JP2014170073A - Optical interferer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To separate arbitrary incident light containing a plurality of wavelengths and a plurality of polarizations in terms of combinations of a wavelength and polarization.SOLUTION: An optical interferer comprises: two photocouplers 16 and 18; first and second arm optical waveguides 20a and 20b which connect the two photocouplers 16 and 18 in parallel; a first port Pprovided at one photocoupler; and second and third ports Pand Pprovided at the other photocoupler. First to third light components C-C, which are different in terms of at least one of the wavelength and polarization, of incident light IN from the first port are output from the second and third ports in accordance with distribution ratios corresponding to settings of three phase adjustment regions 22-22provided along the first and second arm optical waveguides in total.

Description

  The present invention relates to an optical interferometer that separates input light by a combination of wavelength and polarization.

  An optical subscriber communication system (hereinafter referred to as a subscriber) that performs optical transmission (uplink communication) from the subscriber side to the station side and optical transmission (downlink communication) from the station side to the subscriber side using a single optical fiber. In some cases, light of different wavelengths may be used for upstream communication and downstream communication. In this case, an optical element (hereinafter also referred to as an optical multiplexing / demultiplexing element) that multiplexes / demultiplexes light having different wavelengths is required on both the station side and the subscriber side.

  The optical multiplexing / demultiplexing element is spatially optically aligned with the light emitting element and the light receiving element, so that a subscriber side termination device (ONU: Optical Network Unit) or a station side termination device (OLT: Optical Line) of the subscriber system. (Terminal).

  In order to reduce the labor of aligning the optical axis described above, an optical multiplexing / demultiplexing element constituted by an optical waveguide has been developed (see, for example, Patent Documents 1 to 5). In the optical multiplexing / demultiplexing device using the optical waveguide, the light propagation path is limited to the optical waveguide that is formed in advance, so that a lens, a mirror, or the like is not required for the optical multiplexing / demultiplexing device. Furthermore, the light emitting element and the light receiving element may be aligned with the input and output ends of the optical waveguide with reference to a mark previously created in the optical multiplexing / demultiplexing element. Therefore, the labor of strict optical axis alignment of the light beams entering and exiting the light emitting element and the light receiving element is greatly reduced.

In recent years, an optical waveguide (hereinafter also referred to as a Si optical waveguide) is configured by a core made of silicon (Si) and a clad made of silicon oxide (SiO ₂ ) having a large refractive index difference from Si. A demultiplexing element has been reported (for example, see Non-Patent Documents 1 to 3).

Photonics Technology Letters vol. 18, no. 22, p. 2392, November 2006 Photonics Technology Letters vol. 20, no. 23, p. 1968, December 2008 Optics Express vol. 18, no. 23, p. 23891, November 2010 Journal of Lightwave Technology vol. 27, p. 417, Feb 19, 2009 Optics Express vol. 19, no. 19, p. 18614, September 12, 2011 Optics Letters vol. 36, p. 2590, Jul 1, 2011 Optics Express vol. 19, p. 10940, May 23, 2011 Optics Letters vol. 36, no. 20, p. 4047, Oct 15, 2011 Journal of Lightwave Technology vol. 29, p. 1808, Jun 15, 2011

U.S. Pat. No. 4,860,294 US Pat. No. 5,764,826 US Pat. No. 5,960,135 US Pat. No. 7,072,541 JP-A-8-163028

  The Si optical waveguide has a strong light confinement because the refractive index of the core is much larger than the refractive index of the cladding. Therefore, it is possible to realize a curved optical waveguide that bends light with a small curvature radius of about 1 μm. In addition, since a processing technique using a Si electronic device can be used when manufacturing a Si optical waveguide, a very fine submicron cross-sectional structure can be realized. For these reasons, the optical multiplexing / demultiplexing device can be reduced in size by using the Si optical waveguide.

  However, since the Si optical waveguide has a large refractive index of the core, a slight error such as a dimensional error of the core causes a large error in the equivalent refractive index of the optical waveguide. As a result, the equivalent refractive index of the Si optical waveguide with respect to each polarization varies, and there is a problem in that a difference in wavelength separation ability occurs between the polarizations. For example, in wavelength division multiplex communication (WDM: Wavelength Division Multiplex) in which the wavelength interval between adjacent channels is narrow, interference in the wavelength band of the adjacent channel occurs due to variations in the equivalent refractive index for each polarization.

  Therefore, in WDM, it is advantageous to first separate the communication light into a TE wave and a TM wave, combine the wavelengths for each polarization, and then integrate both polarizations again. In order to separate / integrate polarized waves by this method, a polarization separating element (PBS: Polarizing Beam Splitter) is required.

  As a PBS used together with an optical multiplexing / demultiplexing element of a subscriber system, a grating type element (for example, see Non-Patent Document 4), a directional coupler type element (for example, see Non-Patent Documents 5 to 8), and an interferometer A mold element (for example, see Non-Patent Document 9) and the like are known.

  Here, in a GE-PON (Gigabit Ethernet (registered trademark) -Passive Optical Network) system widely used in a subscriber system, light having a wavelength band of 1.31 μm (hereinafter, 1.31 μm light) is upstream communication. In addition, light having a wavelength band of 1.49 μm (hereinafter referred to as 1.49 μm light) is used for downlink communication.

  However, any PBS known so far performs polarization separation of light of a single wavelength, but cannot simultaneously separate light of a plurality of wavelengths. That is, conventionally, there has been no PBS that simultaneously polarizes and separates both 1.31 μm light and 1.49 μm light.

  The present invention has been made with such a technical background. Therefore, the object of the present invention is not limited to 1.31 μm light and 1.49 μm light, but can also be used as PBS that separates arbitrary input light including a plurality of sets of wavelength and polarization by polarization and wavelength. It is to obtain an optical interferometer. Hereinafter, separation of input light by a combination of polarization and wavelength is also referred to as “polarization / wavelength separation”.

  As a result of intensive studies, the inventor has conceived that the above-described object can be achieved by providing the same number of phase adjustment regions as the number of lights to be polarized / wavelength separated in the arm optical waveguide constituting the optical interferometer. .

  Therefore, the first optical interferometer according to the present invention includes two optical couplers and first and second arm optical waveguides provided in parallel between the two optical couplers and connecting the two optical couplers. , A total of j (j is 2) in one or both of the first port provided in one optical coupler, the second and third ports provided in the other optical coupler, and the first and second arm optical waveguides. (Integer above) provided phase adjustment region.

  And the 1st-jth component light from which at least one of the polarization and wavelength input from a 1st port differs is output from a 2nd and 3rd port by the distribution ratio according to setting.

  The second optical interferometer of the present invention is provided in parallel between two optical couplers and two optical couplers, and connects the first to u-th optical waveguides (u is 3). The above-mentioned integer), a first port provided in one optical coupler, and second to s-th ports provided in the other optical coupler (s is an integer of s ≦ u + 1). The first to u-th optical waveguides have different optical path lengths.

  Here, input light including first to r-th component light (r is an integer of 2 or more) having at least one of polarization and wavelength different from each other is input from the first port, and each of the first to u-th optical waveguides In accordance with the lengths of the first to r-th phase adjustment regions in the v-th and v + 1-th optical waveguides (v is an integer of 1 to u−1) that are provided with the first to r-th phase adjustment regions and are adjacent to each other. The first to r-th component lights are output from the second to s-th ports, respectively.

  Since the optical interferometer of the present invention has j phase adjustment regions, the wavelength and polarization of the input light are not limited to 1.31 μm light and 1.49 μm light depending on these settings. Polarization / wavelength separation can be performed on j component lights, at least one of which is different.

It is a schematic diagram which shows roughly the structure of the optical interferometer of this invention. (A) is a schematic diagram conceptually showing the structure and operation of the optical interferometer of Embodiment 1, and (B) shows the specifications of the component light contained in the input light and these component lights are output. It is a figure which shows the relationship with a port. 2 is a plan view schematically showing the structure of the optical interferometer of Embodiment 1. FIG. (A)-(E) are the cut | disconnected end elevations which each cut | disconnected FIG. 3 along the AA line, the BB line, the CC line, the DD line, and the EE line. (A) And (B) is a schematic diagram which shows the output characteristic of the optical interferometer of Embodiment 1. FIG. 6 is a plan view schematically showing the structure of an optical interferometer of Embodiment 2. FIG. It is a characteristic view which shows the output characteristic of the optical interferometer of Embodiment 2. It is a top view which shows roughly the structure of the optical interferometer of Embodiment 3.

  Embodiments of the present invention will be described below with reference to the drawings. In each figure, the shape, size, and arrangement relationship of the components are schematically shown to such an extent that the present invention can be understood. Each of the following embodiments is a preferred example of the present invention, and the material and numerical conditions of each component are merely examples of preferred cases. Accordingly, the present invention is not limited to the following embodiments. Moreover, in each figure, the same code | symbol is attached | subjected to a common component and the description may be abbreviate | omitted.

[Summary of Invention]
The outline of the present invention will be described with reference to FIG. FIG. 1 is a schematic diagram schematically showing the structure of the optical interferometer of the present invention. In FIG. 1, an optical interferometer is simply illustrated in order to help understand the invention. That is, the illustration of the substrate and the clad is omitted, the core is drawn with a simple curve, and each component is drawn with a rectangular box.

  First, with reference to FIG. 1, the direction and dimension of the optical interferometer 10 used in the following description are defined. Considering a right-handed orthogonal coordinate system as shown in FIG. 1, the X direction is the direction from the left to the right of the paper on which the figure is drawn, and is also referred to as the length direction. In addition, the Z direction is a direction from the back surface to the front surface of the paper on which the drawing is drawn, and is also referred to as a height direction or a thickness direction. The Y direction is the direction from the bottom to the top of the paper on which the drawing is drawn, and is also referred to as the width direction. The geometric length measured along the X direction is also referred to as “length”, the geometric length measured along the Y direction is also referred to as “width”, and the geometric length measured along the Z direction. The target length is also referred to as “height” or “thickness”. Here, the light propagation direction of the input light IN is assumed to be the X direction. A section perpendicular to the light propagation direction of a predetermined structure is referred to as a “cross section”. In this example, the main surface of the substrate (not shown) extends parallel to the XY plane (paper surface).

  Next, the configuration of the optical interferometer 10 will be briefly described. The optical interferometer 10 includes two optical couplers 16 and 18 and first and second arm optical waveguides 20a and 20b.

  The first and second arm optical waveguides 20a and 20b are channel-type optical waveguides. The first and second arm optical waveguides 20a and 20b are provided in parallel between the two optical couplers 16 and 18, and connect the two optical couplers 16 and 18. Hereinafter, when both the first and second arm optical waveguides 20a and 20b are shown, they are also referred to as “arm portions 20”.

The first and second arm optical waveguides 20a and 20b are provided with _j phase adjustment regions 22 _{1 to} 22 _j (where j is an integer of 2 or more). These phase adjustment regions 22 _{1 to} 22 _j are configured as channel type optical waveguides having different widths in this example. As a result, the phase adjustment regions 22 _{1 to} 22 _j have different equivalent refractive indexes. The optical path lengths T of the first and second arm optical waveguides 20a and 20b including the phase adjustment regions 22 _{1 to} 22 _j are different from each other. The optical interferometer 10 includes both arm optical waveguides 20a and 20b and j phase adjustment regions 22 _{1 to} 22 _j coupled together, and the deviation of _j component lights C _{1 to} C _j included in the input light IN. Wave / wavelength separation can be performed. The first and second arm optical waveguides 20a and 20b excluding the _j phase adjustment regions 22 _{1 to} 22 _j are configured to have the same optical path length T.

  Here, the “optical path length” is generally an optical length obtained by correcting the geometric length P of the optical waveguide with the equivalent refractive index q of the optical waveguide with respect to light of a certain wavelength and polarization. The optical path length T is given by P × q. Hereinafter, the length (including width, thickness, height, etc.) not described as “optical path length” simply indicates a geometric length.

FIG. 1 shows a configuration example in which the phase adjustment regions 22 _{1 to} 22 _k−1 are provided in the first arm optical waveguide 20 a and the phase adjustment regions 22 _{k to} 22 _j are provided in the second arm optical waveguide 20 b. (K is an integer of 1 ≦ k ≦ j). However, there is no particular limitation on how the phase adjustment regions 22 _{1 to} 22 _j are arranged in the first and second arm optical waveguides 20a and 20b. A suitable number may be arranged in the first and second arm optical waveguides 20a and 20b depending on the design. For example, all the phase adjustment regions 22 _{1 to} 22 _j may be arranged only in one of the first and second arm optical waveguides 20a and 20b.

In this embodiment, the case where the first and second arm optical waveguides 20a and 20b except for the _j phase adjustment regions 22 _{1 to} 22 _j are configured to have the same optical path length T has been described. However, by using the first and second arm waveguides 20a and 20b structures are different from each other, may be both arm optical waveguides 20a and 20b themselves as the phase control region 22 _j. That is, the phase adjustment region 22 _j may be a partial region obtained by removing the phase adjustment regions 22 _{1 to} 22 _j-1 from both arm optical waveguides 20a and 20b. Incidentally, the partial areas of both arm optical waveguides 20a and 20b in the case of the phase control region 22 _j, the optical path length of the two arm optical waveguides 20a and 20b is considered as 0 (zero).

On one of the optical coupler 16 provided with a first port P ₁ for light input and output, the second and third port P ₂ and P ₃ for optical output is provided to the other of the optical coupler 18. In this example, input light IN is input from the first port P ₁ of the optical coupler 16, and output light OUT 1 and OUT 2 subjected to polarization / wavelength separation from the _second and third ports P ₂ and P ₃ of the optical coupler 18. Is output.

  As the optical coupler 16 on the optical input side, a 1-input 2-output or 2-input 2-output 3 dB coupler that equally distributes input light IN to the first and second arm optical waveguides 20 a and 20 b without depending on polarization is used. Can do. When the optical coupler 16 on the optical input side is a polarization-independent 3 dB coupler, the optical coupler 18 on the optical output side is a polarization-independent 3 dB coupler with two inputs and two outputs.

  As a 1-input 2-output coupler for the optical coupler 16, for example, a Y-branch waveguide or the like can be used. As the two-input two-output coupler for the optical couplers 16 and 18, for example, a coupler using a multimode interference (MMI) optical waveguide or a directional coupler can be used.

In addition to the polarization-independent 3 dB coupler, the optical couplers 16 and 18 use the wavelength and polarization of the component light C _i to design polarization / wavelength separation for easy directional coupling. Can be used. The optical couplers 16 and 18 designed in this way will be described in detail in the first embodiment.

Next, the operation of the optical interferometer 10 will be described. Input light IN including _first to j-th component lights C _{1 to} C _j having at least one of polarization and wavelength different from each other is input from the first port P ₁ .

  Here, “polarized wave” refers to a TE wave and a TM wave whose vibration directions of the electric field are orthogonal to each other. The TE wave indicates a polarization that propagates in the light propagation direction (X direction in the figure) of the input light IN and the electric field vibrates in the Y direction. The TM wave indicates a polarization that propagates in the light propagation direction and the electric field vibrates in the Z direction.

The i-th component light C _i (i is an integer satisfying 1 ≦ i ≦ j) is represented by a combination of polarization and wavelength, for example, C _i = (λ (C _i ), TM). This indicates that the i-th component light C _i has a wavelength of λ (C _i ) and a polarization of a TM wave.

In the process of propagating through both arm optical waveguides 20a and 20b, a predetermined phase difference is given to each of the first to j-th component lights C _{1 to} C _j by the phase adjustment regions 22 _{1 to} 22 _j. Wave / wavelength separation is output. More specifically, a phase difference obtained by multiplying the interference order m (C _i ) by 2π is given to each component light C _{1 to} C _j .

When the interference order m (C _i ) is “½ × odd number”, the phase difference given to the component light is “odd multiple of π” and is output from the second port P _{2 as} the output light OUT 1. The When the interference order m (C _i ) is “½ × even”, the phase difference is “even multiples of π” and is output from the third port P ₃ as output light OUT2. Thus, due to the phase difference given to the component light. Each component light is output from a desired port.

Next, a mechanism by which _j phase adjustment regions 22 _{1 to} 22 _j can perform polarization / wavelength separation of _j component lights C _{1 to} C _j as many as the number of regions j will be described.

In the following description, the following variables (1) to (3) are used.
(1) One of the j phase adjustment regions 22 _{1 to} 22 _j is represented as a k-th phase adjustment region 22 _k .
(2) Let the geometric length along the light propagation direction of the k-th phase adjustment region 22 _{k be} L _k .
(3) The equivalent refractive index of the k-th phase adjustment region 22 _k for the i-th component light C _i is n _k (C _i ).

At this time, in order to output the component lights C _{1 to} C _j from the second and third ports P ₂ and P _{3 at a} desired distribution ratio, the interference condition of the following formula (1) needs to be satisfied.

More specifically, the interference conditions of the following formulas (1-1) to (1-j) in which the formula (1) is developed for each of the component lights C _{1 to} C _j must be satisfied. Here, the “distribution ratio” indicates the intensity ratio of the component lights C _{1 to} C _j that are distributed and output to the second and third ports P ₂ and P ₃ .

n ₁ (C ₁ ) × L ₁ + n ₂ (C ₁ ) × L ₂ +... + n _j (C ₁ ) × L _j = m (C ₁ ) × λ (C ₁ ) (1-1) )
n ₁ (C ₂ ) × L ₁ + n ₂ (C ₂ ) × L ₂ +... + n _j (C ₂ ) × L _j = m (C ₂ ) × λ (C ₂ ) (1-2) )
・
・
・
n ₁ (C _j ) × L ₁ + n ₂ (C _j ) × L ₂ +... + n _j (C _j ) × L _j = m (C _j ) × λ (C _j ) (1-j )
In these formulas (1-1) to (1-j), the equivalent refractive indexes n ₁ (C ₁ ) to n _j (C _j ) for each component light are the cross-sectional dimensions of the phase adjustment region and the component light. It can be obtained by simulation using wavelength and polarization. The wavelengths λ (C ₁ ) to λ (C _j ) are also known. Further, m (C _i ) is an interference order of the component light C _i and is a value selected as desired. Thus, the unknowns in the equation (1-1) ~ (1-j ) is only the length _L 1 ~L _j of each phase adjusting region ₂₂ 1 through 22 _j.

Thus, in Formulas (1-1) to (1-j), since the number of unknowns is equal to the number of formulas, the lengths L _{1 to} L _j can be uniquely determined. That is, using these equations, by designing the length L ₁ ~L _j of the phase adjustment region 22 ₁ through 22 _j, the input light IN comprising a plurality of wavelength and polarization and polarization / wavelength separation it can be output in any of the distribution ratio from the second and third port P ₂ and P _3.

Note that the distribution ratio of the _i- th component light C _i can be arbitrarily changed by appropriately selecting the value of the interference order m (C _i ). That is, when “Int” is an integer greater than or equal to 0 and x is a real number between 0 and 1, if the interference order m (C _i ) is “½ × (Int + x)”, the second and third The i-th component light C _i can be output from the port at an arbitrary intensity ratio. For example, if x = 0.5, the phase difference given to the i-th component light C _i becomes “a half integer multiple of π”, and the optical interferometer 10 converts the i-th component light C _i into the second and third components. It functions as a 3 dB coupler that distributes equally to ports P ₂ and P ₃ .

Further, in this example, a case has been described in which channel type optical waveguides having different equivalent refractive indexes by changing the width of the core are used as the phase adjustment regions 22 _{1 to} 22 _j . However, the clad used in the optical waveguide other than the phase adjustment region is provided with one or more partial regions of the optical waveguide in which the equivalent refractive index is changed by providing a phase adjustment clad having a refractive index changed around the core. The phase adjustment regions 22 _{1 to} 22 _j may be used. Specifically, a partial region of the optical waveguide whose cladding material is changed may be used as the phase adjustment regions 22 _{1 to} 22 _j .

[Embodiment 1]
Hereinafter, the optical interferometer of Embodiment 1 will be described with reference to FIGS. In this embodiment, it is assumed that the optical interferometer is a PBS used with the ONU. FIG. 2A is a schematic diagram conceptually showing the structure and operation of this optical interferometer. FIG. 2B is a diagram illustrating a relationship between the specifications of component light included in input light and ports to which these component lights are output. FIG. 3 is a plan view schematically showing the structure of the optical interferometer. 4A shows a cut end view of the optical interferometer cut along the line AA in FIG. FIG. 4B shows a cut end view of the optical interferometer cut along the line BB in FIG. FIG. 4C shows a cut end view of the optical interferometer cut along line CC in FIG. FIG. 4D shows a cut end view of the optical interferometer cut along the line DD in FIG. FIG. 4E shows a cut end view of the optical interferometer cut along the line EE in FIG. 5A and 5B are schematic diagrams showing the output characteristics of the TE wave and TM wave of the optical interferometer, respectively. 2 to 4, components similar to those in FIG. 1 are denoted by the same reference numerals, and redundant description may be omitted. Further, FIG. 2A is simplified similarly to FIG.

(Overview)
First, mainly with reference to FIGS. 2A and 2B, conditions and operations required when the optical interferometer 30 is used as an PBS with an ONU will be outlined.

  More specifically, in GE-PON, which is the mainstream of the current subscriber system, 1.49 μm light is used for downlink communication and 1.31 μm light is used for uplink communication as described above. The 1.49 μm light transmitted from the station reaches the ONU as a mixed light of a TE wave and a TM wave as a result of the polarization plane being randomly rotated in the process of propagating through the optical fiber. The 1.31 μm light is output as a TE wave from the LD (Laser Diode) of the ONU.

Therefore, as shown in FIG. 2B, the light handled by the optical interferometer 30 is the following first to third component lights C _{1 to} C ₃ .

1) First component light C ₁ = (λ (C ₁ ) = 1.49 μm, TE) (hereinafter also referred to as 1.49 TE light)
2) Second component light C ₂ = (λ (C ₂ ) = 1.49 μm, TM) (hereinafter also referred to as 1.49 TM light)
3) Third component light C ₃ = (λ (C ₃ ) = 1.31 μm, TE) (hereinafter also referred to as 1.31 TE light)
In this case, the optical interferometer 30 may perform polarization / wavelength separation of the _three component lights C _{1 to} C ₃ . As described above, since the number of phase adjustment regions equal to the number j (= 3) of component lights to be polarized / wavelength separated is necessary, the arm unit 20 includes a total of three phase adjustment regions 22 _{1 to} 22. ₃ is arranged.

Then, as shown in FIG. 2B, the optical interferometer 30 performs polarization / wavelength separation on the _first to third component lights C _{1 to} C ₃ , and is a first TE wave from the second port P ₂ . and a third component light _{C 1} and _{C 3} is output as OUT1, and output a second light component _{C 2} is a TM wave from the third port _{P 3} as OUT2. That is, the optical interferometer 30 sets the interference order of the first and third component lights C ₁ and C ₃ to “½ × odd”, and sets the interference order of the second component light C ₂ to “½ × “Even number”.

Here, among the component lights included in the input light IN, the TE component light whose polarization is TE wave is put together, and the “TE component light group” and the component light whose polarization is TM wave are put together into “TM component light”. Each is referred to as a “group”. In this case, the optical interferometer 30 gives an interference order of “½ × odd” to the TE component light group composed of the _first and third component lights C ₁ and C ₃ , and the second component light C ₂ An interference order of “½ × even” is given to the TM component light group.

In FIG. 2A, two phase adjustment regions are provided in the first arm optical waveguide 20a and one phase adjustment region in the second arm optical waveguide 20b, respectively, but this is merely an example. There is no particular limitation on the arrangement of the phase adjustment regions 22 _{1 to} 22 ₃ on both arm optical waveguides 20a and 20b.

(Construction)
Referring to FIGS. 3 and 4, the optical interferometer 30 has an optical waveguide 14 composed of a clad 12 provided on a substrate 8 and a core 13, and corresponds to the optical interferometer 10 described above. The interferometer MZ is provided with an input unit 24 and an output unit 26 as optional configurations. The substrate 8, the core 13, and the clad 12 will be described later.

  The Mach-Zehnder interferometer MZ is provided in parallel between the first directional coupler as the optical coupler 16, the second directional coupler as the optical coupler 18, and the first and second directional couplers. First and second arm optical waveguides 20a and 20b connecting the second directional coupler are provided. Hereinafter, in this embodiment, “optical coupler 16” is also referred to as “first directional coupler 16”, and “optical coupler 18” is also referred to as “second directional coupler 18”.

  The first and second arm optical waveguides 20a and 20b have different optical path lengths. In this example, the first arm optical waveguide 20a has a longer optical path length than the second arm optical waveguide 20b.

The first arm optical waveguide 20a includes a first phase adjusting region 22 _1, the third phase adjusting region 22 ₃ and the non-adjustment region 21a. Similarly, the second arm waveguide 20b includes a second phase adjusting region 22 ₂ and the non-adjustment region 21b.

Here, the non-adjustment region 21a, the first arm optical waveguide 20a, a partial region excluding the first and third phase adjusting region 22 ₁ and 22 _3. Similarly, the non-adjustment region 21b, the second arm waveguide 20b, a partial area except the second phase adjusting region 22 _2. Both the non-adjustment regions 21a and 21b are channel-type optical waveguides formed with the same cross-sectional shape, planar shape, and optical path length.

  More specifically, referring to FIG. 4C, the cross-sectional shape of these non-adjustment regions 21a and 21b is a rectangular shape having a width W and a height H of about 300 nm. The optical waveguides 24a, 24b, 26a, and 26b constituting the input unit 24 and the output unit 26 are the same including the cross-sectional shapes and dimensions of the non-adjustment regions 21a and 21b.

Thus, by making the cross-sectional shapes of the non-adjustment regions 21a and 21b and the optical waveguides 24a, 24b, 26a and 26b of the input unit 24 and the output unit 26 rectangular, the polarization rotation in these regions can be performed. Can be prevented. Further, by making the optical path lengths of the optical waveguides 24a and 24b, the optical path lengths of the optical waveguides 26a and 26b, and the optical path lengths of the non-adjustment regions 21a and 21b, respectively, in the process of propagating through these regions, each component light C ₁ phase difference to ~C ₃ does not occur.

The first phase adjusting region 22 ₁ is divided into first provided in the arm optical waveguides 20a, ₁ 2 sub areas 22 L and 22 ₁ R. Both subregions 22 ₁ L and 22 ₁ R are linear channel optical waveguides having the same shape. Specifically, both sub-regions 22 ₁ L and 22 ₁ R, the length along the light propagation direction is _L 1/2, the width as shown in FIG. 4 (A) is a _{W 1,} the thickness Is H. In this example, the lengths L _1/2 of the sub-regions 22 ₁ L and 22 ₁ R are each about 2.79 μm. Thus, the overall length _{L 1} of the first phase adjusting region 22 ₁ is about 5.58μm. Further, the width W ₁ of both the sub-regions 22 ₁ L and 22 ₁ R is about 400 nm, and the thickness H is about 300 nm.

The second phase adjusting region ₂₂₂ is divided into second provided arm optical waveguide 20b, 2 sub area 22 ₂ L and 22 ₂ R. Both subregions 22 ₂ L and 22 ₂ R are linear channel optical waveguides having the same shape. Specifically, both subregions 22 ₂ L and 22 ₂ R, the length along the light propagation direction is _L 2/2, the width as shown in FIG. 4 (D) is _{W 2,} the thickness Is H. In this example, the length _L 2/2 sub-region 22 ₂ L and 22 ₂ R are each about 3.215Myuemu. Thus, the overall length _{L 2} of the second phase adjusting region ₂₂₂ is about 6.43μm. Further, the width W ₂ of both the sub-regions 22 ₂ L and 22 ₂ R is about 500 nm, and the thickness H is about 300 nm.

The third phase adjusting region 22 ₃ is provided in the first arm waveguide 20a, it is divided into two sub-regions 22 ₃ L and 22 ₃ R. Both subregions 22 ₃ L and 22 ₃ R are linear channel-type optical waveguides having the same shape. Specifically, both sub-regions 22 ₃ L and 22 ₃ R, length along the light propagation direction is _L 3/2, the width as shown in FIG. 4 (B) is a _{W 3,} the thickness Is H. In this example, the length _L 3/2 sub-areas 22 ₃ L and 22 ₃ R are each about 0.265Myuemu. Therefore, the total length _{L 3} of the third phase adjusting region 22 ₃ is about 0.53 .mu.m. Further, the width W ₃ of both the sub-regions 22 ₃ L and 22 ₃ R is about 300 nm, and the thickness H is about 300 nm.

A method for determining the lengths L _{1 to} L ₃ of the _first to third phase adjustment regions 22 _{1 to} 22 ₃ will be described in detail in the section of (design conditions).

As described above, the height and width of the core 13 constituting the three phase adjustment regions 22 ₁ , 22 ₂ and 22 ₃ , the non-adjustment regions 21 a and 21 b, the input unit 24 and the output unit 26 are about 200 to 500 nm. It is in the range. By setting the height and width of the core 13 within this range, the optical waveguide 14 can be a single mode optical waveguide in both the height direction and the width direction.

In this example, the case where the lengths of the sub-regions 22 ₁ L and 22 ₁ R, 22 ₂ L and 22 ₂ R, and 22 ₃ L and 22 ₃ R are equal to each other has been described. The lengths of the sub-regions do not have to be equal.

Further, the number of sub-regions constituting each of the phase adjustment regions 22 ₁ , 22 ₂ and 22 ₃ is not limited to two, and may be three or more depending on the design.

In this example, the case where each of the phase adjustment regions 22 ₁ , 22 ₂ and 22 ₃ is a linear channel type optical waveguide has been described. However, the phase adjustment region may be a curved channel type optical waveguide. However, in this case, since the equivalent refractive index at the curved portion is different from that of the linear channel optical waveguide, the cross-sectional shape and the total length need to be determined according to the curved shape.

Referring to FIG. 3, the first directional coupler 16 includes a first optical waveguide 16a and a second optical waveguide 16b. The first and second optical waveguides 16a and 16b are formed in a straight line having the same three-dimensional shape. The first and second optical waveguides 16a and 16b are arranged in parallel to each other with a distance capable of optical coupling. One end of the first optical waveguide 16 a is a first port P ₁ and is connected to the optical waveguide 24 a of the input unit 24. The other end of the first optical waveguide 16a is connected to the first arm optical waveguide 20a. One end of the second optical waveguide 16b is the fourth port _{P 4,} connected to the optical waveguide 24b of the input section 24. The other end of the second optical waveguide 16b is connected to the second arm optical waveguide 20b. In this embodiment, the fourth port P ₄ is a port light is not input, so to speak dummy port, not related in any way to the polarization / wavelength separation.

The second directional coupler 18 is configured identically to the first directional coupler 16. That is, the second directional coupler 18 includes a third optical waveguide 18a and a fourth optical waveguide 18b. The third and fourth optical waveguides 18a and 18b have the same three-dimensional shape as the first and second optical waveguides 16a and 16b, respectively. The third and fourth optical waveguides 18a and 18b are arranged in parallel to each other with a distance equal to the distance between the first and second optical waveguides 16a and 16b. One end of the third optical waveguide 18a is a second port _{P 2,} connected to the optical waveguide 26a of the output section 26. The other end of the third optical waveguide 18a is connected to the first arm optical waveguide 20a. One end of the fourth optical waveguide 18b is a third port _{P 3,} connected to the optical waveguide 26b of the output section 26. The other end of the fourth optical waveguide 18b is connected to the second arm optical waveguide 20b.

When configured as shown in FIG. 2B, the first and third component lights C ₁ and C _{3 that} are TE waves input to the first port P ₁ of the first directional coupler 16 are in the process of propagating through the first and second directional couplers 16 and 18, it is outputted from the second port P ₂ without power transition to the fourth optical waveguide 18b. Thereafter, the light input from the first port P ₁ is to be outputted from the second port P ₂ without causing power shift to the fourth optical waveguide 18b also referred to as "BAR Output".

On the other hand, the second component light C ₂ is a TM wave input to the first port P _1, the power is output from the third port P ₃ to shift to the fourth optical waveguide 18b. Thereafter, the light input from the first port P ₁ is, to the fourth optical waveguide 18b to be outputted from the third port P ₃ to the power transition is also referred to as "CRS Output".

Here, specific dimensions of the first and second optical waveguides 16a and 16b will be described with reference to FIG. The widths of the first and second optical waveguides 16a and 16b are W _DC , the thickness is H _DC , and the distance between the centers of the first and second optical waveguides 16a and 16b is D _DC . In this example, W _DC is about 500 nm, D _DC is about 850 nm, and thickness H _DC is about 300 nm. Further, the length of the first directional coupler 16 is ½ of the complete coupling length of the second component light C ₂ to be CRS output. Thus, the second component light _{C 2} is 1.49TM light can be CRS output a sufficient extinction ratio. A second directional coupler 18 configured identically to the first directional coupler 16 is also formed to this size.

The core 13 is provided in the clad 12 provided on the main surface 8 a side of the substrate 8. In this example, the constituent material of the core 13 is Si having a refractive index of about 3.47. The clad 12 is a layered body extending on the main surface 8a with a uniform thickness. More specifically, the clad 12 covers the upper surface, the lower surface, and both side surfaces of the core 13. The material constituting the clad 12 is, for example, SiO ₂ having a refractive index of about 1.44. As in this example, the material constituting the cladding 12 is preferably a material having a refractive index of 71.4% or less of the core 13. By using a material having a refractive index of this condition for the clad 12, the refractive index difference between the core 13 and the clad 12 becomes sufficiently large, and light can be strongly confined in the optical waveguide 14. As a result, the optical interferometer 10 can be reduced in size, for example, a curved optical waveguide having a radius of curvature of about 5 μm can be formed. Further, as the material of the clad 12, SiO _p N _q (where p and q are 2 ≧ p ≧ 0 and 4/3 ≧ q ≧ 0) may be used.

  The thickness of the clad 12 measured from the main surface 8a of the substrate 8 is, for example, about 3 μm. In order to prevent undesired coupling of light propagating through the optical waveguide 14 to the substrate 8, it is preferable to interpose a cladding 12 having a thickness of 1 μm or more between the core 13 and the substrate 8. In this example, a clad 12 of about 1.5 μm is interposed between the main surface 8 a and the lower surface of the core 13. The substrate 8 is made of Si, for example.

Next, a method for manufacturing the optical interferometer 30 will be briefly described. The optical interferometer 30 is formed using an SOI (Si On Insulator) substrate in which a SiO ₂ layer and a Si layer are stacked in this order on a Si substrate. That is, the core 13 is formed using the uppermost Si layer, and the SiO ₂ layer, which is a BOX (Buried-OXide) layer, is used as the lower layer of the cladding 12. More specifically, the core 13 is formed by patterning the uppermost Si layer by a conventionally known dry etching method or the like. Then, a SiO ₂ layer corresponding to the upper layer of the cladding 12 is formed by a CVD (Chemical Vapor Deposition) method or the like so as to embed the core 13. Thereby, the optical interferometer 30 including the optical waveguide 14 is obtained.

(Design condition)
Next, a design method for the optical interferometer 30 will be described. The optical interferometer 30 used as the PBS in the subscriber system is designed to easily perform polarization / wavelength separation in consideration of the wavelengths and polarizations of the _first to third component lights C _{1 to} C ₃ .

That is, since the third component light C ₃ having a wavelength of 1.31 μm has a shorter wavelength than the _first and second component lights C ₁ and C ₂ , the first and second light beams in the first directional coupler 16. The light interaction between the waveguides is weak and it is difficult to output CRS. The same applies to the second directional coupler 18. Therefore, the third component light C ₃ so as to BAR output, to design the optical interferometer 30 is reasonable.

If the third component light C ₃ is determined as a BAR output in this way, the first component light C ₁ that is the same TE wave as the third component light C ₃ is obtained from the polarization / wavelength separation characteristics required of the optical interferometer 30. the Sadamari a BAR output, the second component light _{C 2} of the TM wave is determined with the CRS output. Thus, in order to output the TE wave as a BAR and output the TM wave as a CRS, as shown in FIG. 4 (E), the confinement ability of the TE wave to the arm optical waveguide 20a is set as W _DC > H _DC. Increased. The specific values of W _DC , H _DC and D _DC were determined by simulation using a finite element method.

By the way, in general, in the directional coupler, it is necessary to strictly match the total length with the coupling length for the light to be output by the CRS, but not so strict for the light to be output by the BAR. Therefore, the total length of the first and second directional couplers 16 and 18 is set to the complete coupling length of the second component light C ₂ to be output as a CRS as described above.

Thus once the output destination of each component light _C 1 -C ₃ (the second or third port _{P 2} or _{P 3),} later accordingly, may be designed to phase adjustment region ₂₂ 1-22 ₃ . Specifically, the following interference conditional expressions (A) to (C) where j = 3 in the above expressions (1-1) to (1-j) may be solved.

n ₁ (C ₁ ) × L ₁ + n ₂ (C ₁ ) × L ₂ + n ₃ (C ₁ ) × L ₃ = m (C ₁ ) × λ (C ₁ ) (A)
n ₁ (C ₂ ) × L ₁ + n ₂ (C ₂ ) × L ₂ + n ₃ (C ₂ ) × L ₃ = [m (C ₁ ) + ½] × λ (C ₂ ) (B)
n ₁ (C ₃ ) × L ₁ + n ₂ (C ₃ ) × L ₂ + n ₃ (C ₃ ) × L ₃ = m (C ₁ ) × λ (C ₃ ) (C)
Here, λ (C ₁ ) and λ (C ₂ ) are 1.49 μm corresponding to the wavelengths of the first and second component lights C ₁ and C ₂ . λ (C ₃ ) is 1.31 μm corresponding to the wavelength of the third component light C ₃ . The interference order m (C ₁ ) is set to 1 taking into account the ports that output the _first to third component lights C _{1 to} C ₃ .

From the formulas (A) to (C), L _{1 to} L ₃ are obtained as the following formulas (D) to (F).

_{L 1 = (λ (C 1} ) × (m (C 1) × (δ 3 Δn 2 -δ 2 Δn 3) -n 2 (C 1) × δ 3/2 + n 3 (C 1) × δ 2/2 )) / (N ₁ (C ₁ ) × (δ ₃ Δn ₂ −δ ₂ Δn ₃ ) −n ₂ (C ₁ ) × (δ ₃ Δn ₁ −δ ₁ Δn ₃ ) + n ₃ (C ₁ ) × (δ ₂ Δn ₁ −δ ₁ Δn ₂ )) (D)
L ₂ = (m (C ₁ ) × (n ₃ (C ₃ ) × λ (C ₁ ) −n ₃ (C ₁ ) × λ (C ₂ )) − L ₁ × (n ₃ (C ₃ ) × n _{1 (C 1) -n 3 (} C 1) × n 1 (C 3))) / (n 3 (C 3) × n 2 (C 1) -n 3 (C 1) × n 2 (C 3) ) ... (E)
L ₃ = (λ (C ₁ ) × m (C ₁ ) −L ₁ × n ₁ (C ₁ ) −L ₂ × n ₂ (C ₁ )) / n ₁ (C ₃ ) (F)
Here, Δn _{1 to} Δn ₃ and δ _{1 to} δ ₃ are defined by the following formulas (G) to (L).

Δn ₁ = n ₁ (C ₁ ) −n ₁ (C ₂ ) (G)
Δn ₂ = n ₂ (C ₁ ) −n ₂ (C ₂ ) (H)
Δn ₃ = n ₃ (C ₁ ) −n ₃ (C ₂ ) (I)
δ ₁ = n ₁ (C ₁ ) / λ (C ₁ ) −n ₁ (C ₃ ) / λ (C ₂ ) (J)
δ ₂ = n ₂ (C ₁ ) / λ (C ₁ ) −n ₂ (C ₃ ) / λ (C ₂ ) (K)
δ ₃ = n ₃ (C ₁ ) / λ (C ₁ ) −n ₃ (C ₃ ) / λ (C ₂ ) (L)
When the above-described values are substituted into the equations (D) to (F) and solved, the above-described L ₁ = 5.58 μm, L ₂ = 6.43 μm, and L ₃ = 0.53 μm are obtained.

(Operation)
Next, the operation of the optical interferometer 30 will be described with reference to FIGS. 5 (A) and 5 (B). 5A and 5B show the output characteristics of the TE wave and TM wave of the optical interferometer 30, respectively. In both FIGS. 5A and 5B, the horizontal axis represents wavelength (μm), and the vertical axis represents intensity (dB). The intensity is a light intensity ratio with respect to input light. These characteristic diagrams were obtained by performing mode calculation by the finite element method for the optical interferometer 30 designed as described above.

Curve I in FIG. 5 (A), a light intensity of the TE wave BAR outputted from the second port _{P 2,} curve II is the intensity of the TE wave CRS output from the third port _{P 3.} Curve I shows that the light intensity is about 0 dB in the entire wavelength range of 1.25 to 1.6 μm, and the intensity of the TE wave output by BAR hardly decreases. On the other hand, curve II shows that the intensity is about −25 dB or less in the entire wavelength range, and the TE wave output by CRS has an intensity less than 1/100 of the TE wave output by BAR. That is, the optical interferometer 30 can output the TE wave including the _first and third component lights C ₁ and C ₃ from the second port P _{2 with} a good extinction ratio.

Curve III in FIG. 5 (B), a light intensity of the TM wave CRS output from the third port _{P 3,} curve IV is the light intensity of the TM wave BAR outputted from the second port _{P 2.} Curve III shows a light intensity of about 0 dB near 1.49 μm, which is the wavelength of the second component light C ₂ , and it can be seen that TM waves near this wavelength are CRS output with almost no loss. In addition, the optical intensity of the TM wave output from the second port P ₂ at this wavelength is less than about −30 dB, and the optical interferometer 30 has a good extinction ratio for the second component light C ₂ that is a TM wave. it can be CRS output from the third port _{P 3.}

  In this embodiment, the case where the optical interferometer 30 is a PBS for the GE-PON system has been described. However, the optical interferometer 30 is not limited to the GE-PON system, and the next generation 10G (10 Gbit / s) -PON system uses 1.577 μm light as the downstream wavelength and 1.27 μm light as the upstream wavelength. It can also be applied to other PBSs.

[Embodiment 2]
Next, the optical interferometer according to the second embodiment will be described with reference to FIGS. 6 and 7. FIG. 6 is a plan view schematically showing the structure of the optical interferometer 40 of the second embodiment. FIG. 7 is a characteristic diagram illustrating output characteristics of the optical interferometer 40 according to the second embodiment.

  Referring to FIG. 6, the optical interferometer 40 corresponds to the optical interferometer 30 according to the first embodiment connected in series over a plurality of stages. That is, the optical interferometer 40 includes first and second optical interferometers 30-1 and 30-2 configured in the same manner as the optical interferometer 30, except that the lengths of the directional couplers are different.

Hereinafter, this difference will be described. The optical interferometer 40 is configured to operate in the same manner as the optical interferometer 30. That is, the first and third component light _{C 1} and _{C 3} is a TE wave BAR output from the second port _P 2 -2 of the second optical interferometer 30-2, the second component light _{C 2} is a TM wave From the third port P ₃ -2 of the second optical interferometer 30-2.

For this purpose, the total length of the four directional couplers 16-1, 18-1, 16-2, and 18-2 included in the optical interferometer 40 is calculated as the completeness of the second component light C ₂ described above. Must be equal to the bond length. That is, the length of each directional coupler 16-1,18-1,16-2 and 18-2, and the respective length of 1/4 complete coupling length of the second component light _{C 2.}

More specifically, the second port P ₂ -1 of the first optical interferometer 30-1 is connected to the first port P ₁ -2 of the second optical interferometer 30-2, and the first optical interferometer The light BAR output from 30-1 is input to the second optical interferometer 30-2. Similarly, the third port P ₃ -1 of the first optical interferometer 30-1 is connected to the fourth port P ₄ -2 of the second optical interferometer 30-2, and the first optical interferometer 30- The light output from CRS 1 is input to the second optical interferometer 30-2.

  Next, the output characteristics of the optical interferometer 40 will be described with reference to FIG. In FIG. 7, the horizontal axis represents wavelength (μm), and the vertical axis represents light intensity. The light intensity is a light intensity ratio with respect to input light. These characteristic diagrams were obtained by performing mode calculation on the optical interferometer 40 by the finite element method.

Curve I in Figure 7 shows the light intensity of the TE wave BAR outputted from the second port _P 2 -2 of the second optical interferometer 30-2. Curve II shows the optical intensity of the TM wave output from the third port P ₃ -2 of the second optical interferometer 30-2 by CRS. A curve III indicates the light intensity of the TM wave output from the second port P ₂ -2 as a BAR. A curve IV represents the light intensity of the TE wave output from the third port P ₃ -2 as a CRS.

Referring to FIG. 7, when the curves I and IV indicating the output of the TE wave are compared, the intensity of the TE wave output from the third port P ₃ -2 in the entire wavelength range of 1.2 to 1.6 μm. (curve IV) is can be seen less than 1/1000 of a second port _P 2 -2 from the TE wave BAR output intensity (curve I). From this, the optical interferometer 40 is polarized / wavelength-separated with a sufficient extinction ratio in the wavelength range used in the subscriber system in terms of the TE wave.

Furthermore, a comparison of curves II and III show the output of the TM wave in the wide wavelength range of a wavelength of about 1.49～1.58Myuemu, the intensity of the TM wave BAR outputted from the second port _P 2 -2 (curve It can be seen that III) is less than 1/50 of the intensity of the TM wave output from the third port P ₃ -2 CRS (curve II). From this, the optical interferometer 40 is polarized / wavelength-separated with a sufficient extinction ratio in the wavelength range used in the ONU of the subscriber system in terms of TM waves.

  7 and 5, in the optical interferometer 40, the wavelength range for CRS output with a practically sufficient extinction ratio can be made wider than that of the optical interferometer 30. Specifically, in the optical interferometer 30, only 1.49TM light is output with a good extinction ratio, whereas in the optical interferometer 40, TM waves in a wide wavelength range of 1.49 to 1.58 μm are generated. CRS is output with a good extinction ratio.

[Embodiment 3]
Next, the optical interferometer of Embodiment 3 will be described with reference to FIG. FIG. 8 is a plan view schematically showing the structure of the optical interferometer 50 of the third embodiment.

  The optical interferometer 50 is an example in which the present invention is applied to an arrayed waveguide grating (AWG).

The optical interferometer 50 is provided in parallel between two optical couplers 50a and 50b and the first to u-th optical waveguides 20-1 connecting the optical couplers 50a and 50b. and to 20-u arrayed waveguide 23 (u is the integer of 3 or more) a, a first port P ₁ for the light input and output provided on one of the optical coupler 50a, provided on the other optical coupler 50b Second to s-th ports P _{2 to} P _s for optical input / output (s is an integer of s ≦ u + 1).

Input light IN including first to r-th component lights (r is an integer of 2 or more) having at least one of polarization and wavelength different from the first port P _{1 is} input to the optical interferometer 50. In this example, u = 6, s = 4 and r = 3. Therefore, the first to third component lights C ₁ , C ₂ and C ₃ included in the input light IN are polarized / wavelength separated in the process of propagating through the first to sixth optical waveguides 20-1 to 20-6. Are output from the _{second to} fourth ports P _{2 to} P ₄ , respectively.

In order to perform polarization / wavelength separation of the first to third component lights, each of the first to sixth optical waveguides 20-1 to 20-6 constituting the arrayed waveguide 23 has a different equivalent refractive index. Three phase adjustment regions are provided. More specifically, the first to sixth optical waveguide 20-1～20-6, first to third phase adjusting region ₂₂ 1 -1～22 ₁ -6,22 ₂ -1～22 _2-6 and 22 ₃ -1～22 _3-6 is provided. In the v-th and v + 1-th optical waveguides 20-v and 20- (v + 1) (v is an integer of 1 to 5) adjacent to each other, the first to third phase adjustment regions 22 ₁ -v and 22 _1- ( v + 1), 22 ₂ −v and 22 ₂ − (v + 1) and 22 ₃ −v and 22 ₃ − (v + 1) are adjusted.

Thus, the optical interferometer 50, the second to the fourth port _P 2 to P _4, it is possible to output the first to third component light polarized / wavelength separation.

  In this embodiment, the case where the number r of component lights to be polarized / wavelength separated is 3 and the number u of optical waveguides constituting the arrayed waveguide 23 is 6 has been described. However, the relationship between r and u is not limited to this, and u ≧ r may be satisfied. However, in order to perform polarization / wavelength separation with a practically sufficient extinction ratio, it is preferable that u ≧ 2r. Furthermore, it is more preferable if u ≧ 4r.

8 Substrate 12 Cladding 13 Core 14, 24a, 24b, 26a, 26b Optical waveguide 10, 30, 40, 50 Optical interferometer 16 Optical coupler (first directional coupler)
16a First optical waveguide 16b Second optical waveguide 18 Optical coupler (second directional coupler)
18a Third optical waveguide 18b Fourth optical waveguide 20 Arm portion 20a First arm optical waveguide 20b Second arm optical waveguides 20-1 to 20-6 First to sixth optical waveguides 21a and 21b Unadjusted regions 22 _{1 to} 22 _j Phase adjustment region (first to jth phase adjustment regions)
22 ₁ -1～22 _1-6 first phase adjusting region ₂₂ 2 -1～22 _2-6 second phase adjusting region ₂₂ 3 -1～22 ₃ -6 third phase adjusting region ₂₂ 1 L, ₂₂ 1 R, 22 ₂ L, 22 ₂ R, 22 ₃ L, 22 ₃ R Subregion 23 Array waveguide 24 Input section 26 Output section 30-1 First optical interferometer 30-2 Second optical interferometer

Claims (15)

It has an optical waveguide composed of a clad and a core provided on the main surface side of the substrate, and the optical waveguide is
Two optical couplers,
First and second arm optical waveguides provided in parallel between the two optical couplers and connecting the two optical couplers;
A first port provided in one of the optical couplers;
Second and third ports provided in the other optical coupler;
A total of j phase adjustment regions (j is an integer of 2 or more) provided in one or both of the first and second arm optical waveguides,
Optical interference characterized in that first to j-th component light having at least one of polarization and wavelength input from the first port is output from the second and third ports at a distribution ratio according to a setting. vessel. The i-th component light C _i (i is an integer from 1 to j) is a light having a wavelength of λ (C _i ) and a polarization of either a TE wave or a TM wave.
Geometric length L _k along the light propagation direction of the k-th phase adjustment region (k is an integer of 1 to j), and the equivalent refractive index n _k of the k-th phase adjustment region with respect to the i-th component light C _i C _i ) and the interference order m (C _i ) (m (C _i ) is a positive real number) relating to the i-th component light C _i satisfy the following formula (1): The optical interferometer described.

  Among the first to j-th component lights, the interference order of the TE component light group whose polarization is a TE wave is ½ × odd, and the interference order of the TM component light group whose polarization is a TM wave is 1 The optical interferometer according to claim 2, which is / 2 × even.   The said jth phase adjustment area | region is a partial area | region of the said 1st and 2nd arm optical waveguide except the said 1st-j-1st phase adjustment area | region, The Claim 2 or 3 characterized by the above-mentioned. Optical interferometer.   The optical interferometer according to any one of claims 2 to 4, wherein the optical path lengths of the first and second arm optical waveguides excluding the first to jth phase adjustment regions are equal to each other.   The phase adjustment cladding is provided around the core in at least one of the j phase adjustment regions, and the refractive index of the phase adjustment cladding is different from the refractive index of the cladding. Item 6. The optical interferometer according to any one of Items 1 to 5.   7. The widths of the j phase adjustment regions that are perpendicular to the light propagation direction and are parallel to the main surface are different from each other. Optical interferometer.   8. The optical interferometer according to claim 1, wherein a material having a refractive index of 71.4% or less of the core is used as the cladding material. The Si is used as a material of the core, and SiO _p N _q (where p and q are 2 ≧ p ≧ 0 and 4/3 ≧ q ≧ 0) is used as the material of the cladding. The optical interferometer according to any one of 6 to 8.   The optical interferor according to any one of claims 1 to 9, wherein the one and the other optical couplers are directional couplers, respectively.   The optical interferor according to claim 1, wherein the one and the other optical couplers are multimode interference optical waveguides.   The optical interferometer according to claim 1, wherein at least one of the j phase adjustment regions includes a plurality of sub-regions.   13. The optical interferometer according to claim 1, wherein a thickness of the core, which is a length perpendicular to the main surface, is a value in a range of 200 to 500 nm.   14. An optical interferometer comprising the optical interferors according to claim 1 connected in series over a plurality of stages. Two optical couplers, a first to a u-th optical waveguide (u is an integer of 3 or more) provided in parallel between the two optical couplers and connecting the two optical couplers; A first port provided in the optical coupler, and second to s-th ports provided in the other optical coupler (s is an integer of s ≦ u + 1),
The first to u-th optical waveguides have different optical path lengths;
Input light including first to r-th component light (r is an integer of 2 or more) having at least one of polarization and wavelength different from the first port is input.
Each of the first to u-th optical waveguides includes first to r-th phase adjustment regions, and the first to r-th optical waveguides in the v-th and v + 1-th optical waveguides (v is an integer of 1 to u−1) adjacent to each other. An optical interferometer, wherein the first to r-th component lights are output from the second to s-th ports, respectively, according to the length of the phase adjustment region.

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