JPS6015986A - Light amplifier - Google Patents

Abstract

PURPOSE:To contrive control of noise and to stabilize the gain of light amplification by absorbing the undesired light properly by using a reflection preventing film for light-input combination of the light amplifier and using a diffraction grating for light-output combination. CONSTITUTION:Between the positive electrode 408 and the negative electrode 409, a bias current flows in a normal direction. At this time, if the signal light 450 having an equal wavelength to the band gap of the active layer 402 is projected, the signal light 450 is amplified by the induced emission effect during wave-guiding of the active layer 402 in a light-amplifying region 420. The amplified light is then transmitted to a connection waveguide path region 430 and the light-amplifying region 420 and the connection waveguide path region 430 are combined without reflection. As the modulation period diffraction grating 405 having the period strucure in which the period becomes slightly shorter from the entering side toward the emitting side is arranged on a boundary plane between the layers 404 and 406 as a light frequency filter, the signal light makes a focus in the outside and is taken out as the output light 460.

Description

DETAILED DESCRIPTION OF THE INVENTION (Non-technical! I!P) The present invention relates to a traveling wave optical amplifier that performs output coupling of light using a diffraction grating.

(Prior Art) An optical amplifier is a device that amplifies a weak optical signal to obtain a strong optical signal without converting it into an electrical signal.

An example of this type of optical amplifier is a semiconductor laser amplifier, which, like a semiconductor laser,
Since it utilizes a gain a structure based on the stimulated emission effect, it has a device structure similar to that of a semiconductor laser.

This kind of conventional traveling wave optical amplifier usually includes a GaInAsP crystal layer (1), 2 as an active layer and a cladding layer on an n-type InP substrate /Q/ as shown in FIG. A p-type InP crystal layer 103 is formed in this order, a negative electrode 10u is attached to the substrate 10/, and a positive electrode 103 is attached to the p-type InP crystal layer 103. Antireflective coatings similar to dielectrics 10B and 1
07, the reflectance at the input/output end face is reduced, and a structure in which gain is obtained by the stimulated emission effect caused by single passage of signal light has been considered.

Since such traveling wave optical amplifiers do not have a Fapley-Bello resonator like the resonant type, the gain frequency bandwidth is widened, and not only stable gain can be obtained, but also the gain saturation characteristics are improved. It has the advantage of being

However, in the traveling wave optical amplifier having the structure shown in FIG. The larger the width, the more noise there is, so there is a drawback that it is necessary to separately prepare an optical frequency filter to remove this noise.

(Objective) Therefore, the first object of the present invention is to provide an advanced wave type optical amplifier with low noise despite a wide range of reflection conditions.

A λ-th object of the present invention is to provide a light amplifier 111 that appropriately absorbs undesired light and suppresses noise.

The third object of the present invention is to appropriately stabilize the optical amplification (f'Ii1) of the optical amplification.
Our mission is to provide the '4M's.

(+Ft composition of the invention) In order to achieve this purpose, an anti-reflection film was applied to the optical input coupling of the optical amplifier.
Use a 1B saw connection.

That is, in order to achieve the first objective of "double water", the present invention attaches an anti-reflection film to the light incident end face of the 11η layer consisting of a double heterojunction, and the mJ is also controlled independently. The bandgap and f's, +'! A signal beam of equal γ length is input from the light incident end surface, and the monopolistic one bow (
Tej (Inject Z flow, lead 1 attack effect, negative 0 self 1
An optical waveguide layer having an equal polarized refractive index is provided at the output end of the active layer so as to amplify the word "ye," and an optical waveguide layer having an equal polarized refractive index is provided at the output end of the active layer. A diffraction grating having a period that does not cause reflection is provided to extract amplified output light from the optical waveguide layer.

In order to achieve the above-mentioned second object, the present invention attaches an anti-reflection film to the light incident end face of an active layer consisting of a double heterojunction, and applies signal light having a wavelength approximately equal to the bandgap of the active layer to the active layer. A current is injected into the active layer to amplify the signal light by a stimulated emission effect, and a current is connected to the active layer at the output end of the active layer. 1; An optical waveguide layer with equal polarized refractive index is provided, a diffraction grating with a period that does not cause regular reflection is provided on one side of the optical waveguide layer, and the amplified output light is extracted from the optical waveguide layer. A light absorbing layer is disposed facing the active layer with the optical waveguide layer in between.

[Achieving the above-mentioned third object] In order to achieve the above-mentioned third object, the present invention attaches an anti-reflection film to the light incident end face of an active layer consisting of a double heterojunction, and coats the active layer with a wavelength approximately equal to the bandgap thereof. Signal light is made incident from the light incident end surface, a current is injected into the active layer, and the signal light is amplified by the stimulated emission effect. , providing optical waveguide layers with equal refractive index on the isolateral side,
A diffraction grating having a period that does not cause specular reflection is provided on one side of the optical waveguide layer, and a V-shaped grating is provided on one side of the optical waveguide layer so as to extract the amplified output light from the optical waveguide layer. A light amplification effect is obtained by arranging a light absorption layer, and arranging an electrode for applying a reverse bias to the light absorption layer.(a) Detecting a change in I, j+ is injected into the active layer according to the change. The amount of current drawn is controlled.

(Implementation j9+, i) The present invention will be described in detail below with reference to the drawings.

FIG. 1 shows the basic structure of the optical amplifier of the present invention.

Here, the semiconductor substrate 200 is composed of a lattice-matched multilayer epitaxial growth layer, and in the optical amplification region 20/, the active layer 202 is formed as a double heterojunction.

The bandgap wavelength of this active layer 202 is the wavelength λ of the incident signal light. shall match. An antireflection film 203 is attached to the light incident end face of the active layer 20.2. 201I is a cladding layer on the active layer 202.

An optical waveguide 20j is connected with low loss adjacent to the active layer-〇2. The isolateral refractive index of this optical waveguide 203 is neff
shall be. On one side of the semiconductor layer constituting the optical waveguide 203, a diffraction grating 201. form. The period N of this diffraction grating 20 is given by neff, where l is a positive number excluding natural numbers. This portion of the optical waveguide extending through the diffraction grating is defined as a connection waveguide region 207. , 201 is a cladding layer on the optical waveguide 20.

Here, a current is injected into the optical amplification region λ02 from the positive electrode 209 and the negative electrode 2IO, and the wavelength λ is applied through the antireflection film 203 under appropriate forward bias conditions. When the signal light 2// is incident, the signal light 21/ is amplified by the stimulated emission effect. Here, by appropriately selecting the refractive indexes and film thicknesses of the connection waveguide region 207 and the optical amplification region 20/, the isolateral refractive index neff can be made approximately equal 7, so that the signal light 2// can be transmitted to the active layer. From 202 to the optical waveguide-! 05 without reflection.

The light coupled to the optical waveguide 2O5 is diffracted by the diffraction grating -20t and extracted to the outside as output light, ! /, becomes 2.

Here, diffraction by the diffraction grating 20B used in the present invention will be explained using FIG. 11S3. In the following, the case of /<#<2 will be explained in particular, but the diffraction by the diffraction grating 20B is the same even in the case of 2<l.

Isolateral refractive index n. 0. It is assumed that a one-notch grating 30/ with a period of n is formed in the optical waveguide medium 300.

Wavelength λ. Suppose that the light is incident on the diffraction grating 30/ in parallel,
The diffraction angle of the diffracted light 303 is assumed to be θ. θ is λ.

is given by Here, m is an integer. On the other hand, 1t1
Let the period of the single-fold lattice 30/ be. Substituting equation (2) into equation (1), sinθ=2
・--t (31!) is obtained.If we calculate the value of θ that satisfies the formula (6), when m=o, 20--wao0(4) When m-/: θ-5in' C '-/ ) (5)
becomes. Here, if we take into account the condition /</ What is obtained for 30.2 is diffracted light 303 and 30
It can be seen that there is no reflected light traveling in the opposite direction to the incident light 30.2.

DBR Nuser and D
In an FB laser, the period of the diffraction grating is l-/.

! , 3. It is given by... The order of the diffraction grating is
For example, if the period is set to correspond to between the seventh order and the first order, the reflected wave f in the incident direction can be eliminated as described above.

FIG. 1 shows a specific embodiment of the optical amplifier of the present invention, where Jio/ is a Zn-doped p-type InP crystal layer (thickness approximately -μm + 927017c) as a cladding layer.
m-5), lIO,2 is an undoped n-type GaInAsP crystal layer (Eg: 0.5 eV, thickness o, 7 μm) as an active layer, and lIO,2 is an S-doped n-type In
It is a P substrate (n=/018 cm-5). Note that the cladding layer lIO/ may be an n-type InP crystal layer. At the output end of the active layer '10.2, there are optical waveguide layers l/, O which are continuous with the active layer po, z and have the same equivalent refractive index.
As II, an undoped n-type GaInAsP crystal haj
(Eg 80 eV, thickness 0.2 μm), and one side of this optical waveguide layer tlOII has a modulation period whose period decreases from the input side to the output side so as not to cause specular reflection. A modulated periodic diffraction grating 1Ios is formed by laser beam interference or the like. The substrate is made of an undoped n-type InP crystal layer (about 2 μm thick) as a cladding layer. An antireflection film ψ07 is attached to the light incident end face of the active layer lIO,2. Furthermore, pog is a positive electrode and poq is a negative electrode.

Furthermore, InP substrate 4!0. ? In the above, GaInA
Opposing the active layer 1102 with the sP crystal @ll0a in between, undoped n-type GaInAsP is used as an absorption layer.
Crystal layer #/J (Eg==0.1 eV, thickness 0.
A p-type InP crystal layer lIl/, doped with Zn as a cladding layer, is disposed on this absorption layer lI/,2.
(approximately 274 m thick, p = 10"a-3). The cladding layer // may be an n-type InP crystal layer. Furthermore, a positive electrode is placed on this InP crystal layer //.
/r is arranged, and a negative electrode≠09 is also arranged on the surface of the substrate 1103 opposite to this positive electrode 11111''.

In the above configuration, the layers lI0.2 and '10/ on the substrate IAOJ form an optical amplification region, the layers t112 and Ill/ form an optical absorption region, the waveguide region ll30 is connected to the layers tioll and tios, and the layers t112 and Ill/ form an optical absorption region, respectively. do.

Next, the operation of the optical amplifier of the present invention shown in FIG.

First, a bias current is caused to flow in the forward direction between the positive electrode 07 and the negative electrode Q. Here, when the signal light tIso having a wavelength approximately equal to the bandgap of the active layer IO2 is incident from the left side of FIG. ≠02 is amplified by the stimulated emission effect while being guided. This amplified light is then transferred to the connecting waveguide region 11.
30, the refractive index of layers 170/, 1103 and I10 is J, /7, the refractive index of layer 1I02 is 3°5/, and the layer thickness is 0.1 μm, and the refractive index of one layer POP is 3.33. If the layer thickness is 0.2 μm, the equivalent refractive index of the optical amplification region 1I20 and the connection waveguide region <t30 will both be approximately 3°λ, and these two head regions will be coupled without reflection.

Next, at the interface between the layers tioti and aOt, a modulated periodic diffraction grating ψOS, which has a periodic structure whose period gradually decreases from the input side to the output side, is placed as an optical frequency filter. From K, the signal light is focused externally and extracted as output light ti6o. Regarding the behavior of light in this diffraction grating, A. KATZIR,
A, O, LIVANO3, J', B, 5HELLAN
.

and A. EEE Journal by YA'RIV
al of Quantum Electronics
, Vol, Lee/3, j6'l, pp, j
It is shown in Waotsu-301/, (/?77).

At this time, since the diffraction angle of the diffracted light differs depending on the wavelength, the frequency distribution is replaced by a spatial distribution.

Therefore, the bandwidth of the optical frequency filter can be determined by the light receiving area of the output light.

In reality, the light diffracted by the diffraction grating OS is
Since the plane on which the AOS is formed is used as the plane of symmetry, it is diffracted in the up and down directions, so there may be a decrease in efficiency, but InP
The thickness d of layer 4106 is λ.

n: By setting the refractive index of the InP layer μ0, the upward diffracted light is InP layer≠06
The optical signal reflected at the interface between the connecting waveguide region 1130 and the outer air layer, and most of which can be extracted downward, is not extracted to the outside in the connecting waveguide region 1130. The light is guided without reflection to the light absorption region≠lIO, where it is absorbed.

Note that by applying a reverse bias between the positive electrode T and the negative electrode G, the light absorption region≠PO has the ability to detect U'C, thereby reducing the fluctuation of the amplification gain. can be detected. Therefore, the gain can be stabilized by negatively feeding the fluctuations detected in this way to the optical amplification region 1I20.

In the above example, a GaInAsP layer with a composition larger in bandgap than the active layer 1102 is used since the semiconductor layer with low absorption IIot is used. Absorption may be reduced by doing this.

(Effects) As explained above, according to the present invention, an optical frequency filter with a wide gain bandwidth and for noise removal using a diffraction grating is integrated into the optical waveguide, thereby widening the range of low reflection conditions. Despite its wide area, a high-performance traveling wave optical amplifier with low noise can be obtained with a simple configuration.

According to the present invention, unwanted light in the optical waveguide layer can be absorbed by the trenched light absorption layer integrated with the optical waveguide layer, which further eliminates noise and improves optical amplification. It can be carried out.

Furthermore, according to the present invention, a reverse bias is applied to the light absorption layer to detect fluctuations in the optical amplification gain, and the optical amplification section is feedback-controlled using the detected output, thereby stabilizing the gain of the optical amplification. You can also do that.

Therefore, by inserting the high-performance traveling wave optical amplifier according to the present invention into a transmission line to construct an optical direct amplification transmission system, the regenerative repeating distance can be greatly expanded.

[Brief explanation of the drawing]

FIG. 7 is a cross-sectional view showing an example of the structure of a traveling wave optical amplifier using a conventional antireflection film, FIG. 2 is a cross-sectional view showing the basic structure of the optical amplifier of the present invention, and FIG. An explanatory diagram of the lattice, FIG. 1 is a sectional view showing the structure of a specific embodiment of the present invention. 10/... n-type InP substrate, 102... GaInAsP crystal layer as active layer, 1
03...p-type InP crystal layer, IO≠...negative electrode, IO! ...Positive electrode, 106, 107...Antireflection film 1. 200...Water root 1. 20/...Light amplification region 1. 202...active layer, one! 03...Anti-reflection film 1. 20g cladding layer, 203... optical waveguide, 206... diffraction grating, 207... connection waveguide region, 201... 1 of cladding j. 20W...Positive electrode, 210...Negative electrode 1. 2/l...Incoming signal light, 2/2...Outgoing light, 300...Optical waveguide medium, 30/...Diffraction grating 302...Incoming light, 303, 303'...Diffracted light, 110 /...p-type InP crystal layer, l/, 0.2-GaInA5P active layer, G03...n
type InP substrate, 1I04/-n-type GaInAsP =-optical waveguide layer, ti
os...Modulation periodic diffraction grating, l/-O-n-type InP crystal layer, '107...Antireflection film, l10za...Positive electrode, l109...Negative electrode, III/...p type InP crystal layer, 1172-GaInAsP light absorption layer, l111...
Positive electrode, Gu20... Optical amplification region, ≠30... Connection waveguide region, Gugu O... Light absorption region 1 HiroSO... Signal light, Guotsu O... Output light. Patent applicant Nippon Telegraph and Telephone Corporation

Claims (1)

[Scope of Claims] 1) An antireflection film is attached to a light incident end face of an active layer formed of a double heterojunction, and a signal light having a wavelength approximately equal to the bandgap of the active layer is made to enter the active layer from the light incident face, A current is injected into the active layer to amplify the signal light by a stimulated emission effect, and a light guide having an equal refractive index on the isolateral side is provided at an output and an opposite end of the active layer, continuous with the active layer. 1. An optical amplifier comprising: a wave layer; one side of the optical waveguide layer is provided with a diffraction grating having a period that does not cause regular reflection; and amplified output light is extracted from the optical waveguide layer. 2) An antireflection film is attached to the light-incidence end face of the active layer made of a double heterojunction, and a signal light having a wavelength approximately equal to the bandgap of the active layer is made to enter the active layer from the light-incidence end face, and a current is applied to the active layer. 7. At the output end of the active layer, an optical waveguide layer having an equal refractive index is provided in succession to the active layer, and the optical waveguide layer is A diffraction grating having a period that does not cause specular reflection is provided on one side of the wave layer to extract amplified output light from the optical waveguide layer, and a diffraction grating is provided on one side of the wave layer to face the active layer with the optical waveguide layer in between. An optical amplifier characterized by disposing a light absorption layer. 5) An antireflection film is attached to the light incident end face of the active layer consisting of a double heterojunction, and fF3'W light of a wave layer approximately equal to the bandgap tl of the active layer is made to enter the active layer from the light incident face. A current is injected into the layer so as to amplify the signal light by a stimulated emission effect, and an optical waveguide layer having an equal refractive index on the isolateral side is provided at the output end of the active layer in succession to the active layer. , a diffraction grating having a period that does not cause specular reflection is provided on one side of the leading waveguide layer so as to extract the amplified output light from the optical waveguide layer, and sandwiching the optical waveguide layer,
A light absorption layer is disposed opposite to the active layer, and an electrode for applying a reverse bias to the light absorption layer is disposed to detect fluctuations in the gain of optical amplification, and inject C into the active layer according to the fluctuations. An optical amplifier characterized in that the amount of current flowing through the amplifier is controlled.