JPH07122723A - Wavelength conversion laser - Google Patents

Abstract

PURPOSE:To convert intensity-modulated light into another intensity-modulated light having another wavelength and the same pattern by providing a laterally injected waveguide crossing a saturable absorption waveguide, reflectivity adjusting layers on the end face of a distributed feedback laser, and another reflectivity adjusting layer on the end face of a second gain waveguide. CONSTITUTION:As the voltage applied across a saturable absorption waveguide 104 is dropped, the light loss in the waveguide 103 increases and, at the same time, the light returning to a distributed feedback laser 102 from the side face of the waveguide 104 on a second gain waveguide 105 side decreases. Because of the two effects, the optical output from the side face of the waveguide 104 on the waveguide 105 side decreases. When the currents injected to the laser 102, gain waveguides 103 and 104, and a laterally injected waveguide 106 are respectively controlled to 80mA, 30mA, and 100mA and the voltage applied across the waveguide 104 is controlled to -1.0V, light is made incident to the waveguide 106. The intensity of outgoing light from a laser 102 can be modulated based on the relation between the intensity of incident light and optional output.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is applicable to optical switches, optical repeaters, etc., which are expected to constitute optical communication or optical information systems, and the same time series is obtained by changing the wavelength of an incident optical pulse train. The present invention relates to a wavelength conversion laser which emits an optical pulse train.

[0002]

2. Description of the Related Art A wavelength conversion laser which has a current-to-light output characteristic and a light input / output characteristic and has a hysteresis characteristic and which oscillates with light having a wavelength different from that of an input light is a high-speed optical switch compatible with wavelength multiplexing. Since it is capable of operations such as optical logic operation and optical memory, it is used as a functional device constituting an optical communication system and an optical information system.

An example of a conventional wavelength conversion laser is shown in FIGS. 16 is a diagram for explaining the schematic configuration of the wavelength conversion laser, FIG. 17 is a diagram for explaining the injection current-optical output characteristics to the gain section of the device shown in FIG. 16, and FIG. FIG. 6 is a diagram for explaining the light input-light output characteristics of the device shown in FIG.

In this wavelength conversion laser, the electrode of the active waveguide portion of the semiconductor laser is divided into three, the forward injection current of one is increased to form a gain portion, and the voltage applied to the other electrode is controlled to saturable absorption. It comprises a bistable laser section that acts as a section and an optical input waveguide section that intersects the saturable absorption section.

Here, reference numeral 201 is a gain portion electrode, 2
02 is an InGaAsP contact layer, 203 is InP
(P) Clad layer, 204 is InGaAsP upper guide layer, 205 is MQW active layer, and 206 is InGaAsP
Lower guide layer, 207 is InP (n) clad layer, 20
8 is an InP (n ⁺ ) substrate, 209 is a bottom electrode, 210 is a saturable absorber electrode, 211 is a front distributed reflector electrode, 21
2 is a rear distributed reflector electrode, 213 is an optical input waveguide electrode, 214 is a separation groove, 215 is a diffraction grating, and 216 is In.
The GaAsP guide layer and 217 are semi-insulating InP layers. As shown in FIG. 17, the threshold characteristic can be obtained by reducing the applied voltage (V _c ) to the saturable absorber from 0.6V to 0.3V. In this figure, the injection current into the gain region is I
FIG. 18 illustrates the light input / output characteristic at this time when the voltage is set to _B and the applied voltage to the saturable absorber is 0.3V. By providing a low-reflection coating on the end face of the lateral injection waveguide, it is possible to obtain a threshold characteristic that does not depend much on the incident wavelength (λ _in ). The emission wavelength (λ _out ) is determined by the current injected into the distributed reflector. As is apparent from FIG. 18, this element emits the same optical pulse train as the incident optical pulse train. Since the emission wavelength can be set independently of the incident wavelength, this element functions as a wavelength conversion laser.

[0006]

However, the conventional wavelength conversion laser described above has the following problems. That is, the bistable laser has a large fluctuation in carrier density in the active layer when the laser is oscillating / non-oscillating. Therefore, relaxation oscillation becomes strong at the time of laser oscillation, and the optical output largely fluctuates. Also,
The so-called pattern effect in which the rise time of oscillation / light intensity changes according to the pattern of the incident signal is remarkable.
Therefore, although it responds at high speed to intensity-modulated light having a simple repetitive waveform, it is difficult to increase the transmission band of the pattern signal. In addition, it is necessary to fine-tune the bias current in order to inject a bias current that is slightly less than the threshold value of the threshold characteristics.If the element characteristics change due to temperature fluctuations or long-term use, the bias current should be adjusted accordingly. The current needs to be readjusted. Therefore, the present invention solves the above-mentioned problems, can convert intensity-modulated light having a high-speed pattern signal into intensity-modulated light having the same pattern at another wavelength, and does not require fine adjustment of operating conditions. An object is to provide a wavelength conversion laser.

[0007]

In order to solve the above problems, a first wavelength conversion laser according to the present invention comprises a semiconductor laser, a first gain waveguide, a saturable absorption waveguide, and a second gain. A laser section in which the waveguides are coaxially connected on the same substrate, a lateral optical injection waveguide intersecting with the saturable absorption waveguide, and a reflectance adjusting layer provided on the end face of the semiconductor laser,
At least a reflectance adjusting layer provided on an end face of the second gain waveguide is provided, and the semiconductor laser is one of a distributed feedback semiconductor laser and a distributed reflection semiconductor laser. .

In the second wavelength conversion laser according to the present invention, the semiconductor laser, the first gain waveguide, the saturable absorption waveguide, the second gain waveguide, and the distributed reflection waveguide are on the same substrate. A laser section coaxially connected, a lateral optical injection waveguide intersecting the saturable absorption waveguide, a non-reflection coating layer provided on the end face of the semiconductor laser, and a non-reflection coating layer provided on the end face of the distributed reflection waveguide. A reflective coating layer is further provided, and the semiconductor laser is one of a distributed feedback semiconductor laser and a distributed reflection semiconductor laser.

The above first and second wavelength conversion lasers are
It preferably has at least one of the following features. That is, (1) a phase adjustment waveguide is provided between the semiconductor laser and the end face of the second gain waveguide.

(2) The wavelength conversion laser is constructed as a curved waveguide.

(3) The lateral optical injection waveguide has a bent portion formed by a total reflection mirror.

(4) The wavelength conversion laser has a plurality of saturable absorption waveguides, each of the saturable absorption waveguides is connected by a gain waveguide, and the light is converted so as to intersect with each of the saturable absorption waveguides. It has a branch waveguide that branches the lateral injection waveguide.

[0013]

The wavelength conversion laser of the present invention controls the return light from the end face provided with the reflectance adjusting layer outside the laser resonator to the laser resonator or the coupling efficiency with the distributed Bragg reflector forming the compound resonator. A saturable absorption waveguide, a first and a second gain waveguide, and a phase adjusting waveguide. The absorption coefficient of the saturable absorption waveguide, that is, the return light or the coupling efficiency is modulated by the light propagating in the lateral optical injection waveguide. As a result, the optical output of the semiconductor laser is intensity-modulated by the light incident on the lateral optical injection waveguide, but the oscillation wavelength of the semiconductor laser is regulated by the distributed reflection structure or distributed feedback structure, while it is saturable. Since the absorption waveguide responds to light within a wide wavelength range, the wavelengths of incident light and emitted light are generally different. Therefore, the device of the present invention functions as a wavelength conversion laser. Since the output light of the semiconductor laser is not modulated by the optical gate outside the laser, but the return light from the end face of the composite resonator by the outer end face is modulated, it is possible to perform deep modulation with weak input light. In addition, the wavelength conversion laser can be configured by using a curved waveguide, or a total reflection mirror can be formed in the lateral optical injection waveguide to input and output light from opposite surfaces of the substrate. Further, a highly efficient wavelength conversion laser can be constructed by dividing the saturable absorption waveguide.

[0014]

Embodiments of the present invention will be described below with reference to the drawings, but these embodiments do not limit the present invention.

<Embodiment 1> FIG. 1 is a view for explaining a schematic configuration of an embodiment of a wavelength conversion laser according to the present invention. In this figure, reference numeral 101 is a semiconductor substrate, 102 is a distributed feedback semiconductor laser, 103 is a first gain waveguide, 104 is a saturable absorption waveguide, and 105 is a second.
, And 106 is a lateral optical injection waveguide.
A cross-sectional view between points AB in this drawing is shown in FIG. here,
Reference numeral 107 is an upper surface electrode, 108 is an InGaAsP contact layer, 109 is an InP (p) clad layer, 110
Is an InGaAsP upper guide layer, 111 is an MQW active layer composed of an InGaAsP well layer (thickness 0.006 μm) having a bandgap wavelength of 1.55 μm and an InGaAsP barrier layer (thickness 0.02 μm) having a bandgap wavelength of 1.3 μm. , 112 are lower guide layers of InGaAsP,
113 is an InP (n ⁺ ) substrate, 114 is a bottom electrode, 11
Reference numeral 5 is an electrode separation groove, 116 is a diffraction grating having a quarter wavelength phase shift, and 117 and 118 are reflectance adjusting layers.
The reflectance is preferably about 5% when the reflectance adjusting layers 117 and 118 are made equal. Figure 3 point CD in Figure 1
Sectional drawing in between is shown. Reference numeral 119 is a non-reflective coating layer (meaning that reflection is negligibly small; hereinafter, also referred to as low-reflection coating layer). FIG. 4 shows a sectional view between points EF in FIG. Reference numeral 120 is an iron-doped high-resistance InP layer, and 121 is an insulating film.

The wavelength conversion laser of this embodiment is manufactured by the following steps (1) to (10). That is,
(1) InGaAs on the InP (n ⁺ ) substrate 113 in order
P lower guide layer 112, MQW active layer 111, InG
The aAsP upper guide layer 110 is epitaxially grown by a MO-VPE apparatus. (2) The distributed feedback diffraction grating 116 is formed on the InGaAsP upper guide layer 110 by etching with saturated bromine water. (3) InP (p) cladding layer 109, InGaA by MO-VPE apparatus
The sP contact layer 108 is grown. (4) A waveguide core is formed by an ECR etching device. (5) MO
Embed the waveguide with high resistance InP by a VPE device. (6) The electrode is vapor-deposited by the vapor deposition device. (7) The electrodes are patterned by an ion milling etching device. (8) Hydrogen ions or Be ions are injected into the electrode separation groove by an ion implanter to increase the isolation resistance. (9) Cleave into chips. (10) The low-reflection coating layer 119 and the reflectance adjusting layers 117 and 118 on the end face are vapor-deposited by a vapor deposition device.

Next, the mechanism of wavelength conversion in the wavelength conversion laser manufactured by such a method will be described. FIG. 5 shows a graph of the suction current-optical output to the distributed feedback semiconductor laser of the device of the present invention. The optical loss in the saturable absorption waveguide 104 increases as the voltage applied to the saturable absorption waveguide 104 decreases, and at the same time, the distributed feedback semiconductor laser 1 from the end face on the second gain waveguide 105 side.
Light returning to 02 is reduced. The second is a combination of two effects
The optical output from the end surface on the gain waveguide 105 side is reduced.
Here, the injection current I to the distributed feedback semiconductor laser 102 is
_LD is 80 mA, the first and second gain waveguides 103, 1
When the injection currents I _g1 and I _g2 to 04 are 30 mA, the applied voltage to the saturable absorption waveguide 104 is −1.0 V, and the injection current to the lateral optical injection waveguide 106 is 100 mA, the lateral optical injection waveguide is Light is incident on 106 (see FIG. 1). FIG. 6 shows the relationship between the light incident intensity (wavelength λ ₁ ) and the light output (wavelength λ ₂ ) at this time. It can be seen from this figure that when the incident light intensity is modulated, the outgoing light intensity is also modulated. The time waveform of the light modulation at this time is shown in FIG. The reason why the light output is modulated by the light incident on the light lateral injection waveguide 106 is that the absorption coefficient of the saturable absorption waveguide 104, that is, the coupling efficiency with the external mirror forming the compound resonator outside the laser resonator is optical. This is because the light is modulated by the light propagating in the lateral injection waveguide 106. However, while the oscillation wavelength of the semiconductor laser is defined by the distributed feedback structure, the saturable absorption waveguide 104 responds to light in a wide wavelength range, so that the wavelengths of incident light and emitted light are generally different and independent. Can be set to. Therefore, the device of the present invention functions as a wavelength conversion laser. Since the output light of the semiconductor laser is not modulated by the optical gate outside the laser, but the return light from the end face of the composite resonator by the outer end face is modulated, it is possible to perform deep modulation with weak input light.

<Embodiment 2> FIG. 8 shows a second embodiment of the present invention. Here, reference numeral 121 is a first distributed reflection waveguide, 122 is a gain waveguide, 123 is a phase adjustment waveguide, 1
Reference numeral 24 denotes a second distributed reflection waveguide, which is the same as the first embodiment except that the distributed reflection type semiconductor laser is constituted by 121 to 124. FIG. 9 shows a sectional view of the device at the point GH in FIG.
Reference numeral 125 is a waveguide core layer that is transparent to the oscillation wavelength of the laser. For example, if the laser oscillation wavelength is 1.55
In the case of μm, In having a band gap wavelength of 1.3 μm
GaAsP can be used as this core layer. Reference numeral 126 is a first distributed reflection diffraction grating and 127 is a second
Is a distributed reflection diffraction grating of. The difference of the second embodiment from the first embodiment is that a distributed reflection laser is used as the semiconductor laser. As is generally known, the distributed _Bragg reflector laser is controlled by controlling the injection currents I _DBR1 and I _DBR2 into the first and second distributed _Bragg reflectors and the injection current I _P1 into the phase adjustment waveguide. The oscillation wavelength can be changed. Therefore, the output wavelength of the wavelength conversion laser can be controlled and the applicable range of the element is expanded. The operation of the element is similar to that of the first embodiment.

<Embodiment 3> FIG. 10 shows a third embodiment of the present invention. Here, reference numeral 128 is a phase adjustment waveguide provided outside the semiconductor laser resonator, and 129 is a distributed reflection waveguide provided outside the semiconductor laser resonator. FIG. 11 shows a sectional view of the element at point IJ in FIG. Reference numeral 130 is a distributed reflector, and 131 and 132 are low reflection coating layers. The difference from the first and second embodiments is that (1) the phase adjustment waveguide 128 is provided and (2) the distributed Bragg reflector 129 is provided. The effect of the above (1) is that the phase of coupling between the mirror (cleavage end face or distributed reflection waveguide) outside the semiconductor laser and the semiconductor laser can be controlled by the injection current I _P2 . Since there is no phase control mechanism in the first and second examples, the coupling phase cannot be adjusted because the coupling phase is determined by the position of the cleaved end face. If the coupling phase is out of phase, the perturbation of the semiconductor laser by the reflected light from the mirror is reduced, and the modulation of the optical output of the wavelength conversion laser when the absorption of the saturable absorption waveguide is modulated is reduced. In the embodiment, this problem can be avoided. The effect of (2) above is the first and second
Although the end face reflectance is adjusted by the reflectance adjusting layer in the above example, it is not easy to set the desired reflectance. According to the distributed Bragg reflector, the depth of the diffraction grating and the length of the waveguide can be easily adjusted. Further, the reflection wavelength of the distributed Bragg reflector can be controlled according to the oscillation wavelength of the laser. The operation of the element is similar to that of the first embodiment. Although the distributed feedback semiconductor laser is used as the semiconductor laser in the present embodiment, it goes without saying that the distributed feedback semiconductor laser of the second embodiment can be used.

<Embodiment 4> FIG. 12 shows a fourth embodiment of the present invention. In this embodiment, the wavelength conversion laser of the first embodiment is composed of a curved waveguide. The advantage of this configuration is that the input and output of optical signals can be performed from opposite end faces, so that it becomes easy to form a module by combining with other optical components. The operation of the element is similar to that of the first embodiment.

<Embodiment 5> FIG. 13 shows a fifth embodiment of the present invention. The present embodiment has a configuration in which a groove 133 whose side surface functions as a total reflection mirror is formed in the lateral optical injection waveguide of the above-described embodiment to obtain the same effect as that of the fourth embodiment.
FIG. 14 shows a sectional view taken along the broken line KL near the total reflection mirror. The side surface 134 of the groove 133 is a total reflection mirror. The operation of the element is similar to that of the first embodiment.

<Sixth Embodiment> FIG. 15 shows a sixth embodiment of the present invention. In this embodiment, it has a plurality of saturable absorption regions,
It differs from the above-described embodiment in that it has a gain waveguide 135 that connects the respective saturable absorption regions, and that the lateral optical injection waveguide 106 has a branch 134 so as to intersect the respective saturable absorption regions. The incident optical signal is amplified in the lateral optical injection waveguide, but generally the efficiency of amplification is better as the width of the lateral optical injection waveguide is narrower. However, if the width is narrowed, the light is incident on only a part of the saturable absorption waveguide, which lowers the modulation efficiency. To avoid this, the saturable absorption waveguide is divided. Therefore, the wavelength conversion efficiency can be increased in the sixth embodiment. The operation of the element is similar to that of the first embodiment.

It goes without saying that a bulk active layer or a strained quantum well active layer can be used in the above embodiments. Needless to say, the same configuration can be made with other material systems such as GaAs semiconductor materials. Further, it goes without saying that the present invention can be realized with another waveguide configuration such as a ridge type waveguide and a pn buried structure waveguide.

[0024]

As described above, in the first wavelength conversion laser according to the present invention, the semiconductor laser, the first gain waveguide, the saturable absorption waveguide, and the second gain waveguide are on the same substrate. A laser section coaxially connected to the optical waveguide, a lateral optical injection waveguide intersecting the saturable absorption waveguide, a reflectance adjusting layer provided on the end face of the semiconductor laser, and an end face of the second gain waveguide. And a second wavelength conversion laser according to the present invention, wherein the semiconductor laser is one of a distributed feedback semiconductor laser and a distributed reflection semiconductor laser. A semiconductor laser, a first gain waveguide, a saturable absorption waveguide, a second gain waveguide, and a distributed reflection waveguide which are coaxially connected on the same substrate, and a saturable absorption waveguide. Crossed optical lateral injection waveguides and The semiconductor laser comprises an antireflection coating layer provided on an end face of the semiconductor laser and an antireflection coating layer provided on an end face of the distributed Bragg reflector waveguide. Further, the semiconductor laser is a distributed feedback semiconductor laser or a distributed reflection semiconductor laser. The first and second wavelength conversion lasers are preferably one of: (1) a phase adjustment waveguide between the semiconductor laser and an end face of the second gain waveguide; (2) The wavelength conversion laser is configured as a curved waveguide;
(3) The optical lateral injection waveguide has a bent portion formed by a total reflection mirror; and / or (4) the wavelength conversion laser has a plurality of saturable absorption waveguides, and the saturable absorption waveguides are arranged between the saturable absorption waveguides. Since it has a branch waveguide that connects the gain lateral waveguide and branches the lateral optical injection waveguide so as to intersect with each saturable absorption waveguide, the optical signal can be converted from any wavelength to another arbitrary wavelength over a wide wavelength range. The wavelength can be converted to a wavelength, and there is little ringing / jitter in the converted waveform, good wavelength conversion is possible, and there is no need for delicate bias adjustment, so there is no need to apply a high-speed electrical signal. Since it is easy to mount and can be made into a smaller module, it is easy to handle and can be incorporated into other devices. It can be used to 置等.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a configuration of a first exemplary embodiment of the present invention.

FIG. 2 is a sectional view of the first embodiment of the present invention.

FIG. 3 is a sectional view of the first embodiment of the present invention.

FIG. 4 is a cross-sectional view of the first embodiment of the present invention.

FIG. 5 is a diagram showing an injection current-optical output characteristic of the first embodiment of the present invention.

FIG. 6 is a diagram showing a light incident intensity-light output characteristic of the first embodiment of the present invention.

FIG. 7 is a diagram showing a time waveform of optical modulation according to the first embodiment of the present invention.

FIG. 8 is a diagram for explaining the second embodiment of the present invention.

FIG. 9 is a sectional view of a second embodiment of the present invention.

FIG. 10 is a diagram for explaining the third embodiment of the present invention.

FIG. 11 is a sectional view of a third embodiment of the present invention.

FIG. 12 is a diagram for explaining the configuration of the fourth exemplary embodiment of the present invention.

FIG. 13 is a diagram for explaining the configuration of the fifth exemplary embodiment of the present invention.

FIG. 14 is a sectional view of a fifth embodiment of the present invention.

FIG. 15 is a diagram for explaining the configuration of the sixth exemplary embodiment of the present invention.

FIG. 16 is a diagram for explaining the configuration of a conventional wavelength conversion laser.

FIG. 17 is a diagram showing an injection current-optical output characteristic to a gain section of a conventional wavelength conversion laser.

FIG. 18 is a diagram showing an optical input-optical output characteristic of a conventional wavelength conversion laser.

[Explanation of symbols]

101 semiconductor substrate 102 distributed feedback semiconductor laser 103 first gain waveguide 104 saturable absorption waveguide 105 second gain waveguide 106 lateral optical injection waveguide 107 upper surface electrode 108 InGaAsP contact layer 109 InP (p) cladding layer 110 InGaAsP upper guide layer 111 MQW active layer 112 InGaAsP lower guide layer 113 InP (n ⁺ ) substrate 114 Lower surface electrode 115 Electrode separation groove 116 Diffraction grating 117, 118 Reflectance adjusting layer 119 Low reflection coating layer (non-reflection coating layer) 120 high-resistance InP layer 121 insulating film 121 first distributed reflection waveguide 122 gain waveguide 123 phase adjustment waveguide 124 second distributed reflection waveguide 125 waveguide core layer 126 first distributed reflection diffraction grating 127 second Distributed reflection diffraction grating 12 Phase adjustment waveguide 129 Distributed reflection waveguide 130 Distributed reflector 131, 132 Low reflection coating layer 133 Groove functioning as a total reflection mirror 134 Total reflection mirror 135 Gain waveguide 201 Gain part electrode 202 InGaAsP contact layer 203 InP (p) clad Layer 204 InGaAsP upper guide layer 205 MQW active layer 206 InGaAsP lower guide layer 207 InP (n) clad layer 208 InP (n ⁺ ) substrate 209 Lower electrode 210 Saturable absorber electrode 211 Front distributed reflector electrode 212 Rear distribution Reflector electrode 213 Waveguide electrode for light input 214 Separation groove 215 Diffraction grating 216 InGaAsP guide layer 217 Semi-insulating InP layer

Claims (6)

[Claims] 1. A laser section in which a semiconductor laser, a first gain waveguide, a saturable absorption waveguide, and a second gain waveguide are coaxially connected on the same substrate, and the saturable absorption waveguide. The semiconductor device further includes at least optical transverse injection waveguides intersecting with each other, a reflectance adjusting layer provided on an end surface of the semiconductor laser, and a reflectance adjusting layer provided on an end surface of the second gain waveguide. A wavelength conversion laser, wherein the laser is either a distributed feedback semiconductor laser or a distributed reflection semiconductor laser. 2. A laser section in which a semiconductor laser, a first gain waveguide, a saturable absorption waveguide, a second gain waveguide, and a distributed reflection waveguide are coaxially connected on the same substrate, and An optical lateral injection waveguide intersecting with a saturated absorption waveguide, a non-reflection coating layer provided on the end face of the semiconductor laser, and a non-reflection coating layer provided on the end face of the distributed Bragg reflector waveguide, Further, the semiconductor laser is either a distributed feedback semiconductor laser or a distributed reflection semiconductor laser, which is a wavelength conversion laser. 3. The wavelength conversion laser according to claim 1, wherein a phase adjustment waveguide is provided between the semiconductor laser and an end face of the second gain waveguide. . 4. The wavelength conversion laser according to claim 1, wherein the wavelength conversion laser is configured as a curved waveguide. 5. The wavelength conversion laser according to claim 1, wherein the lateral optical injection waveguide has a bent portion formed by a total reflection mirror. 6. The wavelength conversion laser according to claim 1, wherein the wavelength conversion laser has a plurality of saturable absorption waveguides, and the gain guide is provided between the saturable absorption waveguides. A wavelength conversion laser, characterized in that a branching waveguide is provided which is connected by a waveguide and further branches the optical lateral injection waveguide so as to intersect with each saturable absorption waveguide.