JP3512974B2 - Laser light source wavelength monitor - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength monitor device for monitoring the wavelength of a laser light source such as a semiconductor laser used for optical communication or the like.

[0002]

2. Description of the Related Art In the present optical communication, wavelength multiplexing communication is used in which optical signals having a large number of wavelengths are multiplexed and communicated with each other to significantly increase the transmission amount as compared with the case of using a single wavelength light. Methods are being considered. In order to realize wavelength division multiplexing communication, laser light of multiple wavelengths is transmitted at intervals of, for example, 1 nm or less within a relatively narrow wavelength band in which an optical signal can be amplified as it is. Therefore, the wavelength of a laser light source can be easily monitored. There is a need to. Also, in optical information processing and optical measurement, it is an important issue to accurately recognize the wavelength of the laser light source.

In order to identify the wavelength of the laser light source, an optical wavelength meter is used which monitors the wavelength by converting the difference from the reference wavelength using an optical interferometer into an electric signal for calculation. Has been. An optical spectrum analyzer for optical spectroscopy is also used, and a spectroscopic device using a grating or a variable filter is used.

[0004]

However, although high accuracy can be obtained by such a conventional interferometer method,
There are drawbacks in that it has moving parts, is expensive, and is difficult to miniaturize. Further, the optical spectrum analyzer has a wide range of applications, but it has a drawback that it is expensive and difficult to miniaturize it by using a grating or a filter.
Further, the spectroscopic device configured to receive light by the photodiode array has a feature that there is no movable part, but has a drawback that the resolution is low and a highly accurate wavelength detection characteristic cannot be obtained.

Particularly in the wavelength division multiplexing communication system, the wavelength range of the light source used is often as narrow as several tens of nm.
Within that range, it is preferable that the wavelength can be accurately monitored with a resolution of, for example, 1 nm or less. However, such a wavelength monitor device has not been realized.

The present invention has been made in view of such conventional problems, and provides a wavelength monitor device for a laser light source capable of accurately monitoring the incident wavelength with an extremely simple structure. With the goal.

The invention according to claim 1 of the present application is arranged between the laser light source and the optical filter, and an optical filter which receives the light of the laser light source and transmits the light of a predetermined wavelength and reflects the other light.
Provided to cut off the central transmission wavelength of the optical filter
Difference between outputs of the first and second light receiving elements, and a cut filter having a wavelength, first and second light receiving elements that respectively receive light transmitted through the optical filter and light reflected by the optical filter On the basis of the output ratio calculated by the output ratio calculating means and an output ratio calculating means for calculating the output ratio by dividing by the sum of the outputs of the first and second light receiving elements. Wavelength output means for outputting the wavelength of the laser light source in a range in which the output changes with respect to the input.

In the invention of claim 2 of the present application, the optical filter is constructed by alternately laminating low refractive index films and high refractive index films having an optical thickness of λ / 4 with respect to the transmission wavelength λ. It is a characterized interference light filter.

In the invention of claim 3 of the present application, the interference light filter is such that its optical thickness is continuously changed so that the transmission wavelength λ continuously changes in a predetermined direction of the substrate. The wavelength monitor device further comprises a slide adjusting mechanism for continuously changing the incident position of the incident light from the laser light source to the interference light filter in the predetermined direction.

[0010]

According to the present invention having such characteristics,
Cut fills laser light of unknown wavelength within measurable range
Incident on the optical filter via the filter. Center transmission of optical filter
Over wavelength cut Filter cut Filter cut off
By setting the wavelength, the wavelength tunability of the optical filter
Only one slope part is specified as the wavelength monitor range
To do. Since this filter transmits light having a predetermined wavelength and reflects the other light, the transmitted light and the reflected light are received by the first and second light receiving elements, respectively, and the output ratio calculation means outputs the first and second light receiving elements. The output ratio is normalized by dividing the difference between the outputs of 1 and 2 by the sum of the outputs of the first and second light receiving elements. Then, the emission ratio of the laser light source can be monitored by giving the output ratio to the wavelength output means and converting it into wavelength data. The invention of claim 2 realizes such an optical filter by an interference optical filter made of a multilayer film. Further, as described in claim 3, the multilayer interference light filter is a variable wavelength interference light filter configured such that the transmission wavelength continuously changes in a predetermined direction, and the light receiving position is changed. With this, the wavelength range in which the laser light can be monitored can be changed.

[0012]

1 is a block diagram showing the overall configuration of a wavelength monitor device according to a first embodiment of the present invention. This wavelength monitor has an optical branching means 1 for branching the incident light, and the incident light is first given to a cut filter 2 as shown in the figure. The cut filter 2 blocks light having a wavelength equal to or shorter than or equal to a predetermined wavelength, and the light passing through the cut filter 2 is given to the interference light filter 3. The interference light filter 3 is configured so that the wavelength to be transmitted continuously changes depending on the incident position. Further, it has a slide adjusting mechanism 4 for mechanically sliding the interference light filter 3 in a minute distance in the X-axis direction, and the slide adjusting mechanism 4 can continuously change the wavelength of light passing through the filter. it can.

A first light receiving element, for example, a photodiode PD1 is arranged at a position passing through the interference light filter 3, and a photodiode serving as a second light receiving element is arranged at a position for receiving the light reflected from the interference light filter 3. Place PD2. The outputs of these photodiodes PD1 and PD2 are given to the output ratio calculating means 5. The output ratio calculation means 5 is a photodiode PD1, which is a first and second light receiving element.
The output ratio of PD2 is calculated. The wavelength of the incident laser light can be recognized based on the output ratio by the output ratio calculating means 5. The output ratio calculated by the output ratio calculation means 5 is converted into wavelength data by the wavelength output means 6 and output.

Next, the output ratio calculation means 5 and the wavelength output means 6
Will be described more specifically. First of the optical branching means 1
The outputs from the second photodiodes PD1 and PD2 are given to the I / V converters 11 and 12 in the output ratio calculating means 5 and converted into voltage signals. The outputs of the I / V converters 11 and 12 are given to the adder 13 and the subtractor 14, and the respective outputs are added and subtracted and given to the divider 15. The divider 15 normalizes the light branched by the optical branching means 1 and outputs a signal corresponding to the wavelength of the input light based on the output ratio of these.

The wavelength output means 6 has an A / D converter 21 for A / D converting the output of the divider 15 and an A / D converter as shown in FIG.
ROM 22, CPU 23, memory 24, ROM holding a conversion table for converting the converted output into wavelength data
It has a D / A converter 25 for converting the wavelength data of 22 into an analog signal and a display 26 for displaying the wavelength data. The D / A converter 25 converts the wavelength data into an analog signal and outputs the analog signal, and the display 26 displays the wavelength data as it is. The CPU 23 is also used to read the conversion table of the ROM 22 based on the A / D conversion output. It is assumed that the ROM 22 is created in advance based on the output of the divider 15 when a laser beam having a known wavelength is incident.

As shown in Japanese Patent Publication No. 7-92530, this interference light filter 3 has high refractive index films and low refractive index films alternately laminated to continuously change the optical thickness of the laminated wavelengths. It was done like this. Next, this interference light filter will be described with reference to FIG. The wavelength tunable interference light filter 3 according to the present embodiment is formed by depositing a substance in multiple layers on a substrate 31 such as glass or silicon. The substrate 31 is made of a material having a high light transmittance in the wavelength range used, and a dielectric or semiconductor is used. In this embodiment, quartz glass is used. On top of this substrate 31, a multi-layer film 32 of a vapor deposition material, a dielectric, a semiconductor or the like having a high light transmittance at the wavelength used is vapor deposited. Multilayer film 3 here
2 is formed of a lower multilayer film 33, a cavity layer 34, and an upper multilayer film 35 as shown. An antireflection film 36 is formed on the lower surface of the substrate 31 by vapor deposition.

[0017] Here, the multilayer film 32, the material used as the deposition material of the antireflection film 36, for example, Si O ₂ (refractive index _{n = 1.46), Ta 2 O} 5 (n = 2.15), Si (n = 3.46)
Al ₂ O ₃ , Si ₂ N ₄ , Mg F, etc. are used. In the present embodiment, the multilayer films 33 and 35 are formed by alternately stacking low refractive index films and high refractive index films and depositing them. Here, the film thickness d, the transmission wavelength λ, and the refractive index n are set to have the following relationships. λ = 4nd (1) That is, each layer has an optical thickness nd of λ / 4. The low-refractive index films and the high-refractive index films are alternately stacked to reduce the full width at half maximum (FWHM) of the transmittance peak. The thickness d _c of the cavity layer 34 is the transmission wavelength λ,
The refractive index n should have the following relationship. λ = 2nd _c (2) That is, the optical thickness nd _c of the cavity layer 34 is λ / 2.

Now, the interference light filter 3 according to the present embodiment.
Since the transmission wavelength and the film thickness have the relationship of the equations (1) and (2), the substrate 31 is an elongated plate-like substrate, the refractive index of the multilayer film 32 is constant, and the film thickness is continuous. To change the transmission wavelength λ. Then, the transmission wavelength of the variable wavelength interference light filter 3 is set to λ _a ~
Let λ _c (λ _a <λ _c ), and let λ _{b be} the transmission wavelength at the center point (x = x _b ). The upper and lower multilayer films 33 and 35 alternately include a first vapor deposition material film having a first refractive index n _{1 and} a second vapor deposition material film having a second refractive index n ₂ having a lower refractive index than this, respectively. It is constructed by stacking. That is, as shown in the enlarged view of the circular portion in FIG. 2A, the thickness of each film is continuously changed. In FIG. 2C, the lower multilayer film 33
33L for the low refractive index film, 33H for the high refractive index film, 35H for the high refractive index film of the upper multilayer film 35, and 35L for the low refractive index film.
And Then, with respect to the transmission wavelength λ _a of the end portion x _a on the X axis of the filter of FIG. 2A, the above formulas (1) and (2) hold for the low refractive index film and the high refractive index film, respectively. To set. The x _b, the transmission wavelength lambda _b at x _c, with respect to lambda _c, the wavelength lambda _b, wherein at lambda _c (1), and sets the film thickness so that holds true (2). The film thickness during that time is also set so that the wavelength changes linearly. Thus, each film thickness of the layer continuously varies with the position x _a ~x _c on the x-axis as shown, the film thickness is increased toward the positive direction of the X axis.

By continuously changing the film thickness in this way, when the multilayer film 32 is formed on the substrate 31 by vapor deposition, the substrate is arranged so that the distance from the vapor deposition source is continuously changed. It can be realized by arranging it at an angle.

Further, the film thickness of the interference light filter 3 is continuously changed, but the film thickness is made constant, and the refractive indices n ₁ and n ₂ of the multilayer film 32 are continuously changed in the X-axis direction. The optical thickness may be continuously changed by changing it.

The interference light filter 3 constructed in this way
Has a narrow band characteristic and is sufficiently stable against temperature changes and the like. Therefore, the transmission wavelength itself can be continuously changed by mechanically moving the position where the light is incident on the interference light filter 3 in the X-axis direction using the slide adjusting mechanism 4.

FIG. 5 is a perspective view of a wavelength monitor device according to this embodiment. In this embodiment, a wavelength monitor device in which a display 26 for monitoring and displaying the wavelength of incident light is provided on a front panel is shown.

Next, the operation of the wavelength monitor device according to this embodiment will be described. 3A is a graph showing characteristics of the cut filter 2, and FIGS. 3B and 3C are graphs showing characteristics of transmittance and reflectance of the interference light filter 3. As is clear from these figures, the cut filter 2
Selects a characteristic in which the central transmission wavelength of the interference light filter 3 is used as a cutoff wavelength and light having a longer wavelength is transmitted and light having a shorter wavelength is blocked. Further, the interference light filter 3 has a characteristic of transmitting light having a predetermined wavelength λ1 and reflecting other light as shown in FIG. For the wavelength λ of the laser light incident at this time, the photodiode PD
1, and the optical outputs obtained in PD2 are shown in FIGS. 3 (d) and 3 (e), respectively.
It will be as shown in. At this time, the photodiode PD1,
The outputs obtained from the PD 2 correspond to the transmittance shown in FIG. 3B and the reflectance shown in FIG. 3C, respectively.

Therefore, assuming that the I / V conversion outputs of the photodiodes PD1 and PD2 are A and B, they are added and subtracted, and divided by the divider 15, and (AB) / (A +).
B) is calculated. The level normalized by the division is shown in FIG. Thus, in the wavelength range of λ1 to λ3, a signal having a level corresponding to the wavelength of the incident laser light can be obtained. The output of the divider 15 is converted into a digital signal by the A / D converter 21. The CPU 23 reads the wavelength data from the ROM 22 in which the conversion table is stored on the basis of the division calculation power. Then, it is output from the D / A converter 25 and displayed on the display 26. In this way, the wavelength of the incident light can be monitored. CPU23 is ROM2
When an intermediate value of the A / D converted values held in the table No. 2 is input, interpolation processing such as proportional distribution may be performed.

The wavelength range monitored here is the range of λ1 to λ3, and as is clear from FIG.
Depends on the characteristics of. To increase the monitor range, an interference light filter with broad characteristics may be used. The resolution can be improved by reducing the monitor range.
In this case, use an interference light filter with steep characteristics .
Yes.

On the other hand, in order to change the wavelength range to be monitored, the slide adjusting mechanism 4 is used and the interference light filter 3 is used.
By changing the incident position of the incident light on
The transmission wavelength λ1 of the interference light filter 3 shown in can be changed. In this case, it is necessary to change the contents of the ROM 22 that stores the conversion table. Therefore, it is preferable that the required wavelength is set by using the slide adjusting mechanism 4 at the time of manufacturing so that the operating portion of the slide adjusting mechanism 4 is not exposed to the outside of the case so that the user cannot adjust the monitor range. In this way, airtight sealing is also facilitated, the user does not need to adjust the monitor range, and a compact and lightweight laser light source monitor device can be realized with an extremely simple configuration.

Next, a second embodiment of the present invention will be described with reference to FIG. In the second embodiment, instead of the interference light filter 3 that can continuously change the transmitted light depending on the incident position, a normal interference light filter that transmits light of a certain wavelength is used. . FIG. 6 is a block diagram showing the overall configuration of a wavelength monitor device for a laser light source according to the second embodiment. The same parts as those in the first embodiment described above are designated by the same reference numerals and detailed description thereof will be omitted. . In this embodiment, instead of the interference light filter 3,
An interference light filter 41 for transmitting light having a constant wavelength is provided in the light branching means 1A. In this case, the slide adjusting mechanism 4 becomes unnecessary. This is sufficient if the wavelength monitor range is within 2 to 3 nm, for example, but if the wavelength can be monitored over a wider range, the angle adjustment for adjusting the angle between the interference light filter 41 and the photodiode PD2 is performed. A mechanism 42 is provided. The angle adjustment mechanism 42 changes the incident angle of the light passing through the cut filter 4 and incident on the interference light filter 41 slightly to continuously change the transmission wavelength λ according to the incident angle. In this case, it is necessary to change the position of the second light receiving element PD2 by the angle adjusting mechanism 42 according to the angle of the interference light filter 3 so that the reflected light can be accurately received. If this angle is made too large, the transmission level will change between P-polarized light and S-polarized light. Further, if the incident angle of the incident light is near 0, the influence of the change in the light intensity due to the polarization component can be reduced, but the reflected light is received, so that the shape of the optical system becomes large. Therefore, it is preferable that the angle adjusting mechanism 42 sets the incident angle within the range of 5 ° so that the position and direction of the photodiode PD2 can be adjusted so that the reflected light can be received according to each incident angle.

In the second embodiment as well, the angle adjustment mechanism 42 is used to change the angles of the interference light filter 41 and the photodiode PD2, but these are adjusted at the same time, and the data in the ROM 22 is changed accordingly. Since it is difficult to make correspondence with each other, it is preferable to adjust this to a predetermined angle in order to set the wavelength of the monitor range at the time of manufacture and then fix this.

In the first and second embodiments described above,
Although an adder, a subtracter, and a divider for calculating the output ratio thereof are provided as the output ratio calculating means, it goes without saying that the ratio of the two I / V converters may be directly calculated. .

[0030]

As described in detail above, according to the inventions of claims 1 to 3 of the present application, the emission wavelength of the light source is monitored from the ratio of the incident light to the reflected light by using the interference light filter. ing. Therefore, without using a movable mechanism such as a wavelength monitor device using a conventional spectroscope,
It can be realized with an extremely simple structure, and can be made compact and lightweight. Moreover, there is an effect that the wavelength of the incident light can be monitored with high accuracy within the measurement range. Further, according to the invention of claim 3, the wavelength range to be monitored can be controlled within a wide range by controlling the incident position on the interference light filter.

[Brief description of drawings]

FIG. 1 is a block diagram showing an overall configuration of a wavelength monitor device for a laser light source according to a first embodiment of the present invention.

2A is a cross-sectional view showing the structure of an interference optical filter having a single-cavity structure according to the first embodiment of the present invention, FIG. 2B is a graph showing a change in transmittance on the X axis, FIG.
(C) is an enlarged sectional view of the circular portion of (a).

FIG. 3 is a graph showing characteristic changes with respect to emission wavelengths of a cut filter, an interference light filter, and photodiodes PD1 and PD2.

FIG. 4 is a graph showing changes in an error signal with respect to wavelength.

FIG. 5 is a perspective view showing a configuration of a wavelength control device according to a second embodiment.

FIG. 6 is a block diagram showing an overall configuration of a wavelength monitor device for a laser light source according to a second embodiment of the present invention.

[Explanation of symbols]

1 Optical branching means 2 cut filter 3,41 Interference light filter 4 Slide adjustment mechanism 5 Output ratio calculation means 6 Wavelength output means 11,12 I / V converter 13 adder 14 Subtractor 15 divider 21 A / D converter 22 ROM 23 CPU 25 D / A converter 26 Display 42 Angle adjustment mechanism PD1, PD2 photodiode

Continuation of front page (56) Reference JP-A-55-142220 (JP, A) JP-A-6-281812 (JP, A) JP-A-5-281480 (JP, A) JP-A-56-103551 (JP , A) JP 5-243664 (JP, A) JP 5-55683 (JP, A) JP 10-209546 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB) G01J 3/00-3/51 G01J 9/00-9/04 H01S 3/00 H01S 3/13-3/139 H01S 5/068-5/0687 H04B 10/00

Claims (3)

(57) [Claims] 1. A light filter, which is provided between the laser light source and the optical filter , wherein a light from a laser light source is incident, a light having a predetermined wavelength is transmitted, and another light is reflected ,
The cutoff wavelength is the center transmission wavelength of the optical filter.
Input filter, the first and second light receiving elements that receive the light that passes through the optical filter and the light that is reflected by the optical filter, respectively, and the difference between the outputs of the first and second light receiving elements is the first , Second
Output ratio calculation means for calculating the output ratio by dividing by the sum of the outputs of the light receiving elements, and the output changes with respect to the input of the optical filter based on the output ratio calculated by the output ratio calculation means. And a wavelength output unit that outputs the wavelength of the laser light source within a range. 2. The optical filter is an interference optical filter configured by alternately laminating low refractive index films and high refractive index films having an optical thickness of λ / 4 with respect to a transmission wavelength λ. The wavelength monitor device for a laser light source according to claim 1, wherein 3. The interference optical filter has an optical thickness continuously changed so that a transmission wavelength λ continuously changes with respect to a predetermined direction of a substrate, and the wavelength monitor device includes: 3. The wavelength of the laser light source according to claim 2, further comprising a slide adjusting mechanism that continuously changes the incident position of the incident light from the laser light source to the interference light filter in the predetermined direction. Monitor device.