JPH0545680A - Light wavelength filter element and light wavelength filter device - Google Patents

Abstract

PURPOSE:To provide a variable wavelength filter which can be widened in the variation range of transmission wavelength and narrowed down in the half-value width of the transmission wavelength. CONSTITUTION:A 1X4 branch 10 is constituted by connecting 1X2 branches 22 in many stages and a connection waveguides 14 which are equal in length are coupled with the respective outputs of the branch 10. A straight waveguide 16 is used as one of the four connection waveguides 14 and straight waveguides 17 which have a lower refractive index than the straight waveguide 16 are coupled as the three remaining waveguides. Those connection waveguides 14 are arranged in parallel. The length of the straight waveguide 16 is made different generating an arithmetical progression so that phase differences between light beams projected from the respective connection waveguides 14 generate an arithmetic progression, and the refractive index of each straight waveguide 16 is electrically varied and controlled so that the quantities of refractive index variation become equal to one another. Then the light beams projected from the respective connection waveguides 14 are multiplexed by a convex lens 24 to cause interference.

Description

Detailed Description of the Invention

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical wavelength filter element and an optical wavelength filter device capable of variably controlling a transmission wavelength.

2. Description of the Related Art Conventionally, as a filter element for separating an optical signal of a specific wavelength λ ₀ from wavelength-multiplexed optical signals, for example, reference I: IEEE Communicative is used.
a-tion Magazine
Communication Magazine) October 1989
Some are disclosed in p53-63. The filter element disclosed in Document I is classified into four types: a: Fabry-Perot type, b: Mach-Zehnder type, c: mode conversion type, and d: Bragg reflection type. Considering changing the transmission wavelength λ _{0 of the} filter from the design reference wavelength λ to λ + Δλ,
For the types a, b and d, the formula (1) of Table 1 is established for the wavelength variation Δλ, and for the type c, the formula (2) of Table 1 is established for the wavelength variation Δλ. It can be expressed as λ ₀ = λ + Δλ. In the formula, Δn is the amount of the refractive index that can be electrically changed with respect to the waveguide included in the filter element, n is the refractive index of the waveguide included in the filter element, and δn is the refractive index difference between modes, for example, between TM and TE modes. Represents the difference in refractive index. Generally, the design reference wavelength λ is a constant that is uniquely determined from the shape, size, forming material, etc. of the filter element constituent element. However, among the c-type, the one utilizing the acousto-optic effect (AO effect) can electrically change the period of the grating for converting the mode of light,
The design reference wavelength λ can be variably controlled. Therefore,
Although there is an upper limit to the refractive index change amount Δn that is electrically variably controlled, the variable range (tuning width) of the transmission wavelength λ ₀ is the widest in the type c. Further, the full width at half maximum Δ of the light transmittance peak in each of the a, b, c and d type filters.
λ _FWHM is expressed by equation (3), equation (4), and
It can be expressed by equations (5) and (6). In the equation, L represents the element length (electrode length) of the filter element, and R represents the reflectance of the input / output end face of the filter element. Since normally δn << n, the half-width Δλ _{FWHM in} the types a, b, and d becomes very narrow as can be understood from the equations (3) to (6), but half in the type c. The value width Δλ _FWHM becomes very wide. Here, the transmission bandwidth (half-value width) per channel of the filter element is Δλ
Assuming _FWHM , the number of channels CH is expressed by the equation (7) in Table 1 for the type a, the equation (8) in Table 1 for the types b and c, and the expression (9) in Table 1 for the type d. Can be expressed as Δ in the formula
n _max represents the maximum Δn in the changeable range. However, in case of type a, FSR (Free Spectral R
Therefore, when the device alone is used, CH =
It becomes pi * R1 / ² / (1-R). Therefore Δn _max ≈
If the value is 0.01, then in the type a, R ≈ 0.9 and the FSR
Due to the limitation of 10 channels (potentially 80 channels if FSR is neglected), 80 channels with L≈1 cm for type b, 8 channels with L≈1 mm for type c and L = 500 μm for type d. Will be 8 channels.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
b, type of d in the filter element, 1 transmission bandwidth [Delta] [lambda] _FWHM narrowly can be tuned width per channel number of channels can not be wide (variable range of transmission wavelength lambda ₀₎ (= Tuning width / 1 per channel The transmission bandwidth) cannot be increased. Further, in the c-type filter element, the tuning width can be widened, but the transmission bandwidth Δλ
_The number of channels cannot be increased because the _FWHM cannot be narrowed.
In consideration of increasing the number of channels, in the types a, b, and d, if the element length L is increased, the transmission bandwidth Δλ _FWHM can be narrowed, so that the number of channels can be increased, but the transmission bandwidth Δλ
_{If the FWHM} becomes too narrow, the filter element becomes difficult to handle and becomes impractical. In the C type, the number of channels cannot be increased unless the element length L is extremely long (for example, L = 1 m). An object of the present invention is to provide an optical wavelength filter device and an optical wavelength filter device capable of narrowing the transmission bandwidth per channel within a practical range and widening the tuning width in order to solve the above-mentioned conventional problems. Especially.

In order to achieve this object, the optical wavelength filter element of the first invention of this application is 1 ×
N branch section and N × 1 interference section, N connection waveguides provided between the output ports of the corresponding branch section and the input port of the interference section, and structural phase difference control section provided in the connection waveguide And a refractive index variable portion, and the length of each structural phase difference control portion is different so as to form an arithmetic progression with the first tolerance, and the length of each refractive index variable portion with the second tolerance. It is characterized in that they are different so as to form an arithmetic sequence. The optical wavelength filter device of the second invention is characterized in that the optical wavelength filter elements of the first invention are connected in multiple stages, and the first tolerances of these optical wavelength filter elements are made different from each other.

According to the first aspect of the invention, the 1 × N branching unit inputs the wavelength-multiplexed light, branches it, and outputs the wavelength-multiplexed light from each of the N output ports. The N × 1 interference unit inputs the wavelength-multiplexed light from each of the N input ports via the connection waveguide and multiplexes them to interfere with the wavelength-multiplexed light from each input port. Due to this interference, light of a specific wavelength is output from the output port of the interference section. The power and phase of the light output from each output port of the branch unit are equal. However, since the connection waveguide is provided with a structural phase difference control unit and a refractive index variable unit,
The light from the branch portion is input to the interference portion through the structural phase difference control portion and the refractive index variable portion. Therefore, a phase difference of the light is generated by the action of the structural phase difference control unit and the refractive index variable unit before the light enters the interference unit from the branching unit. The phase difference of light generated by the structural phase difference controller is a substantially constant fixed value that is not variably controlled. On the other hand, the phase difference of light generated by the refractive index variable unit can be changed by electrically variably controlling the refractive index of the refractive index variable unit,
It changes by an amount corresponding to the amount of change in the refractive index of the variable refractive index portion.
Therefore, the phase difference of the light input to the interference section is a superposition of the phase difference produced by the structural phase difference control section and the phase variation produced by the refractive index variable section. Moreover, the lengths of the structural phase difference controllers are made different so as to form the arithmetic progression, and the lengths of the refractive index variable portions are made different so as to form the arithmetic progression. Therefore, the structural phase difference control unit and the refractive index variable unit whose lengths form the arithmetic progression can make the phase difference of the light input to the interference unit different so as to form the arithmetic progression. ..
By causing the interference section to interfere the wavelength-multiplexed light having such a phase difference, it is possible to prevent the interference section from outputting the light of the specific wavelength and the interference section from outputting the lights of the other wavelengths. The light output from the interference unit is a plurality of lights whose wavelengths are separated by a specific cycle Δλ. Then, when the refractive index of the refractive index variable portion is electrically changed, the magnitude of the phase difference of the light input to the interference portion changes. Therefore, the refractive index of the refractive index variable portion is variably controlled and output from the interference portion. The wavelength of light can be changed. At this time, the wavelength of the light output from the interference section changes while the period Δλ of the wavelength of the light is kept substantially constant. According to the second invention, the optical wavelength filter elements of the first invention are connected in multiple stages, and the first tolerances of these optical wavelength filter elements connected in multiple stages are made different. Thus, the first tolerances are different. Therefore, the light output from the final stage element of the optical wavelength filter elements connected in multiple stages (the light output from the optical wavelength filter device of the second invention) is the light transmitted through all the elements of the optical wavelength filter elements connected in multiple stages. is there. The cycle of the wavelength of the light output from the optical wavelength filter device of the second invention is the least common multiple of the cycles Δλ of all the optical wavelength filter elements connected in multiple stages.

Embodiments of the first and second inventions will be described below with reference to the drawings. It should be noted that the drawings are merely schematic representations so that the present invention can be understood, and therefore the present invention is not limited to the illustrated examples. FIG. 1 is a plan view schematically showing the configuration of the first embodiment of the optical wavelength filter element of the first invention. The optical wavelength filter element of the first embodiment is 1 × N
The branching section 10 and the N × 1 interference section 12, N connecting waveguides 14 provided between the output port of the branching section 10 and the input port of the interference section 12, which correspond to each other, and the structure provided in the connecting waveguide 14. The phase difference control units 16 and 17 and the refractive index varying unit 18 are provided. Then, the lengths of the structural phase difference control units 16 and 17 are made different so as to form an arithmetic progression with the first tolerance, and the lengths of the respective refractive index variable units 18 are made equal with the second tolerance. Different to form a difference sequence. In this embodiment, the branch section 10, the connection waveguide 14, the structural phase difference control section 16 and the refractive index variable section 18 are provided on the same substrate 20.
The substrate 20 is a ferroelectric crystal substrate or a compound semiconductor substrate. The branch unit 10 is formed by connecting 1 × 2 symmetrical Y branches 22 in multiple stages, and for example, the Y branches 22 are connected in two stages to form a 1 × 4 branch unit 10. The i-th Y-branch 22 is connected to the output of the i-th Y-branch 22 one by one.
The input of the Y-branch 22 of the first stage is used as the input port of the branching unit 10, and the input optical fiber 23 is coupled to this input port. The output of each Y branch 22 at the final stage is used as an output port of the branch unit 10. The geometrical distances of the light propagation paths from the input port of the branching unit 10 to each output port of the branching unit 10 are made equal. In the figure, the output surface provided with the output port of the branching unit 10 is indicated by the reference symbol X. Further, the same number of connection waveguides 14 as the output of the branching section 10, for example, four are provided. One connection waveguide 14 is coupled to each output port of the branch unit 10. Each connection waveguide 14 is a waveguide configured by arbitrarily and structurally combining the structural phase difference control units 16 and 17, and the connection waveguide 14 extends from the output face X of the branching unit 10 to the end face Y of the substrate 20. Set up. By making the refractive indexes of the structural phase control units 16 and 17 different and / or the waveguide widths different, each connection waveguide 1
The phase difference of light on the output surface of No. 4 is made different so as to form an arithmetic progression. In this example, the structural phase difference control unit 16
And 17 are linear waveguides having the same waveguide width and different refractive indexes, one of the four connecting waveguides 14 is a linear waveguide constituted by the structural phase difference control unit 16 alone, and the remaining three are structural waveguides. It is a linear waveguide configured by coupling the physical phase difference control units 16 and 17. These structural phase difference control units 16
The phase difference of the light formed by 17 and 17 is a fixed value which is not variably controlled. In the figure, the structural phase difference control unit 16 forming the connection waveguide 14 is represented by a dotted line,
Also, the structural phase difference control unit 17 is represented by a solid line. In the direction along the connecting waveguide 14, the length of each connecting waveguide 14 is made equal, and the length of each structural phase difference control region 16 is made different so as to form an arithmetic progression. Then, these connection waveguides 14 are arranged in parallel with each other. By arranging in parallel, the light emitted from the emission surface Y of the connection waveguide 14 (the end surface of the substrate 20 in this embodiment) can be made into parallel light. Further, in the direction along the connection waveguide 14, the length of each refractive index variable portion 18 is made different so as to form an arithmetic progression, and the refractive index variable portion 18 is provided in a part or the whole of one connection waveguide 14. For example, the structural phase difference control unit 16 and the refractive index variable unit 18 have the same shape, size, and arrangement position, so that the structural phase difference control units 16 and 17 and the refractive index variable unit 18 have different lengths. Let the tolerance of the difference sequence be the same value L. In the figure, the refractive index variable portion 18 is shown surrounded by a rectangular frame of two-dot chain line. The refractive index of the refractive index varying section 18 is electrically variably controlled via an electrode (not shown). When a ferroelectric substrate is used as the substrate 20, an electric field is applied to the refractive index variable section 18 to variably control the refractive index by the electro-optical effect, and when a compound semiconductor substrate is used, the refractive index is changed by the electro-optical effect. The refractive index may be variably controlled, or the refractive index may be variably controlled by injecting carriers into the refractive index variable portion 18 by the plasma effect. With the amount of change in the refractive index of the refractive index variable unit 18 set to zero, the structural phase difference control units 16 have the same refractive index, and the structural phase difference control units 17 have the same refractive index. The refractive indices of the control units 16 and 17 are different. When variably controlling the refractive index of the refractive index variable unit 18, the amount of change in the refractive index of each refractive index variable unit 18 is made equal. The interference section 12 is composed of a medium for propagating light, for example, the atmosphere and a convex lens 24 arranged in the atmosphere. The convex lens 24 inputs the parallel light from each connection waveguide 14 and converges the light at the focal position. Therefore, the lights from the respective connection waveguides 14 combine and interfere at the focal position of the convex lens 24. The light emitted from each connection waveguide 14 propagates through the medium 26 and enters the convex lens 24. The light emitted from the convex lens 24 propagates through the medium 26 and reaches the focal position. In this example, the portion of the medium 26 in contact with the end face of the connection waveguide 14 on the emission surface Y is used as the input port of the interference section 12 and the focal point of the convex lens 24 is used as the output port of the interference section 12, and therefore, the 4-input and 1-output interference section Make up twelve. The output optical fiber 23 is coupled to the focal point of the convex lens 24. The convex lens 24 and the medium 26 may be a waveguide and a waveguide lens provided on the substrate 20. 2A and 2B are cross-sectional views showing an example of a specific configuration of the structural phase difference control units 17 and 16 that form the connection waveguide 14. As shown in FIG. 2A, in this example, the substrate 20 is a LiNbO ₃ substrate, the first diffusion material is diffused into the substrate 20 to form a first diffusion waveguide, and this diffusion waveguide is structurally formed. Phase difference control unit 1
7 Further, as shown in FIG. 2B, the second diffusion material is diffused into the first diffusion waveguide to form a second diffusion waveguide having a higher refractive index than the first diffusion waveguide. The waveguide is the structural phase difference control unit 16. The structural retardation control units 16 and 17 having different refractive indexes are formed by arbitrarily and appropriately setting the types and diffusion concentrations of the first and second diffusing substances and other diffusion conditions. Then, the buffer layer 27 is formed on the substrate 20 on which the structural retardation controllers 16 and 17 are formed.
To provide. Further, electrodes 29 and 31 for electrically variably controlling the refractive index are provided for the structural phase difference control unit 16 which is the refractive index variable unit 18. In the figure, the first diffused substance diffused region of the substrate 20 is indicated by a cross, and the second diffused substance diffused region is indicated by a circle. The waveguide structure of the connection waveguide 14 and the electrode structure of the refractive index variable portion 18 can be arbitrarily changed according to the substrate material. Next, the operating characteristics of the optical wavelength filter element of this embodiment will be described. When the amount of change in the refractive index of the refractive index varying unit 18 is set to zero, the wavelength λ of the light input from the output port of the interference unit 12 to the output optical fiber 23 is approximately as shown in Table 2 (10). Can be represented. However, m is a positive integer, L is the structural retardation control unit 16, 1
7 and the common tolerance of the respective arithmetic progressions formed by the lengths of the refractive index variable portion 18, δn is the structural phase difference control portion 16 in the state where the refractive index change amount of the refractive index variable portion 18 is zero, The refractive index difference of 17 and n _P represent the refractive index of the medium 26 of the interference section 12. The wavelength λ is a wavelength that satisfies the expression (10) in each case where m = 1, 2, 3, ... These plural wavelengths λ have a cycle δλ (m =
They are separated by a difference in wavelength λ when j and m = j + 1. The period δλ can be expressed as shown in Table 2 (11). Incidentally, the period δλ FSR (F ree S pectral R an
ge). Then, the refractive index difference between the structural phase difference control unit 16 and the substrate 20 is electrically changed to change from δn to δn +.
When the wavelength is changed to Δn (Δn represents the amount of change in the refractive index of the refractive index changing unit 18), the wavelength of the light input from the interference unit 12 to the output optical fiber 23 changes from λ to λ + Δλ _t. Then, the amount of wavelength change Δλ _t can be expressed as shown in Table 2 (12). Similar to the wavelength lambda, the wavelength lambda + [Delta] [lambda] _t is the period each plurality presence plurality of wavelength lambda + [Delta] [lambda] _t These δ
Separate by λ. The half-value width (transmission bandwidth) of light of one wavelength λ and the half-value width (transmission bandwidth) of light of one wavelength λ + Δλ _t are equal values Δλ _w , and the transmission bandwidth Δλ _w is It can be expressed as in equation (2). However, N represents the total number of connection waveguides 14 arranged. The analysis up to here is derived from an analogy based on the analysis regarding the diffraction grating (Reference 1: Wolf, "Principles of Optics"). In order to increase the number of channels most efficiently, the wavelength of the light input from the interference section 12 to the output optical fiber 23 is changed from λ to λ +
It is preferable to change it to δλ. Therefore, if the wavelength change amount Δλ _t at the maximum change is expressed as Δλ _tmax , Δλ _t
It is preferable that _tmax = δλ. Maximum wavelength change Δλ
_tmax can be expressed as shown in Expression (14) in Table 2, and Expression (15) is obtained from Expression (14). The maximum number of channels CH _max when Δλ _tmax = δλ can be expressed as shown in Table 2 (16). As is clear from the equation (16), the maximum channel number CH _max is equal to the total number N of the connection waveguides 14, and therefore the maximum channel number CH is increased by increasing the total number N of the connection waveguides 14. _max can be increased. Further, the wavelength change amount Δλ _t is given by the equation (12), and the wavelength change amount is n compared to the Fabry-Perot type optical wavelength filter and the ring resonator type optical wavelength filter having similar operation characteristics to the optical wavelength filter element of this embodiment. It can be increased by a factor of / δn (n is the refractive index of the substrate). FIG. 3 is a plan view schematically showing the configuration of the second embodiment of the first invention.
The constituents corresponding to those of the first embodiment of the first invention are designated by the same reference numerals. In the following description, the points different from the first embodiment of the first invention will be described,
Detailed description of the same points as those of the first embodiment of the first invention will be omitted. The optical wavelength filter element of the second embodiment,
It has the same configuration as the first embodiment of the first invention except that the configuration of the interference unit 12 is different. In this embodiment, in addition to the branch section 10 and the connection waveguide 14, the interference section 12 is provided on the same substrate 20.
Set up in. The interference section 12 is formed by providing a linear waveguide 28 and a planar waveguide 30 on the substrate 20. The planar waveguide 30 has a fan-like shape that spreads from the output surface P toward the input surface Q,
The input surface Q of the planar waveguide 30 has an arc shape. One linear waveguide 28 is provided for each output of each connection waveguide 14.
Of the planar waveguide 3 by connecting the input of
0 to the input surface Q, respectively. A light converging point O is provided on the output surface Q, and the linear waveguides 28 are radially arranged so that extension lines of the axes of the linear waveguide 28 pass through the converging points O, respectively. The light incident on the planar waveguide 30 from the linear waveguide 28 generates a concentric circular wave centered on the focusing point O.
The concentric circular waves are converged at the focal point O, combined, and interfered. The output optical fiber 23 is coupled to the focusing point O on the output surface Q and the vicinity thereof. The operating characteristics of this embodiment are
In principle, it is similar to the case of the first embodiment of the first invention. FIG. 4 is a plan view schematically showing the configuration of the third embodiment of the first invention. The constituents corresponding to those of the first embodiment of the first invention are designated by the same reference numerals.
In the following description, differences from the first embodiment of the first invention will be described, and detailed description of the same points as the first embodiment of the first invention will be omitted. The optical wavelength filter element of the third embodiment has the same configuration as that of the first embodiment of the first invention except that the configuration of the interference section 12 is different. In this example,
In addition to the branching section 10 and the connection waveguide 14, the interference section 12 is provided on the same substrate 20. The interference unit 12 is formed by connecting 2 × 1 symmetrical Y branches 32 in multiple stages, and for example, the Y branches 32 are connected in two stages to form a 4 × 1 interference unit 12. I + 1th stage Y
The i-th stage Y-branch 32 is connected to each of the inputs of the branch 32 one by one. The inputs of the Y-branches 32 of the first stage are used as the input ports of the interference section 12, and the connection waveguides 14 are coupled to the input ports, respectively. The output of the Y branch 32 at the final stage is used as the output port of the interference unit 12, and the output optical fiber 23 is coupled to this output port.
The geometrical distances of light propagation paths from the input ports of the interference unit 12 to the output ports of the interference unit 12 are made equal. The light input to each input port of the interference unit 12 is sequentially combined by the branch 32 of each stage, and all the lights input to each input port of the interference unit 12 are combined and interfered by the branch 32 of the final stage. The operating characteristics of this embodiment are the same as those of the first embodiment of the first invention in principle, but the output intensity K of the light of wavelength λ which is incident on the output optical fiber 23 from the interference section 12 is the same.
Can be expressed as shown in Table 2 (17). FIG. 5 is a plan view schematically showing the configuration of the fourth embodiment of the first invention. The constituents corresponding to those of the third embodiment of the first invention are designated by the same reference numerals. In the following description, points different from the third embodiment of the first invention will be described, and detailed description of the same points as the third embodiment of the first invention will be omitted. The optical wavelength filter element of the fourth embodiment has the same configuration as that of the third embodiment of the first invention except that the configuration of the connection waveguide 14 is different. In this embodiment, four connecting waveguides 1
All 4 are linear waveguides configured by coupling the structural phase difference controllers 16 and 17. The structural phase difference control unit 17 and the refractive index variable unit 18 have the same shape, size, and arrangement position. Also in this embodiment, the structural phase difference control unit 1
The tolerances of the arithmetic progressions formed by the lengths of 6 and 17 and the refractive index variable portion 18 are equal. In principle, the operating characteristics of this embodiment are similar to those of the third embodiment of the first invention. FIG. 6 is a plan view schematically showing the configuration of an embodiment of the second invention. The constituents corresponding to those of the third embodiment of the first invention are designated by the same reference numerals. In the following description, detailed description of the same points as in the third embodiment of the first invention will be omitted. The optical wavelength filter device of this embodiment is formed by connecting the optical wavelength filter elements of the first invention in multiple stages. Then, the first tolerances of the optical wavelength filter elements connected in multiple stages are made different. In this embodiment, for example, the optical wavelength filter elements 34 and 36 of the third embodiment of the first invention are connected in multiple stages. The output of the interference section 12 of the former optical wavelength filter element 34 and the input of the branch section 10 of the latter optical wavelength filter element 36 are coupled to each other, and the input of the input optical fiber to the input of the branch section 10 of the former optical wavelength filter element 34. 23 and the interference section 12 of the optical wavelength filter element 36 in the subsequent stage.
The optical fiber 23 for output is coupled to the output of. Structural phase difference control units 16 and 17 of the optical wavelength filter element 34 in the previous stage
And the tolerance of the arithmetic progression formed by the length of the refractive index variable portion 18 is the same value L1, and the optical wavelength filter element 36 in the subsequent stage is
Structural phase difference control units 16 and 17 and refractive index variable unit 18
The tolerances of the arithmetic progression formed by the lengths of are equal to the value L2 and make these tolerances L1 and L2 different. For example, these tolerances L1 and L2 are determined so as to satisfy the expression (18) in Table 2. However, Δ represents a positive integer smaller than the total number N of the connection waveguides 14. Next, the operating characteristics of this embodiment will be described. First, the rough adjustment of the transmission wavelength will be described. 7 (A) to 7 (C) are explanatory views in the case of roughly adjusting the transmission wavelength in the optical wavelength filter device of FIG. 6 (where N = 4, L2 = L1 · N / (N-1)). FIG. 7 (A) shows the light transmission characteristics of the preceding optical wavelength filter element 34 alone, FIG. 7 (B) shows the optical transmission characteristics of the latter optical wavelength filter element 36 alone, and FIG. 7 (C) shows these optical wavelength filters. 7 shows a combined light transmission characteristic (light transmission characteristic of the light wavelength filter device of FIG. 6) when the elements 34 and 36 are combined. In FIGS. 7A to 7C, the vertical axis represents the optical output intensity and the horizontal axis represents the wavelength. As shown in FIG. 7A, in the light transmission characteristics of the preceding optical wavelength filter element 34 alone, the peak of the optical output intensity appears in every cycle δλ1 of the transmission wavelength of this element 34. Further, as shown in FIG. 7B, in the light transmission characteristics of the latter-stage optical wavelength filter element 36 alone, the peak of the optical output intensity is the cycle δλ2 (δλ2 <δλ1) of the transmission wavelength of this element 36. Appears every time. When coarse adjustment is performed, as shown in FIGS. 7A and 7B, the optical wavelength filter element 34 in the preceding stage is used.
From the state in which the single transmission wavelength and the single transmission wavelength of the subsequent optical wavelength filter element 36 are matched at a certain wavelength, the refractive index of the refractive index variable unit 18 of the subsequent optical wavelength filter element 36 is electrically changed. The transmission wavelength of this element 36 is Δλ _t1 =
Change by δλ2 · (1 / N). Then, as shown in FIG.
As shown in (C), the wavelength of the light transmitted through both the optical wavelength filter elements 34 and 36 in the front and rear stages is δΔλ1.
Only changes. Wavelength of the light transmission wavelength _{(the J} natural number) J · [Delta] [lambda] _t1 which transmits both is varied by upstream and downstream of the optical wavelength filter element of the post-stage optical wavelength filter element 36 changes by J · δΔλ1. Next, the fine adjustment of the transmission wavelength will be described. 8A to 8C show the optical wavelength filter device of FIG. 6 (where N = 4, L2 = L1.N / (N-
FIG. 8A is an explanatory diagram in the case where the transmission wavelength is finely adjusted in FIG. 8A, and FIG. 8A is a light transmission characteristic of the optical wavelength filter element 34 alone in the front stage, and FIG. The light transmission characteristics of the element 36 alone and FIG. 7C show the combined light transmission characteristics when these optical wavelength filter elements 34 and 36 are combined. 8A to 8C, the light output intensity is plotted on the vertical axis and the wavelength is plotted on the horizontal axis. When fine adjustment is performed, as shown in FIGS. 8A and 8B, the transmission wavelength of the optical wavelength filter element 34 in the front stage and the transmission wavelength of the optical wavelength filter element 36 in the rear stage are set to a certain wavelength. From the state where they are matched with each other, the refractive indexes of the refractive index variable portions 18 of the optical wavelength filter elements 34 and 36 at the front stage and the rear stage are electrically changed to change the transmission wavelengths of these elements 34 and 36 by Δλ _t2 (Δλ _t2 <Δλ _t1 ) is changed. Then, as shown in FIG. 8C, the wavelength of the light transmitted through both the optical wavelength filter elements 34 and 36 at the front stage and the rear stage changes by Δλ _t2 . In this embodiment, the variable range of the transmission wavelength can be increased to N-1 times the variable range of the transmission wavelength in the case of the wavelength filter element of the first invention alone. The maximum number of channels CH _{max in} this embodiment is CH
It can be expressed as _max = N (N-1). Therefore, in order to set the desired number N _T of channels, the total number N of connection waveguides 14 to be provided may be set to N≈N _T ^1/2 . In this embodiment, the case where the optical wavelength filter elements of the first invention are connected in two stages is considered, but the optical wavelength filter elements of the first invention may be connected in three or more stages. Next, the size, the number of channels, and the temperature fluctuation of the first and second embodiments will be described with reference to specific numerical examples. For example, Δn = 10 ⁻³ , δn = 10
⁻¹ , n _P = 1 and λ = 1.3 μm, L = 0.
65 mm and m = 1, 2, 3, ..., 100. If N = 32, the total length of the connection waveguide 14 can be 2.1 cm. Therefore, the elements and devices of the embodiments of the first and second inventions can be sufficiently miniaturized, 32 channels in the first invention and 992 in the second invention.
Channel can be realized. The half-width Δλ _w of the transmission wavelength band is Δλ _w = 0.4 nm. In the first and second inventions, the sensitivity to temperature fluctuations Δλ _f is Δλ _f = λ · (δ
L / L) and Δλ _f / Δλ _w are Δλ _f / Δλ _w = N ·
It can be expressed as m · (δL / L). Here, δL / L represents the coefficient of thermal expansion of the connection waveguide 14. The sensitivity Δλ _f in the first invention and the second invention is the same as that of the Fabry-Perot type filter, but since the half width Δλ _{w of} the first and second inventions is larger than that of the Fabry-Perot type, Δλ _f / Δλ _w can be made smaller. is important. Δλ _f / Δ in the first and second inventions
If λ _w is δL / L = 10 ⁻⁵ , then Δλ _f / Δλ _w =
It is 0.032 / ° C, which is practically no problem. The first and second inventions are not limited to the above-mentioned embodiments,
Therefore, the configuration, shape, arrangement position, size, and other conditions of each component can be changed arbitrarily. For example, if the phase difference of light on the output surface of each connection waveguide forms an arithmetic progression, the tolerance of the arithmetic progression formed by the length of the structural phase difference control unit and the length of the refractive index variable portion are The tolerances of the arithmetic progressions to be formed need not be equal, and the shape, the arrangement position and the length of the structural phase difference control unit 16 or 17 and the shape, the arrangement position and the length of the refractive index variable unit 18 match. It is not necessary to do so, and these shapes, arrangement positions and lengths can be arbitrarily changed.

[Table 1]

[Table 2]

As is apparent from the above description, according to the optical wavelength filter element of the first invention, the 1 × N branch section inputs the wavelength-multiplexed light and branches it to output from N output ports. Each outputs wavelength-multiplexed light. The N × 1 interference unit inputs the wavelength-multiplexed light from each of the N input ports via the connection waveguide and multiplexes them to interfere with the wavelength-multiplexed light from each input port. The connection waveguide is provided with a structural phase difference control unit and a refractive index variable unit, and the action of the structural phase difference control unit and the refractive index variable unit causes a phase difference in the light emitted from each connection waveguide. Let Since the lengths of the structural phase difference control units are made different so as to form the arithmetic progression and the lengths of the refractive index variable portion are made different so as to form the arithmetic progression, from each connection waveguide The phase difference of the emitted light forms an arithmetic progression. When light having a phase difference forming an arithmetic progression is interfered in this way, light of a specific wavelength is emitted from the interference part and light of other wavelengths is not emitted. The wavelengths of light can be separated. By electrically variably controlling the refractive index of the refractive index variable unit, the wavelength of light emitted from the interference unit can be changed. The wavelengths of the light emitted from the interference section are separated by a certain period δλ. Moreover, since the light is branched by the branching part and the phase difference is generated in the light branched by the structural phase difference control part and the refractive index changing part, the optical wavelength filter element can be downsized. Further, since light having a specific wavelength is selectively separated by interfering light having a phase difference forming an arithmetic progression, the variable range of the wavelength of the separated light is widened and the transmission bandwidth of the light having the specific wavelength is increased. Can be narrowed. Therefore, the number of channels can be increased. Further, according to the optical wavelength filter device of the second invention, the optical wavelength filter elements of the first invention are connected in multiple stages, and the first tolerances of these optical wavelength filter elements connected in multiple stages are made different. Since the first tolerances of the optical wavelength filter elements connected in multiple stages are different from each other, the wavelength cycle Δλ of the light output from the interference section of each optical wavelength filter element is different. Therefore, the light output from the final stage element of the optical wavelength filter elements connected in multiple stages (the light output from the optical wavelength filter device of the second invention) is the light transmitted through all the elements of the optical wavelength filter elements connected in multiple stages. .. The period of the wavelength of the light output from the optical wavelength filter device of the second invention,
This is the least common multiple with respect to the period Δλ of all the optical wavelength filter elements connected in multiple stages, and as a result, the variable range of the wavelength of the light output from the optical wavelength filter device of the second invention can be further widened.

[Brief description of drawings]

FIG. 1 is a plan view schematically showing the configuration of a first embodiment of the first invention.

FIG. 2A is a diagram showing an example of a specific configuration of a connection waveguide.

FIG. 3 is a plan view schematically showing a configuration of a second embodiment of the first invention.

FIG. 4 is a plan view schematically showing a configuration of a third embodiment of the first invention.

FIG. 5 is a plan view schematically showing a configuration of a fourth embodiment of the first invention.

FIG. 6 is a plan view schematically showing the configuration of an embodiment of the second invention.

7 (A) to 7 (C) are explanatory views in the case of roughly adjusting the transmission wavelength in the embodiment of the second invention.

FIG. 8A to FIG. 8C are explanatory views when fine adjustment of the transmission wavelength is performed in the embodiment of the second invention.

[Explanation of symbols]

 10: Branching part 12: Interference part 14: Connection waveguide 16, 17: Structural phase difference control part 18: Refractive index variable part 34, 36: Optical wavelength filter element

Claims (4)

[Claims] 1. A 1 × N branch section and an N × 1 interference section, and N connection waveguides provided between output ports of corresponding branch sections and input ports of the interference section, and the connection waveguides. The structural phase difference control unit and the refractive index variable unit are provided, and the length of each structural phase difference control unit is changed so as to form an arithmetic progression with the first tolerance, and each refractive index variable unit. The optical wavelength filter element is characterized in that the lengths of the two are different so as to form an arithmetic progression with a second tolerance. 2. The optical wavelength filter element according to claim 1, wherein the refractive index change amounts of the respective refractive index variable portions are made equal to each other. 3. An optical wavelength filter device, comprising the optical wavelength filter elements according to claim 1 connected in multiple stages, wherein the optical wavelength filter elements have different first tolerances. 4. The optical wavelength filter device according to claim 3, wherein the optical wavelength filter elements connected in multiple stages have different second tolerances.