CN103226278B - Based on 8 full optical comparators of quantum spot semiconductor image intensifer - Google Patents

Abstract

The invention discloses a kind of 8 full optical comparators based on quantum spot semiconductor image intensifer, comprise the logic inverter that 1 Mach-Zehnder interferometer is formed, the logic XOR gate that 8 Mach-Zehnder interferometer are formed, time delay is carried out in the output of previous Mach-Zehnder interferometer, as the control signal of next Mach-Zehnder interferometer, together input next Mach-Zehnder interferometer with signal to be compared and carry out logical operation, obtain the cascade of XOR comparative result, described logic inverter and logic XOR gate use quantum spot semiconductor image intensifer as nonlinear element.The signal speed of this full optical comparator process can reach 500Gb/s.Apply it and carry out igh-speed wire-rod production line, to adapt to the development of all-optical network.

Description

Based on 8 full optical comparators of quantum spot semiconductor image intensifer

Technical field

The present invention relates to photoelectron technical field, particularly relate to 8 full optical comparators based on quantum spot semiconductor image intensifer.

Background technology

1. the performance of quantum spot semiconductor image intensifer, structure and principle of work

Semiconductor optical amplifier (SOA) is the key equipment realizing flexible configuration optical-fiber network of future generation, and it not only can carry out signal amplification, also can realize all-optical signal processing, the nonlinear effect of this mainly based semiconductor material.The nonlinear effect of SOA mainly comprises XGM (XGM), Cross-phase Modulation (XPM) and four-wave mixing (FWM) effect etc.

Semiconductor optical amplifier has a wide range of applications in all optical network, and as nonlinear device, it may be used in the optical signal prosessing such as photoswitch, light logic and wavelength conversion.But the performance of conventional bulk is by the restriction of several factors, such as saturation power is low, carrier recovery time is long, pattern effect is large, therefore based on the arithmetic speed of the all-optical logic gates of this SOA mostly at below 40Gb/s, be difficult to the requirement reaching igh-speed wire-rod production line, its stability also has much room for improvement.

In recent years, quanta point material and quantum dot device more and more receive the concern of people.Quantum dot is the nanostructure semiconductor material of accurate zero dimension, in such an embodiment, charge carrier in quantum dot is all bound within the scope of nanoscale on three dimension directions, strong confinement effect makes energy level in quantum dot produce separation, density-of-states distribution becomes a series of δ function, this and atom are similar, so people also call quantum dot " artificial atom " usually.Typical quantum dot size size, at about 10nm, about comprises l ten thousand atoms. and in desirable quanta point material, all sizes are identical, do not have coupling each other, and are arranged in one equably without in the potential barrier of depth stop.Because the quantum dot of nanoscale has strong three-dimensional restriction to charge carrier, show the absorption saturable nonlinear effect etc. of obvious quantum effect, resonance tunnel-through, coulomb blockade and exciton.Just these effects make with the device that quanta point material is made have high characteristic temperature, low-threshold power current density, the high differential gain, without Zhou work and the excellent properties such as wide modulating frequency of singing.Theoretical and experiment shows, has than quantum well and the more superior performance of body material devices using quantum dot as the semiconductor devices of active area.

Because semiconductor quantum dot device is restricted in three dimensions, the quantum dot device of different qualities therefore can be manufactured by the geometric configuration controlling quantum dot.At present, be that the quantum dot device of active area has quantum dot laser, quantum spot semiconductor image intensifer (QD-SOA), quantum dot infrared detector, single-photon light source, quantum computer etc. with quanta point material.These devices are in electricity, and there is very large advantage optical property, vlsi level and low-power consumption aspect, have wide practical use in fields such as nanoelectronics, optoelectronics, bio-science, quantum calculations.

QD-SOA has than quantum well and the more superior performance of body material devices, it has the advantages such as low threshold electric current, high saturation power, wide gain bandwidth (GB) and temperature-insensitive, the release time of its saturated light gain of what is more important is ps magnitude, and this illustrates that it has potential application prospect in high-speed optical signal process.In recent years, QD-SOA obtains extensive research because of the excellent properties of its uniqueness.QD-SOA, as a kind of novel amplifier, can improve the performance of traditional SOA, has very large potentiality in high speed optical communication and all-optical signal processing.Fig. 1 and Fig. 2 is the structural representation of QD-SOA.

The same with common SOA, QD-SOA has two perform regions.One is the linear zone under low optical power, for the Linear Amplifer of light signal; Inelastic region when another is gain saturation, for optical signal prosessing, as shown in Figure 3.

In theory, the key distinction of QD-SOA and traditional SOA is, its active area is made up of many quantum dots (QD) layer, example, gives two-layer QD, below each QD layer in figure as shown in Figure 1, the point material having one deck very thin, is called soakage layer (WL).Charge carrier mainly enters active area in quantum dot by WL layer, and therefore, the characteristic of WL layer is very large to the performance impact of whole equipment.The conduction band structure of what Fig. 2 provided is one deck QD and WL, wherein, supposes that quantum dot comprises two discrete states: excited state (ES) and ground state (GS).Charge carrier in WL layer can enter ES state by photon-and Auger-assisted process, and equally, the charge carrier of ES state also enters GS state through similar process, then carries out Optical pulse amplification.Due to the state that quantum dot system is discrete, in some aspects, we can regard QD-SOA as three-tier system, the state (ES and WL) of more than quantum dot GS can be regarded as the charge carrier storage pool of GS, constantly supplement due to the charge carrier that stimulated radiation consumes in GS, thus make QD-SOA have very fast gain recovery process (p second-time).And traditional SOA is more as bilaminar system, charge carrier memory block and light active area are coupled.Therefore, comparatively speaking, QD-SOA more easily realizes the reversion completely of active area.The three-decker of QD system is similar to Erbium-Doped Fiber Amplifier (EDFA) (EDFA), such as, so it is provided with the Some features of EDFA, and noise factor is low, and pattern effect is little.

QD-SOA can realize high bit rate, multi-wavelength operation, and this is determined by the physical properties of quanta point material, mainly contains two aspects: (1) saturated gain response time is about 100fs magnitude to ps magnitude, and pattern effect is very little; (2) because quantum dot is independent distribution in space, spectrum local effect will be produced, effectively can suppress the crosstalk of each WDM interchannel under gain saturation state.Have the dynamic gain process of Experimental report QD-SOA in early days, research afterwards discloses the Some features that QD-SOA has, and comprising: ultrafast gain recovery (picosecond magnitude), gain band is roomy, noise factor is low, and saturation output power is high, FWM efficiency etc.

People extensively study principle of work and the electronic structure of QD-SOA.Dissimilar quantum dot has different growth techniques and operating wavelength range, and such as, on gaas substrates, InAs Quantum Dots Growth is in InP substrate for In (Ga) As Quantum Dots Growth.

In (Ga) As/GaAs quantum dot can excite being less than 1350nm wavelength coverage, and InAs/InP structure can excite in communication wavelengths 1550nm scope.In fact, the size of quantum dot, shape and local adaptability to changes all cause the fluctuation of quantized level in change, make the uneven broadening of optical transition energy.Gaussian distribution can be adopted to describe quantum dot size distribution.There is now the photoelectric characteristic of experimental study InAs/InP quantum dot.

2. full optical comparator

Current optical fiber communication, just towards hypervelocity, Large Copacity future development, therefore needs to have high packets of information exchange velocity at communication node place.And all-optical packet switching is not because need light-electrical-optical conversion, directly realizing exchanging on photosphere, is therefore one of effective way realizing exchanging at a high speed.Wherein, optical label process is an important technology, and a label contains an address, and out of Memory is included in packets of information, and label is by full light identification, and profit can realize speed-sensitive switch and not need whole packets of information to carry out opto-electronic conversion in this way.Shaven head extracts and identifies it is realize the gordian technique that high speed label exchanges, and shaven head is identified and can be achieved by use full optical comparator.When packets of information enters comparer, if shaven head and a pre-set patterns match, in output power, reasonable time place produces a peak, and then this signal carries out route for controlling a photoswitch.Full optical comparator now one of study hotspot becoming people, for the signal of amplitude modulation(PAM), the method of several smooth comparer has been had to be proved at present, comprise the full optical comparator that the high non-linearity effect based on SOA realizes: B.S.Gopalakrishnapillai proposes the XNOR door based on SOA, its utilize the XGM of SOA realize with or computing export.But compare for multidigit, this device does not possess the function of the comparer of real meaning, and is not suitable for more than 10Gb/s system.The comparer utilizing FBG to realize that comparer based on passive FBG array: J.E.McGeehan and M.C.Hauer proposes, structure is simple, cost is low, the quantity of comparer is determined by the bit needing to compare, but not reconfigurable when signal rate changes or communication network is upgraded.The space 4-f comparer that the people such as DavidF.Geraghty propose, achieve the identification of 4 bit 100Gb/s header signals, but there is the problem of orthogonality and signal drift in system.In addition also have the holographic filter of free space, and there is the speculum etc. of light delay.

All-optical signal processing technology and the device of current based semiconductor image intensifer obtain investigation and application widely.Wherein mainly realize based on nonlinear effects such as the Cross-phase Modulation in SOA, XGM, four-wave mixings.Based on SOA and SOA-MZI(semiconductor optical amplifier Mach-Zehnder interferometer) can realize various all-optical logic, comprise and (AND), or (OR), non-(NOT), XOR (XOR), or non-(NOR) etc.Wherein, the xor logic based on SOA-MZI that HongzhiSun etc. propose, speed reaches 80Gb/s.LASAGNE project team utilizes cascade and feedback two kinds of modes to achieve 2 bit comparators based on SOA-MZI structure respectively, and extinction ratio is 13dB.Current full optical comparator majority is 2 bit comparators.

Summary of the invention

The technical matters that the present invention solves is: how to realize high speed full optical multidigit comparer.

The technical solution adopted for the present invention to solve the technical problems: a kind of 8 full optical comparators based on quantum spot semiconductor image intensifer, comprise the logic inverter that 1 Mach-Zehnder interferometer is formed, the logic XOR gate that 8 Mach-Zehnder interferometer are formed, time delay is carried out in the output of previous Mach-Zehnder interferometer, as the control signal of next Mach-Zehnder interferometer, together input next Mach-Zehnder interferometer with signal to be compared and carry out logical operation, obtain the cascade of XOR comparative result, described logic inverter and logic XOR gate use quantum spot semiconductor image intensifer as nonlinear element.

Beneficial effect of the present invention:

The present invention proposes a kind of 8 full optical comparators realized based on quantum spot semiconductor image intensifer cascade structure.This full optical comparator can realize the signal transacting such as tag recognition, because do not need light-electrical-optical conversion, directly realizing exchanging on photosphere, is therefore one of effective way realizing exchanging at a high speed.The signal speed of this full optical comparator process can reach 500Gb/s.Apply it and carry out igh-speed wire-rod production line, to adapt to the development of all-optical network.

Accompanying drawing explanation

When considered in conjunction with the accompanying drawings, by referring to detailed description below, more completely can understand the present invention better and easily learn wherein many adjoint advantages, but accompanying drawing described herein is used to provide a further understanding of the present invention, form a part of the present invention, schematic description and description of the present invention, for explaining the present invention, does not form inappropriate limitation of the present invention, wherein:

The structural representation of Fig. 1 quantum spot semiconductor image intensifer.

Fig. 2 quantum spot semiconductor image intensifer carrier transition schematic diagram.

The workspace characteristic of Fig. 3 quantum spot semiconductor image intensifer.

Fig. 4 XOR gate schematic diagram.

Fig. 5 not gate schematic diagram.

Figure 68 bit full optical comparator structural representation.

Figure 78 bit full optical comparator result.

Embodiment

Be described with reference to Fig. 1-7 pairs of embodiments of the invention.

For enabling above-mentioned purpose, feature and advantage become apparent more, and below in conjunction with the drawings and specific embodiments, the present invention is further detailed explanation.

Concrete technical scheme is as follows:

1. the basic structure of quantum spot semiconductor image intensifer is obtained by theory calculate.

For obtaining the QD-SOA being applicable to doing signal transacting, utilizing vasp software to calculate the QD-SOA of different structure, obtain the level structure that it is basic, and theory calculate going out the dynamic perfromance of this QD-SOA.

2. realize all-optical XOR logic and NOT logic.

The realization of full optical comparator of the present invention needs to use all-optical XOR logic and NOT logic.

The implementation of all-optical XOR logic as shown in Figure 4.This is the all-optical XOR logic utilizing the Mach-Zehnder interferometer based on quantum spot semiconductor image intensifer to realize.Signal A and the output of signal B after interferometer are XOR(A, B), that is, the result compared is for when A, B are different, and output signal is 1, and when A, B are identical, output is 0.

For meeting the needs that packet header identifies, the Output rusults of system when A=B should be made to be 1, therefore to need to use a not gate, by signal A(or B) reverse.The implementation of not gate as shown in Figure 5.This similar, in the structure of XOR, is also realize based on the Mach-Zehnder interferometer of quantum spot semiconductor image intensifer.Output signal is NOT(A).

Here all-optical XOR logic and NOT logic are all utilize the Cross-phase Modulation effect in semiconductor optical amplifier to realize.

3. the formation of multidigit full optical comparator.

A not gate is connected with an XOR gate, obtains a bit comparator.Multiple XOR is carried out cascade, obtains multidigit full optical comparator.Full light 8 bit comparator is made up of 9 quantum spot semiconductor image intensifer Mach-Zehnder interferometer.First QD-SOAMZI is used for realizing NOT logic, and other QD-SOAMZIs is used for realizing xor logic.As shown in Figure 6.When multiple XOR is carried out cascade, the time delay of each road light signal be carried out, realize the accurate control of multipath light signal delay volume.When speed is 500Gbps, every bit byte only 2ps.

Concrete each modular construction is as follows:

1. the basic structure of quantum spot semiconductor image intensifer: use a kind of InAs/GaAsQD-SOA in device, its active area is formed at the suprabasil 7 layers of InAs quantum dot of GaAs by growing, and the superficial density of quantum dot is about 5.0x10 ¹⁰cm-2, cladding thickness is the InGaAs of 5nm.Quantum dot layer is separated by the GaAs layer that 33nm is thick, can think do not have acting force between two adjacent layers.Level structure comprises conduction band and valence band, and has three and eight non-degenerate energy levels respectively, the energy difference 70meV of conduction band adjacent energy levels, the energy difference 10meV of valence band adjacent energy levels, and the ground state radiation of InAs quantum dot is near 1.3um.

2. utilize quantum spot semiconductor image intensifer to realize XOR and " non-" logic respectively:

A) XOR is realized

The XOR gate realized is the XOR gate based on QD-SOAMZI.Based on ultrafast gain and the phase place dynamic perfromance of QD-SOA, utilize Mach-Zehnder interferometer (MZI) to realize super high speed all-optical signal transacting, its structure as shown in Figure 4.A QD-SOAMZI is made up of 2 QD-SOA, and two QD-SOA are placed on the same position of interferometer two-arm.Ultimate principle is as follows: the signal A(wavelength of different wave length is λ ₁), signal B(wavelength is λ ₃) and gating pulse C(wavelength be λ ₂) inputted by left side.Gating pulse C is divided into two bundles through coupling mechanism, wherein a branch of be coupled with signal A after be input in the upper arm of QD-SOAMZI, another bundle be coupled with signal B after be input in the underarm of QD-SOA-MZI.Control signal C and signal A and signal B transmits in QD-SOA, Cross-phase Modulation effect occurs, and when signal A is identical with signal B, gating pulse C experiences identical phase shift and gain in two QD-SOA, therefore can not export after coupling mechanism is interfered, namely exporting is 0.When signal A is different with signal B, gating pulse C experiences different phase shifts and gain in two SOA, can make to export through coupling mechanism, and the peak power of conditioning signal A and B, can make output the strongest.Therefore output signal is the logical exclusive-OR of signal A and signal B.

Filter center wavelength is aimed at λ ₂(controlling the wavelength of light C), filter out signal light A and B, obtains Output rusults and should be:

$P_{\mathrm{out}}\left(t\right)=\frac{P_{\mathrm{probe}}\left(t\right)}{4}[G_1\left(t\right)+G_2\left(t\right)-2\sqrt{G_1\left(t\right)G_2\left(t\right)}\cos ({\mathrm{\φ}}_1\left(t\right)-{\mathrm{\φ}}_2\left(t\right))\]$

Wherein, P _probet () is the power input of gating pulse C, G ₁, G ₂, φ ₁and φ ₂the gain of detecting light beam and the change of phase place in QD-SOA-MZI two arms.Work as A=B, then G1=G2, φ ₁=φ ₂, therefore P _out=0; If A ≠ B, then, P _out(t) ≠ 0.Visible, now QD-SOAMZI forms a logic XOR gate.

B) " non-" logic is realized.

Similar with XOR gate above, use closely similar QD-SOA-MZI structure to realize logic NOT(non-) door.In XOR structure above, use clock signal to replace data-signal B, the result at this moment obtained will be the XOR result of signal A and " 1 ", and the true value at this moment obtained is exactly NOT(A).Its structure as shown in Figure 5.

3. utilize the cascade structure of quantum spot semiconductor image intensifer to realize full optical comparator:

Based on QD-SOAMZI structure above, multiple xor logic door is carried out cascade, bit full optical comparator more than can be realized.Fig. 6 is exactly the schematic diagram of the 8 bit full optical comparators that we propose, and it is made up of 9 QD-SOAMZI, and wherein, first QD-SOAMZI is used for realizing NOT logic, and other QD-SOAMZI is used for realizing xor logic.

The ultimate principle of 8 bit full optical comparators is as follows: first, and signal A, clock signal 1, clock signal 2 are coupled in first QD-SOAMZI, and for realizing NOT logic, Output rusults is NOT(A).The NOT (A) exported is divided into 8 tunnels, and synchronous signal B is also divided into 8 tunnels.First Bit data of NOT (A) and B carries out logical operation (control signal is a Gaussian monopulse) herein in second QD-SOAMZI, obtains XOR result, " Output1 " namely in figure.Signal " Output1 " is through suitable decay with after postponing, and the second as control signal and NOT (A) and signal B synchronously enters in the 3rd QD-SOAMZI, obtains " Output2 ".By that analogy, the XOR result of the n-th bit realizes xor logic as (n+1) bit synchronous of control signal and signal NOT (A) and B.Finally, the output of the 8th xor logic (last QD-SOAMZI) is exactly the Output rusults of 8 bit full optical comparators.Final comparative result can be expressed as follows:

$\mathrm{Output}=\left\{\begin{array}{ccc}0,& \mathrm{if}& A\≠B\\ 1,& \mathrm{if}& A=B\end{array}\right..$

Concrete outcome is as follows:

Several not homotactic signal A and the result of signal B after 8bit full optical comparator are relatively as shown in Figure 7.Signal A and signal B is 8 bit RZ form intensity-modulated signals, and speed is 500Gbps.The single pulse energy of signal A, signal B and clock signal 2 is all 0.05pJ, and the energy of clock signal 1 and gating pulse is 0.002pJ.The 1/e pulse width of all signals is all 0.5ps.

As can be seen from the results, only when signal A is identical with 8 bits of signal B, the 8th in sequence has light pulse to export.As A ≠ B, in the end signal is not had to export after a QD-SOAMZI.The output pulse width only 0.1ps of 8 bit full optical comparators, extinction ratio is more than 90dB.

Although the foregoing describe the specific embodiment of the present invention, but those skilled in the art is to be understood that, these embodiments only illustrate, those skilled in the art, when not departing from principle of the present invention and essence, can carry out various omission, replacement and change to the details of said method and system.Such as, merge said method step, thus then belong to scope of the present invention according to the function that the method that essence is identical performs essence identical to realize the identical result of essence.Therefore, scope of the present invention is only defined by the appended claims.

Claims (1)

1. 8 full optical comparators based on quantum spot semiconductor image intensifer, it is characterized in that, comprise the logic inverter of 1 Mach-Zehnder interferometer formation and the logic XOR gate of 8 Mach-Zehnder interferometer formations, described logic inverter is connected with first logic XOR gate, obtain a bit comparator, time delay is carried out in the output of previous Mach-Zehnder interferometer logic XOR gate, as the control signal of next Mach-Zehnder interferometer logic XOR gate, together input next Mach-Zehnder interferometer logic XOR gate with signal to be compared and carry out logical operation, obtain the cascade of XOR comparative result, described logic inverter and Mach-Zehnder interferometer logic XOR gate use quantum spot semiconductor image intensifer as nonlinear element, wherein:

The structure of described quantum spot semiconductor image intensifer is a kind of InAs/GaAsQD-SOA: its active area is formed at the suprabasil 7 layers of InAs quantum dot of GaAs by growing, and the superficial density of InAs quantum dot is 5.0x10 ¹⁰cm-2, cladding thickness is the InGaAs of 5nm; Quantum dot layer is separated by the GaAs layer that 33nm is thick, level structure comprises conduction band and valence band, and has three and eight non-degenerate energy levels respectively, the energy difference 70meV of conduction band adjacent energy levels, the energy difference 10meV of valence band adjacent energy levels, the ground state radiation of InAs quantum dot is 1.3um.