JP2509246B2 - Lightwave rangefinder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Field of Industrial Application) The present invention relates to a lightwave distance measuring device in which a distance measuring optical system is integrated into an optical integrated circuit.

(Prior Art) Conventionally, an optical wave rangefinder is known to be equipped with a bulk type rangefinder optical system as shown in FIG. In FIG. 11, LD is a semiconductor, 100 is a chopper, 101 is a reflecting prism forming a part of the external distance measuring optical path I, 102 is an objective lens, and 103 and 104 are all forming a part of the internal reference optical path II. A reflection mirror, 105 is a lens installed between the total reflection mirrors 103 and 104, 106 is a half mirror, and 107 is a light receiving element. The semiconductor laser LD emits a coherent light beam whose intensity is modulated. The chopper 100 has a function of switching the intensity-modulated coherent light beam between the external distance measuring optical path I and the internal reference optical path II, and the light wave distance measuring device is provided with a chopping motor for driving the chopper 100. .

The intensity-modulated coherent light flux is selected by the chopper 100 and guided to either the external distance measurement optical path I or the internal reference optical path II. The coherent light flux guided to the external distance measuring optical path I is reflected by the reflection prism 101, guided through the objective lens 102 to a corner cube (not shown) arranged at the measuring point, and reflected by the corner cube. It returns to the direction in which 102 exists, and is guided to the light receiving element 107 via the reflection prism 101 and the half mirror 106. The coherent light beam guided to the internal reference optical path II is a total reflection mirror.
The light is guided to the light receiving element 107 via the lens 103, the lens 105, the total reflection mirror 104, and the half mirror 106.

The distance to the measuring point digitally counts the phase delay of the coherent light flux reaching the light receiving element 107 via the external distance measuring optical path I, and reaches the light receiving element 107 via the internal reference optical path II. It is obtained by digitally counting the delay of the phase of the coherent light beam and removing the error caused by the time delay of the internal reference optical path II and the electronic circuit.

(Problems to be Solved by the Invention) However, in this conventional bulk type optical distance measuring device, a chopping motor is required for switching between the internal reference optical path II and the external distance measuring optical path I. There are problems such as lack of stability and high reliability due to the large number of mechanical operating parts, such as the need for a variable density ND filter.
There are also problems such as an increase in the size of the optical distance measuring instrument itself, complicated adjustment due to the large number of optical components, and a corresponding increase in cost.

Further, since the configuration is such that the driving current of the semiconductor laser is modulated to modulate the light intensity, it is possible that the oscillation wavelength fluctuates and the ranging accuracy deteriorates, and the upper limit of the modulation frequency is set in terms of response speed. It is about 1GHz, and it is difficult to expect high-speed modulation.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a lightwave distance measuring device having a distance measuring optical system that is small in size and has no mechanical operating portion. .

Configuration of the Invention (Means for Solving the Problems) The feature of the light wave distance measuring device according to the present invention is that the distance measuring optical system is integrated into an optical integrated circuit, and the distance measuring optical system generates a coherent light beam. A light intensity modulation unit for intensity modulation, an optical path switching unit for switching the coherent light flux intensity-modulated by the light intensity modulation unit between the external distance measuring optical path and the reference optical path, and this optical path switching unit for switching to the external distance measuring optical path. And a light receiving system for receiving a reflected light beam reflected by the object, and an external distance measuring optical path between the optical path switching unit and the sending system or the optical path thereof. It is provided with an optical substrate on which a light amount adjusting unit for adjusting the light amount of the coherent light flux passing through the reference optical path between the switching unit and the light receiving system is formed.

(Embodiment) In FIG. 1, reference numeral 1 is a lens barrel which constitutes a part of a distance measuring optical system in the light wave distance measuring sense. The lens barrel 1 is provided with an objective lens 2 at the front part and an eyepiece lens 3 at the rear part. A beam splitter 4 is arranged between the objective lens 2 and the eyepiece lens 3. A concave lens 5 is provided between the beam splitter 4 and the eyepiece range 3.

The lens barrel 1 has an optical substrate 6. As the material of the optical substrate 6, LiNbO ₃ crystal is used here. As shown in FIG. 2, the optical substrate 6 includes a light intensity modulator 7, an optical path switching unit 8, a first light amount adjusting unit 9, and a second light amount adjusting unit.
10. Focusing grating couplers (FGC) 11 and 12 are formed.

The light intensity modulator 7 has an incident optical waveguide 13. Coherent light P _i emitted from a semiconductor laser LD (see FIG. 6) as a coherent light source is incident on the incident optical waveguide 13. The light intensity modulator 7 has branch waveguides 14 and 15 branched from the incident optical waveguide 13. The branch waveguide
14 and 15 are merged again by the merge waveguide 16. A pair of electrodes 17 and 18 are provided near the branch waveguide 14. A voltage V ₁ is applied to the electrode 17, and the electrode 18 is grounded.

The voltage V ₁ is a triangular wave having a predetermined cycle (predetermined frequency) as shown in FIGS. 3 and 5, and the voltage V ₁ is generated by the triangular wave generating circuit 19 shown in FIG. Here, the frequency f of this triangular wave is 15 MHz or 75 KHz. The coherent light P _i is intensity-modulated by the light intensity modulator 7, and modulated light P ₀ as shown in FIG. 3 is emitted from the merging waveguide 16.

The optical path switching unit 8 is composed of a Y-branch waveguide here, and one of the Y-branch waveguides has a first light amount adjusting unit 9
Is the first waveguide 20 leading to the second light quantity adjusting unit 10 and the other is the second waveguide 21 leading to the second light quantity adjusting unit 10. The optical distance of the first waveguide 20 and the optical distance of the second waveguide 21 are equal here. The Y branch waveguide is provided with a pair of electrodes 22 and 23 which are symmetrical with respect to the line of symmetry. A voltage V ₂ is applied to the electrode 22, and the electrode 23 is grounded. This voltage V ₂ is generated by the optical path switching signal generator 24 shown in FIG. The direction of the electric field based on the electrodes 22 and 23 is two directions, and the optical path switching unit 8 having this configuration is known (optical integrated circuit; issue unit Ohmsha; issue date: February 25, 1985).
See pages 310 to 312).

The optical path switching unit 8 has a function of switching the modulated light P ₀ guided to the merging waveguide 16 by the voltage V ₂ between the first waveguide 20 and the second waveguide 21. 2 and 3, Pr
Represents the modulated light P ₀ guided to the first waveguide 20, Pm denotes a modulated light P ₀ which is guided to the second waveguide 21. The generation timing of the voltage V ₂ will be described later.

The first light amount adjusting unit 9 has branch waveguides 25 and 26. A pair of electrodes 27, 28 are provided near the branch waveguides 25, 26. The second light amount adjusting unit 10 has branch waveguides 29 and 30.
A pair of electrodes 31, 32 are provided near the branch waveguides 29, 30. The pair of electrodes 27 and 28, a voltage is V ₃ applied to the pair of electrodes 31 and 32 a voltage V ₄ is applied. The voltage V ₃ and the voltage V ₄ are generated by the control calculation unit 33 shown in FIG. The voltage V ₃ and the voltage V ₄ are voltages having constant values with respect to time.

The first light amount adjusting unit 9 has a waveguide 34 that constitutes a part of the external distance measuring optical path I, and the second light amount adjusting unit 10 has an internal reference optical path II.
Has a waveguide 35 forming a part of the. The modulated light P ₀ passes through the waveguide 34 and the focusing grating coupler (FGC) 1
Guided to 1. The configuration of the condensing grating coupler (FGC) 11 will be described later, and then the intensity modulation,
The principle of light amount adjustment will be described with reference to FIGS. 4 and 5.

FIG. 4 is a schematic diagram showing the relationship between the light intensity modulator 7 and the first light intensity modulator 9 (the same can be considered as the relationship between the light intensity modulator 7 and the second light intensity adjuster 10). Then, coherent light P _i guided to the branch waveguides 14 and 15 is P ₁ and P _2, and modulated light guided to the branch waveguides 25 and 26 is P ₃ and P ₄ . Further, the optical path length of the branch waveguide 15 and the branch waveguide 26 is X, the optical path length of the branch waveguide 14 is X ₁ , and the optical path length of the branch waveguide 25 is X ₂ .
When the optical path length difference of the branch waveguide 14 with respect to the optical path length X of the branch waveguide 15 is δ ₁ , and the optical path length difference of the branch waveguide 25 with respect to the branch waveguide 26 is δ ₂ , the following equation is obtained.

X ₁ = X + δ ₁ X ₂ = X + δ ₂ Here, the modulated light P ′ emitted from the waveguide 34 is a combination of the lights that have passed through the four routes a to d, and each of the routes a to b. The wave function corresponding to Then, the amplitude intensity I of the modulated light P ′ is given based on the following equation. Note that k is the wave number and is 2π / λ.

This equation can be modified as shown below.

4 (1 + cosK δ ₁ ) in this equation is the first optical path length difference δ
_{Since 1} is periodically changed, it is a term that changes the optical amplitude intensity for each cycle, and is a term that includes the modulation frequency. On the other hand, in the expression (1 + cosK δ ₂ ), when the second optical path length difference δ ₂ is adjusted, the maximum amplitude value of the optical amplitude intensity I ₀ changes. That is, (1 + cosK δ ₂ ) is a term that gives the maximum amplitude value of the modulated light.

For example, the voltage V ₃ is adjusted so that the second optical path length difference δ ₂ becomes n ₁ λ
5, the maximum amplitude value of the modulated light P ′ becomes I ₀ , and when the second optical path length difference δ ₂ is set to n ₁ λ + λ / 4, the maximum amplitude value of the modulated light P ′ becomes It becomes I _0/2 . The same applies to the second light amount adjusting unit 10.

The condensing grating coupler (FGC) 11 functions as a transmission system that transmits a coherent light beam toward an object, and as shown in FIG.
36 and a curved chirp grating 37, the modulated light P ′ guided to the waveguide 34 is collimated by the linear grating 36 and guided to the curved chirp grating 37. The light is emitted so as to be converged at a point F, reflected by the beam splitter 4 in the direction in which the objective lens 2 exists, and emitted as a parallel light flux Px toward the measurement point by the objective lens 2.

The condensing grating coupler (FGC) 12 has a function of receiving the reflected light flux reflected by the object, and the curved chirp grating 39 in the opposite direction with the groove 38 as a boundary.
And a linear grating 40. For example, a corner cube 41 is provided at the measuring point.
The parallel light flux Px reflected by 41 (see FIG. 6) returns to the objective lens 2 as a reflected light flux Px ′, passes through this, and is reflected by the beam splitter 4 so as to be condensed at a point F. The reflected light beam Px ′ is then condensed by the curved chirp grating 39, guided as a parallel light beam to the linear grating 40, and condensed by the linear grating 40 on the external distance measuring waveguide 42.

The above-mentioned condensing grating couplers (FGC) 11 and 12 are composed of linear gratings 36 and 40 and curved chirp gratings 37 and 39 that are line-symmetrical with respect to the groove 38, and are formed linearly symmetrically. While the parallel light flux is formed between the linear gratings 39 and 39, the linear gratings 36 and 40 may be omitted as shown in FIG.

Further, as shown in FIGS. 9 and 10, the curved chirp gratings 37 and 39 may be arranged in parallel in a rotationally symmetrical shape so that a parallel light flux enters and leaves the free space. Is a lens for focusing on the point F.

In this way, the focusing grating coupler (FGC) 1
By providing 1 and 12 on the optical substrate 6, the objective lens 2 for point collimation can be used also as the objective lens for distance measurement. If a dichroic mirror that reflects infrared light and transmits visible light is used as the beam splitter 4 and a semiconductor laser LD that generates infrared light is used, the reflected light flux from the corner cube 41 can be reliably collected. It can be guided to the grating coupler (FGC) 12.

The external distance measuring waveguide 42 and the waveguide 35 are merged and optically connected to a light receiving element forming a part of a distance measuring circuit described later.

Next, distance measurement using the lightwave distance measuring device according to the present invention will be described with reference to the distance measuring circuit shown in FIG.

The distance measuring circuit has, in addition to the triangular wave generating circuit 19, the optical path switching signal generator 24, and the control calculating unit 33, the light source power supply circuit 50, the light receiving element 51, the first rectangular wave converter 52, and the second rectangular wave. It has a wave converter 53, a light level detector 54, a clock oscillator 55, a gate circuit 56, and a counter 57. The output of the light source power supply circuit 50 is input to the semiconductor laser LD. The semiconductor laser LD, based on the output of the light source power supply circuit 50,
The coherent light P _{i described} above is emitted.

The voltage V ₁ of the triangular wave generation circuit 19 is applied to the electrode 17 and is also input to the second rectangular wave converter 53 via the inverter. From the second rectangular wave converter 53, the rectangular wave shown in FIG. L ₁
Is output. The rectangular wave L ₁ is an optical path switching signal generator
24 and the set terminal S of the gate circuit 56. The rectangular wave L ₂ (see FIG. 3) output from the first rectangular wave converter 52 is input to the reset terminal R of the gate circuit 56. First
The rectangular wave L ₂ of the rectangular wave converter 52 is generated by the coherent light beams Px ′ and Pm ′ received by the light receiving element 51.

The clock K of the clock oscillator 55 is input to the gate circuit 56, and the first rectangular wave converter is input to the set terminal S.
The gate circuit 56 is opened based on the rising of the rectangular wave L ₁ of 53, and the second rectangular wave converter 52 input to the reset terminal R is input.
The gate circuit 56 is closed based on the rising edge of the rectangular wave L ₂ . The counter 57 is connected to the gate circuit 56 and counts the number of clocks K that have passed through the gate circuit 56.
The counter 57 has its counter value cleared at the rising and falling edges of the voltage V ₂ .

The voltage V ₂ and the count value of the count 57 are input to the control calculation unit 33, and the control calculation unit 33 performs the calculation described later based on the count value and the output of the light quantity adjuster 54. It has a function of setting the values of the voltages V ₃ and V ₄ for adjusting the light amount of the first light amount adjusting unit 9 and the second light amount adjusting unit 10. That is, the control calculation unit 33 controls the light intensity of the coherent light Pm ′ input to the light receiving element 51 via the internal reference optical path II and the coherent light Px input to the light receiving element 51 via the external distance measuring optical path I. It has a function of controlling the first light amount adjusting unit 9 and the second light amount adjusting unit 10 so that the intensity of the light of ‘substantially matches.

The optical path switching signal generator 24 generates the voltage V ₂ for a certain period based on the falling edge of the rectangular wave L ₁ , and as described above, while the voltage V ₂ is being generated, the external distance measuring optical path I Based on the coherent light Px ′ that is input to the light receiving element 51 through
The number N ₁ , N ₁ ′, N ₁ ″ of clocks K counted from the rising edge of the rectangular wave L _{1 to} the falling edge of the rectangular wave L ₂ is input to the control calculation unit 33, and this voltage V ₂ is generated. In the meantime, the clock K counted from the rising of the rectangular wave L _{1 to} the falling of the rectangular wave L ₂ based on the coherent light Pm ′ input to the light receiving element 51 through the internal reference optical path II. The number of N ₂ ,
N ₂ ′ and N ₂ ″ are input to the control calculation unit 33.

Here, there is a time delay based on the distance 1 to the measuring point from when the coherent light P _i is emitted via the external distance measuring optical path I until it is reflected at the measuring point and received by the light receiving element 51. Therefore, assuming that the counting is started based on the emission time of the coherent light P _i and the counting is ended at the light reception time of the coherent light Px ′, the numbers N ₁ , N ₁ ′, N ₁ ″ of the clocks K are It corresponds to the phase difference θ ₁ (time delay based on distance).
There is a time delay based on the optical distance of the internal reference optical path II until P _i is received by the light receiving element 51 via the internal reference optical path II. Therefore, assuming that the counting is started based on the emission time of the coherent light P _i and the counting is ended at the light reception time of the coherent light P m ′, the clock K
The number N ₂ , N ₂ ′, N ₂ ″ corresponds to the phase difference θ ₂ (time delay based on the optical distance). Note that this phase difference θ ₂ also includes an error based on the time delay of the circuit. There is.

Therefore, the difference in phase difference θ = θ ₁ −θ ₂ purely corresponds to the distance to the measurement point.

By the way, there is the following relationship between the phase difference .theta., The wavelength .lamda. (= C / f) and the distance l.

l = (C / f) × (θ / 2π) In the above equation, C means the speed of light, and f =
If the frequency is 15 MHz, the wavelength λ = 20 m, and if f = 75 KHz, the wavelength λ = 4 Km.

The control calculation unit 33 calculates the distance 1 based on the above formula and displays the calculation result on the display 58.

EFFECTS OF THE INVENTION As described above, the optical distance measuring instrument according to the present invention has a structure in which the distance measuring optical system is integrated into an optical integrated circuit and has no mechanical operation part, and is small, stable, and reliable. It has the effect of becoming expensive.

[Brief description of drawings]

FIG. 1 is a layout drawing of a distance measuring optical system of a light wave distance measuring device according to the present invention, FIG. 2 is a layout drawing of each optical element provided on an optical substrate of the distance measuring optical system, and FIG. FIG. 4 is a timing diagram for explaining the light distance measuring device, and FIG. 4 is a schematic diagram for explaining the principle of light intensity modulation and light amount adjustment based on the light intensity modulator and the first light amount adjuster shown in FIG. FIG. 5 is a graph for explaining the principle of light intensity modulation and light amount adjustment, FIG. 6 is a schematic diagram of the distance measuring circuit of the light wave distance measuring device, and FIGS. 7 to 9 are shown in FIG. FIG. 10 is a diagram for explaining a configuration example of a condensing grating coupler (FGC), FIG. 10 is a diagram showing the positional relationship between the optical substrate and the objective lens shown in FIG. 9, and FIG. 11 is a conventional bulk type distance measuring device. It is a figure which shows an example of an optical system. 2 ... Objective lens, 3 ... Eyepiece lens, 4 ... Beam splitter, 6 ... Optical substrate, 7 ... Light intensity modulator, 8 ... Optical path switching unit, 9 ... First light amount adjusting unit, 10 ... Second Light intensity adjuster 11, 12 …… Focusing grating coupler (FGC) 17, 18, 22, 23, 27, 28, 30, 31 …… Electrode LD …… Semiconductor laser, P _i …… Coherent light

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Satoru Nimura 75-1 Hasunuma-cho, Itabashi-ku, Tokyo Within Tokyo Optical Machinery Co., Ltd. (56) Reference JP-A-57-196171 (JP, A) JP-A-62 -5104 (JP, A) JP 62-5105 (JP, A) JP 1-124788 (JP, A) Actually opened 57-82319 (JP, U) Actually opened 1-74581 (JP, U) ) Japanese Patent Publication 6-84884 (JP, B2) Japanese Patent Publication 6-52163 (JP, B2)

Claims (6)

(57) [Claims] 1. A distance measuring optical system, wherein a coherent light beam emitted from a coherent light source is intensity-modulated and transmitted toward an object, and a reflected light beam reflected by the object is received by a light receiving element. In a lightwave distance measuring device for measuring a distance to an object based on detecting a phase of a reflected light beam, the distance measuring optical system includes a light intensity modulator for intensity-modulating the coherent light beam, and the light intensity modulator. An optical path switching unit for switching a coherent light beam whose intensity is modulated by a section between an external distance measuring optical path and a reference optical path, and a delivery system for sending the coherent light beam switched to the external distance measuring optical path by the optical path switching unit toward the object. A light receiving system for receiving a reflected light beam reflected by the object; and an external distance measuring optical path between the optical path switching unit and the sending system or the optical path switching unit and a light receiving system. Laser rangefinder, characterized in that it has an optical substrate and a light-quantity adjusting members are formed for adjusting the light quantity of the reference coherent light beam passing through the optical path between. 2. The light amount adjusting unit is a reference between the first light amount adjusting unit provided in an external distance measuring optical path between the optical path switching unit and the sending system, and between the optical path switching unit and the light receiving system. The lightwave rangefinder according to claim 1, wherein the lightwave rangefinder is formed by a second light amount adjusting portion provided in the optical path. 3. An optical waveguide forming the external distance measuring optical path and the reference optical path is formed on the optical substrate, and the light intensity modulating section, the first light quantity adjusting section, and the second light quantity adjusting section are formed. Has a branch waveguide, and is configured by a Mach-Zehnder interferometer in which an electrode is provided on at least one of the branch waveguides.
Optical rangefinder according to paragraph. 4. The intensity of light received by the light receiving element through the external distance measuring light path and the reference light path through the electrodes of the first light quantity adjusting section and the second light quantity adjusting section. A voltage is applied to the light receiving element so that the intensity of the received light is substantially equal to the intensity of the received light, and a signal having at least two frequencies is selectively applied to the light intensity modulator. The lightwave rangefinder according to claim 3. 5. The optical path switching unit includes a Y-branch optical waveguide, two electrodes are symmetrically arranged along a symmetry line of the Y-branch optical waveguide, and the two electrodes have electric fields in two directions. 3. The optical wave measurement according to claim 2, characterized in that a voltage is applied so that the light travels selectively to the external distance measuring optical path and the reference optical path. Rangefinder. 6. The coherent light flux is infrared light, the objective optical system includes an objective lens, and the objective optical system reflects infrared light from the object toward the light receiving system and The light wave rangefinder according to claim 2, further comprising a dichroic mirror that guides visible light from the object to the eyepiece lens unit.