JPH04357892A - Mode synchronous optical fiber laser apparatus - Google Patents
Mode synchronous optical fiber laser apparatusInfo
- Publication number
- JPH04357892A JPH04357892A JP3133075A JP13307591A JPH04357892A JP H04357892 A JPH04357892 A JP H04357892A JP 3133075 A JP3133075 A JP 3133075A JP 13307591 A JP13307591 A JP 13307591A JP H04357892 A JPH04357892 A JP H04357892A
- Authority
- JP
- Japan
- Prior art keywords
- optical
- optical fiber
- pulse
- section
- compression
- 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.)
- Granted
Links
- 239000013307 optical fiber Substances 0.000 title claims abstract description 67
- 230000001360 synchronised effect Effects 0.000 title 1
- 230000003287 optical effect Effects 0.000 claims abstract description 110
- 239000006185 dispersion Substances 0.000 claims abstract description 35
- 230000010355 oscillation Effects 0.000 claims abstract description 11
- 238000007906 compression Methods 0.000 claims description 35
- 230000006835 compression Effects 0.000 claims description 34
- 230000003321 amplification Effects 0.000 claims description 16
- 238000003199 nucleic acid amplification method Methods 0.000 claims description 16
- 230000005284 excitation Effects 0.000 claims description 11
- 230000008878 coupling Effects 0.000 claims description 9
- 238000010168 coupling process Methods 0.000 claims description 9
- 238000005859 coupling reaction Methods 0.000 claims description 9
- 229910052779 Neodymium Inorganic materials 0.000 claims description 4
- 229910052761 rare earth metal Inorganic materials 0.000 claims description 4
- 229910052691 Erbium Inorganic materials 0.000 claims description 3
- 238000005086 pumping Methods 0.000 claims description 3
- 150000002910 rare earth metals Chemical class 0.000 claims description 3
- 230000002159 abnormal effect Effects 0.000 abstract 1
- 230000000694 effects Effects 0.000 description 11
- 230000002547 anomalous effect Effects 0.000 description 10
- 238000010586 diagram Methods 0.000 description 10
- 239000000835 fiber Substances 0.000 description 10
- 238000000034 method Methods 0.000 description 8
- 230000003595 spectral effect Effects 0.000 description 5
- 230000005374 Kerr effect Effects 0.000 description 4
- 238000001228 spectrum Methods 0.000 description 4
- 229910003327 LiNbO3 Inorganic materials 0.000 description 3
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 2
- 230000005540 biological transmission Effects 0.000 description 2
- 238000012886 linear function Methods 0.000 description 2
- 230000009022 nonlinear effect Effects 0.000 description 2
- 230000010287 polarization Effects 0.000 description 2
- 230000000644 propagated effect Effects 0.000 description 2
- 238000005070 sampling Methods 0.000 description 2
- 239000004065 semiconductor Substances 0.000 description 2
- 229910052777 Praseodymium Inorganic materials 0.000 description 1
- 230000005699 Stark effect Effects 0.000 description 1
- 238000004891 communication Methods 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 230000004069 differentiation Effects 0.000 description 1
- UYAHIZSMUZPPFV-UHFFFAOYSA-N erbium Chemical compound [Er] UYAHIZSMUZPPFV-UHFFFAOYSA-N 0.000 description 1
- 238000000605 extraction Methods 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 238000005457 optimization Methods 0.000 description 1
- 230000001443 photoexcitation Effects 0.000 description 1
- 230000000630 rising effect Effects 0.000 description 1
- 239000000377 silicon dioxide Substances 0.000 description 1
- 230000002269 spontaneous effect Effects 0.000 description 1
- 230000007704 transition Effects 0.000 description 1
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- Lasers (AREA)
Abstract
Description
【０００１】0001
【産業上の利用分野】本発明は、光ソリトン伝送方式、
全光形光スイッチ、電気−光サンプリング、光−光サン
プリング等に使用される１ピコ秒以下の超短光パルスを
発生させるモード同期光ファイバレーザ装置に関する。[Industrial Application Field] The present invention relates to an optical soliton transmission system,
The present invention relates to a mode-locked optical fiber laser device that generates ultrashort optical pulses of 1 picosecond or less for use in all-optical optical switches, electrical-optical sampling, optical-optical sampling, etc.
【０００２】0002
【従来の技術】従来より、レーザの縦モード間の位相を
揃えるモード同期法は、短い光パルス列を発生する方法
として各種レーザに使用されている。しかし、従来のモ
ード同期法で得られる最小の光パルス幅は媒質の利得幅
で定まるため、１μｍより長い長波長帯のレーザ媒質（
Ｎｄ：ＹＡＧ、希土類添加光ファイバ等）では数１０ピ
コ秒が限界である。従って、更に短い光パルスを作るた
め、通常、モード同期で得た光パルスを外部のパルス圧
縮系を用いて圧縮する手段が用いられていた。具体的に
は図８に示すように、まず光ファイバの光カー効果を用
いて広いスペクトル幅でブルーシフトチャーピングをも
つ光パルスを作り、それを回折格子の組合せでチャーピ
ングを補償してパルスを圧縮する。2. Description of the Related Art Conventionally, a mode locking method for aligning the phases between longitudinal modes of a laser has been used in various lasers as a method for generating short optical pulse trains. However, since the minimum optical pulse width obtained with the conventional mode-locking method is determined by the gain width of the medium, the laser medium in the long wavelength band longer than 1 μm (
(Nd:YAG, rare earth doped optical fiber, etc.), the limit is several tens of picoseconds. Therefore, in order to create even shorter optical pulses, means have been used to compress the optical pulses obtained by mode-locking using an external pulse compression system. Specifically, as shown in Figure 8, we first create a light pulse with blue shift chirping over a wide spectral width using the optical Kerr effect of an optical fiber, and then use a combination of diffraction gratings to compensate for the chirping and create a pulse. compress.
【０００３】0003
【発明が解決しようとする課題】しかしながら、上記図
８から明らかなように、この方法ではモード同期レーザ
装置とパルス圧縮装置の２つが必要となるので、小型で
持ち運びが出来るような簡便な装置とはならなかった。
特に、光通信システムではコア径が１０μｍ程度の光フ
ァイバを用いるため、安定かつ低損失に結合させた装置
化が難しくなる。However, as is clear from FIG. 8 above, this method requires two devices: a mode-locked laser device and a pulse compression device. It didn't happen. In particular, since optical communication systems use optical fibers with a core diameter of about 10 μm, it is difficult to create devices that provide stable and low-loss coupling.
【０００４】他方、比較的新しいパルス圧縮法に光ファ
イバを用いた光ソリトン圧縮がある。これは入射パルス
が十分強く、かつその波長が光ファイバの異常分散領域
にあれば光ファイバの非線形効果（光カー効果）により
高次の光ソリトンが生成され、光パルスが特定の長さを
伝搬したときに最短に圧縮されるものである。なお、異
常分散領域とは光パルス波形の伝搬する速度（群速度）
が波長の増加に対して遅くなる領域であり、これに対し
て、波長が長いほどパルスの伝搬速度が速くなる領域が
正常分散領域である。従来構造の石英系光ファイバでは
、零分散波長が１．３μｍ近傍であり、これより短波長
が正常分散領域、長波長が異常分散領域になる。ところ
で、光パルスは少なくともパルス幅の逆数で定まるスペ
クトル広がりを有するので、分散値が零でない光ファイ
バに入射して伝搬されると、長波長成分と短波長成分の
速度が異なるためパルス幅が広がってしまう。これは光
パルスのピーク値があまり大きくない線形領域の話であ
り、光パルスが強くなると光ファイバの光カー効果が誘
起され、異常分散領域ではソリトン効果によるパルス圧
縮が生じる。従来の光ソリトン圧縮は光ファイバレーザ
からの出力光パルスを圧縮する方法として有用であるが
、この効果を得るためには入射させる光パルスが十分高
いピークパワーを持たねばならない。従って、図９に示
すように、モード同期光ファイバレーザ装置からの光パ
ルスを光増幅器を用いて所定のレベルまで増幅し、それ
を異常分散値を持つ光ファイバに入射させる手法が用い
られていた。この方法もモード同期レーザ装置以外に光
増幅系やパルス圧縮系が必要なため、小型化、安定化な
どに問題があった。特に、ソリトン圧縮は入力パワー、
光ファイバ長に依存するため、最適化の制御も必要にな
る。On the other hand, a relatively new pulse compression method is optical soliton compression using an optical fiber. This is because if the incident pulse is strong enough and its wavelength is in the anomalous dispersion region of the optical fiber, high-order optical solitons are generated due to the optical fiber's nonlinear effect (optical Kerr effect), and the optical pulse propagates over a specific length. This is the shortest compression possible when Note that the anomalous dispersion region is the propagation speed (group velocity) of the optical pulse waveform.
This is a region where the pulse propagation speed becomes slower as the wavelength increases, whereas the normal dispersion region is a region where the pulse propagation speed becomes faster as the wavelength becomes longer. In a silica-based optical fiber having a conventional structure, the zero dispersion wavelength is around 1.3 μm, and wavelengths shorter than this are in the normal dispersion region, and wavelengths longer than this are in the anomalous dispersion region. Incidentally, since an optical pulse has a spectral broadening determined by at least the reciprocal of the pulse width, when it is incident on an optical fiber with a non-zero dispersion value and propagated, the pulse width widens because the speeds of the long wavelength component and the short wavelength component differ. It ends up. This refers to the linear region where the peak value of the optical pulse is not very large; when the optical pulse becomes strong, the optical Kerr effect of the optical fiber is induced, and in the anomalous dispersion region, pulse compression occurs due to the soliton effect. Conventional optical soliton compression is useful as a method for compressing output optical pulses from optical fiber lasers, but in order to obtain this effect, the incident optical pulse must have a sufficiently high peak power. Therefore, as shown in Figure 9, a method has been used in which the optical pulse from a mode-locked optical fiber laser device is amplified to a predetermined level using an optical amplifier, and then input into an optical fiber having an anomalous dispersion value. . This method also requires an optical amplification system and a pulse compression system in addition to the mode-locked laser device, so there are problems with miniaturization and stability. In particular, soliton compression requires input power,
Since it depends on the optical fiber length, optimization control is also required.
【０００５】本発明は前記課題を有効に解決するもので
、従来問題であった小型化、簡易化、並びに光ファイバ
との整合性を実現するため、外部のパルス圧縮系を用い
ずに１ピコ秒以下の超短光パルスを発生させることがで
きるモード同期光ファイバレーザ装置の提供を目的とす
る。The present invention effectively solves the above-mentioned problems, and in order to achieve miniaturization, simplification, and compatibility with optical fibers, which were problems in the past, 1 pico pulse compression is achieved without using an external pulse compression system. The object of the present invention is to provide a mode-locked optical fiber laser device that can generate ultrashort optical pulses of less than a second.
【０００６】[0006]
【課題を解決するための手段】前記目的を達成するため
、本発明は、希土類添加光ファイバを用いた光増幅部と
、リング内の光パルスを取り出す光結合部と、光の損失
または位相を変調する光変調部と、片回り光のみを通過
させる光アイソレータ部と、希土類添加光ファイバを光
励起する光励起部とを少なくとも備えたモード同期光フ
ァイバリングレーザ装置において、上記光増幅部は零分
散波長λ０ が発振波長λよりも十分長く、上記光増幅
部と光結合部との間には発振波長λより十分短い零分散
波長を有する光ファイバ圧縮部を備えたことを特徴とす
る。また、本発明の前記希土類は、Ｅｒ，Ｎｄ，Ｐｒな
ど、レーザ遷移を有する元素であれば何でもよい。また
、本発明は、ブルーシフトチャープパルスのチャープ速
度α（ｎｍ／ｐｓ）と光ファイバの群速度分散Ｄ（ｐａ
／ｎｍ／ｋｍ）とで決まる最適な線形圧縮条件長Ｌｏｐ
より短い光ファイバ圧縮部を用いることも含まれる。但
し、Ｌｏｐ＝１／（−αＤ）である。[Means for Solving the Problems] In order to achieve the above object, the present invention provides an optical amplifying section using a rare earth-doped optical fiber, an optical coupling section for extracting optical pulses in a ring, and an optical coupling section for removing optical loss or phase. In a mode-locked optical fiber ring laser device comprising at least an optical modulation section that modulates, an optical isolator section that passes only one-way light, and an optical excitation section that optically excites a rare earth-doped optical fiber, the optical amplification section has a zero dispersion wavelength. The present invention is characterized in that λ0 is sufficiently longer than the oscillation wavelength λ, and an optical fiber compression section having a zero dispersion wavelength sufficiently shorter than the oscillation wavelength λ is provided between the optical amplifying section and the optical coupling section. Further, the rare earth of the present invention may be any element that has a laser transition, such as Er, Nd, Pr, etc. Furthermore, the present invention also provides the chirp speed α (nm/ps) of the blue shift chirp pulse and the group velocity dispersion D (pa
/nm/km) The optimal linear compression condition length Lop is determined by
Also included is the use of shorter optical fiber compression sections. However, Lop=1/(-αD).
【０００７】[0007]
【作用】本発明は次の如くの作用を有する。図１は本発
明のリング共振器内の作用を従来系と比較して模式的に
示した機能ブロック図である。光増幅部では光パルスの
パワー（エネルギー）が増幅されるとともに、光カー効
果（屈折率が光パワーに比例して変化する現象）による
自己位相変調によりスペクトルが広がる。従来系では、
光ファイバの分散値をほぼ零に選んで、光増幅部の利得
幅Δνで定まるパルス幅Δｔがそのまま増幅されるよう
にしている。従って、増幅された光パルスは前記自己位
相変調によるスペクトル広がりにより、パルス幅のフー
リエ変換で与えられるトランスフォーム制限（ＴＬ）の
スペクトル幅より広がってしまう。ΔνとΔｔは、それ
らの積ΔνΔｔの値によってＴＬ条件を示すことができ
る。例えばガウス波形の場合、積の値が０．４４の時に
波形が最もきれいになり、この値からずれるとＴＬ条件
から外れるため、波形は劣化する。即ち、従来法のパル
ス幅は利得幅で制限されるとともに、ＴＬ条件から劣化
する問題がある。本発明では、光ファイバが有する大き
な正常分散特性により、上記自己位相変調の結果生じた
パルスの立ち上がり部に存在する低い周波数（長い波長
）の光は、パルスの立ち下がり部に存在する高い周波数
（短い波長）の光より光ファイバの伝搬速度が速いため
、図２の光増幅部出口に示すように、ほぼ直線のブルー
シフト（ＢＳ）チャーピング（パルス内の波長λが時間
とともに減少する（周波数νは大となる）現象）に変形
された光パルス波形となる。即ち、本発明において光増
幅部の役割は、光パルスのエネルギを増幅すると共に、
利得幅に比べて大きなスペクトル広がりを持つ直線のＢ
Ｓチャープを有する光パルスを生成するものである。次
に、このＢＳチャープパルスは、異常分散値をもつ光フ
ァイバ圧縮部に導かれる。異常分散領域では、周波数が
低い（波長の長い）ほど伝搬速度が遅いので、適当な長
さの光ファイバを伝搬すると、速度が遅いパルスの前半
部分は速度が速いパルスの後半部分に追いつかれる。こ
の時、ＢＳ光パルスはチャープが完全に補償されたので
、前記ＴＬ条件をΔνΔｔが満たすため、自己位相変調
の結果広がったスペクトル幅ΔνＳＦＭ で定まる短い
ＴＬパルス幅Δｔｃｏｍｐに圧縮されたことになる。光
パルスがＴＬパルスに圧縮される条件は、光ファイバの
分散特性がほぼ線形に近似できるので、チャーピング特
性がλ（ｔ）＝λ（０）＋αｔ（但し、αはチャープ速
度で（ｎｍ／ｐｓ）の単位で、本発明では負符号である
）のように時間ｔの一次関数（線形な関数）で近似でき
ることである。パルス幅が不変の従来の増幅条件では自
己位相変調の結果生じるチャーピングは波形の時間微分
で与えられるため、図３に示すように線形条件から大き
くずれてしまう。図２では時間ｔとともに周波数νが大
となる直線となっているが、図３では起伏がある。しか
るに、本発明では、光増幅部の正常分散特性により、チ
ャーピングがほぼ線形に整形されるので（図２参照）、
ほぼＴＬパルスとなるまでパルスが圧縮される。さらに
、より実用性を高める効果として、異常分散領域では非
線形効果が強まると、ソリトン圧縮効果が加わることを
従来用いていた。通常、線形の領域ではパルス幅が最短
になる圧縮条件があり、それは光ファイバの群速度分散
をＤ（ｐｓ／ｋｍ／ｎｍ）、チャープ速度をα（ｎｍ／
ｐｓ）と仮定すると、最適な光ファイバ長Ｌｏｐ（ｋｍ
）がＬｏｐ＝１／（−αＤ）で与えられる。即ち、線形
領域では光ファイバ長ＬがＬｏｐより短かすぎても長す
ぎても良くない。これに反して本発明のパルス圧縮部で
は、線形のチャープ補償に加えて、パルスの圧縮過程で
尖頭値が高まることによるソリトン圧縮効果が生じる。
これにより、線形領域よりも急速にパルス圧縮が進み、
線形領域の最適長Ｌｌｉｎｅａｒ，ｏｐより短い長さＬ
ｎｏｎｌｉｎｅａｒ，ｏｐで線形圧縮で得られる最短パ
ルスより短い光パルスに圧縮される。しかも、これがソ
リトンパルスに収束するため、Ｌｎｏｎｌｉｎｅａｒ，
ｏｐより多少長くなってもパルス幅はそれほど広がらず
、設計や動作条件に対する余裕が大きくなる。以上のこ
とから、本発明では光ファイバ圧縮部の長さの条件を短
くかつ緩くできると共に、非線形によるソリトン圧縮効
果を利用することで、チャーピング幅で定まるＴＬパル
ス幅よりも小さなパルス幅を実現するこができる。[Function] The present invention has the following functions. FIG. 1 is a functional block diagram schematically showing the operation within the ring resonator of the present invention in comparison with a conventional system. In the optical amplification section, the power (energy) of the optical pulse is amplified, and the spectrum is broadened by self-phase modulation due to the optical Kerr effect (a phenomenon in which the refractive index changes in proportion to the optical power). In the conventional system,
The dispersion value of the optical fiber is selected to be approximately zero so that the pulse width Δt determined by the gain width Δν of the optical amplification section is amplified as is. Therefore, due to the spectral broadening caused by the self-phase modulation, the amplified optical pulse becomes wider than the spectral width of the transform limit (TL) given by the Fourier transform of the pulse width. Δν and Δt can indicate the TL condition by the value of their product ΔνΔt. For example, in the case of a Gaussian waveform, the waveform is most beautiful when the product value is 0.44, and if it deviates from this value, the TL condition is violated and the waveform deteriorates. That is, the pulse width of the conventional method is limited by the gain width, and there is a problem that it deteriorates due to the TL condition. In the present invention, due to the large normal dispersion characteristic of the optical fiber, the low frequency (long wavelength) light present at the rising edge of the pulse generated as a result of the self-phase modulation is replaced by the high frequency (long wavelength) light present at the falling edge of the pulse. Because the propagation speed of an optical fiber is faster than that of light with a short wavelength, as shown at the exit of the optical amplification section in Figure 2, almost linear blue shift (BS) chirping (the wavelength λ within the pulse decreases with time The optical pulse waveform is transformed into a phenomenon in which ν becomes large. That is, in the present invention, the role of the optical amplification section is to amplify the energy of the optical pulse, and
Straight line B with a large spectral spread compared to the gain width
This generates a light pulse having an S-chirp. Next, this BS chirp pulse is guided to an optical fiber compressor having an anomalous dispersion value. In the anomalous dispersion region, the lower the frequency (the longer the wavelength), the slower the propagation speed, so if the pulse is propagated through an appropriate length of optical fiber, the first half of the slower pulse will catch up with the second half of the faster pulse. At this time, since the chirp of the BS optical pulse has been completely compensated, ΔνΔt satisfies the above-mentioned TL condition, so it is compressed to a short TL pulse width Δtcomp determined by the spectrum width ΔνSFM widened as a result of self-phase modulation. The conditions under which an optical pulse is compressed into a TL pulse are such that the dispersion characteristics of the optical fiber can be approximately linearly approximated, so the chirping characteristics are λ(t) = λ(0) + αt (where α is the chirp speed (nm/ ps), and can be approximated by a linear function (linear function) of time t, such as (in the present invention, it has a negative sign). Under conventional amplification conditions in which the pulse width remains unchanged, chirping resulting from self-phase modulation is given by the time differentiation of the waveform, resulting in a large deviation from the linear condition as shown in FIG. In FIG. 2, the frequency ν increases with time t, which is a straight line, but in FIG. 3, there are undulations. However, in the present invention, the chirping is shaped almost linearly due to the normal dispersion characteristic of the optical amplification section (see FIG. 2).
The pulse is compressed until it is approximately a TL pulse. Furthermore, as an effect to further improve practicality, it has been conventionally used that when the nonlinear effect becomes stronger in the anomalous dispersion region, a soliton compression effect is added. Usually, there is a compression condition in which the pulse width is the shortest in the linear region, and that is, the group velocity dispersion of the optical fiber is D (ps/km/nm) and the chirp velocity is α (nm/nm).
ps), the optimal optical fiber length Lop (km
) is given by Lop=1/(-αD). That is, in the linear region, it is not good if the optical fiber length L is either too short or too long than Lop. On the other hand, in the pulse compression section of the present invention, in addition to linear chirp compensation, a soliton compression effect occurs due to an increase in the peak value during the pulse compression process. This results in faster pulse compression than in the linear region.
Length L shorter than the optimal length Llinear, op of the linear region
Nonlinear, op compresses the optical pulse to a shorter one than the shortest pulse obtained by linear compression. Moreover, since this converges to a soliton pulse, Lnonlinear,
Even if it becomes somewhat longer than OP, the pulse width will not widen much, and there will be more margin for design and operating conditions. From the above, in the present invention, the length condition of the optical fiber compression section can be shortened and relaxed, and by utilizing the nonlinear soliton compression effect, a pulse width smaller than the TL pulse width determined by the chirping width is realized. I can do it.
【０００８】[0008]
【実施例】以下、本発明の実施例を図面に基づき説明す
る。図４は本発明の実施例を示す図である。図中符号１
は希土類添加光ファイバを用いた光ファイバ増幅器、符
号２１および２２は光アイソレータ、符号３はファイバ
圧縮部、符号４は１（または２）×２の光カップラ、符
号５はモード同期用光変調器、符号６は光励起モジュー
ルである。前記光ファイバ増幅器１に必要な励起光（発
振光より短い波長の光）は光励起モジュール６内にある
光源、例えば半導体レーザ（ＬＤ）から供給される。光
励起モジュール６は図示した如く、励起光と発振光を合
波する２×１カップラの機能を有している。これは励起
光の波長は曲げられ、発振光の波長は直進する波長特性
を有する光ファイバカップラ、またはダイクロイックミ
ラーや回折格子を用いて実現できる。また、直交する偏
波を多重する偏波結合器や、多少の光透過損失を許容す
るならば単にパワーを分割する光カップラを用いてもよ
い。共振器内の光を決められた周波数で変調するモード
同期光変調器５は、光の強度や位相が高速にオン−オフ
できればよく、市販（例えばＢＴ＆デュポン）の電気光
学（Ｅ−Ｏ）効果を用いたマッハツェンダ型または方向
性結合型ＬｉＮｂＯ３（ＬＮ）強度変調器（図５、図６
参照）が使用できる。この他、半導体材料（ＩｎＧａＡ
ｓ等）のフランツケルディシュ効果、Ｅ−Ｏ効果、光シ
ュタルク効果など使う変調器、または市販のモード同期
ＹＡＧレーザに使用される音響光学（Ａ−Ｏ）効果を用
いたＬＮ光変調器も使用できる。Embodiments Hereinafter, embodiments of the present invention will be explained based on the drawings. FIG. 4 is a diagram showing an embodiment of the present invention. Code 1 in the diagram
is an optical fiber amplifier using a rare earth-doped optical fiber, 21 and 22 are optical isolators, 3 is a fiber compression section, 4 is a 1 (or 2) x 2 optical coupler, and 5 is a mode-locking optical modulator , 6 is an optical excitation module. Pumping light (light with a shorter wavelength than the oscillation light) necessary for the optical fiber amplifier 1 is supplied from a light source in the optical pumping module 6, such as a semiconductor laser (LD). As shown, the optical excitation module 6 has the function of a 2×1 coupler that combines excitation light and oscillation light. This can be achieved by using an optical fiber coupler, a dichroic mirror, or a diffraction grating, which has wavelength characteristics in which the wavelength of the excitation light is bent and the wavelength of the oscillation light travels straight. Alternatively, a polarization coupler that multiplexes orthogonal polarized waves or an optical coupler that simply splits the power may be used if some light transmission loss is tolerated. The mode-locked optical modulator 5 that modulates the light inside the resonator at a predetermined frequency only needs to be able to turn on and off the intensity and phase of the light at high speed, and uses commercially available (for example, BT & DuPont) electro-optic (E-O) effect. Mach-Zehnder type or directionally coupled LiNbO3 (LN) intensity modulator using
) can be used. In addition, semiconductor materials (InGaA
Modulators that use the Franz Keldysch effect, E-O effect, optical Stark effect, etc.), or LN optical modulators that use the acousto-optic (A-O) effect used in commercially available mode-locked YAG lasers are also used. can.
【０００９】これらの部品は光ファイバ経由でリング形
状につながっており光学長ＬＣ の片回り（本実施例で
は右回り）のリング共振器を構成している。尚、本実施
例では２個の光アイソレータ２１、２２と１個の光励起
モジュール６を用いているが、それらの配置ならびに個
数は適宜当業者が必要に応じて変更できるものである。
例えば、光アイソレータ２１は光励起モジュール６と光
ファイバ増幅器１との間に配置する構成とすることも可
能であり、光励起モジュール６は光ファイバ増幅器１と
光アイソレータ２２との間に追加する構成とすることも
可能である。[0009] These parts are connected in a ring shape via an optical fiber, and constitute a one-way (clockwise in this embodiment) ring resonator with an optical length LC. In this embodiment, two optical isolators 21 and 22 and one optical excitation module 6 are used, but their arrangement and number can be changed as necessary by those skilled in the art. For example, the optical isolator 21 can be arranged between the optical pump module 6 and the optical fiber amplifier 1, and the optical pump module 6 can be added between the optical fiber amplifier 1 and the optical isolator 22. It is also possible.
【００１０】基本的な動作は、まず光励起モジュール６
で発振閾値以上の光励起を与える。すると、光ファイバ
増幅器１内で発生した自然放出光を種にして片回りリン
グ共振器によりＣＷのレーザ発振が生じる。次に、光変
調器５に共振器の光学長ＬＣ で定まる共振周波数ｆＣ
＝ｋｃ／ＬＣ （但し、ｋは整数、ｃは光速度）の変
調信号（図示せず）を光変調器５に加えると、ｆ０の光
周波数間隔を持つ全ての縦モードの位相が揃い、パルス
列発振となるモード同期が実現する。ところで、数１０
ＭＨｚ程度の駆動周波数では、変調信号としてパルス幅
の小さな矩形パルスが望ましい。光ファイバ増幅器１は
発振波長で正常分散を有しており、ここで大きなＢＳチ
ャープを持つ光パルスが生成され、それが光ファイバ圧
縮部３でチャープレスに圧縮されて光カップラ４の出力
ポートから取り出される。光パルスの幅は、励起光パワ
ーに依存する共振器内部の光パワーと、光ファイバ圧縮
部３の異常分散値と長さで変えることができる。The basic operation begins with the optical excitation module 6.
gives optical excitation above the lasing threshold. Then, CW laser oscillation is generated by the single-turn ring resonator using the spontaneous emission light generated within the optical fiber amplifier 1 as a seed. Next, the resonant frequency fC determined by the optical length LC of the resonator is applied to the optical modulator 5.
When a modulation signal (not shown) of =kc/LC (where k is an integer and c is the speed of light) is applied to the optical modulator 5, the phases of all longitudinal modes with an optical frequency interval of f0 are aligned, and a pulse train is generated. Mode locking resulting in oscillation is realized. By the way, the number 10
At a drive frequency of approximately MHz, a rectangular pulse with a small pulse width is desirable as the modulation signal. The optical fiber amplifier 1 has normal dispersion at the oscillation wavelength, and an optical pulse with a large BS chirp is generated here, which is chirplessly compressed by the optical fiber compressor 3 and output from the output port of the optical coupler 4. taken out. The width of the optical pulse can be changed by the optical power inside the resonator, which depends on the excitation light power, and by the anomalous dispersion value and length of the optical fiber compression section 3.
【００１１】次に、実際の実験系の構成を図７に示す。
ここでは、希土類添加光ファイバとして、Ｅｒ（エルビ
ウム）を添加した長さ５０ｍの正常分散ファイバ（波長
１．５μｍでＤ＝−４５ｐｓ／ｎｍ／ｋｍ）、圧縮ファ
イバとして１．３μｍで零分散となる通常ファイバを１
２０ｍ（波長１．５μｍでＤ＝１６ｐｓ／（ｎｍ・ｋｍ
）、励起パワー３５ｍＷで１ｐｓ幅のＴＬパルスが得ら
れている。従来のパルス圧縮部を用いない系では、せい
ぜい１０ｐｓ程度の幅しか得られなかったが、本発明で
大幅にパルス圧縮された光パルスが得られた。また、チ
ャープ速度の測定結果から、線形領域での最適パルス圧
縮条件は上記圧縮ファイバを用いると約５００ｍ以上と
なるが、これが約５分の１に短くできるという効果を奏
した。Next, the configuration of an actual experimental system is shown in FIG. Here, the rare earth-doped optical fiber is a normal dispersion fiber doped with Er (erbium) with a length of 50 m (D = -45 ps/nm/km at a wavelength of 1.5 μm), and a compressed fiber with zero dispersion at 1.3 μm. 1 normal fiber
20m (D=16ps/(nm・km at wavelength 1.5μm)
), a 1 ps width TL pulse was obtained with an excitation power of 35 mW. In a conventional system that does not use a pulse compressor, a width of only about 10 ps could be obtained at most, but with the present invention, a significantly compressed optical pulse was obtained. Furthermore, from the measurement results of the chirp speed, the optimal pulse compression condition in the linear region is about 500 m or more when the above-mentioned compression fiber is used, but this can be shortened to about one-fifth.
【００１２】尚、希土類元素の種類としては、現在、Ｅ
ｒが１．５μｍ帯、Ｎｄ及びＰｄが１．３２μｍ帯とし
て使用できる。Ｅｒレーザでは群速度分散の条件を満た
すため、光増幅部用はコア系を十分小さくして導波路分
散の寄与を大きくした分散シフトファイバを、光ファイ
バ圧縮部には通常の１．３μｍ零分散ファイバを使用す
ればよい。また、偏波特性の安定化のため、リング共振
器内の光ファイバの全てまたは殆どを偏波保持型光ファ
イバに置き換えてもよい。Ｎｄ及びＰｄの１．３２μｍ
帯では、光増幅用としては通常の１．５５μｍ零分散フ
ァイバ構造を、光ファイバ圧縮部用には１．３０μｍ零
分散ファイバを使用すればよい。[0012] Currently, the types of rare earth elements are E
r can be used as a 1.5 μm band, and Nd and Pd can be used as a 1.32 μm band. In order to satisfy the condition of group velocity dispersion in the Er laser, a dispersion-shifted fiber with a sufficiently small core system to increase the contribution of waveguide dispersion is used for the optical amplification section, and a normal 1.3 μm zero dispersion fiber is used for the optical fiber compression section. You can use fiber. Furthermore, in order to stabilize the polarization characteristics, all or most of the optical fibers in the ring resonator may be replaced with polarization-maintaining optical fibers. 1.32μm of Nd and Pd
In the band, a normal 1.55 μm zero dispersion fiber structure may be used for optical amplification, and a 1.30 μm zero dispersion fiber may be used for the optical fiber compression section.
【００１３】[0013]
【発明の効果】以上説明したように本発明によれば、モ
ード同期光ファイバリングレーザ装置において、光増幅
部に大きな正常分散特性を持つ希土類添加光ファイバを
用い、光増幅部と光をリングから取り出す光結合部との
間に異常分散特性を有する光ファイバ圧縮部を挿入する
ことにより、従来用いられていた外部の光パルス圧縮系
なしに１ｐｓ以下の光パルスを発生させることができ、
小型化、高安定、装置化に適した超短光パルスレーザを
構成することができる等の効果を奏することができる。As explained above, according to the present invention, in a mode-locked optical fiber ring laser device, a rare earth-doped optical fiber having a large normal dispersion characteristic is used in the optical amplification section, and light is transmitted from the optical amplification section and the ring. By inserting an optical fiber compression section with anomalous dispersion characteristics between the optical coupling section and the extraction optical coupling section, it is possible to generate optical pulses of 1 ps or less without the need for an external optical pulse compression system that has been used in the past.
Effects such as being able to construct an ultrashort optical pulse laser suitable for miniaturization, high stability, and deviceization can be achieved.
【図１】本発明の機能ブロック図である。FIG. 1 is a functional block diagram of the present invention.
【図２】本発明の光波形とスペクトルを示す図である。FIG. 2 is a diagram showing an optical waveform and spectrum of the present invention.
【図３】従来の光波形とスペクトルを示す図である。FIG. 3 is a diagram showing a conventional optical waveform and spectrum.
【図４】本発明の実施例を示す構成図である。FIG. 4 is a configuration diagram showing an embodiment of the present invention.
【図５】本発明の実施例の広帯域・低駆動電圧２×２ス
イッチの構造模式の平面図である。FIG. 5 is a plan view of a structural model of a broadband/low drive voltage 2×2 switch according to an embodiment of the present invention.
【図６】本発明の実施例の広帯域・低駆動電圧２×２ス
イッチの構造模式の断面図である。FIG. 6 is a cross-sectional view of a schematic structure of a broadband/low drive voltage 2×2 switch according to an embodiment of the present invention.
【図７】本発明の実施例のモードロックリングレーザ系
の構成図である。FIG. 7 is a configuration diagram of a mode-locked ring laser system according to an embodiment of the present invention.
【図８】従来技術の超短光パルス発生装置の１つの例を
示す構成図である。FIG. 8 is a configuration diagram showing one example of a conventional ultrashort optical pulse generator.
【図９】従来技術の超短光パルス発生装置の他の例を示
す構成図である。FIG. 9 is a configuration diagram showing another example of a conventional ultrashort optical pulse generator.
１ 光ファイバ増幅器 ３ 光ファイバ圧縮部 ４ 光カップラ ５ 光変調器 ６ 光励起モジュール ２１ 光アイソレータ ２２ 光アイソレータ 1 Optical fiber amplifier 3 Optical fiber compression section 4 Optical coupler 5. Optical modulator 6 Photoexcitation module 21 Optical isolator 22 Optical isolator
Claims (3)
部と、リング内の光パルスを取り出す光結合部と、光の
損失または位相を変調する光変調部と、片回り光のみを
通過させる光アイソレータ部と、希土類添加光ファイバ
を光励起する光励起部とを少なくとも備えたモード同期
光ファイバリングレーザ装置において、上記光増幅部は
零分散波長λ０ が発振波長λよりも十分長く、上記光
増幅部と光結合部との間には発振波長λより十分短い零
分散波長を有する光ファイバ圧縮部を備えたことを特徴
とするモード同期光ファイバレーザ装置。Claim 1: An optical amplification section using a rare earth-doped optical fiber, an optical coupling section that takes out the optical pulse in the ring, an optical modulation section that modulates the loss or phase of the light, and a light that allows only one-way light to pass through. In a mode-locked optical fiber ring laser device comprising at least an isolator section and an optical excitation section for optically pumping a rare earth-doped optical fiber, the optical amplification section has a zero dispersion wavelength λ0 that is sufficiently longer than the oscillation wavelength λ, and the optical amplification section and 1. A mode-locked optical fiber laser device comprising an optical fiber compression section having a zero dispersion wavelength sufficiently shorter than the oscillation wavelength λ between the optical coupling section and the optical coupling section.
ｒを添加した希土類添加光ファイバを用いることを特徴
とする請求項１記載のモード同期光ファイバレーザ装置
。[Claim 2] Er, Nd or P as the optical amplification section.
The mode-locked optical fiber laser device according to claim 1, characterized in that a rare earth doped optical fiber doped with r is used.
トチャープパルスのチャープ速度α（ｎｍ／ｐｓ）と光
ファイバの群速度分散Ｄ（ｐｓ／ｎｍ／ｋｍ）とで決ま
る最適な線形圧縮条件長Ｌｏｐ（但し、Ｌｏｐ＝１／−
αＤ）より短い光ファイバを用いることを特徴とする請
求項１記載のモード同期光ファイバレーザ装置。3. As an optical fiber compression section, an optimal linear compression condition length Lop( However, Lop=1/-
2. The mode-locked optical fiber laser device according to claim 1, wherein an optical fiber shorter than αD) is used.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP3133075A JP3011286B2 (en) | 1991-06-04 | 1991-06-04 | Mode-locked optical fiber laser device |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP3133075A JP3011286B2 (en) | 1991-06-04 | 1991-06-04 | Mode-locked optical fiber laser device |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH04357892A true JPH04357892A (en) | 1992-12-10 |
| JP3011286B2 JP3011286B2 (en) | 2000-02-21 |
Family
ID=15096263
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP3133075A Expired - Lifetime JP3011286B2 (en) | 1991-06-04 | 1991-06-04 | Mode-locked optical fiber laser device |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP3011286B2 (en) |
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH0883951A (en) * | 1994-09-09 | 1996-03-26 | Nippon Telegr & Teleph Corp <Ntt> | Mode synchronizing ring laser device |
| JP2002031597A (en) * | 2000-05-09 | 2002-01-31 | Fuji Photo Film Co Ltd | Optical tomographic device |
| JP2003090792A (en) * | 2001-09-20 | 2003-03-28 | Fuji Photo Film Co Ltd | Optical tomographic imaging apparatus |
| JP2005203809A (en) * | 2001-03-16 | 2005-07-28 | Imra America Inc | Mode-locked fiber laser |
| WO2005086299A1 (en) * | 2004-03-05 | 2005-09-15 | The Furukawa Electric Co., Ltd. | Optical fiber laser using rare earth-added fiber and wide band light source |
| JP2007085754A (en) * | 2005-09-20 | 2007-04-05 | Furukawa Electric Co Ltd:The | Optical pulse tester and optical fiber longitudinal direction characteristic test method |
-
1991
- 1991-06-04 JP JP3133075A patent/JP3011286B2/en not_active Expired - Lifetime
Cited By (14)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH0883951A (en) * | 1994-09-09 | 1996-03-26 | Nippon Telegr & Teleph Corp <Ntt> | Mode synchronizing ring laser device |
| JP2002031597A (en) * | 2000-05-09 | 2002-01-31 | Fuji Photo Film Co Ltd | Optical tomographic device |
| JP2009158983A (en) * | 2001-03-16 | 2009-07-16 | Imra America Inc | Passively mode-locked fiber laser |
| JP2005203809A (en) * | 2001-03-16 | 2005-07-28 | Imra America Inc | Mode-locked fiber laser |
| US7782910B2 (en) | 2001-03-16 | 2010-08-24 | Imra America, Inc. | Single-polarization high power fiber lasers and amplifiers |
| US8135048B2 (en) | 2001-03-16 | 2012-03-13 | Imra America, Inc | Single-polarization high power fiber lasers and amplifiers |
| JP2003090792A (en) * | 2001-09-20 | 2003-03-28 | Fuji Photo Film Co Ltd | Optical tomographic imaging apparatus |
| WO2005086299A1 (en) * | 2004-03-05 | 2005-09-15 | The Furukawa Electric Co., Ltd. | Optical fiber laser using rare earth-added fiber and wide band light source |
| EP1729379A1 (en) * | 2004-03-05 | 2006-12-06 | The Furukawa Electric Co., Ltd. | Optical fiber laser using rare earth-added fiber and wide band light source |
| JPWO2005086299A1 (en) * | 2004-03-05 | 2008-01-24 | 古河電気工業株式会社 | Optical fiber laser and broadband light source using rare earth doped fiber |
| CN100438235C (en) * | 2004-03-05 | 2008-11-26 | 古河电气工业株式会社 | Optical fiber laser using rare earth-added fiber and wide band light source |
| EP1729379A4 (en) * | 2004-03-05 | 2009-07-29 | Furukawa Electric Co Ltd | Optical fiber laser using rare earth-added fiber and wide band light source |
| JP5192692B2 (en) * | 2004-03-05 | 2013-05-08 | 古河電気工業株式会社 | Broadband optical pulse generator and noise-like pulse generator |
| JP2007085754A (en) * | 2005-09-20 | 2007-04-05 | Furukawa Electric Co Ltd:The | Optical pulse tester and optical fiber longitudinal direction characteristic test method |
Also Published As
| Publication number | Publication date |
|---|---|
| JP3011286B2 (en) | 2000-02-21 |
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