JP2000105169A - Apparatus for measuring wavelength dispersion - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wavelength dispersion-measuring apparatus which exhibits a wavelength dispersion characteristic highly stably. SOLUTION: The wavelength dispersion-measuring apparatus has a wavelength variable light source 11, a modulation signal source 23 for outputting modulation electric signals, a light intensity modulator 12 for modulating light entering from the wavelength variable light source 11 with the modulation electric signal directly supplied from the modulation signal source 23, and an optical coupler 16 for branching a modulated light signal output from the light intensity modulator 12. The modulated light signal is supplied via the optical coupler 16 to an optical device DUT to be measured. The wavelength dispersion- measuring apparatus is provided with a feedback control loop circuit for feeding back the output of the modulation signal source 23 to an input of the modulation signal source 23 via the light intensity modulator 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chromatic dispersion measuring apparatus, and more particularly, to a chromatic dispersion measuring apparatus for performing chromatic dispersion measurement with high stability.

[0002]

2. Description of the Related Art A conventional example will be described with reference to FIG. FIG.
FIG. 3 is a diagram showing a conventional example of a chromatic dispersion measuring device using a phase shift method. In FIG. 2, reference numeral 20 denotes a network analyzer. Reference numeral 21 denotes a synthesizer that generates the reference clock, 22 denotes a phase synchronization circuit that keeps the amplitude, phase, and frequency constant, 23 denotes a modulation signal source that generates a modulated electric signal having a modulation frequency fm, 24 denotes an electric coupler, and 25 denotes an electric coupler. An intermediate frequency converter, 26 is an A / D converter, 27 is a data processing block, and 27 'is a signal data processing block.

In the network analyzer 20, a modulated electric signal of a modulation frequency fm generated by a modulated signal source 23 is branched and output via an electric coupler 24, and is output by the electric coupler 24, a sampler 251 of an intermediate frequency converter 25,
The feedback is performed via a feedback control loop circuit configured by the phase synchronization circuit 22. That is, one of the modulated electric signals branched via the electric coupler 24 of the modulation signal source 23 is supplied to the sampler 251 of the intermediate frequency converter 25, and is set to an intermediate frequency between the reference signal generated and output by the synthesizer 21. After being converted, it is fed back to the modulation signal source 23 via the phase synchronization circuit 22. Thereby, the modulation signal source 23
The amplitude of the modulated electrical signal at the modulation frequency fm,
The frequency and phase are always kept optimally constant.

The other of the modulated electric signals of the modulated signal source 23 branched via the electric coupler 24 is input to the voltage amplitude variable unit 13 via the output terminal 29. The modulated electric signal output from the modulation signal source 23 is input to the voltage amplitude variable device 13 so as to satisfy the optimum condition of the light intensity modulator 12, and is adjusted to an appropriate frequency and amplitude by manually operating the same. The light is input to the light intensity modulator 12 and used for light intensity modulation.

[0005] Reference numeral 11 denotes a wavelength variable light source. 12 is a light intensity modulator, and 13 is a voltage amplitude variable device. The light intensity modulator 12 modulates light incident from the variable wavelength light source 11 with a modulation electric signal output from a modulation signal source 23 of the network analyzer 20, and outputs a modulated light signal. Here, the modulated optical signal emitted from the optical intensity modulator 12 is incident on an optical fiber or another optical device under test DUT.
The modulated optical signal incident on the optical device under test DUT passes therethrough and is incident on a photoelectric converter indicated by 14, where it is photoelectrically converted, and an electrical detection signal is obtained. The electrical detection signal output from the photoelectric converter 14 is amplified by the amplifier 15, supplied to the signal data processing block 27 ′ via the input terminal 28 of the network analyzer 20, and subjected to various arithmetic analysis processes. The signal data processing block 27 'is a circuit equivalent to a circuit obtained by combining the intermediate frequency converter 25, the A / D converter 26, and the data processing block 27 in the network analyzer 20, and converts an input electrical detection signal into an intermediate signal. The signal is converted into a frequency signal and subjected to A / D conversion.

Here, assuming that the optical device under test DUT is an optical transmission path, the electrical detection signal based on the modulated optical signal that enters the optical device under test DUT and is transmitted therethrough has a transmission time corresponding to the transmission time. Is delayed. Here, the delay time of the electrical detection signal for each wavelength is measured using the optical wavelength as a variable, and the delay time of the signal is differentiated with respect to the wavelength to measure the chromatic dispersion of the optical transmission line as the calculation result. Can be.

[0007]

In the conventional example of the chromatic dispersion measuring apparatus described above, the amplitude of the modulated electric signal of the modulation frequency fm output from the modulation signal source 23 is equal to the voltage amplitude variable device 1.
3 is adjusted and stabilized so as to satisfy the optimum condition of the light intensity modulator 12 and to maximize the extinction ratio by manually operating the input. That is, the modulation signal source 23
The amplitude of the modulated electric signal having the modulation frequency fm output from the electric coupler 24 and the sampler 25 of the intermediate frequency converter 25
1. Although stabilized by a feedback control loop circuit composed of a phase locked loop 22, the light intensity modulator 12 is not included in this feedback control loop circuit.
Since the light intensity modulator 12 is located outside the range of the feedback control loop circuit, no feedback control is applied to the light intensity modulator 12.

As described above, the voltage amplitude of the modulated electric signal is separately adjusted by the voltage amplitude variable device 13 so as to satisfy the optimum condition of the modulator 12 and maximize the extinction ratio. However, after the voltage amplitude variable device 13 is manually operated to appropriately adjust and set the voltage amplitude of the modulated electric signal having the modulation frequency fm, the ambient temperature and other external conditions in which the chromatic dispersion measuring apparatus is used change, or There is a case where the optimum condition of the light intensity modulator 12 changes due to a change in the wavelength of the input light, and as a result, the extinction ratio of the modulated optical signal of the light intensity modulator 12 cannot be sufficiently obtained, and the wavelength dispersion measurement The stability and dynamic range of the signal light may deteriorate.

The present invention solves the above-described problem of performing chromatic dispersion measurement with high stability by automatically stabilizing the extinction ratio of the light intensity modulator 12 in a chromatic dispersion measurement apparatus using a phase shift method. The present invention provides a chromatic dispersion measuring device.

[0010]

A modulated signal source having a tunable light source and outputting a modulated electric signal.
And a light intensity modulator 12 that modulates light incident from the wavelength tunable light source 11 with a modulation electric signal directly supplied from a modulation signal source 23, and branches the modulated light signal output from the light intensity modulator 12 In the chromatic dispersion measuring apparatus which includes an optical coupler 16 for supplying a modulated optical signal to the optical device under test DUT via the optical coupler 16, the output of the modulated signal source 23 is supplied to the modulated signal source via the optical intensity modulator 12. A chromatic dispersion measuring device including a feedback control loop circuit for feeding back to the input of the chromatic dispersion was configured.

In the chromatic dispersion measuring apparatus according to the present invention, the feedback control loop circuit includes a light intensity modulator 12, a feedback photoelectric converter 17 for photoelectrically converting a modulated optical signal, and a modulation signal source. 23 for controlling the phase synchronization circuit 22
A chromatic dispersion measuring device having

[0012]

An embodiment of the present invention will be described with reference to FIG. In FIG. 1, members common to those in FIG. 2 are given the same reference numerals. According to the present invention, an optical coupler 16 for branching a modulated optical signal of an optical intensity modulator 12 and a feedback photoelectric converter 17 are added to a conventional example of a chromatic dispersion measuring apparatus, and the modulated optical signal of the optical intensity modulator 12 is connected to a network. Reference input terminal 2 of analyzer 20
Input to 8 '. That is, the modulated optical signal modulated by the light intensity in the light intensity modulator 12 enters the feedback photoelectric converter 17 via the optical coupler 16 and is converted into an electrical feedback signal.
The reference input terminal 2 which is electrically amplified by the amplifier 18
8 '. The amplified electrical feedback signal input to the reference input terminal 28 'is converted into an intermediate frequency feedback signal via the sampler 251 of the intermediate frequency converter 25. This intermediate frequency feedback signal is then fed back to the phase synchronization circuit 22. As a result, the light intensity modulator 12 is included in the stabilizing feedback control loop circuit of the modulation signal source 23 that generates the modulation electric signal of the modulation frequency fm, and the modulated light signal output from the light intensity modulator 12 has this stability. The feedback control is always constant in the loop feedback control loop circuit. The details will be described below.

In FIG. 1, a network analyzer 2
0 modulation signal source 23 is connected to electric coupler 24 and output terminal 29.
The modulated electric signal which is connected to the optical intensity modulator 12 via the optical modulator 12 is directly supplied to the optical intensity modulator 12 without passing through an adjusting circuit such as a conventional voltage amplitude variable device 13.
The light intensity modulator 12 modulates light incident from the variable wavelength light source 11 with a modulation electric signal output from the modulation signal source 23 and outputs a modulated light signal. The modulated light signal emitted from the light intensity modulator 12 is applied to the light intensity modulator 1 according to the present invention.
The signal is input to the optical coupler 16 connected to the optical coupler 2 and branched. One of the modulated optical signals branched by the optical coupler 16 is:
The light enters the optical fiber or other optical device under test DUT. The modulated optical signal incident on the optical device under test DUT is transmitted therethrough and supplied to the photoelectric converter 14, where it is photoelectrically converted to obtain an electrical detection signal. The electrical detection signal output from the photoelectric converter 14 is amplified by the amplifier 15, input to the signal data processing block 27 ′ via the input terminal 28 of the network analyzer 20, and subjected to various arithmetic analysis processes.

The other of the modulated optical signals branched by the optical coupler 16 is supplied to a feedback photoelectric converter 17 connected to the light intensity modulator 12 via the optical coupler 16 according to the present invention, where it is photoelectrically converted. Thus, an electrical feedback signal is obtained. The electrical feedback signal output from the feedback photoelectric converter 17 is amplified by the amplifier 18 and fed back to the reference input terminal 28 'of the network analyzer 20.

Here, regarding the network analyzer 20, the electrical feedback signal input to the reference input terminal 28 ′ of the network analyzer 20 is then supplied to the sampler 251 of the intermediate frequency converter 25, and the signal generated by the synthesizer 21 is generated. The signal is converted into an intermediate frequency feedback signal between the output signal and the reference signal, and is fed back to the phase synchronization circuit 22. Thus, the amplitude, frequency and phase of the modulated electric signal itself at the modulation frequency fm generated and output from the modulated signal source 23 are always kept constant in the stabilized feedback control loop circuit.

In the above description, the stabilizing feedback control loop circuit of the modulation signal source 23 includes the modulation signal source 23, the electric coupler 24, the output terminal 29 of the network analyzer 20, the light intensity modulator 12, the optical coupler 16, and the feedback photoelectric converter. Converter 17,
It comprises an amplifier 18, a reference input 28 ′ of a network analyzer 20, a sampler 251 of an intermediate frequency converter 25, and a phase locked loop 22. That is, the light intensity modulator 12 is also included in the stabilizing feedback control loop circuit. Therefore, the amplitude of the modulated optical signal output from the light intensity modulator 12 depends on the configuration in the feedback control loop circuit in the network analyzer 20. Not only the components but also the components of the feedback control loop circuit including the optical intensity modulator 12 itself, the optical coupler 16, the feedback photoelectric converter 17, and the amplifier 18, which are components outside the network analyzer 20, are controlled. Feedback is compensated by the stabilizing feedback control loop circuit, so that it is always kept properly.

[0017]

As described above, in the chromatic dispersion measurement using the phase shift method, it is necessary to perform the phase measurement, the delay time measurement, the dispersion characteristic, the amplitude measurement and other measurements of the signal light with high stability. Although the modulated optical signal incident on the measuring optical device DUT must be stabilized, according to the present invention, a change in the light intensity amplitude occurs in the light intensity modulator 12 due to a temperature characteristic, a light wavelength dependence characteristic, and other causes. However, feedback control is rapidly applied to these fluctuation changes, and a constantly modulated optical signal is always incident on the optical device under test DUT, and the phase measurement, delay time measurement, dispersion characteristic, Amplitude measurements and other measurements can be performed.

[Brief description of the drawings]

FIG. 1 illustrates an embodiment.

FIG. 2 illustrates a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Wavelength variable light source 12 Optical intensity modulator 13 Voltage amplitude variable device 14 Photoelectric converter 15 Amplifier 16 Optical coupler 17 Feedback photoelectric converter 18 Amplifier 20 Network analyzer 21 Synthesizer 22 Phase synchronization circuit 23 Modulation signal source 24 Electric coupler 25 Intermediate frequency conversion 251 Sampler 26 A / D converter 27 Data processing block 27 ′ Signal data processing block 28 Input terminal 28 ′ Reference input terminal 29 Output terminal DUT Optical device under test

Claims (2)

[Claims] 1. A light intensity modulation apparatus comprising: a wavelength tunable light source; a modulation signal source for outputting a modulation electric signal; and light intensity modulation for modulating light incident from the wavelength tunable light source with a modulation electric signal directly supplied from the modulation signal source. A wavelength dispersion measuring apparatus comprising: an optical coupler that splits a modulated optical signal output from the optical intensity modulator; and supplies the modulated optical signal to the optical device under measurement via the optical coupler. A chromatic dispersion measuring apparatus comprising a feedback control loop circuit for returning an output to an input of a modulation signal source via an optical intensity modulator. 2. The chromatic dispersion measuring apparatus according to claim 1, wherein the feedback control loop circuit includes a light intensity modulator, a feedback photoelectric converter that performs photoelectric conversion of a modulated optical signal, and a phase locked loop circuit that controls a modulation signal source. A chromatic dispersion measuring apparatus characterized by having: