical packet switching (OPS) system where the bandwidth efficiency can be improved by FWM effect in SOA to achieve optical label processing and reasonable spacing of wavelengths for the payloads and optical label. The feasibility of the proposed method is validated by two experiments of the double 2D-OOCs-based optical label generation and recognition, the effect of the optical label on the payloads is also considered. These results show that the proposed method can (1) reduce effectively the code auto-correlation /cross-correlation requirements of the optical label identification and remove the cross-correlation pulses after optical decoding, (2) increase greatly the coding capacity and the number of the available optical labels, (3) improve the reliability and bandwidth efficiency of the optical label identification. The experimental results also show that the optical label has a high extinction ratio and can be operated easily.

Design of ultra compact all-optical XOR and AND logic gates with low power consumption

We propose a novel ultra-compact all-optical XOR and AND logic gates without using nonlinear optics. In order to realize these devices, we adopt photonic crystal waveguides (PCWs) based on multi-mode interference devices. Numerical results show that the operating bandwidth of the ON to OFF logic-level contrast ratio of not less than 6.79 dB is 35 nm for XOR logic gate and 9 nm for AND logic gate. Proposed logic gates have the potential to be key components for an optical packet switching system due to their small feature sizes and low power consumption.

Photonic Network Technologies for New Generation Network

In this paper, we show the recent progress of photonic network technologies for the new generation network (NWGN). The NWGN is based on new design concepts that look beyond the next generation network (NGN) and the Internet. The NWGN will maintain the sustainability of our prosperous civilization and help resolve various social issues and problems by the use of information and communication technologies. In order to realize the NWGN, many novel technologies in the physical layer are required, in addition to technologies in the network control layer. Examples of cutting-edge physical layer technologies required to realize the NWGN include a terabit/s/port or greater ultra-wideband optical packet switching system, a modulation-format-free optical packet switching (OPS) node, a hybrid optoelectronic packet switching node, a packet-based reconfigurable optical add/drop multiplexer (ROADM) system, an optical packet and circuit integrated node system, and optical buffering technologies.

A QoS optical packet switching system: architectural design and experimental demonstration [Topics in Optical Communications

Optical packet switching has been considered a prominent paradigm for future WDM networks to efficiently support a multitude of applications with diverse quality of service requirements. In this article we present the architectural design and experimental demonstration of a 10 Gb/s QoS optical packet switching system (QOPSS) for WDM networks. It embodies a set of many-to-one space switches, each of which handles the switching solely for a cluster of wavelengths. With the cluster-based optical switch design, QOPSS trades off limited statistical multiplexing gains for higher system scalability. By many-to-one, multiple packets that are carried by different internal wavelengths are scheduled to switch to the same output port but receive different delays afterward. QOPSS adopts downsized feed-forward optical buffers, yielding drastic reduction in packet loss probability in an economical manner. Significantly, through using four-wave-mixing wavelength converters at the output section, QOPSS permits optical packet preemption, thus achieving effectual QoS differentiation. The article presents both simulation and experimental testbed results to demonstrate the feasibility and superior packet loss/QoS performance of the system.

Time-Resolved $Q$-factor Measurement and Its Application in Performance Analysis of 42.6 Gbit/s Packets Generated by SGDBR Lasers

We demonstrate a novel time-resolved Q-factor measurement technique and demonstrate its application in the analysis of optical packet switching systems with high information spectral density. For the first time, we report the time-resolved Q-factor measurement of 42.6 Gbit/s AM-PSK and DQPSK modulated packets, which were generated by a SGDBR laser under wavelength switching. The time dependent degradation of Q-factor performance during the switching transient was analyzed and was found to be correlated with different laser switching characteristics in each case.

Shared-per-wavelength asynchronous optical packet switching: A comparative analysis

This paper compares four different architectures for sharing wavelength converters in asynchronous optical packet switches with variable-length packets. The first two architectures are the well-known shared-per-node (SPN) and shared-per-link (SPL) architectures, while the other two are the shared-per-input-wavelength (SPIW) architecture, recently proposed as an optical switch architecture in synchronous context only, which is extended here to the asynchronous scenario, and an original scheme called shared-per-output-wavelength (SPOW) architecture that we propose in the current article. We introduce novel analytical models to evaluate packet loss probabilities for SPIW and SPOW architectures in asynchronous context based on Markov chains and fixed-point iterations for the particular scenario of Poisson input traffic and exponentially distributed packet lengths. The models also account for unbalanced traffic whose impact is thoroughly studied. These models are validated by comparison with simulations which demonstrate that they are remarkably accurate. In terms of performance, the SPOW scheme provides blocking performance very close to the SPN scheme while maintaining almost the same complexity of the space switch, and employing less expensive wavelength converters. On the other hand, the SPIW scheme allows less complexity in terms of number of optical gates required, while it substantially outperforms the widely accepted SPL scheme. The authors therefore believe that the SPIW and SPOW schemes are promising alternatives to the conventional SPN and SPL schemes for the implementation of next-generation optical packet switching systems.

640 Gbit/s (64-Wavelength$\,\times\,$10 Gbit/s) Data-Rate Wide-Colored NRZ-DPSK Optical Packet Switching and Buffering Demonstration

Abstract-We demonstrated optical packet switching and buffering operation of a DWDM/NRZ-DPSK optical packet, whose payload-data-rate is 640 Gbit/s (64-wavelength × 10 Gbit/s), for transparent optical packet switch systems for the first time. Error-free (bit-error-rate <10-9) operation including 200-Gchip/s PSK optical label processing was achieved for all 64-wavelength-channel 10 Gbit/s DPSK packet-payloads. In addition, the higher tolerance of DPSK format for packet power fluctuation compared with OOK one was verified in an optical packet switch system.

Monolithically Integrated 8:1 SOA Gate Switch With Large Extinction Ratio and Wide Input Power Dynamic Range

A monolithic 8:1 SOA gate switch that integrates an 8-ch SOA gate array, an 8:1 optical coupler, and a 1-ch SOA gate was developed for use in a large scale optical packet switching system. A 250-mum-long compact field-flattened coupler (FFC) produces a very small channel-imbalance together with a compact total chip size of 3.0 times 1.0 mm. The device exhibited a large ON-state gain of >14.3 dB and a small total gain deviation of 3.0 dB. The optimized passive waveguide structure successfully suppressed the stray light, which resulted in a record-high ON-OFF extinction ratio of >70 dB. We used a thin tensile-strained multi-quantum well (MQW) active layer which can attain high-saturation output power, low noise, and polarization insensitivity for SOA gates. Due to the coexistence of a high saturation output power and a low noise figure, the device exhibited a very wide input power dynamic range of 20.5 dB for a 10-Gb/s NRZ signal.