JP2000206349A - Optical module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize a transmission light outputting characteristic of a luminescent element with respect to temperature change and change with the lapse of time under a practical using condition, by arranging a monitoring means for the luminescent element in front of the transmitting direction to monitor directly transmission light. SOLUTION: This module is an optical module wherein transmission signal light emitted from an LD 3 is transmitted from an optical fiber 7 through an optical waveguide circuit 11. A monitor PD5 for receiving the transmission signal light of the LD 3 is provided in a reflection part 102 for reflecting the signal light of the LD 3 within the circuit 11, and the transmission signal light transmitted through a reflection film 61 of the reflection part 102 is directly received to be monitored by the monitor PD5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical module for transmitting and receiving signal light using an optical waveguide circuit.
By arranging monitoring means for monitoring a part of the transmission signal light emitted from the light emitting element in the transmission direction in the optical waveguide circuit, the driving current of the light emitting element is controlled according to the fluctuation of the monitor light amount. The present invention relates to an optical module that can stabilize transmission light output characteristics with respect to a change in temperature and a change with time.

[0002]

2. Description of the Related Art In recent years, demand for communication lines has been increasing due to the spread of the Internet and the like, and demand for subscriber systems as well as trunk systems has been increasing. In particular, the demand for communication costs is strict in the subscriber system, and there is an urgent need to reduce the cost of communication optical devices in order to expand the subscriber optical communication network. As for optical modules for subscribers, optical modules with built-in optical waveguides and integrated transmission / reception functions have been developed for miniaturization and cost reduction.

Hereinafter, a conventional optical module will be described with reference to FIGS. 5 and 6. FIG. FIG. 5 is a plan view showing the configuration of a conventional optical module. FIG. 6 is a graph showing a relationship between an LD current and an optical output in a conventional optical module and a monitor current in a monitor PD.

As shown in FIG. 5, a conventional optical module having an integrated transmitting / receiving function is an LD (Laser) as a light emitting element.
Diode) 3, Receiving PD (Photo Diode) 4 to be a light receiving element
(Optical waveguide circuit: Planar Lig) provided with a monitor PD5, a Y-branch 101, and a directional coupling type reflection unit 102.
ht wave circuit) 11 and an optical fiber 7 mounted and connected to the PLC 11.

The PLC 11 has a common input / output port 21
, An LD port 22, and a reception PD port 23. The optical fiber 7 is mounted on the common input / output port 21 of the PLC 11, and the transmission signal light and the reception signal light from the PLC 11 are efficiently coupled to the optical fiber 7.

[0006] The LD 3 is mounted on the LD port 22 so that the transmission signal light emitted from the LD 3 is efficiently coupled to the PLC 11. A monitor PD5 that receives the monitor light of the LD 3 is provided on the side opposite to the transmission direction of the LD 3.

A receiving PD 4 is mounted on the receiving PD port 23, and a signal light received from the PLC 11 is received by the receiving PD 4.
It is designed to be efficiently coupled to Further, the reflection film 62 is attached to the directional coupling type reflection unit 102 so that the transmission signal light from the LD 3 is totally reflected.

The operation of the conventional optical module having such a configuration will be described. First, the received signal light 111 incident from the optical fiber 7 is transmitted to the common port 2 of the PLC 11.
1 propagates through the PLC and passes through the Y branch 101 to receive PD4.
Is received at. The optical signal is converted into an electric signal by the receiving PD 4 and input to a receiving circuit (not shown) connected to the receiving PD 4.

On the other hand, the transmission signal light emitted from the LD 3 is coupled at the LD port 22 of the PLC 11 and propagated in the PLC. The transmission signal light 114 is totally reflected by the directional coupling type reflection unit 102 having the reflection film 62, and the reflected light 1
14 a is propagated from the common input / output port 21 to the optical fiber 7.

In such a conventional optical module, as shown in FIG. 5, monitor light emitted from one end face (the face opposite to the transmission direction) of the LD 3 to control the fluctuation of the transmission signal light. The monitor PD 5 is mounted so as to receive the signal 115, and the LD driving current is controlled so that the light receiving current in the monitor PD 5 is constant, thereby stabilizing the transmission signal light.

FIG. 6 shows the relationship between the LD current and the optical output in the conventional optical module and the monitor current in the monitor PD. In general, as shown in FIG.
Above the threshold current (reference numeral 251 in FIG. 6A), both the optical output 206 and the monitor current 207 increase in proportion to the increase in current. That is, the optical output of the LD and the monitor current have a proportional relationship as shown by the characteristic 210 as shown in FIG.

Therefore, by observing the amount of change in the monitor current and controlling the LD current so that this value is constant, the transmission signal output can be controlled to be constant as a result. As a result, when the environmental temperature changes and the characteristics of the LD change, it is possible to control the change in the transmission light output using the monitor current value. As such a conventional optical module, there is, for example, an "optical transmission / reception module" disclosed in JP-A-9-184934.

[0013]

In the conventional method of controlling the transmission signal light in the optical module using the monitor light of the LD, the ratio of the amount of light emitted from both end faces of the LD is always constant. And the light emitted from the LD
When the two conditions that the ratio of optically coupling to C, that is, the coupling loss is always constant, are satisfied, the transmission light output can be controlled by the monitor current as described above.

However, under actual use conditions of the optical module, the ratio of the amount of light emitted from both end faces of the LD may vary depending on the temperature, and the coupling loss between the LD and the PLC may also vary with temperature and deterioration with time. It may change depending on factors such as. That is, as a cause of the fluctuation of the transmission signal light in the optical module, actually, not only the fluctuation of the light emission amount of the LD, but also the fluctuation of the coupling between the LD and the PLC, the light amount ratio of the transmission light of the LD to the monitor light also has To change,
In the control method using the monitor light of the LD, it is possible to control the fluctuation of the LD itself, but it is not possible to control the fluctuation caused by the optical coupling between the LD and the PLC. When the transmission signal light fluctuates due to the fluctuation of the coupling between the LD and the PLC, it cannot be suppressed.

For this reason, in the conventional control using the monitor current in the optical module, for example, the temperature is changed and the control shown in FIG.
When the light output 208 and the monitor current 209 change as indicated by the dashed line in FIG. 6A, the characteristic 21 indicated by the dashed line in FIG.
As a result, the light output fluctuates within a certain range, such as 1 and 212.

As described above, in the conventional optical module, monitor light emitted from one end face (the rear face in the transmission direction) of the LD is received by the monitor PD, and the monitor PD controls the fluctuation of the transmission signal light. Since the control of the LD drive current to stabilize the light receiving current in the PD stabilizes the transmission signal light, it cannot cope with the change in the communication environment of the optical module under actual use conditions. Was.

For this reason, in the conventional optical module, the optical fluctuation including the optical coupling portion is measured in advance, and the characteristic fluctuation is controlled so that the fluctuation of the temperature or the characteristic over time is within a certain standard. Had to be screened and only the product used. Such sorting affects the production yield, and has been an obstacle for reducing the cost of the optical module.

Japanese Unexamined Patent Application Publication No. 7-168038 discloses a technique for reducing the size of an optical module and reducing the loss of a transmission / reception signal by using only one multiplexing / demultiplexing section in an optical waveguide circuit. A module has been proposed. However, the technique described in this publication is aimed at miniaturizing the device and reducing the loss of the signal, and there is no description regarding the monitor control of the transmission signal, and it does not solve the above-mentioned conventional problems. Was.

The present invention has been proposed to solve such a problem of the prior art. A monitoring means for monitoring a part of the transmission signal light emitted from the light emitting element is provided with an optical waveguide circuit. By arranging it in the front in the transmission direction, it is possible to control the drive current of the light emitting element according to the fluctuation of the monitor light amount, and to perform control to stabilize the transmission light output characteristic against temperature change and aging change. It is intended to provide an optical module that can be used.

[0020]

According to a first aspect of the present invention, there is provided an optical module comprising: an optical waveguide circuit; an optical fiber mounted on the optical waveguide circuit; and an optical module mounted on the optical waveguide circuit. A light emitting element comprising: a transmission signal light emitted from the light emitting element is transmitted from the optical fiber via the optical waveguide circuit,
A monitor light receiving element for receiving the transmission signal light of the light emitting element is provided, and the monitor light receiving element is arranged in the optical waveguide circuit in a forward direction of the transmission signal light in a transmission direction.

More specifically, in the optical module according to the second aspect, the optical waveguide circuit includes a reflecting portion for reflecting transmission signal light of the light emitting element in the circuit, and the monitor light receiving element includes the reflecting portion. And receiving the transmission signal light. In particular, in claim 3, the reflecting portion is:
A reflection film is provided for transmitting a part of the transmission signal light of the light emitting element, and the monitor light receiving element is disposed behind the reflection film and receives transmitted light of the transmission signal light.

On the other hand, in the optical module according to the fourth aspect,
The optical waveguide circuit includes a branching unit that branches a part of the transmission signal light of the light emitting element in the circuit, and the monitor light receiving element is disposed in front of the branching unit in the branching direction, so that the transmission signal light is transmitted. It is configured to receive the split light.

Further, in the optical module according to the fifth aspect,
A light-emitting element driving circuit that controls the light-emitting element so that the light-receiving current of the transmission signal light received by the monitor light-receiving element is constant. An optical module according to a sixth aspect is configured such that the optical waveguide circuit is an optical module integrated with a transmission / reception function including a light receiving element that receives a reception signal light received from the optical fiber.

According to the optical module of the present invention having such a configuration, a function of directly monitoring is added to the PLC by transmitting or branching a part of the transmission signal light. By controlling the LD drive current according to the fluctuation, it is possible to obtain a stable characteristic without fluctuation of the transmission signal light due to temperature fluctuation or temporal fluctuation.

That is, in the present invention, since a part of the transmission signal light is directly monitored, the fluctuation of the transmission signal light can be directly observed, so that the monitoring is performed by receiving the conventional monitor light. Unlike the method, even if various fluctuation factors occur under actual use conditions, it is possible to control the fluctuations with extremely high accuracy. As a result, in the present invention, it is possible to obtain a stable characteristic with a very small variation of the transmission signal light.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an optical module integrated with a transmitting / receiving function according to the present invention will be described below with reference to the drawings. [First Embodiment] First, a first embodiment of an optical module with an integrated transmission / reception function of the present invention will be described with reference to FIGS. FIG. 1 is a plan view showing an optical module according to the first embodiment of the present invention. FIG. 2 is a block diagram of an LD drive circuit of the optical module according to the present embodiment. FIG. 3 is a graph showing the relationship between the LD current, the optical output, and the monitor current of the monitor PD in the optical module according to the present embodiment.

As shown in FIG. 1, the optical module integrated with a transmission / reception function according to the present embodiment is an optical module with an integrated transmission / reception function, and an LD (Laser) as a light emitting element.
Diode) 3, Receiving PD (Photo Diode) 4 to be a light receiving element
And an optical waveguide circuit 11 (PLC: a monitor PD5, a Y-branch 101, and a reflection unit 102 having a reflection film 61).
A planar light wave circuit) and an optical fiber 7 mounted and connected to the PLC 11.

The PLC 11 has a common input / output port 21
, An LD port 22, a reception PD port 23, and a monitor PD port 24. P
The optical fiber 7 is mounted and connected to the common input / output port 21 of the LC 11, and the transmission signal light and the reception signal light
The coupling between the LC 11 and the optical fiber 7 is efficient.

An LD 3 is mounted on the LD port 21.
The light emitted from the LD 3 is efficiently coupled to the PLC 11. In this embodiment, since the monitor of the LD 3 is performed by the monitor PD 5 located in front of the transmission signal light, all the light emitted from the LD 3 can be emitted in the transmission direction. That is, unlike the conventional LD, it is not necessary to emit monitor light in the direction opposite to the transmission direction for monitoring, and the luminous efficiency of the LD 3 can be improved.

A reception PD 4 is mounted on the reception PD port 23, and a reception signal light from the PLC 11
4 efficiently. The monitor PD port 24 is a reflective film 61 that transmits a certain percentage of light.
Constitute the reflection unit 102 provided with. The reflection film 61 transmits a certain percentage of light, and a monitor PD5 is disposed and mounted behind the reflection film 61. Thereby, a part of the transmission signal light transmitted through the reflection film 61 is efficiently coupled to the monitor PD5.

As described above, the PLC 11 of the present embodiment
Constitutes an optical module integrated with a transmission / reception function including an LD 3 and a reception PD 4. In addition, as a material for forming the PLC 11, there is a material using a quartz material or a plastic material, and the material and the manufacturing method are not particularly limited.

Next, the operation of the optical module according to the present embodiment having such a configuration will be described with reference to FIG. First, the received signal light 111 incident from the optical fiber 7
Propagates through the PLC from the common port 21 of the PLC 11 and is received by the receiving PD 4 via the Y branch 101. The optical signal is converted into an electric signal by the receiving PD 4 and input to a receiving circuit (not shown) connected to the receiving PD 4.

On the other hand, the transmission signal light 1 emitted from the LD 3
12 is connected to the LD port 22 of the PLC 11 and
Propagate inside. Most of the transmission signal light 112 is reflected by the reflector 102 to which the reflection film 61 is added, and the reflected light 11
2 a is propagated from the common input / output port 21 to the optical fiber 7.

On the other hand, the reflection film 61 allows a certain percentage of light to pass therethrough.
The light is received at D5. By observing the received light current output from the monitor PD5, the amount of fluctuation of the transmission signal light 112a can be monitored.

Here, it is necessary to set the ratio between the reflected light and the transmitted light at the reflecting section 102 in accordance with the conditions for using the optical module according to the present embodiment. For example, reflected light: transmitted light = 10: If the ratio is set to be about 1, the transmitted light, that is, the monitor light is about 100 μW with respect to the reflected light, that is, 1 mW of the transmission signal light.

With reference to FIG. 2, the state of control of the transmission signal light in the optical module of the present embodiment will be described. As described above, a part of the transmission signal light 110 emitted from the LD 3 passes through the reflection film 61 and is received by the monitor PD5. Then, the LD drive circuit 8 feeds back the LD drive current so that the received light current has a constant value, and the LD drive circuit 8 controls the LD so that the transmission signal light has a constant value.
3 is controlled.

As described above, L controlled by the LD drive circuit 8
FIG. 3 shows the relationship between the D current, the optical output, and the monitor current. In general, as shown in FIG. 3A, the light output 201 of the LD increases proportionally with an increase in the current above a threshold current (reference numeral 250 in FIG. 3A). Further, since the monitor current 202 observes a part of the transmission light of the LD 3,
It shows the same characteristics as the optical output. Basically, the optical output of the LD and the monitor current are in a proportional relationship as shown by the characteristic 205 in FIG.

In this embodiment, since a part of the transmission light of the LD 3 is directly monitored by transmitting the light through the reflection film 61, the relationship between the optical output of the LD and the monitor current is different from that of the conventional one. , Are not affected by factors such as the ratio of the amount of light emitted from both end faces of the LD, the optical coupling loss between the LD and the PLC, and are hardly affected by other temperature fluctuations and aging.

That is, the transmission signal light emitted from the LD is coupled at the LD port of the PLC, propagates in the PLC, and is largely reflected at the reflection portion provided with the reflection film. Although coupled to the fiber, a certain percentage of the transmission signal light passes through the reflection film and is received by the monitor PD.

For this reason, for example, when the temperature changes, the light output 203 and the monitor current 204 indicated by the dashed line in FIG.
3B, the characteristic 205 shown in FIG. 3B hardly changes. Therefore, by observing the light-receiving current received by the monitor PD and converted into an electric signal, the LD driving current is controlled to provide a stable characteristic in which the fluctuation of the transmission signal light due to the temperature fluctuation and the aging fluctuation of the transmission signal light. Obtainable.

That is, if the LD current is controlled so that this value becomes constant by observing the amount of change in the monitor current, the transmission signal output is controlled to be substantially constant. Therefore,
In the optical module of the present embodiment, it is not necessary to use only a product within a standard in which the amount of optical fluctuation is measured in advance, as is conventionally done.

As described above, in the optical module integrated with the transmission / reception function according to the present embodiment, the function of monitoring a part of the transmission signal light is added to the PLC to control the LD drive current according to the fluctuation of the monitor light amount. By doing so, it is possible to obtain stable characteristics without fluctuation of the transmission signal light due to temperature fluctuation and temporal fluctuation.

That is, in the optical module of this embodiment, since a part of the transmission signal light is directly monitored, the fluctuation of the transmission signal light can be directly observed. Unlike a method of monitoring by receiving light, even if various fluctuation factors occur under actual use conditions, it is possible to control the fluctuations with extremely high accuracy. As a result, in the present embodiment, it is possible to obtain a stable characteristic in which the fluctuation of the transmission signal light is extremely small.

[Second Embodiment] Next, a second embodiment of the optical module with an integrated transmission / reception function of the present invention will be described with reference to FIG. FIG. 4 is a plan view showing an optical module according to the second embodiment of the present invention.

As shown in the figure, the optical module with integrated transmitting / receiving function of this embodiment is a modified embodiment of the optical module with integrated transmitting / receiving function in the above-described first embodiment. Instead of monitoring the light transmitted through the reflection film, a part of the transmission light branched at the branching unit is monitored.

That is, the optical module according to the present embodiment comprises an LD 3, a receiving PD 4, a monitoring PD 5,
PLC consisting of three Y branches 103 and 104
(Optical waveguide circuit) 12 and optical fiber 7.

The PLC 12 has a common input / output port 21
, An LD port 22a, a reception PD port 23, and a monitor PD port 24a. The optical fiber 7 is connected to the common input / output port 21 of the PLC.
Is mounted so that the transmission signal light and the reception signal light are efficiently coupled between the PLC 12 and the optical fiber 7.

The LD 3 is mounted on the LD port 22a, and light emitted from the LD 3 is efficiently coupled to the PLC 12. The receiving PD port 23 has a receiving PD 4
Is mounted, and the received signal light from the PLC 12 is
It is designed to be efficiently coupled to

Further, a monitor PD 5 for receiving a transmission signal light is mounted on the monitor PD port 24a. In this embodiment, as shown in FIG.
3 is transmitted from the common input / output port 21 to the optical fiber 7 via the Y-branch 104 so that one of the signal lights (output transmission signal light 116a) is transmitted to the optical fiber 7. (The monitor transmission signal light 117) is received by the monitor PD5.

Next, the operation of the optical module according to this embodiment having the above configuration will be described. The operation related to the received signal light is the same as that of the first embodiment shown in FIG. The transmission signal light 116 emitted from the LD 3 is transmitted to the LD port 22 of the PLC 12.
a, the signal light 116a is propagated from the common input / output port 21 to the optical fiber 7 via the Y branch 104.

The transmission signal light 117 branched to the other port is received by the monitor PD 5 and converted into an electric signal. By observing the received light current output from the monitor PD5, it is possible to monitor the fluctuation amount of the transmission signal light.

As described above, the same effects as those of the first embodiment can be obtained by the optical module of the present embodiment. That is, in the present embodiment, a part of the transmission signal light of the LD is branched and monitored, and the LD driving current is controlled according to the fluctuation of the monitored light amount. Therefore, the fluctuation of the transmission signal light is directly observed. Therefore, it is possible to obtain stable characteristics without fluctuation of the transmission signal light due to temperature fluctuation and temporal fluctuation.

The optical module integrated with a transmitting / receiving function of the present invention is not limited to the above-described embodiment, and it goes without saying that various modifications can be made within the scope of the present invention. For example, in the above-described embodiment, the optical module constitutes an optical module integrated with a transmission / reception function having both an LD and a reception PD. However, as long as the LD monitor control structure of the present invention is provided, the transmission function is provided. Only an optical module may be used.

[0054]

As described above, according to the optical module with integrated transmission / reception function of the present invention, the monitoring means for monitoring a part of the transmission signal light emitted from the light emitting element is provided in the optical waveguide circuit in the transmission direction. By controlling the driving current of the light emitting element according to the fluctuation of the monitor light amount, it is possible to perform the control for stabilizing the transmission light output characteristic against the temperature change and the aging change.

[Brief description of the drawings]

FIG. 1 is a plan view showing an optical module according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing an LD drive circuit of the optical module according to the first embodiment of the present invention.

FIG. 3 is a graph showing a relationship between an LD current, an optical output, and a monitor current in a monitor PD in the optical module according to the first embodiment of the present invention.

FIG. 4 is a plan view showing an optical module according to a second embodiment of the present invention.

FIG. 5 is a plan view showing a configuration of a conventional optical module.

6 is a graph showing a relationship between an LD current, an optical output, and a monitor current in a monitor PD in the conventional optical module shown in FIG.

[Explanation of symbols]

 REFERENCE SIGNS LIST 3 LD (light emitting element) 4 reception PD 5 monitor PD 7 optical fiber 8 LD drive circuit 11 PLC (optical waveguide circuit) 21 common input / output port 22 LD port 22 a LD port 23 reception PD port 24 monitor PD port 24 a monitor PD port 61 Reflecting film 101 Y branch 102 Reflecting section 103 Y branch 104 Y branch 111 Received signal light 112 Transmitted signal light 112a Reflected light 113 Transmitted light 116 Transmitted signal light 116a Output transmitted signal light 117 Monitor transmitted signal light

Claims (6)

[Claims] An optical waveguide circuit, an optical fiber mounted on the optical waveguide circuit, and a light emitting element mounted on the optical waveguide circuit, wherein a transmission signal light emitted from the light emitting element is transmitted to the optical waveguide circuit. An optical module transmitted from the optical fiber via a wave circuit, comprising: a monitor light receiving element for receiving a transmission signal light of the light emitting element, wherein the monitor light receiving element is the transmission signal in the optical waveguide circuit. An optical module, which is disposed forward in a light transmission direction. 2. The optical waveguide circuit according to claim 1, further comprising: a reflection unit configured to reflect a transmission signal light of the light emitting element in the circuit, and the monitor light receiving element being provided in the reflection unit to receive the transmission signal light. Item 2. The optical module according to Item 1. 3. The reflection section includes a reflection film that transmits a part of transmission signal light of the light emitting element, and the monitor light receiving element is disposed behind the reflection film and transmits the transmission signal light. The optical module according to claim 2, which receives light. 4. The optical waveguide circuit includes a branch section for branching a part of the transmission signal light of the light emitting element in the circuit, and the monitor light receiving element is disposed in front of the branch section in a branch direction. The optical module according to claim 1, wherein the optical module receives the split light of the transmission signal light. 5. The optical module according to claim 1, further comprising a light emitting element driving circuit for controlling said light emitting element so that a light receiving current of a transmission signal light received by said monitor light receiving element becomes constant. 6. The optical module according to claim 1, wherein the optical waveguide circuit includes a light receiving element that receives a signal light received from the optical fiber.