KR100755342B1 - Wavelength division multiplexing device - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength division multiplexing (WDM) device, and connects a MachineZehnder Interferometer (MZI) to an arrayed waveguide grating (AWG) that inputs a plurality of wavelengths and outputs each wavelength having an FSR. Input the wavelengths having FSR from the AWG and output them by wavelength.

Therefore, the present invention can simply increase the number of WDM transmission channels, and can increase the size of the WDM device in preparation for the increase of the transmission channel, thereby miniaturizing the WDM device having the increased number of transmission channels.

Description

Wavelength Division Multiplexing Devices {WAVELENGTH DIVISION MULTIPLEXING DEVICE}

1 is a view showing the structure of a conventional MZI device;

2 is a view showing a connection state of a conventional MZI device;

3 is a view showing the structure of a conventional AWG device;

4 is a view showing the state of the input and output side slab waveguide of the conventional AWG device,

5 shows an FSR of an AWG device;

6 is a view showing the output characteristics of the conventional AWG device,

7 illustrates a wavelength division multiplexing element according to the present invention.

<Description of the symbols for the main parts of the drawings>

41: input waveguide 42: output waveguide

43, 44: slab waveguide 45: waveguide array

100: AWG element 101,102,103: MZI element

The present invention relates to a wavelength division multiplexing (WDM) device, and more particularly, to a WDM device in which a machine-machined interferometer (MZI) device and an arrayed waveguide grating (AWG) device are combined.

Integrated optical devices known to date as WDM devices are MZI and AWG. The MZI is composed of two 3dB couplers C1 and C2 having a length d and path difference waveguides 11 and 12 having lengths L and ΔL as shown in FIG. have. The laser light incident on either of the input stages I ₁ , I ₂ is bisected into two lights having an intensity of 1/2 and a phase difference of 90 ° through the 3dB coupler C1 of the front end. As the light propagates along the waveguides 11 and 12 having different lengths L and L + ΔL to the rear 3dB coupler C2, the phase difference between the two light waves changes. Since the path difference ΔL between the waveguides 11 and 12 existing between the two 3dB couplers C1 and C2 is constant, the phase difference of each optical wave traveling through the two waveguides 11 and 12 is dependent on the wavelength. Will change. At this time, if the phase difference generated by the path difference ΔL is an odd multiple of 180 °, the input light is output to the output terminal O ₂ opposite to the input terminal (for example, I ₁ ) to which the incident light is incident. It is output through (O ₁ ). That is, when the wavelength λ ₁ for generating an odd-numbered phase difference of 180 ° and the wavelength λ ₂ for generating an even-numbered phase difference are incident on the input terminal I ₁ at the same time, the light of the wavelength λ ₁ is transmitted to the terminal ( O ₂ ) and the light having the wavelength λ ₂ is output to the terminal O ₁ , so that the two wavelengths λ ₁ and λ ₂ can be separated. At this time, there is a relationship between the path difference ΔL and the separable wavelength interval Δλ.

Here, N _g means the effective refractive index of the waveguide.

As can be seen in Equation 1, the separable wavelength spacing is inversely related to the path difference ΔL. That is, it can be seen that the larger the distance between wavelengths to be separated, the smaller the path difference ΔL and the smaller the size of the device.

By using the properties of the MZI by connecting the MZI (10, 20, 30) in multiple stages as shown in Figure 2 it is possible to separate the various wavelengths (λ ₁ , λ ₂ , λ ₃ , λ ₄ ).

The AWG has an input waveguide 41, an output waveguide 42, two slab waveguides 43 and 44, and the waveguide array 45 has two slab waveguides 43 and 44 as shown in FIG. ) Is connected. The operation principle of AWG is as follows. When the light incident on the input waveguide 41 is incident on the slab waveguide 43, the light is spread in the slab waveguide 43 because the light is not limited in the horizontal direction as if it proceeds in free space. As shown in FIG. 4A, light incident through the input waveguide 41 is incident on the horizontal waveguide array 45 at the slab waveguide 43. Waveguide adjacent the length of - (L ₈ L ₁₎ are different from each other and the waveguide array (45) (- waveguide array, the light incident to 45 are each waveguide proceeds along a (L ₁ L _8), wherein each waveguide The length difference between L ₁ -L ₈ ) is shown in Equation 2 below.

In Equation 2, s is a length difference between waveguides L ₁ -L ₈ , m is an arbitrary integer, λ _c is a wavelength passing through the center of the output waveguides as a center wavelength, and N _g is a waveguide array portion 45 Is the effective refractive index of.

Considering only the center wavelength λ _c , the path difference between the waveguides L ₁ -L ₈ in the waveguide array 45 is different by an integer multiple of the center frequency λ _c , as shown in Equation 2, respectively. The phases of the light passing through the waveguides L ₁ to L ₈ are equal to each other. As can be seen in FIG. 4B, the distances from the end of each waveguide L ₁ to L ₈ of the waveguide array 45 to the point P, which is the center of the output waveguides L ₉ and L ₁₀ , are the same. Therefore, the distances from the input waveguides L ₁ to L ₈ to the point P, which is the center of the output waveguides L ₉ and L ₁₀ , are all the same. Accordingly, the input waveguide (L ₁ - L ₈₎ through it from the center wavelength (λ _c) the phase difference is because each waveguide of the reach point P in the (L ₁ - L ₈₎ the central wavelength (λ _c) which was divided into the Light is combined at P point. In contrast, the light propagation path from the end of each waveguide (L ₁ -L ₈ ) to the point away from the point P (for example, Q point) depends on each waveguide (L ₁ -L ₈ ) of the waveguide array 45. However, the light travel distance is different and phase difference occurs. Therefore, the light of the center wavelength λ _c is concentrated at the point P.

In contrast to the center wavelength λ _c , that is, the wavelength λ _c + Δλ deviating from the center wavelength, in this case, the length difference between the waveguides L ₁ -L ₈ of the waveguide array 43 is the wavelength λ _{Since they are} not integer multiples of _c + Δλ), the phases at the ends of each waveguide L ₁ -L ₈ are different from each other after passing through the array. As shown in FIG. 4B, when light of the wavelength λ _c + Δλ passing through the waveguides L ₁ -L ₈ of the waveguide array 45 connects lines having an in-phase, the circle O is formed. (O) has an angle (θ) with respect to an in-phase line (that is, a circle formed by the ends of the waveguides L ₁ -L ₈ ) due to the center wavelength λ _c . Since the wavelength λ _c + Δλ has the same phase on the circle O, the wavelength λ _c + Δλ forms a focal point at the point Q on the same principle as in the light of the center wavelength λ _c . That is, light having the wavelength λ _c + Δλ is concentrated at the point Q.

On the other hand, when the circle O is distorted by the angle θ, the path difference from the neighboring waveguides L ₅ -L ₆ to the focal point Q is the path RQ: from the point R to the point Q. Length difference) and the path (TQ: length from point (T) to point (Q)). In ΔSRT, ∠TRS is θ, so the path difference TS between neighboring waveguides L ₅ and L ₆ to circle O is a sin θ ?? aθ. Here, a means an interval between the waveguides L ₅ and L ₆ .

Therefore, in order to form a focal point at the point Q after the wavelength λ leaves the input waveguide 41 and passes through two neighboring waveguides L ₅ and L ₆ , two waveguides L ₅ , ( The path difference s between L ₆ ) must satisfy the following condition (Equation 3).

Where s is the path difference between the waveguides L ₅ and L ₆ , a is the distance between the waveguides, θ is the angle at which the connection point Q of the same phase is twisted, n _g is the effective refractive index in the waveguide array, n _s is the effective refractive index in the slab, and m is an integer.

As can be seen from Equation 3, the phase difference of the wavelength λ by the path difference between the waveguides L ₁ -L ₈ and the path difference aθ between the waveguides L ₁ -L ₈ and the circle O When the phase difference by 2? M forms a focal point at the Q point.

 The relationship between the angle θ and the wavelength λ from Equation 3 is given by Equation 4.

As shown in Equation 4, since the focal position Q is different depending on the wavelength, if the output waveguide is positioned at the focal position Q corresponding to the wavelength λ, only the wavelength λ can be separated.

Here, the relationship between the wavelength interval Δλ and the diffraction angle difference Δθ from Equation 4 is shown in Equation 5.

In Equation 4, a and s are constant, and assuming that n _g and n _s are weak functions of the wavelength λ, the angle θ may have the same value for several wavelengths. That is, if (θ ₁ , m ₁ , λ ₁ ), (θ ₂ , m ₂ , λ ₂ ) satisfy Equation 4 and satisfy Equation 6, the wavelength λ on the same position (same focal point Q) ₁ ), light of (λ ₂ ) is collected.

That is, the wavelengths λ ₁ and λ ₂ may be output through the same output waveguide.

FIG. 5 shows response characteristics of wavelengths output from each output waveguide 1, 2, 3, and 4 in an AWG having four output channels, that is, four output waveguides. As shown, each output waveguide 1, 2, 3, 4 is followed by a wavelength peak of the same type. That is, the output waveguides 1, 2, 3, and 4 output optical signals of different wavelengths. Here, the wavelength interval of the optical signals output from the same output waveguide (1, 2, 3, 4) is referred to as a free spectral range (FSR).

6 shows the results of measuring wavelength response characteristics of silica AWGs designed for use in the 1.55 um wavelength band at 1.55 um and 1.31 um bands, and Table 1 shows the measured performances.

Parameter 1.31um band 1.55 um band Center spacing 1304.8nm 1542nm Center wavelength 1.31 nm 1.6 nm Loss uniformity 2.7 dB 〈2dB Insertion loss 〈6.5dB 〈5dB Cross talk 〈-23dB <-25 dB FWHM 0.54 nm 0.71 nm

Although the wavelength characteristics of the measured AWG as shown are optimized in the 1.55um band, it is not bad even in the 1.31um band. From Equation 6, since the integer value m ₁ when the wavelength λ is 1.31 um is larger than the integer value m ₂ when the wavelength λ is 1.55 um, it can be seen from Equation 5. have.

As described above, in the conventional AWG, each of the output waveguides outputs several wavelengths each having an FSR period, but only one wavelength is selected and used.

On the other hand, the WDM transmission used in the current relay network uses a 1.55um wavelength band to which an optical amplifier can be applied, but the loss of optical fiber is very small over the 1.27um to 1.65um wavelength range, and it can be used in a wavelength band other than 1.55um. As optical amplifiers are currently being studied, the WDM transmission wavelength band is likely to be expanded. In addition, since the optical amplification is not required in the case of WDM transmission in the subscriber network, WDM transmission is possible over the entire wavelength range with low loss.

Therefore, a separate optical device capable of separating multiple wavelengths is required, and in this case, using multiple MZIs and AWGs can separate multiple wavelengths, but such a configuration requires a plurality of optical devices to be used. There is a problem that is complicated and enlarged.

SUMMARY OF THE INVENTION The present invention has been made to solve this problem, and an object of the present invention is to provide a wavelength division multiplexing device capable of simply separating multiple wavelengths.

In order to achieve this object, the present invention provides a wavelength division multiplexing (WDM) device, comprising: an AWG (Arrayed Waveguide Grating) for inputting a plurality of wavelengths and outputting each wavelength having an FSR; It is provided with a MachineZehnder Interferometer (MZI) which inputs wavelengths having FSR from the AWG and outputs them by wavelength.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

7 is a conceptual diagram of the WDM device according to the present invention. As shown, the WDM device of the present invention has a structure in which a plurality of MZI devices 101, 102, and 103 are connected to one AWG device 100.

In the above-described configuration, the input terminals of the AWG element 100 have wavelengths λ ₁₁ , ..., λ _1j , ..., λ _1n , ..., λ _i1 , ..., λ _ij , ... λ _in , ..., λ _m1 , ... λ _mj , ..., λ _mn ) are incident. Here, wavelengths of λ ₁₁ , λ _i1 , λ _m1 , wavelengths of λ _1j , λ _ij , λ _mj , and wavelengths of λ _1n , λ _in , λ _mn have a relationship of FSR. That is, light having wavelengths of λ ₁₁ , λ _i1 , λ _m1 is output to the output terminal O ₁ of the AWG element 100, and light having wavelengths of λ _1j , λ _ij , λ _mj is the AWG element 100. At the output terminal O _j of, the light of ..., λ _1n , λ _in , λ _mn are output to the output terminal O _n of the AWG element 100, respectively.

On the other hand, each output terminal (O _1, .., O _j, ... O _n), the MZI device and (101 102 103) is connected, these MZI device (101 102 103) of the AWG element 100 are the wavelengths having a FSR interval It is configured to output separately. That is, the MZI element 101 inputs and separates wavelengths from the terminal O ₁ of the AWG element 100 to output wavelengths λ ₁₁ , λ _i1 , and λ _m1 , respectively. 102 inputs and separates wavelengths from the terminal O _j of the AWG device 100 to output wavelengths λ _1j , λ _ij , and λ _mj , respectively, and the MZI element 103 is an AWG device. Wavelengths from the terminal (O _n ) of (100) are input and separated, and wavelengths λ _1n , (λ _in ) and (λ _mn ) are separated and output.

On the other hand, as can be seen in Equation 1, as the distance between the wavelengths λ to be separated increases, the path difference becomes smaller and thus the area occupies becomes smaller. That is, in the case of the MZI device of FIG. 1, there is an inverse relationship between the path difference ΔL and the wavelength interval Δλ as shown in equation (7).

For example, a silica planar waveguide having a refractive index difference of 0.75% and an effective refractive index of 1.45, which is commonly used in a clad and core, is used to separate light waves of 1.51 um and 1.55 um having a wavelength interval of 0.04 nm. A path difference of um is required, and when the MZI device is implemented, the area required is 170um in width and 6mm in length.

On the other hand, since a silica AWG device generally requires about 3 cmm × 6 cm, it can be seen that the area increase can be neglected even when the MZI device is additionally configured to the AWG device as described above.

As described above, in the present invention, since the MZI device is connected to the AWG device that outputs the plurality of wavelengths having the FSR through the output waveguide, the plurality of wavelengths having the FSR are separated and output again so that the number of WDM transmission channels can be easily increased. have.

In addition, in the present invention, when the MZI device is connected to the AWG device, the area increase due to the additional configuration of the MZI device may be negligible compared to the size of the AWG device, thereby miniaturizing the WDM device having an increased number of transmission channels. have.

Claims (2)

A wavelength division multiplexing (WDM) device that separates light waves having a wavelength of a free spectral range (FSR) interval, An arrayed waveguide grating (AWG) having a plurality of output terminals and simultaneously outputting a plurality of wavelengths inputted from the output terminals as wavelengths having an FSR interval; A MZI (MachZehnder Interferometer) connected to each output terminal of the AWG and outputting a plurality of wavelengths inputted from the output terminal of the AWG for each wavelength; Wavelength Division Multiplexing Device. delete

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