JP2746488B2 - Optical waveguide loss measurement method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to propagation loss per unit length of light propagating in an optical waveguide (guide loss), scattering due to imperfect structure, or change in the length direction of a waveguide structure. Non-destructive measurement of scattering etc. with high spatial resolution and high sensitivity (that is, very weak scattered light)
Alternatively, the present invention relates to a method for specifying a position of a structural imperfection or the like that causes scattered light.

[0002]

2. Description of the Related Art Methods for measuring the waveguide loss per unit length of a single mode optical waveguide are roughly classified into a destructive measuring method and a non-destructive measuring method. For the former destructive measurement method, generally, a method called a cut back method (Cut back method) is widely used. According to this method, when the length of the optical waveguide is L ₁ , the optical power P incident on the optical waveguide is
Taking the ratio of _i to the emitted optical power P _o , α ₁ = 10 · log ₁₀ (P _o / P _i ) [dB] (1) is determined as the insertion loss of the optical waveguide. Next, after shortening the optical waveguide a little and setting the length to L ₂ , similarly, α ₂ is obtained by taking the ratio of the incident light power and the outgoing light power. Then, the waveguide loss per unit length of the optical waveguide is, for example, when the unit of length is cm, α = (α ₁ −α ₂ ) / (L ₁ −L ₂ ) [dB / cm] ] (2) is required. Since the error increases when only two waveguide lengths are used, generally, the waveguide length is gradually shortened to three or more types, the waveguide length is plotted on the horizontal axis, the value is set as x, and the vertical axis is set on the vertical axis. Taking the insertion loss obtained by equation (1) and setting the value to y, a graph is obtained. If the measurement error of the insertion loss is very small, the measurement points are arranged in a straight line, and y = αx + C. 3) is expressed. Therefore, the slope α of the graph indicates the waveguide loss per unit length, and the intercept with the y-axis indicates the light coupling loss at the incident end. However, in general, a measurement error occurs when the insertion loss is calculated by Expression (1). It measures insertion loss at a certain waveguide length, and then
When the sample is taken out of the measurement system, the waveguide length is shortened, and the same measurement is repeated again, the condition at the incident end (position and angle of the incident beam) must be exactly the same as the previous measurement. This is because the coupling loss varies from measurement to measurement, resulting in an error. Therefore, if the measurement error of the insertion loss at each length cannot be made very small, the measurement points are not aligned, so a straight line corresponding to the equation (3) is obtained by the least square method. For more accurate measurement, if the measurement is performed a plurality of times at each of the waveguide lengths, it is considered that the insertion loss of the equation (1) measured under the condition with the best incident state is almost the optimal incident condition. Therefore, if the insertion loss is repeatedly measured at each waveguide length and the minimum value is graphed, it is possible to obtain a straight line substantially satisfying the expression (3). In any case, this measurement method requires considerable skill to accurately measure, a long time required for the measurement, and
Because of the destructive method, the sample to be measured is shattered after the measurement and cannot be used as a waveguide device.

On the other hand, nondestructive measurement methods include a prism coupler method and a television camera observation method, which have been used for a long time. In the former prism coupler method, light enters and exits the optical waveguide by two prisms pressed on the surface of the optical waveguide as shown in the schematic diagram of FIG. Is changed, and in each case, the ratio between the incident light and the outgoing light is obtained by Expression (1), and is plotted as a function of the prism interval, and the waveguide loss is obtained from the relationship of Expression (3). . Although this method is a non-destructive measurement method, the core surface of the optical waveguide must be exposed because light enters and exits the optical waveguide using a prism (that is, a cladding layer is provided above the core). Must be done). The latter method of observing a television camera is a method of observing, with a television camera, light that is scattered due to imperfect structure of an optical waveguide and leaks out. If the scattering occurs uniformly in the direction of the propagation axis of the optical waveguide, if the propagating light is gradually lost due to the loss due to the scattering, the light leaking to the outside is also gradually weakened in the direction of the propagation axis. Therefore, if it is observed on the screen of the television monitor, the waveguide loss can be measured according to the principle of equation (3). However, since the light receiving sensitivity of the TV camera is not so high, it is not very effective when the scattering is weak (that is, when the waveguide loss is small), and
Since the entire waveguide is observed at once with a television monitor, there is a problem that the spatial resolution is not so high.

In addition, a recently proposed non-destructive measurement method includes an incoherent OTDR (optical Ti
me Domain Reflectometry) method (IEEE / OSA J. Lightwave T).
technology, Vol. 9, No. 5, pp. 6
23-628 (May 1991)). In this method, as shown in a schematic diagram in FIG. 5, light from an incoherent light source (high-intensity light emitting diode) SLD is split into two by an optical fiber directional coupler DC, and one light is split into an optical waveguide S. Incident on Then, the light incident on the optical waveguide S is reflected little by little while propagating due to minute imperfections in the waveguide S, so that the light gradually returns from each point to the original optical fiber. On the other hand, the other light split from the optical fiber type directional coupler DC is converted into a parallel
Use to return to the original optical fiber. Then, the light returning to the optical fiber is combined with the light returning from the other waveguide S again by the directional coupler DC, and is emitted from an end face different from the light source SLD. At that time, the light returned from the mirror M and the light returned from the optical waveguide S are directional couplers D
The optical path length (the product of the refractive index and the actual distance) measured from C is the mirror M
And interferes only with light returning from a point in the waveguide S which is the same as the round trip to. This is because an incoherent light source having a coherence length of only about 10 μm to several tens of μm is intentionally used as the light source SLD. Therefore, light is continuously and gradually emitted from each point in the propagation axis direction of the optical waveguide S. It returns, but only the return light from a specific point can be extracted. In FIG. 5, in order to increase the measurement accuracy, one light is subjected to phase modulation by a modulator PM to heterodyne-detect an interference signal. In order to detect return light from another point in the waveguide S, the mirror M may be moved. Since the return light from a certain point in the waveguide S is proportional to the intensity of the propagating light at that point, if the return light intensity is graphed as a function of the position of the mirror M, a straight line having a gentle slope is obtained as shown in FIG. , The waveguide loss is determined from the slope of the straight line.

The feature of this method is that the waveguide loss can be measured nondestructively, and furthermore, even if a strong scattering point exists in the waveguide, the position can be measured with high spatial resolution. Moreover, since heterodyne detection is performed,
The ability to detect weak backscattered light (return light from the optical waveguide). However, since the light source is an incoherent light source, the intensity of light propagating in the waveguide is at most about several tens to 100 μW. Since the backscattered light is proportional to the intensity of the light propagating in the waveguide, a light detection method with higher sensitivity is required because the intensity of the light propagating in the waveguide is weak. Therefore, if heterodyne detection is performed using a coherent light source (laser) as the light source, the propagation light in the waveguide is strong,
In addition, since even weak light can be detected, incoherent O
Although the dynamic range can be larger than that of the TDR method, the incoherent OTDR method cannot use a coherent light source as a light source in principle.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and has as its object to reduce the dynamic range, which is a drawback of the incoherent OTDR method, by two digits using a completely different principle. It is an object of the present invention to provide a new and improved optical waveguide non-destructive measurement method for an optical waveguide.

[0007]

SUMMARY OF THE INVENTION An optical waveguide loss measuring method according to the present invention uses a coherent light source, divides light from the light source into two optical paths, and divides one of the light into an arbitrary light beam on the side of the optical waveguide to be measured. Irradiating the light to the position, the irradiating light is scattered due to the imperfect structure of the optical waveguide or the like, and is coupled to the waveguide region of the optical waveguide so as to be weakly propagated light; Are combined in or outside the optical waveguide, and the frequency of one of the two divided lights is shifted before being combined, so that the beat component of the combined light is Detecting the intensity of light coupled to the waveguide region by detecting the intensity of the light.

In this case, the multiplexing with the weak propagation light is
The other light is guided from the incident end of the optical waveguide, and the light is guided from the incident end of the optical waveguide, and the light is transmitted after the weakly propagated light is emitted from the optical waveguide. There is.

In addition, when the one light is irradiated to the side surface of the optical waveguide to be measured through an optical fiber, and a light collecting means is provided at an emission end of the optical fiber, the spatial resolution of the measurement can be improved. Is improved. Further, the light from the light source is passed through an optical fiber, and the optical path is divided into two by an optical fiber type branch circuit, so that light emitted from one of the branched optical fibers is irradiated to the side surface of the optical waveguide to be measured, As the optical fiber, one provided with a condensing means at the output end thereof is used, and the output light from the other branch optical fiber is made to enter from the input end of the optical waveguide, and the weak propagation light is transmitted through the optical waveguide. If the optical path is multiplexed, the entire optical path can be made into an optical fiber, and the trouble of adjusting the optical axis of the optical system can be saved.

Further, the irradiation position on the side surface of the optical waveguide to be measured is traced along the waveguide pattern of the optical waveguide, and the intensity of light coupled to the waveguide region is measured as a function of the position. It is possible to measure propagation loss, incomplete structure position, change in the length direction of the waveguide structure, and the like.

In addition, for the optical waveguide to be measured capable of guiding at least two orthogonal polarization modes, both of the two orthogonal polarization modes are excited by the one light, and after the two light beams exit from the optical waveguide, the two are excited. One of the two orthogonal polarization modes is subjected to polarization plane conversion and then interferes with the two orthogonal polarization modes, and
The irradiation position on the side surface of the optical waveguide to be measured is traced along the waveguide pattern of the optical waveguide, and the phase difference is measured using the interference intensity of the two orthogonal polarization modes coupled to the waveguide region as a function of the position. By doing so, by measuring the propagation constant difference between the two orthogonal polarization modes, it is possible to measure the propagation constant difference between the two orthogonal polarization modes.

Another method for measuring the loss of an optical waveguide according to the present invention uses a coherent light source, divides light from the light source into two optical paths, and guides one of the light from the incident end of the optical waveguide to be measured. The guided light is scattered due to imperfections in the structure of the optical waveguide, the scattered light scattered to the outside is extracted from an arbitrary position on the side surface of the optical waveguide, and the other light and the scattered light are combined, and By shifting the frequency of any one of the two divided lights before combining them, and detecting the intensity of the beat component of the combined light, the light is scattered in the waveguide region. This is a method characterized by measuring the intensity of light.

[0013] Also in this case, when the scattered light is taken out by using an optical fiber provided with a condensing means at an incident end as means for taking out the scattered light from the optical waveguide,
The spatial resolution of the measurement is improved. Further, the light from the light source passes through an optical fiber, and the optical path is divided into two by an optical fiber type branch circuit, and the light emitted from one of the branched optical fibers is made incident on the incident end of the optical waveguide to be measured. When the light emitted from the branch optical fiber and the scattered light from the optical waveguide are combined, the entire optical path can be formed into an optical fiber.

Further, a position at which the scattered light from the measured optical waveguide is extracted is traced along the waveguide pattern of the optical waveguide, and the intensity of the scattered light from the waveguide region is measured as a function of the position. This makes it possible to measure the propagation loss, the incomplete structure position, the change in the length direction of the waveguide structure, and the like.

[0015]

According to the present invention, since the coherent light source is used, it is possible to irradiate the measured optical waveguide with strong light,
In addition, since weak light can be detected for heterodyne detection, the dynamic range can be increased. As a result, even when the structural imperfection of the optical waveguide is very small (that is, when the scattering is very weak), the scattering can be detected. In addition, since the irradiation light from the side is collected, the spatial resolution is high and non-destructive measurement is possible.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical waveguide loss measuring method according to the present invention is based on a scattered light heterodyne detection method (heterodyne scatter).
erring Detection method. (HSD method for short), using a coherent laser as a light source, splitting the light from the light source into two optical paths,
One is irradiated from the side of the optical waveguide to be measured, and the irradiated light is scattered due to the imperfect structure of the waveguide and is coupled to the waveguide region (core) of the waveguide to become weakly propagated light. Is guided from the waveguide entrance end, and this light and the above-mentioned weakly propagated light are multiplexed to detect heterodyne. In order to perform heterodyne detection, light in one optical path is modulated and frequency-shifted. Further, in order to enhance the spatial resolution, the light beam irradiated on the side surface of the waveguide is focused to several μm.

According to this configuration, a strong light can be applied to the waveguide because a coherent light source is used, and even a weak light can be detected for heterodyne detection, so that a large dynamic range can be obtained. as a result,
Even when the structural imperfection of the waveguide is very small (that is, when the scattering is very weak), the scattering can be detected. In addition, since the irradiation light from the side surface is condensed, there is a feature that the spatial resolution is high and the measurement can be performed nondestructively. These characteristics are shown in the following table in comparison with the conventional measurement method.

[0018]

From the above table, it can be seen that only the HSD method of the present invention satisfies all the required items. Further, although not shown in this table, the method traces the irradiation beam on the pattern of the optical waveguide (that is, from the side of the waveguide), so that even when the waveguide pattern includes branching or merging, Each optical path can be measured individually. However,
Incoherent OTDR method and OCDR (Optica
l Coherence Domain Reflect
In the tmetry) method, in order to detect backscattered light,
It cannot be determined from which optical path the returned light returns from.

It should be noted that the method of the present invention can be applied to a single-mode optical waveguide and a waveguide-type optical element that have structural imperfections such as a waveguide loss (loss per unit length), a connection point, and a scattering point. Where there are imperfections that cause light scattering), and
The scattering intensity due to its structural imperfections, TE mode and T
The present invention can be applied to a device for non-destructively and highly accurately measuring a difference in propagation constant of the M mode.

Hereinafter, an embodiment of a method for measuring a loss in an optical waveguide according to the present invention will be described with reference to the drawings. FIG. 1 shows an embodiment of a configuration of a measurement system for performing a scattered light heterodyne detection method (HSD method) according to the present invention. Using the coherent laser 1 as a light source, the light from the light source 1 is split into two optical paths by a half mirror 2, one of the laser beams is made incident on an incident end of a polarization-maintaining optical fiber 4 by a lens 3, and the light emitted from the emission end Irradiates the side surface (actually, the upper surface of the substrate) of the optical waveguide S to be measured. Then, most of the optical waveguides have some structure imperfections (when the boundary between the core and the clad of the waveguide is not a perfectly flat surface but has irregularities, or the refractive index is not uniform in the core or the clad and the microscopic When there is a scatterer, etc.), the light irradiated from the side is also scattered in various directions due to its structural imperfection. The light scattered in the direction equal to the propagation angle of the light propagating through the waveguide core (the angle measured from the interface between the core and the clad when the guided light propagates through the core) in the scattered light is incident on the waveguide. The light propagates through the waveguide core as propagating light. This is called coupling of the scattered light to the waveguide core. The light coupled to the waveguide core is very weak, and there is a limit to detection with a normal photodetector. Therefore, in order to detect this weak light with high sensitivity, the other laser light branched by the half mirror 2 is transmitted to the waveguide S by the lens 5.
The light is condensed at the incident end of the core and guided in the waveguide S, and the guided light and the light coupled to the waveguide core are multiplexed and detected in a heterodyne manner.

To perform the heterodyne detection, the optical waveguide S
It is necessary to match the polarization direction of the light when the light beam irradiated to the side surface is coupled to the optical waveguide S with the polarization direction of the light incident on the waveguide S entrance end. Normally,
Adjust to either TE mode or TM mode. Also,
It is necessary to shift the frequency by applying phase modulation to one of the two optical paths branched from the light source 1. In the case of FIG. 1, a polarization-maintaining optical fiber 4 is used in the optical path for irradiating the side surface of the waveguide to apply phase modulation, and an electrostrictive element (ie, a piezo element) is bonded in the optical fiber 4. To form a phase modulator 8 that changes the optical path length by a voltage,
The modulation signal from the oscillator 9 is applied to the phase modulator 8 to perform phase modulation. The modulation voltage waveform used here is a sawtooth wave as shown. By setting the extension of the optical path length in the optical fiber 4 corresponding to the maximum value (amplitude) of the sawtooth wave voltage to be just an integral multiple of the wavelength (that is, the phase change is an integral multiple of 2π), A frequency shift is applied to the light propagating in the fiber 4. However, the method of adding the frequency shift is not limited to this method, and various other methods are available. Now, the light that has undergone the frequency shift and has been coupled to the waveguide core and the light that has not undergone the frequency shift that has been incident from the input end of the waveguide S are multiplexed in the waveguide S, and a DC component has been output from the output end. The light is emitted as a beat component. Since this beat component is proportional to the amplitude of the light coupled to the waveguide core, the outgoing light is photoelectrically converted by, for example, a PIN photodiode 10 and the detection signal is added to a lock-in amplifier 11. By taking the product with the reference signal having the same frequency, the DC component of the output signal is removed, and the intensity of the beat component is obtained as the output signal. To remove the DC component of the output signal,
Instead of the lock-in amplifier, a band-pass filter that passes only the beat component may be used.

Incidentally, in order to enhance the spatial resolution of the measurement, the light beam irradiated on the side surface of the waveguide S is focused to several μm. In the case of FIG. 1, the tip 1 of the polarization-maintaining optical fiber 4
2 is spherically processed and used as a lens.

FIG. 2 shows an example of the result of measurement using the measurement system having the above-described configuration. The sample to be measured in the case of FIG. 2 is a stripe horizontal confinement type ARROW-B (the stripe horizontal confinement structure is described in Japanese Patent Application No. 63-531.
No. 13 for ARROW-B and Japanese Patent Application No. 63-5
3114), core thickness 4 μm, stripe width 5 μm
m. The distribution of the scattering centers of this waveguide is not uniform, but fluctuates somewhat non-uniformly. The waveguide loss per unit length of this waveguide is fitted to a straight line by the least square method using the measurement points in FIG. Then, it is estimated to be 3.7 dB / cm.

The measurement system shown in FIG. 1 is an example, and the principle is the same, but some modifications are conceivable. For example, FIG.
The optical system up to the optical waveguide S can be configured entirely using spatial beam light (that is, using a lens, a modulator for spatial beam light, a half mirror, or the like), or can be configured entirely using an optical fiber (optical fiber type branch). Circuit, an optical fiber type directional coupler or an optical fiber type phase modulator). Also, the optical path to which the frequency shift is applied may be an optical path that enters from the incident end of the waveguide.

In the above, the light from the light source 1 is branched as the other light for heterodyne detection with the weak light coupled to the waveguide core by irradiating from the side surface of the optical waveguide S to be measured. In this case, the light incident from the input end of the waveguide S and guided was used. Instead, the light from the laser 1 was branched from the waveguide side irradiation light by, for example, an optical fiber type branch circuit. Heterodyne detection can also be performed by combining light with the waveguide core-coupled weak light extracted from the emission end of the waveguide S using a light, for example, in an optical fiber type combining circuit, and performing photoelectric conversion.

In the arrangement shown in FIG. 1, when one light from the light source 1 is made incident on the incident end of the waveguide S, contrary to the above case, the light is guided in the waveguide S and the structure becomes inconsistent. Since part of the light is scattered to the outside from the side due to completeness or the like, the scattered light is picked up by the tip 12 of the optical fiber 4,
By detecting the weak light and the other laser light branched by the half mirror 2 in a heterodyne manner,
The loss measurement of the optical waveguide may be performed.

Further, by developing the method of the present invention, the polarization direction of the light beam irradiated from the side surface is inclined with respect to the axial direction, and the TE mode (or also referred to as TE polarization) and T.
Both the M-modes are excited, and the phase difference between the TE-polarized light and the TM-polarized light is detected at the output end of the optical waveguide S by some detection method. When the position of the irradiation beam from the side is traced along the waveguide pattern, the phase difference changes depending on the propagation distance from the time when the light beam irradiated from the side is coupled to the waveguide core to reach the emission end. I understand. Since this change periodically changes depending on the propagation distance, if the period L is obtained, the difference Δβ in the propagation constant between the TE mode and the TM mode can be obtained by Δβ = 2π / L (4). There are various methods for obtaining the phase difference between two polarized lights at the emission end of the optical waveguide. For example, the phase difference itself cannot be measured by a simple device as shown in FIG. That is,
The period L) can be obtained. That is, the light emitted from the exit end of the optical waveguide S is made incident on the polarization-maintaining optical fiber 13, and the TE mode and the TM mode propagating therein are separated by the fiber-type polarization splitter 14. After conversion into the TE mode by the conversion unit 15, the signal is multiplexed with the original TE mode in the merging circuit 16,
The multiplexed light is photoelectrically converted by a photodetector 18 and passed through a filter 19 that allows a beat component to pass therethrough, so that a signal that changes depending on the distance z from the incident end of the optical waveguide S to the side surface irradiation position is obtained. The period L can be obtained. The mode conversion unit 15 may be configured, for example, by cutting a polarization-maintaining optical fiber in the middle and rotating and splicing the intrinsic polarization axes at both ends by 90 ° with respect to each other as shown in the figure. Can be.

[0029]

As described above, according to the optical waveguide loss measuring method of the present invention, the following advantages can be obtained.

Since a laser which is a coherent light source is used as a light source, high-output light can be used as probe light. Therefore, if a photodetector having the same light-receiving sensitivity is used, a smaller scatterer (having a smaller scattering coefficient) can be detected as compared with the interferometric OTDR method that can use only incoherent light with a small output. .

Since heterodyne detection is performed, highly sensitive light detection is possible.

Since the light beam irradiated on the side surface of the waveguide is focused, a high spatial resolution of several μm can be realized. This is from 10 μm to several 1 of the interference type OTDR method.
It is slightly better than 0 μm and two or more digits better than several mm in the OCDR method. It is also much better than the TV camera observation method.

When the light from the light source is divided into two and the other light is made incident on the incident end of the optical waveguide, the two lights are multiplexed using the scattering in the optical waveguide, so that a multiplexer is not required. . Usually, in heterodyne detection, a multiplexer is required to combine two beams, and in particular, multiplexing of spatial beams requires high-precision optical axis adjustment. Also, the multiplexer does not need to adjust the optical axis for multiplexing.

Since the side irradiation beam traces on the pattern of the optical waveguide, each optical path of a complicated optical circuit can be measured independently. This is based on the interference type OTDR method and OCD
It is impossible in principle with a method of detecting reflected return light such as the R method, or it is possible with the method of the present invention.

Measurement can be made nondestructively.

Measurement can be performed even when an upper clad is provided on the upper surface of the optical waveguide. This is not possible with the prism coupler method since the core must be exposed, but it is possible with the interference type OTDR method or the like.

These are summarized in the above table.

[Brief description of the drawings]

FIG. 1 is a diagram showing one embodiment of a configuration of a measuring system for implementing a method for measuring a loss of an optical waveguide according to the present invention.

FIG. 2 shows a result 1 measured using the measurement system having the configuration of FIG.
It is a figure showing an example.

FIG. 3 is a diagram for explaining the configuration and operation of a device for determining the propagation distance dependence of the phase difference between two modes based on the present invention.

FIG. 4 is a schematic diagram for explaining a conventional prism coupler method.

FIG. 5 is a schematic diagram for explaining a conventional incoherent OTDR method.

FIG. 6 is a diagram illustrating an example of a measurement result obtained by the method of FIG. 5;

[Explanation of symbols]

 S: Optical waveguide to be measured 1: Laser 2: Half mirror 3, 5, 7, Lens 4: Polarization-maintaining optical fiber 8: Phase modulator 9: Oscillator 10: PIN photodiode 11: Lock-in amplifier 12: Polarization-maintaining Optical fiber tip 13 ... Polarization-maintaining optical fiber 14 ... Fiber-type polarization separator 15 ... Mode converter 16 ... Merging circuit 18 ... Photodetector 19 ... Filter

Claims (11)

(57) [Claims] 1. A light source for a coherent light source, the light from the light source is divided into two light paths, and one light is irradiated to an arbitrary position on a side surface of the optical waveguide to be measured. Scattered by perfect or the like and coupled to the waveguide region of the optical waveguide to become weakly propagated light, the other light and the weakly propagated light are multiplexed inside or outside the optical waveguide ,
In addition, the frequency of one of the two divided lights is shifted before being combined, and the intensity of the beat component of the combined light is detected, whereby the light is coupled to the waveguide region. A method for measuring the loss of an optical waveguide, comprising measuring the intensity of light. 2. The method according to claim 1, wherein the other light is guided from an incident end of the optical waveguide, and the light guided from the incident end of the optical waveguide is combined with the weakly propagated light. The method for measuring a loss of an optical waveguide according to claim 1. 3. The optical waveguide loss measuring method according to claim 1, wherein the other light and the weakly propagated light are multiplexed after the weakly propagated light exits from the optical waveguide. . 4. The optical fiber according to claim 1, wherein said one light is irradiated to a side surface of an optical waveguide to be measured via an optical fiber, and said optical fiber is provided with a condensing means at an emission end thereof. Item 4. The optical waveguide loss measuring method according to any one of Items 1 to 3. 5. The light from the light source through an optical fiber,
Further, the optical path is divided into two by an optical fiber type branch circuit, and the light emitted from one of the branched optical fibers is irradiated on the side surface of the optical waveguide to be measured, and a light collecting means is provided at the emission end as the optical fiber. The method for measuring a loss of an optical waveguide according to any one of claims 1 to 3, wherein the optical waveguide is used. 6. A method of tracing an irradiation position on a side surface of an optical waveguide to be measured along a waveguide pattern of the optical waveguide, and measuring an intensity of light coupled to the waveguide region as a function of the position. The method for measuring a loss of an optical waveguide according to any one of claims 1 to 3, wherein: 7. An optical waveguide to be measured capable of guiding at least two orthogonal polarization modes, both of the two orthogonal polarization modes are excited by the one light, and after being emitted from the optical waveguide, the two are excited. One of the two orthogonal polarization modes is subjected to polarization plane conversion and then interferes with the two orthogonal polarization modes, and the irradiation position on the side surface of the measured optical waveguide is traced along the waveguide pattern of the optical waveguide. Measuring the difference in propagation constant between the two orthogonal polarization modes by measuring the phase difference using the interference intensity of the two orthogonal polarization modes coupled to the waveguide region as a function of location. 4. The method for measuring a loss of an optical waveguide according to any one of 1 to 3. 8. Using a coherent light source, splitting light from the light source into two optical paths, guiding one light from the incident end of the optical waveguide to be measured, and the guided light is transmitted due to imperfect structure of the optical waveguide. The scattered light scattered and scattered outside is taken out from an arbitrary position on the side surface of the optical waveguide, the other light and the scattered light are combined, and any one of the two divided lights is used. By shifting one of the frequencies before multiplexing, and detecting the intensity of the beat component of the multiplexed light, the intensity of light scattered in the waveguide region is measured. Optical waveguide loss measurement method. 9. The scattered light is extracted by using an optical fiber provided with a condensing means at an incident end as means for extracting the scattered light from the optical waveguide.
A method for measuring a loss of an optical waveguide as described in the above. 10. The optical path of the light from the light source is divided into two paths via an optical fiber and an optical fiber type branch circuit.
The light emitted from one branch optical fiber is made incident on the incident end of the optical waveguide to be measured, and the light emitted from the other branch optical fiber and the scattered light from the optical waveguide are multiplexed. 10. The method for measuring a loss of an optical waveguide according to 8 or 9. 11. A position where the scattered light from the measured optical waveguide is extracted is traced along a waveguide pattern of the optical waveguide, and the intensity of the scattered light from the waveguide region is measured as a function of the position. 11. The method according to claim 8, wherein:
The method for measuring a loss of an optical waveguide according to any one of claims 1 to 7.