JP2813773B2 - Optical code conversion system and cross-connect system and device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical code conversion system, a cross-connect system, and an apparatus for realizing a node function of a future optical communication network aiming at a high throughput capacity of a network.

[0002]

2. Description of the Related Art Multiple division communication is a technique for effectively utilizing a transmission band of a transmission line by sharing a same transmission line by a plurality of communication channels and expanding communication capacity.
In time division multiplexing (TDM), a time slot corresponds to a channel, and in optical frequency division multiplexing (OFDM), an optical frequency corresponds to a channel.

In a conventional time division multiplexing (TDM) network, multiplexing / demultiplexing or node functions require much faster and more complex signal processing than the information rate. Therefore, if the speed further increases beyond multi-gigabit, multiplexing
It is expected that separation and nodes will be bottlenecks and throughput will be limited. In order to drastically solve this problem, it has been considered to adopt OFDM as a multiplex transmission system instead of TDM.

[0004] Next, a cross-connect switch in this OFDM network will be described. FIG. 5 shows a topology in which a general mesh network and a ring network of an optical path network coexist. 51 is a link, and 52 is a node. The node is a cross connect switch or ADM (Add / D
It has a function of “rop multiplexer” and plays a role of setting an optical path between arbitrary nodes.

FIG. 6 is a block diagram of an m × m cross-connect in an optical frequency multiplexing network. Reference numeral 61 denotes an optical amplifier; 62, a demultiplexing unit for n optical frequencies from optical frequency f1 to optical frequency fn; An mn × mn spatial optical switch, 64 is a 3R reproducing unit, 65 is an optical frequency converter, 66 is a multiplexing unit, 67 is a control unit, and 68 is an optical frequency reference oscillator. The operation is as follows.

(1) Optically amplify an input signal. (2) The input signal is spatially separated for each optical frequency and input to the matrix switch. (3) The matrix switch outputs a signal to a predetermined output terminal according to a control signal from the control unit. (4) After reproducing the signal, the optical frequency of the input signal is converted to a predetermined optical frequency. (5) Multiplex the optical frequency converted signals. (6) The multiplexed signal is output after optical amplification.

FIG. 6 shows a route in the case where the signal of the optical frequency fn input to the terminal # 1 is converted into the optical frequency fi and output from the terminal #m.

[0008]

As described above, it is necessary to perform wavelength conversion in the optical FDMA cross-connect. This optical frequency conversion can be realized by using several devices such as an optical frequency tunable semiconductor laser and light wave mixing in an optical fiber, all of which are technically difficult and have the following problems. there were.

(A) It is difficult to strictly control the optical frequency and requires an optical frequency reference. (B) It is difficult to perform optical frequency conversion in a wide optical frequency range. 1.55μm band optical fiber amplifier (EDF
A device capable of changing the optical frequency over the entire range of about 2.5 THz in which A) operates effectively has not yet been prospected for practical use. (C) High-speed devices with a response speed of optical frequency conversion of nanoseconds or less have not been realized at present.

That is, there has been a demand for a technique for realizing a node function of cross connect and ADM without using optical frequency conversion.

[0011]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and assigns a different code to each user and encodes and multiplexes information bits for accessing a network. This allows a plurality of different information to be transmitted at the same time using the same optical fiber transmission line, and each user uses the assigned code as a “key” and uses the same code from the received multiplexed information. CDMA in an optical code division multiple access communication network capable of separating and decoding only encoded information
The demultiplexing unit demultiplexes the optical code division multiplexed signal into different codes # 1 to #n, and selects the # 1 to #n.
Input to the selected optical encoders ENC # 1 to ENC # n ,
An optical code conversion system for performing optical code conversion by generating a new optical code is provided.

According to the present invention, as a method of setting an optical path between any nodes constituting a network, a relay node receives encoded information and converts the code according to the optical code conversion in accordance with control information. The present invention provides a cross-connect scheme for transmitting to the next relay node by using the scheme and finally setting a desired optical path between the departure node and the destination node.

The present invention comprises an optical amplifier, a DEMUX, a matrix switch, an optical code converter, a MUX, an optical amplifier, and a controller. The optical amplifier uses a rare earth element-doped optical fiber amplifier, and the MUX and the DEMU.
For X, a beam splitter is used, and the optical code converter is composed of a pair of an optical decoder and an encoder. The optical encoder and the decoder use an optical tapped delay line or an optical ladder network. A cross-connect device using an n × n optical waveguide type space switch as the matrix switch is provided.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. First, optical code multiplex communication will be described. FIG. 1C shows the principle of optical coding and multiplexing in a conventional optical FD.
M: FIG. 1 (a), TDM; conceptual diagram in comparison with FIG. 1 (b).

Optical encoding multiplexing encodes 1-bit information with a specific time waveform. Even if different codes exist on the same transmission line at the same time, the receiving side distinguishes them by the difference in code patterns. Multiplexing is possible. The detailed description of the optical encoder will be described later with reference to FIG.

As an embodiment to which the optical code conversion principle of the present invention is applied, a cross-connect device will be described. Further, the principle of optical code conversion will also be described. FIG. 2 shows an embodiment of the mxm cross-connect device, wherein 1 is an optical amplifier,
2 is a CDMA demultiplexing unit, 3 is an mn × mn spatial optical switch, 4 is an optical encoder, 5 is a CDMA multiplexing unit, and 6 is a control unit.

The operation of the cross-connect device of this embodiment for inputting a code division multiplex signal is as follows.

(1) The optical amplifier 1 optically amplifies an input signal. (2) The input signal is spatially separated by the CDMA demultiplexer 2 for each optical code, and is input to the mn × mn spatial optical switch 3. (3) The spatial light switch 3 outputs a signal to a predetermined output terminal according to a control signal from the control unit 6. (4) The optical encoder 4 converts the optical code of the input signal into a predetermined optical code. (5) The CDMA multiplexing unit 5 multiplexes a plurality of optically converted signals. (6) The signal multiplexed by the optical amplifier 1 is optically amplified and then output.

FIG. 2 shows #n input to terminal # 1.
The route when the code signal is converted into the # 1 code and output from the terminal #m is shown.

FIG. 3 shows the principle of the present optical code conversion. The CDMA demultiplexing section in FIG. 2 includes a beam splitter 7 and n decoders from # 1 code to #n code as shown by broken lines. 8. # Input to terminal # 1
The signal of the n code is distributed to n decoders 8 by the beam splitter 7, and each decoder 8 performs matched filtering, that is,
Perform correlation calculation.

As a result, when the input signal is a #n code, the pulse width corresponding to the autocorrelation function representing the code coincidence from the #n decoder 8 corresponding to the #n code becomes the chip width (described later). An optical pulse waveform having an equal steep peak is obtained, and a cross-correlation function corresponding to intersymbol interference occurs in other decoders.

Since the intersymbol interference can be extremely reduced by using the orthogonal code sequence, it can be neglected. As a result, the output from the CDMA demultiplexing unit at the input terminal # 1 is output only from the #n decoder 8. And the outputs from the other decoders 8 are almost zero. The output pulse from the #n decoder is guided to the optical encoder # 1 of the output terminal #m via the optical matrix switch, and a # 1 code is generated.
As a result, the signal of the #n code input to the terminal # 1 becomes #
The code is converted into one code and output from the terminal #m.

Coding methods are roughly classified into coherent coding and incoherent coding. Coherent coding with small intersymbol interference is considered to be promising in the future. I do.

FIG. 4 shows an example of the configuration of a coherent optical encoder / decoder. Reference numeral 9 denotes a beam splitter, 10 denotes an optical delay line,
1 is a phase shifter and 12 is an optical switch. Note that the delay time of the i-th optical delay line 10 includes τ _i = (i−1) τ and (i =
1, 2,..., N), and a phase shifter 11 and an optical switch 12 are inserted in each delay line 10.

When an optical pulse is input to this optical encoder, a pulse train composed of N pulses at a time interval τ is generated. As a method of encoding this pulse train, each phase shifter 11 modulates the phase of the corresponding delayed pulse, or cuts off or passes the pulse by the optical switch 12 and modulates the intensity of 0 and 1 with each other. There is a way to do it. At this time, one pulse constituting the code is called a chip. still,
The configuration of the optical decoder is the same as that of the optical encoder.

Next, as the mn × mn spatial optical switch, for example, a 2 × 2 optical waveguide switch is connected in multiple stages or a two-dimensional switch array in which switches are arranged in multiple stages. And a so-called three-dimensional free-space optical switch array or the like, in which light beams are connected in free space.

By using this optical code conversion principle, it is possible to realize not only the cross-connect device but also other node functions such as ADM.

As described above, the present invention has been described based on the embodiments. However, the present invention is not limited to the above-described embodiments, and may be implemented in any way unless the configuration described in the claims is changed. it can.

[0029]

The features of the optical code conversion system of the present invention and the cross-connect device to which the present principle is applied are described below. (A) It is clear that optical code division multiplexing using optical frequency conversion does not require strict control of optical frequency in principle, and as a result, an optical frequency reference is not required. (B) Since the optical code conversion is used, the operation speed is not restricted by the conversion speed, and the present invention can be applied to ultra-high speed communication of multi-gigabit or more. Due to the above-mentioned features, a great effect can be achieved, for example, it can be expected to be an important basic technology for configuring a future optical network that is ultra-high speed and excellent in economy.

[Brief description of the drawings]

FIGS. 1A, 1B, and 1C are conceptual diagrams illustrating the principle of optical multiplexing, where FIG. 1A is an optical FDM, and FIG.
M, (c) is optical coding multiplexing.

FIG. 2 is a block diagram of an mxm cross-connect device according to an embodiment of the present invention.

FIG. 3 is a configuration diagram illustrating the principle of optical code conversion according to the present invention.

FIG. 4 is a configuration diagram of a coherent optical encoder / decoder according to the present invention.

FIG. 5 is a conceptual diagram showing a topology in which a general mesh network and a ring network of a conventional optical path network are mixed.

FIG. 6 shows mx in a conventional optical frequency multiplexing network.
m is a block diagram of a cross-connect device of FIG.

[Explanation of symbols]

 Reference Signs List 1 optical amplifier 2 CDMA demultiplexing unit 3 mn × mn spatial optical switch 4 optical encoder 5 CDMA multiplexing unit 6 control unit 7, 9 beam splitter 8 decoder 10 optical delay line 11 phase shifter 12 optical switch

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H04J 13/00 H04B 10/02

Claims (3)

(57) [Claims] 1. A different code is assigned to each user for access to a network, and information bits are coded and multiplexed to transmit a plurality of different information simultaneously using the same optical fiber transmission line. Each of the users uses the assigned code as a “key” and is capable of separating and decoding only information encoded with the same code from the received multiplexed information. In the network, an optical code division multiplex signal is demultiplexed into different codes # 1 to #n using a CDMA demultiplexer , and
An optical code conversion method characterized in that #n is input to the selected optical encoders ENC # 1 to ENC # n to generate a new optical code and perform optical code conversion. 2. A method according to claim 1, wherein the relay node receives the encoded information and sets the code according to the control information at the relay node. A cross-connect method in which a signal is transmitted to a next relay node by using a code conversion method, and a desired optical path is finally set between a departure node and a destination node. 3. An optical amplifier, a demultiplexer (DEMUX), a matrix switch, an optical code converter, a multiplexer (MUX), an optical amplifier, and a controller using the cross-connect method according to claim 2. A rare earth element-doped optical fiber amplifier is used for the optical amplifier, a beam splitter is used for each of the MUX and the DEMUX, and the optical code converter is constituted by a pair of an optical decoder and an encoder; The encoder and the decoder use an optically tapped delay line.
line) or optical ladder network (ladd)
a cross-connect device, wherein an n × n optical waveguide space switch is used as the matrix switch.