JPH06100737B2 - Light modulator - Google Patents
Light modulatorInfo
- Publication number
- JPH06100737B2 JPH06100737B2 JP63042200A JP4220088A JPH06100737B2 JP H06100737 B2 JPH06100737 B2 JP H06100737B2 JP 63042200 A JP63042200 A JP 63042200A JP 4220088 A JP4220088 A JP 4220088A JP H06100737 B2 JPH06100737 B2 JP H06100737B2
- Authority
- JP
- Japan
- Prior art keywords
- optical waveguide
- face
- light
- incident
- layer
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
- 230000003287 optical effect Effects 0.000 claims description 99
- 238000010521 absorption reaction Methods 0.000 claims description 59
- 239000000969 carrier Substances 0.000 claims description 21
- 230000005684 electric field Effects 0.000 claims description 15
- 239000000758 substrate Substances 0.000 claims description 10
- 238000005253 cladding Methods 0.000 claims description 3
- 239000012535 impurity Substances 0.000 claims 5
- 230000000694 effects Effects 0.000 description 8
- 238000000034 method Methods 0.000 description 8
- 230000006866 deterioration Effects 0.000 description 7
- 238000001228 spectrum Methods 0.000 description 6
- 239000013307 optical fiber Substances 0.000 description 5
- 230000005540 biological transmission Effects 0.000 description 4
- 239000000463 material Substances 0.000 description 4
- 239000004065 semiconductor Substances 0.000 description 4
- 238000009826 distribution Methods 0.000 description 3
- 230000005685 electric field effect Effects 0.000 description 3
- 238000005516 engineering process Methods 0.000 description 3
- 239000000203 mixture Substances 0.000 description 3
- 230000010355 oscillation Effects 0.000 description 3
- 230000008033 biological extinction Effects 0.000 description 2
- 238000004891 communication Methods 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 238000011160 research Methods 0.000 description 2
- 229910000980 Aluminium gallium arsenide Inorganic materials 0.000 description 1
- 229910013641 LiNbO 3 Inorganic materials 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 230000003595 spectral effect Effects 0.000 description 1
- 230000000087 stabilizing effect Effects 0.000 description 1
- 230000003313 weakening effect Effects 0.000 description 1
Description
【発明の詳細な説明】 （発明の技術分野） 本発明は外部から入射される光を変調する光変調素子に
関するもである。TECHNICAL FIELD OF THE INVENTION The present invention also relates to a light modulator for modulating light incident from the outside.
（従来技術とその問題点） 光ファイバ通信技術は光ファイバの超低損失性と光が本
質的に有する超広帯域性を利用して進展し、伝送のます
ますの長距離化と大容量化の研究が世界的に進められて
いる。光ファイバの損失が理論的な限界にまで達した今
日では、特に伝送の高速化，大容量化の研究が重要にな
ってきている。(Conventional technology and its problems) Optical fiber communication technology has progressed by utilizing the ultra-low loss property of optical fiber and the ultra-wide band property inherent in light, and will continue to be used for longer distances and larger capacity transmission. Research is underway worldwide. Nowadays, when the loss of optical fiber reaches the theoretical limit, researches on high-speed and large-capacity transmission have become particularly important.
光信号を高速にオン・オフする技術としては、現在では
一般に半導体レーザを直接変調する方法がとられてい
る。しかし、直接変調方式では、発振素子である半導体
レーザの電流を高速に変化させるため、発振波長が時間
的に大きく変動し、結果的に発振スペクトル幅が変調帯
域のスペクトル幅に比べて異常に大きく広がってしまう
ことになる。従って、長距離あるいは高速の伝送では、
光ファイバの波長分散の影響を大きく受け、受信される
光パルスが歪んでしまうため、良好な伝送特性が得られ
ない。そこで、このような問題を避けるため、半導体レ
ーザの出力は一定に保持し、外部の光変調素子で高速な
変調を行う方法が近年検討されている。As a technique for turning on / off an optical signal at high speed, a method of directly modulating a semiconductor laser is generally used at present. However, in the direct modulation method, the current of the semiconductor laser that is the oscillation element is changed at high speed, so the oscillation wavelength fluctuates greatly with time, and as a result, the oscillation spectrum width is abnormally large compared to the spectrum width of the modulation band. It will spread. Therefore, for long distance or high speed transmission,
Since the received optical pulse is greatly affected by the chromatic dispersion of the optical fiber, good transmission characteristics cannot be obtained. Therefore, in order to avoid such a problem, a method of holding the output of the semiconductor laser constant and performing high-speed modulation with an external light modulator has been studied in recent years.
光変調素子としては、LiNbO3等の強誘電体を用いた光変
調素子やDFBレーザ等の単一波長半導体レーザとモノシ
リックに集積可能な光変調素子などが提案されている
が、中でも後者の変調導波路に電界を印加して電気吸収
効果により強度変調する電気吸収型光変調素子が最も有
望視されている。As optical modulators, optical modulators using ferroelectrics such as LiNbO 3 and optical modulators that can be monolithically integrated with single wavelength semiconductor lasers such as DFB lasers have been proposed. The electro-absorption type optical modulation element that applies an electric field to the waveguide to modulate the intensity by the electro-absorption effect is regarded as the most promising.
第１図は、従来の電気吸収型光変調素子の斜視図であ
る。ｎ型InP基板１の上に、n-−InGaAsP変調導波路層
２、メサ状のｐ型InPクラッド層３及びｐ型InGaAsPキャ
ップ層４が積層されており：さらに、ｐ型電極５及びｎ
型電極６がそれぞれｐ型InGaAsPキャップ層４とｎ型InP
基板１に接するように形成されている。この光変調素子
ではInGaAsP変調導波路層２に光を入射してｐ型電極５
に印加するマイナスと、ｎ型電極６に印加するプラスの
電圧を変化させ、InGaAsP変調導波路層２の吸収係数を
変化させることによって、出射光の強度を変調すること
ができる。電気吸収型変調素子においては、低電圧で変
調できること、高速変調可能なこと及び高速変調時のス
ペクトル広がりが小さいことが重要である。今まで、In
GaAsP変調導波路層２の禁制帯エネルギーEgに入射光フ
ォトエネルギーｈνが近いほど低電圧で吸収係数の変化
が大きくとれ、かつ、素子長Ｌ（InGaAsP変調導波路層
２の入射端面から出射端面までの長さ）を短くできるた
め、高速変調が可能でスペクトル広がりも抑制できると
されていた。従って、従来では両者のエネルギー差ΔEg
（Eg−ｈν）だけに着目し、エネルギー差ΔEgを30〜40
meVに設定すれば、高性能な光変調素子が実現されると
考えられていた。しかし、従来の光変調素子では、入射
光強度が約百μＷ以下の場合には変調電圧，変調帯域幅
及びスペクトル幅ともに良好な特性を示すものの、入射
光の強度が0.1mW以上となるに従い、変調電圧が著しく
増加し、又帯域幅も減少するということが明らかになっ
た。FIG. 1 is a perspective view of a conventional electro-absorption optical modulator. An n -- InGaAsP modulation waveguide layer 2, a mesa-shaped p-type InP cladding layer 3 and a p-type InGaAsP cap layer 4 are laminated on an n-type InP substrate 1: a p-type electrode 5 and an n-type InP substrate.
The type electrodes 6 are p-type InGaAsP cap layer 4 and n-type InP, respectively.
It is formed so as to be in contact with the substrate 1. In this optical modulator, light is made incident on the InGaAsP modulation waveguide layer 2 and the p-type electrode 5
The intensity of the emitted light can be modulated by changing the negative voltage applied to and the positive voltage applied to the n-type electrode 6 to change the absorption coefficient of the InGaAsP modulation waveguide layer 2. In the electro-absorption modulator, it is important that it can be modulated at a low voltage, that it can be modulated at high speed, and that the spectrum spread during high-speed modulation is small. Until now, In
The closer the incident light photoenergy hv is to the forbidden band energy Eg of the GaAsP modulation waveguide layer 2, the larger the change in absorption coefficient can be obtained at a low voltage, and the device length L (from the incident end surface to the emitting end surface of the InGaAsP modulation waveguide layer 2 It is said that high-speed modulation is possible and the spectrum spread can be suppressed because the length of the spectrum can be shortened. Therefore, conventionally, the energy difference ΔEg between the two is
Focusing only on (Eg-hν), the energy difference ΔEg is 30-40
It was thought that a high-performance optical modulator could be realized by setting it to meV. However, in the conventional light modulation element, when the incident light intensity is about 100 μW or less, the modulation voltage, the modulation bandwidth, and the spectral width show good characteristics, but as the incident light intensity becomes 0.1 mW or more, It has been found that the modulation voltage increases significantly and the bandwidth also decreases.
以上述べたように、従来の電気吸収型光変調素子では、
入射光強度が小さい場合には低電圧変調，高速動作及び
狭スペクトル動作が可能なものの、実用レベルの数mWま
で入射光強度を増大させた場合には、これらの特性が著
しく劣化するという欠点があった。As described above, in the conventional electro-absorption optical modulator,
When the incident light intensity is low, low voltage modulation, high-speed operation and narrow spectrum operation are possible, but when the incident light intensity is increased to a practical level of several mW, there is a drawback that these characteristics deteriorate significantly. there were.
（発明の目的及び特徴） 本発明は、上述した従来技術の問題点を解決するために
なされたもので、入射光強度が増大しても低電圧で高速
の変調が可能な光変調素子を実現することを目的とす
る。(Objects and Features of the Invention) The present invention has been made in order to solve the above-mentioned problems of the conventional technology, and realizes an optical modulator capable of performing high-speed modulation with a low voltage even when the incident light intensity is increased. The purpose is to do.
本発明の第１の特徴は、光導波路の入射端面から出射端
面に向かって、吸収係数が大きくなるように光導波路組
成，膜厚，ストライプ幅等を変え、単位長当りの吸収キ
ャリア数を光進行方向についてほぼ一定となるよう構成
した点にある。The first feature of the present invention is to change the optical waveguide composition, film thickness, stripe width, etc. so that the absorption coefficient increases from the incident end face to the emitting end face of the optical waveguide to determine the number of absorption carriers per unit length. The point is that it is configured to be substantially constant in the traveling direction.
本発明の第２の特徴は、第１の特徴に加え光導波路層の
層厚方向の禁制帯幅を連続的もしくは断続的に変化させ
て構成した点にある。The second feature of the present invention is that, in addition to the first feature, the forbidden band width of the optical waveguide layer in the layer thickness direction is changed continuously or intermittently.
本発明の第３の特徴は、第１及び第２の特徴に加え、光
導波路層の禁制帯幅エネルギーが入射光エネルギーより
も平均的に50meV以上としたことにある。The third feature of the present invention is that, in addition to the first and second features, the bandgap energy of the optical waveguide layer is 50 meV or more on average as compared with the incident light energy.
（発明の原理） 入射光強度が増大した場合に現れる変調電圧の増大及び
帯域劣化の現象などの特性劣化を詳細に検討した結果、
光導波路層の禁制帯幅Egと入射光フォトンエネルギｈν
のエネルギー差（ΔEg＝Eg−ｈν）に強く依存し、エネ
ルギー差ΔEgを50meV以下では特性劣化が生じる。又、
素子長依存性については、0.3mmから2.5mmまで素子長を
変えても、ΔEgが30−40meVの場合には、殆ど変化が見
られず特性劣化していることが、同一発明者が同日出願
した特許出願「光変調素子」（１）により確認されてい
る。(Principle of the Invention) As a result of detailed examination of characteristic deterioration such as an increase in modulation voltage and a phenomenon of band deterioration that appear when the incident light intensity increases,
Forbidden band width Eg of optical waveguide layer and incident light photon energy hν
It strongly depends on the energy difference (ΔEg = Eg−hν), and characteristic deterioration occurs when the energy difference ΔEg is 50 meV or less. or,
Regarding the element length dependency, even if the element length was changed from 0.3 mm to 2.5 mm, when ΔEg was 30-40 meV, there was almost no change and the characteristics deteriorated. It is confirmed by the patent application "Light Modulating Element" (1).
以上の実験結果は、入射光強度が大きい場合に、入射端
近傍の非常に光強度が強いわずかな領域でのみ、過剰キ
ャリアによる空間電界効果が生じ、電界強度を弱め、又
変調速度を遅くしていることを示している。この過剰キ
ャリアによる空間電界効果を抑制するひとつの手段とし
て、光導波路層の層厚方向（電圧印加方向）における電
界強度分布を補正するために、光導波路層の層厚方向の
禁制帯幅を連続的もしくは断続的に変える構成について
〔「光変調素子」（２）〕として同一発明者が同日出願
している。ここでは空間電界効果を抑制し、低変調電圧
でかつ高速の変調が可能な他の手段について述べる。The above experimental results show that when the incident light intensity is high, the spatial electric field effect due to excess carriers occurs only in a small region near the incident end where the light intensity is very strong, weakening the electric field intensity and slowing the modulation speed. It indicates that As one means for suppressing the spatial electric field effect due to the excess carriers, in order to correct the electric field strength distribution in the layer thickness direction (voltage application direction) of the optical waveguide layer, the forbidden band width of the optical waveguide layer in the layer thickness direction is continuously set. The same inventor has filed an application for the structure for changing the image intermittently or intermittently [[Light modulation element] (2)]. Here, other means for suppressing the spatial electric field effect and capable of low-modulation voltage and high-speed modulation will be described.
本発明の原理について、以下に説明する。The principle of the present invention will be described below.
光変調器への入射光強度をI(o),吸収係数をα，光導波
路の光閉じ込め係数をΓとすると、入射端面から距離ｘ
の点での光強度I(x)は、 I(x)＝Ioe- αΓｘ （１） と表わすことができ、単位長当りの吸収量は、 となる。式（２）は、単位長当りに吸収されるキャリア
数に比例する。すなわち、従来の光変調素子では、α及
びΓは一定であるため、単位長当りの吸収キャリアは、
ほぼI(x)に比例し、入射端近傍では吸収キャリア数が、
出射端近傍の吸収キャリア数に比べて異常に大きくなっ
ている。入射光強度が小さい場合には、吸収キャリアの
場所的に不均一があっても、バンド構造に影響を与えな
いので問題とはならないが、入射光強度が大きくなる
と、入射端近傍で吸収された過剰な吸収キャリアが、印
加電界を打ち消し、変調電圧や変調速度に影響を与え
る。Assuming that the intensity of light incident on the optical modulator is I ( o ) , the absorption coefficient is α, and the optical confinement coefficient of the optical waveguide is Γ, the distance x from the incident end face is
The light intensity I ( x ) at the point of can be expressed as I ( x ) = Ioe - αΓ x (1), and the absorption amount per unit length is Becomes Expression (2) is proportional to the number of carriers absorbed per unit length. That is, in the conventional light modulator, since α and Γ are constant, the absorption carrier per unit length is
Almost proportional to I ( x ) , the number of absorbing carriers near the entrance end is
It is abnormally large compared to the number of absorbed carriers near the emission end. When the incident light intensity is small, there is no problem even if there is unevenness in the location of the absorbing carriers, since it does not affect the band structure, but when the incident light intensity increases, it is absorbed near the incident end. Excessive absorbed carriers cancel the applied electric field and affect the modulation voltage and the modulation speed.
そこで、本発明者らは、式（２）のαΓI(x)がほぼ一定
となるようにし、光導波路の入射端から出射端で吸収さ
れる吸収キャリア数をほぼ同じにすれば、場所的の過剰
キャリアを発生せずに効率的な光変調が可能となると考
えた。すなわち、光量が多い所では、吸収係数α又は光
閉じ込め係数Γを小さくし、光量が少ない所では、吸収
係数α又はΓを大きくすれば、高強度光入射時にも帯域
劣化や変調電圧の増加がない高性能光変調素子が実現さ
れる。Therefore, if the inventors set α Γ I ( x ) in equation (2) to be substantially constant and make the number of absorption carriers absorbed from the input end to the output end of the optical waveguide substantially the same, the spatial We thought that efficient optical modulation would be possible without generating excess carriers. That is, when the light amount is large, the absorption coefficient α or the light confinement coefficient Γ is reduced, and when the light amount is small, the absorption coefficient α or Γ is increased, so that the band deterioration and the increase of the modulation voltage are caused even when the high intensity light is incident. A high-performance light modulator that does not exist is realized.
（発明の構成及び作用） 以下に図面を用いて本発明を詳細に説明する。(Structure and Action of the Invention) The present invention will be described in detail below with reference to the drawings.
（実施例１） 第２図は、本発明による第１の実施例であり、光変調素
子の側面図である。従来例と異なる点は光導波路層が均
一領域でなく、入射端から出射端に向かって、禁制帯幅
が小さくなっている３つのn--InGaAsP光導波路層7,8及
び９に分割されている点にある。厚さは0.45μm,各導波
路層の長さは200μｍである。入射端側の光導波路層７
の禁制帯幅は、1.55μｍの入射光エネルギより60meV大
きくし、光導波路層８及び９の禁制帯幅は、それぞれ55
meV,50meV大きくしてある。ストライプ幅を３μｍとす
ると、Γ0.77,2V印加時で導波路層内平均電界強度は7
2KV/cm,光導波路層7,8,9の吸収係数は、α＝50cm-1,100
cm-1及び150cm-1である。入射端側の光導波路層７での
吸収係数は小さいため、入射端近傍で局所的に過剰な吸
収キャリアを発生し、空間電荷効果を誘発することはな
い。又、光が光導波路層８及び９へ入射する時点では光
強度はそれぞれ46％及び10％と小さくなっているため、
吸収係数が大きくなっても、吸収キャリア数は増大しな
い。(Embodiment 1) FIG. 2 is a side view of an optical modulator according to the first embodiment of the present invention. The difference from the conventional example is that the optical waveguide layer is not a uniform region, and is divided into three n − -InGaAsP optical waveguide layers 7, 8 and 9 in which the forbidden band width becomes smaller from the entrance end to the exit end. There is a point. The thickness is 0.45 μm, and the length of each waveguide layer is 200 μm. Optical waveguide layer 7 on the incident end side
Of the incident light energy of 1.55 μm is 60 meV, and the forbidden band widths of the optical waveguide layers 8 and 9 are 55 meV.
The meV and 50 meV are enlarged. If the stripe width is 3 μm, the average electric field strength in the waveguide layer is 7 when Γ0.77,2V is applied.
2KV / cm, absorption coefficient of optical waveguide layer 7,8,9 is α = 50cm -1,100
cm -1 and 150 cm -1 . Since the absorption coefficient in the optical waveguide layer 7 on the incident end side is small, excessive absorption carriers are locally generated near the incident end and the space charge effect is not induced. Further, at the time when the light enters the optical waveguide layers 8 and 9, the light intensity is as small as 46% and 10%, respectively.
Even if the absorption coefficient increases, the number of absorption carriers does not increase.
本発明による構成によれば、出射端での消光比は、変調
電圧が2Vで20dB以上とれ、帯域幅は約10GHzとなり、高
強度入射時にも特性劣化のない高性能光変調素子が実現
される。According to the configuration of the present invention, the extinction ratio at the exit end is 20 dB or more at a modulation voltage of 2 V, the bandwidth is about 10 GHz, and a high-performance optical modulator that does not deteriorate in characteristics even at high intensity incidence is realized. .
（実施例２） 第３図は本発明による第２の実施例であり、光変調素子
の側面図である。実施例１では、入射端から出射端に向
けて光導波路層の組成を変えて吸収係数を増加させてい
るのに対し、本実施例では導波路層厚を変えて導波路層
電界強度を変化させ、吸収係数が増大するように構成し
ている。n--InGaAsP変調導波路層10,11,12の禁制帯幅
は、1.55μｍの入射光フォトンエネルギよりも、55meV
大きくしてある。また、ストライプ幅は３μm,各導波路
層10,11及び12の長さは実施例１と同様200μｍである。
光導波路層の10,11,12の膜厚を0.7μm,0.45μｍ及び0.4
μｍとし、2V印加時の電界強度を45KV/cm,72KV/cm及び8
0KV/cmと変え、各導波路層10,11,12の吸収係数を、50cm
-1,100cm-1及び150cm-1としている。光閉じ込め係数が
光導波路層10,11,12で、Γ＝0.89,0.77及び0.73と変化
する事を考慮すると、光導波路層11及び12に入射する光
強度は44％,9％となり、出射端における消光比は2Vで約
20dBとなる。本構成においても、光量の多い入射端近傍
では吸収係数が小さく、又、吸収係数の大きい出射端近
傍では光量が少なくなっているため、局所的過剰キャリ
アを発生することがなく、実施例１と同様高強度入射時
の特性劣化は生じない。(Embodiment 2) FIG. 3 is a side view of an optical modulator according to a second embodiment of the present invention. In the first embodiment, the absorption coefficient is increased by changing the composition of the optical waveguide layer from the entrance end to the exit end, whereas in the present embodiment, the waveguide layer thickness is changed to change the waveguide layer electric field strength. The absorption coefficient is increased. The forbidden band width of the n − -InGaAsP modulation waveguide layers 10, 11 and 12 is 55 meV more than the incident light photon energy of 1.55 μm.
It's big. The stripe width is 3 μm, and the length of each waveguide layer 10, 11 and 12 is 200 μm as in the first embodiment.
The thickness of the optical waveguide layers 10, 11, 12 is 0.7μm, 0.45μm and 0.4μm.
μm, and the electric field strength when applying 2 V is 45 KV / cm, 72 KV / cm and 8
Change to 0KV / cm and change the absorption coefficient of each waveguide layer 10,11,12 to 50cm
-1,100 cm -1 and 150 cm -1 . Considering that the optical confinement coefficient changes in the optical waveguide layers 10, 11 and 12 to Γ = 0.89, 0.77 and 0.73, the light intensity incident on the optical waveguide layers 11 and 12 is 44% and 9%, respectively. Extinction ratio at 2V is about
It becomes 20 dB. Also in this configuration, since the absorption coefficient is small near the incident end where the light amount is large, and the light amount is small near the exit end where the light amount is large, local excessive carriers are not generated, and the first embodiment is different from the first embodiment. Similarly, characteristic deterioration does not occur at high intensity incidence.
（実施例３） 第４図は、本発明による第３の実施例であり、光変調素
子の側面図である。実施例２と同様に本実施例でも、吸
収係数の変化を電界強度の変化で実現している。実施例
２と異なる点は、n--InGaAsP光導波路層13の膜厚は0.4
μｍで一定であり、InGaAsP光導波路層13とInP基板１の
間に厚さが異なるn--InP層14,15を挿入し、導波路層内
電界強度を変化させている点である。n--InP層14及び15
の厚さをそれぞれ0.3μｍ及び0.05μｍとすれば、実施
例２と同様の効果が得られ、高強度の光入射時にも特性
劣化のない光変調素子が実現される。(Embodiment 3) FIG. 4 is a side view of an optical modulator according to a third embodiment of the present invention. Similar to the second embodiment, also in this embodiment, the change of the absorption coefficient is realized by the change of the electric field strength. The difference from Example 2 is that the thickness of the n − -InGaAsP optical waveguide layer 13 is 0.4.
This is that the electric field strength in the waveguide layer is changed by inserting n − -InP layers 14 and 15 having a constant thickness of μm and having different thicknesses between the InGaAsP optical waveguide layer 13 and the InP substrate 1. n -- InP layers 14 and 15
If the respective thicknesses are 0.3 μm and 0.05 μm, the same effect as that of the second embodiment can be obtained, and an optical modulator without characteristic deterioration even when light with high intensity is incident can be realized.
（実施例４） 第５図は本発明による第４の実施例であり、光変調素子
の模式図である。(Embodiment 4) FIG. 5 is a schematic view of an optical modulator according to a fourth embodiment of the present invention.
n--InGaAsP光導波路層13の禁制帯幅と間厚は実施例３と
同様である。入射端から出射端へ向かって吸収係数を変
えることを、本実施例では、ストライプ幅を変化させ、
光閉じ込め係数を変化させることによって実現してい
る。The forbidden band width and the gap thickness of the n − -InGaAsP optical waveguide layer 13 are the same as those in the third embodiment. In this embodiment, changing the absorption coefficient from the entrance end to the exit end changes the stripe width,
This is achieved by changing the light confinement coefficient.
ストライプ幅は、入射端から、出射端へ向かう３つの領
域で、それぞれ１μm,2μｍ及び４μｍとして、光閉じ
込め係数をΓ＝0.48,0.73,0.84と変化させている。2V印
加時の実効的吸収係数は、ストライプ幅1,2及び４μm,
領域で48cm-1,73cm-1及び86cm-1である。各領域長を150
μm,200μm,250μｍとすれば、ストライプ幅２μｍ及び
４μｍに入射する光強度はそれぞれ入射端の強度の48
％,11％となり、実施例３と同様、高光強度入射時にも
特性劣化のない高性能光変調素子が実現される。The stripe width is set to 1 μm, 2 μm, and 4 μm in three regions from the incident end to the emitting end, and the optical confinement coefficient is changed to Γ = 0.48, 0.73, 0.84. Effective absorption coefficient when applying 2V is stripe width 1, 2 and 4μm,
The areas are 48 cm -1 , 73 cm -1 and 86 cm -1 . Each area length is 150
Assuming μm, 200 μm, and 250 μm, the light intensity incident on the stripe widths of 2 μm and 4 μm is 48 times that of the incident end.
%, 11%, so that a high-performance optical modulator without deterioration of characteristics even when a high light intensity is incident can be realized as in the third embodiment.
上述の説明では、光導波路の吸収係数を入射端から出射
端に向かって３段階でかつ段階的に大きくする場合を例
にとり説明したが、２段階以上又は連続的に変化させる
場合にも、本発明が適用できる。また、前述した実施例
１〜４のうち複数を組合わせても良い。In the above description, the case where the absorption coefficient of the optical waveguide is increased in three steps from the entrance end to the exit end and in steps is described as an example. However, even if the absorption coefficient is changed in two or more steps or continuously. The invention can be applied. Further, a plurality of the first to fourth embodiments described above may be combined.
次に本発明の他の実施例として、同一出願人より同日出
願されている光変調素子と組み合わせた場合の例につい
て説明する。Next, as another embodiment of the present invention, an example in the case of combining with an optical modulation element filed on the same day by the same applicant will be described.
まず、組み合わせの具体例を述べる前に同日出願されて
いる２件の光変調素子の概要について説明する。First, before describing specific examples of combinations, the outlines of two light modulation elements applied on the same day will be described.
第１の光変調素子の概要は光導波路層の禁制帯幅Egと入
射光のフォトンエネルギーｈνとのエネルギー差ΔEg
（＝Eg−ｈν）を50meV以上とし、かつ光変調素子の素
子長を予め定めた長さに構成することにある。ここで、
本発明と組み合わせる場合には、層厚方向もしくは入射
端面から出射端面方向の禁制帯幅を変化させているた
め、入射端面側と出射端面側でエネルギー差ΔEgが異な
るが、その平均値であるエネルギー差ΔEgが50meV以上
となる条件があれば良い。The outline of the first optical modulator is the energy difference ΔEg between the forbidden band width Eg of the optical waveguide layer and the photon energy hν of the incident light.
(= Eg−hν) is set to 50 meV or more, and the element length of the light modulation element is set to a predetermined length. here,
When combined with the present invention, since the forbidden band width in the layer thickness direction or from the incident end face to the outgoing end face direction is changed, the energy difference ΔEg differs between the incident end face side and the outgoing end face side, but the average energy It is sufficient if there is a condition that the difference ΔEg is 50 meV or more.
第２の光変調素子の概要は、光導波路層中の電界強度分
布を補正して層厚方向の吸収係数が一定となるように層
厚方向における導波路層の禁制帯幅を連続的もしくは断
続的に変えることにより、光分布と吸収係数の重なりを
大きくして変調電圧の低下と素子長短縮による広帯域化
を図った点にある。又、同時に、吸収係数を均一化する
ことにより、高強度入射時に問題となる局所的過剰キャ
リアによる空間電荷効果を抑制しているものである。The outline of the second optical modulator is that the forbidden band width of the waveguide layer in the layer thickness direction is continuous or interrupted so that the electric field strength distribution in the optical waveguide layer is corrected so that the absorption coefficient in the layer thickness direction becomes constant. This is because the overlap between the light distribution and the absorption coefficient is increased by changing the wavelength, and the modulation voltage is lowered and the element length is shortened to widen the band. At the same time, by making the absorption coefficient uniform, the space charge effect due to local excess carriers, which is a problem at high intensity incidence, is suppressed.
従って、本発明による光変調素子を第３の光変調素子と
した場合、第１と第２の組み合わせによる光変調素子、
第１と第３の組み合わせによる光変調素子、第２と第３
の組み合わせによる光変調素子、第1,第２及び第３の組
み合わせによる光変調素子の４種類の組み合わせが可能
となる。Therefore, when the light modulation element according to the present invention is the third light modulation element, the light modulation element according to the first and second combinations,
First and third combination optical modulators, second and third
It is possible to combine four kinds of combinations, that is, the light modulation element by the combination of the above and the light modulation element by the first, second, and third combinations.
以下に、第1,第２及び第３の組み合わせによる光変調素
子を例にとり説明する。Below, an explanation will be given taking as an example a light modulation element by the first, second and third combinations.
（実施例５） 第６図に本発明による第５の実施例の側面図を示す。(Embodiment 5) FIG. 6 shows a side view of a fifth embodiment according to the present invention.
p-InP基板16上に、入射光のエネルギーより60meV大きい
禁制帯幅を持つn--InGaAsP光導波路層（0.2μｍ積層）1
7を200μｍの領域にわたり形成し、続いて、ΔEg＝55me
Vの禁制帯を持つn--InGaAsP光導波路層（0.2μｍ積層）
18を400μｍの領域にわたり形成している。更に、ΔEg
＝50meVの禁制帯を持つn--InGaAsP光導波路層19を600μ
ｍにわたり形成し、最後にn-InPクラッド層20を積層し
ている。すなわち、本実施例では、同日出願した他の２
件の光変調素子とを全て組み合わせたもので、層厚方向
（電圧印加方向）での電界強度の違いによって生ずる吸
収係数の違いを補正し層厚方向の吸収係数を一定とする
と共に、入射端から出射端に向けての吸収係数を大きく
なるように膜厚（従って電界強度）及び組成を変え長手
方向の吸収の均一化も図り、かつ各光導波路層17,18,19
の禁制帯幅が入射エネルギー（ｈν）より50meV以上と
なるように形成されている。従って、光変調素子の吸収
領域の殆どすべての場所で、吸収の均一化が図られてお
り、高入射光強度下でも高速，低電圧変調が可能な光変
調素子が実現される。n − -InGaAsP optical waveguide layer (0.2 μm laminated) having a band gap of 60 meV larger than the energy of incident light on the p-InP substrate 16 1
7 was formed over the area of 200 μm, and then ΔEg = 55me
N -- InGaAsP optical waveguide layer (0.2μm laminated) with V forbidden band
18 is formed over a region of 400 μm. Furthermore, ΔEg
= 600 mea of n -- InGaAsP optical waveguide layer 19 with a forbidden band of 50 meV
Then, the n-InP clad layer 20 is finally laminated. That is, in this embodiment, the other two
This is a combination of all of the above optical modulators, and the difference in absorption coefficient caused by the difference in electric field strength in the layer thickness direction (voltage application direction) is corrected to make the absorption coefficient constant in the layer thickness direction and at the incident end. The film thickness (and therefore the electric field strength) and composition are changed so that the absorption coefficient from the output end to the output end is increased, and the absorption in the longitudinal direction is made uniform, and each optical waveguide layer 17, 18, 19
Is formed so that the band gap of is 50 meV or more than the incident energy (hν). Therefore, the absorption is made uniform in almost all places in the absorption region of the light modulation element, and a light modulation element capable of high-speed and low-voltage modulation even under high incident light intensity is realized.
なお、実施例５では、第1,第２及び第３の光変調素子の
組み合わせを例にとり説明したが、他の３種類の組み合
わせでも良い。In the fifth embodiment, the combination of the first, second and third light modulation elements has been described as an example, but other three combinations may be used.
光導波路層の伝導型はp-型でも良い。又、材料系として
は、InGaAsP/InP系を例にとり説明したが、AlGaAs/GaAs
系や、AlGaAs/InP系などの他の材料にも同様に適用でき
る。更に、それらの他の材料で構成される多重量子井戸
層を用いることもでき、この場合説明で用いた禁制帯幅
は、量子準位で定まる実効的な禁制帯幅となる。又、横
モード安定化のためのストライプ構造についてはストリ
ップ装荷型を例にとり説明したが、埋め込みストライプ
構造や、リッジ導波路ストライプ構造等の従来の技術が
すべて適用可能である。The conduction type of the optical waveguide layer may be p - type. As the material system, the InGaAsP / InP system has been described as an example.
The same can be applied to other materials such as AlGaAs / InP-based materials. Further, it is possible to use a multiple quantum well layer composed of these other materials, and in this case, the forbidden band width used in the description is an effective forbidden band width determined by the quantum level. Further, although the strip structure for stabilizing the transverse mode has been described by taking the strip loading type as an example, all the conventional techniques such as the embedded stripe structure and the ridge waveguide stripe structure can be applied.
（発明の効果） 以上述べたように、本発明では光強度の大きい入射端側
では吸収係数が小さく、出射端側では吸収係数を大きく
なるよう構成し、単位長当りの吸収キャリア数が均一化
されるように光変調素子を構成しているため、光強度を
増大しても局所的な過剰キャリアを発生し、空間電荷効
果により変調電圧の増加や帯域幅の減少をもたらすこと
がなく、低電圧で高速の光変調が可能な高性能光変調素
子を実現することができる。また、入射端面から出射端
面に向かって吸収係数を大きくするのに加え、光導波路
の層厚方向の禁制帯幅を層厚方向の吸収係数が一定とな
るように連続的もしくは断続的に変化させて構成するこ
とにより、低変調電圧で高速の変調が可能となる。さら
に、入射端面から出射端面に向かって吸収係数を大きく
し、層厚方向の光導波路層の禁制帯幅を変化させるのに
加え、光導波路層の禁制帯幅が入射光のホトンエネルギ
ーよりも平均的に50meV以上となるように構成すること
により、より低変調電圧で高速の変調が可能となる。(Advantages of the Invention) As described above, in the present invention, the absorption coefficient is small on the incident end side where the light intensity is high, and is large on the emission end side, so that the number of absorbing carriers per unit length is uniform. Since the optical modulator is configured as described above, local excess carriers are generated even if the light intensity is increased, and the space charge effect does not increase the modulation voltage or decrease the bandwidth. It is possible to realize a high-performance light modulator capable of high-speed light modulation with voltage. In addition to increasing the absorption coefficient from the entrance end face to the exit end face, the forbidden band width of the optical waveguide in the layer thickness direction is changed continuously or intermittently so that the absorption coefficient in the layer thickness direction becomes constant. With this configuration, high-speed modulation can be performed with a low modulation voltage. Furthermore, in addition to increasing the absorption coefficient from the entrance end face to the exit end face to change the forbidden band width of the optical waveguide layer in the layer thickness direction, the forbidden band width of the optical waveguide layer is more average than the photon energy of the incident light. By configuring so as to be 50 meV or more, it becomes possible to perform high speed modulation with a lower modulation voltage.
また、入射端面から出射端面に向かって吸収係数を大き
くする方法として、禁制帯幅を小さくして行く方法は精
密でかつ正確にできる効果を、層厚を薄くする方法及び
ストライプ幅を大きくする方法は製造方法が簡単である
という効果を有する。この光変調素子はギガビット帯の
超高速，長距離光ファイバ通信等に応用することがで
き、その効果は極めて大である。Further, as a method of increasing the absorption coefficient from the incident end surface to the exit end surface, a method of decreasing the forbidden band width is a precise and accurate effect, a method of reducing the layer thickness and a method of increasing the stripe width. Has the effect that the manufacturing method is simple. This optical modulator can be applied to gigabit band ultra-high speed, long distance optical fiber communication and the like, and its effect is extremely large.
第１図は従来の電気吸収型光変調素子の模式図、第２
図、第３図及び第４図は本発明による第1,第2,第３の実
施例としての光変調素子の構造を示す側面図、第５図は
本発明による第４の実施例である光変調素子の模式図、
第６図は本発明による第５の実施例である光変調素子の
側面図である。 １……n-InP基板、２……n--InGaAsP光導波路層、３…
…p-InPクラッド層、４……p-InGaAsPキャップ層、５…
…ｐ側電極、６……ｎ側電極、7,8,9,10,11,12,13……n
--InGaAsP光導波路層、14,15……n--InP層、16……p-In
P基板、17,18,19……n--InGaAsP光導波路層、20……n-I
nP層。FIG. 1 is a schematic diagram of a conventional electro-absorption optical modulator, FIG.
FIGS. 3, 3 and 4 are side views showing the structures of the light modulation elements as the first, second and third embodiments of the present invention, and FIG. 5 is the fourth embodiment of the present invention. Schematic diagram of light modulator,
FIG. 6 is a side view of a light modulation element which is a fifth embodiment according to the present invention. 1 ... n-InP substrate, 2 ... n--InGaAsP optical waveguide layer, 3 ...
… P-InP clad layer, 4 …… p-InGaAsP cap layer, 5…
… P-side electrode, 6 …… n-side electrode, 7,8,9,10,11,12,13 …… n
--InGaAsP optical waveguide layer, 14,15 …… n--InP layer, 16 …… p-In
P substrate, 17,18,19 …… n--InGaAsP optical waveguide layer, 20 …… nI
nP layer.
Claims (7)
する光導波路層と、該光導波路層よりも屈折率の小なる
第１及び第２の伝導型を有するクラッド層と電極とを有
し、該電極から前記光導波路層へ印加する電界によって
前記光導波路の入射端面に入射する一定強度の入射光に
対する吸収係数を変化させて光強度変調を行って前記光
導波路の出射端面から変調光を取り出す光変調素子にお
いて、 前記光導波路の前記入射端面から前記出射端面でほぼ均
一な吸収キャリア数となるように前記入射端面から前記
出射端面に向かって連続的もしくは段続的に前記入射光
に対して吸収係数が大きくなるように前記光導波路を構
成したことを特徴とする光変調素子。1. An optical waveguide layer having a low impurity concentration and a first conductivity type on a substrate, and cladding layers and electrodes having a first and second conductivity types having a refractive index smaller than that of the optical waveguide layer. From the exit end surface of the optical waveguide by changing the absorption coefficient for incident light of a constant intensity entering the entrance end surface of the optical waveguide by an electric field applied from the electrode to the optical waveguide layer In the light modulation element for extracting the modulated light, the incident light is continuously or stepwise from the incident end face toward the emission end face so that the number of absorption carriers is substantially uniform from the incident end face to the emission end face of the optical waveguide. An optical modulation element, characterized in that the optical waveguide is configured so that an absorption coefficient for the emitted light is large.
する光導波路層と、該光導波路層よりも屈折率の小なる
第１及び第２の伝導型を有するクラッド層と電極とを有
し、該電極から前記光導波路層へ印加する電界によって
前記光導波路の入射端面に入射する一定強度の入射光に
対する吸収係数を変化させて光強度変調を行って前記光
導波路の出射端面から変調光を取り出す光変調素子にお
いて、 前記光導波路の前記入射端面から前記出射端面でほぼ均
一な吸収キャリア数となるように前記入射端面から前記
出射端面に向かって連続的もしくは段続的に前記入射光
に対して吸収係数が大きくなるようにし、かつ前記光導
波路の層厚方向の禁制帯幅を該層厚方向の吸収係数がほ
ぼ一定となるように連続的もしくは断続的に変化させて
構成したことを特徴とする光変調素子。2. An optical waveguide layer having a low impurity concentration and a first conductivity type on a substrate, and cladding layers and electrodes having a first and a second conductivity types having a smaller refractive index than the optical waveguide layer. From the exit end surface of the optical waveguide by changing the absorption coefficient for incident light of a constant intensity entering the entrance end surface of the optical waveguide by an electric field applied from the electrode to the optical waveguide layer In the light modulation element for extracting the modulated light, the incident light is continuously or stepwise from the incident end face toward the emission end face so that the number of absorption carriers is substantially uniform from the incident end face to the emission end face of the optical waveguide. The absorption coefficient for the emitted light is increased, and the band gap in the layer thickness direction of the optical waveguide is continuously or intermittently changed so that the absorption coefficient in the layer thickness direction is substantially constant. This And a light modulator.
する光導波路層と、該光導波路層よりも屈折率の小なる
第１及び第２の伝導型を有するクラッド層と電極とを有
し、該電極から前記光導波路層へ印加する電界によって
前記光導波路の入射端面に入射する一定強度の入射光に
対する吸収係数を変化させて光強度変調を行って前記光
導波路の出射端面から変調光を取り出す光変調素子にお
いて、 前記光導波路の前記入射端面から前記出射端面でほぼ均
一な吸収キャリア数となるように前記入射端面から前記
出射端面に向かって連続的もしくは段続的に前記入射光
に対して吸収係数が大きくなるようにし、かつ前記光導
波路の層厚方向の禁制帯幅を該層厚方向の吸収係数がほ
ぼ一定となるように連続的もしくは断続的に変化させる
と共に、 前記光導波路層の禁制帯幅が前記入射光のエネルギーよ
りも平均的に50meV以上となるように構成したことを特
徴とする光変調素子。3. An optical waveguide layer having a first conductivity type having a low impurity concentration on a substrate, and clad layers and electrodes having first and second conductivity types having a refractive index smaller than that of the optical waveguide layer. From the exit end surface of the optical waveguide by changing the absorption coefficient for incident light of a constant intensity entering the entrance end surface of the optical waveguide by an electric field applied from the electrode to the optical waveguide layer In the light modulation element for extracting the modulated light, the incident light is continuously or stepwise from the incident end face toward the emission end face so that the number of absorption carriers is substantially uniform from the incident end face to the emission end face of the optical waveguide. The absorption coefficient for the emitted light is increased, and the band gap in the layer thickness direction of the optical waveguide is continuously or intermittently changed so that the absorption coefficient in the layer thickness direction is substantially constant, Light modulation element, characterized in that the forbidden band width of Kikoshirube waveguide layer is configured to be average, 50meV more than the energy of the incident light.
ら前記出射端面に向かって連続的もしくは断続的に小さ
くすることにより、 前記光導波路の前記入射端面から前記出射端面でほぼ均
一な吸収キャリア数となるように構成したことを特徴と
する特許請求の範囲第１項，第２項記載又は第３項記載
の光変調素子。4. A band gap of the optical waveguide is reduced continuously or intermittently from the incident end face toward the emission end face, whereby almost uniform absorption is achieved from the incident end face to the emission end face of the optical waveguide. The optical modulator according to claim 1, 2, or 3, wherein the optical modulator is configured to have the number of carriers.
記出射端面に向かって連続的もしくは断続的に薄くする
ことにより、 前記光導波路の前記入射端面から前記出射端面でほぼ均
一な吸収キャリア数となるように構成したことを特徴と
する特許請求の範囲第１項，第２項記載又は第３項記載
の光変調素子。5. An absorption carrier that is substantially uniform from the incident end face of the optical waveguide to the emission end face by reducing the layer thickness of the optical waveguide continuously or intermittently from the incident end face toward the emission end face. The light modulation element according to claim 1, 2, or 3, wherein the light modulation element is configured to have a number.
面から前記出射端面に向かって連続的もしくは断続的に
大きくすることにより、 前記光導波路の前記入射端面から前記出射端面でほぼ均
一な吸収キャリア数となるように構成したことを特徴と
する特許請求の範囲第１項，第２項記載又は第３項記載
の光変調素子。6. A stripe width of the optical waveguide is continuously or intermittently increased from the incident end face toward the emitting end face, so that the absorption carrier is substantially uniform from the incident end face to the emitting end face of the optical waveguide. The light modulation element according to claim 1, 2, or 3, wherein the light modulation element is configured to have a number.
成し、かつ該低不純物濃度で構成されたクラッド層の層
厚を前記入射端面から前記出射端面に向かって連続的も
しくは断続的に薄くすることにより、 前記光導波路の前記入射端面から前記出射端面でほぼ均
一な吸収キャリア数となるように構成したことを特徴と
する特許請求の範囲第１項，第２項記載又は第３項記載
の光変調素子。7. A part of the clad layer is made to have a low impurity concentration, and the layer thickness of the clad layer made to have a low impurity concentration is continuously or intermittently provided from the incident end face toward the emission end face. The thinned film is configured to have a substantially uniform number of absorption carriers from the incident end surface to the emitting end surface of the optical waveguide. The light modulation element described.
Priority Applications (6)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP63042200A JPH06100737B2 (en) | 1988-02-26 | 1988-02-26 | Light modulator |
| US07/311,218 US4913506A (en) | 1988-02-26 | 1989-02-16 | Optical modulation device |
| KR1019890002229A KR0145187B1 (en) | 1988-02-26 | 1989-02-25 | Optical modulation element |
| GB8905098A GB2229287B (en) | 1988-02-26 | 1989-03-06 | Optical modulation device |
| GB9314799A GB2266969A (en) | 1988-02-26 | 1993-07-19 | Optical modulation device |
| GB9314798A GB2266968B (en) | 1988-02-26 | 1993-07-19 | Optical modulation device |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP63042200A JPH06100737B2 (en) | 1988-02-26 | 1988-02-26 | Light modulator |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH01217418A JPH01217418A (en) | 1989-08-31 |
| JPH06100737B2 true JPH06100737B2 (en) | 1994-12-12 |
Family
ID=12629368
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP63042200A Expired - Lifetime JPH06100737B2 (en) | 1988-02-26 | 1988-02-26 | Light modulator |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPH06100737B2 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1999041634A1 (en) * | 1998-02-16 | 1999-08-19 | The Furukawa Electric Co., Ltd. | Optical semiconductor device |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2715864B2 (en) * | 1993-11-15 | 1998-02-18 | 日本電気株式会社 | Nonlinear optical element |
| JP2921397B2 (en) * | 1994-06-14 | 1999-07-19 | 日本電気株式会社 | Nonlinear optical element |
| SE522417C2 (en) * | 1998-10-15 | 2004-02-10 | Ericsson Telefon Ab L M | Electro-absorption modulator (EAM) and method for manufacturing such modulator |
| JP7501819B1 (en) * | 2023-04-26 | 2024-06-18 | 三菱電機株式会社 | Semiconductor optical integrated device |
-
1988
- 1988-02-26 JP JP63042200A patent/JPH06100737B2/en not_active Expired - Lifetime
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1999041634A1 (en) * | 1998-02-16 | 1999-08-19 | The Furukawa Electric Co., Ltd. | Optical semiconductor device |
Also Published As
| Publication number | Publication date |
|---|---|
| JPH01217418A (en) | 1989-08-31 |
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