KR101828257B1 - Opto-electronic oscillator for distance measurement - Google Patents

Abstract

The present invention can improve the accuracy of the distance measurement by constructing a reference loop capable of grasping the basic loop length of the optoelectronic oscillator, and for measuring the distance, which can solve the problem of reducing the free- And to provide an optoelectronic oscillator.

Description

[0001] OPTO-ELECTRONIC OSCILLATOR FOR DISTANCE MEASUREMENT [0002]

The present invention relates to an optoelectronic oscillator for distance measurement.

An optoelectronic oscillator is composed of a light source, a modulator, and a photo detector. A light beam from a light source passes through the modulator and has a modulated signal. The modulated signal is sent to the photodetector And then generates a positive feedback to the modulator, thereby generating a self-oscillating device. However, in the case of a long distance measurement using an optoelectronic oscillator, since the length of the loop becomes long, the free spectral range is reduced and the measurement accuracy is lowered.

It is an object of the present invention to improve the accuracy of distance measurement by constructing a reference loop capable of grasping the basic loop length of an optoelectronic oscillator and to provide a distance measurement capable of solving the problem of reducing the free- To provide an optoelectronic oscillator.

An optoelectronic oscillator according to an embodiment of the present invention includes: a light source for generating light; An electro-optical modulator for modulating the phase of the light; An optical amplifier for amplifying the phase-modulated light; A half wave plate (HWP) for diffracting the polarized light of the amplified light by 45 degrees; A polarization beam splitter which reflects the vertically polarized light of the 45 degrees diffracted polarized light at 90 degrees and passes the horizontally polarized light; A 1/4 quarter wave plate for converting the 90-degree reflected light into horizontal polarized light; A mirror for reflecting horizontal polarized light having passed through the polarizing beam splitter; A first high-speed optical detector for converting the horizontal polarized light converted by the quarter wave plate into a first electrical signal; A second high-speed optical detector for converting the horizontal polarized light reflected by the mirror into a second electrical signal; A combiner for combining the first and second electrical signals; An amplifier for amplifying the combined electric signal; And a power distributor for distributing the amplified electric signal.

In an embodiment of the present invention, the power divider may perform a positive feedback through the electro-optical modulator, the distributed electric signal being the output signal of the power divider.

The present invention can improve the accuracy of a system by configuring a reference loop capable of grasping the basic loop length of the optoelectronic oscillator, and can solve the problem that the free division range due to the long loop is reduced by the double loop composition.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view showing an example of a general form of an optoelectronic oscillator. FIG.
2 is a block diagram of a double-loop type photoelectric oscillator for distance measurement according to an embodiment of the present invention.
3 is a diagram illustrating a frequency spectrum of a multi-mode operation of an optoelectronic oscillator according to an exemplary embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings, which will be readily apparent to those skilled in the art. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In order to clearly illustrate the present invention, parts not related to the description are omitted, and similar parts are denoted by like reference characters throughout the specification.

Throughout the specification, when a part is referred to as being "connected" to another part, it includes not only "directly connected" but also "electrically connected" with another part in between . Also, when a part is referred to as "including " an element, it does not exclude other elements unless specifically stated otherwise.

Herein, the term " part " or " module " means a unit realized by hardware or software, a unit realized by using both, and a unit realized by using two or more hardware Or two or more units may be realized by one hardware.

Hereinafter, a general form of an optoelectronic oscillator will be described with reference to Fig.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram illustrating an optoelectronic oscillator in a general form for explaining the present invention. FIG.

1, the optoelectronic oscillator is composed of a light source 11, an electro-optic modulator 12, an optical fiber 13, a high-speed photodetector 14, an amplifier 15 and a power distributor 16.

As the light beam from the light source passes through the electro-optic modulator, the phase is modulated and the modulated signal is detected by the high-speed photodetector. The signal is amplified in the amplifier and then fed back to the electro-optic modulator. An interference signal is generated between the newly generated phase modulated signal and the looped phase modulated signal in the electro-optical modulator, and only a specific frequency component is generated due to constructive interference and destructive interference.

The boundary condition due to the accumulated phase is expressed by Equation (1).

은 광경로에서의 마이크로파 파수,

는 전기경로에서의 마이크로파 파수를 가리킨다.

은 광경로,

는 전기경로를 가리킨다.

은 정수로

번째 발진 모드를 가리킨다. 수학식 1을 정리하면 광전자 발진기에서 발진 주파수를 수학식 2와 같이 구할 수 있다.In Equation (1)

Is the wave number of the microwave in the optical path,

Quot; refers to the number of microwave waves in the electric path.

A light path,

Indicates an electrical path.

Is an integer

Lt; th > oscillation mode. The oscillation frequency of the optoelectronic oscillator can be obtained as shown in Equation (2).

는 광경로에서의 굴절률,

는 전기경로에서의 굴절률을 가리킨다. 수학식 2에서 자유분광범위(free spectral range, FSR)(

)는 수학식 3과 같이 주어진다. 여기서, c는 광선의 속도를 나타낸다.In the above equation,

The refractive index in the optical path,

Indicates the refractive index in the electric path. In Equation 2, the free spectral range (FSR) (

) Is given by Equation (3). Here, c represents the speed of the light beam.

Equation (3) can be expressed from another viewpoint as shown in Equation (4).

Precise measurement of the free-division range, as in the above equation, allows precise calculation of the overall loop length of the optoelectronic oscillator. Here, except for the electric path, information on the optical path can be obtained. The oscillation frequency can be confirmed through the power distributor 16. By inserting the optical fiber 13 in the middle of the optical path, the length of the loop increased by the optical fiber can be measured.

Hereinafter, the contents of the invention will be described in detail with reference to the accompanying drawings.

2, in order to precisely measure the distance by using an optoelectronic oscillator.

2 is a block diagram of a double-loop type photoelectric oscillator for distance measurement according to an embodiment of the present invention.

As shown in FIG. 2, in the dual loop type photoelectric oscillator for distance measurement according to the embodiment of the present invention,

A light source 21 for generating light (light rays)

An electro-optical modulator 22 for modulating the phase of the light,

An optical amplifier 23 for amplifying the phase-modulated light,

A half wave plate (HWP) 24 for diffracting the polarized light of the amplified light by 45 degrees,

A polarized beam splitter 27 for reflecting vertically polarized light of 45 degrees diffracted by 90 degrees and passing the horizontally polarized light,

A 1/4 quarter wave plate 25 for converting the 90-degree reflected light into horizontally polarized light,

A target mirror 26 for reflecting the horizontal polarized light having passed through the polarized beam splitter 27,

A first photo detector (FPD1) for converting the horizontal polarized light converted by the quarter wave plate 25 into a first electric signal,

A second high-speed optical detector 28 for converting the horizontal polarized light reflected by the target mirror 26 into a second electrical signal,

A power combiner 29 for combining the first and second electrical signals,

An amplifier 210 for amplifying the combined electrical signal, and

And a power distributor 211 for distributing the amplified electric signal.

The power splitter 211 returns its power splitter output signal (distributed electrical signal) back through the electro-optical modulator 22 in a positive manner. The reflective coated QWP 25 is coupled to the polarizing beam splitter 27 via optical bonding. The polarizing beam splitter 27 may comprise the reflective coated QWP 25 integrally.

First, the light beam from the light source 21 is modulated in phase while passing through an electro-optic modulator (EOM) 22, and is amplified to a high light beam power while passing through the optical amplifier 23.

The polarization of the light beam is turned 45 degrees by a half wave plate (HWP), and the vertical polarization is reflected at 90 degrees and the horizontal polarization is passed through a polarization beam splitter (PBS).

The light beam reflected at 90 degrees passes through a quarter-wave plate (QWP) with its back surface coated with a reflective coating, and is then reflected back into horizontal polarized light. After passing through the polarizing beam splitter, it is detected by a fast photo diode (FPD1) and then converted into an electric signal. The signal passes through a power combiner (PC), amplified by an amplifier, and then passed through a power splitter (PS). The power divider output signal is again positive feedback through the electro-optical modulator.

The reflective coated QWP couples to the polarizing beam splitter through optical bonding.

If the power of the light beam is sufficient and the gain is sufficiently given by the amplifier, the frequency component satisfying the phase condition as shown in Equation (1) oscillates by the signal detected by the FPD1. At this time, the free spread range of the loop is expressed by Equation (5).

정도이므로 10 m 루프 길이에 대한 정밀도는

이다. 여기에 q번째로 떨어진 모드끼리의 주파수 차를 이용할 경우 그 이상의 정밀도를 얻을 수 있다.In order to precisely measure the free-division range, the optoelectronic oscillator is operated in multi-mode as shown at 31 in FIG. For example, if the length of the loop is 10 m, the free spectral range is 30 MHz. In order to increase the measurement accuracy, the frequency difference between the q-th mode that is apart from the frequency difference between the closest modes is compared. For example, the Allan deviation of the optoelectronic oscillator is

, The accuracy for 10 m loop length is

to be. If the frequency difference between the q-th mode and the q-th mode is used, more accuracy can be obtained.

Next, the polarized light beam passing through the HWP 24 passes through the polarization beam splitter 27 and then passes through the QWP 25 as described above. And the light beam travels back to the target mirror 26, which lies at the far point to be measured. After passing through the QWP 25 twice, the horizontally polarized light is converted into vertical polarized light, reflected by the polarized beam splitter 27, and detected by the FPD2 28. The FPD2 28 converts the detected signal into an electrical signal and the converted electrical signal passes through the power combiner 29 and the amplifier 210 and the power divider 211 to the optical modulator 22 with a positive feedback do.

The frequency component satisfying the phase condition as shown in Equation (1) oscillates. At this time, the free distribution range of the loop is expressed by Equation (6).

는 정밀하게 측정한 값이고, 자유분광범위를 정밀하게 측정하면 목표 지점까지의 거리에 해당하는

을 정밀하게 측정할 수 있다. 예를 들어, 목표 거울(26)까지의 거리가 1 km라고 하면 자유분광범위는 30kHz에 해당하고, 앨런 편차(Allan deviation)가

정도라고 하면

의 정밀도로 측정할 수 있다. 이를 위해 도 3의 도면부호 32와 같이 광전자 발진기를 다중 모드로 동작시킨 후 모드 간 주파수를 측정한다.In the above equation,

Is a precisely measured value, and when precisely measuring free-range broad-spectrum, it corresponds to the distance to the target point

Can be accurately measured. For example, if the distance to the target mirror 26 is 1 km, the free division range corresponds to 30 kHz, and the Allan deviation

If you say about

Can be measured with accuracy of. To do this, the optoelectronic oscillator is operated in multi-mode as shown by reference numeral 32 in FIG. 3, and the frequency between modes is measured.

까지 올라간다. 이를 수학식으로 나타내면 수학식 7과 같다.3, it is possible to oscillate only a specific mode under the condition of reinforcement and cancellation between two loops through a double loop. By measuring the frequency between modes, the length of the long loop due to the target mirror can be precisely measured at the free-spread range frequency by the short loop. For example, a short loop of 10 m and a long loop of 1 km are simultaneously implemented. Figure 3 shows the operation of the optoelectronic oscillator in a dual mode by a dual loop (33). The measurement of the free spectral range corresponds to 30 MHz and contains 100 modes by 1 km.

Up. This can be expressed by Equation (7).

If the frequency difference between the two modes is obtained, Equation (8) is obtained.

As described above, the present invention can improve the accuracy of the system by constructing a reference loop capable of grasping the basic loop length of the optoelectronic oscillator, and can solve the problem of the free loosening due to a long loop in a double loop composition have.

It will be understood by those skilled in the art that the foregoing description of the present invention is for illustrative purposes only and that those of ordinary skill in the art can readily understand that various changes and modifications may be made without departing from the spirit or essential characteristics of the present invention. will be. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive. For example, each component described as a single entity may be distributed and implemented, and components described as being distributed may also be implemented in a combined form.

The scope of the present invention is defined by the appended claims rather than the detailed description and all changes or modifications derived from the meaning and scope of the claims and their equivalents are to be construed as being included within the scope of the present invention do.

Claims (6)

A dual-loop type photo-electron oscillator for measuring a distance, comprising a reference loop capable of grasping a basic loop length of an opto-electronic oscillator, the opto-electronic oscillator comprising:
A light source for generating light;
An electro-optical modulator for modulating the phase of the light;
An optical amplifier for amplifying the phase-modulated light;
A half wave plate (HWP) for diffracting the polarized light of the amplified light by 45 degrees;
A polarization beam splitter which reflects the vertically polarized light of the 45 degrees diffracted polarized light at 90 degrees and passes the horizontally polarized light;
A 1/4 quarter wave plate for converting the 90-degree reflected light into horizontal polarized light;
A mirror for reflecting horizontal polarized light having passed through the polarizing beam splitter;
A first high-speed optical detector for converting the horizontal polarized light converted by the quarter wave plate into a first electrical signal;
A second high-speed optical detector for converting the horizontal polarized light reflected by the mirror into a second electrical signal;
A combiner for combining the first and second electrical signals;
An amplifier for amplifying the combined electric signal;
And a power divider for distributing the amplified electrical signal,
Wherein the polarizing beam splitter separates the path of light into two. The power splitter of claim 1,
And a positive feedback is performed through the electro-optical modulator, the distributed electrical signal being an output signal of the power divider. The optoelectronic oscillator of claim 1, wherein the quarter wave plate is a quarter-wave plate with a reflective coating. 4. The optoelectronic oscillator of claim 3, wherein the quarter wave plate is coupled to the polarizing beam splitter via optical bonding. delete The optoelectronic oscillator of claim 1, wherein the optoelectronic oscillator operates in multiple modes to measure the distance.

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