JPH11352346A - Optical waveguide type grating array - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a grating of a low cost and high productivity capable of a high density multi-channel operation. SOLUTION: Plural optical waveguides 11-14 are parallelly arranged on a substrate 15, the respective optical waveguides 11-14 are respectively provided with inclination at a certain angle to the grating and the grating provided with the same grating vector is formed on the respective optical waveguides 11-14 by the collective irradiation with ultraviolet light. For the grating on the respective optical waveguides, since inclination angles with the respective optical waveguides 11-14 are different from each other, the pitch is respectively different and thus, the Bragg wavelength is respectively different. As a result, the multi-channel operation is made possible. By arranging the optical waveguides by a high density, the density of channels can be raised as well. Also, since one waveguide formation process and one grating manufacture process are sufficient, the cost is lowered and the productivity is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide type grating array, and more particularly to an optical waveguide type grating array capable of multiplexing / demultiplexing light waves according to their wavelengths and capable of operating in multiple channels.

[0002]

2. Description of the Related Art In recent years, research and development of a wavelength division multiplexing transmission system for transmitting optical signals of a plurality of wavelengths using the same line have been progressing toward increasing the capacity of optical communication. Above all, wavelength intervals of 1.6 nm and 0.8 nm (frequency intervals of 200G each)
In order to multiplex and demultiplex optical signals multiplexed at a high frequency (Hz, 100 GHz), use of a narrow-band wavelength filter in which a grating is formed in an optical fiber or a silica-based optical waveguide has been studied.

This grating is made of germanium (G
Irradiation of ultraviolet light to the quartz glass to which e) has been added is based on a photo-induced refractive index change that increases the refractive index of the glass. As ultraviolet light for changing the refractive index of the quartz glass, an excimer laser of KrF or ArF (wavelengths of 248 nm and 193 nm, respectively), or a second harmonic (wavelength of 244 nm) of an argon laser is used.

FIG. 5 is a diagram showing an example of a grating manufacturing method generally performed in the past. For example, Applied Physics Letters, 1993, No. 6
Volume 2, pages 1035 to 1037 (Applied Physics Lett)
ers, vol. 62, pp. 1035-1037, 1993).

In FIG. 5, a light 55 from the ultraviolet laser 53 is mirrored to an optical fiber on a silicon (Si) substrate 41 or a quartz optical waveguide core 43 through a phase mask 51 made of quartz glass transparent in the ultraviolet region. Irradiate via. The phase mask 51 is a diffraction grating in which periodic fine grooves are carved at a pitch of about 1 μm.
5 is diffracted into 0th, ± 1st, ± 2nd,..., Diffracted light 56. Each diffracted light interferes on the waveguide to form interference fringes,
A periodic pattern of refractive index, that is, a grating 52 is formed in the quartz glass according to the brightness of the stripes. Incidentally, 4
Reference numeral 2 denotes a lower cladding, and 44 denotes an upper cladding.

Usually, ± 1st-order diffracted light from a phase mask is used, and the phase mask pitch Λ and the grating pitch ΛG have a relation of Λ = 2ΛG. The grating, which is a periodic pattern of refractive index, functions as a wavelength filter that reflects a Bragg wavelength light wave propagating through the optical waveguide.
The Bragg wavelength λB is given by λB = 2neff · ΛG = neff · ΛG (1) from the grating pitch ΔG and the equivalent refractive index neff of the optical waveguide.

As a configuration for applying a grating based on a photo-induced refractive index change to a wavelength filter, a Mach-Zehnder type configuration in which the same grating is formed in an arm portion of a Mach-Zehnder interferometer type optical waveguide, a directional coupler type optical waveguide And a configuration in which a grating formed in a linear optical waveguide is used together with an optical circulator.
For each configuration, an optical fiber and a silica-based optical waveguide formed on a substrate such as silicon can be used as the optical waveguide.

FIG. 6 (a) shows, for example, IEE Photonics Technology Letters, 19
1995, Vol. 7, pp. 388-390 (IEEE Photonics
FIG. 2 is a plan view of a Mach-Zehnder type optical waveguide grating reported in Technology Letters, vol. 7, pp. 388-390, 1995). In FIG. 6A, two 3
a Mach-Zehnder interferometer type optical waveguide 61 comprising a dB coupler 62 and two arm portions 63;
Are formed from two identical gratings 16.

[0009] Of the wavelength-division multiplexed optical signals input to the input port 64, the optical signal of the Bragg wavelength represented by the formula (1) is reflected by the grating and is dropped by the drop port 65
And an optical signal is extracted (drop operation). Optical signals other than the Bragg wavelength are output from the through port 66 without being affected by the grating. When an optical signal having a Bragg wavelength is input from the add port 67, this optical wave is reflected by the grating and output from the through port 66, and is added to the optical signal from the input port 64 (add operation).

FIG. 6 (b) shows, for example, IEE Photonics Technology Letters, 19
1996, Volume 8, pages 1331 to 1333 (IEEE Photo
nicsTechnology Letters, vol. 8, pp. 1331-1333, 199
FIG. 6 is a plan view of a directional coupler type optical waveguide grating reported in 6). In FIG. 6B, the directional coupler type optical waveguide 68 and the grating 16 formed on the coupling waveguide section 69 are constituted.

[0011] Of the wavelength multiplexed optical signals input to the input port 64, the optical signal of the Bragg wavelength represented by the equation (1) is reflected by the grating and dropped.
And an optical signal is extracted (drop operation). Optical signals other than the Bragg wavelength are output from the through port 66 without being affected by the grating. When an optical signal having a Bragg wavelength is input from the add port 67, this optical wave is reflected by the grating and output from the through port 66, and is added to the optical signal from the input port 64 (add operation).

[0012]

In order to realize a wavelength filter capable of performing add and drop operations for all channels of a wavelength multiplexed optical signal, it is necessary to prepare a plurality of gratings having different Bragg wavelengths for each channel. There is. According to equation (1), the Bragg wavelength can be changed by changing the equivalent refractive index or the grating pitch. Therefore, as means for producing gratings with different Bragg wavelengths, (A) a method using phase masks with different pitches, (B) changing the relative refractive index difference between the core and clad of the waveguide and the core size to change the equivalent refractive index And (C) a method of changing the equivalent refractive index by uniform irradiation of ultraviolet light without a phase mask after manufacturing the grating.

FIG. 7 is a view showing a process of manufacturing two gratings having different Bragg wavelengths by the method (A). First, a first grating 73 is formed on the first optical waveguide 21 on the substrate 15 using the phase mask 71 having a pitch of (1), and then a second grating is formed on the second optical waveguide 22.
The second grating 7 is formed by using the phase mask 72 of (2).
4 is produced. The Bragg wavelength of the fabricated grating is given by λB (1) = neff · Λ (1) (2) λB (2) = neff · Λ (2) (3) according to equation (1). Can be

The problems with this method are that a plurality of phase masks are required and that ultraviolet light irradiation through the phase mask must be performed a plurality of times. In addition, when a plurality of optical waveguides are densely arranged on a substrate, it is difficult to control the position of ultraviolet light irradiation a plurality of times. Therefore, the cost of fabricating the grating increases, and the productivity decreases.

FIG. 8 is a view showing a process of manufacturing two gratings having different Bragg wavelengths by the method (B). By forming the optical waveguide in a separate step in which the core refractive index is changed, an optical waveguide 21 having an equivalent refractive index neff (1) and an optical waveguide 22 having an equivalent refractive index neff (2) are prepared.
Each of the gratings 7 is
3, 74 are produced. The Bragg wavelength of the manufactured grating is given by λB (1) = neff · Λ (4) λB (2) = neff · Λ (5) according to the equation (1).

The problems with this method are that the process of forming the optical waveguide is complicated and that ultraviolet light irradiation through a phase mask must be performed a plurality of times. Therefore, the productivity of manufacturing a grating is low.

The method (B) can be performed by changing the width of the waveguide core without changing the refractive index of the core.
The problem is that the wavelength width that can change the Bragg wavelength is small. When the method (C) is used, the ultraviolet light irradiation by the phase mask at the time of manufacturing the grating only needs to be performed once, but the uniform irradiation of ultraviolet light after the manufacturing of the grating is required a plurality of times, and refraction that can be further changed after the manufacturing of the grating is performed. The problem is that the rate is limited and it is difficult to change the Bragg wavelength significantly.

An object of the present invention is to solve the above-mentioned problems and to provide an optical waveguide type grating capable of operating at high cost and with high density and multichannel operation at low cost.

[0019]

An optical waveguide type grating array according to the present invention has a structure in which a plurality of optical waveguides are arranged in parallel on a substrate. Each optical waveguide is arranged at an angle to the grating at a certain angle. A grating having the same lattice vector is formed on each optical waveguide by collective irradiation of ultraviolet light.
The gratings on each optical waveguide have different pitches due to different inclination angles with the respective optical waveguides, and therefore have different Bragg wavelengths.

As a result, the optical waveguide type grating array having the structure of the present invention can perform multi-channel operation. By arranging the optical waveguides at a high density, it is possible to increase the channel density. Further, the optical waveguide type grating array of the present invention can be realized with low cost and high productivity because only one waveguide forming step and one grating manufacturing step are required.

[0021]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a plan view showing a first embodiment of the optical waveguide grating array according to the present invention. First linear optical waveguide 1 on substrate 15
1, second straight optical waveguide 12, third straight optical waveguide 1
,..., The eighth linear optical waveguides 14 are arranged on the substrate not parallel to each other but at a certain inclination angle.

A grating having the same lattice vector is formed on each optical waveguide by collective irradiation of ultraviolet light. The angle between the i-th (i = 1 to 8) -th straight optical waveguide and the grating vector of the grating is defined as θi.

FIG. 2 is a view for explaining the operation of the optical waveguide grating array according to the present invention. In the i-th linear optical waveguide 21 having an inclination angle θi with respect to the grating vector of the grating, the grating pitch is 1 / cos θi when there is no inclination, and the Bragg wavelength is λB (i) = 2neff · ΛG / cosθi ... ... (6) Thus, the eight gratings of FIG. 1 will have a total of eight different Bragg wavelengths,
An optical waveguide grating capable of channel operation is realized.

Here, an example of an optical waveguide type grating array capable of operating eight channels has been described. However, the number of operating channels achievable by the present invention can be arbitrarily designed within a range described later, and the operating wavelength can be set to 1.3 μm band. Or in the 1.5 μm band. Further, each optical waveguide may be formed of an optical fiber or a quartz-based optical waveguide formed on a substrate of Si or the like, as long as an ultraviolet light-induced refractive index effect is present.

The number of channels that can be simultaneously manufactured in the optical waveguide grating array of the present invention is limited only by the width of the phase mask. That is, the number of channels can be arbitrarily designed as long as the width of the optical waveguide group arranged in parallel on the substrate does not exceed the width of the phase mask.

FIG. 3 is a plan view showing a directional coupler parallel type optical waveguide type grating array according to a second embodiment of the present invention. Eight directional couplers are arranged in parallel on the substrate 15, and gratings having the same lattice vector are formed by collective irradiation of ultraviolet light on each of the coupling waveguides in a region 16 indicated by a dotted line in the figure. Have been. The coupling waveguide portion of the i-th directional coupler is set to have the grating vector of the grating and the inclination angle θi. Reflecting mirrors 39 are attached to ports on both end faces.

Next, a method of operating the optical waveguide type grating array according to the present invention will be described with reference to FIG. 3 taking the second embodiment as an example. From an input port 35 provided in the first directional coupler 31, an eight-channel optical signal having a wavelength of λ1 to λ8 enters. Of the incident light, only the light wave of wavelength λ1 is reflected by the grating formed in the coupling waveguide section 33 and emitted from the drop port 36.

The light waves having wavelengths λ 2 to λ 8 pass through the coupling waveguide 33 and travel to the through port 37, and are reflected by the reflection mirror 39 mounted on the end face of the substrate, and thereafter the coupling waveguide 3
4 is introduced. In the coupling waveguide 34, only the light wave having the wavelength λ2 is reflected by the grating and emitted from the drop port 38. Thereafter, the same operation is repeated, and the wavelengths λ1 to λ8 are distributed to the respective drop ports.

[0029]

Next, specific examples of the present invention will be described. FIG. 4 is a cross-sectional view when the optical waveguide of FIG. 2 is cut along a broken line. Lower cladding 4 on Si substrate 41
2, an optical waveguide including a core 43 and an upper clad 44 is formed. The composition of the upper and lower claddings is quartz, and the composition of the core is Ge-added quartz. The relative refractive index difference between the core and the clad is 0.4%. The thicknesses of the lower cladding and the upper cladding are 15 μm and 12 μm, respectively, and the cross-sectional size of the core is 6 μm × 6 μm.

A directional coupler is constituted by the above optical waveguides, and eight directional couplers are arranged in parallel as shown in FIG. In the coupling waveguide portion of the directional coupler (69 in FIG. 6B), the gap between the waveguides is 8 μm, and the length is the perfect coupling length.
It is set to 3 mm. According to the method shown in FIG. 5, for example, ArF excimer laser light (wavelength 193n) is emitted as ultraviolet light through a phase mask having a pitch of 1.073 μm.
m) to irradiate to collectively produce gratings in eight directional couplers. The length of the grating is 4 mm.

Referring to FIG. 2, when it is assumed that the coupling waveguide portion of the i-th directional coupler has the grating vector of the grating and the inclination angle θi, θi
And the Bragg wavelength λB (1) are shown in FIG.

The characteristics of each channel of the fabricated optical waveguide grating array are as follows: extinction ratio: -20 dB, bandwidth: 0.6 nm, side lobe: -30 dB, insertion loss: 3 dB
It is. When using an optical fiber as an optical waveguide,
The i-th optical fiber may be fixed to a quartz substrate at an inclination angle θi, and ultraviolet light may be radiated collectively through a phase mask.

The optical waveguide type grating array of the present invention can be constructed even if the grating has a periodic relief structure provided on the optical waveguide. FIG. 9 is a sectional view parallel to the light propagation direction showing the structure of the optical waveguide in this case. 1 and 3, a relief structure 91 is collectively formed by etching the optical waveguide at a period of ΔG, so that an optical waveguide type grating array similar to that of the above embodiment can be manufactured.

As shown in FIG. 6A, the optical waveguide element may be a Mach-Zehnder type optical waveguide, and a structure in which a grating is formed on each of both arms may be used.

[0035]

According to the present invention, an optical waveguide type grating array operable in multiple channels can be realized with low cost and high productivity. Further, by arranging the optical waveguides at a high density, it is possible to increase the channel density.

[Brief description of the drawings]

FIG. 1 is a plan view showing a first embodiment of an optical waveguide grating array according to the present invention.

FIG. 2 is a diagram illustrating the principle of the present invention.

FIG. 3 is a plan view showing a second embodiment of the optical waveguide grating array of the present invention.

FIG. 4 is a sectional view taken along a broken line in FIG.

FIG. 5 is a diagram showing a grating manufacturing method according to the present invention and a conventional example.

6A is a diagram showing an example of a conventional optical waveguide grating and its operation, and FIG. 6B is a diagram showing another example of a conventional optical waveguide grating and its operation.

FIG. 7 is a process chart showing a method for manufacturing a conventional optical waveguide grating.

FIG. 8 is a process chart showing another method for manufacturing a conventional optical waveguide grating.

FIG. 9 is a cross-sectional view showing an example of a grating structure according to the present invention and a conventional example.

FIG. 10 is a diagram showing the relationship between θi and the Bragg wavelength λB (i) shown in FIG. 2;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 1st linear optical waveguide 12 2nd linear optical waveguide 13 3rd linear optical waveguide 14 8th linear optical waveguide 15 board | substrate 16 grating manufacturing area 21 ith linear optical waveguide 22 i + 1 linear optical waveguide 31st One directional coupler 32 second directional coupler 33 coupling waveguide part of first directional coupler 34 coupling waveguide part of second directional coupler 35 incident port 36 of first Bragg wavelength Drop port 37 Through port 38 Drop port of second Bragg wavelength 39 Reflective mirror 41 Si substrate 42 Lower cladding 43 Optical waveguide core 44 Upper cladding 51 Phase mask 52 Grating 53 Ultraviolet laser light source 54 Mirror 55 Ultraviolet laser light 56 Ultraviolet laser diffraction Light 61 Mach-Zehnder optical waveguide 62 3 dB coupler 63 Arm 64 input Launch port 65 drop port 66 through port 67 add port 68 directional coupler type optical waveguide 69 coupling waveguide section 71 phase mask of pitch Λ (1) 72 phase mask of pitch Λ (2) 73 first grating 74 second Grating 81 Pitch Λ phase mask 91 Relief structure

Claims (7)

[Claims] An optical waveguide type grating array comprising: a plurality of optical waveguide elements arranged in parallel on a substrate; and a grating formed on each of the optical waveguide elements, wherein each of the optical waveguide elements and a grating are arranged. An optical waveguide type grating array, wherein angles formed by a lattice vector are set to different angles from each other. 2. An optical waveguide type grating array according to claim 1, wherein said optical waveguide element is a linear optical waveguide. 3. The optical waveguide type grating array according to claim 1, wherein said optical waveguide element is a directional coupler type optical waveguide, and a grating is formed in each coupling waveguide portion. 4. The optical waveguide type grating array according to claim 1, wherein said optical waveguide element is a Mach-Zehnder type optical waveguide, and a grating is formed on each of both arm portions. 5. The optical waveguide type grating array according to claim 2, wherein said optical waveguide device is a flat quartz optical waveguide formed on a silicon or quartz substrate. 6. The optical waveguide type grating array according to claim 2, wherein said optical waveguide element is an optical fiber fixed on a substrate made of a quartz substrate or the like. 7. The optical waveguide type grating array according to claim 2, wherein said optical waveguide device is a flat semiconductor optical waveguide formed on a semiconductor substrate.