JPH03209143A - Method and device for diagnosing optical wave guide circuit - Google Patents

Abstract

PURPOSE:To enable a measurement of branching ratio with high accuracy by making interference for a branch light propagated through optical wave guide circuit and a phase modulated referring light. CONSTITUTION:An incoherent light from a light source 1 is made incident to a pigtail FP 11 of optical fiber coupler 7 through a lens 2 and bifurcated in a light coupling part FC 1. One of them is made incident to the optical wave guide circuit 17 from a port P1 through a pigtail FP 13, and another one is propagated in a pigtail 14 as the referring light and phase-modulated at the optical fiber part wound to a cylindrical electrostrictive oscillator 9. Then, the output light from circuit 17 is made incident to a pigtail FP 21 of optical coupler 8 and coupled with the phase-modulated referring light in a light coupling part FC 2. When a light propagated in a pigtail FP 24 among the coupled lights is collimated by a lens 3 to enter to a Michelson interference device furnished with a delay circuit and the interference is made for the output light and referring light, the branching ratio of a light branching part can be obtained by means of measuring the intensity ratio of beat components of phase modulation frequency in the intensity of interference light.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method and apparatus for diagnosing an optical waveguide circuit used in optical communication, optical information processing, etc. The present invention also relates to an optical waveguide circuit diagnostic method and apparatus for measuring the optical path length difference between optical branching parts.

[Prior Art] FIG. 2 shows an example of a conventional branching ratio measuring device for an optical branching section of an optical waveguide circuit.

In Figure 2, 1 is an incoherent light source, 2 3
4 par lenses, 5.6 are half mirrors 10, 1.1, 1.
2 is a total reflection mirror, l3 is a total reflection mirror sweep stage, l4 is a photodetector, l6 is a waveform monitor, 17 is an optical waveguide G11. G12, G21, G22, G31, G32 and
2×2 boat Pi, P2. This is an optical coupling/branching circuit as an optical waveguide circuit to be illustrated, which has optical branching parts P3 and P4 and two optical branching parts Cl and C2.

Incoherent light from a light source 1 is collimated by a lens 2, and split into two by a half mirror 5 into a reference light and light incident on an optical coupling/branching circuit 17.

The reference light once passes through the half mirror 6 via the total reflection mirror 10, is reflected by the total reflection mirror 12, and enters the half mirror 6 again. On the other hand, the incident light from the half mirror 5 is input to the boat P1 of the optical coupling/branching circuit 17 via the lens 3, and is directed to the optical waveguide, that is, the path Gll.
-G21→G31 and Gll The light that has propagated through -G22-G31 is emitted from the boat P3 with a delay corresponding to the respective propagation optical path lengths, and is further collimated by the lens 4 and then passed through the total reflection mirror 11. and enters the half mirror 6, where it is combined with the reference light described above.

The total reflection mirror l2 is swept in the direction of the arrow on the stage 13, and when the propagation optical path length of each path matches the optical path length of the reference beam, the total reflection mirror l2 is sequentially interfered with the reference beam, and the light is detected. Interference fringes are observed at the detector 14. The propagating light intensity of each path is measured from the peak value of each interference fringe, and the light intensity ratio R1 is calculated.

Similarly, the pathways Gll-lG21→G32 and Gll-G2
The intensity of the propagated light emitted from the boat P4 via 2-G32 is measured, and the light intensity ratio R2 is calculated. Then, the branching ratios of the optical branching section C1 and the optical branching section C2 are calculated from the light intensity ratios R1 and R2, and the optical path length difference between the two optical paths G21 and G22 is calculated from the difference in the position where each interference fringe occurs. You can ask for it.

[Problems to be Solved by the Invention] However, in the conventional measurement method, noise due to vibration of the optical system has a low frequency component comparable to the detected light intensity.
The noise component is easily superimposed on the detection output, the accuracy of branching ratio measurement is low, and the optical axis alignment is difficult because the lens system inputs the light into the optical waveguide circuit, and the optical consistency is poor. Therefore, there is a problem in that extra modes are excited, which affects the accuracy of branching ratio measurement and the measurement of optical path length difference.

Therefore, the present invention has been made in view of the above circumstances, and an object thereof is to be able to measure the branching ratio and the optical path length difference of the optical branching part of an optical waveguide circuit with high accuracy by simply aligning the optical axis. An object of the present invention is to provide a method and device for diagnosing an optical waveguide circuit.

[Means for Solving the Problems] In order to achieve such an object, a first form of the method of the present invention is an optical waveguide circuit diagnostic method for measuring the branching ratio of an optical branching part of an optical waveguide circuit. Coherent light is split into two by an optical fiber coupler type branching means, one branched light is made to enter the input end of the optical waveguide circuit via one optical fiber optical path of the optical fiber coupler type branching means, and the other branched light is is phase-modulated in the other optical fiber optical path of the optical fiber coupler type branching means and used as a reference light;
The output light propagating through each propagation path of the optical waveguide circuit and emitted from the output end and the phase-modulated reference light are caused to interfere with each other by an interferometer having a delay circuit, and the beat component of the phase modulation frequency in the intensity of the interference light is generated. The method is characterized in that the intensity of the light beam is measured, and the branching ratio of the light branching section is determined from the measured intensity ratio.

A second form of the method of the present invention is an optical waveguide circuit diagnostic method for measuring the difference in optical path length between optical branch parts in an optical waveguide circuit, in which incoherent light is split into two by an optical fiber coupler type branching means, One branched light is made to enter the input end of the optical waveguide circuit through one optical fiber optical path of the optical fiber coupler type branching means, and the other branched light is input to the other optical fiber of the optical fiber coupler type branching means. phase-modulated in the optical path to produce a reference light, and the output light propagating through each propagation path of the optical waveguide circuit and emitted from the output end and the phase-modulated reference light are made to interfere with each other by an interferometer having a delay circuit; The present invention is characterized in that the intensity of the beat component of the phase modulation frequency in the interference light intensity is measured, and the optical path length difference between the optical paths is determined from the difference in interference position.

The device of the present invention has a branch ratio of an optical branch part of an optical waveguide circuit and/or
Alternatively, in an optical waveguide circuit diagnostic device that measures the optical path length difference between optical branching parts, an incoherent light source and an optical fiber that branches the emitted light from the incoherent light source into the incident light to the optical waveguide circuit and the reference light. a coupler type branching means;
an optical fiber type phase modulation means coupled to the optical fiber coupler type branching means to apply phase modulation to the reference light; and an output light from the optical waveguide circuit and a reference light phase modulated by the phase modulation means. an optical fiber coupler-type coupling means for coupling; an interferometer for interfering the output light from the optical waveguide circuit with the phase-modulated reference light; The present invention is characterized in that it includes a signal extraction means for extracting a phase modulation frequency component signal.

[Function] According to the present invention, an optical waveguide circuit as a diagnostic target is extracted by extracting an AC signal component of a phase modulation frequency using an optical fiber type coupling/branching optical system and an optical fiber type phase modulation means. The branching ratio of the optical branching sections inside and the optical path length difference between the optical paths between these branching sections can be measured with high accuracy. Moreover, in the present invention, since the coupling/branching optical system connected to the optical waveguide circuit to be diagnosed is constructed from an optical fiber, optical consistency with the optical waveguide circuit is high, and optical axis alignment can be easily performed. be able to.

[Example] Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention.

In Figure 1, ■ is an incoherent light source, 2.3 is a lens, 6 is a half mirror, 7 is a big tail FPII,
FP12, FPl3, FP14 and optical coupling part PCI
an optical fiber coupler as an optical fiber coupler type branching means, 8 is a big tail FP21, FP22;
FP23. An optical fiber coupler as an optical fiber coupler type coupling means having an FP24 and an optical coupling part FC2, 9 a cylindrical electrostrictive vibrator as an optical fiber type phase modulation means, 11. 12 is a total reflection mirror, 13 is a stage that can move the total reflection mirror 8 in the direction of the arrow, l4 is a photodetector, l5 is a selection level meter, 16 is a waveform monitor, 17 is an optical waveguide G11, G12, G21, G22, G31, G3
2, a 2×2 boat, and two optical branches Cl, C2
Optical waveguide as a diagnostic target, optical coupling as a circuit/
It is a branch circuit. Here, the big tail FP 14 of the optical fiber coupler 7 is wound around the cylindrical electrostrictive vibrator 9,
Furthermore, it is coupled to the big tail FP 22 of the optical fiber coupler 8. The cylindrical electrostrictive vibrator 9 vibrates upon application of an alternating current voltage, and expands and contracts the optical fiber wound around the vibrator 9, thereby imparting phase modulation to the propagating light.

Incoherent light from the light source 1 enters from the big tail FPI 1 of the optical fiber coupler 7 via the lens 2, and is split into two at the optical coupling part PCI.

One of them is connected to the optical waveguide circuit l7 via the big tail FPl3.
The light enters from the boat PI, and the other light propagates through the big tail FP 14 as a reference light and undergoes phase modulation in the optical fiber portion wound around the cylindrical electrostrictive vibrator 9. Optical waveguide circuit 17
The output light from is a big tail FP of optical fiber cutter 8.
21 and is coupled to the above-mentioned phase-modulated reference light which has propagated through the big tail FP22 and is coupled by the optical coupler FC2.

Of the combined light, the light that has propagated through the big tail FP 24 is collimated by the lens 3 and then enters the Michelson interferometer. That is, the combined light is split into two by the half mirror 6,
Those branched lights are reflected by a total reflection mirror 11. After being reflected by the mirror 12, it is combined again by the half mirror 6. Here, the total reflection mirror l2 is swept in the direction of the arrow by the stage 13, and the output light and the reference light are caused to interfere at a position where the propagation optical path lengths of the output light and the reference light match, and the interference fringe is detected by the photodetector 14.
Detect with. In the interference light intensity, a beat of the phase modulation frequency occurs on the DC component, so the light intensity of the beat component of this phase modulation frequency is measured by the selection level meter 15. In this way, as in the conventional example, the paths G11→G21→G31 and Gll→G2 are established from the boat P3 of the optical waveguide circuit l7.
2→G31, and Bo}P4 to route Gll -G2
1→G32 and Gll→G22→G32 to determine the respective light intensity ratios R1 and R2. These 2
The branching ratio of the optical branching parts C1 and C2 is calculated from the intensity ratio of the two, and the two paths G2 are determined from the difference in the positions where interference occurs.
The optical path length difference between G1 and G22 is determined.

[Effects of the Invention] As is clear from the above, according to the present invention, an AC signal component of a phase modulation frequency is extracted by using an optical fiber type coupling/branching optical system and an optical fiber type phase modulation means. , it is possible to measure with high precision the branching ratio of the optical branching sections in the optical waveguide circuit to be diagnosed and the optical path length difference between the optical paths between these branching sections. Moreover, in the present invention, since the coupling/branching optical system coupled to the optical waveguide circuit to be diagnosed is constructed from an optical fiber, optical consistency with the optical waveguide circuit is high, and optical axis alignment can be easily performed. I can do it.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the optical waveguide circuit diagnostic device of the present invention, and FIG. 2 is a block diagram showing an example of a conventional optical waveguide circuit branching ratio measuring device. DESCRIPTION OF SYMBOLS 1... Incoherent light source, 2, 3.4... Lens, 5.6... Half mirror 7, 8... Optical fiber coupler, 9... Cylindrical electrostrictive vibrator, to, 11 ．． 12... Total reflection mirror l3... Total reflection mirror sweeping stage, 14... Photodetector, 15... Selection level meter, l6... Waveform monitor, l7... 2×2 boat and an optical coupling/branching circuit having two optical branching sections.

Claims (1)

[Scope of Claims] 1) In an optical waveguide circuit diagnostic method for measuring the branching ratio of an optical branching part of an optical waveguide circuit, an incoherent light is split into two by an optical fiber coupler type branching means, and one branched light is divided into two branches. The branched light is made incident on the input end of the optical waveguide circuit through one optical fiber optical path of the fiber coupler type branching means, and the other branched light is phase-modulated in the other optical fiber optical path of the optical fiber coupler type branching means to produce a reference light. The output light propagating through each propagation path of the optical waveguide circuit and emitted from the output end and the phase-modulated reference light are made to interfere with each other by an interferometer having a delay circuit, and the phase modulation frequency in the intensity of the interference light is determined. A method for diagnosing an optical waveguide circuit, comprising: measuring the intensity of a beat component of the signal; and determining a branching ratio of an optical branching section from the measured intensity ratio. 2) In an optical waveguide circuit diagnostic method for measuring the optical path length difference between optical paths between optical branch parts in an optical waveguide circuit, incoherent light is split into two by an optical fiber coupler type branching means, and one branched light is sent to the optical fiber. The branched light is made incident on the input end of the optical waveguide circuit through one optical fiber optical path of the coupler-type branching means, and the other branched light is phase-modulated in the other optical fiber optical path of the optical fiber coupler-type branching means to form a reference light. None, the output light propagating through each propagation path of the optical waveguide circuit and emitted from the output end and the phase-modulated reference light are made to interfere with each other by an interferometer having a delay circuit, and the phase modulation frequency in the interference light intensity is determined. A method for diagnosing an optical waveguide circuit, comprising: measuring the intensity of a beat component; and determining an optical path length difference between the optical paths from a difference in interference position. 3) In an optical waveguide circuit diagnostic device that measures the branching ratio of optical branching parts of an optical waveguide circuit and/or the optical path length difference between the optical branching parts, an incoherent light source and light emitted from the incoherent light source are guided into the optical waveguide. an optical fiber coupler type branching means for branching into a light incident on the circuit and a reference light; an optical fiber type phase modulation means coupled to the optical fiber coupler type branching means to impart phase modulation to the reference light; an optical fiber coupler type coupling means for coupling the output light from the wave circuit and the reference light phase-modulated by the phase modulation means; and causing the output light from the optical waveguide circuit and the phase-modulated reference light to interfere with each other. An optical waveguide circuit diagnostic apparatus comprising: an interferometer; and a signal extraction means for extracting a signal of a phase modulation frequency component of the phase modulation from an interference signal light obtained from the interferometer.