JP3348701B2 - Waveguide type optical multiplexer / demultiplexer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveguide type optical multiplexer / demultiplexer using an arrayed waveguide grating.

[0002]

2. Description of the Related Art In a waveguide type optical multiplexer / demultiplexer according to the present invention, an important technical problem to be solved is to reduce insertion loss fluctuation depending on wavelength fluctuation of a multiplexed or demultiplexed optical signal. It has become one of. The above loss fluctuation is caused by the fact that the wavelength transmission band characteristic has a sharp single-peak characteristic.

[0003] For this purpose, an array waveguide having a basic structure in which an input channel waveguide, an input slab waveguide, a channel waveguide array, an output slab waveguide, and an output channel waveguide are connected in cascade in the light transmission direction. In the vicinity of the junction between the input / output channel waveguide and the slab waveguide in the diffraction grating type multiplexer / demultiplexer, the above-mentioned insertion loss is obtained by changing the waveguide width of the channel waveguide to widen the wavelength transmission band. A technique of reducing fluctuation is adopted.

However, with this method alone, the shape of the transmission band near the center wavelength becomes large with a unimodal shape close to a parabola. Therefore, when the transmission bandwidth is widened, the crosstalk of the adjacent channel signal with the main signal also increases. When this type of element is used in a wavelength division multiplexing optical transmission system, there is a problem that high quality optical signal transmission cannot be ensured.

Therefore, for example, A.I. Rigny, A .; Br
uno and H.C. Co-authored with Sik and published the journal Elec
tron. Lett. Vol. 33, No. 20, No. 1
In an academic paper published on pages 701 to 1702 (1997), two channel waveguide arrays each composed of a group of waveguides having a waveguide length difference of ΔL1 and ΔL2 are arranged such that the waveguides are alternately arranged. By placing
A technique for superimposing two light transmission wavelength characteristics slightly shifted in center wavelength is disclosed. As a result, a flat wavelength transmission band characteristic is obtained in the vicinity of the center wavelength, and a certain effect is achieved. However, an optical multiplexer / demultiplexer using this method has a wavelength transmission band (FSR) other than the center wavelength due to interference between adjacent channel waveguides belonging to different groups of different waveguide lengths.
ral Range), a new light transmission peak appears, which causes a new problem that the effective wavelength transmission bandwidth is narrowed.

[0006]

An object of the present invention is to provide a FS
Provided is a waveguide-type optical multiplexer / demultiplexer having desired transmission band characteristics such as a flat transmission band shape near a center wavelength without narrowing R and excellent crosstalk characteristics with an adjacent transmission band. It is in.

[0007]

According to the present invention, there is provided a waveguide type multiplexer / demultiplexer which transmits an input channel waveguide, an input slab waveguide, a channel waveguide array, an output slab waveguide, and an output channel waveguide in a light transmission direction. cascade in a waveguide-type demultiplexer arrangement connected to, at least one in one of the slab waveguide of the input and output slab waveguide, said slab waveguide a light image of the slab waveguide entrance end Image in the wave path
Means and means for spatially filtering guided light propagating through the slab waveguide on the image plane . Further, in the waveguide type multiplexer / demultiplexer according to the present invention, the imaging means may provide a lens function to the slab waveguide light.
, And the means for performing the spatial filtering said Ren
Characterized in that it is a spatial filter to provide a spatial modulation to the imaging light image by's. The waveguide type multiplexer / demultiplexer according to the present invention is characterized in that the spatial filters have an array configuration. Further, the waveguide type multiplexer / demultiplexer of the present invention is characterized in that the spatial filter is a spatial filter that applies amplitude modulation to slab waveguide light. Further, the waveguide type multiplexer / demultiplexer of the present invention is characterized in that the spatial filter is a spatial filter that applies phase modulation to slab waveguide light. Moreover, waveguide type demultiplexer of the present invention, the air
Is a spatial filter whose light transmission characteristics can be varied.
It is characterized by that.

[0008]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a plan view of a waveguide type optical multiplexer / demultiplexer according to a first embodiment of the present invention.

On a substrate 1, an input channel waveguide 2, an input slab waveguide 3, a channel waveguide array 4 configured such that the length of the waveguide is sequentially changed by a predetermined length, and an output slab waveguide 5 , Output channel waveguides 6, and the respective waveguide portions are optically connected in this order. A waveguide lens 7 and a spatial filter group 8 are provided inside the input slab waveguide 3. In this figure, the output slab waveguide 5
Has a structure similar to that of the related art without a lens and a spatial filter. For simplification of the drawings, only a few input / output channel waveguides and channel waveguide arrays are shown.

FIG. 2 is a diagram showing the propagation trajectory and field distribution of the guided light in the slab waveguide. Each of the guided lights incident on the input slab waveguide 3 from the input channel waveguide 2 is two-dimensionally image-focused in the slab waveguide by the waveguide lens 7. The spatial filter group 8 is composed of a set of spatial filters 8a located near the imaging points of the respective guided lights. The spatial filter 8a two-dimensionally controls the amplitude and phase of the condensed light in the plane of the slab waveguide. The controlled guided light enters each of the channel waveguides from the light incident end of the channel waveguide array 4 located at a location that has spread again in the slab waveguide.

The one-dimensional distribution in the direction perpendicular to the propagation direction of the amplitude of the respective guided light that enters from each input channel waveguide 2 and propagates through the input slab waveguide 3 is generally approximately Gaussian distribution. By transmitting through the spatial filter 8a, the distribution of the light guided through the slab waveguide 3 after transmission is spatially modulated one-dimensionally, and by appropriately setting the spatial modulation characteristic of the spatial filter 8a, the distribution is, for example, double. The light is coupled to the channel waveguide array 4 in a desired distribution such as a peak Gaussian distribution. In the channel waveguide array section, guided light transmitted through each channel waveguide undergoes a phase delay according to each waveguide length of the transmitted array waveguide,
The amplitude transmitted through each varies only slightly to the extent of the propagation loss and bending loss between the waveguides in the channel waveguide array, and the amplitude distribution between the waveguides is reduced by the incidence of the array waveguide. The light is emitted from the end of the channel waveguide array to the output slab waveguide 5 while maintaining the desired distribution shape formed at the end. The waveguide light collected at the end of the output slab waveguide is coupled to the output channel waveguide 6 in a desired shape such as a bimodal Gaussian distribution having a distribution of amplitude in a direction perpendicular to the propagation direction.

The wavelength transmission characteristic of the optical multiplexer / demultiplexer output from the output channel waveguide is represented by the overlap integral of the guided light amplitude distribution at the end of the output slab waveguide 5 and the propagation mode of the output channel waveguide 6. Since the coupling efficiency depends on the wavelength dispersion of the diffraction angle, the amplitude distribution of the guided light at the end of the output slab waveguide is spatially controlled in the input slab waveguide 3 according to the present invention, so that the transmission band shape is flat or the transmission bandwidth is reduced. A desired wavelength transmission band characteristic such as a large thickness can be obtained.

FIG. 3 is a diagram for explaining the effect of improving the wavelength characteristics in the optical multiplexer / demultiplexer according to the present invention. The amplitude distribution in the direction perpendicular to the propagation direction at the waveguide coupling surface from the output slab waveguide to the output channel waveguide is a Gaussian distribution (conventional example) or a bimodal Gaussian distribution according to one embodiment of the present invention. An example of the calculation result of the light transmission wavelength characteristic of the optical multiplexer / demultiplexer in the case is shown.

According to the present invention, the main transmission wavelength (center wavelength)
An optical multiplexer / demultiplexer having a light transmission characteristic in which the peak shape of the band is flatter than the conventional example can be obtained.

Next, the slab waveguide 3 which is a feature of the present invention will be described.
Examples of the waveguide lens 7 and the spatial filter group 8 provided in the first embodiment will be described.

The waveguide lens 7 for two-dimensionally condensing the slab waveguide light in the slab plane is, for example, a convex lens made of a material having a higher refractive index than the core layer constituting the slab waveguide. Are formed integrally in a slab waveguide by a process including a film forming method such as a CVD method or a sputtering method, etching or the like, or by diffusion of a substance, or a groove is formed in a slab waveguide, and a waveguide is formed in the groove. It can be formed by a method such as inserting a solid cylindrical lens made separately or filling a liquid.

It is also possible to form various thin film lenses such as a mode index lens by loading a film on a desired portion on the slab optical waveguide, a Fresnel lens using a periodic structure, and a grating lens.

Next, a spatial filter 8a for spatially modulating a slab waveguide light into a desired spatial distribution such as a unimodal Gaussian distribution from a bimodal Gaussian distribution or a spatial filter group 8 constituted by a one-dimensional array thereof will be described. Will be described.

For the spatial filtering of the slab waveguide light in the optical system, a method similar to the image improvement by the spatial filtering in the conventional three-dimensional optical system can be adopted. As the spatial filters, there are an amplitude modulation type and a phase modulation type. Can be used. In the amplitude modulation type, for example, the light absorbing substance is distributed in the upper clad layer of the slab waveguide so that the absorption is high near the center of the guided light of Gaussian distribution and the absorption decreases as the distance from the center is increased. It can be provided by a method such as diffusing an absorbing substance into a layer or a core layer or using a lithographic technique. Further, similarly to the above-described waveguide lens 7, a groove may be formed in the slab waveguide, and an amplitude filter may be inserted into this groove.

In the phase modulation type, the guided light having a Gaussian distribution is angle-split into a plurality of guided lights having a Gaussian distribution by a refraction effect or a diffraction effect of a spatial filter, and a plurality of split guided lights are synthesized. Thus, a method of forming a desired distribution can be adopted. For example, a slab waveguide is loaded with a phase shift film that gives a spatial phase delay to the guided light in an aspherical shape to form guided light having a bimodal or one-dimensional amplitude distribution by the effect of refraction, or the phase of a periodic structure. It is possible to employ a method in which a grating layer is loaded on a slab waveguide to form guided light having a bimodal or one-dimensional amplitude distribution by the effect of diffraction. Also here, similarly to the above-described waveguide lens 7, a groove may be formed in the slab waveguide, and a one-dimensional spatial phase filter or a diffraction grating filter may be inserted into this groove.

In the above embodiment, the case where the waveguide lens 7 and the spatial filter group 8 are arranged in the input slab waveguide has been described. However, similar effects can be obtained by providing them on the output slab waveguide side. Can be

Further, as shown in FIG. 4, the waveguide lens 7 may be individually provided at the emission part of each input channel waveguide.

In the above embodiment, the spatial filter is
The case where a passive filter that does not change the transmission characteristics by an external field has been described. For example, the transmission characteristics are changed by an electric field, an electric current, or the like in a spatial filter inserted into a slab waveguide by cutting a groove. Uses an active filter or an electro-optic material or an optical semiconductor material as a substrate or waveguide material for forming a waveguide type optical multiplexer / demultiplexer. The electro-optic effect, electric field light absorption effect, and carrier density change of the material itself. By utilizing a physical optical effect such as a change in light absorption due to light and a change in refractive index due to a change in carrier density, an active spatial filter can be monolithically integrated with a waveguide, a lens, and the like. By employing such a configuration, it is also possible to control the wavelength transmission characteristics of the optical multiplexer / demultiplexer, such as the wavelength transmission bandwidth and crosstalk, by an external field. As the physical external field, not only an electromagnetic field but also a wide range of fields such as a mechanical external force, a temperature change, and light irradiation can be used.

[0024]

As described above, the waveguide type optical multiplexer / demultiplexer according to the present invention is provided with means for spatially modulating the amplitude and phase by the spatial filter in the slab waveguide, and each channel in the channel waveguide array section. By controlling the amplitude distribution and phase distribution of light between waveguides, or the amplitude distribution of light at the optical coupling section between the output slab optical waveguide and the output channel waveguide, the cross-section of the optical multiplexer / demultiplexer with respect to the wavelength transmission bandwidth and the main wavelength is controlled. Wavelength transmission characteristics such as talk can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a waveguide type optical multiplexer / demultiplexer according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a propagation trajectory and a field distribution of guided light in a slab waveguide constituting the configuration of the waveguide type optical multiplexer / demultiplexer according to the first embodiment of the present invention.

FIG. 3 is a diagram showing an effect of improving wavelength characteristics in the waveguide type optical multiplexer / demultiplexer of the present invention.

FIG. 4 is a diagram showing a configuration in a slab waveguide of a waveguide type optical multiplexer / demultiplexer according to another embodiment of the present invention, and a propagation trajectory and a field distribution of guided light.

[Explanation of symbols]

 Reference Signs List 1 substrate 2 input channel waveguide 3 input slab waveguide 4 channel waveguide array 5 output slab waveguide 6 output channel waveguide 7 waveguide lens 8 spatial filter group 8a spatial filter

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-9-133826 (JP, A) JP-A-8-334792 (JP, A) JP-A-11-174250 (JP, A) JP-A 9-133 159848 (JP, A) JP-A-8-234029 (JP, A) JP-A-10-177113 (JP, A) JP-A-2-244105 (JP, A) JP-A-2000-232411 (JP, A) ( 58) Field surveyed (Int. Cl. ⁷ , DB name) G02B 6/12

Claims (6)

(57) [Claims] 1. A waveguide type multiplexer / demultiplexer having a configuration in which an input channel waveguide, an input slab waveguide, a channel waveguide array, an output slab waveguide and an output channel waveguide are connected in cascade in the light transmission direction. In the slab waveguide of at least one of the input and output slab waveguides,
An optical image of the slab waveguide incident end is formed in the slab waveguide.
A waveguide type multiplexer / demultiplexer, comprising: means for imaging; and means for spatially filtering guided light propagating through the slab waveguide on the image plane . Wherein a waveguide lens, wherein the imaging means provides a lens effect to said slab waveguide light, said spatial filtering performed means <br/> spatial modulation to the optical image formed by the lens the waveguide-type demultiplexer according to claim 1, characterized in that a spatial filter to give. 3. The waveguide type multiplexer / demultiplexer according to claim 2, wherein said spatial filter has an array configuration. Wherein said claims 2 and 3 Symbol waveguide type demultiplexer of the mounting characterized in that it is a spatial filter the spatial filter gives an amplitude modulation to the slab waveguide beam. Wherein said claims 2 and 3 Symbol waveguide type demultiplexer of the mounting characterized in that it is a spatial filter the spatial filter providing a phase modulation to the slab waveguide beam. 6. The spatial filter can change light transmission characteristics.
2. The spatial filter according to claim 2, wherein
A waveguide type multiplexer / demultiplexer according to any one of Items 5 to 5.