JP2003315160A - Polarization independent wavelength monitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately monitor wavelength of incident lights having different polarization planes. <P>SOLUTION: An incident light is split by beam splitters 2 to 4, and a pair of almost parallel light beams is received through an etalon 6. In addition, the split lights are received directly or through a slope filter 5. A standard wavelength of the incident light is obtained from a wavelength-transmittance characteristic of the slope filter 5, and the amount of wavelength changed from the standard wavelength is calculated from the transmitted light of the etalon 6. An incident angle of the incident light of the splitters 2 to 4 are adjusted so that the polarization dependent variation of the output from the slope filter is smaller than the transmittance variation of the slope filter per a FSR cycle of the etalon 6, and polarization dependent variation of the output from the etalon is smaller than the transmittance variation of the etalon per wavelength resolving power of a wavelength monitor. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for monitoring a wavelength of a laser light source, a device for monitoring a signal light wavelength of optical communication using the laser light source, and an optical communication device and parts in combination with a variable wavelength laser light source. The present invention relates to a wavelength monitor device used for measurement.

[0002]

2. Description of the Related Art Conventionally, an invention disclosed in Japanese Patent Laid-Open No. 2000-223761 is known as a wavelength monitor which has no movable parts inside and can be operated at high speed and has both wide band and high resolution.
The structure proposed by the present invention is shown in FIG. In the present invention, the incident light from the light source is split by the non-parallel beam sampler 101 to obtain two split lights having slightly different angles. By inputting this branched light into the etalon 102, light having wavelength-transmittance characteristics with phases shifted from each other is obtained, and each light is received by the light receiving element to obtain S1 and S2. Further, the transmitted light of the beam sampler 101 is branched by the beam sampler 103 to obtain the other two branched lights. The branched light is received by the light receiving element directly and via the slope filter 104, and S3 and S4 are obtained. The wavelength-transmittance characteristic is made independent of the light intensity by normalizing the optical signals S1 and S2 with the reference optical signal S3. The optical signal S4 that has passed through the slope filter 104 is normalized by the reference optical signal S3, and the reference wavelength of the incident light is obtained from the wavelength-transmittance characteristic of the slope filter 104. Normalized optical signal S transmitted through the etalon 102
For 1 / S3 and S2 / S3, the wavelength variation from the reference wavelength is calculated by alternately using the wavelength-transmittance curve having good linearity. Then add the reference wavelength and the wavelength change,
The exact wavelength of the incident light is obtained.

[0003]

However, in the wavelength monitor according to this conventional example, the beam samplers 101 and 10 are used.
Light is incident on 2 at an angle of about 45 °. Therefore, the branching ratio of the incident light has a large polarization dependency. Therefore, when measuring the wavelength of a light beam whose polarization state is not constant with this wavelength monitor, there is a problem that the branching ratio fluctuates as the polarization state fluctuates, causing an error in the measured value.

The present invention has been made in view of the above-mentioned problems of the prior art, and is capable of performing high-speed measurement without a moving part inside, and is compatible with both wide band and high resolution, is small in size, and is inexpensive. An object is to provide a wavelength monitor whose accuracy does not depend on the intensity and polarization state of the light under measurement.

[0005]

According to a first aspect of the present invention, there is provided a first beam splitter for splitting a light to be measured, and a second beam splitter for splitting a reflected light obtained by the first beam splitter. And a first beam splitter that includes a third beam splitter that splits the reflected light obtained by the second beam splitter, splits the incident light, and includes first and second split lights that differ from the parallel state by a predetermined angle. -A light branching portion for obtaining a fourth branched light, and first and second light emitted from the light branching portion
, An etalon that transmits the branched light, a slope filter that has a characteristic that the transmittance characteristics with respect to the incident wavelength continuously change, and that transmits the fourth branched light emitted from the optical branching portion, and a etalon that transmits the etalon. The first and second photoelectric conversion units that respectively receive the first and second branched lights, the third photoelectric conversion unit that directly receives the third branched light emitted from the optical branch unit, and By dividing each output of the fourth photoelectric conversion unit that receives the fourth branched light transmitted through the slope filter and the first and second photoelectric conversion units by the output of the third photoelectric conversion unit First and second division units for normalizing each, a switching unit for selecting one of output values in a predetermined range among outputs of the first and second division units, and the fourth photoelectric conversion The third division which normalizes by dividing the output of the unit by the output of the third photoelectric conversion unit A wavelength change amount calculation unit that calculates a wavelength change amount of incident light from a predetermined reference wavelength for each cycle of the wavelength-transmittance characteristic of the etalon based on the output from the switching unit; The output of the wavelength calculator and the wavelength change calculator is added to the wavelength calculator that calculates one of the reference wavelengths of the periodic wavelength-transmittance characteristics of the etalon based on the output of the divider. And an adder that calculates the wavelength of the incident light according to F of the etalon.
The polarization dependent variation of the output intensity of the normalized slope filter is smaller than the transmittance variation of the slope filter per SR cycle, and the transmittance variation of the etalon per wavelength resolution of the wavelength monitor. It is characterized in that the incident angles of the light rays on the first to third beam splitters are set so that the polarization-dependent fluctuation amount of the normalized etalon output intensity becomes smaller than that. .

Here, the optical branching section uses the light transmitted through the first and third beam splitters as the first and second branched lights, and the second branched light.
The light that has passed through the beam splitter is used as the third split light,
The light reflected by the third beam splitter can be used as the fourth branched light.

Further, the optical branching unit makes the light transmitted through the first and third beam splitters the first and second branched lights, and the light transmitted through the second beam splitter as the fourth branched light, Three
The light reflected by the beam splitter can be used as the third branched light.

The light splitting unit sets the light transmitted through the second beam splitter as the first split light, the light reflected by the third beam splitter as the second split light, and the first beam splitter The transmitted light can be used as the third branched light, and the light transmitted through the third beam splitter can be used as the fourth branched light.

Further, the optical branching unit defines the light transmitted through the second beam splitter as the first branched light, the light reflected by the third beam splitter as the second branched light, and the first beam splitter. The transmitted light can be the fourth branched light, and the light transmitted through the third beam splitter can be the third branched light.

According to a second aspect of the present invention, in the wavelength monitor according to the first aspect, the optical branching portion has a pair of glass blocks having substantially parallel flat surfaces, and one surface of the glass block is covered. An antireflection plate having an antireflection film vapor-deposited thereon for incidence of measurement light and the second beam splitter are attached to each other, and the first and third beam splitters are attached to corresponding surfaces of the glass block. The slope filter is configured by being attached to one surface of the glass block.

According to a third aspect of the present invention, in the wavelength monitor according to the first aspect, the optical branching portion has a pair of glass blocks having substantially parallel flat surfaces, and one surface of the glass block is to be measured. An antireflection film for allowing light to enter and a film having a function of the second beam splitter are respectively vapor-deposited, and also have functions of the first and third beam splitters on surfaces corresponding to each other of the glass block. Each of the films is formed by vapor deposition, and the slope filter is characterized in that a film having a function of a slope filter is vapor-deposited on one surface of the glass block.

According to a fourth aspect of the present invention, in the wavelength monitor according to any one of the first to third aspects, the transmittance of the first beam splitter is about 25%, and the transmittance of the second beam splitter is about 25%. Is about 33% and the transmittance of the third beam splitter is about 50%.

According to a fifth aspect of the present invention, in the wavelength monitor according to any one of the first to third aspects, the transmittance of the slope filter monotonically increases in a wavelength range to be used,
Or, it has a characteristic of monotonically decreasing.

According to a sixth aspect of the present invention, in the wavelength monitor according to any one of the first to third aspects, the light intensity wavelength characteristics after passing through the etalon are the first branched light and the second branched light. In order to have a phase difference of 90 ° ± 10 ° with the light,
The angle formed by the first and second branched lights is set.

According to a seventh aspect of the present invention, in the wavelength monitor according to the first aspect, the first to third beam splitters,
Further, the slope filter is characterized in that the back surface thereof is obliquely polished and an antireflection film is vapor-deposited.

The invention according to claim 8 of the present application is the wavelength monitor according to claim 1, characterized in that the slope filter is disposed at a slight inclination from a plane perpendicular to the optical axis of the incident light.

The invention according to claim 9 of the present application is the wavelength monitor according to any one of claims 1 to 3, further comprising temperature adjusting means for keeping at least the temperature of the etalon and the slope filter constant. It is a feature.

According to a tenth aspect of the present invention, in the wavelength monitor according to the second aspect, the substrate of the beam splitter, the substrate of the slope filter, the substrate of the antireflection plate, and the glass block have the same refractive index. The wavelength monitor according to claim 2, wherein the wavelength monitor is a material that has.

The invention of claim 11 of the present application is characterized in that, in the wavelength monitor of claim 2, the back surfaces of the substrate of the antireflection plate, the beam splitter, and the slope filter are obliquely polished. To do.

The twelfth aspect of the invention of the present application is the wavelength monitor according to the second or third aspect, characterized in that the wavelength monitor has a collimator which is made of a rod lens and whose end face is directly bonded to the glass block.

The invention of claim 13 of the present application is the same as claims 1 to 1.
In the wavelength monitor according to any one of item 2, the outputs of the first to fourth photoelectric conversion units are sampled at the same timing.

The invention of claim 14 of the present application is the same as claims 1 to 1.
In the wavelength monitor according to any one of 3 above, the etalon is an etalon having a reflective film having a surface reflectance of 10 to 20%.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (Embodiment 1) FIG. 1 is a block diagram showing the configuration and overall configuration of an optical portion of a polarization independent wavelength monitor according to an embodiment of the present invention. In these figures, the optical parts are a collimator 1 for making a light beam parallel, a first beam splitter 2, a second beam splitter 3, a third beam splitter 4, a slope filter 5, an etalon for splitting a light beam. 6, photoelectric conversion elements 7 to 10 such as photodiodes. The beam splitter 2 is on the optical path of the light beam emitted from the collimator 1,
It is arranged at a slight angle θ1 from the direction perpendicular to the light beam. The beam splitter 3 is arranged on the optical path of the reflected light beam of the beam splitter 2 with respect to the light beam from the vertical direction by a small angle θ.
2 Tilt and place. The beam splitter 4 is arranged on the optical path of the reflected light beam of the beam splitter 3 with a slight angle θ3 inclined from the vertical direction with respect to the light beam. These angles θ1 to θ
3 will be described in detail later. These beam splitters 2 to 4 form an optical branching unit that splits light in four directions. Then, the transmittances of the beam splitter 2 are 25%, the beam splitter 3 is 33%, and the beam splitter 4 is 50% so that the intensity of each of the four branched lights becomes equal.
It is desirable to set so that

In order to prevent interference in each optical element, the beam splitters 2, 3, 4 and the slope filter 5 are obliquely polished on the surface of the interference film opposite to the filter vapor deposition surface, and are given a non-reflective coating. is there. The etalon 6 has a thickness of 1 m, for example.
It is a solid etalon in which two layers of reflection film of about ⅛λ of incident light are applied to both sides of a glass plate of m, and here, for example, 1
The reflective film has a low reflectance of about 5%. Etalon 6
Is arranged so that the first branched light transmitted through the beam splitter 2 and the second branched light transmitted through the beam splitter 4 are transmitted side by side. The photodiode 7 is the etalon 6
It is arranged at a position where it can receive the transmitted light of the beam splitter 2 which has transmitted. The photodiode 8 is arranged at a position where it can receive the transmitted light of the beam splitter 4 that has passed through the etalon 6. The photodiode 9 is arranged at a position where the third branched light transmitted through the beam splitter 3 can be received. The slope filter 5 is the fourth reflected by the beam splitter 4.
It is placed on the optical path of the branched light. In order to prevent interference, the slope filter 5 is arranged at a small angle, for example 1 °, from the vertical direction with respect to the incident light. The photodiode 10 is arranged at a position where the transmitted light of the slope filter 5 can be received. In order to eliminate fluctuations in the characteristics of these optical elements, especially the etalon and slope filter, with respect to temperature,
It is preferable to dispose on one substrate or in the constant temperature bath 11 having an adjusting function for keeping the temperature constant.

Next, the configuration of the signal processing portion will be described. The electric signal outputs of the photodiodes 7, 8, 9 and 10 are given to the amplifiers 21 to 24 in the signal processing section, respectively.
The amplifiers 21 to 24 amplify the electric signal from the photodiodes, and constitute the first to fourth photoelectric conversion units together with the photodiodes 7 to 10, respectively. Amplifier 2
The output of 1 is to the divider 25, and the output of the amplifier 22 is to the divider 2
At 6, the output of amplifier 23 is provided to dividers 25 and 26. The divider 25 divides the output of the first branched light branched from the first beam splitter 2 by the output of the reference third branched light branched from the second beam splitter 3 to output the output. To normalize. Divider 2
Reference numeral 6 normalizes the output of the second branched light branched from the third beam splitter 4 by dividing the output of the second branched light by the output of the third branched light serving as a reference. The outputs of the dividers 25 and 26 are given to the switching unit 27.
The switching unit 27 alternately uses the regions of the etalon 6 having good linearity by switching the outputs of the two split calculation forces excluding the peak portion. The output of the switching unit 27 is input to the A / D converter 28. A / D converter 28
Is for converting an input into a digital signal, and a read-only memory (hereinafter, referred to as ROM) 29 outputs the digital value as an address signal for a wavelength variation within a predetermined period as described later. Here, the A / D converter 28 and the read-only memory 29 are the wavelength of the etalon-
A wavelength change amount calculation unit that calculates a change amount from the wavelength of incident light from a predetermined reference wavelength is configured for each cycle of the transmittance characteristic.

On the other hand, the outputs of the amplifiers 23 and 24 are given to the divider 30, respectively. The divider 30 divides the fourth branched light by the output of the third branched light to normalize it, and the division calculation power is given to the A / D converter 31. The output of the A / D converter 31 is a digital value obtained by normalizing the characteristics of the slope filter 5. The normalized transmittance-wavelength characteristic of the slope filter 5 is held in advance in the ROM 32, and the output of the A / D converter 31 is given to the ROM 32 as an address signal. A / D converter 31 and ROM 32
Is the wavelength of the etalon based on the output of the third division unit −
A wavelength calculation unit that calculates one of the reference wavelengths of the transmittance characteristics is configured. The wavelength data read by the ROM 32 is given to the addition unit 33. In addition, the addition unit 33 is
By adding the outputs of M29 and M32, the wavelength of the incident light is calculated and output. Also constant temperature layer 11
It is assumed that each of the optical elements therein is held by the temperature control unit 34 so as to have a predetermined temperature.

Next, the operation of the wavelength monitor according to this embodiment will be described. When the laser beam to be measured enters the first beam splitter 2 from the optical fiber through the collimator 1, a part of the light is reflected on the surface and the rest is transmitted. The reflected light is incident on the second beam splitter 3 as shown in the figure, a part of which is transmitted and the rest is reflected. Further, the reflected light is further applied to the third beam splitter 4 arranged in parallel with the beam splitter 2, a part of which is transmitted and the rest is reflected. Since the transmittance of each beam splitter is determined as described above, the light intensity of each branched light becomes substantially equal. First of these
The second branched light is incident on the etalon 6 and is received by the photodiodes 7 and 8 via the etalon 6. The third branched light is received by the photodiode 9, and the fourth branched light is received by the photodiode 10 via the slope filter 5. These branched lights are sampled at the same timing.

The levels of the first to fourth branched lights are I1 to I
4, and the outputs obtained from the amplifiers 21 to 24 by photoelectrically converting them are S1 to S4. The characteristics of the etalon 6 with respect to the wavelength of the transmitted light periodically fluctuate, and the period is determined by the free spectrum range (FSR) of the etalon. If this FSR is set to 100 GHz, the fluctuation period becomes about 0.8 nm. The transmittance T of the etalon 6 is calculated by the following equation (1), where R is the reflectance of the boundary surface.

[Equation 1] However, A is represented by the reflectance R as shown in the following equation (2).

[Equation 2] δ is the refractive index of the etalon 6, n is its thickness, φ is the angle of incidence on the etalon 6, and λ is the wavelength of the light incident on the etalon 6.
Then, it is expressed by the following equation (3).

[Equation 3]

As described above, when the reflectance R of the etalon 6 is set to 0.15, for example, the transmittance characteristic represented by the equation (1) becomes close to a sine curve. Therefore, the normalized output obtained from the divider 25 is as shown in FIG. Similarly, the normalized output obtained from the divider 26 is shown in FIG.
It becomes what is shown in (b). These transmittance characteristics are out of phase. This phase shift corresponds to the angular difference between the first and second branched lights that are incident lights on the etalon 6. Therefore, the angle of the beam splitter 3 with respect to the beam splitter 2 is slightly tilted, for example, 0.1 °. As a result, the light rays passing through the etalon 6 are set to be slightly deviated from parallel, and the phase difference between the two light rays is set depending on the installation angle of the etalon 6. Further, the phase difference of the wavelength-transmittance characteristic obtained from the etalon 6 is preferably a phase difference within a range of 90 ° ± 10 ° in order to alternately use parts having good linearity, and the phase difference of 90 ° Most preferably.

The switching unit 27 alternately switches from the outputs of the dividers 25 and 26 to the portion with good resolution shown in bold in FIG. That is, at a certain wavelength λ1, λ5, λ9 ... The transmittance of the branched light I1 transmitted through the etalon 6 has a peak, and the normalized value A is 1.0, that is, 0.4n from this position.
It is assumed that the transmittance is lowest at wavelengths λ3, λ7, λ11, ... λ1 and λ5, λ5
The distance between λ9 and λ9 is 0.8 nm as described above. The switching unit 27 selects the output of the divider 25 if the transmittance is in the range of 0.956 to 0.744, and selects the output of the divider 26 if it has any other value. In that case, the divider 26 is in the range of transmittance 0.956 to 0.744. By doing so, it is possible to switch the high-resolution split calculation power, which is alternately shown in bold according to the wavelength of the incident light.

On the other hand, the slope filter 5 is assumed to have a slope-like wavelength-transmittance characteristic that monotonously changes in the incident wavelength range 1500 to 1600 nm. The photodiodes 9 and 10 receive the third and fourth branched lights, and the amplifiers 23 and 24 convert them into outputs S3 and S4. Then, the characteristic of the slope filter 5 can be normalized by dividing the output S4 of the fourth branched light by the output S3 of the third branched light by the divider 30. FIG. 3A shows this normalized slope filter 5
3B shows an enlarged view of a part thereof, and the wavelength of incident light can be roughly calculated based on the normalized characteristics. The A / D converter 31 converts this into a digital value and reads the discrete wavelength data λ1, λ2, λ3, ... Corresponding to the digital value from the ROM 32, so that FIG. 2A or FIG. The wavelength of either the maximum value or the minimum value of the transmission characteristics of the etalon shown in is selected. At this time, the wavelength to be read is changed depending on which output of any of the dividers 25 and 26 is selected. For example, when the divider 25 is selected, the wavelength-transmittance characteristic at that time causes the data of the shortest wavelength closest to λ1, λ3, λ5 ... to be read as the reference wavelength λr. For example, when it is in the range of λ5 to λ7, the reference wavelength λr is set to λ5. And from the output of the divider 25, λ5
The change Δλ in wavelength from is calculated. When the divider 26 is selected, the data of the wavelength on the short side closest to λ2, λ4, λ6 ... Is read. For example λ2 to λ
When it is within the range of 4, the reference wavelength λr is set to λ2.
Then, from the output of the divider 26, the change Δ in wavelength from λ2
Calculate λ. Thus, based on the transmittance which is the output value of the divider 25 or 26, the reference wavelength λr, for example, λ5 or λ
It is possible to read out different wavelengths Δλ from 2. By adding the reference wavelengths λr and Δλ in the adder 33, the wavelength of the incident light can be accurately calculated and output.

The wavelength read from the ROM 32 is shown in FIG.
Only the peak value of each wavelength-transmittance characteristic of (a) and (b), that is, λ1, λ5 ... Or λ4, λ8 ... Is set, and Δλ is set according to the slope of the rising or falling of the transmittance characteristic. The accurate wavelength value may be obtained by adding or subtracting the value of. Further, the slope filter 5 may hold the data of λn exactly as it is. Alternatively, the transmittance characteristics for a large number of wavelengths having a higher resolution may be held, and the peak values of the two wavelength-transmittance characteristics shown in FIG. 2 may be calculated by linear interpolation or the like. Good. In addition, the variable wavelength range is wide, as shown in FIG.
When the period of the wavelength-transmittance characteristic of the etalon shown in (b) is not a constant value and the period changes according to the wavelength, the period is changed according to the approximate value of the wavelength obtained from the slope filter 5. Alternatively, two wavelength-transmittance characteristics may be switched to calculate Δλ.

Further, in this embodiment, a solid etalon having a coating with a reflectance of 15% is used as the etalon 6. If the reflectance of the etalon 6 is increased, the fluctuation range of the transmittance is increased, but the deviation from the sine wave waveform is increased and the error in calculating the wavelength deviation Δλ by combining the two characteristics is increased. Further, if the reflectance is made smaller, the transmission characteristic becomes closer to that of a sine wave, but the amplitude value becomes smaller, so the resolution becomes lower. Therefore, this reflectance is, for example, 10
It is preferably in the range of ˜20%, and here, the reflectance of the etalon is set to 15%. The FSR can be set to 100 GHz by setting the thickness of the etalon to 1 mm, for example. The larger the thickness, the shorter the cycle of the transmission characteristic, but if the resolution of the slope filter 5 is poor, there is a possibility that an incorrect position will be the reference wavelength. Further, if the thickness of the etalon is reduced, the period of the wavelength-transmittance characteristic of the etalon becomes longer and the resolution of wavelength detection is lowered. Therefore, for example, the transmission characteristic has a period of 0.75 to 0.85.
It is preferably in the range of nm. Further, the etalon is not limited to a solid etalon and may be a void etalon composed of a pair of parallel flat plates.

As a general physical phenomenon, when light is incident on a medium having a different refractive index from another medium, the reflectance and the transmittance vary depending on the incident angle of the light beam, and the variation amount is the polarization of the incident light beam. It depends on the condition. FIG. 4 shows the incident angle dependence of reflectance for S-polarized light and P-polarized light when light is incident on a glass from a medium having a refractive index of 1 to a medium having a refractive index of 1.5, for example, from the air. . The same phenomenon occurs in the beam splitters 2 to 4 and the slope filter 5 used in this embodiment. For example, FIG. 5 shows the reflectance with respect to the incident angle when S-polarized light and P-polarized light are made incident on the beam splitter 3. As described above, in the present embodiment, the beam splitters are arranged so as to be opposed to each other with a slight angle offset, and the incident angle of the light beam to the beam splitter is made as small as possible, whereby the polarization dependence of the entire optical system is reduced. Sex is reduced. For example, when the incident angle θ1, θ2 or θ3 is 3 °, the reflectances of the S-polarized light and the P-polarized light change by only 0.15%. However, the photodiode 7 associated with the change in the polarization state of the measured light
The light intensity measured at -10 varies. Therefore, the angle of incidence on the beam splitter is determined as follows.

In FIG. 6, the transmittance of the slope filter 5 with respect to the wavelength is represented by a curve A, the transmittance of the etalon 6 is represented by a curve B, and the change amount of the transmittance of the slope filter 5 per one cycle (FSR) of the etalon is represented by a curve C. ing. Further, FIG. 7 is an enlarged graph showing the wavelength range of the curve B showing the transmittance of the etalon. When the slope filter 5 and the etalon 6 having such an amount of change in transmittance are combined and the measurement range is from 1525 nm to 1565 nm, the incident angles θ1 to θ3 are determined by the following first and second conditions. . (1) First Condition Since the change amount of the transmittance of the slope filter is about 0.07 dB at the lowest portion from the curve C, the fluctuation of the intensity of the measured light is allowed to be less than this, that is, 0.06 dB. It is assumed that the intensity fluctuation of the measured light is determined only by the polarization state. Here, the received light output S3 is affected by the reflection of the beam splitter 2 and the transmission of the beam splitter 3, and the received light output S4 is affected by the reflection of the beam splitters 2, 3, 4 three times. Therefore, S4 / S of the normalized output in the divider 30
With respect to the polarization dependence of 3, the reflection of one time is canceled, and the influence of reflection twice and transmission once is affected. FIG. 8 is a diagram showing the dependence of the reflectance on the incident angle of P-polarized light and S-polarized light of the beam splitter. FIG. 9 is a diagram showing the dependence of the P-polarized light and S-polarized light transmittance of these beam splitters on the incident angle. Using this beam splitter, the total fluctuation rate of two reflections and one transmission is 0.06.
In order to make it equal to or lower than dB, the incident angle is set to 4.5 ° as shown in FIG. By doing this, 0.015 dB x from Fig. 8
2 = 0.03 dB, which is about 0.03 dB at 4.5 ° from FIG. Therefore, the beam splitters 2, 3,
It is necessary to set the incident angles θ1, θ2, θ3 of the light rays on the beam No. 4 to 4.5 ° or less.

(2) Second Condition Next, for example, the wavelength resolution of the wavelength monitor is set to 10 pm. Then, as shown in FIG. 7, the transmittance of the etalon shows a characteristic, for example, 155 with high resolution and good linearity.
Assuming that the range of 0.1 to 1550.3 is used, the transmittance of the etalon is −200 in this range of 200 pm.
It has changed to 2.4 dB. Therefore, wavelength resolution 10p
The amount of change in the transmittance of the etalon per m is about 0.1 from Fig. 7.
It becomes dB. Therefore, the output S1 is affected by the polarization of one transmission of the beam splitter 2 on the optical path, and the output S3 is affected by the polarization of one reflection and one transmission of the beam splitter. Therefore, the polarization dependence of the normalized outputs S1 / S3 of the etalon becomes only one reflection, because one transmission is canceled. Further, the output S3 of the other etalon is affected by two reflections and one transmission, so that it is canceled out and the normalized output S of the etalon is S3.
2 / S3 is also affected by one reflection. Therefore, when the beam splitter having the angle-dependent characteristics of the P-polarized light and S-polarized light transmittance shown in FIG. 9 is used, the angle at which the difference between the S-polarized light and the P-polarized light is 0.1 dB is about 8 °. Therefore, it is necessary to set the incident angle of the light beam on the beam splitter to 8 ° or less.

Therefore, from the above two conditions, in this case,
Incident angles θ1, θ2, θ on the beam splitters 2, 3, 4
No. 3 needs to be the following conditions. 0 <θ1 <θ2 <θ3 ≦ 4.5 °

These conditions depend on the type of etalon, FSR,
It goes without saying that it changes depending on the slope of the slope filter, the required wavelength resolution, and the like. Although the angle difference between θ1 and θ2 is 0.1 °,
It suffices that a phase difference of 90 ° ± 10 ° can be generated in the change of the intensity of the light beam, and θ1 and θ2 may be other angles as long as they are within the above range.

(Second Embodiment) Next, a second embodiment of the present invention will be described. In this embodiment, as shown in FIG. 10, the optical system for processing the light split by the beam splitters 2 to 4 is changed. This Embodiment 2
Then, as shown in the figure, the light transmitted through the beam splitters 2 and 4 is made incident on the etalon 6 as first and second branched lights. In addition, the light transmitted through the second beam splitter 3
The branched light is received by the photodiode 10 via the slope filter 5. The light reflected by the third beam splitter 4 is used as the third branched light and is received by the photodiode 9. Other configurations are the same as those in the first embodiment.

Next, the angle of incidence on the beam splitter will be described. In this case as well, it is determined by the first and second conditions described above. (1) First Condition The received light output S3 is affected by the three reflections of the beam splitters 2, 3 and 4, and the received light output S4 is affected by the reflection of the beam splitter 2 and the transmission of the beam splitter 3. Therefore, the polarization dependence of the normalized output S4 / S3 in the divider 30 is affected by one reflection and one transmission, because one reflection is canceled. Therefore, similarly to the first embodiment, the incident angles θ1, θ2, θ3 need to be 4.5 ° or less. (2) If the second conditional wavelength resolution is the same as that of the first embodiment, the output S1 of the etalon is affected by the polarization of one transmission of the beam splitter 2, and the output S3 is polarized by three reflections of the beam splitter. It is affected by wave dependence. Therefore, the normalized output S of the etalon
1 / S3 is affected by three reflections and one transmission. The output S2 of the etalon is affected by two reflections and one transmission. Therefore, the normalized output S2 / S3 is affected by one reflection and one transmission. Therefore, the normalized outputs S1 / S3 are more susceptible to the polarization dependence. From FIG. 8, when the incident angle is 5 °, the amount of change from the reflectance is about 0.02 dB × 0.06.
9 dB from FIG. 9, which is about 0.04 dB, and the sum of these is 0.1 dB. Therefore, the angle of incidence on the beam splitter must be 5 ° or less.

Therefore, in this case, from the condition 1, the incident angles θ1, θ2, and θ3 to each beam splitter must be 4.5 ° or less.

(Third Embodiment) Next, a third embodiment of the present invention will be described. In this embodiment, as shown in FIG. 11, the optical system for processing the light split by the beam splitters 2 to 4 is changed. As shown in FIG. 11, the beam is reflected by the beam splitter 2 and is reflected by the beam splitter 3.
The light transmitted through and the light reflected by the beam splitters 2, 3 and 4 are incident on the etalon 6 as first and second branched lights. The light transmitted through the etalon 6 is the same as in the first embodiment.
The light is received by the photodiodes 7 and 8. The light transmitted through the beam splitter 2 is directly received by the photodiode 9 as the third branched light. The light reflected by the beam splitters 2 and 3 and transmitted through the beam splitter 4 is received by the photodiode 10 as the fourth branched light via the slope filter 5. Other configurations are similar to those of the first embodiment.

Next, under the same requirements as in the above-mentioned embodiment,
The angle of incidence on the beam splitter will be described. Regarding the first condition, the normalized output S4 /
The polarization dependence of S3 is two reflections, and the angle of incidence on the beam splitter is 6 ° or less from FIG. As the second condition, the output obtained by normalizing the two inputs to the etalon 6, S,
Of 1 / S3 and S2 / S3, it is S2 / S3 that receives the polarization dependence greatly, and this is three reflections and one transmission. Therefore, similarly, the incident angle to the beam splitter is set to 5 ° or less according to FIGS. 8 and 9. Therefore, in this case, from the second condition, it is necessary that the incident angles θ1, θ2, θ3 on the beam splitter be 5 ° or less.
This makes it possible to obtain the same effects as those of the first embodiment.

(Fourth Embodiment) In the fourth embodiment, the position of the slope filter is different from that of the third embodiment. That is, as shown in FIG. 12, the light reflected by the beam splitter 2 and transmitted through the beam splitter 3 and the light reflected by the beam splitters 2, 3 and 4 are first and second
It is incident on the etalon 6 as the branched light of. The light transmitted through the etalon 6 is received by the photodiodes 7 and 8 as in the first embodiment. The light transmitted through the beam splitter 2 is received by the photodiode 10 as the fourth branched light via the slope filter 5. Beam splitters 2 and 3
The light reflected by the beam splitter 4 and transmitted through the beam splitter 4 is directly received by the photodiode 9 as the third branched light.

Next, the angle of incidence on the beam splitter will be described under the same requirements as in the above-described embodiment. As a first condition, the normalized output S4 / S3 of the slope filter is for two reflections, and the incident angle on the beam splitter is 6 ° or less. As the second condition, of the two normalized inputs to the etalon 6, S1 / S3 and S2 / S3 have the greatest polarization dependence, and S2 / S3 has three reflections.
Times. Therefore, according to FIGS. 8 and 9, the angle of incidence on the beam splitter is set to 6.5 ° or less. Therefore, in this case, from the first condition, the incident angle θ1 to the beam splitter is
θ3 needs to be 6 ° or less. This makes it possible to obtain the same effects as those of the first embodiment.

(Fifth Embodiment) Next, a fifth embodiment of the present invention will be described. In this embodiment, a glass block 41 is used instead of arranging three beam splitters as a light branching part. Then, a glass substrate having a film splitter function and a glass substrate having an antireflection (AR) coating is attached to the glass block 41. These glass substrates preferably have the same refractive index as the glass block. That is, as shown in FIG. 13, an AR substrate 42 having an antireflection coating is attached to the surface of the glass block 41 on which light is incident from the collimator 1. A beam splitter plate 43 having a first beam splitter vapor-deposited on its surface is arranged along the optical axis, and a beam splitter plate 44 serving as a second beam splitter is provided on the symmetrical surface of the glass block along this reflecting surface. paste. Further, a beam splitter plate 45 serving as a third beam splitter is attached to a position where the reflected light on the other surface of the glass block is received, and a slope filter 46 is attached to a position where the reflected light is received. It is preferable that the beam splitter plates 43, 44, and 45 that serve as the first to third beam splitters have transmittances of 25%, 33%, and 50%, respectively, as described above.

In this embodiment, the glass block 41 is used.
Is a glass block having parallel surfaces, and one of the beam splitters 43 and 45 among the beam splitters to be attached to the surfaces on both sides thereof is obliquely (for example, 1 °) polished and attached, The emitted light can be shifted. Alternatively, instead of forming the glass block 41 into parallel glass, the opposite surfaces of the glass plate may be slightly obliquely polished to form a glass block, and parallel beam splitters may be attached. By doing so, as described above, the outputs of the photodiodes 7 and 8 are 90% as shown in FIG.
It can be configured to have a phase difference of °. Other configurations are similar to those of the first embodiment.

According to this embodiment, the incident angle can be made smaller, the effect of reducing the polarization dependence is increased, and the device itself can be miniaturized. Further, as compared with the case where the beam splitter is used as in the first to fourth embodiments, the optical axis alignment becomes unnecessary, and the effect of reducing the man-hour required for production can be obtained.

(Sixth Embodiment) Next, a sixth embodiment of the present invention will be described with reference to FIG. In this embodiment, a glass block 51 similar to that of the fifth embodiment is provided.
Instead of attaching a slope filter or a beam splitter to the glass block 51, the glass block 51
In addition to forming the non-reflective coating 52 on the surface, a film having the functions of the beam splitters 53, 54, 55 and the slope filter 56 is formed. In this case, the outputs of the photodiodes 7 and 8 are 90% as shown in FIG.
It is configured to have a phase difference of °. Other configurations are similar to those of the fifth embodiment. In this case as well, the same effect as that of the fifth embodiment can be obtained, and in addition, the work of attaching a filter or the like to the glass block can be omitted.

(Seventh Embodiment) Next, a seventh embodiment of the present invention will be described with reference to FIG. In this embodiment, the collimator 1 is directly connected to the glass block 51. In this case, the glass block connecting the collimator 1 is obliquely cut to avoid the influence of reflected light. Other configurations are similar to those of the sixth embodiment. Also in this case, the same effect as that of the sixth embodiment can be obtained.

In the fifth to seventh embodiments, the positions of the beam splitter, the slope filter, etc. attached to the glass block are changed as shown in FIGS. 10 to 12, and the positions of the corresponding etalons and photodiodes are changed. Needless to say, the same effect can be obtained.

[0052]

As described above in detail, according to the inventions of claims 1 to 14, the wavelength of the incident light can be accurately monitored regardless of the polarization state of the incident light. The effect is obtained.

According to the wavelength monitor of claims 2 and 3, in addition to such an effect, the incident angle can be reduced,
It is possible to downsize the optical system and simplify the optical axis alignment. Moreover, the excellent effect that the number of parts is reduced and the reliability associated therewith can be improved is obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing an overall configuration of a polarization plane independent type wavelength monitor according to a first embodiment of the present invention.

FIG. 2 is a graph showing normalized wavelength-transmittance characteristics of an etalon according to the present embodiment.

FIG. 3 is a graph showing wavelength-transmittance characteristics of the normalized slope filter of the present invention.

FIG. 4 is a graph showing a change in reflectance with respect to an incident angle for each polarization state of light when light is incident on a glass layer from air.

FIG. 5 shows S-polarized light and P-polarized light with respect to an incident angle of a beam splitter
It is a graph which shows the change of the reflectance with respect to polarized light.

FIG. 6 is a graph showing changes in transmittance of a slope filter and an etalon and changes in transmittance of the slope filter with respect to wavelength.

FIG. 7 is a graph enlarging and showing transmittance wavelength characteristics of an etalon.

FIG. 8 is a graph showing incident angle dependence characteristics of reflectance of P-polarized light and S-polarized light of a beam splitter.

FIG. 9 is a graph showing incident angle dependence characteristics of transmittances of P-polarized light and S-polarized light of a beam splitter.

FIG. 10 is a block diagram showing an overall configuration of a wavelength monitor according to a second embodiment of the present invention.

FIG. 11 is a block diagram showing an overall configuration of a wavelength monitor according to a third embodiment of the present invention.

FIG. 12 is a block diagram showing an overall configuration of a wavelength monitor according to a fourth embodiment of the present invention.

FIG. 13 is a block diagram showing an overall configuration of a wavelength monitor according to a fifth embodiment of the present invention.

FIG. 14 is a block diagram showing a configuration of an optical system portion of a wavelength monitor according to a sixth embodiment of the present invention.

FIG. 15 is a block diagram showing a configuration of an optical system portion of a wavelength monitor according to a seventh embodiment of the present invention.

FIG. 16 is a schematic diagram showing an example of a conventional wavelength monitor.

[Explanation of symbols]

1 Collimator 2, 3, 4 beam splitter 5 slope filter 6 etalon 7,8,9,10 Photodiode 11 Constant temperature layer 21-24 amplifier 25,26,30 divider 27 Switching unit 28,31 A / D converter 29, 32 ROM 33 Adder 34 Temperature controller 41, 51 glass block 42 AR substrate 43,44,45 Beam splitter plate 46 Slope filter plate 52 Anti-reflection coating 53,54,55 beam splitter 56 slope filter

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Park Sung-she             5823 Tonokamisaka, Komaki City, Aichi Prefecture             Suntec Photonics Laboratory Co., Ltd.             Within (72) Inventor Sing Villaham Pal             5823 Tonokamisaka, Komaki City, Aichi Prefecture             Suntec Photonics Laboratory Co., Ltd.             Within F term (reference) 2G020 CB23 CC23 CD16 CD22 CD39                 2H048 GA09 GA13 GA24 GA48 GA61

Claims (14)

[Claims] 1. A first beam splitter that splits a light to be measured, a second beam splitter that splits a reflected light obtained by the first beam splitter, and a reflected light obtained by the second beam splitter. An optical branching unit that includes a third beam splitter that splits the incident light, splits the incident light, and obtains first to fourth branched lights including first and second branched lights that differ from each other by a predetermined angle from the parallel state, An etalon for transmitting the first and second branched lights emitted from the light branching part, and a fourth etalon having a characteristic in which the transmittance characteristic with respect to the incident wavelength continuously changes. A slope filter that transmits branched light, first and second photoelectric conversion units that respectively receive the first and second branched lights that have transmitted the etalon, and third branched light emitted from the optical branching unit. And a third photoelectric conversion unit for directly receiving light , A fourth photoelectric conversion unit that receives the fourth branched light that has passed through the slope filter, and each output of the first and second photoelectric conversion units is divided by the output of the third photoelectric conversion unit. The first and second dividers, which normalize each of them, and a switching unit that selects one of the output values of a predetermined range among the outputs of the first and second dividers, and the fourth. A third division unit that normalizes the output of the photoelectric conversion unit by dividing it by the output of the third photoelectric conversion unit, and each cycle of the wavelength-transmittance characteristic of the etalon based on the output from the switching unit. One of a wavelength change amount calculation unit that calculates a wavelength change amount of incident light from a predetermined reference wavelength for each, and a periodic wavelength-transmittance characteristic of the etalon based on the output of the third division unit. And a wavelength calculation unit that calculates the reference wavelength of the output of the wavelength calculation unit and the wavelength change amount calculation unit. And an addition unit that calculates the wavelength of incident light by adding, and the polarization-dependent variation of the output intensity of the slope filter normalized by the transmittance change amount of the slope filter per FSR cycle of the etalon. The amount is smaller, and the polarization dependent variation of the normalized output intensity of the etalon is smaller than the variation of the transmittance of the etalon per wavelength resolution of the wavelength monitor. A wavelength monitor characterized in that an incident angle of a light beam on a third beam splitter is set. 2. The anti-reflection coating, wherein the light branching portion has a pair of glass blocks having substantially parallel flat surfaces, and an anti-reflection film is vapor-deposited on one surface of the glass block for allowing light to be measured to enter. A plate and the second beam splitter are attached, and the first and third beam splitters are attached to the surfaces of the glass block corresponding to each other, and the slope filter is The wavelength monitor according to claim 1, wherein the wavelength monitor is attached to one surface of the glass block. 3. The light branching section includes a pair of glass blocks having substantially parallel flat surfaces, an antireflection film for allowing light to be measured to enter one surface of the glass block, and the second block. A film having a function of a beam splitter is vapor-deposited, and a film having a function of the first and third beam splitters is vapor-deposited on corresponding surfaces of the glass block. The wavelength monitor according to claim 1, wherein a film having a function of a slope filter is deposited on one surface of the glass block. 4. The transmittance of the first beam splitter is about 25%, and the transmittance of the second beam splitter is about 33%.
%, And the transmittance of the third beam splitter is about 50%. 4. The wavelength monitor according to claim 1, wherein 5. The wavelength monitor according to claim 1, wherein the slope filter has a characteristic that its transmittance monotonously increases or monotonically decreases in a wavelength range to be used. 6. The wavelength characteristic of light intensity after passing through the etalon is 90 ° between the first branched light and the second branched light.
The angle formed by the first and second branched lights is set so as to have a phase difference of ± 10 °.
The wavelength monitor according to any one of 1. 7. The first to third beam splitters and the slope filter have their back surfaces obliquely polished,
The wavelength monitor according to claim 1, wherein an antireflection film is vapor-deposited. 8. The wavelength monitor according to claim 1, wherein the slope filter is arranged so as to be slightly inclined with respect to a plane perpendicular to the optical axis of the incident light. 9. The wavelength monitor according to claim 1, further comprising temperature adjusting means for keeping at least the temperatures of the etalon and the slope filter constant. 10. The wavelength according to claim 2, wherein the substrate of the beam splitter, the substrate of the slope filter, the substrate of the antireflection plate, and the glass block are materials having the same refractive index. monitor. 11. The wavelength monitor according to claim 2, wherein the substrate of the antireflection plate, the beam splitter, and the substrate of the slope filter have their back surfaces obliquely polished. 12. The wavelength monitor according to claim 2, further comprising a collimator which is made of a rod lens and whose end surface is directly adhered to the glass block. 13. The wavelength monitor according to claim 1, wherein the outputs of the first to fourth photoelectric conversion units are sampled at the same timing. 14. The etalon has a surface reflectance of 10
The wavelength monitor according to any one of claims 1 to 13, which is an etalon having a reflection film of 20% to 20%.