JP3778824B2 - Light control element - Google Patents

Description

が要求され、ＳＯＡ長を２００μｍ程度以下にする必要があった。
【００１０】
光の位相変化は、屈折率変化の絶対値と媒質の長さの積で決まるため、長さの短いＳＯＡで所望の位相変化を得るためには、屈折率変化の絶対値を大きくせざるを得ず、動作パワーが増大したり、場合によってはＳＯＡの飽和により所望の屈折率変化が得られないといった問題が生じていた。
【００１１】
本発明は、このような問題に鑑みてなされたもので、その目的とするところは、低パワーで、かつ高速の波長変換機能を有する光制御素子を提供することにある。
【００１２】
【課題を解決するための手段】
本発明は、このような目的を達成するために、請求項１に記載の発明は、任意波長の第１の入力信号光の光強度に応じて、前記第１の入力信号光の波長と異なる波長を有する第２の入力光が変調される光制御素子において、前記第１の入力信号光を分岐させる第１の光分岐手段と、前記第２の入力光を分岐させる第２の光分岐手段と、前記第２の分岐手段により分岐された一方の第２の入力光を遅延させる遅延手段と、前記分岐された一方の第１の入力信号光と前記遅延を受けた一方の第２の入力光とを、第１の合流光ポートに合流させる第１の光結合手段と、前記分岐された他方の第１の入力信号光と前記分岐された他方の第２の入力光とを、第２の合流光ポートに合流させる第２の光結合手段と、前記第１の合流光ポートおよび前記第２の合流光ポートが接続され、前記各々の合流光が相対する方向に伝播して、前記第１の入力信号光の光強度に応じて屈折率が変化する媒質からなる位相変調手段と、を有することを特徴とする。
【００１３】
また、請求項２に記載の発明は、請求項１に記載の発明において、前記第１の入力信号光の光強度に応じて屈折率が変化する媒質からなる位相変調手段として、半導体増幅器を用いることを特徴とする。
【００１４】
【発明の実施の形態】
以下、図面を参照して本発明の実施例について説明する。
図４は、本発明の波長変換を行う光制御素子の一実施例を示す図で、この波長変換回路は、半導体光増幅器（ＳＯＡ）４０１と、このＳＯＡ４０１に接続されたＭＭＩカプラ４０２，４１２と、このＭＭＩカプラ４１２に接続されたＭＭＩカプラ４０３と、このＭＭＩカプラ４０２，４０３間に設けられたループ型干渉回路４０９と、ＭＭＩカプラ４０２，４１２に接続されたＭＭＩカプラ４１３とから構成されている。なお、符号４０５はＣＷ光、４０８は変換光、４１０は変換光出力ポート、４１１はＣＷ光入力ポート、４１４，４１５は信号光導波路を示している。
【００１５】
このような構成により、基本動作は図１に示した従来例のものに準じて動作する。つまり、ＭＭＩカプラ４０３に波長λｊの連続光（ＣＷ光）４０５がポート４１１に入射され、ＭＭＩカプラ４０３で２つに分かれてループ型干渉回路４０９へと導かれる。ループ型干渉回路４０９では、右回りの光と左回りの光に別れてループを一周し、再びＭＭＩカプラ４０３で合波されてポート４１１に出射される。この状態で、波長λｉの信号光４０４をＭＭＩカプラ４０２に入射させる。入射された信号光４０４はＳＯＡ４０１を通過する。このとき、ＳＯＡ４０１内の屈折率が変化する。
【００１６】
ただし、信号光が、図４に示すように、ＭＭＩカプラ４１３で分岐されて信号光導波路４１４，４１５からＳＯＡ４０１に両方向から入射する。そのためループ内を右回りに伝搬する光４０７と左回りに伝搬する光４０６はともに、ＳＯＡ４０１内において、分岐された信号光と同方向伝搬するとともに、逆方向にすれ違う。その結果、右回りに伝搬する光４０７と左回りに伝搬する光４０６の位相変化は、図５（ａ）に示すように、急峻かつ完全に同一波形となる。そのため、変換出力波形は、図５（ｂ）に示すように、立ち上がり、立ち下がりとも急峻となり、高速な出力波形を得ることができる。
【００１７】
本実施例では、ＳＯＡの構造についてはなんら制約を設けるものではない。すなわち、ＳＯＡの活性層に関しては、ＧａＡｓ、ＡｌＧａＡｓ、ＩｎＧａＡｓＰ，ＩｎＧａＡｓ、ＧａＩｎＮＡｓ等、任意の材質について同様な効果が期待できる。また、活性層構造に関しても、バルク、ＭＱＷ、量子細線、量子ドットを問わず、またＳＯＡの導波路構造に関してもｐｎ埋め込み、リッジ構造、半絶縁埋め込み構造、ハイメサ構造等を用いた場合でも同様な効果が期待できる。
【００１８】
また、上述した実施例では、信号光、あるいはＣＷ光を分岐、合流する構造として、ＭＭＩカプラを用いた例を示しているが、方向性結合器を用いてもよい。また、第１の入力光の光強度に応じて屈折率が変化する媒質からなる構造として、ＳＯＡを用いた例を示しているが、ＥＡ変調器等のような光強度に応じて屈折率が変化する構造であれば、すべて適用可能である。
【００１９】
【発明の効果】
以上説明したように本発明によれば、任意波長の第１の入力信号光強度に応じて前記入力信号光の波長と同一または異なる波長を有する第２の入力光が変調される光制御素子において、第１の入力光を分岐させる光分岐手段と、第２の入力光を分岐・遅延させる光分岐・遅延手段と、分岐された第１の入力光の一方を、分岐された第２の入力光の一方と合流する第１の光結合手段と、光結合手段により合流された入力光が伝搬するポートに接続された、第１の入力光の光強度に応じて屈折率が変化する媒質と、媒質からの出力を、分岐された第１の入力光の他方と分岐された第２の入力光の他方とを合流する第２の光結合手段とを有するので、低動作パワーで高速の波長変換機能を有する光制御素子を提供することができる。
【図面の簡単な説明】
【図１】従来の波長変換を行う光制御素子の一例を示す図である。
【図２】従来の波長変換回路の動作原理（その１）を示す図で、（ａ）は位相変化、（ｂ）は光強度を示す図ある。
【図３】従来の波長変換回路の動作原理（その２）を示す図で、（ａ）は位相変化、（ｂ）は光強度を示す図ある。
【図４】本発明の波長変換を行う光制御素子の第一実施例を示す図である。
【図５】本発明の光制御素子の動作原理を示す図で、（ａ）は位相変化、（ｂ）は光強度を示す図ある。
【符号の説明】
１０１ ＳＯＡ
１０２，１０３ ＭＭＩカプラ
１０４ 信号光
１０５ ＣＷ光
１０６ 左回りの光
１０７ 右回りの光
１０８ 出力光（被波長変換光）
１０９ ループ型干渉回路
１１０，１１１ ポート
４０１ ＳＯＡ
４０２，４０３ ＭＭＩカプラ
４０４ 信号光
４０５ ＣＷ光
４０６ 左回りの光
４０７ 右回りの光
４０８ 出力光（被波長変換光）
４０９ ループ型干渉回路
４１０，４１１ ポート
４１２，４１３ ＭＭＩカプラ
４１４，４１５ 信号光導波路[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical control element, and more particularly, in a wavelength division multiplexing optical network, an optical control for modulating light of another wavelength that is the same as or different from the wavelength of the input signal light according to the input signal light intensity of an arbitrary wavelength Regarding technology.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, as an optical transmission system that transmits a plurality of optical signals having different wavelengths, there is an optical transmission system (WDM system) that uses wavelength multiplexing to transmit a plurality of optical signals having different wavelengths by combining them with one optical fiber. . Further, this WDM system is rapidly becoming networked as well as one-to-one transmission.
[0003]
In such a WDM system, an optical control element that performs so-called wavelength conversion that converts the wavelength of an optical signal transmitted through an optical fiber into the same or different wavelength becomes important.
[0004]
FIG. 1 is a diagram showing an example of a conventional optical control element that performs wavelength conversion. This wavelength conversion circuit includes a semiconductor optical amplifier (SOA) 101 and an MMI coupler (multimode) connected to the SOA. Multi-Mode Interference couplers (102, 103) and a loop type interference circuit 109 provided between the MMI couplers (102, 103).
[0005]
With such a configuration, continuous light (CW light) 105 having a wavelength λj is incident on the port 111 to the MMI coupler 103 and is split into two by the MMI coupler 103 and guided to the loop interference circuit 109. In the loop type interference circuit 109, it divides into a clockwise light and a counterclockwise light, makes a round of the loop, is multiplexed again by the MMI coupler 103, and is emitted to the port 111. In this state, the signal light 104 having the wavelength λi is incident on the MMI coupler 102. The incident signal light 104 passes through the SOA 101. At this time, the refractive index in the SOA 101 changes.
[0006]
The light having the wavelength λj guided in the loop undergoes a phase change as shown in FIG. 2A due to the influence of the refractive index change. The clockwise light 107 undergoes a steep phase change, and then returns to the original phase and enters the MMI coupler 103 at a time corresponding to the speed of the carrier change recovery time of the SOA 101. The counterclockwise light 106 is also subjected to the same phase change, but the distance propagating through the loop interference circuit 109 is longer than that of the clockwise light 107 by ΔL. . In the MMI coupler 103, the time when the phase change of the clockwise and counterclockwise light occurs is shifted by Δτ. Only during this Δτ, the light of wavelength λj is emitted to the port 110 due to the interference effect as shown in FIG.
[0007]
That is, the input optical signal having the wavelength λi is transferred to the light having the wavelength λj and is output to the port 110. In the wavelength conversion circuit having this loop type interference circuit, the region restricted by the speed of the carrier change recovery time of the phase change is canceled out, and high-speed wavelength conversion is possible without being restricted.
[0008]
[Problems to be solved by the invention]
However, when the wavelength converter having the loop type interference circuit described above is used, it is necessary that the length of the SOA 101 is sufficiently smaller than ΔL. That is, since the clockwise continuous light 107 propagates in the same direction as the signal light 104, it is affected by the refractive index change over the entire length L _{SOA of the SOA} 101, whereas the counterclockwise continuous light 106 Until it encounters the signal light 104 because it propagates in the opposite direction to the light 104, it is not affected by the change in refractive index, and at the time of rising _tr = 2L _SOA / (c / n _eq ) (c is the speed of light, and n _eq is the SOA speed) Equivalent refractive index).
[0009]
As a result, when the length of the SOA 101 is about the same as ΔL, the phase change of both the clockwise and counterclockwise continuous light is as shown in FIG. 3A and is emitted from the port 110 due to the interference effect. The waveform of the light to be converted is deformed as shown in FIG. Thus, operations such as Δτ is smaller than t _r was impossible. In order to realize about 10 ps as Δτ

And the SOA length had to be about 200 μm or less.
[0010]
Since the phase change of light is determined by the product of the absolute value of the refractive index change and the length of the medium, in order to obtain a desired phase change with a short SOA, the absolute value of the refractive index change must be increased. However, there has been a problem that the operating power is increased, and in some cases, the desired refractive index change cannot be obtained due to the saturation of the SOA.
[0011]
The present invention has been made in view of such problems, and an object thereof is to provide a light control element having a low-power and high-speed wavelength conversion function.
[0012]
[Means for Solving the Problems]
The present invention, in order to achieve the above object, the invention according to claim 1, in accordance with the light intensity of the first input signal light having an arbitrary wavelength, different from the wavelength of the first input signal light in the optical control element in which the second input light having a wavelength is modulated, the first and the first optical branching means for branching the input signal light, the second optical branching means for branching said second input light When the second delay means for delaying the second input light of one which is branched by the branching unit, one of the second input receiving the delayed and the branched one first input signal light A first optical coupling means for combining light with the first combined light port, the second branched first input signal light and the second branched second input light; Second optical coupling means for merging with the merged optical port, the first merged optical port and the second Merging optical port are connected, and wherein each of the merging light propagates in the opposite direction, to have a phase modulation means whose refractive index made from a medium that changes according to the light intensity of the first input signal light It is characterized by.
[0013]
According to a second aspect of the present invention, in the first aspect of the present invention, a semiconductor amplifier is used as the phase modulation means made of a medium whose refractive index changes according to the light intensity of the first input signal light. It is characterized by that.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 4 is a diagram showing an embodiment of an optical control element that performs wavelength conversion according to the present invention. This wavelength conversion circuit includes a semiconductor optical amplifier (SOA) 401 and MMI couplers 402 and 412 connected to the SOA 401. The MMI coupler 403 connected to the MMI coupler 412, the loop type interference circuit 409 provided between the MMI couplers 402 and 403, and the MMI coupler 413 connected to the MMI couplers 402 and 412. . Reference numeral 405 denotes CW light, 408 denotes converted light, 410 denotes a converted light output port, 411 denotes a CW light input port, and 414 and 415 denote signal optical waveguides.
[0015]
With such a configuration, the basic operation operates in accordance with the conventional example shown in FIG. That is, continuous light (CW light) 405 having a wavelength λj is incident on the port 411 to the MMI coupler 403, divided into two by the MMI coupler 403, and guided to the loop interference circuit 409. In the loop type interference circuit 409, the loop is divided into right-handed light and left-handed light, goes around the loop once again, is multiplexed by the MMI coupler 403, and is emitted to the port 411. In this state, the signal light 404 having the wavelength λi is incident on the MMI coupler 402. The incident signal light 404 passes through the SOA 401. At this time, the refractive index in the SOA 401 changes.
[0016]
However, the signal light is branched by the MMI coupler 413 and enters the SOA 401 from the signal optical waveguides 414 and 415 from both directions as shown in FIG. Therefore, both the light 407 propagating clockwise in the loop and the light 406 propagating counterclockwise propagate in the SOA 401 in the same direction as the branched signal light and pass in the opposite direction. As a result, the phase change of the light 407 propagating clockwise and the light 406 propagating counterclockwise has a steep and completely identical waveform as shown in FIG. Therefore, as shown in FIG. 5B, the converted output waveform is steep both rising and falling, and a high-speed output waveform can be obtained.
[0017]
In this embodiment, there is no restriction on the SOA structure. That is, with respect to the active layer of the SOA, the same effect can be expected for any material such as GaAs, AlGaAs, InGaAsP, InGaAs, and GaInNAs. The active layer structure is the same regardless of whether it is a bulk, MQW, quantum wire, or quantum dot, and the SOA waveguide structure is the same even when a pn buried, ridge structure, semi-insulating buried structure, high mesa structure, or the like is used. The effect can be expected.
[0018]
In the above-described embodiments, an example in which an MMI coupler is used as a structure for branching and joining signal light or CW light is shown, but a directional coupler may be used. In addition, although an example using SOA is shown as a structure made of a medium whose refractive index changes according to the light intensity of the first input light, the refractive index varies depending on the light intensity as in an EA modulator or the like. Any structure that changes is applicable.
[0019]
【The invention's effect】
As described above, according to the present invention, in the light control element in which the second input light having the same or different wavelength as the input signal light is modulated according to the intensity of the first input signal light having an arbitrary wavelength. The optical branching means for branching the first input light, the optical branching / delaying means for branching / delaying the second input light, and the second input branching one of the branched first input lights A first optical coupling unit that merges with one of the light; a medium that is connected to a port through which the input light merged by the optical coupling unit propagates and has a refractive index that changes according to the light intensity of the first input light; And a second optical coupling means for combining the output of the medium with the other of the branched first input light and the other of the branched second input light. A light control element having a conversion function can be provided.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an example of a conventional light control element that performs wavelength conversion.
FIGS. 2A and 2B are diagrams showing an operation principle (part 1) of a conventional wavelength conversion circuit, where FIG. 2A shows phase change and FIG. 2B shows light intensity;
FIGS. 3A and 3B are diagrams illustrating an operation principle (part 2) of a conventional wavelength conversion circuit, in which FIG. 3A is a phase change and FIG. 3B is a diagram illustrating light intensity;
FIG. 4 is a diagram showing a first embodiment of a light control element for performing wavelength conversion according to the present invention.
FIGS. 5A and 5B are diagrams showing the operation principle of the light control element of the present invention, where FIG. 5A shows phase change and FIG. 5B shows light intensity.
[Explanation of symbols]
101 SOA
102, 103 MMI coupler 104 Signal light 105 CW light 106 Left-handed light 107 Right-handed light 108 Output light (wavelength converted light)
109 Loop interference circuit 110, 111 Port 401 SOA
402, 403 MMI coupler 404 Signal light 405 CW light 406 Left-handed light 407 Right-handed light 408 Output light (wavelength converted light)
409 Loop type interference circuit 410,411 Port 412,413 MMI coupler 414,415 Signal optical waveguide

Claims (2)

In accordance with the light intensity of the first input signal light having an arbitrary wavelength, the optical control device second input light is modulated with a wavelength different from the wavelength of the first input signal light,
A first optical branching means for branching said first input signal light,
A second optical branching means for branching said second input light,
Delay means for delaying one second input light branched by the second branch means;
First optical coupling means for joining one of the branched first input signal light and one second input light subjected to the delay to a first joining optical port ;
A second optical coupling means for joining the other branched first input signal light and the other branched second input light to a second combined light port;
The first combined light port and the second combined light port are connected, the combined light propagates in opposite directions, and the refractive index changes according to the light intensity of the first input signal light. Phase modulation means comprising a medium that
A light control element comprising: 2. The light control element according to claim 1 , wherein a semiconductor amplifier is used as the phase modulation means made of a medium whose refractive index changes according to the light intensity of the first input signal light.

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