JPH03282344A - Optical device - Google Patents

Abstract

PURPOSE: To reduce the weight and size of an optical time domain reflectivity meter(OTDR) by imparting a strain effectively to an optical pulse thereby limiting the pulse width. CONSTITUTION: An OTDR system 100 comprises a controller 101, an oscillator 103, a phase shifter 105, an amplifier 107, an optical pulse generator 109, an integrated electrooptical circuit(IEOC) 111, a detector 113, a timer 115, a converter 117 and an output unit 119, i.e., a display or a memory. The IEOC 111 comprises a substrate 201, an input optical path 203, a dispersion grating 205, an output optical path 207, a first electrode 209 and a second electrode 211. The electrodes 209, 211 have parallel longitudinal segments 215, 217 and a current flowing through the segments 215, 217 generates a field 319 propagating through the optical path 203. The field 319 induces a phase distortion in the optical pulse and the shorter pulse width thereof realizes reduction in the weight and size of the OTDR and enhancement of the accuracy.

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to optical devices, and more particularly to optical time domain reflectometers (OTDRs) that include a novel pulsed source.

It is an attempt to describe the characteristics of an object by measuring it. For example, 0TDR can be used to evaluate photon devices as well as large optical devices such as photographic lenses. A laser pulse directed at a multi-element lens can generate an echo signal with time-varying intensity.

In this case, intensity corresponds to reflectance and time corresponds to distance from the pulse source. Therefore, by analyzing the echo signals, it is possible to determine how much light each lens surface reflects that should be transmitted therethrough. Mo5he Nazara
thy(IEEB Journal of Li
ghtwave Technology.

Vol -7+ N091 + January 1989) and its references describe the 0TDR.

A typical 0TDR system uses transistors to switch the semiconductor laser that generates the light pulses. It is also possible to start a counter at the same time as the pulse is emitted, stop it at the same time as the pulse is detected, and measure the time required. This required time can be converted into a path distance to locate each reflection source. The accuracy of the range that can be resolved is limited by the characteristic pulse width of the transmitted pulse and the dispersion that occurs between transmission and detection.

By switching the laser diode, 50 picosecond (ps) optical pulses can be easily obtained. This is sufficient to analyze simple lenses consisting of elements spaced one centimeter or more apart. It has become clear that a high-speed laser diode with a time resolution of 1 ops satisfies a resolution on the order of several millimeters.

Some recent photographic lenses, particularly zoom lenses, use 15 or more elements. To provide a reasonably compact lens, the spacing of the lens elements must be small, with typical spacing being a few millimeters or less. Analyzing reflections from such closely spaced device surfaces requires an 0TDR with an initial pulse width on the order of lps.

Edward B., Tracy Journal
of Quantum Electronics Vo
l, QB-5, No, 9. (September 1969) 0p
tical pulse compression w
ithDiffractionC)ratings”
A high power pulsed laser or a large optical compressor can be employed to obtain the desired resolution, as disclosed in . However, the power and weight of these light sources make them expensive and cumbersome. Cost and power requirements preclude their use in applications where convenience is required. There is a need for an economical 0TDR that can characterize optical components with extremely high spatial resolution and resolution, and that also has appropriate size and output conditions.

[Purpose of the invention]

The present invention satisfies the above requirements by providing a convenient and highly accurate optical time domain reflectometer and its related parts.

[Summary of the invention]

A system according to one embodiment of the present invention includes a waveform generator that generates electrical waveforms and a pulse generator that generates optical pulses. The integrated optical circuit includes an optical path that directs the optical pulse to an integrated frequency dispersive reflection filter. The integrated optical circuit also includes electrodes for transmitting electrical waveforms into the optical path so that the electric field propagates along with the optical pulses. The waveform and pulses are synchronized using, for example, a waveform generator that triggers a pulse generator.

Detectors are used that detect the reflection of pulses from the object or other phenomena of interest caused by the incidence of pulses on the object. The time taken from the rise of the pulse to the time of detection is used to measure distance or other parameters of interest in characterizing the object. This duration can be determined by connecting timers to both the waveform generator and detector.

A phase shifter can also be used to provide the desired synchronization between the optical pulse and the electrical waveform. To a first approximation, the light pulse must be centered at the peak of the electrical waveform. Preferably, this synchronization is maintained during simultaneous propagation of the pulse and electric field. When the electric field and optical pulse are propagating at different speeds, this difference is compensated for by adjusting the relative phase so that the accumulated phase delay is maximized. For symmetric Gaussian electric field distribution,
This occurs when the average phase relationship across the common path is equal to the alignment of the peaks.

The method disclosed herein does not require high-power pulsed lasers or similarly cumbersome equipment, and provides greater precision than previously available. The fundamental reason for the accuracy achieved is the much smaller pulse width compared to other convenient types. The present invention provides 1, the above features and other features,
Further, the advantages will become clear from the description given below with reference to the drawings.

[Explanation of Examples]

One embodiment of the present invention provides an optical time domain reflectometer 100 having a convex element 81 and a concave element 82 for characterizing a compound lens 8 DEG as shown in FIG.

Optical time domain reflectometer 100 emits a single or series of 9° pulses through lens 80. Convex element 81
has a convex front surface 83 and a convex rear surface 84, and concave element 82 has a concave front surface 85 and a concave rear surface 86. The energy of lens output 91 is reduced by the energy distributed in each reflection 93-96 from surfaces 83-86. By knowing which surfaces are causing the greatest transmission loss, the optical time-domain reflectometer 100 can, for example,
It can indicate which surfaces are candidates for different optical coatings, etc.

The optical time domain reflectometer system 100 includes a controller 101, an oscillator 1o3, a phase shifter 1o5, an amplifier 107,
Light pulse generator/earthenware 109, integrated electro-optical circuit (IEO)
C) 111, detector 113, timer 115, converter 1
17, and an output device 11 which is a display or storage device.
Consists of 9 parts. When the oscillator 103 is activated by the controller 101 via the wire 121, it generates a waveform on the wire 123.

After this waveform is phase-shifted by a phase shifter 105,
25 and is received by amplifier 107. When amplifier 107 is activated by controller 101 via wire 127, the amplified waveform is sent to wire 129 to trigger optical pulse generator 109.

The optical pulse generator 109 may be a transistor-switched laser diode for generating optical pulses. Preferably, the initial duration is about 10 to 20 ps. This light pulse is
Integrated electro-optic circuit 111 via optical fiber 131
is connected to the optical pulse input OPI of. This optical pulse is compressed by the action of complementary electrical signals from waveform generator 103 on line 141 to input V1 and on line 143 to input V2, as described below. The compressed optical pulses 9 and 0 are sent out from the optical pulse output OPO of the electro-optical circuit 111 toward the lens element 80 .

Detector 113 detects reflections 9 detected from surfaces 83 to 86.
3 to 96, the electrical detection signals are provided. Detector 113 has a variable threshold that gradually decreases during successive transmitted light pulses.

When the threshold is sufficiently lowered, detector 113 provides an electrical pulse corresponding to the strongest of reflections 93-96.

A trigger pulse from amplifier 107 is directed on line 133 to "start" input B of timer 115, and
The output of the detector 113 is connected to the timer 11 on the wiring 135.
5 of 1 end” is directed to the input E. The timer 115 is
It is a time-to-digital converter with an analog interpolation circuit with an accuracy of 6 ps or less. This is similar to Reviewof 5cient, except that the clock rate and interpolation resolution are higher.
ific Instruments, Vol. 57
．． No. 11 (November 1986) “Time-
To-Digital ConverterWith
An Analog Interpolation C
The output of timer 115 is a digital representation of the time between triggering the pulse and detection of the resulting reflection. Transducer 117 takes this timer output on trace 137 and converts the location of the strongest reflection into a distance with approximately 1 millimeter accuracy, sufficient to distinguish surfaces 83 through 86.
39 and displayed or stored by the output device 119.

Amplifier 107 produces a limited output, thereby producing a sharp transition in the optical pulse generator. The operator can adjust controller 101 to select between repeat mode or single shot mode. In the repeat mode, a series of pulse and waveform pairs are sent through the integrated electro-optic circuit 111. In single shot mode, a single pulse is applied to the integrated electro-optic circuit 111.
controller 101 disables amplifier 107 via line 127.

As shown in FIGS. 2 and 3, the integrated electro-optical circuit 111 includes a substrate 201, an input optical path 203, and a dispersion grating 20.
5. Output optical path 207, first electrode 209 and second electrode 2
Contains 11. Note that FIG. 2 is a plan view, and FIG. 3 is a corresponding right side view. The substrate 201 is made of tin cum niobate crystal (Linb03). The optical passage 207 is Dav
id W', AppliedOp by Dolfi
tics, Vol-25, (August 1, 1986)”
Travel=ing Wave 1.3 μm I
interferometer ModulatorWi
th High Bandwidth + Low
Drive Power + and LowLoss
The input optical path 203 exits from the pulse input OPI of the integrated electro-optical circuit 111 and passes through the dispersive grating 205. Pass.

The Fusan grid 205 is based on IEEE Transa. tio
nS on Microwave Theory an
dTechnics Vol, MT T-23
, No. 1 (January 1975) Theory o
f Peri-odic Dielecfric Wa
consists of a series of spatial perturbations 213 formed on the input optical path 203 by refining the process disclosed by S., T., Peng et al. It is reduced from half the longest wavelength delivered to half the shortest wavelength delivered onto input optical path 203.

Spatial perturbations 213 are written by electron beam exposure from a nanolithographic ink system. The spatial perturbation used is generally perpendicular to the first optical path. Furthermore, when using a diffraction grating, a parallel grating obliquely intersecting the first optical path is used.

Longer wavelengths are reflected before shorter wavelengths. The longer wavelength must travel further until it encounters a perturbation in pitch corresponding to the half wavelength required to constructively interfere with the reflection returning on the output optical path 207. In this way, grating 205 serves to create a differential delay as a function of the frequency of the pulse being reflected. Some of the energy of the reflected and counted pulses is transferred to the output optical path 2.
07 and directed to pulse output OPO.

Electrodes 209 and 211 each have parallel longitudinal segments 215 and 217 such that a current therethrough generates an electric field 319 that propagates through input optical path 203, as shown in FIG. Specifically, the electrode 209 is formed on the surface of the substrate 2010 and the input optical path 203, and the electrode 211 is also formed on the surface of the substrate 2o1, but a gap is provided between the electrode 209 and the input optical path 203. Electric field 319 is non-zero when a potential difference exists between electrodes 209 and 211. Electrodes 209 and 211 each have lateral segments 221 and 223 that have minimal interaction with the reflected pulse. segment 22
1 and 223 are connected via a termination resistor 225 formed at the end of the substrate 201.

Electrodes 209 and 211 are formed by electrolytic gold plating to a thickness of approximately 3 μm''1 through a photoresist with a metal pressure pattern. These electrodes have a width of approximately 24 μm;
They are arranged at intervals of approximately 6 μm. Optical paths 203 and 207
is formed by titanium diffusion approximately 6 pm wide and 650 Å thick.

The power transmission line formed by the electrodes 209 and 211 causes the input optical path 203 to have a radian frequency ωm over time.
Establish an electric field that varies sinusoidally at (t) and also varies with location at any given time. The phase shifter 105 is controlled so that the peak of the optical pulse coincides with the peak of the simultaneous electric field, at least near the middle 227 of the length of simultaneous propagation of the pulse and the electric field. The preferred phase relationship between the optical pulse and the electric field 319 is shown by the solid sinusoidal line 429 in FIG.

FIG. 4 shows the effect of velocity mismatch on the total phase excursion accumulated by the light pulses. The abscissa is 0 m(t) in units of phase of the modulated electric field. The ordinate is the total cumulative optical phase r after propagation of the modulating electric field. Solid cosine wave line 3
19 represents the total phase deviation when the speeds of the electric field and the optical pulse 429 having a Gaussian envelope completely match. If the pulse is shorter than the modulating field period, the phase deviation is exclusively of the quadratic type.

Dashed line 431 represents the cumulative phase shift of the optical pulse traveling slower than the co-propagating electric field. It has a phase lag of π/2 radians. A dashed line 433 represents the cumulative phase of a light pulse that is traveling faster than the co-propagating electric field. That is π/2
It has a phase advance of radians.

In either case, the secondary phase is shifted relative to the envelope of the optical pulse, so that the peak phase shift is reduced.

When the phase shifter 105 is used to introduce an optical pulse with a phase lag or lead of π/4, the center of the optical pulse is again located in the quadratic part of the phase curve. However, the phase amplitude peak remains reduced. In general, ΔΦ
The phase shift of can be compensated by a preliminary phase offset of 1 ΔΦ/2.

The electric field 319 causes a phase distortion in the optical pulse 429,
It changes according to the strength of the local electric field.

The duration of the light pulse 429 is such that the light pulse is maintained essentially within a single peak of the electric field 3190.
much shorter than the period. Since the sine wave is approximately quadratic around its peak, the phase distortion applied to optical pulse 429 varies quadratically across its width. Since frequency is the time derivative of phase, and the derivative of a quadratic function is linear, the electric field imparts a linear frequency sweep to light pulse 429.

This frequency-swept pulse is dispersed in time as a function of frequency by the minority grating 205.

This combination of sweeping and dispersion is similar to that of a "chirp" radar. The radar pulse is swept and dispersed, or chirped, to provide high peak power not otherwise available. 0TDR In this application, a reduction in pulse width from about 10 ps to about lps can be obtained. This shorter pulse width results in a higher accuracy of the optical time-domain reflectometer.

Another optical time domain reflectometer 500, as shown in FIG. It consists of a device 513 and an output device 515. Y connector 517 provides optical communication via optical fiber 519 to the optical pulse output OPO of integrated electro-optic circuit 507 and via optical fiber 521 to detector 509.

Output 523 of Y connector 517 can send light pulses through air or other media. Further, the optical quantum circuit can be evaluated by connecting it to the Y connector output 523 using an optical fiber.

The controller 501 maintains a 0 between the signals it activates.
TDR 100 can be programmed to establish the phase relationships described above. Controller 501 can communicate with other components via control bus 525. The electrical waveform generator 505 is connected to the control bus 5 via wiring 527.
25, and the optical pulse generator 503 is connected to the wiring 528
The control bus 525 is connected to the control bus 525. The output of the optical pulse generator 503 is connected to the optical input OPI of the integrated electro-optic circuit 507 by an optical fiber 530.

Optical pulse generator 505, converter 513 and output device 5
15 is basically similar to the corresponding part of the 0TDR system 100. Detector 509 provides a time-varying detection signal corresponding to the detected time-varying intensity. controller 50
1 outputs a synchronization signal to the synchronization human power S of the timer 511 on the bus 525 and wiring 529.

The synchronization signal is used by timer 511 as a reference for evaluating the detection signal. The detection time relative to the pulse trigger is used to determine the relationship between detection strength and delay data. The position data is transferred to the output device 515 on the wiring 533.

The output device may include an oscilloscope for display.

The result is a graph of intensity versus position, which can be used to see which surfaces are reflecting the most light.

Waveform generator 505 may be a frequency generator and is designed to generate a periodic waveform that is approximately quadratic over a half period. The complementary waveform from waveform generator 505 is transmitted to line 5
35 and 537, and are sent to electrical inputs (1) and (2) of the integrated electro-optical circuit 507, respectively.

As shown in FIG.
, and the second from the quadrupled region 605 to the pulse output OPO.
includes a substrate 601 having an optical path 607 of .

The optical paths 603 and 607 are similar to the dispersion area 605,
It is doped with titanium to transmit light.

The valve number region 605 is separated by parallel diffraction gratings 609 and 611 formed on the surface of the substrate 6010. Diffraction grating 609 transfers the received optical pulse to input optical path 603.
The light is arranged so as to be reflected toward the diffraction grating 611 at the top. Diffraction grating 611 further reflects the pulse onto output path 607. Parallel gratings 609 and 61
The effect of 1 is similar to that of the grating of optical time-domain reflectance type system 100.

Integrated electro-optic circuit 507 also has a pair of electrodes 613 and 615 that cooperate to form a power transmission line.

Electrodes 613 and 615 alternate in coverage of input optical path 603, approximately in the shape of a spatial square wave over the length of the simultaneous propagation of the electrical waveform and optical pulse. The length of simultaneous propagation is the length along input optical path 603 that is influenced by the electric field between electrodes 613 and 615. The length of co-propagation corresponds approximately to the longitudinal extent of electrode 615.

The dimensions and materials of electrodes 613 and 615 and optical paths 603 and 607 are similar to those of the corresponding parts shown in FIG. Strictly speaking, electrodes 613 and 615 are connected to optical path 6.
Wider than 03. The inverse relationship is shown in FIG. 6 to better explain the relationship between the electrical and optical paths. For each of electrodes 613 and 615, the vertical segment on optical path 603 is shorter than the vertical segment away from optical path 603. For example, segment 621 of electrode 615 is shorter than segment 623 of electrode 623.

This avoids short-circuiting of the electrodes on the optical path 603.

Electrodes 613 and 615 have resistively coupled lateral force segments 617 and 619. The period of the spatial square wave is related to the speed difference between the optical pulse and the phase modulated electric field. This configuration prevents phase distortion from occurring due to a change in the sign of the electric field. Otherwise, phase distortion will be added to the optical pulse if the velocity difference between the optical pulse and the electric field is relatively large.

The present invention can also be applied to methods other than the embodiments described above.
500 can be applied. If only a single pulse is used to detect defects, the electrical waveform will not be periodic. A single quadratic electrical waveform can be used to cause phase distortion of the optical pulse. Suitable electro-optic materials other than lithium niobate may be used in the substrate of the integrated electro-optic circuit.

Although the above embodiments focus on time-domain reflectance meters,
The invention is equally applicable to other applications. For example, the output of an integrated electro-optic circuit may be used to characterize the detector. In this case, the detector is both part of the system and the object of inspection. In other applications, the detected phenomenon need not be a reflection. For example, a pulse of light may be used to trigger the release of some chemical compound. This release is detected and the delay between the pulse and release is determined by the compound,
Alternatively, it may be used to characterize the release process.

〔Effect of the invention〕

As detailed above, the optical pulse is effectively distorted,
Since the pulse width is narrowed, a time domain reflectometer with high resolution can be obtained.

Furthermore, since the device is small, handling is convenient.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a first optical time domain reflectometer arranged to evaluate lenses using one embodiment of the present invention. FIG. 2 is a plan view of the integrated electro-optic circuit of FIG. 1. FIG. 3 is a front view of the integrated electro-optic circuit of FIG. 1. FIG. 4 is a graph for explaining the preferred synchronization relationship between the electrical waveform and optical pulse of the first optical time domain reflectometer shown in FIG. FIG. 5 is a schematic diagram of a second optical time domain reflectometer using another embodiment of the invention. 6 is a plan view of the integrated electro-optic circuit of FIG. 5. FIG. 80: Complex lens 100: Optical time domain reflectometer 101: Controller 103: Oscillator 105: Phase shifter 107: Amplifier 109: Optical pulse generator 111: Integrated electro-optical circuit (IEOC) 113: Detector 15 17 19 01 03 05 07 209, 13 215, : Timer: Transducer: Output device 7 Two substrates Two human power forward paths Two anvil gratings: Output optical path 211: Electrodes: Spatial perturbation 217: Longitudinal segment.

Claims (1)

[Scope of Claims] 1. An optical device comprising the following (a) to (h). (a) Substrate. (b) A first optical path formed on the substrate and having a first input and a second output. (c) A second optical path having a second input and a second output and formed on the substrate. (d) Provided on the substrate near the first output and the second input to direct the light transmitted through the first optical path from the first output to the second input. Coupling reflection dispersion means. The reflection and dispersion means disperses and reflects the light as a function of frequency. (e) Electric path means formed on the substrate and for propagating an electric field along the first optical path. (f) Optical pulse generator means for generating said optical input pulse having a peak and a characteristic pulse width. (g) Waveform generator means for generating an electrical waveform having a characteristic width and peak that is substantially longer than the characteristic pulse width of the optical input pulse. (h) controller means for activating the optical pulse generator means and the waveform generator means such that the peaks of the optical input pulse and the peaks of the electrical waveform are averagely aligned and propagate in parallel; The electrical waveform imparts phase distortion to the optical input pulse. The phase distortion varies spatially over the pulse length of the optical input pulse. Accordingly, the resulting distorted optical input pulse is reflected by said reflection dispersion means such that the reflected optical output pulse has a pulse width substantially shorter than the characteristic pulse width of said optical input pulse. , from the second output via the second optical path. 2. The optical device of claim 1, wherein said waveform generator means generates a waveform that imparts a quadratically varying phase shift to said optical input pulse. 3. The optical device according to claim 1, further comprising means for adjusting an initial phase difference between the optical input pulse and the electric waveform to offset a propagation speed difference between the optical input pulse and the electric waveform. 4. The optical device of claim 1, wherein said reflection dispersion means includes a grating having a spatial perturbation extending generally perpendicular to said first optical path. 5. Claim 1, wherein the reflection dispersion means comprises a parallel diffraction grating formed on the substrate and extending obliquely to the first optical path.
Optical device as described. 6. The optical device according to claim 1, further comprising means for measuring a time difference between the optical input pulse input to the first input and the reflected optical output pulse output from the second output. .