JPH0895108A - Light signal processor - Google Patents

Abstract

PURPOSE: To realize a filter characteristic having desired sharpness with a small number of steps and to realize arbitrary filter characteristics with one circuit. CONSTITUTION: This light signal processor includes two pieces of first and second optical waveguides 1, 2, (N+1) pieces of first directional coupler groups 3-1 to 3-(N+1) for dividing and coupling these optical waveguides 1, 2 to N pieces regions, second directional coupler groups 4-1 to 4-N which are respectively interposed to either one of the optical waveguides of N pieces of the regions, ring optical waveguide groups 5-1 to 5-N which are respectively coupled to any one of the first and second optical waveguides 1, 2 of N pieces of the regions via these second directional coupler groups 4-1 to 4-N, first phase controller groups 6-1 to 6-N which are respectively interposed in at least one of the optical waveguides 1, 2 of N pieces of the regions and second phase controller groups 7-1 to 7-N which are respectively interposed in the ring optical waveguide groups 5-1 to 5-N. The optical path lengths of the two optical waveguides 1, 2 in N pieces of the regions are respectively equalized to each other and all of the optical path lengths of the ring optical waveguide groups 5-1 to 5-N are equalized to each other.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical signal processor for performing highly optional optical filtering processing in the fields of optical communication, optical switching, and optical computing.

[0002]

2. Description of the Related Art In recent years, in the fields of optical communication, optical switching, and optical computing, optical signal processing capable of performing broadband and high-speed filtering processing without converting an optical signal into an electric signal as it is as an optical signal. The vessel is drawing attention. In particular,
In optical frequency multiplex communication in which optical signals are multiplexed and transmitted, an optical frequency filter that performs a filtering process for each frequency on the propagated frequency multiplexed signal light is an important component.

Conventionally, as an optical signal processor for such a purpose, a transversal type optical signal processor shown in FIG. 8 (Japanese Patent Laid-Open No. 2-128222) has been reported. In this example, variable directional couplers 103-1 to 103-N are arranged on the input ports 101 and 102 side, and optical signals are branched at arbitrary branching ratios to the respective branch waveguides 104-1 to 104-N.
, And N-1 3 dB directional couplers 105-1 to 105-1
The coupling unit 105- (N-1) is used to converge each branched optical signal again. A phase controller 1 for individually controlling the phase of the branched optical signal is provided on each of the branch waveguides 104-1 to 104-N.
06-1 to 106-N are arranged. The 3 dB directional couplers 105-1 to 105- (N-1) have dummy output ports 107-1 to 107- (N-1), and the last 3 dB directional coupler 105-1 (N-). The other output port of 1) becomes the output port 108. In this example, the coupling ratios of the variable directional couplers 103-1 to 103-N are changed, and at the same time, the phase controllers 106-1 to 106-N are changed.
It is possible to realize a desired transmission characteristic by changing the phase shift amount of.

[0004]

However, in order to obtain a sharp cut at the band edge of the filter characteristic in an optical circuit including the above-mentioned conventional example, which does not include a light return path such as a ring portion or a grating. However, there is a problem that the number of stages of the circuit must be increased.

The present invention has been made in view of the above-mentioned prior art, and its object is, first, to realize a desired sharp filter characteristic with a small number of steps, and
Secondly, it is to provide an optical signal processor that achieves a programmable characteristic that realizes an arbitrary filter characteristic with one circuit.

[0006]

In order to achieve the above object, the first aspect of the present invention is to provide two first and second optical waveguides and these two first and second optical waveguides. (N +
1) A first directional coupler group having (N + 1) positive or negative coupling rates, which are coupled at different positions to divide the first and second optical waveguides into N regions. The N
Second directional coupler group having N positive or negative coupling ratios, which are respectively interposed in one of the first and second optical waveguides of the N regions, and these N second directional coupler groups. The first and second regions of the N regions via a directional coupler group of
Group of ring optical waveguides respectively coupled to one of the optical waveguides, and at least one of the first and second optical waveguides of the N regions, respectively, for providing a desired phase shift. And a second phase controller group which is interposed between the ring optical waveguide group and performs a desired phase shift, respectively, and the first optical waveguide and the first optical waveguide in the N regions. In the optical signal processor, the optical path lengths of the second optical waveguide and the ring optical waveguide group are all equal.

According to a second aspect of the present invention, in the first aspect, all or part of the first directional coupler group and the second directional coupler group have positive or negative coupling rates. An optical signal processor characterized by being a variable directional coupler capable of changing to a negative value.

According to a third aspect of the present invention, in the second aspect, the variable directional coupler is a fixed coupling ratio directional coupler having two positive or negative coupling ratios, and the two fixed couplings. Coupling ratio Two optical waveguides sandwiched by directional couplers, and the optical path lengths of the two optical waveguides are equal to each other or deviated by a half wavelength, and at least one of the two optical waveguides is desired. 2. An optical signal processor characterized by having a Mach-Zehnder interferometer configuration provided with a phase controller for performing the phase shift of FIG.

In a fourth aspect of the present invention, in any one of the first to third aspects, the coupling rate θ _1n (−π / 2 to π / 2) of the N + 1 first directional coupler groups. ) And the phase shift amount φ _1n (−π to π) of the N first phase controller groups,
And the coupling rate θ _2n of the N second directional coupler groups
(−π / 2 to π / 2) and the phase shift amount φ _2n (−π to π) of the N second phase controllers are calculated and set based on the following recurrence formula. It is in the optical signal processor.

[0010]

[Equation 3]

However, the recurrence formula is solved in the order of n = N to n = 0, and at the first stage (n = N) of the recurrence formula, h ^[N] (z) = h (z), f ^[N] = (z) f
(Z) and g ^[N] (z) = g (z).

Here, h (z) / g (z) is a desired characteristic in a through port, and f (z) / g (z) is a following when the desired characteristic is realized in a cross port. A polynomial, unitary relationship h (z) h _* (z) + f (z) f _*
(Z) = g (z) g _* (z). Also,

[0013]

[Outside 2]

[0014] j represents √ (−1). Δτ is a delay time corresponding to a constant optical path length difference of the link optical waveguide. Further, γ _n-1 and γ _n are (n−) of g (z).
1) Represents the 0th and nth zeros.

[0015]

[Equation 4]

[0016]

In the optical signal processor of the present invention, a filter characteristic having a sharp band edge can be realized by the feedback action due to the existence of the ring optical waveguide. In addition, the calculation formulas described in “Equation 3” and “Equation 4” give a method of obtaining the coupling ratio of the directional coupler and the phase shift amount of the phase controller for any desired filter characteristic. Therefore, an optical signal processor having an arbitrary filter characteristic can be realized.

Further, by varying the coupling ratio of some or all of the directional couplers within a positive or negative range,
Programmability to achieve arbitrary filter characteristics with a single circuit can be achieved.

[0018]

The present invention will be described in detail below with reference to examples.

(Embodiment 1) The optical signal processor of this embodiment is
It has the circuit configuration shown in FIG. In addition, the coupling ratio of the directional coupler and the phase shift amount of the phase controller, which are unknown circuit parameters, were obtained using the calculation formulas shown in the above-mentioned "Equation 3" and "Equation 4".

As shown in FIG. 1, the first and second optical waveguides 1 and 2 have a first directional coupler group 3-having N positive or negative coupling rates at (N + 1) points.
1 to 3− (N + 1), which are divided into N regions of first optical waveguides (arms) 1-1 to 1-N and second optical waveguides (arms) 2-1 to 2-N, respectively. Has been done. To each of the N first arms 1-1 to 1-N, there are N second directional coupler groups 4-1 to 4-N having a positive or negative coupling ratio, The ring optical waveguide groups 5-1 to 5-N are coupled one by one. Further, each of the N second arms 2-1 to 2-N has a first phase controller group 6-1 for performing a desired phase shift.
1 to 6-N are respectively provided. further,
Each of the ring waveguide groups 5-1 to 5-N is provided with one second phase controller group 7-1 to 7-N for performing a desired phase shift.

The optical signal processor having such a structure is composed of N-stage regions 8-1 to 8-N surrounded by the one-dot chain line.
And one end of the second optical waveguides 1 and 2 is the input port 1
A and 2A and the other ends are output ports 1B and 2B
Is.

Here, the optical path lengths of the first arms 1-1 to 1-N and the second arms 2-1 to 2-N in the N-stage regions 8-1 to 8-N are equal, and , N ring waveguide groups 5-1 to 5-N have the same optical path length.

In the present embodiment, the first phase controller group 6-1 to 6-N is provided in the second arms 2-1 to 2-N of the regions 8-1 to 8-N of N stages, respectively. Although interposed, the first phase controller group may be provided in the first arms 1-1 to 1-N or may be provided in both. Also, the first arm 1-1 to
1-N, the second directional couplers 4-1 to 4-1 are provided.
It may be provided either before or after 4-N or both.
The advantage of providing the first phase controller group in both the first and second optical waveguides is that, in the case of only one, it is necessary to change the phase amount in the range of 0 to 2π in order to control the phase. On the other hand, when they are provided on both sides, the amount of phase change required for each phase controller can be suppressed to half, that is, 0 to π.

In this embodiment, an optical signal processor is manufactured by a plane circuit having excellent mass productivity. Each ring waveguide group 5-
The optical path length of 1 to 5-N is 20 GHz at a wavelength of 1.55 μm
It was set to 10.37 mm corresponding to the frequency interval of.

FIG. 2 shows a cross section taken along the line AA 'of the optical signal processor. In this embodiment, a silicon substrate is used as the substrate 21, the waveguide is formed by the quartz thin film 22 deposited on the substrate by the flame deposition method, and the waveguide structure is manufactured by the photolithography process. Here, the core size of the produced waveguide was determined so as to be a single mode. The optical filter of the present invention realizes filter characteristics by utilizing light interference, branching / coupling, and the presence of higher-order modes inside the waveguide causes performance deterioration. For this,
In this embodiment, all single mode waveguides are used.
The phase controller was manufactured by forming a heater made of a chromium layer on a quartz thin film. This phase controller controls the phase by utilizing the thermo-optic effect that the refractive index changes when heated.

In this embodiment, in order to eliminate the influence of environmental temperature fluctuations, the entire optical circuit is placed on the Peltier device and the temperature of the optical circuit is controlled with an accuracy of about 0.1 degrees.

Since the optical signal processor of the present invention utilizes the coherent interference phenomenon of light, the signal light must be coherent light.

In FIG. 1, the signal light incident from the input port 1A has unit components 8-1 to 8-1 arranged in multiple stages.
It passes through 8-N and is emitted to output ports 1B and 2B. At this time, the signal light is branched into each optical waveguide by each directional coupler. For example, the signal light traveling along the shortest optical path is the arms 1-1, 1-2, ..., Of the first optical waveguide.
1-N, or arms 2-1 and 2- of the second optical waveguide
2, ..., 2-N. Further, the signal light traveling along the longest optical path orbits the ring waveguides 5-1 to 5-N infinitely. The output light from the ports 1B and 2B is expressed as the sum of the signal lights passing through various optical paths. Since this optical signal processor has a ring waveguide, light of infinite circulation exists. Therefore, the complex amplitude of the output light from port 1B is
As represented by Expression (1), the denominator and the numerator are each expressed in the form of a polynomial of z.

[0029]

[Equation 5]

Here, a _k and c _k in the equation (1) are complex expansion coefficients. β represents the propagation constant of the optical waveguide, and ω ₀ represents the period of the frequency characteristic. Further, in the formula (1), the following (a) is considered as a complex number z and the following (b) is expanded to a function h (z) on the complex plane, as is often done in the electric digital filter theory. . On this z complex plane,
The frequency function h (ω) is regarded as a function on the circumference of a radius 1 with an absolute value of z = 1. H (z) of numerator and g (z) of denominator
The polynomials of are both of degree N. g (z) is a polynomial of degree N, and there are N zeros, of which N−M are z
There is a zero at = 0.

[0031]

[Outside 3]

In the equation (1), the through characteristic h (z) /
g (z) is expressed by a polynomial of z. In the field of digital filters, this formula is IIR (Infini
It can be seen that it is equal to the transmission characteristic of a certain type of digital filter with feedback called the teImpulse Response type. This fact plays an important role in the synthesis of the optical filters described below.

Similarly, the light is incident from port 1A and
The output light f (z) / g (z) emitted from B is given by the formula (2)
It is represented as

[0034]

[Equation 6]

Here, the order of f (z) is also h (z), g
N is the same as in (z).

Since this signal processor has 2 inputs and 2 outputs, the transmission matrix S of the entire signal processor is represented by the 2 × 2 matrix expressed by the equation (3).

[0037]

[Equation 7]

Here, the suffix * represents a para-conjugate (h _* (z) = h ^* (1 / z ^* )). Assuming the circuit is lossless, h (z) / g (z) and f (z) / g
A unitary relationship represented by the following expression (4) is established between (z).

[0039]

[Equation 8]

In this embodiment, the cross characteristic f (z) / g
The filter was designed so that (z) has a desired characteristic.

Specifically, the circuit parameters for the cross characteristic (transmission characteristic from the input port 1A to the output port 2B) satisfying the desired filter characteristic were obtained by the following procedure (FIG. 5).

[Design Procedure 1] First, in step S1, a polynomial of z which is a denominator of the equation (2) is obtained so as to satisfy the desired filter characteristic. At this time, it is utilized that the transmission characteristics of the optical filter written in the equation (2) are the same as those of a digital filter called IIR type. Specifically, various approximation methods developed in the field of digital filters are used. For example, the bilinear z-transform method (bilinear exchange method),
The least-squares approximation method, the Fletche-Powell method, and the like are well known (Openheim & Scaf).
er "Digital Signal Processing" Prentice-Ha
ll Inc. 1975). At the time of this calculation, the required expansion order is obtained from the required condition of the desired filter characteristic. This expansion order corresponds to the number N of stages of the unit circuit configuration. When calculating the approximate polynomial, it is important to be careful that the polynomial f (z) / g (z) representing the cross characteristic satisfies the causal rate. Specifically, a polynomial f that represents the cross characteristic
It is necessary that the pole of (z) / g (z), that is, the zero point of g (z) is within the circle with the absolute value of z = 1. Since the optical signal processor of the present invention is a passive circuit, it is essential to satisfy the causal rate.

[Design Procedure 2] In the design procedure 1, the z polynomial of the equation (2) is obtained by using the above-mentioned optimum digital filter method so as to realize the desired filter characteristic. If an optical signal processor is realized by using the obtained polynomial as it is, the absolute value of the amplitude characteristic may exceed 100%.
However, in this signal processor, which is an analog signal processor that uses a physical quantity called light wave, due to the law of energy conservation,
Essentially, the absolute value of the complex amplitude in equation (2) cannot exceed 100%. Therefore, in step S2, the polynomial obtained by the approximation method of the digital filter is standardized by the equation (5) so that the absolute value of the amplitude characteristic does not exceed 100%.

[0044]

[Equation 9]

[Design procedure 3] In step S3, the complex amplitude characteristic having the standardized complex expansion coefficient obtained in the design procedure 2 is used as the cross output of the optical signal processor (from ports 1A to 2).
Output to B), an S matrix representing the transmission characteristics of the present optical signal processor is obtained. Specifically, the remaining unknown transfer function h (z) of the S matrix is obtained from the unitary relation of Expression (4). h (z) h _* (z) is a polynomial f (z) representing the cross characteristic standardized in the design procedure 2 from the unitary relationship.
By using / g (z) and further expanding into the form of a product of a function linear expression to z, it is expressed by Expression (6).

[0046]

[Equation 10]

In this equation (6), a ₀ is obtained as in equation (7).

[0048]

[Equation 11]

Here, γ _N is the Nth zero point of g (z).

In equation (6), h (z) and h _* (z)
From the necessity of being expressed in the form of the product of
The zero point of (z) is obtained as N pairs of {α _k , 1 / α _k ^* }. When finding h (z), the polynomial of h (z) needs to have either one of the root pairs of {α _k , 1 / α _k ^* } as a root. Depending on the way, there are 2 ^N ways to take h (z). Also,
How to select M nonzero points of g (z) is _N P _M
(= (N!) / ( N-M)!) Number there, for each, h (z) is because it is required, in the whole, h (z) is (2 _^N · ^N P _M) number of solutions have. These (2 ^N・_N P
_{The M} ) solutions of h (z) have the same amplitude characteristic but different phase characteristics. As a whole, f (z) is common and h
There are (2 ^N · _N P _M ) S matrices with different (z), and as a result, (2 ^N · _N P _M ) types of circuit parameters are obtained. However, even if a circuit is manufactured with any of these (2 ^N · _N P _M ) circuit parameters, the same cross characteristic can be obtained. In this embodiment, the cross characteristic f (z) is
Since I am interested in the characteristics of / g (z), (2 ^N · _N P _M )
An appropriate one of the h (z) was selected. Of course, it is also possible to select h (z) by appropriately providing criteria for selection such as low element sensitivity and appropriate phase characteristics.

[Design procedure 4] In step S4, in order to obtain the circuit parameters, the S matrix representing the transmission characteristics of the optical signal processing circuit of the N-stage configuration is multiplied by the S matrix representing the transmission characteristics representing the unit configuration. Expand to.

The total S matrix is decomposed as shown in equation (8).

[0053]

[Equation 12]

Here, S _n represents the transmission matrix of the unit circuit of the nth stage.

The unit circuit of the nth stage shown in FIG.
n, 2-n optical waveguides (arms) and 5-n ring waveguides, 3- (n + 1), 4-n two directional couplers, 6-n, 7-n Of the two phase controllers, and the unit configuration circuit of n = 0 is one directional coupler 3-1.
It is composed of

The actual decomposition of the S matrix is performed by the steps S4 and S5 in which the inverse matrix S of the n-th stage unit component transmission matrix S _n is obtained.
_n ⁻¹ = S _n ⁺ (S _n ⁺ is a transposed conjugate matrix of S _n ) is n = n, N
It is performed by sequentially operating from the left side of the S matrix in the order of − to 1, ..., 2, 1, 0.

[0057]

[Equation 13]

Here, S ^[n] = S _n S _n-1 ... S ₂ S ₁ S
Represents ₀ . Each S _n is obtained by this repeated operation.

Specifically, the angle indication θ _n2 of the coupling ratio of the directional coupler connecting the two optical waveguides and the ring waveguide and the phase shift amount φ _n2 of the phase controller on the ring waveguide have cross characteristics. Nth zero of the denominator polynomial g (z) of the polynomial to represent γ _r
It is calculated from the following equation.

[0060]

[Equation 14]

If S ^[n] is known in equation (9), the highest order of the numerator polynomial of the product element of the matrix on the right side of equation (9) is (n + 1) / 2, but equation (9) The highest order of the numerator polynomial of the elements of the matrix on the left side of is (n-1) / 2. In order for the left-hand side and right-hand side equations to hold, it is necessary to match the highest order of the right side with the highest order of the left side. From this condition, the angle indication θ _n1 of the coupling rate of the directional coupler connecting the two optical waveguides can be obtained. Also, [f ^[n] (γ _n )] / [h
The phase shift amount φ _n1 of the phase controller provided on the two waveguides is obtained from the condition that ^[n] (γ _n )] is always a real number (here, it is positive).

[0062]

(Equation 15)

In equation (11), h ^[n] (z), f ^[n]
(Z) is a numerator polynomial of the elements of the n-th unit transmission matrix S ^[n] . γ _n and γ _n-1 are the nth and n-1th zero points of g (z), respectively.

In this way, all circuit parameters are obtained by completing the S matrix decomposition procedure to the final stage. That is, the following recurrence formula is changed to n = N, N-1, ...,
If the solution is performed in the order of 2,1,0, all circuit parameters can be obtained. However, the initial value (n = N) of the recurrence formula is h ^[N] (z) = h (z), f ^[N] obtained in the design procedure 3 ^.
(Z) = f (z) and g (z).

[0065]

[Equation 16]

As described above, in the present invention, (2 ^N · _N P _M ) circuit parameters are obtained for a desired cross filter characteristic (step S6). The same cross filter characteristic can be obtained by using any of these circuit parameters. From this, it is clear that the present invention is not limited to the numerical values regarding the circuit parameters, and the present invention can be applied to all the circuit parameters obtained by the above circuit synthesis method.

In the present embodiment, the circuit parameters are calculated so that the desired filter characteristic is realized by the cross output.
It is also possible to calculate the circuit parameters so as to realize the desired filter characteristics with the through output (output from the ports 1A to 1B).

The results of actually designing the Butterworth filter using the design method described above will be described below.

Optical filter having Butterworth characteristic The Butterworth optical filter is characterized in that the amplitude frequency characteristic is maximum flat in the transmission band. This is
In the Nth-order filter, the 0th to Nth-order squared amplitude frequency characteristics
It means that the derivative up to the first order is zero at the center frequency. In this embodiment, a Butterworth type transmission characteristic is realized in the cross characteristic. The required characteristic values of the optical filter are: frequency interval: 20 GHz, transmission band frequency: -2 GH
The amplitude frequency characteristic of the transmission band of z to 2 GHz is constant within 1 dB, and the stop band characteristic is between 3 GHz and 10 GHz and between (-3 GHz) and (-10 GHz).
It was set to dB.

Here, first, the characteristic function of the analog Butterworth filter satisfying the above-mentioned requirements is obtained, and the characteristic function is calculated by the bilinear conversion method ("Digital signal processing" Prentice-Hall by Openheim & Scafer).
Inc. In 1975), a sixth-order polynomial approximation formula shown in formula (13) was obtained.

[0071]

[Equation 17]

6A and 6B, the transmission amplitude of a 6-stage Butterworth type optical filter (N = 6) produced based on the circuit parameters obtained through the design procedures 1 to 4 of this embodiment was measured. The result. Transmission amplitude 0.5 at ± 2 GHz
A rejection value of 15 dB was achieved at ± 3 GHz.

(Embodiment 2) This embodiment is also implemented to realize the first object.

The circuit configuration of this embodiment is shown in FIG. In addition,
Portions showing the same operation as in FIG. 1 are designated by the same reference numerals, and duplicate description will be omitted.

In Example 1, all the ring waveguides were on the optical waveguide 1 side. In practice, 2 ^N waveguide arrangements are conceivable depending on whether the ring waveguide is arranged on one side or two sides of the two optical waveguides. In this example, an example in which a Butterworth filter similar to that of the example 1 is manufactured by using the following two types of arrangements of 2 ^N waveguides will be described.

[Waveguide arrangement 1] is an arrangement in which ring waveguides appear alternately on the waveguide 1 side and the waveguide 2 side of two optical waveguides.

[Waveguide layout 2] is the unit configuration circuit k =
From 0 to n, there is a ring waveguide on the side of the waveguide 1, and from k = n + 1 to N of the unit configuration circuit, there is a ring waveguide on the side of the waveguide 2.

The circuit parameters for these waveguide arrangements can be easily obtained from the calculation results of the circuit parameters obtained in the first embodiment. This can be easily done by the following procedure.

[Procedure 2]: Similar to the first embodiment, the circuit parameters for realizing the Butterworth filter are obtained when the ring waveguides are all on the waveguide 1 side.

[Procedure 2] is for waveguides 1 and 2 in which the ring waveguide is on the waveguide 2 side in the desired waveguide arrangement.
The directional couplers at both ends of the symmetric Mach-Zehnder interferometer composed of are both reduced by π. This operation is repeated for all symmetrical Mach-Zehnder interferometers in which the ring waveguide is on the waveguide 2 side.

As a result of producing a filter circuit for each waveguide arrangement and measuring the filter characteristics, the same filter characteristics as in Example 1 were obtained.

As can be seen from this embodiment, in the present invention, for all 2 ^N kinds of waveguide arrangements which are different depending on whether the ring waveguide is provided on the waveguide 1 side or the waveguide 2 side,
Equivalent circuit parameters can be designed. From this, it is apparent that the present invention includes all circuit configurations that are optically equivalent to those in FIG.

(Third Embodiment) This embodiment is an example in which a configuration for realizing the second object is implemented.

The variable directional coupler used in this embodiment is shown in FIG.
Shown in. The advantages of using a variable directional coupler are:
It is possible to obtain the programability in which one circuit can realize arbitrary circuit characteristics. The variable directional coupler of FIG.
A symmetrical Mach-Zehnder interferometer is constituted by two optical waveguides 11 and 12 having the same optical path length and 3 dB directional couplers 13-1 and 13-2 arranged at both ends thereof. Phase controllers 14-1 and 14-2 made of a chrome heater are arranged on each optical waveguide. Even if this phase controller is installed only on one waveguide, a variable directional coupler is constructed. The present variable directional coupler can change the coupling ratio from 100% to 0% by changing the phase difference between the two optical waveguides from 0 to π by the phase controller. Specifically, the phase controller 14A,
When the phase shift amount of 14B is 0, the directional coupler is 100% coupling, and when the phase shift amount is π, the directional coupler is 0% coupling. Although not adopted here, it is also possible to shift the optical path lengths of the two waveguides by half a wavelength in advance so that when the phase shift amount of the phase controller is 0, a directional coupler with 0% coupling is obtained. It is possible. Although not used here, the 3 dB directional coupler 1 which constitutes the variable directional coupler 1
It is also possible to replace 3-1 and 13-2 with the variable directional coupler having the symmetrical Mach-Zehnder interferometer configuration shown in FIG. The variable directional coupler is 0-100 as designed.
To be completely variable up to% coupling, configure 3d
The coupling rate of the B coupler needs to be 3 dB with considerable accuracy. It is an effective means to replace the 3 dB coupler with a variable directional coupler in order to accurately set the coupling rate of the 3 dB coupler to 3 dB. Furthermore, 3 dB directional couplers 13-1 and 13-2 forming a variable directional coupler
Is an asymmetric Mach-Zehnder interferometer-based wavelength-independent directional coupler (Electon
ics Letters; "Mach-Zehnde
r Interferometer type op
tidal wave guide couler wi
th wavelength-flattened c
"upling ratio", Vol. 26, No.
17, pp. 1326 to 1327, 1990). In this way, the manufactured optical signal processor can operate regardless of the wavelength.

Also in this embodiment, the same 6 as in the first embodiment is used.
A stepped Butterworth filter was made. It was also confirmed that a Chebyshev characteristic filter can be realized with the same circuit. The present embodiment is characterized in that it is more resistant to manufacturing errors than the first embodiment. This is because error correction is possible because the variable directional coupler is used.

Although the configuration and the designing method of the present invention have been described with reference to the embodiments, the present invention is not limited to the embodiments. For example, although a quartz planar optical circuit is used in the present invention, a semiconductor such as InGaAsP-based semiconductor, LiNbO _{3 is used.}
It is also possible to form the planar circuit with another material such as an electro-optical material such as, or an organic optical material. It is also possible to use an optical fiber instead of the planar circuit. In the present embodiment, the thermo-optical effect and the electro-optical effect were used to perform the phase control, but as the method of the phase control, other physical phenomena, for example, a nonlinear optical effect represented by the Kerr effect,
It is also possible to use the magneto-optical effect or the like. As described above, the present invention relates to a circuit composition method for calculating a circuit parameter by giving a circuit configuration showing a combination of elements and a desired filter characteristic, and is not restricted by a physical realizing means of the circuit.

Although the present invention has a large number of optically equivalent circuit configurations as shown in the second embodiment, all of them can be regarded as the same, and therefore, a circuit optically equivalent to the circuit configuration of the present invention. All configurations are subject to the rights of the present invention. For example, 2
If the coupling ratio of the directional coupler that connects the optical waveguide of the book and the ring optical waveguide is 0, the presence of the ring optical waveguide becomes unnecessary, so it is conceivable to use a circuit configuration in which unnecessary ring optical waveguides are removed in advance. . Also in this case, setting the coupling rate of the directional coupler to 0 and removing the corresponding ring optical waveguide in advance are optically equivalent, and thus can be considered to be the same circuit configuration.

What is characteristic of the claims of the present invention is that, in addition to the circuit configuration, a design procedure for obtaining circuit parameters is additionally required. In order to actually realize the desired characteristic, a calculation formula for calculating the circuit parameter for realizing the desired characteristic is required. It is actually impossible to obtain circuit parameters by trial and error,
Even if a computer is used to obtain the circuit parameters by the successive approximation method, it is almost impossible to obtain the optimum circuit parameters. The design method required by the present invention is unique to the present invention, and is different from the iterative approximation method in that the optimum circuit parameter can be obtained with a finite number of calculations. Even if a patent having a circuit configuration similar to that of the present invention exists, the present invention asserts the distinction from other patents due to the existence of the design method unique to the present invention. Specifically, the frequency filter described in the embodiments has characteristics that cannot be obtained without using this design method, and even when the circuit configurations are similar, by comparing the embodiments, it is possible to distinguish from other patents. Can be converted.

[0089]

As described above, the optical signal processor of the present invention adopts the above-mentioned circuit configuration and design method to perform arbitrary filtering processing with a maximum transmittance of 100%, which could not be realized in the past. Made feasible. In particular, the present invention is characterized in that by providing a ring waveguide, a steep filter characteristic can be realized with a small number of stages by utilizing a feedback action similar to that of a thin film filter. Further, by using a variable directional coupler that freely describes the coupling rate and a phase controller that can give an arbitrary phase shift as circuit components, it is possible to realize an arbitrary filter characteristic in the same circuit. It also has the feature.

The optical signal processor of the present invention having such excellent characteristics is to provide a high performance optical signal processor in the field of advanced information processing such as frequency multiplex communication, which requires high speed and wide bandwidth. Is possible.

[Brief description of drawings]

FIG. 1 is a diagram showing a circuit configuration of an optical signal processor according to a first embodiment of the present invention.

FIG. 2 is a sectional view taken along the line AA ′ of the optical signal processor according to the first exemplary embodiment.

FIG. 3 is a diagram showing a circuit configuration of the variable directional coupler used in the first embodiment.

FIG. 4 is a diagram showing an n-th stage unit component circuit of the circuit configuration of the first embodiment.

FIG. 5 is a flowchart showing a design procedure of the first embodiment.

FIG. 6 is a diagram showing Butterworth transmission characteristics of an optical frequency filter realized by the circuit configuration of the first embodiment.

FIG. 7 is a diagram illustrating two types of waveguide configurations according to a second embodiment.

FIG. 8 is a diagram showing a circuit configuration of a transversal type optical signal processor according to a conventional example.

[Explanation of reference numerals] 1, 2 optical waveguides 1-1, 1-N, 2-1 to 2-N arm 1A, 2A input port 1B, 2B output port 3-1, 3- (N + 1), 4-1 to 4-1 4-N Fixed (variable) directional coupler having positive or negative coupling rate 5-1 to 5-N Ring waveguide 6-1 to 6-N, 7-1 to 7-N Phase controller

Claims (4)

[Claims] 1. Two first and second optical waveguides, and these two first and second optical waveguides are coupled at (N + 1) different positions, and the first and second optical waveguides are connected. One of a first directional coupler group having (N + 1) positive or negative coupling rates for dividing the waveguide into N regions, and the first and second optical waveguides in the N regions. A second directional coupler group having N positive or negative coupling rates, which are respectively interposed on one side, and the N regions of the N regions via the N second directional coupler groups. A ring optical waveguide group coupled to either one of the first and second optical waveguides, and a desired phase inserted in at least one of the first and second optical waveguides in the N regions. A first phase controller group for shifting and a ring optical waveguide group are respectively interposed. A second phase controller group for performing a desired phase shift, and the first phase controller in the N regions.
2. The optical signal processor, wherein the optical path lengths of the optical waveguide and the second optical waveguide are equal, and the optical path lengths of the ring optical waveguide group are all equal. 2. The combination according to claim 1, wherein all or part of the first directional coupler group and the second directional coupler group can change the coupling rate to a positive or negative value. An optical signal processor, which is a variable directional coupler. 3. The variable directional coupler according to claim 2, wherein the variable directional coupler is sandwiched between two fixed coupling ratio directional couplers having a positive or negative coupling ratio and the two fixed coupling ratio directional couplers. A phase controller for performing a desired phase shift on at least one of the two optical waveguides, the optical path lengths of the two optical waveguides being equal to or different from each other by half a wavelength. An optical signal processor having a Mach-Zehnder interferometer configuration provided with. 4. The coupling rate θ _1n (−π of each of the N + 1 first directional coupler groups according to claim 1.
/ 2 to π / 2), the phase shift amount φ _1n (−π to π) of the N first phase controller groups, and the coupling rate θ of the N second directional coupler groups. _{2n (-π} / _2~π / 2) and the N second phase controller of the phase shift amount φ _2n (-π~
An optical signal processor, characterized in that π) is calculated and set based on the following recurrence formula. [Equation 1] However, the recurrence formula is to be solved in the order of n = 0 to n = 0. In the first stage of the recurrence formula (n = N), h ^[N]
(Z) = h (z), f ^[N] (z) = f (z), g ^[N]
(Z) = g (z). Where h (z) / g (z)
Is a through characteristic of the desired characteristic, and f (z) / g (z) is a polynomial expressed below when the desired characteristic is realized by the cross port. The unitary relation h (z) h _* (z) +
It is obtained from f (z) f _* (z) = g (z) g _* (z). Also, [Outer 1] Is. j represents √ (−1). Δτ is a delay time corresponding to a constant optical path length difference of the link optical waveguide.
Further, γ _n-1 and γ _n represent the (n-1) th and nth zero points of g (z). [Equation 2]