JP2767635B2 - Multi-wavelength optical modulator - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-wavelength light modulator used for a color display or the like using a white laser.

[Conventional technology]

Conventionally, as this kind of multi-wavelength optical modulator, an acousto-optic modulator as shown in FIG. 5 is known. This acousto-optic modulator receives, as incident light IL, laser light having a plurality of different wavelength components that have propagated on the same incident optical path, and independently modulates the intensity of the plurality of wavelength components of the incident light IL. is there.

Acousto-optic modulator includes an acousto-optic medium 100 having an incident surface 100a which enters the incident light IL at Bragg angles theta _B. In this example, it is assumed that the incident light IL incident on the acousto-optic medium 100 has first to third wavelengths λ ₁ , λ _2, and λ ₃ different from each other. On the side surface 100b perpendicular to the incident surface 100a of the acousto-optic medium 100, piezoelectric elements corresponding to the _{first to} third wavelengths λ ₁ , λ ₂ and λ ₃ , respectively, along the traveling direction of the incident light IL. First to third transducers 111, 1
12 and 113 are attached. First through third transducers 111, 112 and 113, respectively, with the first to third frequency f _1, f ₂ and f ₃ is supplied from the first to third driving circuits 301, 302 and 303 Driven by the first to third high frequency signals. First to third drive circuits 301 and 302
And 303 each include a high-frequency oscillator and a power intensifier (not shown). Therefore, the first to third drive circuits 30
1, 302 and 303 are first to third ultrasonic waves 121, 1 having first to _third frequencies f ₁ , f ₂ and f ₃ inside the acousto-optic medium 100.
Generates 22 and 123.

First to third drive circuits 301, 302 and 303, respectively, first, second and third modulated input terminals 311 and 312 first to third input voltage V _1, V ₂ and V ₃ are applied and It has 313. This first through third input voltage V _1, V ₂ and V _3, the first through third respective drive circuits 301, 302 and 303
The intensity of the first to third high frequency signals output from is changed. Therefore, the acousto-optic medium 100, respectively,
The first through which the first to third ultrasonic waves 121, 122 and 123 propagate
And third to third ultrasonic wave propagation regions 131, 132 and 133. In this example, the center axis CX ₁ of the first ultrasonic wave 121 propagating in the first ultrasonic wave propagation area 131 and the second ultrasonic wave
Of the second ultrasonic wave 122 propagating through the ultrasonic wave propagation region 132
The distance between the propagation direction central axis CX ₂ (hereinafter, referred to as 1-2 ultrasonic propagation distance.) Propagation and L _1-2, the second propagation direction central axis CX ₂ and the third ultrasonic propagation region 133 The distance between the central axes CX3 in the _third propagation direction of the third ultrasonic wave 123 (hereinafter referred to as 2-3 ultrasonic wave propagation distance) _L2-3 is equal to L.

The combination of the first ultrasonic wave propagation region 131, the first drive circuit 301, and the first transducer 111 serves as a first acousto-optic modulator for modulating the _first wavelength λ1 component of the incident light IL. Works. Similarly, the second ultrasonic wave propagation region
132, the second drive circuit 302 and the second transducer 11
The combination of the two functions as a second acousto-optic modulator for modulating the _second wavelength λ ₂ component of the incident light IL. The combination of the third ultrasonic wave propagation region 133, the third drive circuit 303, and the third transducer 113 serves as a third acousto-optic modulator for modulating the _third wavelength λ ₃ component of the incident light IL. Operate.

In general, it is known that when light enters an acousto-optic medium through which ultrasonic waves propagate, the incident light is diffracted by an acousto-optic effect. At this time, when viewed from the air, if the wavelength of the light is λ, the frequency of the ultrasonic wave is f, and the speed of sound in the acousto-optic medium is v, When light is incident on the ultrasound wavefront consisting angle theta _B,
Bragg diffraction occurs.

First to third Bragg when components of the first to _third wavelengths λ ₁ , λ ₂ and λ ₃ of the incident light IL are Bragg diffracted by the first to third ultrasonic waves 121, 122 and 123, respectively. Let the angles be θ _B1 , θ _B2 and θ _B3 respectively. These first to third Bragg angles θ _B1 , θ _B2, and θ _B3 are incident angles θ
The first to third frequencies f ₁ , f ₂ and f ₃ are set to be equal to _B. This can be easily realized by satisfying the following equation.

λ ₁ · f ₁ = λ ₂ · f ₂ = λ ₃ · f _{3 In} the incident light IL incident at the Bragg angle θ _B , only the first wavelength λ ₁ component in which the first ultrasonic wave 121 propagates Is subjected to Bragg diffraction in the ultrasonic wave propagation region 131, and becomes the first primary diffracted light 141. Similarly, only the component of the second wavelength λ ₂ is subjected to Bragg diffraction in the second ultrasonic wave propagation region 132 where the second ultrasonic wave 122 propagates, and becomes the second primary diffracted light 142. Also,
Only the component of the third wavelength λ ₃ is subjected to Bragg diffraction in the third ultrasonic wave propagation region 133 where the third ultrasonic wave 123 propagates, and becomes the third primary diffracted light 143. Since the first to third primary diffracted lights 141, 142 and 143 are diffracted at the same Bragg angle, they become parallel lights at an interval d represented by the following equation by the above-described distance L. '.

d = 2L · tan θ _B / cos θ _B (2) Accordingly, the first to third first-order diffracted lights 141, 142, and 143 of the first to _third wavelengths λ ₁ , λ _2, and λ ₃ components are emitted.
Are not completely aligned. However, if the interval d between the parallel lights is within a range that can be ignored compared to the beam diameter w ₀ , it can be considered that the optical axes coincide practically. First to third first-order diffracted lights 14 that have been subjected to Bragg diffraction
The light amounts of 1, 142 and 143 are the first to third ultrasonic waves 121, 12
Depends on the strength of 2 and 123. Therefore, the first to third modulation input terminals 3 of the first to third drive circuits 301, 302 and 303
First to third input voltages applied to 11, 312 and 313
By independently varying V ₁ , V _2, and V ₃ , the light of the _{first to} third wavelengths λ ₁ , λ _2, and λ ₃ can be modulated independently.

[Problems to be solved by the invention]

In general, the multi-wavelength optical modulator using an acoustic optical element, the intensity modulation possible modulation bandwidth Delta] f _m is determined by the sound velocity v and the beam diameter w ₀ in the acoustooptic medium, represented by the following formula.

Δf _m = 0.54 · v / w ₀ (3) Therefore, in order to increase the modulation bandwidth Δf _m , the beam diameter w ₀
Needs to be smaller. However, in the above-described conventional multi-wavelength optical modulator, since a plurality of wavelength components are diffracted at different positions, a plurality of modulated lights cannot be completely propagated on the same optical path.
Therefore, when the small beam diameter w ₀ is the deviation of the optical path d it can not be ignored, since the color shift occurs, there is a drawback that can not be wider modulation bandwidth Delta] f _m.

Accordingly, it is an object of the present invention to provide a wide band capable of independently modulating light of a plurality of wavelength components having different wavelengths propagating on the same optical path at high speed independently without shifting the optical path of each wavelength component. An object of the present invention is to provide a multi-wavelength optical modulator.

[Means for solving the problem]

A multi-wavelength optical modulator according to the present invention receives incident light having first to n-th (n is an integer of 2 or more) wavelength components that have propagated on the same incident optical path, and receives the first to n-th light components of the incident light. n
Is a multi-wavelength optical modulator that independently modulates each of the wavelength components and propagates as output light onto the same output optical path, wherein the multi-wavelength optical modulator receives the incident light, and receives the first to n-th wavelength components of the incident light. Are independently modulated into first to n-th primary modulated lights, and the first to n-th primary modulated lights are inclined by a first predetermined angle with respect to the same incident optical path. A primary acousto-optic modulator that propagates on first to n-th diffraction optical paths parallel to each other, and receives the first to n-th primary modulated light and receives the first to n-th primary modulated light The light is independently modulated into first to n-th secondary modulated light, and the first to n-th secondary modulated light is transmitted to the first to n-th diffraction optical paths. A second acousto-optic modulator that is inclined at a second predetermined angle and propagates as the outgoing light on the same outgoing light path. .

[Action]

The incident light is modulated twice independently by the primary acousto-optic modulator and the secondary acousto-optic modulator for each wavelength component,
The light is propagated as outgoing light on the same outgoing light path.

〔Example〕

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

Referring to FIG. 1, a multi-wavelength optical modulator according to a first embodiment of the present invention has a primary acousto-optic modulator and a secondary acousto-optic modulator arranged symmetrically with respect to a virtual plane IP.

The primary acousto-optic modulator has the same structure as the acousto-optic modulator shown in FIG.

That is, primary acousto-optic modulator has a primary acoustooptic medium 100 having a primary entrance surface 100a incident at Bragg angle theta _B the laser beam as an outgoing light IL from the laser 400. As the primary acousto-optic medium 100, for example, AOT-
44B tellurite glass can be used. In this embodiment, a hollow cathode He-Cd laser is used as the laser 400. The hollow cathode type He-Cd laser 400 emits blue light having a wavelength of 441.6 nm, and light having wavelengths of 533.7 nm and 537.8 nm, respectively, as light having the _{first to} third wavelengths λ ₁ , λ ₂ and λ _3.
, And red light having wavelengths of 636.5 nm and 636.0 nm are simultaneously emitted.

The primary side surface 100b perpendicular to the primary incidence surface 100a of the primary acousto-optic medium 100 corresponds to the _{first to} third wavelengths λ ₁ , λ ₂ and λ ₃ along the traveling direction of the incident light IL, respectively. , First to third primary piezoelectric transducers 111, 112
And 113 are attached. First to third primary piezoelectric transducer 111, 112 and 113, respectively, first to third frequency f _1, f ₂ and f ₃ is supplied from the first to third driving circuits 301, 302 and 303 First to third with
Driven by the high-frequency signal. First to third drive circuits 30
Although not shown, each of 1, 302, and 303 includes a high-frequency oscillator and a power amplifier. Accordingly, the first to third driving circuits 301, 302 and 303, first to third frequency f _1, the first to third f ₂ and f ₃ of the primary ultrasonic waves in the interior of the primary acoustooptic medium 100 Generate 121, 122 and 123.

In this embodiment, the first to third frequencies f ₁ , f ₂ and
f ₃ is set so as to satisfy the following relationship.

_{f 1: f 2: f 3} = (636.0 + 636.5) / 2: (533.7 + 537.8) / 2:
441.6 For example, if f ₁ = 80 MHz, f ₂ = 67.7 MHz and f ₃ = 55.8
MHz. The Bragg angle θ _{B at} this time is θ _B = 5.3 mrad from the equation (1).

First to third drive circuits 301, 302 and 303, respectively, first, second and third modulated input terminals 311 and 312 first to third input voltage V _1, V ₂ and V ₃ are applied and It has 313. This first through third input voltage V _1, V ₂ and V _3, the first through third respective drive circuits 301, 302 and 303
The intensity of the first to third high frequency signals output from is changed. Therefore, the primary acousto-optic medium 100 includes first to third primary ultrasonic wave propagation regions 131, 132 and 13 through which the first to third primary ultrasonic waves 121, 122 and 123 respectively propagate.
It is divided into three.

First primary ultrasonic wave propagation region 131, the combination of the first driving circuit 301 and the first primary piezoelectric transducer 111, a first primary sound for modulating the first wavelength lambda ₁ of the component of the incident light IL Acts as an optical modulator. Similarly, the combination of the second primary ultrasonic wave propagation region 132, the second drive circuit 302, and the second primary piezoelectric transducer 112 provides a _second component for modulating the component of the incident light IL at the second wavelength λ2. Acts as a primary acousto-optic modulator. The combination of the third primary ultrasonic wave propagation region 133, the third driving circuit 303, and the third primary piezoelectric transducer 113 forms a third primary acoustic wave for modulating the _third wavelength λ ₃ component of the incident light IL. It operates as an optical modulator.

In the incident light IL incident at the black angle θ _B , only the blue light of the first wavelength λ ₁ is subjected to Bragg diffraction in the first primary ultrasonic wave propagation region 131 where the first primary ultrasonic wave 121 propagates, and It becomes the first-order diffracted light (first-order modulated light) 141. Similarly, only green light of the second wavelength λ ₂ is subjected to Bragg diffraction in the second primary ultrasonic wave propagation region 132 in which the second primary ultrasonic wave 122 propagates, and the second primary diffracted light (second primary modulation light) Light 142). Further, only the red light of the third wavelength λ ₃ is subjected to Bragg diffraction in the third primary ultrasonic wave propagation region 133 where the third primary ultrasonic wave 123 propagates, and becomes the third primary diffracted light (third primary modulated light). 143). These first to third primary modulated lights 141, 142, and 143 are diffracted at the same Bragg angle, become parallel lights, and are emitted from the emission surface 100c.

Similarly, the secondary acousto-optic modulator outputs the first to third primary modulated light 14 emitted from the primary acousto-optic modulator.
Primary incidence surface 20 for incidence of 1, 142 and 143 at Bragg angle θ _B
0c is included in the secondary acousto-optic medium 200. Secondary side surface 200b perpendicular to the secondary incident surface 100c of the secondary acousto-optic medium 200
Include first to third primary piezoelectric transducers 111, 1
First to third secondary piezoelectric transducers arranged symmetrically with respect to each other with respect to a virtual plane IP with 12 and 113 respectively
211, 212 and 213 are attached. First to third
Of the second piezoelectric transducers 211, 212 and 213 have first to third frequencies f ₁ , f ₂ and f ₃ supplied from the first to third drive circuits 301, 302 and 303, respectively.
To a third high-frequency signal. Accordingly, the secondary acousto-optic medium 200 is divided into first to third secondary ultrasonic wave propagation regions 213, 232, and 233 through which the first to third secondary ultrasonic waves 221, 222, and 223 propagate, respectively. You.

The combination of the first secondary ultrasonic wave propagation region 231, the first driving circuit 301 and the first secondary piezoelectric transducer 211 is used to modulate the first primary modulated light 141.
As a secondary acousto-optic modulator. Similarly, the combination of the second secondary ultrasonic propagation region 232, the second drive circuit 302, and the second secondary piezoelectric transducer 212 provides a second primary modulated light 142 for modulating the second primary modulated light 142. Acts as a secondary acousto-optic modulator. Third secondary ultrasonic wave propagation region 23
3. The combination of the third drive circuit 303 and the third secondary piezoelectric transducer 213 operates as a third secondary acousto-optic modulator for modulating the third primary modulated light 142.

The first to third primary modulated light 141, 142 and 143 incident at the black angle θ _B are respectively in the first secondary ultrasonic wave propagation region 231 where the first secondary ultrasonic wave 221 propagates, Second
Second secondary ultrasonic wave propagation region 2 through which the secondary ultrasonic wave 222 propagates
At 32 and in a third secondary ultrasound propagation region 233 where the third secondary ultrasound 233 propagates, the first and second
And the third secondary-modulated light, and the first to third secondary-modulated light are emitted from the emission surface 200a as the emission light OL onto the same emission optical path.

Referring to FIG. 2, a multi-wavelength optical modulator according to a second embodiment of the present invention has the same configuration as that of the first acousto-optic medium 100 and the second acousto-optic medium 200 except that a single acousto-optic medium 500 is used. It has a configuration similar to that shown in FIG. In this embodiment, the angle α between the primary side surface 100b and the secondary side surface 200b is set to twice the angle of the Bragg angle θ _B (α = θ _B ). In this embodiment, there is no air layer between the primary acousto-optic modulator and the secondary acousto-optic modulator. Therefore, the angle shift due to the wavelength dispersion of the refractive index at the time of incidence of the incident light is not canceled. Therefore, the first to third wavelengths λ ₁ , λ ₂ and λ
The ratio of the _three components of the Bragg angles θ _B needs to be changed slightly so that the first, second and third primary modulated light 141, 142 and 143 are parallel to each other.

Referring to FIG. 3, a multi-wavelength optical modulator according to a third embodiment of the present invention is similar to that of FIG. 1 except that the arrangement of the secondary acousto-optic modulator is different from that of FIG. It has a configuration similar to that shown. That is, are arranged in point symmetry with each other with respect to the primary acoustooptic medium 100 and the secondary acoustooptic medium 200 cusp O _2. However, the first to third secondary piezoelectric transducers 211, 212 and 213, respectively, point to the first to third primary piezoelectric transducer 111, 112 and 113, with respect to the point O _1, O ₂ and O ₃ They are arranged in symmetrical positions. This embodiment has an advantage that the incident light and the outgoing light are parallel to each other.

Referring to FIG. 4, a multi-wavelength optical modulator according to a fourth embodiment of the present invention is different from the first embodiment in that the primary acousto-optic medium 100 and the secondary acousto-optic medium 200 are combined into one acousto-optic medium 600. It has a configuration similar to that shown in FIG. In this embodiment, the primary side 100b and the secondary side 200b are parallel to each other.

In the embodiment described above, a hollow cathode type light source is used as a light source.
Although a He-Cd laser is used, other light sources emitting a plurality of wavelength components may be used. In this case, needless to say, it is necessary to adjust the frequency of the high-frequency signal for driving the transducer. Alternatively, light obtained by combining laser beams from a plurality of light sources, such as an Ar laser and a He-Ne laser, may be used. Further, the acousto-optic medium is not limited to tellurite glass, and another glass or crystal may be used.

〔The invention's effect〕

As is clear from the above description, the multi-wavelength optical modulator of the present invention has the same wavelength component of the output light propagates on the same output optical path. The modulation bandwidth can be widened. In addition, since the multi-wavelength optical modulator of the present invention includes two acousto-optic modulators, a higher extinction ratio can be obtained than that of a single acousto-optic modulator.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a multi-wavelength optical modulator according to a first embodiment of the present invention. FIG. 2 is a diagram showing a configuration of a multi-wavelength optical modulator according to a second embodiment of the present invention. FIG. 4 is a diagram showing a configuration of a multi-wavelength optical modulator according to a third embodiment of the present invention, FIG. 4 is a diagram showing a configuration of a multi-wavelength optical modulator according to a fourth embodiment of the present invention, and FIG. FIG. 11 is a diagram illustrating a configuration of a conventional multi-wavelength optical modulator. 100,200,500,600 ... acousto-optical media, 111,112,113,211,21
2,213… Transducer, 301,302,303… Drive circuit, 40
0 ... Laser.

Claims (1)

(57) [Claims] An incident light having first to n-th (n is an integer of 2 or more) wavelength components propagating on the same incident optical path, and receiving the first to n-th wavelength components of the incident light. A multi-wavelength optical modulator that independently modulates and propagates as outgoing light on the same outgoing optical path, receives the incident light, and independently converts the first to n-th wavelength components of the incident light into first to n-th wavelength components. The first to n-th primary modulated lights are modulated to the first to n-th primary modulated lights, and the first to n-th primary modulated lights are inclined by a first predetermined angle with respect to the same incident optical path, and are respectively parallel to the first parallel light. A primary acousto-optic modulator for propagating on the first to n-th diffraction optical paths, and receiving the first to n-th primary modulated light, and independently receiving the first to n-th primary modulated light. The light is modulated into the first to n-th secondary modulated light, and the first to n-th secondary modulated light is modulated. , The first through inclined second predetermined angle with respect to the n-th diffracted light path, multi-wavelength optical modulator and a secondary acousto portion to propagate as the outgoing light to the same emission optical path.