JPS6322568B2 - - Google Patents
Info
- Publication number
- JPS6322568B2 JPS6322568B2 JP59053221A JP5322184A JPS6322568B2 JP S6322568 B2 JPS6322568 B2 JP S6322568B2 JP 59053221 A JP59053221 A JP 59053221A JP 5322184 A JP5322184 A JP 5322184A JP S6322568 B2 JPS6322568 B2 JP S6322568B2
- Authority
- JP
- Japan
- Prior art keywords
- light
- window
- thickness
- coherence
- value
- 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
Links
- 230000010355 oscillation Effects 0.000 claims description 12
- 238000004891 communication Methods 0.000 description 10
- 239000004065 semiconductor Substances 0.000 description 10
- 239000013307 optical fiber Substances 0.000 description 7
- 238000010586 diagram Methods 0.000 description 6
- 238000000034 method Methods 0.000 description 5
- 230000001427 coherent effect Effects 0.000 description 4
- 230000003287 optical effect Effects 0.000 description 4
- MDPILPRLPQYEEN-UHFFFAOYSA-N aluminium arsenide Chemical compound [As]#[Al] MDPILPRLPQYEEN-UHFFFAOYSA-N 0.000 description 2
- 239000011248 coating agent Substances 0.000 description 2
- 238000000576 coating method Methods 0.000 description 2
- 230000003111 delayed effect Effects 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000001228 spectrum Methods 0.000 description 2
- JBRZTFJDHDCESZ-UHFFFAOYSA-N AsGa Chemical compound [As]#[Ga] JBRZTFJDHDCESZ-UHFFFAOYSA-N 0.000 description 1
- 241000282461 Canis lupus Species 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 230000000737 periodic effect Effects 0.000 description 1
Classifications
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/42—Coupling light guides with opto-electronic elements
- G02B6/4201—Packages, e.g. shape, construction, internal or external details
- G02B6/4204—Packages, e.g. shape, construction, internal or external details the coupling comprising intermediate optical elements, e.g. lenses, holograms
- G02B6/4206—Optical features
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/42—Coupling light guides with opto-electronic elements
- G02B6/4201—Packages, e.g. shape, construction, internal or external details
- G02B6/4204—Packages, e.g. shape, construction, internal or external details the coupling comprising intermediate optical elements, e.g. lenses, holograms
- G02B6/4207—Packages, e.g. shape, construction, internal or external details the coupling comprising intermediate optical elements, e.g. lenses, holograms with optical elements reducing the sensitivity to optical feedback
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Light Receiving Elements (AREA)
- Optical Couplings Of Light Guides (AREA)
Description
【発明の詳細な説明】
(a) 発明の技術分野
本発明は、半導体レーザを光源として、光フア
イバを伝送されてきた光を受光する装置に係り、
特に半導体レーザ光の可干渉性により、受光装置
の窓の厚さに起因して発生する多重反射による
歪，雑音を最小限にする為の、上記窓の厚さの設
定方法に関する。[Detailed Description of the Invention] (a) Technical Field of the Invention The present invention relates to a device for receiving light transmitted through an optical fiber using a semiconductor laser as a light source.
In particular, the present invention relates to a method for setting the thickness of the window in order to minimize distortion and noise due to multiple reflections caused by the thickness of the window of a light receiving device due to the coherence of semiconductor laser light.
(b) 技術の背景
最近の光フアイバによる光通信の著しい進歩，
高度化に伴つて、高いビツト速度のデイジタル通
信，或いはアナログ通信等が行われるようになつ
てきた。(b) Technical background Recent remarkable progress in optical communication using optical fibers,
With the advancement of technology, high bit rate digital communication, analog communication, etc. have come into use.
デイジタル通信の場合、ビツト速度が早くなる
につけて、伝送帯域幅が広くなり、該帯域幅に比
例して雑音のパワーが増加し、Ｓ／Ｎ比が悪くな
ることになり、アナログ通信の場合はAM通信と
なるので、デイジタル通信に比較して高いＳ／Ｎ
比が要求されることになる。 In the case of digital communication, as the bit speed increases, the transmission bandwidth becomes wider, and the noise power increases in proportion to the bandwidth, resulting in a worse S/N ratio.In the case of analog communication, Since it is AM communication, the S/N is higher than digital communication.
A ratio will be required.
従つて、かかる高いビツト速度のデイジタル通
信、或いはアナログ通信に対しても、Ｓ／Ｎ比の
良い、光フアイバによる光通信の方法が要望され
ていた。 Therefore, for such high bit rate digital communication or analog communication, there has been a demand for an optical communication method using optical fibers with a good S/N ratio.
(c) 従来技術と問題点
従来、半導体レーザを光源として、光フアイバ
を伝送されてきた光を受光する場合、該光受光器
の窓については、該窓の厚さに対する考慮が払わ
れていなく、無反射コーテイングを施してある
が、残留反射があり、その為の多重反射光が干渉
を起こし、半導体レーザ光の可干渉性が高いこと
と相まつて、干渉性の歪，雑音を発生していると
云う欠点があつた。(c) Prior art and problems Conventionally, when a semiconductor laser is used as a light source to receive light transmitted through an optical fiber, no consideration is given to the thickness of the window of the optical receiver. Although it is coated with a non-reflective coating, there is residual reflection, which causes multiple reflected light to cause interference, which, combined with the high coherence of the semiconductor laser light, causes coherent distortion and noise. There was a drawback that there was.
(d) 発明の目的
本発明は上記従来の欠点に鑑み、受光器の窓の
厚さを特定の厚さに設定することにより、該窓の
厚さに起因する多重反射に伴う歪，雑音の発生を
最小限に抑止した受光装置を提供することを目的
とするものである。(d) Purpose of the Invention In view of the above-mentioned conventional drawbacks, the present invention eliminates distortion and noise caused by multiple reflections caused by the thickness of the window by setting the thickness of the window of the photodetector to a specific thickness. The object of the present invention is to provide a light-receiving device that minimizes the occurrence of such occurrences.
(e) 発明の構成
そしてこの目的は、本発明によれば、窓の厚さ
がｄである受光装置において、該窓の厚さｄを光
が往復する時間におけるコヒーレンス関数の値が
小さくなるように、該ｄの値を設定し、可干渉性
により発生する歪，雑音を最小限に抑えるように
する方法も提供することによつて達成され、受光
器の窓の反射による干渉性歪，雑音の発生が最小
限に抑えられるので、高品質なアナログ情報，デ
イジタルデータ等の伝送に適した受光装置が実現
できる利点がある。(e) Structure of the Invention According to the present invention, in a light receiving device whose window has a thickness d, the value of the coherence function in the time it takes for light to travel back and forth through the thickness d of the window is reduced. This is achieved by also providing a method for setting the value of d to minimize the distortion and noise caused by coherence, and the interference distortion and noise caused by reflection from the receiver window. This has the advantage that a light receiving device suitable for transmitting high-quality analog information, digital data, etc. can be realized because the occurrence of .
(f) 発明の実施例
本発明の主旨を要約すると、本発明は、窓の厚
さがｄである受光装置において、該窓の厚さｄを
光が往復する時間におけるコヒーレンス関数の値
が小さくなるように、該ｄの値を設定することに
より、干渉性歪，雑音の発生を抑えるようにした
ものである。(f) Embodiments of the Invention To summarize the gist of the present invention, the present invention provides a light receiving device having a window with a thickness d, in which the value of the coherence function in the time it takes for light to travel back and forth through the window thickness d is small. By setting the value of d, the generation of coherent distortion and noise is suppressed.
以下本発明の実施例を図面によつて詳述する。
第１図は本発明を適用した受光装置をブロツク図
で示した図，第２図は半導体レーザに対して、高
速度変調を行つた時の多縦モード発振のスペクト
ルを示す図，第３図は厚さｄの媒質におけるレー
ザ光の反射状況を示す図，第４図はコヒーレンス
関数Ｃ（τ）の値をグラフで表示した図である。 Embodiments of the present invention will be described in detail below with reference to the drawings.
Fig. 1 is a block diagram of a light receiving device to which the present invention is applied, Fig. 2 is a diagram showing the spectrum of multi-longitudinal mode oscillation when high-speed modulation is performed on a semiconductor laser, and Fig. 3 4 is a diagram showing the state of reflection of laser light in a medium having a thickness of d, and FIG. 4 is a diagram showing the value of the coherence function C(τ) in a graph.
第１図において、１は光フアイバ，２は本発明
に関連する受光装置、２１は厚さがｄである受光
窓，２２が受光素子，３，４は受光素子２２の出
力線である。 In FIG. 1, 1 is an optical fiber, 2 is a light-receiving device related to the present invention, 21 is a light-receiving window having a thickness of d, 22 is a light-receiving element, and 3 and 4 are output lines of the light-receiving element 22.
光フアイバ１から半導体レーザ光が受光装置２
の窓２１を通して、受光素子２２に投射される
と、該レーザ光の強弱に対応した電気信号が出力
され、出力線３，４を通じて外部に出力される。 Semiconductor laser light is transmitted from optical fiber 1 to light receiving device 2
When the laser beam is projected onto the light receiving element 22 through the window 21, an electric signal corresponding to the intensity of the laser beam is outputted and outputted to the outside through the output lines 3 and 4.
この場合、受光器２の窓２１は屈折率ｎの媒質
で構成されており、屈折率の異なる空気に対する
面が反射面を構成している。前述のように、通常
この反射面は無反射コーテイングをしてあるが、
残留反射があり、それによる多重反射光が干渉を
起こし、干渉性歪，雑音を発生させる原因となつ
ている。本発明は、かかる状態での反射光を抑止
する方法を関している。 In this case, the window 21 of the light receiver 2 is made of a medium with a refractive index n, and the surface facing air having a different refractive index constitutes a reflective surface. As mentioned above, this reflective surface is usually coated with a non-reflective coating.
There is residual reflection, and the resulting multiple reflections cause interference, causing coherent distortion and noise. The present invention relates to a method for suppressing reflected light under such conditions.
一般に、半導体レーザは、該レーザ光に対して
高速度変調（例えば、数10〜数100MHz，又は
Mb／Ｓ以上）を行うと、第２図に示す多縦モー
ドの発振を起こす。 Generally, a semiconductor laser modulates the laser light at high speed (for example, several tens to several hundreds of MHz, or
Mb/S or more), multi-longitudinal mode oscillation as shown in FIG. 2 occurs.
第２図において、該縦モード発振の周波数間隔
をΔνとすると、該Δνは以下のようにして求めら
れる。即ち、それぞれの縦モード発振の周波数を
νとすると、
ν＝Ｃ／λ
ここで、Ｃ：真空中の光速度
λ：縦モード発振の波長
である。 In FIG. 2, if the frequency interval of the longitudinal mode oscillation is Δν, then the Δν is obtained as follows. That is, if the frequency of each longitudinal mode oscillation is ν, then ν=C/λ where C: speed of light in vacuum λ: wavelength of longitudinal mode oscillation.
従つて、上式を微分すると、 dν／dλ＝−Ｃ／λ2 ∴dν＝−Ｃ・dλ／λ2 即ち、Δν＝−Ｃ・dλ／λ2となる。 Therefore, when the above equation is differentiated, dν/dλ=-C/λ 2 ∴dν=-C·dλ/λ 2 , that is, Δν=-C·dλ/λ 2 .
このΔνの値は、0.8μ帯のガリウム・アルミニ
ウム・砒素（GaAlAs）／ガリウム・砒素
（GaAs）レーザにおいては、200GHz程度である。
そして、γは１本の縦モード発振レーザの帯域幅
を示している。 The value of Δν is approximately 200 GHz in a 0.8 μ band gallium aluminum arsenide (GaAlAs)/gallium arsenide (GaAs) laser.
Further, γ indicates the bandwidth of one longitudinal mode oscillation laser.
今、半導体レーザ光の光路中に、第３図に示す
ような２つの反射面を持つ媒質（例えば、前述の
受光器の窓の媒質）があり、その２つの反射面の
距離がｄであるとすると、該反射面からの反射光
Ｒによるレーザ光の遅れ時間τは以下の式で表さ
れる。即ち
τ＝2dn／Ｃ ……
ここで、Ｃ：真空中の光速度
ｎ：上記媒質の屈折率
直進光Ｔと、τだけ遅れた反射光Ｒとの可干渉
性（コヒーレンス度という）をＣ（τ）とすると、
Ｃ（τ）は
Ｃ（τ）
＝（Imax−Imin）／（Imax＋Imin）
ここで、Ｉ：干渉した光の強度を示す。 Now, in the optical path of the semiconductor laser light, there is a medium with two reflective surfaces as shown in Figure 3 (for example, the medium of the window of the photodetector mentioned above), and the distance between the two reflective surfaces is d. Then, the delay time τ of the laser beam due to the reflected light R from the reflecting surface is expressed by the following formula. That is, τ=2dn/C... Here, C: speed of light in vacuum n: refractive index of the above medium The coherence (referred to as degree of coherence) between the straight light T and the reflected light R delayed by τ is expressed as C( τ), then
C(τ) is as follows: C(τ) = (Imax-Imin)/(Imax+Imin) where I: indicates the intensity of the interfered light.
で表される。It is expressed as
上式を導く過程については、公知資料：
「PRINCIPLES OF OPTICS」（BORN＆
WOLF著，PERGAMON社，1970版，316ペー
ジ，§7.5.8）に示されているので、ここでは特
に示さないが、上記Ｃ（τ）の値（可干渉性度）
をグラフにすると、第４図の通りとなり、実線で
示したように、周期的にピーク値を持つた特性を
示し、該ピークの値は点線で示したように、exp
（−γτ）で減衰する。ここで、γは第２図で示し
た、複数個の縦モード発振における発振周波数の
帯域幅である。 Regarding the process of deriving the above equation, please refer to the publicly known materials:
"PRINCIPLES OF OPTICS" (BORN &
WOLF, PERGAMON, 1970 edition, page 316, §7.5.8), so it is not specifically shown here, but the value of C(τ) above (degree of coherence)
When made into a graph, it becomes as shown in Figure 4, which shows a characteristic with periodic peak values as shown by the solid line, and the value of the peak is exp as shown by the dotted line.
(−γτ). Here, γ is the bandwidth of the oscillation frequency in a plurality of longitudinal mode oscillations shown in FIG.
この図において、Ｘ軸は光の遅れ時間τ，Ｙ軸
は可干渉性度Ｃ（τ）の値を示しており、最も可
干渉性度が大きい値を示すτの値は、図から明ら
かな如く、
０，１／Δν，２／Δν……
である。従つて、最も可干渉性度が小さくなるτ
の値は、
1/2Δν，3/2Δν……
となる。 In this figure, the X-axis shows the light delay time τ, and the Y-axis shows the value of the degree of coherence C(τ).The value of τ, which indicates the largest value of the degree of coherence, is clearly As in, 0, 1/Δν, 2/Δν... Therefore, the degree of coherence is the smallest τ
The values of are 1/2Δν, 3/2Δν...
従つて、上記式から最も可干渉性度が小さく
なるτに関して、以下の関係式が得られる。即
ち、
τ＝2dn／Ｃ＝1/2Δν
＝3/2Δν
〓
上式から、可干渉性度が最も小さくなる距離ｄ
を求めると、
ｄ＝Ｃ／4nΔν
＝3C／4nΔν
〓
＝（2m＋１）Ｃ／4nΔν
となる。ここで，ｍ＝０，１，２，３……であ
る。 Therefore, from the above equation, the following relational expression can be obtained regarding τ at which the degree of coherence is the smallest. That is, τ=2dn/C=1/2Δν =3/2Δν 〓 From the above formula, the distance d where the degree of coherence is the smallest
d=C/4nΔν =3C/4nΔν 〓 =(2m+1)C/4nΔν. Here, m=0, 1, 2, 3....
２つの反射面の間の距離ｄ（即ち、受光器の窓
の厚さｄに対応）を上式の値になるように選べ
ば、第３図における反射光Ｒと透過光Ｔとの間の
干渉は非常に小さくすることができることにな
る。 If the distance d between the two reflecting surfaces (that is, corresponding to the thickness d of the window of the receiver) is chosen to be the value of the above formula, the distance between the reflected light R and the transmitted light T in Fig. 3 is It follows that the interference can be made very small.
尚、第４図のグラフから明らかな如く、可干渉
性度を小さくする為の距離ｄは、上式で決まる一
点ではなく、その近傍の任意の位置を考えても、
可干渉性度は無視できる程度に小さくできること
が理解できる。 As is clear from the graph in Figure 4, the distance d for reducing the degree of coherence is not determined by the above equation, but is determined by any arbitrary position in the vicinity.
It can be seen that the degree of coherence can be made small enough to be ignored.
(g) 発明の効果
以上、詳細に説明したように、本発明の受光装
置は、窓の厚さがｄである受光装置において、該
窓の厚さｄを光が往復する時間において、コヒー
レンス関数の値〔Ｃ（τ）の値〕が小さくなるよ
うに、該ｄの値を設定したものであるので、該受
光器の窓による反射に起因する干渉性歪，雑音の
発生を最小限に抑えることができ、高品質のアナ
ログ情報，デイジタル情報等の伝送に適した受光
装置を実現することができる効果がある。(g) Effects of the Invention As explained above in detail, in the light receiving device of the present invention, the coherence function is Since the value of d is set so that the value of [C(τ)] is small, the generation of coherent distortion and noise caused by reflection by the window of the light receiver is minimized. This has the effect of realizing a light receiving device suitable for transmitting high quality analog information, digital information, etc.
第１図は本発明に関連する受光装置をブロツク
図で示した図，第２図は半導体レーザに対して、
高速度変調を行つた時の多縦モード発振のスペク
トルを示す図，第３図に厚さｄの媒質におけるレ
ーザ光の反射状況を示す図，第４図はコヒーレン
ス関数Ｃ（τ）の値をグラフ表示した図である。
図面において、１は光フアイバ，２は受光装
置，２１は窓，２２は受光素子，３，４は受光素
子２２の出力線，νは半導体レーザの多縦モード
発振周波数，λは該多縦モードレーザ光の波長，
γは１本の縦モード発振レーザ光の帯域幅，ｄは
２つの反射面を有する媒質の距離（即ち、受光器
の窓の厚さに対応），Ｃ（τ）は透過光Ｔと，τだ
け遅れた反射Ｒとの可干渉性度，をそれぞれ示
す。
FIG. 1 is a block diagram of a light receiving device related to the present invention, and FIG. 2 is a diagram showing a semiconductor laser.
Figure 3 shows the spectrum of multi-longitudinal mode oscillation when performing high-speed modulation, Figure 3 shows the state of reflection of laser light in a medium with thickness d, and Figure 4 shows the value of the coherence function C(τ). It is a figure displayed graphically. In the drawing, 1 is an optical fiber, 2 is a light receiving device, 21 is a window, 22 is a light receiving element, 3 and 4 are output lines of the light receiving element 22, ν is the multi-longitudinal mode oscillation frequency of the semiconductor laser, and λ is the multi-longitudinal mode. wavelength of laser light,
γ is the bandwidth of one longitudinal mode oscillation laser beam, d is the distance of the medium with two reflecting surfaces (that is, corresponds to the thickness of the window of the receiver), C(τ) is the transmitted light T, and τ The degree of coherence with the reflection R delayed by
Claims (1)
ザ光を電気信号に変換し、外部へ出力する受光装
置において、該窓の厚さｄを、 ｄ＝（2m＋１）Ｃ／4nΔν ｍ：自然数 Ｃ：真空中の光速度 ｎ：該窓の屈折率 Δν：該レーザ光に対して高速度変調を行つた
場合の縦モード発振の周波数間隔 とすることを特徴とする受光装置。[Claims] 1. In a light receiving device that converts laser light input through a window with a thickness of d into an electrical signal and outputs it to the outside, the thickness d of the window is d=(2m+1) C/4nΔν m: natural number C: speed of light in vacuum n: refractive index of the window Δν: frequency interval of longitudinal mode oscillation when high-speed modulation is performed on the laser beam Device.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP59053221A JPS60221711A (en) | 1984-03-19 | 1984-03-19 | Photodetecting device |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP59053221A JPS60221711A (en) | 1984-03-19 | 1984-03-19 | Photodetecting device |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPS60221711A JPS60221711A (en) | 1985-11-06 |
| JPS6322568B2 true JPS6322568B2 (en) | 1988-05-12 |
Family
ID=12936765
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP59053221A Granted JPS60221711A (en) | 1984-03-19 | 1984-03-19 | Photodetecting device |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPS60221711A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH0345871A (en) * | 1989-07-10 | 1991-02-27 | Sanden Corp | Refrigerant flow divider for freezing circuit |
Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5548993A (en) * | 1978-10-04 | 1980-04-08 | Nec Corp | Semiconductor laser device |
-
1984
- 1984-03-19 JP JP59053221A patent/JPS60221711A/en active Granted
Patent Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5548993A (en) * | 1978-10-04 | 1980-04-08 | Nec Corp | Semiconductor laser device |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH0345871A (en) * | 1989-07-10 | 1991-02-27 | Sanden Corp | Refrigerant flow divider for freezing circuit |
Also Published As
| Publication number | Publication date |
|---|---|
| JPS60221711A (en) | 1985-11-06 |
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