JP2750903B2 - Orthogonal polarization type optical frequency shifter - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an orthogonal polarization type optical frequency shifter used for optical heterodyne measurement.

2. Description of the Related Art Conventionally, as this kind of orthogonal polarization type optical frequency shift, one shown in FIG. 5 as disclosed in Japanese Patent Application Laid-Open No. 61-169820 is known.

Referring to FIG. 5, a conventional orthogonal polarization type optical frequency shifter is a He-Ne gas laser which emits a laser beam 102 which is a linearly polarized light having a frequency f ₀ and an electric field component of 45 degrees with respect to the paper surface. It has 101. The laser light 102 emitted from the He-Ne gas laser 101 enters the first polarizing beam splitter 103 as incident laser light, where it is linearly polarized light having a horizontal electric field component (hereinafter abbreviated as P-polarized light). ) And reflected laser light 105 which is linearly polarized light (hereinafter abbreviated as S-polarized light) having an electric field component perpendicular to the plane of the drawing. That is, the first polarization beam splitter 103 includes the incident laser light and the transmitted laser light 104
And a reflected laser beam 105.
Transmitted laser beam 104 is incident in a compatible angle (Bragg angle) theta _B to the Bragg condition to the first acousto-optic device 106. The first transducer 1 includes a first transducer 1
The first transducer 108 is excited by a first high frequency signal from the first drive circuit 107, for example, having a center frequency of 80 MHz. Thus, the medium body of the first acousto-optic device 106, the first ultrasonic signal having a wavefront forming the Bragg angle theta _B with respect to the rectilinear direction of the transmitted laser beam 104 propagates. The transmitted laser light 104 incident on the first acousto-optical element 106, in which the first ultrasonic signal propagates, has a Bragg angle θ _{B with} respect to the 0th-order diffracted light that goes straight here and the wavefront of the first ultrasonic signal. Diffracted by 1
The light is split into the next order diffracted light 110 and emitted from the first acousto-optic element 106. Here, the first-order diffracted light 110 is used. Since the first-order diffracted light 110 has a frequency f ₀ shifted up by 80 MHz which is the center frequency of the first ultrasonic signal propagating through the first acousto-optic element 106, the frequency is f ₀ +80 MHz. Therefore, this first-order diffracted light 110
Is referred to herein as the first shifted up laser light. The first shifted laser light 110
Is reflected by the first mirror 111 and its trajectory is 90
After being changed by degrees, the light enters the second polarization beam splitter 112. The second polarization beam splitter 112 has a property of transmitting P-polarized light and reflecting S-polarized light. As described above, the first shifted-up laser beam 110 is P-polarized, and therefore transmits through the second polarization beam splitter 112.

On the other hand, the reflected laser beam 105 reflected by the first polarizing beam splitter 103 is reflected by the second mirror 113, and its trajectory is changed by 90 degrees, and then the second acousto-optic element 114 meets the Bragg condition. angle (Bragg angle) incident at theta _B. A second transducer 116 is attached to the second acousto-optic element 114, and the second transducer 116 is 1 MHz lower than the first high-frequency signal from the second drive circuit 115, for example, a center frequency of 79 MHz. The second with
Is excited by the high-frequency signal. Thus, the medium body of the second acousto-optic device 114, as in the case of the first acoustooptic device 106 described above, with a wavefront forming the Bragg angle theta _B with respect to the rectilinear direction of the reflected laser beam 105 A second ultrasonic signal propagates. The reflected laser beam 105 incident on the second acousto-optic element 114 in which the second ultrasonic signal propagates
, Similar to that described above, wherein divided into first-order diffracted light 117 is diffracted at the Bragg angle theta _B relative to the wavefront of the zero-order diffracted light and the second ultrasonic signal travels straight, the second acousto-optic device 114 Is emitted. Here, the first-order diffracted light 117 is used.
This first-order diffracted light 117 has a frequency f ₀ shifted up by 79 MHz, which is the center frequency of the second ultrasonic signal propagating through the second acousto-optic element 114, so that the frequency is f ₀ +79 MHz. Therefore, this first-order diffracted light 1
17 is referred to herein as the second shifted up laser light. This second shifted laser light 110
Is incident on the second polarizing beam splitter 112, but is S-polarized as described above, and is reflected by the second polarizing beam splitter 112. The second shifted laser beam 110 reflected by the second polarization beam splitter 112 is transmitted along the first shifted laser beam 110 passing through the second polarization beam splitter 112 on the same optical path. From the second polarizing beam splitter 112. That is, the second polarization beam splitter 112 emits orthogonal two-frequency laser light having polarization planes orthogonal to each other and a frequency difference of 1 MHz as emission laser light. In other words, the second polarization beam splitter 112 acts as an optical coupler that combines the first shifted up laser light 110 and the second shifted up laser light 110.

[Problems to be Solved by the Invention] In an orthogonal dual-frequency light source for optical heterodyne measurement, an orthogonal 2
Since the deviation of the optical axis of the high-frequency laser light affects the measurement accuracy,
The parallelism of the optical axis must be within 120 micro radians (24 seconds). However, in the conventional orthogonal polarization type optical frequency shifter, since each optical element is composed of a separate optical component, in order to accurately combine orthogonal two-frequency laser light on the same optical path, each optical component is It is necessary to fine-tune the position. Since this position adjusting mechanism must be provided for each of the optical components, there is a disadvantage that the apparatus becomes large. Furthermore, since the conventional orthogonal polarization type optical frequency shifter is configured by combining a number of optical components such as a polarization beam splitter, an acousto-optic device, and a mirror, the cost becomes high and the input / output end face of each optical component is increased. Orthogonal 2 emitted for surface reflection at
There is a disadvantage that the loss of the high frequency laser light is large.

Accordingly, an object of the present invention is to provide a small orthogonal polarization type optical frequency shifter which does not require position adjustment for combining orthogonal two-frequency laser beams on the same optical path.

It is another object of the present invention to provide an inexpensive orthogonal polarization type optical frequency shifter with few components.

Still another object of the present invention is to provide an orthogonal polarization type optical frequency shifter capable of obtaining low-loss orthogonal two-frequency laser light with little surface reflection at an end face.

[Means for Solving the Problems] An orthogonal polarization type optical frequency shifter to which the present invention is applied includes an incident light having a predetermined incident frequency and including first and second linearly polarized light having electric field components orthogonal to each other. An orthogonal polarization type optical frequency shifter that receives laser light and emits outgoing laser light having frequencies shifted by first and second frequencies having a predetermined frequency difference from the incident frequency.
According to the present invention, the orthogonal polarization type optical frequency shifter has a bottom surface, a top surface, and two side surfaces, respectively, and the first and second bottom surfaces are opposed to each other and arranged close to each other.
Acousto-optic medium. The two side surfaces near the bottom surface of the second acousto-optic medium are provided with an incident surface for receiving the incident laser light and an emission surface for emitting the emitted laser light, respectively. . The orthogonal polarization type optical frequency shifter according to the present invention, wherein the incident surface is provided between the bottom surfaces of the first and second acousto-optic media in contact with the bottom surface and near the incident surface. A light separating unit that transmits the first linearly polarized light as transmitted laser light and reflects the second linearly polarized light as reflected laser light, and the transmitted laser light is Proceeding along one of the two side surfaces of the first acousto-optic medium, being reflected at the top surface of the first acousto-optic medium and traveling along the other of the two side surfaces of the first acousto-optic medium A first shift unit that outputs a first shifted laser beam with the incident frequency of the transmitted laser beam being the first frequency shift, and the reflected laser beam is a second acousto-optic medium. Along one of the two sides While traveling along the other of the two side surfaces of the second acousto-optic medium while being reflected at the upper surface of the second acousto-optic medium, changing the incident frequency of the reflected laser light to the second A second shift means for outputting a second shifted laser beam by shifting the frequency of the first and second acousto-optic media, in a state in contact with the bottom surface, and And an optical coupling means provided near the emission surface for coupling the first and second shifted laser lights and emitting the combined laser light as the emission laser light from the emission surface.

[Operation] The orthogonal polarization type optical frequency shifter according to the present invention has first and second acousto-optic media, and has a first and a second acousto-optic medium sandwiched between a bottom surface thereof and an optical separation unit and an optical coupling unit. Since the orthogonal polarization type optical frequency shifter has an integral structure using the upper surface of the acousto-optic medium as a reflection means, there is no need for position adjustment for combining orthogonal two-frequency laser light emitted therefrom on the same optical path. ,
It is possible to obtain a quadrature two-frequency laser beam that is small, has few components, is inexpensive, has little surface reflection at the end face, and has low loss.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a sectional view showing an orthogonal polarization type optical frequency shifter according to one embodiment of the present invention.

The orthogonal polarization type optical frequency shifter of the illustrated embodiment includes He.
Has a predetermined incident frequency f ₀ which is emitted from -Ne gas laser 13 and the laser beam receiving the incident laser beam 14 comprising first and second linearly polarized light having an electric field components perpendicular to each other, than the incident frequency f ₀ The emitted laser beam has a frequency shifted by the first and second frequencies f ₁ and f _{2 having a} predetermined frequency difference Δf from each other. Here, it is assumed that the first linearly polarized light is linearly polarized light (P-polarized light) having an electric field component horizontal to the paper surface, and the second linearly polarized light is linearly polarized light (S-polarized light) having an electric field component perpendicular to the paper surface. Suppose there is.

The orthogonal polarization type optical frequency shifter has a bottom surface 29, a top surface 7,
A first acousto-optic medium 1 having a trapezoidal cross section having two slopes 30 and 31, similarly a bottom surface 32, a top surface 8, and two slopes 3
And a second acousto-optic medium 2 having a trapezoidal cross section having 3,34, and these are arranged with their bottom surfaces 29,33 facing each other and close to each other.

Two slopes 33, 3 near the bottom surface 32 of the second acousto-optic medium
4 is provided with an incident surface 11 for entering the incident laser light 14 and an emission surface 12 for emitting the emitted laser light, respectively. Each of the entrance surface 11 and the exit surface 12 is a non-reflective film made of a dielectric multilayer film.

Between the bottom surfaces 29 and 32 of the first and second acousto-optical media 1 and 2 and in contact with the bottom surfaces 29 and 32, and near the incident surface 11, an optical separator 9 as a first polarizing film is provided. Is provided. The light separator 9 transmits the first linearly polarized light (P-polarized light) as the transmitted laser light 15 and converts the second linearly polarized light (S-polarized light) out of the incident laser light 14 incident through the incident surface 11. It is reflected as reflected laser light 16.

The transmitted laser light 15 travels along one of the two slopes 30 of the first acousto-optic medium 1, is totally reflected by the upper surface 7 of the first acousto-optic medium 1, and While traveling along the other 31 of the two slopes, during this time, the incident frequency f ₀ of the transmitted laser light 15 is changed by a first frequency shifter described later.
Are shifted by a _first frequency f ₁ . The first frequency shifter outputs a first shifted laser beam having a first frequency f ₁ shifted frequency to the incident frequency f _0. The first frequency shifter of the present embodiment includes a first transducer 3 mounted on a slope 30 and
And a first acousto-optic medium 1 for supplying a first high-frequency signal of a first frequency f ₁ to the transducer 3.

On the other hand, the reflected laser light 16
Traveling along one of the two slopes 33, the second acousto-optic medium 2
Is totally reflected by the upper surface 8 of the second acousto-optic medium 2 and travels along the other of the two slopes 34 of the second acousto-optic medium 2.
The incident frequency f ₀ of the reflected laser light 16 is shifted by the second frequency f _{2 by} the frequency shifter of (1). This second frequency shifter has a second frequency f _{2 with} respect to the incident frequency f ₀ .
And outputting a second shifted laser beam having the shifted frequency. The second frequency shifter of the present embodiment has a slope
A second transducer 4 attached to 33, for supplying a first of the second high-frequency signal having a predetermined frequency difference by different second frequency f ₂ to the frequency f ₁ to the second transducer 4 It is constituted by a combination of the second drive circuit 6 and the second acousto-optic medium 2.

Between the bottom surfaces 29 and 32 of the first and second acousto-optic media 1 and 2 and in contact with the bottom surfaces 29 and 32 and near the exit surface 12, an optical coupler 10 serving as a second polarizing film is provided. Is provided. The optical coupler 10 combines the first and second shifted laser lights 18 and 20 to form the combined laser lights 18 ′ and 18 ′.
20 'is emitted from the emission surface 12 as emission laser light.

At the center of the bottom surface 29 of the first acousto-optic medium 1, the bottom surface 29
Has a nonparallel surface inclined at, for example, 5 degrees, and is excited by the first transducer 3 to absorb the first ultrasonic wave transmitted through the first acousto-optic medium 1.
Recess 35 is formed. Similarly, the central portion of the bottom surface 32 of the second acousto-optic medium 2 has a non-parallel surface inclined at, for example, 5 degrees with respect to the bottom surface 32, and the second transducer 4
The second concave portion 36 for absorbing the second ultrasonic wave excited by the second acoustic wave medium 2 and propagated in the second acousto-optic medium 2 is formed. By disposing a heat conductive adhesive or a metal plate (not shown) between the concave portions 35 and 36, a heat radiation effect can be obtained.

Next, a more detailed configuration and manufacturing method of the orthogonal polarization type optical frequency shift shown in FIG. 1 will be described with reference to FIG.

Each of the first and second acousto-optic media 1 and 2 is, for example, a trapezoidal prism of an acousto-optic medium made of tetral glass. Bottom surfaces of first and second acousto-optic media 1 and 2
When the surfaces 29 and 32 are symmetrical, the upper surface 7 of the first acousto-optic medium 1 and the upper surface 8 of the second acousto-optic medium 2 are plane-symmetric. That is, the bottom surface 29 and the top surface 7 of the first acousto-optic medium 1
Distance h _1, are equal to each other the distance h ₂ between the second bottom surface 32 and the top surface 8 of the acoustooptic medium 2 between. Further, the slope 30 of the first acousto-optic medium 1 on which the first transducer 3 is mounted and the slope 33 of the second acousto-optic medium 2 on which the second transducer 4 is mounted also have a plane-symmetric relationship. That is,
Angle α between bottom surface 29 and slope 30 of first acousto-optic medium 1
_1, are equal to each other an angle alpha ₂ of the second bottom surface 32 and inclined surface 33 of the acoustic-optic medium 2. In the present embodiment, the angles α ₁ and α ₂ are selected to be 45 degrees.

When the first acousto-optic medium 1 and the second acousto-optic medium 2 are separately manufactured, it is difficult to satisfy the above-described conditions, but by manufacturing as follows, the acousto-optic medium having a predetermined shape is manufactured. Can be obtained.

That is, as shown in FIG. 3 (a), a trapezoidal prism 39 having a thickness of 2n (n is a natural number) is polished to a predetermined shape by polishing, and then shown in FIG. 3 (b). 1 and 2 by cutting to a predetermined thickness.
Predetermined acousto-optic media 40, 41, 42 and the like, such as the first and second acousto-optic media 1 and 2 shown in the figure, can be easily manufactured.

Next, near the bottom surface 32 of the slopes 33, 34 of the second acousto-optic medium 2, anti-reflection films 11, 12 made of a dielectric multilayer film are provided, respectively.
To form On a slope 30 of the first acousto-optic medium 1, a first transducer 3 including a lower electrode 23 made of, for example, tin, a piezoelectric element 24 made of, for example, lithium niobate, and an upper electrode 25 made of, for example, gold is provided. Attach. Similarly, on the inclined surface 33 of the second acousto-optic medium 2, the lower electrode 26,
The second transducer 4 including the piezoelectric element 27 and the upper electrode 28 is mounted. First and second polarizing films 9 and 10 made of a dielectric multilayer film are respectively provided at positions corresponding to the anti-reflection films 11 and 12 on the bottom surface 32 of the second acousto-optic medium 2 by, for example, a vacuum evaporation method. Form. Next, the bottom surface 29 of the first acousto-optic medium 1 thus formed and the bottom surface 32 of the second acousto-optic medium 2 are placed so that the slopes 30 and 33 to which the transducers 3 and 4 are attached are adjacent to each other. Then, by bonding using an optical adhesive, the first and second polarizing films 9, 10 and the first and second acousto-optical media 1, 2 as shown in FIG. An integrated, orthogonally polarized optical frequency shifter is manufactured.

Next, the operation of the orthogonal polarization type optical frequency shifter according to the present embodiment will be described with reference to FIG.

Laser beam 14 emitted from the He-Ne gas laser 13, the wavelength is 633 nanometers, incident frequency f ₀ is has 474THz,
This is linearly polarized light having an azimuth of 45 degrees with respect to the paper surface. This laser light 14 passes through the incident surface 11 of the anti-reflection film and the second acousto-optic medium 2, and the first and second acousto-optic media 1 and 2
Incident on the first polarizing film 9 provided between the bonding surfaces (bottom surfaces 29, 32) and having a polarization separation function. The first polarizing film (light separator) 9 transmits the P-polarized light as the transmitted laser light 15 and reflects the S-polarized light as the reflected laser light 16 of the incident laser light to separate the incident laser light into two laser lights. I do.

In this case, the transmitted laser beam 15 (P-polarized light of the incident laser beam 14), from the first driving circuit 5, for example, first the first frequency f ₁ is excited by the first high-frequency signal of 80MHz The laser beam is emitted from the He-Ne gas laser 13 by the transducer 3 so as to enter the wavefront of the first ultrasonic signal 37 propagating in the first acousto-optic medium 1 at a Bragg angle θ _B1. 14 enter the second acousto-optic medium 2. Thereby, the transmitted laser light (P-polarized light) 15
Zero-order diffracted light 17 that is black-diffractive at the wavefront of the first ultrasonic signal 37 propagating in the first acousto-optic medium 1 and travels straight
And 1 which is reflected at an angle 2θ _B1 with respect to the transmitted laser light 15
It is separated into the next diffraction light 18. In this embodiment, the first-order diffracted light 18
Use The first-order diffracted light 18 has a frequency obtained by shifting up the incident frequency f ₀ of the transmitted laser light 15 by the first frequency f ₁ (= 80 MHz) which is the driving frequency of the first acousto-optic medium 1, that is, f _0. Has + 80MHz. Therefore, the first-order diffracted light 18 is called the first shifted laser light. The first shifted laser light 18 is totally reflected by the upper surface 7 of the first acousto-optic medium 1 having a surface of about 45 degrees with respect to the
Through the second polarizing film (optical coupler) 10 provided between the bonding surfaces (bottom surfaces 29, 32) of the acousto-optic media 1 and 2 and the second acousto-optic medium 2 and the second anti-reflection film And is emitted as a first emission laser light (P-polarized light) 18 '.

On the other hand, the reflected laser light (S-polarized light of the laser light 14) 16 reflected by the first polarizing film (light separator) 9 is transmitted to the second transducer 4 from the second drive circuit 6, for example, by the second driving circuit 6. frequency f ₂ is incident at the Bragg angle theta _B1 against the wavefront of the second ultrasonic signal 38 that propagates through the second acousto-optic medium within 2 by supplying the second high-frequency signal of 79.9MHz. At this time, although the reflected laser beam 16 does not strictly satisfy the Bragg condition for the second ultrasonic signal 38,
Since the frequency f ₁ and the second frequency f ₂ are similar, practically, it can be considered to be satisfied almost Bragg condition. The reflected laser light (S-polarized light) 16 is black-diffractive at the wavefront of the second ultrasonic signal 38 propagating in the second acousto-optic medium 2, and has an angle 2θ with respect to the zero-order diffracted light 19 and the reflected laser light 16. _The light is separated into first-order diffracted light 20 reflected by _B2 . In this embodiment, the first-order diffracted light 20 is used. here,
The first-order diffracted light 20 has a frequency obtained by shifting up the incident frequency f ₀ of the reflected laser light (S-polarized light) 16 by the second frequency f ₂ (= 79.9 MHz) which is the driving frequency of the second acousto-optic medium 2. That is, it has f ₀ +79.9 MHz. Therefore, the first-order diffracted light 20 is called a second shifted up laser light. The second shifted laser light 20 is totally reflected by the upper surface 8 of the second acousto-optic medium 2 at an angle of about 45 degrees with respect to the laser light 20, and then the second polarizing film (optical coupler) 10), passes through the second acousto-optic medium 2 and the exit surface 12, which is a second non-reflective film, and exits as a second exit laser beam (S-polarized) 20 '. The second outgoing laser light 20 'and the first outgoing laser light 18' are combined on substantially the same optical path and emitted as orthogonal two-frequency laser light having a frequency difference of 0.1 MHz.

Here, the angle Δθ between the first outgoing laser beam (P-polarized) 18 ′ and the second outgoing laser beam (S-polarized) 20 ′ of the outgoing two-frequency laser beam is given by the following equation. .

Δθ = 2 (θ _B1 −θ _B2 ) As described above, the first and second transducers 3 and 4 of the first acousto-optic medium 1 and the second acousto-optic medium 2 are attached thereto. Slope 30, 33, and upper surface 7,
8 are the first and second acousto-optic media 1 and 2 respectively.
Are symmetrical with respect to the bonding surface (bottom surfaces 29, 32) of the first and second emission laser beams (P-polarized light) 18 'and the second emitted laser light (S-polarized light) 20' on the same plane. There, both the angle Δθ of is equal to the twice of the difference between the first acousto-optic medium 1 of the black angle theta _B1 and second Bragg angle theta _B2 of the acoustooptic medium 2. Therefore, the first emission laser light (P-polarized light)
Strictly speaking, 18 'and the second emitted laser beam (S-polarized light) 20' do not propagate on the same optical path. However, the wavelength of the laser beam 14 emitted from the He-Ne gas laser 13 is 633 nanometers, and each of the first and second acousto-optical media 1 and 2 is, for example, tellurite glass manufactured by Hoya Corporation. AOT
When -5 is used, the relationship between the driving frequency and the black angle is approximately 182 micro radians / MHz, so that when the frequency difference Δf = 0.1 MHz, Δθ = 18.2 μm.
Radian (about 4 seconds), which is practically negligible.

As a method of evaluating the superposition of the orthogonal two-frequency laser light by the optical frequency shifter, the degree of modulation of the optical beat obtained by synthesizing the two frequency components with the polarizer set at an azimuth of 45 degrees with respect to the orthogonal two-frequency laser light is used. There is evaluation. According to this, it is generally found that a modulation degree of 95% or more is sufficient.

Referring to FIG. 4, the beam diameter of the laser light used is
In the case of 1 mm or less, there is a relationship between Δθ and the modulation factor γ as shown in FIG.
There is no practical problem up to a radian, that is, a frequency difference of about Δf = 0.71 MHz.

In this embodiment, a He-Ne gas laser is used as the laser light source, but a gas laser other than the He-Ne gas laser, a semiconductor laser, a dye laser, a solid-state laser, or the like may be used.
Further, the acousto-optic medium is not limited to tellurite glass, but may be another glass. Even in the case of an optical crystal, it can be used by appropriately setting the direction of the crystal axis. The drive frequency of the acousto-optic medium is not limited to 80 MHz and 79.9 MHz, but may be, for example, 60 MHz and 60.1 MHz. The method for manufacturing the acousto-optic medium is not limited to the above-described method using polishing, but may be, for example, a method using a glass mold. Also, the upper surface 7 of the first acousto-optic medium 1 and the upper surface 8 of the second acousto-optic medium 2 need not necessarily be plane-symmetric. Further, the first and second transducers 3 and 4 are provided on the slopes 3 of the first and second acousto-optic media 1 and 2, respectively.
1, 34 may be provided. In the embodiment, since the first and second acousto-optical media 1 and 2 have the same shape, the outgoing light 1
Slight displacement on the optical axis of 8 ', 20' or displacement of the incident angle with respect to the ultrasonic signal propagating to each medium occurred, but if not limited to the same shape, the slope on which the transducer was disposed, Alternatively, the above-described deviation can be resolved by appropriately selecting the inclination angle of the upper surface. In the above-described embodiment, the first and second acousto-optic media have a trapezoidal cross section having a bottom surface, a top surface, and two slopes, respectively. May be provided.

[Effects of the Invention] As is apparent from the above description, according to the present invention, the polarization beam splitter and the mirror, which are conventionally provided separately, can be eliminated, and the orthogonal two-frequency laser light is combined on the same optical path. Therefore, it is possible to provide an orthogonal polarization type optical frequency shifter that does not require a position adjustment mechanism for obtaining a low-cost, small-size, low-loss orthogonal two-frequency laser light.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an orthogonal polarization type optical frequency shifter according to an embodiment of the present invention, and FIG. 2 is a cross section for explaining a detailed configuration and a manufacturing method of the orthogonal polarization type optical frequency shifter of FIG. FIG. 3 is a perspective view for explaining a method for manufacturing an acousto-optic medium used in the orthogonal polarization type optical frequency shifter of the present invention, and FIG. 4 is a perspective view showing orthogonal light emitted from the orthogonal polarization type optical frequency shifter. FIG. 5 is a diagram showing a relationship between an angle Δθ formed by a two-frequency laser beam and a modulation factor γ, and FIG. 5 is a sectional view showing a conventional orthogonal polarization type optical frequency shifter. 1,2: acousto-optic medium, 3,4: transducer, 5,6
...... Drive circuit, 7,8 ... Top surface (total reflection surface) of acousto-optic medium, 9,10 ... Polarizing film.

Claims (1)

(57) [Claims] An incident laser beam having a predetermined incident frequency and including first and second linearly polarized lights having electric field components orthogonal to each other is received, and first and second laser beams having a predetermined frequency difference from the incident frequency are received. An orthogonal polarization type optical frequency shifter that emits outgoing laser light having a frequency shifted by a second frequency has a bottom surface, a top surface, and two side surfaces, respectively, wherein the bottom surfaces face each other. And first and second acousto-optic media disposed in close proximity to each other, and incident on the two side surfaces near the bottom surface of the second acousto-optic medium, respectively, for injecting the incident laser light. A surface and an emission surface for emitting the emitted laser light, provided between the bottom surfaces of the first and second acousto-optic media in contact with the bottom surface and near the incident surface. And
Of the incident laser light incident through the incident surface,
A light separating unit that transmits the first linearly polarized light as transmitted laser light and reflects the second linearly polarized light as reflected laser light, wherein the transmitted laser light is applied to the two side surfaces of the first acousto-optic medium. Traveling along one side, reflected at the upper surface of the first acousto-optic medium,
A first shift means for shifting the incident frequency of the transmitted laser light by the first frequency and outputting a first shifted laser light while traveling along the other of the two side surfaces; Light travels along one of the two sides of the second acousto-optic medium, is reflected at the top surface of the second acousto-optic medium, and is coupled to the second acousto-optic medium.
A second shift unit that shifts the incident frequency of the reflected laser light by the second frequency and outputs a second shifted laser light while traveling along the other of the two side surfaces; And in a state in contact with the bottom surface between the bottom surface of the second acousto-optic medium and near the exit surface,
An optical coupling unit that combines the first and second shifted laser lights and emits the combined laser light from the emission surface as the emission laser light.