JPS5842636B2 - Kouha Heterodyne Souch - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a light wave heterodyne device using a laser.

The light wave heterodyne method takes advantage of the fact that it can receive extremely weak light that is close to the detection limit of a photodetector.
Its application to radar is attracting attention.

When the reflected light from a moving object is received by heterodyne detection, the reflected light undergoes a Doppler shift corresponding to the speed of the moving object and changes its frequency to the high frequency side or the low frequency side.

The amount of frequency shift is 2υν.

It is given by ± (H2).

Here, C is the speed of light and υ is the moving speed of the object ν.

is the frequency of light. Therefore, by receiving the reflected light using the light wave heterodyne method and knowing the frequency difference between the intermediate frequency generated by light mixing and the intermediate frequency preset at υ-0, the moving speed of the object could be determined.

In order to realize this method, the frequency of the transmitting laser must be set in advance to either a higher frequency side or a lower frequency side than that of the local laser.

In order to achieve this setting, the conventional method has been to use a scanning interferometer to observe and adjust the frequency relationship between the transmitting and local lasers. It required a shaped interferometer and special optical equipment, and when it was used, it required complicated operations to align the light wavefronts.

An object of the present invention is to eliminate the drawbacks of the prior art described above, and to provide a light wave heterogain device that can detect the frequency relationship between a transmitting laser and a local laser using a simple device and set the frequency relationship to suit the purpose. It is on offer.

For light wave heterodyne devices, the inventor has already filed a patent application showing that setting the frequency of the transmitting laser near the center frequency of the line profile of the laser medium is an effective method.

Therefore, in order to achieve the above objective, it is sufficient to consider a method for setting the frequency of the local laser to the high frequency side or the low frequency side with respect to the center of the line profile of the laser medium.

The oscillation output of the laser increases or decreases in response to changes in the frequency of the mode in the sloped portion of the line profile, and as shown in FIG. 1, the mode is at the center frequency ν of the line profile.

On the other hand, when the mode is on the low frequency side ν1, the output increases when the mode causes a slight shift to the high frequency side, and when the mode is on the high frequency side ν2 of the line profile, the output decreases.

Therefore, by applying slight frequency modulation to the mode and detecting the phase between the modulation signal and the oscillation output, it is possible to determine whether the mode of the local laser exists on the low frequency side or on the high frequency side with respect to the center frequency of the line profile. It is possible to detect the presence of

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention shown in the drawings will be described in detail below.

FIG. 2 shows an embodiment of the present invention.

In the figure, 1 is a transmitting laser, 2 is a local laser, 3 is an electrostrictive element for finely adjusting the frequency of the local laser, and 4'J
, - and 5 are semi-transparent mirrors, 6 is a square law detector, 7 is a limiter 18a, 8b is an FM discriminator having mutually opposite frequency characteristics, 9 is an operational amplifier, 10 is a DC amplifier, 11 is a wave detector, 12 is a phase detector, 13 is an indicator, 14 is a signal source, 1
5.16 is a circuit changeover switch.

The operation of the embodiment will be described below with reference to the figures.

Laser beams oscillated from the transmitting laser 1 and the local transmitting laser 2 are collected into a single beam by semi-transparent mirrors 4 and 5.
It is guided to a square law detector 6.

The intermediate frequency signal generated by the square law detector is branched into two paths and enters a limiter 7 and a detector 11.

The signal entering the former is generated by the FM discriminator 8a to generate an error signal from the target intermediate frequency, is amplified by the operational amplifier 9 and the DC amplifier 10, and is applied to the electrostrictive element 3 to keep the intermediate frequency constant. A loop is formed for this purpose.

On the other hand, a signal having a lower frequency than the intermediate frequency signal generated by the signal source 14 is superimposed on the error signal by the operational amplifier 9, and serves to slightly fluctuate the oscillation frequency of the local laser.

On the other hand, the intermediate frequency signal is detected by a wave detector 11, and the low frequency signal component is detected by a phase detector 12 to detect the phase difference with the signal from the signal source 14, and after determining whether the signal is in phase or out of phase, is displayed on an indicator. .

Calibrate the indicator display in advance according to the frequency-phase relationship shown in Figure 1, and if it does not match the desired indication when the loop is closed, turn switches 15 and 16 from side A to side B. ) The desired frequency relationship can be achieved by reversing the phase relationship.

As described above, according to the present invention, the frequency relationship between the transmitting laser and the local laser can be determined purely electrically, without the need for complicated operations.

Furthermore, the detector 11, phase detector 12, and
The indicator 13 and the signal source 14 do not need to be built into individual devices, but can be provided as adjustment devices, which has the effect of reducing costs.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram showing the relationship between the frequency and output of laser light,
FIG. 2 is a configuration diagram of an apparatus showing an embodiment of the present invention. Explanation of symbols 1...Transmission laser, 2...Local laser, 3...Piezoelectric element, 4, 5...
・Semi-transparent mirror, 6... Square law detector, 7...
・Limiter, 8a, 8b...FM discriminator, 9・
... operational amplifier, 10 ... direct current amplifier,
11...Detector, 12...Phase detector, 13...Indicator, 14...Signal source,
15, 16... Switch.

Claims (1)

[Claims] I Extracts the FM modulation component from the intermediate frequency signal generated by heterodyne detection of the FM-modulated local laser beam and the unmodulated transmitted laser beam, and determines the phase relationship between the transmitting laser and the local station by knowing the phase relationship with the modulated wave. A light wave heterogain device characterized by setting the frequency relationship of an emitting laser.