JPS63296006A - Bidirectional optical multiplexing and demultiplexing device for three wavelengths - Google Patents

Abstract

PURPOSE:To reduce an insertion loss and the crosstalk of a device by providing three kinds of optical filters for transmission and reflection, for which wavelengths of optical signals are specific, respectively. CONSTITUTION:The titled device 4 is constituted of a first and a second optical multiplexer and demultiplexer 5, 6, and a transmission device 7. Also, optical filters 54, 64 allow optical signal whose wavelengths are lambda1, lambda2 to transmit through and reflect an optical signal whose wavelength is lambda3, an optical filter 55 allows lambda1 to transmit through and reflects lambda2, and an optical filter 65 allows lambda2 to transmit through and reflects lambda1, and they are in relation of lambda1<lambda2<lambda3 or lambda1>lambda2>lambda3. According to such constitution, a signal of lambda1 which made incident on an end part 51b of an optical fiber 51 transmits through the filters 55, 54 and 64, and thereafter, reflected by the filter 65 and emitted from an optical fiber 63. In the same way, a signal of lambda2 which is made incident on an end part 61b of an optical fiber 61 is emitted from an optical fiber 53, and a signal of lambda3 which is made incident on an optical fiber 62 is emitted from an optical fiber 52.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a three-wavelength bidirectional optical multiplexing/demultiplexing device used in wavelength multiplexed optical communication.

(Prior Art) In optical communications using optical fibers as transmission paths, attempts have been made to achieve wavelength multiplexing optical communications using a plurality of mutually different wavelengths. In particular, recently, two-way multiplex communication systems have been developed that are capable of mutual communication between centers such as telephone and data services and subscriber homes, as well as one-sided communication from centers such as image communication services to subscriber homes. is attracting attention.

Figure 4 shows a conventionally known two-wavelength two-way optical multiplexer/demultiplexer as a two-way optical multiplexer/demultiplexer used in such wavelength multiplexing communications. The optical demultiplexer includes a first optical multiplexer/demultiplexer 1 and a second optical multiplexer/demultiplexer 2 connected to the first optical multiplexer/demultiplexer 1 via a transmission line 3 made of an optical fiber. The first optical multiplexer/demultiplexer 1 includes a first optical fiber 11 whose one end is connected to the transmission line 3 and constitutes a main path, and a first optical filter disposed at a branch point A of the optical fiber 11. 13 and a second optical fiber 12 joined to the side surface of the first optical fiber at a branch point A. On the other hand, the second optical multiplexer/demultiplexer 2 has one end connected to the transmission line 3, a third optical fiber 21 constituting the main path, and a second optical fiber 21 disposed across the branch point of the optical fiber 21. The fourth optical fiber 22 is connected to the side surface of the first optical fiber at the branch point B.

In such a configuration, the optical filters 13.23 are each disposed diagonally in the optical path of the optical fiber 11.21, and the optical fiber 12.22 is such that the optical signal incident on the optical fiber 11.21 from the transmission line 3 passes through the optical filter. They are joined so that when reflected at 13 and 23, their leading axes align with the light IL 21, respectively.

Further, the optical filter 13 transmits the optical signal with the wavelength λl and reflects the optical signal with the wavelength λ2, and the optical filter 23
reflects the optical signal of wavelength λl and transmits the optical signal of wavelength λ2. Therefore, as shown in the figure, the optical signal of wavelength λ1 incident on the optical fiber 11 of the first optical multiplexer/demultiplexer 1 passes through the optical filter 13, propagates through the transmission line 3, and enters the optical fiber 21. The light is reflected by the optical filter 23 and output from the fourth optical fiber 22. on the other hand,
The optical signal of wavelength λ2 that is incident on the optical fiber 21 of the second optical multiplexer/demultiplexer 2 passes through the optical filter 23, propagates through the transmission line 3, enters the light 11, and is reflected at the optical filter 13. The light is emitted from the second optical fiber 12. In this way, two-wavelength bidirectional optical communication can be performed.

In the optical multiplexing/demultiplexing device described above, the optical fibers 11 and 21 constituting the main path are the same as the optical fibers constituting the transmission line 3, considering the coupling efficiency with the light source (not shown) and the connection loss with the transmission line 3. On the other hand, the optical fibers 12 and 22 connected to the photoreceiver (not shown) each have a connection loss (specifically, loss due to connection length) with the optical fiber 11 and 21 taken into consideration. Then, it is preferable that the core diameter is larger than that of the optical fiber 11.21, or that it has a higher numerical aperture, or both.

(Problems to be Solved by the Invention) Recently, as various data communication systems using telephone lines have become popular, two-wavelength multiplex communication as described above is no longer sufficient, and, for example, three-wavelength two-way multiplex communication has become popular. system is desired.

However, the details of the configuration of the 3-wavelength optical multiplexer/demultiplexer used in the 3-wavelength multiplexed bidirectional communication system, that is, the combination of wavelengths and optical fiber parameters, are not yet known, and the details of the combination of wavelength and optical fiber parameters are not yet known. There is an increasing demand for a three-wavelength bidirectional optical multiplexing/demultiplexing device with low crosstalk.

The present invention was made in response to such conventional demands, and an object of the present invention is to provide a bidirectional optical multiplexer/demultiplexer for three wavelengths with low insertion loss and low crosstalk.

(Means for Solving the Problems) In order to achieve the above object, according to the three-wavelength bidirectional optical multiplexer/demultiplexer of the present invention, one end portion is connected to one end of the transmission line,
A first optical fiber having first and second branch points in order from the one end, first and second optical filters respectively disposed at the first and second branch points, and first and second optical fibers. At the branch point, the optical signal that has entered the first optical fiber from the transmission path is
and a first optical multiplexing/demultiplexing comprising second and third optical fibers that are joined so that their tip axes align with the optical axis of the first optical fiber when reflected by the second optical filter. a fourth optical fiber having one end connected to the other end of the transmission line and having third and fourth branch points in order from the one end, disposed at the third and fourth branch points, respectively; The optical signal that has entered the fourth optical fiber from the transmission path is transmitted to the third and fourth optical filters that are
When reflected by the respective optical filters, the leading axes are the fourth
and a second optical multiplexer/demultiplexer consisting of fifth and sixth optical fibers spliced so as to align with the optical axes of the optical fibers, and the first and third optical filters have wavelengths λl and λ.
The second optical filter transmits the optical signal of wavelength λ1 and reflects the optical signal of wavelength λ3, and the second optical filter transmits the optical signal of wavelength λ1 and reflects the optical signal of wavelength λ2. The optical filter reflects an optical signal with wavelength λ1 and transmits an optical signal with wavelength λ2, and has wavelengths λl, λ2, and λ3.
It is assumed that there is a relationship of λ1 < λ2 × λ3 or λ1 > λ2 > λ3.

(Operation) The optical signal with wavelength λ1 is transmitted through the first optical fiber of the first optical multiplexer/demultiplexer and the sixth optical fiber of the second optical multiplexer/demultiplexer, and the optical signal with wavelength λ2 is transmitted through the first optical fiber of the first optical multiplexer/demultiplexer. The third optical fiber of the first optical multiplexer/demultiplexer is connected to the fourth optical fiber of the second optical multiplexer/demultiplexer, and the optical signal of wavelength λ3 is transmitted to the second optical fiber of the first optical multiplexer/demultiplexer.
Transmission and reception of light is performed using the optical fiber of the second optical multiplexer/demultiplexer and the fifth optical fiber of the second optical multiplexer/demultiplexer. At this time, crosstalk is reduced by establishing the relationship λl - λ2 - λ3 or λ1 > λ2 > λ3 between each wavelength, and
The optical fiber for transmitting and receiving optical signals with wavelength λ3 is placed at a branch point close to the transmission line to minimize insertion loss due to reflection. and/or reduce insertion loss by using a high numerical aperture.

(Embodiment) Hereinafter, an embodiment of the three-wavelength bidirectional optical multiplexing/demultiplexing device of the present invention will be described in detail based on the accompanying drawings.

In FIG. 1, the three-wavelength bidirectional optical multiplexing/demultiplexing device 4 is
It consists of an optical multiplexer/demultiplexer 5, a second optical multiplexer/demultiplexer 6, and a transmission line 7 made of an optical fiber connecting these. The first optical multiplexer/demultiplexer 5 has one end 51a connected to one end of the transmission line 7, and a first optical fiber 51 constituting a main path.
, first and second branch points C and D formed on the optical fiber 51 in order from the one closest to the one end 51a, and first and second branch points disposed obliquely at these branch points C and D, respectively. Optical filters 54, 55, optical fibers 51 at the branch point C%D
It is composed of second and third optical fibers 52 and 53 that constitute a branch path, respectively, and are connected to each other. These optical fibers 5
2.53 are respectively arranged so that when the optical signal entering the optical fiber 51 from the transmission line 7 is reflected by the optical filter 54, 55, the tip axis thereof is aligned with the optical fiber 51.

The second optical multiplexer/demultiplexer 6 has one end 61a connected to one end of the transmission line 7, and a fourth optical fiber 61 constituting the main path, which is formed in the optical fiber 61 in order from the one closest to the one end 61a. The third and fourth branching points E and F, these branching points E,
Third and fourth optical filters 64 are respectively disposed diagonally in F.
．． 65, it is composed of fifth and sixth optical fibers 62 and 63, which constitute a branch path, which are respectively joined to the optical fiber 61 at the above-mentioned branch points E and F. These optical fibers 62.
The optical fibers 63 are arranged so that the optical axes thereof are aligned with the optical fibers 61 when the optical signals entering the optical fibers 61 from the transmission line 7 are reflected by the optical filters 64 and 65, respectively.

In this configuration, the optical filters 54 and 64 both transmit optical signals with wavelengths λ1 and λ2 and reflect optical signals with wavelength λ3, and optical filters 55 transmit optical signals with wavelength λl and reflect optical signals with wavelength λ2. The optical filter 65 reflects the optical signal of wavelength λ1 and transmits the optical signal of wavelength λ2. That is, in the above three-wavelength bidirectional optical multiplexing/demultiplexing device 4, the optical fiber 5
The other ends 51b and 61b of 1 and 61 are used as input ports for an optical signal with a wavelength λ1 and an optical signal with a wavelength λ2, respectively, and the optical fiber 62 is used as an input port for an optical signal with a wavelength λ3. The optical fibers 63, 53 and 52 have wavelengths λ1 and λ, respectively.
It is an output port for optical signals of λ2 and λ3.

Specifically, the optical signal of wavelength λ1 that entered the other end 51b of the optical fiber 51 was transmitted through the optical filters 55 and 54, entered the optical fiber 61 via the transmission line 7, and transmitted through the optical filter 64. Thereafter, the light is reflected by the optical filter 65 and emitted from the optical fiber 63. The other end 6 of the optical fiber 61
The optical signal of wavelength λ2 incident on 1b is passed through optical filter 65.6.
4, enters the optical fiber 51 via the transmission path 7, passes through the optical filter 54, is reflected by the optical filter 55, and is emitted from the optical fiber 53. In addition, the optical signal of wavelength λ3 that is incident on the optical fiber 62 is reflected by the optical filter 64, enters the optical fiber 51 from the optical fiber 61 via the transmission line 7, is reflected by the optical filter 54, and is transmitted to the optical fiber 52. It is emitted from.

At this time, the optical fibers 51, 61, and 62, which serve as input ports for optical signals of each wavelength, may have the same parameters as the optical fibers constituting the transmission line 7, but they serve as output ports for optical signals of each wavelength. In order to reduce insertion loss as much as possible, the optical fibers 63, 52 and 53 should have a larger core diameter or a higher numerical aperture than the optical fibers constituting the transmission line 7, or satisfy both. Furthermore, in the case of the input/output configuration of optical signals of each wavelength as described above, in order to reduce crosstalk between each optical signal, between wavelengths λ1, λ2, and λ3, λ1<λ2< λ
It is necessary to select each wavelength so that the relationship λ1>λ2>λ3 holds.

In the above configuration, the transmitted light loss and reflected light loss between each optical fiber are, for example, αl for the transmitted light loss between the same optical fibers, α2 for the reflected light loss between different types of optical fibers,
If the reflected light loss between the same optical fibers is α3, then α1
, α2 < α3, and the insertion loss for each wavelength between the -m optical multiplexer/demultiplexer 5.6 is as follows for the wavelength λ1:
3αl+α2), for wavelength λ2 (3αl+α2)
, for the wavelength λ3, it becomes (α2+α3), that is, the loss α3 is large, so in the optical multiplexing/demultiplexing device of the present invention, the optical fiber 62 for transmitting the optical signal of the wavelength λ3 and the optical fiber for receiving the light 52 at branch points E and C close to the transmission line 7, and by not interposing an optical filter between the two, the insertion loss is reduced as much as possible.

The bidirectional optical multiplexer/demultiplexer for three wavelengths of the present invention can be manufactured, for example, by assembling each optical multiplexer/demultiplexer on a substrate having a guide groove. FIG. 2 is a diagram showing the case where the optical multiplexer/demultiplexer 5 is manufactured.
After placing and fixing 1.52.53, the optical fiber 51
A slit 9.10 is formed at each branch point C, D, and an optical filter 54.5 is placed in the slit 9, 10, respectively.
Insert and fix 5. The optical filters 54 and 55 may be formed by vapor deposition on the obliquely cut end faces of the optical fiber 51, but in general, in the optical fiber 51 constituting the main path,
It is necessary to accurately control the length of the portion sandwiched between the optical filters 54 and 55 in μm units, and the above process, that is, the process of vapor depositing and forming the filter on the end face after cutting the optical fiber 51, is difficult in terms of accuracy. However, it is preferable to process the slit using, for example, a guising tool, since this has the advantage that the position of the slit can be accurately controlled in micrometer units.

The three-wavelength bidirectional optical multiplexing/demultiplexing device 4 shown in FIG. 1 was assembled under the conditions shown below.

(1) Wavelength λ1=1.3μm, λ2=1.45μm.

λ3 = 1.6 μm (2) Optical fiber characteristics ff1j UL single mode fiber (Δ-0.3%, spot size 5 μm 1 cutoff wavelength 1.2 μm) 1 fiber 5 pieces, 61.62: Same fiber for transmission line 52.53 .63: 31 fiber (Δ=2%, core diameter 80 μm) (3) Optical filter Optical filter 54.64: Short-wavelength transmission filter Tomoe Dosha Kori: Bandpass filter Dogue Kamatatane:
Band Pass Filter The transmittance of each of the above optical filters in the wavelength band is shown in FIG.

In the three-wavelength bidirectional optical multiplexing/demultiplexing device configured as described above, each of the losses α1, α2, and α3 described above is 0.3.
0.3.1.0 dB, and the insertion loss for each wavelength calculated from the above formula is 1.2 to 1.3 dB, confirming that it is a bidirectional optical multiplexing/demultiplexing device with extremely low insertion loss. It was done.

(Effects of the Invention) As explained above, according to the present invention, a first optical fiber whose one end is connected to one end of a transmission line and which has first and second branch points in order from the one end; The first and second optical filters are arranged at the first and second branch points, respectively. a first optical multiplexer/demultiplexer comprising second and third optical fibers that are spliced so that their optical axes align with the optical axes of the first optical fiber when reflected by the second optical filter; , a fourth optical fiber having one end connected to the other end of the transmission path and having third and fourth branch points in order from the one end, and arranged at the third and fourth branch points, respectively. Third and fourth optical filters, the optical axis of the optical signal incident on the fourth optical fiber from the transmission path is reflected at the third and fourth optical filters, respectively. a second optical multiplexer/demultiplexer consisting of fifth and sixth optical fibers spliced so as to align with the optical axis of the fourth optical fiber, and the first and third optical filters The second optical filter transmits optical signals with wavelengths λ1 and λ2 and reflects optical signals with wavelength λ3.
The fourth optical filter transmits the optical signal of wavelength λ2 and reflects the optical signal of wavelength λ2, and the fourth optical filter reflects the optical signal of wavelength λl and transmits the optical signal of wavelength λ2.
1, between λ2 and λ3, λ1 and λ2<λ3 or λ
Since we determined that there is a relationship of 1>λ2>λ3, we can realize a three-wavelength bidirectional optical multiplexing/demultiplexing device with low insertion loss and reduced crosstalk between wavelengths, which is extremely useful in wavelength division multiplexing communication systems. It is useful and has high industrial value.

[Brief explanation of the drawing]

Fig. 1 is a conceptual configuration diagram showing an embodiment of the 3-wavelength bidirectional optical multiplexing/demultiplexing device of the present invention, and Fig. 2 shows an example of the manufacturing process of the 3-wavelength bidirectional optical multiplexing/demultiplexing device of the present invention. A plan view, Figure 3 is a graph showing the transmittance of the optical filter versus wavelength, Figure 4 is a graph showing the transmittance of the optical filter versus wavelength.
The figure is a conceptual configuration diagram showing a conventional two-wavelength bidirectional optical multiplexing/demultiplexing device. 4... Three-wavelength bidirectional optical multiplexer/demultiplexer, 5.6... Optical multiplexer/demultiplexer, 8... Substrate, 9.10... Slit,
51゜52.53.61.62.63...Optical fiber, 54.55.64.65...Optical filter, 81.8
2.83...Guide groove.

Claims (2)

[Claims] (1) a first optical fiber whose one end is connected to one end of a transmission path and which has first and second branch points in order from the one end;
First and second optical filters are respectively disposed at the first and second branch points, and the optical signal incident on the first optical fiber from the transmission path is transmitted to the first and second branch points. and a first optical multiplexing/demultiplexing comprising second and third optical fibers joined so that their optical axes are aligned with the optical axis of the first optical fiber when reflected by the second optical filter, respectively. one end of which is connected to the other end of the transmission line, and a third
and a fourth optical fiber having a fourth branch point;
and third and fourth optical filters disposed at the third and fourth branch points, respectively, so that the optical signals incident on the fourth optical fiber from the transmission path are transmitted to the third and fourth branch points. a second optical multiplexer/demultiplexer consisting of fifth and sixth optical fibers spliced so that their optical axes align with the optical axes of the fourth optical fibers when reflected by the respective optical filters; The first and third optical filters transmit optical signals of wavelengths λ1 and λ2 and reflect the optical signals of wavelength λ3, and the second optical filter transmits optical signals of wavelength λ1 and wavelength λ
The fourth optical filter reflects the optical signal of wavelength λ1 and transmits the optical signal of wavelength λ2. Between the wavelengths λ1, λ2, and λ3, there is a λ
A bidirectional optical multiplexing/demultiplexing device for three wavelengths, characterized in that there is a relationship of 1<λ2<λ3 or λ1>λ2>λ3. (2) The first, fourth, and fifth optical fibers are optical fibers having the same parameters as the optical fibers constituting the transmission line, and the second, third, and sixth optical fibers are the optical fibers that constitute the transmission line. The core diameter and/or
The bidirectional optical multiplexing/demultiplexing device for three wavelengths according to claim 1, characterized in that the device has a high numerical aperture.