JPH02194332A - Optical spectrum analyzer - Google Patents

Abstract

PURPOSE:To accurately detect light to be measured with high S/N by providing a means for detecting the frequency of surface acoustic waves at the time of detecting the light to be measured with the aid of a photodetector means based on component fetched from a filter means. CONSTITUTION:A light beam L projected from a light source 21 is incorporated in a light guide 12 from an end face 12a through an optical fiber 22, a coupler 23 and an optical fiber 24. The light beam L is allowed to be the collimated beam of light by a light guide lens 13 and guided in the light guide 12. Next, the light beam L4 projected from the light guide 12 passes a pin hole 30a and is detected by a photodetector 31. The guided light L1 made incident on the surface acoustic wave 15 is modulated in modulation frequency (fr) through a modulation control circuit 26. Therefore, a light quantity signal S1 outputted from the photodetector 31 is modulated in frequency (fr) and is supplied to a lockin amplifier 35. In the amplifier 35, the component same as the frequency (fr) is fetched from a signal S1 by an incorporated BPF and outputted as the light quantity signal S'1. By making the light pass the BPF, the light is detected with high S/N.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to an optical spectrum analyzer that performs optical spectrum analysis, and particularly relates to an optical spectrum analyzer that analyzes optical spectrum using the acousto-optic effect. .

(Prior Art) Various types of optical spectrum analyzers for analyzing optical spectra are known.

As one of the optical spectrum analyzers that have been widely used in practical use, for example, there is known a so-called Zzerny-Turner type optical spectrum analyzer. This optical spectrum analyzer rotates a diffraction grating that diffracts the irradiated light to be measured, thereby moving the diffracted light on a slit, and detecting the diffracted light through the slit based on the rotation angle of the diffraction grating. This method analyzes the optical spectrum.

Such optical spectrum analyzers are capable of analyzing optical spectra with high resolution.

However, such optical spectrum analyzers are large and heavy, making them difficult to handle, making them unsuitable for portable use, for example. Various optical spectrum analyzers that can be made small and lightweight have been considered, but many of these have the problem of low resolution.

Therefore, the applicant first proposed an optical spectrum analyzer that can be made small and lightweight and has high resolution (
(Patent Application No. 180779/1982). This optical spectrum analyzer includes an optical waveguide formed of a material that allows surface acoustic waves to propagate, and a waveguide that is arranged in a direction that intersects the optical path of guided light as measured light that is input into the optical waveguide and travels within the optical waveguide. Proceed,
A surface acoustic wave generating means for generating a surface acoustic wave whose frequency changes continuously to diffract and deflect the guided light in a thick optical waveguide; The present invention is characterized in that it is comprised of a light detection means for detecting the thick light to be measured, and a frequency detection means for detecting the frequency of the surface acoustic wave when the light detection means detects the light to be measured.

When guided light guided in an optical waveguide intersects with a surface acoustic wave propagated in this optical waveguide, it is diffracted and deflected due to acousto-optic interaction. This deflection angle δ is δ−2θ, where θ is the incident angle of the guided light with respect to the traveling direction of the surface acoustic wave. The wavelength of the guided light is λ, and the effective refractive index of the optical waveguide is N.
Let e be the wavelength, frequency, and velocity of the surface acoustic wave, respectively.
S f.

If ■, then λ. Since Ne and V are constant, if the incident angle θ and the surface acoustic wave frequency f at which the guided light is most efficiently diffracted satisfying the Bragg condition expressed by this equation are known, the guided light, that is, the light to be measured, can be determined. The wavelength λ of is known.

Further, when the guided light (light to be measured) includes a plurality of spectral components having very close wavelengths, each spectral component can be separated by the diffraction effect of the surface acoustic wave. Therefore, for example, if a pinhole plate or the like is placed in front of the photodetector so that the light of each spectral component can be detected individually, each spectral component can be detected even if the wavelengths are close to each other as described above. Components can be measured accurately.

(Problems to be Solved by the Invention) An object of the present invention is to enable the above-mentioned optical spectrum analyzer to detect light to be measured with a high S/N ratio.

(Means for Solving the Problems) The optical spectrum analyzer according to the present invention has an optical spectrum analyzer that includes an optical waveguide as described above, a surface acoustic wave generating means, a light detecting means, and a frequency configuration H4 means. In the analyzer, an optical waveguide is formed from a material exhibiting an electro-optic effect, an optical switch is provided for the electro-optic optical path in the optical waveguide portion of the optical waveguide, and voltage application to the electro-optic optical switch is controlled by the surface elasticity. ON-Or'l below the modulation frequency lower than the wave frequency
a switching circuit that controls and periodically switches the optical path of the optical waveguide between an optical path toward the photodetector and an optical path away from the photodetector; , filter means for extracting only a component of the same frequency as the modulation frequency from the detection signal, and the frequency detection means detects the light to be measured by the light detection means based on the component extracted from the filter means. The present invention is characterized in that it is configured to detect the frequency of the surface acoustic wave at the time.

(Function) If the optical path of the optical waveguide is switched as described above, the light to be measured detected by the photodetector is turned on at the above modulation frequency.
-OFF modulation is performed. Therefore, if the same frequency component as the modulation frequency is extracted from the output signal of this photodetector, it becomes a component based almost only on the light to be measured.

Therefore, even if the output signal of the photodetector contains noise, it can be removed and the light to be measured can be detected with a high S/N ratio.

In addition to modulating the guided light as described above, it is also possible to modulate the applied alternating voltage to the surface acoustic wave that diffracts the guided light by ON-OFF I. In this case, the modulation frequency must be set relatively low so as not to reduce the diffraction efficiency of the guided light. In other words, if the modulation frequency of the surface acoustic waves is made too high, the surface acoustic waves will be interrupted at random within the beam width of the guided light.

On the other hand, when the light to be measured is switched and modulated using an electro-optic optical switch, the above-mentioned restrictions are not imposed, and the modulation frequency can be sufficiently increased.

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

FIG. 1 shows an optical spectrum analyzer according to a first embodiment of the present invention. This optical spectrum analyzer 10 includes an optical waveguide I2 formed on a substrate 11, a waveguide lens 13 formed on this optical waveguide 12,
Focusing diffraction grating for light beam output
rating coupler (hereinafter referred to as FCC) 14, these lenses 13 and FGC 14
A pair of Chlb interdigitated electrodes generates a surface acoustic wave 15 that travels in a direction intersecting the optical path of the guided light L1 that travels between
alT transducer (hereinafter referred to as chirp IDT) 17, a high frequency amplifier 19 that applies a high frequency alternating voltage to this chirp IDT 17 in order to generate the surface acoustic wave 15, and a high frequency amplifier 19 that continuously changes (sweeps) the frequency of the voltage. an electro-optic grating (E Iectr
29 (hereinafter referred to as EOG), an EOG drive circuit 25 that applies a voltage to this EOG 29, and a switching element in this drive circuit 25 to control the operation of the voltage application to ON-01'P. The modulation control circuit 2B has a modulation control circuit 2B.

Further, a pinhole plate 30 and a photodetector 3) such as a photodiode for measuring the intensity of the light beam L& are arranged at a position where the light beam L4 emitted from the light beam emission FGC 14 is irradiated. ing.

The light amount signal S1 outputted from this photodetector 31 is amplified by a lock-in amplifier 35, which will be described later, and the output signal S1-' of this lock-in amplifier 35 is inputted to an arithmetic processing circuit 33, which outputs it. Light amount signal S
3 is input to the display device 34.

In this embodiment, as an example, the substrate l] is made of LiNbO.
The optical waveguide J2 is formed by using three wafers and providing a Ti diffusion film on the surface of the wafer. Note that substrate 1
As 1, a crystalline substrate made of sapphire, 81, etc. may also be used. In addition, the optical waveguide 12 is not limited to the Ti diffusion described above, but other materials may be sputtered onto the substrate 11.
It can also be formed by vapor deposition or the like. However, this optical waveguide 12 must be formed of a material, such as the above-mentioned Ti diffusion film, that allows surface acoustic waves (described later) to propagate and exhibits an electro-optic effect. Further, the optical waveguide may have a laminated structure of two or more layers.

Charb IDT 17 and EOG 29 are manufactured by, for example, applying a positive electron beam resist to the surface of the optical waveguide 12, further depositing an Au conductive thin film thereon, drawing an electrode pattern with an electron beam, and developing after peeling off the Au thin film. , then Cr
The thin film can be formed by depositing an AI thin film and then performing lift-off in an organic solvent. Note that if the substrate 11 and the optical waveguide 12 are made of a piezoelectric material, the Charb IDT 17 can generate the surface acoustic wave 15 even if it is installed directly inside the optical waveguide 12 or on the substrate 11. If not, a piezoelectric thin film made of, for example, ZnO is formed on a part of the substrate 11 or the optical waveguide 12 by vapor deposition, sputtering, etc., and the IDT 17 is attached thereto.
All you have to do is set it up.

For example, a light beam L emitted from a light source 21 such as a semiconductor laser and subjected to spectrum analysis is transmitted through an optical fiber 22 connected to the light source 21, a coupler 23, and an optical waveguide 1.
The optical fiber 24 is introduced into the optical waveguide 12 from the end face 1.2a of the optical fiber 2 through the optical fiber 24 directly coupled to the end face 1.2a. This light beam L (divergent beam) is transmitted to the waveguide lens 13
The beam is made into a parallel beam and guided in the optical waveguide 12. This guided light L1 is incident on the EOG 29 portion. When a predetermined voltage is applied to this EOG 29 from the EOG drive circuit 25, the EOG 29 acts as a diffraction grating,
At this time, the guided light L1 is diffracted and travels in the direction indicated by the solid line in FIG. On the other hand, if the above voltage is not applied, the guided light Ll travels in the direction indicated by the broken line in FIG. If the Bragg condition expressed by the above equation (1) is satisfied, the diffracted waveguide light L1 is diffracted (Bragg diffraction). The diffracted waveguide light L2 is focused and emitted to the outside of the optical waveguide 12 by the action of FGCl,4.

Hereinafter, the diffraction and deflection of the guided light L1 by the surface acoustic wave 15 will be explained in detail with reference to FIG. 2.3. Figure 2 shows a detailed enlarged view of the chirp IDT 1.7, and Figure 3 shows the guided light 1 and surface acoustic wave 1.
The wave number vector of 5 is shown. As shown in FIG. 2, the guided light L1 is incident at a constant angle θ with respect to the traveling direction of the surface acoustic wave 15.

In addition, the wave number vectors of the guided light L1 before entering the surface acoustic wave I5 and the guided light L2 after passing through the surface acoustic wave I5 are respectively Ik
, t, Ik2, and the wave number vector of the surface acoustic wave I5 is IKl. When the Bragg condition shown in equation (1) above is satisfied, Ikl +I as shown in FIG.
K1 = Ikz −・= (2J, and the waveguide light L
The deflection angle for the guided light L1 of 2 is δ-2θ. If this incident angle θ is constant as described above, the deflection angle δ when the above (2J formula holds) is also constant. Therefore, the light beam L6 that completely satisfies the Bragg condition and exits from the optical waveguide 12 is emitted in a fixed direction.The pinhole plate 30 in front of the photodetector 31 is arranged so that the light beam L4 emitted in the fixed direction passes through the pinhole 30a.

The wavelength of the guided light Ll (measured light) is λ, and the surface acoustic wave 1
If the wavelength of 5 is A, then Ikl l-2π/λ and the wavelength of the guided light L2 is also λ, so IJ
l −11kz l −2π/λ. Therefore, the value of IIK knee 2π/A that satisfies the above formula (2) is:
Since the incident angle θ is fixed, only one exists for each 11kl+. Therefore, when (2 equations hold) (
In other words, the wavelength λ can be determined from the value of IIKII (when the light beam L4 passes through the pinhole 30a and is detected by the photodetector 31), that is, from the value of the wavelength of the surface acoustic wave 15.

This wavelength λ can of course be determined from the above equation (1), but it is also possible to determine the wavelength λ using the incident angle θ and the optical waveguide 1 for the guided light Ll.
Even if the refractive index Ne of 2 is unknown, it can be determined.

That is, it is assumed that a reference guided light having a known frequency (denoted as λrat) is made to enter the optical waveguide 12, and at that time, this reference guided light is diffracted by a reference surface acoustic wave having a wavelength Arer. In FIG. 3, if the wave number vector of the reference waveguide light is PQ, and the wave number vector of the diffracted reference waveguide light is OQ, then Δ0PQcoΔSPR, so OP PQ OP-2yr/λrerS PQ-2yr/Aref
Therefore, λ-λref (A/Aref') Here, the speed and frequency of the surface acoustic wave 15 are ■ and f, respectively, and the speed and frequency of the reference surface acoustic wave are ■rer and f rer, respectively.
Then, v −f A, vref −frerIAref,
Since it is v-vrer, λ-λref(frer/f) --(3) is obtained from equation 1. In other words, if the wavelength λref of the reference guided light and the frequency f ref' of the reference surface acoustic wave are checked in advance, the wavelength λ of the measured light can be determined from equation (3).

As mentioned above, when performing optical spectrum analysis, the frequency of the high-frequency alternating voltage applied to the Chirb IDT 1.7 is changed from fwin to fIIlax by the sweeper 20.
is continuously swept up to. Also, at this time, the modulation control circuit 2
6 repeatedly turns on and off the voltage application to the EOG 29 by the EOG drive circuit 25 at a predetermined modulation frequency fr. As a result, the guided light L1 incident on the surface acoustic wave 15
is modulated (ON-OFI) at a modulation frequency fr. This modulation frequency fr is set to a value lower than the frequency of the alternating voltage applied to the IDT 17.

As mentioned above, the frequency of the alternating voltage, that is, the surface acoustic wave 15
When the frequency of is swept, the above fmin, fffia
If the value of X is appropriately set, a certain surface acoustic wave frequency f (fmin≦f≦fWaX
), the guided light L1 is diffracted most efficiently. At this time, the light beam L4 emitted from the optical waveguide 12 passes through the pinhole 30a and is detected by the photodetector 31.

Here, since the guided light L1 incident on the surface acoustic wave 15 is ON-OFF modulated as described above, the light beam L diffracted by the surface acoustic wave 15 also has a modulation frequency fr
Therefore, the light amount signal S1 output from the photodetector 31 is also modulated at the modulation frequency fr. Lock-in amplifier 35 from the above-mentioned modulation control circuit 2B
A clock signal C having a frequency fr is input to the . The lock-in amplifier 35 uses a built-in band-pass filter to extract a component of the same frequency as the frequency fr from the light amount signal S1, amplifies the component, and generates the light amount signal Sl.
' Output as '. Generally, the light amount signal S1 contains various noises other than the signal component detected by the light beam L4, but by passing it through the band pass filter as described above, the light amount signal S1' can be converted to a high S/N signal that cuts out various noises.
It can be of. In this manner, the present device can accurately detect the intensity of the diffracted light beam L4. Note that the upper limit of the modulation frequency fr of the guided light 11 is essentially limited by the capacitance of the EOG 29 and the resistance of the circuit connected to the EOG 29. Since there are no restrictions as in the case of modulation, it is possible to make this modulation frequency fr sufficiently high, for example on the order of IGHz.

A frequency measuring circuit 32 connected to the sweeper 20 receives a high frequency signal Sf that the sweeper 20 sends to the high frequency amplifier ■9.
Then, the ever-changing alternating voltage frequency, that is, the surface acoustic wave frequency f, is determined. This continuously changing frequency f
A signal S2 indicating this is input to the arithmetic processing circuit 33. This arithmetic processing circuit 33 has the wavelength λ of the reference waveguide light mentioned above.
ref and the frequency f rer of the reference surface acoustic wave are stored in advance, and the arithmetic processing circuit 33 uses these wavelengths λ
From the surface acoustic wave frequency f indicated by ref', frequency frcr, and signal S2, guided light L is calculated based on equation (3) above.
In addition to calculating the wavelength λ of 1, the relationship between the detected light amount and the wavelength λ is determined based on the light amount signal Sl' synchronized with the signal S2.

A signal s3 indicating the relationship between the guided light L1, that is, the wavelength λ of the light to be measured, and the detection e,'-it obtained in this way is output from the arithmetic processing circuit 33, and is sent to a display device such as a liquid crystal display device or a phototube display device. 34, and this signal S3
Based on this, the relationship between the amount of light and the wavelength λ is displayed in a graph as an example. Therefore, if the wavelength λ at the time when the light beam L4 is detected, that is, when the Bragg condition is satisfied, is found from this display, it becomes the wavelength of the light to be measured.

Note that the display device 34 may be replaced with a suitable recording device or the like. Further, in this embodiment, the wavelength λ of the light to be measured corresponding to the surface acoustic wave frequency f is calculated by the arithmetic processing circuit 33.
is calculated and determined, but such calculations may be performed separately manually. That is, if at least the surface acoustic wave frequency f when the photodetector 31 detects the light beam L4 is detected, the wavelength λ of the light to be measured can be determined.

Furthermore, as in the embodiment described above, not only when the photodetector 31 detects the light beam L4, but also when the surface acoustic wave 15
While sweeping the frequency, find the frequency f,
It goes without saying that the light amount signal Sl' may be continuously sent to the arithmetic processing circuit 33 regardless of whether the open beam L4 is detected or not. In this way, the display device 34 clearly shows a wavelength range in which the light beam L4 is not detected at all (that is, a range in which no spectral component exists).

In such a case, since noise components are generally included in the light amount signal S1-' etc., the detected light amount display is often not O (zero) even in the wavelength region where the light beam L4 is not detected. Even if this happens, there is no problem as long as it is known in advance that up to a certain level of the light amount display is a noise component.

Furthermore, in order to avoid such a situation, a predetermined level slightly higher than the thick noise component may be displayed as the light ff1O (zero) level. Furthermore, if this predetermined level is set even higher than above, the spectrum (
It is also possible to display only wavelengths near the center wavelength of the longitudinal mode (one or more longitudinal modes may be used).

Furthermore, in the above embodiment, the relationship between the detected light amount of the light to be measured and the wavelength λ is determined by analog processing, but the light amount signal output from the photodetector 31 is digitized, and the above relationship is determined by digital processing. You can also ask for

In addition to inputting the light beam L into the optical waveguide 12 as in the above embodiment, for example, the light beam L emitted into the air from the optical fiber 24 is narrowed to a flat shape by a cylindrical lens, and the end face of the optical waveguide is It is also possible to perform this by irradiating the light beam L onto a diffraction grating formed on the surface of the optical waveguide 2a and causing it to be diffracted there.

Here, the optical spectrum analyzer of the present invention is capable of measuring each spectral component with high resolution even when the light to be measured is composed of a plurality of spectral components whose wavelengths are very close to each other. This point will be explained in detail below.

For example, the light to be measured has wavelengths λ1, λ2, λ that are close to each other.
3 (λ1 × λ2<λ3).

As shown in FIG. 4, it is assumed that the Bragg condition is satisfied between the guided light having the intermediate wavelength λ2 and the surface acoustic wave 15, and the diffracted light is emitted in the direction of the vector lk2. At this time, the guided lights of wavelengths λ1 and λ3 also almost satisfy the Bragg condition, although not completely, with respect to the surface acoustic wave 15. Therefore, the guided lights of these wavelengths λ] and λ3 are also diffracted by the surface acoustic wave 15 and exit from the optical waveguide 12.

However, the diffraction angles of these lights are different from the diffraction angles of light with wavelength λ2, and as shown in Figure 4, the diffraction angles of these lights are
, the direction of the vector lk (in Fig. 4, 0
1 and G3 are the starting points of the wave number vector of the guided light with wavelengths λ1 and λ3, respectively). Therefore, the light beam emitted from the optical waveguide 12 is separated into each spectral component. If each spectral component is completely separated on the pinhole plate 30 in this way, when the frequency of the alternating voltage is swept, three beam spots move on the pinhole plate 30, and light of each wavelength is are sequentially individually pinholes 30a
pass through.

Therefore, the relationship between the amount of light detected by the photodetector 31 and the alternating voltage frequency, that is, the surface acoustic wave frequency is as shown in FIG. In other words, the wavelengths λ1, λ2, λ
The three spectral components are individually detected when the surface acoustic wave frequencies are f□, fZ, and f3, respectively. If these surface acoustic wave frequencies f, , fZ, f3 are detected,
The wavelengths λ1, S2, and λ3 can be determined in the same manner as described above.

Next, a second embodiment of the present invention will be described with reference to FIGS. 6.7 and 8. In FIGS. 6 to 8, the same elements as those already explained are given the same reference numerals, and the explanation thereof will be omitted unless particularly necessary. As shown in FIGS. 6 and 7, in the optical spectrum analyzer 50 of this embodiment, the optical waveguide 1
2 is provided with a second chirb IDT 18 in addition to the chirb IDT 17. This Charb lDT 1g
generates a second surface acoustic wave 16, which diffracts and deflects the guided light Lz that has been diffracted and deflected by the first surface acoustic wave 15 in a direction that further amplifies the deflection. let In this example, sweep alternating voltages having the same frequency are applied from the high frequency amplifier 19 to the first and second chirped IDTs 17 and 18. Therefore, the first and second surface acoustic waves 1
The frequencies of 5.16 change continuously, always keeping the same value. This is also similar to the first embodiment, but
The guided light 1.1 is turned on at a modulation frequency fr lower than the frequency of the alternating voltage applied to the Chirb IDT 17.18.
OFF modulated.

In this case, the wave number vectors of the guided light L1, the guided light L2 after being diffracted by the first surface acoustic wave 15, and the guided light L3 after being diffracted by the second surface acoustic wave 1G are lkl, respectively.
, lk2, lk3, and the first and second surface acoustic waves 15
．． If the wave number vector of 16 is "'I S lk2,"
When the above two diffraction times are performed, lkl +lJ
−tic2 1k 2 +IK 2 = lk 3 . And the guided light L for the first surface acoustic wave 15
1 and the guided light L for the second surface acoustic wave 1G.
Chilb I so that the incident angles of 2 and 2 are equal to each other at θ
If DT17.18 is placed, the frequency f1 of the first and second surface acoustic waves I5.1B, that is, I
Based on the value of the frequency of the alternating voltage applied to DT17, ]8, the wavelength λ of the constant light of 1i111 can be determined. Also in this embodiment, since the light amount signal S1 output from the photodetector 31 is passed through the lock-in amplifier 35, the intensity of the light beam L4 can be accurately detected with a high S/N.

In this example, if the reference guided light and the reference surface acoustic wave (in this example, the first and second reference surface acoustic waves having the same frequency are used) as described above, the above equation (3) is used. The wavelength λ of the light to be measured can be determined based on . In other words, in Fig. 8, the wave number vector of the reference waveguide light is OP, and the wave number vector of the first reference surface acoustic wave is PQ.
, if the wave number vector of the reference guided light diffracted by the first reference surface acoustic wave is OQ, and the wave number vector of the reference guided light diffracted from the second reference surface acoustic wave is 61, then Δ0PQcoΔSPR is also obtained in this case. Therefore, the above formula (3) holds true after all.

However, in this example, the deflection angle δ of the guided light L3 after the second diffraction with respect to the guided light L1 is the first surface acoustic wave 1 of the guided light beam.
If the angle of incidence on 5 is θ, it becomes 4θ. This is the first
This is twice the deflection angle δ-2θ in the example, and therefore, in this example, the resolution of spectrum analysis can be higher than in the first example. This point will be explained in detail below.

For example, in FIG. 4, vector lk2 and vector I
The angle formed by k or lk5 becomes larger as the angle formed by the vector lk2 with respect to the vector lk1 becomes larger, that is, as the diffraction angle of the guided light by the surface acoustic wave becomes larger. That is, the difference in the emission angles of several light beams simultaneously emitted from the optical waveguide 12 increases as the deflection angle δ of the guided light increases, and each light beam is spaced at a larger interval on the pinhole plate 30 described above. It becomes separated after a while. If this happens, it will be possible to separate spectral components with closer wavelengths, so that the larger the deflection angle δ is, the better the resolution of spectrum analysis will be. This will be explained below using specific numerical examples. Since the deflection angle δ in the case of second diffraction is 4θ as described above, from the above equation (1), the following is obtained. Therefore, the amount of change Δδ in the deflection angle with respect to the minute amount of change Δλ in wavelength is approximately as follows. Here, considering the optical waveguide 12 made of X-cut LiNbO3, N c -2,2, v -3483m
/ss Also, assuming f-1.5GHz and the distance from the diffraction point to the pinhole plate 30 to be 9J-90mm, a beam spot of 10 μm will be formed on the pinhole when the incident light beam diameter is D-15mm. , the separation amount of the beam spot on the pinhole plate 30 is approximately Δδ,
In air, it becomes Δδ-2,2×35.400xΔλ-77,880.
It becomes XΔλ. If the beam spot separation iu, -Δδ is secured by the beam spot diameter at the minimum, it becomes possible to separate and detect the two light beams. Therefore, if the light beam L4 is focused by the light beam output FGC 14 to a spot diameter of 10 μm, which is equal to the core diameter of an optical fiber for optical communication, then if 77.880XΔλ−10 μm, two lights with a wavelength difference of Δλ The beams can be separated and detected. Solving the above equation, Δλ is approximately 0.13n
m. In other words, this second embodiment device has a thickness of approximately 0.1 nm.
Spectral analysis can be performed in units.

In addition, when forming this optical spectrum analyzer for, for example, optical spectrum analysis of a semiconductor laser, the above Δ
λ is usually about several nrn, and it is sufficient to assume Δλ−1oontn, so as mentioned above, the surface acoustic wave frequency is set to 1. ．． If it is about 5 GHz, the band is 50
It is sufficient to secure a frequency of about 1.00 MHz.

In the device of the second embodiment described above, the frequencies of the first and second surface acoustic waves 15 and I6 are always made equal; The frequencies of may be set to take different values while always maintaining an equal ratio.

Further, the guided light, which is the light to be measured, may be diffracted three or more times by three or more surface acoustic waves. As mentioned earlier, the resolution of spectral analysis improves as the deflection angle δ of the guided light increases, so if diffraction is performed multiple times in this way, the resolution of spectral analysis can be improved without significantly increasing the frequency of the surface acoustic wave. It is preferable because it can be improved.

(Effects of the Invention) As described in detail above, the optical spectrum analyzer of the present invention enables optical spectrum analysis with high resolution. Furthermore, the optical spectrum analyzer of the present invention has a structure in which the light to be measured enters the optical waveguide and is diffracted by surface acoustic waves, so it is small and lightweight, and has two mechanical operating parts. Since it is not equipped with, durability and reliability are also high.

Furthermore, in the optical spectrum analyzer of the present invention, the diffracted light to be measured is subjected to ON-OFF modulation, and a component of the same frequency as the modulation frequency is extracted from the output signal of the light to be measured detection means to generate the light to be measured. Since the light is used for detection, the light to be measured can be detected with high S/N and high accuracy. Therefore, according to this apparatus, optical spectrum analysis can be performed extremely accurately. Furthermore, since the above-mentioned modulation of the light to be measured is performed electrically, unlike the case where this modulation is performed using a mechanical chopper, the light to be measured is
/N, there is no need to significantly increase the size of the device in order to enable accurate detection.

Furthermore, since the ON-OFF modulation of the light to be measured is performed by switching the light to be measured using an electro-optic optical switch, the application of an alternating voltage to the surface acoustic wave is turned ON.
Compared to the case where the measured light is modulated with -OFF, the modulation frequency can be sufficiently increased, and the sweep speed of the alternating voltage applied to the surface acoustic wave can be increased, allowing optical spectrum analysis to be performed within a short time. can be done.

[Brief explanation of the drawing]

Fig. 1 is a schematic perspective view showing a first embodiment of the device of the present invention, Fig. 2 is a plan view showing an enlarged part of the first embodiment of the device, and Fig. 3 is an L-end box 1 embodiment device. FIG. 4 is an explanatory diagram illustrating the separation of optical spectra in the device of the present invention; FIG. 5 is a graph showing the relationship between the amount of light detected in the device of the present invention and the surface acoustic wave frequency; FIG. 6 is a schematic perspective view showing the device of the second embodiment of the present invention, FIG. 7 is a plan view showing an enlarged part of the device of the second embodiment, and FIG. 8 is the device of the second embodiment of the invention. FIG. 3 is an explanatory diagram illustrating light beam deflection. 1.0.50... Optical spectrum analyzer 11.
...Substrate 12...Optical waveguide 13...
Waveguide lenses 14... FCC15 for forward beam output
...First surface acoustic wave 1G...Second surface acoustic wave I7...First chirp IDT 18...Second chirp IDT 19...High frequency amplifier 20...Sweeper 21
...Light source 25...EOG drive circuit 2
6... Modulation control circuit 29... EOG30...
・Pinhole plate 30a...Pinhole 31...
・Photodetector 32...Frequency measurement circuit 33・
...Arithmetic processing circuit 34...Display device 35...
lock-in amplifier

Claims (1)

[Scope of Claims] An optical waveguide formed of a material that allows surface acoustic waves to propagate and exhibits an electro-optic effect, and guided light as measured light that is incident on the optical waveguide and travels within the optical waveguide. Proceeding in a direction intersecting the optical path of
a surface acoustic wave generating means for generating in the optical waveguide a surface acoustic wave whose frequency changes continuously to diffract and deflect the guided light; and the measured light that is deflected by the surface acoustic wave and emitted out of the optical waveguide. an electro-optic optical switch disposed in the guided optical path portion of the optical waveguide; and a voltage applied to the electro-optic optical switch at a modulation frequency lower than the frequency of the surface acoustic wave. a switching circuit that performs ON-OFF control to periodically switch the optical path of the optical waveguide between an optical path toward the photodetector and an optical path away from the photodetector; and a filter means for extracting only a component of the same frequency as the modulation frequency from the detection signal; An optical spectrum analyzer consisting of frequency detection means for detecting the frequency of elastic waves.