JPH06252890A - Optical add drop wavelength multiplexer demultiplexer - Google Patents

Abstract

PURPOSE:To insert an optical signal of an optional wavelength from a 1st stage and to extract a desired optical signal among plural optical signals at a final stage at a low cost and low loss by providing proper delay and phase shift to optical transmission lines in plural optical distributers connected in series each having a couple of input terminal and output terminal. CONSTITUTION:Optical distributers each having optical input and output terminal in pairs are connected in series by using an optical guide path to form a coherent optical transversal filter. A couple of optical guide paths between the optical distributers are adjusted to have the same delay based on the length and the phase is shifted based on the optical signal wavelength. Then a delay time T and a phase shift theta1-n-1 are set by a predetermined equation together with distribution ratio of the optical distributers C1-Cn by using optical delay lines D1-n-1. Then optical signals lambda1, 2-lambdad1, 2- An are inputted to one of the distributer C1 and optical signals lambdaa1, 2- are inputted to the other. Thus, the optical signals lambdad1, 2- are extracted from the distributer Cn and the signals lambdaa1,2- are inserted at a low cost and low loss.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical add / drop wavelength demultiplexing device that can be used in, for example, an optical wavelength multiplexing communication network.

[0002]

2. Description of the Related Art As is well known, an optical filter with a narrow bandwidth is required to realize an optical wavelength division multiplexing communication network for carrying out large capacity information communication. In particular, an optical add / drop wavelength demultiplexer (hereinafter referred to as an optical ADM) that inserts (adds) an optical signal of a specific wavelength from a node into an optical fiber trunk line, removes an optical signal of a specific wavelength (drop), and sends the optical signal to a node Called) is required. An optical ADM incorporated in an optical fiber trunk line of a conventional optical wavelength multiplex communication network is basically configured as shown in FIG.

In FIG. 3, 11 is an optical circulator 1.
1, and a plurality of wavelengths λ 1, λ 2, from an optical fiber trunk line (not shown) are provided at the light input end of the optical circulator 11.
, .Lambda.d, ... .lambda.n are multiplexed to provide a multiplexed optical signal. The optical circulator 11 once sends the input multiplexed optical signal to the Fabry-Perot resonator filter 12.

This Fabry-Perot resonator filter 12
Has a characteristic of transmitting light of one specific wavelength and reflecting light of other wavelengths. Now, assuming that the wavelength of the specific passing light of the Fabry-Perot resonator filter 12 is λd, the wavelength of λd in the multiplexed optical signal from the optical circulator 11 is
Of the optical signal passes through the filter 12 and the other wavelengths λ
The optical signals of 1, λ2, ..., λn are reflected by the filter 12 and output from the optical circulator 11. As a result, only the optical signals of the selected wavelength can be removed and the optical signals of other wavelengths can be passed.

The optical output of the optical circulator 11 is supplied to one optical input end of the directional coupler 13 and is sent from one optical output end to the optical fiber trunk line. Here, if an optical signal of an arbitrary wavelength λa is given to the other optical input end of the directional coupler 13, the optical signal is multiplexed (inserted) with the optical signal from the optical circulator 11 and is transmitted to the optical fiber trunk line. Can be sent out.

However, the conventional optical AD as described above is used.
In M, an optical circulator which is not only expensive but also has a large insertion loss must be used. Further, since only one wavelength can be selected by the Fabry-Perot resonator filter 12, only light of one wavelength can be removed, which limits the performance of the communication network. When it is desired to remove light of a plurality of wavelengths, a plurality of optical circulators and Fabry-Perot resonator filters are required, resulting in significant increase in cost and loss.

Furthermore, since the directional coupler is used only for inserting an optical signal, both the passing light and the inserting light suffer a large loss. In reality, in order to compensate for this loss, an optical amplifier is inevitably required, and the cost is increasing.

[0008]

As described above, in the conventional optical add / drop wavelength demultiplexer, it was difficult to insert and remove optical signals of a plurality of wavelengths at low cost and low loss.

The present invention has been made in order to solve the above problems, and is an optical add / drop wavelength demultiplexing device which is low in cost and low in loss and which can easily insert and remove optical signals of a plurality of wavelengths. The purpose is to provide.

[0010]

In order to achieve the above object, an optical add / drop wavelength demultiplexing apparatus according to the present invention takes in optical signals from a pair of optical input terminals and outputs a pair of optical signals at a predetermined distribution ratio. Distributing to the optical output terminal, a certain transmission delay difference is generated in the optical connection between the plurality of optical distributors that are optically connected in series with each other and the pair of optical input / output terminals between the optical distributors. And a transmission delay means for phase-shifting an optical signal of an arbitrary wavelength between the respective optical distributors,
By setting the distribution ratio and the amount of phase shift, the optical signal of an arbitrary wavelength is output from one optical output end of the final stage optical distributor, and the other optical signal is output from the other optical output end. .

[0011]

In the optical add / drop wavelength demultiplexer having the above-described structure, a plurality of optical distributors having a pair of optical input / output terminals are connected in series, and delay and phase shift suitable for optical signal transmission between the optical distributors are provided. , We realize a coherent optical transversal filter, insert an optical signal of arbitrary wavelength in the first stage optical distributor of this filter, and use the optical circulator and Fabry-Perot resonator filter by utilizing the complementary function of the filter. Instead, the optical signal of the desired wavelength or wavelengths is removed by the final stage optical distributor.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of an optical ADM according to the present invention, where C1 to Cn are optical distributors. Each of the light distributors C1 to Cn has a pair of light input / output terminals and is directly connected using an optical waveguide. This constitutes a coherent optical transversal filter.

The lengths of a pair of optical waveguides connecting the optical distributors C1 to Cn are adjusted so as to produce the same transmission delay difference, and the phases are shifted according to the wavelength of the optical signal to be removed. So that it is adjusted between stages. Directional couplers can be used as the light distributors C1 to Cn.
Each distribution ratio is determined according to the wavelength of the optical signal to be removed.

In FIG. 1, for easy understanding, delay and phase shift are performed by the optical delay lines D1 to Dn-1.
It is assumed that there is no delay or phase shift in the connection part. Further, T represents a delay time, and θ1, θ2, ... Represent a phase shift amount.

When applied to an optical wavelength division multiplexing network, optical signals λ 1, λ 2, from an optical fiber trunk line (not shown)
…. , λn are supplied to one of the optical input terminals of the same optical distributor C1, and optical signals (inserted optical signals λa1, λa2, ...) From a node (not shown) are supplied to the other side of the first-stage optical distributor C1. Of the final stage optical demultiplexer Cn and the optical signals λ1, λ2, ... λa1,
, λn are led to the optical fiber trunk line, and the optical signals (decoupled optical signals) λd1, λ output from the other optical output end
Derives d2, ... To the nodes. Optical ADM with the above configuration
The transfer function of is given by

[0017]

[Equation 1]

Here, ak is a complex number that is a function of the distribution ratio of each optical distributor C1 to Cn and the phase shift amount between stages, and T is an optical delay line D1 to Dn-1. This filter configuration is logically lossless. Therefore, an optical signal not output from one optical output end is output from the other optical output end. This is a very effective characteristic for realizing an optical ADM.

The optical input of the first-stage optical distributor C1 becomes the input of the entire optical ADM (optical transversal filter). The two inputs of the optical distributor C1 are the main line light of the communication network and the light that is injected at the node. The two optical outputs are the optical signal to the trunk line and the decoupled optical signal to the node.

Further, a four-stage optical ADM will be specifically described as an example. The transmission characteristics of this optical ADM can be calculated by the transmission matrix method. First, the output signal of this optical ADM is expressed by the following equation.

[0021]

[Equation 2]

Where Eo is the output signal matrix and Ei
Is an input signal matrix, Ck is a transmission matrix of the kth optical distributor, and Dk is a transmission matrix of the kth optical delay line. According to the configuration of FIG. 2, Eo, Ei and Dk are expressed as follows.

[0023]

[Equation 3] On the other hand, if a directional coupler having a distribution ratio of 50:50 is used for the optical distributors C1 to Cn, Ck is expressed by the following equation.

[0024]

[Equation 4]

From the above, the delay amount T is set to 10 ps, and the phase shift amount τ is θ1 = −π / 2, θ2 = π, θ3.
= -Π / 2, each optical output end of the final stage optical distributor Cn (through the line sending side is a tap, and the node sending side is a tap)
Then, as shown in FIGS. 2A and 2B, mutually contradictory wavelength transmission characteristics can be obtained. In this case, it becomes possible to insert and remove the optical signal of the wavelength λo, and the wavelengths λ1, λ2, λ3
The optical signal can be passed without loss.

The channel frequency interval of each wavelength depends on the delay amount and the number of optical distributors. In this case, since there are four stages, the channel interval is 1 / (4 * (10 ps)) = 25.
GHz.

Therefore, the optical ADM having the above structure is
Optical signals of arbitrary wavelengths can be easily inserted and removed. In this case, the optical circulator and the Fabry-Perot resonator filter are not used, and only the relatively inexpensive directional coupler and the optical waveguide can be used, so that the cost can be reduced.

In particular, by adopting the coherent optical transversal filter structure, it is not necessary to use an optical amplifier, and a great effect can be obtained in reducing loss. Further, it is possible to insert and remove optical signals of a plurality of wavelengths at the same time, and it is possible to dramatically improve the performance of the communication network. The present invention is not limited to the above-described embodiments, and the present invention can be similarly implemented even if various modifications are made without departing from the scope of the present invention.

[0029]

As described above, according to the present invention, it is possible to provide an optical add / drop wavelength demultiplexing device which is low in cost and low in loss and which can easily insert and remove optical signals of a plurality of wavelengths. You can

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of an optical add / drop wavelength demultiplexing device according to the present invention.

FIG. 2 is a characteristic diagram showing output characteristics when a four-stage configuration is used in the embodiment.

FIG. 3 is a block diagram showing a configuration of a conventional optical ADM.

[Explanation of symbols]

11 ... Optical circulator, 12 ... Fabry-Perot resonator filter, 13 ... Directional coupler, C1 to Cn ... Optical distributor, D1 to Dn-1 ... Optical delay line.

Claims (3)

[Claims] 1. A plurality of optical distributors, each of which receives an optical signal from a pair of optical input terminals and distributes the optical signal to a pair of optical output terminals at a predetermined distribution ratio, the optical distributors being optically connected to each other in series. And a transmission delay means for causing a constant transmission delay difference in optical transmission between a pair of optical input / output terminals between the optical distributors and for phase-shifting an optical signal of an arbitrary wavelength between the optical distributors. The optical signal having an arbitrary wavelength is output from one optical output end of the final stage optical distributor by setting the distribution ratio and the phase shift amount, and the other optical signal is output from the other optical output end. An optical add / drop WDM demultiplexer characterized by the above. 2. The optical add / drop wavelength demultiplexer according to claim 1, wherein the optical distributor is a directional coupler. 3. The light distributor is configured by connecting two light distributors in series, and the second light distributor is adjusted by adjusting the phase difference of light at the input of the second light distributor. 2. The optical add / drop wavelength demultiplexing device according to claim 1, wherein the distribution ratio of the output of the optical device can be set to a predetermined value.