JPS584322B2 - light modulator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a light modulation device that modulates light intensity using a sound wave, for example, an audio signal.

Optical fiber transmission systems are attracting attention as a promising next-generation method for transmitting large amounts of information over long distances at low cost.

When transmitting voice signals using this optical transmission line as a telephone line, it is currently assumed that conventional acoustic-to-electrical converters will be used.

That is, after converting an audio signal into an electrical signal, the electrical signal is used to modulate light, thereby transmitting the audio signal as an optical signal.

However, when considering the introduction of optical fibers to subscriber lines of telephone lines, this type of system requires a complicated and expensive terminal device (telephone device), so equipment that directly converts voice signals into optical signals is required. development is desired.

In view of this situation, the present invention provides a new device that directly modulates light using sound waves without converting sound waves such as audio signals into electrical signals.

According to this invention, two diffraction gratings are used, a diaphragm is vibrated by sound waves, and the two diffraction gratings are relatively displaced by the vibration.

One of the two diffraction gratings is irradiated with light, and the light from that diffraction grating is irradiated onto the other diffraction grating, thereby obtaining light whose intensity is modulated by the sound wave from the diffraction grating.

As will be explained later, one of the diffraction gratings may be a non-existent virtual diffraction grating.

FIG. 1 shows an embodiment of the present invention, in which the front side of a case 11 whose back side is closed off is closed off by a diaphragm (or vibrating thin film) 12.

The front side of the diaphragm 12 is covered with a sound collecting protective cover 13.

Diffraction gratings 14 and 15 facing each other are arranged inside the case 11, and one end of one of the diffraction gratings 14 is fixed to the center of the diaphragm 12.

The other diffraction grating 15 is fixed to the case 11.

Optical fibers 16 and 17 are introduced into the case from both side walls of the case 11, and self-occurring lenses 18 and 19 are attached to the inner ends of these optical fibers 16.

The light from one optical fiber 16 is converted into parallel light 21 by a self-occurring lens 18 and is incident on the diffraction grating 14, and the transmitted light passes through the diffraction grating 15 and is converted into light 22 and is incident on the lens 19.

The diaphragm 12 vibrates due to the sound pressure of the external sound coming through the sound collection cover 13, and the diaphragm 12 changes in response to the audio signal.

The diffraction grating 14 has stripes arranged in the direction in which the diaphragm 12 is displaced.

The stripes of the diffraction grating 15 are also arranged similarly to those of the diffraction grating 12.

When the diaphragm 12 vibrates and is displaced by sound, the diffraction gratings 14 and 15 are relatively displaced in the direction in which their stripes are arranged.

The light transmitted through the optical fiber 16 is collimated by the self-occurring lens 18 and illuminated on the diffraction gratings 14 and 15, and the light 22 diffracted by the diffraction gratings 14 and 15 is condensed by the self-occurring lens 19 and sent to the optical fiber 17. transmitted within.

At this time, the light intensity of the light diffracted by the diffraction gratings 14 and 15 and transmitted through the optical fiber 17 is modulated by the relative displacement of the diffraction gratings 14 and 15, as will be explained later.

In this way, the audio signal of the diaphragm 12 vibrated by the sound pressure (sound) of the sound wave can be directly transmitted as an optical signal.

FIG. 2 shows another embodiment of the invention, in which parts corresponding to those in FIG. 1 are given the same reference numerals.

The case 11 includes a cylindrical portion 1lb and a flange portion 11a protruding forward from the front outer periphery of the cylindrical portion 1lb, and a diaphragm 12 is attached to the front surface of the flange portion 11a.

A diffraction grating 15 is attached to the boundary between the collar portion 11a and the cylindrical portion 11b.

A mirror 23 is attached to the diaphragm 12 facing the diffraction grating 15.

The mirror 23 is displaced along with the displacement of the diaphragm 12, and the distance between the diffraction grating 15 and the virtual image formed by the mirror 23, that is, the virtual diffraction grating, changes.

Optical fibers 16 and 17 are attached to the back plate of the cylindrical portion 11b.

The light transmitted by the optical fiber 16 is converted into parallel light 21 by the self-occurring lens 18, and is then collimated by the diffraction grating 15.
is irradiated.

The light that has passed through the diffraction grating 15 is reflected by the mu 23, and the diffracted light 22 that has passed through the diffraction grating 15 again is collected by the self-occurring lens 19, confined in the optical fiber 17, and sent.

At this time, when the position of the mirror 23 is displaced by the vibration of the diaphragm 12, the light intensity of the diffracted light 22 is modulated in accordance with this displacement, as will be explained later, and an audio signal is directly transmitted as an optical signal. I can do it.

The principle of this system is based on the fact that the distance between the virtual image of the diffraction grating 15 produced by the mirror 23 and the diffraction grating 15 changes in accordance with the displacement of the mirror 23, as shown in FIG.

With the above configuration, the system that transmits light through optical fibers can be used as a microphone or even as a transmitter of a telephone.

The operating principle of modulating light intensity by causing relative displacement of two diffraction gratings within the same plane or by changing the spacing between the two diffraction gratings will be briefly described below.

Here, as a simple example, the aperture ratio of the two diffraction gratings is 1.
/2 binary diffraction grating (for example, in the case of an absorption grating, the diffraction grating blocks the light by half the pitch,
It has stripes lined up that transmit light at only half the pitch.

), and the pitches of the two diffraction gratings are assumed to be equal.

At this time, the two diffraction gratings are made to face each other, and the parallel likelihood is set to θ
When the light is incident at an angle of 1) I=KSin2(δ)cos2(πY±1) (phase type + phase type diffraction grating) (2) T =K{1+Sin(δ)sin(2πY±1)}(
absorption type + phase type diffraction circuit) (3).

Here, K is a proportionality constant, and δ is the amount of phase shift of the phase type diffraction grating.

Y±1 is Y=±1=d/p-λZ/p2(p/λsin
θ±1/2) (4).

p is the pitch of the diffraction grating, λ is the wavelength to be used, d is the relative displacement between the two diffraction gratings in the same plane, Z
is the gap between the two diffraction gratings.

As shown in equations (1), (2), and (3), in any combination of diffraction gratings, the intensity of diffracted light is a sine with respect to the relative displacement between the diffraction gratings and the gap between the diffraction gratings. It can be seen that it is modulated in a wave-like manner.

Therefore, keeping the gap Z between the two diffraction gratings constant,
Considering the case where only a change in relative displacement occurs, the third
A change in light intensity occurs as shown in the figure.

In other words, a sinusoidal change in the intensity of the diffracted light with a period p on which a DC bias is applied is generated.

Therefore, the gap Z between the two diffraction gratings and the angle θ of the incident light
If the initial setting is made to be the output of bias point B and the relative displacement amount d is configured to be in the linear region, the light will be modulated by the audio signal in Figure 1. .

For example, if an elastic thin film is used as the diaphragm 12 in FIG.
A displacement of 4 μm occurs.

Therefore, if the period p of the diffraction grating is set to 5 to 10 μm, the aforementioned sound waves can be converted into optical signals.

On the other hand, if the relative displacement d of the two diffraction gratings is kept constant and only the gap Z between the two diffraction gratings changes, the intensity of the diffracted light will change as shown in Figure 4. arise.

That is, for ±1st-order diffracted light, Sinθ=±λ/2
At times other than p, the period indicates a change in light intensity.

In particular, if sin θ=0, the period becomes 2p2/λ.

Therefore, the pitch of the diffraction grating is selected and initialized (initial setting of the gap Z between the diffraction gratings so that the bias point is B) so that the displacement of the diaphragm caused by the sound wave is converted into an optical signal.
By doing this, a light modulation device can be constructed.

As explained above, light is modulated by changing the relative displacement amount d of the two diffraction gratings or the gap Z between the two diffraction gratings.

The embodiment shown in FIG. 1 is an example in which the relative displacement amount d of two diffraction gratings is changed by the displacement of the diaphragm 12.

On the other hand, the embodiment shown in FIG. 2 is an example in which the gap between two diffraction gratings is equivalently changed by displacement of a mirror 23 attached to a diaphragm.

In the above explanation, the periods are equal and the aperture ratio is 1/2.
However, the case is generally not limited to these, but the aperture ratio is other than 1/2, especially the case where the period of one diffraction grating is an integral multiple of the period of the other diffraction grating, and Even when two diffraction gratings have different periods, the intensity of diffracted light changes depending on the relative position of the two diffraction gratings, and there is a region where the change in light intensity is linear.

Further, although the explanation has been made regarding a binary diffraction grating, it goes without saying that the present invention is not limited to binary diffraction gratings such as a sinusoidal diffraction grating and a blazed diffraction grating.

Further, even if a reflective diffraction grating is used in place of the mirror 23 in the arrangement shown in FIG. 2, the light can be similarly modulated by the displacement of the diaphragm 12.

Furthermore, in FIG. 2, a mirror 23 is used to equivalently change the gap between the two diffraction gratings, but in the same way, by using a mirror and a prism, the relative displacement d of the two diffraction gratings can be equivalently changed. Alternatively, various configurations can be adopted in which the gap Z is changed.

Although the configuration shown in FIGS. 1 and 2 can be used as a microphone or a telephone transmitter, an example of the configuration of a telephone incorporating a transmitter and a receiver will be described below.

First, FIG. 5 shows a conceptual diagram of a telephone network using optical fibers.

In FIG. 5, for example, 24a among subscribers 24 and subscriber 2
When the subscriber 24a and the subscriber 24b communicate with each other, first, a line between the subscriber 24a and the subscriber 24b is secured by the exchange of the telephone office 25.

At this time, the light source 26 is installed at the telephone office, and for example, the light sent from the light source 26a of the telephone office 25 to the subscriber 24a is optically modulated by the voice signal at the transmitter of the telephone of the subscriber 24a. Thereafter, it is optically transmitted again to the telephone of subscriber 24b via the telephone office.

The optical signal is demodulated into a voice signal by the telephone of subscriber 24b,
Received as audio.

Similarly, voice is also transmitted and received from the telephone of subscriber 24b to the telephone of subscriber 24a.

In this way any two of the subscriber telephones can communicate with each other.

FIG. 6 shows an embodiment in which the present invention is applied to a transmitting section of a telephone.

The light from the optical fiber 16 that transmits the light from the light source of the telephone office passes through the diffraction grating 14 in the transmitting section 28 at one end of the body 27,
15 is irradiated.

The modulated optical signal passes through an optical fiber 29, and further, an optical coupler 3 for transmission and reception splits and combines the light for transmission and reception.
1 to a bidirectional optical fiber 17.

The light from the bidirectional optical fiber 17 is transmitted to the optical coupler 31
and further via an optical fiber 32 to a photoelectric converter 34 provided in the receiver 33, and a speaker 35 is driven by its electrical output.

The transmitting section 28 of the optical telephone shown in FIG. 6 is constructed using the acoustic-to-optical signal conversion method using the transmission type diffraction grating shown in FIG. 1, and light is modulated by an audio signal.

Needless to say, even if the modulation method shown in Fig. 2 is used,
An optical telephone is constructed in the same manner.

In FIG. 6, the light transmitted from the light source of the telephone office through the optical fiber 16 is transmitted to the diaphragm 12, the diffraction grating 14,
15, the signal is optically modulated by an audio signal.

This optically modulated light is introduced into the optical fiber 29,
The signal is transmitted via the optical coupler 31 and the bidirectional fiber 17 to the central office and to the telephone subscriber of the other party.

On the other hand, the optical signal transmitted from the other party through the optical fiber 17 is transmitted to the optical coupler 31 and the optical fiber 3.
2, it is converted into an electrical signal modulated by the audio signal by a photoelectric converter 34.

Furthermore, this electrical signal is demodulated into sound by a receiver (speaker) 35 and received as sound.

In this way, audio signals can be transmitted and received as optical signals.

In the above explanation, the light source was installed on the central office side, but the light source could also be built into the phone.Moreover, although we talked about bidirectional communication using one optical fiber, there are two optical fibers, one for transmitting and one for receiving. It goes without saying that a communication system using optical fibers may be constructed.

As explained above, since this invention is an optical modulation device that can directly convert a sound wave signal into an optical signal, it has the advantage of making it possible to create microphones and telephones suitable for optical fiber transmission with a simple configuration, as well as being economically inexpensive. It has the advantage of being easily fabricated.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing one embodiment of the present invention, FIG. 2 is a sectional view showing another embodiment of the invention, and FIG. 3 is a diffraction light corresponding to the relative displacement of two diffraction gratings. Figure 4 is a diagram showing changes in light intensity due to changes in the gap between two diffraction gratings, Figure 5 is a conceptual diagram of a telephone network using optical fibers, and Figure 6 is a diagram showing changes in light intensity. 1 is a diagram showing an embodiment of an optical telephone to which the present invention is applied. 12: Vibration plate, 14, 14: Diffraction grating, 16, 17, 2
9, 32: Optical fiber, 18, 19: Self-occurring lens, 21: Incident parallel light, 22: Diffracted light, 23: Mirror.

Claims (1)

[Claims] 1 a first diffraction grating, a diaphragm vibrated by a sound wave,
A second diffraction grating whose relative position with respect to the first diffraction grating is changed by being displaced by the vibration of the diaphragm and one of the first and second diffraction gratings, and the light from the diffraction grating. and means for projecting the light onto the other of the first and second diffraction gratings to obtain light whose intensity is modulated by the sound waves from the diffraction grating.