JPH01438A - Chromatic dispersion characteristic measurement system and its optical signal transmitting unit and optical signal receiving unit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention relates to a system for measuring the chromatic dispersion characteristics of a source fiber, an optical signal transmitting unit thereof, and an optical signal receiving unit thereof. The present invention relates to a system for measuring chromatic dispersion of an optical fiber, an optical signal transmitting unit thereof, and an optical signal receiving unit thereof.

[Prior Art] The wavelength dispersion characteristics of an optical fiber are very important in determining the information transmission speed of an optical fiber communication path. Currently, the method for measuring chromatic dispersion of single mode optical fiber is
I mainly study the following things.

(1) No. 9 combining fiber Ramanrede and spectroscopy 4
Luss delay time difference measurement method +21 Baseband phase comparison method using a combination of LED and spectrometer (3) Baseband phase comparison method using multiple radar diodes LDs with different wavelengths (4) Applying the coherence of light Among these interferometry methods, (
3) The baseband phase comparison method will be described. Generally, optical signals having different wavelengths have different group velocities of the light source due to material dispersion and structural dispersion of the fiber, and a difference occurs in the phase of the optical signals after the propagation. The baseband phase comparison method takes advantage of this fact. First, an optical signal generator such as a radar diode with different wavelengths is placed in the optical signal transmitter to generate two types of optical signals whose intensity is modulated by a sinusoidal f-tone signal, namely a reference optical signal and a measurement optical signal. let

The above two types of optical signals are respectively input to a reference fiber and an optical fiber to be measured. Next, in the optical signal receiving section, based on the reference optical signal emitted from the reference optical fiber, the phase between the 41A signals of each wavelength of the measurement optical signal emitted from the optical fiber to be measured is determined. Determine the group delay time M from the sum. Furthermore, if the measurement result is approximated by an appropriate function τ (λ), then by analytically differentiating that function, the desired chromatic dispersion D (λ) = dτ
(λ)/dλ is found. The relationship between the group delay time difference and the wavelength is shown in a graph as shown in FIG.

By the way, a measuring instrument using the conventional baseband phase comparison method has an optical signal transmitter 1 and an optical signal receiver 10 arranged as shown in FIG. A fiber 1 and a fiber to be measured 12 are connected. The optical signal transmitter 1 sends a CpTJ 2 and this CPU which issue necessary commands at predetermined timing.
A modulation signal generation unit 3 generates modulation signals '1 * '2 + f3 and f4 of a sine wave frequency in response to a signal selection command from the modulation signal generation unit 3, and a branch circuit 4 from this modulation signal generation unit 3.
The modulated signal fl yf! +f3
A radar diode M that emits a radar light of a predetermined wavelength to input a reference optical signal obtained by intensity modulating with +f4 into a reference fiber 1, and a channel selection unit 6 that sequentially selects output end channels in response to a switching command from the CPU 2. , a Raded diode LDI-LD4 that emits Raded light of different wavelengths and outputs a measurement optical signal obtained by sequentially intensity-modulating the modulating signal, for example, f, inputted from the modulated signal generator 3 through the branch circuit 4; radar diode LDI with
- An optical switch 81 having a function of reflecting only the intensity-modulated measurement optical signal from the LD 4 and passing the other incident light.

82, r83, m84, etc.

9 is! It's the rhythm.

On the other hand, the signal receiving section 10 converts the reference optical signal and the measurement optical signal emitted from the reference fiber 11 and the measured fiber 12, respectively, into electrical signals and performs 4i tuning. After that, 4
The chromatic dispersion characteristic is obtained by determining the phase difference between the two signals that have been tuned to 1.

Furthermore, a measuring instrument using the conventional baseband phase comparison method has an optical signal transmitter 210 and an optical signal receiver 220 arranged as shown in Figure @11.
A reference fiber 23 and a measured fiber 232 are connected between the fibers 220 and 220 . This optical signal transmitter 210 is
A reference optical signal obtained by intensity-modulating light emitted from a reference light source such as a Raded diode with at least l types of modulation signals of predetermined frequencies is input into the reference fiber 231, and similarly, at least l types of modulation signals of predetermined frequencies are input into the reference fiber 231. The measurement light signal obtained by intensity modulating the light emitted from a measurement light source such as a laser diode with a modulation signal of a predetermined frequency of the fji class is made to enter the fiber under test 232.

On the other hand, on the optical signal receiving section 220 side, photoelectric conversion sections 221r and 221t are connected to the output sides of the reference fiber 231 and the measured fiber 232, respectively, and here, each of the seven eyeglass
3, a rear terminal @ device 222r that converts the emitted optical signal from 232 into an electrical signal.

222t, and amplified the signal to an appropriate level, and further amplified the signal to the local oscillator 2 using subsequent demodulation mixers 223r and 223t.
Demodulation is performed using a local oscillation signal of a predetermined frequency output from 24. Then, these demodulated signals are sent to a filter 22.
After passing the signal of the required frequency through 5r and 225t,
The signal is supplied to the phase measuring section 226. In this phase measuring section 226, both filters 225r.

After measuring the phase from the output of 225t and determining the phase difference from these two phases, this phase difference is converted into a voltage signal, further converted into a digital signal, and sent to a post-processing device (not shown).

By the way, in the wavelength dispersion measuring instrument as described above, the photoelectric conversion section 2 disposed on the receiving input end side of the optical signal receiving section 220
21r and 221t have the range to convert electrical signals KK with good linearity within a certain optical input level range. Therefore, if an optical signal with a level exceeding the above-mentioned range is emitted from the fibers 231 and 232, it cannot be converted into an electrical signal with high accuracy.

Therefore, conventionally, when the optical signal level emitted from the fibers 231 and 232 is expected to change significantly from a practical or empirical point of view, the photoelectric conversion units 221r and 221
An optical attenuator or the like is provided on the input side of t, and the optical signal level is adjusted by manually adjusting the attenuator.
1r and 221t, the optical input level is within the range where linearity conversion is possible.

[Problems to be Solved by the Invention] However, the optical signal transmission unit of the conventional chromatic dispersion characteristic measurement system that uses such a baseband phase comparison method requires a reference optical signal to be obtained in addition to the measurement optical signal generator. A dedicated light source such as a radar diode is separately provided just for this purpose. This is not only disadvantageous in reducing the size of the measuring instrument, but also poses an obstacle to cost reduction due to the redundant use of very expensive radar diodes and other related components.

Furthermore, the optical signal receiving unit of the conventional wavelength dispersion characteristic measurement system has a photoelectric conversion section to convert the optical signals emitted from the fiber under test and the reference fiber into electrical signals. However, although it has the ability to convert optical signals within a certain level range into electrical signals with a high degree of nearness,
If it exceeds the range of the above-mentioned level, there is a problem that it cannot be converted into an electric signal with a high degree of +7. For this reason, when the optical signal level is expected to change significantly, an optical attenuator or the like is provided at the input of the photoelectric conversion section, and the level of the optical signal is limited while manually adjusting this attenuator.

This manual method of adjusting the attenuation value is not satisfactory in terms of the speed of measurement.

In addition, since the loss caused by the difference in the length of the fiber under test and the connection condition differs each time, it is recommended to adjust the optical signal level appropriately when there is an unpredictable change in the optical signal level. This can also cause deterioration of the light receiving element.

Therefore, an essential object of the present invention is to provide a chromatic dispersion characteristic measurement system and its optical signal transmission unit that reduce the number of optical signal generators required in the optical signal transmission unit, resulting in cost reduction and miniaturization. Our goal is to provide the following.

In addition to the above, another object of the present invention is to be able to automatically adjust the level of the original IM signal emitted from the optical fiber, and to convert the optical signal into an electrical signal with good linearity at all times. An object of the present invention is to provide a wavelength dispersion characteristic measurement system and an optical signal receiving unit thereof.

[Means for Solving the Problem] In order to achieve the above object, the optical signal transmission unit of the wavelength dispersion characteristic system of the present invention transmits an optical signal having a wavelength corresponding to each of the n wavelength points to be measured into a measurement light. n light source means provided for selectively generating a signal, one of which serves also for generating a reference optical signal; and a modulation signal for generating a modulation signal having at least one predetermined frequency. generating means; first control signal generating means for specifying the n light source means in a predetermined order to generate the measurement signal and the reference optical signal; the first control signal generating means, the modulation signal generating means; a particular light source means of the n light source means coupled between the means and the n light source means and designated by the first control signal for generation of the measurement light signal; and generation of the reference light signal; a light source switching means for selectively supplying the modulation signal to the light source means that also serves as the light source means or for supplying the modulation signal only to the light source means that generates the measurement optical signal and the reference optical signal; a second control signal generating means for generating a second control signal having a predetermined synchronization relationship with the control signal; n optical signal input terminals disposed corresponding to each of the n light source means; The above-mentioned optical signal having a single measurement optical signal output terminal and a single reference optical signal terminal is selectively input to the n optical signal input terminals in response to a second control signal from the 1g2 control signal generation means. The measurement optical signal from the specified light source means among the n light source means is commonly led to the measurement optical signal output terminal, and one of the n light source means
The present invention is characterized in that it comprises an optical switch means for guiding the reference light signal No. 1 generated by the reference light signal to the reference light signal output terminal.

Furthermore, the optical signal receiver (22) of the wavelength dispersion characteristic system of the present invention is coupled to the photoelectric converter and the photoelectric converter that converts the reference optical signal and the measurement light No. 1B into electric wave signals, respectively, and current monitoring means for detecting the level of an electrical signal from the photoelectric converter and generating a control signal corresponding to the level of the detected electrical signal; and the reference light that is combined with the photoelectric converter ICM and input to the photoelectric converter. It is characterized by comprising a programmable optical attenuator that automatically adjusts the level of the signal and the measurement optical signal.

Further, the chromatic dispersion characteristic system of the present invention is provided for selectively generating optical signals having wavelengths corresponding to n wavelength points to be determined as measurement optical signals, one of which is a reference optical signal. n light source means for generating a modulation signal having at least one predetermined frequency; and a modulation signal generation means for generating a modulation signal having at least one predetermined frequency; a first control signal generating means for specifying the n light source means in a predetermined order; a control signal for the 5gl coupled between the first control signal generating means, the modulation signal generating means and the n light source means; selectively supplying the modulated signal to a specific light source means of the n light source means designated to generate the measurement optical signal and a light source means also used to generate the reference optical signal; or light source switching means for supplying the modulation signal only to the light source means that generates the measurement optical signal and the reference optical signal; a second control signal generating means for generating a second control signal having a predetermined synchronization relationship with the ff1J# signal; n optical signal input terminals disposed corresponding to each of the n light source means; 6 has a single measurement optical signal output end and a reference optical signal end, and receives a second control signal from the second control signal generating means and selectively inputs the n optical signal input ends. The measurement optical signal from the n light source means that is added to the n light source means is commonly led to the measurement optical signal output terminal, and the reference is generated by one of the n light source means. an optical signal transmitting unit comprising source switching means for guiding the optical signal to the reference optical signal output end; and an optical signal transmitting unit having one end and the other end, the one end of the reference optical fiber being configured to receive the reference optical signal. A reference optical fiber is connected to the reference optical signal output end of the source switching means, and the optical switch has one end and the other end, and the one end of the optical fiber to be measured receives the measurement optical signal. an optical fiber to be measured connected to the measurement optical signal output end of the optical fiber to be measured; a photoelectric converter for converting the reference optical signal and the measurement optical signal into electrical signals, respectively; , current monitoring means for detecting the level of the electrical signal from the itc converter and generating a control signal corresponding to the level of the detected electrical signal; and the reference coupled to the photoelectric converter and input to the photoelectric converter. The present invention is characterized in that it comprises an optical signal receiving unit comprising an optical signal and a programmable optical attenuator that automatically adjusts the level of the measurement optical signal to vI41!Il.

[Effect] The operation of the means of the invention is as follows.

Optical signal transmission of the wavelength dispersion characteristic measurement system of the present invention22;
has n optical signal input terminals, six single measurement optical signal output terminals and six reference optical signal terminals, and the n light sources selectively enter the n optical signal input terminals. Among the means, the measurement optical signals from the light source means connected to each other are commonly led out to the measurement optical signal output terminal, and the reference optical signal generated by one of the n light source means is outputted to the reference optical signal. Since an optical switch means for guiding the signal to the signal output terminal is provided, it is not possible to use one of the n light source means for generating the reference optical signal, and a light source exclusively for the reference optical signal is not required.

Further, the optical signal receiving unit of the wavelength fractional characteristic measurement system of the present invention is coupled to a photoelectric converter, detects the level of the electrical signal from the optical IF converter, and detects the level of the electrical signal corresponding to the detected/flipped electrical signal. The present invention includes current monitoring means for generating all control signals, and a programmable optical attenuator that is coupled to the photoelectric converter and automatically adjusts the levels of the reference optical signal and the measurement optical signal that are input to the photoelectric converter. The photoelectric converter automatically adjusts the levels of the reference optical signal and the measurement optical signal to KgI4 and DiC.

Furthermore, the chromatic dispersion characteristic measurement system of the present invention has an optical signal transmitting unit having n optical signal input ends, six single measurement optical signal output ends, and six single reference optical signal ends, The measurement light signal from the specified light source means among the n light source means selectively input to the signal input terminal is commonly led to the measurement light signal output terminal, and the n light source means Since an optical switch means is provided for guiding a reference optical signal generated by one of the n light source means to the reference optical signal output terminal, it is possible to use one of the n light source means for generating the reference optical signal. This eliminates the need for a dedicated source for the reference optical signal, and incorporates a photoelectric converter into the optical signal receiving unit.
current monitoring means for generating a control signal corresponding to the level of the detected electrical signal across the level of the electrical signal from the photoelectric converter; Since a programmable optical attenuator that automatically adjusts the levels of the reference optical signal and the measurement optical signal is provided, the photoelectric converter can automatically adjust the levels of the reference optical signal and the measurement optical signal.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to FIG. In FIG. 1, one end of the reference fiber 6 is connected to the reference optical signal output @REF OtJ'r of the optical signal transmitter 20 of the wavelength dispersion characteristic measurement system of the present invention, and one end of the measured fiber 62 is connected to the transmitter 20. Measurement optical signal output terminal TEST 0UTK! Continued.

Furthermore, the other end of the reference fiber 61 is the reference optical signal input end ftfEF I of the optical signal receiving section 400 of the system of the present invention.
N, and the other end of the fiber under test 62 is connected to the measurement optical signal input end TEST IN of the receiving section 40.

First, the transmitter 20 of the wavelength dispersion characteristic measurement system of the present invention will be explained. The modulation signal generation circuit 22 is composed of four crystal oscillators having four different oscillation frequencies 1l-f4. This modulation signal generation circuit 22 is connected to a branch circuit 23 consisting of a resistor. One of the outputs of the branch circuit 23 is a channel switching circuit U;
One radar diode 9 of the light source group 25 consisting of LD4
Connected to LD4. Driving selection of the four crystal oscillators is performed in response to a selection signal from the CPU 21.

The switching operation by the channel switching circuit 24 is also controlled by a switching command from the CPU 21. In this system, the four frequencies fl-f4 are 5.50. Zoo, 800 MHz is used,
It is not limited to this frequency, but may be any other suitable frequency. As described above, a resistor is used for the branch circuit 2311C, and a high frequency relay matrix is used for the channel switching circuit 24, but other suitable elements may be used. Of the light source #25, the Raded diode L
DI-LD 3 is the channel switching circuit N124.
is placed on the output side of Furthermore, on the output side of the radar diode LDI-LD3, the radar diode L
Three optical switches 261-263 constituting optical switch #26 are arranged corresponding to each of DI-LD3. The three optical switches are connected to the output of the radar diode LD4.

A half mirror 27 is arranged in relation to the channels 261-263. Further, the prism 28 is connected to the optical switch 261-
26311C. Radede diodes LDI-LD4 are used for the light source group 25, but other suitable light sources may be used.

The number of radar diodes used in the wavelength dispersion characteristic measurement system of the present invention is not limited to four.

The wavelength of the radar diode LDI-LD4 is 3μ
In the light 7 eyeglasses with zero dispersion wavelength of m, respectively, 26. , 30. , 34. , 53 μm wavelengths are used, and 50. , 53. , 56. , 59 μm are used, although other suitable wavelengths may be used.

There may be.

As shown in FIG. 4(m) and FIG. 4(b), each of the light source groups 25 includes the radar diode LDI-
In addition to the LD4, there is also an optical isolator 351, a ball lens 356, and a mirror 3 for removing noise generated due to the influence of reflected light from the radar diode LDI-LD4.
52, a Peltier element 353, a mister 357, a heat radiation fin 359, and a modulation circuit 358. These elements, including the radar diode LDI-LD4, are extremely high-voltage.

Therefore, reducing the number of expensive light sources by even one will reduce the overall cost. It is easy to see that the performance is greatly affected.

As shown in FIG. 5, the optical switch 261-26
3 respectively include the half mirror 27 and the condenser lens 2.
67, and a triangular prism 265, which is arranged to be slightly offset from the parallelogram prism 264. This 2
The two prisms are connected to the radar diode LDI-LD3.
It is arranged at such a position that the light emitted from the prism passes through the triangular prism 265 and the parallelogram prism 264 and toward the condensing lens 267. The parallelogram prism 26
4, when the emitted light is reflected by the half mirror 27 and heads toward the optical fiber, its position is changed by a sliding movement, and the blocked optical path is opened, so that the emitted light is directed from the half mirror 27. Straight into the optical fiber is a ball lens. Furthermore, reference numerals 267 and 268 are condenser lenses.

On the other hand, in the optical signal receiving section 40 shown in FIG.
and avalanche photodiode APD 4 J
, 44 are arranged in the order just described. As shown in Figure 3, the above! Logramaple Hikari, Tenator 4, 42
Each of them has three optical attenuation elements 411, 412 and 413 arranged in series, and is integrally connected to, for example, the avalanche photodiode APD 441c.

Reference numeral 414 in the figure is an optical resegmentacle.

The diameters of the optical attenuation elements 411, 412, and 413 are all 8 mm, and the three attenuation elements 411, 412, and 412 are 8 mm in diameter.
The reduction Nt of 413 is 4 dB and 8 dB, respectively.

Although the diameter is 16 dB, the diameter and the attenuation amount may have other suitable values. Each of these attenuation elements 411° 412
．． 413 can be programmably turned ON or OFF, eight types of attenuation can be set up to a maximum of 28 dB.

In FIG. 1, the APD 4 J, 44 is the! It has a function of converting the optical signals output from the log-simal optical tenators 4 and 42 into electrical signals. Said AP
A current monitor 45 is connected to D 43 and 44.
and 46. This detects the output current from the APD 43.44, controls the attenuation of the programmable optical attenuators 4 and 42 according to the magnitude of the detected current, and sends an optical signal at a predetermined level to the APD 43.44. It has an input function. Said APD 43, 44
The demodulated signal photoelectrically converted is input to mixers 47 and 4B. The local signal generation circuit 49 consists of four crystal oscillators having four different generation frequencies 1l-f4.

Driving selection of the four crystal oscillators is made by a selection signal from the CPU 53. The mixers 47, 411 perform frequency conversion using local signals of selected frequencies. The frequency-converted electrical signal is sent to a phase measurement section 52, where the phase difference between each wavelength is measured.

In order to better understand the operation of the chromatic dispersion measurement system of the present invention, the overall operation sequence will be explained with reference to FIG. First, the CPU 21 gives a signal selection command to the modulation signal generation circuit 22 at a predetermined timing to generate a modulation signal f1 of f = 5 MHz, for example. This modulation signal f1 is branched into two by the branch circuit 23, and one of the outputs is sent to the channel switching circuit 23.
sent to. In response to a switching command from the CPU 21, the channel switching circuit 24 performs a learning operation to select one output. The radar diode L receives the selected output and corresponds to the selected output.
One of the DI-LD3, for example the radar diode LDI, is driven. As a result, an optical signal whose intensity is modulated by the modulation frequency f1 is generated at the output of the LDI. This optical signal hits the optical switch 261 corresponding to the radar diode LDI. As described above, the selection of the optical switch 261 is performed by the switching command pressure from the CPU. Thereafter, the optical signal is reflected by the prism 28, and is sent to the optical signal transmitter 28 as a measurement optical signal.
The measurement optical signal enters one end of the fiber to be measured 62 via the measurement optical signal output terminal TEST OUT. On the other hand, the other output of the branch circuit 23 is directly supplied to the radar diode LD4. Therefore, the radar diode L
An optical signal whose intensity is modulated by the modulation frequency f1 is generated at the output of D4. The generated optical signal is branched into two by the half mirror 27. One of them is used as a reference optical signal at the reference optical signal output terminal RE of the optical signal transmitter 200.
F OUT is input to one end of the reference fiber 61, and the other side is reflected to the prism 28 via the optical switch group 261-263, and the measurement optical signal output from the optical signal transmitter 20 is output as a measurement optical signal. The light is input to one end of the fiber to be measured 62 via TgNT OUT.

Next, the CPU Z I again gives a channel switching command to the channel switching section 24 and the optical switch 26. As a result, the output terminal of the channel switching unit 24 is newly selected, and one of the radar diodes LD2-LDJ different from the radar diode LD7, for example, LD, ?, is selected by inputting the modulation signal f1. to drive. The optical signal generated by this drive is reflected by the corresponding optical switch 262 and heads toward the prism 28 . The optical signal reflected by this prism 211tlC is transmitted to the measurement optical signal output terminal TENTOU.
The light is incident on the seventh eyeper 62 to be measured via T.

The CPU21tt-1, the radar diode LDI
- Issue a switching command to the channel switching unit 24 and the optical switch 26 until all of the LDs 4 are selected.

As a result, the operation of emitting the reference optical signal and the measurement optical signal to the reference optical fiber 6I and the measurement target light 7 eyeper 62iC, respectively, is repeated.

After the repetitive operation is completed, the CPU j I issues a new selection command to the modulation signal generation circuit 22.

As a result, a crystal oscillator with a frequency different from the modulation frequency f1, for example, f2=50 MHz, is driven, and the repeating operation is performed also at the frequency of f2. Similarly, the repetitive operation is performed at the frequency f 3 =
200 MHz, and also the frequency t4=80 (MHz).

FIG. 6 shows the modulated signal 1l in relation to the repetitive operation.
This is a timing chart showing a state in which -f4 is transmitted sequentially. The (,) in the 6th prisoner is for the f7 fiber with a zero dispersion wavelength of 3 μm, and (b) in Figure 6
This is about an optical fiber whose zero dispersion wavelength is in the 55 μrn band.

The receiving section will be described. The signal level of the reference optical signal and the measurement optical signal emitted from the reference optical fiber 6 and the optical fiber to be measured 62, respectively, is adjusted to IJd by the programmable optical fiber 4, 42.
l(, ri the APD (3.

Accepted at 44. Output signals from the APDs 43 and 44 are input to the mixers 47 and 48t/C. The mixers 47 and 411 frequency-convert the input signal using the local signal of the frequency generated by the local signal generation circuit 49. After the frequency conversion, the signal passes through the filter 50.51 to the phase measurement unit 5.
2.

The baseband phase comparison method of the wavelength dispersion characteristic measurement system of the present invention will be further described with reference to the graph of FIG. In the uninvented system, four wavelengths λ1
-λ4 is used, but here we assume multiple light sources with different wavelengths λ1-λ□ of m 1vA. adjacent 2
The phase difference (internal phase difference) inside the measuring instrument between wavelengths is expressed as θ'(n
l) Let n be the phase difference between the two wavelengths on the receiving side after propagation through the optical fiber to be measured. Furthermore, let the modulation frequency be f, and the delay time difference be τ(n-1)n. Therefore, θ(n-rin: θI<n-rire+2πfτ(n-1
)n (n"2e 3°-m) holds.Here, the length of the optical fiber to be measured is t, and the phase difference between the two wavelengths is φ(n
-1) If n, φ is one. =θ(n-1)n-θ'
(n-1)n, so the unit length (n==2.J...
It can be expressed as m).

This group delay time difference Δτ(n-1). The relationship between the wavelength λ1-λ□ is shown in a graph as shown in FIG. The curve in FIG. 2 is expressed by several approximate equations, but since the wavelength dispersion characteristic measurement system of the present invention uses four light sources, the quadratic equation τ(λ)=aλ2-1-b-1-cλ- 2
Use.

Phase measurement in the chromatic dispersion characteristic measurement system of the present invention is performed for each combination of the four wavelengths λ1-λ4 and the four modulation frequencies 1l-f4 in connection with the repetitive operation.

Among them, the data in which no phase rotation occurs and the data having the largest modulation frequency fl-f4 is selected, and the group delay time difference between the respective wavelengths is determined. From this measurement result, the CPU 5J calculates the quadratic equation τ(λ)=1λ2+b-1-cλ-2 using the least squares method. Furthermore, by differentiating the obtained quadratic equation with respect to the wavelength λ, the wavelength fractional characteristic D(λ)−dτ(λ)/dλ can be obtained. The measurement results are output as graphs and numerical values to the built-in CRT 54 and the printer 55, and can also be output to an external printer/plotter (not shown) via the GPIB ss.

Next, another embodiment of the present invention will be described in detail with reference to FIG. In FIG. 7, the chromatic dispersion measuring device of the present invention has an optical signal transmitting section 20 and an optical signal receiving section 130 connected to a reference fiber 1.
41 and a fiber to be measured 142.

The optical signal receiving section 20 is similar to the conventional one in that it includes a CPU 2, a modulation signal generation circuit 22, a branch circuit 23, a channel switching circuit 24, etc., but the difference is that the output side of the channel switching circuit 24 is One less radar diode LD, -LDn-, than n radar diodes LD1 -LDn, which emit radar light with different wavelengths, is connected to A radar diode, for example LDn, is connected to the branch end of the branch circuit 23 on the side opposite to the channel switching circuit 24 side.

The output side of the radar diode LD1-Ll)n-1 reflects the measurement optical signal only when the measurement optical signal is incident from the corresponding radar diode LD1-LDn-, and other than that, it reflects the measurement optical signal. Part one when measuring optical signals! Ma. Optical switches 261 to 26n-1 are provided to allow the optical signal to pass through, and a half mirror 2 as an optical branch circuit that branches the optical signal into two is provided on the output side of the remaining one radar diode LDn.
7 is placed. This half mirror 27 splits the intensity-modulated optical signal from the radar diode LDn into two, one of which is a straight beam that enters the reference fiber 14 as a reference optical signal, and the other beam that is reflected by the beam for measurement. l
, the optical switches 261-26. j and the grism 28 to enter the fiber 142 to be measured.

On the other hand, the signal receiving section 130gJJJ
.

142, an electric signal converter 13 is provided on the light emitting end side of each of the parts 142,
The electrical signal converted here is amplified by amplifiers 133 and 134 and sent to a phase measuring circuit 135. This phase measurement circuit 135 demodulates the outputs of the amplifiers 133 and 134 based on the command from the CPU 136, determines the phase difference between both numbers 43 after this demodulation, and then converts this phase difference into a voltage signal, and It has a function of converting it into a Digimel signal and sending it to a post processing section (not shown).

Next, the operation of the device configured as described above will be explained. First, the CPU 21 gives a signal selection command to the modulation signal generation circuit 22 based on a predetermined timing to generate, for example, a modulation signal fl. As a result, for example, the Raded light generated from the Raded diode LDn is the modulated signal f! of the modulated signal generation circuit 22! intensity modulated by 7%
7 is sent to the mirror 27, where it is split into two, one of which is input to the reference fiber 141 as a reference optical signal, and the other light is sent to each party switch 26fl-1+ as a measurement optical signal.
..., 26I, is reflected by the prism 28, and enters the fiber under test 142. Continuing, CPU 21
When a channel switching command is given to the channel switching circuit 24 and the optical switch group 26, the channel switching circuit 24
An optical switch 261 whose output terminals are sequentially selected and corresponds to the selection of the output terminals in synchronization with the selection of the output terminals.

26! ... are turned on sequentially, and the measurement optical signals obtained by intensity modulating the radar light of each of the one-dediodes LDI, LD, ... with the modulation signal 'fl are sent to the corresponding optical switches 261, 262, . ...and enters the fiber under test 142 through the prism 28.

At this time, on the optical signal receiving section 130 side, both fibers 141
, 142 are sequentially received by electrical signal converters 131 and 132,
Here, after converting the electrical signal Kf, it is sent to the phase measuring circuit 135. This phase measuring circuit 135 performs demodulation processing, and determines the phase θref and wavelengths λ1 to λ of a reference optical signal having a specific wavelength λ1 from the demodulated signal as shown in FIG. The phase θ1-2 of the measurement optical signal related to each different channel.

At the same time, these phase differences are converted into a voltage signal, and further converted into a dinotal signal and output.

Although the above description has been made regarding the modulation signal fl, if there are other modulation signals '2r'3+f4, the above-described operation is repeated for each modulation signal.

Therefore, according to the configuration of the embodiment as described above, in the optical signal transmitter 20, one of the plural measurement light sources having different wavelengths is directly connected to the branch circuit 23, and such one
The optical signal intensity-modulated by the modulation signal output from the 7% light source is split into two by the 7% mirror 27, one of the lights is input to the reference fiber 141 as a reference optical signal, and the other light is used for measurement, f Since the signal is input to the fiber under test 141 as a signal, it is possible to send out the reference optical signal using a measurement light source without having to have a dedicated reference light source. By reducing by 11d, it is possible to downsize and reduce the cost of the device, and also to reduce the failure rate due to failure.

Note that although a Raded diode was used as a light source in the above embodiment, other light emitting elements may be used.

In addition, the optical switch 26. , 26. For example, a rotating mirror or a prism is used, but other switches may be used as long as they have the same function.

Further, another embodiment of the invention will be described in detail with reference to FIG. In FIG. 8, the wavelength dispersion measuring instrument of the present invention is
The optical signal transmitting unit 240 and the optical signal receiving unit 250 are arranged with a predetermined distance therebetween.

The optical signal transmitter 240 obtains a reference 1δ signal and a measurement optical signal by sequentially modulating the intensity of light tubes emitted from the reference light source and the measurement light source, respectively, using modulation signals fl, r, +fN*f4 having different frequencies, for example. The optical signal receiver 250 uses the standard 722/
A Grogrammaggle optical attenuator 251 r on the output end side of the λ fiber 2 eyer Φ → and the fist-sized fiber optic to be measured, respectively; 51 t and photoelectric conversion 1fls
They are arranged in the order of 252r and 252t. These glogrammaple light a, tenators 251r, 251* are set to the maximum a, tenatility value when not measuring, and are automatically set to the appropriate attenuation value by an external control signal at the start of measurement. The optical signal output from the fiber connector J-IP-Ik is controlled to an appropriate level. The y [conversion units 252r and 252t have a function of converting the optical signals output from the glogramma pull source attenuators 251r and 2:51t into electrical No. 16 signals, and have linearity conversion characteristics within a predetermined optical signal level range. It is something that converts.

Reference numerals 253r and 253t are current monitors, which detect the output currents of the photoelectric conversion units 252r and 252t, and adjust the magnitude of the detected currents to determine the a and tenancy values of the glogram pull optical attenuators 251r and 251t. 7 &:
It has the ability to control and input optical signals of a predetermined level to the photoelectric conversion units 252r and 21r2t. Further, automatic gain control circuits 254r and 254t are connected to the output sides of the photoelectric conversion sections 252r and 252t. These automatic gain control circuits 254r and 254t convert the distorted wave signal into an optical signal into a subsequent demodulating mixer 255r,
It has a control function to maintain a breakthrough level in order to remove 255 in a well-balanced manner. This demodulation mixer 255r.

255t receives local signals of different frequencies depending on the frequency of the modulation signal generated from the local@oscillator circuit 256 and performs demodulation processing operation. 257r and 257t are filters,
258 is a phase measuring circuit.

Next, the operation of the device having one or more IC configurations will be explained. The intensity of the reference light source and the measurement light source is modulated by a modulation signal with a specific number of frequencies, and the reference light signal and measurement light signal obtained thereby are the reference light signal emitted from the reference light source and the sub-circuit (i). is input to the ramapul source attenuators 25) r and 251t, and is converted into electrical signals by the photoelectric conversion units 252r and 252t, respectively. The optical attenuators 251r and 251 monitor the output current of the output current and program a signal to control the output current according to the magnitude of the current.
For example, when the level of the optical signal is high, the attenuation value is set in the direction of suppressing the optical signal, and conversely, when the level of the optical signal is low, the attenuation value is set in the direction of increasing the level of the optical signal. Set the value.

As a result, programmable optical a.

The levels of the optical signals output from the tenators 251r and 251t can always be kept within a predetermined level range, so that the photoelectric converters 252r and 252t can perform signal conversion operations with good linearity. Moreover, by providing automatic gain control circuits 254r and 254t on the output side of the photoelectric conversion sections 252r and 252t and controlling the gain to a desired level, it is possible to remove distorted waveforms in a well-balanced manner, for example, during demodulation processing.

The signals that have been set to the desired level as described above are demodulated by the demodulating mixers 255r and 255t, and the phase difference between the demodulated signals is determined by the phase measuring circuit 258.

Therefore, according to the configuration of the embodiment as described above, the output currents of the photoelectric conversion units 252r and 252t are monitored, and the programmable optical attenuator 2 is adjusted according to the magnitude of the monitored current.
Since the A and Ten values of 51r and 251t are controlled, the level of the optical signal can be successively and automatically varied depending only on the level of the optical signal that changes instantaneously, and
Wavelength dispersion measurement can be performed by constantly converting signals within the signal conversion range with good linearity of the photoelectric conversion units 252r and 252t, and therefore highly accurate measurement can be achieved. Also,
Since the level is automatically controlled according to the magnitude of the optical signal level, it greatly contributes to streamlining measurement work, and can quickly respond to optical signal losses caused by various causes without reducing measurement accuracy. can be measured.

[Effects of the Invention] As described above, since the half mirror is disposed at the output of one of the radar diodes constituting the light beam group in the optical signal transmission unit of the wavelength dispersion characteristic measurement system of the present invention, the laser The optical signal from one of the dediodes can be split into two and one can be used as the reference optical signal and the other as the measurement optical signal.

Therefore, since a dedicated light source for generating the reference optical signal is not required, it is possible to reduce the number of light sources.

Therefore, it is possible to provide a chromatic dispersion characteristic measurement system that is cost-reduced and miniaturized.

Furthermore, since the optical signal receiving unit of the uninvented wavelength fractional characteristic measurement system is provided with the programmable optical attenuator and the current monitor, the level of the optical signal emitted from the reference optical fiber and the measured optical fiber can be automatically adjusted. It is possible to adjust.

Therefore, photoelectric conversion with good linearity is provided.

Although the invention has been shown and described with respect to three exemplary embodiments, various other modifications are within the capabilities of those skilled in the art.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the chromatic dispersion characteristic measurement system according to the invention, and FIG. 2 shows the relationship between group delay time difference and wavelength when chromatic dispersion characteristics are measured according to the principles of the present invention. 3 is a block diagram showing the attenuator according to the present invention; FIGS. 4(&) and 4(b) are block diagrams of the light source used in the wavelength dispersion characteristic measurement system of the present invention; @Figure 5 is a configuration diagram of an optical switch used in the wavelength dispersion characteristic measurement system of the present invention, and Figures 6 (breath) and 6 (b) are diagrams showing the timing at which modulation No. 18 is transmitted. (a) is an #IJ group with a zero dispersion wavelength of 3 μm, and (b) a diagram showing the case where r'i has a zero dispersion wavelength of 55 μm. Figure 7 shows the wavelength dispersion according to the present invention. A configuration diagram showing another embodiment of the characteristic measuring system, its optical signal transmitting unit, and its optical signal receiving unit. FIG. 8 is a configuration diagram showing another embodiment of the optical signal receiving unit of the wavelength dispersion characteristic measuring system according to the present invention. Fig. s9 Fig. #'i is a phase characteristic diagram showing the results of wavelength dispersion characteristic measurement in the embodiment of Fig. 7; FIG. 10 is a configuration diagram showing an optical signal transmitting unit of a chromatic dispersion characteristic measuring system for illustrating a conventional example of the embodiment shown in FIG. Fig. 5g11 is a configuration diagram showing an optical signal receiving unit of a chromatic dispersion characteristic measuring system to show a conventional example of the embodiment shown in Fig. 8. 20... Optical signal transmitter, 2no... CPU, 22...
・Modulation signal generation circuit, 24... channel switching circuit,
25...Light source group, 26 (261-263n...°
Optical switch, 2 full optical attenuators, 4, 42...attenuators, 43.44...Apara/she photodiodes 1'; 4r
7 now 25yo #... automatic gain control circuit, +4,61...
・Measurement #J Hll- Fiber, → 2, Nflaa, 4xz-4x
y... Light area N element, 414... Original receptacle, 3
51...Former Einrater, 352...Mirror, 35
3...Beltier cable 5ss4...Selfoc lens, 355...Light receiving cable, 356...Ball lens, 3
57... Thermistor, 358... Modulation circuit, 359
...radiating fin, 264...parallelogram! rhythm,
265...Triangular grism, 261,268...Goku lens. Out-jindai mass entry Bue burial Suzue Takehikoλ1λ2
λ3−−−−−−Jm−+λm tear k λ Fig. 2 Fig. 3 Fig. 4 (a) Fig. 4 (b)

Claims (1)

[Claims] 1. In a system that includes an optical signal transmitting unit and an optical signal receiving unit and measures the wavelength dispersion characteristics of an optical fiber based on a baseband phase comparison method, each of the optical signal transmitting units performs measurement. n light sources provided to selectively generate optical signals having wavelengths corresponding to the n wavelength points to be measured as measurement optical signals, one of which is provided to also serve as a reference optical signal generation; means for generating a modulated signal having at least one predetermined frequency; and a modulating signal generating means for generating a modulated signal having at least one predetermined frequency; 1 control signal generation means, and the n light source means are coupled between the first control signal generation means, the modulation signal generation means, and the n light source means, and are designated by the first control signal to generate the measurement optical signal. a light source that selectively supplies the modulation signal to a specific light source means of the light source means and the light source means also used for generating the reference optical signal, or generates the measurement optical signal and the reference optical signal; light source switching means for supplying the modulation signal to only the means; second control signal generating means for generating a second control signal having a predetermined synchronization relationship with the first control signal; and each of the n light source means. and a single measurement optical signal output terminal and a reference optical signal terminal, each of which is arranged to correspond to a second control signal from the second control signal generating means. In response, the measurement optical signal from the specified light source means among the n light source means selectively input to the n optical signal input terminals is commonly led to the measurement optical signal output terminal. , and optical switch means for guiding a reference optical signal generated by one of the n light source means to the reference optical signal output terminal. 2. In a system that includes an optical signal transmitting unit and an optical signal receiving unit and measures the wavelength dispersion characteristics of an optical fiber based on a baseband phase comparison method, the optical signal receiving unit transmits a reference optical signal and a measurement optical signal. a current monitor coupled to the photoelectric converter and detecting the level of the electrical signal from the photoelectric converter and generating a control signal corresponding to the level of the detected electrical signal. and a programmable optical attenuator that is coupled to the photoelectric converter and automatically adjusts the levels of the reference optical signal and the measurement optical signal that are input to the photoelectric converter. . 3. In a system for measuring chromatic dispersion of an optical fiber based on the baseband phase comparison method, to selectively generate optical signals having wavelengths corresponding to n wavelength points to be measured as measurement optical signals. n light source means, one of which is provided for the purpose of generating a reference optical signal; a modulation signal generation means for generating a modulation signal having at least one predetermined frequency; and the measurement signal. and a first control signal generating means for specifying the n light source means in a predetermined order to generate the reference optical signal; the first control signal generating means, the modulation signal generating means, and the n light source means. a specific light source means of the n light source means which is coupled between the n light source means and which is designated by the first control signal to generate the measurement optical signal, and a light source means which is also used for generating the reference optical signal; light source switching means that selectively supplies the modulation signal or supplies the modulation signal only to the light source means that generates the measurement optical signal and the reference optical signal; and a predetermined synchronization relationship with the first control signal. a second control signal generating means for generating a second control signal having a second control signal; n optical signal input terminals disposed corresponding to each of the n light source means; and each single measurement optical signal output. and a reference optical signal end, and receives a second control signal from the second control signal generating means and selectively enters the n optical signal input ends of the n light source means. Among them, the measurement optical signals from the specified light source means are commonly led out to the measurement optical signal output terminal, and the reference optical signal generated by one of the n light source means is led out to the reference optical signal output terminal. an optical signal transmitter comprising an optical switch means for guiding the reference optical signal to the reference optical fiber; and an optical signal transmitter having one end and the other end, the reference optical signal output end of the optical switch means having one end of the reference optical fiber inputting the reference optical signal. a reference optical fiber connected to the optical switch means; and a reference optical fiber having one end and the other end, the one end of the optical fiber to be measured being connected to the measurement optical signal output end of the optical switch means to receive the measurement optical signal. A measurement optical fiber, a photoelectric converter that converts the reference optical signal and the measurement optical signal into electrical signals, respectively, and is coupled to the photoelectric converter and detected by detecting the level of the electrical signal from the photoelectric converter. current monitoring means for generating a control signal corresponding to the level of the electrical signal applied to the photoelectric converter; and a programmable current monitor means for automatically adjusting the levels of the reference optical signal and the measuring optical signal coupled to the photoelectric converter and input to the photoelectric converter. 1. A chromatic dispersion characteristic measurement system, comprising: an optical signal receiving section having an optical attenuator.