JP4802916B2 - Bidirectional optical module and optical pulse tester using the same - Google Patents

Description

  The present invention relates to a bidirectional optical module having a light source that emits light and a light receiving unit that receives incident light, and an optical pulse tester using the bidirectional optical module. An optical pulse that realizes a bidirectional optical module that can receive light with high accuracy, and that can accurately measure an optical fiber to be measured through which an optical signal for optical communication is transmitted using the bidirectional optical module. It relates to a tester.

  An optical communication system or a measuring instrument using light (for example, an optical fiber sensor) requires a transmission unit (light source) that outputs light and a reception unit (light reception unit) that receives light. In addition, in a measuring instrument for maintaining and managing an optical communication system, a light source that outputs measurement light to the optical fiber to be measured and a light receiving unit that receives light transmitted by the optical fiber to be measured are essential. .

  For example, in an optical communication system that performs data communication using an optical signal, it is important to monitor an optical fiber that transmits the optical signal. An optical pulse tester (hereinafter abbreviated as OTDR (Optical Time Domain Reflectometer)) is used for laying and maintaining optical fibers. The OTDR repeatedly inputs pulsed light into the optical fiber to be measured, and measures the level of the reflected light and backscattered light from the optical fiber to be measured and the light receiving time. Measure state.

  In addition, modules that have a transmitter unit and a light receiver unit in one are called bi-directional optical modules, BIDI (Bi-Directional) modules, etc., and the price will become lower with the recent spread of FTTH (Fiber To The Home). In addition to OTDR, it is also used in a large amount in other measuring devices and optical communication systems.

  FIG. 6 is a diagram illustrating a configuration of an OTDR using a bidirectional optical module (see, for example, Patent Documents 1 and 2). In FIG. 6, a measured optical fiber F1 of the measured line is a line for transmitting an optical signal, and is an optical fiber to be measured.

  The OTDR 200 has an input / output end measurement connector CN connected to the optical fiber F1 to be measured, and emits pulsed light from the measurement connector CN to the optical fiber F1 to be measured. In the OTDR 200, return light (reflected light or backscattered light) of the pulsed light emitted to the optical fiber F1 to be measured is incident via the measurement connector CN.

  The OTDR 200 includes a bidirectional optical module M1, an LD driving unit M2, a sampling unit M3, a signal processing unit M4, and a display unit M5. The bidirectional optical module M1 outputs pulsed light to the measured optical fiber F1 via the measurement connector CN and receives return light from the measured optical fiber F1. The LD driving unit M2 drives the light source in the bidirectional optical module. The sampling unit M3 converts the electrical signal (photocurrent) from the light receiving unit in the bidirectional optical module M1 into a voltage and samples it. The signal processing unit M4 outputs pulsed light to the bidirectional optical module M1 via the LD driving unit M2, causes the sampling unit M3 to perform sampling, and performs an arithmetic processing on the electrical signal as a sampling result. The display unit M5 displays the processing result of the signal processing unit M4.

  Next, FIG. 7 is a diagram showing a configuration of a conventional bidirectional optical module M1 (see, for example, Patent Documents 1 to 3). In FIG. 7, a laser diode (hereinafter abbreviated as LD (Laser Diode)) 1 outputs light of wavelength λ1. The lens 2 converts the light from the LD 1 into parallel light. The LD 3 outputs light having a wavelength λ2. The lens 4 makes the light from the LD 3 parallel light. The multiplexing / demultiplexing filter (multiplexing means) 5 multiplexes the light with wavelengths λ 1 and λ 2 from the lenses 2 and 4. The lens 6 condenses the light from the multiplexing filter 5. One end of the first optical fiber 7 is provided at the condensing position of the lens 6, and the other end is connected to the optical fiber F1 to be measured by the measurement connector CN. A beam splitter (hereinafter abbreviated as BS (Beam Splitter)) 8 is a reflecting means, and is provided between the multiplexing / demultiplexing filter 5 and the lens 6. The lens 9 condenses the return light branched by the BS 8. An avalanche photodiode (hereinafter abbreviated as APD (Avalanche Photodiode)) 10 is provided at a condensing position of the lens 9 and receives return light.

  LD1 and LD3 are light sources, and APD 10 is a light receiving unit. Also, the use of a plurality of LD1 and LD3 having different wavelengths uses light of wavelengths such as 1310 [nm] and 1550 [nm] for domestic working lines, and 1650 [nm] for monitoring wavelengths. Since light of a wavelength is used, the user can perform measurement at a desired wavelength depending on the application.

The operation of such an apparatus will be described.
The signal processing unit M4 sets the pulse width of the pulsed light in the LD driving unit M2 in advance. Then, timing generation means (not shown) in the signal processing unit M4 sends a timing signal to the LD driving unit M2 at a predetermined interval. Then, the LD driver M2 outputs pulsed light to the LD1 or LD3 in synchronization with the timing signal. Then, the pulsed light from the LD 1 becomes parallel light at the lens 2. Further, the pulsed light from the LD 3 becomes parallel light at the lens 4. Then, the multiplexing / demultiplexing filter 5 transmits the light from the LD 1, reflects the light from the LD 3, and emits it to the BS 8. Further, transmitted light (light from LD 1) and reflected light (light from LD 3) from the multiplexing / demultiplexing filter 5 pass through BS 8 and are collected by the lens 6, and enter one end of the first optical fiber 7. To do.

  Then, the light incident on one end of the first optical fiber 7 enters the optical fiber F1 to be measured through the other end of the first optical fiber and the measurement connector CN. Rayleigh scattering occurs in the optical fiber F1 to be measured, and a part thereof travels in the direction opposite to the traveling direction of the pulsed light and returns to the OTDR 200 as backscattered light. Further, Fresnel reflected light generated at the connection point or break point of the optical fiber F1 to be measured returns to the OTDR 200.

  Then, the return light from the measured optical fiber F1 enters the measurement connector CN and the other end of the first optical fiber 7. Further, the return light emitted from one end of the first optical fiber 7 becomes parallel light by the lens 6 and is branched by the BS 8. Of the branched return light, the return light reflected in the direction of the lens 9 is collected by the lens 9 and received by the APD 10. Further, the APD 10 converts the incident return light into an electrical signal (photocurrent) corresponding to the optical power of the return light, and outputs it to the sampling unit M3.

  Then, an IV conversion circuit (not shown) in the sampling unit M3 converts the photocurrent from the APD 10 into a voltage, a multistage amplifier (not shown) in the sampling unit M3 amplifies the electric signal, and An AD conversion circuit (not shown) in the sampling unit M3 AD-converts an analog electrical signal into a digital signal using the timing signal of the signal processing unit M4 as a time reference, and outputs the digital signal to the signal processing unit M4 To do.

  Furthermore, the signal processing unit M4 obtains the time from when the pulsed light is emitted to the LD1 and LD3 until the return light is received by the APD 10 based on the timing when the timing signal is output and the digital signal from the sampling unit M3. The distance of the optical fiber F1 and the optical signal level of the return light are measured, and the measurement result is displayed on the display unit M5 with the horizontal axis indicating the distance and the vertical axis indicating the optical signal level of the return light.

  Further, since the signal level of the return light is very weak, the pulse light is repeatedly output to the optical fiber F1 to be measured, and the signal processing unit M4 attempts to reduce noise by averaging the measurement values obtained a plurality of times. .

  Next, FIG. 8 is a block diagram showing another example of a conventional bidirectional optical module (see, for example, Patent Document 4). Here, the same components as those in FIGS. 6 and 7 are denoted by the same reference numerals, and the description thereof is omitted. In FIG. 8, 2 × 2 (two inputs and two outputs) optical couplers 11 and 12 are provided instead of the multiplexing / demultiplexing filter 5, the lens 6, the first optical fiber 7, and the BS 8.

  LD1 pulsed light is incident on one input end 11a of the optical coupler 11, and LD3 pulsed light is incident on the other input end 11b. Then, both lights from LD 1 and LD 3 are incident on one input end 12 a of the optical coupler 12 from one output end 11 c of the optical coupler 11. Further, the light incident on the optical coupler 12 is emitted from the one output end 12c of the optical coupler 12 to the measured optical fiber F1.

  Then, the return light from the measured optical fiber F1 enters from the output end 12c of the optical coupler 12, exits from the other input end 12b, and is received by the APD 10.

  The other output end 11d of the optical coupler 11 and the other output end 12d of the optical coupler 12 are processed so as to be non-reflective ends. Further, one output end 12c of the optical coupler 12 and the optical fiber F1 to be measured are connected by a measurement connector CN. Then, the lens 2 that collects the light from the LD 1 and couples it to the input end 11 a of the optical coupler 11, the lens 4 that collects the light from the LD 3 and couples it to the input end 11 b of the optical coupler 11, and the optical coupler 12. The lens 9 that collects light from the input end 12b and couples it to the APD 10 is not shown.

JP 2001-305017 A JP-A-4-296812 JP-A-8-166526 JP-A-10-336106

  The light receiving area of the APD 10 is predetermined according to the specification. However, there is a portion that outputs a photocurrent when light is incident even if it is outside the range determined by the specification. A portion that receives light even if it is not the light receiving area is called outside the light receiving area. Usually, the manufacturer of the APD 10 defines only a portion with good characteristics (for example, frequency characteristics) as a light receiving area.

  Here, FIG. 9 is a diagram schematically showing output characteristics (frequency characteristics) of the APD 10 with respect to incident light. In FIG. 9, the horizontal axis is time, the upper (a) is the incident light to the ADP 10, the middle (b) is the output when received in the light receiving area, and the lower (c) is outside the light receiving area. The output when receiving light is shown. As shown in FIG. 9, the output when the light is received in the light receiving area rises and falls sharply following the incident pulse light. On the other hand, the output when receiving light outside the light receiving area has poor frequency characteristics and a slow response.

  Therefore, when the bidirectional optical module shown in FIG. 7 is manufactured, the BS 8, the lens 9, the APD 10, etc. are aligned so that the return light is incident only on the light receiving area of the APD 10.

  However, in the pigtail type bidirectional optical module shown in FIG. 7, the optical components 1 to 6 and 8 to 10 are housed in a metal case (dotted line in FIG. 7), and only the ferrule portion on one end side of the optical fiber 7 is included. Fixed to the case (other parts are outside the case) and modularized. Each optical component 1 to 10 is fixed to a metal case by a metal component (not shown) or the like. Therefore, pulse light and return light from the LDs 1 and 3 are reflected / scattered on the end surfaces of the optical components 1 to 10, metal parts, metal cases and other parts / metal surfaces, and stray light is generated.

  Then, the return light emitted from one end of the optical fiber 7 into the bidirectional optical module is reflected / scattered to generate stray light. Further, the generated stray light is repeatedly attenuated and enters the outside of the light receiving area of the APD 10 having poor frequency characteristics. FIG. 10 illustrates the vicinity of the light receiving area of the lens 9 and the APD 10, and schematically illustrates the return light and stray light entering the APD 10. FIG. 10 shows an example in which the return light 100a enters the light receiving area 10a and the stray light 100b of the return light 100a enters the outside light receiving area 10b.

  In this way, when stray light 100b is received outside the light receiving area 10b with poor frequency characteristics, the tailing (referred to as an attenuation dead zone) when measuring the breaking point / connection point of the optical fiber F1 to be measured is caused to occur in the light receiving area 10. There is a problem that the distance on the distance axis is larger than that when only the light is received, and the measurement accuracy for obtaining the breaking point / connection point is deteriorated. Here, FIG. 11 is a diagram showing an example of the measurement result of OTDR200. The horizontal axis is the distance (the time from when the pulse light is emitted until it is received by the APD 10 is converted into the distance), and the vertical axis is the optical signal level of the return light.

Further, the polarization dependence of the BS 8 of the reflecting means (hereinafter also abbreviated as PDL (Polarization Dependent Loss)) is the normal of the branch surface of the BS 8 and the light of the return light incident on the branch surface. The worse the angle of incidence with the axis, the worse. Here, FIG. 12 is a diagram showing the incident angle to the BS 8 and the polarization dependence characteristics. In the apparatus shown in FIG. 7, since the return light is branched and reflected by the BS 8 in a direction orthogonal to the optical axis, the incident angle to the BS 8 is large (usually about 45 [deg]), and the polarization dependency is also deteriorated. . As a result, there is a problem in that it is difficult to accurately measure the optical power of the return light incident on the bidirectional optical module, and it is difficult to accurately measure the measured optical fiber F1.

  In addition, in order to drive LD1 and LD3 with high accuracy, it is necessary to shorten the wiring of electrical signals from the drive unit M2 to the LD1 and LD3, and the LD1, LD3 and the drive unit M2 are physically close to each other. There must be. Similarly, a weak photocurrent from the APD 10 is converted into a voltage by the sampling unit M3, and a large amplification and AD conversion are performed. To accurately sample the photocurrent, an electrical path between the APD 10 and the sampling unit M3 Should be shortened and physically closer.

  However, in the pigtail type bidirectional optical module shown in FIG. 7, LD1, LD3, and APD 10 are physically close to each other. Therefore, the electric signal of the driving unit M2 that is larger than the electric signal from the APD 10 affects the light receiving side (APD10, sampling unit M3) that needs to be detected with high sensitivity and low noise. That is, there is a problem that the light receiving side is easily affected by the light emitting side (LD1, LD3, driving unit M2), and the electric signal on the light emitting side becomes noise to the light receiving side.

  On the other hand, in the fiber coupler type bi-directional optical module shown in FIG. 8, unnecessary reflected light and scattered light generated inside the optical system are difficult to enter the APD 10, so that the above-mentioned tailing is small and the influence of PDL is also exerted. Few. Further, since the LDs 1 and 3 and the APD 10 can be physically separated, the influence of the driving unit M2 on the sampling unit M3 is small.

  However, the use of the optical couplers 11 and 12 increases the component cost, and the optical fiber cannot be bent smaller than a predetermined curvature. Therefore, the size of the bidirectional optical module is reduced with the fiber forming of the optical couplers 11 and 12. There was a problem that it was difficult to convert.

  Accordingly, an object of the present invention is to realize a bidirectional optical module that can receive light with high accuracy while being small and inexpensive, and to accurately measure an optical fiber to be measured using the bidirectional optical module. It is to realize an optical pulse tester capable of

The invention described in claim 1
In a bidirectional optical module having a light source that emits light and a light receiving unit that receives incident light,
A first optical fiber that enters the light from the light source from one end and exits from the other end to the own module; the incident light enters from the other end and exits from the one end into the own module;
A lens that collimates incident light from one end of the first optical fiber;
The collimated light from the lens, a reflecting means for reflecting to said lens,
One end is provided at the focal position of the lens , and there is provided a second optical fiber that enters the reflected light reflected by the reflecting means and collected by the lens from one end and exits from the other end to the light receiving unit. ,
The distance between the lens and the reflecting means is set equal to the focal length of the lens, and one ends of the first optical fiber and the second optical fiber are arranged point-symmetrically with respect to the center of the lens. The distance between the ends of the fiber is set to be sufficiently shorter than the focal length of the lens .
The invention according to claim 2 is the invention according to claim 1,
The reflecting means is provided perpendicular to the optical axis of incident light emitted from one end of the first optical fiber.
The invention according to claim 3 is the invention according to claim 1 or 2,
The incident angle of the incident light incident on the reflecting means is equal to the outgoing angle of the reflected light reflected by the reflecting means.
The invention according to claim 4 is the invention according to any one of claims 1 to 3,
A ferrule is provided to hold one end of the first optical fiber and one end of the second optical fiber in parallel, and the distance between the lens and the end face of the ferrule is set equal to the focal length of the lens. It is characterized by.
The invention according to claim 5
In an optical pulse tester that emits pulsed light to a measured optical fiber to which an optical signal for optical communication is transmitted, and measures the measured optical fiber based on the return light of the emitted pulsed light,
The pulse light is emitted from the other end of the first optical fiber to the optical fiber to be measured, and the return light is incident on the other end of the first optical fiber as incident light. A bidirectional optical module;
A drive unit that emits pulsed light to the light source of the bidirectional optical module;
A sampling unit for sampling the output from the light receiving unit of the bidirectional optical module;
A timing signal is output to the driving unit and the sampling unit, and a signal processing unit that measures the optical fiber to be measured by an output from the sampling unit is provided.

The present invention has the following effects.
According to the first to fourth aspects, since one end of the second optical fiber that emits light to the light receiving portion is provided at the focal position of the collimating means, even if stray light of incident light is generated in the own module, it is reflected. Unless it enters the collimating means at the same angle as the reflected light reflected by the means, it does not enter the second optical fiber. Further, the incident position on the light receiving unit is determined by the positional relationship with the second optical fiber. Accordingly, unnecessary stray light generated by the incident light is not easily incident on the second optical fiber, and is not received except at a desired position of the light receiving unit, and the light can be received with high accuracy by the light receiving unit. In addition, the size and cost can be reduced as compared with a configuration using an optical coupler.
According to claim 2, since the incident light from the first optical fiber is incident on the reflecting means substantially perpendicularly, the polarization dependence of the reflecting means is reduced, and the optical power of the incident light is accurately received, Can be measured.
According to the fifth aspect, since the bidirectional optical module according to any one of the first to fourth aspects is used for an optical pulse tester, the return light from the optical fiber to be measured can be received with high accuracy. Thereby, the optical fiber to be measured can be measured with high accuracy.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram showing an embodiment of the present invention. 6 and 7 are denoted by the same reference numerals, description thereof is omitted, and further illustration is omitted. This is an example in which the bidirectional optical module of the present invention is applied to the OTDR 200 shown in FIG. 6 instead of the conventional bidirectional optical module M1 shown in FIGS.

  In FIG. 1, BS13 is provided instead of BS8. The BS 13 is a reflection means, which splits the return light emitted from one end of the first optical fiber 7 and converted into parallel light by the lens 6 with a predetermined ratio of optical power, reflects one to the lens 6 again, and the other. Transparent. In addition, BS13 of FIG. 1 has shown only the branch surface.

  A second optical fiber 14 is newly provided. Return light reflected by the BS 13 and collected by the lens 6 enters one end of the second optical fiber 14. Then, the return light incident and transmitted from the other end of the second optical fiber 14 is emitted to the lens 9. The lens 9 condenses the return light emitted from the other end of the second optical fiber 14. The second optical fiber 14, the lens 9, the APD 10, etc. are aligned so that the light emitted from the second optical fiber 14 enters only the light receiving area 10 a of the APD 10.

  FIG. 2 shows the other end of the optical fiber 14, the lens 9, and the vicinity of the light receiving area of the APD 10, and schematically shows that light emitted from the other end of the optical fiber 14 enters the lens 6 and the APD 10. It is.

  FIG. 3 is a diagram showing in detail the one end of each of the optical fibers 7 and 14, the lens 6, BS 13, the return light 100 a from the optical fiber 7, and the reflected light 100 a ′ of the return light from the BS 13. In FIG. 3, the ferrule 15 holds one end of the first optical fiber 7 and one end of the second optical fiber 14 in parallel. Also, the alternate long and short dash line in FIG. 3 indicates the optical axes of the return light 100a and the reflected light 100a '.

  FIG. 4 is a configuration diagram showing the directions of the optical fibers 7 and 14 from the lens 6 side, and the illustration of the ferrule 15 is omitted. In FIG. 3, the optical fibers 7 and 14 are arranged point-symmetrically with respect to the center of the lens 6.

  3 and 4, the return light 100 a is light emitted from one end of the first optical fiber 7, and the reflected light 100 a ′ is the return light 100 a branched by the BS 13. It is the light reflected by.

  One end of each of the optical fibers 7 and 14 is arranged as close as possible in the same ferrule 15. For example, if the diameters of the optical fibers 7 and 14 are 125 [μm], they are close to the distance ΔL = 250 [μm] between the centers of the optical fibers 7 and 14 (for example, JP-A-10-111433, JP-A-2001-356240). Of course, the distance ΔL may be any value, for example, ΔL = 125 [μm]. However, a commercially available two-core ferrule is generally 250 [μm]. Further, the longitudinal axes of the optical fibers 7 and 14 are parallel, and the end face of the ferrule 15 may be either flat or oblique. Further, the optical axis of the return light 100a emitted from the optical fiber 7 to the lens 6 and the optical axis of the reflected light 100a 'from the lens 6 to the optical fiber 14 are parallel to each other.

  When the focal length of the lens 6 is f, the distance between the BS 13 and the lens 6 is f, and the distance between the lens 6 and the end face of the ferrule 15 (that is, the end face of one end of each of the optical fibers 7 and 14) is also f. . As an example, the focal length f of the lens 6 is several [mm] to several tens [mm] with respect to the distance 250 [μm] between the fibers, and there is a difference of 2 to 3 digits in the distance.

  The normal line of the branch surface of the BS 13 is parallel to the optical axis of the return light 100 a emitted from one end of the first optical fiber 7. That is, the branch surface of the BS 13 is provided perpendicular to the optical axis of the return light 100 a that is emitted from the optical fiber 7 and reaches the lens 6.

  Note that the branch surface of the BS 13 is perpendicular to the optical axis of the return light 100a immediately after being emitted from the optical fiber 7, but in reality, in the alignment of the BS 13, the lens 6, the ferrule 15, and the like, the branch of the BS 13 is branched. It is difficult to make the surface completely perpendicular to the optical axis. Therefore, the term “perpendicular to the optical axis” includes an inclination due to such an alignment error (usually 1 [deg] or less).

  In addition, when the distance between the branch surface of the BS 13 and the lens 6 is f and the distance between the lens 6 and the end surface of the ferrule 15 is also f, the reflected light 100a ′ obtained by reflecting the return light 100a at the BS 13 is transmitted to the optical fiber 14. It is very important for efficient coupling.

The operation of such an apparatus will be described.
LD1 or LD3 emits pulsed light according to the drive signal from the LD drive unit M2. Which LD1 or LD3 is driven may be switched depending on the application. Then, the pulsed light from the LD 1 becomes parallel light at the lens 2. Further, the pulsed light from the LD 3 becomes parallel light at the lens 4. Then, the multiplexing / demultiplexing filter 5 transmits the light from the LD 1, reflects the light from the LD 3, and emits it to the BS 13. Further, transmitted light (light from LD 1) and reflected light (light from LD 3) from the multiplexing / demultiplexing filter 5 pass through the BS 13 and are collected by the lens 6, and enter one end of the first optical fiber 7. To do.

  Then, the light incident on one end of the first optical fiber 7 enters the optical fiber F1 to be measured through the other end of the first optical fiber and the measurement connector CN. Rayleigh scattering occurs in the optical fiber F1 to be measured, and a part thereof travels in the direction opposite to the traveling direction of the pulsed light and returns to the OTDR 200 as backscattered light. Further, Fresnel reflected light generated at the connection point or break point of the optical fiber F1 to be measured returns to the OTDR 200.

Then, the return light from the measured optical fiber F1 enters the other end of the first optical fiber 7 via the measurement connector CN. Further, the return light 100 a emitted from one end of the first optical fiber 7 is converted into parallel light by the lens 6. At this time, since the optical axis of the return light 100a emitted from the first optical fiber 7 is shifted from the center of the lens 6 (on the xy plane in the figure), the optical axis of the return light 100a is inclined by the lens 6 ( In the figure (-y) axial direction), the light beam is incident on the branch surface of the BS 13 at a slight angle (incident angle: θin = tan ⁻¹ ((ΔL / 2) / f)) close to normal incidence. The light is branched into transmitted light (not shown) and reflected light 100a ′.

  Then, the BS 13 reflects the return light 100a incident on the BS 13 at the incident angle θin at the emission angle θout (= θin). Further, the reflected light 100 a ′ reflected by the BS 13 is collected by the lens 6 and enters one end of the second optical fiber 14. As described above, since the focal length f is 2-3 orders of magnitude larger than the distance ΔL between the centers of the fibers 7 and 14 of several hundred [μm], the incident angle θin and the outgoing angle θout are almost 0 [deg]. ] Normal incidence. As an example, if ΔL = 250 [μm] and f = 2 to 5 [mm], the incident angle θin is about 1.4 to 3.6 [deg]. In addition, as shown in FIG. 12, the PDL of the BS 13 increases exponentially rather than linearly with respect to the incident angle θin. Therefore, compared with the incident angle (about 45 [deg]) as shown in FIG. 7, the PDL at the BS 13 can be remarkably reduced.

  Then, the reflected light 100 a ′ incident on one end of the second optical fiber 14 is transmitted by the optical fiber 14 and emitted from the other end. The emitted reflected light 100 a ′ is collected by the lens 9 and received by the light receiving area 10 a of the APD 10. Further, the APD 10 converts the incident light into an electrical signal (photocurrent) corresponding to the optical power of the light, and outputs it to the sampling unit M3.

  On the other hand, the return light 100a emitted from one end of the optical fiber 7 into the bidirectional optical module is reflected / scattered by the end surfaces of the optical components 1 to 7, 13, and 14, metal parts, metal cases and other parts / metal surfaces. And stray light is generated. However, the generated stray light is not collected at the end face of the second optical fiber 14 and does not enter the second optical fiber 14 unless it enters the lens 6 at the same angle as the reflected light 100a '. Further, even if stray light enters the second optical fiber 14, the stray light 100b emitted from the other end of the second optical fiber 14 is received only by the light receiving area 10a of the APD 10, and has a poor frequency characteristic. Light is not received outside the area 10b.

  The other operations (driving unit M2, sampling unit M3, signal processing unit M4, display unit M5, etc.) other than those described above are the same as those of the apparatus shown in FIG. Here, FIG. 5 is a diagram showing an example of a measurement result of the OTDR 200 using the bidirectional optical module shown in FIG. The horizontal axis is the distance (the time from when the pulse light is emitted until it is received by the APD 10 is converted into the distance), and the vertical axis is the optical signal level of the return light. In FIG. 5, in the present invention, since the light is received only by the light receiving area 10a, it can be seen that the tailing is improved as compared with the case where the bidirectional optical module shown in FIG. 7 is used (FIG. 11).

  In this way, since one end of the second optical fiber 14 that emits light to the APD 10 is provided at the focal position of the lens 6, even if stray light of the return light 100a is generated in the own module, it is reflected by the BS 13 The light does not enter the second optical fiber 14 unless it enters the lens 6 at the same angle as the reflected light 100a ′. Further, the incident position of the APD 10 on the light receiving area 10 a is determined by the positional relationship with the second optical fiber 14. As a result, stray light is unlikely to enter the second optical fiber 14, and the reflected light 100 a ′ is not received outside the light receiving area 10 a of the APD 10, and the reflected light 100 a ′ can be received with high accuracy by the APD 10. Further, it can be made smaller and less expensive than the configuration shown in FIG. 8 using an optical coupler.

  Even if stray light is incident on the second optical fiber 14, the stray light is always received only by the light receiving area 10a of the APD 10. Therefore, the stray light does not deteriorate the trailing edge and the measurement accuracy does not deteriorate. .

  That is, the light (stray light) to the outside of the light receiving area 10b of the APD 10 that has a poor frequency characteristic and deteriorates tailing is removed before being incident on one end of the second optical fiber 14 before being coupled to the APD 10. Therefore, measurement with less tailing is possible while being smaller and less expensive than the bidirectional optical module shown in FIG. Thereby, the measurement accuracy can be improved.

  Further, since the return light 100a from the first optical fiber 7 is incident on the branch surface (reflection surface) of the BS 13 almost perpendicularly, the polarization dependency of the BS 13 is reduced, and the optical power of the reflected light 100a ′ is accurately measured. It can receive light well. Thereby, the measurement of the optical fiber F1 to be measured by the OTDR 200 can be performed with high accuracy.

  In addition, since the reflected light 100a ′ is transmitted by the second optical fiber 14, the degree of freedom of arrangement of the APD 10 is increased, and the physical distance between the LD1, LD3, and the APD 10 can be increased. It is easy to separate the circuit on the light receiving side. Thereby, the influence on the light-receiving side by the light-emitting side can be suppressed. Therefore, measurement with higher sensitivity and lower noise than the conventional bidirectional optical module shown in FIG. 7 can be performed, and measurement accuracy can be improved.

  In the present invention, a so-called two-core fiber (two-core ferrule) has been present, but in the present invention, when the reflected light 100a ′ of the return light 100a is guided to the APD 10, it is parallel to the vicinity of the first optical fiber 7. In the conventional bidirectional optical module, the second optical fiber 14 for guiding to the APD 10 is arranged to remove stray light to the outside of the light receiving area 10b of the APD 10 and reduce PDL. An extremely high performance bidirectional optical module can be realized.

The present invention is not limited to this, and may be as shown below.
Although the configuration in which the bidirectional optical module of the present invention is used for the OTDR 200 has been shown, it may be used for other measuring equipment (for example, an optical fiber sensor) or a transmission / reception unit of an optical communication system. In short, it may be used for devices, systems, and the like in which a transmitter (light source) that outputs light and a receiver (light receiver) that receives light are essential.

  Although the configuration using two light sources LD1 and LD3 is shown, the number of LDs may be one or three or more, and the wavelength of the LD may be determined depending on the application, and any wavelength may be used. For example, when only the LD 1 is used as the light source, the LD 3, the lens 4, and the multiplexing / demultiplexing filter 5 may be removed from the apparatus shown in FIG.

  The configuration in which LD1 and LD3 are used as the light source and is directly modulated by the driving unit M2 is shown. However, the light source is configured by LD1, LD3 and the intensity modulator, and the light emitted from LD1 and LD3 is pulsed by the intensity modulator. It may be light.

  Moreover, although the structure which provides a beam splitter as an example of a reflection means was shown, a half mirror etc. may be sufficient.

  In addition, although the configuration in which the APD 10 is used for the light receiving portion is shown, other photodiodes (silicon photodiode, compound semiconductor photodiode, PIN photodiode, or the like) may be used.

  Moreover, although the structure which uses the lens 6 was shown as an example of a collimator means, a concave mirror, a parabolic mirror, etc. may be sufficient.

  In the apparatus shown in FIG. 1, the lenses 2, 4, 6, and 9 are shown as a single lens, but a plurality of types of lenses may be combined. In particular, the lenses 6 and 9 are preferably configured to suppress aberrations (chromatic aberration, top aberration, etc.). As a result, the reflected light 100a 'can be efficiently incident on the second optical fiber 14 and the light receiving area 10a of the APD 10.

It is the block diagram which showed one Example of this invention. It is the figure which showed the other end of the optical fiber 14, the lens 9, and the light-receiving area vicinity of APD10 in detail. It is the figure which showed each end of the optical fibers 7 and 14, the lens 6, and BS13 in detail. It is the block diagram which showed the optical fibers 7 and 14 direction from the lens 6 side. It is the figure which showed an example of the measurement result of OTDR200 using the bidirectional | two-way optical module shown in FIG. It is the figure which showed the structure of the optical pulse tester. It is the block diagram which showed an example of the conventional bidirectional | two-way optical module. It is the block diagram which showed the other example of the conventional bidirectional | two-way optical module. It is the figure which showed typically the output characteristic (frequency characteristic) with respect to the incident light of APD10. It is the figure which showed typically the light-receiving area vicinity of the lens 9 and APD10. It is the figure which showed an example of the measurement result of OTDR200 at the time of using the bidirectional | two-way optical module shown in FIG. It is the figure which showed typically the characteristic of the polarization dependence with respect to an incident angle.

Explanation of symbols

1, 3 Laser diode (light source)
6 Lens (collimating means)
7 First optical fiber 10 APD (light receiving part)
13 BS (reflection means)
14 Second optical fiber 200 OTDR
F1 Optical fiber to be measured M1 Bidirectional optical module M2 Drive unit M3 Sampling unit M4 Signal processing unit

Claims (5)

In a bidirectional optical module having a light source that emits light and a light receiving unit that receives incident light,
A first optical fiber that enters the light from the light source from one end and exits from the other end to the own module; the incident light enters from the other end and exits from the one end into the own module;
A lens that collimates incident light from one end of the first optical fiber;
The collimated light from the lens, a reflecting means for reflecting to said lens,
One end is provided at the focal position of the lens , and there is provided a second optical fiber that enters the reflected light reflected by the reflecting means and collected by the lens from one end and exits from the other end to the light receiving unit. ,
The distance between the lens and the reflecting means is set equal to the focal length of the lens, and one ends of the first optical fiber and the second optical fiber are arranged point-symmetrically with respect to the center of the lens. A bidirectional optical module, wherein a distance between one ends of the fibers is set to be sufficiently shorter than a focal length of the lens . Said reflecting means, said first bidirectional optical module according to claim 1, wherein the relative end optical axis of the incident light emitted from the optical fiber, and which are located vertically.   3. The bidirectional optical module according to claim 1, wherein an incident angle of incident light incident on the reflecting means is equal to an outgoing angle of reflected light reflected by the reflecting means. A ferrule is provided to hold one end of the first optical fiber and one end of the second optical fiber in parallel, and the distance between the lens and the end face of the ferrule is set equal to the focal length of the lens. The bidirectional optical module according to claim 1, wherein: In an optical pulse tester that emits pulsed light to a measured optical fiber to which an optical signal for optical communication is transmitted, and measures the measured optical fiber based on the return light of the emitted pulsed light,
The pulse light is emitted from the other end of the first optical fiber to the optical fiber to be measured, and the return light is incident on the other end of the first optical fiber as incident light. A bidirectional optical module;
A drive unit that emits pulsed light to the light source of the bidirectional optical module;
A sampling unit for sampling the output from the light receiving unit of the bidirectional optical module;
An optical pulse tester comprising: a signal processing unit that outputs a timing signal to the driving unit and the sampling unit, and measures the optical fiber to be measured by an output from the sampling unit.

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