CN1417604A - Double-ring coupled all optical buffer storage - Google Patents

Abstract

A double-ring coupling all-optical buffer based on 3×3 fiber coupler, which not only stores optical signals (photons), but also reads and writes as required under the control of another optical signal. It forms a double-ring structure with the ports on both sides of the 3×3 optical fiber coupler through optical fiber feedback, and uses the middle port as the input and output ports of the buffer. Introduce and export the control light through two WDM fiber couplers on a fiber ring, use the cross phase modulation (XPM) effect to change the phase difference of the signal light on the two rings, and realize the writing and reading of optical signals in the fiber ring . The optical signal that controls the read and write operations can use both positive logic and secondary logic. According to needs, optical amplifiers can be added in the fiber ring for power compensation. It can also be composed of a plurality of such buffers (such as 8 such buffers), an all-optical buffer of parallel signals formed under the control of the same read-write control optical signal, such as a parallel byte with 8 bits as a parallel byte All-optical buffer.

Description

Dual-loop coupled all-optical buffer

1. Technical field

The invention relates to an all-optical buffer implemented based on a 3*3 fiber coupler. The all-optical buffer not only caches optical signals, but also controls the read and write operations by optical signals instead of electrical signals, and can be read randomly as needed. It is the basic component of optical information processing and will be widely used in optical fiber communication, optical signal (information) processing, optical packet switching, optical computing and other fields. It is mainly used to temporarily store high-speed optical signals.

2. Background technology

Just as the electrical buffer temporarily stores the electrical signal in the chip for a period of time, and then reads it out under the control of the electrical control signal as needed, the optical buffer buffers the optical signal in a special device and can control the signal. A device for writing and reading under control. International research on all-optical buffers is still in some laboratory stages, mainly in the following three categories:

One is based on the "delay line + optical switch" scheme, which uses the delay (about 1m is 5ns) characteristic of photon transmission in the optical fiber, and adjusts the delay time with the optical switch. When two data packets collide, a packet with a lower priority can be temporarily stored on the delay line for a period of time before being output, thus forming a "Switched Delay Line" (Switched Delay Line----SDL). But it is not a buffer in the real sense, but just a delayer, not only the temporary storage time is very limited, but also the read-out time cannot be controlled. For example, to temporarily store a data packet with a length of 40-80 bytes, for a 2.5Gb/s system, about 1-3km of optical fiber is required, and the temporary storage time is difficult to reach the order of ms. At the same time, it is also difficult to adjust the temporary storage time. For more complex adjustment requirements, and it can only be controlled by electrical signals, it will lead to an increase in the number of nodes, thereby increasing costs, losses, and crosstalk.

The second type is based on the scheme of "reflecting optical fiber (FP cavity) + optical switch", which is formed by adding a mirror with adjustable transmittance (reflectance) at both ends of an optical fiber. By adjusting the transmittance (reflectivity) of the mirrors at both ends, the optical signal is written and read, so that the optical signal is temporarily stored in the FP cavity between the two mirrors of the optical fiber. The advantage of this solution is that it is a buffer in the true sense, and the buffer time can be changed within a relatively large time range, so as to realize random readout according to needs. Moreover, it is difficult to achieve 100% total reflection, so the storage loss is relatively large, and power compensation needs to be performed on it. "The ability is weak, and it is difficult to realize technically.

The third category is a solution based on Fiber Loop. In a fiber optic ring with power compensation, if the accumulation of noise is not considered, photons can theoretically survive in it for a long time. The key is how to introduce photons (write operation) and output photons (read operation). According to different input, output and optical switches used, researchers have proposed a variety of structural schemes based on optical fiber rings:

1. Adopt the scheme of 2×2 optical coupler input and optical 2×2 coupler output.

The simplest way of input and output can be realized with fiber coupler. K.Hall (K.Hall, et al, "All-Optical Buffering of 40 Gb/s Data Packets" IEEE, P.T.L., V.10, 1998.) of MIT in the United States and others in 1998, and K.Bose of I.I.T (Kushawaha, S.K.Bose, et al, "Analytical Modeling for Performance Studies of an FLBM-Based All-Optical Packet Switch", IEEE Communication Lett.V.5, 4, pp227, 2001.) and others in 2001 adopted both This scheme. The difference is that K.Hall uses the electroabsorption modulator EOM as the delay control of the optical signal in the ring, while K.Hall uses the SOA optical switch as the delay control of the optical signal. At the input end, first convert the wavelength of the packet to be buffered to a specific wavelength, and then turn on the corresponding optical switch. To buffer for several cycles, the EOM or SOA is turned on for several cycles. The advantage of this solution is that multiple packets can be processed in parallel at the same time, but because the output of the coupler is used, the optical signal must be output once every time the optical signal circulates in the ring, which does not meet the requirements of the buffer.

2. Adopt the scheme of optocoupler input and optical switch output.

This scheme is somewhat similar to the former, proposed by Y.Chai et al. of the University of Maryland in 1998 (Y.Chai, et al. "Optical DRAM Using Refreshable WDM Loop Memory", ECOC'98 pp171.), the difference is the use of What is used is a 1×2 optical switch. When the output is required, the optical switch is switched to the output wavelength division multiplexer, thus overcoming the shortcomings of scheme 1.

3. The scheme of adopting 2×2 optical coupler input and demultiplexer output.

Proposed by SLDanielsen et al. (L Danielsen, et.al, "10Gb/s operaion of a multiwavelengthbuffer architecture employing a monolithically integrated all-optical interferometric michelsonwavelength converter," IEEE Phot.Teehnol.Lett.8(1996) 434.). On the input side, the wavelength of the packet in the buffer is first converted to a specific wavelength: if one needs to be stored for one cycle cycle, it will be converted to wavelength _λ2 before entering the buffer, demultiplexed The wavelength λ ₂ is then converted to λ ₁ by a device and a wavelength converter. Since λ ₁ is the output wavelength of the buffer, this will cause the signal to be output after a circle in the optical fiber ring. Similarly, if a packet needs to be stored for two cycles, it will be converted to wavelength λ ₃ , and the signal will be converted to λ ₂ and then converted to λ ₁ in the buffer, so that the signal loops around the fiber for two weeks. By analogy, a package can store n cycles through n wavelength converters. Thus, if two packets arrive at the same time, one packet is switched to _λ1 wavelength and the other packet is switched to _λn wavelength. As a result, both packages are preserved.

4. The solution of using optical fiber ring + TOAD optical switch

AJPoustie et al. proposed a TOAD-based regenerative all-optical buffer solution (AJPoustie, KJBlow, RJManning, "Storage threshold and amplitude restoration in an all-optical regenerative memory," Optics Communications 146 (1998) 262.). It consists of two cascaded TOADs and a fiber delay line (DELAYLINE). Each TOAD consists of a fiber coupler, two wavelength-division multiplexing couplers for importing and exporting switching pulses, a polarization controller, and an SOA slightly off the center of the ring. The fiber delay line (DELAY LINE) and the erbium-doped fiber amplifier (AMPLIFY) are used to control the pulse arrival time and the switching energy of TOAD respectively. The input signal with a certain data format and a wavelength of _λ1 enters the buffer through the input end of TOAD1, and its data format is copied to the clock control signal wavelength _λ2 , and enters the optical fiber storage ring. The function of TOAD2 is a wavelength converter, which re-copy the data format of λ ₂ to wavelength λ ₁ , thus completing the regeneration of the input signal in TOAD1. The stored signal is amplified by the amplifier and fed back to the input of TOAD1, and the cyclic regeneration can keep the signal in the optical fiber ring for a long time. SOA-based TOAD (or SLALOM) only requires extremely low switching energy (typically 1pJ/pulse), and its relatively compact structure can minimize the delay in optical signal processing.

As far as the optical fiber is used as the buffer of the storage body, there is also a scheme of AWG structure (K. Guild, et.al, "A Novel Routing and Buffering in an All-Optical Node", CLEO'99, pp1279.). In addition to the above three types of buffers using optical fibers as storage bodies, various other storage body buffers have been proposed. But all the schemes are based on the single-fiber ring structure of 2×2 coupler, not only the structure is complicated, but also the symmetry and stability are poor, and the storage time is relatively short.

3. Contents of the invention

The invention proposes a dual-fiber ring all-optical buffer based on a 3*3 fiber coupler, which is suitable for storing optical signals with a rate above Gb/s (p second level). The invention has the advantages of simple structure, large storage capacity, and can control the readout time according to needs, and has strong practicability.

The dual-ring coupled all-optical buffer of the present invention is composed of a 3×3 optical fiber coupler, a connecting optical fiber or a connecting optical waveguide, and two wavelength division multiplexing couplers (WDM), and is characterized in that: a parallel arrangement of 3× 3 Optical fiber coupler, the two sides of the coupler are connected to the fiber feedback to form a double-ring structure, and the middle port of the coupler is used as the input and output ports of the buffer, and two wavelength division multiplexing couplers are installed on a fiber ring ( WDM) is used to introduce and export control light, and use the cross-phase modulation (XPM) effect to change the phase difference of the signal light on the two rings, so as to realize the writing and reading of optical signals in the optical fiber ring.

The writing of the optical signal of the present invention does not require any additional control, even for some occasions that require control, only an optical switch needs to be added in front. Since the present invention controls the entire frame, it does not need control pulses with extremely high synchronization requirements and high power like NOLM, and the input control is relatively simple. Because the optical signal is controlled by phase modulation in the optical fiber ring, the optical signal can be stored for a long time. In principle, as long as the coupler is well done, the symmetry of the loop is good, and the power compensation is appropriate, it can be stored for a long time. Due to the phase control, the readout of the optical signal is very easy, as long as the control optical signal is turned off. The control light that maintains the optical signal has only one-way signal, unlike the Sagnac interferometer, which has a two-way signal, so it is not sensitive to the walk-off in the optical fiber, the XPM effect of the reverse signal, etc., and is easy to control. It is not necessary to use light pulses synchronized with the signal light to control the light, as long as the entire frame is controlled. Another solution can also be used to control the maintenance and readout of the control light: the upper and lower rings are mechanically adjusted to a fixed phase difference of π radians, so that the signal can always be stored in the ring and no longer needs to be controlled. Light. When it is to be read out, the control light is used to make one of the rings produce a π radian phase difference, so as to read out. This approach is useful for long-latency RAM.

4. Description of drawings

FIG. 1 is a schematic diagram of a 3×3 fiber coupler used in a dual-ring coupling all-optical buffer of the present invention.

FIG. 2 is a schematic diagram of a double-ring coupling all-optical buffer based on a 3×3 fiber coupler in the present invention.

Fig. 3 is a schematic diagram of an all-optical buffer for an eight-bit parallel signal made by a double-loop coupled all-optical buffer.

5. Specific implementation

Example 1:

In Fig. 2, compared with Fig. 1, it can be seen that the double-ring coupling all-optical buffer of the present invention is that the two side arms of the 3 * 3 coupler are connected and sealed into two equal-length optical fiber rings with optical fiber materials, and the middle arm As the input and output ports of the all-optical buffer. Two WDMs are connected to one of the optical fiber rings to import and export control light. The 3×3 coupler used here is made to conform to the following matrix during the fabrication process: $\left[\begin{array}{c}{\mathrm{E.}}_1\\ {\mathrm{E.}}_2\\ {\mathrm{E.}}_3\end{array}\right]\left(z\right)=\left[\begin{array}{ccc}1/2& j\sqrt{2}/2& -1/2\\ j\sqrt{2}/2& 0& j\sqrt{2}/2\\ -1/2& j\sqrt{2}/2& 1/2\end{array}\right]\left[\begin{array}{c}{\mathrm{E.}}_1\\ {\mathrm{E.}}_2\\ {\mathrm{E.}}_3\end{array}\right]\left(0\right)$

As shown in Figure 2, the specific working process of the buffer is as follows:

When the input optical signal is input from the 2 ends, according to the above matrix, it is divided into two paths after coupling and enters two optical fiber rings from the 1' and 3' ends respectively. Since the lengths of the two optical fiber rings are equal, when no control light is added , the two optical pulses will be fed back to the input terminals 1 and 3 at the same time, and after the interference of the optical coupler, they will be output from the 2' terminal again, which is only delayed by one loop period. When the optical signal is to be temporarily stored, the optical signal added to the optical fiber ring (33') of the WDM is under the action of the control light, and the phase shift of π radians is generated by cross-phase modulation, so that after the interference of the optical coupler, the optical signal It will be redistributed into the two fiber loops and not output from the 2' end. In this way, as long as the control light is always present, the light pulses will always be exchanged in the two rings, forming an all-optical buffer. When reading is required, just turn off the control light. The present invention can adopt the light level signal of positive logic (that is, the logic "1" when there is light, and the logic "0" when there is no light) as the write control, and the negative logic (that is, "0" when there is light, and "1" when there is no light) ) as a readout control. The present invention can also adopt the light level signal of negative logic (that is, the logic "0" when there is light, and the logic "1" when there is no light) as the write control, and the positive logic (that is, "1" when there is light, and "0" when there is no light) ”) as a readout control. The control light here does not necessarily need to use light pulses synchronized with the signal light, as long as the entire frame is controlled.

Example 2:

As shown in Figure 2, based on the different control modes of the control light for maintenance and readout, the double-ring coupled all-optical buffer of the present invention can also adopt another scheme: other methods can be used to make the upper and lower optical fiber rings (11' and 33') have different lengths, so that the optical signal generates a fixed phase difference -π radians (or its integer multiples) when passing through it, so that the signal can be stored in the ring all the time, and no need to control the light. When it is to be read out, the control light is used to make one of the rings produce a π radian phase difference, so as to read out. This approach is useful for long-latency RAM.

In embodiment 1 and embodiment 2, what the storage of photon adopts is the optical fiber loop, along with the further development of optical waveguide technology and manufacturing technology, this optical fiber loop also can adopt other optical waveguide material to make; In order to compensate optical coupler and the power loss in the fiber ring, a one-way amplifier can be added in the two fiber rings as needed to compensate for the energy loss of photons in the fiber ring. In this way, photons in the fiber ring can survive for a long time. When it is necessary to read out, it is only necessary to turn off the control light (equivalent to adding a low light level effective signal). The unidirectional amplifier here can be an erbium-doped fiber amplifier, a semiconductor optical amplifier or other optical amplifiers.

Example 3:

On the basis of embodiment 1 or embodiment 2, a plurality of such all-optical buffers (such as 8 such buffers) can be utilized to form an all-optical buffer of parallel signals under the control of the same read-write control optical signal device. For example, as shown in FIG. 3 , an all-optical buffer for a parallel signal with 8 bits as a parallel byte.

Claims (7)

1. double-ring coupled full optical buffer, by one 3 * 3 fiber coupler, connect optical fiber or connect optical waveguide, and two wave division multiplex couplers (WDM) constitute, it is characterized in that: adopt 3 * 3 fiber couplers that are arranged in parallel, both sides port (1 with coupling mechanism, 1 ' and 3,3 ') constitute twin nuclei (ring 11 ' and ring 33 ') through connecting the optical fiber feedback, with the input (2) of the Centronics port of coupling mechanism as buffer, output (2 ') port, two wave division multiplex couplers (4) are installed in order to introduce and to derive control light on a fiber optic loop, utilize cross-phase modulation (XPM) effect to change the phase differential of flashlight on two rings, realize light signal writing and reading in fiber optic loop.

2. double-ring coupled full optical buffer according to claim 1 is characterized in that: thus the both sides output port of 3 * 3 fiber couplers is connected to the fiber optic loop that the corresponding input end mouth constitutes two equal lengths with optical fiber.

3. according to claim 1 or 2 described double-ring coupled full optical buffers, it is characterized in that: (it is logical one that light is promptly arranged can to adopt the flat signal of light of positive logic, unglazed is logical zero) as writing control, adopt negative logic (it is " 0 " that light is promptly arranged, and unglazed is " 1 ") as reading control.

4. according to claim 1 or 2 described double-ring coupled full optical buffers, it is characterized in that: (it is logical zero that light is promptly arranged can to adopt the flat signal of light of negative logic, unglazed is logical one) as writing control, adopt positive logic (it is " 1 " that light is promptly arranged, and unglazed is " 0 ") as reading control.

5. according to claim 1 described double-ring coupled full optical buffer, it is characterized in that: the length of two fiber optic loop (11 ' and 33 ') is different about using, make light signal therein by the time produce fixing differing-the π radian, thereby can make signal in ring, store always, no longer need to control light, in the time will reading, make one of them ring produce the π radian with control light again and differ, thereby read.

6. according to claim 1 or 2 or 5 described double-ring coupled full optical buffers, it is characterized in that: when cache-time is longer, can in two rings of light, introduce image intensifer as required, in order to the energy loss of compensation photon in fiber optic loop.

7. according to claim 1 or 2 or 5 described double-ring coupled full optical buffers, it is characterized in that: can utilize a plurality of such buffers, under the control of same read-write control light signal, constitute the full optical buffer of parallel signal.