JPS62159129A - Optical analog to digital converter - Google Patents

Abstract

PURPOSE:To easily realize an optical analog to digital converter with superior speediness by performing analog to digital conversion by using an acoustooptic means. CONSTITUTION:An acoustooptic element 13-1 diffracts input light by its acoustooptic effect and outputs the diffracted light. The intensity of the diffracted light in this case relates to the level of a modulated signal applied to the acoustooptic element. For the purpose, an analog signal modulating means 20 modulates an analog signal by using a carrier consisting of a sine wave signal having, for example, an amplitude 2<k-1>.V1 (k=1-n and V1 is a reference amplitude voltage) and applies the modulated signal to the acoustooptic element, so that (n) diffraction output light beams corresponding to the analog signal are obtained. Those (n) diffraction output light beams are converged by an output light lens 19 and the intensity is detected by, for example, a photodiode 14 and converted by a comparing circuit 15 into a digital signal consisting of '1' and '0'.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical analog-to-digital converter, and particularly to an optical analog-to-digital converter that is fast and easy to implement.

[Conventional technology]

Conventional optical analog-to-digital converters are described in the literature (
1) is known. FIG. 4(a) is an explanatory diagram showing the configuration of this conventional optical analog-to-digital converter, and shows a 4-bit optical analog-to-digital converter.

In this conventional example, input light 1. an input light laser-1 that generates input light 1. is connected to each branch of this branched blade wave path 2, and each electrode is connected to the input highway 7, and an analog signal Va is input. 4 phase modulators 3-
1 to 3-4, and output light 1. from each of the phase modulators 3-1 to 3-4, respectively. - Photodiodes 4-1 to 4-4 receive the light I4, detect its intensity, and convert it into an electrical signal, and the electrical signals from these photodiodes 4-1 to 4-4 are input to one side, and a certain predetermined signal is input. The threshold voltage A is used as the other input, and the electric signal is converted into a digital signal Vat~
It includes four comparison circuits 5-1 to 5-4 which convert the voltage to Vd4 and output it to output highways 6-1 to 6-4. Note that here, the branch, the shaped vane wave path 2 and the electrode are connected to the input highway 7.
The phase modulation circuits 3-1 to 3-4 connected to each other constitute an optical modulation means 8 that converts the analog signal Va into an electrical signal.

Next, the operation of this conventional example will be explained. An input light beam from an input light laser 1 is input to a branched blade waveguide 2, and is branched into four channels of light. As shown in FIG. 4(b), the branched four-channel light is expressed as Ls==2'-'Ll(k=1.2.3. 4) is input to four phase modulators 3-1 to 3-4 provided with the following signals. At this time, when the analog signal Va from the input highway 7 is applied to the electrodes of each phase modulator 3-1 to 3-4, the following (
Given the phase delay amount shown in equation (2), output lights (1 to I) having the intensity (1) shown in equation (3) are obtained.

Δl'=2 to -1, π・V(t)/Vm(k=
1.2.3.4) −−−−−−−(2)1,=
A, cos” (Δrk + ψk) (k=1.2.3
, 4) ...------(3) However, v(t)
: Amplitude voltage of analog signal Va m : Maximum voltage A0 of analog signal Va : Modulation amplitude ψ1 Phase shift of each input light when inputting to a two-phase modulator Therefore, for example, apply an appropriate DC voltage to the analog signal Va to each electrode. By applying in addition, ψ, −π/4
, −−−−−−・−(4), then
The relationship between the analog signal Va and the intensity of the output light 1)-14 is as shown in FIG.

Here, as shown in Fig. 4, the intensity of the output lights 18 to 4 is detected by a photodiode, converted to electrical power 18, and then thresholded by comparison circuits 5 to 1 to 5-4. By comparing the voltage and each of the above electrical signals,
If it is determined to be "1" or "0", a binary digital signal with the most significant bit on the output light 1) side and the least significant bit on the output light 14 side is generated.6. ~Vd4 are output to output highways 6-1 to 6-4, respectively.

[Problem that the invention seeks to solve]

The conventional optical analog-to-digital converter described above performs analog-to-digital conversion by delaying the phase of light.
Compared to analog-to-digital conversion using electric circuits, it is superior in speed, but the electrode length of n phase modulators (1, 1
,) as Lm = 2'-' ・Ll (k = 1~n)
-(1) It is necessary to change and integrate as shown in '. Incidentally, such a phase modulator uses a ferroelectric material such as lithium niobate, which has a large electro-optical effect, and has the disadvantage that it is difficult to finely adjust the length of each electrode.

An object of the present invention is to provide an optical analog-to-digital converter that is easy to manufacture and implement by eliminating the above-mentioned drawbacks.

[Means for solving problems]

The present invention includes an optical modulation means that generates n (n is a natural number of 2 or more) lights having different phases from input light according to an analog signal, and converts the output light from the optical modulation means into n electrical signals. In the optical analog-to-digital converter, the light modulating means converts the input light into parallel light. an input optical lens; an acousto-optic means for diffracting the parallel light from the input optical lens to generate n lights each having a different phase; It is characterized in that it includes an analog signal modulation means for applying a signal to the acousto-optic means, and an output light lens for condensing the output light of the acousto-optic means.

Further, in the present invention, it is preferable that the acousto-optic means is composed of n acousto-optic elements, and that the carrier waves have the same frequency.

Further, in the present invention, the acousto-optic means is composed of one acousto-optic element, the carrier waves are n carrier waves each having a different frequency, and the outputs of the respective modulation circuits are superimposed and applied to the acousto-optic element. Preferably, it includes multiple coupling circuits.

[Effect]

The present invention performs analog-to-digital conversion using an acousto-optic element instead of a conventional phase modulator using optical phase delay. The acousto-optic element diffracts input light and outputs diffracted light due to its acousto-optic effect. The intensity of the diffracted light in this case is related to the intensity of the modulation signal applied to the acousto-optic element.

Therefore, the analog signal is converted into, for example, 25-'·■ by analog signal modulation means.

(k = 1 ”” n s V I is the reference amplitude voltage)
modulated using a carrier wave consisting of a sine wave signal with an amplitude of
By applying this to the acousto-optic element, n diffracted output lights corresponding to analog signals are obtained. And this n
The diffracted output light of
, is converted into a digital signal of "0".

Here, the modulated signal may be given to n acousto-optic elements using a carrier wave with the same frequency, or may be given to one acousto-optic element by using n carrier waves with different frequencies and superimposing the modulated signal. Good too.

As described above, the present invention requires only one or n identical acousto-optic elements, which are relatively easy to manufacture, and the others are constructed from electrically or optically simple elements, allowing easy optical analog-to-digital conversion. It is possible to obtain equipment.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 (al is an explanatory diagram showing the configuration of a first embodiment of the present invention, and shows a 4-bit optical analog-to-digital converter.

Further, FIG. 1 (bl is a partial detailed explanatory diagram showing the light receiving state of the photodiode).

In this embodiment, an optical modulation means 18 generates four lights having different phases from input light rt from an input optical laser 1) using an analog signal Va, and output light I3 from this optical modulation means 18 is divided into four lights. photodiodes 14-1 to 14-4 as light receiving means for converting the photoelectric signals into digital signals V with a constant threshold voltage 7 as a reference;
Comparison circuit 15 as comparison means for converting dl to Va4
-1 to 15-4, the light modulation means 18 includes an input light lens 12 that converts the input light (1) into parallel light;
acousto-optic elements 13-1 to 13-4 that diffract parallel light from the source and generate four lights each having a different phase, and an acousto-optic element 13-1 that modulates an analog signal Va, respectively.
4 modulation circuits 20-1 to 20- applied to ~13-4
4, and each of the modulation circuits 20-1 to 20-4 receives a sine wave signal having the same frequency f0 as a carrier wave and an amplitude of 2 to -1·V+ (k=1-2.3.4). The output light lens 19 includes four oscillators 21-1 to 21-4 that provide energy, and an output light lens 19 that condenses the output light of the acousto-optic elements 13-1 to 13-4.

The feature of the present invention is that in FIG.
-13-4 is provided.

Next, the operation of the present embodiment will be explained.

Input light 1i from an input light laser 1) is input to an input light lens 12 and converted into parallel light. This parallel light is input to the acousto-optic elements 13-1 to 13-4. The other modulation circuit 20-1
~20-4 input the analog signal Va input through the input highway 17 from the oscillators 21-1~21-4 at the same frequency f0 and VII=21'-1・■1 (k=1.2 .3.4, ■1 is the reference amplitude voltage and in this case, the one with =1 is used as the reference.) It is modulated by a sine wave signal with an amplitude of .

At this time, the parallel light input to the acousto-optic elements 13-i to 13-4 at the same angle is θ
=r0λ/V...-(5) However,
λ: wavelength of input light V: diffracted in the direction of sound speed of the acousto-optic element, intensity L(t) of output light is as follows (6)
It is given by the formula (see literature (2)).

1m (t) = Io 5in2 (K ・Vlt) ・2
"-' ・V+) (k=1.2.3.4) ...(
6) However, ■. Two-person force intensity K: constant V(t) specific to the acousto-optic element: analog signal voltage Vl: modulation amplitude voltage of the acousto-optic element 13-1. Therefore, when creating each modulation signal in advance, by applying an appropriate DC bias voltage to the analog signal Va, 1m(t)=1. sin”(K ・V(t) ・2
'-' ・V, ・ψ (k=1.2.3.4) φ, = −π/4 ・・−(7)
, and a format similar to equation (3) of the above conventional example can be obtained.

FIG. 2 illustrates the intensity Ih(t) of the output light in equation (7), and is similar to FIG. 5 of the conventional example.

Therefore, the output light ■5 is focused by the output light lens 18,
The photodiodes 14-1 to 14-4 detect and obtain a photoelectric signal, and the comparison circuits 15-1 to 15-4 detect the threshold voltage V7 as "1" or "0".
”, the output light 1. Binary digital signal with the most significant bit on the side and the least significant bit on the output light I4 side■6
．． ~va4 are output highways 16-1 to 16, respectively.
-5 is output.

In addition, in the first embodiment, the modulation circuits 20-1 to 20-
4 and 4 oscillation standards 21-1 to 21-4 each, but here the oscillation frequencies are the same and only the output levels are different (it can be said that the output levels of the modulation circuits are different). , one oscillator and one modulation circuit, and the output level of the modulator may be doubled by a level adjuster and applied to the acousto-optic elements 13-1 to 13-4.

According to the second embodiment, there is no manufacturing complexity such as integrating a plurality of n phase modulators with different electrode lengths as in the prior art. This can be realized using an acousto-optic element including a piezoelectric element such as.

FIG. 3(a) is an explanatory diagram showing the configuration of a second embodiment of the present invention. Further, FIG. 3(b) is a partial detailed explanatory diagram showing the light receiving state of the photodiode. In the second embodiment, the light modulation means 18 in the configuration of the first embodiment shown in FIG. 1 is replaced with a light modulation means 18a. The optical modulation means 18a includes one acousto-optic element 13-5 into which parallel light is input through the input optical lens 12, and four modulation circuits 2O-1a to 2O-4 that modulate the analog signal Va.
a, and each of the modulation circuits 2O-1a to 2O-4a has a different frequency r, -r4 as a modulation signal, and the amplitude is 2 to -1·vI (Vt is the modulation amplitude voltage of the reference modulation signal) Four oscillation circuits 2l-1 that give a sine wave signal with an amplitude of
a to 2l-4a and each modulation circuit 2O-1a to 2O-4
It includes a multiplex coupling circuit 22 which superimposes the output of the acousto-optic element 13-5.

Next, the operation of the second embodiment will be explained.

The input light (■) with wavelength λ from the input light laser 1) becomes parallel light by the input light lens 12, and is converted into parallel light by the acousto-optic element 13-5.
is input. On the other hand, the modulation circuits 2O-1a to 2O-4a convert the level analog signals Va input through the input highway 17 to frequencies f and -f from the oscillators 2l-1a to 2l-4a, respectively, and Vk = 2 -''V+ (k = 1, 2, 3, 4) It is modulated by a sine wave signal with an amplitude of (k = 1, 2, 3, 4).

At this time, the parallel light input to the acousto-optic element 13-5 independently corresponds to the angular frequency f, ~f4, and has the following equation in θ=fk λ/V (5)'
The intensity 1t, (t) of each output light beam 3 is given by the following equation (8).

L(t) = Ioαsin'' (K HV[tl ・2 to 1' ・V,) (k=1.2.3.4) ・・−(
8) However, Io: input light intensity α: proportional constant: constant V (tl: electric analog signal voltage) specific to the piezoelectric element; I: modulation amplitude voltage of the modulation signal with frequency f1. , by applying an appropriate DC bias voltage to the analog signal Va, I m(tl
= I oα5in2 (K ・ Vat) ・ 2
ni' ・V++φm) (k=1, 2, 3,
4) φ5 = -π/4 -・-
・-(91), which has the same form as equation (7), and the same relationship as shown in FIG.
-1 to 14-4 detected 1. Comparison circuits 15-1 to 15-
4, the same digital signal d as in the first embodiment above is generated.
I~d4 are obtained.

The second embodiment requires only one acousto-optic element and can be manufactured more easily than the first embodiment.

Although the above explanation assumes that the number of bits is 4, it goes without saying that the present invention can be applied to a plurality of n-bit optical analog-to-digital converters.

Literature (1): Henry F.
.

Taylor) r optical analog to digital converter
Design and Analysis J (rAn 0ptical Anal
og-to Digital Con-vertorJ
), I, E, E, E, Journal of
Quantum Electronics (IEEE E, Jour
nal of Quantum Electro
nics) QE-15 volume, NO, 4, 1979
April, 210 pages.

Literature (2): Yuki Sugiura “Acousto-optic modulator/deflector” Op.
lug 8 February 1985, page 86.

〔Effect of the invention〕

As explained above, according to the present invention, analog-to-digital conversion is performed using an acousto-optic means using an acousto-optic element that is easy to manufacture, instead of a conventional optical delay phase modulator. Optical analog with excellent high speed
A digital converter can be easily realized, and its effects are great.

[Brief explanation of drawings]

Figure 1 (al is an explanatory diagram showing the configuration of the first embodiment of the present invention. Figure 1 (bl is a detailed explanatory diagram of the part thereof. Figure 2 shows the relationship between the optical output intensity and the electrical analog signal voltage. Characteristic diagram. Fig. 3(a) is an explanatory diagram showing the configuration of the second embodiment of the present invention. Fig. 3 (Tb) is a partial detailed explanatory diagram thereof. Fig. 4 (al is an explanatory diagram showing the configuration of the conventional example) Fig. 4(b) is a detailed explanatory diagram of the part. Fig. 5 is a characteristic diagram showing the relationship between the optical output intensity and the electrical analog signal voltage. 1.1) Input optical laser, 2... Branched blade wave path, 3-1 to 3-4... Phase modulator, 4-1 to 4-4.
14-1~14-4...Photodiode, 5-1~
5-4.15-1 to 15-4... Comparison circuit, 6-1 to
6-4.16-1 to 16-4... Output highway, 7
．． 17...Input highway, 8.18.18a...
Light modulation means, 12... input light lens, 13-1 to 13
-5... Acousto-optic element, 19.19a... Output light lens, 20-1 to 20-4.2O-1a to 20 to 4a
・-・Modulation circuit, 21-1 to 21-4.2l-1a to 2
l-4a... Oscillator, 22... Multiple coupling circuit, Ii
...Input light, I, 1. ~■4... Output light, Va.
...Analog signal, V0 to Vd4...Digital signal. Agent Patent attorney Nao Takashi Ide 6) 2; 5 Example 2 Figure 5 Conventional example also Figure 5

Claims (3)

[Claims] (1) Optical modulation means that generates n (n is a natural number of 2 or more) lights having different phases from input light according to an analog signal, and converts the output light from this optical modulation means into n electrical signals. In an optical analog-to-digital converter including a light receiving means and a comparing means for converting the electrical signal into a digital signal based on a certain threshold, the optical modulating means has an input for converting the input light into parallel light. an optical lens, an acousto-optic means for diffracting parallel light from the input optical lens to generate n lights each having a different phase, and a signal modulated by carrier waves each having a different amplitude using the analog signal as a modulation input. An optical analog-to-digital converter comprising: analog signal modulation means for providing the acousto-optic means with an output light of the acousto-optic means; and an output light lens for condensing the output light of the acousto-optic means. (2) The optical analog-to-digital converter according to claim (1), wherein the acousto-optic means is composed of n acousto-optic elements, and the carrier waves have the same frequency. (3) The acousto-optic means is composed of one acousto-optic element, the carrier waves are n carrier waves each having a different frequency, and the outputs of the respective modulation circuits are superimposed and multiple-coupled to be applied to the acousto-optic element. Claim No. 1 containing a circuit (
The optical analog-to-digital converter according to item 1).