JPH02194342A - Optical spectrum analyzer - Google Patents

Abstract

PURPOSE:To analyze an extremely fine spectral width by effectively utilizing an element for performing the ordinary analysis of light spectrum and using a delay self heterodyne method or a delay self homodyne method. CONSTITUTION:A light beam L from a light source 23 is branched to two systems through optical fibers 24 and 26, a collimator lens 27 and a beam splitter 50. The light beam L passing through the beam splitter 50 is diffracted by a diffraction grating 28 for correcting wavelength fluctuation and incorporated in a light guide 12. A part of the guided light L1 is diffracted in terms of a surface acoustic wave 16 and advances as the guided light 5. However, the guided light L1 passing through the acoustic wave 16 as 0-th order light is diffracted by an acoustic and optical interaction with the surface acoustic wave 15 generated from a chirp interdigital transducer 17. The diffracted guided light L2 is diffracted through a linear diffraction grating 14 for outputting a light beam. It is because the spectrum of a beat signal is made to appear in an area distant from zero frequency that the light beam L is diffracted with the surface acoustic wave 16 to perform frequency shift in the delay self heterodyne method.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a spectrum analyzer that performs optical spectrum analysis, and particularly relates to a spectrum analyzer that analyzes optical spectrum using an 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 Zernitana-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 present applicant has previously proposed a spectrum analyzer that can be made small and lightweight and has high resolution (Japanese Patent Application No. 1.80779/1982). 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,
surface acoustic wave generating means for generating a surface acoustic wave whose frequency changes continuously to diffract and deflect the guided light in the optical waveguide; and the measured light that is deflected by the surface acoustic wave and emitted out of the optical waveguide. The present invention is characterized in that it is comprised of a light detection means for detecting the 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 Q be the wavelength, frequency, and velocity of the surface acoustic wave, respectively.
, f.

If ■, then λ. Since NO and V are constant, if the incident angle θ and the surface acoustic wave frequency f at which the guided light is diffracted most efficiently satisfying the Bragg condition expressed by this equation are known, the guided light, that is, the measured light 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.

(Problem to be solved by the invention) Conventionally, distributed feedback type (D
jsirjbuLed Feedback: D
F B ) Semiconductor laser or distributed reflection type (D jstr
ibuted Bragg Rer 1ecto
r: DBR) semiconductor lasers are known.

When these semiconductor lasers are used for long-distance communications, for example, the spectral width is a factor that determines the transmission distance limit, so there is a demand for accurate measurement of this spectral width. However, the spectral width (full width at half maximum) of these semiconductor lasers is on the order of 1/IQQpm, and such a minute spectral width cannot be measured even using the optical spectrum analyzer as described above.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide an optical waveguide type optical spectrum analyzer that can also obtain an extremely narrow spectral width as described above.

(Means and effects for solving the problems) The first optical spectrum analyzer according to the present invention is composed of the above-mentioned optical waveguide, surface acoustic wave generation means, light detection means, and frequency detection means. This is an optical spectrum analyzer that makes effective use of the above components to be able to measure minute spectral widths using the delayed self-heterodyne method.Specifically, in addition to each of the above components, , a second surface acoustic wave generating means for generating in the optical waveguide a surface acoustic wave with a constant frequency that propagates in a direction intersecting the optical path of the guided light and causes the guided light to be diffracted and deflected; and the surface where the frequency changes. a branching means for branching a part of the light to be measured before it is incident on the elastic wave and the surface acoustic wave with a constant frequency; a multiplexing means disposed in the branching means; an optical transmission system for guiding the light to be measured branched by the branching means to the multiplexing means; and an optical delay means made of, for example, a single mode optical fiber bundle of several kilometers in length, which is sufficiently longer than the optical path length from the means to the multiplexing means via a surface acoustic wave with a constant frequency; and the multiplexing means. and a high-frequency spectrum analyzer that analyzes the frequency of the electrical signal output by the second light detection means. .

FIG. 7 schematically shows a spectral width measurement system in the above configuration, and the measurement of spectral width will be described below with reference to FIG. 7. Note that FIG. 7 does not particularly show the measurement system for determining Apj of the optical spectrum as described above. The light to be measured emitted from the light source 23 such as the DFB semiconductor laser is split into two systems by a beam splitter 50 as a splitting means, one of which is input into the optical waveguide 12, and the other is a light beam formed by a single mode optical fiber 51. sent to the transmission system. The light to be measured that enters the optical waveguide 12 and is guided through the optical waveguide 12 is diffracted by the second surface acoustic wave 16 with a constant frequency traveling through the optical waveguide 12, and is emitted to the outside of the optical waveguide j2 as a light beam L6. On the other hand, the single mode optical fiber 51 has a length of 1.5 km, for example.
The optical delay means 51. It forms A. The 11 all constant light beams passing through the optical delay means 5iA are combined with the light beam L6 at the beam splitter 52, and received by the 1'th and 2nd light detection means 53 as the first beam L8. The signal S5 outputted by the photodetecting means 53 is sent to a high frequency spectrum analyzer 54 and subjected to spectrum analysis.

Here, the center frequency of the guided light is ν, and the frequency variation corresponding to the spectral width (full width at half maximum) is Δν. This guided light is diffracted by the second surface acoustic wave 16, so that
The frequency is shifted by the frequency fA of the surface acoustic wave 16.

On the other hand, the frequency of the constant light L7 to be measured 71IIJ remains (ν" - Δν), and this light to be measured L7 and the frequency
When the 11 all constant beams L6 of A) are combined, they interfere there. Due to this interference, a beat component due to the difference in frequency between the two is superimposed on the light to be measured L8, but since the light to be measured L7 is delayed, the frequency components that appear irregularly within the fluctuation range of both are superimposed on each other. They randomly interfere with each other, and a component that fluctuates with a full width at half maximum of about 2Δν is left in the beat component. In other words, the detection signal S5 of the "-2 light to be measured L8 has a center frequency of fA, as shown in FIG.
Then, the full width at half maximum appears as Δf'=2Δν. Therefore, this signal S5 is transmitted to the high frequency spectrum analyzer 5.
4 to find the above Δf, about half of that value is Δν
becomes.

If the speed of light is C1, the wavelength of light is λ, and the frequency is ν, then λ2 Δλ = −□ Δν, so if Δ is known, the vector width Δ can be calculated from the above equation.
λ can be found.

On the other hand, a second optical spectrum analyzer according to the present invention is a spectrum analyzer comprising the above-mentioned optical waveguide, surface acoustic wave generation means, light detection means, and frequency detection means. By making effective use of these elements, it is possible to measure even minute spectral widths using the delayed self-homodyne method. Specifically, in addition to the above-mentioned elements, the frequency propagating in the optical waveguide is continuously a branching means for branching a part of the light to be measured before it is incident on the changing surface acoustic wave; and a branching means arranged to receive the light to be measured that passes through the surface acoustic wave as zero-order light and is emitted outside the optical waveguide. a combining means for combining the light to be measured branched by the branching means; an optical transmission system for guiding the light to be measured branched by the branching means;
an optical delay means that is sufficiently longer than the optical path length from the branching means to the multiplexing means via the surface acoustic wave; and a second optical detection unit that detects the 11p constant light multiplexed by the multiplexing means. and a high-frequency spectrum analyzer for frequency-analyzing the electrical signal output by the second photodetecting means.

Spectral width i+p of this optical spectrum analyzer
In the j constant system, compared to the 71I+1 constant system in FIG. The difference is that they are structured as follows. Therefore, in that case, the light to be measured is not diffracted by the surface acoustic wave 16 and the frequency is not shifted by the surface acoustic wave frequency fA, so the detection signal S5 outputted from the light detection means 53 has the following characteristics as shown in FIG. The center frequency is f
A beat with 0 (zero) instead of A and a full width at half maximum of Δf'=2Δν appears. In this case, Δf' cannot be directly confirmed, but Δf'/2 is known.

The value of Δf'/2 is approximately equal to the frequency variation Δν corresponding to the desired spectral width Δλ.

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

FIG. 1 shows the planar shape of an optical spectrum analyzer according to an embodiment of the present invention, and FIG. 2 shows the side surface shape of the peripheral portion of the optical waveguide 12 of this optical spectrum analyzer. This optical spectrum analyzer includes an optical waveguide 12 formed on a substrate 11 and a linear diffraction grating (Lincar GraLing Coup) for outputting a light beam formed on the surface of this optical waveguide 12.
ler (hereinafter referred to as LGC) 13 and a light beam output LGC 14, and a chirped intersecting comb that generates a first surface acoustic wave 15 whose frequency changes, which travels in the optical waveguide 12 in a direction intersecting the optical path of the guided light L1. Electrode pair (
Chirped 1nter-D jgital
transducer (hereinafter referred to as chirp DT) 17, an IDT 1.8 that generates a second surface acoustic wave 16 of a constant frequency in the optical waveguide 12, and the first
Chirb IDT1 to generate surface acoustic wave I5 of
a high-frequency amplifier 19 that applies a high-frequency alternating voltage to 7;
a sweeper 20 that continuously changes (sweeps) the frequency of the voltage; a high-frequency amplifier 40 that applies an alternating voltage of a constant frequency to the IDT 1.8 in order to generate the second surface acoustic wave 16; It has an oscillator 41 that inputs an oscillation signal of a constant frequency.

Further, the optical path of the light beam L4 emitted from the optical waveguide 12 includes a focusing lens 29, a pinhole plate 30, and a photodiode or the like that measures the intensity of the light beam L4 focused into a small spot by the focusing lens 29. 1 photodetector 31
is located. The light amount signal S1 outputted from the photodetector 31 is A/D converted by an A/D converter 32, and the digital light amount data S2 obtained thereby is input to an arithmetic processing section 33. . On the other hand, the light beam L4 is emitted in a different direction from the focusing lens 29.
A beam splitter 52 as a combining means and a second photodetector 53 such as a photodiode for detecting the amount of light beam L8 emitted from the beam splitter 52 are disposed on the optical path of the light beam L6 that has passed through the beam splitter 52. has been done. A photodetection signal S5 output from this photodetector 53 is input to a high frequency spectrum analyzer 54.

In this embodiment, as an example, the substrate 11 has LiNbO
The optical waveguide 12 is formed by using three wafers and providing a Ti diffusion film on the surface of the wafer. Note that substrate 1
1 may also be a crystalline substrate made of sapphire, Si, or the like. Furthermore, the optical waveguide 12 is not limited to the above-mentioned Ti diffusion, but may also be formed by sputtering, vapor depositing, or the like other materials on the substrate 11. However, this optical waveguide 12 must be formed of a material such as the above-mentioned Ti diffusion film that can propagate surface acoustic waves, which will be described later. Further, the optical waveguide may have a laminated structure of two or more layers.

Charb IDT17 and IDT18 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 A1 thin film and then performing lift-off in an organic solvent. Note that the Charb IDT 17 and IDT 18 are connected to the substrate 11 and the optical waveguide 1.
If 2 is made of a piezoelectric material, the surface acoustic wave 1 may be installed directly within the optical waveguide 12 or on the substrate 11.
5.16, but if this is not the case, a part of the substrate 11 or the optical waveguide 12 is coated with, for example, Zn.
A piezoelectric thin film made of O or the like may be formed by vapor deposition, sputtering, etc., and the IDTs 17 and 18 may be installed there.

For example, a light beam L emitted from a light source 23 such as a semiconductor laser and subjected to spectrum analysis is emitted as diverging light from the end face of an optical fiber 26 via an optical fiber 24 connected to the light source 23 and a coupler 25. This light beam L is made into parallel light by the collimator lens 27,
Next, the beam splitter 50 branches the beam into two systems. The first beam L transmitted through the beam splitter 50 is diffracted by the reflection type wavelength fluctuation correction diffraction grating 28, and the end beam L passes through the diagonally cut substrate end face 1.1. Through a L G C13
is incident on the optical waveguide 1, where it is diffracted and efficiently connected to the optical waveguide 1.
It is taken into 2.

This light is guided in the optical waveguide 12 in the form of a parallel beam.

Note that the optical input efficiency of the above-mentioned LGCl3 varies depending on the wavelength of the light beam L. The above-mentioned wavelength fluctuation correction diffraction grating 28 stabilizes the light input efficiency in LGCl3 by changing the output angle thereof (that is, the angle of incidence on LGCl3) according to the wavelength fluctuation of the light beam L. It is something to do. As this diffraction grating 28, a transmissive type may be used in addition to a reflective type. Regarding such a diffraction grating for wavelength fluctuation correction, the present applicant filed a patent application (2) on December 16, 1988 (Representative Yanagi [
A detailed description is given in the specification of η Seishi et al.

The device of this embodiment has a center wavelength λ=1°55μ as an example.
Based on the premise of spectrum analysis of a cliff conductor laser beam of m, the Charb IDT17 has 1. An alternating voltage whose frequency is swept around GHz is applied, while a voltage of 0.2G is applied to the IDT18.
An alternating voltage with a constant frequency of B(z) is applied. Also, the incident angle θ° of the guided light I, 1 to the second surface acoustic wave 1G is:
The angle is set to satisfy the Bragg condition shown in equation (1) above.

Therefore, a part of the waveguide light L1 is diffracted by the surface acoustic wave 16 and travels through the optical waveguide 12 as a waveguide light Ls (this will be described later), but the surface acoustic wave 16 is considered to be the zero-order light (passed by 7°C). If the Bragg condition shown in (1) above is satisfied, the guided light undergoes diffraction i5 (Bragg diffraction) due to acousto-optic interaction with the surface acoustic wave 15 emitted from the Chubb IDT 17.

Diffraction [7] The guided light L2 is diffracted at LGCl, 4↑h
The light then passes through the prism 21 and exits to the outside of the optical waveguide 12. The light beam L4 emitted from η11 is focused into a small spot by a focusing lens 29.

Hereinafter, the diffraction and deflection of the guided light within the optical waveguide 12 will be explained in detail with reference to FIGS. 3 and 4.

FIG. 3 shows an enlarged detailed view of the chirp IDT 17 and iDTlg, and FIG. 4 shows the wave number vectors of the guided light L1 and the surface acoustic wave 15. As shown in Fig. 3, the second surface acoustic wave 1
The guided light L1 that has passed through 6 as the zero-order light is the surface acoustic wave 1
The light is incident at a constant angle θ with respect to the direction of travel of the vehicle. Also,
The wave number vectors of the guided light L1 before entering the surface acoustic wave 15 and the guided light L2 after passing through the surface acoustic wave 15 are 1 kl and 1, respectively.
2 and the wave number vector of the surface acoustic wave 15 is lK1. When the Bragg condition shown in equation (1) is satisfied, Ik 1 + IK 1-1k 2... ( 2), and the deflection angle of the guided light L2 with respect to the guided light T,1 is δ-2θ. If the incident angle θ is constant as described above, the deflection angle δ when the above equation (2) is satisfied is also constant. Therefore, the light beam L4 that completely satisfies the Bragg condition and is emitted out of the optical waveguide 12 is emitted in a fixed direction. - The light beam L5 rotated by the blade surface acoustic wave 1B is incident on the first surface acoustic wave 15 at an angle that does not satisfy the Bragg condition, so it is not diffracted there, and the light beam L6 The light beam L is emitted in a fixed direction different from the light beam L.

The pinhole plate 30 is arranged so that when the light beam 1.4 is emitted in a certain direction of "-2", the light beam L4 narrowed to a small spot passes through the pin pole 30a. The light beam L4 that passed through the pinhole plate 30 is
The light is received by the photodetector 31. Note that a slit plate may be used instead of the pinhole plate 30.

Here, if the wavelength of the guided light (light to be measured) is λ and the wavelength of the surface acoustic wave 15 is A, then 1=2π/λ, and since the wavelength of the guided light L2 is also λ. , lkl
1 = l Ik2 1 = 2π/λ. Therefore, since the incident angle θ is fixed, only one value of 1=2π/A for 11 exists for each 11 that satisfies the equation (2). Therefore, when this equation (2) holds true (that is, when the light beam L4 passes through the pinhole 30a and is detected by the photodetector 31), the value of 11 changes from the value of 11 to the wavelength of the surface acoustic wave 15. From the value, the wavelength λ
is sought after.

This wavelength λ can of course be determined from the above-mentioned equation (1), but it can also be determined even if the incident angle θ and the effective refractive index Ne of the optical waveguide 12 with respect to the guided light L1 are unknown. That is, when a reference guided light having a known frequency (assumed as λrer) is made to enter the optical waveguide 12, this reference guided light is diffracted by a reference surface acoustic wave having a wavelength A rer and detected by the photodetector 31. do. In Fig. 4, the wave number vector of the reference guided light is OP1, the wave number vector of the reference surface acoustic wave of wavelength A is PQ, and the wave number vector of the diffracted reference guided light is O.
If Q, then ΔOPQωΔSPR, so 0P=2π/λrar, PQ=2π/Aref
', therefore, λ-λrer(A/Arer) Here, the velocity and frequency of the surface acoustic wave 15 are respectively v5f
, the velocity and frequency of the reference surface acoustic wave are Vref, respectively.
, f ref, then v=fA, vrcf = frcf −Δref, v
-vref, so from the above equation, λ-λref (f ref / f ) -43
). 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 light to be measured can be determined from equation (3).

The frequency of the high-frequency alternating voltage applied to the chirb IDT 17 when performing optical spectrum analysis is the same as that of the sweeper 20.
is swept from f min to f max. Note that the timing of this frequency sweep is controlled based on the clock signal C output by the overall control section 95. When the frequency of the alternating voltage, that is, the frequency of the first surface acoustic wave 15 is swept in this way, if the value of f min Sf max is appropriately set, a certain surface acoustic wave frequency that satisfies the above equation (1) The light guided by the surface acoustic wave 15 of f (fmin≦f≦fmax) is most efficiently diffracted.

The light amount signal S1 outputted by the photodetector 31 is passed through an A/D converter 32 and digitized. The sampling period at this time is controlled based on the clock signal C output by the overall control section 95, and corresponds to the frequency sweep period of the surface acoustic wave 15. Therefore, the A/D converter 32
Of the digital light quantity data S2 outputted from the digital light amount data S2, it is automatically known at what Hz the frequency of the surface acoustic wave 15 is.

In other words, if this light amount data S2 is shown continuously, it can show the relationship between the surface acoustic wave frequency f (horizontal axis) and the detected light amount, as shown in FIG. Note that, as is clear from the above description, in this example, the overall control unit 95 controls the light beam L4.
It constitutes a frequency detection means for detecting the surface acoustic wave frequency f when is detected.

After the frequency sweep of the surface acoustic wave 15 is completed, the arithmetic processing unit 33 compares the light amount data S2 indicating the relationship between the surface acoustic wave frequency and the detected light amount with the wavelength λref of the reference guided light inputted in advance. Frequency of surface acoustic wave f ref
, and is converted into data indicating the relationship between the guided light wavelength and the amount of detected light based on the above equation (3). The converted light amount data S3 indicates the light amount of the light beam L4 in association with its wavelength. This light amount data S3 is, for example, C
The information is input to a display device 34 such as an RT. As an example, the display device 34 displays the relationship between the amount of light and the wavelength of the light beam L4 in the form of a graph. 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. Furthermore, in the above embodiment, not only when the photodetector 31 detects the light beam L4, but also when the surface acoustic wave 1
While the frequency of the light beam L4 is being swept, the frequency f is continuously determined, and the light amount signal S1 is continuously sent to the A/D converter 32 regardless of whether the open beam L4 is detected. Although the relationship between the amount of light and the wavelength is displayed in a graph, the wavelength λ when the light beam L4 is detected is automatically detected, and only the value of that wavelength λ is displayed on the display device.
Alternatively, it may be recorded. However, if the above embodiment is adopted, in the display device 34, the light beam L
This is more preferable because it clearly shows the wavelength range where 4 is not detected at all (that is, the range where no spectral component exists). In this case, since noise components are generally included in the light amount signal S, etc., the detected light amount display is often not O (zero) even in the wavelength region where the light beam L 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. Also, to avoid this,
The light ff1 is set at a predetermined level slightly higher than the above 7 noise components.
It may also be displayed as O (zero) level. Furthermore, if this predetermined level is set higher than "-", the spectrum (the number of longitudinal modes may be one or more)
It is also possible to display only wavelengths near the center wavelength.

Furthermore, in the embodiments described above, the relationship between the detected amount of light to be measured and the wavelength λ is determined by digital processing, but the relationship can also be determined by analog processing.

Here, the optical spectrum analyzer according to the present invention is
Even when the target A11l constant light rH consists of a plurality of spectral components whose wavelengths are extremely close to each other, each spectral component can be measured with high resolution.

This point will be explained below. For example, if the wavelengths λ1, A2, A3 (A1 × A2 <A
3) shall consist of the spectral components.

(7) As shown in FIG. 5, it is assumed that the Bragg condition is satisfied between the guided light with the intermediate wavelength λ2 and the surface acoustic wave I5, and the diffracted light is emitted in the force direction of the vector lk2. Then, the guided light of wavelength λj and A3 is also a surface acoustic wave 15
In contrast, the Bragg condition is almost, although not completely, satisfied. Therefore, the guided lights of these wavelengths λ1 and A3 are also diffracted by the surface acoustic wave 15, and are transmitted through the optical waveguide 12.
Emits from.

However, the diffraction angles of these lights are different from the diffraction angles of light with wavelength λ2, and as shown in FIG.
, the direction of the vector I.lk5 (in FIG. 5, G 1 and G 3 are the starting points of the wave number vectors of the guided lights of wavelengths λ1 and A3, respectively). So optical waveguide 1
The light beam emitted from 2 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 bin pole 3
Pass through 0a.

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, A2, A
The 3 spectral components are individually detected when the surface acoustic wave frequencies are fl, fl, and f3, respectively. Once these surface acoustic wave frequencies f1, fl, and f3 are detected, wavelengths λ1, A2, and A3 can be determined in the same manner as described above.

Here, when the light source 23 is the above-mentioned DFB flat conductor laser or the like, the relationship between the amount of light and the wavelength displayed on the display device 34 as described above is as shown in FIG. 10.

In other words, the number of longitudinal modes is 1-, and the spectral width Δλ(
(full width at half maximum) is extremely narrow. Hereinafter, the point of determining this spectral width Δλ will be explained. As shown in FIG. 2, a light beam L7 reflected by the beam splitter 50 and split from the destination beam I heading toward the optical waveguide I2 is focused by a focusing lens 55.
The light is input into a single mode optical fiber 51. This single mode optical fiber 51 is, for example, 1. ．． A length of approximately 5 km is wound around the drum 57, and this wound fiber bundle constitutes the optical delay means 51A.

This optical delay means 51. The light beam L7 that has passed through A exits from the single mode optical fiber 51 as a diverging light, is condensed by a condenser lens 56, and enters the beam splitter 52 mentioned above at -C1.

On the other hand, the light beam L6 emitted from the optical waveguide 12 is focused by the focusing lens 29 and enters the beam splitter 52, where it is combined with the light beam L7. At this time, due to diffraction by the second surface acoustic wave 16, the frequency of 0.2 GHz
The frequency-shifted light beam L6 and the original target 4I11
Interference occurs as described above with the light beam LT, which remains at a constant frequency. The combined light beam L8 is detected by a second photodetector 53, and its photodetection signal S5 is input to a high frequency spectrum analyzer 54 for frequency analysis. The fact that the frequency fluctuation range Δν of the light to be measured can be obtained from the beat component as shown in FIG.
This is as described with reference to the figures.

Furthermore, in determining the frequency fluctuation width Δν using the delayed self-heterodyne method described above, the reason why the light beam L is diffracted by the second surface acoustic wave 16 and shifted in frequency is based on the spectrum of the beat signal shown in FIG. This is to make the spectrum appear in a region away from 0 (zero) frequency, with the center frequency being fA. Therefore, the frequency fluctuation width Δν corresponding to the spectral width Δλ is
Considering that FB semiconductor lasers etc. usually do not reach 100MHz, the above frequency shift width, that is, the second
It is sufficient to set the frequency of the surface acoustic wave 16 to around 1.00 MHz.

Next, a second embodiment of the present invention will be described with reference to FIGS. 11.12 and 13. In FIGS. 11 to 13, the same elements as those already described are given the same reference numerals, and the description thereof will be omitted unless particularly necessary (the same applies hereinafter). Figure 11 and 1
As shown in FIG. 2, in the optical spectrum analyzer of this embodiment, the chirp IDT is connected to the optical waveguide 12.
In addition to 17, another chirp IDT 17° is provided. This chirp ID 717'' also generates a surface acoustic wave 15' whose frequency changes, and this surface acoustic wave 15' further amplifies the guided light L2 that has been diffracted and deflected by the surface acoustic wave 15. In this example, sweep alternating voltages of the same frequency are applied to these chirp IDTs 17.17° from a high frequency amplifier I9.Therefore, surface acoustic waves 1.5.1 The frequencies of .5'' change continuously, always keeping the same value.

In this case, the wave number vectors of the guided light L1, the guided light L2 after being diffracted by the surface acoustic wave 15, and the guided light L3 after being diffracted by the surface acoustic wave 15' are Ik1 and lk, respectively.
2. If Ik3 and the wave number vectors of surface acoustic wave 15.15' are IKl and IK2, then when the above two diffraction is performed, the following Bragg diffraction conditions are satisfied: Ikl + lKl - 1kz 1 to 2 + IK2 Snow 1 to 3 It is supposed to be done.

And the angle of incidence of the guided light L1 with respect to the surface acoustic wave 15,
The chirped IDT 17 and 17' are set so that the incident angles of the guided light beam 2 and the surface acoustic wave 15' are equal to each other at θ.
If you place , surface acoustic waves 15.15
The wavelength λ of the light to be measured can be determined based on the frequency f1 of ゛, that is, the frequency value of the alternating voltage applied to the IDT 17.17'.

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. 13, the wave number vector of the reference guided light is 5 below, and the wave number vector of the first reference surface acoustic wave is P.
Q, the wave number vector of the reference guided light diffracted by this first reference surface acoustic wave is OQ, the wave number vector of the second reference surface acoustic wave is QT, the reference guided light diffracted by this second reference surface acoustic wave is If the wave number vector of the wave light is OT, then also in this case, Δ0PQ(1)ΔSPR, so the above equation (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 40, where θ is the angle of incidence of the guided light L1 on the surface acoustic wave 15. This is twice the deflection angle δ-2θ in the previously described embodiment, and therefore, in this embodiment, the resolution of the spectral analysis is higher than in the previous embodiment. This point will be explained in detail below.

For example, in FIG. 5, vector Ik2 and vector l
The angle formed by k or Ik5 becomes larger as the angle formed by the vector Ik2 with respect to the vector Ik1 is larger, that is, the larger the diffraction angle of the guided light by the surface acoustic wave. 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.
-, they will be separated by a larger ljl interval. In this case, it becomes possible to separate spectral components of wavelengths that are closer to each other, so that the larger the deflection angle δ, the lower the resolution of spectrum analysis.

In the embodiments described above, surface acoustic waves 15.
The frequencies of the surface acoustic waves 15' may always be equal, or the frequencies of these surface acoustic waves 15.15' may always maintain an equal ratio and take different values.

Further, the guided light, which is the light to be measured, may be refracted three times by three or more surface acoustic waves whose frequencies change continuously. As mentioned earlier, a large deflection angle δ of the guided light will affect the resolution of spectral analysis, so if diffraction is performed multiple times in this way, the frequency of the surface acoustic wave can be reduced to a very small spectral value. This is preferable because the resolution of analysis can be improved.

In addition, in the apparatus shown in FIG. 11, from the light beam L,
The branching stage that branches the destination beams I and 7 to be sent to the first optical delay stage 51A, and the technique of r) wave-forming the light beams L7 and L6 are different from those in the apparatus shown in Fig. 1. . That is, as the above-mentioned branching means, an optical fiber coupler 70 is used which branches the light beam L sent from the optical fiber 24 into equal amounts of 1J. In addition, as the combining means, the bifurcated portion on one end side or the optical waveguide 1
The optical fiber 7 into which the light beam L6 emitted from the light beam L6 is inputted
1 and a fiber optic coupler 72 connected to the optical fiber 51 that guides the light beam L7.

A second photodetector 53 is coupled to the other end of the optical fiber coupler 72, and the optical beams 1, I-6 and L7 that interfere with each other (7) are combined by this photodetector 53. Detected.

Next, referring to FIG. 14, a third embodiment of the present invention will be described. Compared to the smaller device shown in FIG. 11, this device does not include a means for generating surface acoustic waves 16, and instead of generating surface acoustic waves with a constant frequency, means for generating surface acoustic waves with a varying frequency is used. It is also used. That is, in this apparatus, the normal spectrum analysis and the operation for determining the spectral width Δλ are performed separately over time.

When determining the spectral width Δλ, the frequency of the surface acoustic wave I5 is fixed to a certain predetermined value within the sweep range.

As a result, in this case, a surface acoustic wave 15 of a constant frequency is emitted. After diffraction in this surface acoustic wave 15,
The guided light L2 that has passed through the surface acoustic wave 15'' as zero-order light is outputted to the outside of the optical waveguide 12 as a light beam L6, and thereafter is converted into a light beam L7 in the same manner as in the apparatus shown in FIG.
It is combined with

For example, in the case of the aforementioned DFB semiconductor laser, etc., the center wavelength is roughly determined in advance, so if the above predetermined value is determined according to that value, the light beams I and 6 can be emitted in a certain direction. can be done.

Also, without doing so, for example, the frequency of the surface acoustic wave 15 is set to the maximum value or minimum value within the sweep range, and the light beam L6 whose emission direction changes depending on the wavelength of the light to be measured.
The light beam L6 may be detected by a photodetector having a relatively large light-receiving surface, or in the apparatus shown in FIG. 14, the optical fiber 1' half 1 may be appropriately moved to detect the light beam L6.

Further, a switch may be provided between the high frequency amplifier 19 and the IDT 17° so that the surface acoustic wave 15' is not generated when the spectral width Δλ is analyzed. This is preferable because the amount of light beam L6 increases.

In this device, since the frequency of the light beam L6 is shifted by the surface acoustic wave 15 as described above, this frequency shift ffi f A becomes extremely high, for example, IGHz.

Therefore, in this device, the detection signal S5 output from the photodetector 53 is sent to the mixer 76 and mixed with the local oscillation signal S8 output from the local oscillator 75.

For example, the frequency of elastic wave 15 in Table 1f11 is 1. GHz
In this case, if a 0.9 GHz signal is used as the local oscillation signal S8, the signal S9 output from the mixer 76 and sent to the high frequency spectrum analyzer 54 will be 0.1 GH2+2Δ
It can have a beat component of ν.

Note that in the first embodiment device shown in FIG. 1 and the second embodiment device shown in FIG.
and 15゛ may be prevented from occurring. This is preferable because the guided light will not be diffracted by these surface acoustic waves 15,15', and the amount of light detected in spectral width analysis can be increased. This also applies to the fourth embodiment described below.

Next, referring to FIG. 15, a fourth embodiment of the present invention will be described. The optical spectrum analyzer shown in Fig. 15 is configured to obtain the spectral width Δλ by the delayed self-homodyne method described above. Only a chirp IDT 17 that generates an elastic wave 15 is provided. Of the guided light L1 that has entered the surface acoustic wave 15, the guided light that has passed through the surface acoustic wave 15 as zero-order light is not diffracted and therefore does not undergo a frequency shift. The guided light L9 exits from the optical waveguide 12 and enters the beam splitter 52 as a light beam L6, where it enters the optical delay means 51. It is combined with the light beam L7 that has passed through A.

In this case, since the light beam L6 has not been frequency shifted, the beat signal shown on the high frequency spectrum analyzer 54 will be as shown in FIG. The frequency fluctuation width Δν of the beam L can be determined, and from this value the spectral width Δλ
I understand.

Further, in this embodiment, the light beam L that has been made parallel by the frimeter lens 27 is passed through the cylindrical lens 80 and focused into a flat shape, and the direction in which this light beam L is focused coincides with the thickness direction of the optical waveguide I2. The optical waveguide end face 1 is
, 2a, the light is input into the optical waveguide 12.

Note that even in this case, the optical fiber coupler 72 shown in FIG. 1I can combine the light beams L6 and L7.

(Effects of the Invention) As described above in detail, the three-spectrum optical spectrum analyzer of the present invention enables optical spectra to be analyzed with high resolution. Moreover, the optical spectrum analyzer of the present invention has a structure in which the light to be measured enters the optical waveguide and the light to be measured is diffracted by surface acoustic waves.
It is small and lightweight, and has no mechanical operating parts, so it is highly durable and reliable.

Moreover, the optical spectrum analyzer of the present invention effectively utilizes the elements for performing ordinary optical spectrum analysis, and uses the delayed self-heterodyne method or the delayed self-homodyne method to form an extremely small spectrum width that can be analyzed. Its range of use is wide and it can be extremely convenient in practice.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing a device according to a first embodiment of the present invention, FIG. 2 is a side view showing a part of the device of the above embodiment, and FIG. 3 is a plan view showing an enlarged part of the device of the above embodiment. FIG. 4 is an explanatory diagram for explaining the optical beam deflection in the above-mentioned embodiment device, FIG. 5 is an explanatory diagram for explaining the separation of the optical spectrum in the device of the present invention, and FIG. 6 is an explanatory diagram for explaining the amount of light detected in the device of the present invention, A graph showing the relationship between surface acoustic wave frequencies, FIG. 7 is a system diagram schematically showing the spectral width measurement system of the above embodiment device, and FIG. 8 is a schematic diagram showing the beat signal by the delayed self-heterodyning method according to the present invention. 9 is a graph showing an outline of a beat signal obtained by the delayed self-homodyne method according to the present invention. FIG. 1O is a graph showing an example of the oscillation spectrum of a semiconductor laser. FIG. Plan view showing the device, 1st
FIG. 2 is an enlarged plan view of a part of the device shown in FIG. 11, FIG. 13 is an explanatory diagram illustrating light beam deflection in the device shown in FIG. 11, and FIGS. 14 and 15 are, respectively, FIG. 7 is a plan view showing devices according to third and fourth embodiments of the present invention. Moon...Substrate 12...Optical waveguide T3...
・・LGC14 for optical input・LGC15, 15' for optical output
...First surface acoustic wave 1G...Second surface acoustic wave 17.17' ...Chirp IDT 18...I
DT19.40...High frequency amplifier 20...Sweeper 23...Light source 27...Collimator lens 29.55.5G...Condensing lens 30...Pinhole plate 31...First Photodetector 32... A/D converter 33... Arithmetic processing unit 3
4... Display device 41... Oscillator 50.52
...Beam splitter 51...Single mode optical fiber 51A...Optical delay means 53...Second photodetector 54...High frequency spectrum analyzer 70.72
...Optical fiber coupler 75...Local oscillator 76...Mixer 80.
...Nlindrical lens 95...Overall control section

Claims (2)

[Claims] (1) An optical waveguide formed of a material through which surface acoustic waves can propagate; ,
a first surface acoustic wave generating means that generates in the optical waveguide a surface acoustic wave whose frequency changes continuously to diffract and deflect the guided light; a second surface acoustic wave generating means for generating in the optical waveguide a surface acoustic wave having a constant frequency that diffracts and deflects the wave light; a first light detection means for detecting light; a frequency detection means for detecting the frequency of the surface acoustic wave when the light detection means detects the light to be measured; and a surface acoustic wave whose frequency changes and the frequency thereof. branching means for branching a part of the light to be measured before it is incident on the surface acoustic wave having a constant frequency; and a branching means arranged to receive the light to be measured that has been deflected by the surface acoustic wave having a constant frequency and emitted to the outside of the optical waveguide. combining means; an optical transmission system that guides the light to be measured branched by the branching means to the combining means; and an optical transmission system provided in the optical transmission system, the optical path length of the optical transmission system being controlled from the branching means to a constant frequency. an optical delay means that is sufficiently longer than the optical path length from the surface acoustic wave to the multiplexing means; a second optical detection means that detects the light to be measured that has been multiplexed by the multiplexing means; An optical spectrum analyzer comprising a high frequency spectrum analyzer that frequency-analyzes the electrical signal output by the second optical detection means. (2) An optical waveguide formed of a material through which surface acoustic waves can propagate; ,
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. a first light detection means for detecting the light to be measured; a frequency detection means for detecting the frequency of the surface acoustic wave when the light to be measured is detected by the light detection means; and a frequency detection means for detecting the frequency of the surface acoustic wave before being incident on the surface acoustic wave. branching means for branching a part of the light; a combining means disposed to receive the light to be measured that passes the surface acoustic wave as zero-order light and exits out of the optical waveguide; an optical transmission system that guides the light to be measured to the multiplexing means; and an optical transmission system provided in this optical transmission system, the optical path length of the optical transmission system being set by an optical path from the branching means to the multiplexing means via the surface acoustic wave. a second light detection means for detecting the light to be measured that is multiplexed by the multiplexing means; and a frequency analysis of the electrical signal outputted by the second light detection means. An optical spectrum analyzer consisting of a high frequency spectrum analyzer and a high frequency spectrum analyzer.