JP2012128243A - Optical module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to shield or reduce light from a reverse direction to a light receiving unit and ensure a dynamic range of measurement of light intensity of light incident on the light receiving unit from an incident side.SOLUTION: An optical module comprises: an incidence fiber collimator 11; an optical filter 13 that allows passage of incident light L10 incident from the incidence fiber collimator 11 and reflects a part of the light by a filter surface 13a on a front surface; an emission fiber collimator 12 that emits the light passing through the optical filter 13 to the outside; and a light receiving unit 15 that receives the light reflected by the filter surface 13a of the optical filter 13. An incident position of the incident light to the optical filter 13 is set to be deviated from a center O of the filter surface 13a to the light receiving unit side.

Description

  The present invention relates to an optical module used in an optical communication system or the like, and more specifically to an optical module used for monitoring a part of light to be communicated and controlling the light to be communicated.

  For example, an optical amplifier used in an optical communication system is configured to monitor a part of the output light and control the output power of the pumping light source in order to stabilize the amplified light output. In addition, in a transmission / reception module used in an optical communication system that transmits light whose wavelength is controlled, a configuration is adopted in which a part of the light is monitored and controlled so that the oscillation wavelength is stabilized. This type of optical module is disclosed in, for example, Patent Document 1.

  FIG. 1A shows an example of the configuration of such an optical module. As shown in the figure, this optical module includes an incident fiber collimator 1, an optical filter 2 (fixed at a predetermined angle with a holder 3), an optical isolator 4, and an output fiber collimator 5 in the order of the optical path of light. Arranged in order. Light incident from the incident fiber collimator 1 is applied to the filter surface 2 a of the optical filter 2. Most of the irradiated light L is refracted by the irradiated filter surface 2 a, travels through the optical filter 2 through a predetermined path, exits from the back surface to the outside, and passes through the optical isolator 4 to be an outgoing fiber collimator. 5 is emitted.

  Moreover, a part of light irradiated to the filter surface 2a of the optical filter 2 is reflected there. The optical filter 2 is reflected by the filter surface 2a of the optical filter 2 because the filter surface 2a on the incident fiber collimator 1 side is inclined at a predetermined angle with respect to the optical path of the light L incident from the incident fiber collimator 1. The reflected light L1 travels obliquely at a predetermined angle with respect to the optical path of the incident light L. The light receiving unit 6 is disposed at the tip of the optical path of the reflected light. Information (light intensity, wavelength, etc.) of the light received by the light receiving unit 6 is given to a control unit (not shown), and the control unit controls light incident from the incident fiber collimator 1.

JP 2002-185074 A

  In the configuration shown in FIG. 1A, as shown in FIG. 1B, the light received by the light receiving unit 6 is a forward light such as the reflected light L1 reflected by the filter surface 2a of the optical filter 2 described above. In addition to light, there is light L3 in the reverse direction based on return light L2 from the output fiber collimator 5 side. The light L3 in the reverse direction enters the optical filter 2, and the reflected light L2 is repeatedly reflected inside the optical filter 2 to generate irregular reflection at the cut surface 2b that is not optically polished, and a part of the irregular reflection component. Includes light that has finally emerged from the filter surface 2a.

  The ratio of the incident intensity of the reflected light L1 from the forward direction to the light receiving unit 6 and the incident intensity of the light L3 in the reverse direction to the light receiving unit 6 (PD crosstalk) is deteriorated by the irregular reflection component. Yes.

  In particular, with the recent miniaturization of electronic devices and apparatuses, this type of optical module is also miniaturized, the size of the optical filter is reduced, and the return light L2 that has entered the optical filter 2 is about once to several times. The cut surface 2b is reached with a small number of reflections, and irregular reflection is caused there to easily cause the above problem.

  In order to solve the above problems, the present invention provides (1) an incident fiber collimator, an optical filter that allows incident light incident from the incident fiber collimator to pass therethrough and reflects a part of the incident light on the surface filter surface; An output fiber collimator that emits light that has passed through the optical filter to the outside, and a light receiving unit that receives the light reflected by the optical filter, and the incident position of the incident light on the optical filter is the filter surface It is set to the light-receiving part side from the center of.

  The optical filter is disposed at a predetermined angle with respect to the optical path of the incident light so that the light reflected by the filter surface is received by the light receiving unit. In addition, the front and back surfaces of the optical filter through which regular light in the forward direction and the reverse direction pass are polished, but the other cut surfaces are usually not polished. In such a configuration, when light in the reverse direction from the emission fiber collimator reaches the back surface of the optical filter, it passes through the optical filter and enters the optical filter, reaches the filter surface, and is partially reflected there. The reflection component travels again through the optical filter toward the back surface, and is reflected when it reaches the back surface. Further, as described above, an optical filter is inclined with respect to the incident light so that a part of the forward light (incident light) is reflected by the filter surface and received by the light receiving unit, and the filter surface is on the light receiving unit side. Therefore, when entering the optical filter, the light in the opposite direction moves away from the light receiving unit while repeatedly reflecting on the front surface (filter surface) and back surface of the optical filter. It reaches the cut surface on the far side. Since the cut surface is not polished, irregular reflection occurs there, and a part of the irregularly reflected light tries to go to the light receiving unit side, but the incident position of incident light on the filter surface is changed from the center of the filter surface. Since the filter surface (optical filter) has the same size and shape, the distance from the incident position to the cut surface is compared to the conventional setting near the center (cut surface side). Can be taken longer. Then, even if the reflection is irregularly performed on the cut surface, the irregular reflection component can be prevented from being directly transmitted through the filter surface and received by the light receiving unit.

  In addition, due to the reverse nature of the light, the position where the light in the reverse direction is first irradiated on the filter surface is the same as the incident position, and a long distance to the cut surface can be secured. As a result, the number of times that the light in the opposite direction is reflected from the inside of the optical filter to the cut surface after repeated reflection is increased. Then, since the total reflection is not performed, the light amount of the reflection component is attenuated each time the light is reflected, so that the light amount of the irregular reflection component is also reduced. Therefore, even if a part of the irregular reflection component reaches the light receiving unit, the amount of light can be suppressed. Therefore, the light received by the light receiving unit can be suppressed as much as possible by the irregular reflection component at the cut surface, and control based on the light received by the light receiving unit can be performed with high accuracy.

  (2) While the reflection component on the filter surface of the light that has entered the inside through the back surface of the optical filter from the output collimator is reflected on the back surface and reaches the filter surface again. The optical filter may be sized and shaped so as not to enter the cut surface of the optical filter. If it does in this way, the possibility that the irregular reflection component in a cut surface will be received by a light-receiving part can be suppressed as much as possible.

  (3) It is possible to adopt a configuration in which an optical isolator is disposed between the incident fiber collimator and the output fiber collimator.

  (4) The exit fiber collimator includes a ferrule whose tip is obliquely polished, an optical fiber fixed to the ferrule, and a lens, and the obliquely polished apex of the ferrule tip is on the light receiving unit side. It should be arranged. In this way, the optical path of the light incident / exited from the ferrule can be shifted to the light receiving unit side, so that the amount of light received in the reverse direction by the light receiving unit can be further reduced.

  In the present invention, light from the reverse direction to the light receiving unit can be blocked and reduced, and a dynamic range for measuring the light intensity of light incident on the light receiving unit from the incident side can be ensured.

It is a figure which shows an example of the optical module used as the origin of this invention. It is a figure which shows suitable embodiment which concerns on this invention. It is a figure explaining an effect | action. It is a figure which shows other embodiment.

  Hereinafter, preferred embodiments of the optical module 10 according to the present invention will be described. An optical module 10 according to the present invention includes an input fiber collimator 11 and an output fiber collimator 12 that are arranged in parallel while shifting the optical axis, and an optical filter that is arranged along the forward direction between the two fiber collimators 11 and 12. 13, an optical isolator 14, and a light receiving unit (photodetector) 15 that receives reflected light reflected by the optical filter 13 out of the forward light incident from the incident fiber collimator 11.

  The optical filter 13 is composed of a dielectric filter, and functions as a beam splitter that reflects a part of the light on the front filter surface 13 a facing the incident fiber collimator 11. In the present embodiment, about 3 to 5% of the light irradiated on the filter surface 13a is reflected and the rest is transmitted. The angle θ formed by the normal direction of the optical filter 13 (filter surface 13a) and the optical path of the incident light L10 incident from the incident fiber collimator 11 is set to 10 degrees or more. As a result, the angle formed between the incident light L10 and the reflected light L11 with respect thereto is 2θ. Therefore, the optical path of the reflected light L11 deviates from the incident fiber collimator 11, and the reflected light L11 is received by the light receiving unit 15. The light receiving unit 15 is connected to a control unit (not shown), monitors light characteristics such as the light intensity of the reflected light received and detected by the light receiving unit 15, and the incident light incident from the incident fiber collimator 11 is stable. Control to do. In the present embodiment, the light receiving unit 15 uses a photodiode and detects the light intensity. The control based on this monitor can use various types of controls including conventionally known ones, and will not be described in detail.

  In addition, the optical filter 13 is held in an inclined shape at a predetermined angle by a cylindrical holder 16 having front and rear openings. This predetermined angle is set corresponding to the angle θ formed between the incident light L10 and the normal direction of the optical filter 13, and when the axis of the holder 16 and the axis of the incident fiber collimator 11 are adjusted to be parallel, An angle θ formed by the normal direction of the incident light L10 and the optical filter 13 is set to a desired angle.

  In addition, an antireflection film 13 b is provided on the back surface of the optical filter 13. The light transmitted through the filter surface 13a is refracted and travels through the optical filter 13, and is emitted to the outside from the back surface side. Since the optical filter 13 of the present embodiment uses a parallel plate, the outgoing light L12 emitted to the outside is parallel to the incident light L10 (deviated by the above refraction).

  Since the optical isolator 14 and the outgoing fiber collimator 12 are arranged on the optical path of the outgoing light L12, the outgoing light L12, which is forward light, is emitted from the outgoing fiber collimator 12 to the outside.

  Here, in the present embodiment, the incident position of the incident light L10 from the incident fiber collimator 11 to the optical filter 13 is shifted from the center O of the filter surface 13a of the optical filter 13 to the light receiving unit 15 side (the upper side in the drawing). ing. In other words, this type of optical component is usually arranged so that the respective axes are aligned in consideration of the efficiency and ease of assembly work. Therefore, in terms of the relationship between the incident fiber collimator 11 and the optical filter 13, the assembly is performed so that the incident fiber collimator 11 and the axial center (center) of the holder 16 coincide. These adjustments are made in accordance with the outer shape exposed to the outside. Therefore, as shown in FIG. 1B, when the optical filter 2 is mounted in the holder 3 obliquely (toward the light receiving unit 6), the optical filter of the light L from the incident fiber collimator 1 is inevitably produced. 2 (filter surface 2a) is on the far side (lower side in the figure) when viewed from the light receiving unit 6 with respect to the center O, but in this embodiment, it is intentionally close to the light receiving unit 15 side. I am doing so.

  As a result, the distance D between the incident position of the incident light L10 and the cut surface 13c far from the light receiving portion 15 of the optical filter 13 while using the same size and shape of the optical filter 13 as in the past. Can be lengthened. As a result, the light receiving unit 15 receives the light that the return light L13 from the emission fiber collimator 12 side enters the optical filter 13 from the antireflection film 13b side of the optical filter 13 due to the effects described below. The amount of light can be suppressed.

  That is, as shown in FIG. 3A, the return light L13 enters the optical filter 13 and reaches the filter surface 13a on the surface side, part of which is refracted and output to the outside, and part of it is reflected. Then, it proceeds through the optical filter 13 and reaches the antireflection film 13b on the back surface. Part of this antireflection film 13b also reflects. In this way, by making the distance D long, as indicated by the solid line in the figure, the light that has entered the optical filter 13 from the return light L13 is between the filter surface 13a of the optical filter 13 and the antireflection film 13b. And proceeding while repeating reflection several times inside, approaching the cut surface 13c. In the illustrated example, even if it is reflected twice on each surface, it does not reach the cut surface 13c. Of course, although specific illustration is omitted, even in the case of FIG. 3 (a), the light reflected by the filter surface 13a for the third time is irradiated to the cut surface 13c and causes irregular reflection there. Therefore, the amount of light applied to the cut surface 13c is greatly attenuated compared to the amount of the return light L13, and the light component irregularly reflected by the cut surface 13c is received by the light receiving unit 15. Until it is necessary to repeat reflection between the filter surface 13a of the optical filter 13 and the antireflection film 13b a plurality of times, the light component of the return light L13 is not received by the light receiving unit 15 or is received. Even so, it is suppressed as much as possible and is attenuated to such an extent that it has substantially no influence.

  On the other hand, as shown in FIG. 3B, in contrast to the above, the irradiation position of the incident light L on the optical filter 2 is shifted from the center of the filter surface 2a to the lower side (cut surface 2b side) in the drawing. In the case of setting, the return light L2 passes through the antireflection film 2c on the back side of the optical filter 2 and enters the inside, and is reflected by the filter surface 2a, and the reflection component is reflected by the antireflection film surface 2c. The incident light is incident on the cut surface 2b of the optical filter 2 while reaching the filter surface 2a again, and is diffusely reflected there, and a part of the light L3 of the irregular reflection component is received by the light receiving unit. Cause deterioration.

  In the example of FIG. 3A, the cut surface 13c was not reached even if it was reflected twice on each of the filter surface 13a and the antireflection film 13b. However, the present invention is not limited to this. Each time of reflection, that is, the reflection component at the filter surface 13a of the light that has entered the optical filter 13 from the return light L13 is reflected by the antireflection film surface 13b and again reaches the filter surface. Even if the light is not incident on the cut surface 13c of the optical filter (up to the filter surface 13a), a sufficient effect can be expected.

  Moreover, although the optical path shown in FIG. 3 is indicated by a line, the actual light has a certain width. Therefore, even when the center line is not received by the light receiving unit, part of the light in the vicinity of the outer periphery may be received, and the diffuse reflection component diffuses in all directions because of irregular reflection at the cut surface 13c. In some cases, the amount of light is small.

  When the crosstalk was obtained by changing the incident position on the filter, the crosstalk was 30 dB in the product of the present invention shown in FIG. 3A, but in the case of the comparative example shown in FIG. The superiority of the present invention was confirmed. Here, the crosstalk was obtained as follows.

  That is, the light intensity from the light source is P0 (unit: watts: W). Then, the light (light intensity P0) incident from the incident collimator is reflected by the filter, the light intensity of the light received by the light receiving unit is measured, and the light intensity at that time is defined as P1. Here, when a photodiode is used as the light receiving unit, the unit of P1 is ampere [A] in order to observe a current according to the light reception intensity.

The light receiving sensitivity Pin from the incident collimator is expressed by the ratio of P0 and P1,
Pin = P1 / P0 [A / W] (1)
It becomes. Similarly, when light having a light intensity P0 [W] is incident from the output collimator, and the light intensity that passes through the filter and is dried at the light receiving unit is P2 [A], the light reception sensitivity Pout from the output collimator is
Pout = P2 / P0 [A / W] (2)
It becomes. The crosstalk is expressed by the logarithm of the ratio of the light receiving sensitivity Pout of the output collimator and the light receiving sensitivity Pin of the incident collimator, and becomes −10 × log10 (Pout / Pin) [dB].

And specifically, it measures in the following procedures.
1. The light intensity from the light source is measured with an optical power meter. Thereby, P0 [W] is obtained.
2. The light source is connected to the incident collimator, and the output current value of the photodiode of the light receiving unit is measured with an ammeter. As a result, P1 [A] is obtained.
3. The light receiving sensitivity Pin from the incident collimator is calculated from P0 and P1 obtained in the above 1 and 2, using the above equation (1).
4). The light source is connected to an output collimator, and the output current value of the photodiode of the light receiving unit is measured with an ammeter. As a result, P2 [A] is obtained.
5. The light receiving sensitivity Pout from the output collimator is calculated from P0 and P2 obtained in 1 and 4 using the above equation (2).
Using Pin and Pout obtained in 6.3 and 5, calculate −10 × log 10 (Pout / Pin) to obtain the crosstalk.

  FIG. 4 shows another embodiment of the present invention. In this embodiment, the installation state of the output fiber collimator 12 is devised. In other words, the outgoing fiber collimator 12 includes a ferrule 12a whose tip is obliquely polished, an optical fiber 12b fixed to the ferrule 12a, and a lens 12c disposed at the tip. The optical fiber 12b fixed to the ferrule 12a is disposed at the center of the lens 12c.

  The tip 12a 'of the ferrule 12a may be obliquely polished by about 8 to 10 degrees in order to prevent the light reflected by the tip surface from returning. Therefore, the apex P of the oblique polishing of the tip 12a 'of the ferrule 12a is in the same direction as the light receiving unit 15, that is, on the light receiving unit 15 side (upper side in the drawing) in the plane orthogonal to the optical axis of the emitted light L12. Be placed.

  In this way, light entering and exiting the ferrule 12a passes through an oblique optical path toward the upper side (vertex P side) from the optical fiber 12b (center of the lens 12c) and is above the center of the lens 12c (light receiving unit). 15 side). As a result, the return light L13 becomes closer to the light receiving unit 15 side from the center of the antireflection film 13b of the optical filter 13, and the distance from the cut surface becomes longer. As a result, of the light component of the return light L13, the amount of light received by the light receiving unit 15 can be further suppressed.

  In addition, arrangement | positioning of each optical component in the optical module mentioned above is an example, For example, the structure which is not provided with an optical isolator can also be taken, and it does not prevent adding another optical component.

Claims (4)

An incident fiber collimator;
An optical filter that allows the incident light incident from the incident fiber collimator to pass therethrough and reflects a part of the incident light by the filter surface of the surface;
An output fiber collimator for emitting the light that has passed through the optical filter to the outside;
A light receiving portion for receiving light reflected by the optical filter;
With
An optical module, wherein an incident position of the incident light on the optical filter is set closer to the light receiving unit than a center of the filter surface.   The optical filter is configured such that a reflection component on the filter surface of light that has passed through the back surface of the optical filter from the output collimator and enters the inside is reflected on the back surface and reaches the filter surface again. The optical module according to claim 1, wherein the optical module is configured not to be incident on a cut surface of the filter.   The optical module according to claim 1, wherein an optical isolator is disposed between the incident fiber collimator and the output fiber collimator. The exit fiber collimator includes a ferrule whose tip is obliquely polished, an optical fiber fixed to the ferrule, and a lens.
The optical module according to any one of claims 1 to 3, wherein a vertex of the ferrule tip that is obliquely polished is disposed on the light receiving unit side.

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