JPH0915091A - Reflection point measuring apparatus - Google Patents

Abstract

PURPOSE: To obtain an apparatus for measuring the position of a reflection point occurring in an optical element with a high resolution. CONSTITUTION: An optical probe pulse P1 generated from a short pulse light generating means 10 is condensed through a condenser lens 14 and transmitted on an optical transmission path 15. A condenser lens 17A condenses the light from the optical transmission path 15 and directs the light toward a first optoelectric conversion means D1. The optical probe pulse P1 picked up at the outgoing end C of an optical fiber coupler constituting a reflected light acquiring means 16 is made incident on an variable delay means 20 through the optical transmission path 15. An delayed optical probe pulse P2 is projected to a second optoelectric conversion means D2. On the other hand, a sample voltage signal is detected by a detector 31 and converted through an AD converter 32 into a digital signal and then subjected to deconvolution processing by an arithmetic unit 33 before being presented on a display 34 thus measuring a reflection point occurring in an optical element.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflection point measuring device used for specifying a reflection point of a reflected wave generated in an optical element.

[0002]

2. Description of the Related Art Conventional OTDR (Optical Time Domain)
The Refrectometer made an optical pulse generated by a laser diode (LD) incident on the DUT, detected reflected light by the photodiode, and measured the reflection point from the time waveform. In this method, due to the large pulse width of the light pulse and the band of the light receiving system, the resolution of the reflection point was at most about several tens of centimeters. Further, the resolution of an interference type OTDR using an incoherent light source is only a few millimeters.

[0003]

In an optical component such as a laser diode module, reflection of light in an optical circuit leads to deterioration of the characteristics of the module. In order to improve the characteristics of the module, it is necessary to reduce reflection,
In the conventional OTDR, the resolution is low and it has been impossible to identify the reflection point. In the module, optical parts such as lenses, fibers, and semiconductor elements are arranged at intervals of several millimeters, and sub-millimeter resolution OTDR is required to identify the reflection point.

An object of the present invention is to provide a high resolution OTDR.

[0005]

According to the invention of claim 1 of this application, a short pulse light generator for generating an optical pulse having an extremely narrow pulse width is used as a light source. A narrow optical probe pulse is generated, and this optical probe pulse is made incident on the object to be measured through the optical transmission line. Provided is a reflected light acquisition unit that separates and acquires reflected light returned from the object to be measured from the optical transmission path, and the reflected light acquired by this reflected light acquisition unit is incident on the optical-electrical conversion unit, and this optical-electrical conversion is performed. By means, short electrical pulses with a narrow pulse width are obtained on the signal conductor.

At the same time, a part of the optical probe pulse is applied to the variable delay means, and the optical probe pulse delayed by the variable delay means is formed between the signal conductor and the signal extraction electrode provided in the vicinity of the signal conductor. The second optical-electrical converting means is irradiated and the short electrical pulse generated on the signal conductor is sampled and taken out. This claim 1
According to the invention, since the pulse width of the light pulse generated by the light source is extremely narrow and the pulse width of the electric pulse converted by the first optical-electrical converting means is narrow, the distance measuring performance with high resolution can be obtained. You can

The reflection point measuring device proposed in claim 2 of this application is provided with a pair of short pulse light generating means for generating optical probe pulses having slightly different frequencies, and is emitted from one of the short pulse light generating means. Short pulsed light is applied to the object to be measured, and the reflected light is acquired by the reflected light acquisition means, and first
An electric short pulse having a narrow pulse width is generated on the signal conductor by applying it to the opto-electric conversion means.

At the same time, the short pulse light emitted from the other short pulse light generating means is applied to the second photoelectric conversion means formed between the signal conductor and the signal extraction electrode provided in the vicinity of the signal conductor. Then, the short electrical pulse generated on the signal conductor is sampled. In this sampling, the frequency of the optical probe pulse generated by the pair of short pulse light generating means is slightly different, so that the sampling position is slightly shifted.

As a result, according to the invention of claim 2,
The electric pulse generated on the signal conductor can be sequentially sampled in the time axis direction without using the variable delay means. The reflection point measuring apparatus proposed in claim 3 of the present application constitutes a reflection point measuring apparatus for measuring an electrically operating circuit element by utilizing the structure of the reflection point measuring apparatus proposed in claim 2. Is.

Therefore, according to the reflection point measuring apparatus proposed in the third aspect, the reflection point measuring apparatus in which the electrically operating circuit element is in measurement symmetry can be configured without using the variable delay means. As a result, it is possible to provide a reflection point measuring device having a simple structure. In the reflection point measuring apparatus proposed in claim 4, an electro-optical element having a reflection surface is joined on a signal conductor as sampling means, and the optical probe pulse delayed by the variable delay means or the frequency is slightly different from this electro-optical element. Irradiate an optical probe pulse. The electro-optical element gives a polarization rotation amount to the reflected light of the optical probe pulse according to the electric potential of the electric pulse generated in the signal conductor. This is a proposal of a reflection point measuring device that detects the polarization rotation amount and samples the electric pulse generated in the signal conductor.

[0011]

FIG. 1 shows an embodiment of a reflection point measuring device proposed in claim 1 of this application. In the figure, 10 indicates a short pulse light generating means. As the short pulse light generating means 10, for example, a semiconductor laser generator or another laser generator can be used. In this example, a mode-locked laser oscillator including a main laser oscillator 11, an excitation laser oscillator 12, and a synchronization circuit 13 is used. Main laser oscillator 11
A titanium sapphire laser oscillator can be used as the laser oscillator, and an argon laser oscillator can be used as the excitation laser oscillator 12. As the mode-locked laser oscillator having such a structure, for example, a mode-locked titanium sapphire laser oscillator manufactured by Spectra Physics, Inc. in the United States can be used. This mode-locked titanium sapphire laser oscillator has a laser pulse repetition frequency of 80 MHz,
Optical probe pulse P with a pulse width of 80 fs (10 ^-15 seconds)
1 can be obtained.

The optical probe pulse P1 generated by the short pulse light generating means 10 is condensed by the condenser lens 14 and is incident on the optical transmission line 15. The optical transmission line 15 can use an optical fiber. The DUT to be measured is coupled to the tip of the optical transmission line 15. The reflected light acquisition means 16 is provided at an intermediate portion of the optical transmission line 15. The reflected light acquisition means 16 can use an optical coupler generally called an optical fiber coupler. The optical coupler passes the optical probe pulse P1 incident from the incident end A to the emission ends B and C, and the reflected light P _DUT (FIG. 3B) reflected by the DUT to be measured is extracted to the emission end D.

The reflected light P _DUT taken out at the output end D is passed through the optical transmission line 15 made of an optical fiber to a condenser lens 17
A. The condenser lens 17A converges the light emitted from the optical transmission path 15 and irradiates the first photoelectric conversion unit D1. The first photoelectric conversion means D1 is, for example, a conductive pattern J1 shown enlarged in FIG. 2 on the surface of the semi-insulating substrate 19 in which a trace amount of iron (Fe) is doped on a substrate formed of indium phosphorus (InP) or the like. And J2 can be formed. The facing portions of the conductive patterns J1 and J2 have a comb-teeth shape, and the comb-teeth are intricately arranged so that a large light irradiation area can be obtained. Here, the conductive pattern J1
Will be referred to as a signal conductor, and the first photoelectric conversion means D1 constituted by the signal conductor J1 and the conductive pattern J2 will be referred to as a first photoelectric conversion means.

The area between the signal conductor J1 and the conductive pattern J2 becomes conductive when irradiated with light. Therefore, the direct current voltage V is applied to the conductive pattern J2 from the direct current power source 18, and the reflected light P _DUT is applied to the portions facing each other in a comb shape, whereby the intensity of the direct current voltage V and the reflected light P _DUT is applied to the signal conductor J1. Electrical pulse signals W ₁ , W ₂ , W having peak values corresponding to
₃ ... (Fig. 3G) occurs. The pulse width of the electric pulse signals W ₁ , W ₂ , W ₃ , ... Is made extremely narrow due to the extremely narrow pulse width of the optical probe pulse P1 and the structure of the optical-electrical converting means D1. be able to. That is, it is possible to obtain an electric pulse signal having an extremely short pulse width with a half width of about 0.1 to 1 ps. Note that FIG.
Reference symbol JE indicates a ground conductor. By arranging the ground conductor JE, the signal conductor J1 and the conductor pattern J2 are arranged.
J3 has a coplanar line structure and is configured so that its characteristic impedance has a predetermined characteristic impedance.

On the other hand, the optical probe pulse P1 extracted at the emission end C of the optical fiber coupler which constitutes the reflected light acquisition means 16 is incident on the variable delay means 20 through the optical transmission line 15. The variable delay means 20 is a moving mirror 21 in this example.
And a stage driver 2 for driving this moving mirror 21
2 shows the case of being constituted by 2 and. Stage driver 2
2 moves the moving mirror 21 stepwise or continuously in the front-back direction with respect to the traveling direction of the optical probe pulse P1 according to a timing signal given from the controller 30,
The optical probe pulse P1 is provided with a delay time τ stepwise or continuously. In addition, here, in order to facilitate understanding of the description, a case where the moving mirror 21 is moved stepwise will be described.

The optical probe pulse P2 delayed by the variable delay means 20 is applied to the second photoelectric conversion means D2.
As shown in FIG. 2, the second optical-electrical converting means D2 is connected to the comb teeth, the comb teeth formed by branching from the signal conductor J1, the comb teeth formed intricately with the comb teeth, and the comb teeth. It can be constituted by the signal extraction electrode J3. By irradiating the second optical-electrical converting means D2 with the optical probe pulse P2 delayed by the variable delay means 20, the potential on the signal conductor J1 at the time of the irradiation (delay timing) is taken out to the signal taking-out electrode J3. You can That is,
Can be sampled.

The voltage signal sampled by the signal extraction electrode J3 is extracted by the detector 31 which is composed of, for example, a lock-in amplifier. The digital signal is converted by the AD converter 32, deconvoluted by the arithmetic unit 33, restored to the original waveform data on the time axis, and displayed by the display unit 34.
Will be displayed. The state of sampling is shown in FIGS. FIG. 3C shows a state in which the movable mirror 21 is moved one step from the initial position and the optical probe pulse P2 is delayed by Δτ. The optical probe pulse to which the delay time Δτ has been given is shown with reference numeral P2 ₁ . Optical probe pulse P2 ₁ Light - continues to be irradiated to electrical conversion means D2, continues to sample the potential on the signal conductor J1 at the position of the delay time .DELTA..tau, continue to enter the potential detector 31. For example, a lock-in amplifier or the like is used as the detector 31, and the AD converter 32 is caused to perform an AD conversion operation at the time when a response time (for example, about several ms) has elapsed, and the value of the waveform data at the delay time Δτ is determined. To do.

The AD converter 32 ends the AD conversion operation.
Then, the controller 30 instructs the variable delay means 20 to change the delay time.
Output In response to this instruction, the variable delay means 20 moves.
The moving mirror 21 is moved to the next step. Shown in FIG. 3D
You P2_TwoIs given by the delay time 2Δτ at the next stop position
3 shows an optical probe pulse generated. This optical probe pulse
P2_TwoIs given to the second photoelectric conversion means D2?
The time until the output of the detector 31 stabilizes
And AD converter 32 are the waveform data at delay time 2Δτ
The value of is AD-converted and taken into the computing unit 33. This behavior
The moving mirror 21 repeatedly moves to the maximum moving position,
The maximum delay time τ for the optical probe pulse P2 _maxGive this
Maximum delay time τ_maxBut with AD converter 32, the waveform data
Take in.

The arithmetic unit 33 connects the waveform data at each delay timing AD-converted by the AD converter 32, performs deconvolution processing, restores the original waveform data on the time axis, and displays it on the display unit 34 on the time axis. Display as a waveform. FIG. 3G shows the electric pulse waveform of the reflected light P _DUT restored to the original waveform data on the time axis. The example in the figure shows a state in which reflected waves W ₁ , W ₂ , W ₃ and W ₄ are generated. The _first reflected wave W ₁ can be regarded as a reflected wave generated at the coupling portion between the optical transmission line 15 and the DUT to be measured. The reflected waves W ₂ , W ₃ , and W ₄ generated following this reflected wave W ₁ can be regarded as the reflected waves generated inside the DUT to be measured. Therefore, based on the peak point position of the reflected wave W ₁ , W ₁ ~
From the time τ _X1 during W ₂ , the distance from the entrance portion of the DUT to be measured to the first reflection point can be known. Similarly, the time τ _X2 between W _{1 and} W ₃ and W _{1 to} W ₄
It is possible to know the distances to the second reflection point and the third reflection point from the time τ _X3 between.

The maximum value of the delay time τ is given by the maximum value of the moving amount of the moving mirror 21. The maximum amount of movement is 5
When the delay time is 0 mm, the maximum delay time τ _max is τ _max = 2 × 50 × 10 ⁻³ / 3 × 10 ⁸ = 3.333 × 10 ¹⁰ (sec) = 333.3 (psec).

Reading resolution (1 step Δ of delay time
τ) is determined by the moving step interval of the moving mirror 21. For example, if one step is 0.5 μm, one step of delay time Δτ is Δτ = 2 × 0.5 × 10 ⁻⁶ / 3 × 10 ⁸ = 3.333 × 10 ⁻¹⁵ (sec) = 333.3 (fsec ).

That is, the waveform generated at the time of 333.3 (psec) can be sampled with the resolution of 3.333 (fsec) = 3.333 × 10 ⁻¹⁵ sec and the waveform data can be fetched. FIG. 4 shows an embodiment of the reflection point measuring device proposed in claim 2 of this application. This embodiment proposes a method of gradually shifting the sampling timing in the time axis direction without using the variable delay means 20.

That is, in this embodiment, two short pulse light generating means 10A and 10B are prepared. The short pulse light generating means 10A and 10B emit the optical probe pulse P1.
And P1 'are set to slightly different frequencies. For example, when the frequency of the optical probe pulse P1 emitted by the short pulse light generation means 10A is 80 MHz, the optical probe pulse P1 'emitted by the short pulse light generation means 10B.
The frequency of 80 MHz-10 Hz to 80 MHz-100 Hz is selected. Along with this, the short pulse light generating means 1
A synchronizing circuit 35 is connected between 0A and 10B to synchronize the oscillations of the short pulse light generating means 10A and 10B. That is, the optical probe pulses P1 and P1 ′ emitted from both sides are provided for each period of the frequency generated at the difference frequency by providing the oscillation frequencies with a difference and synchronizing the oscillation states.
Are synchronized (phases match).

The reflected light obtained by the reflected light obtaining means 16 in which the optical probe pulse P1 emitted from the short pulse light generating means 10A is incident on the DUT to be measured through the optical transmission line 15 is transmitted to the first optical-electrical converting means D1. Irradiate. With this,
The optical probe pulse P1 'emitted from the short pulse light generation means 10B is applied to the second photoelectric conversion means D2 for sampling through the optical transmission line 15. A non-reflecting means 36 is attached to the emitting end D to absorb the optical probe pulse taken out to the emitting end C.

With this configuration, the optical probe pulse P1 'with which the optical-electrical converting means D2 is irradiated has a slightly different frequency from the other optical probe pulse P1. T ₀ (see FIG. 5)
Therefore, the phases of P1 and P1 'are shifted by ΔT for a slight time. In the example of FIG. 5, the optical probe pulse P
The case where the frequency of 1'is made slightly lower than the frequency of the optical probe pulse P1 is shown. Therefore, due to the frequency difference, the phase of the optical probe pulse P1 'shifts in the direction in which the phase of the optical probe pulse P1 is sequentially delayed. When the frequency of the optical probe pulse P1 is 80 MHz and the frequency of the optical probe pulse P1 'is 80 MHz-10 Hz, the phase shift amount ΔT is ΔT = λ ₁ −λ ₂ = 1 / (80 MHz-10 Hz) -1/80 MHz = 0 It becomes 0.1 μs. In other words, it is possible to sample with a resolution of 0.1 μs.

According to this embodiment, there is an advantage that the movable variable delay means 20 need not be used. The signal sampled by the detector 31 has a frequency of the optical probe pulse P1 of 80 MHz and a frequency of the optical probe pulse P1 'of 80 M
Assuming that the frequency is Hz-10 Hz, a result obtained by sampling the time of 1/80 MHz with a resolution of 1 / (80 MHz-10 Hz) can be obtained at a cycle of 10 times per second. By connecting an oscillograph to the detection output of the detector 31, the waveform of the reflected wave can be observed. FIG.
In the embodiment, the output of the detector 31 is AD-converted by the AD converter 32.
Conversion, and the AD conversion output is arithmetically processed by the arithmetic unit 33,
A reflected wave generated at the entrance of the DUT to be measured, for example, the distance is calculated from the delay time τ _X1 from the peak point of W1 to the next reflected wave W2 shown in FIG. 3, or the intensity of the peak point of the reflected wave, Calculate the peak intensity ratio of the reflected waves,
A waveform signal is output to the display 34 through the controller 37 to display the reflected waveform. In addition to this waveform display, the distance data calculated by the calculator 33 is displayed. Although the optical probe pulse P1 'is selected to have a frequency slightly lower than P1 in the above description, either P1 or P1' may be high or low.

FIG. 6 shows a case where the DUT to be measured is an electric circuit in the embodiment shown in FIG. In this case, the optical probe pulse P1 is applied to the first optical-electrical converting means D1, and the short electric pulse signal generated at the time of the irradiation is input to the electrical input terminal of the DUT under measurement through the signal conductor J1. The optical probe pulse P1 'is applied to the second photoelectric conversion means D2 which constitutes the sampling means. By providing the optical probe pulses P1 and P1 ′ with a slight frequency difference, these optical probe pulses P1 and P1
As described with reference to FIG. 5, 1'increases the phase difference for each pulse from the synchronized timing, so that the sampling timing by the optical probe pulse P1 'gradually moves. As a result, the signal generated by irradiating the optical-electrical converting means D1 with the optical probe pulse P1 and the measured object DU.
The reflected wave that returns from T and returns can be sampled and captured in the detector 31. The signal waveform is shown in FIG. 7C. A1 is a short electrical pulse generated by irradiating the first optical-electrical converting means D1 with the optical probe pulse P1, A
2, A3 and A4 represent reflected waves generated from the DUT to be measured. Since the reflected wave A2 can be seen as a reflection generated at the input point of the DUT to be measured, by measuring the time τ _X between the peak point of this reflected wave A2 and the peak point of the next reflected wave A3, It is possible to know the distance from the input point of the DUT to the internal first reflection occurrence point. Thereby, the position of the reflection point on the electric circuit can be measured.

FIG. 8 shows an embodiment of the reflection point measuring apparatus proposed in claim 4 of this application. This embodiment is different from the embodiment shown in FIG. 1 in the sampling portion. The sampling means shown in this embodiment is a signal conductor J.
1 and the half mirror 41 that reflects the optical probe pulse P2 reflected by the electro-optical element 40 toward the polarization amount detecting means 42. The polarization amount detecting means 42 is the analyzer 4
3 and the photodetector 44.

For the electro-optical element 40, an electro-optical crystal body such as zinc tellurium (ZnTe) can be used. An electric field generated in the signal conductor J1 is applied to the electro-optical element 40 to polarize the optical probe pulse P2 reflected at the bottom of the electro-optical element 40. The polarized optical probe pulse P2 is branched by the half mirror 41, is incident on the polarization amount detecting means 42, and is converted into an electric signal according to the polarization amount. The electric signal detected by the polarization amount detecting means 42 is input to the detector 31, and the following is AD-converted by the same operation as described above and taken in as waveform data by the calculator 33. The configuration of this sampling means is as shown in FIGS.
It can also be applied to the embodiment shown in FIG.

[0030]

As described above, according to the present invention, the reflection generated inside the optical element can be measured. In particular, since the pulse width of the optical probe pulses P1 and P1 'generated by the optical probe pulse generator is extremely short, the distance from the entrance of the DUT to be measured to the reflection point generated inside is measured with high resolution. be able to.

When adopting the method of using two optical probe pulses P1 and P1 'having a slight frequency difference as in the embodiment shown in FIGS. 4 and 6, the variable delay means shown in FIG. There is no need to use 20. Therefore, since it is not necessary to equip a mechanically operating part, there is an advantage that the entire measuring device can be reduced in size and weight.

[Brief description of the drawings]

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

FIG. 2 shows first and second light used in the embodiment shown in FIG.
The top view for demonstrating the structure of an electrical conversion means.

FIG. 3 is a waveform diagram for explaining the operation of the present invention.

FIG. 4 is a block diagram showing a modified embodiment of the present invention.

5 is a waveform diagram for explaining the operation of the embodiment shown in FIG.

FIG. 6 is a block diagram for explaining still another embodiment of the present invention.

7 is a waveform diagram for explaining the operation of the embodiment shown in FIG.

FIG. 8 is a block diagram for explaining still another embodiment of the present invention.

[Explanation of symbols]

 10, 10A, 10B Short pulse light generation means P1, P1 'Optical probe pulse 15 Optical transmission line 16 Reflected light acquisition means DUT DUT 1st optical-electrical conversion means D2 2nd optical-electrical conversion means 18 DC power supply 19 Semi-insulating substrate 20 Variable delay means 21 Moving mirror 22 Stage driver 31 Detector 32 AD converter 33 Operator 34 Display

Claims (4)

[Claims] 1. A. First Embodiment A short pulse light generating means for generating an optical probe pulse having a narrow pulse width; An optical transmission line for making an optical probe pulse emitted from the short pulse light generating means incident on the object to be measured; A reflected light acquisition unit that acquires reflected light returned from the device under test to the optical transmission path; and D. A first optical-electrical converting means for converting the reflected light acquired by the reflected light acquiring means into a short electric pulse; Variable delay means for delaying the optical probe pulse emitted by the short pulse light generation means, and F. It has a signal conductor to which the electric pulse converted by the first optical-electrical converting means is applied, and a signal extraction electrode arranged in the vicinity of this signal conductor, and between the signal conductor and the signal extraction electrode. Second optical-electrical conversion means for irradiating the optical probe pulse delayed by the variable delay means and sampling the potential on the signal conductor at the irradiation timing of the optical probe pulse delayed by the variable delay means. A reflection point measuring device characterized in that 2. A. A pair of short pulse light generating means for generating optical probe pulses having a narrow pulse width and slightly different frequencies; An optical transmission line for causing an optical probe pulse generated by one of the pair of short pulse light generating means to enter the object to be measured; A reflected light acquisition means for acquiring the reflected light of the optical probe pulse incident on the object to be measured, and D. A first optical-electrical converting means for converting the reflected light acquired by the reflected light acquiring means into a short electric pulse; It is provided with a signal conductor to which an electric signal converted by the first optical-electrical converting means is given, and a signal take-out electrode arranged in the vicinity of the signal conductor, and the signal take-out electrode is provided between the signal electrode and the signal take-out electrode. An optical probe pulse emitted from the other of the pair of short pulse light generation means is irradiated, and the potential of the signal on the signal electrode is sampled by the signal extraction electrode.
An optical-electrical conversion means is provided and it comprised, The reflection point measuring apparatus characterized by the above-mentioned. 3. A. A pair of short pulse light generating means for generating optical probe pulses having a narrow pulse width and slightly different frequencies; A first optical-electrical converting means for generating an electric pulse having a narrow pulse width by being irradiated with an optical probe pulse generated by one of the pair of short pulse light generating means; A signal conductor for transmitting the electric pulse converted by the first optical-electrical converting means to the device under test, and D. The signal conductor has a signal extraction electrode arranged in the vicinity of the signal conductor, and an optical pulse generated by the other of the pair of short pulse light generation means is applied between the signal conductor and the signal extraction electrode. A reflection point measuring device comprising: a second photoelectric conversion means for extracting the potential of the above signal to the signal extraction electrode. 4. The reflection point measuring device according to any one of claims 1 to 3, wherein an electro-optical element is deposited on the signal conductor, and the electro-optical element is provided with an electric pulse generated in the signal conductor. A polarization rotation amount is applied to the reflected light of the optical probe pulse whose frequency is slightly different from that of the delayed optical probe pulse applied to the electro-optical element or the optical probe pulse applied to the measured object by applying an electric field corresponding to the intensity. give,
A reflection point measuring device characterized in that the potential on the signal conductor is sampled by detecting the polarization rotation amount by a polarization amount detecting means.