JPH01119785A - Semiconductor laser distance measuring equipment - Google Patents

Abstract

PURPOSE:To miniaturize an equipment and allow highly accurate distance measurement by providing a semiconductor laser, an oscillator and a synthesizer. CONSTITUTION:Light emitted from a semiconductor laser 1 is incident on an acoustic optical element 3 through a light isolator 2 and divided into diffracted light 12 and transmitted light 13 different in frequency by the frequency of an oscillator 4. The lights are synthesized 5, one output is output by a photodiode 8, the the other output is reflected by a reflecting mirror 7 through a light transmitting and receiving telescope 6 and detected by a photodiode 9 through the telescope 6 again. The signals of the diodes 8, 9 are amplified 10, 10' respectively and the phase differece is detected by a phase difference meter 11. The phase difference corresponds to optical path difference of two optical paths reaching the diodes 9, 10 after being emitted from the synthesizer 5. Therefore, the equipment can be miniaturized and highly accurate distance measurement is enabled.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an optical distance measuring device using a semiconductor laser.

BACKGROUND OF THE INVENTION In recent years, there has been an increasing demand for measuring dimensions and distances in areas of several meters in a short time and with high precision.

Optical distance measuring devices that use light wave interference have become popular recently because of their high resolution.

Conventionally, a distance measuring device has been proposed that utilizes the wavelength of a beat obtained from two modes within one oscillation line of an internal mirror helium neon (He-Ne) laser. He-Nev
- In the case of visible laser (632,8 nm), 15
~30α, 25-36 for infrared laser (1153nm)
Bimodal oscillation occurs when the resonator length is approximately α. And 2
A laser oscillating in modes emits a beat-modulated beam due to the frequency difference between the modes. The beat frequency f at this time is determined by the wavelength of the laser tube, and when the above-mentioned laser tube is used, f is several hundred MH2. In the case of an internal mirror V-ZA that oscillates in two modes, the polarization directions of the modes are orthogonal to each other, so to obtain the beat signal, the polarizer must be moved so that its axes are aligned with each other, as shown in Figure 3. Insert it at an angle of 45 degrees from the polarization direction of the mode. When this modulated wave is detected by a high-speed photodiode, a sine wave signal of several hundred MH2 is obtained.

An outline of a method for measuring distance using such a modulated wave will be explained using FIG. 4. In Figure 4, 40 is 2
mode laser, 41 is a polarizer, 42 is a beam splitter (BS), 43 is a transmitting/receiving telescope, 44 is a reflecting mirror placed at the measurement point, 45 is a photodiode (PDl),
46 is a photodiode (PD2), 47.47 is an amplifier, 48 is a frequency counter, and 49 is a phase difference meter. 2
The light beam emitted from the mode laser 40 passes through a polarizer 41 and enters a beam splitter 42 . One of the two divided beams immediately enters the photodiode (PDI) 45, and the other beam travels back and forth between the reflecting mirror that is the object of distance measurement, and then enters the photodiode (PD2) 46 and is detected. Ru. The optical path difference between these two beams is determined by the signal from the photodiode (, PIh) 45 and the photodiode (P
Since it appears as a phase difference with the signal detected by D2) 46, the distance can be determined from the phase difference between both signals.

Problems to be Solved by the Invention When the beat of the two-mode laser described above is used for distance measurement, it is desired that the beat frequency f be sufficiently accurate. However, even with beat wavelength stabilization, the He-He laser is only stable at about IKHz (±2 x 10-6), which is lower than the modulation frequency stability (1 x
1O-8), actual measurement using frequency was essential. Furthermore, when a gas laser such as a He-No laser is used, there is a drawback that the apparatus becomes large in size.

A means for solving the problem, that is, the present invention, includes a single longitudinal mode semiconductor laser whose oscillation frequency is stabilized, a means for converting the frequency of a part of the output light of the semiconductor laser, and a means for converting the frequency of a part of the output light of the semiconductor laser and the output light of the semiconductor laser. means for combining the frequency-converted output lights of the semiconductor lasers, first detection means for detecting a part of the beat of the two output lights of the combined semiconductor lasers, and a means for combining the two output lights of the combined semiconductor lasers; By having a second detection means for irradiating the object to be measured and detecting the beat of the reflected light, and means for detecting a phase difference between the beat signals of the first detection means and the second detection means. In particular, the above-mentioned problems are solved by using an acousto-optic element as a means for converting the frequency of a part of the output light of a semiconductor laser.

Function The function of the present invention is that the conventional bimodal oscillation gas laser is
A semiconductor laser that oscillates in a single longitudinal mode is replaced by a frequency conversion element such as an acousto-optic element. Frequency conversion of light by an acousto-optic element will be explained using FIG. 2.

In FIG. 2, 21 is incident light, 22 is transmitted light, 23 is diffracted light, 24 is an acousto-optic element, and 25 is an oscillator. f
When light 21 of frequency f is incident on an acousto-optic element driven at a frequency of ). This diffracted light 2
3 and the transmitted light 22 and detect the beat, the difference frequency between the two lights becomes f-. However, this frequency is electrically generated by the oscillator 25 and has a high stability of 1.times.10@-8 or less. Furthermore, the DFB type semiconductor laser that has been reported in recent years has a stable oscillation wavelength and a coherence length of about several tens of meters, and can be used for highly accurate distance measurement in a range of several tens of meters or less.

Example An embodiment of the present invention will be described with reference to FIG.

In FIG. 1, 1 is a DFB type semiconductor laser with an oscillation wavelength of 1.3 μm, 2 is an optical isolator, 3 is an acousto-optic element,
4 is an oscillator, 5 is a 2-manpower x 2-output light combiner, 6 is a telescope for transmitting and receiving light, 7 is a reflector placed at the measurement point, 8 is a photodiode (PD), and 9 is a photodiode. (
PD2), 10°10' is an amplifier, 11 is a phase difference meter, 1
2 is a diffracted light by the acousto-optic element, 13 is a transmitted light of the acousto-optic element, 14 is a mirror, and 15 is a mirror.

The light emitted from the semiconductor laser 1 enters the acousto-optic element 3 via the optical isolator 2 and is divided into diffracted light 12 and transmitted light 13 whose frequencies differ by the frequency of the oscillator 4. These two lights are combined using a combiner 5 such as a directional coupler, one output is outputted by a photodiode 8, and the other output is sent to a reflecting mirror 7 via a transmitting/receiving telescope 6. It is reflected and passes through the transmitting/receiving telescope 6 again to the photodiode 9
Detect with. The signals from the two photodiodes are amplified by amplifiers 10 and 10', respectively, and a phase difference meter 11 detects the phase difference. This phase difference corresponds to the optical path difference between the two optical paths that reach the photodiodes 8 and 9 after leaving the combiner 5. When the acousto-optic element is driven at a frequency of 100 MH2, a phase difference of 2π is obtained for every 3 m of optical path difference. Also, the spectral linewidth is 10
When using a MHz DFB type semiconductor laser, so
A coherence length on the order of m can be obtained and can be used to measure distances on the order of 1 om.

Note that the optical isolator 2 used in the example prevents instability due to the return of light to the semiconductor laser 1, and by using this, more stable measurements can be performed. Further, even if the excavation wavelength of the semiconductor laser to be used is other than 1.3 μm, the effects of the present invention will not be impaired in any way.

Effects of the Invention The present invention has the effect of improving the stability, which was a problem in the prior art, and further making it possible to miniaturize the device due to the above-described configuration. This has the significance of making it possible to easily use a high-precision distance measuring device, and has great industrial significance.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram of a semiconductor laser distance measuring device according to an embodiment of the present invention, Fig. 2 is an explanatory diagram of frequency conversion using an acousto-optic element, and Fig. 3 is an explanatory diagram of gas laser characteristics used in a conventional ranging device. , FIG. 4 is a block diagram of a conventional distance measuring device. 1... Semiconductor laser, 2... Optical isolator, 3... Acousto-optic element, 4...
Oscillator, 5...Synthesizer, 6...Telescope for transmitting and receiving light, 7...Reflector, 8.9...
・Photodiode, 11... Phase difference meter, 12
...Diffracted light, 13...Transmitted light. Name of agent: Patent attorney Toshio Nakao and one other person? I
-Human radiation 922- Transmitted light 23-11 Sight light 24- Acousto-optic element par Emitter No. 21! !

Claims (2)

[Claims] (1) A single longitudinal mode semiconductor laser with a stabilized oscillation frequency, a means for converting the frequency of a part of the output light of the semiconductor laser, and combining the output light of the semiconductor laser and the frequency-converted output light of the semiconductor laser. a first detection means for detecting a part of the beat of the two output lights of the combined semiconductor laser; and a first detection unit that irradiates the object to be measured with the two output lights of the combined semiconductor laser, and detects the reflected light thereof. a second detection means for detecting the beat of the first detection means and the second detection means;
A semiconductor laser ranging device having means for detecting a phase difference of a beat signal with a detecting means. (2) The semiconductor laser distance measuring device according to claim 1, wherein the means for frequency converting a part of the output light of the semiconductor laser uses an acousto-optic element.