JP2001264167A - Optical spectrum analyzer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize an optical spectrum analyzer(OSA) having a small size, a light weight, a long lifetime and high reliability. SOLUTION: The OSA analyzes an optical power density depending a wavelength of a light to be measured. The OSA comprises an optical circulator, a fiber grating(FG), an FG drive circuit, and a photodetector. The OSA elongates and contracts the FG by using the drive circuit, reflects a part of the light to be measured incident from the circulator to the FG by the FG, and then potodetects the light by the photodetector via the circulator.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical spectrum analyzer and, more particularly, to a technique effective when applied to an optical system such as an optical communication system, an optical signal processing system, and an optical measurement.

[0002]

2. Description of the Related Art A first prior art optical spectrum analyzer (hereinafter referred to as OSA) is shown in FIG. In FIG. 6, 1 is an optical fiber, 2 is a connector, 4 is a light receiver,
7 is a control circuit, 8 is an output display, 21A and 21B are lenses, 22 is a diffraction grating pair, 23 is a diffraction grating drive circuit, 2
4 is a slit.

In the first prior art OSA, as shown in FIG. 6, the light to be measured emitted from the connector 2 of the optical fiber 1 is collimated by a lens 21A, guided to a diffraction grating pair 22, and By utilizing the diffraction phenomenon in the above, a wavelength-dependent diffraction angle is obtained. The collimated light emitted from the diffraction grating pair 22 is passed through a slit 24 for removing an extra light beam, and then focused on the light receiver 4 using a lens 21B.
Since the diffraction angle depends on the wavelength of the light to be measured, the diffraction grating pair 22 is formed by using the driving circuit 23 as shown in FIG.
By rotating, a measured light component having a wavelength corresponding to the rotation angle can be received. That is, spectrum analysis of the measured light can be performed.

[0004] The optical power value obtained by the light receiver 4 is given to the control circuit 7 as an electric signal such as a voltage level. Further, output is performed such as displaying the wavelength corresponding to the rotation angle and the optical power obtained by the light receiver 4 on an output display unit.

A typical size of a diffraction grating pair is about 10 cm in length and width and about 5 cm in height. Also. The diffraction grating pair 22 is provided on an optical surface plate in order to perform stable spectroscopy. Further, the optical surface plate is mechanically driven and installed on a rotary stage.

A second prior art OSA is disclosed in
No. 0-2796. In the second prior art OSA, not the diffraction grating pair but the ultra-high-speed optical switch and the incident light transmission type in the first configuration (see FIG. 1 of JP-A-10-2796). , A total reflection plate, and a control device.

In the second configuration, an ultra-high-speed optical switch, a plurality of wavelength-selective reflectors having a fixed wavelength, a delay line disposed adjacent to each of the wavelength-selective reflectors, a total reflector, The device is used. It is shown that the tunable filter is a Fabry-Perot etalon or a tunable filter having a dielectric multilayer structure. In the second prior art OSA, the light to be measured is guided to a light receiver by using the spectral means and the optical circulator of the first and second configurations.

[0008]

However, in the first prior art shown in FIG. 6, the OSA is large because the diffraction grating pair 22 and the optical surface plate and the rotary stage associated therewith are large and heavy. , Large weight and expensive.

In addition, there is a problem that the large mechanical drive portion has a short life and low reliability.

The second prior art has a problem that the number of components is large and the OSA is large, heavy, and expensive. In particular, the number of the wavelength-selective reflectors and the delay lines is required by the number of measurement points to be measured (from a constant of 10 or more to several hundreds).

An object of the present invention is to provide a small and lightweight OSA.
Is to provide. It is another object of the present invention to provide a technique capable of expanding the sweep wavelength range of OSA. Another object of the present invention is to provide a small, lightweight, long-lived and highly reliable OSA. The above and other objects and novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

[0012]

The outline of the invention disclosed in the present application is briefly described as follows. (1) O to analyze the wavelength-dependent optical power density of the measured light
SA, an optical circulator, and a wavelength-tunable fiber grating (hereinafter, referred to as a wavelength-tunable FG)
And a drive circuit for the variable-wavelength FG, and a photodetector. The drive circuit expands and contracts the variable-wavelength FG, and converts the light to be measured incident on the variable-wavelength FG from the optical circulator. A part of the light is reflected by the variable wavelength FG, and then received by the light receiver via the optical circulator.

(2) An OSA for analyzing the wavelength-dependent optical power density of the light to be measured, comprising: an optical circulator, a plurality of tunable FGs, a drive circuit for each of the tunable FGs, and a switch. , A light receiver, the expansion and contraction of each of the wavelength variable type FG using the drive circuit individually and sequentially in accordance with the switching by the changeover switch,
A part of the light to be measured incident on the tunable FG from the optical circulator via the changeover switch is reflected by the tunable FG, and then received by the light receiver via the changeover switch and the optical circulator. It is.

That is, in the means (1), a variable wavelength type FG is used as the spectroscopic means of the light to be measured instead of the diffraction grating pair used in the prior art. Tunable FG
OSA is made of small and lightweight optical fiber,
An optical circulator, a variable-wavelength FG, a light receiver, and a drive circuit for the variable-wavelength FG, the FG is expanded and contracted using the drive circuit, and the circulator is incident on the variable-wavelength FG from the optical circulator. After a part of the measured light is reflected by the variable wavelength FG, the light is received by the light receiver via the optical circulator.

In the means (2), the sweep wavelength range is expanded for applications in which the sweep wavelength range of the OSA in the means (1) is not sufficiently wide. OS
Since the sweep wavelength range of A is determined by the variable wavelength width of the variable wavelength FG, a plurality of variable wavelength FGs and changeover switches are used.

Hereinafter, the present invention will be described in detail with reference to the drawings together with embodiments (examples) according to the present invention.

[0017]

(Embodiment 1) FIG. 1 is a block diagram showing a schematic configuration of an OSA according to Embodiment 1 of the present invention, wherein 1 is an optical fiber, 2 is a connector, 3 is an optical circulator, and 4 is 5 is a wavelength-variable FG, 6 is a wavelength-variable FG drive circuit, 7 is a control circuit, 8 is an output display, 9
Is a reflectionless terminator.

In the OSA of the first embodiment, as shown in FIG. 1, an optical circulator 3 is provided on the input side of the light to be measured.
The light to be measured is guided to the optical circulator 3 by the optical fiber 1 and the connector 2. The variable-wavelength FG 5 is provided at the subsequent stage of the optical circulator 3 and reflects the measured light component having the reflection wavelength of the variable-wavelength FG 5. A non-reflection terminator 9 is provided downstream of the tunable FG 5 in order to prevent reflection from the end face of the optical fiber pigtail. As an example of the non-reflection terminator 9, there is diagonal polishing of the end face of the optical fiber, which can be easily and inexpensively installed.

The light component to be measured reflected by the tunable FG 5 returns to the optical circulator 3, is guided downward from the third port of the optical circulator 3 in FIG. 1, and is detected by the light receiver 4. . As the light receiver 4, for example, a photodiode is used.

The optical power of the measured light component detected by the light receiver 4 is transmitted to the control circuit 7 as an electric signal such as a voltage. The control circuit 7 drives the tunable FG 5 to expand and contract through the drive circuit 6. The wavelength-variable FG5 changes its reflection center wavelength due to expansion and contraction.
The control circuit 7 displays the reflection center wavelength and the optical power of the measured light component through the output display 8.

The grating of the tunable FG5 is installed in the optical fiber 1 as a change in the refractive index period, and the typical value of the length in the fiber axis direction is 2 mm. FIG. 2 shows a specific configuration example of the wavelength-tunable FG5.
Shown in

As shown in FIG. 2, the tunable FG 5 is an optical fiber 1 having a grating 5A installed therein.
A and an optical fiber 1A on which a grating 5A is installed.
Element (piezo element) 5B for expanding and contracting the part
A fixing portion 1B for fixing the portion of the optical fiber 1A to the piezoelectric element 5B; and an optical fiber guide 1C for preventing the optical fiber 1A from bending when the optical fiber 1A is expanded and contracted. . In FIG. 2, the fixed portion 1B
Is drawn for convenience of drawing so as to be installed in contact with the entire portion of the optical fiber 1A, but the fixing portion 1B
May be installed in contact with a part of the piezoelectric element 5B and a part of the optical fiber 1A.

The drive circuit 7 applies a voltage to the piezoelectric element 5B to expand and contract the piezoelectric element 5B, and the portion of the optical fiber 1A fixed by the fixing portion 1B expands and contracts. The change in the reflection center wavelength of the tunable FG 5 is proportional to the expansion and contraction rate of the optical fiber 1A.

In particular, from the strength of the optical fiber 1A, a change in the optical fiber length that is greater in compression than in expansion can be obtained (Reference 1: Alessandro et al., OFC, ThJ1, pp. 132-134, 1).
999).

The expansion and contraction of the portion of the optical fiber 1A is performed by applying stress to the portion of the optical fiber 1A using a piezoelectric element 5B, and in addition to applying a stress to the portion of the optical fiber 1A using an electric magnet. In addition, there is a method in which the temperature of the portion of the optical fiber 1A is changed or a method in which the temperature is changed (Reference 2: Jin et al., OFC, ThJ2, pp. 135 to 1137, 1999, and Reference 3: Bock et al. ., ECOC, PD, pp. 48-49, 1999).

FIG. 3 shows an example of the reflectance spectrum of the tunable FG5 (see Document 1). 3 shows three representative reflectance spectra. That is, the spectrum is shown near both ends and the center of the wavelength variable range. Said O
An example of the reflectance width which is an index of the resolution of SA is the reflectance of 3
dB, 10 dB, 30 dB lower overall width (1/2, 1/1
0, 1/1000 times lower overall width).
5 nm, 1.0 nm, and 1.5 nm. Therefore, it shows a sufficiently high resolution and a sufficiently high dynamic range.

The reflectance width can be variously made in addition to the above, and a typical width of 10 dB reduction is 0.1 nm to 10 nm.
nm.

On the other hand, the wavelength variable range is 1520 to 156.
It is 5 nm and its change range is 45 nm. This wavelength region conveniently covers a wavelength region that is important as a typical gain wavelength region of an erbium-doped fiber amplifier (EDFA). The expansion and contraction of the optical fiber portion is performed by compression using a piezoelectric element.

The tunable range of the tunable FG5 is as follows.
Since it differs depending on the degree of expansion and contraction of the portion of the optical fiber 1A,
Different values are shown depending on each technique of the prior art of the above-mentioned document.
Typical values are from 10 nm to several tens of nm. The wavelength tunable range determines the sweep wavelength range of the OSA of the present invention. However, in comparison with the OSA of the prior art, the sweep range of the OSA of the present invention is not sufficiently wide. An enlargement method is shown in a second embodiment described later.

As described above, the tunable FG5, which is the spectral means of the first embodiment, is small and lightweight.
The wavelength variable means is also small and lightweight. Further, since the light to be measured is guided only by the optical fiber 1, the waveguide optical system of the first embodiment is more resistant to vibration and highly stable than the conventional waveguide optical system using a lens. And has a long service life.

The first embodiment and a second embodiment described later.
The difference between the first embodiment and the second configuration of the second prior art, which are similar in the drawings, will be specifically described below.

That is, in the first configuration of the second prior art, the set of the incident light transmission type variable wavelength filter and the total reflection plate has a function similar to that of the variable wavelength type FG5 of the first embodiment. However, in addition to them, an ultra-high-speed optical switch and a control device are essential.

Further, in the first embodiment and the second embodiment,
While only one or a plurality of FGs are required, in the second configuration of the second prior art, an ultrafast optical switch, a number of wavelength selective reflectors of a fixed wavelength, a number of delay lines,
A total reflection plate and a control device are essential.

Since the wavelength variable range differs depending on the degree of expansion and contraction of the optical fiber portion, different values are shown depending on each method described in the above document. Typical values are from 10 nm to several tens of nm. The wavelength tunable range determines the sweep wavelength range of the OSA of the present invention, but for applications where the sweep wavelength range of the OSA of the present invention is not sufficiently wide as compared to prior art OSAs, Example 2 of which enlargement method is described later
Is shown in

As described above, the FG, which is the spectroscopic means of this embodiment, is small and light, and the wavelength variable means is also small and light. In addition, since the light to be measured is guided only by the optical fiber, the waveguide optical system of the present embodiment is, as compared with the conventional waveguide optical system using a lens,
It has advantages such as high resistance to vibration, high stability and long life.

(Embodiment 2) FIG. 4 is a block diagram showing a schematic configuration of an OSA according to Embodiment 2 of the present invention, wherein 1 is an optical fiber, 2 is a connector, 3 is an optical circulator,
Denotes a light receiver, 6A and 6B denote drive circuits of a wavelength variable FG, 7
Is a control circuit, 8 is an output display, 9 is a non-reflection terminator, 10
Is a changeover switch, 101 is a drive circuit of the changeover switch, 501 is a wavelength variable type FG for long wavelength band light to be measured,
Reference numeral 502 denotes a tunable FG for light to be measured in a short wavelength band.

As shown in FIG. 4, the OSA according to the second embodiment is an embodiment in which the wavelength sweeping long range in the OSA according to the first embodiment is expanded.
This is a configuration using two wavelength bands of 1,502.

Generally, by changing the grating period of the FG, the reflection center wavelength can be set to an arbitrary wavelength in a normal state at room temperature without external stress. The difference from the first embodiment will be described. The tunable FG 501 reflects the measured light in the long wavelength band, and the tunable FG 502 reflects the measured light in the short wavelength band. At the time when the measured light in the long wavelength band is measured by the control circuit 7, the changeover switch 10 causes the light to be measured to be incident only on the tunable FG 501, and measures the measured light in the short wavelength band. In time, the light to be measured is a tunable F
It is made to enter only G502. Tunable FG5
The control of the reflection center wavelengths 01 and 502 is performed by the control circuit 7 in the same manner as in the first embodiment. Changeover switch 1
The drive of 0 is performed by the drive circuit 101 in synchronization with the control of the wavelength variable FGs 501 and 502 by the control circuit 7.

FIG. 5 shows a wavelength tunable F according to the second embodiment.
4 shows an arrangement of wavelength tunable wavelength ranges of G501 and G502 and switching wavelengths of a changeover switch 10. That is, the wavelength tunable wavelength ranges of the wavelength tunable FGs 501 and 502 (1525-1570 nm and I565-16, respectively).
10 nm), and the wavelength-tunable FG
When the sweep wavelength 501 becomes the switching wavelength set in the overlapping wavelength range, the switching switch 10 is driven to switch the propagation direction of the measured light. Thereafter, a wavelength sweep is performed using the wavelength-tunable FG502, and the wavelength-tunable FG5 is
When the sweep using 02 is completed, the changeover switch 10 is driven again to enable the sweep by the tunable FG 501. By repeating the above operation, continuous wavelength sweeping of the wave wavelength band using the two wavelength bands is realized. The wavelength band conveniently covers the short wavelength band and the long wavelength band, which are important as typical gain wavelength ranges of the EDFA.

The second embodiment relates to a two-wavelength band configuration.
A configuration of three or more wavelength bands is possible by changing to a port or more.

As described above, the invention made by the present inventor is:
Although specifically described based on the embodiment (example),
The present invention is not limited to the above-described embodiment (example), and it is needless to say that various changes can be made without departing from the gist of the present invention.

[0042]

The effects obtained by the invention disclosed in the present application will be briefly described as follows. (1) Since the variable wavelength FG is used as the spectroscopic means of the light to be measured, a small-sized and long-life OSA can be realized. (2) The swept wavelength range of the OSA can be expanded by using a plurality of tunable FGs and a changeover switch. (3) A small, long-life, highly reliable OSA can be realized.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a schematic configuration of an OSA according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram showing a specific configuration of the wavelength variable FG of the first embodiment.

FIG. 3 is a diagram illustrating an example of a reflectance spectrum of the tunable FG according to the first embodiment.

FIG. 4 is a block diagram illustrating a schematic configuration of an OSA according to a second embodiment of the present invention.

FIG. 5 is a diagram illustrating a wavelength tunable wavelength range of a wavelength tunable FG and an arrangement of switching wavelengths of a changeover switch according to a second embodiment.

FIG. 6 is a diagram showing a first prior art OSA.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Optical fiber, 1A ... Optical fiber with the grating installed inside, 1B ... Fixed part, 1C ... Optical fiber guide, 2 ... Connector, 3 ... Optical circulator, 4 ... Receiver, 5 ... Variable wavelength FG, 5A ... Grating, 5B
... Piezoelectric elements (piezo elements), 6, 6A, 6B... Drive circuit of variable wavelength FG, 7... Control circuit, 8.
... Non-reflection terminator, 10... Changeover switch, 101... Changeover switch drive circuit, 501... Tunable FG for long wavelength band light to be measured, 502. , 21B: lens, 22: diffraction grating pair, 23: diffraction grating driving circuit, 24: slit.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Noboru Kochio 2-3-1 Otemachi, Chiyoda-ku, Tokyo Inside Nippon Telegraph and Telephone Corporation (72) Inventor Katsumi Iwazuki 2-chome Otemachi, Chiyoda-ku, Tokyo No. 1 Nippon Telegraph and Telephone Corporation F-term (reference) 2G020 AA03 BA02 CA02 CB02 CB04 CC32 CC49 CC55 CC65 CD13 2G086 BB01 BB04

Claims (2)

[Claims] 1. An optical spectrum analyzer for analyzing a wavelength-dependent optical power density of light to be measured, comprising: an optical circulator;
A variable wavelength type FG), a drive circuit for the variable wavelength type FG, and a light receiver. The wavelength variable type FG is expanded and contracted by using the drive circuit, and the wavelength variable type FG is transmitted from the optical circulator. An optical spectrum analyzer characterized in that a part of the light to be measured incident on the optical fiber is reflected by the variable wavelength type FG, and then received by the light receiver via the optical circulator. 2. An optical spectrum analyzer for analyzing a wavelength-dependent optical power density of light to be measured, comprising: an optical circulator, a plurality of variable wavelength FGs, a drive circuit for each of the variable wavelength FGs, and a switch. And a light receiver, and expands and contracts each of the wavelength tunable FGs individually using the drive circuit in accordance with switching by the changeover switch. The wavelength tunable FG is transmitted from the optical circulator through the changeover switch. An optical spectrum analyzer, wherein a part of the light to be measured incident on the FG is reflected by the variable wavelength type FG and then received by the light receiver via the changeover switch and the optical circulator.