JPH08227014A - Tunable wavelength filter, manufacturing method thereof, and tunable light source - Google Patents

Abstract

(57) [Summary] [Purpose] To continuously change wavelength characteristics over a wide wavelength range without causing deterioration of transmittance and steepness. [Structure] A glass substrate 11 and a dielectric multilayer film 12 including a large number of high refractive index dielectric layers and low refractive index dielectric layers alternately formed on the glass substrate 11 are provided, and the dielectric multilayer film 12 is provided. The thickness of each dielectric layer is linearly and continuously changed according to the position of the substrate, and the position of the light incident on the multilayer film 12 is changed to allow the light of different wavelengths to pass through.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength tunable filter, a method of manufacturing the same, and a wavelength tunable light source using the wavelength tunable filter.

[0002]

2. Description of the Related Art Conventionally, as a wavelength tunable filter, there has been known a structure in which a wavelength characteristic of the filter is continuously changed by changing an incident angle to a dielectric multilayer filter. That is, when the incident angle is changed, the optical film thickness is changed, so that the wavelength characteristic of the filter can be changed. In addition, several kinds or dozens of narrow-band bandpass filters with adjacent transmission wavelengths are made, these are finely processed, arranged in parallel in the order of wavelength, and one of them is selected to change the wavelength characteristic. Known as an analytical instrument.

[0003]

However, when the incident angle to the dielectric multilayer filter is changed, there is an allowable range for the incident angle change, and if the incident angle is exceeded, the transmittance and steepness deteriorate. There is. That is, when the optical film thickness is changed by changing the incident angle, the amount of change of the optical film thickness with respect to the change of the incident angle is different in the layers having different refractive indices, so that the transmittance and the steepness are lowered. Therefore, the wavelength characteristics cannot be changed in a wide range by changing the incident angle.

Further, if several kinds or dozens of adjacent narrow band band pass filters are arranged, the structure is complicated and the manufacturing is difficult, and the manufacturing cost becomes high. Moreover, there is a problem that light leaks at the joint portion of the bandpass filters arranged in parallel, and the wavelength characteristic cannot be continuously changed.

In view of the above, it is an object of the present invention to provide a wavelength tunable filter having a simple structure capable of continuously changing wavelength characteristics in a wide wavelength range.

Another object of the present invention is to provide a method of manufacturing a wavelength tunable filter, which can easily manufacture a wavelength tunable filter whose wavelength characteristics can be continuously changed in a wide wavelength range. .

Further, by using a wavelength tunable filter capable of continuously changing the wavelength characteristic in a wide wavelength range, the wavelength characteristic of the emitted light can be continuously changed in a wide range and further downsizing is possible. Another object is to provide a variable wavelength light source.

[0008]

In order to achieve the above object, in a wavelength tunable filter according to the present invention, a substrate, a high refractive index dielectric layer and a low refractive index dielectric layer which are alternately formed in large numbers on the substrate are provided. It is characterized in that it is composed of a body layer and the film thickness of these dielectric layers continuously changes depending on the position of the substrate.

The film thickness of each of the above dielectric layers may be linearly and continuously changed according to the position of the substrate.

The film thickness of each of the above dielectric layers may vary non-linearly and continuously depending on the position of the substrate.

Further, according to the present invention, there is provided a manufacturing method for manufacturing a wavelength tunable filter capable of continuously changing the wavelength characteristic in a wide wavelength range, in which a high refractive index dielectric material evaporation source and a low refractive index are provided in a vacuum deposition container. The evaporation sources of the dielectric constant material are arranged substantially alternately, and the substrates are held in the vacuum vapor deposition container so that the distance of the substrate surface to the evaporation sources varies depending on the position of the substrate, and Is characterized in that the materials evaporated from the above two evaporation sources are alternately deposited.

In the above manufacturing method, the substrate may be held linearly.

Further, in the above manufacturing method, the substrate may be curved and held.

Further, the wavelength tunable light source according to the present invention comprises:
It is characterized by comprising a semiconductor laser element and a wavelength tunable filter in which the film thickness of each layer is continuously changed depending on the position and is inserted in the optical path of the emitted light so that the position can be changed. .

In addition, the variable wavelength light source according to the present invention is inserted in the optical path between the external reflection mirror constituting the optical resonator so that the position can be changed, and the film thickness of each layer according to the position. It is also possible to use a semiconductor laser device having a wavelength tunable filter whose wavelength changes continuously.

[0016]

A dielectric multilayer filter can be formed from a high-refractive-index dielectric layer and a low-refractive-index dielectric layer that are alternately laminated on a substrate. Then, if the film thickness of each of these layers is continuously changed depending on the position of the substrate, the wavelength characteristics will change depending on the position. That is, the wavelength of the passing light changes when the position where the light is incident is changed. Therefore, the wavelength characteristic can be continuously changed by changing the position where the light is incident. Since the incident angle of light does not change, the incident angle does not exceed the allowable range and the transmittance is not deteriorated or the steepness of the wavelength characteristic is not deteriorated, and the wavelength variable range can be widened.

If the film thickness of each dielectric layer is determined so as to change linearly and continuously according to the position of the substrate,
The wavelength tunable filter can have a narrow band.

If the film thickness of each dielectric layer is determined so that it changes non-linearly and continuously depending on the position of the substrate, a wide band wavelength tunable filter can be obtained.

In the vacuum vapor deposition container, the substrate is arranged such that the distance of the substrate surface with respect to the evaporation source varies depending on the position of the substrate.
By holding and evaporating the material evaporated from the evaporation source on the surface of this substrate to form each dielectric layer, the multilayer film in which the film thickness of each dielectric layer continuously changes depending on the position is formed. Can be made. As a result, the variable wavelength filter can be manufactured easily and easily.

In this case, if the substrate is held linearly, the film thickness of each dielectric layer can be linearly and continuously changed according to the position of the substrate, and a narrow band wavelength tunable filter can be easily constructed. Easy to manufacture.

Further, if the substrate is curved and held, the film thickness of each dielectric layer can be continuously changed non-linearly according to the position of the substrate, and a wide band tunable filter can be easily and easily provided. Can be manufactured.

By inserting the wavelength tunable filter in which the thickness of each layer is changed in this way into the optical path of the emitted light of the semiconductor laser device and continuously changing the position, the wavelength of the emitted light is continuously changed. Can be changed. This light source is a wavelength tunable light source in which the intensity of emitted light and the steepness in wavelength characteristics are stable in a wide wavelength range.

A reflection mirror is provided outside the semiconductor laser element to form an external optical resonator, and in the optical path of the external optical resonator,
When a wavelength tunable filter in which the film thickness of each layer is changed is inserted, only the light of the wavelength that has passed through this wavelength tunable filter resonates and oscillates. In this way, an external optical resonator having wavelength selectivity can be formed, and its oscillation wavelength can be continuously changed by continuously changing the position of the wavelength tunable filter with respect to the optical path. Therefore, the wavelength of the emitted light obtained from this semiconductor laser device can be continuously changed, and the steepness in the intensity and wavelength characteristics of the emitted light can be stabilized in a wide wavelength range.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the drawings. The wavelength tunable filter shown in FIG. 1 has a glass substrate 11 on which a multi-layered film 12 composed of a large number of dielectric thin films is formed. Glass substrate 1
Optical glass is used as 1. The multilayer film 12 includes a large number of alternating layers of high refractive index material such as titanium dioxide and low refractive index material such as silicon dioxide (for example, 30 to 50).
Layers are laminated, and due to the coherence of light, it becomes an interference film filter that passes only light having a wavelength of four times the film thickness of each layer.

In the embodiment shown in FIG. 1, the thickness of each layer of the multilayer film 12 is gradually increased linearly in one direction in both the high refractive index layer and the low refractive index layer at the same ratio with respect to the position. And
Therefore, the transmission wavelength characteristics differ in proportion to the incident position of light. That is, as shown in FIG. 1, if a thin light beam is transmitted, the transmission wavelength is set to 1 depending on the position of the light beam.
It can be continuously changed in the range of about 200 nm to 1400 nm.

In this case, different wavelength characteristics are obtained only by changing the incident position of light, so that it is possible to change the wavelength characteristics in a wide wavelength range without lowering the transparency or steepness in the transmission characteristics. That is, the problem of changing the wavelength characteristic by tilting the entire multilayer filter to change the incident angle of light is solved.

In the embodiment shown in FIG. 2, the thickness of each layer of the multilayer film 12 is gradually increased non-linearly in one direction in both the high refractive index layer and the low refractive index layer at the same ratio with respect to the position. Has been done.
The wavelength tunable filter of FIG. 2 is designed so that the pass wavelength band is wide. When the pass wavelength band is wide in this way, the wavelength λ
The film thickness dλ in the above equation is determined by the following mathematical formula 1.

[Equation 1] In Equation 1, λ is the center wavelength of the design of the filter, θ0 is the incident angle from the incident medium having the refractive index n0, and nλ is the refractive index of each layer at the wavelength λ.

Therefore, in this case, the relationship between the film thickness dλ and the wavelength λ is expressed by the solid line in FIG. The dotted line indicates the case where the wavelength band of the pass wavelength is narrow where the wavelength dispersion of the refractive index of each layer can be ignored. As shown by the solid line in FIG. 4, the film thickness dλ with respect to the position on the glass substrate 11.
, The wavelength characteristics change at each position,
A wavelength tunable filter having a wide pass wavelength band can be obtained.

Ignoring the wavelength dispersion, the relationship between the position on the substrate and the film thickness dλ becomes linear as shown by the dotted line in FIG. That is, the wavelength tunable filter shown in FIG. 1 is based on this, and the wavelength tunable filter of FIG. 1 becomes a filter having a narrow pass wavelength band. In this case, the central wavelength of the passing wavelength changes linearly from the dotted lines in FIGS. 3 and 4 according to the position on the substrate.

Next, an embodiment of a method of manufacturing the above wavelength tunable filter will be described. Basically, as shown in FIG. 5, the glass substrate 11 is placed in a vacuum deposition container (bell jar or chamber) 21, and the high and low refractive index materials evaporated from the evaporation source 23 are transferred to the glass substrate 11. Evaporate on surface. More specifically, the glass substrate 11 is supported on a dome-shaped rotary support 22. As the evaporation source 23, a high refractive index material such as titanium dioxide,
A low refractive index material such as silicon dioxide is arranged on a concentric circle centered on the rotation center of the dome-shaped rotation support base 22 described above,
A large number of high refractive index layers and low refractive index layers are alternately formed by heating by an electron beam heating method or the like to evaporate these materials and by alternately shielding with a suitable shutter. At that time, in order to control the thickness of each layer,
The film thickness formed on the monitor substrate 24 is detected by an optical film thickness detector 25 using reflected light.

The glass substrate 11 is a dome-shaped rotary support base 2
Although it is revolved by being supported by 2, it may be rotated separately. Normally, by arranging the surface of the glass substrate 11 at a right angle to the straight line connecting the evaporation source 23 and the glass substrate 11,
The distance from the evaporation source 23 to the surface of the glass substrate 11 is made as uniform as possible at each position on the surface so that the vapor deposition layer has a uniform thickness at each position. In order to provide a gradient in the film thickness of the glass substrate 1
It is assumed that the surface of No. 1 is inclined from a right angle with respect to the straight line connecting the evaporation source 23 and the glass substrate 11.

That is, as shown in FIGS. 6A and 6B, the glass substrates 11 are held by the holders 31 and 32 while being tilted on the rotation support base 22. At this time, the two evaporation sources 23
The inclination should be the same. As shown in FIGS. 6A and 6B, when the glass substrate 11 is tilted and vapor deposition is performed while keeping it straight, each layer can be formed so that the film thickness changes linearly with respect to the position. A narrow band wavelength tunable filter as shown in FIG. 1 can be produced. In this case, one side of the glass substrate 11 is, for example, 10 to 50.
A square having a size of about mm is used. The inclination angle of the glass substrate 11 is preferably 1 ° or more and less than 90 °, and ideally 10 ° or more and 60 ° or less with respect to the above-mentioned reference right angle.

Further, as shown in FIG. 6C, if a holder 33 that bends the glass substrate 11 and holds it on the rotary support 22 is used, the film thickness changes non-linearly with respect to the position. Each layer can be formed as described above, and a wide band tunable filter as shown in FIG. 2 can be manufactured. If the glass substrate 11 having a thickness of, for example, about 20 μm is used, there is no problem even if it is curved in this way. Depending on the bending curvature, it is possible to use the glass substrate 11 having a thickness of about 100 μm or less.

A wavelength tunable light source can be constructed by using the wavelength tunable filter as shown in FIGS. 1 and 2 thus produced. In the embodiment shown in FIG. 7, the light emitted from the semiconductor laser device 41 is made incident on the wavelength tunable filter 10 (shown in FIGS. 1 and 2) via the lens 42, and the light passing therethrough is collected by the lens 43. The light is guided to the ferrule 44 and made incident on the optical fiber 45. An optical connector 46 is provided at the other end of the optical fiber 45.

In the wavelength tunable light source configured as shown in FIG. 7, the wavelength of the light transmitted through the wavelength tunable filter 10 is changed by moving the position of the wavelength tunable filter 10 with respect to the optical path as shown by the arrow in the figure. It can be arbitrarily selected. That is, the wavelength of the light emitted from the optical connector 46 is continuously variable depending on the position of the tunable filter 10 and is configured as a tunable light source.

In the embodiment shown in FIG. 8, the light from the semiconductor laser device 41 is converged by the lens 42 at one end of the ferrule 44, is made incident on one end of the optical fiber 45, and is emitted from the optical connector 46. The tunable filter 10 is inserted in the middle of the optical fiber 45. That is, in the planar optical circuit 51, the groove 5 is formed so as to cut the waveguide 53 provided on the waveguide substrate 52.
4 is formed, the tunable filter 10 is put in the groove 54, and the tunable filter 10 is movable in the length direction of the groove 54. Then, one end of the optical fiber 45 is formed into a spherical shape (so-called a spherical optical fiber) to be optically coupled with one end of the waveguide 53, and one end of the optical fiber 47 on the side connected to the optical connector 46 is also formed into a spherical shape (a spherical shape). An optical fiber) and is optically coupled to one end of the waveguide 53. When the wavelength tunable filter 10 is moved along the groove 54, the position where the light passes (the position of the waveguide 53) changes, so that the wavelength characteristic of the light passing through the wavelength tunable filter 10 continuously changes. As a result, the wavelength of the light emitted from the optical connector 46 changes continuously.

In FIGS. 7 and 8, the wavelength characteristic of the light emitted from the optical connector 46 is continuously changed by changing the position of the wavelength tunable filter 10 with respect to the optical path. Therefore, the wavelength characteristic is changed in a wide wavelength range. Can be configured as a wavelength tunable light source in which the intensity of emitted light and the wavelength characteristic (steepness) are stable. By the way, if the multilayer filter is tilted to change the incident angle as in the conventional case, the transmittance of the multilayer filter deteriorates if the allowable angle range is exceeded, and the output light intensity is stable. No, and the steepness in the wavelength characteristic is deteriorated, but there is no such inconvenience.

Since the wavelength tunable filter 10 may be inserted in the optical path of the outgoing light so that the position thereof is continuously changed, the wavelength tunable filter is provided in the incident path to the ferrule 44 as described above. 10 or inserting the tunable filter 10 in the middle of the optical fiber 45 by providing the planar optical circuit 51, the optical fiber 45 itself (after being reinforced by the reinforcing V groove member) It is possible to adopt a configuration in which the tunable filter 10 is cut into parts and the tunable filter 10 is inserted into the cut parts so that the position can be changed.

In the embodiment shown in FIG. 9, the semiconductor laser device 41 is used.
When the total reflection mirror 48 is arranged outside one end of the above to form an external optical resonator together with the lens 42, the position variable wavelength tunable filter 10 is inserted into the external optical resonator. With this, since the wavelength selective external optical resonator can be configured, the wavelength characteristic of the light emitted from the other end can be continuously changed depending on the position of the tunable filter 10.
That is, it is possible to continuously change the wavelength characteristic of the light emitted from the other end of the semiconductor laser element 41, guided to the ferrule 44 through the lens 43, and further emitted from the optical connector 46 through the optical fiber 45.

In these wavelength tunable light sources (FIGS. 7 to 9), only the small wavelength tunable filter 10 is movably incorporated, so that the structure is simple and the size can be reduced, and the intensity of the light emitted from the optical connector 46 can be increased. Also, a stable wavelength tunable light source can be obtained in which the steepness in wavelength characteristics does not decrease in a wide wavelength range.

[0041]

As described above with reference to the embodiments, according to the wavelength tunable filter of the present invention, in a wide wavelength range,
It is possible to continuously change the wavelength characteristics without lowering the transmittance or deteriorating the steepness of the wavelength characteristics. Further, according to the method of manufacturing the wavelength tunable filter according to the present invention, the wavelength tunable filter as described above can be easily and easily manufactured. Further, by forming a wavelength tunable light source using the wavelength tunable filter as described above, the wavelength characteristics of the emitted light can be adjusted in a wide range without causing a decrease in the intensity of the emitted light or deterioration of the steepness in the wavelength characteristics. It is possible to obtain a variable wavelength light source that can be continuously changed and can be miniaturized.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a wavelength tunable filter according to an embodiment of the present invention and its characteristics.

FIG. 2 is a schematic diagram showing a wavelength tunable filter according to another embodiment.

FIG. 3 is a graph showing the relationship between the wavelength of transmitted light and the thickness of each multilayer film.

FIG. 4 is a graph showing the relationship between the position on the substrate and each film thickness of the multilayer film.

FIG. 5 is a schematic view showing an example of a manufacturing method.

FIG. 6 is a partially enlarged sectional view schematically showing an example of holding a glass substrate.

FIG. 7 is a schematic diagram showing an embodiment of a variable wavelength light source.

FIG. 8 is a schematic view showing another embodiment of the variable wavelength light source.

FIG. 9 is a schematic view showing still another embodiment of the variable wavelength light source.

[Explanation of symbols]

 10 wavelength tunable filter 11 glass substrate 12 multilayer film 21 vacuum deposition container 22 dome-shaped rotary support 23 evaporation source 24 monitor substrate 25 film thickness detector 31, 32, 33 glass substrate holder 41 semiconductor laser device 42, 43 lens 44 Ferrule 45, 47 Optical fiber 46 Optical connector 48 Total reflection mirror 51 Planar optical circuit 52 Waveguide substrate 53 Waveguide 54 Groove

Claims (8)

[Claims] 1. A substrate, and a high-refractive-index dielectric layer and a low-refractive-index dielectric layer, which are alternately formed in large numbers on the substrate, and the film thickness of these dielectric layers depends on the position of the substrate. A wavelength tunable filter characterized by continuously changing. 2. The wavelength tunable filter according to claim 1, wherein the film thickness of each dielectric layer changes linearly and continuously according to the position of the substrate. 3. The wavelength tunable filter according to claim 1, wherein the film thickness of each dielectric layer changes non-linearly and continuously according to the position of the substrate. 4. An evaporation source of a high-refractive-index dielectric material and an evaporation source of a low-refractive-index dielectric material are substantially alternately arranged in a vacuum deposition container, and the distance of the substrate surface to the evaporation source is the position of the substrate. The method of manufacturing a wavelength tunable filter, characterized in that the substrate is held in the vacuum vapor deposition container and the materials evaporated from the two evaporation sources are alternately deposited on the surface of the substrate so as to differ depending on the above. 5. The method of manufacturing a wavelength tunable filter according to claim 4, wherein the substrate is held linearly. 6. The method of manufacturing a wavelength tunable filter according to claim 4, wherein the substrate is curved and held. 7. A semiconductor laser device and a wavelength tunable filter in which the film thickness of each layer is continuously changed according to the position, and is inserted in the optical path of the emitted light so that the position can be changed. A variable wavelength light source characterized in that 8. A position changeable in a semiconductor laser device, an external reflecting mirror forming an optical resonator of the semiconductor laser device, and an optical path between the semiconductor laser device and the external reflecting mirror. And a wavelength tunable filter in which the film thickness of each layer is continuously changed according to the position.