JP2706621B2 - Infrared diffraction lens - Google Patents
Infrared diffraction lensInfo
- Publication number
- JP2706621B2 JP2706621B2 JP6103700A JP10370094A JP2706621B2 JP 2706621 B2 JP2706621 B2 JP 2706621B2 JP 6103700 A JP6103700 A JP 6103700A JP 10370094 A JP10370094 A JP 10370094A JP 2706621 B2 JP2706621 B2 JP 2706621B2
- Authority
- JP
- Japan
- Prior art keywords
- lens
- diffractive lens
- infrared
- wavelength
- refractive index
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
Description
【発明の詳細な説明】
【０００１】
【産業上の利用分野】本発明は、赤外光用の集光特性が
よく、作製容易な赤外用回折型レンズに関するものであ
る。
【０００２】
【従来の技術】従来の屈折型フレネルレンズに加え、近
年、小型軽量で再現性がよく、収差が小さい回折型レン
ズが注目されている。この回折型レンズは、例えば電子
ビーム描画等の微細加工によって製造を行うため、フレ
ネルマイクロレンズまたはマイクロフレネルレンズとも
呼ばれている。
【０００３】従来の回折型レンズは、屈折型フレネルレ
ンズ同様ガラスやアクリル樹脂等屈折率ｎが１．５前後
のもので作られていたため、レンズの位相変調量に対応
した溝の深さは、最大集光効率を得ようとした場合、入
射光の波長の１／（ｎ−１）倍つまり２倍の値にする必
要がある。例えば、可視光のＨｅ−Ｎｅレーザの０．６
３２８μｍを入射光とする場合、溝の深さは１．３μｍ
であるが、これが近赤外の波長が１．５μｍ用のものに
なると回折型レンズの溝の深さは３μｍとする必要があ
る。
【０００４】
【発明が解決しようとする課題】しかしながら、従来例
のように、屈折率が１．５前後の物質で近赤外用の回折
型レンズを作ると、溝の深さが深いため、正確なレンズ
形状を実現するのは難しく、つまりは集光特性のよい赤
外用回折型マイクロレンズが得られにくいという問題点
を有していた。
【０００５】本発明は、上記問題点を解決するもので、
集光特性のよい赤外用回折型レンズを提供することを目
的とする。
【０００６】
【課題を解決するための手段】本発明は、上記目的を達
成するため、入射光の波長に依存し、レンズの位相変調
量に応じた凹凸部がレンズ表面に形成された赤外用回折
型レンズであって、前記入射光の波長は１．８μｍから
２３μｍの領域にあり、前記凹凸部は、屈折率が３以上
で、かつ、ＧｅもしくはＧｅを含む材料をエッチングす
ることにより垂直部分を有するように形成されたもので
ある。
【０００７】
【作用】本発明は上記した構成により、構成物質の屈折
率が高いため回折型レンズの溝の深さを浅くでき、又、
エッチングすることにより垂直部分を有するように凹凸
部が形成されるため、前記凹凸部の垂直部分で生じる不
要な多重反射光が少なくなり、作製容易で、高効率な集
光特性のよい赤外用回折型レンズを実現するものであ
る。
【０００８】
【実施例】以下本発明の実施例について、図面を参照し
ながら説明する。図１(a),(b)はそれぞれ本発明の一実
施例における回折型の赤外用レンズ（以下回折型レンズ
と称す）を示す断面図、平面図である。
【０００９】図１において、１はＧｅ結晶であり、表面
に断面が鋸歯状のレンズの位相変調量に応じた凹凸部２
が施してある。鋸歯状の凹凸部２の溝の深さｔは、レン
ズの集光効率が最大になるために、レンズを構成してい
る物質の屈折率ｎ、及び入射光の波長λを用いて、ｔ＝
λ／（ｎ−１）と設定する必要がある。近赤外で透明な
Ｇｅの屈折率は、ｎ＝４．０であり、本実施例では、入
射光としてλ＝１０．６μｍの半導体レーザ光を用いた
ので溝の深さをｔ＝３．５μｍとした。従来例のように
ガラスやアクリル, 電子ビームレジスト等の屈折率が
１．５前後のもので作製した回折型レンズの場合、溝の
深さｔはλ＝１０．６μｍに対してｔ＝２１μｍとする
必要があったから、本実施例の回折型レンズにより、溝
の深さｔが従来例の１／６程度で、薄い回折型レンズが
実現できたと言える。その結果、凹凸部の垂直部分で生
じる不要な多重反射光が大幅に少なくなり、この多重反
射光に起因した回折効率の低下を防止して、集光特性に
優れた赤外用回折型レンズを容易に実現できる。
【００１０】また、入射光の反射を減少させるために、
少なくともレンズの入射側または反射側のどちらか一方
の面に無反射コーティングを行うと集光効率がさらに良
くなる。
【００１１】次に、図２を用いて作製工程を説明する。
まず図２(a)のＧｅ結晶１上に図２(b)のように電子ビー
ムレジスト３をコーティングし、電子ビームリソグラフ
ィにより、図２(c)のようにレンズのパターンを作製し
た。次に、イオンビームエッチングを行い、図２(d)の
ように電子ビームレジスト３の形をＧｅ結晶１に転写し
て凹凸部２を形成した。この時電子ビームレジスト３の
コーティング厚さを制御し溝の深さｔが最適になるよう
にした。
【００１２】尚、レンズとして作用するのはＧｅ結晶１
表面の凹凸のある部分であるので、この部分がＧｅであ
りさえすれば良く、凹凸のない部分は他の物質でもよ
い。
【００１３】以上のように本実施例によれば、溝の深さ
が従来例に比べて約１／６まで薄くなったこととエッチ
ングにより形成することにより、だれのない正確な凹凸
形状が実現でき、溝の深さが薄くなったことと、正確な
凹凸形状が実現できたことにより、その結果集光特性の
よい回折形レンズが実現でき、またイオンビームエッチ
ングでパターンの転写をする時間も短くなり作製が容易
である。
【００１４】以上の説明はＧｅを用いた回折型レンズに
ついて行ったが、屈折率が３以上の物質であればよく、
Ｇｅを含み、屈折率が３以上の材料から構成された回折
型レンズについても同様の効果が得られる。
【００１５】尚、Ｇｅの透過波長領域は、１．８μｍ〜
２３μｍであり、しかもＧｅはこの領域で屈折率が３以
上である。従って、入射光が結晶の透過波長領域ならど
の波長でも、同様の効果が得られる。
【００１６】
【発明の効果】以上のように本発明によれば、高屈折率
な物質、例えばＧｅで回折型レンズの凹凸部をエッチン
グにより垂直部分を有するように形成したことによっ
て、前記凹凸部の垂直部分で生じる不要な多重反射光が
少なくなり、溝の深さが浅くて、かつ正確なレンズ形状
を実現でき、その結果、集光特性のよい回折型の赤外用
レンズを容易に実現できる。Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an infrared diffractive lens which has good light-collecting characteristics for infrared light and is easy to manufacture. [0002] In addition to the conventional refraction type Fresnel lens, in recent years, a diffraction type lens having small size, light weight, good reproducibility and small aberration has been attracting attention. This diffractive lens is also called a Fresnel micro lens or a micro Fresnel lens because it is manufactured by fine processing such as electron beam drawing. A conventional diffractive lens is made of glass, acrylic resin or the like having a refractive index n of about 1.5 like a refractive Fresnel lens. Therefore, the depth of a groove corresponding to the amount of phase modulation of the lens is: In order to obtain the maximum light collection efficiency, it is necessary to set the value to 1 / (n-1) times, that is, twice the wavelength of the incident light. For example, 0.6 of visible light He-Ne laser
When 328 μm is the incident light, the depth of the groove is 1.3 μm
However, when the wavelength of the near-infrared ray is 1.5 μm, the depth of the groove of the diffractive lens needs to be 3 μm. However, if a near infrared diffractive lens is made of a material having a refractive index of about 1.5 as in the conventional example, the depth of the groove is large. It is difficult to realize a suitable lens shape, that is, it is difficult to obtain an infrared diffractive microlens having a good light-collecting property. The present invention solves the above problems,
It is an object of the present invention to provide an infrared diffractive lens having good light collecting characteristics. SUMMARY OF THE INVENTION In order to achieve the above object, the present invention is directed to an infrared light having an irregular portion formed on a lens surface, which depends on the wavelength of incident light and corresponds to the amount of phase modulation of the lens. A diffractive lens, wherein the wavelength of the incident light is from 1.8 μm
The uneven portion has a refractive index of 3 or more and is formed so as to have a vertical portion by etching Ge or a material containing Ge. According to the present invention, since the refractive index of the constituent material is high, the depth of the groove of the diffractive lens can be reduced.
Unevenness to have vertical part by etching
Formed at the vertical portion of the uneven portion.
It is an object of the present invention to realize an infrared diffractive lens with reduced required multiple reflected light , easy production, high efficiency and good light-collecting characteristics. Embodiments of the present invention will be described below with reference to the drawings. 1A and 1B are a sectional view and a plan view, respectively, showing a diffractive infrared lens (hereinafter referred to as a diffractive lens) according to an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a Ge crystal, and its surface has an uneven portion 2 corresponding to the amount of phase modulation of a lens having a sawtooth cross section on the surface.
Is given. The depth t of the groove of the saw-toothed uneven portion 2 is determined by using the refractive index n of the material constituting the lens and the wavelength λ of the incident light so that the light collection efficiency of the lens is maximized.
It is necessary to set λ / (n−1). The refractive index of near infrared transparent Ge is n = 4.0. In this embodiment, since the semiconductor laser light of λ = 10.6 μm is used as the incident light, the depth of the groove is set at t = 3.0. The thickness was 5 μm. In the case of a diffractive lens made of glass, acrylic, electron beam resist or the like having a refractive index of about 1.5 as in the conventional example, the groove depth t is λ = 10.6 μm and t = 21 μm. Therefore, it can be said that the diffraction lens of the present embodiment has realized a thin diffraction lens having a groove depth t of about 1/6 of the conventional example. As a result, unnecessary multiple reflection light generated in the vertical portion of the uneven portion is significantly reduced, and a reduction in diffraction efficiency due to the multiple reflection light is prevented. Can be realized. In order to reduce the reflection of incident light,
If at least one of the surfaces on the incident side or the reflection side of the lens is provided with a non-reflection coating, the light collection efficiency is further improved. Next, a manufacturing process will be described with reference to FIG.
First, an electron beam resist 3 was coated on the Ge crystal 1 shown in FIG. 2A as shown in FIG. 2B, and a lens pattern was formed as shown in FIG. 2C by electron beam lithography. Next, ion beam etching was performed to transfer the shape of the electron beam resist 3 to the Ge crystal 1 as shown in FIG. At this time, the coating thickness of the electron beam resist 3 was controlled to optimize the groove depth t. It is noted that the Ge crystal 1 acts as a lens.
Since the surface is a portion having irregularities, it is sufficient that this portion is made of Ge, and the portion having no irregularities may be another material. As described above, according to this embodiment, the depth of the groove is reduced to about 1/6 of that of the conventional example and the groove is formed by etching, thereby realizing a precise uneven shape without any droop. The depth of the groove was reduced, and the accurate uneven shape was achieved.As a result, a diffractive lens with good light-collecting characteristics was realized, and the time required to transfer the pattern by ion beam etching was improved. It is short and easy to manufacture. Although the above description has been made with respect to a diffractive lens using Ge, any substance having a refractive index of 3 or more may be used.
Similar effects can be obtained for a diffractive lens including Ge and having a refractive index of 3 or more. The Ge transmission wavelength range is from 1.8 μm to 1.8 μm.
23 μm, and Ge has a refractive index of 3 or more in this region. Therefore, the same effect can be obtained regardless of the wavelength of the incident light as long as it is in the transmission wavelength region of the crystal. As described above, according to the present invention, the concave / convex portion of the diffraction lens is formed to have a vertical portion by etching with a material having a high refractive index, for example, Ge.
Unnecessary multiple reflected light generated in the vertical portion of the uneven portion
The number of grooves is small , the depth of the groove is small , and an accurate lens shape can be realized. As a result , a diffractive infrared lens having good light-collecting characteristics can be easily realized.
【図面の簡単な説明】
【図１】(a) 本発明の一実施例における赤外用回折型
レンズの断面図
(b) 本発明の一実施例における赤外用回折型レンズの
平面図
【図２】(a)〜(d) 本発明の一実施例の赤外用回折型レ
ンズの作製工程図
【符号の説明】
１ Ｇｅ結晶
２ 凹凸部BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 (a) Cross-sectional view of an infrared diffractive lens according to an embodiment of the present invention (b) Plan view of an infrared diffractive lens according to an embodiment of the present invention (A) to (d) Manufacturing steps of an infrared diffractive lens according to one embodiment of the present invention [Explanation of reference numerals] 1 Ge crystal 2
───────────────────────────────────────────────────── フロントページの続き (56)参考文献 特開 昭59−137908（ＪＰ，Ａ) 特開 昭51−110347（ＪＰ，Ａ) 特開 昭57−200010（ＪＰ，Ａ) ＪｏｕＲＮａＬ ｏｆ ＯＰＴＩＣＡ Ｌ ＳＯＣＩＥＴＹ ＯＦ ＡＭＥＲＩ ＣＡ，51［１］（1961），Ｐ．17−20 ────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-59-137908 (JP, A) JP-A-51-110347 (JP, A) JP-A-57-200010 (JP, A) JouRNal of OPTICA L SOCIETY OF AMERI CA, 51 [1] (1961); 17−20
Claims (1)
た凹凸部がレンズ表面に形成された赤外用回折型レンズ
であって、前記入射光の波長は１．８μｍから２３μｍ
の領域にあり、前記凹凸部は、屈折率が３以上で、か
つ、ＧｅもしくはＧｅを含む材料をエッチングすること
により垂直部分を有するように形成されたことを特徴と
する赤外用回折型レンズ。 ２．凹凸部は、前記凹凸部を構成する材料の屈折率ｎと
入射光の波長λとに対して、λ／（ｎ−１）の溝の深さ
を有する鋸歯形状であることを特徴とする請求項１記載
の赤外用回折型レンズ。 ３．少なくとも表面又は裏面に無反射コーティングを施
したことを特徴とする請求項１記載の赤外用回折型レン
ズ。 ４．凹凸部は、透過型の回折型凸レンズ形状であること
を特徴とする請求項１記載の赤外用回折型レンズ。 ５．凹凸部は、マスクの断面形状をＧｅもしくはＧｅを
含む材料に転写して形成されたことを特徴とする請求項
１記載の赤外用回折型レンズ。(57) [Claims] An infrared diffractive lens having a concave-convex portion formed on a lens surface depending on a wavelength of incident light and in accordance with a phase modulation amount of the lens, wherein the wavelength of the incident light is from 1.8 μm to 23 μm.
Located in the region, the uneven portion, a refractive index of 3 or more, and infrared diffractive lens characterized by being formed to have a vertical portion by etching a material comprising Ge or Ge. 2. The uneven portion has a sawtooth shape having a groove depth of λ / (n−1) with respect to a refractive index n of a material forming the uneven portion and a wavelength λ of incident light. Item 2. An infrared diffractive lens according to item 1. 3. 2. An infrared diffractive lens according to claim 1, wherein an anti-reflection coating is applied on at least the front surface or the back surface. 4. The concave and convex portions have a transmission-type diffraction-type convex lens shape
The infrared diffractive lens according to claim 1, wherein: 5. The concave / convex portions are formed by using Ge or Ge
Claims: formed by transferring to a material containing
2. The infrared diffractive lens according to 1.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP6103700A JP2706621B2 (en) | 1994-05-18 | 1994-05-18 | Infrared diffraction lens |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP6103700A JP2706621B2 (en) | 1994-05-18 | 1994-05-18 | Infrared diffraction lens |
Related Parent Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP59245078A Division JPH0679081B2 (en) | 1984-11-20 | 1984-11-20 | Infrared Fresnel lens |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH0756010A JPH0756010A (en) | 1995-03-03 |
| JP2706621B2 true JP2706621B2 (en) | 1998-01-28 |
Family
ID=14361042
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP6103700A Expired - Lifetime JP2706621B2 (en) | 1994-05-18 | 1994-05-18 | Infrared diffraction lens |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP2706621B2 (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP3758072B2 (en) * | 1999-11-11 | 2006-03-22 | 三菱電機株式会社 | Infrared optical system |
| WO2022185716A1 (en) * | 2021-03-01 | 2022-09-09 | パナソニックＩｐマネジメント株式会社 | Fresnel lens and sensor system |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5124247A (en) * | 1974-08-22 | 1976-02-27 | Yokogawa Electric Works Ltd | KOTAIIKIRENZU |
| US3947084A (en) * | 1975-02-28 | 1976-03-30 | Hughes Aircraft Company | Long-wave infrared afocal zoom telescope |
| JPS5336250A (en) * | 1976-09-16 | 1978-04-04 | Toshiba Corp | Fresnel lens |
-
1994
- 1994-05-18 JP JP6103700A patent/JP2706621B2/en not_active Expired - Lifetime
Non-Patent Citations (1)
| Title |
|---|
| ＪｏｕＲＮａＬ ｏｆ ＯＰＴＩＣＡＬ ＳＯＣＩＥＴＹ ＯＦ ＡＭＥＲＩＣＡ，５１［１］（１９６１），Ｐ．１７−２０ |
Also Published As
| Publication number | Publication date |
|---|---|
| JPH0756010A (en) | 1995-03-03 |
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