JPH11223735A - Tunable polymer waveguide diffraction grating and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a tunable polymer waveguide diffraction grating having a large thermo-optical const. and excellent heat resistance, transmittance of light in the optical communication wavelength range, and formability by forming either or both of the core and the clad of a waveguide diffraction grating from a polymer material. SOLUTION: The clad and the core material consists of a polymer material which is transparent in a near infrared region as an optical communication wavelength range of the waveguide material, especially near 1.3 and 1.55 μm wavelengths and which has a large thermo-optical const. and excellent heat resistance. Especially, by using a fluorinated polyimide having high heat resistance as about at >=300 deg.C, the most excellent long-term stability can be obtd. As for a fluorinated polyimide having good balance in transmittance and heat resistance, a fluorinated polyimide or its polymer synthesized from 2,2-bis(3,4- dlcarboxyphenyl) hexafluoropropane dianhydride (6FAD) and diamine is preferably used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tunable polymer waveguide diffraction grating used for optical communication and the like, and a method of manufacturing the same.

[0002]

2. Description of the Related Art Research and development of waveguide type optical devices have been actively pursued in order to advance optical communication systems. Above all, a waveguide diffraction grating is an optical circuit that can reflect or transmit only a specific wavelength, and is expected to be applied to a wavelength division multiplexing system.

In general, application of an optical waveguide to an optical device requires various conditions such as ease of fabrication, control of the refractive index of the waveguide material, and heat resistance. At present, quartz is most often used as an optical waveguide material, and the optical waveguide exhibits a low optical loss of 0.1 dB / cm or less at a wavelength of 1.3 μm. However, there are problems such as a complicated manufacturing process and difficulty in increasing the area, and it is difficult to obtain a waveguide diffraction grating which is excellent in economy and versatility. Further, quartz has a small thermo-optic (TO) constant indicating the temperature dependence of the refractive index of 1 × 10 ⁻⁵ / ° C., and the wavelength tuning region by the TO effect is as narrow as about 1 nm.

On the other hand, since a polymer optical waveguide can be formed by a spin coating method, it is easier to manufacture than a quartz optical waveguide. In addition, polymer materials are one-quarter compared to quartz.
In many cases, the TO constant is at least 0 times larger, so that the tuning region of the transmission wavelength of the diffraction grating can be theoretically increased by 10 times or more than that of the silica-based waveguide diffraction grating. However, there has been no tunable polymer waveguide diffraction grating made of a polymer material having excellent heat resistance that can withstand practical use and light transmittance in an optical communication wavelength band.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a TO
An object of the present invention is to provide a tunable polymer waveguide diffraction grating having a large constant, excellent heat resistance, excellent light transmittance in an optical communication wavelength band, and excellent workability, and a method for manufacturing the same.

[0006]

As a result of studying from these viewpoints, the present inventors have found that fluorinated polyimide has low loss in the near infrared region of wavelengths of 1.3 μm and 1.55 μm,
Excellent heat resistance, thermo-optic (TO) constant indicating the temperature dependence of the refractive index is 10 ⁻⁴ / ° C. or more, 10 times larger than quartz, and fabrication of tunable polymer waveguide diffraction grating using thermo-optic effect Has the required processability for external radiation,
The inventors have found that the refractive index changes due to the light-induced effect of irradiation with electron beams, ultraviolet rays, or near-infrared rays, and that the reflectivity of the produced diffraction grating is large. Thus, the present invention has been completed.

[0007] [Claim 1] of the present invention based on such knowledge.
The tunable polymer waveguide diffraction grating according to the present invention includes a heating unit using an external heat source, and in the tunable waveguide diffraction grating using a thermo-optic effect, one or both of the core and the clad of the waveguide diffraction grating are provided. It is made of a polymer material.

[0008] A tunable polymer waveguide diffraction grating according to claim 2 of the present invention includes a heating means using a resistor formed on the waveguide diffraction grating, and provides a tunable waveguide using a thermo-optic effect. In the waveguide grating, one or both of the core and the clad of the waveguide grating are made of a polymer material.

According to a third aspect of the present invention, there is provided a tunable polymer waveguide diffraction grating according to the second aspect, wherein the shape of the resistor is repeatedly bent so as to intersect the optical axis, and the repetition width thereof. In addition, one or both of the film thicknesses at the respective repetitive portions of the resistor gradually change in a chirped shape in the optical axis direction.

[0010] A tunable polymer waveguide diffraction grating according to claim 4 of the present invention is characterized in that in claim 1 to 3, the polymer material is a fluorinated polyimide.

[0011] In a tunable polymer waveguide diffraction grating according to claim 5 of the present invention, in claim 1 to 4, both surfaces of the diffraction grating portion made of the polymer material do not contact any object. It is characterized by being configured in a self-holding shape.

According to a sixth aspect of the present invention, there is provided a method of manufacturing a tunable polymer waveguide diffraction grating, comprising a heating means using an external heat source or a resistor formed on the waveguide diffraction grating; A method of manufacturing a tunable polymer waveguide diffraction grating using an effect, comprising: forming a diffraction grating made of the polymer material on a substrate; and separating the diffraction grating from the substrate. I do.

[0013] A method of manufacturing a tunable polymer waveguide diffraction grating according to claim 7 of the present invention is characterized in that in claim 6, there is provided a step of heat-treating the diffraction grating separated from the substrate.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below, but the present invention is not limited to these embodiments.

The clad and core materials applicable to the present invention are as follows: 1) The waveguide material is transparent in the near-infrared region, which is an optical communication wavelength band, particularly at a wavelength of 1.3 or 1.55 μm
2) The thermo-optic constant of the clad and core materials is large;
3) Any polymer material can be used as long as it satisfies excellent heat resistance. However, when a fluorinated polyimide having heat resistance as large as 300 ° C. or more is used, a tunable high-grade resin having the best long-term stability can be obtained. A molecular waveguide diffraction grating is obtained. The fluorinated polyimide can be produced from a fluorinated tetracarboxylic acid or a derivative thereof and a diamine, from a tetracarboxylic acid or a derivative thereof and a fluorinated diamine, or from a fluorinated tetracarboxylic acid or a derivative thereof and a fluorinated diamine. These fluorinated polyimides can be used not only alone, but also fluorinated polyimide copolymers and those obtained by adding additives and the like as necessary.

Among the above-mentioned fluorinated polyimides, those having a good balance of light transmittance and heat resistance include 2,2-
Fluorinated polyimide synthesized from bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FAD) and diamine or copolymer thereof, and 1,4
-Bis (3,4-dicarboxytrifluorophenoxy) tetrafluorobenzene dianhydride (10FEDA)
And a fluorinated polyimide synthesized from a diamine or a copolymer thereof.

[0017]

Hereinafter, the present invention will be described in more detail with reference to the drawings, but the present invention is not limited to these examples. In this embodiment, fluorinated polyimide is used for the polymer material, silicon is used for the substrate, and Ti is used for the metal film. However, it goes without saying that other materials may be used. For example, as a substrate material, Al, polyimide, indium phosphide, gallium arsenide, gallium nitride, glass, and as a material for forming a resistor thin film, Ti, Cr, Al, gold, silver, copper, platinum, tin oxide, oxide Indium, indium tin oxide, a mixture thereof, and a stacked film of these thin films can be used.

Example 1 2,2-bis (3,4-dicarboxylphenyl) hexafluoropropane dianhydride (6FDA) and 2,2'-bis (trifluoromethyl)
Polyimide synthesized from -4,4'-diaminobiphenyl (TFDB) (6FDA / TFDB) and polyimide synthesized from 6FDA and 4,4'-oxydianiline (4,4'-ODA) (6FDA / 4,4 A process for producing a tunable polymer waveguide diffraction grating using a copolymer of '-ODA) (copolymerization ratio includes 1: 0) will be specifically described with reference to FIG. First, (6FDA / TFDB):
A 15 wt% solution of a fluorinated polyamic acid, which is a precursor of a fluorinated polyimide copolymer having a copolymerization ratio of (6FDA / 4,4′-ODA) of 1: 0, in DMAc 15 wt% was applied to a silicon substrate 1.
After spin-coating on 1, the mixture was heated in an oven at 380 ° C. for 1 hour to imidize the lower cladding layer 12 (refractive index: n _TE ; 1.520, n _TM at a wavelength of 1.3 μm;
N _{TE at} 510, 1.55 μm; 1.518, n _TM ;
1.508). Next, on the lower cladding layer 12, (6FDA / TFDB) :( 6FDA / 4,4'-
DMAc1 of a fluorinated polyamic acid which is a precursor of a fluorinated polyimide copolymer having a copolymerization ratio of ODA) of 4: 6
A 5 wt% solution was spin-coated so that the film thickness after heat imidization became 8 μm. Then 380 in the oven
1 hour heating the core layer 13 (refractive index perform imidization ℃, when the wavelength of _{1.3μm n TE; 1.538, n TM} ; 1.
531, n _TE at 1.55 μm; 1.538, n _TM ;
1.530) (FIG. 1A). Next, after a photoresist was spin-coated on the core layer 13, the Cr mask pattern of the optical waveguide was transferred to the resist by a photolithographic method (FIG. 1B). Next, by developing the photoresist, a mask pattern 14 of the optical waveguide is formed on the core layer 13, and the core layer 13 on which the mask pattern 14 is formed is etched by using the RIE method to form a light guide. The core pattern 15 of the waveguide was formed (FIGS. 1C and 1D). Next, on the core pattern 15 of the optical waveguide, fluorinated polyamic acid D, which is a precursor of the same fluorinated polyimide copolymer as the lower cladding layer 12, is added.
After spin-coating a 15 wt% MAc solution, the solution was heated in an oven at 380 ° C. for 1 hour to perform imidization, thereby forming an upper cladding layer 16 having the same refractive index as the lower cladding layer 12 (FIG. 1E). Finally, by irradiating radiation through a transmission type X-ray mask 17 of a diffraction grating, the refractive index was changed, and a diffraction grating 18 was formed in the core (FIG. 1).
(F)). By such a method, a tunable polymer waveguide diffraction grating using a fluorinated polyimide optical waveguide was formed.

In this embodiment, emitted light is used as light for producing a diffraction grating. However, electron beams, ultraviolet rays, near-infrared rays, or the like may be used, or a phase mask or the like may be used as a mask for producing a diffraction grating. Further, a diffraction grating can be manufactured by scanning with an electron beam without using these masks.

The prepared tunable polymer waveguide diffraction grating 21 was placed on a sample table 22 on which a Peltier element was mounted (FIG. 2), and the optical characteristics were measured. The incident light 23 is transmitted to the optical waveguide 24.
As a result, only a specific wavelength satisfying the diffraction condition of the incident light 23 was reflected by the diffraction grating 26. The wavelength of the reflected light 27 at room temperature is 1561.1 nm.
(TE polarized light) and 1550.9 nm (TM polarized light), the extinction ratio was 23 dB, and the half width was 0.6 nm, and excellent reflection characteristics were observed (FIG. 3). Next, when the entire surface was uniformly heated to 100 ° C. using a Peltier element, a wavelength shift of 10 nm or more was observed due to the effect of a thermo-optic constant that was 10 times or more larger than that of quartz contained in the fluorinated polyimide copolymer. . This is ten times the value of the quartz waveguide diffraction grating. Furthermore, even after variable insertion loss, half width and 100 ° C
The shift amount of the center wavelength at the time of heating did not change, and exhibited characteristics excellent in environmental resistance and long-term stability.

(Embodiment 2) FIG. 4 shows a manufacturing process of a tunable polymer waveguide diffraction grating having a heating electrode.
As shown in FIG. 4, a Ti metal film 43 as a heating electrode was formed on a tunable polymer waveguide diffraction grating 41 manufactured in the same manner as in Example 1 by vacuum evaporation (FIG. 4).
(A), (b)). After spin coating a photoresist on the Ti metal film 43, an electrode mask pattern 44 was formed at a position above the optical waveguide 42 by a photolithographic method (FIG. 4C). Finally, using a photoresist as a mask, Ti is etched to form an electrode 45 (FIG. 4D), and then the mask pattern 44 is peeled off to produce a tunable polymer waveguide diffraction grating having a heating electrode. (FIG. 4E).

FIG. 5 is a schematic view of a tunable polymer waveguide diffraction grating with a heating electrode using the fluorinated polyimide optical waveguide thus produced. The heating electrode 51 formed on the diffraction grating has a periodic structure along the optical waveguide 52, and the entire diffraction grating can be uniformly heated by electric heating. When the tunable polymer waveguide diffraction grating is heated up to 100 ° C. by using the electrode and heated by heating, the wavelength shift amount is 10 times that of the quartz waveguide diffraction grating, and the wavelength can be changed with low power consumption. It turned out to work as a tunable wavelength filter. The tunable polymer waveguide diffraction grating did not change its characteristics even after heat treatment at 100 ° C., and was excellent in environmental resistance and long-term stability.

In the present invention, the shape and the periodic structure of the electrodes are not limited to the structures shown in this embodiment, and it goes without saying that any structure can be used. Also, the folded portion of the electrode need not be a right angle, and an arc having a certain curvature can be used.

Embodiment 3 As shown in FIG. 6, a tunable polymer waveguide diffraction grating having a heating electrode in which the pattern period of the heating electrode 61 formed on the diffraction grating is changed along the optical waveguide 62. Was produced in the same manner as in Example 2. Since the electrode period of the heating electrode 61 formed on the diffraction grating changes along the optical waveguide 62, a temperature gradient can be formed in the diffraction grating portion by conducting and heating. As a result of conducting heating using this electrode, the tunable polymer waveguide diffraction grating functioned as a chirped diffraction grating, and an arbitrary reflection wavelength spectrum corresponding to the electrode structure could be obtained. Chirp means not only shifting the wavelength of the reflection peak from the diffraction grating, but also controlling the shape of the reflection spectrum to an arbitrary shape. For example, a singular peak of Gaussian distribution is converted to a doublet or triplet, the half-width or peak intensity is changed, or a combination of the two is possible. Wave path diffraction gratings include tunable filters, WDM multiplexers / demultiplexers, dispersion compensators,
Application to a gain compensator or the like is possible.

In the present invention, the shape and the periodic structure of the electrodes are not limited to the structures shown in this embodiment, and any structure can be used. The folded portions of the electrodes need not be right angles, and arcs of any curvature can be used. It is needless to say that the same effect can be obtained by forming a heating electrode having a resistance value changed along the waveguide direction (for example, changing the width, thickness, or both of the electrodes).

(Embodiment 4) FIG. 7 shows a process for producing a film-like tunable polymer waveguide diffraction grating. A tunable polymer waveguide diffraction grating 71 as shown in FIG. 7A fabricated on a substrate in the same manner as in Example 1 was used as shown in FIG.
As shown in FIG. 7, a film-shaped tunable polymer waveguide diffraction grating 73 having self-holding properties and flexibility as shown in FIG. As a result of measuring the reflection spectrum of the film-like tunable polymer waveguide diffraction grating, it was found that the difference in the reflection peak wavelength due to the plane of polarization of the incident light was small and the polarization dependence was extremely small. The results show that the peeling and annealing of the substrate and the refractive index (n _TE ) in the polarization direction parallel to the substrate surface due to the residual stress in the fluorinated polyimide (due to the difference in thermal expansion coefficient with the substrate) and the substrate surface Refractive index in the direction of polarization perpendicular to (n _TM )
This is because the difference (birefringence) becomes small or almost zero. Further, the extinction ratio and the half width also showed the same characteristics as before the separation.

Further, the peeled film tunable polymer waveguide diffraction grating was placed in an oven at 350 ° C. for 1 hour.
Time annealing was performed. In this film tunable polymer waveguide grating, the birefringence was further reduced by annealing, the difference in the reflection peak wavelength was further reduced, and the polarization dependence was eliminated. Due to the polarization independence, the application of the tunable polymer waveguide diffraction grating to optical communication has greatly expanded.

The film-shaped tunable polymer waveguide diffraction grating has a large shift of the reflection peak wavelength of 10 nm or more due to external heating (100 ° C.) of the entire diffraction grating using a Peltier element as in the case of the substrate. The value was shown. Further, the film-shaped tunable polymer waveguide diffraction grating is used as a chirped diffraction grating by performing heating by applying a temperature gradient using a heating electrode having a period changed in the waveguide direction as shown in the third embodiment. Functioning, it was possible to obtain an arbitrary reflection wavelength spectrum without polarization.

This tunable polymer waveguide diffraction grating is excellent in flexibility due to the flexibility of polyimide, and can be tunable and chirped by bending the diffraction grating portion, so that it can be applied to a bending sensor and the like. it can.

[0030]

According to the present invention, the fluorinated polyimide used as a waveguide material has a large TO effect,
A tunable polymer waveguide diffraction grating having a large wavelength variable range of 10 nm or more and capable of performing chirping by heating with a temperature gradient can be provided. As a result, a tunable polymer waveguide diffraction grating that consumes low power, is economical, and has excellent versatility can be manufactured. The tunable polymer waveguide diffraction grating can be applied to a wavelength tunable filter, a WDM multiplexer / demultiplexer, a dispersion compensator, a gain compensator, and the like.

[Brief description of the drawings]

FIG. 1 is a manufacturing process diagram of a tunable polymer waveguide diffraction grating made of fluorinated polyimide.

FIG. 2 is a diagram of a tunable polymer waveguide diffraction grating installed on a sample stage on which a Peltier element is mounted.

FIG. 3 is a reflection spectrum diagram of a tunable polymer waveguide diffraction grating made of fluorinated polyimide.

FIG. 4 is a manufacturing process diagram of a tunable polymer waveguide diffraction grating with a heating electrode made of fluorinated polyimide.

FIG. 5 is a schematic view of a tunable polymer waveguide diffraction grating with a heating electrode.

FIG. 6 is a schematic view of a tunable polymer waveguide diffraction grating with a heating electrode.

FIG. 7 is a process chart for producing a film-like tunable polymer waveguide diffraction grating made of fluorinated polyimide.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Substrate 12 Lower cladding layer 13 Core layer 14 Mask pattern 15 Core pattern 16 Upper cladding layer 17 Transmissive X-ray mask 18 Diffraction grating 21 Tunable polymer waveguide diffraction grating 22 Peltier element mounted sample stand 23 Incident light 24 Light guide Waveguide 25 Incident end face 26 Diffraction grating 27 Reflected light 41 Tunable polymer waveguide diffraction grating 42 Optical waveguide 43 Ti metal film 44 Mask pattern 45 Electrode 51 Heating electrode fabricated on diffraction grating 52 Optical waveguide 61 Fabricated on diffraction grating Heating electrode 62 optical waveguide 71 tunable polymer waveguide diffraction grating 72 acid 73 film tunable polymer waveguide diffraction grating

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Toru Maruno 3-19-2 Nishishinjuku, Shinjuku-ku, Tokyo Nippon Telegraph and Telephone Corporation

Claims (7)

[Claims] 1. A tunable waveguide diffraction grating comprising a heating means using an external heat source and using a thermo-optic effect, wherein one or both of a core and a clad of the waveguide diffraction grating are made of a polymer material. Tunable polymer waveguide diffraction grating. 2. A tunable waveguide diffraction grating using a thermo-optic effect, comprising heating means using a resistor formed on the waveguide diffraction grating, wherein one of the core and the clad of the waveguide diffraction grating or A tunable polymer waveguide diffraction grating, wherein both are made of a polymer material. 3. The resistor according to claim 2, wherein the resistor has a shape repeatedly bent so as to intersect the optical axis, and one or both of the repetition width and the film thickness at each of the repeating portions of the resistor are set. A tunable polymer waveguide diffraction grating characterized by gradually changing into a chirp in the optical axis direction. 4. The tunable polymer waveguide diffraction grating according to claim 1, wherein the polymer material is a fluorinated polyimide. 5. The tunable polymer waveguide according to claim 1, wherein both surfaces of the diffraction grating portion made of the polymer material are formed in a self-holding shape so as not to contact any object. Wave grating. 6. A method of manufacturing a tunable polymer waveguide diffraction grating using a thermo-optic effect, comprising a heating means using an external heat source or a resistor formed on the waveguide diffraction grating, A method for manufacturing a tunable polymer waveguide diffraction grating, comprising: forming a diffraction grating made of a molecular material; and separating the diffraction grating from the substrate. 7. The method for manufacturing a tunable polymer waveguide diffraction grating according to claim 6, further comprising a step of heat-treating the diffraction grating separated from the substrate.