JPH10257026A - Wavelength multiplex optical communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wavelength multiplex optical communication system that is accessed simply at a low cost in an optical communication network having branched optical fiber lines. SOLUTION: The wavelength multiplex optical communication system is provided with a 1st system where a signal light at a 1st wavelength band sent from a 1st optical transmitter 1-1 to optical subscribers 6-1-6-8 via a passive optical communication network and with a 2nd system where a signal light at a 2nd wavelength band sent from a 2nd optical transmitter 1-2 to the optical subscribers 6-1-6-8 via a passive optical communication network. The passive optical communication network is provided with an optical transmission line 2, a branching device 3, a 2nd optical filter 4 and an optical fiber line 5, the 1st optical transmitter 1-1 is provided with a light source 7, a 1st optical filter 8 and a multiplier 9, and each light guide path being a component of the 1st optical filter 8 and the 2nd optical filter 4 has a wavelength band pass filter element that passes one wavelength but stops other wavelength in the 1st wavelength band.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength division multiplexing optical communication system capable of efficiently accessing optical information to a subscriber.

2. Description of the Related Art Initially, as a network structure of an optical subscriber system, wavelength division multiplexing optical communication has been carried out by using a branch optical line network or the like laid in a district or a building. After that, the construction of long-distance optical transmission lines has progressed, and the form of an optical communication network over a wide area integrating these has been promising, and studies have begun (for example, the 1996 IEICE Communications Society Conference: B-977). Or 22nd ECOC '96, We
B.1.5).

2. Description of the Related Art As optical communication networks have become wider, high-speed multiplexing is required.
(0.8 nm) intervals are defined.

[0003]

When multiplexing or demultiplexing such narrow-band wavelengths, it is necessary to form a multilayer film by controlling the film thickness with high precision using a conventional dielectric filter. In addition, since wavelength characteristics vary depending on the mounting form of the dielectric multilayer filter, it is not easy to multiplex / demultiplex light having wavelengths specified at 0.8 nm intervals.

On the other hand, D which has been devised as a narrow band light source has been proposed.
The FB-LD, the DBR-LD, and the like have a problem in manufacturing because the diffraction grating is configured to be incorporated in the light source. Also,
Although it seems that a narrow band light source using an acousto-optic modulator or the like has been developed, the number of components increases and the structure becomes complicated.

An object of the present invention is to provide a wavelength-division multiplexed optical communication system that can be accessed simply and inexpensively in an optical communication network having a branched optical fiber line.

[0006]

SUMMARY OF THE INVENTION A wavelength division multiplexing optical communication system according to the present invention comprises: a first optical transmission apparatus;
A first system for transmitting a signal light in a wavelength band to an optical subscriber through a passive optical communication network; and a second system for transmitting a signal light from a second optical transmission device.
A second system for multiplexing the signal light of the wavelength band with the signal light of the first wavelength band and transmitting the multiplexed signal light to the optical subscriber via the passive optical communication network. Is an optical transmission line through which the signal light transmitted from the first optical transmission device and the second optical transmission device propagates, a splitter for splitting the signal light transmitted through the optical transmission line, and a splitter for each of the split signal lights. A second optical filter having an optical waveguide passing therethrough; and an optical fiber line connected to each output port of the optical waveguide constituting the second optical filter, wherein the first optical transmission device has a phase in a first wavelength band. A light source that oscillates signal light for each different wavelength,
A first optical filter having an optical waveguide passing through each of different wavelengths transmitted from each light source; and a multiplexer for collecting each output port of the optical waveguide into one, the first optical filter and the second optical filter. Each of the optical waveguides constituting the filter has a wavelength bandpass element that passes one different wavelength in the first wavelength band but blocks another wavelength, and the signal light in the first wavelength band and the second wavelength band. In the present invention, the demultiplexing elements of the first optical filter and the second optical filter are formed by an optical waveguide type diffraction grating, and the optical waveguide type diffraction grating has the same shape and the same shape. It preferably has characteristics (Embodiment 1).

According to the wavelength division multiplexing optical communication system of the present invention, since a system is constituted by combining a plurality of systems, it is easy to use a dedicated line and a general purpose line easily according to the frequency of use, the type of information, and the like. It can be used effectively. Further, since the signal light is cut out by passing through an optical filter having a sharp wavelength characteristic, a narrow band signal light can be easily obtained, and a normal light emitting element can be used as the oscillation light source. The first optical filter and the second
Since the optical filter is formed of an optical waveguide type diffraction grating and has the same shape and the same characteristics, a filter having a sharp wavelength characteristic can be obtained at low cost.

In the wavelength division multiplexing optical communication system of the present invention, the monitoring light in the first wavelength band transmitted from the optical monitoring device is transmitted to the optical subscriber through the passive optical communication network, and the monitoring light is passively transmitted. An optical monitoring system for receiving, by a light receiving device, return light generated when propagating in an optical communication network; and a passive optical communication network after multiplexing the signal light of the second wavelength band transmitted from the optical transmitting device with the monitoring light. In a wavelength division multiplexing optical communication system provided with an optical communication system for transmitting to an optical subscriber via an optical communication system, a passive optical communication network comprises a signal light transmitted from an optical transmitting device and a pulse-like monitoring signal transmitted from an optical monitoring device. An optical transmission path through which light propagates, a splitter that splits signal light and monitoring light that have propagated through the optical transmission path, and a second optical filter including an optical waveguide that passes through each of the split signal light and monitoring light, Light constituting the second optical filter An optical fiber line connected to each output port of the wave path, wherein the optical monitoring device comprises: a monitoring light source that oscillates light in the first wavelength band; and an optical waveguide that passes through the different wavelengths transmitted from the monitoring light source. A monitoring light generating device comprising a first optical filter provided and an optical pulse gate for forming light in a pulse form by passing light transmitted from the first optical filter through a gate which opens and closes at a predetermined cycle; A light receiving device that processes return light generated when the light propagates through the passive optical communication network for each wavelength by an OTDR (optical time dommain reflectometer); and each optical waveguide configuring the first optical filter and the second optical filter includes: It has a wavelength band-pass element that passes one different wavelength in the first wavelength band but blocks another wavelength, and has a function of receiving return light and monitoring a passive optical communication network. The features, in the present invention, the first optical filter and the second
The demultiplexing element included in the optical filter is formed by an optical waveguide type diffraction grating, and it is preferable that the optical waveguide type diffraction grating has the same shape and the same characteristics (Embodiment 2).

According to this wavelength division multiplexing optical communication system, since a device for constantly monitoring the characteristics of the transmission path through which the signal light propagates is provided, a highly reliable system can be obtained. Since the first optical filter and the second optical filter using the optical waveguide type diffraction grating having the same characteristics are formed, the configuration is simplified, and a filter having sharp wavelength characteristics can be obtained at low cost.

[0010]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description.

(Embodiment 1) FIG. 1 is an overall view of a wavelength division multiplexing optical communication system according to a first embodiment of the present invention.
It is composed of two optical communication systems.

In FIG. 1, a first system includes a first wavelength band (for example, 1.5 wavelength band) transmitted from a first optical transmission device 1-1.
The signal light λ _i (λ ₁ , λ ₂ ... λ _n ) of the μm band) propagates through the optical transmission line 2 and is then power-divided by the splitter 3. Each of the split signal lights λ ₁ , λ ₂ ... Λ _n is selected in wavelength by the second optical filter 4, and the signal light λ ₁ is transmitted to the optical fiber line 5-1. Light λ _n
Only sent. On the other hand, the second system is the second optical transmitter 1-
The signal light λ _{S of} the second wavelength band (for example, 1.3 μm band) transmitted from the optical coupler 10 passes through the optical transmission line 2 together with the signal light λ _i of the first wavelength band via the optical coupler 10 and passes through the splitter 3. , And the signal light of λ _S is transmitted to each subscriber 6 through the second optical filter 4.

[0013] In this way each _{subscriber, λ 1, λ 2 ·· λ} n
And a dedicated line consisting of any one of the wavelengths λ _S
And general-purpose lines.

The first optical transmission device 1-1 includes separate light sources 7 (7-1... 7-n) for oscillating signal lights of different wavelengths λ _{1 to} λ ₈ in the first wavelength band, respectively. Light source 7-1
A first optical filter 8 having an optical waveguide transmitted from the 7-n for each different wavelength, and a multiplexer for collecting each output port of the optical waveguide into one and sending out to the optical transmission line 2 9 is provided.

The light sources 7 are formed of light emitting elements that oscillate signal lights of different wavelengths. As the wavelength multiplexing speeds up, the oscillation wavelength of each light source approaches, so that the oscillation characteristics overlap each other at the bottom as shown in FIG. In this state, interference occurs between signals. Here, there is a method using a light source with a narrow wavelength band, but it is complicated,
It will be expensive. Therefore, the present invention is to obtain a narrow-band signal light as shown in FIG. 2B by using together the first optical filter 8 having a sharp wavelength characteristic.

The first optical filter 8 is for cutting off the skirt portion where the light source 7 oscillates and cutting out a signal light having a narrow wavelength band. The structure of the first optical filter 8 is as shown in FIG.
a (8a-1, 8a-2... 8a-n) and the optical waveguide type diffraction grating 8b (8b-1, 8b-2...) in which the refractive index of each core of the optical waveguide changes periodically in the core axis direction.・ 8b-n)
And formed. The diffraction grating 8b-1 has a band-pass characteristic that passes λ ₁ of the signal light in the first wavelength band but blocks wavelengths of λ ₂ ... Λ _n (see FIG. 4A). Less than,
Similarly, the diffraction grating 8b-n provides the λ of the signal light in the first wavelength band.
_n passes, but has a bandpass characteristic of blocking wavelengths of λ ₁ , λ ₂ ... (see FIG. 4C). Method of the refractive index of the core periodically changes is obtained by irradiating the interference fringes of ultraviolet light to the core doped with GeO _2. Since the bandpass element of the present invention is formed of an optical waveguide type diffraction grating, a filter having a passband of 1 nm or less can be easily obtained.

The multiplexer 9 multiplexes and sends out the signal light λ _i of the first wavelength band oscillated in parallel, and is formed by combining a half mirror or an optical coupler. FIG. 5 shows a multiplexer for multiplexing eight signal lights by combining optical couplers for splitting into 50%. A splitter combined with an optical coupler is preferable because it has good wavelength preservation properties and is inexpensive.

By configuring the first optical transmission device 1-1 in this way, high-speed wavelength multiplexing can be performed with a normal light emitting element without using a high-speed oscillation device.

The second optical transmitter 1-2 transmits the multiplexed signal light having the wavelength λ _S.

Next, the configuration of the passive optical communication network will be described.

The optical transmission line 2 is usually several km to several tens km, and a multi-mode optical fiber or a single-mode optical fiber is used. The multi-mode optical fiber is made of silica-based glass having a refractive index increasing dopant such as Ge.
It is formed of a core having an outer diameter of several tens of μm to which O ₂ is added, and a cladding having an outer diameter of 125 μm covered with quartz glass on the outer periphery of the core. Further, the single mode optical fiber is formed of a core having a diameter of several μm obtained by adding GeO ₂ to silica glass and a cladding having an outer diameter of 125 μm covered with silica glass on the outer periphery of the core. It is used as a long-distance link because it has less loss and smaller chromatic dispersion compared to.

The splitter 3 splits and supplies the first and second signal lights in accordance with the number of subscribers 6 and has the same configuration as the multiplexer 9.

The second optical filter 4 converts the branched signal lights λ ₁ , λ _2, ... Λ _n of the first wavelength band into any one of the optical fiber lines 5 (# 1, # 2,. And the branched signal light λs of the second wavelength band is directly sent to the optical fiber line 5 (# 1, # 2, #n). Such a second optical filter 4 is required to have the same characteristics as the first optical filter 8, and has the same configuration and the same characteristics as the first optical filter 8. Therefore, it is preferable to arrange the optical waveguide constituting the first optical filter 8 and the optical waveguide constituting the second optical filter 4 side by side, and simultaneously irradiate the core portion with ultraviolet rays to form a diffraction grating. is there. That is, an optical waveguide type diffraction grating in which the refractive index of each core changes periodically in the core axis direction is formed in the optical waveguide forming the second optical filter 4, and each diffraction grating has one wavelength in the first wavelength band. Has a bandpass characteristic of passing but blocking other wavelengths.

The branched optical fiber lines 5 (# 1, # 2
.. #N) generally use multimode optical fibers, and are connected to subscribers 6 (6-1, 6-2,..., 6-n), respectively.

The optical coupler 10 has a signal light λ in the first wavelength band.
_i and the signal light λ _S of the second wavelength band are multiplexed and sent out to the optical transmission line 2. For example, as shown in FIG. It has a part 10-1. Between the coupling portions 10-1, light can gradually move from one optical fiber to the other. When light from the input end a-1 of the wavelength lambda _a optical coupler 10 having such a configuration is incident, the incident light lambda _a is gradually moved to the optical fiber b from the optical fiber a, optical fiber again after finishing moving all The movement from b to the optical fiber a is repeated until the coupling interval S ends. On the other hand, when the light from the input end b-1 of the wavelength lambda _b of the optical coupler 7 is incident, as well as light of wavelength lambda _b moves between the optical fiber b and the optical fiber a. At this time, the input terminal a-1 and the input terminal b
Since the two lights incident from −1 have different wavelengths, the two light beams have different periods of movement between the optical fiber b and the optical fiber a. By selecting the bond distance S to its predetermined length, it is possible to emit light of both wavelengths lambda _a and the wavelength lambda _b to the output terminal b-2 of the optical fiber b. That is, the signal light λ _{i in} the first wavelength band and the signal light λ _{S in} the second wavelength band
Can be sent out to the optical transmission line 2.

The passive optical communication network is constituted by passive elements that do not include active elements such as optical amplifiers, and has a property of no directivity. Therefore, the optical communication from the station to the subscriber has been described, but the optical communication can also be performed from the subscriber to the station.

Next, the propagation path of the optical communication system will be described. The first path is the first path oscillated by each light source 7-1... 7-n in the first optical transmission device 1-1.
Each of the signal lights λ ₁ , λ ₂ ... Λ _n in the wavelength band is shaped up to a predetermined wavelength band by the first optical filter 8 so that no interference occurs between the signal lights. Each of the shaped signal lights λ ₁ , λ ₂ ... Λ _n of the first wavelength band is multiplexed by the multiplexer 9 and then transmitted to the optical transmission line 2 through the optical coupler 10. After sending the signal lights lambda ₁ was, the lambda ₂ · · lambda _n propagated through the optical transmission line 2, is the power divided by the splitter 3, each of the divided signal light lambda ₁ was, the lambda ₂ · · lambda _n first The two optical filters 4 separate optical fiber lines # 1, # 2, #n for each wavelength.
Assigned to. Each optical fiber line # 1, # 2, #n
Are connected to the subscribers 6-1, 6-2,..., 6-n, respectively.

In the second path, the signal light λ _{S in} the second wavelength band transmitted from the transmitting device 1-2 passes through the optical coupler 10 and is transmitted to the optical transmission line 2 together with the signal light in the first wavelength band. The transmitted signal light λ _S propagates through the optical transmission line 2 and is then power-divided by the splitter 3. The split signal light λ _S passes through each optical waveguide forming the second optical filter 4 and is transmitted as it is to each of the optical fiber lines 5-1, 5-2,. , 6-2... 6-n.

That is, according to this system, each subscriber 6
Can obtain common information by using the signal light λ _S of the second wavelength band, and further obtain the signal light λ ₁ of the first wavelength band,
by lambda ₂ · · lambda _n can obtain only information communication.

(Embodiment 2) FIG. 7 is an overall view of a wavelength division multiplexing optical communication system according to a second embodiment of the present invention.
It consists of an optical monitoring system and an optical communication system.

In FIG. 7, the optical monitoring system is an optical monitoring device 1
1st wavelength band (for example, 1.5 μm)
(m band) pulsed monitoring light λ _i (λ ₁ , λ ₂ ·· λ _n )
After being propagated through the optical transmission line 12, the power is divided by the splitter 13. Each monitoring light lambda ₁ is divided, λ ₂ ·· λ _n
Is wavelength-selected by the second optical filter 14, and the signal light λ ₁ is applied to the optical fiber line # 1, and similarly, the optical fiber line #n
Is sent only the monitoring light λ _n . The return light generated when the monitoring light propagates through the passive optical communication network is received by the light receiving device.

On the other hand, the optical communication system transmits the signal light (for example, 1.3 μm) of the second wavelength band transmitted from the optical transmission device 11-2.
The signal light λ _S of the (m band) passes through the optical transmission line 12 together with the monitoring light λ _i of the first wavelength band via the optical coupler 26, is power-divided by the splitter 13, and passes through the second optical filter 14. A signal light of λ _S is sent to each subscriber 6.

The configurations of the optical transmission device 11-2 and the passive optical communication network are the same as in the first embodiment.

The optical monitoring device 11-1 includes a monitoring light source 21 for oscillating light in a first wavelength band, and an optical waveguide through which light of different wavelengths λ _{1 to} λ _n transmitted from the monitoring light source 21 passes for each wavelength. A first optical filter 23 having a first optical filter 2
A monitoring light generator 20 comprising an optical pulse gate 25 for transmitting a pulsed monitoring light by a gate which opens and closes the light transmitted from the light source 3 at a predetermined cycle, and processes the return light of the monitoring light for each wavelength by the OTDR. A light receiving device 30 is provided.

The monitoring light source 21 has a wavelength λ _{1 of} the first wavelength band.
Formed by the light-emitting element that oscillates to [lambda] _n.

The first optical filter 23 separates the monitoring light oscillated by the monitoring light source 21 by wavelength, and has the same structure and characteristics as the first optical filter 8 (or the second optical filter 4) in the first embodiment. It has the same configuration. That is, the first optical filter 23 is an optical waveguide (8a-
1, 8a-2... 8a-n) and optical waveguide type diffraction gratings (8b-1, 8b-2... 8b-) in which the refractive index of each core of these optical waveguides changes periodically in the core axis direction. n). The diffraction grating 8b-1 is a filter having a band-pass characteristic that allows passage of λ ₁ of the monitoring light in the first wavelength band but blocks wavelengths of λ ₂ ... Λ _n (see FIG. 4A). Hereinafter, similarly, the diffraction grating 8b-n has a bandpass characteristic of blocking the wavelengths of λ ₁ , λ _2, ... While passing the monitoring light λ n of the first wavelength band (see FIG. 4C). .

A first coupler 22, for example, an optical switch is disposed between the first optical filter 23 and the monitoring light source 21 to sequentially switch the monitoring light source 21 and each port of the first optical filter 23. It is possible. When the optical switch is connected to the port 1, the diffraction grating 8b-1 causes λ ₁
Is output only. Next, when the optical switch is connected to the port 2, monitoring light of λ ₂ is output, and similarly, monitoring light of a different wavelength is sequentially output as the optical switch is switched. FIG. 8A shows these states.

As means for collecting and sending out the monitoring light sequentially output from each port of the first optical filter 23 as described above, for example, as shown in FIG.
The second switch 24 that can be switched in synchronization with the second switch 24 can be used.

The optical pulse gate 25 opens and closes at a predetermined cycle to shape the light passing through the gate into a pulse, and the monitoring light output from the second coupler 24 (see FIG. 8A). Is incident on the optical pulse gate 25, as shown in FIG. 8B, a pulse-like monitoring light λi having a pulse width t and a pulse interval T is obtained. The pulse interval T is a sufficiently large value with respect to the monitoring distance.

The light receiving device 30 includes a photodiode that receives return light generated when the pulse-like monitoring light λ _i output from the optical pulse gate 25 propagates through the passive optical communication network, and a passive diode that receives the return light. OTDR for measuring the state of the optical communication network.

When the pulse-like monitoring light λ _i propagates through these transmission media and components, Rayleigh scattering due to loss of the transmission medium, Stokes light and anti-Stokes light due to Raman scattering, or reflection due to structural non-uniformity light is generated, return light corresponding to the monitoring light lambda _i is received by the light receiving device 8. In the light receiving device 8, the return light is separated for each wavelength by a wavelength separator, and is converted into a current by the light receiver. These current signals are processed by a signal processor,
As shown in FIG. 9, the relationship of the return light corresponding to the monitoring distance is displayed. In particular, each of the optical fiber lines # 1, # 2, #n
Since monitoring light of different wavelengths propagates through the optical fiber line, the situation of each optical fiber line can be monitored. In this embodiment, the optical switches 22 and 24 are connected to both of the first optical filters 23.
However, as shown in FIG. 10A, the same result is obtained even in the case of an optical switch and a multiplexer, or as shown in FIG. 10B, in the case of a splitter and an optical switch. can get.

The reliability of the transmission path is improved by adding a monitoring device to the optical communication system. In addition, the above monitoring device employs an optical filter using a diffraction grating having a simple structure, so that it is inexpensive and high quality. The characteristics of
Since the optical filter and the second optical filter have exactly the same structure, the configuration can be simplified.

[0043]

The present invention is embodied in the form described above and has the following effects.

In the first embodiment of the present invention, since the system is configured by combining a plurality of systems, the dedicated line and the general-purpose line can be easily used depending on the frequency of use, the type of information, and the like, and the line can be effectively used. Can be used.

In the second embodiment of the present invention, since a device for constantly monitoring the characteristics of the transmission path for optical communication is provided, the reliability of the system is improved, and the first optical filter and the second optical filter are used.
Since the optical filter is formed by an optical waveguide type diffraction grating, the configuration is simplified, and a filter having sharp wavelength characteristics can be obtained at low cost.

[Brief description of the drawings]

FIG. 1 is an overall view of a wavelength division multiplexing optical communication system according to a first embodiment.

FIG. 2 is a diagram showing an output waveform (a) of each light source and an output waveform (b) of a first optical filter.

FIG. 3 is a diagram illustrating a configuration of an optical filter.

FIG. 4 is a diagram illustrating reflection characteristics of an optical filter.

FIG. 5 is a detailed diagram showing a configuration of a multiplexer.

FIG. 6 is a detailed diagram illustrating a configuration of an optical coupler.

FIG. 7 is an overall view of a wavelength division multiplexing optical communication system according to a second embodiment.

FIG. 8 is a diagram showing a waveform (a) of the monitoring light output from each port of the first optical filter and a waveform (b) of the monitoring light output from the optical pulse gate.

FIG. 9 is a diagram showing a display unit of the optical monitoring device.

FIG. 10 is a diagram showing another configuration of the coupler used before and after the first optical filter.

[Explanation of symbols]

1-1: first optical transmitter, 1-2: second optical transmitter, 2
... optical transmission line, 3 ... branch device, 4, 8 ... optical filter,
5, 15 ... optical fiber line, 6, 16 ... subscriber, 7 ...
-Light source, 9 ... multiplexer, 10, 26 ... optical coupler, 11-1
... optical monitoring device, 11-2 ... optical transmitting device, 20 ... monitoring light generating device, 21 ... monitoring light source, 22, 24 ... optical switch, 25 ... optical pulse gate, 30 ... light receiving device, λ _i ...
Light in the first wavelength band, λ _S ... Light in the second wavelength band

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI H04B 10/12 10/02 10/28 10/26 10/04 10/06

Claims (4)

[Claims] 1. A first system for transmitting signal light of a first wavelength band transmitted from a first optical transmission device to an optical subscriber via a passive optical communication network, and a first system transmitted by a second optical transmission device. A wavelength division multiplexing optical communication system comprising: a second system that combines the signal light of the two wavelength band with the signal light of the first wavelength band and transmits the multiplexed signal light to the optical subscriber via the passive optical communication network. The passive optical communication network includes an optical transmission line through which the signal light transmitted from the first optical transmission device and the second optical transmission device propagates, and a branching device that branches the signal light transmitted through the optical transmission line. A second optical filter including an optical waveguide that passes through each of the branched signal lights, and an optical fiber line connected to each output port of the optical waveguide that forms the second optical filter; The optical transmitting device transmits a signal for each different wavelength of the first wavelength band. A light source that oscillates light, a first optical filter including an optical waveguide that passes through each of the different wavelengths transmitted from each of the light sources, and a multiplexer that collects output ports of the optical waveguide into one. The optical waveguides forming the first optical filter and the second optical filter are different from each other in the first wavelength band.
A wavelength-division multiplexing optical communication system having a wavelength band-pass element that passes one wavelength but blocks another wavelength, and has an optical communication function using signal light of the first wavelength band and the second wavelength band. . 2. The wavelength band-pass element included in each of the first optical filter and the second optical filter is formed of an optical waveguide type diffraction grating, and the optical waveguide type diffraction gratings have the same shape and the same characteristics. The wavelength division multiplexing optical communication system according to claim 1, wherein 3. The pulse-like monitoring light of the first wavelength band transmitted from the optical monitoring device is transmitted to an optical subscriber via a passive optical communication network, and the monitoring light propagates through the passive optical communication network. An optical monitoring system that receives the return light generated by the light receiving device, and after multiplexing the signal light of the second wavelength band transmitted from the optical transmitting device with the monitoring light, the light is transmitted through the passive optical communication network. In a wavelength division multiplexing optical communication system comprising an optical communication system for transmitting to an optical subscriber, the passive optical communication network includes a signal light transmitted from the optical transmitting device and a pulse-like monitoring signal transmitted from the optical monitoring device. An optical transmission line through which light propagates, a branching device that branches the signal light and the monitoring light that have propagated through the optical transmission line, and an optical waveguide that passes through each of the branched signal light and the monitoring light. A two-light filter; An optical fiber line connected to each output port of an optical waveguide constituting an optical filter, wherein the optical monitoring device comprises: a monitoring light source that oscillates light in the first wavelength band; and a phase transmitted from the monitoring light source. A first optical filter having an optical waveguide that passes for each different wavelength, and an optical pulse gate that forms a pulse-like monitoring light by passing light transmitted from the first optical filter through a gate that opens and closes at a predetermined period. And a return light generated when the monitor light propagates through the passive optical network.
A light receiving device that performs processing for each wavelength by TDR, wherein each of the optical waveguides configuring the first optical filter and the second optical filter has a different one in the first wavelength band.
A wavelength multiplexing optical communication system comprising: a wavelength band-pass element that passes one wavelength but blocks another wavelength; and has a function of receiving the return light and monitoring the passive optical communication network. 4. A wavelength bandpass element included in each of the first optical filter and the second optical filter is formed by an optical waveguide type diffraction grating, and the optical waveguide type diffraction gratings have the same shape and the same characteristics. The wavelength division multiplexing optical communication system according to claim 3.