JP2702883B2 - Infrared diffraction lens - Google Patents
Infrared diffraction lensInfo
- Publication number
- JP2702883B2 JP2702883B2 JP6103699A JP10369994A JP2702883B2 JP 2702883 B2 JP2702883 B2 JP 2702883B2 JP 6103699 A JP6103699 A JP 6103699A JP 10369994 A JP10369994 A JP 10369994A JP 2702883 B2 JP2702883 B2 JP 2702883B2
- Authority
- JP
- Japan
- Prior art keywords
- lens
- infrared
- diffractive lens
- inp
- incident light
- 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
Landscapes
- Diffracting Gratings Or Hologram Optical Elements (AREA)
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１.０μｍから
１４μｍの領域にあり、前記凹凸部は、屈折率が３以上
で、かつ、ＩｎＰもしくはＩｎＰ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、か
つ、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よ
うな形状であることを特徴とする。
【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ＩｎＰ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。
【００１０】近赤外で透明なＩｎＰの屈折率は、ｎ＝
３．３であり、本実施例では、入射光としてλ＝１．５
５μｍの半導体レーザ光を用いたので溝の深さをｔ＝
０．６７μｍ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＝１．
５５μｍに対してｔ＝３．１μｍ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１／５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。
【００１１】又、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。
【００１２】次に、図２を用いて作製工程を説明する。
まず図２(a)のＩｎＰ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ＩｎＰ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。
【００１３】なお、レンズとして作用するのは、ＩｎＰ
結晶１表面の凹凸のある部分であるので、この部分がＩ
ｎＰ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。
【００１４】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１／５まで薄くなったこととエッチ
ングにより形成したことにより、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
よい回折型レンズが実現でき、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。
【００１５】以上の説明はＩｎＰ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、ＩｎＰ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。
【００１６】尚、ＩｎＰの透過波長領域は、１．０μｍ
〜１４μｍであり、しかもＩｎＰ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。
【００１７】
【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ＩｎＰを用い、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, an accurate groove is formed due to a deep groove. There is a problem that it is difficult to realize a lens shape, that is, it is difficult to obtain an infrared diffractive microlens having good light-collecting characteristics. 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 uneven portion formed on a lens surface depending on the wavelength of incident light and in accordance with the amount of phase modulation of the lens. A diffractive lens, wherein the wavelength of the incident light is in a range of 1.0 μm to 14 μm, and the uneven portion has a refractive index of 3 or more and is formed by etching a material containing InP or InP to form a vertical portion. Is formed to have
First, the refractive index n of the material forming the uneven portion and the wave of the incident light
Has a groove depth of λ / (n−1) with respect to the length λ.
It is characterized in that it has a shape like that. 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.
Since the uneven portion is formed so as to have a vertical portion by etching, unnecessary multiple reflection light generated in the vertical portion of the uneven portion is reduced, and it is easy to manufacture, and it is easy to manufacture and has a high efficiency. It realizes a shaped lens. 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 an InP crystal, and a surface thereof has an uneven portion 2 corresponding to the amount of phase modulation of a lens having a sawtooth cross section. 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 in order to maximize the light collection efficiency of the lens.
= Λ / (n-1). The refractive index of near infrared transparent InP is n =
3.3, and in this embodiment, λ = 1.5 as incident light.
Since a semiconductor laser beam of 5 μm was used, the depth of the groove was t =
0.67 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 = 1.
Since it was necessary to set t = 3.1 μm with respect to 55 μm, it can be said that the diffraction lens of this embodiment can realize a thin diffraction lens having a groove depth t of about １ ／ 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 the incident light, if a non-reflection coating is applied to at least one of the entrance side and the reflection side of the lens, the light collection efficiency is further improved. Next, a manufacturing process will be described with reference to FIG.
First, an InP crystal 1 shown in FIG. 2A was coated with an electron beam resist 3 as shown in FIG. 2B, and a lens pattern was formed by electron beam lithography as shown in FIG. 2C. Next, ion beam etching is performed, and FIG.
As described above, the shape of the electron beam resist 3 was transferred to the InP crystal 1 to form the uneven portion 2. At this time, the coating thickness of the electron beam resist 3 was controlled to optimize the groove depth t. It is noted that InP acts as a lens.
Since this is a part of the surface of crystal 1 having irregularities, this part
What is necessary is just nP, and the part without unevenness may be another substance. As described above, according to this embodiment, since the depth of the groove is reduced to about 1/5 of that of the conventional example and the groove is formed by etching, an accurate uneven shape without any droop is realized. The depth of the groove was reduced, and the accurate uneven shape was achieved.As a result, a diffractive lens with good focusing characteristics was realized, and the time required to transfer the pattern by ion beam etching was increased. It is short and easy to manufacture. The above description has been made with respect to a diffractive lens using InP. However, any material having a refractive index of 3 or more may be used. A diffractive lens made of a material containing InP and having a refractive index of 3 or more may be used. Has the same effect. The transmission wavelength range of InP is 1.0 μm
１４14 μm, and InP 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, by using a material having a high refractive index, for example, InP, the concave and convex portions of the diffraction lens are formed so as to have vertical portions by etching. Unnecessary multiple reflected light generated in the vertical part of the uneven part is reduced, the depth of the groove is small, and an accurate lens shape can be realized. As a result, it is easy to produce a diffractive infrared lens with good focusing characteristics realizable.
【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 ＩｎＰ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 InP crystal 2 Uneven portion
───────────────────────────────────────────────────── フロントページの続き (56)参考文献 特開 昭53−36250（ＪＰ，Ａ) 特開 昭59−137908（ＪＰ，Ａ) 特開 昭59−116602（ＪＰ，Ａ) 特開 昭59−92444（ＪＰ，Ａ) 特開 昭59−69444（ＪＰ，Ａ) 久保田広他編 「光学技術ハンドブッ ク（増補版）」 朝倉書店 （1975. ７．20） ＰＰ．674〜677 ＪＯＵＲＮＡＬ ＯＦ ＴＨＥ ＯＰ ＴＩＣＡＬ ＳＯＣＩＥＴＹ ＯＦ Ａ ＭＥＲＩＣＡ 51（１） ＰＰ．17〜20 ────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-53-36250 (JP, A) JP-A-59-137908 (JP, A) JP-A-59-116602 (JP, A) JP-A-59-92444 (JP, A) JP-A-59-69444 (JP, A) Hiroshi Kubota et al. “Optical Technology Handbook A (extended edition) "Asakura Shoten (1975. 7.20) PP. 674-677 JOURNAL OF THE OP TICAL SOCIETY OF A MERICA 51 (1) PP. 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１.０μｍから１４μｍの領域にあ
り、 前記凹凸部は、屈折率が３以上で、かつ、ＩｎＰもしく
はＩｎＰ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、かつ、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ような形状であることを
特徴とする赤外用回折型レンズ。 ２．凹凸部は、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ＩｎＰもしくはＩｎ
Ｐ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 an uneven portion formed on a lens surface depending on the wavelength of incident light and corresponding to a phase modulation amount of the lens, wherein the wavelength of the incident light is in a range of 1.0 μm to 14 μm, The concavo-convex portion has a refractive index of 3 or more and is formed to have a vertical portion by etching InP or a material containing InP .
Λ / λ with respect to the refractive index n of the material and the wavelength λ of the incident light.
An infrared diffractive lens having a shape having a groove depth of (n-1) . 2. 2. The infrared diffractive lens according to claim 1, wherein the uneven portion has a sawtooth shape . 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. 2. The infrared diffractive lens according to claim 1, wherein the concave and convex portions have a transmission type diffractive convex lens shape. 5. The uneven portion is formed by changing the cross section of the mask to InP or In
2. The infrared diffractive lens according to claim 1, wherein the diffractive lens is formed by being transferred to a material containing P.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP6103699A JP2702883B2 (en) | 1994-05-18 | 1994-05-18 | Infrared diffraction lens |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP6103699A JP2702883B2 (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 |
|---|---|
| JPH0749408A JPH0749408A (en) | 1995-02-21 |
| JP2702883B2 true JP2702883B2 (en) | 1998-01-26 |
Family
ID=14361017
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP6103699A Expired - Lifetime JP2702883B2 (en) | 1994-05-18 | 1994-05-18 | Infrared diffraction lens |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP2702883B2 (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6649092B2 (en) * | 2001-04-04 | 2003-11-18 | Lockheed Martin Corporation | Plastic laminated infrared optical element |
-
1994
- 1994-05-18 JP JP6103699A patent/JP2702883B2/en not_active Expired - Lifetime
Non-Patent Citations (2)
| Title |
|---|
| ＪＯＵＲＮＡＬ ＯＦ ＴＨＥ ＯＰＴＩＣＡＬ ＳＯＣＩＥＴＹ ＯＦ ＡＭＥＲＩＣＡ ５１（１） ＰＰ．１７〜２０ |
| 久保田広他編 「光学技術ハンドブック（増補版）」 朝倉書店 （１９７５．７．２０） ＰＰ．６７４〜６７７ |
Also Published As
| Publication number | Publication date |
|---|---|
| JPH0749408A (en) | 1995-02-21 |
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