JP3346440B2 - Manufacturing method of transmission type fiber grating filter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates are those which relate to the production how the transmission fiber grating filter that realizes only by the grating on the optical fiber bandpass filter.

[0002]

2. Description of the Related Art It has been known that a fiber grating filter having a narrow band and excellent wavelength selectivity can be obtained by irradiating the core of an optical fiber with ultraviolet rays to form a grating. However, a normal fiber grating filter is a reflection type filter, and since it must be used together with a fiber coupler or an optical circulator to use it as a transmission type filter, that is, a bandpass filter, it is compared with a dielectric multilayer filter. Therefore, there is a problem that the structure is complicated, miniaturization is difficult, and the cost is high.

On the other hand, as an attempt to realize a band-pass filter using only a grating on an optical fiber (hereinafter referred to as a transmission fiber grating filter), when a chirp grating is formed by a two-beam interference exposure system, There is a report that a part of an exposed part is shielded to form a missing part in a chirped grating to obtain transmission of light of a wavelength corresponding to the part (for example, Electronics Letters, Vol. 30, No. 11). , 199
4, MCFarries et al., "Very broad reflection band
width (44nm) chirped fiber gratings and narrow bandp
ass filters produced by the use of an amplitude ma
sk ", pp. 891-892).

[0004]

However, in the above-described method, when an attempt is made to form a chirped grating in a wide wavelength range, it is necessary to expand the ultraviolet beam.
For this reason, there is a problem that the effect of the aberration of the focusing lens is greatly affected, and good characteristics cannot be obtained.

An object of the present invention is to provide a way capable of producing a good transmission fiber grating filter characteristics.

[0006]

FIG. 1 shows an outline of an apparatus for carrying out a method of manufacturing a transmission type fiber grating filter according to the present invention. In FIG.
2 is a mirror, 3 is a shielding plate, 4 is a phase shift mask, 5 is an optical fiber, and 6 is a fixed base.

Generally, the grating formed on the core of the optical fiber 5, that is, the reflection wavelength λ _B of the fiber grating is represented by λ _B = 2nΛ (1). Here, n is the refractive index of the core, and Λ is the pitch of the grating.

[0008] By the way, if the pitch of the mask pattern of the phase shift mask 4 and Λ _PM, a relationship of _{2Λ = Λ PM ...... (2)} . Therefore, when forming the fiber grating through the phase shift mask 4 becomes _{λ B = nΛ PM ...... (3} ). Therefore, when the phase shift mask 4 having a mask pattern in which the pitch Λ _PM changes linearly is used, a chirped grating is formed.

Therefore, if a sufficiently thin shielding plate 3 is previously placed on the phase shift mask 4 or is sandwiched between the phase shift mask 4 and the optical fiber 5, a portion where no grating is formed occurs, and light of a wavelength corresponding to the grating is formed. Is transmitted.

[0010] In addition, when the laser beam diameter is appropriately narrowed and scanning irradiation is performed, if the irradiation is intentionally interrupted at a certain portion,
A portion where no grating is formed occurs, and light having a wavelength corresponding to the portion is transmitted.

If a predetermined pitch is deleted in advance in the phase shift mask 4 having a mask pattern in which the pitch Λ _PM changes linearly, when a chirp grating is formed, light having a wavelength corresponding to the missing pitch is generated. The light passes through without being reflected (however, in this case, the wavelength to be transmitted cannot be changed unless the phase shift mask is replaced).

The grating formed in the core of the optical fiber 5 by the light-induced refractive index change does not disappear in a normal environment. The refractive index also increases where no index change occurs, the periodic change in the refractive index decreases, and eventually all the refractive indexes become uniform, and the grating disappears. Therefore, when a predetermined portion is irradiated with ultraviolet light as it is after the formation of the chirped grating, the grating in that portion disappears, and light of the corresponding wavelength passes without being reflected.

[0013]

According to the present invention, when a chirped grating is formed in an optical fiber using a phase shift mask having a mask pattern whose pitch changes linearly, a portion corresponding to the wavelength to be transmitted can be omitted. Thus, a transmission type fiber grating filter having good characteristics can be manufactured.

[0014]

FIG. 2 shows a state in which a chirped grating is formed by the apparatus shown in FIG. 1. A phase shift mask 4 having a mask pattern 4a having a linearly changing pitch is fixed to an optical fiber 5 in close contact therewith. Then, a case where a chirp grating is formed by irradiating the ultraviolet laser light 7 is considered.

In order to widen the reflection wavelength range, it is necessary to make the chirp grating sufficiently long. It is desirable to move the optical fiber 5 at a constant speed in the longitudinal direction or to move the mirror 2 that reflects the ultraviolet laser light 7 to perform scanning irradiation.

By irradiating the ultraviolet laser light 7 from one end to the other end of the mask pattern 4a of the phase shift mask 4, a chirped grating having the same length as the mask pattern 4a is formed. FIG. 3 shows the reflection spectrum at this time, where λ _S is the shortest wavelength and λ _L is the longest wavelength.

Here, the X-axis is set in the center axis direction of the optical fiber 5 with the end corresponding to the shorter wavelength side of the mask pattern 4a as the origin, and the length of the mask pattern 4a (the length of the grating) is set to L. Then, the reflection wavelength of an arbitrary portion P (x) on the grating is represented by λ _B (P) = (λ _L −λ _S ) x / L + λ _S (4) Therefore, when the wavelength to be transmitted is determined, the portion P (x) is determined in reverse to the equation (4).

Therefore, as shown in FIG. 4, when the shielding plate 3 is disposed on the portion P on the optical fiber and the ultraviolet laser beam 7 is irradiated, a chirped grating 8 in which the grating is missing is formed. The light of the wavelength corresponding to the portion passes. Note that this transmission wavelength is λ
_It can be set arbitrarily between _S and λ _L.

Assuming that the length of the missing portion is Δx, the transmission band Δλ _B is given by Δλ _B = (λ _L −λ _S ) Δx / L (5) Therefore, to control the Δx by adjusting the width of the shielding plate 3 can be adjusted a transmission band [Delta] [lambda] _B. The reflection spectrum at this time is as shown in FIG.
There is no reflection in the vicinity of _B because light is transmitted.

In the present invention, a transmission type fiber grating filter is manufactured in this way. When a chirp grating is formed using a phase shift mask,
Unlike the case of the two-beam interference exposure system, the length L of the grating can be increased in principle, so that the transmission band Δλ _B can be made sufficiently small, and the transmission wavelength can be accurately controlled.

For example, when the pitch is from 1.03 μm to 1.1
If a phase shift mask having a mask pattern having a length of 20 mm that changes linearly to 0 μm is used, the wavelength becomes 1.5 μm.
20 mm long with reflection band from m to 1.6 μm
Are formed on the dispersion-shifted fiber. At this time, as shown in FIG.
If a 1 mm shielding plate is arranged at a position of x = 10 mm on the phase shift mask and irradiated with ultraviolet laser light, the wavelength becomes 1.
A filter having a light transmission band of 55 μm and a width of 5 nm is realized. FIG. 6 shows the reflection spectrum.

Further, when a shielding plate of Δx = 1 mm is x = 4,
By irradiating ultraviolet laser light at a position of 8, 12, or 16 mm, wavelengths of 1.52, 1.54, 1.56,.
A filter having a light transmission band of 58 μm and a width of 5 nm is realized. FIG. 7 shows the reflection spectrum.

[0023]

As described above, according to the present invention, when a chirped grating is formed on an optical fiber using a phase shift mask, a portion corresponding to a predetermined wavelength, that is, a wavelength to be transmitted, is missing. Since a chirped grating can be formed, a transmission type fiber grating filter having good characteristics can be manufactured. Current,
Wavelength multiplexing transmission is promising as one of the methods for increasing the capacity of optical transmission lines, and wavelength conversion technology using four-wave mixing, which is a nonlinear optical effect, has recently been receiving attention. Requires a narrow-band bandpass filter. Therefore, according to the present invention, it is considered that the cost can be suppressed lower than that of a filter using a conventional dielectric multilayer film, and mass production becomes possible.

[Brief description of the drawings]

FIG. 1 is a diagram showing an outline of an apparatus for implementing a method of manufacturing a transmission type fiber grating filter of the present invention.

FIG. 2 is a diagram showing how a chirp grating is formed on an optical fiber using a phase shift mask.

FIG. 3 is a diagram illustrating an example of a reflection spectrum of a chirp grating.

FIG. 4 is a diagram showing how a chirped grating is formed according to the present invention.

FIG. 5 is a diagram showing a reflection spectrum of a chirp grating having a light transmitting portion.

FIG. 6 is a diagram showing an example of a reflection spectrum of a transmission type fiber grating filter according to the present invention.

FIG. 7 is a diagram showing another example of the reflection spectrum of the transmission type fiber grating filter according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Ultraviolet laser light source, 2 ... Mirror, 3 ... Shielding plate, 4 ...
Phase shift mask, 4a: mask pattern, 5: optical fiber, 6: fixed base, 7: ultraviolet laser beam, 8: chirp grating.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-52-48334 (JP, A) UK Patent Application Publication 2272075 (GB, A) FARRIES, M.A. C. et al. , Very broad reflection bandwidth (44 nm), chipped fiber gratings and near bandpass filters produced, ELECTRON ICS LETERS, UK, IE, May 26, 1994, IEol. 30 No. 11, p. 891-892 MARTIN, J.M. et al. , Novel writing technique of long and high reflexive in-fibre gratings, ELECTRONICS LETTER S, United Kingdom, IEEE, May 12, 1994, Vol. 30 No. 10, p. 811-812 (58) Field surveyed (Int. Cl. ⁷ , DB name) G02B 6/00-6/02 G02B 6/10 G02B 6/16-6/22 G02B 6/44 JICST file, JQUICK file ( JOIS) IEEE / IEEE ELECTRONI C LIBRARY

Claims (1)

(57) [Claims] 1. A mask pattern whose pitch changes linearly.
A phase shift mask with
And the length of the phase shift mask
UV laser light is radiated at a constant speed along the direction, and the phase shift mask is removed from the mask pad of the optical fiber.
UV only at the pitch corresponding to the predetermined wavelength of the turn
Transmission type irradiating the X-ray laser light again
Manufacturing method of ibug rating.