JP2001099709A - Wavelength monitoring device and optical product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive and small-sized wavelength monitoring device having a small insertion loss. SOLUTION: A long-period fiber grating element 110 possesses a transmission characteristic changing monotonously in a prescribed wavelength band. Power of light transmitted through the long-period fiber grating element 110 and detected by a light-receiving element 120 is dependent on a wavelength, and wavelength dependence of the power agrees with the transmission characteristic of the long-period fiber grating element 110, and changes monotonously in the prescribed wavelength band. In an operation part 130, the wavelength of light in the prescribed wavelength band inputted into the long-period fiber grating element 110 is obtained, based on the power detected by the light-receiving element 120.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a wavelength monitor for monitoring the wavelength of light and an optical product including the wavelength monitor.

[0002]

2. Description of the Related Art Wavelength division multiplexing (WDM) for multiplexing and transmitting multi-wavelength signal light.
It is important to monitor the wavelength of light in optical communication using a transmission method, optical information processing, optical measurement, and the like. As a conventional wavelength monitor, a device that monitors a wavelength based on a difference from a reference wavelength obtained using an optical interferometer,
2. Description of the Related Art There is known an apparatus for monitoring a wavelength by dispersing light with a spectrum analyzer or the like. Further, Japanese Patent Application Laid-Open No. 10-25345
The wavelength monitoring device disclosed in Japanese Patent Application Publication No. 2002-139,197 makes light to be monitored incident on an interference filter, detects respective powers of transmitted light and reflected light from the interference filter, and detects light based on a ratio of these powers. Is obtained.

[0003]

However, among the above conventional examples, a wavelength monitor using an optical interferometer has a movable portion, and a wavelength monitor using a spectrum analyzer is expensive and large. Further, Japanese Patent Application Laid-Open No. 10-2534
The wavelength monitoring device disclosed in Japanese Patent Publication No. 52 uses an interference filter, and therefore has a large insertion loss and a large size.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to provide an inexpensive and compact wavelength monitor device having a small insertion loss, and an optical product including the wavelength monitor device. I do.

[0005]

A first wavelength monitoring apparatus according to the present invention comprises: (1) a long-period fiber having a transmission characteristic that monotonically changes in a predetermined wavelength band and inputting light to be wavelength monitored; A grating element, (2) a light-receiving element that receives light transmitted through the long-period fiber grating element of the light input to the long-period fiber grating element and detects the power of the light, and (3) a light-receiving element that detects the light power. And a calculating unit for calculating the wavelength of the light input to the long-period fiber grating element based on the obtained power.

According to the first wavelength monitoring device, the power of the light transmitted through the long-period fiber grating element and detected by the light receiving element depends on the wavelength. It matches the transmission characteristics of the fiber grating element and changes monotonously in a predetermined wavelength band. The arithmetic unit calculates the wavelength of light within the predetermined wavelength band input to the long-period fiber grating element based on the power detected by the light receiving element.

A second wavelength monitoring device according to the present invention comprises:
(1) A long-period fiber grating having a transmission characteristic in which a first polarization component monotonically increases and a second polarization component monotonically decreases in a predetermined wavelength band, and which inputs light to be wavelength monitored. (2) a polarization splitting element that splits the light transmitted through the long-period fiber grating element into light of a first polarization component and light of a second polarization component and outputs the separated light; ) A first light receiving element for receiving the light of the first polarization component output from the polarization separation element and detecting the power of the light; and (4) a second light reception element for outputting the power of the polarization separation element. A second light receiving element for receiving the polarized component light and detecting the power of the light; and (5) a long period fiber grating element based on the power detected by each of the first and second light receiving elements. And a calculation unit for calculating the wavelength of the light input to the device.

According to the second wavelength monitoring device, the power of the light of the first polarization component detected by the first light receiving element via the long-period fiber grating element and the polarization splitting element depends on the wavelength. The wavelength dependence of the power matches the transmission characteristic of the long-period fiber grating element for the first polarization component, and monotonically increases in a predetermined wavelength band. On the other hand, the power of the light of the second polarization component detected by the second light receiving element via the long-period fiber grating element and the polarization separation element also depends on the wavelength, and the wavelength dependence of the power is long. The transmission characteristic of the periodic fiber grating element coincides with the transmission characteristic of the second polarization component, and decreases monotonously in the predetermined wavelength band. The arithmetic unit obtains the wavelength of the light within the predetermined wavelength band input to the long-period fiber grating element based on the power detected by each of the first and second light receiving elements.

A third wavelength monitoring device according to the present invention comprises:
(1) an optical splitting element for splitting the input light into a first light and a second light and outputting the split light; and (2) a first light having a transmission characteristic that monotonically increases in a predetermined wavelength band. (3) a second long-period fiber grating element having a transmission characteristic that monotonously decreases in the predetermined wavelength band, and a second long-period fiber grating element that inputs second light; 4) First
A first light receiving element for receiving light transmitted through the first long-period fiber grating element of the first light input to the long-period fiber grating element and detecting the power of the light; (6) a second light receiving element for receiving light transmitted through the second long-period fiber grating element among the second lights input to the second long-period fiber grating element and detecting the power of the light; First and second
An arithmetic unit for determining the wavelength of light input to the optical branching element based on the power detected by each of the light receiving elements;
It is characterized by having.

According to the third wavelength monitor, the power of the first light detected by the first light receiving element via the optical branching element and the first long-period fiber grating element depends on the wavelength. , The wavelength dependence of its power is
It coincides with the transmission characteristic of the first long-period fiber grating element, and monotonically increases in a predetermined wavelength band. On the other hand, the power of the second light detected by the second light receiving element via the optical branching element and the second long-period fiber grating element also depends on the wavelength, and the wavelength dependence of the power is as follows:
The transmission characteristic coincides with the transmission characteristic of the second long-period fiber grating element, and monotonically decreases in the above-mentioned predetermined wavelength band. The arithmetic unit calculates the wavelength of the light within the predetermined wavelength band input to the optical branching element based on the power detected by each of the first and second light receiving elements.

In the third wavelength monitoring device, the first
The temperature dependence of the transmission characteristics of each of the first and second long-period fiber grating elements is characterized in that the absolute values are substantially the same and the polarities are different from each other. In this case, even if the transmission characteristic of each of the first and second long-period fiber grating elements changes due to a change in temperature, in this wavelength monitoring device, the change in the transmission characteristic is obtained by calculating the ratio in the arithmetic unit. Are canceled, and the wavelength can be accurately monitored regardless of the temperature change.

A fourth wavelength monitor according to the present invention comprises:
(1) Has a loss characteristic that changes monotonically in a predetermined wavelength band,
A long-period fiber grating element for inputting the light to be wavelength-monitored; and And (3) an arithmetic unit for calculating the wavelength of light input to the long-period fiber grating element based on the power detected by the light receiving element.

According to the fourth wavelength monitoring device, the power of light leaked from the long-period fiber grating element to the outside and detected by the light receiving element depends on the wavelength, and the wavelength dependence of the power is as follows: It coincides with the loss characteristic of the long-period fiber grating element, and changes monotonously in a predetermined wavelength band. The arithmetic unit calculates the wavelength of light within the predetermined wavelength band input to the long-period fiber grating element based on the power detected by the light receiving element.

In the fourth wavelength monitoring device, the long-period fiber grating element has a predetermined range on the downstream side covered with a medium having a refractive index different from the refractive index of the cladding region. Receiving the light leaked from the portion covered with. In this case, the cladding mode light converted from the core mode light by the long-period fiber grating element can be efficiently leaked to the outside, which is preferable. It is preferable that the refractive index of this medium is equal to or larger than the value of the refractive index of the cladding region of the long-period fiber grating element. This medium is preferably a resin for coating an optical fiber, or is preferably made of the same material as the cladding region of the long-period fiber grating element.

A fifth wavelength monitor according to the present invention comprises:
(1) Has a loss characteristic that changes monotonically in a predetermined wavelength band,
A first long-period fiber grating element for inputting light to be wavelength-monitored, and (2) a loss characteristic that is provided in series downstream of the first long-period fiber grating element and monotonically changes in a predetermined wavelength band. And (3) receiving light leaked from the first long-period fiber grating element out of the light input to the first long-period fiber grating element, A first light receiving element for detecting the power of
(4) a second light receiving element for receiving light leaked from the second long-period fiber grating element to the outside of the light input to the second long-period fiber grating element and detecting the power of the light; (5) An arithmetic unit for calculating the wavelength of light input to the first long-period fiber grating element based on the power detected by each of the first and second light receiving elements.

According to the fifth wavelength monitor, the first
The power of light leaked from the long-period fiber grating element to the outside and detected by the first light receiving element depends on the wavelength, and the wavelength dependence of the power depends on the loss of the first long-period fiber grating element. It coincides with the characteristic and changes monotonously in a predetermined wavelength band. Further, the power of light leaked to the outside from the second long-period fiber grating element provided in series downstream of the first long-period fiber grating element and detected by the second light receiving element depends on the wavelength. Wavelength dependence of the power
, And monotonously changes in a predetermined wavelength band. The arithmetic unit obtains the wavelength of the light within the predetermined wavelength band input to the first long-period fiber grating element based on the power detected by each of the first and second light receiving elements.

In the fifth wavelength monitor, the first
The temperature dependence of the loss characteristic of each of the first and second long-period fiber grating elements is characterized in that the absolute values are substantially the same and the polarities are different from each other. In this case, even if the loss characteristic of each of the first and second long-period fiber grating elements changes due to a change in temperature, in this wavelength monitor device, the change in the loss characteristic is obtained by calculating the ratio in the arithmetic unit. Are canceled, and the wavelength can be accurately monitored regardless of the temperature change.

A sixth wavelength monitor according to the present invention comprises:
(1) Has a loss characteristic that changes monotonically in a predetermined wavelength band,
A first long-period fiber grating element for inputting light to be wavelength-monitored, and (2) a second light-entering and propagating light leaked from the first long-period fiber grating element.
And (3) of the light input to the second long-period fiber grating element,
A light-receiving element that receives light transmitted through the second long-period fiber grating element and detects the power of the light;
(4) Based on the power detected by the light receiving element, the first
And a calculation unit for calculating the wavelength of light input to the long-period fiber grating element.

According to the sixth wavelength monitoring device, the first
The light leaked from the long-period fiber grating element to the outside is input to the second long-period fiber grating, propagated, and detected by the light receiving element. The power of the light detected by the light receiving element depends on the wavelength, and the wavelength dependence of the power matches the loss characteristic of the first long-period fiber grating element and changes monotonously in a predetermined wavelength band. . The arithmetic unit calculates the wavelength of light within the predetermined wavelength band input to the first long-period fiber grating element based on the power detected by the light receiving element.

An optical product according to the present invention has any one of the first to sixth wavelength monitoring devices. For example, when the optical product also has a semiconductor laser light source, by monitoring the wavelength of the laser light output from the semiconductor laser light source with a wavelength monitoring device, by adjusting the temperature of the semiconductor laser light source, The oscillation wavelength can be kept constant. In particular, any one of the fourth to sixth wavelength monitoring devices can be provided on the main line, and light transmitted through the long-period fiber grating element in the wavelength monitoring device can be propagated further downstream on the main line. .

[0021]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description.

(First Embodiment) First, a first embodiment of the wavelength monitoring apparatus according to the present invention will be described. FIG.
1 is a schematic configuration diagram of a wavelength monitor device 100 according to a first embodiment. Wavelength monitor device 100 according to the present embodiment
Includes a long-period fiber grating element 110, a light receiving element 120, and a calculation unit 130.

Long-period fiber grating element 110
Has a transmission characteristic that changes monotonically in a predetermined wavelength band,
Light to be wavelength monitored arrives via the optical fiber 10 is input. The long-period fiber grating element 110
The core of the optical fiber is formed with a long-period (a period of about several hundred μm) refractive index modulation, and a loss is given to the core mode light due to the coupling between the core mode light and the cladding mode light. The transmission characteristics of the long-period fiber grating element 110 depend on the period of the refractive index modulation, the length at which the refractive index modulation is formed, the degree of modulation of the refractive index modulation, and the like. Transmission characteristics are obtained. FIG. 2 shows a wavelength monitor 10 according to the first embodiment.
5 is a graph illustrating transmission characteristics of a long-period fiber grating element 110. As shown in this graph, the transmittance T of the long-period fiber grating element 110 monotonically changes (monotonically decreases in this figure) with respect to the wavelength λ in the band of the wavelength λ ₁ to the wavelength λ ₂ .

The light receiving element 120 receives the light transmitted through the long-period fiber grating element 110 from the light input to the long-period fiber grating element 110 and detects the power of the light. As the light receiving element 120, for example, a photodiode is suitably used. FIG. 3 is a graph showing the relationship between the power I of light detected by the light receiving element 120 of the wavelength monitoring device 100 according to the first embodiment and the wavelength λ. The graph (FIG. 3) showing the relationship between the power I of the light detected by the light receiving element 120 and the wavelength λ is the same as the graph (FIG. 2) showing the transmission characteristics of the long-period fiber grating element 110, and the wavelength λ ₁ as the wavelength lambda is longer in a band of ~ wavelength lambda _2, a small power I of light detected by the light receiving element 120.

The arithmetic unit 130 obtains the wavelength λ of the light input to the long-period fiber grating element 110 based on the power I detected by the light receiving element 120. The calculation unit 130 stores the relationship between the output value I of the light receiving element 120 and the wavelength λ (that is, the relationship shown in FIG. 3) obtained in advance, and stores the power I detected by the light receiving element 120. To the memorized relationship between the two,
The wavelength λ of the light input to the long-period fiber grating element 110 is obtained.

The wavelength monitor 100 according to the present embodiment
Can monitor the wavelength of light in the band of wavelengths λ ₁ to λ ₂ where the transmission characteristics of the long-period fiber grating element 110 monotonously change. This wavelength monitoring device 100
Since the long-period fiber grating element 110, which is a fiber-type optical component, is used, it is inexpensive, small, and has a small insertion loss.

(Second Embodiment) Next, a wavelength monitor according to a second embodiment of the present invention will be described. FIG.
FIG. 3 is a schematic configuration diagram of a wavelength monitoring device 200 according to a second embodiment. Wavelength monitor device 200 according to the present embodiment
Includes a long-period fiber grating element 210, a polarization splitting element 240, a first light receiving element 221, a second light receiving element 222, and an arithmetic unit 230.

Long-period fiber grating element 210
Has a transmission characteristic in which a first polarization component X monotonically increases and a second polarization component Y monotonically decreases in a predetermined wavelength band, and inputs light to be wavelength monitored. The long-period fiber grating element 210 has a long period (period of about several hundred μm) in the core of the optical fiber having the polarization characteristic.
And a loss is given to the core mode light due to the coupling between the core mode light and the cladding mode light. Long period fiber grating element 21
The transmission characteristic of 0 depends on the polarization state of the core mode light, in addition to the period of the refractive index modulation, the length at which the refractive index modulation is formed, the degree of modulation of the refractive index modulation, and the like. FIG. 5 is a graph showing transmission characteristics of the long-period fiber grating element 210 of the wavelength monitor 200 according to the second embodiment. As shown in this graph, in the band of wavelength λ ₁ to wavelength λ ₂ , the transmittance T of the long-period fiber grating element 210 is
The polarization component X monotonically increases with respect to the wavelength λ, and the polarization component Y monotonically decreases with respect to the wavelength λ. For example, a long-period fiber grating element in which a long-period grating is formed on an optical fiber having a noncircularity (= 1− (short axis diameter / long axis diameter)) of 1.6% has a polarization component X
Since the loss peak wavelengths of Y and Y differ by about 20 nm, the width of the wavelength range that can be monitored can be about 20 nm.

The polarization splitting element 240 splits the light transmitted through the long-period fiber grating element 210 into a polarized light component X and a polarized light component Y and outputs the separated light. As the polarization separation element 240, for example, a polarization coupler or a polarization beam splitter is suitably used.

The first light receiving element 221 is a polarization separation element 2
The light of the polarization component X output from 40 is received, and the power of the light is detected. As the light receiving element 221, for example, a photodiode is preferably used. FIG. 6 shows the first light receiving element 221 of the wavelength monitoring device 200 according to the second embodiment.
5 is a graph showing the relationship between the power _{IX of} light detected by the method and the wavelength λ. A graph (FIG. 6) showing the relationship between the power _{IX of the} light detected by the light receiving element 221 and the wavelength λ is shown in FIG.
Polarization component X of long-period fiber grating element 210
Is the same as the graph (FIG. 5) showing the transmission characteristics of the light-receiving element 221. The longer the wavelength λ in the wavelength band from λ ₁ to λ ₂ , the greater the power _{IX of the} light detected by the light receiving element 221.

The second light receiving element 222 is a polarization separation element 2
The light of the polarization component Y output from 40 is received, and the power of the light is detected. As the light receiving element 222, for example, a photodiode is suitably used. FIG. 7 shows the second light receiving element 222 of the wavelength monitoring device 200 according to the second embodiment.
5 is a graph showing the relationship between the power I _{Y of} light detected by the method and the wavelength λ. A graph (FIG. 7) showing the relationship between the power I _{Y of the} light detected by the light receiving element 222 and the wavelength λ is shown in FIG.
Polarization component Y of long-period fiber grating element 210
Is the same as the graph (FIG. 5) showing the transmission characteristics of the light-receiving element 222. The longer the wavelength λ in the wavelength band from λ ₁ to λ ₂ , the smaller the power I _{Y of the} light detected by the light receiving element 222.

The arithmetic unit 230 includes light receiving elements 221 and 2
The wavelength λ of the light input to the long-period fiber grating element 210 is obtained based on the powers I _X and I _Y detected by the respective elements 22. The arithmetic unit 230 determines the relationship between the output values I _X , I _{Y of} the light receiving elements 221 and 222 and the wavelength λ, which are obtained in advance (that is, the relationship shown in FIGS. 6 and 7).
Is stored, and the powers I _X and I _Y detected by the light receiving elements 221 and 222 are applied to the stored relationship between the two to obtain the wavelength λ of the light input to the long-period fiber grating element 210. You may. However, more preferably, the arithmetic unit 230 has the configuration shown in FIG. 8 and calculates the wavelength λ based on the value of the ratio ((I _X −I _Y ) / (I _X + I _Y )).
Ask for.

FIG. 8 is a block diagram of the calculation unit 230 of the wavelength monitor 200 according to the second embodiment. The arithmetic unit 230 includes an I / V converter 231 and an I / V converter 23
2, a subtractor 233, an adder 234, a divider 235, and a CPU 236. I / V converter 231 inputs the current signal outputted from the light receiving element 221 is converted into a voltage signal representative of the value of the power I _X of the light of the polarization component X that is detected by the light receiving element 221 outputs I do. I / V converter 2
Reference numeral 32 receives the current signal output from the light receiving element 222, converts the current signal into a voltage signal representing the value of the power I _Y of the light of the polarization component Y detected by the light receiving element 222, and outputs the voltage signal.

The subtractor 233 receives the voltage signal output from each of the I / V converters 231 and 232 and outputs a voltage signal representing the difference between the two. The adder 234 calculates I
The voltage signals output from the / V converters 231 and 232 are input, and a voltage signal representing the sum of the two is output. The divider 235 includes a subtractor 233 and an adder 234.
The voltage signal output from each is input, and a voltage signal indicating the ratio between the two is output. The voltage signal output from the divider 235 indicates the value of the ratio ((I _X -I _Y ) / (I _X + I _Y )). Then, the CPU 236 inputs the voltage signal output from the divider 235, and based on the voltage signal, the long-period fiber grating element 210
Is obtained.

In this embodiment, the light that reaches the long-period fiber grating element 210 needs to be randomly polarized. If the light is not randomly polarized light, a depolarizer is provided in front of the long-period fiber grating element 210 to make the light input to the long-period fiber grating element 210 into random polarized light.

The wavelength monitor 200 according to the present embodiment
Can monitor the wavelength of light in the band of wavelengths λ ₁ to λ ₂ in which the transmission characteristic of the long-period fiber grating element 210 monotonically increases for the polarization component X and monotonically decreases for the polarization component Y. . This wavelength monitor 200
Uses the long-period fiber grating element 210, which is a fiber-type optical component, so that it is inexpensive, small, and has a small insertion loss. In the present embodiment, even if the transmission characteristic of the long-period fiber grating element 210 changes due to a temperature change or the like, the transmission characteristic shows a change in an inverse characteristic within the band of wavelengths λ _{1 to} λ _2. By determining the ratio at, the change is offset. Therefore, the wavelength monitoring device 200 according to the present embodiment can accurately monitor the wavelength λ regardless of a temperature change or the like.

(Third Embodiment) Next, a wavelength monitor according to a third embodiment of the present invention will be described. FIG.
FIG. 9 is a schematic configuration diagram of a wavelength monitoring device 300 according to a third embodiment. Wavelength monitor 300 according to the present embodiment
Includes an optical branching element 350, a first long-period fiber grating element 311, a second long-period fiber grating element 312, a first light receiving element 321, a second light receiving element 322, and an arithmetic unit 330.

The light splitting element 350 splits the input light into a first light and a second light and outputs the split light. For example, an optical fiber coupler is preferably used. As shown in FIG. 10, the first long-period fiber grating element 311 has a transmission characteristic that monotonously increases in a band of wavelengths λ ₁ to λ ₂ , and receives the first light output from the optical branching element 350. I do. The second long-period fiber grating element 3
Numeral 12 has a transmission characteristic that monotonously decreases in a band of wavelengths λ ₁ to λ ₂ as shown in FIG. 11, and receives the _second light output from the optical branching element 350. Each of the long-period fiber grating elements 311 and 312 also has a long-period (a period of about several hundred μm) refractive index modulation formed in the core of the optical fiber, and is caused by the coupling between the core mode light and the clad mode light. It gives a loss to core mode light. The transmission characteristics of the long-period fiber grating elements 311 and 312 also depend on the period of the refractive index modulation, the length in which the refractive index modulation is formed, the degree of modulation of the refractive index modulation, and the like. As a result, desired transmission characteristics can be obtained.

The first light receiving element 321 receives the light transmitted through the long-period fiber grating element 311 out of the first light input to the long-period fiber grating element 311 and detects the power I ₁ of the light. . The second light receiving element 322 is a long-period fiber grating element 31.
The light transmitted through the out long period fiber grating element 312 of the second light input to the 2 by receiving, detecting the power I ₂ of the light. As each of the light receiving elements 321, 322, for example, a photodiode is suitably used. Graph showing the relationship between the power I ₁ and the wavelength lambda of the light detected by the light receiving element 321 is a graph isomorphic showing the transmission characteristics of the long-period fiber grating device 311, a band of wavelengths lambda ₁ ~ wavelength lambda ₂ The longer the wavelength λ, the light receiving element 32
Large power I ₁ of the light detected by one. On the other hand, the power I _{2 of the} light detected by the light receiving element 322 and the wavelength λ
Is the same as the graph showing the transmission characteristics of the long-period fiber grating element 312. The longer the wavelength λ in the wavelength band from λ ₁ to λ ₂ ,
The power I _{2 of the} light detected by 22 is small.

The operation unit 330 includes light receiving elements 321 and 3
The wavelength λ of the light input to the optical branching element 350 is obtained based on the powers I ₁ and I ₂ detected by the respective elements 22.
The calculation unit 330 is provided with the light receiving element 32 obtained in advance.
The relationship between the output values I ₁ , I _{2 of} I.1, 322 and the wavelength λ is stored, and the powers I ₁ , I ₂ detected by the light receiving elements 321, 322 are applied to the stored relationship between the two. Thus, the wavelength λ of the light input to the optical branching element 350 may be obtained. However, more preferably, the calculation unit 330 determines the ratio ((I ₁ −I ₂ ) / (I ₂ ) in the same manner as in the second embodiment.
_The wavelength λ is obtained based on the value of ₁ + I ₂ )). in this case,
Arithmetic unit 330 has the same configuration as arithmetic unit 230 shown in FIG.

FIG. 12 is a diagram for explaining the temperature dependence of the transmission characteristics of each of the long-period fiber grating elements 311 and 312 in the wavelength monitor 300 according to the third embodiment. FIG. 6A shows the transmission characteristics at a temperature θ ₁ , and FIG. 6B shows the transmission characteristics at a temperature θ ₂ (where θ ₁ ≠ θ ₂ ). As shown in FIG.
_By changing from ₁ to θ ₂ , the transmission characteristic of the long-period fiber grating element 311 shifts to the short wavelength side, and the transmission characteristic of the long-period fiber grating element 312 shifts to the long wavelength side. The temperature dependency of the transmission characteristics of each of the long-period fiber grating elements 311 and 312 has substantially the same absolute value (the absolute value of the shift amount) and different polarities (the direction of the shift). Since each of the long-period fiber grating elements 311 and 312 has such characteristics, even if the transmission characteristic of each of the long-period fiber grating elements 311 and 312 changes due to a change in temperature, the wavelength monitor according to the present embodiment may be used. In the device 300, the operation unit 33
By determining the ratio at 0, the change in the transmission characteristics is canceled, and the wavelength λ can be monitored accurately regardless of the temperature change.

The wavelength monitor 300 according to the present embodiment
Indicates that the transmission characteristic of the long-period fiber grating element 311 monotonously decreases and the long-period fiber grating element 311
It is possible to monitor the wavelength of light in the band of wavelengths [lambda] _{1 to} [lambda] ₂ at which the transmission characteristics of the light source 12 monotonously increase. Since the wavelength monitor device 300 uses the long-period fiber grating elements 311 and 312 which are fiber-type optical components, it is inexpensive, small, and has a small insertion loss.

(Fourth Embodiment) Next, a wavelength monitor according to a fourth embodiment of the present invention will be described. FIG.
FIG. 3 is a schematic configuration diagram of a wavelength monitor device 400 according to a fourth embodiment. Wavelength monitor device 40 according to the present embodiment
Reference numeral 0 includes a long-period fiber grating element 410, a light receiving element 420, and a calculation unit 430.

Long-period fiber grating element 410
Has a transmission characteristic that changes monotonously in a predetermined wavelength band, and inputs light to be wavelength monitored. The long-period fiber grating element 410 has a core region 4 of the optical fiber.
A refractive index modulation having a long period (period of about several hundred μm) is formed in 10a, and a loss is given to the core mode light due to the coupling between the core mode light and the cladding mode light.
That is, the long-period fiber grating element 410
Has a loss characteristic that changes monotonically in a predetermined wavelength band. The loss characteristic of the long-period fiber grating element 410 depends on the period of the refractive index modulation, the length at which the refractive index modulation is formed, the modulation degree of the refractive index modulation, and the like. A loss characteristic is obtained.

In the long-period fiber grating element 410, a cladding region 410b surrounding the core region 410a is preferably covered with a medium 410c in a predetermined range downstream of the region where the refractive index modulation is formed. is there. This medium 410c has a refractive index different from that of the cladding region 410b. The refractive index of the medium 410c is preferably equal to or greater than the value of the refractive index of the cladding region 410b. The medium 410c is preferably an optical fiber coating resin, and is also preferably made of the same material as the cladding region 410b. By doing this,
It is possible to increase the ratio of clad mode light emitted to the outside.

The light receiving element 420 converts the light input to the long-period fiber grating element 410 into clad mode light,
The light leaked from 10 to the outside is received, and the power of the light is detected. Long period fiber grating element 410
Is covered with the medium 410c, the light receiving element 420 receives light leaked from the part covered with the medium 410c. As the light receiving element 420, for example, a photodiode is suitably used.

The calculating section 430 obtains the wavelength of the light input to the long-period fiber grating element 410 based on the power detected by the light receiving element 420. The arithmetic unit 430 stores the relationship between the output value of the light receiving element 420 and the wavelength determined in advance, and applies the power detected by the light receiving element 420 to the stored relationship between the two. The wavelength of the light input to the long-period fiber grating element 410 is obtained.

The wavelength monitor 400 according to the present embodiment
Can monitor the wavelength of light in the wavelength band λ ₁ to λ ₂ where the loss characteristic of the long-period fiber grating element 410 monotonically changes. This wavelength monitor device 400
Since the long-period fiber grating element 410, which is a fiber-type optical component, is used, it is inexpensive, small, and has a small insertion loss.

In this embodiment, since the power of light leaked from the long-period fiber grating element 410 to the outside is detected, the light transmitted through the long-period fiber grating element 410 can be further propagated downstream. Therefore, the wavelength monitor 400 can be inserted on the main line.

(Fifth Embodiment) Next, a fifth embodiment of the wavelength monitor according to the present invention will be described. FIG.
FIG. 4 is a schematic configuration diagram of a wavelength monitor device 500 according to a fifth embodiment. Wavelength monitor device 50 according to the present embodiment
0 is the first long-period fiber grating element 51
1, the second long-period fiber grating element 512,
A first light receiving element 521, a second light receiving element 522, and a calculation unit 530 are provided.

Long-period fiber grating element 511
And 512 have transmission characteristics that change monotonically in a predetermined wavelength band, and input light to be wavelength monitored. Each of the long-period fiber grating elements 511 and 512 is formed in series on one optical fiber, and a long-period (a period of about several hundred μm) refractive index modulation is formed in the core region 510a of the optical fiber. In addition, a loss is given to the core mode light due to the coupling between the core mode light and the cladding mode light. That is, each of the long-period fiber grating elements 511 and 512 has a loss characteristic that changes monotonously in a predetermined wavelength band. The loss characteristics of each of the long-period fiber grating elements 511 and 512 depend on the period of the refractive index modulation, the length in which the refractive index modulation is formed, the modulation degree of the refractive index modulation, and the like.
By properly designing these, desired loss characteristics can be obtained.

Each of these long-period fiber grating elements 511 and 512 has a cladding region 510b surrounding a core region 510a in a predetermined range on the downstream side of the region where the refractive index modulation is formed.
Preferably, it is covered with c. These media 511
c and 512c have a refractive index different from the refractive index of the cladding region 510b. It is preferable that the refractive indexes of the media 511c and 512c be equal to or higher than the value of the refractive index of the cladding region 510b. Also, the media 511c and 512c are preferably optical fiber coating resin, and are also preferably made of the same material as the cladding region 510b. By doing so, it is possible to increase the ratio of the clad mode light emitted to the outside.

The light receiving element 521 converts the light input to the long-period fiber grating element 511 into clad mode light, and
The light leaked from 11 to the outside is received, and the power of the light is detected. Long period fiber grating element 511
Is covered by the medium 511c, the light receiving element 521 receives light leaked from the portion covered by the medium 511c. The light receiving element 522 receives the light that has been converted into cladding mode light and leaked out of the long-period fiber grating element 512 out of the light input to the long-period fiber grating element 512 and detects the power of the light. I do. When a part of the long-period fiber grating element 512 is covered with the medium 512c, the light receiving element 522 receives light leaked from the part covered with the medium 512c. Light receiving elements 521 and 522
For each, for example, a photodiode is suitably used.

The calculating section 530 includes light receiving elements 521 and 5
The wavelength λ of the light input to the long-period fiber grating element 511 is obtained based on the powers I ₁ and I ₂ detected by the respective elements 22. The calculation unit 530 stores the relationship between the output values I ₁ and I _{2 of} the light receiving elements 521 and 522 and the wavelength λ, which has been obtained in advance, and stores the light receiving elements 521 and 522.
The wavelengths λ of the light input to the long-period fiber grating element 511 may be obtained by applying the powers I ₁ and I ₂ detected by the above to the stored relationship between the two. However, more preferably, the arithmetic unit 530 determines the ratio ((I ₁ −I ₂ ) / (I ₁ + I ₂ )) as in the case of the second embodiment.
Is obtained based on the value of. In this case, the operation unit 53
0 is the same as the configuration of the arithmetic unit 230 shown in FIG.

FIG. 15 is a diagram for explaining the temperature dependence of the loss characteristics of each of the long-period fiber grating elements 511 and 512 in the wavelength monitor 500 according to the fifth embodiment. FIG. 7A shows the loss characteristics at the temperature θ ₁ , and FIG. 7B shows the loss characteristics at the temperature θ ₂ (where θ ₁ ≠ θ ₂ ). As shown in FIG.
_By changing from ₁ to θ ₂ , the loss characteristic of the long-period fiber grating element 511 shifts to the shorter wavelength side, and the loss characteristic of the long-period fiber grating element 512 shifts to the longer wavelength side. The temperature dependences of the loss characteristics of the long-period fiber grating elements 511 and 512 have substantially the same absolute value (the absolute value of the shift amount) and different polarities (the direction of the shift). Since each of the long-period fiber grating elements 511 and 512 has such characteristics, even if the loss characteristic of each of the long-period fiber grating elements 511 and 512 changes due to a change in temperature, the wavelength monitor according to the present embodiment can be used. In the device 500, the arithmetic unit 53
By calculating the ratio at 0, the change in the loss characteristic is canceled out, and the wavelength λ can be accurately monitored regardless of the temperature change.

The wavelength monitor 500 according to the present embodiment
Are the long-period fiber grating elements 511 and 5
12 wavelengths λ ₁ to λ _{2 at which} respective loss characteristics change monotonically
The wavelength of light in this band can be monitored. Since the wavelength monitoring device 500 uses the long-period fiber grating elements 511 and 512, which are fiber-type optical components, it is inexpensive, small, and has a small insertion loss.

In this embodiment, since the power of the light leaked from the long-period fiber grating elements 511 and 512 is detected, the light transmitted through the long-period fiber grating elements 511 and 512 goes further downstream. Can be propagated,
The wavelength monitoring device 500 can be inserted on the main line.

(Sixth Embodiment) Next, a sixth embodiment of the wavelength monitor according to the present invention will be described. FIG.
FIG. 6 is a schematic configuration diagram of a wavelength monitor device 600 according to the sixth embodiment. Wavelength monitor device 60 according to the present embodiment
0 is the first long-period fiber grating element 61
1, the second long-period fiber grating element 612,
A light receiving element 620 and a calculation unit 630 are provided.

Long-period fiber grating element 611
Has a transmission characteristic that changes monotonously in a predetermined wavelength band, and inputs light to be wavelength monitored. The long-period fiber grating element 611 is the core region 6 of the optical fiber.
A refractive index modulation having a long period (a period of about several hundred μm) is formed in 11a, and a loss is given to the core mode light due to the coupling between the core mode light and the cladding mode light. That is, the long-period fiber grating element 611 has a loss characteristic that changes monotonously in a predetermined wavelength band. The loss characteristics of the long-period fiber grating element 611 depend on the period of the refractive index modulation, the length at which the refractive index modulation is formed, the modulation degree of the refractive index modulation, and the like. A loss characteristic is obtained.

Long-period fiber grating element 612
In a predetermined range downstream of the long-period fiber grating element 611, a long-period (period of about several hundred μm) refractive index modulation is formed in the core region 612a of the optical fiber adjacent via the refractive index matching member 660. It is a thing. The long-period fiber grating element 612 receives light leaked from the long-period fiber grating element 611 as clad mode light, and converts the clad mode light into core mode light.

The light receiving element 620 receives the light transmitted through the long-period fiber grating element 612 out of the light input to the long-period fiber grating element 612 and converted into the core mode, and detects the power of the light. . As the light receiving element 620, for example, a photodiode is suitably used.

The calculating section 630 obtains the wavelength λ of the light input to the long-period fiber grating element 611 based on the power detected by the light receiving element 620. The arithmetic unit 630 stores the relationship between the output value of the light receiving element 620 and the wavelength determined in advance, and applies the power detected by the light receiving element 620 to the stored relationship between the two. The wavelength of the light input to the long-period fiber grating element 611 is obtained.

The wavelength monitor 600 according to the present embodiment
Can monitor the wavelength of light in a wavelength band in which the loss characteristic of the long-period fiber grating element 611 monotonically changes. The wavelength monitoring device 600 includes a long-period fiber grating element 611 which is a fiber-type optical component.
And 612, the insertion loss is small and inexpensive.

In this embodiment, since the power of light leaked from the long-period fiber grating element 611 to the outside is detected, light transmitted through the long-period fiber grating element 611 can be further propagated downstream. Therefore, the wavelength monitor device 600 can be inserted on the main line.

(Seventh Embodiment) Next, a seventh embodiment will be described. FIG. 17 is a schematic configuration diagram of an optical product 700 according to the seventh embodiment. An optical product 700 according to the seventh embodiment includes a wavelength monitor device 710, a semiconductor laser light source 720, a power supply 730, a temperature controller 740, and an optical branching element 750, and outputs laser light of a constant wavelength.

The wavelength monitoring device 710 is a wavelength monitoring device according to any one of the first to sixth embodiments described above.
Of the laser light output on 60, the one split by the optical splitter 750 is input, the wavelength of the input laser light is monitored, and an electric signal corresponding to the wavelength is output. The semiconductor laser light source 720 is supplied with power from a power supply 730 and outputs laser light. The wavelength of the laser light depends on the temperature of the semiconductor laser light source 720. The temperature controller 740 adjusts the temperature of the semiconductor laser light source 720 based on the electric signal output from the wavelength monitoring device 710, and controls the wavelength of the laser light output from the semiconductor laser light source 720 to a constant wavelength.

For example, when the semiconductor laser light source 720 is a distributed feedback semiconductor laser light source, the temperature dependence of the oscillation wavelength is about 0.08 nm / ° C. In such a case,
The temperature of the semiconductor laser light source 720
By performing the feedback control so that the wavelength of the laser light monitored by the wavelength monitoring device 710 becomes a constant value, the wavelength of the laser light output from the semiconductor laser light source 720 is stably maintained at a constant value. You.

(Eighth Embodiment) Next, an eighth embodiment will be described. FIG. 18 is a schematic configuration diagram of an optical product 800 according to the eighth embodiment. The optical product 800 according to the eighth embodiment includes a wavelength monitor 810, a semiconductor laser light source 820, a power supply 830, and a temperature controller 840.
And outputs laser light of a constant wavelength.

The wavelength monitoring device 810 is a wavelength monitoring device according to any one of the fourth to sixth embodiments described above, and is provided on the main line 860, and is provided on the main line 860 from the semiconductor laser light source 820. Monitor the wavelength of the laser light output to the controller and output an electric signal corresponding to the wavelength. The semiconductor laser light source 820 is supplied with power from a power supply 830 and outputs laser light. The wavelength of the laser light depends on the temperature of the semiconductor laser light source 820. The temperature controller 840 adjusts the temperature of the semiconductor laser light source 820 based on the electric signal output from the wavelength monitoring device 810, and controls the wavelength of the laser light output from the semiconductor laser light source 820 to a constant wavelength.

Also in this embodiment, the semiconductor laser light source 820
The temperature of the laser light output from the semiconductor laser light source 820 is adjusted to a constant value by adjusting the temperature of the laser light by the temperature controller 840 and performing feedback control so that the wavelength of the laser light monitored by the wavelength monitoring device 810 becomes a constant value. Is kept stable. In particular, in this embodiment, since the wavelength monitor 810 that detects the power of light leaked from the long-period fiber grating element to the outside is used, the wavelength monitor 810 can be inserted on the main line, Light transmitted through the fiber grating element can be propagated further downstream on the main line 860.

The present invention is not limited to the above embodiment, and various modifications are possible. For example, in the second embodiment, the calculation unit 230 calculates the ratio (I _X / (I _X +
The wavelength λ may be obtained based on the value of I _Y )), or the wavelength λ may be obtained based on the value of the ratio (I _X / I _Y ). The same applies to the third and fifth embodiments. Further, the optical product including the wavelength monitoring device is not limited to those described in each of the seventh and eighth embodiments, but may be other types.

[0072]

As described above in detail, according to the first wavelength monitoring apparatus of the present invention, the power of light transmitted through the long-period fiber grating element and detected by the light receiving element depends on the wavelength. The wavelength dependence of the power coincides with the transmission characteristics of the long-period fiber grating element, and changes monotonously in a predetermined wavelength band. The arithmetic unit calculates the wavelength of light within the predetermined wavelength band input to the long-period fiber grating element based on the power detected by the light receiving element.

Further, according to the second wavelength monitoring device of the present invention, the first light-receiving element detected by the first light-receiving element via the long-period fiber grating element and the polarization splitting element.
The power of the polarized component light depends on the wavelength, and the wavelength dependence of the power matches the transmission characteristic of the long-period fiber grating element for the first polarized component, and is monotonic in a predetermined wavelength band. To increase. On the other hand, the power of the light of the second polarization component detected by the second light receiving element via the long-period fiber grating element and the polarization separation element also depends on the wavelength, and the wavelength dependence of the power is long. The transmission characteristic of the periodic fiber grating element coincides with the transmission characteristic of the second polarization component, and decreases monotonously in the predetermined wavelength band. The arithmetic unit obtains the wavelength of the light within the predetermined wavelength band input to the long-period fiber grating element based on the power detected by each of the first and second light receiving elements.

According to the third wavelength monitoring apparatus of the present invention, the power of the first light detected by the first light receiving element via the optical branching element and the first long-period fiber grating element is equal to the wavelength. The wavelength dependence of the power coincides with the transmission characteristic of the first long-period fiber grating element, and monotonically increases in a predetermined wavelength band. On the other hand, the power of the second light detected by the second light-receiving element via the optical branching element and the second long-period fiber grating element also depends on the wavelength. It coincides with the transmission characteristics of the long-period fiber grating element, and monotonically decreases in the above-mentioned predetermined wavelength band. The arithmetic unit calculates the wavelength of the light within the predetermined wavelength band input to the optical branching element based on the power detected by each of the first and second light receiving elements.

According to the fourth wavelength monitoring apparatus of the present invention, the power of light leaked from the long-period fiber grating element to the outside and detected by the light receiving element depends on the wavelength. The wavelength dependence coincides with the loss characteristic of the long-period fiber grating element, and changes monotonously in a predetermined wavelength band. The arithmetic unit calculates the wavelength of light within the predetermined wavelength band input to the long-period fiber grating element based on the power detected by the light receiving element.

According to the fifth wavelength monitoring apparatus of the present invention, the power of light leaked from the first long-period fiber grating element to the outside and detected by the first light receiving element depends on the wavelength. The wavelength dependence of the power coincides with the loss characteristic of the first long-period fiber grating element, and changes monotonously in a predetermined wavelength band. Also,
The power of light leaked from the second long-period fiber grating element provided in series downstream of the first long-period fiber grating element and detected by the second light receiving element depends on the wavelength. The wavelength dependence of the power coincides with the loss characteristic of the second long-period fiber grating element, and changes monotonously in a predetermined wavelength band.
The arithmetic unit obtains the wavelength of the light within the predetermined wavelength band input to the first long-period fiber grating element based on the power detected by each of the first and second light receiving elements.

According to the sixth wavelength monitoring apparatus of the present invention, the light leaked from the first long-period fiber grating element to the outside is input to the second long-period fiber grating, propagates, and receives the light. Detected by the element.
The power of the light detected by the light receiving element depends on the wavelength, and the wavelength dependence of the power matches the loss characteristic of the first long-period fiber grating element and changes monotonously in a predetermined wavelength band. . The arithmetic unit calculates the wavelength of light within the predetermined wavelength band input to the first long-period fiber grating element based on the power detected by the light receiving element.

These wavelength monitoring devices according to the present invention are:
Since a long-period fiber grating element, which is a fiber-type optical component, is used, it is inexpensive, small, and has low insertion loss.

Further, the second, third and fifth embodiments according to the present invention
In each of the wavelength monitoring devices, it is preferable that the temperature dependence of the transmission characteristics (or loss characteristics) of each of the first and second long-period fiber grating elements have substantially the same absolute value and different polarities. In this case, the wavelength can be accurately monitored irrespective of a temperature change or the like.

Further, the optical product according to the present invention comprises the first to sixth optical products.
Of any one of the above. For example, when the optical product also has a semiconductor laser light source, by monitoring the wavelength of the laser light output from the semiconductor laser light source with a wavelength monitoring device, by adjusting the temperature of the semiconductor laser light source, The oscillation wavelength can be kept constant. In particular, any one of the fourth to sixth wavelength monitoring devices can be provided on the main line, and light transmitted through the long-period fiber grating element in the wavelength monitoring device can be propagated further downstream on the main line. .

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a wavelength monitor device according to a first embodiment.

FIG. 2 is a graph showing transmission characteristics of a long-period fiber grating element of the wavelength monitor device according to the first embodiment.

FIG. 3 is a graph showing a relationship between a power I of light detected by a light receiving element of the wavelength monitoring device according to the first embodiment and a wavelength λ.

FIG. 4 is a schematic configuration diagram of a wavelength monitoring device according to a second embodiment.

FIG. 5 is a graph showing transmission characteristics of a long-period fiber grating element of the wavelength monitor according to the second embodiment.

FIG. 6 is a graph showing a relationship between a power _{IX of} light detected by a first light receiving element of the wavelength monitoring device according to the second embodiment and a wavelength λ.

FIG. 7 is a graph showing the relationship between the power I _{Y of} light detected by a second light receiving element of the wavelength monitoring device according to the second embodiment and the wavelength λ.

FIG. 8 is a block diagram of a calculation unit of the wavelength monitor device according to the second embodiment.

FIG. 9 is a schematic configuration diagram of a wavelength monitor device according to a third embodiment.

FIG. 10 shows a first example of the wavelength monitor device according to the third embodiment.
6 is a graph showing transmission characteristics of a long-period fiber grating element.

FIG. 11 shows a second example of the wavelength monitor device according to the third embodiment.
6 is a graph showing transmission characteristics of a long-period fiber grating element.

FIG. 12 is a diagram illustrating the temperature dependence of the transmission characteristics of each long-period fiber grating element in the wavelength monitor according to the third embodiment.

FIG. 13 is a schematic configuration diagram of a wavelength monitor device according to a fourth embodiment.

FIG. 14 is a schematic configuration diagram of a wavelength monitor device according to a fifth embodiment.

FIG. 15 is a diagram illustrating the temperature dependence of the loss characteristics of each long-period fiber grating element in the wavelength monitor according to the fifth embodiment.

FIG. 16 is a schematic configuration diagram of a wavelength monitor device according to a sixth embodiment.

FIG. 17 is a schematic configuration diagram of an optical product according to a seventh embodiment.

FIG. 18 is a schematic configuration diagram of an optical product according to an eighth embodiment.

[Explanation of symbols]

100: wavelength monitor device, 110: long-period fiber grating element, 120: light receiving element, 130: arithmetic unit,
Reference numeral 200: wavelength monitor, 210: long-period fiber grating element, 221: first light receiving element, 222: second light receiving element, 230: arithmetic unit, 240: polarization splitting element, 300: wavelength monitoring apparatus, 311 ... First long-period fiber grating element, 312 ... second long-period fiber grating element, 221 ... first light receiving element, 2
22 second light receiving element, 330 arithmetic unit, 350 optical branching element, 400 wavelength monitor device, 410 long-period fiber grating element, 420 light receiving element, 430
Arithmetic unit, 500: wavelength monitor device, 511, 512: long-period fiber grating element, 521, 522: light receiving element, 530: arithmetic unit, 600: wavelength monitor device, 6
11,612 ... long-period fiber grating element, 6
Reference Signs List 20: light receiving element, 630: calculation unit, 660: refractive index matching member, 700: optical product, 710: wavelength monitoring device, 72
0: semiconductor laser light source, 730: power supply, 740: temperature controller, 750: optical branching element, 800: optical product, 8
10 wavelength monitor device, 820 semiconductor laser light source, 8
30 ... power supply, 840 ... temperature controller.

Claims (14)

[Claims] 1. A long-period fiber grating element having a transmission characteristic that monotonically changes in a predetermined wavelength band and inputting light to be wavelength-monitored; A light-receiving element that receives light transmitted through the fiber grating element and detects the power of the light; and an operation for obtaining a wavelength of the light input to the long-period fiber grating element based on the power detected by the light-receiving element. A wavelength monitor comprising: a unit; 2. A long period for inputting light to be wavelength-monitored, the transmission characteristic having a monotonically increasing first polarization component and a monotonically decreasing second polarization component in a predetermined wavelength band. A fiber grating element; and a polarization splitting element that splits the light transmitted through the long-period fiber grating element into the first polarization component light and the second polarization component light and outputs the separated light. A first light receiving element that receives the light of the first polarization component output from the polarization separation element and detects a power of the light; and a second light reception element that outputs the power of the polarization separation element. A second light receiving element for receiving light of a polarization component and detecting the power of the light; and a long-period fiber grating element based on the power detected by each of the first and second light receiving elements. The wavelength of the light input to Wavelength monitor apparatus characterized by comprising: a calculating unit, the that. 3. An optical splitter for splitting input light into first light and second light and outputting the split light, the first light having a transmission characteristic that monotonically increases in a predetermined wavelength band, A first long-period fiber grating element, which has a transmission characteristic that monotonously decreases in the predetermined wavelength band;
A second long-period fiber grating element for inputting the second light; and a light transmitted through the first long-period fiber grating element among the first lights input to the first long-period fiber grating element. And a first light receiving element for detecting the power of the light, and the second light input to the second long-period fiber grating element is transmitted through the second long-period fiber grating element. A second light receiving element for receiving light and detecting the power of the light; and a wavelength of light input to the optical branching element based on the power detected by each of the first and second light receiving elements. And a calculation unit for obtaining the following. 4. The temperature dependency of the transmission characteristics of each of the first and second long-period fiber grating elements has substantially the same absolute value and different polarities. The wavelength monitor as described in the above. 5. A long-period fiber grating element that has a loss characteristic that changes monotonously in a predetermined wavelength band, and that inputs light to be wavelength-monitored; A light receiving element that receives light leaked from the periodic fiber grating element to the outside and detects the power of the light; and a wavelength of light input to the long period fiber grating element based on the power detected by the light receiving element. And a calculation unit for obtaining the following. 6. The long-period fiber grating element has a predetermined range on the downstream side covered with a medium having a refractive index different from the refractive index of the cladding region, and the light receiving element has a portion covered with the medium. The wavelength monitor according to claim 5, wherein the light leaks from the device. 7. The wavelength monitor according to claim 6, wherein the refractive index of the medium is equal to or greater than the refractive index of the cladding region of the long-period fiber grating. 8. The wavelength monitor according to claim 6, wherein the medium is a resin for coating an optical fiber. 9. The wavelength monitor according to claim 6, wherein the medium is made of the same material as the cladding region of the long-period fiber grating element. 10. A first long-period fiber grating element having a loss characteristic that changes monotonously in a predetermined wavelength band and inputting light to be monitored, and a downstream side of the first long-period fiber grating element. A second long-period fiber grating element having a loss characteristic that changes monotonously in a predetermined wavelength band, and the first long-period fiber grating element of the light input to the first long-period fiber grating element. A first light receiving element that receives light leaked from the periodic fiber grating element to the outside and detects the power of the light; and a second long cycle of light input to the second long cycle fiber grating element. A second light receiving element that receives light leaked from the fiber grating element to the outside and detects the power of the light; and the first and second light receiving elements. Based on the power detected by each light receiving element, a wavelength monitoring device, characterized in that it comprises an arithmetic unit for determining the wavelength of light input to the first long-period fiber grating devices. 11. The temperature dependence of loss characteristics of each of the first and second long-period fiber grating elements has absolute values substantially the same and polarities different from each other. The wavelength monitor as described in the above. 12. A first long-period fiber grating element that has a loss characteristic that changes monotonously in a predetermined wavelength band and receives light to be wavelength-monitored, and leaks from the first long-period fiber grating element. A second long-period fiber grating element for injecting and propagating light, of the light input to the second long-period fiber grating element, receiving light transmitted through the second long-period fiber grating element; A light receiving element for detecting the power of the light; and a calculation unit for obtaining a wavelength of the light input to the first long-period fiber grating element based on the power detected by the light receiving element. Wavelength monitoring device. 13. An optical product having the wavelength monitoring device according to claim 1. Description: 14. An optical product having the wavelength monitoring device according to claim 5 on a main line.