JPS63285031A - Test circuit for light transmitter - Google Patents

Abstract

PURPOSE:To test the semiconductor laser and photodetector by providing a loopback circuit having a means varying the transmitting characteristic and reflecting characteristic with respect to the polarized wave of light between an output terminal of a light source circuit and an input terminal of a light receiving circuit. CONSTITUTION:An optical transmitter 1a includes a loopback circuit 1-8 provided between an output terminal of a light source 1-3 and a photodetector 1-4 and an optical transmitter 2a includes a loopback circuit 2-8. Then the light source 1-3 of the optical transmitter 1a and the photodetector 2-4 of the optical transmitter 2a are coupled by an optical fiber 3-2 and the light source 2-3 of the optical transmitter 2a and the photodetector 1-4 of the optical transmitter 1a are arranged so as to be coupled by an optical fiber 3-2. A polarized wave dependence optical switch 4-1 included in the loopback circuits 1-8, 2-8 is brought into the electric field application state at the test and the P-wave component in the optical signal radiated from, e.g., a light source is transmitted through the polarized wave dependence optical switch 4-1 and made incident on the photodetector 1-4. Thus, the loopback circuit is formed and the test is conducted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical transmission device using light as a medium, and more particularly to an optical transmission device test circuit with an improved signal folding circuit for testing the same.

[Conventional technology]

FIG. 7 shows an example of a conventional optical transmission device circuit.

The optical transmission device 1 and the optical transmission device 2 are connected by an optical fiber cable 3. The electrical signal is input to the input terminal 1-1 of the optical transmission device 1.
, is inputted from the light source driving circuit 1-2 and the light source 1-3, is converted into an optical signal, is transmitted to the light-receiving element 2-4 of the optical transmission device 2 via the optical fiber 3-1, and is reconverted into an electrical signal. Output terminal 2- after being amplified by amplifier 2-5
Taken from 6. Signal transmission from the optical transmission device W2 to the optical transmission device 1 is performed at the input terminal 2 in the opposite direction to the above signal flow.
-1, light source drive circuit 2-2, light source 2-3, optical fiber 3
-2, light receiving element 1-4, amplifier 1-5 and output terminal 1
-6.

When a failure occurs in a transmission path, it is necessary to isolate the point of failure. For this reason, a test switch l-7 is provided in the optical transmission device 1, and during the test, this switch is closed and the signal input from the input terminal 1-1 is reflected back and observed at the output terminal 1-6. Or, a method has been used to determine whether it is an optical element or an optical fiber at a later stage. The optical transmission device 2 also has the same configuration and is provided with a test switch 2-7.

[Problem that the invention seeks to solve]

However, in reality, failures in optical transmission equipment often occur in optical elements, which have lower reliability than electrical circuits, especially semiconductor lasers used as light sources, and light receiving elements, so there is a drawback that it is not possible to isolate the failure point sufficiently. there were.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical transmission device test circuit that has a folding circuit using an optical film for testing in the event of a failure, and is capable of testing semiconductor lasers and light receiving elements.

[Means for solving problems]

In the present invention, an optical transmission device including a light source circuit that emits an optical signal to a transmitting optical fiber and a light receiving circuit that receives an optical signal incident from a receiving optical fiber is connected via an optical fiber cable. The optical transmission system is characterized in that a folding circuit having means for varying transmission characteristics and reflection characteristics with respect to polarized light is provided between the output end of the light source circuit and the input end of the light receiving circuit. do.

Further, in the present invention, for an optical signal incident at an angle θ, the folding circuit reflects the S-wave component and the P-wave component when no electric field is applied, and reflects the S-wave component and the P-wave component when an electric field is applied. It can be a polarization-dependent optical switch that has a liquid crystal layer that transmits light and two pieces of high refractive index glass that sandwich this liquid crystal layer.

Further, in the present invention, for an optical signal incident at an angle θ, the folding circuit reflects the S-wave component and the P-wave component when no electric field is applied, and reflects the S-wave component and the P-wave component when an electric field is applied. A polarization-dependent optical switch has a liquid crystal layer to be transmitted and two pieces of high refractive index glass provided with the liquid crystal layer sandwiched therebetween, and the optical signal emitted from the light source circuit is polarized by 180 degrees to polarize the polarization-dependent optical switch. It can include two mirrors that enter the optical switch, and two mirrors that polarize the optical signal output from the polarization-dependent optical switch by 180 degrees and make it enter the light receiving circuit.

Further, in the present invention, for an optical signal incident at an angle θ, the folding circuit reflects the S-wave component and the P-wave component when no electric field is applied, and reflects the S-wave component and the P-wave component when an electric field is applied. A polarization-dependent optical switch that has a liquid crystal layer for transmission and two pieces of high refractive index glass sandwiched between the liquid crystal layer is used to transmit an optical signal incident from a light source circuit in the absence of an electric field to an optical fiber for transmission. a first polarization-dependent optical switch that emits light; and a second polarization-dependent optical switch that transmits the P-wave component of the optical signal that has passed through the first polarization-dependent optical switch when a voltage is applied and outputs it to the light receiving circuit. Two mirrors may be provided to polarize the P-wave component emitted from the first polarization-dependent optical switch by 180 degrees and input the P-wave component into the second polarization-dependent optical switch.

Further, in the present invention, for an optical signal incident at an angle θ, the folding circuit reflects the S-wave component and the P-wave component when no electric field is applied, and reflects the S-wave component and the P-wave component when an electric field is applied. A polarization-dependent optical switch that has a liquid crystal layer for transmission and two pieces of high refractive index glass sandwiched between the liquid crystal layer is used to transmit an optical signal incident from a light source circuit in the absence of an electric field to an optical fiber for transmission. a first polarization-dependent optical switch that emits light, and a second polarized light that reflects an optical signal incident from the reception optical fiber in the absence of an electric field and outputs it to the light-receiving circuit via the first polarization-dependent optical switch. A polarization-dependent optical switch is provided, and the plane of polarization of the optical signal emitted from the second polarization-dependent optical switch is rotated by 90 degrees, and a 90-degree polarized wave is input to the first polarization-dependent optical switch. A rotating element may be included.

[Effect]

Between the output end of the light source circuit and the input end of the light receiving circuit, a folding circuit having means for varying the transmission characteristics and reflection characteristics with respect to the polarization of light may be used, for example, for an optical signal incident at an angle θ. When an electric field is applied, the S-wave component (TBP wave component) whose polarization direction is perpendicular to the plane of incidence (senkerecht) and the P-wave component whose polarization direction is perpendicular to the plane of incidence (pa-rallel) (TM acid component is reflected, and when an electric field is applied, the S-wave component A polarization-dependent optical switch is provided, which has a nematic liquid crystal layer that reflects the P-wave component and transmits the P-wave component, and two pieces of high refractive index glass sandwiching this liquid crystal layer. At times, the polarization-dependent optical switch is kept in an electric field-free state, and during testing, it is controlled to be in an electric field applied state.

In this way, under normal conditions, the optical signal emitted from the light source circuit is reflected by the liquid crystal layer through the high refractive index glass on one side of the polarization-dependent optical switch and is emitted to the transmission optical fiber. The optical signal input from the receiving optical cable is reflected by the liquid crystal layer through the high refractive index glass on the other side and input to the light receiving circuit, and communication is performed normally. On the other hand, during testing, the S-wave component of the optical signal emitted from the light source circuit is reflected and emitted to the transmission optical fiber, but the P-wave component is transmitted and input to the light receiving circuit.

Therefore, by using a light source circuit that emits an optical signal containing a P-wave component as the light source circuit, the optical signal can be folded back by the optical film, making it possible to test including the laser diode and the light receiving element.

Note that the configuration of the folding circuit allows the transmission optical fiber and the reception optical fiber to be placed on one side of the device by combining one polarization-dependent optical switch and four mirrors.

Furthermore, by combining the two polarization-dependent optical switches and the two mirrors, it is possible to similarly arrange a transmitting optical fiber and a receiving optical fiber on one side of the device.

Further, the folding circuit can be constructed by combining two polarization-dependent optical switches and one 90-degree polarization rotation element.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a first embodiment of the present invention.
This figure shows the basic configuration of the present invention.

In this embodiment, an optical transmission device 1a and an optical transmission device 2a are connected via an optical fiber cable 3.

The optical transmission device 1a includes, as light source circuits, a light source drive circuit 1-2 whose input is connected to the input end 1-1, and a light source 1-3 whose input is connected to the output of the light source drive circuit 1-2. The light receiving circuit includes a light receiving element 1-4 and an amplifier 1-5 whose input is connected to the output of the light receiving element 1-4 and whose output is connected to the output terminal 1-6, and the output of the light source 1-3. It includes a folding circuit 1-8 provided between the end and the light receiving element 1-4. Similarly, the optical transmission device 2a includes, as light source circuits, a light source drive circuit 2-2 whose input is connected to the input terminal 2-1, and a light source 2 whose input is connected to the output of the light source drive circuit 2-2.
-3, as a light receiving circuit, includes a light receiving element 2-4, an input is connected to an output of the light receiving element 2-4, and an output is an output terminal 2.
-6, and a folding circuit 2-8 provided between the output end of the light source 2-3 and the input end of the light receiving element 2-4. The light source 1-3 of the optical transmission device 1a and the light receiving element 2-4 of the optical transmission device 2a are coupled by the optical fiber 3-1, and the light source 2-3 of the optical transmission bag device 2a and the light receiving element of the optical transmission device 1a 1-4 and optical fiber 3-2
are arranged so that they are joined by

FIGS. 2(a) to (e) show folding circuits 1-8 in FIG.
and 2-8 are explanatory diagrams of polarization-dependent optical switches included in FIG. This polarization-dependent optical switch 4 connects a nematic liquid crystal layer 4-3 with an ordinary refractive index n0 and an extraordinary refractive index n, (no > no) to a liquid crystal j! A transparent electrode layer 4-4 for applying an electric field for driving the liquid crystal is provided on the surface in contact with the liquid crystal layer 54-3, and a transparent electrode layer 4-4 is provided to apply an electric field for driving the liquid crystal. An alignment treatment layer 4-5 that has been subjected to processing (rubbing method or cultivation method vapor deposition) is provided, and an optical signal incident on the liquid crystal surface at an angle θ is transmitted to the extraordinary light refractive index n of the liquid crystal layer 4-3. It is constructed by filling between two pieces of high refractive index glass 4-6 processed into a shape such that the optical signal is incident at an angle determined by the condition of total reflection with respect to the ordinary light refractive index n0. Note that 4-7 is a control terminal for applying an electric field to the electrode layer 4-4.

When no electric field is applied to this liquid crystal 1i4-3,
The liquid crystal N4-3 is oriented as shown in FIG.
As shown in Figure (a), the optical signal consists of an S-wave component whose polarization direction is perpendicular to the plane of incidence (represented by the → axis in the figure) and a P-wave component whose polarization direction is parallel to the plane of incidence (indicated by the + axis in the figure). (represented by ←) is also totally reflected. When applying an electric field,
The liquid crystal layer 4-3 is arranged as shown in FIG. 2(d), and the optical signal incident at an angle θ is S as shown in FIG. 2(b).
The wave component is totally reflected, and the P wave is transmitted. Note that the light source circuit in Fig. 1 uses a polarization-controlled light source (semiconductor laser, L
(ED), an optical signal containing a P-wave component is emitted.

Therefore, under normal conditions, by placing the polarization-dependent optical switch 4 in an electric field-free state, for example, the optical signal emitted from the light source 1-3 is emitted as it is to the transmission optical fiber 3-1, and during testing, By applying an electric field to the polarization-dependent optical switch 4, for example, the P-wave component of the optical signal emitted from the light source 3-1 is transmitted through the polarization-dependent optical switch 4, and the light-receiving element 1-4 is transmitted through the polarization-dependent optical switch 4. By injecting the beam into the beam, a folded circuit can be formed and tested.

The feature of the present invention is that in FIG. 1, FIGS.
) A folding circuit 1 including a polarization-dependent optical switch 4 shown in
-8 and 2-8 were provided.

FIGS. 3(a) and 3(b) are block diagrams showing a second embodiment of the present invention, taking one end of the optical transmission device shown in FIG. 1 as an example. In the optical transmission device 1c shown in FIG. 3, 1-1 is an input terminal, 1-2 is a light source drive circuit, 1-3 is a light source, 1-4 is a light receiving element, 1-5 is an amplifier, 3-1 and 3
-2 is an optical fiber, and 4-1 is a polarization-dependent optical switch shown in FIG. 2(e).

Under normal conditions, the polarization-dependent optical switch 4-1 is kept "off" (no electric field) as shown in FIG. -1, both the P wave component and the S wave component are reflected to the optical fiber 3-1.
is combined with The incident optical signal from the optical fiber 3-2 is reflected by the polarization-dependent optical switch 4-1 as both the P-wave component and the S-wave component, and is coupled to the light receiving element 1-4.

During the test, the polarization-dependent optical switch 4-1 is turned on (an electric field is applied) as shown in FIG. 3(b). The optical signal emitted from the light source 1-3 is polarized by a polarization-dependent optical switch 4-1, and the P-wave component is transmitted and the S-wave component is totally reflected.

The transmitted P wave component is coupled to the light receiving element 1-4.

FIGS. 4(a) and 4(b) are block diagrams showing a third embodiment of the present invention. The optical transmission device 1d of this third embodiment has mirrors 5-1, 5-2, and 5-2 in the second embodiment shown in FIG.
．． 5-3 and 5-4, and optical fiber 3-1.3
This is an example in which 2-2 are grouped together on the same side.

Under normal conditions, the polarization-dependent optical switch 4-1 is turned off as shown in FIG. reflected by 2,
The light enters the polarization-dependent optical switch 4-1. The incident optical signal is reflected by the polarization-dependent optical switch 4-1 as both the P-wave component and the S-wave component, and is coupled to the optical fiber 3-1. The incident optical signal from the optical fiber 3-2 is reflected by the mirror 5-4 and then by the mirror 5-3, enters the polarization-dependent optical switch 4-1, and is converted into a P-wave component by the polarization-dependent optical switch 4-1. and S wave components are also reflected and coupled to the light receiving element 1-4.

During the test, the polarization-dependent optical switch 4-1 is turned on as shown in Fig. 4 (Figure 4). The output optical signal from the light source 1-3 is reflected by the mirror 5-1 and then by the mirror 5-2, and enters the polarization-dependent optical switch 4-1. The polarization is separated by a polarization-dependent optical switch 4-1, and the P-wave component is transmitted and the S-wave component is totally reflected. The transmitted P wave component is coupled to the light receiving element 1-4.

FIGS. 5(a) and 5(b) are block diagrams showing a fourth embodiment of the present invention. Optical transmission bag W of this fourth embodiment
1e is two polarization-dependent optical switches 4-1 and 4-2.
This is an embodiment composed of two mirrors 5-1 and 5-2.

During normal operation, the polarization-dependent optical switches 4-1 and 4-2 are kept "off" as shown in FIG. 5 (al).

The output optical signal from the light source 1-3 is transmitted through a polarization-dependent optical switch 4-
1, both the P-wave component and the S-wave component are reflected and coupled to the optical fiber 3-1. The incident optical signal from the optical fiber 3-2 enters the polarization-dependent optical switch 4-2, is reflected by both the P-wave component and the S-wave component, and is coupled to the light receiving element 1-4.

During the test, the polarization-dependent optical switches 4-1 and 4-2 are turned on as shown in FIG. 5(b).

The output optical signal from the light source 1-3 is transmitted through a polarization-dependent optical switch 4-
1 for polarization separation, the P wave component is transmitted and the S wave component is totally reflected. The transmitted P wave component is reflected by the mirror 5-1 and then by the mirror 5-2, enters the polarization-dependent optical switch 4-2, and after passing through the polarization-dependent optical switch 4-2, enters the light receiving element 1-4. Join.

FIGS. 6(a) and 6(b) are block diagrams showing a fifth embodiment of the present invention. In the optical transmission device 1f in FIG. 6, 4-1 and 4-2 are polarization-dependent optical switches,
6-1 is a 90 degree polarized concave element.

The rest is the same as the second embodiment shown in FIG.

During normal operation, the polarization-dependent optical switches 4-1 and 4-2 are kept "off" as shown in FIG. 6(a).

The output optical signal from the light source 1-3 is transmitted through a polarization-dependent optical switch 4-
1, both the P-wave component and the S-wave component are totally reflected and coupled to the optical fiber 3-1. The incident optical signal from the optical fiber 3-2 undergoes total reflection of both the P-wave component and the S-wave component at the polarization-dependent optical switch 4-2. The totally reflected light passes through the 90 degree polarization rotation element 6
-1, is converted into an S-wave component and a P-wave component, enters the polarization-dependent optical switch 4-1, and is totally reflected by the light-receiving element 1-1.
Combine with 4.

During the test, the polarization-dependent optical switches 4-1 and 4-2 are turned on as shown in FIG. 6('b).

The output optical signal from the light source 1-3 is transmitted through a polarization-dependent optical switch 4-
1 for polarization separation, the P wave component is transmitted and the S wave component is totally reflected. The transmitted P wave component is coupled to the light receiving element 1-4. The incident optical signal from the optical fiber 3-2 is polarized by a polarization-dependent optical switch 4-2, and the P-wave component is transmitted and the S-wave component is totally reflected. The transmitted P wave component is transferred to a 90 degree polarization rotation element 6-
1 and is converted into an S-wave component and polarization-dependent optical switch 4
-1 is transmitted.

〔Effect of the invention〕

As described above, the present invention is capable of non-mechanically folding back signals using an optical film using an optical film by applying an electric field in an optical transmission device, so that automatic testing of transmission lines can be effectively performed.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention. FIGS. 2(a) to (Ql are explanatory diagrams of polarization-dependent optical switches used in the folding circuit. FIGS. 3(a) and (b) are block diagrams showing a second embodiment of the present invention. 4(a) and (b) are block diagrams showing a third embodiment of the present invention. FIGS. 5(a) and cb+ are block diagrams showing a fourth embodiment of the present invention. ) and (b) are block diagrams showing a fifth embodiment of the present invention. Fig. 7 is a block diagram showing a conventional example. ■, la to le, 2.2a = optical transmission device, 1-1.2 −
1... Input terminal, 1-2.2-2... Light source drive circuit, l-3, 2-3... Light source, 1-4.2-4... Light receiving element, 1-5. 2-5...Amplifier, 1-6.2-6
...Output terminal, 1-7.2-7...Test switch, 1-8.2-8...Return circuit, 3...Optical fiber cable, 3-1.3-2...・Optical fiber, 4.
4-1.4-2...Polarization-dependent optical switch, 4-3...
・Liquid crystal layer, 4-4... Electrode layer, 4-5... Alignment processing layer, 4-6... High refractive index glass, 4-7... Control terminal, 5-1.5-2 .5-3.5-4...Mirror, 6
...90 degree polarization rotation element. Patent applicant: Nippon Telegraph and Telephone Corporation-'+S. Agent: Patent Attorney Naotaka Ide ：＼、
/ ~ No・Noichi-* as an example Oabe M 1 Kuchihen = 夾继例のcyclic 'WJ 3 Illustrated Three Great Demon Examples of the Makibo system 4 口 (0) Normal cry Fu IIg * Brother's example lecture凰shoulda 5 In the example shown in Figure 5, 1) 18 shoulders 6 田conventional@0礪入、￥i 7 口

Claims (5)

[Claims] (1) An optical transmission device including a light source circuit that emits an optical signal to a transmitting optical fiber and a light receiving circuit that receives an optical signal incident from the receiving optical fiber is connected via an optical fiber cable. The optical transmission system is characterized in that a folding circuit is provided between the output end of the light source circuit and the input end of the light receiving circuit, the folding circuit having means for varying transmission characteristics and reflection characteristics with respect to polarized light. Optical transmission equipment test circuit. (2) The folding circuit reflects the S wave component and the P wave component when there is no electric field for the optical signal incident at an angle θ,
The claim is a polarization-dependent optical switch comprising a liquid crystal layer that reflects an S-wave component and transmits a P-wave component when an electric field is applied, and two pieces of high refractive index glass sandwiching this liquid crystal layer. The optical transmission device test circuit according to paragraph (1). (3) The folding circuit reflects the S wave component and the P wave component when there is no electric field for the optical signal incident at an angle θ,
A polarization-dependent optical switch includes a liquid crystal layer that reflects the S-wave component and transmits the P-wave component when an electric field is applied, and two pieces of high refractive index glass sandwiching this liquid crystal layer, and a polarization-dependent optical switch that reflects the S-wave component and transmits the P-wave component. two mirrors that polarize the optical signal output from the polarization-dependent optical switch by 180 degrees and input it into the polarization-dependent optical switch; and two mirrors that polarize the optical signal output from the polarization-dependent optical switch by 180 degrees and input it to the light receiving circuit. An optical transmission device test circuit according to claim (1). (4) The folding circuit reflects the S wave component and the P wave component when there is no electric field for the optical signal incident at the angle θ,
A polarization-dependent optical switch, which has a liquid crystal layer that reflects S-wave components and transmits P-wave components when an electric field is applied, and two pieces of high refractive index glass sandwiching this liquid crystal layer, is used as a light source when no electric field is applied. A first polarization-dependent optical switch that outputs an optical signal input from the circuit to a transmission optical fiber, and a P-wave component of the optical signal that passes through this first polarization-dependent optical switch when a voltage is applied. A second polarization-dependent optical switch that outputs light to a light receiving circuit is provided, and the P-wave component output from the first polarization-dependent optical switch is polarized by 180 degrees to produce the second polarization-dependent light. An optical transmission device test circuit according to claim 1, which includes two mirrors that enter the switch. (5) The folding circuit reflects the S wave component and the P wave component when there is no electric field for the optical signal incident at the angle θ,
A polarization-dependent optical switch, which has a liquid crystal layer that reflects S-wave components and transmits P-wave components when an electric field is applied, and two pieces of high refractive index glass sandwiching this liquid crystal layer, is used as a light source when no electric field is applied. a first polarization-dependent optical switch that outputs an optical signal incident from the circuit to a transmitting optical fiber; and a first polarization-dependent optical switch that reflects an optical signal incident from the receiving optical fiber in the absence of an electric field. and a second polarization-dependent optical switch that outputs the optical signal to the light receiving circuit via the switch, and rotates the plane of polarization of the optical signal output from the second polarization-dependent optical switch by 90 degrees. 90 incident on one polarization-dependent optical switch
An optical transmission device test circuit according to claim (1), which includes a degree polarization rotation element.