JP2000214392A - Optical wave length filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical wavelength filter having arbitrary transmission or cut-off characteristics and a tuning capability. SOLUTION: The optical wavelength filter is provided with a waveguide substrate 100 in which a waveguide 101, a first slab waveguide, waveguide array and a second slab waveguide are connected in this order; provided with a reflection type spatial filter 105 arranged in proximity to an image forming focal plane against the waveguide array 103, near the end face on the side opposite from the end face in which the second slab waveguide is connected to the waveguide array 103; and provided with a fine adjustment mechanism for positional adjustment of the reflection type spatial filter 105. Further, the wavelength filter is designed to control a frequency profile through the positional adjustment of the reflection type spatial filter 105.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical wavelength filter, and more particularly to an optical wavelength filter capable of arbitrarily adjusting transmission characteristics or cutoff characteristics.

[0002]

2. Description of the Related Art In recent years, with the development of erbium-doped optical fiber amplifiers, optical signals can be easily amplified. However, in optical signal transmission, since noise increase due to incoherent spontaneous emission light generated from the erbium-doped optical fiber amplifier becomes a problem, an optical wavelength filter having a bandwidth equal to or slightly wider than the signal bandwidth is used. It is common practice to cut off unnecessary spontaneous emission light. Conventionally, a Fabry-Perot type optical interferometer is used for the optical wavelength filter. In recent years, in order to increase the frequency use efficiency of optical signal transmission, the use of a single sideband (SSB) system or a vestigial sideband (VSB) system as a transmission system has been studied. The single sideband (SSB) method requires an optical wavelength filter having a steep frequency cutoff characteristic, and the vestigial sideband (VSB) method requires an optical wavelength filter having a linear frequency cutoff characteristic. Conventionally, since it is difficult to configure an optical wavelength filter having such a frequency cutoff characteristic, a wavelength transmission characteristic of a Mach-Zehnder interferometer is often used approximately.

[0003]

Since it is difficult to control the frequency characteristics of these conventional optical wavelength filters, an optical band-pass filter having a rectangular transmission characteristic that is steep with respect to the frequency, and a filter having a cut-off frequency. A tunable optical wavelength filter could not be constructed. SUMMARY OF THE INVENTION It is an object of the present invention to provide a tunable optical wavelength filter having an arbitrary transmission or blocking characteristic in order to solve the above-mentioned problems.

[0004]

In order to solve the above-mentioned problems, a first optical wavelength filter of the present invention comprises a waveguide, a first slab waveguide, a waveguide array, and a second slab waveguide in this order. And the second slab waveguide has an imaging focal plane for the waveguide array near the end face opposite to the end face connected to the waveguide array, and a reflective spatial filter is arranged near the imaging focal plane. Have been. Further, the first optical wavelength filter described above may be provided with a fine movement mechanism for adjusting the position of the reflective spatial filter, and controlling the frequency profile by adjusting the position of the reflective spatial filter. In this case, the first configuration example of the reflection type spatial filter has a reflection surface in one region divided by a straight line perpendicular to the waveguide substrate. Further, the above-described second configuration example of the reflection type spatial filter has a reflection surface in a region sandwiched between two straight lines perpendicular to the waveguide substrate. In the above-described third configuration example of the reflection type spatial filter, the reflection surface is provided in the trapezoidal region. In the first optical wavelength filter described above, the reflectance may be continuously changed by changing the thickness of a medium serving as a mirror in the reflection type spatial filter spatially. In the first optical wavelength filter described above, the reflection type spatial filter is:
The position in the direction parallel to the waveguide substrate at the boundary of the reflection region may periodically change in the beam diameter in the direction perpendicular to the waveguide substrate.

Further, the second optical wavelength filter of the present invention comprises:
The first waveguide, the first slab waveguide, the first waveguide array, and the second slab waveguide are connected in this order, and the third slab waveguide, the second waveguide array, the fourth slab waveguide, and the second waveguide are connected. The second slab waveguide has an imaging focal plane for the first waveguide array near an end face opposite to the end face connected to the first waveguide array, and the third slab waveguide is connected to the third slab waveguide. A waveguide having an imaging focal plane for the second waveguide array near an end face opposite to the end face connected to the second waveguide array;
A transmission spatial filter and an imaging focal plane of the third slab waveguide for the second waveguide array are arranged near the imaging focal plane of the slab waveguide for the first waveguide array. Further, the second optical wavelength filter described above may be provided with a fine movement mechanism for adjusting the position of the transmission spatial filter and controlling the frequency profile by adjusting the position of the transmission spatial filter. In this case, the first configuration example of the transmission-type spatial filter includes a transmission surface in one region divided by a straight line perpendicular to the waveguide substrate. Further, the above-described second configuration example of the transmission-type spatial filter has a structure that is perpendicular to the waveguide substrate.
A transmission surface is provided in a region sandwiched between the straight lines of the book. Further, the above-described third configuration example of the transmission type spatial filter has a transmission surface in a trapezoidal region. In the second optical wavelength filter described above, the position of the transmission type spatial filter in the direction parallel to the waveguide substrate at the boundary of the transmission region periodically changes within the beam diameter with respect to the direction perpendicular to the waveguide substrate. You may do so.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. First, a first embodiment of the present invention will be described. FIG. 1 is a configuration diagram of a reflection type optical wavelength filter according to a first embodiment of the present invention.
The reflection type optical wavelength filter 1 according to the first embodiment is a bandpass filter, and includes a waveguide substrate 100 and a reflection type spatial intensity filter 105. The waveguide substrate 100 includes a waveguide 101, a first slab waveguide 102,
A waveguide array 103 and a second slab waveguide 104 are provided, which are connected on a single-crystal silicon substrate 106 in the above order. These waveguides are composed of a core and a clad surrounding the core, and the core and the clad are formed of transparent glass films having different refractive indexes.
The waveguide 101 is composed of a core having a rectangular cross section of 7 μm in width and 7 μm in height, and is connected to the tip of the arc-shaped end of the first slab waveguide 102. First slab waveguide 102
Is constituted by a core having a rectangular cross section having both ends in an arc shape. The waveguide array 103 is composed of 340 waveguides each having a rectangular cross section having a width of 7 μm and a height of 7 μm, and its diffraction order (the value obtained by dividing the optical path length difference between adjacent waveguides by the wavelength) is 59. . These waveguides are connected to the respective arc-shaped ends of the first slab waveguide 102 and the second slab waveguide 104 on a one-to-one basis. The second slab waveguide 104 is
The end face connected to the waveguide array 103 has a circular arc shape, and is formed of a core having a rectangular cross section in which the opposite end face is flat.

The reflection type spatial intensity filter 105 is a bandpass filter, and as shown in FIG.
It comprises a gold mirror 302 provided at the center of one surface and an anti-reflection coating 303 provided outside thereof. 3A is a plan view showing the structure of a reflection type optical bandpass filter, and FIG. 3B is a cross-sectional view taken along line AA. The quartz substrate 301 has a smooth surface and a frosted glass-like fine unevenness on the back surface, and has a thickness of 1 mm or 1.5 mm.
Is transparent quartz. The gold mirror 302 is a rectangular gold film having a thickness of 300 nm or more. In the first embodiment, the frequency transmission bandwidth 304 is set to 100 GHz.
Therefore, the width is set to 50 μm. The anti-reflection coating 303 is a multilayer film in which SiO 2 and TiO 2 are alternately stacked.

[0008] The reflection type spatial intensity filter 105 is attached to a fine movement mechanism comprising a micrometer and capable of fine movement on five axes via an adapter. This fine movement mechanism
It is possible to move back and forth, left and right and up and down, rotate around a front and rear axis, and rotate around a vertical axis. The reflection type spatial intensity filter 105 is used for the waveguide array 10 of the second slab waveguide 104.
3 is fixed to a common base together with the waveguide substrate 100 so as to be arranged on the imaging focal plane for the waveguide array 103 near the end face opposite to the end face connected to the waveguide board 100.

In such a configuration, the signal light incident on the waveguide 101 is guided to the first slab waveguide 102, where it is distributed to each waveguide of the waveguide array 103. The signal light that has passed through the waveguide array 103 is subjected to time-space conversion and is incident on the second slab waveguide 104, where it is Fourier-transformed and forms an image on a focal plane. At this time, the linear dispersion on the focal plane is 2 GHz / μm, and the frequency resolution is about 10 GHz. After that, the reflection type spatial intensity filter 105 arranged on the focal plane causes a frequency transmission bandwidth 3 within 50 GHz each above and below the center frequency 305.
The signal light of a certain wavelength in 04 is selectively reflected, multiplexed by following the path at the time of incidence in reverse, and emitted from the waveguide 101. As a result, a signal light consisting of only light having a wavelength within the frequency transmission bandwidth 304 is obtained. Here, the reflection type spatial intensity filter 105 is connected to the waveguide substrate 1 using a fine movement mechanism.
Fine movement in parallel to 00 changes the wavelength of light incident on the frequency transmission band, so that the center frequency of the frequency transmission band of the reflection type optical wavelength filter can be changed.

The output of a white light or erbium-doped optical fiber amplifier is input to this reflection type optical wavelength filter, and the filter characteristics are evaluated by an optical spectrum analyzer. As a result, as shown in FIG. A rectangular frequency transmission characteristic was obtained. The frequency transmission bandwidth 304 was 102 GHz, which coincided with the designed value of 100 GHz within the range of the frequency resolution. The reflectivity for the incident light at the center frequency is 98.3%, and the extinction ratio is 40 dB.
Met. As described above, the reflection-type optical wavelength filter of the first embodiment has a rectangular frequency transmission characteristic, and has an effect that its center frequency can be varied.

Next, the waveguide substrate 100 and the reflection type spatial intensity filter 105 constituting the reflection type optical wavelength filter 1 will be described.
A method of manufacturing the device will be described. The waveguide substrate 100 is manufactured as follows. First, a glass microparticle film is deposited on a single crystal silicon substrate in the order of a lower cladding layer and a core layer using a flame hydrolysis deposition method, and then placed in an annealing furnace and heated to convert the glass microparticle film into a transparent glass film. And Next, after applying a resist on the core layer, patterning is performed in the form of a waveguide by photolithography, and unnecessary core layers are removed by dry etching. Next, a glass fine particle film serving as an upper clad layer is deposited by using a flame hydrolysis deposition method, and then is placed in an annealing furnace and heated to convert the glass fine particle film into a transparent glass film.

The reflection type spatial intensity filter 105 is manufactured as follows. First, after a resist is applied on a quartz substrate, the resist of the gold mirror pattern is removed by photolithography. Next, after depositing gold to a thickness of 300 nm or more, the resist and the gold film on the resist are removed by immersion in an organic solvent. Next, after applying a resist on the quartz substrate, the resist is left only on the pattern of the gold mirror by photolithography. Next, after forming a multilayer film by alternately depositing SiO2 and TiO2 by sputtering, the resist and the multilayer film on the resist are removed by immersion in an organic solvent.

In the first embodiment, a waveguide substrate in which a waveguide is formed of glass on a single-crystal silicon substrate is used. However, the present invention is not limited to this.
A semiconductor layer such as InP is used as a cladding layer, and a semiconductor layer having a semiconductor structure with a refractive index higher than that of the cladding such as InGaAsP is used as a core layer, or a core formed of deuterated PMMA is used. It goes without saying that the same function can be obtained even if a material having a waveguide structure made of a polymer formed of an ultraviolet curable resin is used. In this case, it is desirable that the material be sufficiently transparent in the wavelength region to be used.

Next, a second embodiment of the present invention will be described. The reflection type optical wavelength filter of the second embodiment of the present invention is a band elimination filter, except that the reflection type optical band pass filter of the first embodiment is a reflection type optical band elimination filter. This is the same as the first embodiment. Here, the waveguide substrate and the fine movement mechanism are the same as those in the first embodiment, and thus the description is omitted.

As shown in FIG. 4, the reflection type optical band elimination filter includes a non-reflection coating 403 provided at the center of the surface of a quartz substrate 401 and a gold mirror 402 provided outside the coating. I have. 3A is a plan view showing the structure of a reflection type optical band elimination filter, and FIG. 3B is a sectional view taken along line AA. The quartz substrate 401 is 1 mm or 1.5 mm thick transparent quartz having a smooth surface and frosted glass-like fine irregularities on the back surface. The anti-reflection coating 403 is made of SiO
2 and TiO2 are alternately laminated. In the second embodiment, the frequency cutoff bandwidth 404 is set to 100
In order to make it GHz, it is a rectangle having a width of 50 μm. The gold mirror 402 is a gold film having a thickness of 300 nm or more.

In such a configuration, the signal light incident on the waveguide substrate has a center frequency of 405 due to the reflection type optical band elimination filter disposed on the focal plane.
The signal light of a wavelength other than the wavelength within the frequency cutoff bandwidth 404 within each of the upper and lower 50 GHz is selectively reflected, multiplexed by reversing the path at the time of incidence, and emitted from the waveguide substrate.
As a result, light having a wavelength within the frequency cutoff bandwidth 404 is removed from the signal light. Here, when the reflection type optical band elimination filter 400 is finely moved in parallel with the waveguide substrate using the fine movement mechanism, the wavelength of the light incident on the frequency cutoff band changes. The center frequency of the band can be changed.

The output of a white light or erbium-doped optical fiber amplifier is input to this reflection type optical wavelength filter, and the filter characteristics are evaluated by an optical spectrum analyzer. As a result, as shown in FIG. A rectangular frequency cutoff characteristic was obtained. The frequency cutoff bandwidth 404 was 100 GHz, and the reflectance for incident light at frequencies outside the frequency cutoff band was 98.3%. As described above, the reflection type optical wavelength filter of the second embodiment has a rectangular frequency cutoff characteristic, and has an effect that its center frequency can be varied. The manufacturing method of the waveguide substrate and the reflection type optical band elimination filter which constitute this reflection type optical wavelength filter is the same as that of the first embodiment, and therefore the explanation is omitted.

Next, a third embodiment of the present invention will be described. The reflection type optical wavelength filter according to the third embodiment of the present invention is a low-pass filter. The first embodiment is different from the first embodiment except that the reflection type optical band-pass filter according to the first embodiment is a reflection type optical low-pass filter. It is the same as the form of. Here, the waveguide substrate and the fine movement mechanism are the same as those in the first embodiment, and thus the description is omitted.

As shown in FIG. 6, the reflection type optical low-pass filter includes a non-reflection coating 503 provided on the right half surface of the surface of the quartz substrate 501 and a gold mirror 502 provided on the left half surface thereof. . 3A is a plan view showing the structure of a reflection type optical low-pass filter, and FIG.
Is a sectional view taken along the line A-A. The quartz substrate 501 is 1 mm or 1.5 mm thick transparent quartz having a smooth surface and frosted glass-like fine irregularities on the back surface. The anti-reflection coating 503 is a multilayer film in which SiO 2 and TiO 2 are alternately stacked. The gold mirror 502 is a gold film having a thickness of 300 nm or more.

In such a configuration, the signal light incident on the waveguide substrate is selectively reflected by the reflection type optical low-pass filter disposed on the focal plane, at a low frequency of 505 or less. The light is multiplexed by following the path at the time of incidence in reverse, and is emitted from the waveguide substrate. As a result,
Light having a frequency higher than the cutoff frequency 505 is removed from the signal light. Here, if the reflection type optical low-pass filter 500 is finely moved in parallel with the waveguide substrate using the fine movement mechanism, the wavelength of light incident on the frequency transmission band 504 changes. Can be changed.

The output of a white light or erbium-doped optical fiber amplifier is input to the reflection type optical wavelength filter, and the filter characteristics are evaluated by an optical spectrum analyzer. As a result, as shown in FIG. A rectangular frequency transmission characteristic was obtained. The reflectance for the incident light in the frequency transmission band 504 was 98.3%. As described above, the reflection type optical wavelength filter of the third embodiment has a rectangular frequency transmission characteristic, and has an effect that its cutoff frequency can be varied. The manufacturing method of the waveguide substrate and the reflection type optical low-pass filter which constitute this reflection type optical wavelength filter is the same as that of the first embodiment, and the explanation is omitted.

Next, a fourth embodiment of the present invention will be described. The reflection type optical wavelength filter according to the fourth embodiment of the present invention is a bandpass filter capable of changing the frequency transmission bandwidth, and the reflection type optical bandpass filter according to the first embodiment is replaced with a variable bandwidth optical bandpass. This is the same as the first embodiment except that a filter is used. here,
Since the waveguide substrate and the fine movement mechanism are the same as those in the first embodiment, the description is omitted.

The variable bandwidth optical bandpass filter is shown in FIG.
As shown in the figure, the quartz mirror 601 comprises a gold mirror 602 provided at the center of the surface of the quartz substrate 601 and an anti-reflection coating 603 provided outside thereof. 3A is a plan view showing the structure of the variable bandwidth optical bandpass filter, and FIG. 3B is a cross-sectional view taken along line AA. Quartz substrate 6
01 is a transparent quartz of 1 mm or 1.5 mm in thickness having a smooth surface and frosted glass-like fine irregularities on the back surface. The gold mirror 602 is a gold film having a thickness of 300 nm or more. In the fourth embodiment, the shape is trapezoidal in order to make the frequency transmission bandwidth variable between 20 GHz and 400 GHz. 10 μm on the side, 2 on the long side
It is set to 00 μm. The anti-reflection coating 603 is S
It is a multilayer film in which iO2 and TiO2 are alternately stacked.

In such a configuration, the variable bandwidth optical band-pass filter disposed on the focal plane of the waveguide substrate is moved in a direction perpendicular to the waveguide substrate by the fine movement mechanism, so that the incident signal light is reduced. Gold mirror 60 to be reflected
2 is 10 μm on the short side 604a to 2 μm on the long side 604b.
It varies between 00 μm. Thereby, the frequency transmission bandwidth can be changed between 20 GHz and 400 GHz. Further, as in the first embodiment, when the variable bandwidth optical bandpass filter is finely moved in parallel with the waveguide substrate by the fine movement mechanism, the center frequency of the frequency transmission band can be changed.

As described above, the reflection type optical wavelength filter of the fourth embodiment has a rectangular frequency transmission characteristic, and has an effect that its center frequency and frequency transmission bandwidth can be varied. The manufacturing method of the waveguide substrate and the variable bandwidth optical bandpass filter constituting the reflection type optical wavelength filter is the same as that of the first embodiment, and the description is omitted.

Next, a fifth embodiment of the present invention will be described. The reflection type optical wavelength filter according to the fifth embodiment of the present invention is a high-pass filter having a transmittance that changes linearly with frequency, and reflects the reflection type optical band-pass filter according to the first embodiment. This is the same as the first embodiment except that a filter whose rate changes linearly is used. Here, the waveguide substrate and the fine movement mechanism are the same as those in the first embodiment, and thus the description is omitted.

As a method of changing the reflectivity linearly,
The film thickness dependence of the light reflectance of gold can be used. FIG.
Is a graph showing the film thickness dependence of the light reflectance of gold. According to this graph, the light reflectivity of gold increases logarithmically with the film thickness, and becomes constant at a film thickness of 300 nm or more (9).
8.3%).

As shown in FIG. 10, the high-pass filter 700 having a transmittance that changes linearly with the frequency using this method has a film thickness provided at the center of the surface of the quartz substrate 701 which varies depending on the position. A gold mirror 702 comprising a region 705 and a region having a constant film thickness, an anti-reflection coating 703a provided outside the region having a constant film thickness, and a region having a constant film thickness from a region 705 having a different film thickness depending on a position. Anti-reflective coating 703 provided at the same width as
The quartz substrate 701 is exposed between the region 705 where the thickness of the gold mirror 702 varies depending on the position and the anti-reflection coating 703b. 3A is a plan view showing the structure of a high-pass filter having a transmittance that changes linearly with frequency, and FIG. 3B is a cross-sectional view taken along line AA. The quartz substrate 701 has a smooth surface and a frosted glass-like fine unevenness on the back surface, and has a thickness of 1 m.
m or 1.5 mm transparent quartz. Gold mirror 702
Has a thickness of 300 nm or more in a region where the film thickness is constant, has a reflectance of 50% at the center frequency in a region 705 where the film thickness varies depending on the position, and changes linearly in the region. This is a gold film whose film thickness is controlled. The anti-reflection coatings 703a and 703b are multilayer films in which SiO2 and TiO2 are alternately stacked.

In such a configuration, the signal light incident on the waveguide substrate is reflected by the high-pass filter 700 disposed on the focal plane with a reflectance that varies linearly with frequency, and reverses the path at the time of incidence. And are emitted from the waveguide substrate. As a result, light having a frequency lower than the cutoff frequency 707 is removed from the signal light, and light having a frequency incident on the region 705 having a different thickness depending on the position is attenuated. Here, when the high-pass filter 700 is finely moved in parallel with the waveguide substrate using the fine movement mechanism,
Since the wavelength of light incident on the frequency transmission band 704 changes, the center frequency 705 of the high-pass filter 700 can be changed.

The output of a white light or erbium-doped optical fiber amplifier was input to this reflection type optical wavelength filter, and the filter characteristics were evaluated by an optical spectrum analyzer. As a result, as shown in FIG. Frequency transmission characteristics were obtained. The frequency transmission bandwidth of this filter is
The band of the region showing a linear cutoff characteristic at 3200 GHz was 100 GHz.

As described above, the reflection type optical wavelength filter of the fifth embodiment has a linear frequency transmission characteristic with respect to the frequency, and has an effect that the center frequency can be varied. Such a filter can be applied to the vestigial sideband (VSB) system. The manufacturing method of the waveguide substrate and the reflection type optical high-pass filter which constitute this reflection type optical wavelength filter is the same as that of the first embodiment, and the explanation is omitted.

Next, a sixth embodiment of the present invention will be described. The reflection type optical wavelength filter according to the sixth embodiment of the present invention is a high-pass filter having a transmittance that changes linearly with frequency, and reflects the reflection type optical band-pass filter according to the first embodiment. This is the same as the first embodiment except that a filter whose rate changes linearly is used. Here, the waveguide substrate and the fine movement mechanism are the same as those in the first embodiment, and thus the description is omitted.

As a method of linearly changing the reflectance,
The reflectance profile can be controlled by spatially changing the light reflection area. As shown in FIG. 12, a high-pass filter 800 having a transmittance that changes linearly with frequency using this method includes a comb-shaped gold mirror 802 provided at the center of the surface of a quartz substrate 801, And the anti-reflection coating 803, and the gold mirror 8
The quartz substrate 801 is exposed between the comb teeth portions 02. 3A is a plan view showing the structure of a high-pass filter having a transmittance that changes linearly with frequency, and FIG. 3B is a cross-sectional view taken along line AA. Quartz substrate 801
Is 1 mm or 1.5 mm thick transparent quartz having a smooth surface and frosted glass-like fine irregularities on the back surface. The gold mirror 802 is a gold film having a comb-like shape and a periodic area that changes in the vertical direction. The anti-reflection coating 803 is made of Si
This is a multilayer film in which O2 and TiO2 are alternately stacked.

In such a configuration, the signal light incident on the waveguide substrate is reflected by the high-pass filter 800 disposed on the focal plane with a reflectance that changes linearly with frequency, and reverses the path at the time of incidence. And are emitted from the waveguide substrate. As a result, light having a frequency lower than the cutoff frequency is removed from the signal light, and light having a frequency incident on the comb-shaped region is attenuated. Here, if the high-pass filter 800 is finely moved in parallel with the waveguide substrate using the fine movement mechanism, the wavelength of the light incident on the frequency transmission band 804 changes, so that the center frequency 806 of the high-pass filter 800 may be changed. it can.

As described above, the reflection type optical wavelength filter of the sixth embodiment has a linear frequency transmission characteristic with respect to the frequency, and has an effect that the center frequency can be changed. The manufacturing method of the waveguide substrate and the reflection type optical high-pass filter which constitute this reflection type optical wavelength filter is the same as that of the first embodiment, and the explanation is omitted.

Next, a seventh embodiment of the present invention will be described. FIG. 13 is a configuration diagram of a transmission type optical wavelength filter according to a seventh embodiment of the present invention. This seventh
The transmission type optical wavelength filter 2 according to the embodiment is a band-pass filter, and includes the first waveguide substrate 100, the transmission type spatial intensity filter 205, and the second waveguide substrate 200. The description of the first waveguide substrate 100 is omitted because it is the same as that of the first embodiment. Second waveguide substrate 20
0 is the third slab waveguide 206, the second waveguide array 20
7, a fourth slab waveguide 208 and a second waveguide 209, which are connected on the single crystal silicon substrate 201 in the above order. Since the structure of the second waveguide substrate 200 is the same as that of the first waveguide substrate 100, the description is omitted.

The transmission type spatial intensity filter 205 is a band pass filter, and as shown in FIG.
01, a rectangular opening 902 is provided.
3A is a plan view showing the structure of a transmission type optical bandpass filter, and FIG. 3B is a cross-sectional view taken along line AA. The transmission-type spatial intensity filter 205 is attached via an adapter to a fine movement mechanism that can be finely controlled by five axes and includes a micrometer. This fine movement mechanism can move back and forth, left and right and up and down, rotate around a front and rear axis, and rotate around a vertical axis.
The slab waveguide 104 is fixed to a common base together with the first waveguide substrate 100 so as to be arranged on an imaging focal plane for the waveguide array 103 near the end face opposite to the end face connected to the waveguide array 103. I have. Further, the second waveguide substrate 200 is provided with a transmission type spatial intensity filter on an imaging focal plane for the second waveguide array near the end face opposite to the end face connected to the second waveguide array of the third slab waveguide. 205 is fixed to a common base so as to be arranged.

In such a configuration, the signal light incident on the waveguide 101 is guided to the first slab waveguide 102, where it is distributed to each waveguide of the waveguide array 103. The signal light that has passed through the waveguide array 103 is subjected to time-space conversion and is incident on the second slab waveguide 104, where it is Fourier-transformed and forms an image on a focal plane. Thereafter, signal light having a wavelength within a frequency transmission bandwidth 904 within 50 GHz below and above the center frequency 905 is selectively transmitted by the transmission type spatial intensity filter 205 disposed on the focal plane, and the third slab waveguide is formed. The light is incident on 206, is multiplexed through the second waveguide array 207 and the fourth slab waveguide 208, and is emitted from the second waveguide 209. As a result, signal light composed of only light having a wavelength within the frequency transmission bandwidth 904 is obtained. Here, if the transmission type spatial intensity filter 205 is finely moved in parallel with the first waveguide substrate 100 using the fine movement mechanism, the wavelength of light incident on the frequency transmission band changes, so that the frequency of the transmission type optical wavelength filter is changed. The center frequency of the transmission band can be changed. As explained above,
The transmission type optical wavelength filter according to the seventh embodiment has a rectangular frequency transmission characteristic, and has an effect that its center frequency can be varied.

In a transmission type optical wavelength filter,
An optical elimination filter, an optical low-pass filter, and an optical high-pass filter can be realized similarly to the reflection type optical wavelength filter. For example, an optical elimination filter can be obtained by using the filter of FIG. 2, an optical band-pass filter can be obtained by using the filter of FIG. 4, and an optical low-pass filter can be obtained by inverting the filter of FIG. Also, by inverting the relationship between the gold mirror and the anti-reflection coating of the filter of FIG. 8, a variable bandwidth optical bandpass filter is obtained. In addition, by inverting the pattern of the gold mirror of the filter in FIG. 12, a high-pass filter having a frequency transmission characteristic that is linear with respect to frequency can be obtained. When using these filters, it is necessary to smooth the back surface of the quartz substrate.

In this embodiment, the tunable wavelength filter is constituted by finely moving the spatial filter by the fine movement mechanism. However, the filter is bonded to the focal plane without using the fine movement mechanism, or the filter is directly patterned on the focal plane. If a pattern mirror is arranged by vapor deposition of a metal such as gold, a fixed filter having extremely high stability can be obtained at low cost, although wavelength variability is lost.

[0041]

As described above, according to the present invention,
By combining the waveguide array and the spatial intensity filter, it is possible to obtain an optical wavelength filter having an arbitrary frequency transmission characteristic which has been difficult in the past.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a reflection-type wavelength filter according to a first embodiment of the present invention.

FIG. 2 is a structural diagram of a reflective optical bandpass filter according to the first embodiment of the present invention.

FIG. 3 is a characteristic diagram of the reflection-type wavelength filter according to the first embodiment of the present invention.

FIG. 4 is a structural diagram of a reflection type optical elimination filter according to a second embodiment of the present invention.

FIG. 5 is a characteristic diagram of a reflection-type wavelength filter according to a second embodiment of the present invention.

FIG. 6 is a structural diagram of a reflection type optical low-pass filter according to a third embodiment of the present invention.

FIG. 7 is a characteristic diagram of a reflective wavelength filter according to a third embodiment of the present invention.

FIG. 8 is a structural diagram of a variable bandwidth optical bandpass filter according to a fourth embodiment of the present invention.

FIG. 9 is a graph showing the film thickness dependence of the reflectance of a gold thin film.

FIG. 10 is a structural diagram of a reflective optical high-pass filter according to a fifth embodiment of the present invention.

FIG. 11 is a characteristic diagram of a reflection-type wavelength filter according to a fifth embodiment of the present invention.

FIG. 12 is a structural diagram of a reflective optical high-pass filter according to a sixth embodiment of the present invention.

FIG. 13 is a configuration diagram of a transmission type wavelength filter according to a seventh embodiment of the present invention.

FIG. 14 is a structural diagram of a transmission type optical bandpass filter according to a seventh embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Reflection type optical wavelength filter, 2 ... Transmission type optical wavelength filter, 100, 200 ... Waveguide substrate, 101, 209 ... Waveguide, 102, 104, 206, 208 ... Slab waveguide, 103, 207 ... Waveguide array , 105: reflection type spatial intensity filter, 106, 201: single crystal silicon substrate, 205: transmission type spatial intensity filter, 300: reflection type optical bandpass filter, 301, 401, 501, 60
1,701,801 ... quartz substrate, 302,402,50
2, 602, 702, 802 ... gold mirror, 303, 40
3, 503, 603, 703a, 703b, 803 ... non-reflective coating, 304, 604a, 604b, 70
4,804: frequency transmission bandwidth, 305, 405, 60
5,706,806,905 ... center frequency, 306,4
06, 506, 708: filter waveform, 400: reflection type optical elimination filter, 404: frequency cutoff bandwidth, 500: reflection type optical low-pass filter, 505, 70
7: cut-off frequency, 600: variable bandwidth optical bandpass filter, 700, 800: reflective optical high-pass filter, 9
00: a transmission type optical bandpass filter; 901, a thin metal plate; 902, an opening.

Claims (13)

[Claims] 1. A waveguide, a first slab waveguide, a waveguide array, and a second slab waveguide are connected in this order, and the second slab waveguide is opposite to an end face connected to the waveguide array. An optical wavelength filter having an imaging focal plane for the waveguide array in the vicinity of the end face of the optical filter, and a reflective spatial filter arranged in the vicinity of the imaging focal plane. 2. The optical wavelength filter according to claim 1, further comprising a fine movement mechanism for adjusting a position of said reflection type spatial filter, wherein a frequency profile is controlled by adjusting a position of said reflection type spatial filter. 3. The first waveguide, the first slab waveguide, the first waveguide array, and the second slab waveguide are connected in this order, and the third slab waveguide, the second waveguide array, and the fourth slab waveguide are connected. A waveguide and a second waveguide are connected in this order; and an imaging focal plane for the first waveguide array near an end surface opposite to the end surface where the second slab waveguide is connected to the first waveguide array. Wherein the third slab waveguide has an imaging focal plane for the second waveguide array near an end face opposite to the end face connected to the second waveguide array; A light wavelength, wherein a transmission spatial filter and an imaging focal plane of the third slab waveguide for the second waveguide array are arranged in the vicinity of an imaging focal plane of the waveguide for the first waveguide array. filter. 4. The optical wavelength filter according to claim 3, further comprising a fine movement mechanism for adjusting a position of said transmission type spatial filter, wherein a frequency profile is controlled by adjusting a position of said transmission type spatial filter. 5. The optical wavelength filter according to claim 1, wherein the reflection type spatial filter has a reflection surface in one region divided by a straight line perpendicular to the waveguide substrate. . 6. The optical wavelength filter according to claim 3, wherein the transmission-type spatial filter has a transmission surface in one region divided by a straight line perpendicular to the waveguide substrate. Wavelength filter. 7. The optical wavelength filter according to claim 1, wherein the reflection type spatial filter has a reflection surface in a region sandwiched between two straight lines perpendicular to the waveguide substrate. Optical wavelength filter. 8. The optical wavelength filter according to claim 3, wherein the transmission-type spatial filter has a transmission surface in a region sandwiched between two straight lines perpendicular to the waveguide substrate. Optical wavelength filter. 9. The optical wavelength filter according to claim 1, wherein said reflective spatial filter has a reflective surface in a trapezoidal region. 10. The optical wavelength filter according to claim 3, wherein said transmission-type spatial filter has a transmission surface in a trapezoidal region. 11. The optical wavelength filter according to claim 1, wherein the reflection type spatial filter changes the reflectance continuously by spatially changing the thickness of a medium serving as a mirror. An optical wavelength filter. 12. The optical wavelength filter according to claim 1, wherein the position of the reflective spatial filter in the direction parallel to the waveguide substrate at the boundary of the reflection region is perpendicular to the waveguide substrate within the beam diameter. On the other hand, an optical wavelength filter characterized by periodically changing. 13. The optical wavelength filter according to claim 3, wherein the transmission-type spatial filter is arranged such that a position of a boundary of a transmission region in a direction parallel to the waveguide substrate is perpendicular to the waveguide substrate within a beam diameter. On the other hand, an optical wavelength filter characterized by periodically changing.