JP3114698B2 - Array waveguide grating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an arrayed waveguide grating (AWG), and more particularly to an arrayed waveguide grating used as a wavelength selective filter or an add-drop (ADM) filter used in a high-density wavelength division multiplexed optical fiber communication system. It is about.

[0002]

2. Description of the Related Art Array waveguide gratings are wavelength-selective filters used in high-density wavelength division multiplexed optical fiber communication systems,
It is important as an add-drop max filter, and research and development are being actively conducted inside and outside. Such an arrayed waveguide filter is a multi-input multi-output type filter device, and when a wavelength-multiplexed signal is introduced to a certain input terminal,
Each output terminal has a function of separating the multiplexed signal, and it is possible to perform the reverse operation. The use of a quartz waveguide is particularly important because a low insertion loss operation of about several dB can be realized in coupling with a fiber.

FIG. 7 is an overall view of a conventional arrayed waveguide grating. The array waveguide is described in, for example, Proc.
-3p162, several input waveguides 1, an input side slab waveguide 2 incident from the input waveguide 1, and a number of input waveguides 1 attached to opposite ends of the input side slab waveguide 2. An array waveguide 3 composed of a waveguide, an output-side slab waveguide 4 attached to the other end of the array waveguide 3,
It consists of several output waveguides 5 attached to the other end of the slab waveguide 4.

An optical signal incident from an input waveguide 1 is incident on an input side slab waveguide 2 and is incident on an arrayed waveguide 3 composed of a number of waveguides at an equal phase. The input end of the array waveguide 3 and the output end of the input waveguide 1 are arranged on the circumference, respectively, and the radius of the circumference where the input end of the array waveguide 3 is arranged is determined by the output end of the input waveguide 1. 2 of the radius of the placed circle
The center of the circumference where the input end of the arrayed waveguide 3 is arranged is arranged on the circumference where the output end of the input waveguide 1 is arranged.

[0005] In the arrayed waveguide 3, each waveguide is adjusted so as to give a phase difference at equal intervals, and an output side slab waveguide 4 is arranged at the other end of the arrayed waveguide 3. As for the arrangement of the array waveguide 3, the output side slab waveguide 4, and the output waveguide 5, the output end of the array waveguide 3 and the input end of the output waveguide 6 are arranged on the circumference similarly to the input side. The radius of the circumference where the output end of the array waveguide 3 is arranged is twice the radius of the circumference where the input end of the output waveguide 5 is arranged, and the circle where the output end of the array waveguide 3 is arranged. The center of the circumference is arranged on the circumference where the input end of the output waveguide 5 is arranged.

One of the performance indexes of the arrayed waveguide grating is crosstalk, which is defined by the ratio of the power of light of another wavelength to the power of light of the wavelength to be selected and indicates signal leakage between channels. In order to realize high-quality communication, low crosstalk must be realized. Conventionally, several methods have been considered to achieve low crosstalk. One of them is K. Takada, H. Yamada, Y. Inoue, Opt
ical Low Coherence Method for Characterizing Silic
a-Based Arrayed-Waveguide, Journal of Lightwave Te
As described in Chnology, Vol. 114, No. 7, 1996, the phase and distribution power of the waveguides in the arrayed waveguide are measured, and each waveguide in the arrayed waveguide is measured so as to cancel the phase error. This is a method of reducing crosstalk by adjusting the optical path length.

According to this method, it is shown that a relatively low crosstalk level of -39 dB can be realized at a channel spacing of 100 GHz and -29 dB can be realized at a channel spacing of 10 GHz. However, the cause of the crosstalk degradation is not only the phase error but also the power distribution error in the array waveguide, and it is difficult to suppress the crosstalk degradation due to the power distribution error in the conventional method. Has become.

[0008]

In the conventional array waveguide section, the phase of the light is controlled by controlling the refractive index to improve the crosstalk. In addition to the error, there are also power distribution errors due to errors in the power branching ratio in the slab waveguide portion and errors in the propagation loss of each array waveguide,
The error degrades crosstalk.

An object of the present invention is to provide an arrayed waveguide grating capable of improving a crosstalk characteristic of the arrayed waveguide grating by suppressing a power distribution error in the arrayed waveguide portion.

[0010]

According to the present invention, one or more input waveguides, an input slab waveguide connected to the input waveguide, and an optical path length connected to the input slab waveguide are provided. An array waveguide having a plurality of different waveguides, an output slab waveguide connected to the array waveguide, and a plurality of output waveguides connected to the output slab waveguide. An arrayed waveguide grating is obtained, wherein each waveguide in the arrayed waveguide section has a variable optical power mechanism.

The operation of the present invention will be described. In the array waveguide, an optical power variable mechanism is provided for each waveguide forming the array waveguide, and the optical power of the waveguide forming the array waveguide is calibrated to a required power by adjusting the optical power. An arrayed waveguide grating having more excellent crosstalk than a conventional arrayed waveguide grating can be manufactured.

By changing the optical power in the optical power variable mechanism formed in each waveguide forming the arrayed waveguide, the optical power variable mechanism can freely change the optical power of each waveguide. Along with this, a change occurs in the phase difference of the arrayed waveguide portion, and the change is adjusted by changing the refractive index / geometric parameter in the straight waveguide portion after adjusting the optical power. can do.

[0013]

Next, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is an overall view of an arrayed waveguide grating according to the first embodiment, and the same parts as those in FIG. 7 are denoted by the same reference numerals. Referring to FIG. 1, the arrayed waveguide grating includes several input waveguides 1, an input-side slab waveguide 2 incident from the input waveguide 1,
An arrayed waveguide 3 composed of a number of waveguides attached to the opposite end of the input side slab waveguide 2 and an optical power variable mechanism 6 connected to the waveguides constituting the arrayed waveguide 3 and capable of controlling a coupling ratio. An output section 8 for extracting light branched from the array waveguide by the optical power variable mechanism 6, an output slab waveguide 4 attached to the other end of the array waveguide 3, And several output waveguides 5 attached to the ends.

The power and phase distributed to each waveguide constituting the arrayed waveguide can be measured in advance. For example, the measurement method is a low coherent Fourier measurement method (K. Takada, H. Yamada, Y. Inoue, Optical Low Coherenc).
e Method for Characterizing Silica-Based Arrayed-Wav
eguide, Journal of Lightwave Technology, Vol114, N
o.7., 1996).

The coupling ratio can be controlled by changing the refractive index or the shape in the optical power variable mechanism 6 based on the data measured by this method or the like.
The input waveguide 1 and output waveguide 5 of the arrayed waveguide grating
By injecting more optical signals and measuring the optical power of each port of the output unit 8, the amount of change in the coupling ratio can be accurately measured, and the on-site measurement that is being adjusted is also possible.

After the power is adjusted using the above method, the phase is measured again using the above-described low coherent Fourier measurement method or the like, and the power and phase in the array waveguide section are completely controlled by performing the phase adjustment. And thereby high crosstalk performance can be obtained.

FIG. 2 is a diagram for explaining the operation of an ideal arrayed waveguide grating. The operation of the arrayed waveguide grating will be described with reference to FIG. 2. In FIG. 2, for simplicity, the structures of the input-side and output-side slab waveguides 2 and 4 are shown as trapezoids. basically it is the same as that of FIG. 7, also the input waveguide path 1 is the only one for simplicity, the output waveguides 5 3
Only one book and only four array waveguides 3 are shown.

The optical mode of the waveguide of the input waveguide 1 is substantially Gaussian, and the distribution 9 of the electric field when entering the input side slab waveguide 2 is also substantially Gaussian. The light propagating through the input side slab waveguide 2 propagates while maintaining the shape of the Gaussian distribution. At the exit of the input side slab waveguide 2, the electric field distribution 11 is Gaussian and the arc distribution is like a phase distribution 10. Becomes The light is distributed to the respective waveguides of the array waveguide 3 while maintaining the electric field and the phase profile, and the equally spaced optical path lengths provided in the respective waveguides of the array waveguide 3 are provided. And is introduced into the output of the optical array waveguide 3.

Considering only the current wavelength, the phase distribution 12 and the electric field distribution 13 are the phase distribution 10 and the electric field distribution 11
When the output waveguide 5 has the same shape as that described above, a beautiful Gaussian shape is formed at the input end of the output waveguide 5 which is transmitted and coupled through the output slab waveguide 4.
At this time, it is obvious that the crosstalk level becomes the lowest.

FIG. 3 is an explanatory diagram of crosstalk degradation of the arrayed waveguide grating. The deterioration of the operation of the arrayed waveguide grating will be described with reference to FIG. As in the description of FIG. 2, light propagates through the arrayed waveguide section 3 and enters the output slab waveguide 4. At this time, variations in the refractive index of the waveguide in the arrayed waveguide section, variations in the shape of the waveguide, etc. The optical path length difference is different from the design value due to the above factor, and the phase distribution 12 'is shifted from the theoretical value phase distribution 12, and the electric field distribution 13' is different from the theoretical value electric field distribution 13 due to the variation at the time of manufacturing the waveguide. A shift occurs. Due to this, an aberration occurs in the image formed in the output slab waveguide, and the electric field distribution 14 'at the input end of the output waveguide 5 to be coupled does not have a beautiful Gaussian shape but has a noise-like side lobe. And the crosstalk is degraded.

The improvement of crosstalk in the present invention will be described with reference to FIG. Since the variation in power and the variation in phase between each waveguide in the arrayed waveguide can be measured by the aforementioned low coherent Fourier measurement method, it is necessary to control the refractive index or the shape of the optical power variable mechanism 6 based on the data. Thus, the power is adjusted so that the electric field distribution at the output portion of the arrayed waveguide approaches the shape of the electric field distribution 14.

The power is adjusted by, for example, using a quartz waveguide doped with germanium as a constituent material of the variable optical power mechanism 6 and irradiating the variable optical power mechanism 6 with ultraviolet rays. Change) is simple, but the optical power variable mechanism 6
A thermo-optic effect generated by forming a heater electrode on the substrate and passing a current may be used, or an electro-optic effect may be used if a medium having an electro-optic effect is used as an optical waveguide material. It is also possible to change the optical power by mounting an active device such as a semiconductor optical amplifier that can change the gain and changing the injection current.

When the electric field distribution at the output portion of the arrayed waveguide 3 is controlled in this manner, the phase generally shifts because the refractive index generally changes. Therefore, the phase error was measured again by the low coherent Fourier measurement method, and the above-mentioned literature (K. Takada, H. Yamada, Y. Inoue, Optical Low Coherenc
e Method for Characterizing Silica-Based Arrayed-W
aveguide, Journal of Lightwave Technology, Vol114,
As in the example of No.7, 1996), by controlling the refractive index of the waveguides that make up each array waveguide, the phase error is minimized, and not only the phase but also the electric field distribution is optimized. The obtained arrayed waveguide grating is obtained.

FIG. 6 is a diagram for explaining the operation of the arrayed waveguide grating after all adjustments have been completed. It can be seen that the electric field distribution 13 and the phase distribution 12 at the output of the arrayed waveguide section 3 are close to ideal values, and the electric field distribution 14 imaged at this time is of a Gaussian type, so that the crosstalk level can be reduced.

[0025]

FIG. 4 is a sectional view of an embodiment of an arrayed waveguide grating according to the present invention. Referring to FIG. 4, a lower cladding layer 16, a core 17 whose refractive index is adjusted to be higher than that of the lower cladding layer 16, and an upper cladding layer 18 whose refractive index is adjusted to be lower than that of the core 17 are formed on a substrate 15. ing. As a material of the substrate 15, a substrate such as silicon, a glass substrate, and a ceramic substrate is generally used.
It is considered preferable to use a silicon substrate which is low in cost, can easily form a fiber guide by anisotropic etching, and is suitable for hybridization of electric circuits.

Core layer 17, lower layer and upper clad layer 1
The materials 6 and 18 are made of a material in which phosphorus, germanium, titanium, boron, fluorine and the like are added to quartz, and the cores 9 and 10 through which light passes are controlled to have a higher refractive index than the claddings 8 and 11. It can be obtained by: As a method for forming a quartz layer, a normal pressure CVD method, a flame deposition method, a sputtering method,
Spin coating, electron beam evaporation, and the like are mainly used.

After the core layer 17 is formed, a region for forming a waveguide is transferred to the core layer 17 using photolithography, and a reactive ion etching (RIE) apparatus, a reactive ion beam etching (RIBE) apparatus, or the like is used. The core layer 17 is etched by a dry etching method to be used, and thereafter, an upper clad layer 18 whose refractive index is adjusted to be lower than that of the core layer 17 is formed. The optical power variable mechanism uses a directional coupler, and by changing its refractive index, the complete coupling length changes, the coupling rate changes, and the power can be adjusted.

FIG. 5 is a diagram for explaining the operation before the adjustment of the arrayed waveguide grating. FIG. 6 is an explanatory diagram of the operation after the adjustment. The phase distribution and electric field distribution obtained as a result of measuring the phase and power of the array waveguide portion 3 of the array waveguide grating obtained by cutting out the chip by dicing are represented by 12 'and 13'. First, after detecting a deviation from the corrected ideal value 13 of the electric field distribution 13 ', the refractive index of the optical power variable mechanism 6 was changed by a change in the refractive index of the ultraviolet irradiation so as to correct the deviation. At this time, the ultraviolet rays used an ArF excimer laser, and the change in the refractive index was controlled by the number of shots.

Next, the phase of the array waveguide is measured again,
The array waveguide was irradiated with an ArF excimer laser so as to adjust the phase error. KrF or Ar as ultraviolet rays
SHG of ion laser can also be used. When the adjustment is completed, the electric field distribution and the phase distribution of the arrayed waveguide grating are 1
In this case, deviations of the variations can be made extremely small.

According to the present method, the device whose crosstalk has been improved only up to -30 dB by adjusting the phase error alone, has a crosstalk of -50 dB by using this method.
It became possible to adjust to less than dB.

The operation of the arrayed waveguide grating will be described with reference to FIG. The optical mode of the waveguide of the input waveguide 1 is substantially Gaussian, and the distribution 9 of the electric field when entering the input side slab waveguide 2 is also substantially Gaussian. The light propagating through the input side slab waveguide 2 propagates while maintaining the shape of the Gaussian distribution. At the exit of the input side slab waveguide 2, the electric field distribution 11 is Gaussian and the arc distribution is like a phase distribution 10. Becomes

The light is distributed to the respective waveguides of the arrayed waveguide 3 while maintaining the electric field and the phase profile, and the optical waveguides are provided with the equally spaced optical path length differences provided in the respective waveguides of the arrayed waveguide 3, and are different for each wavelength. The phase difference is given to the output portion of the optical array waveguide 3. The power variation in the arrayed waveguide is adjusted by the optical power variable mechanism 6 to be Gaussian on the incident side of the output side slab waveguide 4, and the output side slab waveguide 4 in the arrayed waveguide section 3 is adjusted. The phase error on the incident side is adjusted to be zero. For this reason, the electric field distribution on the surface where the output waveguide 5 is set becomes a beautiful Gaussian shape, and the crosstalk level is extremely suppressed.

Instead of using a directional coupler for the optical power variable mechanism 6, it is also possible to use a Mach-Zehnder switch and adjust the power by changing the refractive index of the arm. As a method of changing the refractive index, a thermo-optic effect, an electro-optic effect, or the like can be used instead of the ultraviolet-irradiation refractive index. In addition, focusing on the fact that power can be changed by changing the equivalent refractive index, the power is adjusted by changing the shape of the optical power variable mechanism 6 by annealing, dry etching, or the like. The technique is also effective.

It is also possible to change the optical power by mounting an active device such as a semiconductor optical amplifier whose gain can be varied and changing the injection current.
However, in this case, since there is no output section 8 for the light branched from the optical power variable mechanism 6, the adjustment cannot be performed while monitoring the optical power. However, it is easy to know the injection current and the optical power change in advance, and therefore,
It is easy to adjust the optical power. Similarly, EO
The power can be easily adjusted by inserting a variable attenuator using effects or other methods.

[0035]

The first effect is to improve the crosstalk of the arrayed waveguide grating. The reason is that while the conventional method could only improve the crosstalk by improving the phase error, the present method provides an improvement of the power distribution error and provides a method of improving the crosstalk more than before. Because he did.

The second effect is that the yield of the arrayed waveguide grating can be increased. The reason is that it is possible to improve the production yield which has conventionally occurred due to the variation in crosstalk.

[Brief description of the drawings]

FIG. 1 is an overall view of an arrayed waveguide grating according to the present invention.

FIG. 2 is a diagram illustrating the operation of an ideal arrayed waveguide grating.

FIG. 3 is an explanatory diagram of crosstalk degradation of an arrayed waveguide grating.

FIG. 4 is a sectional view of an arrayed waveguide grating according to an embodiment of the present invention.

FIG. 5 is an explanatory diagram of an operation before adjustment of an arrayed waveguide grating.

FIG. 6 is an explanatory diagram of the operation after adjustment of the arrayed waveguide grating.

FIG. 7 is an overall view of a conventional arrayed waveguide grating.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Input waveguide 2 Input side slab waveguide 3 Array waveguide 4 Output side slab waveguide 5 Output waveguide 6 Optical power variable mechanism 8 Output part 9 Electric field distribution at the entrance of input side slab waveguide 10 Input side slab waveguide Phase distribution at exit 11 Electric field distribution at exit of input slab waveguide 12 Phase distribution at entrance of output slab waveguide 12 'Phase distribution at entrance of output slab waveguide 13 Electric field distribution at entrance of output slab waveguide 13 'Electric field distribution at the entrance of the output side slab waveguide 14 Electric field distribution at the exit of the output side slab waveguide 14' Electric field distribution at the exit of the output side slab waveguide 15 Silicon substrate 16 Lower cladding layer 17 Core layer 18 Upper cladding layer

Claims (8)

(57) [Claims] An array waveguide having one or more input waveguides, an input slab waveguide connected to the input waveguide, and a plurality of waveguides connected to the input slab waveguide and having different optical path lengths. An array waveguide grating comprising: a waveguide section, an output slab waveguide connected to the array waveguide section, and a plurality of output waveguides connected to the output slab waveguide, wherein the array waveguide An arrayed waveguide grating having an optical power variable mechanism in each waveguide of the section. 2. The arrayed waveguide grating according to claim 1, wherein said optical power variable mechanism comprises an optical coupler that varies power by varying a coupling ratio. 3. The arrayed waveguide grating according to claim 1, wherein said optical power variable mechanism comprises a semiconductor type optical amplifier. 4. The arrayed waveguide grating according to claim 1, wherein said optical power variable mechanism comprises a directional coupler. 5. The arrayed waveguide grating according to claim 1, wherein said optical power variable mechanism is constituted by a Mach-Zehnder interferometer. 6. The arrayed waveguide grating according to claim 1, wherein quartz is used as a material of the waveguide, and a heater is used as a mechanism for adjusting power distribution of the optical power variable mechanism. 7. The array waveguide according to claim 1, wherein quartz is used as a material of the array waveguide, and an ultraviolet-induced refractive index change is used to adjust power distribution of the optical power variable mechanism. lattice. 8. The method according to claim 1, wherein quartz is used as the material of the waveguide, and the distribution ratio is changed by using a change in the shape of the waveguide caused by annealing or the like as the optical power variable mechanism. 2. The arrayed waveguide grating of claim 1.