JP5360399B2 - Diffraction grating phase mask - Google Patents

Description

  The present invention relates to a phase mask for producing a diffraction grating, and in particular, a phase mask for producing a fine diffraction grating on the surface or inside of a photosensitive material such as a photoresist, or an ultraviolet laser in an optical fiber used for optical communication or the like. The present invention relates to a phase mask for producing a diffraction grating using light.

  In the following, the production of an optical fiber diffraction grating will be described as an example.

  Optical fiber has revolutionized global communications, enabling high-quality, high-capacity transoceanic telephone communications, but conventionally, a refractive index profile has been created periodically in the core along this optical fiber, A black diffraction grating, and the wavelength of the diffraction grating for optical communication is determined by determining the reflectivity level and width of the wavelength characteristics according to the period and length of the diffraction grating and the size of the refractive index modulation. It is known that it can be used as a splitter, a narrow-band high-reflection mirror used for a laser or a sensor, a wavelength selection filter for removing an extra laser wavelength in an optical fiber amplifier, and the like.

  However, since the attenuation of quartz optical fiber is minimized and the wavelength suitable for the long-distance communication system is 1.55 μm, in order to use the optical fiber diffraction grating at this wavelength, the grating interval needs to be about 500 nm. It is said that it is difficult to make such a fine structure in the core at first, and side polishing, photoresist process, holographic exposure, reactive ions are used to create a black diffraction grating in the core of the optical fiber. Many stages of complicated processes, such as beam etching, were taken. For this reason, the production time was long and the yield was low.

  However, recently, a method of irradiating an optical fiber with an optical fiber and directly changing the refractive index in the core to make a diffraction grating has been known, and this method of irradiating the ultraviolet light does not require a complicated process. It has come to be implemented gradually as technology advances.

  In the case of this method using ultraviolet light, since the grating interval is as small as about 500 nm as described above, an interference method in which two light beams interfere with each other (a single diffraction grating surface is formed by condensing a single pulse from an excimer laser). There are a method of writing each point), a method of irradiating using a phase mask having a grating, and the like.

  The interference method that causes the two light beams to interfere with each other has a problem in the quality of the beam in the lateral direction, that is, spatial coherence, and the method of writing by each point requires precise step control of submicron size. In addition, it is required to write a lot of surfaces by taking in a small amount of light, and there is a problem in workability.

For this reason, an irradiation method using a phase mask has been attracting attention as a method that can cope with the above problem. However, as shown in FIG. 1A, this method has a concave groove on one surface of a quartz substrate. Using a phase mask 21 provided at a predetermined depth with a predetermined repetition period, KrF excimer laser light (wavelength: 248 nm) 23 is irradiated onto the mask 21 to directly change the refractive index of the core 22A of the optical fiber 22. A grating (grating) is produced. In FIG. 1A, the interference fringe pattern 24 in the core 22A is shown in an easily enlarged manner. FIG. 1B and FIG. 1C show a sectional view of the phase mask 21 and a part of a top view corresponding thereto. The phase mask 21 has a binary phase type diffraction grating-like structure in which a concave groove 26 having a repetition period Λ and a depth d is provided on one surface, and a ridge 27 having substantially the same width is provided between the concave grooves 26. It is.

  The depth d of the groove 26 of the phase mask 21 (the difference in height between the ridge 27 and the groove 26) d is selected so as to modulate the phase of the excimer laser beam (beam) 23 as the exposure light by π radians. The 0th-order light (beam) 25A is suppressed to 5% or less by the phase mask 21, and the main light (beam) emitted from the mask 21 includes the plus-first-order diffracted light 25B including 35% or more of the diffracted light. And the first-order diffracted light 25C. Therefore, irradiation of interference fringes with a predetermined pitch is performed by the plus first-order diffracted light 25B and minus first-order diffracted light 25C, and a refractive index change at this pitch is brought into the optical fiber 22.

JP 2009-103786 A

“SPIE” Vol. 883 (1988), p. 8-11 “Holography” written by Junpei Takiuchi (published on November 5, 1997, Ryokabo Inc.), p. 55

  The cross-sectional shape of the phase mask 21 is such that the depth d of the groove 26 shifts the phase of the exposure light 23 having the wavelength λ by π radians as described above, and the width w of the ridge 27 and the repetition period Λ. It is said that the diffraction efficiency of the 0th-order light component 25A is minimized when the duty ratio f of the ridge 27 defined by the ratio w / Λ is 0.5 (scalar diffraction theory).

  However, if the period becomes the wavelength order due to the miniaturization of the repetition period, the 0th-order light component 25A is transmitted by several percent or more. Therefore, the 0th-order light component 25A becomes noise during transfer, and the transferred optical waveguide diffraction There was a problem that noise was generated in the reflection spectrum of the grating.

  Furthermore, especially when the pitch approaches the exposure wavelength or when a high refractive index is used for the phase mask material, there is a problem that the transmitted zero-order light 25A cannot be reduced to 0%, or the transmitted ± first-order lights 25B and 25C are reduced. is there. That is, when the pitch approaches the exposure wavelength, the transmission zero-order light 25A cannot be gradually reduced to 0%, or the transmission ± first-order light 25B, 25C is reduced. In Patent Document 1, a high refractive index is used for the phase mask material. However, on the other hand, there is a problem that the efficiency of the reflected light is increased and the transmitted ± first-order light 25B and 25C is reduced, or the transmitted zero-order light cannot be reduced to 0% again at a smaller pitch.

  The present invention has been made in view of such problems of the prior art, and its purpose is to minimize the zero-order light component that is transmitted without being diffracted and to increase the diffraction efficiency of the transmitted ± first-order light as much as possible. Another object of the present invention is to provide a diffraction grating manufacturing phase mask in which noise is not generated in the reflection spectrum of a diffraction grating of an optical waveguide such as a transferred optical fiber.

The phase mask for producing a diffraction grating of the present invention that achieves the above object is provided with a repetitive pattern of concave grooves and ridges having a substantially rectangular cross section in the form of a grating on one surface of a transparent substrate, and transmission ± primary light by the repetitive pattern In the phase mask in which the diffraction grating is formed in the photosensitive material by the interference, the cross-sectional shape dimensions of the repetitive pattern of the concave groove and the convex stripe are d: groove depth of the concave groove, w: width of the convex stripe, Λ: repeating Period, λ: exposure wavelength, n ₂ : refractive index of transparent substrate, n ₁ : refractive index of surrounding (atmosphere or liquid), d ₀ = λ / {2 (n ₂ −n ₁ )}, f = w / Λ , Λ ′ = Λ / λ, and n ₁ Λ ′, n ₂ / n ₁ , d / d ₀ , f are the following conditional expressions (1) to (3), (5), (6) It is characterized by satisfying.

In the interval 1.0 <n ₁ Λ ′ <2.2, where 1.0 <n ₁ Λ ′ ≦ 1.5,
-23.150 (n ₁ Λ ′) ⁵ + 83.283 (n ₁ Λ ′) ⁴ −65.102 (n ₁ Λ ′) ³
−78.080 (n ₁ Λ ′) ² +131.966 n ₁ Λ ′ −46.905
≦ n ₂ / n ₁ ≦ 118.085 (n ₁ Λ ′) ⁵ −510.61 (n ₁ Λ ′) ⁴
+638.55 (n ₁ Λ ′) ³ +78.771 (n ₁ Λ ′) ² −642.31 n ₁ Λ ′ +321.06
... (1)
Section 2 in the range of 1.0 <n ₁ Λ ′ <2.2: 1.5 <n ₁ Λ ′ ≦ 1.9
13.239 (n ₁ Λ ′) ³ −64.220 (n ₁ Λ ′) ² +103.117 n ₁ Λ ′ −53.40
≦ n ₂ / n ₁ ≦ 61.5374 (n ₁ Λ ′) ⁶ −385.3323 (n ₁ Λ ′) ⁵
+328.953 (n ₁ Λ ′) ⁴ +2844.835 (n ₁ Λ ′) ³ −8978.233 (n ₁ Λ ′) ²
+ 10245.56n ₁ Λ ′ −4207.135 (2)
Section 3 in the range 1.0 <n ₁ Λ ′ <2.2: For 1.9 <n ₁ Λ ′ <2.2,
^{_{10.443 (n 1 Λ ') 2}} -42.926n 1 Λ' +45.36
≦ n ₂ / n ₁ ≦ -8.393 (n ₁ Λ ′) ² +32.374 n ₁ Λ ′ −29.674 (3)
And,
In the range of 1.0 <n ₁ Λ ′ <2.2,
2.8090 + 0.7790 / {(n ₁ Λ ′ + 4.7488) (n ₂ / n ₁ −1.1687)}
≦ d / d ₀ ≦
3.6885 + 0.1488 / {(n ₁ Λ ′ + 2.6126) (n ₂ / n ₁ −1.1233)} (5)
And,
In the range of 1.0 <n ₁ Λ ′ <2.2,
0.7123−3.8871 / {(n ₁ Λ ′ + 1.7055) (n ₂ / n ₁ +0.7117)}
≦ f ≦ 0.7740−1.7142 / {(n ₁ Λ ′ + 1.7095) (n ₂ / n ₁ −0.3275)}
(6).

In this case, 1.0 <n ₁ Λ ′ <2.2
n ₂ / n ₁ = −1.5543 (n ₁ Λ ′) ⁵ +8.1107 (n ₁ Λ ′) ⁴
−13.048 (n ₁ Λ ′) ³ +3.248 (n ₁ Λ ′) ² +7.476 n ₁ Λ ′
-2.141 (4)
It is desirable to satisfy.

  According to the phase mask for producing a diffraction grating of the present invention, the cross-sectional shape of the repetitive pattern of the concave grooves and the ridges is substantially rectangular, and the cross-sectional shape dimension of the repetitive pattern of the concave grooves and the ridges is approximately 3π radians. Since the transmission zero-order light diffraction efficiency is minimized and the contrast of the transmission ± first-order light with respect to the transmission zero-order light is maximized, this phase grating mask is irradiated with ultraviolet exposure light. Then, the interference fringes having a predetermined pitch are exposed in a photosensitive material such as an optical fiber by the interference of the ± 1st order diffracted beams, and a refractive index change of the pitch of the interference fringes is generated in the photosensitive material to produce a diffraction grating. By manufacturing the above, it is possible to manufacture a high-quality diffraction grating that does not generate noise in the diffracted light. In particular, by using a highly refractive material for the phase mask, the diffraction angle in the atmosphere or the diffraction angle converted into the atmosphere can be increased, so that finer interference fringes can be recorded on the exposed side such as resist and optical fiber grating. Can do.

In addition, in the region where the phase difference of the exposure light is in the vicinity of π radians and the transmission zero-order light cannot be reduced to 0%, the transmission zero-order light can be reduced and the diffraction efficiency of the transmission ± first-order light can be reduced. In addition, the contrast of the transmitted ± first order light with respect to the transmitted zero order light can be improved. Thereby, the exposure time can be shortened, and it becomes possible to save energy, suppress the influence of vibration, and the like.

It is a figure for demonstrating the phase mask of this invention used for optical fiber processing. It is sectional drawing which shows the basic arrangement | positioning in the case of producing a diffraction grating using the phase mask for diffraction grating production of this invention. FIG. 6 is a graph in which the optimization range according to the present invention is plotted on a graph with n ₁ Λ ′ on the horizontal axis and n ₂ / n ₁ on the vertical axis. FIG. 5 is a diagram in which d / d ₀ as an optimization range according to the present invention is taken as n ₂ / n ₁ and n ₁ Λ ′ as variables. The f to be optimized range of the present invention. FIG taking n ₂ / n ₁ and n ₁ lambda 'as variables.

  In the present invention, the depth of the concave groove of the phase mask for producing a diffraction grating shifts the phase of the exposure light to around 3π radians, so that the phase of the transmitted ± primary light is shifted from the case where the phase is shifted to around π radians. It has been completed by discovering that the diffraction efficiency or the contrast with respect to the transmitted zero-order light can be increased.

FIG. 2 is a cross-sectional view showing a basic arrangement in the case of producing a diffraction grating using the diffraction grating production phase mask of the present invention. The phase mask 21 for producing a diffraction grating according to the present invention has a groove 26 and a ridge 27 which are parallel to each other and substantially rectangular in cross section with respect to a photosensitive material 22 such as an optical fiber for exposing an interference fringe pattern 24 (FIG. 1). The refractive index of the transparent substrate of the phase mask 21 is arranged between the photosensitive material 22 such as an optical fiber on which the interference fringe pattern 24 is exposed and the repeated pattern surface 28 of the phase mask 21. In this state, exposure light 23 such as KrF excimer laser light is irradiated from the surface opposite to the repeated pattern surface 28 of the phase mask 21, and the concave grooves 26 and the ridges 27 are repeated. diffraction efficiency T ₀ of the zero-order light of the 0-order light 25A which passes without being diffracted pattern surface 28 with 5% (repeated pattern surface 28. repetition path of the transparent substrate of the phase mask 21 It does not include attenuation on the surface opposite to the curved surface 28 and attenuation in the transparent substrate. The photosensitive material 22 is irradiated with interference fringes having a predetermined pitch by the plus first-order diffracted light 25B and the minus first-order diffracted light 25C, and the diffraction grating is exposed therein to change the refractive index. It is used for producing.

In such a binary phase type diffraction grating having a concave groove 26 parallel to each other and having a substantially rectangular cross section and a repetitive pattern surface 28 of the convex stripes 27, d: groove depth of the concave groove 26, w: width of the convex stripe 27 , Λ: repetition period, λ: exposure wavelength, n ₂ : refractive index of transparent substrate, n ₁ : refractive index of surrounding (gas or liquid), f = w / Λ, Λ ′ = Λ / λ, d ₀ = λ Q value is determined as / {2 (n ₂ −n ₁ )} and is defined by Q = 2πλd / (nΛ ² ) (Non-patent Document 2). In the case of the phase mask as shown in FIG. 2, the average refractive index n = fn ₂ + (1−f) n ₁ , and when Λ ′ = Λ / λ is substituted, Q = (2πd / λ) / {fn ₂ + ( 1-f) n ₁ } Λ ′ ² Here, when Q ≦ 1, since the diffraction grating can obtain a diffraction grating with high accuracy by scalar diffraction theory, Q> 1 that cannot be accurately handled by scalar diffraction theory in the present invention, that is,
2πd / λ> {fn ₂ + (1−f) n ₁ } Λ ′ ² (1)
The binary phase type diffraction grating (phase mask) 21 that satisfies the above is the object.

When Q> 1, which is difficult to apply in scalar theory, is assumed to be in the vicinity of d / d ₀ = 3, 5, 7,... (An odd number of 3 or more), the diffraction efficiency T of transmitted ± first-order light 25B, 25C It turns out that ₁ can be made relatively large. The physical meaning is considered to be that an antireflection effect occurs due to the deep groove of the diffraction grating, and the reflected light can be distributed to T ₁ . Further, in the region where the efficiency T ₀ of the transmitted zero-order light 25A cannot be reduced to 0% in the vicinity of d / d ₀ = 1, d / d ₀ should be larger than the vicinity of 3 in the region (n ₂ / n ₁ , n ₁ Λ ′). Thus, the transmitted zero-order light 25A can be reduced as compared with the case where d / d ₀ is in the vicinity of 1. As a result, the contrasts T ₀ / T ₁ and T ₁ can be improved. However, in practice, d / d ₀ = 5,7, in (5 or more odd number) or because they or each other have wavy presence of such solution, d / d ₀ = Consider around 3

  As described above, the diffraction efficiency of each diffraction order of the binary phase type diffraction grating (phase mask) 21 as shown in FIG. 2 can be strictly determined by the vector diffraction theory (Non-Patent Document 1). The diffraction efficiency is the diffraction efficiency when diffracting from the inside of the phase mask 21 immediately before the diffraction grating to the outside immediately after the diffraction grating, and when entering the inside of the substrate from outside the previous substrate. Reflection and reflection at the interface when the substrate is made of a laminate of materials having different refractive indexes are not considered.

Accordingly, first, by using the vector diffraction theory, in a 1 near vicinity d / d ₀ 3, with respect to n ₁ lambda 'and n ₂ / n ₁ set, the d / d ₀ and f as parameters, T ₀ was minimized, and T ₀ (%), T ₀ / T ₁ , and T ₁ (%) when the _value was minimized were obtained. The results are shown in the following Table 1 and Table 2, respectively. When d / d ₀ is close to 3, the values of d / d ₀ and f when T ₀ is minimized are also displayed.

ただし、Ｔ₀ 、Ｔ₁ の値は、計算誤差のため、また作製誤差で０．１％程度の誤差が生じるため、０．０１（％）の桁で四捨五入している。

However, the values of T ₀ and T ₁ are rounded to the nearest 0.01 (%) because of calculation errors and production errors of about 0.1%.

When Table 1 and Table 2 are compared, T ₀ may be smaller and T ₁ may be larger when d / d ₀ is near 3 than when it is near ₁ .

there,
_{[1] d / d 0 =} 1 near the corresponding _{(n 1 Λ ', n 2} / n 1) as compared to, d / d ₀ = 3 contrast near equivalent or more (T ₀ / T ₁ is equal to or less ),
[2] T ₀ ≦ 5% (except for the values where T ₀ is black and white inverted in both Table 1 and Table 2),
[3] T when ₀ = 0% is, d / d ₀ = 1 near the largest T ₁ (T ₁ of Table 2 is black and white reversal when T ₀ = 0% in each of n ₁ lambda ' T ₁ near d / d ₀ = 3 is equal to or greater than this,
[4] One region continuous from the smaller side of n ₂ / n ₁ for each n ₁ Λ ′,
The range that satisfies the above condition is the range enclosed by the double frame in Table 1 (if T ₀ ≠ 0%, [1] and [2], and if T ₀ = 0%) , [1] and [2] and [3], both satisfying [4]).

When the range surrounded by the double frame in Table 1 is plotted on the graph with n ₁ Λ ′ on the horizontal axis and n ₂ / n ₁ on the vertical axis, it is as shown in FIG. The maximum and minimum values of n ₂ / n ₁ for each n ₁ Λ ′ are shown. Between the maximum and minimum values, d / d ₀ near 3 is more than 1 near. When T ₀ ≠ 0%, T ₀ / T ₁ is small and the contrast is large, and when T ₀ = 0%, T ₁ is large. It also shows that T ₀ / T ₁ is minimum (T ₁ is maximum when T ₀ = 0%) between the maximum and minimum values.

The curves connecting the points of the maximum value and the minimum value in FIG. 3 are approximated by polynomials as follows. However, the horizontal axis n ₁ Λ ′ is divided into 1.0 <n ₁ Λ ′ ≦ 1.5 (section 1), 1.5 <n ₁ Λ ′ ≦ 1.9 (section 2), and 1.9 <n ₁ Λ ′ <2.2 (section 3). Curve approximation.

In interval 1: 1.0 <n ₁ Λ ′ ≦ 1.5,
Minimum value: n ₂ / n ₁ = -23.150 (n ₁ Λ ′) ⁵ +83.283 (n ₁ Λ ′) ⁴
−65.102 (n ₁ Λ ′) ³ −78.080 (n ₁ Λ ′) ² +131.966 n ₁ Λ ′ −46.905
Maximum value: n ₂ / n ₁ = 118.085 (n ₁ Λ ′) ⁵ −510.61 (n ₁ Λ ′) ⁴
+638.55 (n ₁ Λ ′) ³ +78.771 (n ₁ Λ ′) ² −642.31 n ₁ Λ ′ +321.06
That is,
In interval 1: 1.0 <n ₁ Λ ′ ≦ 1.5,
-23.150 (n ₁ Λ ′) ⁵ + 83.283 (n ₁ Λ ′) ⁴ −65.102 (n ₁ Λ ′) ³
−78.080 (n ₁ Λ ′) ² +131.966 n ₁ Λ ′ −46.905
≦ n ₂ / n ₁ ≦ 118.085 (n ₁ Λ ′) ⁵ −510.61 (n ₁ Λ ′) ⁴
+638.55 (n ₁ Λ ′) ³ +78.771 (n ₁ Λ ′) ² −642.31 n ₁ Λ ′ +321.06
... (1)
Section 2: 1.5 <n ₁ Λ ′ ≦ 1.9
Minimum value: n ₂ / n ₁ = 13.239 (n ₁ Λ ′) ³ −64.220 (n ₁ Λ ′) ²
+103.117 n ₁ Λ '-53.40
Maximum value: n ₂ / n ₁ = 61.5374 (n ₁ Λ ′) ⁶ −385.3323 (n ₁ Λ ′) ⁵
+328.9526 (n ₁ Λ ′) ⁴ +2844.835 (n ₁ Λ ′) ³
−8978.233 (n ₁ Λ ′) ² +10245.557 n ₁ Λ ′ −4207.134
That is,
Section 2: 1.5 <n ₁ Λ ′ ≦ 1.9
13.239 (n ₁ Λ ′) ³ −64.220 (n ₁ Λ ′) ² +103.117 n ₁ Λ ′ −53.40
≦ n ₂ / n ₁ ≦ 61.5374 (n ₁ Λ ′) ⁶ −385.3323 (n ₁ Λ ′) ⁵
+328.953 (n ₁ Λ ′) ⁴ +2844.835 (n ₁ Λ ′) ³ −8978.233 (n ₁ Λ ′) ²
+ 10245.56n ₁ Λ ′ −4207.135 (2)
Section 3: 1.9 <n ₁ Λ ′ <2.2
Minimum value: n ₂ / n ₁ = 10.443 (n ₁ Λ ′) ² −42.926 n ₁ Λ ′ +45.359
Maximum value: n ₂ / n ₁ = -8.3928 (n ₁ Λ ′) ² +32.374 n ₁ Λ ′ −29.672
That is,
Section 3: 1.9 <n ₁ Λ ′ <2.2
^{_{10.443 (n 1 Λ ') 2}} -42.926n 1 Λ' +45.36
≦ n ₂ / n ₁ ≦ -8.393 (n ₁ Λ ′) ² +32.374 n ₁ Λ ′ −29.674 (3)
It becomes.

Further, when a curve connecting points where T ₀ / T ₁ is minimized is approximated by a polynomial, it is as follows. In this case (the horizontal axis n ₁ Λ ′ is in the range of 1.0 <n ₁ Λ ′ <2.2),
n ₂ / n ₁ = −1.5543 (n ₁ Λ ′) ⁵ +8.1107 (n ₁ Λ ′) ⁴
−13.048 (n ₁ Λ ′) ³ +3.248 (n ₁ Λ ′) ² +7.476 n ₁ Λ ′
-2.141 (4)
It becomes.

By the way, when (n ₁ Λ ′, n ₂ / n ₁ ) is in a range surrounded by the double frame in Table 1 (T ₀ ≠ 0%, [1] and [2], T ₀ = 0 %, [1] and [2] and [3], both of which satisfy [4]), that is, when the conditional expressions (1) to (3) are satisfied, d FIGS. 4 and 5 show what range / d ₀ and f should satisfy, respectively.

When the graph shown as “original data” in FIG. 4 is in the range surrounded by the double frame in Table 1,
It is a diagram in which d / d ₀ is taken as n ₂ / n ₁ and n ₁ Λ ′ as variables, and the graphs shown as “maximum side envelope surface” and “minimum side envelope surface” are “original data” FIG. 6 is a diagram in which approximate curved surfaces are determined so that errors are reduced by contacting curved surfaces from above and below d / d ₀ , respectively. In FIG. 4, the vertical axis is d / d ₀ , the horizontal axis is n ₂ / n ₁ , and the other is n ₁ Λ ′.

The range of d / d ₀ sandwiched between the minimum side envelope surface and the maximum side envelope surface in the case of FIG. 4 is as follows.

2.8090 + 0.7790 / {(n ₁ Λ ′ + 4.7488) (n ₂ / n ₁ −1.1687)}
≦ d / d ₀ ≦
3.6885 + 0.1488 / {(n ₁ Λ ′ + 2.6126) (n ₂ / n ₁ −1.1233)} (5)
It becomes.

In addition, the graph shown as “original data” in FIG. 5 is a diagram in which f is n ₂ / n ₁ and n ₁ Λ ′ as variables in the range surrounded by the double frame in Table 1. In the graphs shown as “maximum side envelope surface” and “minimum side envelope surface”, the approximate curved surface is determined so that the error is reduced by contacting the curved surface of “original data” from the lower side and the upper side of f, respectively. FIG. In FIG. 5, the vertical axis is f, the horizontal axis is n ₂ / n ₁ , and the other is n ₁ Λ ′.

  The range of f sandwiched between the minimum envelope surface and the maximum envelope surface in the case of FIG. 5 is as follows.

0.7123−3.8871 / {(n ₁ Λ ′ + 1.7055) (n ₂ / n ₁ +0.7117)}
≦ f ≦ 0.7740−1.7142 / {(n ₁ Λ ′ + 1.7095) (n ₂ / n ₁ −0.3275)}
... (6)
As is apparent from the above, when the conditional expressions (1) to (3), (5), and (6) are satisfied at the same time, the depth d of the concave groove 26 of the phase mask 21 changes the phase of the exposure light in the vicinity of π radians. How to be shifted to 3π vicinity than manner shifted in is, T ₀ / T ₁ transmission ± 1-order light 25B for small 0-order light 25A, it is possible to increase the contrast of 25C (T ₀ ≠ 0% Or the diffraction efficiency T ₁ of the transmission ± first-order light 25B, 25C can be increased (when T ₀ = 0%).

Next, some examples of the phase mask for producing a diffraction grating according to the present invention will be shown. Examples 1-1, 2-1, 3-1, 4-1, 5-1, 6-1 shown in Table 3 below are examples based on the present invention, and Examples 1-2, 2-2 Reference numerals 3-2, 4-2, 5-2, and 6-2 are comparative examples. The polarizations used in these examples and comparative examples, and parameters n ₁ , n ₂ , Λ, f, d / λ, d / d ₀ , T ₀ , T ₁ , T _RT , Q are shown. Here, _TRT is the sum of reflection diffraction components. Here, the units of T ₀ , T ₁ and T _RT are%.
[Table 3]
Example Polarization n ₁ n ₂ Λ f d / λ d / d ₀ T ₀ T ₁ T _RT Q
1-1 S 1.00 1.834 1.1 0.354 1.756 2.928 2.2 34.6 28.7 7.04
1-2 S 1.00 1.834 1.1 0.291 0.618 1.031 3.1 29.4 38.2 2.58

2-1 S 1.00 2.00 1.1 0.345 1.487 2.975 0.0 37.5 25.1 5.74
2-2 S 1.00 2.00 1.1 0.281 0.543 1.085 0.3 29.9 39.8 2.20

3-1 S 1.00 2.00 1.4 0.389 1.640 3.279 0.0 38.7 22.5 3.78
3-2 S 1.00 2.00 1.4 0.390 0.551 1.102 0.0 37.4 25.2 1.27

4-1 P 1.00 1.80 1.2 0.409 2.311 3.698 3.9 45.7 4.7 7.60
4-2 P 1.00 1.80 1.2 0.403 0.777 1.243 4.3 43.8 8.0 2.56

5-1 S 1.50 2.80 0.7 0.331 1.125 2.925 0.3 38.1 23.5 7.47
5-2 S 1.50 2.80 0.7 0.315 0.386 1.002 3.2 25.0 46.8 2.59

6-1 P 1.50 2.70 0.8 0.409 1.541 3.698 3.9 45.7 4.7 7.60
6-2 P 1.50 2.70 0.8 0.403 0.518 1.243 4.3 43.8 8.0 2.56
.

Examples 1-1, 2-1, 3-1, 4-1, 5-1, 6-1 are cases where d / d ₀ is optimized in the vicinity of 3 based on the present invention. 2, 2-2, 3-2, 4-2, 5-2, 6-2 are cases where d / d ₀ is optimized in the vicinity of 1, and in any case, the examples of the present invention are comparative examples. It can be seen that T ₀ is smaller and T ₁ is larger than.

  When the interference fringe pattern 24 is exposed to the photosensitive material 22 such as an optical fiber by using the diffraction grating manufacturing phase mask 21 according to the present invention, the direction of the electric field of the transmission ± primary light 25B and 25C that interfere with each other is taken into consideration. Then, the exposure efficiency is improved by using S-polarized light rather than using P-polarized light.

  As described above, the phase mask for producing a diffraction grating of the present invention has been described based on the principle and examples. However, the present invention is not limited to these examples, and various modifications are possible.

  According to the phase mask for producing a diffraction grating of the present invention, the cross-sectional shape of the repetitive pattern of the concave grooves and the ridges is substantially rectangular, and the cross-sectional shape dimension of the repetitive pattern of the concave grooves and the ridges is approximately 3π radians. Since the transmission zero-order light diffraction efficiency is minimized and the contrast of the transmission ± first-order light with respect to the transmission zero-order light is maximized, this phase grating mask is irradiated with ultraviolet exposure light. Then, the interference fringes having a predetermined pitch are exposed in a photosensitive material such as an optical fiber by the interference of the ± 1st order diffracted beams, and a refractive index change of the pitch of the interference fringes is generated in the photosensitive material to produce a diffraction grating. By manufacturing the above, it is possible to manufacture a high-quality diffraction grating that does not generate noise in the diffracted light. In particular, by using a highly refractive material for the phase mask, the diffraction angle in the atmosphere or the diffraction angle converted into the atmosphere can be increased, so that finer interference fringes can be recorded on the exposed side such as resist and optical fiber grating. Can do.

  In addition, in the region where the phase difference of the exposure light is in the vicinity of π radians and the transmission zero-order light cannot be reduced to 0%, the transmission zero-order light can be reduced and the diffraction efficiency of the transmission ± first-order light can be reduced. And the contrast of the transmission ± primary light with respect to the transmission zero-order light can be improved. Thereby, the exposure time can be shortened, and it becomes possible to save energy, suppress the influence of vibration, and the like.

21 ... Phase mask (phase mask for diffraction grating fabrication)
22. Optical fiber (photosensitive material)
22A ... optical fiber core 23 ... exposure light 24 ... interference fringe pattern 25A ... 0th order light 25B ... plus first order diffracted light 25C ... minus first order diffracted light 26 ... concave 27 ... convex 28 ... repeat pattern surface 29 ... gas Or liquid

Claims (2)

Repeating pattern of grooves and the ridges of the lattice-like substantially rectangular cross-section is provided on one surface of the transparent substrate, a phase mask for forming a diffraction grating in the photosensitive material by interference of the transmitted ± 1-order light by the repetition pattern , The sectional shape dimensions of the repeating pattern of the concave groove and the convex stripe are d: groove depth of the concave groove, w: width of the convex stripe, Λ: repetition period, λ: exposure wavelength, n ₂ : refractive index of the transparent substrate , N ₁ : refractive index of surrounding (atmosphere or liquid), d ₀ = λ / {2 (n ₂ −n ₁ )}, f = w / Λ, and Λ ′ = Λ / λ, n ₁ Λ ′ , N ₂ / n ₁ , d / d ₀ , f satisfy the following conditional expressions (1) , (5), (6) at the same time, or (2), (5), (6) at the same time, Or the phase mask for diffraction grating production characterized by satisfying (3), (5), and (6) simultaneously .
1.0 <n ₁ Λ '<2.2 range interval of _1: 1.0 <n 1 Λ' in ≦ 1.5,
-23.150 (n ₁ Λ ′) ⁵ + 83.283 (n ₁ Λ ′) ⁴ −65.102 (n ₁ Λ ′) ³
−78.080 (n ₁ Λ ′) ² +131.966 n ₁ Λ ′ −46.905
≦ n ₂ / n ₁ ≦ 118.085 (n ₁ Λ ′) ⁵ −510.61 (n ₁ Λ ′) ⁴
+638.55 (n ₁ Λ ′) ³ +78.771 (n ₁ Λ ′) ² −642.31 n ₁ Λ ′ +321.06
... (1)
1.0 <n ₁ Λ '<2.2 in the range of the section 2: 1.5 <n ₁ Λ' in ≦ 1.9,
13.239 (n ₁ Λ ′) ³ −64.220 (n ₁ Λ ′) ² +103.117 n ₁ Λ ′ −53.40
≦ n ₂ / n ₁ ≦ 61.5374 (n ₁ Λ ′) ⁶ −385.3323 (n ₁ Λ ′) ⁵
+328.953 (n ₁ Λ ′) ⁴ +2844.835 (n ₁ Λ ′) ³ −8978.233 (n ₁ Λ ′) ²
+ 10245.56n ₁ Λ ′ −4207.135 (2)
1.0 <n ₁ lambda '<2.2 range interval 3: 1.9 <n ₁ Λ' by <2.2,
^{_{10.443 (n 1 Λ ') 2}} -42.926n 1 Λ' +45.36
≦ n ₂ / n ₁ ≦ -8.393 (n ₁ Λ ′) ² +32.374 n ₁ Λ ′ −29.674 (3)
In the range of 1.0 <n ₁ Λ ′ <2.2,
2.8090 + 0.7790 / {(n ₁ Λ ′ + 4.7488) (n ₂ / n ₁ −1.1687)}
≦ d / d ₀ ≦
3.6885 + 0.1488 / {(n ₁ Λ ′ + 2.6126) (n ₂ / n ₁ −1.1233)} (5)
In the range of 1.0 <n ₁ Λ ′ <2.2,
0.7123−3.8871 / {(n ₁ Λ ′ + 1.7055) (n ₂ / n ₁ +0.7117)}
≦ f ≦ 0.7740−1.7142 / {(n ₁ Λ ′ + 1.7095) (n ₂ / n ₁ −0.3275)}
... (6) In claim 1,
In the range of 1.0 <n ₁ Λ ′ <2.2,
n ₂ / n ₁ = −1.5543 (n ₁ Λ ′) ⁵ +8.1107 (n ₁ Λ ′) ⁴
−13.048 (n ₁ Λ ′) ³ +3.248 (n ₁ Λ ′) ² +7.476 n ₁ Λ ′
-2.141 (4)
A phase mask for producing a diffraction grating characterized by satisfying

Images