JP2007178791A - Fiber type narrow band wavelength selective filter - Google Patents

Abstract

A fiber-type narrowband wavelength selective filter that has low loss and can selectively transmit a plurality of narrowband signals and has a high degree of design freedom.
A fiber-type Fabry-Perot etalon that selectively transmits a plurality of narrowband signals, and a fiber grating that selectively blocks unnecessary signals among signals selected by the fiber-type Fabry-Perot etalon. Yes.
[Selection figure] None

Description

  The present invention relates to a fiber type narrow band wavelength selective filter that selectively transmits a narrow band signal of an arbitrary wavelength.

  In optical fiber communication, when there are a plurality of signals in a certain wavelength range and only a specific signal is transmitted, wavelength filters such as a dielectric multilayer filter, a Fabry-Perot etalon, and a fiber grating are used. In particular, Fabry-Perot etalon is used when the signal wavelength band is as narrow as 0.1 nm or less. However, spatial coupling is required, and there are practical problems with respect to loss and assembly cost. As means for solving these problems, a fiber Fabry-Perot etalon disclosed in Non-Patent Document 1 below is used.

IEICE “2005 General Conference Proceedings” p. 216 Issued March 7, 2005

  However, since the fiber-type Fabry-Perot etalon of Non-Patent Document 1 has a constant transmission wavelength interval, when transmitting only a specific signal, it is necessary to combine a plurality of fiber-type Fabry-Perot etalon, As a filter that transmits, there is a problem that the degree of freedom in design is low.

  Accordingly, an object of the present invention is to provide a fiber-type narrowband wavelength selective filter that has low loss and can selectively transmit a plurality of narrowband signals and has a high degree of design freedom.

  The fiber-type narrowband wavelength selective filter of the present invention selectively selects an unnecessary signal among a fiber-type Fabry-Perot etalon that selectively transmits a plurality of narrowband signals and a signal selected by the fiber-type Fabry-Perot etalon. And a fiber grating for blocking.

  According to the present invention, it is possible to provide a fiber-type narrowband wavelength selective filter with low loss and capable of selectively transmitting a plurality of narrowband signals and having a high degree of design freedom.

  Hereinafter, a fiber type narrow band wavelength selective filter according to an embodiment of the present invention will be described with reference to the drawings. The fiber type narrowband wavelength selective filter of the present embodiment selectively selects an unnecessary signal from the fiber type Fabry-Perot etalon that selectively transmits a plurality of narrowband signals and the signal selected by the fiber type Fabry-Perot etalon. And a fiber grating for blocking.

  The fiber type Fabry-Perot etalon is a transmission type narrow band wavelength filter. This fiber-type Fabry-Perot etalon, for example, heat-stretches a base material while inserting a single-mode optical fiber into the central axis of a cylindrical crystallized glass base material, and fuses the optical fiber inside the crystallized glass. Can be produced.

  The fiber grating is a device that reflects (cuts off) only a specific wavelength corresponding to the period, utilizing a phenomenon called light-induced refractive index change that increases the refractive index when an optical fiber is irradiated with ultraviolet rays. This fiber grating is formed by forming interference fringes by ultraviolet rays irradiated from the side surface on an optical fiber made of quartz or the like, and writing the pattern of the interference fringes into the optical fiber by light-induced refractive index change. Some are based on the beam interference method and some are based on the phase mask method.

  In the two-beam interference method, as shown in FIG. 1, irradiation light 12 having a predetermined wavelength such as ultraviolet rays is divided into two directions by a beam splitter 13, reflected by mirrors 14 and 15, and irradiated onto the core 11 of the optical fiber. In this method, the interference fringes 16 are formed by the interference of light to give a periodic refractive index change. The light source requires irradiation light 12 such as a laser having high coherence. However, since a fiber grating having an arbitrary reflection wavelength can be manufactured by changing the incident angle of irradiation light 12, the degree of freedom in manufacturing is higher than that of the phase mask method. high.

  For example, as shown in FIG. 2, the phase mask method has a predetermined wavelength such as ultraviolet rays through a phase mask (phase mask) 23 in which a diffraction grating composed of grooves 22 is formed with a period twice that of the interference fringe 21. In this method, interference light 24a is generated by irradiating the irradiation light 24 onto the core 25 of the optical fiber to form an interference pattern. Note that this method requires a plurality of phase masks corresponding to the grating period, which is disadvantageous in cost compared to the two-beam interferometry, but provides stable characteristics and is excellent in mass productivity. , Often used.

  By these methods, a wavelength called a uniform grating having a constant period in the longitudinal direction of the fiber has a sharp peak wavelength characteristic (in the case of the optical fiber cores 11 and 254 in FIGS. 1 and 2), and the period changes in the longitudinal direction. It is possible to form various types of gratings such as a chirped grating having a wide-band waveform (optical fiber core 32 having interference fringes 31 in FIG. 3).

  Next, a fiber type narrow band wavelength selective filter according to an embodiment of the present invention will be described with reference to the drawings.

  The fiber type Fabry-Perot etalon used in the examples according to the present invention is manufactured by Nippon Electric Glass Co., Ltd. (similar to the FIX-FFPE described in Non-Patent Document 1 above). FIG. 4 shows a graph of the waveform of the transmission spectrum in this fiber type Fabry-Perot etalon. From this graph, it can be seen that a plurality of narrowband signals can be selectively transmitted with low loss.

  The fiber grating used in the example according to the present invention was the one disclosed in Example 1 of JP-A-2005-181980. FIG. 5 shows a graph of the waveform of the reflection spectrum in the fiber grating used in this example.

  FIG. 6 is a graph showing a spectrum of a fiber type narrow band wavelength selective filter according to an embodiment of the present invention. The graph of FIG. 6 is the same as the composite of the transmission spectrum of the fiber Fabry-Perot etalon in FIG. 4 and the reflection spectrum of the fiber grating in FIG. Therefore, it can be seen that a specific signal can be selected and transmitted among the signals obtained by collapsing the fiber Fabry-Perot etalon with low loss.

  The present invention can be changed in design without departing from the scope of the claims, and is not limited to the above-described embodiments and examples.

It is a figure for demonstrating the two-beam interferometry of the formation method of a fiber grating. It is a figure for demonstrating the phase mask method of the formation method of a fiber grating. It is a figure which shows the chirped grating formed by the two-beam interference method or the phase mask method. It is a graph which shows the waveform of the transmission spectrum in the fiber type Fabry-Perot etalon used in the Example of this invention. It is a graph which shows the waveform of the reflection spectrum in the graph of FIG. 1, and the fiber grating used in the Example of this invention. It is a graph which shows the waveform of the spectrum of the fiber type narrow band wavelength selective filter which concerns on the Example of this invention.

Explanation of symbols

11, 25, 32 Core 12, 24 Irradiation light 13 Beam splitter 14, 15 Mirror 16, 21, 31 Interference fringe 22 Groove

Claims (1)

A fiber Fabry-Perot etalon that selectively transmits multiple narrowband signals;
A fiber type narrow band wavelength selective filter, comprising: a fiber grating for selectively blocking unnecessary signals among signals selected by the fiber type Fabry-Perot etalon.

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