JPH01183204A - High frequency sweep device - Google Patents

Abstract

PURPOSE:To improve the accuracy of frequencies through the use of a voltage controlled oscillator by providing a high frequency output limitation means. CONSTITUTION:The title device consists of a comparator 51 as a control circuit controlling the state of an attenuator 59, a CPU(central processing unit) 52, a counter 53, a ROM 54, a D/A converter 55, the voltage controlled oscillator 56, a CR circuit 57, a branching device 58, the attenuator 59 and a frequency- divider 60. In such a case, a first setting value (lower limit value) and a second setting value (upper limit value) corresponding to the lowest frequency f1 and the highest frequency f2 of a high frequency which is impressed on a couple of cross comb type electrodes of a light deflection device, for example, are set in the comparator 51. Even if the characteristic of the voltage controlled oscillator 56 changes due to the change of a peripheral temperature, the attenuator 59 is operated when the frequencies of the high frequency RF actually show f1 and f2, the high frequency RF which is frequency-swept between f1 and f2 is always transmitted to the IDTs.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention provides a high frequency sweep device that outputs a high frequency wave whose frequency has been swept. The present invention relates to a high-frequency sweeping device that is configured to have a high frequency.

(Prior Art) For example, mechanical optical deflectors such as galvanometer mirrors and polygon mirrors and EOD (electro-optic optical deflectors) have been used as optical deflection devices for deflecting light beams in optical scanning recording devices, optical scanning reading devices, etc. AOD (acousto-optic optical deflector) is widely used. However, mechanical optical deflectors have problems such as poor durability and tend to be bulky.On the other hand, EOD and AOD do not have a large optical deflection angle, so the beam optical path becomes long, and optical scanning recording devices etc. There is a problem in that it leads to an increase in size.

Recently, as an optical deflection device that can solve the above-mentioned problems,
Optical deflection devices using a guiding waveguide are attracting attention. This optical deflection device consists of a slab-shaped leading waveguide made of a material that allows surface acoustic waves to propagate, and a surface whose frequency changes continuously as it travels in the direction intersecting the light beam guided inside the optical waveguide. A means for generating an elastic wave in the optical waveguide (for example, composed of a pair of crossed comb-shaped electrodes and a driver that applies a high-frequency alternating voltage whose frequency changes continuously to the pair of intersecting comb-shaped electrodes). . In this optical deflection device, the light beam guided in the guide waveguide undergoes Bragg diffraction due to acousto-optic interaction with the surface acoustic wave, and this diffraction angle changes depending on the surface acoustic wave frequency, so the surface acoustic wave By varying the frequency as described above, the light beam can be continuously deflected within the guide wavepath. The light beam deflected in this manner can be emitted out of the leading waveguide by, for example, a diffraction grating (grating coupler) or a prism coupler formed on the surface of the leading waveguide. Further, such a light deflecting device is described in detail in, for example, Japanese Patent Laid-Open No. 62-77761.

On the other hand, for example, Japanese Patent Application No. 62-18077 filed by the applicant of the present application
As shown in Specification No. 9, an optical spectrum analyzer that measures the wavelength of a light beam by propagating a surface acoustic wave whose frequency changes continuously in an optical waveguide, similar to the above-mentioned optical deflection device, has also been proposed. There is. In this optical spectrum analyzer, when a light beam guided through an optical waveguide is diffracted by a surface acoustic wave, the diffraction angle changes depending on the surface acoustic wave frequency as described above, and also changes depending on the wavelength of the light beam. The wavelength of the light beam is determined based on the surface acoustic wave frequency when the light beam is diffracted at a predetermined angle.

In the optical deflection devices and optical spectrum analyzers that use the optical waveguides described above, it is necessary to sufficiently increase the frequency accuracy of surface acoustic waves in order to improve the scanning accuracy of the optical beam or the accuracy of optical wavelength analysis. is necessary. As mentioned earlier, this surface acoustic wave is generally generated by applying a swept high-frequency alternating voltage to a pair of intersecting comb-shaped electrodes, so in this case, the frequency accuracy of the high frequency applied to the pair of electrodes is Increasing the frequency accuracy of surface acoustic waves will inevitably improve.

More specifically, a high-frequency sweep device that generates a swept high-frequency wave is a voltage-controlled oscillator (VCO) that outputs a high-frequency wave whose frequency changes depending on the value of an input voltage signal.
: Voltage ControlledOsci
Conventionally, a device consisting of a voltage controlled oscillator (l 1ator ) and a signal generation source that inputs a gradually increasing or decreasing voltage signal to this voltage controlled oscillator has been widely used. Such a high frequency sweep device is advantageous in reducing the size and cost of an optical deflection device and an optical spectrum analyzer compared to a synthesizer, etc., since the voltage controlled oscillator is relatively inexpensive and compact.

(Problem to be Solved by the Invention) However, on the other hand, the above voltage controlled oscillator has inferior frequency stability compared to a synthesizer or the like, and therefore has the problem of low frequency accuracy as described above. In other words, this voltage controlled oscillator is
Generally, it has instability of about several MHz to several tens of MHz. For example, when the above-mentioned optical deflection device is applied to an optical scanning recording device, if the surface acoustic wave frequency, that is, the frequency of the high frequency applied to the interdigitated electrode pair is swept between 500 and 100,100 O, the frequency sweep range is 500 MHz.
Therefore, in order to obtain 2000 resolution points, a frequency accuracy of 500 MHz/2000=0.25 MHz is required. Conventionally, it has been impossible to satisfy such requirements when using a voltage controlled oscillator with low frequency stability as described above.

SUMMARY OF THE INVENTION An object of the present invention is to provide a high frequency sweep device that uses a voltage controlled oscillator and can sufficiently increase frequency accuracy to the above value.

(Means for Solving the Problems) The high frequency sweep device of the present invention includes, in addition to a voltage controlled oscillator and a signal generation source that inputs a voltage signal that gradually increases or decreases to the voltage controlled oscillator as described above, a voltage controlled oscillator. a first state that allows the high frequency output from the oscillator to pass, and a second state that limits this passing.
a high frequency output limiting means that can selectively take a state of 1; a frequency measuring means for measuring the frequency of the high frequency; and receiving the output of the frequency measuring means, the frequency measured by the means has reached a first set value. and a control circuit that sets the high frequency output limiting means to the first state when the frequency reaches a second set value, and sets the high frequency output limiting means to the second state when the frequency reaches a second set value. That is.

(Function) As mentioned above, the frequency of the high frequency output from the voltage controlled oscillator was actually measured, and this 11! If the high frequency is outputted from the high frequency output limiting means when the J constant value reaches the first set value, and the output is limited when the J constant value reaches the second set value,
The output limiting means outputs a high frequency wave whose frequency is accurately swept between the first set value and the second set value. The instability of the high frequency output from the voltage controlled oscillator is caused by a parallel shift in the characteristic curve of the input voltage signal versus the output frequency. If the frequency is accurately suppressed, the frequency will always change with the characteristic between the paths even within these value ranges.

(Example) Hereinafter, the present invention will be described in detail based on an example shown in the drawings.

FIG. 1 shows a high frequency sweeping device 50 according to an embodiment of the present invention, and FIGS. 2 and 3 show an optical deflection device that deflects a light beam by receiving the high frequency waves swept by this high frequency sweeping device 50. A device 10 is shown. First, the optical deflection device IO will be explained with reference to FIGS. 2 and 3. This optical deflection device IO constitutes an optical scanning recording device as an example, and includes a slab-shaped leading waveguide 11 formed on a transparent substrate 16 and intersecting comb-shaped electrodes provided at the side ends of this optical waveguide 11. Pair (Inter D 1g1
transducer (hereinafter referred to as IDT) 15, and a linear diffraction grating (LlnearG) for light incidence provided spaced apart from each other on the surface of this optical waveguide 11.
It has a ratlng coupler (hereinafter referred to as LGC) 20 and a light emitting LGC 21. Moreover, on the surface lea on the opposite side to the leading waveguide ti of the substrate IB,
A light input prism 30 and a light output prism 31 are attached. The light entrance prism 30 has a triangular cross section, and has a first light passing surface 30a and a second light passing surface 30.
b, and the first light passing surface 30a is the substrate surface tea.
It is tightly fixed to the surface 16a by being strongly pressed against it or by using an adhesive with a high refractive index. The light output prism 31 is also the light input prism 30.
It has the same shape as the first light passing surface 318% and the second light passing surface Blb, and the substrate surface lea
is fixed.

In this embodiment, as an example, the substrate 18ELiNbO
, wafer is used, and an optical waveguide U is formed by providing a Ti diffusion film on the surface of this wafer. Note that the substrate te
Alternatively, a crystalline substrate made of sapphire, Si, etc. may be used. Furthermore, the optical waveguide 11 is not limited to the above-mentioned Ti diffusion, but can also be formed by sputtering, vapor depositing, or the like other materials on the substrate 16. Regarding optical waveguides, see, for example, Inch-Grated Obtique 7.
rated 0ptlcs) J() Bix in Applied Physics (Topics 1n Ap
pHed Physlcs) Volume 7) Sbringer
Detailed descriptions can be found in published works such as Sprlnger-Verlag (1975); Nishihara, Onna, and Suhara co-authors ``Optical Integrated Circuits'' published by Ohmsha (1985). Any of the following optical waveguides can be used. However, this guide wave path 11 is formed from a material such as the above-mentioned Ti diffusion film that allows surface acoustic waves to propagate, which will be described later. Further, the optical waveguide may have a laminated structure of two or more layers.

The semiconductor laser 18 that emits recording light emits a light beam (
It is arranged so as to emit a laser beam) 13. This light beam 13, which is a diverging beam, is made into a parallel beam by a collimator lens 25, and then enters the light entrance prism 30 from the second light passing surface 30b,
The light passes through the first light passing surface 30a and enters the substrate 1B, passes through the optical waveguide 11, and enters the portion of the LGC 20 formed on the surface thereof. Thereby light beam 1
3 is diffracted by this LGC 20, enters the leading waveguide 11, and travels in the direction of arrow A within the optical waveguide 11 in a waveguide mode.

When recording an image, the photoreceptor 23 is set on a transport means 22 such as an endless belt.

Then, the semiconductor laser IB is driven by the laser drive circuit 19.
The IDT 15 is driven to emit a laser beam 13, and at the same time, a high frequency alternating voltage whose frequency changes continuously is applied from a high frequency sweep device 50 to the IDT 15 (the generation of this high frequency will be described in detail later). ). The laser drive circuit 19 is controlled by a modulation circuit 24 to change the optical output according to the image signal S (i.e., the intensity of the light beam 13, the number of pulses and the pulse width when emitting the light beam 13 in a pulsed manner). ) the semiconductor laser 18 is driven so as to change the

The IDT 15 is made up of a large number of electrode fingers arranged in parallel with line widths that are changed little by little, and by applying the above-mentioned voltage to the IDT 15, the surface acoustic wave 12 is generated.
occurs. This surface acoustic wave 12 travels on the surface of the optical waveguide 11 in the direction of arrow B in FIG.

The IDT 15 is arranged so that the surface acoustic wave 12 travels in a direction intersecting the 13° optical path of the guided light (parallel beam). Therefore, the guided light 13° is the surface acoustic wave 1
At this time, the guided light 13° undergoes a Bragg (
Bragg) Diffraction.

Bragg diffraction of guided light by surface acoustic waves has been known for some time, but will be briefly explained here. The traveling direction of the surface acoustic wave 12 propagating in the leading waveguide 11 and the guided light 1
If the angle (Bragg angle) formed by the 3° traveling direction is θ, then the deflection angle (diffraction angle) δ of the guided light 13' due to the acousto-optic interaction with the surface acoustic wave 12 is δ-2θ.

The wavelength of the guided light 13° and the effective refractive index are λ and Ne, and the wavelength, frequency, and speed of the surface acoustic wave 12 are AS, respectively.
If fSv, 2θ-25in-1(λ/ (2Ne
@A) 1 λ/(Ne@A) 1λ·f/(Ne−v), and 2θ, that is, δ is approximately proportional to the frequency f of the surface acoustic wave 12. As mentioned above, the high frequency sweep device 50 is the IDT1.
Since an alternating voltage whose frequency changes continuously is applied to 5, the frequency of the surface acoustic wave 12 changes continuously, and the deflection angle δ changes continuously. In other words, as shown by arrow C, this guided light 13° is diffracted and deflected so that the diffraction angle changes continuously. The guided light beam 13° thus deflected is diffracted by the LGC 21 and output from the optical waveguide 11 to the substrate 16 side. In this way, the light beam 13'' emitted from the leading waveguide 11 and turned into external light passes through the first light passing surface 31a of the light emitting prism 31, enters the prism 31, and enters the second light passing surface. The light passes through the atb vertically and exits the prism.

The light beam 1 emitted to the outside of the guiding waveguide 11 as described above
The beam 3' passes through a scanning lens 2B made of, for example, an fθ lens, is focused into a small beam spot Q, and scans (main scans) the photoreceptor 23 in the direction of arrow U.

At the same time, the photoreceptor 23 is transferred by the transfer means 22 in the direction of arrow V, which is substantially perpendicular to the main scanning direction, to perform sub-scanning, so that the photoreceptor 23 is two-dimensionally scanned by the light beam 13''. .As mentioned above, this light beam 13"
is modulated based on the image signal S, so the photoreceptor 2
3, an image carried by this image signal S is recorded.

Note that in order to synchronize the image signal S for one main scanning line with the main scanning of the light beam 13'', the blanking signal sb included in this image signal S is used as a trigger signal.
The timing of voltage application to the IDT 15 may be controlled.

Furthermore, by controlling the driving timing of the transfer means 22 using this blanking signal sb, the main scanning and sub-scanning can be synchronized.

Here, if the frequency of the alternating voltage applied to the IDT 15 is accurately swept between a predetermined value fl to ft (assuming fl < ft), the deflection angle range of the light beam 13'' becomes constant and its photosensitive Although the scan area (range between the scan start point and end point) on the body 23 is kept constant, if this frequency sweep range changes, the scan area changes and the recorded image becomes distorted. Hereinafter, we will explain how the occurrence of such problems can be prevented.As shown in FIG.
Comparator 51 as a control circuit that controls the state of 9.
, CPU (central processing unit) such as a microprocessor 5
2, counter 53, ROM 54, D/A converter 55,
It is composed of the voltage controlled oscillator 5B as described above, a CR circuit 57 inserted between the voltage controlled oscillator 5B and the D/A converter 55, a brancher 58, an attenuator 59, and a frequency divider 60. There is. When deflecting a light beam, first CP
U52 starts the counter 53 and begins sending clock pulses. The counter 53 counts these clock pulses and sends a digital signal Sd indicating the count value to the ROM 54.

The ROM 54 constitutes a table for correcting nonlinearity, etc. of the voltage controlled oscillator 5B, and the digital signal Sd is converted and outputted so that this nonlinearity is corrected. This conversion signal Sd' is sent to the D/A converter 55 and converted into an analog voltage signal Sv. This voltage signal Sv
corresponds to the count value of the clock pulse, and since this count value gradually increases, the voltage signal S
The level of v gradually increases over time. This voltage signal Sv is smoothed by the CR circuit 57 and then input to the voltage controlled oscillator 58. The voltage controlled oscillator 5B has characteristics as shown in FIG. 4, and outputs a high frequency RF (alternating voltage) having a frequency f corresponding to the value V of the voltage signal Sv. This high frequency RF is branched by a splitter 58, sent to an attenuator 59, and also sent to a frequency divider BO. The frequency divider 60 divides the frequency f of the high frequency RF into 1/M, and sends a signal Sf indicating the frequency f/M to the comparator 5.
Send to 1. This comparator 51 has a first set value (lower limit value) that is the lowest frequency f1 and highest frequency f2 of the high frequency applied to the IDT 15, each multiplied by 1/M.
/Mt and a second set value (upper limit) F2-f2/M are set, and the comparator 51 attenuates the gate open signal GO when the frequency indicated by the signal Sf reaches the first set value F1. The signal is sent to the attenuator 59 to set the attenuator 59 to a state with an attenuation rate of O (zero) dB. Thereby, the high frequency RF passes through this attenuator 59 and is sent to the IDT 15, generating the surface acoustic wave 12 as described above. As is clear from the above, the frequency f of the high frequency RF at this time is the lowest frequency f
It is l. Thereafter, as the voltage signal Sv gradually increases,
The frequency f of the high frequency RF gradually increases, and thereby the deflection angle of the guided light 13° gradually increases.

In this way, the frequency f of the high frequency RF gradually increases,
When the maximum frequency f2 is reached, the frequency indicated by the signal Sf input to the comparator 51 becomes the second set value F2.
reach. When this state is reached, the comparator 51 sends the gate close signal Gc to the attenuator 59, and sets the attenuator 59 to the state with the maximum attenuation rate. As a result, the high frequency RF
It is no longer sent to the DT 15, or is sent at a very low level, and the generation of the surface acoustic wave 12 is stopped there. As explained above, the frequency of the high frequency RF sent to the IDT 15 changes continuously between the lowest frequency f1 and the highest frequency f2 in any case. Therefore, the frequency of the surface acoustic wave 12 is
It always changes continuously between the lowest frequency fl and the highest frequency f2, and the deflection angle range of the guided light 13° is kept constant.

In other words, even if the characteristics of the voltage-controlled oscillator 5B shown in FIG. 4 change as indicated by the broken line due to changes in ambient temperature, for example, the attenuator 59 is not activated when the frequency f of the high-frequency RF becomes fl or ft. Since it is being operated, it is always f1 to f2.
High frequency RF whose frequency has been swept between 1 and 2 is now sent to the IDT 15.

By the way, if the input voltage V to the voltage controlled oscillator 5B is v
When setting the frequency range of the high-frequency RF by controlling it to take a value of 1 to v2, if the characteristics in Fig. 4 fluctuate as shown by the broken line, the frequency of the high-frequency RF sent to the IDT 15 changes. The range is fl' shown in the figure
It fluctuates within a range of f2°. Furthermore, the characteristic fluctuation shown in FIG. 4 is such that the characteristic curve moves vertically in parallel in the figure, so as mentioned above, the lowest frequency f1 of the high frequency RF
As long as the maximum frequency f2 and f2 are suppressed, the frequency change characteristics between them will be - in any case.

The comparator 51 outputs the gate close signal Gc as described above, and at the same time outputs the signal S indicating the end of deflection to the CPU 52.
Send e. Upon receiving this signal Se, the CPU 52 stops outputting the aforementioned clock pulse and resets the counter 53 at the same time. Thereafter, the CPU 52 starts outputting clock pulses at a timing corresponding to the input of the blanking signal sb, and thereafter the operations described above are repeated, and the deflection of the light beam 13' is repeated. In addition, FIG. 5 shows the frequency f of the high frequency RF sent to the IDT 15.
This shows the changes over time.

As is clear from the above description, the value of the voltage signal Sv input to the voltage controlled oscillator 56 is set so that the oscillator 56 starts sweeping from a frequency slightly lower than the lowest frequency f1. The frequency at which this sweep starts is the lowest frequency f
How much lower than 1 to set is determined by the voltage controlled oscillator 5.
It is sufficient to grasp the extent to which the characteristic variation of B may occur, and to appropriately determine it accordingly. Further, the deflection speed of the light beam 13'' can be appropriately determined by adjusting the frequency of the clock pulse outputted from the CPU 52.

As mentioned earlier, the frequency sweep range is 5 with the lowest frequency f, -500MHz21 and the highest frequency fz-1000MHz.
00MHz, in order to obtain 2000 resolution points, at least 0.0MHz is required. It is necessary to sweep the frequency in 25 MHz steps, and a frequency accuracy of 6 digits is required. At present, comparators 51 having an accuracy of eight digits or more are available, so the above requirement can be met. Further, if the frequency divider 60 is, for example, a 1/160 frequency divider, the comparator 51 has a maximum of 6.25M.
A signal of Hz (=1000/160) is input, but if the value is around this level, the comparator 51 can execute the above-mentioned processing with sufficient accuracy.

In the embodiment described above, the frequency of the high frequency RF is swept so as to gradually increase, but on the contrary, this frequency is swept so as to gradually decrease, and when the frequency reaches a predetermined maximum frequency, the high frequency RF is the high frequency output limiting means (
In the above embodiment, the high frequency RF may be passed through the attenuator 59), and when the frequency reaches a predetermined minimum frequency, the output limiting means may limit the passage of the high frequency RF.

Further, the high frequency sweep device 50 of the embodiment described above is applied to an optical deflection device, but the high frequency sweep device of the present invention is applied to the above-mentioned optical spectrum analyzer.

It can be applied to any device that requires high frequencies in a precise frequency range, including isers.

(Effects of the Invention) As explained in detail above, the high frequency sweep device of the present invention actually changes the frequency of the high frequency output from the voltage controlled oscillator to n.
1 constant, and when this 191 constant value reaches the first set value, the high frequency is output from the limiting means, and when the second set value is reached, the output is limited, so that the high frequency sweep device A high frequency wave whose frequency is accurately swept between the first and second setting values is always sent to the device receiving the high frequency wave from the above. Therefore, if this high frequency sweep device is applied to the above-mentioned waveguide type optical deflector, the scanning accuracy can be sufficiently increased, and if it is applied to the above-mentioned optical spectrum analyzer, the accuracy of optical wavelength analysis can be sufficiently increased. Furthermore, since the high frequency sweep device of the present invention uses a voltage controlled oscillator, it can be made extremely inexpensive and compact compared to a synthesizer or the like.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a high frequency sweep device according to an embodiment of the present invention, FIGS. 2 and 3 are a side view and a schematic perspective view showing an optical deflection device using the above high frequency sweep device, respectively, and FIG. The figure is a graph showing the relationship between the input signal voltage and the output frequency of the voltage controlled oscillator according to the present invention, and FIG. 5 is a graph showing the frequency sweep characteristics of high frequencies by the above-mentioned high frequency sweep device. lO... Optical deflection device 11... Optical waveguide 12
...Surface acoustic wave 13...Light beam 13'
... Waveguide light 13" ... Light beam 15 emitted from the optical waveguide...
IDT 50...High frequency sweep device 51.
... Comparator 52 ... CPU 53 ... Counter 55 ... D/A converter 56 ... Voltage controlled oscillator 59 ... Attenuator 60 ... Frequency divider Fig. 1

Claims (1)

[Scope of Claims] A voltage controlled oscillator that outputs a high frequency whose frequency changes depending on the value of an input voltage signal, a signal generation source that inputs a voltage signal that gradually increases or decreases to the voltage controlled oscillator, and the voltage a high frequency output limiting means connected to a controlled oscillator and capable of selectively taking a first state in which the high frequency passes through and a second state in which the passage is restricted; and a frequency measuring means for measuring the frequency of the high frequency. , upon receiving the output of the frequency measuring means, when the frequency measured by the means reaches a first setting value, the high frequency output limiting means is set to the first state, and this frequency becomes a second setting value; and a control circuit that sets the high frequency output limiting means to the second state when the high frequency output limiter reaches the second state.