JP5983255B2 - Optical receiver module - Google Patents

Description

  The present invention relates to an optical receiver module, and more particularly to an optical receiver module that receives so-called coherent light.

  In a next-generation long-distance large-capacity optical communication system that requires high speed and large capacity as communication traffic increases, the introduction of multilevel modulation / demodulation coding techniques such as QPSK, DP-QPSK, and QAM is being studied.

  These systems have a narrower signal band than conventional binary intensity modulation (OOK) systems, can improve frequency utilization efficiency and increase transmission distance, and can be expected to have higher sensitivity.

  In these modulation systems, an optical receiver module equipped with a 90-degree hybrid circuit that causes phase-modulated light or quadrature amplitude-modulated signal light to interfere with reference local oscillation light and outputs interference light converted into an orthogonal relationship is provided. It is used a lot.

  Here, a conventional optical receiver module will be described with reference to FIG. As shown in FIG. 1A, a conventional optical receiver module 1 is a 90-degree hybrid optical circuit that generates local oscillation light 6 and signal light 5 emitted from a light source (not shown) that emits coherent light such as a semiconductor laser. The interference light that is introduced into 2 and caused to interfere is converted into an electrical signal by the light receiving element 3, amplified by the amplifier 4, and output.

  Then, a part of the input light is branched by a branching element 7 (optical coupler in FIG. 1) provided outside the optical receiving module 1 and converted into an electric signal by the light receiving element 8 and further introduced into the gain adjusting circuit 9. Thus, the gain of the amplifier 4 is adjusted.

  Also, as shown in FIG. 1B, when the signal light 5 input to the optical receiver module 1 is adjusted by the intensity varying means 10, the amount of change needs to be adjusted according to the intensity of the signal light 5. The input light 5 to the receiving module needs to be branched by the branch element 7 and monitored.

  However, as shown in FIG. 1, when a mechanism for monitoring and adjusting the signal light 5 is provided outside the receiving module 1, the configuration of the entire receiving system is complicated. Furthermore, when various optical components increase in the receiving system, the optical power of light input to the receiving module may be attenuated.

  The problem to be solved by the present invention is to solve the above-mentioned problem, without complicating the structure of the entire receiving system, and preventing the optical power of the signal light input to the receiving module from being attenuated. An optical receiver module is provided.

In order to solve the above-described problem, the invention according to claim 1 is directed to a 90-degree hybrid optical circuit that outputs an interference light between an input modulated signal light and a local oscillation light, and receives the interference light into an electrical signal. Modulated signal light input to the 90-degree hybrid optical circuit in an optical receiving module having a first light receiving element that converts and outputs, and an amplifying element that amplifies an electrical signal output from the first light receiving element And a second light receiving element that receives the branched modulated signal light, converts it into an electrical signal, and outputs the electric signal. The light branching element is a spatial optical system or a planar lightwave circuit. In order to suppress the local oscillation light from entering the second light receiving element, a light shielding means is provided between the 90-degree hybrid optical circuit and the second light receiving element, and the second light receiving element Based on the electrical signal output by And performing gain adjustment of the device.

  The invention according to claim 2 is the invention according to claim 1, wherein the 90-degree hybrid optical circuit is formed of a spatial optical system or a planar lightwave circuit.

According to a third aspect of the present invention, in the optical receiver module according to the first or second aspect, a ratio of the optical branching element branching the modulated signal light is 10% or less .

  According to a fourth aspect of the present invention, in the optical receiver module according to any one of the first to third aspects, the amplification element is a TIA, and an electric signal output from the second light receiving element is input to the TIA, The gain adjustment of the TIA is performed according to the signal.

According to the first aspect of the present invention, a 90-degree hybrid optical circuit that outputs interference light between the input modulated signal light and local oscillation light, and a first that receives the interference light, converts it into an electrical signal, and outputs the electrical signal. In an optical receiving module having a light receiving element and an amplifying element for amplifying an electric signal output from the first light receiving element, an optical branching element that branches the modulated signal light input to the 90-degree hybrid optical circuit; A second light receiving element that receives the modulated signal light that has been branched, converts the light into an electrical signal, and outputs the electric signal. The light branching element includes a spatial optical system or a planar lightwave circuit, and the second light receiving element. Since the gain of the amplifying element is adjusted based on the electrical signal output from the element, there is no need to place optical components outside the receiving module, and the entire receiving system is not complicated or enlarged, and the input signal light Can also decay There.
In addition, since the light shielding means is provided between the 90-degree hybrid optical circuit and the second light receiving element, the signal light introduced into the second light receiving element is influenced by slight scattering and reflection of the local oscillation light. Therefore, the signal light can be monitored stably.

  According to the second aspect of the present invention, since the 90-degree hybrid optical circuit is formed of a spatial optical system or a planar lightwave circuit, it is possible to realize a cost-effective receiving module such as wiring by printing.

According to the third aspect of the present invention, since the ratio at which the optical branching element splits the modulated signal light is 10% or less, the signal light monitoring by the second light receiving element is a slight reflection of the locally transmitted light. Therefore, the light shielding means as in claim 1 is extremely useful.

  According to the invention of claim 4, the amplification element is a TIA, and the electrical signal output by the second light receiving element is input to the TIA, and the gain adjustment of the TIA is performed according to the electrical signal. Other optical components for adjusting the optical power of the signal light are not required, and the overall configuration of the receiving system can be further reduced.

It is a figure explaining the conventional optical receiver module. It is a figure explaining the 1st Example of the optical receiver module of this invention. It is a figure explaining the 2nd Example of the optical receiver module of this invention. It is a figure explaining the 3rd Example of the optical receiver module of this invention. It is a figure explaining the 4th Example of the optical receiving module of this invention.

Hereinafter, the present invention will be specifically described with reference to preferred examples.
FIG. 2 is a diagram for explaining a first embodiment of the optical receiver module of the present invention. The optical receiver module 1 of the present invention includes a 90-degree hybrid optical circuit 2 that outputs interference light between the input modulated signal light 5 and the local oscillation light 6, and receives the interference light and converts it into an electrical signal for output. Modulation signal input to the 90-degree hybrid optical circuit 1 in the optical receiver module 1 having the first light-receiving element 3 that performs and the amplification element 4 that amplifies the electric signal output from the first light-receiving element 3 An optical branching element 7 that branches the light 5 and a second light receiving element 8 that receives the branched modulated signal light, converts it into an electrical signal, and outputs the electrical signal. The optical branching element 7 is a spatial optical system or A gain of the amplifying element 4 is adjusted on the basis of an electric signal output from the second light receiving element 8, which is composed of a planar lightwave circuit.

  As in the present invention, a mechanism for monitoring and adjusting signal light from the branch element 7 and the light receiving element 8 and the like is arranged inside the optical receiving module 1, so that the entire receiving system is complicated as in the prior art. In addition, the signal light incident on the receiving module can be prevented from being attenuated.

  As the 90-degree hybrid optical circuit, various circuits that can convert synthesized light waves such as a polarization beam splitter into an orthogonal relationship are used. As a method for forming the same, it is formed by a planar lightwave circuit (PLC), a spatial optical system, or the like as in the prior art.

  In the receiving module 1 shown in FIG. 2, a TIA (Trans Impedance Amplifier) with a gain adjusting function is used as the amplifying element 4. The light receiving element 8 converts the signal light branched by the branching element 7 into an electric signal and introduces it into the gain control circuit 9, converts it into a gain control signal and introduces it into the TIA 4, and adjusts the amount of amplification at the TIA 4. To do.

  As the branching element 7 for branching the signal light 5 incident on the receiving module 1, a so-called spatial optical system or planar light wave such as a half mirror or an optical coupler that reflects a certain percentage of the light wave passing therethrough and passes the remaining light wave. Circuit can be used. Further, the ratio of the signal light to be branched is preferably about 10% or less in order to keep the ratio of the signal light introduced into the 90-degree hybrid circuit 2 above a certain level.

FIG. 3 is a diagram for explaining a second embodiment according to the receiving module of the present invention. The receiving module in FIG. 3 is different from the receiving module in FIG. 2 in that the intensity varying means 10 is provided outside the receiving module, and the signal light branched by the branch element 7 is introduced into the intensity varying means 10. The amount of change of the signal light 5 is controlled.

Various means such as a VOA (Variable Optical Attenuator) and an amplifier can be used as the intensity varying means. Further, by adopting a configuration in which only the signal light is adjusted as shown in FIG. 3 , unlike the case of FIG. 2 in which the TIA is adjusted, the intensity of the signal light 5 can be reliably increased without being affected by the local oscillation light 6. Can be adjusted. Further, in the present embodiment, the intensity varying means 10 is arranged outside the optical receiving module, but the branching element 7 and the light receiving element 8 are arranged inside the receiving module, so that reception is performed in the same manner as the receiving module in FIG. It is possible to prevent the entire system from becoming complicated.

  FIG. 4 shows a third embodiment of the receiving module of the present invention. The receiving module 1 shown in FIG. 4 is different from the receiving modules shown in FIGS. 2 and 3 in that a light shielding means 11 is provided between the 90-degree hybrid optical circuit 2 and the light receiving element 8.

  Usually, the signal light 5 input to the receiver is much smaller than the local oscillation light 6 (for example, the signal light intensity is 10 μw and the local oscillation light intensity is 40 mw). It becomes smaller (about 1 μw when the reflectance at the branch element 7 is about 10%). Therefore, the monitoring of the signal light by the light receiving element 8 is affected by slight reflection and scattering of the local oscillation light 6.

  Therefore, in the present embodiment, the light shielding means 11 is provided between the 90-degree hybrid optical circuit 2 to which the local oscillation light 6 is input and the light receiving element 8, and reflection and scattering of the local oscillation light 6 are signal light in the light receiving element 8. This is to prevent the monitor from being affected.

  As the light shielding means 11, a light shielding wall made of, for example, a black colored resin is formed in FIG. 4, but a light-absorbing substance can be applied in addition to the light shielding wall.

  Further, in FIG. 4, the output destination of the electric signal from the branch element 7 is not particularly shown, but this is introduced into the TIA and / or the VOA as shown in FIGS. Can be adjusted.

  FIG. 5 shows a fourth embodiment of the receiving module of the present invention. The receiving module 1 shown in FIG. 5 is different from the receiving modules shown in FIGS. 2 to 4 in that not only the signal light 5 but also the local oscillation light 6 is controlled.

  When the local oscillation light 6 is also subject to control as shown in FIG. 5, for example, as shown in FIG. 5, the receiving module 1 includes a branch element 7 that branches a part of the local oscillation light 6 and a branch element 7. A light receiving element 8 for receiving the branched local oscillation light and converting it into an electric signal is provided, and the electric signal from the light receiving element 8 is introduced into the gain control circuit 9 to convert it into a gain control signal. Based on the gain control signal The output of the local oscillation light in the light source 12 of the local oscillation light 6 is controlled. As the light source 12, various light sources that emit coherent light such as a semiconductor laser can be used as in the conventional case.

  By controlling the local oscillation light 6 as shown in FIG. 5, the entire output can be easily adjusted in accordance with the output of the signal light 5. Also in this case, since it is not necessary to separately arrange an optical component outside the receiving system, the entire receiving system can be made compact.

  In FIG. 6, the gain is adjusted by controlling the TIA, but it is also possible to control the output of each of the signal light and the local oscillation light using the VOA as shown in FIG.

  As mentioned above, although this invention was demonstrated based on the Example, this invention is not limited to said Example, It cannot be overemphasized that a design change is possible suitably in the range which does not deviate from the meaning of this invention.

  According to the present invention, it is possible to provide an optical receiving module that does not complicate the structure of the entire receiving system and that can prevent the optical power of signal light input to the receiving module from being attenuated.

DESCRIPTION OF SYMBOLS 1 Optical receiving module 2 90 degree optical hybrid circuit 3, 8 Light receiving element 4 Amplifying element 5 Signal light 6 Local oscillation light 7 Branch element 9 Control circuit 10 Intensity variable means 11 Light shielding means 12 Light source

Claims (4)

A 90-degree hybrid optical circuit that outputs interference light between the input modulated signal light and the local oscillation light;
A first light receiving element that receives the interference light, converts it into an electrical signal, and outputs the electrical signal;
In an optical receiving module having an amplification element that amplifies an electrical signal output from the first light receiving element,
An optical branching element that branches the modulated signal light input to the 90-degree hybrid optical circuit;
A second light receiving element that receives the branched modulated signal light, converts it into an electrical signal, and outputs the electrical signal;
The optical branching element is composed of a spatial optical system or a planar lightwave circuit,
In order to suppress the local oscillation light from entering the second light receiving element, a light shielding means is provided between the 90-degree hybrid optical circuit and the second light receiving element,
An optical receiver module, wherein the gain of the amplifying element is adjusted based on an electric signal output from the second light receiving element. The optical receiver module according to claim 1,
The optical receiver module, wherein the 90-degree hybrid optical circuit is formed by a spatial optical system or a planar lightwave circuit. The optical receiver module according to claim 1 or 2,
A ratio of the optical branching element branching the modulated signal light is 10% or less . The optical receiver module according to claim 1, wherein
The amplifying element is TIA;
An optical receiving module, wherein an electrical signal output from the second light receiving element is input to the TIA, and gain adjustment of the TIA is performed in accordance with the electrical signal.

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