JP2007292947A - Method and apparatus of measuring optical waveguide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To shorten the waveguide loss estimation time of an optical waveguide for shortening the depelopment process of the optical waveguide. <P>SOLUTION: The estimation time is shortened, by simultaneously manufacturing optical waveguides having different lengths, and using an optical fiber array having the same interval and the same cut angle as those of the optical waveguide. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method and a measurement apparatus that are mainly used in optical products and can easily measure the waveguide loss value of an optical waveguide.

  In recent years, the development of information communication technology has been remarkable, and optical communication is an indispensable communication means for next-generation broadcasting because it has excellent features such as ultra-high speed and large capacity. Also, in terms of infrastructure, a high-speed communication service “FTTH (Fiber to the home)” for laying optical fibers to homes is provided, and the number of subscribers is increasing. In order to spread the optical fiber network, a device including an optical waveguide such as an optical multiplexer / demultiplexer or an optical switch (hereinafter referred to as an optical waveguide device) is a key device.

An optical waveguide device is a circuit component for processing such as multiplexing and demultiplexing of a communication optical signal, and is used in combination with a communication optical fiber or a light emitting / receiving element. Therefore, the communication characteristics of the optical waveguide device have an important role in determining the characteristics of the optical signal processing module such as the band and the signal intensity. The optical waveguide device has, in its configuration, a portion where the refractive index is higher than that of the surroundings (hereinafter referred to as an optical waveguide or a core) and a portion surrounding the core (hereinafter referred to as a clad). The main optical waveguide fabrication methods are (1) a method using photolithography and anisotropic etching, (2) a stamp-type replication fabrication method using a transparent material such as metal or quartz, and (3) UV-curing resin mask exposure. For example, a direct exposure method for curing by the above method may be used.

The optical characteristics evaluated after the above-described optical waveguide is manufactured include, for example, a connection loss value indicating attenuation of signal intensity at a connection point between the optical fiber and the optical waveguide, and a unit length when the optical signal propagates through the optical waveguide. For example, a waveguide loss value indicating signal strength attenuation per hit. As a method for measuring the waveguide loss value, for example, the length of the same waveguide is gradually shortened by cutting for each measurement, and the unit loss is obtained from the slope of the linear regression curve of the insertion loss value at each length. There is a cut back method for calculating a waveguide loss value and calculating a connection loss value from an intercept of the linear regression curve (for example, Non-Patent Document 1).
Nishihara Hiroshi, Haruna Masamitsu, Sugawara Toshiaki, “Optical Integrated Circuits”, revised edition, Ohm, August 1993, p263

  As the above-described optical waveguide device, for example, a wavelength demultiplexer that demultiplexes an optical signal obtained by multiplexing a plurality of optical signals having different wavelengths into light of each wavelength, or a single optical signal into a plurality of optical signals. Therefore, there is a demand for optical waveguide devices having various functions such as a branching device that branches at an arbitrary strength. The waveguide loss value indicating the optical signal intensity attenuated per unit length varies depending on the material used for waveguide fabrication, the waveguide fabrication process, etc., and determines the length of the optical waveguide that can be manufactured in the design of the optical waveguide device. It becomes a big element.

  However, the conventional method for measuring the waveguide loss value of an optical waveguide is to shorten the length of the same optical waveguide by a certain length by cutting, and measure the loss at each waveguide length. Therefore, there has been a problem that it takes time to repeat cutting and alignment / measurement, resulting in a long measurement time.

  In view of the above circumstances, an object of the present invention is to provide a measurement method and a measurement apparatus that reduce the waveguide loss evaluation time of an optical waveguide in order to shorten the development process of the optical waveguide device.

  The method for measuring an optical waveguide of the present invention that has solved the above-described problem is that a plurality of optical waveguides having different waveguide lengths are formed on the same substrate, an insertion loss value of each optical waveguide is measured, and each optical waveguide is measured. From this measurement result, the gist is obtained by calculating the waveguide loss value of the optical waveguide per unit length.

  The optical waveguide measurement apparatus of the present invention includes a substrate unit on which a measurement target substrate in which a plurality of optical waveguides having different waveguide lengths are formed on the same substrate, and measurement light connected to the substrate unit. The incident portion or the light receiving portion is formed at the end portion of each optical waveguide, and the incident portion or the light receiving portion is connected to the one end of the optical waveguide to be measured. Measuring the loss value of the optical waveguide by measuring the light intensity of the measurement light when the measurement light is incident from the incident part and the light reception part is connected, and the loss value is measured in a plurality of ways. The gist of the present invention is that of the optical waveguide.

  In the measurement method of the present invention, since optical waveguides having different lengths can be produced at a time, it is possible to reduce the time required for waveguide loss measurement. In addition, the evaluation time can be further shortened by using a measuring device capable of simple evaluation including an optical fiber array having the same waveguide interval and cutting angle as the optical waveguide.

  The waveguide loss measurement method using the optical waveguide measurement method of the present invention cuts the substrate at an arbitrary angle with respect to the waveguide direction of the optical waveguide, and produces a plurality of optical waveguides having different lengths at a time. A step of measuring a waveguide loss value using the optical waveguide, and a step of calculating a waveguide loss value per unit length from the measurement result.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments relating to the optical waveguide measuring method of the present invention will be described in detail below with reference to the drawings.

  First, a process of manufacturing a plurality of optical waveguides having different waveguide lengths at once will be described. FIG. 1 is a perspective view of an original optical waveguide sample to be measured, and FIG. 2 is a perspective view of the optical waveguide to be measured.

  The optical waveguide 1 includes a substrate (not shown), a core 2, and a clad 3. In this embodiment, as shown in FIG. 1, a rectangular optical waveguide sample is used as viewed from above. Note that five cores 2 are formed and have a parallel positional relationship (see FIG. 3 which is a plan view of the optical waveguide of FIG. 2 cut in the plane direction for the positional relationship of the cores 2). One waveguide end face of the optical waveguide 1 is cut by a precision cutting device such as a dicing saw with a cut surface 4 having an arbitrary angle θ. As a result, as shown in FIG. 2, the optical waveguide 1 having a pair of non-parallel waveguide end faces is formed, and five optical waveguides (cores 2) having different waveguide lengths are produced at one time. The waveguide length of each optical waveguide (core 2) is the same as that of the two waveguides (core 2) adjacent to the angle θ of the cut surface 4 when each optical waveguide (core 2) is formed in parallel. It is determined by the distance (hereinafter referred to as pitch). The waveguide length of each optical waveguide (core 2) is not particularly limited, and the angle θ may be appropriately selected according to the number of measurements (number n) and the pitch. In the present embodiment, the cut surface 4 is formed with the angle θ in the range of 5 ° to 60 °. Although the loss values were measured at various cutting angles, it was confirmed that the dependency of the loss values on the cutting angle θ was not recognized (see FIG. 4).

  Next, the process of measuring the waveguide loss value of the optical waveguide shown in FIG. 2 will be described. As shown in FIG. 3, the waveguide loss value measurement process in the present embodiment is first measured at one end of one of the cores 2 of the optical waveguide 1 (the left end in FIG. 3 as viewed from the top of the paper). The optical fiber 5 for installation is installed, and the optical fiber 6 for light reception is installed at the other end (upward side in FIG. 3). Next, measurement light having an arbitrary light intensity is incident on the core 2 of the optical waveguide 1 from the measurement optical fiber 5, and the measurement light propagated in the core 2 is received by the light reception optical fiber 6 to measure the insertion loss value. To do. In FIG. 3, this measurement is repeated five times, and the insertion loss value of each optical waveguide (each core 2) is measured.

  Although not shown, a measurement optical fiber array in which five measurement optical fibers are formed in an array and a light reception optical fiber array in which five light reception optical fibers are formed in an array are used. The number of measurements may be one. The number of measurements and the number of optical fibers in the optical fiber array are not particularly limited, and may be determined as necessary.

  Further, the type, core diameter, numerical aperture (NA), incident mode, etc. of the measurement optical fiber 5 and the light receiving optical fiber 6 are not particularly limited, and are appropriate according to the wavelength used for measurement and the NA of the optical waveguide. May be used. The core diameter of the measurement optical fiber 5 is preferably smaller than the core diameter of the core 2 of the optical waveguide 1 on the incident side, and the core diameter of the optical fiber 6 for reception is larger than the core diameter of the core 2 of the optical waveguide 1. An optical fiber having

  Further, the clad diameter of the measurement optical fiber 5 is not particularly limited, but a gap may be formed between the core of the light receiving optical fiber 6 and the core 2 of the optical waveguide 1 depending on the angle θ of the cut surface 4. End up. That is, there is a possibility that the cladding of the light receiving optical fiber 6 is in contact with the cladding 3 of the optical waveguide 1 and the core of the light receiving optical fiber 6 and the core 2 of the optical waveguide 1 cannot be sufficiently close to each other. In consideration of this configuration, the cladding diameter of the light receiving optical fiber 6 is preferably small. In addition, when a gap arises between the optical waveguide 1 and the optical fiber 6 for light reception, what is necessary is just to fill the gap with the refractive index adjustment liquid etc. with an appropriate refractive index. For example, the diameter of the core 2 is 70 μm (NA 0.39), the core diameter of the measurement optical fiber 5 is 50 μm (cladding diameter 125 μm, NA 0.22), the core diameter of the light receiving fiber 6 is 200 μm (cladding diameter 230 μm, NA 0.48), As a result of the measurement, it has been found that the relationship between the angle θ of the cut surface 4 and the waveguide loss value in the case of using a refractive index adjusting liquid having a refractive index of 1.56 is almost independent of the angle θ (see FIG. 4). reference).

  Next, a process of calculating a waveguide loss value per unit length from the measurement result will be described. As described above, after measuring the waveguide loss value of each optical waveguide having a plurality of different waveguide lengths, the waveguide loss value per unit length is determined from the slope of the linear regression curve of the insertion loss value at each length. In addition, a connection loss value is calculated from the intercept of the linear regression curve. When five optical waveguides as shown in FIG. 3 are formed, after measuring five insertion loss values, the optical waveguide 1 (core 2) is determined from the slope of the linear regression curve of the insertion loss value at each length. The waveguide loss value of is obtained.

  Next, an optical waveguide measuring device will be described. The measuring device is not particularly limited, but for example, a multi-channel measuring device including the measuring optical fiber array and the receiving optical fiber array, or measuring according to the pitch of the optical waveguide 1 and the angle θ of the cut surface 4. It is preferable to use an automatic alignment device provided with an optical fiber moving mechanism for moving the optical fiber 5 and the light receiving optical fiber 6.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated, this invention is not limited to these.

Example << Cut optical waveguide >>
A polymer optical waveguide having a core diameter of 70 μm was fabricated on a silicon wafer. The length of the optical waveguide was 42.5 mm. Using a dicing saw, a trapezoidal measurement sample having a θ of 45 degrees was cut from the silicon wafer substrate. An interval between the waveguides (cores) was 250 μm, and an optical waveguide in which the waveguides (cores) whose length changed from 42.5 mm to 23 mm was formed at intervals of 250 μm was produced by a single cutting operation.

<< Measurement of waveguide loss in optical waveguide >>
Using the above measurement sample having a maximum length of 42.5 mm, waveguide loss was measured with a light source having a wavelength of 850 nm. For comparison, a conventional cutback method was also used for evaluation using the same substrate. The results are shown in FIG. The waveguide loss value was calculated to be 0.08 dB / cm in the method of the present invention, and 0.09 dB / cm in the cutback method (measured with respect to the waveguide 1 and the waveguide 2).

It is a perspective explanatory view explaining the optical waveguide measuring method of the present invention. It is an isometric view explanatory drawing of the measurement sample of the optical waveguide measuring method of the present invention. It is the top view which looked at the surface direction cross section of the measurement sample of FIG. 2 from the top. It is a graph which shows the angle ((theta)) dependence of the insertion loss in the optical waveguide measuring method of this invention. It is a graph which shows the measurement result of the insertion loss in the optical waveguide measuring method of the present invention, and the measurement result of the insertion loss in the cutback method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical waveguide 2 Optical waveguide core 3 Optical waveguide clad 4 Optical waveguide cut surface 5 Optical fiber for measurement 6 Optical fiber for light reception

Claims (5)

Forming multiple optical waveguides with different waveguide lengths on the same substrate,
Measure the insertion loss value of each optical waveguide,
A method for measuring an optical waveguide, comprising: calculating a waveguide loss value of the optical waveguide per unit length from a measurement result of each optical waveguide.   The method for measuring an optical waveguide according to claim 1, wherein the optical waveguides are formed in parallel.   3. The method of measuring an optical waveguide according to claim 2, wherein each of the optical waveguides is manufactured at a time by cutting the substrate at an arbitrary angle with respect to the optical axis direction of the optical waveguide. A substrate unit on which a substrate to be measured in which optical waveguides having different waveguide lengths are formed on the same substrate;
The measuring light incident portion and the light receiving portion connected to the substrate unit,
A connection structure of the incident part or the light receiving part is formed at the end of each optical waveguide,
The incident portion is connected to one end of the optical waveguide to be measured, the light receiving portion is connected to the other end, the measurement light is incident from the incident portion, and the light intensity of the measurement light is measured by the light receiving portion. To measure the loss value of the optical waveguide,
An apparatus for measuring an optical waveguide, wherein the loss value is measured by a plurality of the optical waveguides.   The optical waveguide measuring device according to claim 4, wherein a plurality of the incident portions and the light receiving portions are provided.

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