JPS58147718A - Optical digital-to-analog converting device - Google Patents

Abstract

PURPOSE:To effectively utilize an optical waveguide layer, by converting a digital value shown by each light group propagated on each switched optical path, to an analog value shown by power of light which is propagated on a prescribed optical path and is emitted, in order. CONSTITUTION:When titanium is thermally diffused onto the surface of a single crystal 11 of lithium niobate being an acoustic optical crystal, an optical waveguide layer 12 having thickness of several mu or so is formed. On the incident side end part of this optical waveguide layer 12, an optical coupling part 13 is formed and on its emitting side end part, grating lenses 14, 15 are formed, respectively, an optical gruop PA consisting of parallel light P0-P7 of 8 beams is led into the optical waveguide layer 12 from the optical coupling part 13, and light which is subjected to optical D/A conversion in the process of propagating in the optical waveguide layer 12 is condensed by the lenses 14, 15, so as to be optically coupled and emitted to optical fibers 16, 17, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical DA converter that converts digital optical data represented by a plurality of parallel input light rays into an analog quantity called optical power, and more specifically, an optical D/A converter that converts digital optical data represented by a plurality of parallel input light beams into an analog quantity called optical power. The present invention relates to an optical DA conversion device that utilizes the phenomenon.

2. Description of the Related Art In recent years, optical application technology has made remarkable progress, and various optical functional elements are required accordingly. Among optical functional elements, optical DA conversion elements can be applied to optical communications, optical disks, optical sensors, etc., and although there is a great need for them, they have not yet been realized.

The present invention provides an optical DA converter that can be used for optical applications and can effectively utilize the optical waveguide layer. Optical switching means for switching the propagation optical path in the optical waveguide layer of a light group constituted by a collection of lights to either of two directions, and sequentially diffracting the six lights of each light group propagating on each switched optical path. A surface acoustic wave generator that generates a surface acoustic wave that is deflected from the optical path by the optical switching means, and a control circuit that controls the timing between switching the optical switching means and generating the surface acoustic wave, and propagating on each switched optical path. It is characterized in that the digital quantity represented by each light group is sequentially converted into an analog quantity represented by the power of the light propagated through the predetermined optical path and emitted. By condensing the light emitted from the leading wave layer, converting it into an electrical signal, and then integrating this, the optical signal converted into an analog quantity can be extracted as an electrical signal.

As the light input/output means of the optical waveguide layer, grating,
Prisms and other optical coupling elements can be used. The surface acoustic wave generator is preferably a comb-shaped electrode ultrasonic transducer (
The transducer is an inter-digital transducer (hereinafter referred to as IDT), but Gunn diodes and other devices may also be used. The optical switching means includes a large number of IDs.
In addition to the IDT array, which is constructed by arranging Ts and to which a DC voltage is applied, there is a Y-shaped leading waveguide with two branches extending at an angle twice the Bragg angle θ. Preferably, the Y-shaped waveguide is formed monolithically on the substrate on which the waveguide layer is formed, and its two branches are optically coupled to the optical waveguide layer.

In the optical DA conversion device according to the present invention, most of the device can be manufactured on one substrate, and since the structure is very simple, it can be easily mass-produced and provided at low cost. I can be scared. Furthermore, since it can be manufactured together with other optical functional devices on a cold chip, it is possible to integrate many devices on the same substrate. In particular, this invention is equipped with a control circuit that controls the timing of switching the optical switching means and generation of surface acoustic waves, so that the optical path on the leading wave layer of one light group is switched to perform two-plane optical DA conversion. Or, 2
It becomes possible to perform optical DA conversion on a group of light beams, making it possible to effectively utilize the optical waveguide layer on the substrate and increasing the degree of integration.

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

Figures 1 and 2 illustrate the principle of this invention, that is, the deflection of light using the acousto-optic effect of surface acoustic waves, and when two parallel beams of light and the surface acoustic wave intersect, the surface acoustic wave The time point at which the two beams are deflected by is the time required for the surface acoustic wave to propagate through the mutual distance between the two beams.
This shows that it differs depending on the propagation position of the light.

In FIG. 1, two lines of light (PI) (P2) are incident in parallel on an optical waveguide layer formed of an acousto-optic material. IDT (11) is provided on this optical waveguide layer.

By applying an ultrasonic voltage signal to ID Til+, a surface acoustic wave (hereinafter referred to as SAW), which is a periodic refractive index fluctuation, is generated on the surface of the optical waveguide layer, as shown by the parallel broken line.
is generated, and the SAW propagates on the surface of this waveguide layer at the propagation speed of sound. Since the SAW wavefront acts as a diffraction grating for light, light (P 1) (P 2) incident on the SAW wavefront at a small angle θ will be completely reflected by the SAW when the following conditions are satisfied. , its direction of travel is 2
Only 0 changes.

Here, λ: wave layer of light, 4: period of SAW This is the deflection of light by Bragg diffraction using SAW.

The time point at which the ultrasonic signal is printed on ID T11) is t.

shall be. The light (P2) is incident at a position closer to the IDT (1) than the light (Pl). SAW propagation speed VS,
I D Til+ (7) From the tip, light (PI) (P2
) is deflected by the SAW (diffraction point) by l! Let it be l, /2.

The light (P2) begins to be deflected by the SAW at time 2, also after 1!2/VS(7) time has elapsed from time 0. The light (PI) is slower than this, from time tQ to /l/VS
At time t1, the beam begins to be deflected by the SAW. The lights CP, l) and (P2) are the S of these lights
In the propagation direction of the AW, the time point at which the AW begins to be deflected is shifted by a time (1-42) proportional to the mutual spacing (/1-/2). This situation is shown in FIG.

3 to 5 show embodiments of the invention. In Figure 3, the acousto-optic crystal lithium niobate (
LiNb03) By thermally diffusing titanium (Ti) on the surface of a single crystal circle at a temperature of about 1000°C, a leading wave layer with a refractive index higher than that of the crystal substrate αD by about 3 to 5×10 and a thickness of about several μm! 12 are formed. This optical waveguide layer (
An optical coupling unit (IJ) is formed at the input side end of 12, and a grating lens (]41 (151) is formed at the output side end of the light group (151), which consists of eight parallel beams (PO) to (Pl). P A) is introduced into the optical waveguide layer α2 from the optical coupling part OJ, and in the process of propagating within the optical waveguide layer, the light is converted into an optical DA as described later and is focused by the lens Q41 (151). , and are optically coupled to optical fibers ao u'71 and emitted.

On the light incident side on the optical waveguide layer az, 6 light (PO) ~ (
IDT@~啼 are arranged in a line at the positions where they intersect with Pl), and an IDT string ω is formed by connecting these IDTs. Each electrode of IDTl2G-■ is provided at intervals satisfying the period A of the (υ equation),
And it intersects with the lights (PQ) to (Pl) at an angle θ. When a DC voltage is applied to the IDT column by the DC power supply Q81, a periodic refractive index change occurs directly under each IDT due to the electro-optic effect, and this is caused by a diffraction grating for the six lights (PO) to (Pl). Acts as. The timing control circuit controls signals (Ql) (Q2) (Fig. reference)
This outputs the following. At time tQ the signal (Ql)
is output and when direct current electrons are applied to the IDT column, the light group, which was traveling straight (RA) as shown by the broken line, is deflected by 20 degrees by Bragg diffraction and is guided to the optical fiber U61 through the lens circle. It will be destroyed.

The leading wave layer has an ID on the light output side than the IDT row above.
ID that generates a SAW whose wavefront intersects the light group (PA) deflected by the T array circle at an angle θ that satisfies the first mountain equation.
T 140) is provided.

An ultrasonic voltage signal generated from an ultrasonic signal generator a9 is applied to this IDTlα at time to by a signal (Q2). Light polarized by the IDT train (
Diffraction points of P O) to (P7) by SAW and IDT
The distance between the tip of +4Ql is 1OSl each! 1
,・柟・16,I! Set it to 7. I! O<j'l<...
<1!6<lr.

Referring to FIG. 4, at time tQ, the IDT column (to)
When a series voltage is applied to IDTlα and an ultrasonic voltage signal is applied to IDTlα, the light (PO) to (P7) first passes through the IDT string ■
deflected by At this point, the SAW has not reached the optical path of the customer, so the six lights (PO) to (P7) enter the optical fiber ae through the lens σΦ. From time Lo to time t! .

After /VS has passed, the SAW reaches the diffraction point of the light (PO), so the light (PO) is diffracted by the SAW and is no longer connected to the lens circle and the optical fiber αe.
It will no longer be incident on . Optical fiber (PO) +161
The time it is incident on is l! O/VS. Similarly, (Pi)-, , (P5) are sequentially deflected by the SAW, and finally the light (P7) is deflected from 0 to 1!7/VS
is deflected by the SAW when the time has elapsed. When the light (Pi) (i=0~7) is deflected by the SAW, these lights no longer reach the lens α4 and the optical fiber (1
6) is not incident. As is clear from the above-mentioned distance relationship, 10/VS </1/VS (,,.

Gu16/vSkuI! 7/■S.

After being deflected by the light (Pi) or the IDT array (to), S
Since the time T until the light is deflected by the AW is T = l i / VS as mentioned above, the time T can be changed by changing the incident position of the light, that is, the distance /i.
can be changed. If the power Pd of light (Pi) is constant with respect to time, the time T can be controlled by changing the incident position of the light, and the light (Pi) passes through the lens cone into the optical fiber (
The power Pd5j'i/-VS of light input to 161 can be controlled.

In this way, as the distance/i becomes smaller, the optical fiber +
The power of light incident on 161 decreases monotonically. Therefore, the light (PO) with the smallest distance/i is set to the least significant bit L
A weight of 2 is assigned as SB, and a weight of 2 is assigned to the light with the largest distance is (P7) as the topmost beam (P7). Similarly, other lights (pi>) are given a weight of 2i.This weighting is based on the distance I! for the LSB light [PO]. This can be realized by setting distance/i for 6 lights (Pi) to a distance expressed by the following formula, where 0 is a unit distance.

l! 1=2i,I! o0. , (2° For example, when distance I!0 is 20 μm, each distance is as shown in the table below.

As a result of the above, light (PO) is expressed as an 8-bit binary number, with light (PO) as LSB and light (P7) as MSB.
It will be understood that the digital quantity expressed by (P7) is converted into an analog quantity of the optical power incident on the optical fiber (5) through the lens a.
It shows the waveform of an optical signal that enters the optical fiber f161 when the lights (PO) to (P7) representing 011O101 are input. Here, 1 means the presence of light and 0 means no light.

The SAW generated from I D T +401 will continue over time. Therefore, at an appropriate time t3 after the light (P7) is deflected, the control of the signal (Ql) is stopped and the IDT
08AW, which immediately stops the application of DC voltage to the column (2), may be continued or stopped. Then, the light group (PA) travels straight again as shown by the broken line and hits the lens (15
1 and enters the optical fiber 0η. This straight traveling light group (PA) also satisfies equation (1) between it and the SAW.

I
The point where DTi4Ql took a distance of 11m1!0 is (Al
The distance between this point tAI and the tip of IDTi41 is l! Let it be d. Then, the above point 13 is also 3−*
0=ld/VP;>17/VS'fr: Satisfied point of time.

As a result, the light (PO) to (P7) indicated by the broken line is
Similarly to the above case, after time t3, the light is sequentially diffracted by the SAW and is diverted from the optical path of incidence on the lens (151).Therefore, after time t3, the light that passes through the lens 051 and enters the optical fiber aη has a slope of the lens a. The waveform becomes exactly the same as that of the light that enters the optical fiber through the optical fiber, and the light group (P
A) will be optically DA converted twice.

If the light group (PA) is incident on the optical waveguide layer αa after time LO, the light before time to also enters the lens (15).
through the optical fiber u'? ), but either an appropriate optical switch is provided on the optical waveguide layer G2, or the optical group (PA)
By making the incident timing of LO coincide with the LO or by providing an optical switch in the optical fiber (171),
It is easily possible to extract only the light incident on the optical fiber (171) after 3.

In this embodiment, when one group of optical digital signals is optically DA converted and extracted and used as two groups of optical analog signals (
Especially suitable. For example, check the optical DA conversion by comparing the optical analog signals extracted from the α61 plane of both optical fibers. I can do something.

In this embodiment, the optical signals (PO) to (P7) are weighted using binary numbers, but it goes without saying that arbitrary weighting can be performed depending on the incident position of the light. Moreover, the optical waveguide layer is L i N b O3
Although it is formed by thermally diffusing Ti, it can also be realized with other acousto-optic materials and other methods.

Further, in the above embodiment, in the first optical DA conversion, the distance 10 is the distance corresponding to the weighted LSB, and the application of DC voltage to the IDT array and the ultrasonic signal to the IDT is applied at the same time, but by slightly delaying the driving of the IDT array compared to the driving of the 1D T IQI, the distance lO can be set longer.
The reverse is also possible.

6 and 7 show other embodiments. In FIG. 6, in addition to the above-mentioned light group A (PA), the optical waveguide layer (1) is weighted according to the position similarly to this light group (PA). A light group (PB) consisting of mutually parallel lights (P10) to (Pi7) has an incident angle different from that of the light group (PA) by 20, and the light group (PA) is on the IDT mountain range. The DA-converted light is emitted through the optical coupling part (2), and is received by the photodetectors t4a and ta through the lenses 14υ (Incorporated).Each photodetector (4
The output electrical signal of 2i is integrated by an integrator Nini. Both detectors Ω2145 are controlled by the signal (Q2), and the detector - receives light when the signal (Q2) is at the H level, and the detector - receives light when the signal (Q2) is at the L level. Detect each light.

Control signal (Ql) output from timing control circuit 4
(Q2) is different from the embodiments shown in FIGS. 3 to 5. Referring to Figure 7, both optical groups (PA)
(PB) is input into the optical waveguide layer (12). At time tQ, a DC voltage is applied to the IDT string (to),
Ultrasonic signals are applied to the IDT ([).The incident light group (PA) (PR) is
Be biased. Therefore, first, the six lights of the light group (PA) are I
The light DA is changed by being sequentially deflected by the SAW generated from the DTl 401, and the light until it is deflected is detected by the detector 14Z. And from time to l! At the time point 3 when the time d/vS has elapsed, the signal (Q2) is inverted from the H level to the L level. At this point, the generation of SAW from the IDT side stops, but the SAW generated between time tO and L3 is
As the AW propagates further, the light group (PB) is subsequently subjected to optical DA conversion by the SAW and the light is detected by a detector.

At time t4 after the MSB light (P17) in the light group (PB) is deflected, the signal (Ql) is inverted to L level and the signal (Q2) is inverted to H level. therefore,
At the time, (after L4, no DC voltage is applied to the IDT string ω, so both light groups (P A) (P B)
travels straight without being deflected by the IDT array. For this reason, first the light group (PB) is IDT (401 occurrence t
The light is deflected by S A, Mulberry W, is converted into DA, and is detected by the detector (
The light is received four times. At time t5, when /d/VS has elapsed from time t4, the signal (Q2) is inverted to L level, but the light group (PA) is then optically DA converted by the SAW that has already been generated and propagated. , detected by a detector.

In this example, the light D by the SAW of -10,000 light groups is
Immediately after the A conversion is completed, the signal (Q2) is inverted to L level, and the generation of SAW is stopped. Then, the other light group is subjected to optical DA conversion by this <SAW that has already occurred and is progressing. Therefore, the light DA of the other light group
When the conversion is completed, there is already an SA on the optical path of both light groups.
Since W no longer exists, it is possible to immediately proceed to the next optical DA conversion, and the repetition period N of light and A conversion can be shortened.

[Brief explanation of the drawing]

Figures 1 and 2 are for illustrating the principle of this invention. Figure 1 is an explanatory diagram showing how the light is deflected, and Figure 2 is an explanatory diagram showing the timing at which the light is deflected.・Chart, FIG. 3 shows an embodiment of the present invention, and FIG. 4 is a block diagram of an optical DA converter, and FIG.
A time chart showing the optical signal output from the A conversion device, FIG. 5 is a waveform diagram showing the output signal of the photodetector, FIG. 6 is a configuration diagram showing another embodiment, and FIG. 3 is a time chart illustrating the operation of the device shown in the figure. flllal~so t4111@as ID TS(1
11*ss L i N b 03 board, (1z...
Optical waveguide layer, (131(2)... optical coupling part, α leakage [1
51(411(4416,, lens, 161(171@
-Optical fiber, Ql @ * * ~ (P7) (PIO)
~(PI3)---Light, (PA) (PB)...
・Light group. Patent applicants: Tateishi Electric Co., Ltd., and 4 others

Claims (1)

[Claims] +11 An optical waveguide layer formed of an acousto-optic material, a propagation optical path in the optical waveguide layer of a light group constituted by a set of a plurality of lights incident parallel to each other and weighted by the propagation position. an optical switching device that switches the optical path to one of two predetermined directions, and an elastic device that generates surface acoustic waves that sequentially diffract the six lights of the respective light groups traveling on each switched optical path, thereby deflecting the optical path from the optical path. A control circuit controls the timing of switching the surface wave generator and optical switching means and generation of surface acoustic waves, and sequentially controls the digital quantity represented by each light group transmitted on each switched optical path to the above-mentioned predetermined value. An optical DA converter that converts the light transmitted along the optical path of the light into an analog quantity expressed by the power of the emitted light. +21 An optical DA conversion device according to claim 11, wherein two light groups having different incident directions are sequentially subjected to optical DA conversion.