JPH02122292A - distance measuring device - Google Patents

Abstract

PURPOSE:To simplify the structure, to decrease the number of parts and to facilitate the integration by providing a laser generating means by which light sources of two kinds of light beams execute an oscillation simultaneously in a mode TE and TM whose oscillation wavelength is different from each other. CONSTITUTION:Light beams of two kinds of modes emitted from a semiconductor laser 1 are allowed to branch to an exit light and a reference light by a Y branching part 2. The exit light is converged to parallel rays by a collimator lens 3 and an object to be measured is irradiated with the above rays. The reference light is made incident on a TE-TM mode splitter 4. A reflected light from the object to be measured of the exit light is converged to parallel rays by a collimator lens 5, and made incident on a second TE-TM mode splitter 6. The splitter 4 demultiplexes the incident reference light to a TE wave and a TM wave. The splitter 6 demultiplexes the incident reflected light to a TE wave and a TM wave. These reference light and reflected light which are demultiplexed are coupled by a TE wave Y branching part 7 and cause an interference, and made incident on a photodiode 8 and 10. The diodes 8, 10 convert an interference light to an electric signal, and inputs it to a phase difference gauge 11.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a distance measuring device using interferometry using two types of light having different wavelengths.

(Prior Art) Two types of distance measuring devices using light have been proposed. One of these methods is an interferometry method that uses two types of light with different wavelengths. FIG. 4 shows an optical system of an example of a conventional distance measuring device using interferometry using a semiconductor laser as a light source.

This distance measuring device uses two semiconductor lasers 20a20b.
have. The wavelength λ3. which is emitted from each of the two semiconductor lasers 20a and 20b. Of the laser beams of wavelength λ2 (λ1≠λ2), the laser beam of wavelength λ1 is incident on the polarization splitting prism 22 through the λ/2 plate 21, and the laser beam of wavelength λ2 is reflected by the mirror 23 and sent to the polarization splitting prism 2.
2. The wavelength λ7. which is multiplexed by the polarization separation prism 22. The laser beam of λ2 is split into two by a half mirror 24, one of which is irradiated onto the object to be measured, and the other is incident on a polarization separation prism 25 as a reference beam. The light reflected by the object to be measured is incident on the polarization separation prism 25 through the λ/2 plate 26.

The reflected light and the reference light incident on the polarization splitting prism 25 are split into light with a wavelength λ1 and light with a wavelength λ2, respectively.
The reflected light of wavelength λ1 and the reference light interfere, and the reflected light of wavelength λ2 and the reference light interfere. Interfering light with wavelength λ1 and wavelength λ
The two interference lights are converted into electrical signals by photodiodes 27 and 28, respectively. Both electrical signals are input to a phase difference meter 29. The phase difference meter 29 measures the phase difference between the interference light of wavelength λ1 and the interference light of wavelength λ2.

The optical path of the reflected light is longer than the optical path of the reference light, which corresponds to twice the distance from the distance measuring device to the object to be measured. As a result, there is a wavelength of λ1 between the two reflected lights and the reference light. λ
A phase difference occurs for each of the two. The phase difference for light with wavelength λ1 is θ The phase difference for light with wavelength λ2 is θ
2 and the optical path difference between the reflected light and the reference light is L, then 1
The following relational expression holds true.

Since the phase difference meter 29 obtains the value on the left side of equation (1), (
1) The optical path difference is determined based on the formula.

(Problems to be Solved by the Invention) In the distance measuring device shown in FIG. 4, two semiconductor lasers are required to obtain two light beams having different wavelengths. In addition, a λ/2 plate or a polarization separation prism J is required as a demultiplexing means for causing the reflected light from the object to be measured to interfere with the reference light from the semiconductor laser that has emitted the reflected light. Since conventional distance measuring devices require such a large number of light emitting elements and optical components, they not only have a complicated structure and high cost, but also are extremely difficult to integrate. A Fabry-Perot type semiconductor laser is usually used as the light emitting element. Since the oscillation wavelength of a Fabry-Perot type semiconductor laser tends to change due to changes in temperature, etc., conventional distance measuring devices using this type have a drawback in terms of measurement accuracy.

The present invention was made in view of the current situation, and
The purpose is to provide a distance measuring device with a simple structure, a small number of parts, and easy integration.

(Means for Solving the Problems) The distance measuring device of the present invention is a distance measuring device using an interferometry method using two types of light having different wavelengths, in which the light sources of the two types of light have oscillation wavelengths that are different from each other. is provided with a laser generating means that simultaneously oscillates in different TE mode and TM mode, thereby achieving the above object.

The distance measuring device of the present invention preferably includes a laser generating means that simultaneously oscillates in a TE mode and a TM mode having different oscillation wavelengths, and a reference light and a light beam emitted from the laser generating means that irradiates a measurement object. means for branching into
The TE mode light and the T'M mode light contained in the reflected light from the measurement object are respectively interfered with the TE mode light and the TM mode light contained in the reference light to generate TE mode interference light and TM mode interference light. A means for obtaining light, a means for detecting the TE mode interference light and the TM mode interference light, and a phase difference between the TE mode interference light and the TM mode interference light based on the signal output from the detection means. It is equipped with a means to detect.

(Example) The invention will now be described with reference to examples.

FIG. 1 shows an optical system according to an embodiment of the present invention. In this embodiment, the optical system is premised on integration, and optical components are connected by optical waveguides. Semiconductor laser 1
is at a given injection current value.

T E (Transvers) whose oscillation wavelengths are different from each other
e-Electric) mode and T M (Tran
This is a distributed feedback (DFB) laser that simultaneously oscillates in the sverse-magnetic mode. The DFB laser used as the semiconductor laser 1 does not exhibit current-output characteristics as shown in FIG. 2, for example. DFB Rayleigh' is also compared to Fabry-Perot type lasers used in conventional distance measuring devices.

It has the advantage that fluctuations in the oscillation wavelength due to changes in the environment such as temperature are small. The semiconductor laser 1 is.

The laser may be a DFB laser as long as it can oscillate simultaneously in TE mode and TM mode.For example, a distributed reflection (DBR) laser may be used.

The two modes of light emitted from the semiconductor laser 1 are
The light is branched into an emitted light and a reference light at a Y branch portion 2 of the optical waveguide. The emitted light is focused into parallel light beams by the collimator lens 3 and irradiated onto the object to be measured. The reference light is input to the first 'Vl'', -TM mode splitter 4. The reflected light generated when the output light is irradiated onto the measurement object is focused into a parallel beam by the collimator lens 5, and then is input to the T E-TM mode splinter 6 .

The first TE-TM mode splitter 4 splits the incident reference light into a TE wave and a TM wave. The second TE-TM mode splitter 6 splits the incident reflected light into TE waves and TM waves.
It splits into waves. 'rI? , -TM mode sprinter 4
, TE of the reference destination TE wave and reflected light after being demultiplexed by
The waves combine at the Y branch 7 of the optical waveguide and cause interference, resulting in T
The E-wave interference light is incident on the photodiode 8.

Similarly, the reference TM wave and the reflected TM wave are combined at the Y branch 9 of the optical waveguide to cause interference, and are incident on the photodiode 10 as TM wave interference light.

The photodiodes 8 and 10 receive the TE wave interference light and the T
Convert each M-wave interference light into an electrical signal.

The electrical signal is input to the phase difference meter 11. The phase difference meter 11 measures the phase difference between the TE wave interference light and the TM wave interference light based on the input electrical signal.

A phase difference occurs between the reflected light and the reference light corresponding to the optical path difference between the two. Therefore, the TE wave of the reflected light split by the second TETM mode splint 6 has a phase difference between it and the TE wave of the reference light according to the optical path difference. Similarly, the TM wave of the reflected light has a phase difference between it and the reference TM wave according to the optical path difference.

When the TE wave of the reference light and the TE wave of the reflected light interfere, T
The E-wave interference light has a phase θ1 corresponding to the phase difference between the two. Similarly, the TM wave of the reference light and the T wave of the reflected light
The interference with the M wave produces TM wave interference light having a phase difference θ2 corresponding to the phase difference between the two. The phase difference (θ1-θ2) between these two interference lights is measured by two phase difference meters 11.
Detected in As already mentioned, the optical path difference can be found from the phase difference (θ1-θ2). Thus,
The distance from the distance measuring device to the object to be measured is measured.

FIG. 3 is a perspective view of an example of an optical integrated circuit in which the distance measuring device shown in FIG. 1 is integrated.

The substrate 12 is made using L+NbO. The optical waveguide 13 is formed by partially selectively thermally diffusing Ti onto the substrate 12 using a first lithography technique.
It is formed. The TE-TM mode splints 4 and 6 are adjacent parallel optical waveguide portions 13a.

The optical waveguide portion 1 is placed on the optical waveguide portion 13b of the optical waveguide portion 13b.
3b is loaded with aluminum 14 which induces a large negative dielectric constant. In the TE-TM mode splitter 46, loading of aluminum 14 reduces the effective refractive index of the optical waveguide portion 13b for TM waves;
The power transfer rate between the two becomes extremely small. As a result, T
The M wave travels through the optical waveguide portion 13a that is not loaded with aluminum 14, and the TE wave travels through the leading waveguide bone 13b that is loaded with aluminum 14.

A semiconductor laser 1. is mounted on the substrate 12 as described above. Collimator lenses 3, 5 and photodiodes 8.10 are attached. The phase difference meter Il and the connections between it and the photodiodes 8, 10 are not shown in FIG. The operation of the optical integrated circuit shown in Fig. 3 is as follows.

It is similar to the distance measuring device shown in FIG.

Although the embodiments described above are examples of optical integrated circuits or optical systems based on optical integrated circuits, the present invention is also applicable to cases where no integration is performed.

(Effects of the Invention) In the distance measuring device of the present invention, since the necessary light can be obtained with a single laser generating means, not only the number of laser generating means themselves but also the number of required optical parts can be significantly reduced. structure is simplified.

Therefore, the distance measuring device of the present invention is very easy to integrate. When the distance measuring device is integrated, it becomes less susceptible to vibrations, etc., which ensures stable alignment between the components, which has a great effect on stabilizing measurements.In addition, the configuration is simple. When a DFB laser or a DBR laser is used as the laser generating means of the distance measuring device of the present invention, these lasers are used in the conventional distance measuring device. Compared to the Fabry-Perot semiconductor laser, the oscillation wavelength does not change easily due to changes in the environment such as temperature, so stable measurement results can be obtained.

↓-Rule I Of course■ Simple phlegm Kai Figure 1 shows the optical system of one embodiment of the present invention, while Figure 2 shows the characteristics of the DFB laser used in the embodiment of Figure 1.
FIG. 3 is a perspective view of an optical integrated circuit in which the embodiment of FIG. 1 is integrated, and FIG. 4 is a diagram showing a conventional optical system.

DESCRIPTION OF SYMBOLS 1... Semiconductor laser, 2... Y branch part, 4... First TE-TM mode splitter, 6... Second TE
TM mode splitter, 7, 9...Y branch, 8゜1
0...Photodiode, 11...Phase difference meter.

that's all

Claims (1)

[Claims] 1. A distance measuring device using interferometry using two types of light with different wavelengths, the light source of the two types of light being a laser generating means that simultaneously oscillates in a TE mode and a TM mode with different oscillation wavelengths. A distance measuring device.