Fast dynamic configurable smooth packet buffer in the all-optical network
Technical field
The present invention relates to the light packet buffer in a kind of all-optical network, relate in particular to a kind of buffer memory and time gas exchange structure of dynamic fast configurable light grouping, be applicable to the optical cross connection node in the all-optical network.Belong to the optical communication technique field.
Background technology
(optical packet switching, OPS) network because possess fine-grained allocated bandwidth and superfast exchange capacity, are widely regarded as the developing goal of optical-fiber network of future generation in full light packet switch.It has higher network throughput, abundant network routing function and outstanding dirigibility.In order to realize these performance objectives, practical, cost performance is high, the all-optical buffer device of favorable expandability is just essential.It can be used for light packet synchronization (packet synchronization) at least, competition solves (contention resolution), light packet switch (packet switching) and traffic shaping aspects such as (traffic shaping).
Existing smooth caching technology comprises two big classes at present: 1) slower rays buffer (slow-light buffer), by reducing the group rate of light, postpone light in transmission medium transmission time and reach the buffer memory effect, this technology has advantages such as little, the easy of integration and retardation continuous variable of physical size, but since its limited buffer memory ability, less shortcomings such as delay bandwidth product in all-optical network, never reused; 2) fiber delay line cache device (optical delay line), in fibre delay line, transmit one section long distance by light signal and obtain delay buffer, this technology has bigger transmission bandwidth, less loss, signal format and polarization state is had advantages such as certain transparency, high cost performance and reliability, becomes at present a kind of up-and-coming smooth caching technology and obtains extensive studies and application.
According to the difference of structure, the fiber delay line cache device roughly can be divided into following three classes.
People such as T.Sakamoto have delivered on J.Lightwave Technol 2004 and have been entitled as " Performanceanalysis of variable optical delay circuit using highly nonlinear fiber parametricwavelength converters; " article, (Re-circulating) light buffer structure that proposed to recirculate utilizes photo-coupler or fast optical switch based to be directed to light signal in the fiber optic loop and circle transmission constantly.Though this light buffer structure has less physical size, but the ASE of amplifier in the fiber optic loop (Amplifiedspontaneous emission) noise has seriously reduced signal quality, and the length restriction of fiber optic loop the extensibility of this structure (fiber optic loop is longer, cause the buffer memory granularity bigger, efficient is not high; Fiber optic loop is shorter, has limited the length of buffer memory light grouping again).
P.R.Pruncal, people such as C.Guillemot are respectively at J.Quantum Electron 1993, deliver " Optically processed self-routing; synchronization; andcontention resolution for 1D and 2D photonic switching architectures; " on the J.LightwaveTechnol.1998 article has proposed two kinds of feedforwards of cascaded-switch and broadcast-and-select (Feed-forward) light buffer structure respectively.Though this structure has overcome the restriction of said structure to the light block length, has bigger physical size, extendability is relatively poor, the more high shortcoming of cost.
People such as Y.K.Yeo is successively at ECOC2005 and J.Lightwave Technol. then, deliver many pieces of articles on 2006, (" Dynamically Reconfigurable Optical Buffer with Integrated; Simultaneous Wavelength Conversion Capability for Multi-wavelength Packets; " ECOC2005, " Performance characterization and optimization of high-speed; ON-OFFoptical signal reflectors in a folded-path time-delay buffer; " IEEE J.LightwaveTechnol., 2006,24 (1), 365-378) hops in tandem (Folded-path) light buffer structure has been proposed.This structure has n section delay line, and each section delay line is based on the reflection of high speed SOA and the function of absorbing light signal, dynamically the cache path of selective light grouping.But this structure is very big to the loss of light packet power, and each section delay line progression is unsuitable excessive, and ASE (the Amplified spontaneous emission) noise of amplifier has also seriously reduced signal quality after every section delay line.
In recent years, the all-optical buffer structure is still the focus and emphasis of research, people such as Caroline P.Lai, Songnian Fu, Xinwan Li deliver many pieces of articles on the International Technology periodical, propose miscellaneous thoughts and argument on structure, device and the algorithm of optical buffer.The optical buffer structure that has now proposed all has its relative merits separately, but does not have a kind of optical buffer to obtain generally acknowledging and widespread use of academia, industry member.
Summary of the invention
The objective of the invention is at the deficiencies in the prior art, design provides fast dynamic configurable smooth packet buffer in a kind of optical-fiber network, the cache-time of can be dynamic fast configurable light grouping, can hold simultaneously a plurality of light grouping carrying out buffer memorys and realize the functions such as time gas exchange of a plurality of light groupings, advantage such as have that light cache-time dynamic range is big, the time of reshuffling is short, physical size is little, power consumption is low and extensibility is strong.
For achieving the above object, technical scheme of the present invention is that M Sagnac interference ring and the space welding of M volume fibre delay line with " reflection and transmission " function is together in series, head and the tail two ends optical fiber is welding together with a pair of input/output terminal of one 2 * 2 fast optical switch based again, constitute a big buffer memory fiber optic loop, another of 2 * 2 fast optical switch baseds to input/output terminal respectively as the input end and the output terminal of optical packet signal.In fact the optical buffer structure that the present invention proposes is exactly in traditional (Re-circulating) fiber optic loop (loop) structure that recirculates based on 2 * 2 fast optical switch baseds, at interval nested M Sagnac interference ring and M roll up fibre delay line, increased the buffer memory ability of the fiber optic loop that recirculates, provide multiple cache path to select, can hold the time gas exchange that a plurality of light groupings are carried out buffer memory simultaneously and can be realized a plurality of light groupings.
The concrete structure of fast dynamic configurable smooth packet buffer of the present invention is: be made up of M Sagnac interference ring, M volume fibre delay line, 2 * 2 fast optical switch baseds.M Sagnac interference ring and the M volume fibre delay line with reflection and transmission function is together in series apart from one another by welding, head and the tail two ends optical fiber is welding together with the input/output terminal of one 2 * 2 fast optical switch based again, constitute a buffer memory fiber optic loop, another of 2 * 2 fast optical switch baseds to input/output terminal respectively as the input end and the output terminal of optical packet signal.At input side, there is not fibre delay line between M Sagnac interference ring and the fast optical switch based, and at outgoing side, between the 1st Sagnac interference ring and 2 * 2 fast optical switch baseds one section fibre delay line is arranged, make that the minimal cache time delay of this optical buffer is 2 τ.The direct access path of the optical packet signal of coming in from input end by 2 * 2 fast optical switch baseds 2 directly is transferred to output terminal or enters the buffer memory fiber optic loop counterclockwise by the cross connection path and carry out buffer memory.In the buffer memory fiber optic loop, be applied to driving voltage on each Sagnac interference ring by change, control is reflected or transmissive through the optical packet signal of Sagnac interference ring, selects different fiber optic loop cache paths for optical packet signal, promptly has different caching delay; When caching delay arrived, the light grouping must be transferred to output terminal via the cross connection path of M Sagnac interference ring and fast optical switch based.
The Sagnac interference ring that among the present invention, has " reflection and transmission " function is the control element of optical packet signal transmission path, and by changing its driving voltage, the optical packet signal of process Sagnac interference ring can be reflected, also can transmissive.M volume fibre delay line has identical or different length, and optical packet signal transmits therein and introduces certain time delay τ.
In fact this optical buffer structure is exactly in traditional recirculating (Re-circulating) fiber optic loop structure, at interval nested M Sagnac interference ring is between per two Sagnac interference rings, embed one section fibre delay line again between outgoing side Sagnac interference ring and the fast optical switch based.Wherein each Sagnac interference ring has " reflection and transmission " function, and promptly incident optical signal can pass through interference ring, also can be reflected by interference ring.Like this,, can select the transmission path of optical packet signal in buffer flexibly, thereby realize quick dynamic configurable time delay size by the on off state (cross-bar) of regulating and controlling fast optical switch based and " reflection and transmission " state of interference ring.Notice, between M Sagnac interference ring of input side and fast optical switch based, do not have fibre delay line, and one section fibre delay line is arranged that design makes that the minimal cache time delay of this optical buffer is 2 τ like this between outgoing side Sagnac interference ring and fast optical switch based.
The Sagnac interference ring that has " reflection and transmission " function described in the present invention comprises the Sagnac interference ring of based semiconductor image intensifer SOA and based on the Sagnac interference ring of phase-modulator PM (phase modulator).In the SOA-Sagnac interference ring, light signal is by behind 50/50 the photo-coupler, enter SOA from two different directions respectively, wherein the light signal of propagating counterclockwise directly enters SOA, and the light signal of propagating clockwise at first by a section single-mould fiber (SMF) again through entering SOA behind the attenuator (Attenuator).Because the power difference that two light signals of propagating in the other direction enter SOA, the phase change of its experience are also different.Corresponding change takes place by the driving voltage that changes gain control SOA in consequent phase differential.When its phase differential is π, signal " full impregnated "; When phase differential was 0, signal " was all-trans ".And the PM-Sagnac interference ring utilizes the LiNbO3 phase-modulator incident optical signal to be produced that the principle of different phase change realizes under TE and TM different working modes.Change the driving voltage of PM, respective change also takes place in the phase differential between the incident optical signal of different mode.When its phase differential is π, signal " full impregnated "; When phase differential was 0, signal " was all-trans ".The light buffer structure that the present invention proposes is exactly by SOA or the driving voltage of PM and the on off state of fast optical switch based in the control Sagnac interference ring, has selected the cache path of the light signal that is buffered flexibly fast, i.e. caching delay.
Compare with prior art, the invention solves the variety of issue of conventional art.The buffer structure of the present invention a plurality of light groupings of buffer memory simultaneously, caching delay is configurable fast flexibly, also can realize the functions such as time gas exchange of a plurality of light groupings, satisfies the demand of crack exchange network of full light time.It is less that the optical buffer that the present invention proposes has physical size, and cost is lower, and function is more complete, control easy, buffer memory granularity flexibility and changeability, efficient advantages of higher.In a word, utilize technology of the present invention, can simplify the structure of full Optical Switch Node, reduction designs and controls cost, and improves the performance of switching node, finally promotes the realization early of all-optical network.
Smooth packet buffer of the present invention is applicable to fields such as light packet switch, light burst-switched and microwave photon.
Description of drawings
Fig. 1 is the structural representation of fast dynamic configurable smooth packet buffer of the present invention.
Among Fig. 1,1 is the Sagnac interference ring, and 2 is 2 * 2 fast optical switch baseds, and 3 is the single-mode fiber lag line.
Fig. 2 is two kinds of specific implementations of Sagnac interference ring 1 of the present invention.
Among Fig. 2, a) SOA-Sagnac interference ring, b) PM-Sagnac interference ring.4 is the 100m single-mode fiber, and 5 is adjustable attenuator, and 6 is semiconductor optical amplifier SOA, and 7 is photo-coupler, and 8 is the consistent welding point of polarization maintaining optical fibre, and 9 is phase-modulator PM, and 10 is the quadrature welding point of polarization maintaining optical fibre, and 11 is polarization maintaining optical fibre.
Fig. 3 is the cache path synoptic diagram in light the is grouped in buffer of the present invention.
Fig. 4 is that a plurality of light are grouped in the time gas exchange synoptic diagram in the buffer of the present invention.
Embodiment
In order to understand technical scheme of the present invention better, embodiment is further described below in conjunction with accompanying drawing.
Fig. 1 has provided in the all-optical network that the present invention proposes fast the dynamically structural representation of configurable smooth packet buffer.This structure is made up of M Sagnac interference ring 1, M volume fibre delay line 3,2 * 2 fast optical switch baseds 2.2 * 2 fast optical switch baseds 2 can use the LiNbO3 photoswitch (E.J.Murphy, T.O.Murphy, " 16 * 16 strictly nonblocking guided-wave optical switching system; " Journal ofLightwave Technology, 1996,14,352-358).M has the Sagnac interference ring 1 of " reflection and transmission " function and M volume fibre delay line 3 and is together in series apart from one another by welding, and head and the tail two ends optical fiber is welding together with a pair of input/output terminal of one 2 * 2 fast optical switch based 2 again, constitutes a big buffer memory fiber optic loop.Another of 2 * 2 fast optical switch baseds 2 to input/output terminal respectively as the input end and the output terminal of optical packet signal.
M volume fibre delay line 3 has identical or different length, and optical packet signal transmits therein and introduces certain time delay τ.Note, at input side, there is not fibre delay line 3 between M Sagnac interference ring 1 and 2 * 2 fast optical switch baseds 2, and at outgoing side, between the 1st Sagnac interference ring 1 and 2 * 2 fast optical switch baseds 2 one section fibre delay line 3 is arranged, design makes that the minimal cache time delay of this optical buffer is 2 τ like this.The optical packet signal of coming in from input end can directly be transferred to output terminal (not having caching delay) by the direct access path of 2 * 2 fast optical switch baseds 2, also can enter the buffer memory fiber optic loop counterclockwise by the cross connection path and carry out buffer memory.In the buffer memory fiber optic loop, be applied to driving voltage on each Sagnac interference ring by change, control is to be reflected through the optical packet signal of Sagnac interference ring, or transmissive, thereby selected different fiber optic loop cache paths for optical packet signal, promptly had different caching delay.When caching delay arrived, the light grouping must be transferred to output terminal via the cross connection path of M Sagnac interference ring and 2 * 2 fast optical switch baseds.
The optical buffer that the present invention proposes is exactly by the on off state (cross-bar) of control fast optical switch based and " reflection and transmission " state of interference ring, select the transmission path of optical packet signal in buffer flexibly, thereby realized quick dynamic configurable time delay size.
The Sagnac interference ring that has " reflection and transmission " function among the present invention also has article to propose (Lilin Yi, Weisheng Hu, " A polarization-independent subnanosecond 2 * 2 optical multicastswitch using a sagnac interferometer ", IEEE Photonic Technology Letters, 20 (8), 539-541,2008, one of author of the present invention), and experimental verification, two kinds of implementations are arranged at present: the Sagnac interference ring of based semiconductor image intensifer SOA and based on the Sagnac interference ring of phase-modulator PM (phase modulator).
Fig. 2 has provided two kinds of implementations of Sagnac interference ring among the present invention: a) SOA-Sagnac interference ring; B) PM-Sagnac interference ring.
The SOA-Sagnac interference ring comprises 100m single-mode fiber 4, adjustable attenuator 5, SOA semiconductor optical amplifier 6 and photo-coupler 7.
The PM-Sagnac interference ring comprises consistent welding point 8, the PM phase-modulator 9 of polarization maintaining optical fibre, quadrature welding point 10, photo-coupler 7 and the polarization maintaining optical fibre 11 of polarization maintaining optical fibre.
In the SOA-Sagnac interference ring, because of SOA has cross-gain modulation (XGM) and cross-phase modulation effects such as (XPM) simultaneously, enter SOA simultaneously for fear of two opposite direction transmission signals, in ring, introduce a section single-mould fiber 4, make one road signal carry out suitable delay.After light signal separates by 50/50 photo-coupler 7, phase change takes place through entering semiconductor optical amplifier SOA after 4 delays of 100m single-mode fiber, attenuator 5 decay earlier respectively in optical packet signal clockwise, light signal passes through identical decay, delay after being introduced into SOA generation phase change more counterclockwise, because the luminous power difference when two light signals enter SOA has produced phase differential thus.Change the driving voltage that is applied on the gain driving SOA, the phase differential of two light signals also changes thereupon.
In the PM-Sagnac interference ring, replace SOA with LiNbO3 phase-modulator PM, it produces different phase differential to incident optical signal under TE and TM different working modes.This just requires in the Sagnac interference ring all is polarization maintaining optical fibre 11, phase-modulator PM keeps two optical fiber pigtail fast and slow axis consistent (consistent welding point 8) with photo-coupler 7 when wherein a side is coupled, opposite side requires two optical fiber pigtail fast and slow axis quadratures, and promptly two fused fiber splice angles are 90 ° (quadrature welding points 10).Like this, polarization mode is identical at the beginning for two reverse optical signals that photo-coupler through 50/50 separates, clockwise light signal directly enters phase-modulator PM by polarization maintaining optical fibre 11, and optical signals enters PM then in wherein polarization maintaining optical fibre quadrature welding and emergence pattern changes counterclockwise.The out of phase variation takes place respectively and has produced phase differential in two reverse optical signals in PM.Change the driving voltage that is applied on the phase-modulator PM, the phase differential of two light signals also changes thereupon.When its phase differential is π, two reverse optical signals, the place interferes and light signal " full impregnated " at photo-coupler; When phase differential was 0, two reverse optical signals interfered and light signal " is all-trans ".
When adopting the SOA-Sagnac interference ring, the insertion loss that the enlarging function of SOA can avoid passive device to bring has reduced the power attenuation of buffer memory transmission, but the XGM effect of SOA to the bag progress row of input signal restriction.When adopting the PM-Sagnac interference ring, owing to there is not a nonlinear effect, the bag length of signal has not been had any restriction, and the cost of PM is lower than SOA, be suitable for the optical buffer spare that makes up large-scale low-cost, but need to introduce extra optical signal amplifier with compensation buffer memory loss.
Fig. 3 has provided four kinds of possible cache paths of the optical buffer that the present invention proposes (illustrate 6 Sagnac rings): 1. circumferential path buffer memory counterclockwise, 2. reflexed path buffer memory, 3. point-to-point transmission oscillation path buffer memory, 4. clockwise circumferential path buffer memory.
When switching node did not have the output port conflict, the light grouping was directly exported from the direct access path of 2 * 2 fast optical switch baseds 2, without any time delay.When output port conflicts, then enter the buffer memory fiber optic loop counterclockwise.In the buffer memory fiber optic loop, can be counterclockwise along the circumferential path buffer memory, also can be at a certain Sagnac interference ring 1 place's reflexed clockwise along the circumferential path buffer memory, also can be at 1 oscillatory type buffer memory of two Sagnac interference rings.When caching delay arrived, the light grouping must be transferred to output terminal via the cross connection path of M Sagnac interference ring and fast optical switch based.Note a bit not having fibre delay line between M Sagnac interference ring and fast optical switch based, design makes that the minimal cache time delay of this optical buffer is 2 τ like this.
Fig. 4 has provided the process that the optical buffer that the present invention proposes (illustrating 5 Sagnac to encircle, counterclockwise numbering) is finished four light grouping time gas exchange.The light grouping of input is followed successively by A, B, C, D, wishes that the optical buffer output order that proposes by the present invention is D, C, A, B.This shows that last light grouping D requires first output, first three light grouping just must enter this light packet buffer successively so.A, the B light counterclockwise circumferential path buffer memory that divides into groups need be through longer buffer delay, and C light is grouped in reflexed path buffer memory between Sagnac interference ring 1 and the ring 5, through less buffer delay, only allows light grouping D directly output earlier.After light grouping D output, light grouping C is via " reflection " of Sagnac interference ring 1 and the cross connection path output of fast optical switch based, and the light grouping A and the B of last one circle of circumference buffer memory counterclockwise export successively.