JP2891756B2 - Tunable semiconductor laser - Google Patents
Tunable semiconductor laserInfo
- Publication number
- JP2891756B2 JP2891756B2 JP2204157A JP20415790A JP2891756B2 JP 2891756 B2 JP2891756 B2 JP 2891756B2 JP 2204157 A JP2204157 A JP 2204157A JP 20415790 A JP20415790 A JP 20415790A JP 2891756 B2 JP2891756 B2 JP 2891756B2
- Authority
- JP
- Japan
- Prior art keywords
- semiconductor laser
- barrier layer
- layer
- wavelength
- waveguide
- 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 - Fee Related
Links
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/06—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium
- H01S5/062—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium by varying the potential of the electrodes
- H01S5/0625—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium by varying the potential of the electrodes in multi-section lasers
- H01S5/06255—Controlling the frequency of the radiation
- H01S5/06256—Controlling the frequency of the radiation with DBR-structure
Landscapes
- Semiconductor Lasers (AREA)
Description
【発明の詳細な説明】 ［産業上の利用分野］ 本発明は、半導体超格子構造が印加電圧を制御するこ
とでその屈折率を変えることを利用した半導体装置、特
に波長可変半導体レーザに関するものである。Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device using a semiconductor superlattice structure to change its refractive index by controlling an applied voltage, and more particularly to a wavelength tunable semiconductor laser. is there.
［従来の技術］ 従来、波長可変半導体レーザとしては、活性導波路及
び回折格子が形成された外部導波路を有する分布反射型
半導体レーザにおいて、その外部導波路に電流注入して
キャリア密度を変化させ、これにより外部導波路の屈折
率を変化させる（プラズマ効果）ことで回折格子のブラ
ッグ反射波長を変化させ、発振波長を可変としたものが
知られている（Electronics Letters,23,403（1987）
参照）。[Prior Art] Conventionally, as a wavelength tunable semiconductor laser, in a distributed reflection type semiconductor laser having an active waveguide and an external waveguide on which a diffraction grating is formed, current is injected into the external waveguide to change the carrier density. It is known that the Bragg reflection wavelength of the diffraction grating is changed by changing the refractive index of the external waveguide (plasma effect), thereby making the oscillation wavelength variable (Electronics Letters, 23, 403 (1987)).
reference).
また、回折格子と量子井戸構造を有する外部導波路に
電界を印加すると量子準位エネルギー近傍の光の吸収が
大きくなる（量子閉じ込めシュタルク効果、QCSE）こと
により屈折率が変化し、回折格子のブラッグ反射波長が
変化して発振波長を変化させるものも知られている（特
開昭64−35978参照）。In addition, when an electric field is applied to an external waveguide having a diffraction grating and a quantum well structure, the absorption of light near the quantum level energy increases (quantum confined Stark effect, QCSE), which changes the refractive index and the Bragg of the diffraction grating. It is also known that the reflection wavelength changes to change the oscillation wavelength (see JP-A-64-35978).
［発明が解決しようとする課題］ しかしながら、上記従来例では、電流注入または電界
印加によってレーザの発振波長を変化させると、それに
伴って回折格子を有する外部導波路の吸収損失が大きく
なる為、ブラッグ反射特性が変化してしまい、その結
果、レーザ特性の変化、特に発振スペクトル線幅の増大
が生じてしまうという欠点があった。[Problems to be Solved by the Invention] However, in the above-mentioned conventional example, when the oscillation wavelength of the laser is changed by current injection or electric field application, the absorption loss of the external waveguide having the diffraction grating increases with the change. There is a drawback that the reflection characteristics change, and as a result, the laser characteristics change, particularly the oscillation spectrum line width increases.
従って、本発明の目的は、上記の課題に鑑み、超格子
構造を用いつつもQCSEなどを利用しないで屈折率を吸収
損失の増大を伴わないで大きく変化させることが可能な
構成を有する波長可変半導体レーザを提供することにあ
る。Therefore, in view of the above problems, an object of the present invention is to provide a wavelength tunable device having a structure capable of greatly changing the refractive index without using QCSE or the like without using an QCSE while using a superlattice structure without increasing absorption loss. It is to provide a semiconductor laser.
［課題を解決する為の手段］ 上記目的を達成する本発明の分布反射型波長可変半導
体レーザにおいては、外部導波路層の回折格子を形成し
ている領域から光波長以内の距離に２層以上の量子井戸
とその間の障壁層を含む半導体光導波路が設けられ、量
子井戸がｐ型およびｎ型の一方の導電型に形成され、障
壁層が高抵抗層で形成され、また、該障壁層は光導波路
に印加する電圧の制御によって該量子井戸間の結合状態
を変化可能な様な厚さ、形状に形成されており、光導波
路に電圧を印加するための手段が設けられている。[Means for Solving the Problems] In the distributed reflection type wavelength tunable semiconductor laser according to the present invention that achieves the above object, two or more layers are arranged at a distance within a light wavelength from a region of the external waveguide layer where the diffraction grating is formed. A semiconductor optical waveguide including a quantum well and a barrier layer therebetween is provided, the quantum well is formed of one of p-type and n-type conductivity types, the barrier layer is formed of a high-resistance layer, and the barrier layer is formed of a high-resistance layer. It is formed in a thickness and shape such that the coupling state between the quantum wells can be changed by controlling the voltage applied to the optical waveguide, and means for applying a voltage to the optical waveguide is provided.
より具体的には、量子井戸がAlxGa1-xAs、障壁層がAl
yGa1-yAs（０≦ｘ＜ｙ≦１）で形成され、障壁層の厚さ
が3nm以上、15nm以下である様に形成されたりする。More specifically, the quantum well is Al x Ga 1-x As and the barrier layer is Al
It is formed of yGa 1-y As (0 ≦ x <y ≦ 1), and the barrier layer is formed to have a thickness of 3 nm or more and 15 nm or less.
本発明の動作原理は次の如きものである。超格子構造
において、障壁層が薄く量子井戸が結合状態にある場
合、この超格子構造の屈折率（n1とする）は、障壁層と
量子井戸層を混ぜ合せた混晶（超格子構造に含まれる各
成分をこれと同量の割合で含む様な混晶）の屈折率（nA
とする）にほぼ等しいが（n1≒nA）、障壁層が比較的厚
く、量子井戸層が結合状態にない場合の超格子構造の屈
折率（n2とする）は広い波長範囲においてnAより0.1程
度大きくなること（nA＋0.1≦n2）が知られている（Jou
rnal of Electronic Materials,vol.12,p397（198
3）参照）。The principle of operation of the present invention is as follows. In the superlattice structure, when the barrier layer is thin and the quantum well is in a coupled state, the refractive index of the superlattice structure (referred to as n 1 ) is a mixed crystal in which the barrier layer and the quantum well layer are mixed (in the superlattice structure). The refractive index (n A ) of the mixed crystal that contains each component contained in the same amount.
(N 1 ≒ n A ), but when the barrier layer is relatively thick and the quantum well layer is not in a coupled state, the refractive index of the superlattice structure (n 2 ) is n over a wide wavelength range. It is known that it is about 0.1 larger than A (n A + 0.1 ≦ n 2 ) (Jou
rnal of Electronic Materials, vol. 12, p397 (198
3)).
従って、超格子構造の比較的厚い障壁層に電界を印加
してここのポテンシャル分布を変化させ、実効的に障壁
層の高さ、形成を変化させることにより、量子井戸間の
結合状態が変化することになり、その結果、超格子構造
の屈折率が大きく変化する（量子井戸間が結合状態にあ
るときは比較的屈折率が小さく、結合状態にないときは
比較的屈折率が大きくなる）。この際、QCSEの様に吸収
端の変動を利用しないので吸収損失の増大は生じない。Therefore, by applying an electric field to a relatively thick barrier layer having a superlattice structure to change the potential distribution therein, and effectively changing the height and formation of the barrier layer, the coupling state between quantum wells changes. As a result, the refractive index of the superlattice structure changes greatly (the refractive index is relatively small when quantum wells are in a coupled state, and relatively large when not coupled). At this time, since the fluctuation of the absorption edge is not used unlike QCSE, the absorption loss does not increase.
本発明は、この超格子構造への電圧印加による吸収損
失の増大を伴わない大きな屈折率変化を利用して、波長
可変半導体レーザを実現したものである。The present invention realizes a wavelength tunable semiconductor laser by utilizing a large change in refractive index without increasing absorption loss due to application of a voltage to the superlattice structure.
超格子構造の井戸、障壁層をどの様な材料、厚さ、形
状で構成するか、回折格子と超格子構造の光導波路層の
位置関係をどの様に設定するか等は、活性領域の構造、
発振される光の波長、デバイスの全体構造等を考慮して
適当に決定すればよい。The material, thickness and shape of the well and barrier layer of the superlattice structure, and the positional relationship between the diffraction grating and the optical waveguide layer of the superlattice structure are determined by the structure of the active region. ,
It may be appropriately determined in consideration of the wavelength of the emitted light, the overall structure of the device, and the like.
［実施例］ 第１図は本発明による波長可変半導体レーザの実施例
の側断面図である。Embodiment FIG. 1 is a side sectional view of an embodiment of a wavelength tunable semiconductor laser according to the present invention.
同図において、ｎ−GaAs基板１上に、ｎ−AlGaAsクラ
ッド層２、厚さ5nmのｎ−GaAs井戸層31を10層、厚さ6nm
の高抵抗AlGaAs層32を11層交互に積層した超格子導波路
層３、GaAs活性層４、及び活性層４の保護層（不図示）
を、順次、MBE法などの適当な方法で成長した。この
後、位相制御領域21の活性層を除去し、また外部導波路
部の表面に周期約260nmの２次の回折格子５を形成し
た。In FIG. 1, an n-AlGaAs cladding layer 2, ten n-GaAs well layers 31 each having a thickness of 5 nm, and a thickness of 6 nm are formed on an n-GaAs substrate 1.
Superlattice waveguide layer 3 in which 11 high-resistance AlGaAs layers 32 are alternately stacked, GaAs active layer 4, and protective layer of active layer 4 (not shown)
Were sequentially grown by a suitable method such as the MBE method. Thereafter, the active layer in the phase control region 21 was removed, and a secondary diffraction grating 5 having a period of about 260 nm was formed on the surface of the external waveguide.
次に、ｐ−AlGaAsクラッド層６、ｐ−GaAsキャップ層
７を成長した後、電極８、10、11、12及び電極分離溝９
を形成した。Next, after growing the p-AlGaAs cladding layer 6 and the p-GaAs cap layer 7, the electrodes 8, 10, 11, 12 and the electrode separation groove 9 are formed.
Was formed.
こうして、第１図に示す様な活性領域20、位相制御領
域21、DBR（分布反射型）領域22から成る分布反射型波
長可変半導体レーザが作製される。Thus, a distributed reflection type wavelength tunable semiconductor laser including the active region 20, the phase control region 21, and the DBR (distributed reflection type) region 22 as shown in FIG. 1 is manufactured.
このレーザは、電極８を介して閾値以上の電流を注入
し電極10、11に電圧をかけない無バイアス時には、回折
格子５のブラッグ波長で決まる875nmの発振波長を示し
た。ここにおいて、超格子導波路層３の吸収端は約820n
mであり、この発振波長に対して十分低損失となってい
る。This laser showed an oscillation wavelength of 875 nm determined by the Bragg wavelength of the diffraction grating 5 when no current was applied through the electrode 8 and a current higher than the threshold was applied and no voltage was applied to the electrodes 10 and 11. Here, the absorption edge of the superlattice waveguide layer 3 is about 820n.
m, and the loss is sufficiently low for this oscillation wavelength.
次に、DBR領域22の電極11に−5Vの負バイアスを加え
ると、発振波長は約10nm短くなった。Next, when a negative bias of -5 V was applied to the electrode 11 in the DBR region 22, the oscillation wavelength was shortened by about 10 nm.
以上のことは次の様に説明される。無バイアス時は、
超格子導波路層３の障壁層（高抵抗AlGaAs層）32に印加
される電界が自己バイアス（ｎ−クラッド層２とｐ−ク
ラッド層６によるもの）のみなので、障壁層32のポテン
シャル分布の傾斜は小さく量子井戸31間の結合程度は小
さい。よって、超格子導波路層３の屈折率は、これと同
一Al組成割合の混晶AlGaAsの屈折率の値に比べて、およ
そ0.1程度大きな値を持つ。一方、負バイアスを電極11
に印加すると、井戸層31はｎ型にドープされているた
め、電界は全て障壁層32に印加されてこの層32のポテン
シャルの傾斜が大きくなる。よって、実効的に障壁層32
のポテンシャルの高さが低くなり量子井戸31間の結合程
度が大きくなり、その結果、導波路層３の屈折率は、同
一Al組成割合の混晶AlGaAsの値に近付くため、小さくな
る。The above is explained as follows. When there is no bias,
Since the electric field applied to the barrier layer (high-resistance AlGaAs layer) 32 of the superlattice waveguide layer 3 is only the self-bias (the one due to the n-cladding layer 2 and the p-cladding layer 6), the potential distribution of the barrier layer 32 is inclined. And the degree of coupling between the quantum wells 31 is small. Therefore, the refractive index of the superlattice waveguide layer 3 has a value that is approximately 0.1 larger than the refractive index of mixed crystal AlGaAs having the same Al composition ratio as this. On the other hand, a negative bias is applied to electrode 11
, Since the well layer 31 is doped n-type, all the electric field is applied to the barrier layer 32, and the potential gradient of this layer 32 increases. Therefore, the barrier layer 32 is effectively
And the degree of coupling between the quantum wells 31 increases, and as a result, the refractive index of the waveguide layer 3 approaches the value of mixed-crystal AlGaAs having the same Al composition ratio, and thus decreases.
こうして、負バイアス印加時には回折格子５のブラッ
ク波長が短くなり、発振波長が短波長側にシフトする。Thus, when a negative bias is applied, the black wavelength of the diffraction grating 5 becomes shorter, and the oscillation wavelength shifts to the shorter wavelength side.
この際、位相制御領域21とDBR領域22に印加する電圧
を調整することにより、準連続的に発振波長を変化させ
ることができる。また、このとき、導波路層３の屈折率
の変化に対し、光吸収の増大が生じないので、発振スペ
クトル線幅の増大も生じず、良好なレーザ特性を維持で
きる。At this time, the oscillation wavelength can be changed quasi-continuously by adjusting the voltage applied to the phase control region 21 and the DBR region 22. Further, at this time, since the light absorption does not increase with respect to the change in the refractive index of the waveguide layer 3, the line width of the oscillation spectrum does not increase, and good laser characteristics can be maintained.
第２図、第３図、第４図は別の変形例を示し、超格子
導波路層３のポテンシャル分布の模式図を示す。2, 3 and 4 show another modified example, and show schematic diagrams of the potential distribution of the superlattice waveguide layer 3.
第２図の例では、フラットバンド状態で障壁層32のポ
テンシャルが傾斜している様に超格子導波路層３、クラ
ッド層２、６を形成している。In the example of FIG. 2, the superlattice waveguide layer 3 and the cladding layers 2 and 6 are formed such that the potential of the barrier layer 32 is inclined in a flat band state.
第３図の例では、障壁層32のポテンシャルが傾斜しつ
つ段階状になる様に超格子導波路層３等を形成してい
る。In the example of FIG. 3, the superlattice waveguide layer 3 and the like are formed such that the potential of the barrier layer 32 becomes stepwise while being inclined.
第４図の例では、障壁層32が更に短周期の超格子で形
成されている。In the example of FIG. 4, the barrier layer 32 is formed of a superlattice having a shorter period.
これらの例では、電圧を印加した際に量子井戸31間の
結合が容易に生じることになる。In these examples, coupling between the quantum wells 31 easily occurs when a voltage is applied.
第５図は本発明の第２実施例である波長変換レーザの
側断面図である。第１図の波長可変レーザとこの第２実
施例とが異なる点は、活性領域が活性領域I20A、活性領
域II20b、および可飽和吸収領域23で構成され、そして
光入力λinが活性領域に入射されることである。尚、8
1、82は活性領域Ｉ、II20a,20bに形成された電極であ
る。FIG. 5 is a side sectional view of a wavelength conversion laser according to a second embodiment of the present invention. The point where the second embodiment and the tunable laser of FIG. 1 are different, the active region is an active region I20A, is composed of an active region II20b, and the saturable absorption region 23, and the optical input lambda in incidence in the active region Is to be done. In addition, 8
Reference numerals 1 and 82 denote electrodes formed in the active regions I and II 20a and 20b.
第２実施例の動作は次の様に行なわれる。 The operation of the second embodiment is performed as follows.
活性領域I,II20a,20bへの注入電流を発振閾値より僅
かに低い状態にし、ここにλinの光を入射すると、可飽
和吸収領域23の吸収損失が低下し、素子がレーザ発振状
態になる。Active region I, II20a, the current injected into 20b and slightly lower than the oscillation threshold and now to light having a lambda in, reduced absorption loss of the saturable absorption region 23, the element is a laser oscillation state .
この時、光出力λoutの波長はDBR領域22のブラッグ波
長で決定される。従って、位相制御領域21及びDBR領域2
2への印加電圧を変えることにより、ブラッグ波長が変
化し、光出力λoutの波長を任意に変換できることにな
る。At this time, the wavelength of the optical output λ out is determined by the Bragg wavelength of the DBR region 22. Therefore, the phase control area 21 and the DBR area 2
By changing the voltage applied to 2, the Bragg wavelength changes, and the wavelength of the optical output λ out can be arbitrarily converted.
第２実施例の作製方法は、第１実施例と同様である。 The manufacturing method of the second embodiment is the same as that of the first embodiment.
［発明の効果］ 以上説明した様に、本発明によれば、２層以上の量子
井戸を含む半導体光導波路において、障壁層に印加され
る電界の制御によって量子井戸間の結合状態が変化し、
これに伴ない屈折率も大きく変化する現象を利用して発
振波長を変化させている。従って、QCSEなどの現象を利
用せず、吸収損失の増大を伴わないので、波長を変化し
た際の発振スペクトル線幅の変化が少ない良好な特性の
波長可変レーザが得られる。[Effects of the Invention] As described above, according to the present invention, in a semiconductor optical waveguide including two or more quantum wells, the coupling state between the quantum wells changes by controlling the electric field applied to the barrier layer,
The oscillation wavelength is changed by utilizing the phenomenon that the refractive index is greatly changed. Therefore, since a phenomenon such as QCSE is not used and the absorption loss is not increased, a wavelength tunable laser having good characteristics with a small change in the oscillation spectrum line width when the wavelength is changed can be obtained.
第１図は本発明の第１実施例である波長可変レーザの側
断面図、第２図は導波路の障壁ポテンシャルが傾斜して
いる例の模式図、第３図は導波路の障壁ポテンシャルの
傾斜を階段状で構成した例の模式図、第４図は導波路の
障壁を更に短周期の超格子構造で構成した例のポテンシ
ャルの模式図、第５図は本発明の第２実施例である波長
変換レーザの側断面図である。 １……ｎ−GaAs基板、２……ｎ−AlGaAsクラッド層、３
……超格子光導波路層、４……GaAs活性層、５……２次
の回折格子、６……ｐ−AlGaAsクラッド層、７……ｐ−
GaAsキャップ層、8,81,82……活性領域20、20a、20bの
電極、９……電気的分離の為の溝、10……位相制御領域
21の電極、11……DBR領域22の電極、12……共通電極、2
3……可飽和吸収領域、31……超格子光導波路層の井戸
層、32……超格子光導波路層の障壁層FIG. 1 is a side sectional view of a wavelength tunable laser according to a first embodiment of the present invention, FIG. 2 is a schematic view of an example in which a barrier potential of a waveguide is inclined, and FIG. FIG. 4 is a schematic diagram of an example in which the inclination is configured in a stepwise manner, FIG. 4 is a schematic diagram of a potential in an example in which the waveguide barrier is formed of a superlattice structure having a shorter period, and FIG. It is a sectional side view of a certain wavelength conversion laser. 1... N-GaAs substrate, 2... N-AlGaAs cladding layer, 3
... superlattice optical waveguide layer, 4 ... GaAs active layer, 5 ... secondary diffraction grating, 6 ... p-AlGaAs cladding layer, 7 ... p-
GaAs cap layer, 8, 81, 82 ... electrodes of active regions 20, 20a, 20b, 9 ... grooves for electrical isolation, 10 ... phase control region
21 electrodes, 11 ... DBR region 22 electrodes, 12 ... common electrodes, 2
3 saturable absorption region, 31 well layer of superlattice optical waveguide layer, 32 barrier layer of superlattice optical waveguide layer
Claims (6)
て、外部導波路層の回折格子を形成している領域から光
波長以内の距離に２層以上の量子井戸とその間の障壁層
を含む半導体光導波路が設けられ、前記量子井戸がｐ型
およびｎ型の一方の導電型に形成され、前記障壁層が高
抵抗層で形成され、また、前記障壁層は、前記導波路に
印加する電圧によって量子井戸間の結合状態を変化可能
な厚さ及び形状に形成されており、且つ前記導波路に電
圧を印加するための手段が設けられていることを特徴と
する波長可変半導体レーザ。In a distributed reflection type wavelength tunable semiconductor laser, a semiconductor optical waveguide including two or more quantum wells and a barrier layer therebetween at a distance within a light wavelength from a region of the external waveguide layer forming a diffraction grating. Is provided, the quantum well is formed of one of p-type and n-type conductivity types, the barrier layer is formed of a high-resistance layer, and the barrier layer is formed by a voltage applied to the waveguide. A wavelength tunable semiconductor laser having a thickness and a shape capable of changing a coupling state between the waveguides and a means for applying a voltage to the waveguide.
いる請求項１記載の半導体レーザ。2. The semiconductor laser according to claim 1, wherein said barrier layer is formed of a short-period superlattice.
ド状態で傾斜している様に形成されている請求項１記載
の半導体レーザ。3. The semiconductor laser according to claim 1, wherein the potential of the barrier layer is formed so as to be inclined in a flat band state.
段状である様に形成されている請求項１記載の半導体レ
ーザ。4. The semiconductor laser according to claim 1, wherein the potential of said barrier layer is formed so as to be stepwise while being inclined.
AlyGa1-yAs（０≦ｘ＜ｙ≦１）で形成され、そして障壁
層の厚さが3nm以上、15nm以下である請求項１記載の半
導体レーザ。5. The method according to claim 1, wherein the quantum well is Al x Ga 1 -x As, and the barrier layer is
2. The semiconductor laser according to claim 1, wherein the semiconductor laser is formed of Al y Ga 1-y As (0 ≦ x <y ≦ 1), and the thickness of the barrier layer is 3 nm or more and 15 nm or less.
長変換半導体レーザとして構成されている請求項１、
２、３、４又は５記載の半導体レーザ。6. A wavelength conversion semiconductor laser having a saturable absorption region between active regions.
6. The semiconductor laser according to 2, 3, 4, or 5.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2204157A JP2891756B2 (en) | 1990-08-01 | 1990-08-01 | Tunable semiconductor laser |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2204157A JP2891756B2 (en) | 1990-08-01 | 1990-08-01 | Tunable semiconductor laser |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH0488687A JPH0488687A (en) | 1992-03-23 |
| JP2891756B2 true JP2891756B2 (en) | 1999-05-17 |
Family
ID=16485782
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP2204157A Expired - Fee Related JP2891756B2 (en) | 1990-08-01 | 1990-08-01 | Tunable semiconductor laser |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP2891756B2 (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP5189956B2 (en) * | 2008-11-05 | 2013-04-24 | 日本電信電話株式会社 | Optical signal processing device |
-
1990
- 1990-08-01 JP JP2204157A patent/JP2891756B2/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| JPH0488687A (en) | 1992-03-23 |
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