JPS61264890A - Optical time switch - Google Patents

Abstract

PURPOSE:To simplify a circuit connected with the first and the second delay circuits by providing a delay time at the second delay circuit with changing an attribute, such as a wave length, etc., before distributing an optical signal to a delay element. CONSTITUTION:Each time slot time-division-multiple accessed optical signal on an inputting optical transmission line 30 is converted to one of the wave lengths lambda0-lambdam-1 and is outputted to an optical transmission line 31. Afterwards, the optical signal is distributed at an lxm optical switch 1 and it is delayed, for example, at a delay element 1i by iXt and is inputted to an (n) optical coupler 2. The optical signal outputted from the (n) optical coupler 2, after wave length-multiplexed on an optical transmission line 32, is inputted selectively from a delay element 20 to a delay element 2(m-1) according to the wave length by an m branching filter 3. The light of lambdaj, after delayed by jX(nXt), is coupled or synthesized with other rays of light at an (m) coupler or an (m) wave synthesizer 4 and is outputted to an output optical transmission line 33. To constitute the optical time switch of N-multiple, it is possible to reduce the number of the delay element by selecting (n) and (m) so as to satisfy (m-1)n <N<=mn.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a time switch for an optical time division exchange that exchanges time division multiplexed optical signals as they are.

(Prior art) Conventional devices of this type include those using optical delay elements;
Some devices use optical memory using optical bistable elements. In order to exchange N multiplexed optical signals, N optical delay elements are used in the former case, and N1 optical delay elements are used in the latter case (l is 1 time). The number of pits in a slot) is required as an optical memory, and as the time division multiplexing degree N increases, the amount of hardware required for the delay circuit and memory circuit increases. In Fig. 3, optical delay elements are arranged in parallel and an input optical signal is distributed to appropriate delay elements 11 by IXN optical switch lot, and the delay time is 1.
-t (t is the time of one time slot), and then output to the output optical transmission line 103. In addition, the applicant previously used two types of delay circuits, the first and the second. proposed a method to reduce the amount of hardware (
Patent application 1978-178144>. FIG. 4 shows an example thereof. Delay elements 10 to 1 (n-1) have a delay unit of time t of one time slot (0, t, 2t, .
..., (n-1)・t), and from the delay element to 2(m-
1) uses time n-t as the unit of delay (0+ n
-t, 2n-t,..., (m-1)・(n-
t)).

The optical signal input from the input optical transmission line lot is delayed by it in the delay element 11 in the first delay circuit.

Delay element 2 in the second delay circuit by the nxm optical switch
guided by j, and after a delay of j・(nt) there,
Output to the output optical transmission line. Although this method requires fewer delay elements than the method shown in FIG. 3, a non-blocking time switch cannot be constructed unless a non-blocking optical switch is used to connect the first and second delay circuits.

(Problems to be Solved by the Invention) An object of the present invention is to improve the above-mentioned drawbacks, and to exchange optical signals by using fewer optical delay elements than the number of time division multiplexes, and to achieve a number of times one time division multiplex. The object of the present invention is to provide an optical time switch which is more economically advantageous than conventional devices.

(Means for Solving the Problems) The features of the present invention for achieving the above object include a delay circuit whose unit of delay is t (time of one time slot), and nt ( This is realized by a combination of two types of delay circuits, one in which the unit of delay is an integral multiple of t, and the amount of delay that should be given by the second delay circuit before the optical signal enters the first delay circuit. The purpose is to set the amount of delay in the second delay circuit by converting the attributes of the optical signal into corresponding attributes.

(Function) Since the number of elements in each delay circuit is smaller than the number of time slots, two or more signals are distributed to the same time slot at the output of the first delay circuit.

These signals are distributed by a second delay circuit into individual time slots according to their wavelength or phase attributes. Therefore, an optical time switch is provided with a much smaller number of delay circuits than the number of time division multiplexers.

(Embodiment) FIG. 1 shows an embodiment of the present invention in which wavelengths are used to add attributes, and 1 is an lxn optical switch capable of switching light of a plurality of wavelengths.

2 is an n optical coupler, 3 is an m demultiplexer, 4 is an m optical coupler or m multiplexer, 5 is a wavelength conversion circuit, 6 is a first delay circuit, 7
is the second delay circuit, 30, 31, 32, 0 is the optical signal transmission line, 40, 41...4 (n-1) is the output of the lxn optical switch, 50, 51... 5 (n- 1) is the input of the n optical coupler, 60, 61, -6 (m-1) is the output of the m demultiplexer, 70, 71...7 (m-1) is the m optical coupler or m multiplexer. The input of the device is Ruru. The operation will be explained below.

First, an overview of the operation will be explained. The time-division multiplexed (multiplicity N) optical signal of each time slot on the input optical transmission line (9) is converted by the wavelength conversion circuit 5 to any wavelength from λ0 to λ771-1, and then transferred to the optical transmission line 31. come out on top. Thereafter, the optical signal is distributed by an Lxn optical switch 1, delayed by it by, for example, a delay element 1i, and enters an m optical coupler 2. Delay elements 10 to 1 (n-1) use time t of one time slot as a unit of delay, and delay elements 10 to 1 (n-1)
is the delay time O1, the delay time it is for the delay element 11, and the delay time (n-1)·t for the delay element 1 (n-1). Delay elements 10 to 1 (n-1) input to m optical coupler 2
λ subjected to delay. The optical signal with a wavelength of 2m-1 from The light with the wavelength λH-t is added to the delay element 2 (m-
1) is selectively input. That is, the light converted into the wavelength λj by the wavelength conversion circuit 5 is inputted to the delay element 2j by the m demultiplexer 3. The light of λj becomes j・(n・
After the delay, the light is combined or multiplexed with other light by an m-optical coupler or m-combiner 4 and output onto an output optical transmission line 33.

2 (m-1) from the delay element addition uses nt as the unit of delay, and the delay element addition..., 2j..., 2(m-
1) are delay times O2..., j・(nt), respectively.
....

(m-1)·(nt).

In this way, the wavelength conversion circuit 5 converts λjK to lx
The optical signals selected for n-optical Swiss inch power 41 have a total of (
i+j−n)·t(i−t in the first delay circuit 6.

The second delay circuit 7 causes a delay of j·(nt). Although a plurality of optical signals may exist simultaneously in the n optical coupler 2, since these lights have different wavelengths, they can be separated by an m demultiplexer.

Next, a method for selecting delay elements in the first and second delay circuits 6 and 7 will be explained. Considering the case where a delay of xt is given to the optical signal in a certain time slot on the input transmission path I (X is a natural number smaller than the multiplicity N), X is x=i+jn
Therefore, instead of giving a delay of xt, ixt and jX
nt delays may be applied separately and consecutively. Here.

For x and n where 0≦X≦N-1 1≦n≦N, i where 0≦i≦n-1 and O≦j
, j are uniquely determined, so using i and j, elements 11 and 2j can be selected from among the delay elements in the first and second delay circuits 6.7. (m-1), which is the maximum value of n and j, is a natural number that satisfies (m-1)n<N≦mn.

L(n-1) from the delay element 10 and 2(m-1) from the delay element 10
) are the lengths corresponding to the delay times, respectively, and λ. From λ□
This can be realized by using an optical fiber that transmits light with a wavelength of −1. The wavelength conversion circuit 5 is a light receiving circuit capable of receiving light having the wavelength of the optical signal on the input optical transmission line I, and a wavelength λ. from λ□−
This can be realized with a light emitting circuit consisting of m laser diodes that emit light at one wavelength.

FIG. 2 shows an implementation of the lxn optical switch 1. 8 is n
The branch, 80.81, -.8(n-1), is a laser diode switch. The laser diode switch is described in the literature [V-Switching characteristics of the diode switch J,
IEEE vow QE-19, pp. 157-164
.

1983 ([M, Ikeda, “3witching
Characteristic of La5er D
iode 5w1tch,” IEEEJ, Quan
tum Elect -ron,, vol, QE-
19, pp157-164.1983J), the output light can be turned on/off by changing the applied current.
OFF is possible, and the document "Separation characteristics of laser diode optical switch", Journal Op Applied,
Physics, voA'561 A51 page 131
9-1324, 1984 + (“M, Ikeda
, “l5olationCharacteristi
cs for La5er Diode 0ptica
l 5w1tches.

'J, Appl, Phys, voL56. no
,5. pp1319-1324゜1984J)
As shown in g, 11, switching operation is possible over a certain wavelength range. Therefore, the switching range of wavelengths of the laser diode switch is λ. If λm-t is selected from
An lxn optical switch capable of switching light of wavelengths up to m-1 can be realized.

In order to make the wavelength of the optical signal on the output optical transmission line coincide with the wavelength of the optical signal on the input optical transmission line I, λ.

From λ. A wavelength conversion circuit is added on the output optical power transmission line 33, which is a combination of a light receiving circuit capable of receiving light with a wavelength of −1 and a light emitting circuit consisting of a laser diode that emits light at the wavelength of the optical signal between the input optical transmission lines. do it.

With such a configuration, an N-multiplex optical time switch can be realized with one wavelength conversion circuit, n0m delay elements, and some passive optical components, and when the multiplicity N is large, the conventional configuration can be realized. It is possible to significantly reduce the number of elements compared to optical time switches.

(Description of Effects) As explained above, according to the present invention, n and m are used to configure an N-multiplex optical time switch.

(m-1) By appropriately selecting n<N≦mn, the number of delay elements can be reduced, and before distributing the optical signal to the delay elements, attributes such as wavelength can be changed to By setting the delay time in the delay circuit, the circuit connecting the first and second delay circuits can be simplified.

[Brief explanation of drawings]

Fig. 1 is an example of a time switch according to the present invention, Fig. 2 is an example of an Lxn optical switch capable of wavelength multiplexing, Fig. 3 is a diagram showing an experimental example of current-light output characteristics of a laser diode switch, and Fig. 4 is a diagram showing an example of an experiment on current-light output characteristics of a laser diode switch. This is an example of an optical time switch proposed in Japanese Patent Application No. 59-178144. [Explanation of symbols in the diagram] 1...lxn optical switch 2...n optical coupler 3...m demultiplexer 4...m optical coupler or m multiplexer 5...Wavelength conversion Circuit 6...First optical delay circuit 7...Second optical delay circuit 8...n optical splitter 10, 11,..., 1(n-1)...1 time slot Adding delay elements in units of time t, 21. ..., 2(m-1)...Delay element force in units of nt, 31, 32.33... Optical transmission line 40.41, --..., 4 (n -L)-1xn light Switch output 50.51. ..., 5(n-1)...
Input of n optical coupler 60.61,...,6(m-1)
... m demultiplexer output cuff 0.71. ..., 7(m-1
)...m optical coupler or m multiplexer input 80.81. ..., 8(n-1)... Laser diode switch 100... Input optical transmission line 101... lxN optical switch 102... N optical coupler 103... Output optical transmission line 104... lxn optical switch 105...nxm optical switch 106...m optical coupler

Claims (1)

[Scope of Claims] An optical time switch for exchanging time slots on a highway of time-division multiplexed optical signals, including an attribute adding circuit that adds a wavelength or phase attribute to an input optical signal for each time slot in advance, and a connection to the output thereof. and 1 or n(n
is a natural number smaller than the time division multiplexing number) Delay elements whose delay time units are time slots are connected in parallel or in series, and the input optical signal is distributed to the delay elements according to the amount of delay, and the attributes added by the attribute adding circuit are A first optical delay circuit, which functions independently of and a second optical delay circuit that selects a delay element accordingly.