JPH08122545A - Waveguide type optical multiplexer/demultiplexer - Google Patents

Abstract

PURPOSE: To extend one band without narrowing the other band. CONSTITUTION: In the waveguide type optical multiplexer/demultiplexer which allows light of the band including wavelengths λ1 and λ3 to pass through and couples light of the band including a wavelength λ2 , waveguide length differences ΔL1 and ΔL2 of phase difference giving parts 11, 14, and 17 and a coupling rate κ(λ2 ) of the wavelength λ2 of directional couplers 5 to 8 satisfy conditional formulas ΔL1 =(N1 ±0.5).λ3 /neff(λ3 ), Pc(λ2 )=4.κ(λ2 ). 1-κ(λ2 )}.cos<2> neff(λ2 ).π.ΔL1 /λ2 }=0.5, 2.N2 =λ1 /neff(λ1 )/|λ1 /neff(λ1 )-λ2 /neff(λ2 )|, and ΔL2 =(N±0.5).λ1 /neff(λ1 )=N.λ2 /neff(λ2 ) where N1 and N2 are integers and neff (λ) is the equivalent refractive index of waveguides 2 and 3 to light of the wavelength λ.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Mach-Zehnder type waveguide type optical multiplexer / demultiplexer for multiplexing / demultiplexing light in two bands.

[0002]

[Prior art]

(Conventional Example 1) A waveguide type Mach-Zehnder interferometer type optical multiplexer / demultiplexer (hereinafter referred to as an optical multiplexer / demultiplexer) to which the principle of the Mach-Zehnder interferometer is applied is conventionally configured as shown in FIG. 4 (a). That is, in this optical multiplexer / demultiplexer, the coupling ratio of the light intensity is κ.
(Λ) two directional couplers 28 and 29 and a length Δ
It is composed of a waveguide 30 and a phase difference providing unit 32 composed of a waveguide 31 which are different from each other by L ₂ . When the light having the wavelength λ _{1 and} the light having the wavelength λ ₂ are made incident from the input port 25 which is one end of the waveguide, the light having the wavelength λ ₁ is extracted from the transmission port 27 which is the other end of the waveguide. The light of wavelength λ ₂ is extracted from the coupling port 26 at the end.

The condition of the phase difference imparting part necessary for multiplexing and demultiplexing the light of wavelength λ _{1 and} the light of wavelength λ ₂ is the equivalent refractive index neff of the waveguide.
Optical path length difference neff Considering (λ) (λ) · ΔL 2 is, when any of the integer and the _{N 2, neff (λ) ·} ΔL 2 = (N 2 ± 0.5) · λ 1 = N 2・ It is given by the relation of λ ₂ (5). As can be seen from the equation (5), the wavelengths λ ₁ and λ ₂ are not obtained arbitrarily, but {λ ₁ / neff (λ ₁ )} / | λ ₁ / neff (λ ₁ ) −λ ₂ / neff (Λ ₂ ) | = 2 · N ₂ (6) Only wavelength combinations satisfying the condition are restricted. Note that the formula
In (6), the wavelength dependence of the equivalent refractive index neff (λ) of the waveguide is considered.

Expression (5) is rewritten as ΔL ₂ = (N ₂ ± 0.5) · λ ₁ / neff (λ ₁ ) = N ₂ · λ ₂ / neff (λ ₂ ) (7), and each port is rewritten. The pass wavelength and stop wavelength at
It can be set with high accuracy by determining ΔL ₂ in the equation (7).

In this optical multiplexer / demultiplexer, the input port 25
The coupling of light into the coupling port 26 from the P _2-3, when the transmittance of light from the input port 25 to the permeate port 27 and _{P 2-4, P 2-3 = 4 ·} {1-κ (λ )} ・ Κ (λ) ・ cos ² {neff (λ) ・ π ・ ΔL ₂ / λ} (8) P _2-4 = {1-2 ・ κ (λ)} ² +4 ・ κ (λ) ・ { 1-κ (λ)} · sin ² {neff (λ) · π · ΔL ₂ / λ} (9) The propagation loss and scattering loss of the waveguide are ignored here. Focusing on κ (λ) in Equations (5) to (9), the wavelength λ that is the light extracted from the port 26
_It can be seen that an optical multiplexer / demultiplexer with low loss and zero crosstalk can be constructed by setting the coupling ratio κ (λ ₂ ) of the light intensity of ₂ to 0.5.

With this design method, the wavelength λ ₁ = 1.31 μ
The characteristics of the optical multiplexer / demultiplexer designed with m and wavelength λ ₂ = 1.53 μm are shown in FIG. 3 (b).

(Reference 1: IEICE Transactions C-
I Vol.J73-CI No.5 pp.354-359 May 1990) (Conventional example 2) The pass wavelength band and the stop wavelength band of the optical multiplexer / demultiplexer described in (Conventional example 1) are narrow and practical. Therefore, it was necessary to expand the bandwidth. Therefore, an optical multiplexer / demultiplexer as shown in FIG. 5 has been developed. (Reference 2: T. Kominato et al; Optical
multi / demultiplexer with a modified Mach-Zender in
terferometer configuration; OEC'94, Technical di
gest pp.174-175, July 12-15,1994) The point of the optical multiplexer / demultiplexer of (Conventional example 2) is to replace the directional coupler of (Conventional example 1) with a Mach-Zehnder interferometer type optical multiplexer / demultiplexer. In addition to the wavelength λ ₁ of (conventional example 1), the wavelength λ ₃ is added due to the multiplexing / demultiplexing characteristics of the Mach-Zehnder interferometer type optical multiplexer / demultiplexer (hereinafter abbreviated as daughter MZ multiplexer / demultiplexer).
Is to be transparent. As shown in FIG. 5 (a), the structure is such that the waveguide 42 and the waveguide 4 differ in length by ΔL _1.
A daughter MZ multiplexer / demultiplexer composed of a phase difference imparting unit 44 composed of 3 and directional couplers 38 and 39 having a coupling ratio of κ (λ), and a waveguide 48 and a waveguide having lengths different by ΔL _1. Four
A daughter MZ multiplexer / demultiplexer composed of a phase difference providing unit 50 made of 9 and directional couplers 40 and 41 having a coupling ratio of κ (λ) is arranged upside down, and the two daughter MZs are arranged upside down.
This is a structure in which the multiplexer / demultiplexer is connected by waveguides 45 and 46 whose lengths differ by ΔL ₂ .

In this optical multiplexer / demultiplexer, the input port 35
Let P _{2-3 be} the light transmittance from the input port 35 to the transmission port 37 and P _2-4 be the light coupling ratio from the input port 35 to the coupling port 36, then P _2-4 = {1-2 · Pc (λ )} ² + 4 · Pc (λ) · {1-Pc (λ)} · sin ² {neff (λ) · π · ΔL ₂ / λ} (10) P _2-3 = 4 · {1-Pc (λ )} · Pc (λ) · cos 2 {neff (λ) · π · ΔL 2 / λ} (11) Pc (λ) = 4 · {1-κ (λ)} · κ (λ) · cos 2 { neff (λ) · π · ΔL ₁ / λ} (13) Here, ΔL ₂ is the same as in (conventional example 1), expressed by equations (5), (6),
Determined from (7).

Here, the coupling ratio κ (λ) of the directional coupler and the waveguide length difference ΔL of the phase difference providing section of the daughter MZ multiplexer / demultiplexer.
₁ is given by _{neff (λ) · ΔL 1 =} (N 1 ± 0.5) · λ 2/2 = N 1 · λ 3/2 (14) κ (λ 2) = 0.5 (15) . Here, N ₁ is an integer and λ ₃ is a wavelength close to the wavelength λ ₁ .

With the above design method, the wavelength λ ₁ = 1.
31 μm, wavelength λ ₂ = 1.53 μm, wavelength λ ₃ = 1.2
Figure 5 shows the multiplexing / demultiplexing characteristics of the optical multiplexer / demultiplexer designed to be 76 μm.
The solid line is shown in (b). For comparison, the multiplexing / demultiplexing characteristic (conventional example 1) is also shown by the dotted line in FIG. 5 (b).

[0011]

In (Conventional example 2), one band has been successfully expanded as compared with (Conventional example 1). However, unless the width of the waveguide or the refractive index is changed, the combination of (λ ₁ , λ ₂ ) is determined corresponding to the integer N ₂ in the conditional expression (7). Further, from the conditional expression (14), the combination of (λ ₂ , λ ₃ ) is decided corresponding to the integer N ₁ . To further extend the band, λ ₃ is limited to a wavelength close to λ ₁ . Therefore, if the integers N ₂ and λ ₂ are decided, all other design parameters are decided without choice, and there is a problem that the degree of freedom in design is small.

Further, as can be seen from FIG. 5 (b), the (passivation example 2) has a wider pass and stop wavelength band in the 1.3 μm band than the (passive example 1), but conversely in the 1.5 μm band. The pass and stop wavelength bands are narrower than those of (conventional example 1). Without narrowing one band like this,
There was a problem that the other band could not be expanded.

An object of the present invention is to solve the above problems and to expand the other band without narrowing one band.

[0014]

The gist of the present invention according to claim 1 is to have a port 1 and a port 2 which are input ports, a port 3 and a port 4 which are output ports, and connect the ports 1 and 3 together. A total of two waveguides, that is, a waveguide connecting the port 2 and the port 4 has a coupling ratio of the light intensity at the wavelength λ of κ.
(Λ) Two directional couplers and a phase difference providing section connecting the two directional couplers are formed. In the phase difference providing section, the waveguide connecting the ports 1 and 3 is the port 2 It has two Mach-Zehnder interferometer type waveguide optical multiplexers / demultiplexers having a length longer than the waveguide connecting port 4 by ΔL ₁ and one port of the Mach-Zehnder interferometer type waveguide optical multiplexer / demultiplexer 4 and the port 1 of the other Mach-Zehnder interferometer type waveguide optical multiplexer / demultiplexer are connected by one waveguide, and one Mach-Zehnder interferometer type optical multiplexer is connected by a waveguide longer by ΔL ₂ than this waveguide. A waveguide-type optical multiplexer / demultiplexer that connects the port 3 of the demultiplexer and the other port 2 and transmits light in the band including wavelengths λ ₁ and λ ₃ and couples light in the band including wavelength λ _2. , N ₁ and N ₂ are integers and neff
When (λ) is an equivalent refractive index for light having a wavelength λ in the waveguide, the waveguide length differences ΔL ₁ and ΔL ₂ in the phase difference providing unit, the coupling rate κ (λ ₂ ) at the wavelength λ _{2 in} the directional coupler. Is the following conditional expression, ΔL ₁ = (N ₁ ± 0.5) · λ ₃ / neff (λ ₃ ) (1) Pc (λ ₂ ) = 4 · κ (λ ₂ ) · {1-κ ( λ ₂ )} ・ cos ² {neff (λ ₂ ) ・ π ・ ΔL ₁ / λ ₂ } = 0.5 (2) 2 ・ N ₂ = λ ₁ / neff (λ ₁ ) / | λ ₁ / neff (λ ₁ ) −λ ₂ / neff (λ ₂ ) | (3) ΔL ₂ = (N ± 0.5) · λ ₁ / neff (λ ₁ ) = N · λ ₂ / neff (λ ₂ ) (4) Especially.

Further, the gist of the present invention according to claim 2 is a function of the wavelength expressed by the conditional expression (2), Pc (λ) = 4 · κ (λ) · {1-κ (λ)} · cos ^{2 {neff (λ) · π} · ΔL 1 / λ} differential dPc (λ) / dλ are formed so that the wavelength lambda ₂ or lambda 0 ₂ near wavelengths, the conjugation rate of the directional coupler κ
(Λ), the equivalent refractive index neff (λ) of the waveguide, and the waveguide length difference ΔL ₁ of the phase difference providing section.

[0016]

In the present invention, the conditional expression (14) in (Conventional example 2),
Instead of (15), the above conditional expressions (1) and (2) are used to improve the design flexibility.

In (Conventional example 2), if λ ₂ is determined, the equation (1
From 4), λ ₃ has a one-to-one correspondence (to be precise, there is a ± sign, so a one-to-two correspondence).

On the other hand, in the present invention, conditional expression (1),
By using (2), λ ₃ can be determined independently of λ ₂ .

(Conventional Example 2) is a conditional expression (15) in which κ (λ ₂ )
However, the present invention eliminates the limitation, and instead introduces conditional expression (2),
λ ₃ is released from the one-to-one correspondence with λ ₂ .

The present invention according to claim 2 provides the following conditional expression:
By designing using (18), it is possible to expand one band rather than narrowing the other band slightly, and to expand the other band.

Pc (λ) = 4 · {1-κ (λ)} · κ (λ) · cos ² {neff (λ) · π · ΔL ₁ / λ} dPc (λ ₂ ) / dλ = 0 (18 ) In order to split the light of wavelength λ to the coupling port, neff (λ) · ΔL ₁ = N ₁ · λ (19) Pc (λ) = {1-κ (λ)} · 4 · κ ( It is necessary to satisfy the condition of λ) · cos ² {neff (λ) · π · ΔL ₁ /λ}=0.5 (20). Wavelength λ ₂ is conditional expression (5)
(2) and (2) satisfy Eqs. (19) and (20), so they are demultiplexed.
To widen the band, use the formulas (19) and (20) at wavelengths near λ _2.
It is necessary to approach the state of satisfying. Therefore,
In the present invention, the rate of change of the function Pc (λ) of wavelength (dPc (λ) /
dλ) is designed to be the smallest near λ ₂ .

6 to 15 are views for explaining the operation of the present invention. In the following description, in the phase difference providing unit of the optical multiplexer / demultiplexer, only the waveguide length difference is taken into consideration (that is, the length of the waveguide 58 in the phase difference providing unit 60 is ΔL ₁ , The length of 59 is regarded as 0. There is no theoretical problem with this.

FIG. 6 is a diagram for explaining the electric field amplitude and the phase of the output light when the light having the electric field amplitude of E ₀ and the phase of 0 is incident from the input port 53a of the optical multiplexer / demultiplexer. Here, the electric field amplitude of the light output from the coupling port 55 is E ₁ , the phase is θ ₁ , the electric field amplitude of the light output from the transmission port 54 is E ₂ , and the phase is θ ₂ . At that time, θ ₁ and θ ₂ are the coupling rates κ of the directional couplers 56 and 57.
(Λ), the waveguide length difference ΔL _{1 of} the phase difference providing unit 60, and the propagation constant β (λ) of the waveguide, the following equation can be used.

[0024]

[Equation 1]

FIG. 7 shows a state in which light having a conjugate relationship with the light output in FIG. 6 is incident in the opposite direction. This means that the light whose electric field amplitude is E ₁ and whose phase is −θ ₁ is coupled port 5
5, when light having an electric field amplitude of E ₂ and a phase of −θ ₂ is simultaneously incident from the transmission port 54, the input port 53a
Means that light having an electric field amplitude of E ₀ is emitted from. That is, if light having a conjugate relationship with the light emitted from the coupling port 55 and the transmission port 54 when the light is input from the input port 53a enters the coupling port 55 and the transmission port 54, the light returns to the input port 53a. That's what it means. It should be noted that, here, it will be described in the explanation of FIG. 9 that only the relative relationship between the phases needs to be considered.

FIG. 8 is a diagram for explaining the electric field amplitude and the phase of the output light when the light having the electric field amplitude of E ₀ and the phase of 0 is incident from the input port 53b of the same optical multiplexer / demultiplexer as in FIG. Here, the electric field amplitude of the light output from the port 54 is E ₁ , the phase is φ ₁ , the electric field amplitude of the light output from the port 55 is E ₂ , and the phase is φ ₂ . Then φ ₁ , φ
₂ is the coupling ratio κ (λ) of the directional coupler, the waveguide length difference ΔL of the phase difference providing unit, and the propagation constant β (λ) of the waveguide,
It can be expressed by the following formula.

[0027]

[Equation 2]

Light having a conjugate relationship with the light output in FIG.
FIG. 9 shows a state in which light having the same phase difference between the port 55 and the port 54 and the same electric field amplitude is incident in the opposite direction.
This means that in FIG. 9, the electric field amplitude is E ₁ and the phase is port 54.
When light that is advanced by φ ₁ -φ ₂ from the port 55 and light whose electric field amplitude is E ₂ and the phase is delayed by φ ₁ -φ ₂ from the port 55 at the same time from the port 54, the light is input from the input port 53b. It means that light is emitted. That is, when the light is input from the input port 53b, the phase difference between the output light and the ports 55 and 54 is opposite, and if the light having the same electric field amplitude is input in the opposite direction, the light returns to the input port 53b. That is.

Next, the operation of the present invention will be described using the concept described with reference to FIGS.

As shown in FIG. 10, the optical multiplexer / demultiplexer according to the present invention is divided into three regions for the purpose of explanation, and the movement of the light in each region when the light is incident from the incident port is shown in FIG.
It will be described with reference to FIG.

FIG. 11 is a diagram for explaining the electric field amplitude and phase of light in the region 1. When the light having the electric field amplitude E ₀ enters from the input port 61, the electric field amplitude of the combined light is E
₁ , the phase is θ ₁ , the electric field amplitude of the transmitted light is E ₂ , and the phase is θ ₂ , then from the conditional expression (2) shown in the claims, the wavelength λ
_In the case of the light of ₂ , E ₁ = E ₂ , and from the conditional expression (1),
It can be seen that E ₁ = 0 and E ₂ = E ₀ for light of wavelength λ ₃ .

In FIG. 12, the light emitted in the area 1 is converted into the area 2
It shows what kind of phase change is made upon incidence on. Here, regarding the phase, it suffices to consider only the difference between the waveguides 71 and 72 with respect to the lights incident simultaneously. Therefore, light with an electric field amplitude of E ₁ and a phase of θ ₁ −θ _{2 in} the waveguide 71, and electric field amplitude of E ₂ in the waveguide 72 is E ₂ ,
It is assumed that light having a phase of 0 is incident. In the incident light, the electric field amplitude does not change in the area 2, but only the phase changes. The phase of the light emitted from the waveguide 71 is θ ₁ −θ ₂ + β
(Λ) · ΔL ₂ , and the phase of the light emitted from the waveguide 72 is 0. Here, the conditional expression (3), (4), the wavelength lambda _1, the _{β (λ 1) · ΔL 2} = (2 · N 2 ± 1) · π, the wavelength _{λ 2, β (λ 2)} · It can be seen that ΔL ₂ = 2 · N ₂ · π. FIG. 13 is a diagram for explaining how the light of wavelength λ ₁ emitted in the region 2 enters the region 3 and is emitted to the transmission port. Here, although detailed description is omitted, for the wavelength λ ₁ , (φ ₂ −φ ₁ ) − (θ ₁ −
θ ₂ ) = − π holds. Therefore,

[0033]

(Equation 3)

It becomes

As described above, with respect to the wavelength λ ₁ , the phase of the light entering the waveguide 75 is larger than that of the light entering the waveguide 74 by θ ₁ −θ ₂ + (2 · N ₂ ± 1) · Advance by π ”means that the light entering the waveguide 75 has a phase φ ₁ more than the light entering the waveguide 74.
It is delayed by −φ ₂ ”(the phase of an integral multiple of 2 · π is the same as 0). Therefore, in this case, the electric field amplitude is E _{1 in the} waveguide 74 and the phase is − (Φ ₁
The light of −φ ₂ ) is incident on the waveguide 75 with the electric field amplitude of E ₂ and the phase of 0. This is the same as the case of FIG. 9 (upside down FIG. 9). You can see it well).
Therefore, it can be seen that the light of wavelength λ ₁ is output to the transmission port.

FIG. 14 is a diagram for explaining how the light of wavelength λ ₂ emitted in the region 2 enters the region 3 and is emitted to the coupling port.

[0037]

[Equation 4]

Where, for wavelength λ ₂ , E ₁ = E ₂
Therefore, as shown in the figure, “light having an electric field amplitude of E ₁ and a phase of θ ₁ −θ ₂ enters the waveguide 74 and light of an electric field amplitude of E ₂ and a phase of 0 enters the waveguide 75. That is, “light having an electric field amplitude E ₂ and a phase of 0 is incident on the waveguide 74, and light having an electric field amplitude of E ₁ and a phase of − (θ ₁ −θ ₂ ) is incident on the waveguide 75”. And can be converted as shown in FIG. This is the same as in the case of FIG.
Therefore, it can be seen that the light of wavelength λ ₂ is output to the coupling port. According to the second aspect of the present invention, the rate of change of E ₁ and E ₂ with respect to the wavelength is minimized at the wavelength λ ₂ , and λ
_At a wavelength close to ₂ , the band is prevented from narrowing by setting E ₁ ≈E ₂ . FIG. 15 is a diagram for explaining how the light of wavelength λ ₃ emitted in the region 2 enters the region 3 and is emitted to the transmission port. For light of wavelength λ ₃ ,
Since E ₁ = 0 and E ₂ = E _0, it is the same as when light is incident only on the waveguide 75. Waveguide 74 through region 3
Let E ₁ be the electric field amplitude of the light emitted from the waveguide and E ₂ be the electric field amplitude of the light emitted from the waveguide 75. Again, from the conditional expression (1), E ₁ = 0 and E ₂ = E ₀ I know there is. Therefore, the light of wavelength λ ₃ is output to the transmission port.

[0039]

Embodiments of the present invention will be described below with reference to FIGS. FIG. 1 is a diagram showing a waveguide type optical multiplexer / demultiplexer according to this embodiment. FIG. 1 (a) is a plan view and FIG.
(b) is a sectional view taken along the line aa '. FIG. 2 is a diagram showing a loss wavelength characteristic of a waveguide type optical multiplexer / demultiplexer according to an embodiment of the present invention (claim 1). FIG. 2 (a) is a coupling port when light is input from the input port 18. Figure 20 shows the loss wavelength characteristic at 20.
(b) shows loss wavelength characteristics at the transmission port 19 when light is input from the input port 18. FIG. 3 is a diagram showing a loss wavelength characteristic of a waveguide type optical multiplexer / demultiplexer according to an embodiment of the present invention (claim 2). FIG. 3 (a) is a coupling port when light is input from the input port 18. Loss wavelength characteristics at 20
FIG. 6B shows the loss wavelength characteristic at the transmission port 19 when light is input from the input port 18.

As shown in FIG. 1, the waveguide type optical multiplexer / demultiplexer of this embodiment is formed by extending the waveguides 2 and 3 linearly or bending them at a bending radius of 30 mm.
It is composed of two directional couplers 5, 6, 7, and 8 and phase difference providing units 11, 14, and 17 connecting them. Same figure
As shown in (b), the waveguides 2 and 3 are obtained by covering the cores 2 a and 3 a formed on the substrate 1 with the cladding 4.
The directional couplers 5, 6, 7, and 8 as shown in FIG.
The waveguides 2 and 3 are arranged in parallel with a gap Gap, and the length of the parallel portion is represented by LC. The phase difference providing unit 11 makes the waveguide 9 longer than the waveguide 10 by ΔL ₁ , and the phase difference providing unit 14 makes the waveguide 12 longer than the waveguide 13 by ΔL ₂ Reference numeral 17 gives a phase difference by making the waveguide 16 longer than the waveguide 15 by ΔL ₁ .

The refractive index of the substrate 1 and the clad 4 is 1.45.
8. The refractive index of the core is 1.4624, and the height and width of the core are 8 μm. As for the material, the substrate 1 is SiO ₂ , and the clad 4
There _{SiO 2 -B 2 O 5 -P 2} O 3, the core is SiO ₂ -T
iO ₂ .

In FIG. 1, Gap of the directional coupler is 3.5 μm, the length LC of the parallel portion is 213 μm, the waveguide length difference ΔL ₁ between the phase difference providing portions 11 and 17 is 1.293 μm,
The waveguide length difference ΔL ₂ of the phase difference providing unit 14 is 3.171 μm.
The loss wavelength characteristic of the waveguide type optical multiplexer / demultiplexer of the above example is shown by the solid line in FIG. Here, the wavelength λ ₁ ,
λ ₂ and λ ₃ are λ ₁ = 1.31 μm and λ ₂ = 1.53 μ
m and λ ₃ = 1.25 μm. In FIG. 2, for comparison, a broken line shows the loss wavelength characteristic of the waveguide type optical multiplexer / demultiplexer of (Conventional example 2). The characteristics shown by the solid line cannot be realized by the conventional design method. For example, suppose here that the target is 25 dB or more at the wavelength λ = 1.24 to 1.32 μm at the coupling port (the spectral curve may pass outside the frame 21),
0.05 dB or less at the wavelength λ = 1.525 to 1.535 μm (the spectral curve should pass outside the frame 22), and 0.1 dB or less at the transmission port at the wavelength λ = 1.24 to 1.32 μm (frame 23 The spectral curve should pass outside the
20 dB or more at 1.525 μm to 1.535 μm (frame 24
If the spectroscopic curve should pass outside of, the present invention can achieve the target because the characteristics of the solid line can be realized.
It cannot be achieved conventionally. As described above, the waveguide type optical multiplexer / demultiplexer of the present invention is excellent in the degree of freedom in designing according to the target.

In FIG. 1, Gap of the directional coupler is 3.84 μm, the length LC of the parallel portion is 27 μm, and the waveguide length difference ΔL ₁ between the phase difference applying portions 11 and 17 is 3.156 μm.
The waveguide length difference ΔL ₂ of the phase difference providing unit 14 is 2.115 μm.
The loss wavelength characteristic of the waveguide type optical multiplexer / demultiplexer of the above example is shown by a solid line in FIG. For comparison, the loss wavelength characteristics of the waveguide type optical multiplexer / demultiplexer (conventional example 1) are shown by a broken line in FIG. Conventionally, as shown in FIG. 5 (b), and as described above, there is a problem that when one band is widened, the other band becomes narrower. As shown in FIG. 3, the demultiplexer has a width of 1.53 μm even though the band is wide in the 1.3 μm band.
The band is not narrow in the band. Rather, the band is wide even in the 1.53 μm band. As described above, the waveguide type optical multiplexer / demultiplexer of the present invention is excellent in that both of the demultiplexing bands can be widened.

In addition to the materials used in the examples, SiO ₂ —GeO ₂ is often used as the core.

As the substrate, the clad and the core material, other than the above-mentioned materials, other dielectric materials, semiconductor materials and organic materials can be used.

[0046]

【The invention's effect】

(1) According to the present invention described in claim 1, it is possible to easily realize a waveguide type optical multiplexer / demultiplexer in which one band is widened without narrowing one band.

(2) According to the present invention as set forth in claim 2, it is possible to widen the other band without narrowing one band, and to expand the other band.

[Brief description of drawings]

1A and 1B are views showing an embodiment of the present invention, in which FIG. 1A is a plan view and FIG. 1B is a sectional view taken along the line aa '.

FIG. 2 is a graph of loss wavelength characteristics of the optical multiplexer / demultiplexer according to the embodiment of the present invention (claim 1).

FIG. 3 is a graph of loss wavelength characteristics of an optical multiplexer / demultiplexer according to an embodiment of the present invention (claim 2).

4A and 4B are diagrams showing a conventional example, FIG. 4A is a plan view of a conventional optical multiplexer / demultiplexer, and FIG. 4B is a graph of loss wavelength characteristics.

5A and 5B are diagrams showing a conventional example, FIG. 5A is a plan view of a conventional optical multiplexer / demultiplexer, and FIG. 5B is a graph of loss wavelength characteristics.

FIG. 6 is a diagram illustrating the operation of the present invention.

FIG. 7 is a diagram for explaining the operation of the present invention.

FIG. 8 is a diagram illustrating the operation of the present invention.

FIG. 9 is a diagram for explaining the operation of the present invention.

FIG. 10 is a diagram illustrating the operation of the present invention.

FIG. 11 is a diagram illustrating the operation of the present invention.

FIG. 12 is a diagram for explaining the operation of the present invention.

FIG. 13 is a diagram for explaining the operation of the present invention.

FIG. 14 is a diagram for explaining the operation of the present invention.

FIG. 15 is a diagram for explaining the operation of the present invention.

[Explanation of symbols]

 1 Substrate 2, 3 Waveguide 4 Clad 5, 6, 7, 8 Directional Coupler 9, 10, 12, 13, 15, 16 Waveguide 11, 14, 17 Phase Difference Giving Part 18 Input Port 19 Transmission Port 20 Coupling port

Claims (2)

[Claims] 1. A total of two waveguides having input ports, port 1 and port 2, output ports, port 3 and port 4, connecting port 1 and port 3 and connecting port 2 and port 4. The two waveguides form two directional couplers having a coupling ratio of light intensity at the wavelength λ of κ (λ) and a phase difference providing section connecting the two directional couplers. In the applying part, the waveguide connecting port 1 and port 3 is port 2
Of two Mach-Zehnder interferometer type waveguide optical multiplexers / demultiplexers having a structure that is longer than the waveguide connecting the port 4 and port 4 by ΔL ₁ The port 4 and the other port 1 of the Mach-Zehnder interferometer type waveguide optical multiplexer / demultiplexer are connected by one waveguide, and one Mach-Zehnder interferometer type waveguide type is formed by a waveguide longer by ΔL ₂ than this waveguide. A waveguide type optical multiplexer / demultiplexer configured to connect the port 3 of the optical multiplexer / demultiplexer and the other port 2 and transmit the light in the band including the wavelengths λ ₁ and λ ₃ and couple the light in the band including the wavelength λ _2. In the wave filter, N ₁ and N ₂ are integers,
When neff (λ) is an equivalent refractive index for light having a wavelength λ of the waveguide, the waveguide length differences ΔL ₁ and ΔL _{2 of} the phase difference providing unit,
The coupling ratio κ (λ ₂ ) of the wavelength λ ₂ of the directional coupler is expressed by the following conditional expression: ΔL ₁ = (N ₁ ± 0.5) · λ ₃ / neff (λ ₃ ) (1) Pc (λ ₂ ) = 4 · κ (λ ₂ ) · {1-κ (λ ₂ )} · cos ² {neff (λ ₂ ) · π · ΔL ₁ / λ ₂ } = 0.5 (2) 2 · N ₂ = λ ₁ / neff (λ ₁ ) / | λ ₁ / neff (λ ₁ ) −λ ₂ / neff (λ ₂ ) | (3) ΔL ₂ = (N ± 0.5) ・ λ ₁ / neff (λ ₁ ) = N · λ ₂ / neff (λ ₂ ) (4) is a waveguide type optical multiplexer / demultiplexer. 2. A function of wavelength expressed by the conditional expression (2) according to claim 1, Pc (λ) = 4 · κ (λ) · {1-κ (λ)} · cos ² {neff (λ ) · Π · ΔL ₁ / λ} differential dPc (λ) / dλ is 0 at the wavelength λ ₂ or at a wavelength near λ ₂ so that the coupling ratio κ of the directional coupler is κ.
(Λ), the equivalent refractive index neff (λ) of the waveguide, and the waveguide length difference ΔL ₁ of the phase difference providing section, wherein the waveguide type optical multiplexer / demultiplexer is characterized.