JP2004159032A

JP2004159032A - Spatial optical communication system

Info

Publication number: JP2004159032A
Application number: JP2002322002A
Authority: JP
Inventors: Masahiro Toyoda; 雅宏豊田
Original assignee: Communications Research Laboratory
Current assignee: Communications Research Laboratory
Priority date: 2002-11-06
Filing date: 2002-11-06
Publication date: 2004-06-03

Abstract

<P>PROBLEM TO BE SOLVED: To properly perform directivity control and alignment adjustment in spatial optical communication between both stations in the case of interconnecting two points spatially apart from each other by means of the spatial optical communication. <P>SOLUTION: Both of the first and second communication stations for performing the spatial optical communication have an optical reflector 2, a light receiving means 3 receives reflected laser beams 5a', 5b' resulting from transmission laser beams 5a, 5b emitted from a laser transmitter 1 of its own station and reflected in the optical reflector 2 of an opposite communication station, and a communication control means 4 adjusts the strength, the spread angle, and the emission direction of the transmission laser beams 5a, 5b on the basis of the reception strength of the reflected laser beams 5a', 5b' to automatically perform the proper directivity control and alignment adjustment. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、空間的に離れた２地点の通信局をレーザ光を用いた空間光通信で接続する空間光通信システムに関し、特に、通信相手方へのレーザ光の照射を迅速かつ的確に行い得る技術に関する。
【０００２】
【従来の技術】
従来より行われている空間光通信システムは、離れた２つの建築物（建物の屋根や塔など）に空間光通信用端末を設置し、これら空間光通信用端末を備える通信局間でレーザ光を用いた空間光通信を行うものである。空間光通信用端末の建築物への設置に際しては、設置する２地点の各建築物の双方に人員を配置して、互いに連絡を取り合い、各空間光通信用端末が送信したレーザ光が相手側に受光されているかを確認しながら、空間光通信機端末の指向方向を調節するのである。
【０００３】
【非特許文献１】
オプトロニクス社編集部，「光空間通信ネットワーク技術資料集」，株式会社オプトロニクス社，平成１２年３月１０日
【０００４】
この場合には、レーザ光の拡がり角を十分に大きく設定することによって、人手による大雑把な指向方向の調節を可能としていた。さらに、空間光通信用端末のレーザ出射方向がずれたり、建築物の歪みによって空間光通信用端末のレーザ出射方向がずれたりすると、レーザ通信回線が途切れることを避けるためにも、レーザ光の拡がり角は大きく取られていた。
【０００５】
【発明が解決しようとする課題】
しかしながら、上述したような空間光通信用端末の設置方法では、複数の人員の配置と、人員間の密接な連絡が必要なため、設置に手間が掛かっていた。
【０００６】
また、レーザ光の拡がり角を人手で対応できるように十分に大きくしていたため、使用するレーザ光源の強度を強くすることが要求され、また、通信の相手方までの距離も制限されていた。そのため、通信のデータレートを高くできない欠点や、拡がりが大きいために弱まった光を受けることから受信側の受光口径を大きくし、また、信号検出性能を上げたりとの負荷が加わっていた。
【０００７】
さらに、霧や雨などの空間伝送路の状況に柔軟に対応できないため、相手側へ照射するレーザ光の強度にマージンを持たせた設計となっていたため、空間光通信用端末の光学的な性能を十分に利用することができなかった。
【０００８】
加えて、何らかの要因により、片方のレーザ光が相手側に照射されなくなった時には、再度の設置作業が必要となり、復旧への迅速な対応が困難であった。
【０００９】
そこで、本発明は、２局間で光通信を用いた良好な通信状態を確立するための空間光通信用端末における設定を、人手を煩わすことなく、迅速かつ的確に行うことができる空間光通信システムの提供を目的とする。
【００１０】
【課題を解決するための手段】
上記の課題を解決するために、請求項１に係る発明は、空間的に離れた２地点の通信局をレーザ光を用いた空間光通信で接続する空間光通信システムであって、双方の通信局は、それぞれ、送信レーザ光を出射するレーザ送信手段と、入射した光線を到来方向と逆方向へ反射する光反射器と、レーザ光を受光する受光手段と、上記レーザ送信手段を制御して相手側通信局への信号送信を行うと共に上記受光手段が受光した相手側通信局からの信号を受信処理する通信制御手段と、を含む空間光通信用端末を備え、且つ、両通信局のレーザ送信装置がそれぞれ出射する送信レーザ光は、互いに識別可能なように光特性を異ならせておき、上記通信制御手段は、相手側通信局へ出射した送信レーザ光が相手側通信局から反射されて戻った反射レーザ光の受光強度を上げるようにレーザ光の出射方向を調整することで、送信レーザ光の出射方向を相手側通信局へ向けるようにしたことを特徴とする。
【００１１】
また、請求項２に係る発明は、上記請求項１に記載の空間光通信システムにおいて、上記通信制御手段は、送信レーザ光の拡がり角を狭めることで、相手側での受光強度を上げるように、通信状態を調整するようにしたことを特徴とする。
【００１２】
【発明の実施の形態】
次に、添付図面に基づいて、本発明に係る空間光通信システムの実施形態を説明する。
【００１３】
図１に示すのは、空間的に離れた２地点の通信局をレーザ光を用いた空間光通信で接続する空間光通信システムを構成する第１通信局と第２通信局の概略構成であり、第１通信局に設けた空間光通信端末Ａと第２通信局に設けた空間光通信端末Ｂとは、実質的に同じ構成である。すなわち、空間光通信用端末Ａおよび空間光通信用端末Ｂは、それぞれ、送信レーザ光を出射するレーザ送信手段１と、入射した光線を到来方向と逆方向へ反射する光反射器２と、レーザ光を受光する受光手段３と、レーザ送信手段１を制御して相手側通信局への信号送信を行うと共に受光手段３が受光した相手側通信局からの信号を受信処理する通信制御手段４と、を備える。
【００１４】
上記通信制御手段４は、上記レーザ送信手段１を制御して相手側通信局への信号送信を行うと共に上記受光手段３が受光した相手側通信局からの信号を受信処理するものである。加えて、通信制御手段４は、送信用レーザの強度、受光端でのビーム径（照射側におけるレーザ光源のビーム径と拡がり角に加えて両通信局間の距離で決まるビーム径。以下、特に断らない限り、「ビーム径」は「受光端でのビーム径」の意味で用いる。）および照射方向を制御する機能も有する。上記レーザ送信手段１より出射するレーザ光の強度は、通信制御手段４からのレーザ強度制御信号により制御される。また、本実施形態で示すレーザ送信手段１は、少なくとも、出射方向調整部１１とビーム径調整部１２とレーザ強度調整部１３とを備え、通信制御手段４からの制御に応じて、送信レーザ光の出射方向を変えたり、ビームの拡がり角を調整して受光端でのビーム径を拡げたり絞ったり、良好な通信状態とするのに十分なレーザ強度に調整したりできる。
【００１５】
ここで、空間光通信用端末Ａのレーザ送信手段１から出射される送信レーザ光５ａと空間光通信用端末Ｂのレーザ送信手段１から出射される送信レーザ光５ｂとは、分離が可能なように光特性（例えば、波長や偏光）を異ならせておく。本実施形態においては、第１通信局と第２通信局とで、異なる波長のレーザ光を用いて通信するものとした。
【００１６】
よって、レーザ送信手段１より出射された送信レーザ光５ａが相手側通信局である第２通信局の光反射器２で反射されて戻った反射レーザ光５ａ′と、第２通信局のレーザ送信手段より出射された送信レーザ光５ｂとを同時に受光する受光手段３は、その光特性により、反射レーザ光５ａ′と送信レーザ光５ｂとを分離して受光することができる。同様に、第２通信局の受光手段３も、送信レーザ光５ｂが相手側通信局である第１通信局の光反射器２で反射されて戻った反射レーザ光５ｂ′と、第１通信局のレーザ送信手段より出射された送信レーザ光５ａとを同時に受光して、これらを分離することができる。本実施形態においては、このような光分離機能を担う光分離部３１を受光手段３に設けるものとし、通信光受光強度信号と反射光受光強度信号を通信制御手段４へ送信するものとした。
【００１７】
なお、空間光通信用端末Ａおよび空間光通信用端末Ｂの各受光手段３の視野は十分に広く設定すると共に、各レーザ送信手段１から出射した送信レーザ光５ａ，５ｂの方向は、受光手段３の視野方向のほぼ中央に配置されるように、端末設置時に調整しておく。地上の固定２地点間の光通信では、通信距離が短いため、視野を狭くして、受光感度を上げる必要性が低いことから、受光系の視野をやや広めに設定しておけば、視野の方向を固定としても、十分な受信強度を確保できるのである。しかし、低出力のレーザ光を用いるような制限が課されて、視野を狭くして受光感度を高めなければならないような場合には、受光方向調整部を設けて、受光方向を微調整するようにしても良い。
【００１８】
また、入射した光線を到来方向と逆方向へ反射する光反射器２としては、互いに直角をなしている３面の鏡面で構成された光学機器であるＣＣＲ（ＣｏｒｎｅｒＣｕｂｅＲｅｔｒｏ―ｒｅｆｌｅｃｔｏｒ）を用いることができ、このＣＣＲの有効入射角度は数十度と非常に広いため、空間光通信用端末Ａ，Ｂにおける光反射器２の取り付け時の方向の精度は要求されない。なお、光反射器２の反射面の大きさや光反射器２の設置個数は特に限定されるものではなく、空間光通信用端末Ａ，Ｂの光送受信の性能、両通信局間の距離、通信データレート等の諸条件に応じて、適宜に設計すれば良い。
【００１９】
上記のように構成した空間光通信用端末Ａと空間光通信用端末Ｂとを外観の一例を示したのが、図２であり、建築物に設置された空間光通信用端末Ａ，Ｂの各レーザ送信手段１と光反射器２と受光手段３とが相対する空間中に遮蔽物が存在しないことで、屋外における空間光通信を実現できる。なお、本実施形態においては、空間光通信用端末Ａ，Ｂの各レーザ送信手段１，光反射器２，受光手段３を治具によって建築物等に取り付けるものとした。治具の取り付け時の角度を調節することによって、相手側通信局へおおよその方向を向けておくのである。なお、通信制御手段４は、屋外に設置される治具の適所に内蔵しても良いし、屋内に設けるようにしても良い。
【００２０】
次に、図３に基づいて、レーザ送信手段１における出射方向調整部１１とビーム径調整部１２の一具体例と、受光手段３における分離部３１の一具体例を説明する。なお、ここでは第１通信局の空間光通信用端末Ａを例に説明するが、第２通信局の空間光通信用端末Ｂも同様の構成である。
【００２１】
先ず、レーザ送信手段１について説明する。レーザ光の発光源であるレーザ光源１４は、三次元方向移動装置１５の移動ステージ上に設置され、通信制御手段４からのレーザ強度制御信号に応じた強度で予め定められた波長のレーザ光を出力する。このようにして出力されたレーザ光は、送信レンズ１６を通って、その焦点距離に応じた拡がり角の送信レーザ光５ａとして相手側通信局（第２通信局）へ出射される。
【００２２】
ここで、上記三次元方向移動装置１５は、レーザ送信手段１のケーシング適所に固着される固定ステージに対して、レーザ光源１４が定置された移動ステージを３次元の各方向に微動できる装置であり、通信制御手段４より入力された位置制御信号に応じて移動ステージの位置を変えるものである。このように、レーザ送信手段１のケーシングに固定された送信レンズ１６に対し、レーザ光源１４の位置（レーザ光の照射位置）を相対的に変化させることで、レーザ光の出射方向や受光端でのビーム径を変化させることができる。
【００２３】
すなわち、本実施形態で用いるレーザ送信手段１においては、送信レンズ１６に対してレーザ光源１４を三次元方向へ相対的に移動させることが可能な三次元方向移動装置１５によって、出射方向調整部１１およびビーム径調整部１２の両機能を実現するのである。また、レーザ強度調整部１３の機能は、レーザ光源１４が有する。
【００２４】
例えば、レーザ光の伝搬方向と平行なｘ軸とこれに直交するｙ軸がほぼ水平面に位置してｚ軸が鉛直面に位置すると仮定した場合、レーザ光の伝搬方向と平行なｘ軸方向にステージを移動させることによって、送信レンズ１６を通って出射される送信レーザ光５ａの拡がり角を調節でき、レーザ光の伝搬方向と垂直な方向に移動ステージを動かすことによって、送信レンズ１６を通って出射される送信レーザ光５ａの出射方向（ｙ軸方向に移動させた場合には左右方向、ｚ軸方向に移動させた場合には上下方向）を微調節できる。
【００２５】
なお、ＤＣモーターの回転動作を適宜なギアで直進動作に変換したマイクロメーター（いわゆる微動装置）機構にエンコーダを付けてフィードバック制御を行い１μｍ程度の動作精度を実現した機器（数ｃｍ長の筒状のもの）が市販されており、これをｘ−ｙ−ｚの３軸に組み合わせて移動ステージを各軸方向へ移動できるようにすれば、三次元方向移動装置１５を実現できる。
【００２６】
次いで、受光手段３について説明する。相手側通信局である第２通信局より出射された送信レーザ光５ｂと、自局のレーザ送信手段１より出射して第２通信局の光反射器２で反射されて戻った反射レーザ光５ａ′は、集光レンズ３２を介して内部へ導き、光学フィルタ３３を経て太陽光などの背景光が除去された後、ビームスプリッタ３４へ到達する。このビームスプリッタ３４には波長選択性を持たせてあり、自局の送信レーザ光５ａ（反射レーザ光５ａ′）の波長の光を反射し、相手側通信局の送信レーザ光５ｂの波長の光を透過するので、送信レーザ光５ｂと反射レーザ光５ａ′を分離することができる。
【００２７】
すなわち、本実施形態で用いる受光手段３においては、２つの通信局毎に定めたレーザ光の波長を透過もしくは反射して分離できるビームスプリッタ３４によって、光分離部３１の機能を実現できるのである。
【００２８】
上記のようにして分離された反射レーザ光５ａ′は反射光受光器３５によって、第２通信局からの送信レーザ光５ｂは通信光受光器３６によって、各々光電変換され、反射光受光強度信号および通信光受光強度信号が通信制御手段４へ供給される。なお、ビームスプリッタ３４によって分離された反射レーザ光５ａ′と送信レーザ光５ｂを光信号のまま光ファイバ等で通信制御手段４へ導き、通信制御手段４内で光電変換するようにしても良い。
【００２９】
そして、上述した構成の空間光通信用端末Ａ，Ｂにおいて、送信元から出射した送信レーザ光５ａ，５ｂが、相手側通信局の受光手段３に照射されていれば、その光反射器２で反射され、反射レーザ光５ａ′，５ｂ′は到来方向と逆の方向へ伝搬するため、送信元通信局の受光手段３を照射することとなる。よって、受光手段３の反射光受光器３５から反射光受光強度信号が通信制御手段４へ送られることとなり、反射レーザ光５ａ′，５ｂ′の受光強度を通信制御手段４が取得できる。
【００３０】
一方、受光手段３が反射レーザ光５ａ′，５ｂ′を受光していないときには、反射光受光器３５から反射光受光強度信号が送信され無い（もしくは、極めて低い値を示す反射光受光強度信号が送信される）ために、通信制御手段４は、レーザ光源１４から出る送信レーザ光の強度を上げるようにレーザ強度制御信号をレーザ光源１４へ送ると共に、レーザ光源１４を送信レンズ１６に近付ける方向（図３中、ｘ軸方向）に移動ステージを動かすように位置制御信号を三次元方向移動装置１５へ送り、送信レーザ光５ａ，５ｂの強度および拡がり角を大きくし、確実に相手側通信局の光反射器２を照射するように調整する。
【００３１】
この調整が適切なビーム強度と拡がり角を満たせば、送信レーザ光５ａ，５ｂが相手側通信局の光反射器２を照射して、その反射光である反射レーザ光５ａ′，５ｂ′が送信元通信局の受光手段３を照射することとなり、反射光受光器３５から出力される反射光受光強度信号によって反射レーザ光５ａ′，５ｂ′の受光強度を通信制御手段４が取得できる。
【００３２】
反射レーザ光５ａ′，５ｂ′の受光強度を取得した通信制御手段４は、反射光の受光強度を更に上げるように、送信レンズ１６から等距離面内（図３中、ｙ軸およびｚ軸方向）でレーザ光源１４を動かすように位置制御信号を三次元方向移動装置１５へ送る。すなわち、通信制御手段４が、相手側通信局へ出射した送信レーザ光５ａ，５ｂが相手側通信局から反射されて戻った反射レーザ光５ａ′，５ｂ′の強度を上げるようにレーザ光の出射方向を調整することで、送信レーザ光５ａ，５ｂの出射方向を相手側通信局へ自動的に向けることが可能となる。
【００３３】
なお、通信制御手段４による指向制御（レーザビームの送信方向を相手側通信局へ向ける制御）において、その制御手法は特に限定されるものではなく、最適なビーム照射方向（反射レーザ光５ａ′，５ｂ′の受信強度が最も強くなるポイント）を見つけるようにビーム走査を行って行くようにしても良いし、空間光通信を行う上で必要十分な基準値として予め定めた基準受信強度をクリアするビーム送信方向が見つかった時点で、そこをビーム照射方向と設定するようにしても良い。
【００３４】
また、通信制御手段４は、最適なビーム照射方向となるように三次元方向移動装置１５に対する動作制御（ｙ軸およびｚ軸方向の制御）を行った後、レーザビームの拡がり角を狭めるように三次元方向移動装置１５に対する動作制御（ｘ軸方向の制御）を行い、送信レーザ光５ａ，５ｂの拡がり角を狭めることに伴って反射レーザ光５ａ′，５ｂ′の受信強度が高くなるので、この反射レーザ光５ａ′，５ｂ′の受信強度が適切な値となるようにレーザ光源１４に対するレーザ強度制御を行うことで、通信相手局に適した照準となる通信状態の調整（アライメント調節）を自動で行えるようにしても良い。
【００３５】
加えて、上述した指向制御とアライメント調節を行った後、更に指向制御を行って、より正確なビーム照射方向を定め、再びアライメント調整を行うような制御手法をとれば、一層微妙な指向制御とアライメント調節を行うことができる。
【００３６】
以上のように、両通信局間で指向制御とアライメント調節が完了すると、相手側通信局の光反射器２での反射光である反射レーザ光５ａ′，５ｂ′を反射光受光器３５で受光し、かつ、相手側通信局の送信レーザ光５ａ，５ｂを通信光受光器３６で受光しているので、反射光受光器３５からの反射光受光強度信号および通信光受光器３６からの通信光受光強度信号により、通信制御手段４は、両通信局間の空間光通信回線が成立していると判定できる。
【００３７】
しかしながら、相手側通信局からの送信レーザ光５ａ、５ｂのみを受光していたときには、自局の送信レーザ光４ａ，５ｂが相手側を照射していないことを意味するので、指向制御とアライメント調節の手順を再度行えば良い。このように、本実施形態に係る空間光通信システムにおいては、自局の送信レーザ光５ａ，５ｂの反射光（反射レーザ光５ａ′，５ｂ′）を受光しているか否かによって、レーザ送信手段１の送信方向がずれていることを検知している。
【００３８】
一方、自局の送信レーザ光５ａ，５ｂの反射光（反射レーザ光５ａ′，５ｂ′）のみを受光していた場合には、相手側通信局のレーザ指向方向が適切でないことを意味する。この場合には、相手側通信局においても、自ら出射した送信レーザ光５ａ，５ｂの反射光（反射レーザ光５ａ′，５ｂ′）が検出されていない筈であるから、相手側通信局で指向制御とアライメント調節が自動で行われて、相手側通信局の送信レーザ光５ａ，５ｂを受信できるようになり、双方向のレーザ回線が回復する。なお、相手側通信局からの送信レーザ光５ａ，５ｂを受光できなくなってから、所定の猶予時間が経過しても相手側通信局からの送信レーザ光５ａ，５ｂを受光できない場合は、相手側通信局に何らかの障害が発生している可能性があるので、エラー発生としてレーザ回線を遮断する制御としても良い。
【００３９】
次に、本実施形態に係る空間光通信システムにおいて、両通信局間で良好な通信状態を設定するために通信制御手段４が行う具体的な制御手順について説明する。なお、以下の説明は、第１通信局の空間光通信用端末Ａにおける通信制御手段４が行う制御についてであるが、第２通信局の空間光通信用端末Ｂにおける通信制御手段４が行う制御も同様である。
【００４０】
上述した図２のように、見通しの利く２地点に、空間光通信用端末Ａおよび空間光通信用端末Ｂが設置されており、双方の受光手段３の視野は、設置における角度精度より十分広く設定しておく。例えば、相手側通信局へ向けて取り付けるときの精度が±５度とすると、受光手段３の視野は±１０度とする。なお、光反射器２の視野は幾何光学的には±３７．３度であり、受光手段３よりも十分広い視野となる。
【００４１】
一方、ビームの拡がり角は、光反射器２や受光手段３の角度と比較して数桁小さくすることができ、コリメートさせた場合（ビームの回折限界の拡がり角で送信する場合）、例えばレーザの波長が１μｍで１ｃｍ直径のビームであれば、全角で１２２μｒａｄ＝０．００７度の円錐状となる。ビームの拡がり角は、狭いほど相手への放射照度が高くなるため、通信においては、速度を上げられるなどの利点がある。よって、相手側での受光強度を上げる観点からは、受光端でのビーム径が光反射器２の開口と受光手段３の開口をギリギリ照射するサイズとなるように、出射側でビームの拡がり角を小さく抑えるような調整を行うことが理想である。
【００４２】
また、空間光通信を行う際の両通信局の共通設定事項として、ビームの拡がり角を設置精度（±５度）のＸ分の一に設定する。Ｘが１であれば、拡がり角は±５度であり、Ｘが５であれば、拡がり角は±１度となる。このＸの値によって、光反射器２で反射した光を送信元で受光したときの強度が決まる。受光系の感度との比較によって、Ｘの値が決まる。光反射器２の面積や、受光手段３の受光口径はあまり大きくすることは望ましくないため、ここでは、Ｘの値を５とし、拡がり角を±１度とする。
【００４３】
《手順１》：先ず、レーザ光源１４の発光強度を設定範囲内の最大とする。半導体レーザの場合、許容出力の最大７割程度で使うのが一般的で、レーザ光源は発光強度が低いほど寿命が長くなり、また、レーザの空間伝搬の放射強度（出射強度と拡がり角に依存）に関して人体に対する安全上の規制もあるので、それに応じた設定範囲を予め設定しておき、その最大値で第２通信局へ送信レーザ光５ａを照射する。
【００４４】
《手順２》：次いで、レーザビームの走査を開始する。ビーム走査の方法は特に限定されるものではないが、一般に、図４に示したスパイラル走査とラスター走査の２つの方法が知られている。本図において、点線が設置精度の方向の範囲を示したもので、この点線内のどこかに、ビームを向ければ、光反射器２に当たり、反射光を受光できる。
【００４５】
図４（ａ）に示すスパイラル走査では、始点から渦を巻くようにビーム照射方向を移動させて、黒点のビーム照射方向で止め、順に照射方向を変えて行く。ここでは、次の黒点との角度差を１．５度とした。また、図４（ｂ）のラスター走査では、予め定めた走査領域を始点からスイープして行く。これらのビーム走査は、通信制御手段４が三次元方向移動装置１５へ位置制御信号を出力して移動ステージを動かすことにより実現される。
【００４６】
《手順３》：走査中に、反射レーザ光５ａ′を受光して、反射光受光器３５からの反射光受光強度信号を受けると、その位置で三次元方向移動装置１５の移動ステージを停止させ、走査を停止する。
【００４７】
《手順４》：レーザ光源１４へのレーザ強度制御信号により発光強度を５０％下げる。なお、レーザ強度を下げる割合は、特に限定されるものではなく、この時のビーム拡がり角や受信系の感度によって、適宜に定めても良い。無論、レーザ光源１４の設計仕様（発熱対策や電力）や安全上の規制も考慮することが望ましい。
【００４８】
《手順５》：三次元方向移動装置１５へ位置制御信号を出力して移動ステージを動かすことで、ビームの拡がり角を数分の一にする。なお、レーザビームの絞り込みの割合も特に限定されるものではなく、ここでは、±０．２度とする。
【００４９】
《手順６》：再び、ビームの走査を開始する。上記手順２と同様のビーム操作方法でも良いし、異なるビーム操作方法を用いても良いが、上記手順２よりも走査精度を上げる必要がある。ここでは、黒点間の角度差を、０．３度と小さくして走査を行う。
【００５０】
《手順７》：走査中に、反射レーザ光５ａ′の受光量が増加しなくなったところで、ビームの走査を停止する。
【００５１】
《手順８》：反射レーザ光５ａ′の受光強度が予め定めた設定値を上回るまで、上記の手順５〜手順７を繰り返し、受光強度が設定値を上回ると、指向制御とアライメント調節が完了したものとする。なお、この設定値は、２つの通信局の離隔距離、空間光通信用端末Ａ，Ｂの光送受信性能、光反射器２の面積、発光しているレーザの強度などに基づいて、適宜に決めれば良い。
【００５２】
上記の手順１〜手順８を通信制御手段４が行うことで、相手側通信局である第２通信局には、所望の通信を行うための十分な放射照度のビームを照射していることとなる。なお、レーザ送信手段１の送信レーザ光５ａの出射方向がきちんと相手側通信局に向けられていれば、手順１でレーザ光源１４の発光強度を設定範囲内の最大とした時点、反射レーザ光５ａ′を受光できるので、手順２，３を行うことなく手順４を行えば良い。また、通信制御手段４が行うアライメント調整においては、両局間で最適な通信状態（送信効率と受信効率が最良）となるまでビームの拡がり角を狭める制御を行わず、相手側通信局の受光強度が必要十分なレベルに達したと判定できた時点で、アライメント調整動作を終了するようにしても良い。
【００５３】
また、レーザ伝搬路における状況変化に起因したレーザの減衰やレーザ送信手段１の設置方向の変化等の理由により、上記手順８において、反射レーザ光５ａ′の受光強度が設定値を上回る前に、ビームの拡がり角が規定値（最小ビーム径として定めたサイズのビーム径で相手側を照射する状態となるように予め設定した拡がり角の値）まで小さくなった場合には、それ以上ビームを狭める動作は行わず、手順６，７を行って指向方向を調整した後、反射レーザ光５ａ′の受光強度が設定値を上回るように、レーザ光源１４の発光強度を上げていく。このようにすれば、一応のレーザリンクを確立できる。なお、ビームの拡がり角の規定値は、主に空間光通信用端末Ａ，Ｂの取り付け地点の安定性に応じて決めるものであり、例えば、電柱の上部に設置した場合など、電柱自体の揺れを想定したレーザビームの拡がり角を設定して、送信範囲に余裕を持たせておかないと、すぐにレーザリンクが切れてしまい、通信が不安定になってしまうからである。
【００５４】
上述したのは、最初に相手側通信局へのレーザ送信状態を適切に設定するために通信制御手段４が行う手順であるが、通信制御手段４は、レーザ送信状態の初期設定が完了した後に環境変化など（霧や雨などによる伝搬路の透過率の低下、指向方向のずれなど）で送信状態が悪化した場合に、これを自動検知して自動再設定するようにも構成できる。
【００５５】
例えば、通信制御手段４は、常時、反射レーザ光５ａ′の受光強度をモニタするものとし、反射レーザ光の受光強度が予め定めた許容受光強度を下回った場合を送信状態の悪化と判定し、レーザビームの出射方向やビーム径などの再設定を行うようにする。
【００５６】
この再設定の手順は、特に限定されるものではないが、降雨等によるケースが最も多いと思われるので、先ず、発光強度を上げるようにレーザ光源１４へレーザ強度制御信号を送って送信レーザ光５ａの発光強度を上げ、反射レーザ光５ａ′の受光強度が許容受光強度以上になった時点で再走査を行わせることが望ましい。もし、それ以上に受光強度が強まるポイントがなければ、伝搬路の悪化によるものと看做せるので、送信レーザ光５ａの強度を上げたまま送信を行い、伝搬路が復旧すると受信強度が強くなり、予め定めた基準受光強度を超えるので、それを機に送信レーザ光５ａの強度などの再設定を行えば良い。一方、受光強度がさらに強まるポイントがあった場合には、自局のレーザ照射方向がずれたか、相手側通信局の位置がずれたと考えられるので、通常の設定と同様に、手順６〜手順８を行えば良い。
【００５７】
なお、通信制御手段４が、受光強度の変化を時系列に判断できるように設定しておけば、降雨等によって短時間のうちに反射レーザ光５ａ′を受信できなくなったのか、経年の位置ずれにより再指向が必要になったのかを判別できるので、そのケースに応じた適切な手順で再設定を行わせることが可能となる。
【００５８】
上述したように、本実施形態に係る空間光通信用システムにおいては、２局間の通信開始時の設定を容易にできるだけでなく、空間光通信回線の維持や復旧を自動で行うこともでき、高い利便性と信頼性を備えるシステムとなる。
【００５９】
上述した実施形態においては、三次元方向移動装置１５を用いてレーザ光源１４のレーザ出力位置を機械的に動作させ、出射方向調整部１１およびビーム径調整部１２の機能を実現する方式について説明したが、これに限定されるものではなく、電気光学効果を有する素子等を用いて、レーザ光源１４と送信レンズ１６の間の屈折率の分布を電気的に調節することによって、送信レーザ５ａの拡がり角や出射方向を微調節する手段としても良い。
【００６０】
先ず、電気光学結晶を用いたビーム方向制御の概念を図５（ａ）に基づき説明する。ビーム方向制御素子６は、電気光学結晶のｃ軸（結晶の光軸）を逆向きにした２つの電気光学結晶よりなるプリズム６ａ，６ｂを組み合わせ、電極６ｃ，６ｃ間に電圧を印加できるようにしたもので、電極６ｃ，６ｃ間に電圧を印加して電界を生じさせると、プリズム６ａ，６ｂの結晶の光学的性質が変化し、屈折率が僅かに変化する。変化量をΔｎとすると、プリズム６ａとプリズム６ｂは結晶の光軸が逆になっているため、例えば、プリズム６ａではΔｎ減少し、プリズム６ｂでΔｎ増加する。したがって、両プリズム６ａ，６ｂの接合面でビームが屈折してレーザビームの方向が変わるのである。
【００６１】
そして、電気光学結晶における屈折率の変化量Δｎは、電極６ｃ，６ｃ間への印加電圧によって制御できるため、レーザビームの方向を微調節することが可能である。従って、レーザビームの伝搬方向に垂直な２方向（レーザビームの伝搬方向をｘ軸方向とすると、ｙ軸およびｚ軸の２方向）への方向制御を行える組み合わせとなるように、レーザビームの出力経路に沿って２つのビーム方向制御素子６を配置しておけば、レーザビームの出射方向を自在に変えることが可能となる。なお、図５（ａ）に示すビーム方向制御素子６は、レーザビームの伝搬方向（ｘ軸）に対して、ｙ軸方向への方向制御を行えるように配置した例である。
【００６２】
次に、電気光学結晶を用いたビーム拡がり角調整の概念を図５（ｂ）に基づき説明する。ビーム拡がり角制御素子７は、キューブ型の電気光学結晶７ａを相対向する面に電極７ｂ，７ｂを設けて、電気光学結晶のｃ軸方向に電圧を印加できるようにしたもので、電極７ｂ，７ｂ間に電圧を印加すると、電気光学結晶７ａの屈折率がΔｎ増えるようにしてある。それによって、ビームの入射面と出射面で屈折が生じるので、光源からの出射位置が前方に移動された場合と同様に、レーザビームの拡がり角が大きくなる。
【００６３】
そして、屈折時の角度は、電気光学結晶における屈折率の変化量Δｎにより調節でき、この屈折率の変化量Δｎは電極７ｂ，７ｂ間への印加電圧によって制御できる。従って、レーザビームの出射位置と送信レンズ１６との間にビーム拡がり角制御素子７を配置しておけば、レーザビームの拡がり角を自在に変えることが可能となる。
【００６４】
従って、上述したビーム方向制御素子６とビーム拡がり角制御素子７を組み合わせることによって、レーザビームの出射方向と拡がり角を高精度に制御でき、機械的駆動部品を用いることなく出射方向調整部１１およびビーム径調整部１２の機能を実現できる。なお、現状の技術では、上述した三次元方向移動装置１５を用いて出射方向調整部１１およびビーム径調整部１２の機能を実現した方が、低コストで済む。
【００６５】
【発明の効果】
以上説明したように、請求項１に係る空間光通信システムによれば、レーザ送信手段より出射したレーザ光が相手側通信局の光反射器で反射されて戻ってくる反射レーザ光を受光し、その反射レーザ光の受光強度を利用して、相手側通信局への指向を通信制御手段が自動的に行うので、従来の如く、両通信局の通信端末へ人員を配置して互いに連絡を取り合ったりしながら、レーザ光の出射方向や受光方向を調整する必要がない。
【００６６】
しかも、両通信局の空間光通信用端末でのレーザ光出射方向を適切に設定した後に、空間光通信用端末自体のレーザ光出射方向がずれたり、空間光通信用端末が設置されている建築物の歪みなどによってレーザ光出射方向がずれたりして、相手側通信局への指向を再調整する必要が生じても、自局が出射した送信レーザ光が反射されて戻ってくる反射レーザ光を随時モニタすることで、回線断となる前に光軸の補正が必要な状態を的確に知ることができ、空間光通信用端末間のレーザ回線を保ちながらレーザ光の出射方向を自動的に補正できるので、光軸のずれに対して柔軟性を持たせることができ、光軸のずれが生じても回線断とはなり難い。よって、信頼度の高い空間光通信を行うことができる。
【００６７】
また、請求項２に係る空間光通信システムによれば、通信制御手段が、送信レーザ光の拡がり角を狭めることで、相手側での受光強度を上げるように、通信状態を調整するものとしたので、相手側通信局への指向制御に加えて、アライメント調節も自動で行うことができ、一層利便性の高いものとなる。
【図面の簡単な説明】
【図１】同等の空間光通信用端末を備える第１通信局と第２通信局とからなる空間光通信システムの概略構成図である。
【図２】空間光通信用端末Ａと空間光通信用端末Ｂの外観斜視図である。
【図３】空間光通信用端末における受光手段とレーザ送信手段と通信制御手段の概略機能図である。
【図４】レーザ光の出射方向を定める際の走査例を示す説明図である。
【図５】レーザ送信手段における出射方向調整部とビーム径調整部の他の例を示す概略機能図である。
【符号の説明】
Ａ空間光通信用端末
Ｂ空間光通信用端末
１レーザ送信手段
１１出射方向調整部
１２ビーム径調整部
１３レーザ強度調整部
２光反射器
３受信手段
３１光分離部
４通信制御手段
５ａ，５ｂ送信レーザ光
５ａ′，５ｂ′ 反射レーザ光[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a spatial optical communication system that connects communication stations at two spatially separated points by spatial optical communication using laser light, and in particular, a technique capable of quickly and accurately irradiating a communication partner with laser light. About.
[0002]
[Prior art]
In the conventional spatial optical communication system, a spatial optical communication terminal is installed on two distant buildings (such as a building roof and a tower), and laser light is transmitted between communication stations having the spatial optical communication terminal. Is used to perform spatial optical communication. When installing a spatial optical communication terminal on a building, personnel are allocated to both buildings at the two locations where they are to be installed to communicate with each other, and the laser light transmitted by each spatial optical communication terminal is transmitted to the other side. The directional direction of the space optical communication terminal is adjusted while checking whether the light is being received.
[0003]
[Non-patent document 1]
Optronics, Editorial Department, "Optical Space Communication Network Technical Documents", Optronics, Inc., March 10, 2000.
[0004]
In this case, by setting the divergence angle of the laser beam to be sufficiently large, it is possible to manually adjust the pointing direction roughly. Furthermore, if the laser emission direction of the spatial optical communication terminal shifts or the laser emission direction of the spatial optical communication terminal shifts due to the distortion of the building, the laser beam spreads to avoid interruption of the laser communication line. The horn was large.
[0005]
[Problems to be solved by the invention]
However, in the method of installing a terminal for spatial optical communication as described above, since the arrangement of a plurality of personnel and close communication between the personnel are required, the installation is troublesome.
[0006]
In addition, since the spread angle of the laser light is sufficiently large so that it can be handled manually, it is required to increase the intensity of the laser light source to be used, and the distance to the communication partner is also limited. Therefore, there are disadvantages that the data rate of the communication cannot be increased, and that the light receiving port receives a weakened light due to a large spread, so that the light receiving aperture on the receiving side is increased and the load of improving the signal detection performance is added.
[0007]
In addition, because it is not possible to flexibly cope with the situation of the spatial transmission path such as fog and rain, the design has a margin for the intensity of the laser beam irradiated to the other party, so the optical performance of the terminal for spatial optical communication Could not be fully utilized.
[0008]
In addition, when one of the laser beams is no longer irradiated to the other side due to some factor, a re-installation operation is required, and it is difficult to quickly respond to the recovery.
[0009]
Accordingly, the present invention provides a spatial optical communication system that can quickly and accurately perform settings in a spatial optical communication terminal for establishing a good communication state using optical communication between two stations without any need for human intervention. The purpose is to provide the system.
[0010]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, the invention according to claim 1 is a spatial optical communication system that connects two spatially separated communication stations by spatial optical communication using laser light. The station controls the laser transmitting means for emitting the transmission laser light, the light reflector for reflecting the incident light beam in the direction opposite to the arrival direction, the light receiving means for receiving the laser light, and the laser transmitting means, respectively. A communication control means for transmitting a signal to the other communication station and receiving and processing a signal from the other communication station received by the light receiving means; and a laser for both communication stations. The transmission laser light emitted from each of the transmission devices has different optical characteristics so that they can be distinguished from each other, and the communication control means reflects the transmission laser light emitted to the other communication station from the other communication station. The reflection ray returned By adjusting the emission direction of the laser beam to increase the received light intensity of the light, characterized in that the emission direction of the transmitted laser beam was set to direct to the other communication station.
[0011]
According to a second aspect of the present invention, in the spatial optical communication system according to the first aspect, the communication control means increases a light receiving intensity at the other party by narrowing a spread angle of the transmission laser light. The communication state is adjusted.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, an embodiment of a spatial optical communication system according to the present invention will be described with reference to the accompanying drawings.
[0013]
FIG. 1 shows a schematic configuration of a first communication station and a second communication station that constitute a spatial optical communication system that connects two spatially separated communication stations by spatial light communication using laser light. The spatial optical communication terminal A provided in the first communication station and the spatial optical communication terminal B provided in the second communication station have substantially the same configuration. That is, the spatial optical communication terminal A and the spatial optical communication terminal B each include a laser transmitting unit 1 that emits a transmission laser beam, a light reflector 2 that reflects an incident light beam in a direction opposite to the arrival direction, and a laser beam. A light receiving means 3 for receiving light; a communication control means 4 for controlling the laser transmitting means 1 to transmit a signal to the other communication station and for receiving and processing a signal from the other communication station received by the light receiving means 3; , Is provided.
[0014]
The communication control means 4 controls the laser transmission means 1 to transmit a signal to the communication station of the other party, and also receives and receives the signal received by the light receiving means 3 from the communication station of the other party. In addition, the communication control means 4 controls the intensity of the transmitting laser, the beam diameter at the light receiving end (the beam diameter determined by the distance between the two communication stations in addition to the beam diameter and divergence angle of the laser light source on the irradiation side. Unless otherwise specified, "beam diameter" is used to mean "beam diameter at the light receiving end.") And has a function of controlling the irradiation direction. The intensity of the laser light emitted from the laser transmission means 1 is controlled by a laser intensity control signal from the communication control means 4. Further, the laser transmitting means 1 shown in the present embodiment includes at least an emission direction adjusting unit 11, a beam diameter adjusting unit 12, and a laser intensity adjusting unit 13, and transmits the transmitting laser light under the control of the communication control unit 4. The beam diameter at the light receiving end can be increased or decreased by changing the emission direction of the laser beam, or by adjusting the divergence angle of the beam, or can be adjusted to a laser intensity sufficient for achieving a good communication state.
[0015]
Here, the transmission laser light 5a emitted from the laser transmission means 1 of the spatial optical communication terminal A and the transmission laser light 5b emitted from the laser transmission means 1 of the spatial optical communication terminal B are separated. The optical characteristics (for example, wavelength and polarization) are different. In the present embodiment, the first communication station and the second communication station communicate with each other using laser beams having different wavelengths.
[0016]
Therefore, the transmission laser light 5a emitted from the laser transmission means 1 is reflected by the optical reflector 2 of the second communication station, which is the other communication station, and returns as reflected laser light 5a '. The light receiving means 3, which simultaneously receives the transmission laser light 5b emitted from the means, can separate and receive the reflected laser light 5a 'and the transmission laser light 5b, depending on its optical characteristics. Similarly, the light receiving means 3 of the second communication station also includes a reflected laser beam 5b 'returned by reflecting the transmission laser light 5b by the optical reflector 2 of the first communication station, which is the other communication station, and a first communication station. And the transmission laser light 5a emitted from the laser transmission means is simultaneously received and separated. In the present embodiment, the light separating unit 31 having such a light separating function is provided in the light receiving unit 3, and the communication light receiving intensity signal and the reflected light receiving intensity signal are transmitted to the communication control unit 4.
[0017]
The field of view of each light receiving means 3 of the spatial optical communication terminal A and the spatial optical communication terminal B is set to be sufficiently wide, and the directions of the transmission laser beams 5a and 5b emitted from each laser transmitting means 1 are determined by the light receiving means. Adjustment is made at the time of installing the terminal so that it is arranged almost at the center of the viewing direction of No. 3. In optical communication between two fixed points on the ground, since the communication distance is short, it is not necessary to narrow the field of view and increase the light receiving sensitivity.Therefore, if the field of view of the light receiving system is set slightly wider, Even if the direction is fixed, sufficient reception strength can be ensured. However, in the case where restrictions such as the use of low-power laser light are imposed and the light receiving sensitivity must be increased by narrowing the field of view, a light receiving direction adjustment unit is provided to finely adjust the light receiving direction. You may do it.
[0018]
Further, as the light reflector 2 for reflecting the incident light beam in the direction opposite to the arrival direction, a CCR (Corner Cube Retro-reflector) which is an optical device composed of three mirror surfaces which are perpendicular to each other is used. Since the effective incident angle of the CCR is as wide as several tens of degrees, the direction accuracy at the time of attaching the light reflector 2 in the spatial optical communication terminals A and B is not required. The size of the reflecting surface of the light reflector 2 and the number of the light reflectors 2 are not particularly limited, and the optical transmission and reception performance of the spatial optical communication terminals A and B, the distance between the two communication stations, the communication What is necessary is just to design suitably according to various conditions, such as a data rate.
[0019]
FIG. 2 shows an example of the external appearance of the spatial optical communication terminal A and the spatial optical communication terminal B configured as described above, and FIG. 2 shows the spatial optical communication terminals A and B installed in a building. Since there is no shield in the space where each of the laser transmitting means 1, the light reflector 2 and the light receiving means 3 are opposed to each other, spatial optical communication outdoors can be realized. In this embodiment, the laser transmitting means 1, the light reflector 2, and the light receiving means 3 of the spatial optical communication terminals A and B are attached to a building or the like with a jig. By adjusting the angle when the jig is attached, the approximate direction is directed to the communication station on the other side. Note that the communication control means 4 may be built in an appropriate place of a jig installed outdoors or may be provided indoors.
[0020]
Next, a specific example of the emission direction adjusting unit 11 and the beam diameter adjusting unit 12 in the laser transmitting unit 1 and a specific example of the separating unit 31 in the light receiving unit 3 will be described with reference to FIG. Here, the spatial light communication terminal A of the first communication station will be described as an example, but the spatial light communication terminal B of the second communication station has the same configuration.
[0021]
First, the laser transmitting means 1 will be described. A laser light source 14, which is a light source of laser light, is installed on a moving stage of a three-dimensional direction moving device 15, and emits laser light of a predetermined wavelength with an intensity according to a laser intensity control signal from the communication control means 4. Output. The laser light output in this way passes through the transmission lens 16 and is emitted to the other communication station (second communication station) as transmission laser light 5a having a divergence angle corresponding to the focal length.
[0022]
Here, the three-dimensional direction moving device 15 is a device that can finely move the moving stage on which the laser light source 14 is fixed in each of three-dimensional directions with respect to a fixed stage fixed to a proper position of the casing of the laser transmitting means 1. The position of the moving stage is changed according to a position control signal input from the communication control means 4. As described above, by changing the position of the laser light source 14 (the irradiation position of the laser light) relative to the transmission lens 16 fixed to the casing of the laser transmission means 1, the emission direction of the laser light and the light receiving end are changed. Can be changed.
[0023]
That is, in the laser transmission means 1 used in the present embodiment, the emission direction adjustment unit 11 is provided by the three-dimensional direction moving device 15 which can relatively move the laser light source 14 in the three-dimensional direction with respect to the transmission lens 16. Thus, both functions of the beam diameter adjusting unit 12 are realized. The function of the laser intensity adjusting unit 13 is provided by the laser light source 14.
[0024]
For example, assuming that the x-axis parallel to the laser light propagation direction and the y-axis orthogonal thereto are located substantially on a horizontal plane and the z-axis is located on a vertical plane, the x-axis direction is parallel to the laser light propagation direction. By moving the stage, the divergence angle of the transmission laser light 5a emitted through the transmission lens 16 can be adjusted, and by moving the moving stage in a direction perpendicular to the propagation direction of the laser light, It is possible to finely adjust the emission direction of the emitted transmission laser light 5a (the left-right direction when moved in the y-axis direction and the up-down direction when moved in the z-axis direction).
[0025]
In addition, a device (a several centimeter-long cylinder) that realizes an operation accuracy of about 1 μm by attaching an encoder to a micrometer (so-called fine movement device) mechanism that converts the rotation operation of the DC motor into a straight-ahead operation with an appropriate gear and performing feedback control ) Is commercially available, and if this is combined with three axes of x, y, and z so that the moving stage can be moved in each axis direction, the three-dimensional direction moving device 15 can be realized.
[0026]
Next, the light receiving means 3 will be described. A transmission laser beam 5b emitted from the second communication station, which is the other communication station, and a reflected laser beam 5a emitted from the laser transmission means 1 of the own station, reflected by the optical reflector 2 of the second communication station, and returned. Is guided to the inside through the condenser lens 32, passes through the optical filter 33, and after the background light such as sunlight is removed, reaches the beam splitter 34. The beam splitter 34 has wavelength selectivity, reflects light having the wavelength of the transmission laser light 5a (reflected laser light 5a ') of its own station, and has light having the wavelength of the transmission laser light 5b of the other communication station. , The transmission laser beam 5b and the reflected laser beam 5a 'can be separated.
[0027]
That is, in the light receiving unit 3 used in the present embodiment, the function of the light separating unit 31 can be realized by the beam splitter 34 that can transmit or reflect and separate the wavelength of the laser light determined for each of the two communication stations.
[0028]
The reflected laser light 5a 'separated as described above is photoelectrically converted by the reflected light receiver 35, and the transmission laser light 5b from the second communication station is photoelectrically converted by the communication light receiver 36. The communication light reception intensity signal is supplied to the communication control means 4. The reflected laser beam 5a 'and the transmission laser beam 5b separated by the beam splitter 34 may be guided to the communication control means 4 by an optical fiber or the like as an optical signal, and photoelectrically converted in the communication control means 4.
[0029]
Then, in the spatial optical communication terminals A and B having the above-described configuration, if the transmission laser beams 5a and 5b emitted from the transmission source are irradiated on the light receiving means 3 of the other communication station, the light reflector 2 is used. Since the reflected laser beams 5a 'and 5b' are reflected and propagate in the direction opposite to the direction of arrival, they irradiate the light receiving means 3 of the source communication station. Therefore, the reflected light reception intensity signal is transmitted from the reflected light receiver 35 of the light receiving unit 3 to the communication control unit 4, and the communication control unit 4 can acquire the reception intensity of the reflected laser beams 5a 'and 5b'.
[0030]
On the other hand, when the light receiving means 3 does not receive the reflected laser beams 5a 'and 5b', the reflected light receiving intensity signal is not transmitted from the reflected light receiver 35 (or the reflected light receiving intensity signal indicating an extremely low value is not transmitted). Communication control means 4 sends a laser intensity control signal to the laser light source 14 so as to increase the intensity of the transmission laser light emitted from the laser light source 14, and at the same time, moves the laser light source 14 closer to the transmission lens 16 ( A position control signal is sent to the three-dimensional moving device 15 so as to move the moving stage in the x-axis direction (in FIG. 3, the x-axis direction), and the intensities and spread angles of the transmission laser beams 5a and 5b are increased. Adjustment is made so that the light reflector 2 is irradiated.
[0031]
If this adjustment satisfies the appropriate beam intensity and divergence angle, the transmission laser beams 5a and 5b irradiate the optical reflector 2 of the other communication station, and the reflected laser beams 5a 'and 5b' are transmitted. By irradiating the light receiving means 3 of the former communication station, the communication control means 4 can acquire the received light intensity of the reflected laser beams 5a 'and 5b' based on the reflected light received intensity signal output from the reflected light receiver 35.
[0032]
The communication control means 4 having acquired the received light intensities of the reflected laser beams 5a 'and 5b', in the plane equidistant from the transmission lens 16 (in the y-axis and z-axis directions in FIG. 3) so as to further increase the received light intensity of the reflected light. ), A position control signal is sent to the three-dimensional direction moving device 15 so as to move the laser light source 14. That is, the communication control means 4 emits the laser beams so that the transmission laser beams 5a and 5b emitted to the partner communication station are reflected from the partner communication station and the intensity of the reflected laser beams 5a 'and 5b' is increased. By adjusting the direction, it is possible to automatically direct the emission directions of the transmission laser beams 5a and 5b to the partner communication station.
[0033]
In the pointing control (control for directing the transmission direction of the laser beam to the communication station on the other side) by the communication control means 4, the control method is not particularly limited, and the optimum beam irradiation direction (the reflected laser beam 5a ', The beam scanning may be performed so as to find a point where the reception intensity of 5b 'is the strongest), or a reference reception intensity predetermined as a reference value necessary and sufficient for performing spatial optical communication is cleared. When the beam transmission direction is found, it may be set as the beam irradiation direction.
[0034]
Further, the communication control unit 4 controls the three-dimensional movement device 15 to perform an operation control (a control in the y-axis direction and the z-axis direction) so as to obtain the optimum beam irradiation direction, and then reduces the divergence angle of the laser beam. Since the operation control (control in the x-axis direction) of the three-dimensional direction moving device 15 is performed, and the spread angle of the transmission laser beams 5a and 5b is reduced, the reception intensity of the reflected laser beams 5a 'and 5b' increases. By controlling the laser intensity of the laser light source 14 so that the reception intensity of the reflected laser beams 5a 'and 5b' becomes an appropriate value, the communication state adjustment (alignment adjustment) suitable for the communication partner station can be performed. You may make it automatic.
[0035]
In addition, after the above-mentioned pointing control and alignment adjustment are performed, further pointing control is performed, a more accurate beam irradiation direction is determined, and if a control method of performing the alignment adjustment again is adopted, a more subtle pointing control can be achieved. Alignment adjustments can be made.
[0036]
As described above, when the pointing control and the alignment adjustment between the two communication stations are completed, the reflected laser beams 5a 'and 5b', which are the reflected light from the optical reflector 2 of the other communication station, are received by the reflected light receiver 35. Since the transmission laser beams 5a and 5b of the other communication station are received by the communication light receiver 36, the reflected light reception intensity signal from the reflected light receiver 35 and the communication light from the communication light receiver 36 are received. Based on the received light intensity signal, the communication control means 4 can determine that a spatial optical communication line between both communication stations has been established.
[0037]
However, when only the transmission laser beams 5a and 5b from the partner communication station are received, it means that the transmission laser beams 4a and 5b of the own station are not irradiating the partner, so that the pointing control and the alignment adjustment are performed. The above procedure may be repeated. As described above, in the spatial optical communication system according to the present embodiment, the laser transmitting means depends on whether or not the reflected light (reflected laser light 5a ', 5b') of the transmission laser light 5a, 5b of the own station is received. It is detected that the transmission direction of No. 1 is shifted.
[0038]
On the other hand, when only the reflected light (reflected laser light 5a ', 5b') of the transmission laser light 5a, 5b of the own station is received, it means that the laser pointing direction of the other communication station is not appropriate. In this case, since the reflected light (reflected laser light 5a ', 5b') of the transmission laser light 5a, 5b emitted by itself must not be detected at the communication station of the other party, the pointing of the laser beam at the communication station of the other party is not performed. Control and alignment adjustment are automatically performed, and the transmission laser beams 5a and 5b of the other communication station can be received, and the bidirectional laser line is restored. If the transmission laser beams 5a and 5b from the partner communication station cannot be received even after a predetermined delay time has elapsed after the transmission laser beams 5a and 5b from the partner communication station cannot be received, Since there is a possibility that some trouble has occurred in the communication station, control may be performed to shut off the laser line as an error.
[0039]
Next, a specific control procedure performed by the communication control means 4 in order to set a good communication state between both communication stations in the spatial optical communication system according to the present embodiment will be described. The following description is about the control performed by the communication control means 4 in the spatial light communication terminal A of the first communication station, but the control performed by the communication control means 4 in the spatial light communication terminal B of the second communication station. The same is true for
[0040]
As shown in FIG. 2 described above, the spatial optical communication terminal A and the spatial optical communication terminal B are installed at two places with good visibility, and the field of view of both light receiving means 3 is sufficiently wider than the angle accuracy in the installation. Set it. For example, assuming that the accuracy at the time of attachment toward the partner communication station is ± 5 degrees, the field of view of the light receiving unit 3 is ± 10 degrees. Note that the field of view of the light reflector 2 is ± 37.3 degrees in terms of geometrical optics, and is a field of view sufficiently wider than the light receiving means 3.
[0041]
On the other hand, the divergence angle of the beam can be made several orders of magnitude smaller than the angles of the light reflector 2 and the light receiving means 3, and when collimated (when transmitted at the divergence angle of the beam diffraction limit), for example, a laser If the wavelength is 1 μm and the beam has a diameter of 1 cm, the conical shape is 122 μrad = 0.007 degrees in all angles. The smaller the spread angle of the beam is, the higher the irradiance to the other party is. Therefore, there is an advantage that the speed can be increased in communication. Therefore, from the viewpoint of increasing the light receiving intensity on the other side, the beam divergence angle on the emission side is set so that the beam diameter at the light receiving end is the size that allows the opening of the light reflector 2 and the opening of the light receiving means 3 to be barely irradiated. Ideally, the adjustment should be made so as to keep the value small.
[0042]
In addition, as a common setting item for both communication stations when performing spatial optical communication, the divergence angle of the beam is set to 1 / X of the installation accuracy (± 5 degrees). If X is 1, the divergence angle is ± 5 degrees, and if X is 5, the divergence angle is ± 1 degrees. The intensity of the light reflected by the light reflector 2 when the light is received at the transmission source is determined by the value of X. The value of X is determined by comparison with the sensitivity of the light receiving system. Since it is not desirable to make the area of the light reflector 2 or the light receiving aperture of the light receiving means 3 too large, here, the value of X is 5 and the divergence angle is ± 1 degree.
[0043]
<< Procedure 1 >>: First, the emission intensity of the laser light source 14 is set to the maximum within a set range. In the case of a semiconductor laser, it is common to use it at a maximum of about 70% of the allowable output. The lower the light emission intensity, the longer the life of the laser light source. In addition, the radiation intensity of the spatial propagation of the laser (depending on the emission intensity and the divergence angle) There is also a restriction on the human body regarding ()), so a setting range corresponding to the restriction is set in advance, and the transmission laser beam 5a is irradiated to the second communication station at the maximum value.
[0044]
<< Procedure 2 >>: Next, scanning of the laser beam is started. The method of beam scanning is not particularly limited, but generally, two methods of spiral scanning and raster scanning shown in FIG. 4 are known. In this figure, the dotted line indicates the range of the direction of the installation accuracy, and if the beam is directed to somewhere within the dotted line, it hits the light reflector 2 and can receive the reflected light.
[0045]
In the spiral scan shown in FIG. 4A, the beam irradiation direction is moved so as to form a vortex from the start point, stopped at the beam irradiation direction at the black point, and changed in order. Here, the angle difference from the next black point is 1.5 degrees. In the raster scanning shown in FIG. 4B, a predetermined scanning area is swept from a starting point. These beam scans are realized by the communication control unit 4 outputting a position control signal to the three-dimensional direction moving device 15 to move the moving stage.
[0046]
<< Procedure 3 >>: During scanning, when the reflected laser beam 5a 'is received and the reflected light receiving intensity signal from the reflected light receiver 35 is received, the moving stage of the three-dimensional moving device 15 is stopped at that position. Stop scanning.
[0047]
<< Procedure 4 >>: The emission intensity is reduced by 50% by the laser intensity control signal to the laser light source 14. The rate at which the laser intensity is reduced is not particularly limited, and may be appropriately determined depending on the beam divergence angle and the sensitivity of the receiving system at this time. Of course, it is desirable to consider the design specifications (heat generation measures and power) and safety regulations of the laser light source 14.
[0048]
<< Procedure 5 >>: By outputting a position control signal to the three-dimensional direction moving device 15 to move the moving stage, the divergence angle of the beam is reduced to a fraction. The ratio of narrowing down the laser beam is not particularly limited, and is set to ± 0.2 degrees here.
[0049]
<< Procedure 6 >>: Beam scanning is started again. The same beam operation method as in the above procedure 2 may be used, or a different beam operation method may be used. However, it is necessary to increase the scanning accuracy more than in the above procedure 2. Here, scanning is performed with the angle difference between black points as small as 0.3 degrees.
[0050]
<< Procedure 7 >>: When scanning does not increase the amount of reflected laser light 5a 'received, beam scanning is stopped.
[0051]
<< Procedure 8 >>: The above Steps 5 to 7 are repeated until the received light intensity of the reflected laser beam 5a 'exceeds a predetermined set value. When the received light intensity exceeds the set value, the pointing control and the alignment adjustment are completed. Shall be. This set value is appropriately determined based on the separation distance between the two communication stations, the optical transmission / reception performance of the spatial optical communication terminals A and B, the area of the optical reflector 2, the intensity of the emitting laser, and the like. Good.
[0052]
By performing the above-mentioned procedure 1 to procedure 8 by the communication control means 4, the second communication station, which is the other communication station, is irradiated with a beam having sufficient irradiance for performing desired communication. Become. If the emission direction of the transmission laser light 5a of the laser transmission means 1 is properly directed to the communication station on the other side, the time when the emission intensity of the laser light source 14 is set to the maximum within the set range in the procedure 1, the reflected laser light 5a 'Can be received, so that the procedure 4 may be performed without performing the procedures 2 and 3. In the alignment adjustment performed by the communication control means 4, the control for reducing the beam divergence angle is not performed until the optimum communication state (the best transmission efficiency and the best reception efficiency) is obtained between the two stations. The alignment adjustment operation may be terminated when it is determined that the intensity has reached a necessary and sufficient level.
[0053]
Further, in the above procedure 8, before the received light intensity of the reflected laser beam 5a 'exceeds the set value, due to the attenuation of the laser caused by a change in the situation in the laser propagation path or a change in the installation direction of the laser transmitting means 1, for example. When the divergence angle of the beam is reduced to a specified value (a divergence angle set in advance so that the other side is irradiated with the beam diameter of the size determined as the minimum beam diameter), the beam is further narrowed. After performing the procedures 6 and 7 to adjust the directional direction without performing the operation, the emission intensity of the laser light source 14 is increased so that the reception intensity of the reflected laser beam 5a 'exceeds the set value. In this way, a temporary laser link can be established. The specified value of the divergence angle of the beam is mainly determined according to the stability of the mounting point of the spatial optical communication terminals A and B. For example, when the pole is installed on the pole, the swing of the pole itself This is because unless the divergence angle of the laser beam is set assuming that the transmission range has a margin, the laser link is immediately cut, and communication becomes unstable.
[0054]
What has been described above is a procedure performed by the communication control means 4 to appropriately set the state of laser transmission to the communication station of the other party first. If the transmission state deteriorates due to environmental changes (such as a decrease in the transmittance of the propagation path due to fog or rain, etc.), this can be automatically detected and automatically reset.
[0055]
For example, the communication control means 4 always monitors the received light intensity of the reflected laser light 5a ', and determines that the transmission state is deteriorated when the received light intensity of the reflected laser light is lower than a predetermined allowable light receiving intensity. The laser beam emission direction and beam diameter are reset.
[0056]
The resetting procedure is not particularly limited. However, since it is considered that there are most cases due to rainfall or the like, first, a laser intensity control signal is sent to the laser light source 14 so as to increase the emission intensity, and the transmission laser It is desirable to increase the light emission intensity of 5a and perform re-scanning when the light reception intensity of the reflected laser light 5a 'is equal to or higher than the allowable light reception intensity. If there is no point where the received light intensity is further increased, it can be considered that this is due to the deterioration of the propagation path. Therefore, the transmission is performed while the intensity of the transmission laser light 5a is increased, and when the propagation path is restored, the reception intensity increases. Since the light intensity exceeds the predetermined reference light receiving intensity, the intensity of the transmission laser light 5a or the like may be reset using the light intensity as a reference. On the other hand, if there is a point at which the received light intensity further increases, it is considered that the laser irradiation direction of the own station has shifted or the position of the partner communication station has shifted. Should be done.
[0057]
If the communication control means 4 is set so as to be able to judge the change of the received light intensity in a time series, it may be impossible to receive the reflected laser light 5a 'within a short time due to rainfall or the like, Thus, it is possible to determine whether or not the re-pointing is necessary, so that the resetting can be performed in an appropriate procedure according to the case.
[0058]
As described above, in the system for spatial optical communication according to the present embodiment, not only can the setting at the start of communication between two stations be easily performed, but also the maintenance and restoration of the spatial optical communication line can be performed automatically, The system has high convenience and reliability.
[0059]
In the above-described embodiment, the method of mechanically operating the laser output position of the laser light source 14 using the three-dimensional direction moving device 15 to realize the functions of the emission direction adjustment unit 11 and the beam diameter adjustment unit 12 has been described. However, the present invention is not limited to this, and by using a device having an electro-optical effect or the like to electrically adjust the refractive index distribution between the laser light source 14 and the transmission lens 16, the transmission laser 5 a can be spread. Means for finely adjusting the angle and the emission direction may be used.
[0060]
First, the concept of beam direction control using an electro-optic crystal will be described with reference to FIG. The beam direction control element 6 combines two prisms 6a and 6b composed of two electro-optical crystals with the c-axis (optical axis of the crystal) of the electro-optical crystal reversed, so that a voltage can be applied between the electrodes 6c and 6c. When an electric field is generated by applying a voltage between the electrodes 6c, the optical properties of the crystals of the prisms 6a, 6b change, and the refractive index slightly changes. Assuming that the amount of change is Δn, the prism 6a and the prism 6b have opposite optical axes of the crystal. For example, the prism 6a decreases Δn and the prism 6b increases Δn. Therefore, the beam is refracted at the joint surface between the two prisms 6a and 6b, and the direction of the laser beam changes.
[0061]
Since the change amount Δn of the refractive index in the electro-optic crystal can be controlled by the voltage applied between the electrodes 6c, it is possible to finely adjust the direction of the laser beam. Therefore, the output of the laser beam is set so as to be a combination capable of controlling the direction in two directions perpendicular to the propagation direction of the laser beam (two directions of the y-axis and the z-axis when the propagation direction of the laser beam is the x-axis direction). By arranging two beam direction control elements 6 along the path, it is possible to freely change the emission direction of the laser beam. Note that the beam direction control element 6 shown in FIG. 5A is an example in which the direction control in the y-axis direction can be performed with respect to the propagation direction (x-axis) of the laser beam.
[0062]
Next, the concept of beam divergence angle adjustment using an electro-optic crystal will be described with reference to FIG. The beam divergence angle control element 7 is provided with electrodes 7b, 7b on surfaces opposing a cube-shaped electro-optic crystal 7a so that a voltage can be applied in the c-axis direction of the electro-optic crystal. When a voltage is applied between the electrodes 7b, the refractive index of the electro-optic crystal 7a is increased by Δn. Thereby, refraction occurs on the incident surface and the exit surface of the beam, so that the divergence angle of the laser beam increases as in the case where the exit position from the light source is moved forward.
[0063]
The angle at the time of refraction can be adjusted by the change Δn in the refractive index of the electro-optical crystal, and the change Δn in the refractive index can be controlled by the voltage applied between the electrodes 7b. Therefore, if the beam divergence angle control element 7 is arranged between the laser beam emission position and the transmission lens 16, the divergence angle of the laser beam can be freely changed.
[0064]
Therefore, by combining the above-described beam direction control element 6 and beam divergence angle control element 7, the emission direction and divergence angle of the laser beam can be controlled with high precision, and the emission direction adjustment unit 11 and the The function of the beam diameter adjusting unit 12 can be realized. In the current technology, it is cheaper to realize the functions of the emission direction adjuster 11 and the beam diameter adjuster 12 using the three-dimensional direction moving device 15 described above.
[0065]
【The invention's effect】
As described above, according to the spatial optical communication system according to claim 1, a laser beam emitted from a laser transmitting unit receives a reflected laser beam reflected by an optical reflector of a partner communication station and returned, The communication control means automatically uses the intensity of the reflected laser light to direct the communication station of the other party, so that personnel are allocated to the communication terminals of both communication stations to communicate with each other, as in the past. However, it is not necessary to adjust the emission direction and the light reception direction of the laser light.
[0066]
In addition, after appropriately setting the laser beam emission direction of the spatial optical communication terminal of both communication stations, the laser beam emission direction of the spatial optical communication terminal itself is shifted or the building in which the spatial optical communication terminal is installed. Even if the emission direction of the laser beam shifts due to distortion of the object, etc., and it is necessary to readjust the pointing toward the communication station on the other end, the reflected laser beam emitted from the own station is reflected and returned. Can be accurately monitored before the line is disconnected, and the state in which the optical axis needs to be corrected can be accurately known.The laser beam emission direction can be automatically determined while maintaining the laser line between the spatial optical communication terminals. Since the correction can be made, flexibility can be given to the shift of the optical axis, and even if the shift of the optical axis occurs, the line hardly breaks. Therefore, spatial optical communication with high reliability can be performed.
[0067]
According to the spatial optical communication system of the second aspect, the communication control means adjusts the communication state so as to increase the light receiving intensity at the other party by narrowing the spread angle of the transmission laser light. Therefore, in addition to the directivity control to the communication station of the other party, the alignment adjustment can be automatically performed, which is more convenient.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a spatial optical communication system including a first communication station and a second communication station having equivalent spatial optical communication terminals.
FIG. 2 is an external perspective view of a space optical communication terminal A and a space optical communication terminal B.
FIG. 3 is a schematic functional diagram of a light receiving unit, a laser transmitting unit, and a communication control unit in the space optical communication terminal.
FIG. 4 is an explanatory diagram showing an example of scanning when determining the emission direction of laser light.
FIG. 5 is a schematic functional diagram showing another example of the emission direction adjustment unit and the beam diameter adjustment unit in the laser transmission unit.
[Explanation of symbols]
A Terminal for space optical communication
B Space Optical Communication Terminal
1 Laser transmission means
11 Emission direction adjustment unit
12 Beam diameter adjustment unit
13 Laser intensity adjustment unit
2 Light reflector
3 receiving means
31 Light separation unit
4 Communication control means
5a, 5b Transmission laser light
5a ', 5b' reflected laser light

Claims

空間的に離れた２地点の通信局をレーザ光を用いた空間光通信で接続する空間光通信システムであって、
双方の通信局は、それぞれ、送信レーザ光を出射するレーザ送信手段と、入射した光線を到来方向と逆方向へ反射する光反射器と、レーザ光を受光する受光手段と、上記レーザ送信手段を制御して相手側通信局への信号送信を行うと共に上記受光手段が受光した相手側通信局からの信号を受信処理する通信制御手段と、を含む空間光通信用端末を備え、且つ、両通信局のレーザ送信装置がそれぞれ出射する送信レーザ光は、互いに識別可能なように光特性を異ならせておき、
上記通信制御手段は、相手側通信局へ出射した送信レーザ光が相手側通信局から反射されて戻った反射レーザ光の受光強度を上げるようにレーザ光の出射方向を調整することで、送信レーザ光の出射方向を相手側通信局へ向けるようにしたことを特徴とする空間光通信システム。A spatial optical communication system for connecting two spatially separated communication stations by spatial optical communication using laser light,
The two communication stations each include a laser transmitting unit that emits a transmission laser beam, a light reflector that reflects an incident light beam in a direction opposite to an arrival direction, a light receiving unit that receives a laser beam, and the laser transmitting unit. A communication control means for controlling and transmitting a signal to the other communication station and receiving and processing a signal from the other communication station received by the light receiving means. The transmission laser light emitted by the laser transmission devices of the station has different optical characteristics so that they can be distinguished from each other,
The communication control means adjusts the emission direction of the laser light so as to increase the light receiving intensity of the reflected laser light that is reflected by the transmitted laser light emitted from the other communication station and returned to the other communication station. A spatial optical communication system, wherein a light emission direction is directed to a communication station on the other side.

上記通信制御手段は、送信レーザ光の拡がり角を狭めることで、相手側での受光強度を上げるように、通信状態を調整するようにしたことを特徴とする請求項１に記載の空間光通信システム。2. The spatial optical communication according to claim 1, wherein the communication control means adjusts a communication state so as to increase a light receiving intensity at the other party by narrowing a spread angle of the transmission laser light. system.