JPS62156535A - Light frequency network analyzer - Google Patents

Abstract

PURPOSE:To measure with a high accuracy an amplitude, a phase characteristic, etc., by comparing an electric output of the first filter part, and an electric signal related to a frequency difference of the first and the second optical outputs, and executing a signal processing. CONSTITUTION:The titled analyzer is provided with a light frequency sweeper 1 for generating the first optical output for sweeping a frequency and the second optical output related to said first optical output and emitting the first optical output to a measuring object, the first heterodyne detecting parts 33, 43 for inputting a light beam related to the emitted light of the measuring object based on the first optical output and the second optical output, the first filter parts 34, 44 for inputting an electric output of this first optical heterodyne detecting part, comparing means 35, 36, 45 and 46 for comparing an electric output of the first filter part and an electric signal related to a frequency difference of the first and the second optical outputs, and a signal processing means 50 for inputting an electric output of this comparing means and executing a signal processing. In this way, a light frequency network analyzer which can measure an amplitude, a phase characteristic, etc. with a high accuracy is obtained.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to an optical fiber, an optical waveguide, and a wavelength demultiplexer.

This invention relates to an optical frequency network analyzer that measures optical transmission characteristics, optical reflection characteristics, etc. of optical components such as optical switches and 0EfC.

(Prior Art) FIG. 12 is a block diagram showing a conventional optical fiber 10 wavelength loss characteristic measuring device. The output light of the variable wavelength light source VL enters the fiber under test MF, and the output light is sent to the photodetector P.
After detection at D, it is output to amplification/display means DP. The wavelength characteristic of optical fiber loss is measured from the change in optical power when the output wavelength of the variable wavelength light source V[- is swept.

FIG. 13 is a block diagram showing a conventional nine-fiber wavelength dispersion characteristic measuring instrument. The variable wavelength light source VL and the reference wavelength light source SL are modulated at frequency f (amplitude modulated by No. 8 source Et. The output light of the variable wavelength light source VL is applied to the fiber under test MF and the reference wavelength light source SL is added to the reference wavelength light source SL. The output optical power of the fiber SF is detected by the optical detection unit PD, and the phase difference between the frequency f component of both is detected by the phase measurement unit P.
By detecting with S, the propagation WI delay time with respect to the wavelength of the fiber under test MF is measured.

(Problems to be Solved by the Invention) However, the measuring instrument configured as described above has a drawback in that it cannot measure the phase propagation characteristics of light with high precision.

Also, although it is possible to measure objects with a good optical path, such as fibers,
Short waveguides cannot be measured. future coheren i・
Performance tests of optical fibers, leading waveguides, wavelength demultiplexers, optical switches, 0EICs, etc., which are important components of optical application technology, include measurement of propagation characteristics (loss, gain, phase, 11 extension) and anti-fault characteristics! i! However, the above measuring instruments are not sufficient.

The present invention has been made to solve these problems, and therefore, it is an object of the present invention to realize an optical frequency network analyzer that can measure amplitude two-phase characteristics and the like with high precision.

<Means for solving the l/It problem) The optical frequency network analyzer according to the invention generates a first optical output with a frequency h1 subtracted and a second optical output related to this first optical output. an optical frequency sweeper that emits a first optical output to a measurement object; and a first optical header-in detection that inputs light related to the output light of the measurement object based on the first optical output and the second optical output. a first filter section into which the electrical output of the first optical heterodyne detection section is input, and a filter related to the frequency difference between the electrical output of the first filter section and the first and second optical outputs; The present invention is characterized in that it includes a comparing means for comparing the electric signal with the air signal, and a signal processing means for inputting the electric output of the comparing means and processing the signal.

(Example) The present invention will be explained in detail below using the drawings.

FIG. 1 is a block diagram showing an embodiment of an optical frequency network analyzer according to the present invention. 1 generates a frequency-sweeping optical output (see Figures 2 to 11).
The optical frequency sweeper 23 is this optical frequency sweeper 1.
An optical heterodyne detection section 24 inputs the first and second output lights of the optical heterodyne detection section 24;
2 is an optical directional coupler that inputs the first output light of the surface frequency sweeper 1, 3 is an output end that outputs the output light from this optical directional coupler 2, and 10 is an output light from this output end 3. 4 is an input end for inputting the output light from the measurement pair 110, and 41 is a magneto-optical effect crystal (YIG, lead glass, etc.) for inputting the incident light from the input end 4. The polarization control unit used, 42 is an optical amplification unit that inputs the output light of this polarization control unit 41, and 43 is a PIN photodiode, an avalanche photodiode, etc.
[An optical heterodyne detection section that inputs the i-width section 42 and the second output J light of the optical frequency sweeper 1; 44 is a filter consisting of a bandpass filter that inputs and amplifies the electrical output of this optical heterodyne detection section 43; section, t+5 is a width comparison section which inputs the electrical output from the filter sections 44J5 and 24, and 46 is a width comparison section nQ, which inputs the electric outputs from the filter sections 44J5 and 24.
31 is a polarization control unit similar to 41 through which the reflected light from the measurement object 10 enters the optical directional coupler 2, and 32 is a polarization control unit for this polarization control unit. an optical amplifying section 33 similar to 42 into which the output light of section 31 is input;
is an optical amplifier 32 and a gain detection section similar to 43 which inputs the second output light of the optical frequency sweeper 1, and 34 is a gain detection section similar to 44 which inputs the electrical output of the optical heterodyne detection section 33. 35 is an amplitude comparison section similar to 45 which receives the electrical outputs from the filter sections 34 and 24; 36 is an amplitude comparison section 46 which inputs the electrical outputs from the filter sections 34 and 24; A similar phase comparison section 50 is the phase comparison section 35.
45 and the phase comparator 36, 71.6 is a processing/display section. 33. 43 is the first optical heterodyne detection section, 34, 44 is the first filter section, 23 is the second optical heterodyne detection section, 24 is the second filter section, 35.36, 45. 46 constitutes a comparison means, and 50 constitutes a signal processing means. The optical amplification section 32゜42 is a Q@AIAs laser (78
0nm band) and uGaAsP laser (1500nm band)
The following three methods can be used.

(a) Both are called 1-axis type semiconductor laser amplifiers, which perform linear optical amplification through stimulated emission by flowing a bias current with an oscillation threshold of 1 and inputting signal light into a laser diode.

(D) This is called an optical synchronous amplifier and controls the optical frequency and phase of the oscillated light by inputting a signal light into an oscillating laser diode.

(c) Called a traveling wave laser amplifier, both end surfaces of the laser diode depth are coated with a non-repulsion coating, and light is amplified only by transmitting signal light.

The operation of the optical frequency network analyzer having the J: U configuration will be described in detail below.

Optical frequency sweeper 1 sweeps the optical output in frequency to achieve high precision.
Outputs with high stability and high spectral purity (details will be described later)
. The first optical output at frequency ω0 of the optical frequency sweeper 1 is transmitted to the optical directional coupler 2. It enters the measurement object 10 through the output rA terminal 3, and this measurement pair @! The emitted light from 10 is input to the polarization control section 41 via the input end 4. The polarization control unit 41 controls the applied magnetic field by utilizing the optical rotation of the magneto-optic effect crystal, thereby changing the polarization plane of the input light into the locally oscillated light (the second
The polarization plane is controlled to be the same as the optical output (optical output). The optical output of the polarization control section 41 is amplified by the optical amplification section 42 and combined with the local oscillation light from the optical frequency sweeper 1 using a shallow half mirror (not shown), and the optical heterodyne detection section 43 detects the difference in image frequency. It is converted into an electrical signal with a frequency of ω0+Δω)−ω0−Δω. Part of the electrical output of the optical header-in detection unit 43 passes through the bandpass characteristic of the filter 44 . In addition, the first output light (frequency ω0) from the optical frequency sweeper 1 is directly transmitted to the local oscillation light (frequency ω0) by a half mirror or the like.
0-tΔω), and is converted by the optical heterodyne detection unit 23 into an electrical signal having a frequency equal to the image frequency difference Δω. The electrical output of the optical heterodyne detection section 23 is transmitted through the filter 24.
A part of the signal passes through the bandpass characteristic of the signal and becomes the reference signal. The output of the i output and the output of the reference 243 which has not been subjected to the evaluation of the characteristics of the object to be measured by the filter 44 are determined by the film width comparison section 45. The amplitudes are compared, and the phases of both numbers are compared in the phase comparator 46.The electrical outputs of the 1i width comparator 45 and the phase comparator 46 are signal-processed in the processing/display unit 50, and the 111 Sung The propagation characteristics of the measurement countermeasure are displayed as .The reflected light outputted from the optical coupler 2 from the measurement countermeasure 10 via the output end 3 is also transmitted to the polarization control section 31.The optical amplification section 3
2. Optical heater [1 dyne detection section 33, filter 34 . The amplitude comparison section 351, the phase comparison section 36J5, and the signal processing/display section 50 perform similar processing, and as a result, the reflection characteristics of the measurement target are displayed. When an optical waveguide is the object of measurement, the propagation loss of the waveguide, the wavelength characteristics of the phase difference, etc. can be measured. When measuring an optical fiber, the wavelength characteristics of propagation loss and delay t/1'? ! It can be measured using a fiber with a short f. When a laser diode optical amplifier is to be measured, wavelength characteristics of amplification gain, phase delay, etc. are measured. Also, the reflection loss at the optical connection point can be measured from the characteristics of the reflected light.

According to the optical frequency network analyzer having such a configuration, amplitude, phase, wavelength characteristics, etc. can be measured with high precision.

In addition, the propagation characteristics of the measurement target are loss 1 phase.

It is possible to measure both gain and reflection characteristics simultaneously and easily.

Note that WNt<
Tungsten, nickel) point contact diodes or Josephson elements can also be used.

Further, in the above embodiment, a bandpass filter was used as the filter section 24, 34°44, but this is limited to one vortex,
A low pass filter may also be used. In that case, Δω〒
It becomes ○.

FIG. 2 is a configuration block diagram of an optical frequency synthesizer sweeper which is an example of the configuration of the optical frequency sweeper 1 shown in FIG. 11 is a reference wavelength light source unit whose wavelength is stabilized;
Reference numeral 2 denotes an optical frequency PLL section which inputs the output light of this reference wavelength light source section 11, 13 an optical modulation section that modulates the output light of this optical frequency PLL section 12, and 14 amplifies the output light of this optical modulation section 13. The optical amplifying section 15 is an optical frequency shifter section that shifts the output frequency of the optical amplifying section 14. optical frequency P
In the LL section 12, 121 is an optical heterodyne detection section which receives the output light of the reference wavelength light source section 11 as one input;
123 is a variable wavelength light source section that controls the oscillation wavelength of output light by the output of this optical heterodyne detection section 121; 123 is an optical frequency shifter section that shifts the frequency of the output light of this variable wavelength light source section 122; Shifter section 123
This is an optical frequency multiplication section that multiplies the frequency of the output light of the optical system and uses the output light as the other manual power of the optical heterodyne detection section 121.

The operation of the device having such a configuration will be explained next.

When the output light from the reference wavelength light source section 11 is input to the optical frequency PLL section 12, the optical frequency PLL section 12 is! The wavelength of the optical output is fixed (locked) to the wavelength corresponding to the oscillation wavelength of the third sub-wavelength light source section 11. That is, the optical header login detection section 121 compares the output light from the reference wavelength light source section 11 and the output light from the optical frequency multiplication section 124, and controls the variable wavelength light source section 122 so that the difference between them becomes small. The optical frequency shifter section 123 in the feedback circuit adds an offset frequency to the output light of the variable wavelength light source section 122, and the optical frequency multiplier section 124 increases the ratio of the output optical frequency of the variable wavelength light source section 122 and the output optical frequency of the reference wavelength light source section 11. Establish. The light modulation section 13 modulates the output horn light of the optical frequency PLL section 12,
The optical amplification section 14 amplifies the output light of the optical modulation section 13 to generate an output of the optical frequency synthesizer sweeper (as a first optical output), and the optical frequency shifter section 15 amplifies the output light of the optical amplification section 14. The output light whose frequency is shifted by Δω is generated (as a locally pumped light output).

FIG. 3 is a block diagram showing a further embodiment of the configuration shown in FIG. In the reference wavelength light source section 11, L D
1 is Raded diode, CL is 1Mb gas or Cs
HMl is a half mirror into which the output light of the absorption cell CL is incident; PD1 is the half mirror into which the output light of the laser diode 11 is incident;
△1 is a control circuit that inputs the electric output of this photodiode PD1 and controls the current of the laser diode i D 1 with the corresponding output; [81 is the half mirror-HMl; Isolake for preventing return light from passing through, O△1
is an optical amplification element into which the light transmitted through this isolator 181 is input. The optical frequency P l-1 is J'3 in the section 12, HM2 is the reference wavelength W, and the half mirror 1PD2 which receives the output light from the source section 11 is the optical heterodyne detection section 12.
A PIN photodiode (consisting of an avalanche diode, etc.) that composes 1 and inputs the transmitted light of the half mirror 11M2, and EC inputs a reference frequency from a crystal etc. The 511 oscillator MXI that generates the signal is a mixer (mixing) circuit to which the electrical output of this oscillator EC and the electrical output of the optical heterodyne detection section PD2 are connected.This mixer' (mixing) circuit MX
In the variable wavelength light source section 122 to which the output of F is connected,
C is an optical frequency modulation circuit to which the output of the above-mentioned mixer circuit MX1 is connected, and VL1 to VL3 are variable wavelength laser diodes to which the output of this optical frequency modulation circuit FC is input. 8
2 is made of YIG (yttrium iron garnet) and the variable wavelength laser diode v[-1 to VL
The isolator O81 through which the output light of No. 3 passes is an optical switch through which the light that has passed through a small number (three in FIG. 3) of isolators 132 enters. 8M3 is this optical switch O8
The half mirror 1OA2 whose output light is 0A1J is an optical amplification element U which inputs the reflected light of this half mirror 8M3.
Ml is an ultrasonic modulator that constitutes the optical frequency shifter section 123 and inputs the output light of the optical amplification element OΔ2, and NL is an optical frequency modulator (constituting the 8th section and a nonlinear material that inputs the output light of this optical frequency shifter section). The leading waveguide O△3 is an optical amplification element that amplifies the output light of this optical waveguide NL.

In the optical modulation section 13 into which the output light of the optical frequency P L 1 section 12 is input, eight M1. PMI is an amplitude modulator d3 and a phase modulator using electro-optic crystals such as L+NbO5, respectively, and LMl is a polarization modulator all using magneto-optic crystals such as YIG. OA4 is an optical amplification element that constitutes the optical amplification section 14 and amplifies the output light of the optical modulation section 13. The optical frequency shifter section 15 is composed of an ultrasonic modulator similar to 123.

The operation of the apparatus having such a configuration will be described in detail below.

The reference wavelength light source section 71 has Rb (
Or Cs) Control the oscillation wavelength of the laser diode by 1t11 to the absorption line of the atom and use the absolute wavelength? Part 33, highly stabilized (
10-12 or more). Laser diode L
The output horn light of D1 becomes L when it passes through the absorption cell CL.
When the wavelength of the output light of Dl matches the absorption line of Rb gas (or C5 gas), it is absorbed, and an absorption characteristic as shown in the characteristic curve diagram of FIG. 4(A) appears. FIG. 5 is an explanatory diagram showing one unit of energy of Rb gas, and the absorption line of Rb is 02 line at 78 Orlm.

The DI line is 795 nm, and when multiplied by 2, it becomes 15
60 nm and 1590 nm, which is convenient because it coincides with the 1500 nm band, which is the optical fiber communication length s. This is also a wavelength range that is easy to use in the field of optical applied δ1 measurement.

The part of the output light of the absorption cell CL that is reflected by the half mirror 1'Ml is detected by the photodetector PD1, and the control circuit Δ1 controls the current of the laser diode LDI in accordance with the output of the photodetector PDI. By controlling the LD at the absorption center
Lock the output wavelength of l. For example, in Figure 4 (A>a
When it is desired to lock to a point, the control circuit A1 uses the lock-in amplifier f-, etc. to obtain the differential waveform of FIG.
It is fixed at six points (points where the differential waveform value becomes O) in the figure (B). This method is called the linear absorption method, and as shown in Figure 4 (A), the absorption spectrum becomes thicker, but the saturated absorption method (Hori, Kaida, Kitano, Yabusaki, Ogawa: Semiconductor using saturated absorption spectroscopy) Laser frequency stabilization fji science and technology tfI 0QE82-
116) to detect the absorption line of the hyperfine structure hidden in the Donplaschiff 1~, and connect it to the laser diode 1-D.
If the oscillation wavelength of l is locked, even higher stability will be achieved. Note that the temperature of the laser diode LD1 is stabilized in a constant temperature bath. The light transmitted through the half mirror HMl is passed through the isolator f.
incident on s1. The isolake Is1 prevents return light due to reflection from the outside from entering the laser diode LDI and becoming noise. The output light of the isolake IS1 is amplified by the optical amplification probe OAI as necessary.

As described below, the optical frequency PLL section 12 has a function of locking the oscillation wavelength of the variable wavelength light source section 122 to the oscillation wave hc of the J3 quasi-wavelength light source section 11 with a predetermined ratio and a predetermined off bit. have The output light from the reference wavelength light source section 11 passes through the half mirror 1M2 and enters the photodiode PD2 of the optical heterodyne detection section 121. The feedback light from the optical frequency multiplier 124 is also reflected by the half mirror HM2 via the optical amplification element OA3, and then enters the photodiode PD2. The output of the reference wavelength light source section 11 and the optical frequency of the feedback light are respectively ωS
,ω! Then, the frequency ω2 of the output electrical signal of the optical heterodyne detection section 121 becomes ω2-1ωS-ω11. When the output frequency of the oscillator EC is ω3, the output ω4 of the mixer circuit (phase detection circuit) MXl is obtained by adding an offset frequency to the output frequency ω2 of the optical heterodyne detection section 121, and becomes ω4=ω2−ω. The output electricity No. 13 ω4 of the MIKI υ circuit MX1 is input to the optical frequency modulation circuit FC of the variable wavelength light source section 122, and the optical frequency modulation circuit FC adjusts the optical frequency of the variable wavelength laser diodes VL1 to L3 so that ω4=0. Control. Here, the variable wavelength laser diode V
For LI to VL3, a resonator is constructed using reflection from a diffraction grating built into the radar diode chip, and the oscillation frequency is determined by the pitch of the diffraction grating, so the wavelength is relatively stable and FB (Distributed Fee)
dback) laser or DBR (D i st r 1
Butted Brag(] Reflector)
ADFB (Acoustic [)1] is a type of laser.
:B) Laser (Yamanishi M, et.

al, :QaAB ACOuSjiCDistrib
uted Feedback La5erS,
, ) pn, J, Ap p 1.
Phys, , 5LJI)t)1.1B-
1, p. 355.1979). The ADFB laser generates a surface acoustic wave (SAW) perpendicular to the diffraction grating in the DBR radar, and the SAW and the diffraction grating built into the chip form a ring resonator of light by black diffraction. When the wavelength of the SAW is swept, the resonance wavelength of the ring resonator changes, and the oscillation wavelength can be swept. In this embodiment, the oscillation wavelength is set to 1560 nm band. DFB with long resonator length, DI3 R A D
FB laser has a narrow oscillation spectrum (also has the advantage of good spectral purity. One Al) I=B
If the variable wavelength range of the laser is insufficient, a plurality of ΔDFB lasers (VL1 to VL3) can be used and switched by an optical switch or optical multiplexer as shown in FIG. That is, the output lights of the variable wavelength laser diodes VLI to VL3 are input to the optical switch O81 via the isolator IS2 for preventing return light, respectively, and are selected within a predetermined variable wavelength range. A part of the output light from the optical switch 081 is reflected by the half mirror 1-IM3 and input to the optical amplification element OA2.

The output light of the optical amplifying element OA2 is input to the optical frequency shifter section 123, and then input to the ultrasonic modulator UM1 to output S-order diffracted light of 13 ragg. If the frequency of the ultrasonic wave supplied from a reference frequency source such as crystal le & 5 is ω5,
The optical frequency of the diffracted light is shifted by SO2.

The output light of the optical frequency shifter section 123 is transmitted to the optical frequency multiplier section 12.
4) and outputs the second harmonic of the incoming saw light through an optical waveguide NL using a nonlinear material. In other words, a tunable wavelength laser diode output of 1560 nm is inputted via an optical amplifier, and a second harmonic of 780 nm is output. As a waveguide, a four-layer slab guided waveguide of Air-T (02ZTLS-glass) using a nonlinear thin film of ZTIS and a linear thin film of TiO2 is used to efficiently generate the nonlinear effect.

Although this embodiment uses second-order harmonics, any n-order harmonics may be used.

The output light from the optical frequency multiplier 124 is amplified by the optical amplification element OΔ3, and then merges with the output light from the reference wavelength light source 11 by the Hartz mirror HM2 as feedback light, as described above.

Through the above operation, the optical frequency ω0 of the optical output of the optical frequency F) part 12 becomes ω0=(ωS±ω3)/n±Sω5 (note that the signs are not in the same order). However, in this embodiment, the optical frequency multiplication number n=2. That is, ω is the absolute wavelength and is locked to a highly accurate and highly stable optical frequency ωS via a predetermined ratio n, and furthermore, it can be set to any arbitrary frequency ω, /n or ω5.
becomes an optical frequency with an offset of . ω3 or θ
) 5, a highly accurate optical frequency sweep can be realized. Here, since ω3°ω5 are electrical signals, high accuracy and high stability can be easily obtained.

The optical output of the optical frequency P[-1 part 12 is input to the optical modulation section 13, is amplitude modulated by the amplitude modulator ΔM1, and is modulated by the phase modulator P.
The phase is modulated by M1, and (Ia
The direction of light is changed. The optical output of the optical modulation section 13 is amplified by the optical amplification element O△4 of the optical amplification section 14, and then
r output (first optical output). Also, the optical amplification element 0△4
The output frequency of the optical output is shifted △ω by the ultrasonic transformer of the optical frequency shifter section 15, and the optical output is localized at the frequency ω0 + Δω.
R, is output as a vibration (second optical output).

In the above configuration example, the optical amplification elements OA1 to OΔ4 are the same as the amplification sections 32 and 42.

In the above configuration example, by replacing the optical frequency thick section 123 and the original frequency (by inserting 1 of the 13 section 12-'l), the frequency ω0 of the optical output of the optical frequency P L 1 section 12 is set to ωo=< It may also be ωS ±ω3 ± SO2)/n.

In addition, in the optical frequency P L 1 section 12, the mixer circuit M
Both the XI J5 and the optical frequency shifter section 123 are for adjusting the offset frequency, and either one can be omitted.

Also, there is a3 in the optical frequency PLL section 12, and the multiplication is ¥1. If n is set to 1, the optical frequency multiplier 124 can be omitted.

Further, in the above configuration example, in the reference wavelength light source section 11, Rb
Or, the absorption line of Cs is used, but it is not limited to these, but any absorption line with high precision and high stability at the absolute wavelength, such as N
It is also possible to use the absorption line (1500 nm band) of H) or H2O. In this case, the optical frequency multiplier 124 becomes unnecessary. Although it is possible to stabilize the wavelength by using the well-known 71 Bribelow TT oscillator as a wavelength detector, the characteristics are better obtained by using the m-son standard absorption line as described above.

Also, in the device shown in Fig. 3, instead of ω3, ω3'-ω, +Ω
(Ω is the light f, ′ when the FMgMg wave frequency frequency No. 18 is input to the mixer circuit MXI when a lock-in amplifier is used in the reference wavelength light source section 11)] Wave number PLL section 12
Unnecessary FM modulation components can be removed from the optical output.

In addition, the variable wavelength radar diodes VL1 to VL3 are not limited to ADFB as in the above configuration example, but an external resonator using a diffraction grating is added outside the laser diode chip, and the wavelength can be selected by rotating the diffraction grating. It may also be possible to make the wavelength variable by taking advantage of its properties. External cavity laser diodes have the excellent feature of narrow spectrum.

Further, as the variable wavelength laser diodes V1-1 to VL3, a device in which a wavelength selective element is inserted into a resonator as shown in FIG. 6 may be used. In the figure, LD2 is a semiconductor laser, 51.52 is a non-reflection core provided at both ends of the semiconductor laser (Ll) 2, and LSl is a parallel light emitted from the non-reflection tool 1 to 51. lens, M
l is a mirror on which the light transmitted through this lens LS1 is reflected, and LS2 is a mirror on which the light emitted from the non-reflection coating portion 52 is reflected.
tJM2 is a first ultrasonic modulator into which the light transmitted through the lens LS2 enters; UM3 is a second ultrasonic modulator into which the light emitted from this ultrasonic modulator UM2 enters; M2 reflects the light emitted from this ultrasonic modulator UM3! l) j mirror, DRl is the ultrasonic modulator LJM2. This is an oscillator that excites UM3 at frequency F. FIG. 7 shows an ultrasonic modulator UM2.A3 in the device shown in FIG.
FIG. 3 is an operation explanatory diagram showing how the UM3 performs wavelength selection and frequency sweeping operations. The light emitted from the non-reflection coating portion 51 of the semiconductor laser γLD2 is converted into parallel light by the lens LSI, and is reflected by the mirror M1. The reflected light from the mirror M1 returns to the original optical path, becomes a semiconductor laser again, and enters D2. Frequency 1' emitted from the non-reflection coating section 52
The o+ light is made into parallel light by the lens l-32, and the light from the first IB
>N-wave enters the modulator UM2. In this case, the diffraction line 1'1
Therefore, there is a relationship as shown in the following equation between the incident angle θ132 on the diffraction grating 63 caused by the ultrasonic wave 61, the output angle θO++ after diffraction, the wavelength λo J5 of the light, and the wavelength Δ0 of the ultrasonic wave.

sin θ7++ sin θOI=λ0/Δ0 (1) In other words, the wavelength λ0 of the light passing through the optical path such that both the incident angle θi1 and the output angle θo1 are equal to the wavelength of the ultrasonic wave. It will change if it changes. The emitted light undergoes a Doppler shift due to the ultrasound, and in this case, it is first-order diffracted light (the direction of the ultrasound and the direction of diffraction are the same), so its frequency is f
o+ 10F. The light emitted from the ultrasonic modulator UM2 is ultrasonic modulated! Again with AUM3] r! Fold it. Similar to the library record, the angle of incidence θ on the diffraction grating 64 caused by the ultrasonic wave 62
L2 + diffraction output angle θ02. There is a relationship between the wavelength λ0 of light and the wavelength Δ0 of ultrasound as shown in the following equation.

Sl"]θ(2+sinθo2=λ./△.

...(2) However, in equation 2), λ due to the Doppler shift of the ultrasonic modulator UM2. Since the change in is small, no T and S2 are performed. Here, the relationship between the ultrasonic traveling wave 62 and the diffracted light is opposite to that in the ultrasonic modulator UM2, and it becomes -1st order diffracted light, so the Doppler shift l-fil becomes -F, and the output light of the ultrasonic modulator UM3 The frequency of is fo+ ←F F
=fo+. The emitted light from the ultrasonic modulator (JM3) is reflected by the mirror M2, travels backward along the optical path, and enters the semiconductor laser LD2 again.When going backwards, the frequency of the emitted light from the UM3 changes to f due to Doppler shift. +F and U
The frequency of the light emitted from M2 becomes the original frequency f'o+ (fo+F+F=fo+) and returns to the semiconductor laser l-D2, so that the resonance state continues. In order to increase the diffraction efficiency, the Bragg incident condition is satisfied, and the following relationship is established between the incident angle θ (++ outgoing angle θOI + incident angle θL2 and outgoing angle θo2) when the wavelength of the ultrasonic wave is 0. .

θi+−θOI−θt2=θ02 With this configuration, the wavelength of the ultrasonic wave is △. If you change θLI+
θ01+ θ, 2. The likely wavelength λ0 that satisfies θo2 and resonates can be swept as shown in the following equation.

sinθf++5ij1θo1-(λ0+Δλ)/(△
. 4・Δ△) Also, variable wavelength laser + f diode V L 1-V L
3, a resonator in which an element capable of controlling the refractive index is inserted into the resonator as shown in FIG. 8 may be used. Components that are the same as those in FIG. 6 are given the same ad symbols and their explanations will be omitted. EOl is an electro-optical element made of L i N b O 3 and sodium obate, etc., and has anti-reflection coatings on both sides and receives the output light from the lens LS2. 71 is a power source that controls this electro-optical element [EOl]. The light emitted from the semiconductor laser L1]2 becomes parallel light through the lens LS2, passes through the electro-optical element EOI, is reflected by the mirror M2, and then travels backward along the optical path.
The light enters the semiconductor laser LD2 again. As a result, mirror M
A resonator can be constructed between the mirror M1 and the mirror M2. Mirror M1
If we take the distance excluding the length Q along the optical path of the electro-optical element EO1 between the mirror M2 and the mirror M2, and take the refractive index of the electro-optical element Eo1 as n, the speed of light as C, and p as an integer, then the oscillation frequency "02 is fo 2 = p-C/2 (L+n (V) Q)・
...(3) becomes. In other words, the refractive index n can be changed by changing the electric field strength of the electro-optical element E01 using the power source 71, and as a result, the oscillation frequency f02 can be swept.

FIG. 9 is a block diagram showing the configuration of the variable wavelength radar diode of FIG. 8 in a double resonator type. The same parts as in FIG. 8 are given the same symbols and the explanation is omitted. BSL
is a beam splitter that divides the emitted light from lens LS2 into two directions, and EO2 is this beam splitter [
An electro-optical element that receives the light transmitted through 3S1, a mirror that reflects the light emitted from the electro-optical element E02 on the side of M2i, and E
O3 is an electro-optical element that receives the light reflected by the beam splitter 881, and M3 is a mirror that reflects the output Di9 of the electro-optical element FO3. electro-optical element EO2,
The length of EO3 in the optical path direction is Q+, Q2, and refraction', respectively.
A5 respectively nI+n2, the distance excluding Q+ along the optical path between mirrors M1 and M2 is 1-1, mirror M1. If the distance excluding Q2 is 12, and Q is an integer, then the oscillation frequency [03 of this easy case is fos = q - C/21 (L+ +n
+ (V+)j+-(12+-n2 (
V2) Q2) I-
(4) becomes. Since the denominator of equation (4) can be made smaller than that of equation (3), the variable range of the oscillation frequency can be made larger than in the case of the device shown in FIG.

FIG. 10 is a construction diagram showing the tunable wavelength laser diode of FIG. 8 integrated on one chip. 91 is G
A laser diode composed of aAQΔs, EnGaAs Ph, etc., 92 is an optical amplification section arranged at the junction of the single diode 91, 9ζ3 is also a waveguide outdoor resonator, and 94.95 is the laser diode 91. 06 is an electrode provided on the surface of the laser diode 91 corresponding to the optical amplification section 92;
Reference numeral 97 denotes an electrode provided on the surface of the radar diode 91 corresponding to the waveguide outdoor resonator 93.

A current of 1t, o is applied to the junction through the electrode 9G, and a current is applied to the optical amplification section 92 to generate a laser beam, and a current IF is applied to the waveguide type external oscillator 93 through the electrode 97. By changing the refractive index of the flowing waveguide outdoor resonator 93, the oscillation frequency is lowered by one. The quality along the junction of the optical amplification section 92 and the waveguide type external co-imager 93 is 93 N, respectively.
(!4, if the refractive index is n3, n4, and r is an integer, the oscillation frequency fod is fo 4-r-C/2 (n
3 Q3 +n4 (fF) Q.

Further, a WNt (tungsten, nickel) point contact diode or a George Fson element can also be used for the optical heterodyne detection section 121. These cables have the functions of both a transmitter 8 and a mixer, so ωS, ω1. The mixer circuit M that can be operated manually at the same time as ω3 is shown in Figure 3.
X1 becomes unnecessary.

In this case, the input signal of the optical frequency modulation circuit FC from the output point 1j of these elements is ω4−ωS−ω1±mω3 (
Port 1 is the multiplication number). Also ω4=ωs2ω1±mω3
In this case, the optical frequency signal 12
4 becomes unnecessary.

FIG. 11 is a configuration block diagram showing an example of the configuration of a song of the optical hete I codine detection section 121. oC is a local oscillator with a first frequency using a second wavelength stabilized light source, and OX is an optical output of this local oscillator OC and the optical frequency multiplier 1.
OD is an optical frequency mixer using a nonlinear optical crystal into which the optical output of 24 is inputted via the optical amplification cable OA3, and OD is a combination of the optical output of this optical frequency Meyari OX and the reference wavelength light source section 11.
inputs the output light from J and outputs it to the variable wavelength light source section 122.
The photodetector is composed of a P r N photodiode or a 7-balanced 4-diode <T.

According to such a configuration, the optical output frequency ω6 of the optical frequency mikina oX becomes (!J6−ω1+
It becomes ωL. In the configuration shown in Figure 3, the optical frequency multiplier allows
(Apart from the offset frequency) ωS - ω1 = ntt)
Although only a limited ω1 determined by Q can be obtained, the configuration shown in FIG. 11 can output light of various wavelengths. For example, Rb
The wavelength of ωS is determined by using the absorption line of λs=780nm, C6
If the wavelength of ωL is chosen as λL=852nm using the absorption line of , then the relationship when the feedback loop is balanced is ωs=ω
6 to ωS, ω1. Each wavelength of ωL λ5°λ1.
Since there is a relationship between λL of 1/λs=1/λ1+1/λL, it becomes λIl-9230n.

The optical frequency synthesizer sweeper described above has the following features: (a) Its optical output can be locked to absorption lines such as Rb and Cs with high precision and high stability at the absolute wavelength. Preliminary standard with stability of 1Q-12 or higher (conventional frequency standard is Cs <9Gl-1z), Rb
(Using microwave resonance of >6 GHz) can be obtained.

(b) Also, variable wavelength laser diodes V11 to V1-3
Since the resonator length is changed to ΔDFB or an S-type diode is used, the Q of the co-imager is high and the oscillation spectrum width can be narrowed.

(c) Also, since the principle of optical frequency PLL is used, highly accurate optical frequency sweeping is possible.

(d) Also, by using Rb absorption lines (780 nm, 795 nm) and the doubling method, optical communication fibers can transmit light in the 1500 nm band with the lowest optical transmission 1 (+1 loss) with high precision and high stability. Since it can be output, it is highly practical.

(e) With the configuration shown in Figure 11, various 4
Can emit r-light frequency.

An example of the operation of the optical frequency applied to the optical frequency network analyzer configured as described in the embodiment of FIG. 1 will be described below.

Wavelength of ωS: 780 nm (Lock the wavelength of the laser diode to the absorption line of Rb) Wave of ω0 1n: 1560 nm±50 n +nΔω Frequency fl: 100MI-IZ In this operation example, the measurement light is passed through an optical fiber (optimum of g) It is particularly effective for measuring optical communication devices in wavelengths.

Note that in the above embodiment of the optical frequency network analyzer, a synthesizer sweeper is used as an optical frequency sweeper, but this is limited to a synthesizer sweeper.
A high g+good sweeper that is not J-ized may also be used.

Furthermore, in the embodiment described in section 1, the reference signal of the comparison means is obtained using the second nine-heterodyne detection section 23 and the second filter section 24, but the invention is not limited to this, for example, the optical frequency shown in FIG. A modulation electrical signal corresponding to the shift frequency Δω applied to the optical frequency shifter 15 of the synthesizer sweeper may be used. In this case, the configuration can be simplified by omitting the second optical heterodyne detection section and the second filter section.

In addition, the light emitted from the optical frequency network analyzer to the measurement target is not limited to continuous light, but pulsed light is used, and in synchronization with this pulsed light, the optical frequency (1) can be subtracted by Properties can also be measured.

(Effects of the Invention) As described above, according to the present invention, it is possible to realize an optical frequency network analyzer that can measure amplitude and one-phase characteristics with high precision.

[Brief explanation of drawings]

FIG. 1 is a configuration block diagram showing one embodiment of the present invention, and FIG.
The figure is a block diagram showing a configuration example of the optical frequency sweeper 1 used in the present invention, FIG. 3 is a block diagram showing a configuration example embodying the configuration of FIG. Figure 3 is a characteristic curve diagram to explain the operation of the device, Figure 5 is an explanatory diagram to explain the operation of the device in Figure 3, and Figures 6 and 8 to 1o are the variable wavelength diagrams in Figure 3. A configuration explanatory diagram showing another configuration example of the laser diode, FIG. 7 is an operation explanatory diagram for explaining the operation of the device in FIG. 6, and FIG. 11 is a diagram showing a partial modification of the device in FIG. 3. Conjunction block diagram, 12th
The figure is a block diagram of the hob configuration of a conventional optical fiber loss wavelength characteristic measuring instrument, and Figure 13 is a conventional optical)? FIG. 2 is a conjunctive block diagram showing a device for measuring wavelength dispersion characteristics. 1... Optical frequency sweeper, 10... Measurement object, 23
...Second optical heterodyne detection section, 24...Second filter section, 33.43...First optical heterodyne detection section, 34,4.4...@1 filter section ,35,
36.45.46... Comparison means, 50... Signal processing T: stage.・′、−＼

Claims (9)

[Claims] (1) an optical frequency sweeper that generates a first optical output that sweeps a frequency and a second optical output related to the first optical output and emits the first optical output to a measurement target; a first optical heterodyne detection unit that inputs the light related to the output light of the measurement target based on the output and the second optical output; and a first filter that inputs the electrical output of the first optical heterodyne detection unit. a comparing means for comparing the electrical output of the first filter section and an electrical signal related to the frequency difference between the first and second optical outputs; and signal processing by inputting the electrical output of the comparing means. An optical frequency network analyzer characterized in that it is equipped with a signal processing means. (2) comprising a second optical heterodyne detection section into which the first and second optical outputs are input; and a second filter section into which the electrical output of the second optical heterodyne detection section is input; 2. The optical frequency network analyzer of claim 1, wherein the electrical output of the second filter section is compared with the electrical output of the first filter section. (3) Equipped with a polarization control section that inputs the output light of the measurement target and controls the polarization plane, and an optical amplification section that amplifies the output light of this polarization control section, and converts the output of the optical amplification section into a first optical heterodyne. The optical frequency network analyzer according to claim 1, wherein the optical frequency network analyzer is configured to input the signal to a detection section. (4) The optical frequency network analyzer according to claim 1, wherein the comparing means comprises amplitude comparing means. (5) The optical frequency network analyzer according to claim 1, wherein the comparison means includes phase comparison means. (6) The optical frequency network analyzer according to claim 1, wherein the filter section is constituted by a band pass filter having a transmission frequency band corresponding to the difference between two output frequencies of the optical frequency sweeper. (7) The optical frequency sweeper includes a reference wavelength light source section and an optical frequency PLL section that controls the wavelength of the optical output to a wavelength corresponding to the oscillation wavelength of the reference wavelength light source section, and the optical frequency PLL section has an optical output. 2. The optical frequency network analyzer according to claim 1, which uses an optical frequency synthesizer sweeper that makes the wavelength of the optical frequency variable. (8) D_2 (78
0nm) line or D_1 line (795nm)
The optical frequency network according to claim 7, wherein the optical frequency PLL section outputs light in a wavelength band twice as large as each of the oscillation wavelengths, using a laser diode whose R oscillation wavelength is controlled in two absorption spectra. analyzer. (9) An optical heterodyne detection section in which the optical frequency PLL section receives the output light of the reference wavelength light source section as one input, and a variable oscillation wavelength of the output light is controlled by an output related to the electrical output of this optical heterodyne detection section. 8. The optical frequency network analyzer according to claim 7, further comprising a wavelength light source section, wherein light related to the output light of the variable wavelength light source section is inputted to the other input of the optical heterodyne detection section.